Silicon-Nanowire-Type Polarization-Diversified CWDM Demultiplexer for Low Polarization Crosstalk

Abstract

Coarse wavelength division multiplexing (CWDM)-targeted novel silicon (Si)-nanowire-type polarization-diversified optical demultiplexers were numerically analyzed and experimentally verified. The optical demultiplexer comprised a hybrid mode conversion-type polarization splitter rotator (PSR) and a delayed Mach–Zehnder interferometric demultiplexer. Si-nanowire-based devices were fabricated using a commercially available Si photonics foundry process, exhibiting nearly identical spectral responses regardless of the polarization states of the input signals under the PSR. The experiment demonstrated a low insertion loss of 1.0 dB and a polarization-dependent loss of 1.0 dB, effectively suppressing spectral crosstalk from other channels by less than −15 dB. Furthermore, a TM-mode rejection-filter-integrated optical demultiplexer was designed and experimentally validated to mitigate unwanted TM-mode-related polarization crosstalk that arose from the PSR. It exhibited an improved polarization crosstalk rejection efficiency of −25 dB to −50 dB within the whole CWDM spectral range.

Silicon-Nanowire-Based 100-GHz-Spaced 16λ DWDM, 800-GHz-Spaced 8λ LR-8, and 20-nm-Spaced 4λ CWDM Optical Demultiplexers for High-Density Interconnects in Datacenters

“…Previous studies have noted that DI-based optical DeMUXs offer technical benefits, including a compact footprint, minimal IL, low spectral crosstalk, and a flat-topped spectral response [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. However, these advantages tend to diminish when the channel count exceeds 8 and the channel spacing narrows below 400 GHz, especially when the optical demultiplexing function is achieved passively rather than through external active control [15].…”

“…Additionally, CWDM devices must properly work within a wavelength range exceeding 60 nm, as the operating point is spaced by 20 nm [5][6][7]11]. Furthermore, the optical DeMUX at the receiver's end must possess the capability to handle arbitrary polarization input signals [28,30,35,36,40,42,47,49]. To date, various methods have been investigated to manage randomly polarized CWDM signals for use in the optical receiver, which can be categorized into three groups: the zero-birefringence scheme [28], the polarization compensation scheme [30,40], or the polarization diversity schemes [35,36,47,49], applied to silicon nitride (SiN) [28,40,47] and silicon (Si) [30,35,36,49] materials.…”

“…Silicon photonics stands out as a highly promising technological platform for the development of photonic integrated circuits (PICs) characterized by high bandwidth and low energy consumption. Considering silicon-based PICs [8][9][10][11][12][13][14][15], together with several photonic components such as laser diodes, optical modulators, and photodetectors, optical waveguide type demultiplexers (DeMUXs) such as microring resonators [16][17][18][19], delayed interferometers (DIs) [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36], or arrayed waveguide gratings (AWGs) [37][38][39][40][41][42][43][44][45][46][47][48] are normally needed to filter the WDM optical signals spatially out to each photodetector to be decoded.…”

“…It should be noted that the contribution of other higher order modes can be neglected since the main two states of polarization are difficult to couple to any other higher order polarization states. In this investigation, we devised, theoretically identified, and experimentally validated two varieties of ADC structures [36]. Figure 3 shows the simulated propagation characteristics for the above-mentioned ADC-based mode split areas: (a) the long-length ADC (L-ADC)-based mode split area and the structure parameters for the taper-type L-ADC, (b) the propagating mode profile along the full L-ADC region (λin = 1.31 µm), (c) the short-length ADC (S-ADC)-based mode split area, and (d) the propagating mode profile along the full S-ADC region (λin = 1.31 µm).…”

“…Proposed device integrated with TM 00 -mode elimination cutters[36] 2. Wavelength crosstalk from adjacent nanowires 3.…”