A fully integrated CMOS burst-Mode Optical transmitter for gigabit-level passive optical network applications

Abstract

Motivated by the huge data transmission capacity required for multimedia communications, passive optical network (PON) based on fiber-to-the-home (FTTH) is considered an emerging access network technology to solve the last mile problem of communications. A typical PON system is basically a point-to-multipoint (PtMP) optical network with no active elements in the signal path. Based on TDMA, this passive PtMP ability shares a single optical fiber making it feasible to implement a cost effective solution for the subscriber line that supports broad-band voice, data, and even video services. A key component of such a PON system is the burst-mode up-stream transmitter located inside each subscriber optical network unit (ONU). For real burst-mode operation, together with the stable transmitted optical power under wide temperature variation from -40$\deg$C to +85$\deg$C, laser turn-on/turn-off delay is one of the critical performance parameters of the up-stream transmitter. In addition to this, an extinction ratio (ER) should be kept constant and suitably high to guarantee no errors in the OLT receiver. However, the inherent characteristics of the laser diode (LD), which depend strongly on ambient temperature and aging, make it very difficult to keep the transmitter constant. Laser output power is roughly proportional to the laser current above the threshold ($\It{I_{th}}$) at which the LD starts lasing and increases with ambient temperature. Note that the optical gain beyond $\It{I_{th}}$, known as the slope efficiency ($\eta$), decreases with the ambient temperature. Therefore, for obtaining a reliable and constant laser operation, both the modulation and the bias current of the LD must be properly regulated according to the desired values of averaged optical power and extinction ratio. This results in the optical transmitter compulsorily adopting temperature compensation circuits. In this thesis, a fully integrated burst-mode upstream transmitter chip for giga...