Study of High-Speed Tunable Wavelength Converter

光波长转换器在构建高功能光子网络中起着重要的作用。在本研究中，我们对工作在宽输入信号波长范围内的全光波长转换器进行了探索性研究。提出了一种新型的全光波长转换元件。该波长转换器基于非线性布拉格反射器（NBR-WC），其工作原理是将输入的连续波探测光与作为泵浦的信号光进行切换。利用泵浦光引起的折射率变化调制连续波探测光。通过数值计算，估计了信号门控功率、光栅耦合系数对波长的依赖性、转换效率和信号调谐范围。此外，还制作了所提出的波长转换器，并阐明了其特性。NBR-WC具有较宽的输入信号波长调谐范围，可扩展到掺铒光纤放大器的c波段和l波段。我们使用GaInAsP/InP波导制备了NBR-WC。核心层由GaInAsP组成，带隙波长为1430nm。在1530-1565 nm波长范围内，当输入信号峰值功率为10dBm时，器件的转换效率几乎恒定在-9dB。采用垂直光栅黄铜反射器的高台面波导结构可以消除NBR-WC的偏振依赖性。进一步讨论了提高消光比和转换效率等问题。此外，我们还利用NBR-WC作为波长转换元件，研究了转换波长（即探测波长）的可调性。

An optical wavelength converter plays an important role in constructing highly-functional photonic networks. In this research, we conducted the exploratory study on the all-optical wavelength converter that operates in a wide range of input signal wavelength.A novel all-optical wavelength conversion element is proposed. The wavelength converter is based on a nonlinear Bragg reflector (NBR-WC), and it works as a wavelength converter by switching an input CW probe light with a signal light applied as a pump. The refractive index change induced by the pump light is used to modulate the CW probe light. The signal gating power, the wavelength dependence on the grating coupling coefficient, the conversion efficiency, and the signal tuning range are estimated based on numerical calculations. Also, the proposed wavelength converter is fabricated, and its characterization is clarified. The NBR-WC exhibits a wide tuning range of input signal wavelength, which potentially extends over the C-band and L-band of Erbium doped fiber amplifier. We fabricated NBR-WC using a GaInAsP/InP waveguide. The core layer was composed of GaInAsP with a band gap wavelength of 1430nm. The fabricated device provided almost constant conversion efficiency of -9dB for 10dBm input signal peak power in the signal wavelength range of 1530-1565 nm. Also, the polarization dependence of NBR-WC could be removed by using high-mesa waveguide structure with a vertical grating Brass reflector.Further issues such as improvement of an extinction ratio and conversion efficiency are discussed. Also, using the NBR-WC as a wavelength conversion element, we investigated the tunability of the converted wavelength, i.e., the probe wavelength.