Search

Directional couplers are widely used as one of the key components of optical integrated circuits. However, the coupling efficiency of the conventional directional coupler is highly sensitive to wavelength. This sensitivity degrades the characteristics of devices that contain directional couplers for wavelength division multiplexing transmission. A curved directional coupler has been proposed using silica optical waveguide as one of the coupler which realize wavelength insensitive, small footprint and tolerant to fabrication. In this paper, we theoretically investigated this curved coupler using Si wire waveguide and got results that the curved coupler whose bending radius of 21 μm and coupling length of 7.40 μm can reduce the wavelength dependence and achieve about a sevenfold enhancement of operational bandwidth in the transmittance variation range of -3 ± 0.1 dB compared with conventional directional coupler. [ABSTRACT FROM PUBLISHER]

This paper presents our recent progress with the integration of silicon (Si) photonic devices for optical telecommunications. To integrate Si wire waveguides, germanium (Ge) photodetectors (PDs) and silica waveguides, we have developed processes for the selective epitaxial growth of Ge on a Si waveguide core and for the low-temperature deposition of silica waveguide film and introduced spot size converters (SSCs) for coupling Si-wire and silica waveguide with low loss. Using these processes and SSCs, we have managed to monolithically integrate Si variable optical attenuators (VOAs) and Ge PDs, and Si VOAs and a silica arrayed waveguide grating (AWG). In the integrated VOA-PD, the Ge PD accurately detects the attenuation of light power in the Si VOA. The 3-dB cutoff frequency in VOA-PD synchronous operation is around 100 MHz, which is limited by the VOA. The integrated VOA-AWG provides high-speed power-level adjustment independently in every channel of the AWG with a response time of 15 ns. These integrated Si photonics devices exhibit sufficient performance for application to future telecommunications systems that combine WDM and burst-mode packets. [ABSTRACT FROM PUBLISHER]

We propose a novel Mach-Zehnder interferometric optical switching device with micro-electro-mechanical systems (MEMS) phase shifters. Analytical results show that the stretch length per phase shifter is 70 nm at an applied voltage of 100 V. Phase switching can be achieved by the cascade connections of fifteen phase shifters. [ABSTRACT FROM AUTHOR]

This work presents our recent progress in the development of an Si wire waveguiding system for microphotonics devices. The Si wire waveguide promises size reduction and high-density integration of optical circuits due to its strong light confinement. However, large connection and propagation losses had been serious problems. We solved these problems by using a spot-size converter and improving the microfabrication technology. As a result, propagation losses as low as 2.8 dB/cm for a 400×200 nm waveguide and a coupling loss of 0.5 dB per connection were obtained. As we have the technologies for the fabrication of complex, practical optical devices using Si wire waveguides, we used them to make microphotonics devices, such as a ring resonator and lattice filter. The devices we made exhibit excellent characteristics because of the microfabrication with the precision of a few nanometers. We have also demonstrated that Si wire waveguides have great potential for use in nonlinear optical devices. [ABSTRACT FROM PUBLISHER]