Matsumoto Ryosuke, Konoike Ryotaro, Matsuura Hiroyuki, Suzuki Keijiro, Inoue Takashi, Ikeda Kazuhiro, Namiki Shu, Sato Ken-Ichi
Opt Lett. 2022 Aug 1;47(15):3680-3683. doi: 10.1364/OL.461951.
A wavelength-routing optical switch uses a wavelength-tunable laser at each input port, and this transmitter implements output port selection by tuning the wavelength that is associated with each output port. With coherent transmission, loopback modulation of a local oscillator (LO) carrier generated at the output port can eliminate the need for a wavelength-tunable laser. However, loopback modulation can be unstable since the power fluctuates because fiber traversal by the light creates polarization rotation. Here, we propose a simple polarization-alignment circuit and verify its effectiveness in creating a high-port-count optical switch system. The proposed circuit consists of passive components and aligns the polarization state of the supplied LO carrier to be linearly polarized along the x-direction of a TE-input dual-polarization (DP) IQ modulator. The circuit is shown to yield stable modulation with Q-variation of less than 0.8 dB, regardless of any birefringence along the transmission path. The proposal's effectiveness is verified in optical switch system experiments with DP-QPSK signals; 1,856 × 1,856 switch scale is achieved with loopback modulation.
波长路由光开关在每个输入端口使用一个波长可调谐激光器，该发射机通过调谐与每个输出端口相关联的波长来实现输出端口选择。对于相干传输，在输出端口生成的本地振荡器（LO）载波的回环调制可以消除对波长可调谐激光器的需求。然而，回环调制可能不稳定，因为光在光纤中传播会产生偏振旋转，导致功率波动。在此，我们提出一种简单的偏振对准电路，并验证其在创建高端口数光开关系统中的有效性。所提出的电路由无源元件组成，可将提供的LO载波的偏振态对准，使其沿TE输入双偏振（DP）IQ调制器的x方向线性偏振。结果表明，无论传输路径上存在何种双折射，该电路都能产生稳定的调制，Q值变化小于0.8 dB。通过使用DP-QPSK信号的光开关系统实验验证了该方案的有效性；采用回环调制实现了1856×1856的开关规模。
