The difference between single-mode and multi-mode in optical modules

The optical module (opTicalmodule) is composed of optoelectronic devices, functional circuits and optical interfaces. The optoelectronic devices include two parts: transmitting and receiving. In the optical module, there are single-mode and multi-mode points. So, what is an optical module, and what is the difference between single-mode and multi-mode in optical modules?

ZR Cable Optical Module

1. What is an optical module

The optical module (opTicalmodule) is composed of optoelectronic devices, functional circuits and optical interfaces. The optoelectronic devices include two parts: transmitting and receiving. The transmitting part is: the input electrical signal with a certain code rate is processed by the internal driver chip to drive the semiconductor laser (LD) or light emitting diode (LED) to emit a modulated optical signal of the corresponding rate. The output optical signal power remains stable. The receiving part is: the optical signal with a certain code rate is converted into an electrical signal by the light detection diode after being input into the module. After the preamplifier, the electrical signal of the corresponding code rate is output.

Simply put, the function of the optical module is photoelectric conversion. The transmitting end converts the electrical signal into an optical signal, and after transmission through the optical fiber, the receiving end converts the optical signal into an electrical signal.

2. What is the difference between single-mode and multi-mode in optical modules

1. Different wavelengths

Generally, the wavelength of multi-mode light is 850nm, and the wavelength of single-mode light is mainly 1310nm and 1550nm. Multi-mode optical modules can only be used for short-distance transmission (SR) due to serious inter-mode dispersion; while single-mode optical modules are mostly used for long-distance transmission such as LR, ER, and ZR. Under normal circumstances, the transmission distance of less than 2km is called a multi-mode module; the transmission distance of more than 2km is called a single-mode module.

2. Different scope of application

Multi-mode optical modules are mostly used in networks with relatively low transmission rates and relatively short transmission distances, such as local area networks, etc. Such networks usually have many nodes, many joints, many detours, large amounts of connectors and couplers, and units. The length of the optical fiber uses the characteristics of a large number of light sources. The use of multi-mode optical modules can effectively reduce network costs; single-mode optical modules are mostly used in lines with long transmission distances and relatively high transmission rates, such as long-distance trunk transmission and metropolitan area network construction. Wait.

3. Different fiber types

The single mode in the optical module actually only refers to the type of optical fiber. According to the transmission mode of the optical module in the fiber, it can be divided into single-mode fiber and multi-mode fiber.

Multimode fiber is referred to as MMF, and the fiber diameter is generally 50/125μm or 62.5/125μm.

Single-mode fiber is referred to as SMF, and the fiber diameter is 9/125 μm.

4, the cost is different

The devices used in single-mode optical modules are twice as many as multi-mode optical modules, so the overall cost of single-mode optical modules is much higher than that of multi-mode optical modules.

5. Different light sources

The light source of a multi-mode optical module is a light-emitting diode or a laser, while the light source of a single-mode optical module is an LD or an LED with narrow spectral lines.

6. Different transmission distances

Single-mode optical modules are often used for long-distance transmission, and the transmission distance can reach 150 to 200 km. Multimode optical modules are used in short-distance transmission, and the transmission distance can reach 5km.

3. How to distinguish single-mode and multi-mode optical film blocks

In addition to the difference between the two above, it can also be distinguished from the manufacturer:

(1) Manufacturer 1

1. Multimode optical module

Model: GLC——SX——MM

Description: SFP, 1000Base - SX Gigabit Optical Module, 850nm, Multimode 550m

2. Single-mode optical module

Model: GLC-LH-SM

Description: SFP, 1000Base - LX Gigabit Optical Module, 1310nm, Single Mode 10km

(2) Manufacturer 2

1. Multimode optical module

Model: eSFP——850nm——1000Base——Sx/FC200MM

Description: Optical transceiver module (eSFP, 850nm, 2.125Gb/s multi-rate, -9.5dBm -2.5dBm, -17dBm, LC, multimode, 0.5km)

2. Single-mode optical module 10km

Model: eSFP - 1310nm - 1000Base - Lx SM

Description: Optical transceiver module - eSFP - 1310nm - 1. 25Gb/s - 9dBm - 3dBm - 20dBm - LC - single mode - 10km

In fact, the single mode in the optical module actually only refers to the type of optical fiber, and the multi-mode optical module is an optical module that uses optical components and multi-mode optical fibers to obtain the best transmission characteristics. The bandwidth potential of single-mode in single-mode optical modules makes it the best choice for high-speed and long-distance data transmission, while multi-mode optical modules limit the frequency of transmitting digital signals due to large inter-mode dispersion, so they are generally used for short distances. transmission.