Xu Hongnan, Dai Daoxin, Shi Yaocheng
Opt Express. 2021 Jun 21;29(13):20617-20631. doi: 10.1364/OE.428352.
The O-band coarse wavelength-division (de)multiplexing (CWDM) has been extensively used in data-center optical communications, whereas it's still challenging to reduce crosstalk and enhance fabrication tolerances for a CWDM filter. In this paper, we propose and experimentally demonstrate a low-crosstalk and fabrication-tolerant four-channel CWDM filter by utilizing dispersion-engineered Mach-Zehnder interferometers. The multi-sectional phase shifters are exploited to eliminate the phase errors induced by width deviations, leading to ultra-precise phase shifts and ultra-large width-error tolerances. The random-phase errors are also inhibited by using multi-mode waveguides as phase-shifting sections. The two-stage-coupler scheme is utilized to flatten the strong coupling-ratio dispersions for directional couplers, so that low crosstalk can be achieved over the whole O-band. The experimental results show both low insertion losses (< 1.2 dB) and low crosstalk (< -22.2 dB) over the whole working wavelength range. The measured width-error tolerance is also as large as ≈ 70 nm.
O波段粗波分复用（CWDM）已在数据中心光通信中得到广泛应用，然而，降低CWDM滤波器的串扰并提高制造容差仍然具有挑战性。在本文中，我们提出并通过实验证明了一种利用色散工程马赫曾德尔干涉仪的低串扰且制造容差大的四通道CWDM滤波器。利用多段移相器消除由宽度偏差引起的相位误差，从而实现超精确的相位偏移和超大的宽度误差容差。通过使用多模波导作为移相段，还抑制了随机相位误差。采用两级耦合器方案来平坦定向耦合器的强耦合比色散，以便在整个O波段实现低串扰。实验结果表明，在整个工作波长范围内，插入损耗低（<1.2 dB）且串扰低（< -22.2 dB）。测得的宽度误差容差也高达约70 nm。
