What are the optical module parameters?

In the summary of modern information networks, optical fiber communication occupies a dominant position. With more and more extensive network coverage and the continuous increase of communication capacity, the upgrading of communication links is also an inevitable development. The optical module realizes the conversion of photoelectric signals in an optical communication network and is one of the main components of optical fiber communication. However, we usually say optical module, then, what are the parameters of the optical module? You know what? In this article, TRANSCOM will give you a detailed introduction.

1. Central wavelength

The working wavelength of the optical module is actually a range, and the parameter of the central wavelength is used for the convenience of description. The unit of the center wavelength is a nanometer (nm). The general center wavelengths are 850nm, 1310nm, and 1550nm, as well as 1270nm-1610nm (interval 20nm) of the CWDM series and 1528nm-1623nm (interval 0.8nm or 0.4nm) of the DWDM series.

1) 850nm (MM, multi-mode, low cost but short transmission distance, generally only 500m);

2) 1310nm (SM, single mode, large loss but small dispersion during transmission, generally used for transmission within 40km);

3) 1550nm (SM, single mode, small loss but large dispersion in the transmission process, generally used for long-distance transmission over 40km, and can directly transmit 120km without a relay).

2. Transmission distance

Because the optical fiber itself has side effects such as dispersion and loss of the optical signal. Therefore, the light emitted by different types of light sources can travel different distances. When connecting to an optical interface, select the optical module and optical fiber based on the farthest signal transmission distance. The transmission distance of the optical module is divided into three types: short distance, medium distance, and long distance. It is generally considered that 2km and below are short distances, 10-20km are middle distances, and 30km, 40km, and above are long distances.

3. Transmission rate/Date rate

The transmission rate refers to the number of bits (bit) of data transmitted per second, in bps. The transmission rate is as low as 100M and as high as 400Gbps. There are five commonly used rates of 1Gbps, 10Gbps, 25Gbps, 40Gbps, and 100Gbps. In addition, in the optical fiber storage system (SAN), the optical module has three rates of 2Gbps, 4Gbps, and 8Gbps.

After understanding the above three optical module parameters, do you have a preliminary understanding of the optical module? If you want to know more, let's take a look at other parameters of the optical module!

A.Loss and dispersion

Loss is the loss of light energy due to the absorption, scattering, and leakage of the medium when light is transmitted in the optical fiber. This part of the energy is dissipated at a certain rate as the transmission distance increases.

Dispersion is mainly due to the fact that electromagnetic waves of different wavelengths propagate at different speeds in the same medium, resulting in different wavelength components of the optical signal arriving at the receiving end at different times due to the accumulation of transmission distances, resulting in pulse broadening, which makes it impossible to distinguish signals value.

Generally, the link loss is calculated at 0.35dBm/km for 1310nm optical transceivers, and 0.20dBm/km for 1550nm optical transceivers. The calculation of the dispersion value is very complicated and is generally only for reference. These two parameters are mainly used to define the transmission distance of the product. The optical transmission power and receiving sensitivity of optical modules with different wavelengths, transmission rates, and transmission distances will be different.

B.Laser category:

At present, FP and DFB are the most commonly used lasers. The semiconductor materials and resonant cavity structures of the two are different. DFB lasers are expensive and are mostly used for optical modules with transmission distances greater than 40km; FP lasers are cheap and are generally used for transmission. Optical modules with distances within 40km.

C.Optical fiber interface:

Refers to the interface where the optical module is connected to the fiber jumper, generally, there are several types of MPO, duplex LC, simplex LC, and simplex SC. The MPO optical port can be subdivided into MPO 12 (for 8 or 12 optical fibers) and MPO24 (for 16 or 24 optical fibers) according to the number of optical fibers required for optical module transmission. SFP optical modules are all LC interfaces, GBIC optical modules are all SC interfaces, and other interfaces include FC and ST.

D.Output optical power:

Output optical power refers to the output optical power of the light source at the transmit end of the optical module. Can be understood as the intensity of light, the unit is W or mW, or dBm. Among them, W or mW is a linear unit, and dBm is a logarithmic unit. In communication, we usually use dBm to represent optical power.

Formula: P (dBm) = 10Log (P/1mW)

Under the normal working conditions of the module, the optical power output by the optical module and the transmitted optical power (light intensity at the transmitting end) are important parameters that affect the transmission distance. When two optical modules are interconnected, the transmit optical power should meet the range requirements of the received optical power.

E.Maximum receiving sensitivity:

Receive sensitivity refers to the minimum received optical power of an optical module under a certain rate and bit error rate, unit: dBm. In general, the higher the rate, the worse the receiving sensitivity, that is, the greater the minimum received optical power, the higher the requirements for the receiving end components of the optical module. Considering the increase of link loss caused by fiber aging or other unforeseen factors, the optimal received optical power range is controlled from 2-3dB above the receiving sensitivity to 2-3dB below the overload point.

F.Extinction ratio:

The extinction ratio is one of the parameters used to measure the quality of optical modules. The minimum value of the ratio of the average optical power of the signal to the average optical power of the space under full modulation conditions indicates the ability to distinguish between 0 and 1 signal. Two factors affect the extinction ratio in the optical module: bias current (bias) and modulation current (Mod), let's regard it as ER=Bias/Mod. The value of the extinction ratio is not that the larger the optical module is, the better it is, but the optical module whose extinction ratio meets the 802.3 standards is better.

7. Light saturation:

Also known as saturated optical power, it refers to the maximum input optical power when a certain bit error rate (10-10~10-12) is maintained at a certain transmission rate, unit: dBm.

It should be noted that the photodetector will appear photocurrent saturation phenomenon under strong light irradiation. When this phenomenon occurs, the detector needs a certain period of time to recover. At this time, the receiving sensitivity decreases, and the received signal may be misjudged. It will cause bit errors, and it is very easy to damage the detector at the receiving end. During use and operation, try to avoid exceeding its saturated optical power.

8. Maximum power consumption:

The power consumption of modules with different model parameters is different, and each brand of the same model is also slightly different. Gigabit is generally about 1W; SFP+ 10G is generally 1.2-1.5W; XFP 10G is 1.5-2W for short distances and 3.5W for long distances; 100G is generally 3.5-9W depending on the package.

9. The service life of the optical module:

International unified standard, 7×24 hours of uninterrupted work for 50,000 hours (equivalent to 5 years).

10. Environment:

The temperature of the commercial grade optical module: 0~+70℃; the temperature of the extended optical module: -20~85℃; the temperature of the industrial grade optical module: -40~85℃; the working voltage: 3.3V; working level: TTL.