Miniaturized spectrometers using integrated optics

In this work, two different integrated-optics based spectrometer designs are presented. The first one is called interleaved arrayed waveguide grating (AWG) spectrometer provides large bandwidth (i.e. 30 nm) and high resolution (i.e. 0.1 nm) for a compact size (i.e. 2.4 cm × 3 cm). The second spectrometer is called ultra-high resolution Fourier transform (FT) spectrometer provides 1 pm of resolution for only 2 cm × 0.5 cm (1 cm2) device size at 1.3 μm. For the interleaved AWG spectrometer, the primary AWG has narrow closely spaced passbands (that equal the final desired channel spacing) that repeat N times in the desired wavelength range, using the frequency-cyclic nature of the AWG. The channel spacing of the secondary AWGs should be equal to the free spectral range (FSR) of the primary AWG. In this configuration, the FSR of the secondary AWGs defines the FSR of the overall configuration whereas the channel spacing (resolution) of the primary AWG defines the overall system resolution. The ultra-high resolution FT spectrometer is formed by sequentially-activated 60 Mach-Zehnder interferometers that are connected to photodetectors through very-low-loss beam combiners based on two-mode interference. The long optical delays are provided by tapping the propagating light out at certain locations on the optical waveguides by using electro-optically-controlled directional couplers. A design example with a spectral resolution of 500 MHz (~1 pm) and bandwidth of 15 GHz is presented for a device size of only 2 cm × 0.5 cm (1 cm2).