Abstract

We present a new, direct laser-written integrated Bragg grating spectrometer, with large bandwidth due to the large blaze angle of the grating. Integrated cost-effective solutions to spectral monitoring are highly desirable for both quick and portable measurements in the lab and miniaturised rugged interrogation systems. Blazed, chirped, Bragg gratings in a planar silica-on-silicon platform provide a route to this. Blazed gratings direct light out of a waveguide mode into radiation modes, the direction of which is dependent on the wavelength of the light. Chirping the blazed grating correctly creates a focus with wavelength-dependent position. Spectra can thus be resolved by interrogating the focal plane using a CCD (Fig. 1). Planar waveguides formed by FHD glass layers ensure light is guided in the device plane, eliminating the requirement to refocus the other dimension. Small blaze-angle devices (<15º) have been previously shown [1,2]. In contrast this work uses large-angle devices (45º) which offer increased bandwidth and are polarisation sensitive. The direct UV-writing method [3] allows for a high grating period detuning range, as well as a high detuning rate, both of which are required to make high resolution devices with short focal length.

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