In this Letter, we propose a simple structure of an orthogonal type double Michelson interferometer. The orthogonal detection method overcomes the problems of uneven ranging sensitivity and the inability of traditional interferometers to determine the displacement direction. The displacement measurement principle and signal processing method of the orthogonal double interferometer are studied. Unlike the arctangent algorithm, the displacement analysis uses the arc cosine algorithm, avoiding any pole limit in the distance analysis process. The minimum step size of the final experimental displacement system is 5 nm, which exhibits good repeatability, and the average error is less than 0.12 nm.

光学频率梳在光通信、光谱学等领域有广泛的应用。平坦度是光学频率梳重要的性能指标。使用级联相位调制器和强度调制器产生光学频率梳的方法，是让叠加的谐波驱动调制器，通过调节驱动电信号的幅度和相位以及强度调制器的偏置电压，可以实现平坦度好的光学频率梳。首先，建立光学频率梳的优化问题模型，通过差分进化算法得到上述各个参数，并得到在不同叠加微波驱动信号下的平坦光学频率梳。其次，固定某一微波驱动信号的相位，在同一优化问题下使用同样方法得到微波驱动信号的其他参数，并分析生成的平坦光学频率梳性能。最后，搭建实验系统，根据仿真得到的优化参数确定实验参数，并得到相应的光学频率梳。研究表明，当采用基频和三次谐波驱动相位调制器、采用四次谐波驱动强度调制器时，可以产生13根谱线的光学频率梳，仿真和实验时的平坦度分别为0.27 dB和0.83 dB。当采用基频、三次谐波和五次谐波同时驱动相位调制器和强度调制器时，可以产生19根谱线的光学频率梳，仿真显示其平坦度为0.56 dB。以上仿真和实验结果证明了所提方法的可行性和鲁棒性。

We propose a concept of wavelength synchronization to ensure the stability of ultra-dense channels in an ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON) transmitter. A mode-locked laser is used to provide wavelength references for users. By injection locking the semiconductor laser, the separation of the wavelength reference is realized in an optical line terminal. The downlink and uplink wavelength references are interlaced and distributed to facilitate the synchronization of uplink carriers. In the optical network unit, the uplink optical carriers are filtered by injection locking semiconductor lasers, which achieve wavelength synchronization for the uplink users. In this Letter, an adaptive wavelength synchronization transmitter for UDWDM-PON is realized with a channel spacing of 5 GHz.