A novel bidirectional optical coupling module for subscribers

To overcome drawbacks and limitations of planar lightwave circuit based mod ules for bidirectional communications, such as the demand for several chips and in consequence more packaging efforts, we have recently developed a no vel optical coupling technique using our unique 155 Mbps bidirectional lase r chip. Since the chip is structured with a pin-photodiode monolithically i ntegrated on a laser diode's waveguide, the optical coupling requires only the alignment of the chip with a fiber. To optically couple the laser diode and photodiode simultaneously with a single fiber, we have designed an unu sual coupling structure using a fiber having a cleaved surface whose normal is 35 degrees angled to the fiber core axis, and using a index controlling medium with a refractive index of similar to1.3. The bidirectional chip is flip-chip bonded and the fiber is passively aligned using a V-groove on th e same substrate of 2.5 x 1.3 mm(2) in size. Even with this extremely small and simple scheme for bidirectional optical coupling, we could obtain an o ptical output power of -7 similar to -10 dBm and a responsivity of < -30 dB m, which are satisfactory to the STM-1 level telecommunications specificati ons.