ROSA Basic Structure

As TDM PONs are being deployed on a large scale, significant effort has been put into designing an optical transceiver with improved performance, lower cost, and better reliability. The key challenges in developing optical transceivers for FTTx applications are a higher level of integration, cost-effective packaging, and burst-mode optical transmission technologies in the upstream link. For integration and packaging, optical transceivers are evolving toward planar light-wave circuits and monolithic photonic integrated circuits.

Continuous-Mode and Burst-Mode Transmission

Burst-Mode Laser Drivers

A burst-mode transmitter has to show fast turn-on time as well as good power suppression. The design challenges for burst-mode laser/modulator drivers are rise and fall times and automatic power control. Conventional driver circuits are designed to maintain a constant bias current and voltage. However, good optical power suppression in the idle state requires that the bias be turned off quickly. Driver circuits have to be designed to have short turn-on/off performance. For automatic power control, conventional circuits often use slow monitor photodiode and/or analog filters to average the signal and an analog control loop to analog control loops. It is necessary to monitor optical output sampled at appropriate points in burst waveform.

Burst-Mode Receivers

Conventional optical receivers cannot be used for burst-mode detection because they are not able instantaneously to handle various packets arriving with large differences in optical power and phase alignment. It is therefore necessary to design receivers that can adapt to the variation in optical power and phase alignment on a packet-by-packet basis. The design challenges for burst-mode receivers are dynamic sensitivity recovery, level recovery, and fast clock recovery.

When a weak burst follows a strong burst, it is difficult to detect the weak signal. Dynamic sensitivity recovery is necessary for detection of the weak signal. The recovery of the weak burst is limited by photodiode carrier transport effects, amplifier slew and charging rates, and unintentional automatic gain control effects.

For level recovery, a burst-mode receiver can be designed with a feedback or feed forward structure. For the feedback design, a differential input/output transimpedance amplifier and peak detection circuit form a feedback loop, whereas in the feed forward design, the signal from the preamplifier is feed forward into a peak detection circuitry. Both designs have been implemented in practice. A feedback structure enables the receiver to work more reliably, but a different input/output preamplifier is needed. A feed forward receiver has a faster response time and a conventional decoupled preamplifier can be used, but the circuitry needs to be designed carefully to prevent oscillation in the receiver. Level recovery circuits with simple and robust design and good performance are still an open issue that requires further investigation.

We provide optical transceivers not only for TDM PONs; we also offer compatible transceiver modules worldwide. Welcome to visit our website where you can find the modules you want to buy. Our optical modules can be compatible with all brands, such as the SFP modules.

For purchasing more high quality fiber optic transceivers with low cost or for more products’ information, please contact a Sopto representative by calling 86-755-36946668, or by sending an email to info@sopto.com.