What are the core components of the optical module
2021-11-04
As an important part of optical fiber communication system, optical module plays the role of photoelectric conversion. This article will introduce the core devices of the optical module. 1. Tosa: it is mainly used to realize the conversion of electrical signal to optical signal, mainly including laser, MPD, TEC, isolator, MUX, coupling lens and other devices, including TO-can, gold box, COC (chip on chip), cob (chip on board) In order to save cost, TEC, MPD and isolator are not necessary for optical modules used in data centers. MUX is only used in optical modules requiring wavelength division multiplexing. In addition, LDDS of some optical modules are also encapsulated in Tosa. In the chip manufacturing process, epitaxial circles are made into laser diodes. Then, laser diodes are combined with filters, metal covers and other components , package into to can (transmitter outline can), then package the to can and ceramic sleeve into optical sub module (OSA), and finally match with electronic sub module. 2. LDD (laserdiode driver): converts the output signal of CDR into the corresponding modulation signal to drive the laser to emit light. Different types of lasers need to select different types of LDD chips. In short-range multimode optical modules (such as 100g Sr4), generally speaking, CDR and LDD are integrated on the same chip. 3. Rosa: its main function is to realize optical signal to power signal. The built-in devices mainly include Pd / APD, demux, coupling components, etc. the packaging type is generally the same as that of Tosa. PD is used for short-range and medium-range optical modules, and APD is mainly used for long-range optical modules. 4. CDR (clock and 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, which is simply to recover the clock. At the same time, CDR can also compensate the loss of signal on wiring and connector. CDR optical modules are generally used, most of which are high-speed and long-distance transmission optical modules. For example, 10g-er / Zr are generally used. Optical modules using CDR chips will be locked in speed and cannot be used with frequency reduction. 5. TIA (transimpedance amplifier): used with detector. The detector converts the optical signal into a current signal, and TIA processes the current signal into a voltage signal with a certain amplitude. We can simply understand it as a large resistance. Pin-tia, pin-tia optical receiver is a detection device used to convert weak optical signals into electrical signals in optical communication system and amplify the signals with a certain intensity and low noise. Its working principle is as follows: when the photosensitive surface of pin is irradiated by the detection light, due to the reverse bias of p-n junction, the photogenerated carriers drift under the action of electric field and generate photocurrent in the external circuit; The photocurrent is amplified and output through a transimpedance amplifier, which realizes the function of converting the optical signal into an electrical signal and then amplifying the electrical signal. 6. La (limiting amplifier): the output amplitude of TIA will change with the change of received optical power. The role of La is to process the changed output amplitude into equal amplitude electrical signals to provide stable voltage signals to CDR and decision circuit. In high-speed modules, La is usually integrated with TIA or CDR. 7. MCU: responsible for the operation of underlying software, DDM function monitoring related to optical module and some specific functions.
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