Integration of roof-top reflector laser diodes and waveguide by twin-guide structure

Abstract

Integration of optical devices and waveguide is a key to the realization of the optical integrated circuit. Integrated twin guide laser diode (ITG LD) with etched roof-top reflectors (RTR) at both side is proposed as a integrated light source. Since RTR can totally reflect incident beams threshold current (Ith) of ITG LD can be reduced by adopting RTR. Conical microlens arrays are formed on a glass plate by simply spin-coating spin-on-glass film on the glass and patterning photoresist, then etching the glass in HF solution. These arrays can be used for obtaining more uniform irradiance profiles from non uniform incoherent sources. Transverse electric field distributions in the twin-guide structure and power coupling between active and passive guiding layers are calculated by rigorous normal mode method. Threshold gain (Gth) and transmission into the outer single guide according to cavity length are also obtained. Optimum layer design parameters are determined. Characteristics of twin-guide can be significantly changed by lasing wavelength variation and fluctuations in material parameters. Twin-guide LD layers are grown by AP-MOCVD and etched RTR mirrors are formed by chemically assisted ion beam etching (CAIBE). Light-current characteristics are measured for LD with various mirror configurations. As stripe width increases, RTR gives lower threshold current than cleaved facet or etched straight mirror. This is because RTR has higher reflectivy for most region, but has radiation and scattering loss at the corner region. Carrier distribution and lateral modes of gain-guided stripe LD are obtained. Near field patterns of RTR LD are similar to those of cleaved facet LD up to stripe width of 10$\mu m$. But, RTR LD strongly favors odd mode operation for stripe width of 20$\mu m$. Longtudinal mode selection property of coupled cavity is seen in spectra. Reflection modulation according to wavelength occurs in twin-guide LD with etched RTR. This gives threshold gain modu...