Category: Fiber Transceivers

 MM fiber Concept

MM fiber is a fiber that transmits multiple modes at a given working wavelength. When the geometric size of the fiber is much larger than the wavelength of the light wave, there will be dozens or even hundreds of propagation modes in the fiber. Different propagation modes have different propagation velocities and phases, resulting in time delay and widening of optical pulses after long-distance transmission. Therefore, the bandwidth of MM fiber will be narrowed and its transmission capacity will be reduced, so MM fiber is only suitable for optical fiber communication with small capacity.

SM fiber Concept

Generally, when V is less than 2.405, only one wave peak passes through the fiber, so it is called a SM fiber. Its core is very thin, about 8-10 microns, and the modal dispersion is very small. The main factor affecting the bandwidth of optical fiber transmission is various dispersion. The dispersion of SM fiber is small, so it can transmit light over a long distance with a wide frequency band, so SM fiber is especially suitable for large-capacity optical fiber communication.

Differences between SM fiber and MM fiber

1. Appearance color

The most obvious difference between SM fiber and MM fiber is the color of the outer jacket. The SM fiber patch cord OS2 is yellow, while the MM fiber OM1 and OM2 is orange outer jacket, OM3 is aqua outer jacket, and OM4 is Purple.

2. Fiber diameter

The core diameter of MM fiber is generally 50µm (OM1) or 62.5µm (OM2, OM3, OM4), and the core diameter of SM fiber is 9µm (OS2).

3. Light source

The light source of SM fiber transmission is laser, and the light source of MM fiber transmission is LED.

4. Bandwidth

MM fiber narrows the bandwidth due to modal dispersion, while SM fiber allows only one mode to propagate in the fiber, and the rest of the high-order modes are all cut off, avoiding the problem of modal dispersion, so SM fiber has a very wide bandwidth.

5. Price

The price of MM fiber is cheaper than that of SM fiber. Because MM fiber is suitable for short-distance transmission and relatively low cost, it is widely used in data centers, while SM fiber is suitable for long-distance transmission,so it is mainly used in backbone network and metropolitan area network.

6. Transmission distance

The transmission distance of MM fiber is within 2KM, while the transmission distance of SM fiber can reach hundreds of kilometers.

7. Application scenarios

SM fiber is mainly used in metropolitan area network, backbone network, PON and other scenarios, while MM fiber is mainly used in enterprise, data center and other scenarios.

In general, SM optical modules need to be used with SM fiber patch cord, and MM optical modules need to be used with MM fiber patch cords. In addition, indoor and short-distance applications are dominated by MM fibers, and outdoor and long-distance applications are dominated by SM fibers.

 by http://www.fiber-mart.com

When selecting optical modules, we should not only consider the stability and reliability of optical module functions, but also consider the price and quality, as well as whether they meet the requirements of network equipment compatibility and data transmission. Here, fiber-mart.com will introduce which optical module parameters should be explained to the manufacturer when selecting the optical module, hoping to be helpful to you.

1. Interface Rate

Before selecting the rate of an optical module, you need to confirm the rate supported by the switch port, and then select the rate of the optical module based on the rate supported by the switch. The rates of optical modules can be FE(155M), GE(1.25G), 10GE, 25GE, 40GE, 100GE, or 400GE. In addition, there are commonly used for storage network (SAN) fiber channel 8G, 16G rate (widely used by Brocade devices)

2. Transmission Distance

Optical modules with different rates, wavelengths, and packages support different transmission distances. Therefore, it is important to determine the transmission distances.For example,SFP-10G-SR 10G multimode optical module can only reach 300m, and SFP-10G-ZR 10G single mode optical module can reach 80km.

The luminescence of optical modules varies with the distance specifications. Note that (usually during field tests), the transmitted optical power of a long-distance optical module is greater than the overload optical power. Therefore, you need to pay attention to the length of the optical fiber to ensure that the actual received optical power is less than the overload optical power. If the length of the optical fiber is short, use the optical attenuation (dB/km) of the optical fiber to avoid burning out the peer optical module.

3. Optical Fiber Type

Optical fibers can be classified into single mode and multimode optical fibers. The central wavelength of a single mode optical module is 1310nm and 1550nm, which are used together with single mode optical fibers. Single mode fiber has transmission frequency bandwidth and large transmission capacity, suitable for long distance transmission. The central wavelength of a multimode optical module is 850nm, which is used together with multimode optical fibers. Multimode fiber has the defect of mode dispersion, and its transmission performance is worse than that of single mode fiber, but its cost is low, and it is suitable for small capacity and short distance transmission.

4. Optical Fiber Interface

Common module interfaces include LC,SC, MPO, etc., but the cost of the project and future upgrade and expansion should be considered comprehensively. For example, 40G QSFP+ multimode interface is generally an MPO interface, using MPO patch cord, the cost of optical module is low, but the cost of MPO patch cord laying is high. 40G QSFP+ also has LC interface specifications, using LC patch cord, cable laying cost is lower. So this is the need to combine the actual situation to make a comprehensive decision. In addition, the optical fiber interface of different optical modules is different, so we need to know the corresponding optical fiber interface of the optical module before purchasing the suitable optical fiber patch cord. For example, the interface type of 1.25G BiDi simplex optical module includes LC and SC, which needs to be confirmed with the manufacturer.

5. Operating Temperature

The operating temperature of the optical module ranges from 0℃-70℃ for commercial, -20℃-85℃ for expansion, and -40℃-85℃ for industrial. Optical modules with the same package, rate, and transmission distance are available in commercial and industrial versions. Industrial-grade products are more expensive because they use devices that are more resistant to temperature. You need to set the operating temperature of the optical module based on the actual operating environment.

6. Compatibility

Because major equipment vendors tend to close the ecosystem in order to provide consistent products and services. As a result, optical modules cannot be mixed with devices of different brands. When purchasing an optical module, you need to explain the devices on which the optical module is to be used to avoid incompatible devices.

7. Price

Generally,the price of optical modules that the brand of optical modules and the equipment brand of the same is expensive,The performance and quality of third-party optical modules are the same as those of brand optical modules, but the price has obvious advantages.

8. Quality and After-sales Service

Optical modules usually have no problems in the first year of use and most of them appear in the later period. So try to choose suppliers with stable quality.

The above is some information we need to provide to the merchants when we buy optical modules. As a professional optical module manufacturer, fiber-mart.com carries out product parameter performance test, appearance test, compatibility and interoperability test and optical end face cleaning before all products leave the factory to ensure that users can get high-quality optical modules.

 After a optical module is made into a finished product, it must go through multiple steps of testing before shipment that ensure the quality of the product. In the test, several parameters are very important. Only when these parameters meet the relevant standards, the optical module performance can be optimized. These parameters include: transmitted optical power, receiving sensitivity, bias current, saturated optical power, extinction ratio, and operating temperature.

First we need to understand what is the transmitted optical power.

The transmitted optical power refers to the output optical power of the optical source at the transmitting end of the optical module, it taking dBm as the unit. It is an important parameter of the optical module and will directly affect the quality of the network communication.

What are the causes of poor power of optical transceiver?

v Power does not match with resistance

v Defective patch or poor performance of drive chip  

v Poor transmitter TOSA or PD+ pin solder joint false 

v Magnetic beads on LD+ and LD- signal lines are defective or missing

v The components (capacitance, resistance, inductance or magnetic bead) at the foot of the storage chip are defective or missing

How to test the optical power of optical module?

The general tools have optical power meter and optical fiber attenuator. The test steps are as follows:

v The power meter is used to measure the optical output power of the optical fiber transmitter.Industry standards define the optical input power of specific network standards for transmitters and receivers.The receiver and transmitter shall be matched, and the optical output power of the transmitter shall be within the specified range;

v Connect the transmitter to the receiver, check whether it can work properly under the maximum optical input power provided by the transmitter, and then test the receiver with the minimum optical input power that can be received by the receiver to see whether the receiver can still provide the best performance;

v Calculate the attenuation level required for the test.Calculation method: if the optical output power of the transmitter is -15 dBm, and the minimum optical output power of the receiver is -32 dBm, the difference between the two is 17dB. The 17 dB optical fiber attenuator can be used and the receiver can be retested.

Doing business is not simply to sell products, but to show professional service and product technical knowledge to customers, which some salesmen lack. Just imagine, if you don’t know anything about product testing, how can customers trust you with orders?Therefore, to become a master of foreign trade, we also have to learn from the basic knowledge, know everything!

 10G SFP+ CWDM optical transceiver is a kind of coarse wavelength division multiplexing optical transceiver, usually used with single mode optical fiber. This kind of optical transceiver uses the CWDM technology to save optical fiber resources, which significantly improves networking flexibility, economy, and reliability. Moreover, the optical transceiver has very low power consumption.

The wavelength interval of the CWDM optical transceiver is generally 20nm. The CWDM technology solves the two problems of optical fiber shortage and transparent multi-service transmission. It is mainly apply to the convergence or access level of medium and shortdistance’s MAN. The CWDM optical  transceiver uses DFB laser, which does not need to use EDFA as optical amplifier. The device is cheap, and the CWDM modulation laser uses uncooled laser, which does not need to be cooled.

When the temperature changes from 0 to 70℃, the wavelength of the laser changes about 6nm. Considering the discrete type caused by the production process, there is a wavelength change of ±3nm, with a total of about 9nm wavelength change, which requires low wavelength stability.

The transmission distance of 10G SFP+ CWDM optical  transceiver can be up to 100KM, and the common transmission distance is 10KM, 20KM, 40KM, and 80KM. The optional wavelength of 10KM and 20KM products is 1270-1610nm, and the wavelength interval is 20nm. The optional wavelength of 40KM and 80KM products is 1470-1610nm, with a wavelength interval of 20nm.

The CWDM Optical transceiver  is mainly used for MAN. When the CWDM system is connected to a high-performance routing switch, a broadband IP MAN can be formed. The CWDM transmission device can also be directly connected to a routing switch, which drives optical transmission devices directly. The routing switch can divide and plug all wavelengths and data streams. The simplest case is to use an optical fiber (TX/RX) to transmit data directly (directly running GE services) in the initial stage. If access business increase or bandwidth requirements increase, the CWDM system can be used to gradually add wavelength channels to this optical fiber according to business requirements.

Laying optical fiber to increase fiber core resources from a long-term point of view, is the ultimate solution. But the construction cycle is long, the construction is difficult, the cost of investment is high, and most of the large customers hope to quickly open business, using CWDM as a MAN construction solution is the best choice.

 1. Lower fiber loss

OM5 is the name given to a new type of broadband multimode fiber, with attenuation reduced from 3.5 dB/km to 3.0 dB/km for previous OM3 and OM4 fibers, and additional bandwidth requirements at 953nm wavelengths. The geometry of OM5 (50μm core and 125μm cladding) is the same as that of OM3 and OM4, making it compatible with these types of fibers downward.

2. Support higher bandwidth applications

OM5 optical fiber also supports future 400G Ethernet, for faster 400G Ethernet applications such as 400G Base-SR4.2 (4 pairs of optical fibers with 2 wavelengths, 50G PAM4 per channel) or 400G Base-SR4.4(4 pairs of optical fibers with 4 wavelengths, 25GNRZ per channel), Only 8-core OM5 optical fiber is required. OM5 optiacl fiber is a laser-optimized multimode fiber (MMF) that has specified bandwidth characteristics for wavelength division multiplexing (WDM). The aim of this new optiacl fiber classification method is to support a wide range of “short” wavelengths between 850nm and 950nm, which are suitable for high-bandwidth applications after polymerization.

The OM5 optical fiber patch cord at a wavelength of 850/1300 nm and supports at least four wavelengths. The usual operating wavelengths of OM3 and OM4 are 850nm and 1300nm. That is to say, the traditional OM1, OM2, OM3, OM4 multimode optical fiber has only one channel,while the OM5 has four channels and it’s transmission capacity increased by four times.

Combining shortwave wavelength division multiplexing (SWDM) and parallel transmission technology, OM5 requires only 8-core wideband multimode optical fiber (WBMMF) to support 200/400G Ethernet applications, greatly reducing the number of optical fiber cores and significantly reducing network wiring costs.

3. The transmission distance of OM5 optical fiber is longer than that of OM3 and OM4

OM5 optical fiber has more scalability and flexibility, and can support higher speed network transmission with fewer multimode optical fiber cores, while the cost and power consumption are far lower than single mode optical fiber. Therefore, it will be widely used in 100G/400G/1T super-large data centers in the future.In order to distinguish different optical fiber patch cord, different colors outer sheath are used.For non-military purposes, single mode optical fibers generally use yellow outer sheath. In the multimode optical fiber, OM1 and OM2 are orange, OM3 and OM4 are aqua blue, and OM5 is aqua green. After understanding the color appearance of OM5, then let us understand the OM5 optical fiber patch cord has what advantages.

 The English translation of high-speed cable is Direct Attach Cable, or DAC for short. This article will introduce several key factors that affect the transmission performance of DAC high-speed cable.

1. Cable attenuation

Cable attenuation refers to the reduction or loss of signal energy that occurs during the transmission of information to the device through the cable. During the transmission of high-speed cables, as the frequency increases, the attenuation will increase. In addition to the increase in frequency attenuation, temperature will also increase the attenuation of the cable. For every 10°C increase in temperature, the signal attenuation of the cable will increase by 4%.

2. Cable crosstalk

Crosstalk is also an important factor affecting cable performance. Crosstalk is a harmful interference signal, which comes from the coupling effect between pairs. This type of noise will cause random changes in signal amplitude, which will limit the receiver’s ability to monitor changes in signal waveforms, thereby affecting the bit error rate and reliability of the transmitted signal.

 3. The cable is excessively bent

Cable bending will weaken the transmission signal, the cable is easy to bend, and the recovery ability after bending is relatively poor. In addition, the cable insulation part is a foamed structure, which has poor mechanical properties and is easily squeezed or stretched. It will be deformed to damage the foam layer structure. Therefore, in the process of using high-speed cables, we should try our best to avoid twisting and bending the insulated core wire, which will cause the conductor to bend and affect the performance.

4. Wiring environment

The operating environment will also affect the performance and service life of high-speed cables. Factors such as high temperature, ultraviolet radiation, and too much humidity will affect the transmission performance of high-speed cables. Therefore, when we lay out cables outdoors, we should lay them out under the eaves. In a place protected from light, moisture, and shade.

5. Electromagnetic and radio frequency interference

Copper cables are most afraid of EMI/RFI (electromagnetic interference/radio frequency interference) during application. Although high-speed cables are generally resistant to electromagnetic/radio frequency interference, we should also avoid potential Source of interference.

6. Grounding

Correct grounding is the key to effective shielding. Failure to ground or incorrect grounding may reduce the effectiveness of the shielding. The ideal shield grounding should have only a single contact. When the interference signal is coupled to the shielding layer, the current will be led to the ground, avoiding the influence of the wire pairs under the shielding layer.