Expand this Topic clickable element to expand a topic
OSA Publishing

Early Posting

Accepted papers to appear in an upcoming issue

OSA now posts prepublication articles as soon as they are accepted and cleared for production. See the FAQ for additional information.

Transmission enhancement in periodic chiral metamaterials with dispersion and gain

Yan Huang, Qingqing Zhu, Xiaowei Zhang, Xiang Yu, Hongli Chen, and Chonggui Zhong

DOI: 10.1364/JOSAB.393096 Received 17 Mar 2020; Accepted 09 Jul 2020; Posted 10 Jul 2020  View: PDF

Abstract: The transmission properties are presented for the periodic metamaterials composed of dispersive and gain chiral media. Our numerical results predict that for transverse electric (TE) and transverse magnetic (TM) incident waves, the co-polarization transmission enhancement can be realized as the transmittance is larger than 0.9. As the parameters of the unit cell are fixed, the multi-band of the co-polarization transmission enhancement with broad bandwidth will be obtained for both TE and TM waves as varying the angle of incidence. Meanwhile, the co-polarization transmission enhancement in an ultra-wide incidence angle range (0~78°, 0~86.3°) can be achieved for the certain frequency (35.5GHz, 35.3GHz). Furthermore, the co-polarization transmission enhancement for TM wave appears in the whole frequency band (15~120GHz) as the angle of incidence satisfies the range of (54.9°~65.9°). Finally, the suitable frequency band and broad bandwidth of the transmission enhancement for both TE and TM waves can be modulated by adjusting the period T and the thickness of chiral layer a. We anticipate that this work offers the opportunity in obtaining the broadband and wide-angle transmission enhancement for TE and TM waves, which will shed light on the future design of the microwave filters.

Defective Jones matrices: Geometric phase and passivity condition

Julio Gutierrez-Vega

DOI: 10.1364/JOSAB.400167 Received 12 Jun 2020; Accepted 09 Jul 2020; Posted 10 Jul 2020  View: PDF

Abstract: A defective Jones matrix is a 2x2 matrix that only has one polarization eigenstate, contrary to the more common case of diagonalizable matrices that have two eigenstates. We analyze the properties of a defective optical system and characterize the optical phase shift ψ (dynamic and geometric) introduced by the system. Two scenarios are identified: (a) ψ has a finite range, leading to the existence of two particular input states that experiment minimum and maximum phase shifts. (b) ψ spans the complete range from -π to π, leading to the existence of two input states whose output states are orthogonal. We solve the inverse problem of designing an optical system for both scenarios. Additionally, we determine the conditions to get physically realizable defective Jones matrices satisfying the passivity condition. Finally, we introduce a new defectivity parameter to characterize the degree of defectiveness of a Jones matrix.

Optically pumped HBr master oscillator power amplifier operating in the mid-infrared region

Wayne Koen, Cobus Jacobs, M J Daniel Esser, and Hencharl Strauss

DOI: 10.1364/JOSAB.398697 Received 01 Jun 2020; Accepted 08 Jul 2020; Posted 09 Jul 2020  View: PDF

Abstract: An optically end-pumped HBr master oscillator power amplifier has been demonstrated for the first time. It produced up to 10.3 mJ per pulse at 4.20 and 4.34 μm when pumped with a single-frequency Ho:YLF MOPA system at a pulse repetition frequency of 50 Hz. Wavelength selection with the use of an intra-cavity CO2 absorption cell was also demonstrated, forcing the oscillator to emit at 3.89, 4.13 and 4.16 µm simultaneously, with a maximum output energy of 6.5 mJ per pulse after amplification.

Measuring the Nonlinear Optical Properties of Indium Tin-Oxide Thin Film Using fs Laser Pulses

Mona Ahmed, Abdalla Shehata, Mohamed Ashour, Wael Tawfik, Reinhold Schuch, and Tarek Hassan

DOI: 10.1364/JOSAB.396327 Received 13 May 2020; Accepted 07 Jul 2020; Posted 10 Jul 2020  View: PDF

Abstract: We have investigated the nonlinear optical properties of Indium Tin Oxide (ITO) thin film coated on soda-lime glass substrate using Z-scan technique. With 100 fs laser pulses the nonlinear absorption coefficient and nonlinear refractive index are measured at different excitation wavelengths and at different incident intensities. The nonlinear optical absorption shows a competition between saturable absorption and reverse saturable absorption at the different excitation wavelengths and incident intensities. A transition from saturable to reverse saturable absorption was observed with increasing excitation wavelengths. The measured nonlinear refractive index was found to be dependent on wavelength with a maximum value of 5.34×10−12 cm2/ W at wavelength of 900 nm.

Atoms in axially-shifted tightly focusedcounter-propagating beams: the role of the Gouy andcurvature phases

Koray Köksal, Vassilis Lembessis, Mohamed Babiker, and Jun Yuan

DOI: 10.1364/JOSAB.396097 Received 28 Apr 2020; Accepted 07 Jul 2020; Posted 07 Jul 2020  View: PDF

Abstract: We consider the interaction of atoms with two tightly focused and axially-shifted counter-propagating optical beams. At sub-wavelength focusing, we find that the scattering force potential in the threedimensional space between the shifted focal planes changes from a feature with a saddle-point to a three-dimensional trapping potential. Further analysis shows that due to the tight focusing, the trapping depends on significant contributions arising from the Gouy and curvature phase gradients of the interfering beams. The physics and its effects are illustrated with reference to the sub-wavelength trapping of sodium atoms.

Optical properties of water relaxing after intense laser exposure

Vitali Kononenko, Viktor Gololobov, Evgeny Zavedeev, and Vitaliy Konov

DOI: 10.1364/JOSAB.397826 Received 18 May 2020; Accepted 07 Jul 2020; Posted 07 Jul 2020  View: PDF

Abstract: The dynamics of the optical properties of water bulk exposed to femtosecond radiation (Ti-sapp laser, wavelength 800 nm, intensity ~ 10^{13} W/cm^2) was studied in the time window of ~ 1.5 ns using a pump--probe technique. Both the refractive index and absorbance were measured by femtosecond interferometric microscopy, which allowed us to gather deconvoluting quantitative data about the induced processes: solvatation of excess-electrons, geminate recombination and development of cavitation. We found that the number of electrons produced by a strong NIR field in the cavitation regime (< 10^{19} cm^{-3}) is much lower than was thought previously. The obtained data clarify the mechanisms of laser energy deposition in water and are of crucial importance to understanding intensive light action on aqueous-based systems.

On plasmonic devices modeling: overview

Afaf Said, Khaled Atia, and Salah Obayya

DOI: 10.1364/JOSAB.399121 Received 02 Jun 2020; Accepted 07 Jul 2020; Posted 07 Jul 2020  View: PDF

Abstract: Plasmonics offers strong light localization into subwavelength dimensions beyond the diffraction limit. Therefore, plasmonics has a significant impact on realizing nano-scale photonic devices for a wide range of applications such as integrated optics, sensing, solar cells, microscopy, etc. The computational modelling of plasmonic devices provides a fundamental understanding of the relying physics. However, computational modelling of these devices is still a challenge as some of the existing modeling techniques fail to capture the correct behaviour of plasmonic devices. In this regard, this article focuses on reviewing the existing computational modeling tools for analysing plasmonic devices and highlighting their salient features and shortcomings.

Reflective photonic hook achieved by dielectric-coated concave hemi-cylindrical mirror

Cheng-Yang Liu, Hung-Ju Chung, and Hsuan-Pei E

DOI: 10.1364/JOSAB.399434 Received 05 Jun 2020; Accepted 07 Jul 2020; Posted 07 Jul 2020  View: PDF

Abstract: In this study, we propose a new design of the dielectric-coated concave hemi-cylindrical mirror for efficient generation of the reflective photonic hook (PH). The numerical approaches based on the finite-difference time-domain technique are used to investigate the physical mechanism of the reflective PH formation. The field intensity distributions and the photonic fluxes near the concave mirror are analyzed for working in the reflection mode. The asymmetric vortexes of Poynting vectors cause the reflective PH with large bending angle. By changing the refractive index of the dielectric film, the shape and the curvature of the reflective PH can be efficiently adjusted. Moreover, the narrow waist of the reflective PH is obtained beyond the half of the incident wavelength. This compact dielectric-coated concave mirror has proved its practicability for integrated photonic circuits and surface optical tweezers in the reflection mode.

Raman converter of noisy double-scale pulses into coherent pulses

Alexey Kokhanovskiy, Sergey Kobtsev, and Sergey Smirnov

DOI: 10.1364/JOSAB.398581 Received 27 May 2020; Accepted 07 Jul 2020; Posted 08 Jul 2020  View: PDF

Abstract: We propose and analyse a new mechanism for conversion of noise-like pulses into coherent ones with the help of Raman process. The conditions were identified that ensure conversion efficiency exceeding 45%. Parameter ranges were established, within which the proposed mechanism can be implemented. We also define the condition of generation of stable Raman solion molecules. The possibility of efficient conversion of noise-like pulses into coherent ones opens up new broad application fields for high-energy double-scale pulses.

Efficient method for determining pulse-front distortion in an ultra-intense laser

Zhaoyang Li and Junji Kawanaka

DOI: 10.1364/JOSAB.399433 Received 03 Jun 2020; Accepted 07 Jul 2020; Posted 08 Jul 2020  View: PDF

Abstract: We proposed a simplified method to quickly determine the pulse-front of an ultra-intense laser, which usually possesses a very long beamline and hundreds of cascaded optical elements. By deriving the wave-front and pulse-front of a pulsed beam in paraxial optical systems, we show that, in some conditions, the pulse-front overlaps with the wave-front of a specific “wavelength” whose refractive-index equals the group refractive-index. In this case, by using the commercial ray-tracing software, the pulse-front of an ultra-intense laser can be quickly determined by calculating the wave-front of this “wavelength”, and the distorted spatiotemporal optical field can also be obtained eventually. We believe this method could significantly simplify the design of an ultra-intense laser.

Enhanced Hole Transport in AlGaN Deep Ultraviolet Light-Emitting Diodes Using Double-Sided Step Graded Superlattice Electron Blocking Layer

Barsha Jain, Ravi Teja Velpula, Swetha Velpula, Hieu Nguyen, and Hoang-Duy Nguyen

DOI: 10.1364/JOSAB.399773 Received 08 Jun 2020; Accepted 07 Jul 2020; Posted 08 Jul 2020  View: PDF

Abstract: In this article, deep ultraviolet AlGaN light-emitting diodes (LEDs) with novel double-sided step graded superlattice (DSGS) electron blocking layer (EBL) instead of conventional EBL has been proposed for ~254 nm wavelength emission. The enhanced carrier transport in DSGS structure results in reduced electron leakage into the p-region, improved hole activation and hole injection, enhanced output power and external quantum efficiency. The calculations show that output power of DSGS structure is ~3.56 times higher and electron leakage is ~12 times lower, compared to conventional structure. Moreover, the efficiency droop at 60 mA in the DSGS LED was found to be ~9.1% that is ~4.5 times lower than the regular LED structure.

Coupled-mode theory for microresonators with quadratic nonlinearity

Dmitry Skryabin

DOI: 10.1364/JOSAB.397015 Received 07 May 2020; Accepted 06 Jul 2020; Posted 06 Jul 2020  View: PDF

Abstract: We use Maxwell's equations to derive several models describing the interaction of the multi-mode fundamental field and its second harmonic in a ring microresonator with quadratic nonlinearity and quasi-phase-matching. We demonstrate how multi-mode three-wave mixing sums entering nonlinear polarisation response can be calculated via Fourier transforms of products of the field envelopes. Quasi-phase-matching gratings with arbitrary profiles are incorporated seamlessly into our models. We also introduce several levels of approximations allowing to account for dispersion of nonlinear coefficients and demonstrate how coupled-mode equations can be reduced to the envelope Lugiato-Lefever-like equations with self-steepening terms. An estimate for the $\chi^{(2)}$ induced cascaded Kerr nonlinearity, in the regime of imperfect phase-matching, puts it above the intrinsic Kerr effect by several orders of magnitude.

Chirp-dispersion management inducing regeneration of truncated Airy pulses in fiber-optics links

Crépin Heuteu, Lucien Mandeng Mandeng, and Tchawoua Clement

DOI: 10.1364/JOSAB.394237 Received 14 Apr 2020; Accepted 06 Jul 2020; Posted 07 Jul 2020  View: PDF

Abstract: In this paper we introduce another technic of Airy pulsesregeneration in fiber links using the interaction between the groupvelocity dispersion (GVD) and the initial value of frequency-chirp(C). This technic, called the chirp-management dispersion (CDM),consists to manage the product of GVD chirp over each piece of fiberline in the case of zero third-order dispersion (TOD). Thealternation of both the initial chirp and GVD that conducts thisregeneration, follows the work done by [R. Driben et al, Phys. Rev.A 89, 043817 (2014)] for nonzero-TOD systems. Through numericalresults in the linear optical system, we show that the first case ofalternation with a starting condition GVD × chirp > 0, is the bestone able to yield an interesting regeneration both for a singlefinite energy Airy pulse (FEAP) and for symmetric FEAP (SFEAP)previously defined by [S. Xiaohui et al, Optics Communications 399,16- (2017)]. The main parameter which is beneficial for this kindof CDM-regeneration of Airy pulses in fiber links is found to be theinitial frequency chirp while the temporal gap and the nonlinearityhave deleterious impact on the regeneration.

Improving Visible Light Communication LocalizationSystem Using Kalman Filter

Eman Amer, Mohamed El-Shimy, Amr Mokhtar, El-Sayed El-Badawy, and Hossam Shalaby

DOI: 10.1364/JOSAB.395056 Received 13 Apr 2020; Accepted 06 Jul 2020; Posted 07 Jul 2020  View: PDF

Abstract: Two techniques are proposed for improving the accuracy of localization estimation in indoor visible lightcommunications (VLC) systems, namely averaging and Kalman filtering with averaging schemes. In theaveraging technique, the receiver position is estimated using received signal strength (RSS) indicationmethod for multiple times (e.g., N samples) and the acquired estimations are averaged over all samples.For further improving the localization, Kalman filtering algorithm is adopted to estimate the receivedpower over N samples, followed by applying RSS technique on the average received power. The proposedtechniques are analyzed mathematically, considering the effects of both line-of-sight (LOS) andfirst-reflection from non-line-of-sight (NLOS) propagations. The performance of the proposed techniquesis determined by evaluating the positioning errors at a typical room. The results are compared to that oftraditional RSS system. Simulation results reveal that an improvement of about 33.3% in the averagepositioning error is achievable when using the averaging scheme as compared to that of traditional RSSscheme. This improvement increases to 72.2% when adopting proposed Kalman filtering scheme. © 2020Optical Society of America

Sub-surface modifications in silicon with ultra-short pulsed lasers above 2 microns

Roland Richter, Nikolai Tolstik, Sébastien Rigaud, Paul Valle, Andreas Erbe, Petra Ebbinghaus, Ignas Astrauskas, Vladimir L. Kalashnikov, Evgeni Sorokin, and Irina Sorokina

DOI: 10.1364/JOSAB.396074 Received 27 Apr 2020; Accepted 05 Jul 2020; Posted 06 Jul 2020  View: PDF

Abstract: Nonlinear optical phenomena in silicon such as self-focusing and multi-photon absorption are strongly dependent on the wavelength, energy and duration of the exciting pulse, especially for the wavelengths >2 μm. We investigate the sub-surface modification of silicon using ultra-short pulsed lasers at wavelengths in the range of 1950-2400 nm, at a pulse durationbetween 2-10 ps and the pulse energy varying from 1 μJ to 1 mJ. We have performed numerical simulations and experiments using fibre-based lasers built in-house that operate in this wavelength range for the surface and sub-surface processing of Si-wafers. The results have been compared to the literature data at 1550 nm. Due to a dip in the nonlinear absorption spectrum and a peak in the spectrum of the third-order non-linearity, the wavelengths between 2000-2200 nm prove to be more favourable for reating sub-surface modifications in silicon. This is the case even though those wavelengths do not allow as tight focusing as those at 1550 nm. This is compensated by an increased self-focusing due to the nonlinear Kerr-effect around 2100 nm at high light intensities, characteristic for ultra-short pulses.

Polarization based optical fiber acoustic sensor for geological applications

James Farai Jena, Shukree Wassin, Lucian Bezuidenhout, Moctar Doucoure, and Tim Gibbon

DOI: 10.1364/JOSAB.396565 Received 30 Apr 2020; Accepted 02 Jul 2020; Posted 06 Jul 2020  View: PDF

Abstract: An interferometric fiber sensor was developed and used to detect polarization changes resulting from varying the amplitude and frequency of an acoustic signal. The sensor was designed to be suited to geological activities such as seismic tomography, detection of sinkholes, and early-warning earthquake detection. The fiber sensor and a commercial geophone were subjected to the same tests to compare their characteristic response to different vibrations. The average signal sensitivities were 9.15 a.u./mJ and 8.37 a.u./mJ for the fiber sensor and geophone, respectively. The ability of each sensor to distinguish between short, successive events showed that the fiber sensor has superior sensitivity and resolution. This is attributed to the short recovery time of the optical fiber sensor. The geophone is limited in this regard by its inherent Faraday magnet and coil damping mechanism. The bandwidth of the optical fiber sensor is shown to be 3.349 kHz, more than 20 times that of the commercial geophone.

Claddless optical fiber sensor based on evanescent wave absorption for monitoring water polluted by methylene bleu

Azil Kenza, kouider Ferria, and Bouzid Said

DOI: 10.1364/JOSAB.396646 Received 01 May 2020; Accepted 02 Jul 2020; Posted 06 Jul 2020  View: PDF

Abstract: In this paper, we present a claddless optical fiber sensor intended for distilled water solution polluted with methylene blue analysis. The optical fiber sensor is essentially based on evanescent wave absorption by the surrounding medium, at the core-liquid cladding interface. The response of the optical fiber sensor is mainly relevant to the methylene blue concentration as well as its refractive index. In this context, theoretical and experimental investigation were carried out to check the sensitivity of the proposed sensor. The obtained results have shown that the designed sensor gives a significant response at the concentration range from 6 to 50 mg/l.

Theoretical and experimental study on the enhancement of seed injection in terahertz-wave generation

Weipeng Kong, Zeyu Li, Qiang Yan, Mingrui Zou, Xun Zhou, and Yu Qin

DOI: 10.1364/JOSAB.393661 Received 25 Mar 2020; Accepted 02 Jul 2020; Posted 06 Jul 2020  View: PDF

Abstract: We have studied on the seed enhancement of injection-seeded terahertz-wave parametric generator (is-TPG) with the help of the theoretical model. During the simulation, the power of the seed beam varied from 1 W to 1 MW as the initial condition, while the pump power is set to 18.5 MW. When the peak power of the seed beam reaches megawatt level, the output power of THz wave increases rapidly and the peak position for the THz output dramatically moves towards the front of the crystal. The calculated output power of the injection pulse-seeded TPG (ips-TPG) with 0.3 MW pulsed seed is 3.4 kW in the case of surface-emit configuration and 14 kW in the case of Si-prism coupled output configuration. The enhancement ratios are 3.5 and 1.4 times respectively compared with the watt level CW-seeded is-TPG. Guided by the simulation, we experimentally demonstrated an 11 kW peak power Si-prism output coupled ips-TPG. The enhancement ratio is 1.6 times. The energy of the pulsed seed is 30 μJ (0.3 MW). The pump energy is 7.2 mJ which is about half of the typical is-TPG with the same output power. Compared with typical is-TPG, most of the THz power in ips-TPG accumulates in the front of the crystal, thus is easier to collect. One obvious advantage of ips-TPG is that the output THz energy can be increased while keeping the pump power at the safe level.

The use of FTIR microspectroscopy and chemometric analysis in the discrimination between Egyptian ancient bones: A case study

Ahmed Mohamed kamel, Ibraheem Yousef, and Mohamed Kasem

DOI: 10.1364/JOSAB.397419 Received 18 May 2020; Accepted 02 Jul 2020; Posted 07 Jul 2020  View: PDF

Abstract: Bones are one of the hardest tissues in human body as they are mostly composed of analogous volume fractions of collagen as organic material and apatite as minerals. Bones undergo several complicated depositional variation in the calcified tissues after being buried. These processes are known as diagenesis. The latter is affected and influenced by multiple cross linked factors such as the nature of burial soil, temperatures, humidity, pH and many intrinsic factors. But since bones are hard tissues, they could withstand for a longer period such extrinsic and intrinsic components when compared to other tissues. Subsequently, they can confer many crucial and vital data by their elemental and molecular investigations. Fourier Transform Infrared FTIR microspectroscopy is a powerful molecular spectroscopic tool that can trace the molecular changes that were caused by diagenesis with high spatial resolution and hence indicate the preservation degree of the specimen under study. The current research is a case study that aimed to probe the diagenetic changes across different depth sections of bone shafts. The bone shafts belong to two ancient Egyptian dynasties namely Roman Greek (RG) and Late Period (LP) and they were collected from Saqqara, Egypt. We used FTIR microspectroscopy for generating IR chemical images for those bones. The technique is characterized by precision, accuracy and reproducibility. Identifying the morphology and the size of apatite crystal of the bone were investigated by transmission electron microscopy (TEM). Chemometric analysis namely principal component analysis (PCA) was applied to elucidate its capabilities by analysing the FTIR spectra for the differentiation between the two bones samples as well as the different regions in the same bones according to the diagenetic changes. Five main molecular bands were investigated using the PCA: Amide I (1700-1600 cm-1), phosphate (1145 cm-1- 980 cm-1), carbonyl (1485-1450 cm-1) V2 carbonate (885-870 cm-1 and V3 carbonate (1432-1365 cm-1).The chemical images showed clearly different diagenetic changes throughout the different regions of the same bone section via the changes in the contents of Amide I, carbonate and phosphate bands as well as using the indices of Amide I/phosphate and V3-Carbonate/Phosphate ratios. PCA efficiently discriminated between the two dynasties bones as well as differentiated between various depth regions from the same bone section using the above mentioned molecular bands. Finally, TEM demonstrated that the apatite crystals of LP bone shaft were shown to be less abundant, needle shape and ranging between 15 to 30 nm in size, while those of RG bone shaft were smaller with a size of about 10 nm and irregular thin platelet shape.

Theory of coherent active convolved illumination for superresolution enhancement

Durdu Guney, Anindya Ghoshroy, and Wyatt Adams

DOI: 10.1364/JOSAB.395122 Received 15 Apr 2020; Accepted 01 Jul 2020; Posted 01 Jul 2020  View: PDF

Abstract: Recently an optical amplification process called the plasmon injection scheme was introduced as an effective solution to overcoming losses in metamaterials. Implementations with near-field imaging applications have indicated substantial performance enhancements even in the presence of noise. This powerful and versatile compensation technique, which has since been renamed to a more generalized active convolved illumination, offers new possibilities of improving the performance of many previously conceived metamaterial-based devices and conventional imaging systems. In this work, we present the first comprehensive mathematical breakdown of active convolved illumination for coherent imaging. Our analysis highlights the distinctive features of active convolved illumination, such as selective spectral amplification and correlations, and provides a rigorous understanding of the loss compensation process. These features are achieved by an auxiliary source coherently superimposed with the object field. The auxiliary source is designed to have three important properties. First, it is correlated with the object field. Second, it is defined over a finite spectral bandwidth. Third, it is amplified over that selected bandwidth. We derive the noise variance for the image spectrum and show that utilizing the auxiliary source with the above properties can significantly improve the spectral signal-to-noise ratio and resolution limit. We find that the resolution limit for an arbitrary object can be in the end extended by more than $70\%$ using a passive spatial filter with a bandwidth of $4k_0$, where $k_0$ is the free space wavenumber, centered around $10k_0$ and illuminated with an intensity of about $0.03mW/{\mu}m^2$. Beyond enhanced superresolution imaging, the theory can be potentially generalized to the compensation of information or photon loss in a wide variety of coherent and incoherent linear systems including those, for example, in atmospheric imaging, time-domain spectroscopy, ${\cal PT}$ symmetric non-Hermitian photonics, and even quantum computing.

Pre-chirp managed self-phase modulation for efficient generation of wavelength tunable energetic femtosecond pulses

Guoqing Chang and Runzhi Chen

DOI: 10.1364/JOSAB.395275 Received 15 Apr 2020; Accepted 01 Jul 2020; Posted 02 Jul 2020  View: PDF

Abstract: Self-phase modulation Enabled Spectral Selection (SESS) allows generation of widely tunable femtosecond pulses. We propose pre-chirp managed SESS, in which the excitation pulse is properly pre-chirped to control the fiber-optic nonlinear spectral broadening and hence generate separated spectral lobes—a feature demanded by SESS. Besides offering improved efficiency compared with conventional energy-tuned SESS, this new method is able to reshape an input flat-top pulse into a bell-shape pulse that is desired for implementing SESS. The excellent energy scalability of pre-chip managed SESS can produce megawatt-level femtosecond pulses widely tunable in the wavelength range of 0.86-1.3 µm. Such a powerful source is well suited to drive multiphoton microscopy to achieve deep tissue imaging.

Efficient formation and tunability of optical scattering directivity of surface-waves by a linear array of nanoantennas on a metallic film

Mahdi Hosseinmardi and Tavakol Pakizeh

DOI: 10.1364/JOSAB.397025 Received 07 May 2020; Accepted 01 Jul 2020; Posted 02 Jul 2020  View: PDF

Abstract: Photonic spin-Hall effect (PSHE) related to spin-orbit interaction (SOI) of light leads to spin-momentum locking of longitudinal-spin photons of a pump beam into transverse-spin photons of an inherently circularly-polarized (CP) surface wave like surface plasmon polaritons (SPPs). An excited nanoparticle (NP) above a metal-dielectric interface (MDI) optically couples a pump beam and the SPP, though an array of NPs may provide a desired and remarkable scattering directivity pattern (SDP). Here, we show that how a linear array of alike nanoantennas (NAs) illuminated by an optical beam with different wave-polarizations and incidence directions forms the unique SDPs, and how the PSHE affects on the propagation direction of the scattered SPPs and their SDPs. The scattering patterns for the excited surface-wave with remarkable tunability and functionality are studied in two principle cases, namely broadside and endfire, in which the PSHE may efficiently emerge. The theoretical results developed based on Green’s tensor approach (GTA) accompanied by the mode matching technique and quasistatic modeling are in good agreement with the computational results. In this way, crucial parameters effects on the SDPs such as the elements’ spacing and number in the array are thoroughly investigated. The reported results pave a way to adaptively engineer the scattering formation of the SPP-type waves for surface optics and photonics applications.

MGSI, A Single Source Formulation for the Analysis of Electromagnetic Penetrable Objects

Hoda Ameri and Reza Faraji-Dana

DOI: 10.1364/JOSAB.386663 Received 02 Jan 2020; Accepted 30 Jun 2020; Posted 01 Jul 2020  View: PDF

Abstract: Modified Global Surface Impedance (MGSI) formulation, a fast and efficient single source integral equation for analyzing penetrable objects including plasmonic circuits and dielectric periodic structures is proposed. Using the equivalence principle, a single source formulation for the exterior region of the desired problem is constructed. Then the assumed equivalent source (surface electric current) is written as the sum of two surface electric currents, one related to the other based on the global surface impedance (GSI) model. Thus, the conventional surface integral equation (SIE) for the exterior problem will be modified by this new single source formulation. The interior problem is also formulated using the GSI model resulting in our proposed MGSI formulation. MGSI, eliminates the need for equivalent magnetic current in the SIE formulation. It also helps one to formulate the interior and exterior problems independently. Moreover, in our approach material property does not affect the problem convergence, while the convergence of conventional SIE deteriorates for a plasmonic structure and also for a dielectric object with high contrast to its surrounding medium. The accuracy and efficiency of the proposed formulation are demonstrated by comparing its results with the conventional SIE in solving several examples.

Spiking dynamics of frequency up-converted field generated in continuous-wave excited rubidium vapours

Alexander Akulshin, Nafia Rahaman, Sergey Suslov, Dmitry Budker, and Russell McLean

DOI: 10.1364/JOSAB.395087 Received 14 Apr 2020; Accepted 30 Jun 2020; Posted 01 Jul 2020  View: PDF

Abstract: We report on spiking dynamics of frequency up-converted emission at 420 nm generated on the 6P3/2-5S1/2 transition in Rb vapour two-photon excited to the 5D5/2 level with laser light at 780 and 776 nm. The spike duration is shorter than the natural lifetime of any excited level involved in the interaction with both continuous and pulsed pump radiation. The spikes at 420 nm are attributed to temporal properties of the directional emission at 5. μm generated on the population-inverted 5D5/2-6P3/2 transition. A link between the spiking regime and cooperative effects is discussed. We suggest that the observed stochastic behaviour is due to the quantum-mechanical nature of the cooperative effects rather than random fluctuation of the applied laser fields.

Theory of fifth harmonic generation in cubic centrosymmetric crystals

Hiroki Nishizawa

DOI: 10.1364/JOSAB.396073 Received 23 Apr 2020; Accepted 30 Jun 2020; Posted 01 Jul 2020  View: PDF

Abstract: We derive wave equations for fifth harmonic generation in cubic centrosymmetric crystals generated in direct and indirect processes when an incident electric field propagates along a cubic axis. We elucidate the dependence of fifth harmonic fields on crystal length and polarization directions of an incident field. We devise a method to measure elements of a fifth-order nonlinear susceptibility tensor in the transparent regime by measurement of fifth harmonic intensity in crystals of different lengths.

Combining FDTD and coupled-mode theory for self-pulsing modeling in coupled nonlinear microring resonators

Nessim Jebali, Loic Bodiou, Joel Charrier, Andrea Armaroli, and Yannick Dumeige

DOI: 10.1364/JOSAB.399879 Received 09 Jun 2020; Accepted 30 Jun 2020; Posted 01 Jul 2020  View: PDF

Abstract: By means of finite-difference time-domain (FDTD) simulations, the stationary and dynamic responses of coupled optical microring resonators made with a material exhibiting an instantaneous Kerr non-linearity are numerically investigated. We compare the results with the coupled mode theory (CMT) and find a good agreement. We demonstrate by integrating Maxwell's equations that this system can show a self-pulsing operation in the normal dispersion regime. Finally this work shows that FDTD simulations can be combined with a CMT analysis for the purpose of designing optical functions whose operation is based on nonlinear coupled micro-resonators.

Investigation of analog signal distortion introduced by a fiber phase sensitive amplifier

debanuj chatterjee, Yousra Bouasria, Weilin Xie, Tarek Labidi, Fabien Bretenaker, Fabienne Goldfarb, and Ihsan Fsaifes

DOI: 10.1364/JOSAB.397469 Received 11 May 2020; Accepted 29 Jun 2020; Posted 29 Jun 2020  View: PDF

Abstract: We numerically simulate the distortion of an analog signal carried in a microwave photonics link containing a phase sensitive amplifier (PSA), focusing mainly on amplitude modulation format. The numerical model is validated by comparison with experimental measurements. By using the well known two-tone test, we compare the situations in which a standard intensity modulator is used with the one where a perfectly linear modulator would be employed. We also investigate the role of gain saturation on the nonlinearity of the PSA. Finally, we establish the conditions, in which the signal nonlinearity introduced by the PSA itself can be extremely small.

Influence of chirped pump shape on the two-pump fiber optical parametric amplification

ZhenYu Zhu, Hongna Zhu, Hao Sui, Le Cheng, lei Yu, Yufeng Zhang, Stefano Taccheo, and Bing Luo

DOI: 10.1364/JOSAB.399524 Received 04 Jun 2020; Accepted 29 Jun 2020; Posted 02 Jul 2020  View: PDF

Abstract: The gain performance of two-pump fiber optical parametric amplifier (FOPA) pumped by different kinds of chirped pump pulses are investigated numerically. It shows that, the gain performances of FOPA are evidently influenced by the shapes of chirped pump pulse. The highest and broadest gain spectrum is obtained with the 10th order super-Gaussian pulse in case of identical energy and full width at half maximum of the pump pulse. Besides, the signal gain is also affected by the poor symmetry of pump pulse which leads to a low gain performance.

Suppressing amplified spontaneous emission in high-power 1018-nm monolithic fiber laser by decreasing the feedback from the inner reflections

Jiading Tian, Qirong Xiao, Dan Li, Zhoutian Liu, Weilong Yu, Ping Yan, and Mali Gong

DOI: 10.1364/JOSAB.396541 Received 05 May 2020; Accepted 28 Jun 2020; Posted 30 Jun 2020  View: PDF

Abstract: We showed that to decrease the feedback that comes from the inner reflections of the counter-propagating light could suppress the amplified spontaneous emission (ASE) in the output of 1018-nm fiber lasers. With a simulation model to solve power spectrum of multiple signals, we calculated the values of the feedback required for the aimed power scaling. We realized the low feedback by modifying the counter-propagating side of the setup, which included a home-made cladding light stripper on a no-core fiber that was angle-cleaved. With that, we demonstrated a 1018-nm monolithic fiber laser producing 506.4 W with 1.58-M2 beam quality, 84.9% optical-optical efficiency and 148-pm linewidth. The maximum intensity of the ASE noises was >50-dB lower than that of the 1018-nm signal, which could allow further power scaling with safety and stability.

Laser research on the African continent

Hubertus Von Bergman

DOI: 10.1364/JOSAB.398821 Received 28 May 2020; Accepted 27 Jun 2020; Posted 29 Jun 2020  View: PDF

Abstract: This article reviews the history and current state of laser and laser related research on the African continent. The major laser centres in North, West and Southern Africa are discussed and their current research activities reviewed. Laser related networks operating on the continent are introduced and their impact on the development of laser centres discussed. Commercial companies involved in laser manufacture are identified and finally an outlook on future developments will be attempted.

Tunable radiative cooling based on stretchable selective optical filter

Xinhang Liu, Sijie Pian, Rong Zhou, Hao Shen, Xu Liu, Qing Yang, and Yaoguang Ma

DOI: 10.1364/JOSAB.394671 Received 17 Apr 2020; Accepted 27 Jun 2020; Posted 06 Jul 2020  View: PDF

Abstract: Radiative cooling has the potential to drastically improve a wide range of energy conversion and utilization processes on Earth. However, the lack of tunability may limit its application in practical scenarios such as buildings, vehicles, and textiles. In this paper, we propose a new approach to achieve tunable radiative cooling through a stretchable multilayer filter. The cooling power can be continuously modulated by mechanical stretching which only requires a small among of energy. This filter can be combined with existing static radiative cooling systems to achieve efficient and continuous regulation of cooling power.

Terahertz wave generation in aperiodically poled lithium niobate by cascaded difference frequency generation with efficiency in excess of 30% at cryogenic temperature

zhongyang li, Xiangqian Sun, Hongtao Zhang, Yongjun Li, Bin Yuan, Binzhe Jiao, Jia Zhao, Lian Tan, Bing Pibin, Zhan Wang, and Jian-Quan Yao

DOI: 10.1364/JOSAB.390137 Received 10 Feb 2020; Accepted 27 Jun 2020; Posted 29 Jun 2020  View: PDF

Abstract: In this work, we investigate the characteristics of cascaded difference frequency generation (CDFG) generating terahertz (THz) waves and explore the essential factors that affect the THz intensity. Based on the analysis results we propose a high-efficiency THz wave generation approach by CDFG with an aperiodically poled lithium niobate (APPLN) crystal at cryogenic temperature. The APPLN crystal with desirable poling periods along crystal length determines phase mismatches of each-order CDFG, resulting in a decrement of phase mismatches in cascaded Stokes processes and an increment of phase mismatches in cascaded anti-Stokes processes simultaneously. This is in contrast to previous works on CDFG, where THz wave is generated with irreversible phase mismatches in cascaded Stokes and anti-Stokes processes. The variations of phase mismatches enhance the evolution of optical spectra in cascaded Stokes processes, and restrain the evolution of optical spectra in cascaded anti-Stokes processes, yielding unprecedented energy efficiencies in excess of 30% from optical wave to THz wave with APPLN at a temperature of 10 K. Compared with the maximum THz intensity from traditional CDFG using periodically poled lithium niobate (PPLN), the maximum THz intensities are enhanced by 2.5 and 2.8 times using APPLN with stepwise changing and gradually changing poling periods, respectively.

Degenerate four-wave mixing in THz with standing-wave graphene resonators

Thomas Christopoulos, Odysseas Tsilipakos, and Emmanouil Kriezis

DOI: 10.1364/JOSAB.395461 Received 21 Apr 2020; Accepted 27 Jun 2020; Posted 29 Jun 2020  View: PDF

Abstract: Graphene is one the most promising 2D materials for functional electromagnetic components. Harnessing graphene’s high third-order nonlinearity, a standing-wave resonant system is proposed that realizes low-power and high-conversion-efficiency degenerate four-wave mixing in the THz regime. The proposed system is analyzed in depth, utilizing a recently developed nonlinear framework based on perturbation theory and temporal coupled-mode theory, which allows for efficient design, accurate results and physical insight into the system performance. Following robust design guidelines derived from the developed framework, a clear design path is highlighted, covering two possible realizations of the coupling scheme using one or two waveguides as physical ports. The two systems are compared on the basis of input power and conversion efficiency performance metrics, accurately extracted taking into account all relevant nonlinear phenomena including the nonlinear resonance frequency shifts due to self- and cross-phase modulation in graphene, owing to the Kerr effect. The reported values of 10% conversion efficiency and sub-mW power requirements are highly promising for practical applications, highlighting the potential of graphene-based structures in the far-infrared.

Nonlinear dynamical control of giant resonant Goos-Hanchen shift

Alexander Zharov, Nina Zharova, and Alexander Zharov

DOI: 10.1364/JOSAB.395162 Received 15 Apr 2020; Accepted 25 Jun 2020; Posted 25 Jun 2020  View: PDF

Abstract: An analytical approach is developed for the calculation of dynamical Goos-Hanchen (GH) shift in a layered dielectric structure, which provides waveguiding of a high-quality-factor leaky eigenmode and lateral energy transfer.The analysis is based on the master equation for slow amplitude of the mode excited by impinging light, and it allows to relate reflected and transmitted fields to the incident radiation in a general case of nonlinear and non-stationary processes.The corresponding numerical calculations demonstrate giant GH shifts for the reflected and transmitted beams.It is shown that the value and sign of the GH shift for the reflected and transmitted beamscan be controlled by the incident field intensity and/or incident pulse duration.

From unexceptional to doubly exceptional surface waves

Akhlesh Lakhtakia and Tom Mackay

DOI: 10.1364/JOSAB.399403 Received 03 Jun 2020; Accepted 25 Jun 2020; Posted 26 Jun 2020  View: PDF

Abstract: Anexceptional surface wave can propagate in an isolated direction, whenguided by the planar interface of two homogeneous dielectricpartnering mediums of which at least one is anisotropic,providedthat the constitutive parameters of the partnering mediums satisfy certain constraints.Exceptional surface waves are distinguished from unexceptional surface waves by their localization characteristics: the fieldsof an exceptionalsurface wave in the anisotropic partnering medium decayas a combined linear-exponential function of distance from the interface, whereas the decay is purelyexponential for an unexceptional surface wave. If both partnering mediums are anisotropic then a doubly exceptional surface wave can exist for an isolated propagation direction. The decay of this wave in both partnering mediums is governed by a combined linear-exponential function of distance from the interface.

Random laser spectroscopy of solvent-rich polymer thin film waveguide

Priyanka Choubey, Anirban SARKAR, Shailendra Varshney, and Shivakiran Bhaktha B.N.

DOI: 10.1364/JOSAB.399091 Received 01 Jun 2020; Accepted 24 Jun 2020; Posted 29 Jun 2020  View: PDF

Abstract: We present the statistical analysis of random lasing intensity fluctuations in a 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminos-styryl)-4H-pyran (DCM) doped polyvinyl alcohol (PVA) thin film waveguide subjected to a constant heat-treatment. The microscopic changes occurring in the density of the polymer thin film during the various stages of solvent evaporation are probed using the changes in the statistics of random laser (RL) emission intensities. In the solvent rich wet-film, stronger RL emission intensity fluctuations are observed compared to the dried film, leading to a relatively slower decay of the survival function distribution of the emission intensities for a mode at the gain maxima of the averaged spectrum. The mode interactions in the wet and dried films, studied using covariance between lasing mode intensities, are found to be different. Further, replica symmetry breaking studies indicate the changes in the mode interactions with the microscopic modifications in the system during solvent evaporation at constant pump energy above the lasing threshold. The statistical analyses of the RL emission intensity fluctuations are proposed as a spectroscopic tool to probe material properties.

Tailoring the waveguide dispersion of nonlinear fibers for supercontinuum generation with superior intrapulse coherence

Chao Mei and Gunter Steinmeyer

DOI: 10.1364/JOSAB.396511 Received 29 Apr 2020; Accepted 24 Jun 2020; Posted 25 Jun 2020  View: PDF

Abstract: Spectral coherence is an important prerequisite for many applications of femtosecond supercontinua, including precision frequency metrology, attosecond science, and high-field physics. These applications often critically depend on measurement of the carrier-envelope phase via f -2 f interferometry. As modelocked laser sources cannot directly provide octave-spanning spectra, one typically resorts to spectral broadening in highly nonlinear optical fibers to generate the necessary spectral coverage. This process comes with a caveat as coherence can be severely degraded in the broadening process. This degradation can be mitigated by suitable choice of a fiber dispersion profile. Here we numerically investigate prototypical fiber designs and analyze their susceptibility to coherence degradation. It is found that the generally favored soliton fission process provides the best broadening efficiency at the expense of rather scarce coherence conditions. Sufficient pulse energy provided, all-normally dispersive fiber designs fare far better in terms of spectral coherence. Finally, fiber designs with flattened normal dispersion provide the best compromise between efficiency and resulting spectral coherence. Our study indicates that the spectral width of a supercontinuum may be deceiving. Even when compressible into a short pulse, this does not automatically qualify for sufficient spectral coherence to conduct carrier-envelope-phase sensitive experiments. The numerical simulations in this study provide a guideline for coherent spectral broadening. In turn, these guidelines may help to improve carrier-envelope phase stabilization and, in particular, to enable stabilization of laser oscillators, which have previously proven difficult to stabilize.

Observing the Goos Hanchen Shift for a planarinterface of dielectric and general anisotropic medium

Waleed waseer, Rashda Ali, QAisar Naqvi, and M.J. Mughal

DOI: 10.1364/JOSAB.391973 Received 12 Mar 2020; Accepted 24 Jun 2020; Posted 24 Jun 2020  View: PDF

Abstract: Goos Hanchen (GH) shift from a planar interface of dielectric and generalanisotropic medium is determined and investigated. Knowing the fact thatwavevector plane for anisotropic medium can be divided into four regions: supporting propagating, propagating & evanescent, evanescent, and non-uniform(ghost) waves. Tangential components of the incident wavevector are adjusted in order to address these regions one by one. Possibility of existence/non-existence of GH shift for waves related to these regions is reported.

Whispering gallery modes in triple microdisks of triangular configurations

Jung-Wan Ryu and Sunghwan Rim

DOI: 10.1364/JOSAB.392994 Received 18 Mar 2020; Accepted 24 Jun 2020; Posted 25 Jun 2020  View: PDF

Abstract: We study whispering gallery modes in triple microdisks of equilateral and isosceles triangular configurations. The characteristic properties of resonant modes in three microdisks on vertices of an equilateral triangle are explained by discrete rotational symmetry of the triangle. The avoided crossings of resonant modes in three microdisks on vertices of an isosceles triangle are also studied in terms of a combination of single and coupled microdisks. In addition, we propose the matrix models which well explain the resonant modes in triple microdisks.

Long-lived quantum coherence and Nonlinear Properties of a Two-Dimensional Semiconductor Quantum Well

Doaa Abukahla

DOI: 10.1364/JOSAB.393367 Received 24 Mar 2020; Accepted 24 Jun 2020; Posted 25 Jun 2020  View: PDF

Abstract: In this paper, we present an analytical solution for the Maxwell-Bloch equations of the two-level semiconductor quantum well, GaAs\AlGaAs. In addition, we discuss the effects of the coherent Rabi oscillations Ω(t) and the frequency of the semiconductor system υ(t) on the atomic occupation probabilities, ρ11(t) and ρ22(t), the population inversion, ρz(t), and the information entropies, H(σx), H(σy) and H(σz). We observe clearly the emergence of Long-lived quantum coherence and the decay in the curvesfor some special cases of Ω(t) and υ(t). Besides, we show that the dynamic nonlinear properties of the system can be controlled by changing the values of the coherent Rabi oscillations Ω(t) and the frequency of the semiconductor system υ(t). Due to the lack of mathematical treatment of such systems, our study promises significant advantages for a large number of nonlinear dynamic systems, opening up a wide range of applications for semiconductors quantum wells.

Cylindrical silicon near-IR optical amplifier driven by direct current

Aleksei Abramov, Igor Zolotovskii, Alexey Kadochkin, Sergey Moiseev, Dmitry Sannikov, Vyacheslav Svetukhin, Marina Yavtushenko, and Andrei Fotiadi

DOI: 10.1364/JOSAB.390277 Received 10 Feb 2020; Accepted 23 Jun 2020; Posted 24 Jun 2020  View: PDF

Abstract: We propose the mechanism enabling amplification of the surface tunneling modes propagating over the semiconductor cylinder surface pumped by a direct current. Amplification of a whispering gallery mode with a net gain as high as 103 cm^( -1) is demonstrated.

Rectangular Maxwell’s fisheye lens via transformation optics as a crossing medium for dissimilar waveguides

Seyed Hadi Badri, Mohsen Mohammadzadeh Gilarlue, and Hemed Taghipour-Farshi

DOI: 10.1364/JOSAB.392644 Received 10 Mar 2020; Accepted 23 Jun 2020; Posted 09 Jul 2020  View: PDF

Abstract: Different material platforms, each offering a set of unique advantages, have been introduced for photonic integrated circuits. These platforms may be used in the same photonic chip to explore their advantages. Consequently, the in-plane crossing of dissimilar waveguides may be inevitable. In this paper, we investigate for the first time, to our knowledge, the crossing of silicon nitride (Si3N¬4) and silicon (Si) strip waveguides. Recently, the imaging property of the Maxwell’s fisheye lens has been exploited to design waveguide crossings. However, the refractive indices of Si3N¬4 and Si are different by about 1.45 so the crossing medium should have different refractive indices at its edges to minimize reflection from the interface of the waveguide and the crossing medium. We utilize quasi-conformal transformation optics to design a rectangular Maxwell’s fisheye lens as a crossing medium of Si3N¬4 and Si strip waveguides. We implement the rectangular lens with graded photonic crystal and numerically evaluate the performance of the designed waveguide crossing.

Coupling coefficients of waveguide gratings with double-negative material films

Abdollah Hassanzadeh and Nazanin KAKOOLAKI

DOI: 10.1364/JOSAB.386117 Received 20 Dec 2019; Accepted 22 Jun 2020; Posted 22 Jun 2020  View: PDF

Abstract: The propagation of waves in waveguide gratings with a double negative film but double-positive cover and substrate is studied. Perturbation theory is used to derive expressions that approximate the transverse and longitudinal coupling coefficients for coupling between various transverse magnetic guided modes in a three-layer waveguide with a rectangular grating profile at the film-cover interface. An analytical method is then used to draw the coupling coefficients curves as functions of the film thickness. The curves of the waveguide gratings with double negative material film differ significantly from that of the conventional waveguide gratings and those with double negative cover. Numerical results show that the obtained coupling coefficients are much higher than that of conventional waveguide gratings. Waveguide gratings with double negative film possess a number of unusual properties. We show that the coupling coefficient of the fundamental mode does not exist and the first-order mode is confined within a narrow film thickness range and cannot couple to any other mode. The coexistence of both the longitudinal and transverse coupling coefficients with the same order of magnitude, double degeneracy of the modes and double degeneracy of the coupling coefficients near the cutoff are other unusual properties of the proposed structure.

Numerical analysis of amplified spontaneous emission of thin disk laser with adjustable ring pump spot

Keming Chen, Guangzhi Zhu, Biaoping Gu, Hailin Wang, Kozlov Aleksei, and Xiao Zhu

DOI: 10.1364/JOSAB.394928 Received 13 Apr 2020; Accepted 22 Jun 2020; Posted 22 Jun 2020  View: PDF

Abstract: The amplified spontaneous emission (ASE) effect is a major factor affecting large size, high gain Yb:YAG thin disk lasers. In this paper, considering the reabsorption effect of the quasi-three-level Yb:YAG crystal, an adjustable ring rump spot (ARPs) is proposed to suppress the ASE effect. A numerical integration model is built to calculate the output power density, the distribution of ASE photon flux density, and gain coefficient of the ARPs. Compared with the circle pump spot (CPs), hollow pump spot (HPs), the reabsorption effect in the ring shaped un-pumping region of the ARPs has a good balance between the ASE photon amplification in the pumping areas and attenuation in the un-pumping area in the thin disk crystal. Significant improvement of suppression ability of ASE effect can be achieved by using the ARPs with an optimal position of the ring shaped un-pumping area, especially for the larger pump spot.

Ultrathin, Polarization-Insensitive Multi-Band Absorbers Based on Graphene Metasurface with THz Sensing Application

Saeedeh Barzegar-Parizi and Amir Ebrahimi

DOI: 10.1364/JOSAB.396266 Received 29 Apr 2020; Accepted 22 Jun 2020; Posted 23 Jun 2020  View: PDF

Abstract: This article presents multi-band plasmonic absorbers based on graphene array at terahertz frequencies. The absorbers are made of a very simple structure including a graphene disk array printed on the top surface of a dielectric spacer backed by a metallic ground plane. Multi-band performance is achieved with more than 90% absorption in 1 – 8 THz frequency range by exciting surface plasmon polaritons of graphene. It is shown that the resonance frequencies of the proposed absorber can be tuned by varying the chemical potential between 0.8 – 1 eV for triple-band absorber and 0.7 – 0.9 eV for quad-band one, while keeping more than 80% absorption. The results obtained by means of the simulation are verified with the results obtained by the analytical circuit model. The proposed absorbers are polarization-insensitive and provide stable absorption performance for both of the TE and TM polarizations. As an application, we designed a refractive index sensor based on the triple-band absorber. The results verify that the absorption bands are sensitive to the variations of the refractive index of the coating layer.

Routes to Chaos and characterization of limit-cycleoscillations in wide-band time-delayed optoelectronicoscillators with nonlinear filters.

Jimmi Hervé Talla Mbé, JULIETTE STEVIA DEUMI KAMAHA, and Paul Woafo

DOI: 10.1364/JOSAB.396596 Received 30 Apr 2020; Accepted 20 Jun 2020; Posted 22 Jun 2020  View: PDF

Abstract: In this paper, we show that the novel cubic-nonlinear optoelectronic oscillator (CN-OEO) [1] depicts the phenomena of amplitude jump and crenelated oscillations in its routes to chaos. The amplitude jump is characterized by a sudden variation of the frequency of the limit-cycle oscillations. Using the normal form of the system, we characterize the limit-cycle oscillations. The amplitude and the frequency of these limit-cycle oscillations are determined mathematically and analyzed in terms of the system parameters such as the time-delay and the feedback gain. It is analytically confirmed that the CN-OEO displays limit-cycle oscillations whose frequencies remain greater than those of a standard optoelectronic oscillator (the one with a standard band-pass filter in the electrical path). Our experimental measurements are in good agreement with the analytical and numerical results.

Exceptional Point of Sixth Order Degeneracy in a Modified Coupled Resonators Optical Waveguide

Mohamed Nada and Filippo Capolino

DOI: 10.1364/JOSAB.385198 Received 05 Dec 2019; Accepted 19 Jun 2020; Posted 22 Jun 2020  View: PDF

Abstract: We demonstrate for the first time the occurrence of a sixth order exceptional point of degeneracy (EPD) in a realistic multimode optical photonic structure by using a modified periodic coupled resonators optical waveguide (CROW), at the optical wavelength λe=1550 nm . The 6th order EPD is obtained in a CROW without the need of loss or gain and such an EPD corresponds to a very special band edge of the periodic photonic structure where six eigenmode coalesce, so we refer to it as the 6th order degenerate band edge (6DBE). Moreover, we report a new scaling law of the quality factor Q of an optical cavity made of such a periodic 6DBE-CROW with cavity length as Q=N^7 , when operating near the 6DBE with N being the number of unit cells in the periodic finite-length CROW. Furthermore, we elaborate on two applications of the 6DBE: highly sensitive sensor, and ultra-low-threshold lasers. We present a novel scaling law of the lasing threshold that scales as N^{-7} when operating near the 6DBE. Also, we show the superiority of the threshold scaling of the 6DBE-CROW to the scaling of another CROW with the same size operating near a 4th order EPD that is often referred to as the degenerate band edge (DBE). The lasing threshold scaling of the DBE-CROW is shown for the first time in this paper. The proposed 6DBE-CROW may also find applications in modulators, optical switches, nonlinear devices, and Q-switching cavities.

Optimal quantum phase estimation with generalized multi-component cat states

Seung-Woo Lee, Su-Yong Lee, and Jaewan Kim

DOI: 10.1364/JOSAB.393200 Received 31 Mar 2020; Accepted 19 Jun 2020; Posted 22 Jun 2020  View: PDF

Abstract: We are interested in detecting the presence of a nearby object which is phase-sensitive, where a traveling light works out under a low photon loss rate. Here we investigate the optimal quantum phase estimation with generalized multi-component cat states. We show the optimal conditions of the generalized multi-component cat states for the phase estimation in a lossless scenario. We then demonstrate that the generalized multi-component cat states beat the performances of a NOON state in the presence of small loss, while maintaining the quantum advantage over the standard quantum limit which is attainable by coherent states. Finally, we propose a generation scheme of the entangled multi-component cat states with current or near-term optical technologies.

Slow Light Assisted Electrical Tuning in Hollow Optical Waveguide via Carrier Depletion in Silicon and Indium Tin Oxide Sub-wavelength Gratings

SWATI RAJPUT, VISHAL KAUSHIK, Sourabh Jain, and Mukesh Kumar

DOI: 10.1364/JOSAB.390741 Received 18 Feb 2020; Accepted 18 Jun 2020; Posted 19 Jun 2020  View: PDF

Abstract: An electrically tunable hollow optical waveguide based on Silicon-Indium Tin Oxide (ITO) gratings is proposed to achieve phase modulation. The hollow waveguide consisting of Si-ITO gratings as top and bottom reflectors supports the propagation of slow light mode with a high group index of 71 and a loss of 0.1dB/cm in a narrow 1μm thick air-core at 1550nm. Carrier depletion in p-type Si and n-type ITO enables electrically controlled phase modulation of the guided slow light mode. With the slow light effect 180° phase modulation is obtained in a short device-length of 3mm with a maximum reverse bias of -5Volts and 3dB modulation bandwidth of 63 GHz.

Investigation of C-band pumping for extended L-band EDFAs

Chengmin Lei, Hanlin Feng, Younes Messaddeq, and Sophie LaRochelle

DOI: 10.1364/JOSAB.392291 Received 10 Mar 2020; Accepted 18 Jun 2020; Posted 19 Jun 2020  View: PDF

Abstract: In this study, we present systematic numerical and experimental analysis of high-power C-band light pumping in extended L-band EDFAs. We investigate, for the first time to our best knowledge, how C-band light sources can be used as pump sources to extend the bandwidth of L-band EDFAs beyond 1610 nm. Results show that, when using a C-band light source as the sole pump, efficient amplification is obtained over the extended L-band but at the expense of higher noise figure. However, the advantage of C-band pumping in terms of power conversion efficiency can be exploited when using a two-stage EDFA, with a first stage pumped by 1480 nm to maintain good noise figure performance and a high-power C-band light source (up to several hundred mW) as the pump source for the second stage. Thus, a 20-dB gain covering 1570-1618 nm with a maximum noise figure of 5.7 dB is demonstrated.

Coexistence of bright and dark soliton Kerr combs inzero, normal, and anomalous group-velocity dispersion resonators: a switching wave approach

Jimmi Hervé Talla Mbé and Yanne Chembo

DOI: 10.1364/JOSAB.396610 Received 30 Apr 2020; Accepted 18 Jun 2020; Posted 19 Jun 2020  View: PDF

Abstract: We propose a theoretical study to analyze how both stable dark and bright soliton Kerr combs can be generated within the various regimes of the group-velocity dispersion, namely normal, anomalous, and null.The coexistence of these solitonic structures in each regime is shown to appear around a critical optical cavity pump. We also evidence that these solitons are built up owing to the mechanism of oscillation locking of switching waves connecting the upper and the lower homogenous steady states.

Single channel high transmission optical band-pass filter based on plasmonic Nano-cavities

Masoud Mardani, Samane Vahidi, hassn ghafoorifard, and Mahsa Valizadeh

DOI: 10.1364/JOSAB.392042 Received 10 Mar 2020; Accepted 13 May 2020; Posted 19 Jun 2020  View: PDF

Abstract: This paper is concerned with the investigation of an optical band-pass filter based on sub-wavelength surface plasmon polariton. The transmission characteristics are numerically analyzed by the finite difference time domain method and simulation results reveal that the structure has a band-pass filtering characteristic. The metal-insulator-metal plasmonic nanostructure is implemented by several vertical rectangular cavities across an optical waveguide. The metal and dielectric materials utilized for the realization of the filter are silver and air, respectively. Furthermore, the performance can be efficiently modified by tuning the geometric parameters such as the cavities' length and width and the coupling distance between them. The output transmission spectrum shows a single transmission peak over a wide wavelength range of 400 nm to 2000 nm while the full width at half maximum is about 200 nm. The high extinction ratio beyond 40dBc with the low insertion loss make this filter comparable to those of other proposed band-pass filters. Besides, the operating wavelength of this filter can be expeditiously tuned by adjusting the geometric parameters, mainly the length of the center cavity. The small footprint of the structure contributes to the achievement of wavelength selection systems for optical communications in ultra-dense plasmonic integrated circuits.

Select as filters

    Select Topics Cancel
    © Copyright 2020 | The Optical Society. All Rights Reserved