Planar lightwave circuit (PLC) chips based on III-V semiconductor MQW rib waveguide promise to be not only a solution to information access, but also direct the issues of bandwidth, pin count, reliability and complexity. Nanopositioning and precision alignment addresses vital importance in high-efficient connectivity between PLC chips and fiber arrays. Refractive-index mismatching between fused silica and III-V compound is one of the most serious problem which remains unsolved on one hand as well as mode field mismatching which can be mitigated in other hand through gradient geometry structure such as tapered spot size converter (SSC) and specialty fibers such as wedge-shaped fiber (WSF). Spherical gradient refractive-index (SGRIN) media intervened between WSF and MQW rib waveguide is put forward. The GRIN media virtually eliminates the reflection losses associated with the fused silica-air interface and III-V semiconductor-air interface. The beam spot emitted from WSF are observed by digital camera and the fundamental mode of MQW rib waveguide was calculated out. Lightwave propagation and mode field evolution in the WSF-SGRIN-PLC system is simulated by FDTD method with the coupling loss of 8.54dB at a wavelength of 1.55μm. An LED signal is injected into WSF, transmitted along GRIN media and PLC waveguide and output through single mode fiber (SMF). Optical power meter-based measurement verifies the whole system coupling loss to be consistent with the numeric estimation. The approach provides an experimental prototype for coupling and packaging technique of integrated photonic devices, hence supplying foundation for photonic network.
An optimal design of Photonic crystal waveguide (PCW) directional coupler (DC) with adiabatic coupling is presented in this paper. Planar wave expand (PWE) method and FDTD method are used to analyze and optimize PCW-DC. It is shown that use this PCW-DC can achieve efficient transmission ratio in cross state, bar state and power division state at different coupling length. The simulation results show that the coupling ratio can be higher than 90% in some selective wavelength in these states. With the help of adiabatic coupling and bent PCW, the coupling coefficient of two parallel SMFs whose distance from each other at standard interval of 125μm can be higher than 90%. This also suggests that this device can realize a very efficient add/drop filter device which can be used in WDM system.