As an important part of the optical fiber communication system, the optical module plays the role of photoelectric conversion.
1. TOSA: Its main function is to convert electrical signals into optical signals. It mainly includes lasers, MPDs, TECs, isolators, Mux, coupling lenses and other devices, including TO-CAN, Gold-BOX, COC (chip on chip), COB ( chip on board) and other packaging forms. For optical modules used in data centers, in order to save costs, TEC, MPD, and isolators are not necessary. Mux is also only available in optical modules that require wavelength division multiplexing. In addition, the LDD of some optical modules are also packaged in TOSA. In the chip manufacturing process, the epitaxial wafer is made into a laser diode. The laser diode is then packaged into a TO can (Transmitter Outline can) with components such as filters and metal covers. This TO can is then packaged with ceramic sleeves and other components into an optical sub-module (OSA), and finally it is combined with electronics. sub-module.
2. LDD (LaserDiode Driver): Converts the CDR output signal into the corresponding modulation signal to drive the laser to emit light. Different types of lasers require different types of LDD chips. In short-range multi-mode optical modules (such as 100G SR4), generally CDR and LDD are integrated on the same chip.
3. ROSA: Its main function is to convert optical signals into electrical signals. The built-in devices mainly include PD/APD, DeMux, coupling components, etc. The packaging type is generally the same as TOSA. PD is used for short-distance and medium-distance optical modules, and APD is mainly used for long-distance optical modules.
4. CDR (Clock and Data Recovery): Translated as clock data recovery, the function of the clock data recovery chip is to extract the clock signal from the input signal and find out the phase relationship between the clock signal and data. Simply put, it is to recover the clock. At the same time, CDR can also compensate for signal losses on wiring and connectors.
The clock recovery circuit (Clock Data Recovery, CDR for short) is a key component of the optical module. The main function of the CDR is to extract the data sequence from the received signal and recover the clock timing signal corresponding to the data sequence, thereby Restore the specific information received. CDR bandwidth is an important indicator of CDR. It mainly affects the data lock time and jitter indicators of the optical module, and determines the key performance of the optical module. If the value of the CDR bandwidth is relatively large, the data locking time of the optical module will be relatively short, but the jitter performance will be worse; conversely, if the value of the CDR bandwidth is relatively small, the jitter performance will be better, but the locking time will be worse. becomes longer. In severe cases, the data on individual system boards may be lost, causing the optical module to be unable to be used normally.
CDR has two main functions. The first is to provide clock signals for various circuits at the receiver end; the second is to judge the received signals to facilitate the recovery and subsequent processing of data signals.
Because when an optical signal is transmitted to a certain distance, usually a long distance, its waveform will be distorted to a certain extent. The signal received by the receiving end is a pulse signal of different lengths. At this time, at the receiving end, we cannot Get the data we need. Therefore, signal regeneration is required at this time. The signal regeneration functions are re-amplification, re-shaping and re-timing. Re-timing refers to CDR clock data recovery.
In short, the biggest role of the CDR clock data recovery function in the optical module is to keep the signal at the receiving end consistent with the signal at the transmitting end. Generally, CDR optical modules are used. Most of them are high-speed, long-distance transmission optical modules. For example, 10G SFP+ ER/10G SFP+ ZR are generally used. Optical modules using CDR chips will be rate-locked and cannot be used. Use at reduced frequency.
5. TIA (Transimpedance amplifier): used with detectors. The detector converts the light signal into a current signal, and the TIA processes the current signal into a voltage signal of a certain amplitude, which we can simply understand as a large resistor. PIN-TIA, PIN-TIA optical receiver is a detection device used in optical communication systems to convert weak optical signals into electrical signals and amplify the signals with a certain intensity and low noise. Its working principle is: the photosensitive surface of PIN is detected When light is irradiated, because the pn junction is in reverse bias, the photogenerated carriers drift under the action of the electric field, and a photocurrent is generated in the external circuit; the photocurrent is amplified and output through the transimpedance amplifier, thus realizing the conversion of the optical signal into an electrical signal. And then the function of preliminary amplifying the electrical signal.
6. LA (Limiting Amplifier): The TIA output amplitude will change as the received optical power changes. The function of LA is to process the changing output amplitude into a constant amplitude electrical signal to provide a stable voltage for the CDR and decision circuit. Signal. In high-speed modules, LA is usually integrated with TIA or CDR.
7. MCU: Responsible for the operation of the underlying software, DDM function monitoring related to optical modules and some specific functions.