Study of all-optical logic devices

为了实现由激光二极管提供能量的光控制波导光开关器件，进行了此项研究。在整个研究过程中获得的结果总结为结束语如下。从理论上估计了直接带隙半导体的强度相关折射率和非线性吸收系数。通过数值计算，估计在1550nm波长下，控制由GaInAsP组成的波导DFB双稳器件所需的功率为几十mW。对于具有均匀耦合系数的传统DFB结构，导态透过率随输入强度的增大而减小。然而，通过在DFB结构中引入加权耦合系数来克服这个缺点。通过数值计算表明，采用加权DFB结构的光双稳器件具有提高导通率和降低阈值强度的特点。此外，还提出了加载布拉格反射器（BR-NLDC）的非线性定向耦合器，该耦合器作为双稳器件，具有两个输出端口与输入端口分离，用于光信号处理应用。非对称BR=NLDC的开关功率通常比传统的非线性定向耦合器低1/10。最后，在具有分布式反馈结构的GaInAsP波导中成功地实现了全光开关。在与光集成电路兼容的波导结构中，首次观察到全光集复位操作。通过本实验，光开关操作的阈值功率范围为20 ~ 80mw。虽然实验证实器件的响应时间小于2.5nsec，但没有研究开关速度的限制。为了将来的实际应用，必须这样做。

The research was carried out in order to realize the waveguide optical switching devices controlled with light whose power is obtainable by a laser diode. The results obtained throughout this research are summarized as concluding remarks in the following.The intensity-dependent refractive index and the nonlinear absorption coefficient were theoretically estimated in direct bandgap semiconductors. Through the numerical calculation, the required power to control a waveguide DFB bistable device composed of GaInAsP was estimated to be a few tens mW at a wavelength of 1550nm.In case of conventional DFB structures with a uniform coupling coefficient, the on-state transmittance decreases as input intensity increases. This drawback, however, was overcome by introducing a weighted coupling coefficient in DFB structure. Through numerical calculations, it has been shown that optical bistable device with the weighted DFB structure exhibits improved on-state transmittance together with reduced threshold intensity. Also, nonlinear directional couplers loaded with a Bragg reflector (BR-NLDC), which work as a bistable device having two output ports separated from the input one, were proposed for optical signal processing applications. The swiching power of an asymmetric BR=NLDC is typically 1/10 less compared with a conventional nonlinear directional coupler.Finally, all-optical switching was successfully demonstrated in the GaInAsP waveguide with a distributed feedback structure. The first observation of all-optical set-reset operation has been obtained in the waveguide structure compatible with optical integrated circuits. Through the present experiment, the threshold power for the optical swiching operation ranges from 20 to 80 mW.Although it is experimentally confirmed that the response time of devices is less than 2.5nsec, the limitation of the switching speed was not investigated. This must be done for practical applications in the future.