Crosstalk analysis in in-line transceiver

An in-line diplexer optical transceiver chip based on an integrated DFB laser and photodiode has been demonstrated and analyzed. The transceiver transmits at 1310nm for upstream signal and receives at 1490nm for downstream signal. For the in-line integrated device, crosstalk between the transmitting and receiving channels become a key issue of system performance. Such crosstalk includes optical-optical, electrical-electrical, and electrical-optical crosstalk. The optical-optical crosstalk is caused by the limited optical isolation between the DFB laser and the photodiode. The electrical-electrical crosstalk is the result of electrical interference between transmitter driver and receiver amplifier. In the in-line transceiver design, the 1490nm downstream signal goes through the DFB laser cavity. When the laser is modulated, the 1490nm signal will experience modulation through the gain and refractive index change in the cavity. This electrical-optical crosstalk has been confirmed by numerical simulation and experimental measurement. The results show that the electrical-optical crosstalk power is proportional to the received 1490nm power and dependent on modulation depth of the DFB laser. A bit error rate model is also presented to describe the impact of the modulation crosstalk from the system performance point of view.