高橋 浩

A wavelength-division multiplexer with no polarization dependence is demonstrated. It is based on an arrayed-waveguide grating fabricated with silica-based optical waveguides on a silicon substrate. The polarization dependence that is due to the birefringence of the waveguide is eliminated by inserting a quartz lambda/2 plate in the middle of the arrayed waveguide. Moreover the grating is designed to operate in the 115th order for high wavelength resolution. The polarization insensitivity and the high resolution lead to the successful multiplexing of 13 wavelength channels with 1-nm spacing. A passband width of 0.3 nm and a cross-talk level of -30 dB are achieved.

11 channel optical-frequency-division multiplexing with a 10GHz channel spacing is achieved with an arrayed-waveguide grating consisting of SiO2-GeO2/SiO2 waveguides on a silicon substrate.

The fabrication and performance of a wavelength-insensitive 8 x 8 star coupler is described. The integrated-optic star coupler consists of two fan-shaped channel waveguide arrays facing each other and a slab waveguide region located in between. The wavelength-insensitive light splitting was realized by properly tailoring the mode coupling in the input array region. The coupler exhibits low-average excess losses of alpha = 1.4 dB (standard deviation sigma = 0.40 dB) at lambda = 1.3-mu-m and alpha = 1.7 dB (sigma = 0.44 dB) at lambda = 1.55-mu-m, respectively.

A 1 x 128 optical power splitter is fabricated by integrating 127 Y-branch waveguide elements on a 3 inch silicon wafer using silica waveguide technology. The average measured excess loss of this splitter is 3.2dB including fibre-waveguide coupling loss.

The design and fabrication of an integrated-optic 8 x 8 star coupler is described. The coupler consists of two fan-shaped channel waveguide arrays facing each other and a slab waveguide region located in between them. The coupler geometry was designed and optimised by using the beam propagation method (BPM). The coupler was fabricated on silicon substrate using high-silica planar lightwave circuit (PLC) technology. The device exhibits low loss (average excess loss alpha = 1.42 dB) and good coupling uniformity (standard deviation sigma = 0.49 dB), which agree quite well with the BPM simulations.