The high-speed, high-efficient, compact phase modulator array is indispensable in the Optical-phased array (OPA) which has been considered as a promising technology for realizing flexible and efficient beam steering. In our research, two methods are presented to utilize high-contrast grating (HCG) as high-efficient phase modulator. One is that HCG possesses high-Q resonances that origins from the cancellation of leaky waves. As a result, sharp resonance peaks appear on the reflection spectrum thus HCGs can be utilized as efficient phase shifters. Another is that low-Q mode HCG is utilized as ultra-lightweight mirror. With MEMS technology, small HCG displacement (~50 nm) leads to large phase change (~1.7π). Effective beam steering is achieved in Connie Chang-Hasnian’s group. On the other hand, we theoretically and experimentally investigate the system design for silicon-based optical phased array, including the star coupler, phased array, emission elements and far-field patterns. Further, the non-uniform optical phased array is presented.
A novel hollow-core (HW) Y-branch waveguide splitter based on high-contrast grating (HCG) is presented. We calculated and designed the HCG-HW splitter using Rigorous Coupled Wave Analysis (RCWA). Finite-different timedomain (FDTD) simulation shows that the splitter has a broad bandwidth and the branching loss is as low as 0.23 dB. Fabrication is accomplished with standard Silicon-On-Insulator (SOI) process. The experimental measurement results indicate its good performance on beam splitting near the central wavelength λ = 1550 nm with a total insertion loss of 7.0 dB.
We discuss the relationship between Sagnac effect and "slow light" phenomenon, and point out that although the medium and waveguide dispersion can in no way affect the magnitude of Sagnac effect, the highly dispersive structure is still beneficial to the enhancement of Sagnac effect and can be utilized to detect absolute rotation for navigation purpose.
Based on the EIT-like property of coupled resonator structure, a miniature highly sensitive gyroscope is possible. This EIT-like phenomenon occurs through a classical mean in a coupled resonator structure due to all-optical classical interference, called coupled resonator induced transparency (CRIT). With the analogy between optical and atomic parameters, we treat Sagnac effect as a phase perturbation to resonators' optical parameters, and then analyze Sagnac effect in a CRIT structure with a transfer function approach and derive the explicit expression of relative Sagnac phase shift. We find that Sagnac effect is enhanced as a factor as light slows, and can be tailored by adjusting the optical parameters of structure.
Furthermore, as a potential highly sensitive, compact size rotation sensor, some issues for the implementation of CRIT structure based gyroscope are discussed and considered, such as the fabrication possibility, line-width, shot noise limit sensitivity and integration issues. With the improvement of micro-fabrication technique, this gyroscope should have all-solid configuration, compact size and also be expected to achieve comparable sensitivity to common optic-fiber gyroscope. It would be easily integrated to all-optical application and construct a high performance rotation sensor.