Application of optical module in video optical transceiver

The dramatic increase in demand for the video optical transceiver market has brought new demands for fiber bandwidth capacity and device management. In order to meet the requirements of such changes, the types of optical transceiver modules, which are one of the core devices, have also become more and more numerous. The requirements have become higher and higher, and the complexity has also grown at an alarming rate. However, as a general trend, optical modules are moving toward miniaturization, low power consumption, high speed, long distance, hot swapping, and intelligentization.

High rate

With the continuous expansion of the security market and the increasing difficulty in the construction of optical fibers, the number of optical fibers for optical transceivers is increasing. As a result, ultra-high-speed optical modules have gradually been used on optical transceivers. The higher the transmission rate and the greater the capacity, the lower the cost of transmitting each video. Now 2.5G and CWDM optical modules have been applied to video optical transceivers. Higher 4G, 8G and 10G modules are also mature. At present, SDH single-channel optical systems are impacting at 40 Gbit/s. From the current circuit technology, 40Gbit/s is close to the limit of "electronic bottleneck". The high rate, resulting in signal loss, power dissipation, electromagnetic radiation (interference) and impedance matching and other issues difficult to solve, and the current price is too high, the video optical transceiver is not yet mature applications, with the continuous reduction in costs and supporting The maturity of the IC program is believed to be applied soon.

miniaturization

With the popularization of optical fibers, the current global optical communications market is developing in the direction of all-optical networks, and the amount of optical communications equipment is becoming larger and larger. Therefore, the volume requirements of the equipment are getting smaller and smaller. The interface boards contain more and more interfaces, which further exacerbates the density of devices. In order to adapt to the requirements of communication devices for optical devices, optical modules are being developed into highly integrated small packages. The interface of optical modules has evolved from ST and FC to SC and smaller size LC and MT-RJ type connectors, and the corresponding optical transceiver module has also grown from plastic packages to metal packages. The pin arrangement and package are developed from a single row of 9 feet, a double row of 5 feet or 10 feet to the gold finger. The Small Form Factor (SFF) small-package optical module uses advanced precision optics and circuit integration technology. It is only half the size of an ordinary duplex SC (1X9) optical fiber transceiver module, and can double the number of optical ports in the same space. Increase line port density and reduce system cost per port. Because the SFF small package module uses an MT-RJ interface similar to the copper network, the size is the same as the common computer network copper interface, which is conducive to the transition from the existing copper-based network equipment to the higher-speed optical fiber network. To meet the rapid growth of network bandwidth requirements, specific applications, some optical transceiver manufacturers have been using SFF, SFP modules, as well as manufacturers use a single row of 9-pin module plus the pigtail LC interface to achieve miniaturization. The smaller size of communication equipment brings about a problem of heat dissipation, which requires the development of optoelectronic devices in the direction of low power consumption. The current small-package (SFF, SFP) optical modules have all been powered by a low-voltage 3.3v to ensure the normal operation of the system equipment.

Hot swap

All future optical modules all support hot-swap functionality, which means that the module can be connected or disconnected from the device without shutting off the power supply. Because the optical module is hot-swappable, network managers can implement replacement or expansion without shutting down the network. This will not affect the continuous operation of the system. This will greatly reduce maintenance and upgrade costs and make the end user better able to Manage their equipment. The hot-swappable optical modules currently have GBIC and SFP optical modules. Since the SFP is relatively small in appearance, it can be directly inserted on a circuit board and has a wide application area.

Distance

Another development direction of the optical module is long distance. The vast territory of China, coupled with the continuous expansion of the application of optical transceivers makes the transmission distance requirements become higher and higher. If optical modules of FP type and 1310 nm wavelength lasers are used, the eight-channel video optical transceivers are in a typical G652 optical fiber system. The transmission distance can also reach more than 20km, while the one-way or two-way optical transmitter can reach a transmission distance of more than 40km. If a DFB-type, 1550 nm wavelength laser is used, the eight-channel video optical transceiver can also achieve 80 km transmission. Of course, the price is also much more expensive. It is worth mentioning that in order to save optical fiber resources, many optical transceivers now use a single-fiber bidirectional transmission mode, and a single-fiber bidirectional module is also used on the optical module. The forward and reverse transmissions are paired using the 1310nm and 1550nm wavelength lasers, respectively. Depending on the cost, FP type lasers are generally used. At this time, it should be noted that the 1550 nm wavelength light has a relatively large dispersion characteristic in the optical fiber, thus limiting its transmission distance. Generally, it can only be guaranteed at low speeds. 40km, if you need to transmit longer distances, use a DFB type laser. For example, Shenzhen Star Optical Communication Technology Co., Ltd.'s conventional products can meet the transmission needs of eight-channel video within 70 kilometers, while the use of APD module can achieve 8 video transmission 100 kilometers.

Intelligent

The SFP (short for Small Form Pluggable) module can be simply understood as an upgraded version of GBIC. However, the SFP module is half the size of the GBIC module, and more than double the number of ports can be configured on the same panel. It is an SFP intelligent optical module that uses digital diagnostics. The intelligentization of optical modules is reflected in two aspects.

The first is that the built-in IC of the optical module has parameters such as monitoring the temperature of the optical module, the power supply voltage, the laser bias current, and the transmitted and received optical power. In addition to the acquisition and conversion circuits, the implementation of these five parameters is converted into digital data by the analog-to-digital conversion circuit inside the module and is provided to the user in binary form. Through these parameters, the working status of the optical transceiver can be monitored.

The second is that the optical module has a digital diagnostic function. In the SFF-8472 MSA, the digital diagnostic function and details about the SFF-8472 are regulated. SFF-8472 retains the original SFP/GBIC address mapping at address A0h and adds a 256-byte memory location at address A2h. In addition to providing parameter detection information, this storage unit also defines alarm flags or alarm conditions and the status mirror of each pin. According to the specification, the parameter signals are detected and digitized on the circuit board inside the module. Then, provide calibrated results or provide digitized measurements and calibration parameters. The monitored information is stored in a standard memory structure and read through a dual cable serial interface. The digital diagnostic function in the optical module provides a performance monitoring method for the system, which can help the system manage the life of the predicted optical module, locate and isolate the system fault. The fault isolation feature allows system administrators to quickly locate the location of a link failure, either within the module or on the wire, on the local module or on the remote module. By quickly locating the fault, the system's fault recovery time is reduced.

In addition, in order to cooperate with the hot-swappable features of the optical module, the intelligent module also reserves a certain storage unit. Customers can write passwords, protocols, and other information in the storage unit, restricting unauthorised replacement of SFP modules at random, thereby ensuring the manufacturer’s intellectual property and customer benefits.

Due to the ease of interchangeability of SFP modules, optical or fiber optic networks are easier to upgrade and maintain than traditional solder modules. Instead of replacing the entire circuit board containing multiple solder modules, a single module may be removed or replaced instead of a single module. This can greatly reduce the cost of maintenance and upgrades. And SFP has a variety of advantages: (1) high performance, outstanding mechanical and optoelectronic characteristics, and user-friendly; (2) long interconnection distance, support 1000Base-LH standard, the longest distance when using single-mode fiber 70km; (3) A variety of optical fibers can be connected, except for SFPs that support the 1000Base-LH standard and SFPs that support the 1000Base-SX and 1000Base-LX standards.

Although on the current video optical transceiver, a single-row 9-pin module occupies most of the applications. However, in terms of the development trend of the module, the SFP optical module having the above advantages has gradually become a mainstream optical module. The hot spots of future optical components are mainly concentrated in three large blocks, wide area networks, access (PON) networks, and LAN/SAN network markets. Active devices based on MSA modules and PON networks will be a very popular market, with The rapid increase of metro access and data communications, and the emergence of SFP optical modules to meet the subsequent development needs of video optical transceivers. As with the growing communications system, intelligent SFP module technology represents the development trend of the next generation of optical modules. The cornerstone of a high-speed optical module.