Optical
Optical Communication Chip
Optical chips and electrical chips are the most important devices that determine the performance of optical modules.
Optical chips and electrical chips are the core components of optical devices.
In optical devices, optical chips are used for the conversion of photoelectric signals. According to different types, it can be divided into active optical chips and passive optical chips.
Active optical chips are divided into laser chips (transmitter) and detector chips (receiver). At the transmitting end (laser chip), the optical transmitting module converts the electrical signal into an optical signal; at the receiving end (detector chip), the optical signal is restored to an electrical signal and introduced into an electronic device. The performance and transmission rate of the optical chip directly determine the transmission efficiency of the optical fiber communication system.
The value of laser chips is large, and the technical barriers are high. It is the "pearl" of optical chips. According to the type of light emission, it is divided into surface emission and side emission. Among them, surface-emitting lasers are mainly VCSEL (vertical cavity surface-emitting lasers); there are many types of edge-emitting lasers, including FP (Fabry–Pérot, Fabry-Perot laser), DFB (Distributed Feedback Laser, distributed feedback laser) Lasers) and EML (Electroabsorption Modulated Laser), traditional FP laser chips have gradually narrowed their applications in the field of optical communication due to large losses and short transmission distances. There are three main types of core laser chips: DFB and EML And VCSEL.
(1) DFB is the most commonly used direct modulation laser, which is based on the FP through the built-in Bragg grating, so that the laser is highly monochromatic, reducing loss and increasing the transmission distance. At present, DFB lasers are mainly used for medium and long-distance transmission. The main application scenarios include: FTTx access network, transmission network, wireless base station, and internal interconnection of data centers.
(2) EML lasers add an electro-absorption sheet (EAM) as an external modulator on the basis of DFB. The chirp and dispersion performance are better than DFB, and are more suitable for long-distance transmission. The main application scenarios of EML are: high-speed, long-distance telecommunications backbone network, metropolitan area network and data center interconnection (DCI network).
(3) VCSEL has the characteristics of single longitudinal mode, circular output spot, low price and easy integration, but the luminous transmission distance is short, suitable for short distance transmission within 500m. The main application scenarios are: internal data center, consumer electronics (3D). A
There are two types of detector chips: PIN (PN diode detector) and APD (avalanche diode detector). The former has relatively low sensitivity, which is used in short and medium distances, and the latter has high sensitivity, which is used in medium and long distances.
On the one hand, the electric chip realizes supporting support for the operation of the optical chip, such as LD (laser driver), TIA (transimpedance amplifier), CDR (clock and data recovery circuit), on the one hand, realizes the power adjustment of the electric signal, such as MA (main amplifier ), On the other hand, to achieve some complex digital signal processing, such as modulation, coherent signal control, serial-parallel / parallel-serial conversion, etc. There are also some optical modules with DDM (Digital Diagnostic Function), corresponding with MCU and EEPROM. Electric chips are usually used together, and mainstream chip manufacturers will generally introduce a set of products for a certain type of optical module.
Regardless of whether it is an optical chip or an electrical chip, depending on the substrate (substrate) material, it can be divided into the following categories: indium phosphide (InP), gallium arsenide (GaAs), silicon-based (Si), etc .:
Matching use of optical chip and electrical chip: At the transmitting end, the electrical signal is modulated internally or externally by CDR, LD and other signal processing chips, driving the laser chip to complete the electro-optical conversion; at the receiving end, the optical signal is converted into electrical pulses by the detector chip , And then amplitude modulation is performed through power processing chips such as TIA and MA, and finally a continuous electrical signal that can be processed by the terminal is output. The cooperation of the optical chip and the electronic chip realizes the realization of the main performance indicators such as transmission rate, extinction ratio, and transmitted optical power, and is the most important device that determines the performance of the optical module.
Optical device chips have extremely high technical barriers and complicated process flows, so they are the largest part of the optical module BOM cost structure. The cost of optical chips is usually 40% -60%, and the cost of electric chips is usually 10% -30%. The higher the speed, the higher the cost of high-end optical module electric chips.