A hybrid integrated optical module composed of a silica-based planar lightwave circuit (PLC), a laser diode with an integrated monitor-photodiode, and a pin-photodiode is fabricated for use in high-performance, compact and cost-effective fiber optic subscriber systems. Its applicability to a wavelength-division-multiplex (WDM) system with a 1.3-µm bi-directional signal and a 1.5-µm one-way signal is demonstrated. The PLC was fabricated by a combination of flame hydrolysis deposition (FHD) and reactive ion etching (RIE), and it simultaneously achieved 1.3-µm/1.5-µm multi/demultiplexing and 1.3-µm Y-branching functions. The optical module exhibited insertion losses of 4.1dB at 1.31µm (including a Y-branch circuit loss of 3dB) and 0.5dB at 1.53µm. An optical output power of more than -4dBm was obtained from the optical module and the crosstalk was sufficiently low at less than -20dB between wavelengths of 1.3µm and 1.5µm. Temperature cycle tests on the optical module showed reliable and stable operation with an optical power fluctuation of less than 0.3dB for 500 cycles.

An influence of a waveguide facet reflection on hybrid-integrated LD gate characteristics was studied. The gate gain is sensitive to a change in the waveguide-gate gap width. An AR coating of the waveguide facet is essential for suppressing the gain-ripple due to a change in the gap width.

A multilayered optical coupler is described which is used to couple a laser beam into a thin film waveguide. This device adopts an evanescent-field coupling technique based on a tapered-gap prism coupler. The multilayered coupler configuration without moving parts results in a mechanically stable coupling function. Experimentally, coupler insertion loss of 3 dB, including coupling imperfection loss, Fresnel reflection loss, and waveguide loss in the coupling region, was achieved in coupling an He-Ne laser beam with 0.633 µm wavelength into a 0.33 µm thick SiO2-Ta2O5 waveguide.