All-Optical Signal Processing

All-Optical Routing System
Optically-Controlled Optical Devices

All-Optical Routing System

The system where transmitted optical signals are routed according to their address information is investigated. We propose the optical circuit enabling separation of transmitted information cell stream into data and address bits in an all-optical manner, i.e. without optical-to-electrical signal conversion. A control pulse and a synchronous signal are generated from the information cell. Generation of the control pulse and all-optical routing are demonstrated successfully.

Published Papers

Demonstration of All-Optical Routing

From a transmitted cell, address bits are successfully extracted.

Optical Switching in Nonlinear Directional Couplers

The coupling characteristic of directional coupler is controlled with the intensity of lightwave through the refractive index change produced by an optical Kerr effect. The output port is switched by applying a control light as indicated in the following figure.

1)without control light

2)with control light

Third-Order Optical Nonlinearity in III-V Semiconductors

Third-Order optical nonlinearity is investigated in direct transition semiconductors to exploit the applicability to optically-controlled devices operating in a fiber-optic communication wavelength range. The intensity-dependent refractive index change, as well as nonlinear absorption, is extensively studied based on so-called two-state energy approximation model. The wavelength of control light effective for reducing an optical switching power is discussed in relation to the bandgap of the material and a signal wavelength.

Optically-Controlled Optical Devices

Optical devices controlled with lightwave are investigated. They are based on an optical Kerr effect, in which refractive index changes as a function of lightwave intensity. We investigate waveguide bistable devices and nonlinear directional couplers. The third-order nonlinearity at near infra-red range is also investigated in III-V compound semiconductors for application to fiber-optic communication.

Waveguide Bistable Devices

A bistable device takes on- and off- states (high- and low- transmittance) for an identical input intensity. The device functions as an optical memory and an optical logic. A novel structure of waveguide resonator with weighted DFB is proposed in this study to reduce the switching power of the device and to improve the on/off ratio. The operation of the device is successfully demonstrated.

Published Papers

Demonstration of Optical Bistability

The measured response of a fabricated device is shown in the following figure.
The output is suppressed in a low level in the initial state where holding light is incident on the device.
Afer injecting a set pulse, the output is set to a high state and holds the state before injecting a reset pulse.
Again, when a reset pulse is injected, the output retains to a low level.