A Burst-Mode Laser Transmitter with Fast Digital Power Control for a 155 Mb/s Upstream PON

摘要

This paper presents an innovative 155 Mb/a burst-mode laser transmitter chip, which was designed and successfully demonstrated, and contains several new subsystems: a digitally programmed current source, programmable up to 120mA with a resolution of 0.1 mA, a fast but accurate intermittent optical level monitoring circuit, and a digital Automatic Power Control (APC) algorithm. This generic and intelligent chip was developed in a standard digital 0.35 μm CMOS process. Extensive testing showed a high yield and algorithm stability, as well as excellent performance. During initialization, when the transmitter is connected to the Passive Optical Network (PON) for the first time, maximum three Laser Control Fields (LCF) are needed, with a length of 17 bytes (0.88 microsecond at 155 Mb/s), to stabilize the laser output power. In this short time, the chip can regulate the launched optical output power of any FSAN (Full Service Access Network) compliant laser diode to the required level, even in the extreme circumstances caused by outdoor operation or by battery backup operation during power outages. Other tests show that the chip can further stabilize and track this launched optical power with a tolerance lower than 1 dB over a wide temperature range, during the burst mode data transmission. The APC algorithm intermittently adjusts the optical power to be transmitted in a digital way, starting from loosely-specified but safe preset values, to the required stable logic "1" and "0" level. No laborious calibration of the laser characteristic curve and storage of the calibration values in lookup tables are needed, nor any off-chip adjustable component. The power consumption is significantly reduced by disabling inactive circuitry and by gating the digital high-speed clock. Although this laser transmitter was developed for FSAN PON applications, which are standardized at a speed of 155 Mb/s upstream, the design concept is quite generic and can be applied for developing a wide range of burst mode laser transmitters, such as required for Gigabit PON systems or other TDMA networks.