Passband-flattened arrayed-waveguide grating design using an aspheric output star coupler

Custom Arrayed Waveguide Gratings with Improved Performance

“…For example, the high loss and small passband due to the Gaussian transfer function of the primary AWG filters are still substantial problems of conventionally cascaded systems. An AWG with a flat transmission response can be achieved in several ways [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] . Takada et al has demonstrated a partially integrated low-loss multiplexer/demultiplexer configuration by cascading bulky thin-film interference filters as primary filters and five AWGs as secondary filters in order to reduce the overall system loss 26 .…”

“…For compactness, the AWGs are physically interleaved 34 . • Making the star couplers have two focal points 35 or a parabolic shape 36 .…”

“…[25] Copyright 2022, OSA. since they create interference between the first and second modes [31] ; 3) introducing an excess path length to the AWs: it can be done either by inducing a phase difference at the outer arms [32] or creating a sync-like distribution of the spectrum at the output of the array [33] ; 4) using two AWGs with slightly different path length differences, i.e., ΔL: for compactness, the AWGs are physically interleaved [34] ; 5) making the star couplers have two focal points [35] or a parabolic shape [36] ; and 6) employing Multimode interference (MMI) couplers directly preceding the first star coupler. [29,37] The flat-top passband is a highly desired feature, especially in cascaded AWG systems.…”

“…An AWG with a flat transmission response can be achieved in several ways. [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] Takada et al has demonstrated a partially integrated low-loss multiplexer/demultiplexer configuration by cascading bulky thin-film interference filters as primary filters and five AWGs as secondary filters to reduce the overall system loss. [26] Although the loss decreased considerably, the thin-film interference filters were still not integrated on-chip, which is a typical bottleneck for such filters.…”

“…Custom AWG designs have been developed to provide a high‐performance AWG device while addressing the needs of each application. [ 10–60 ] Compared to computational spectrometers, [ 61 ] a rapidly growing field, custom AWGs can provide higher resolution and larger operation bandwidth. Moreover, the accuracy of computational spectrometers is proportional to the amount of training data that has to be well characterized and well labeled, and doing so could be quite time‐consuming and difficult.…”