Yuri Petropavlovsky

In June 2017, the production of another type of high-tech products began in Russia - the company Fiber Trade LLC launched a plant for the production of fiber-optic transceivers in Novosibirsk. According to the company itself and the opinion of other experts in this field, this is the first and so far the only plant with a full cycle of mass production of such devices in Russia. It should be noted that other companies are also involved in the development and production of optoelectronic components, including optical transceivers, in Russia, for example, FTI-Optronik from St. A. F. Ioffe Russian Academy Sciences. Readers should also be reminded that not all, even the world's leading electronic companies, have their own production of microelectronics and other electronic components. Companies that do not have their own production are called Fabless companies; microelectronics for them is produced by specialized enterprises (Foundries-companies) on orders.

Before considering the features of fiber optic transceivers, let's give some data about the company itself. private company Fiber Trade LLC was founded in 2010 in Novosibirsk by Aleksey Valentinovich Yunin, born in 1974 (Figure 1), who previously worked for Novotelecom and Vimpelcom. The main activity of the company at that time was the supply of telecommunications equipment to the Russian market. In 2012, the company was assigned the code of the development organization FCRD in accordance with GOST 2.201-80 (changed in 2011), which made it possible to start developing and designing products under its own FiberTrade (FT) trademark.

Practical work on the creation of the production of transceivers began in 2015 and ended in 2017 with the launch of the plant. During this time, the difficult tasks of creating clean rooms of the 7th class and installing high-precision test equipment from leading world manufacturers have been solved. Financing of the project (about 40 million rubles) was carried out at the expense of Alexey Yunin's own funds and other private investors, while no third-party companies were involved in the process of creating the plant. The expected volume of production will be 960 thousand transceivers per year, and the amount of revenue - 3.8-4.2 billion rubles per year. Payback is planned for 2020.

By the end of 2018, it is planned to increase the number of the company's staff to 70 people (now there are 22 development engineers and 23 production engineers and other specialists). Due to the lack of qualified specialists with experience in the company's profile, the possibility of attracting university graduates with further training is being considered.

Currently, the company cooperates on a permanent basis with leading telecommunications and IT companies, including PJSC VimpelCom, OJSC MegaFon, PJSC Rostelecom, PJSC MTS, Vkontakte LLC, Mail Ru LLC Group", CJSC "Comstar-Region" and a number of others. In the future, the enterprise may take up to 50% of the market of fiber-optic transceivers in Russia; the main export directions are the CIS countries. Taking into account the fact that the company already has projects that have no analogues in the world, the possibility of exporting products to European countries is being considered.

One of these projects includes multi-vendor transceivers that allow their operation in telecommunications equipment of various vendors (up to 5 at the same time). October 19, 2017 Federal Service for intellectual property issued a Certificate of state registration of the computer program "Formation of a unified definition of the SFR + module in switching equipment various manufacturers". Fiber Trade multi-vendor transceivers allow companies to reduce costs using equipment from different manufacturers in their systems, as well as avoid additional costs for maintaining a warehouse of modules from different vendors (vendor - supplier and owner of the trademark).

Another project is optical modules with data cryptoprotection support.

Some "expert theorists" consider the production of microelectronics in Russia to be difficult and unpromising. Indeed, such production requires large financial costs, and from the very beginning. To implement projects in this area, specialists are needed who not only have a good profile education and extensive work experience, but also, according to Alexei Yunin, a great desire to develop this area in Russia. Nevertheless, the production of domestic fiber optic transceivers has a number of advantages.

The fundamental disadvantages of foreign devices are the impossibility of changing the software to the requirements of operators and the likelihood of undeclared functionality supplied devices. Cheaper Chinese transceivers are also characterized by a higher percentage of defects, which requires additional costs from consumers for the return / replacement of defective modules. According to Alexey Yunin, one of the main goals of the production of fiber-optic transceivers is to ensure the security of the country. When developing products and software for them in Russia, the manufacturer knows literally everything about his products and can control them. In this case, we can actually talk about compliance information security in the era of cyber warfare and hacker attacks. Another important advantage of the production of radio electronics products in the country is a much greater flexibility in relations with domestic customers on all emerging issues.

The main consumers of the plant's products are the country's leading telecom operators and data centers. In the future, the company has big plans, for example, covering up to 50% of the needs of the Russian market in fiber-optic transceivers and entering foreign markets. There is a desire to become a member of the import substitution project (IMWEI), which will help to significantly increase sales in the domestic market. The need for transceivers will only increase, for example, in Russia by 2024, 5G networks in one form or another are planned to be deployed in cities with a population of over 300 thousand inhabitants, which will require the replacement of base station equipment and a significant increase in their number.

Tests of the Fiber Trade equipment, including those carried out by the country's leading telecommunications operators, have shown the competitiveness of the company's fiber-optic transceivers with European counterparts in terms of reliability and functionality.

The catalogs of the company in 2017, in addition to the actual transceivers, also include other types of products: media converters, channel sealing equipment, equipment for long lines, passive equipment.

Fiber Optic Transceivers

Fiber-optic transceivers (FOTS) or optoelectronic transceivers are designed to convert optical signals transmitted over fiber-optic communication lines (FOCL) into electrical signals and vice versa - electrical signals into optical ones. The need for VOT arose as early as the 1990s, when the active introduction of fiber-optic networks for broadband access by network and mobile operators connections. At that time, WOT were performed on printed circuit boards active telecommunications equipment. However, due to the growth in the range of such devices (switches, multiplexers, routers, media converters), there is a need to separate information processing and data transmission devices. Moreover, the devices themselves for transmitting signals over FOCL for the purpose of unification must be standardized in one way or another.

For quite a long time, BOTs from various manufacturers have been unified compact plug-in modules installed in standardized electrical ports of active telecommunications equipment. This approach to the creation of a network infrastructure makes it possible to optimize costs in the design and, most importantly, in the reconstruction of optical networks, for example, to increase the data transfer rate, the amount of information transmitted and the range of signal transmission over FOCL.

BOT modules are produced in various designs - form factors. SFP (Small Form-factor Pluggable) modules are currently the most widely used, shown in Figure 2. SFP modules are compact units in metal cases, providing protection of the electronic components of the modules from electromagnetic radiation and mechanical damage. The modules usually have two optical ports - a laser emitter (TX - transmitter) and a photodetector (RX - receiver), which ensure the operation of the module in a two-wave mode (Figure 3). Single-wavelength SFP modules have only one port, while multiplexing is used to change the direction of transmission.

On the printed circuit boards of the modules, in addition to emitters and photodetectors, other electronic components and components are installed - laser diode control circuits, signal converters into a linear code, photodiode bias circuits, various amplifiers and filters, digital circuits monitoring. The module boards also contain an EEPROM (Electrically Erasable Reprogrammable Memory) with a control software(a variant of the block diagram of the SFP module is shown in Figure 4).

Various mechanical and electrical characteristics BOT is not defined by international standards, but by MSA (Multi-source Agreement) specifications, developed on the basis of agreements between various equipment manufacturers. This "nature" of the process of developing multiple specifications is characterized by the "indefinite range" of companies participating in MSA agreements. To effectively develop MSA specifications, back in 1990, a group (committee) Small Form Factor Committee (SFF Committee) was created in the USA to determine form factors in the information storage industry. Among the dozens of committee members are the largest producers electronics and computer technology- Dell, Foxconn, Fujitsu, Hewlett Packard, Hitachi, IBM, Intel, Pioneer, Samsung, Seagate, Sun Microsystem, Texas Instruments, Toshiba. In 2016, the organization changed its name to SNIA SFF Technology Affiliate. To date, the partners of the SFF Committee, in addition to those listed above, are other leading companies - Microsoft, Broadcom, Cisco, Huawei, Lenivo, Micron, Microsemi, GiGNET and a number of others (more than 50 companies in total).

We examined what optical transceivers of the SFP and SFP + form factor are in general. In this one, we would like to take a closer look at a few more subtle points.

In particular, we will focus on the classification of transceivers by the type of optical connector, standards and technology of spectral division multiplexing.

Cable trimming

An optical cable for connecting to SFP modules must be terminated into an LC (Lucent/Little/Local Connector) or SC (Subscriber/Square/Standard Connector) connector.

Accordingly, the modules are available with two types of cable connectors: SC and LC.

Here it should be noted that two-fiber optical transceivers of SFP, SFP+ formats almost always come with an LC connector, since SC is larger, and two such connectors will not fit in a duplex module. The use of SC is possible only in single-fiber.

SC is one of the first ceramic connectors designed to facilitate the connection of optical cables to a variety of devices and protect the cable cut from contamination and mechanical damage. Given the microscopic thickness of the fibers of an optical cable, even one speck of dust can cause a significant deterioration in the quality of communication or a connection break.

The LC connector was developed by Lucent as an improvement over the SC. It is half the size and has a snap-off, which makes it easier to handle optical cables in high-density connections/fibers.

In general, Ethernet standards allow the use of both one and the second connector, however, most manufacturers still install LC connectors on their modules. Even single-fiber SFP WDM modules, which have always come standard with an SC connector, are now also available with an LC connector.

You can read more about optical connectors in this article.

Standards

Optical transceivers operate in Ethernet networks and therefore must meet one of the relevant standards. For convenience, we have summarized the parameters of those in the table.

Reception-transmission speed	Standard		Standard	Number of fibers	fiber type	Emitter wavelength, nm
					multimode, full duplex
					multimode, half duplex with guaranteed collision detection
	TIA/EIA-785-1-2002				multimode
					single mode
					single mode
					multimode
					single mode
					multimode
					single mode
					single mode
					single mode
					single mode
					multimode
					multimode	1275, 1300, 1325, 1350
					single mode	1275, 1300, 1325, 1350
					single mode
					single mode
					multimode
					multimode
					single mode
					single mode
					multimode
					single mode	1295, 1300, 1305, 1310
					single mode	1295, 1300, 1305, 1310

Transparency windows of optical single-mode fiber

The vast majority of modern optical cable belongs to the SMF G.652 standard different versions. latest version standard, G.652 (11/16) was released in November 2016. The standard describes the so-called standard single-mode fiber.

The transmission of light through an optical fiber is based on the principle of total internal reflection at the interface between media with different optical densities. For implementation this principle, the fiber is made two- or multi-layered. The light-conducting core is surrounded by layers of transparent shells made of materials with lower refractive indices, due to which total reflection occurs at the layer boundary.

Optical fiber, as a transmission medium, is characterized by attenuation and dispersion. Attenuation is the loss of signal power during the passage of the fiber, expressed as the level of loss per kilometer of distance (dB/km). The attenuation depends on the material of the transmission medium and the wavelength of the transmitter. The wavelength dependence of the absorption spectrum contains several peaks with minimal attenuation. It is these points on the graph, also called transparency windows or telecommunications windows, that were chosen as the basis for selecting emitters..

There are six transparency windows of single-mode fiber:

• O-band (Original): 1260-1360 nm;
• E-band (Extended): 1360-1460 nm;
• S-band ( Short wavelength: 1460-1530 nm;
• C-band ( Conventional): 1530-1565 nm;
• L-band ( Long wavelength): 1565-1625 nm;
• U-band ( Ultra-long wavelength): 1625-1675 nm.

Approaching fiber properties within each range can be considered approximately the same. The peak of transparency is, usually , to the long wave end E-band . Specific attenuation in O-band about one and a half times higher than in S- and C-band , specific chromatic dispersion - vice versa, has a zero minimum at a wavelength of 1310 nm and above zero at C-band .

Initially, to organize a duplex connection using an optical cable, pairs of fibers were used, each responsible for its own transmission direction. This is convenient, but wasteful in relation to the resource of the cable being laid. To level this problem, the technology of spectral division multiplexing, or, in other words, wave multiplexing, was developed.

Wave multiplexing technologies, WDM/CWDM/DWDM

WDM

At the heart of WDM technology, Wavelength Division Multiplexing, is the transmission of several light streams with different light lengths over a single fiber.

The basic WDM technology allows the creation of one duplex connection, with the most commonly used wave pair 1310/1550 nm, from the O- and C-band, respectively. To implement the technology, a pair of “mirror” modules is used, one with a 1550 nm transmitter and a 1310 nm receiver, the other, on the contrary, with a 1310 nm transmitter and a 1550 nm receiver.

The difference in the wavelength of both channels is 240 nm, which makes it possible to distinguish both signals without the use of special detection tools. The main used pair 1310/1550 allows you to create stable connections at distances up to 60 km.

In rare cases, pairs 1490/1550, 1510/1570 and other options from transparency windows with lower specific attenuation relative to the O-band are also used, which allows organizing more “long-range” connections. In addition, the combination 1310/1490 occurs when a cable television signal is transmitted in parallel with data at a wavelength of 1550 nm.

CWDM

The next stage of development was Coarse WDM, CWDM, coarse spectral multiplexing. CWDM allows you to transmit up to 18 data streams in the wavelength range from 1270 to 1610 nm with a step of 20 nm.

CWDM modules in the vast majority of cases are two-fiber. There are BiDi, bidirectional SFP CWDM modules, in which reception and transmission go over one fiber, but in Ukraine they are still quite rare for sale.

SFP and SFP+ CWDM transmitters (modules) transmit at one particular wavelength.

The receiver of such modules is broadband, that is, it receives a signal at any wavelength, which allows you to organize a single duplex channel with any two modules certified for CWDM compliance. For simultaneous transmission of several channels, passive multiplexers-demultiplexers are used, which collect data streams from “color” SFP modules (each of which has a transmitter with its own wavelength) into a single beam for transmission over fiber and parse it into individual streams at the end point . The versatility of receivers provides greater flexibility in networking.

DWDM

The latest development to date - Dense WDM (DWDM), dense spectral multiplexing, allows you to organize up to 24, and in custom-made systems - up to 80 duplex communication channels, in the wavelength range of 1528.77-1563.86 nm with a step of 0, 79-0.80 nm.

Naturally, the denser the placement of the channels, the tighter the tolerances in the manufacture of emitters become. While a wavelength error within 40 nm is acceptable for conventional modules, for WDM transceivers this error is reduced to 20-30 nm, for CWDM it is already 6-7 nm, and for DWDM it is only 0.1 nm. The smaller the tolerances, the more expensive the production of emitters.

Nevertheless, despite the much higher cost of equipment, DWDM has the following significant advantages over CWDM:
1) transfer noticeably more channels on one fiber;
2) transmission more channels over long distances, due to the fact that DWDM operates in the most transparent range (1525-1565 nm).

Finally, it should be mentioned that, unlike the original WDM standard, in CWDM and DWDM, each individual channel can deliver data at speeds of both 1 Gb / s and 10 Gb / s. In turn, the 40 Gb and 100 Gb Ethernet standards are implemented by combining the bandwidth of several 10 Gb channels.

What are OADM modules and WDM filters (dividers)?

Despite the consonant name, the OADM module is not an optical transceiver, but rather an optical filter, one of the multiplexer types.

In the picture: OADM module.

Optical Add Drop Multiplexor (OADM) nodes are used to separate data streams at intermediate points. OADM, otherwise Add-Drop module, is an optical device that is installed in the gap of an optical cable and allows filtering two data streams from a common beam. OADM, like all multiplexers, unlike SFP and SFP + transceivers, are passive devices, so they do not require power supply and can be installed in any conditions, up to the most severe ones. A properly planned OADM package allows you to do without the end multiplexer and "distribute" data streams to intermediate points.

The disadvantage of OADM is the reduction in the power of both the separated and transit signals, and hence the maximum range of stable transmission. According to various sources, the power reduction is from 1.5 to 2 dB on each Add-Drop.

An even more simplified device, the WDM filter, allows you to separate only one channel with a certain wavelength from the total stream. Thus, it is possible to assemble OADM analogs based on arbitrary pairs, which increases the flexibility of building a network to the maximum.

In the picture: WDM filter (divider).

The WDM filter can be used both in networks with WDM multiplexing, and with CWDM, DWDM multiplexing.
Just like CWDM, the DWDM specification is based on the use of OADM and filters.

Multi-source agreements (MSAs)

Often in the accompanying documentation for SFP and SFP + transceivers you can see information about MSA support. What it is?

MSAs are industry agreements between module manufacturers that ensure end-to-end compatibility between transceivers and network equipment from different companies and that all manufactured transceivers comply with generally accepted standards. Installing MSA-compliant SFP ports in equipment expands the range of compatible modules and ensures a competitive market for interchangeable products.

MSA for SFP/SFP+ set the following parameters:

1. Mechanical interface:

• module dimensions;
• parameters of the mechanical connection of connectors with the board;
• placement of elements on the printed circuit board;
• an effort, necessary to insert the module into/remove from the slot;
• labeling standards.

2. Electrical interface:

• pinout;
• power options;
• timings and I/O signals.

3. Software interface:

• type of PROM chip;
• data formats and preset firmware fields;
• I2C control interface parameters;
• DDM functions ( Digital Diagnostics Monitoring).

To date, the SFP/SFP+ format modules include three MSA specifications issued by the SNIA SFF committee, which most market participants have committed to comply with:
SFP - Download as pdf
SFP+ - Download as pdf
DDM - Download as pdf

SFP, SFP+, XFP modules technical description(rus.) Download in pdf format

website

Fiber-optic communication lines are a type of communication in which information is transmitted through optical dielectric waveguides, known as "optical fiber". Optical fiber is currently considered the most advanced physical medium for transmitting information, as well as the most promising medium for transmitting large flows of information over long distances.

Broadband optical signals are due to the extremely high carrier frequency. This means that information can be transmitted over an optical communication line at a rate of about 1.1 Terabit/s. Those. One fiber can transmit 10 million at the same time. telephone conversations and a million video signals. The data transfer rate can be increased by transmitting information in two directions at once, since light waves can propagate in one fiber independently of each other. In addition, two light signals can propagate in an optical fiber. different polarizations, which doubles throughput optical communication channel. To date, the limit on the density of information transmitted over optical fiber has not been reached.

The most important component is the fiber optic cable. There are several dozen companies in the world that produce optical cables for various purposes. The most famous of them are: AT&T, General Cable Company (USA); Siecor (Germany); BICC Cable (UK); Les cables de Lion (France); Nokia (Finland); NTT, Sumitomo (Japan), Pirelli (Italy). The cost of optical cables is commensurate with the cost of standard "copper" cables. The use of fiber-optic signal transmission means is still constrained by the relatively high cost of equipment and the complexity of installation work.

To transmit data through optical channels, the signals must be converted from electrical to optical, transmitted over a communication line, and then converted back to electrical at the receiver. These conversions take place in transceivers, which contain electronic assemblies along with optical components.

In general, the organization of an optical channel is similar to IrDA. Significant differences are the range of optical waves and the speed of the transmitted data. In this regard, semiconductor lasers are used as emitters, and high-frequency photodiodes are used as receivers. The block diagram of the optoelectronic data receiver is shown in fig. 5.19, and in fig. 5.20 - data transmitter.

Rice. 5.19. Optoelectronic data receiver

Rice. 5.20. Optoelectronic data transmitter

To transmit information over a fiber optic channel, two wavelength ranges are used: 1000 ^ 1300 nm (second optical window), and 1500 ^ 1800 nm (third optical window). In these ranges - the smallest signal loss in the line per unit cable length.

Various optical sources can be used for optical transmission systems. For example, light emitting diodes (LEDs) are often used in low cost local networks for short distance communication. However, a wide spectral emission band and the impossibility of operating in the wavelengths of the second and third optical windows do not allow the use of the LED in telecommunication systems.

Unlike an LED, an optically modulated laser transmitter can operate in a third optical window. Therefore, for ultra-long range and WDM transmission systems, where cost is not the main consideration, but high efficiency is a must, a laser optical source is used. For optical communication channels Various types Directly modulated semiconductor laser diodes have an optimal cost/performance ratio. The devices can operate in both the second and third optical windows.

All semiconductor laser diodes used for direct modulation typically have a DC bias current requirement to set the operating point and modulation current for signal transmission. The amount of bias current and modulation current depends on the characteristics of the laser diode and may differ from type to type and from each other within the same type. The range of these characteristics with time and temperature must be taken into account when designing the transmitter unit. This is especially true for economically more profitable uncooled types of semiconductor lasers. It follows that the laser driver must provide a bias current and modulation current in a range sufficient to allow different optical transmitters with a wide choice of laser diodes to operate for a long time and at different temperatures.

To compensate for the deteriorating performance of the laser diode, an automatic power control (APC) device is used. It uses a photodiode that converts the light energy of the laser into a proportional current and supplies it to the laser driver. Based on this signal, the driver outputs a bias current to the laser diode so that the light output remains constant and matches the original setting. This maintains the "amplitude" of the optical signal. The photodiode found in the APC circuit can also be used in automatic modulation control (AMC).

Clock recovery and serialization require clock pulses to be synthesized. This synthesizer can also be integrated into a parallel-to-serial converter and usually includes a phase locked loop circuit. The synthesizer plays an important role in the transmitter of an optical communication system.

Optical receivers detect signals transmitted over a fiber optic cable and convert it into electrical signals, which then amplify, restore their shape and clock signals. Depending on the baud rate and system specifics of the device, the data stream can be converted from serial to parallel format. The key component that follows the amplifier in the receiver is the clock and data recovery (CDR) circuitry. CDR performs clocking, decides on the amplitude level of the incoming signal and outputs the restored data stream.

There are several ways to maintain synchronization (external SAW filter, external control clock signal, etc.), but only an integrated approach can effectively solve this problem. The use of a phase locked loop (PLL) system is an integral part in synchronizing the clock pulses with the data stream, this ensures that the clock signal is aligned with the middle of the information word.

Laser modules of the LFO-1 series (Table 5.15) are manufactured based on high-performance MQW InGaAsP/InP and AlGaInP/GaAs laser diodes and are available in standard uncooled coaxial packages with single-mode or multi-mode optical fiber. Individual models, along with uncooled versions, can be produced in DIL-14 housings with a built-in micro-cooler and thermistor. All modules have a wide operating temperature range, high radiation power stability, service life of more than 500 thousand hours and are the best radiation sources for digital (up to 622 Mbps) optical communication lines, optical testers and optical telephones.

	Radiation power, (mW)	Wavelength, (nm)	tych. fibers	micro-refrigerator	Type of shell

Photodetector modules of the PD-1375 series (Table 5.16) for the spectral range 1100-1650 nm are made on the basis of InGaAs PIN photodiodes and are available in an uncooled version with single-mode (model PD-1375s-ip) or multimode (PD-1375m-ip), optical fiber, as well as in an "optical socket" type housing for docking with SM and MM fibers terminated with a "FC / PC" connector (model PD-1375-ir). The modules have a wide operating temperature range, high spectral sensitivity, low dark currents and are designed to operate in analog and digital fiber-optic communication lines with data transfer rates up to 622 Mbps.

	Wavelength, (nm)	tych. fibers	Sensitivity, (A/W)	Receiving speed, (Mbps)	Type of shell
					"socket"

Chipset manufactured by MAXIM for transceivers allows conversions in SDH/SONET optical transmission systems. SDH is the European standard for fiber optics for data transmission. SONET is a standard that defines speeds, signals, and interfaces for synchronous data transmission at rates greater than one gigabit/sec over a fiber optic network.

The MAX3664 and MAX3665 amplifiers (Figure 5.21) convert the current from the photodiode sensor into a voltage that is amplified and output as a differential signal. In addition to the photocurrent amplifier, microcircuits have Feedback to compensate for the constant component, which depends on the magnitude of the dark current of the photodetector and has a very low temperature and time stability. A typical MAX3665 wiring diagram is shown in fig. 5.22. The main purpose of these amplifiers is to restore the amplitude of the electrical signal and transmit the restored signal for further processing.

The MAX3675 (MAX3676) chip performs clock recovery and clocking from the received data stream. The block diagram of the MAX3676 is shown in Figure 1. 5.23. Signal processing algorithms in these devices are much more complex. As a result of signal conversion, together with the restoration of the digital data stream, a clock signal is extracted, which is necessary for further correct processing. A typical MAX3676 wiring diagram is shown in fig. 5.24. The MAX3676 takes the signal from the photocurrent amplifier and converts the signal to output differential data and clock signals with standard logic levels. It must be taken into account that all these conversions are performed with signals arriving in serial format at a very high speed.

Rice. 5.21. MAX3665 photocurrent amplifier block diagram

Rice. 5.22. Typical switching circuit MAX3665

Rice. 5.23. Functional diagram MAX3676

Rice. 5.24. Typical switching circuit MAX3676

To transmit signals generated as a result of reception via standard interfaces MAXIM offers MAX3680 and MAX3681, these are serial-to-parallel converters. The MAX3680 converts a 622 Mbps serial data stream to a 78 Mbps eight-bit word stream. The data and clock output is compatible with TTL levels. Power consumption - 165 mW with a supply of 3.3V. The MAX 3681 converts a 622 Mbps serial data stream to a 155 Mbps four-bit word stream. Its differential data and clock support the low-voltage differential signal of the LVDS interface (Figure 5.25).

The MAX3693 chip (Figure 5.26) converts four 155 Mbps LVDS data streams to a 622 Mbps serial stream. The clock required for transmission is synthesized using a built-in phase-locked loop, which contains a voltage-controlled oscillator, a loop filter amplifier, and a phase-frequency detector that requires only external clock references. With a 3.3 V supply, the power consumption is 215 mW. The serial data output signals are standard positive-emitter-coupled-logic differential signals.

The main purpose of the MAX3669 laser driver (Figure 5.27) is to supply bias current and modulation current to directly modulate the laser diode output. For added flexibility, the differential inputs accept PECL data streams as well as differential voltage swings up to 320 mV (p-p) at Vcc=0.75 V. By changing the external resistor between the BIASSET pin and ground, the bias current can be adjusted from 5 to 90 mA, and the resistor between the MODSET pin and ground can adjust the modulation current from 5 to 60 mA. A typical diagram of connecting the MAX3669 to the laser module is shown in fig. 5.28. The data is received in parallel 4-bit code and is clocked into a serial data stream by the MAX3693 converter. From this converter, signals in serial format are transmitted to the MAX3669 laser driver, which generates a modulating signal with the required parameters to control the emission of a laser diode.

A fairly detailed selection of materials on the use of these components can be found on the website www.rtcs.ru, Rainbow Technologies, the official distributor of MAXIM in the CIS countries.

Rice. 5.25. Connecting an optical receiver to the data bus using an LVDS interface

Rice. 5.26. MAX3693 block diagram

Rice. 5.27. MAX3669 block diagram

MAXIM also releases the MAX38xx series IC kit for building a 2.5Gb/s fiber optic interface. For example, the MAX3865 laser driver with automatic modulation control (Fig. 5.29) has the following distinctive features:

Unipolar supply voltage 3.3 or 5 V;

Consumption 68 mA

Work with performance up to 2.5 Gbps (NRZ);

Controlled feedback;

Programmable bias and modulation currents;

Falling/rising edge duration 84 ps;

Monitoring of modulation and bias currents;

Failure detector;

ESD protection.

Rice. 5.28. Typical scheme for connecting MAX3669 to a laser module

Rice. 5.29. Typical scheme for connecting MAX3865 to a laser module

SKEO supplies transceivers of all available types, common modules are kept in stock at the company's warehouse. The line of SKEO optical modules is designed for installation in critical areas of the communication network, the modules have guaranteed stable characteristics, the warranty for this series is 5 years. These transceivers can replace expensive modules offered by vendors.

The choice of SKEO optical modules is optimal for use in standard carrier networks where the cost-effectiveness of the equipment is highly valued.

Optical transceivers (transceiver, transmitter - transmitter and receiver - receiver) are replaceable modules for telecommunications equipment. The task of an optical transceiver is to convert an electrical signal into an optical signal.

Using Optical Transceivers

Optical transceivers have replaced transceivers built into equipment. The disadvantages of built-in transmitters were the impossibility of changing the data transmission medium and the complexity of maintenance in the network device in case of failure.

Equipment with interchangeable optical transceivers supports multiple transmission media (single mode or multimode fiber, copper twisted pair, etc.) and can be easily replaced in the event of a breakdown. In the case of data transmission over single-mode optical fibers, the length of the line can reach 200 km without regeneration and amplification (for 155 Mbps).

Various transceiver form factors

Optical transceivers have several form factors, which are determined by the SFF Committee (Small Form Factor Committee), whose working groups include leading manufacturers of telecommunications equipment. The most common optical transceiver form factors are GBIC, SFP, SFP+, X2, XENPAK, XFP, CFP, qSFP. These transceivers support various protocols and data rates from 100 Mbps to 100 Gbps.

The parameters of transceivers can vary greatly, but the following classification is valid for the most common types of modules:

• GBIC and SFP 155 Mbps, 622 Mbps, 1.25 Gbps, 2.5 Gbps, 4 Gbps (protocols STM-1, STM-4, Gigabit Ethernet (Fiber Channel), STM-16)
• XENPAK, X2, XFP, SFP+ 10Gb/s (protocols 10GE, 10G Fiber Channel, OC-192, STM-64, 10G OTU-2)
• QSFP+, CFP 40 Gb/s, 100 Gb/s (40GE, 100G OTU-4 protocols)

The transmission distance limit is determined by the optical budget and the chromatic dispersion tolerance. Here, the optical budget refers to the difference between the radiation power of the transmitter and the sensitivity of the receiver. By analogy with the list of correspondence between form factor and speed / protocol, you can make a list of distances, again for common transceivers:

• GBIC and SFP 0.1, 0.3, 3, 20, 40, 80, 120, 160 km
• XENPAK, X2, XFP, SFP+ 0.3, 10, 40, 80 km
• QFSP28 - 10 or 40 km

Standard distance designations for transceivers up to 500 meters - SR, up to 20 km - LR, up to 60 km - ER, after 60 km - ZR.

CWDM and DWDM Optical Transceivers

To provide support for xWDM technologies, transceivers are produced with transmitters with an operating wavelength from the CWDM / DWDM mesh. For CWDM systems, transceivers are produced with 18 different wavelengths, for DWDM 44 wavelengths (100 GHz grid) or 80 wavelengths (50 GHz grid).

Optical transceivers allow you to control your own state parameters through the monitoring function. This feature is called DDM (Digital Diagnostics Monitoring) or DOM (Digital Optical Monitoring). With this function, you can monitor standard parameters operation of the transceiver, such as electrical characteristics, temperature, radiated power, and signal strength at the detector. This information helps prevent data transmission failures by detecting negative line changes in a timely manner.

"Firmware" of optical transceivers is a short record in the non-volatile memory of an optical module that contains classification information about the module, which may include serial number, manufacturer name, form factor, transfer range and more. Some manufacturers use firmware to block the operation of their own equipment with third-party transceivers. To do this, the equipment controls the presence of the correct record and the total checksum in the memory of the installed transceiver.