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Optical modules, optical interfaces and optical fiber knowledge

Date: 2018/4/12 14:35:09    Hits:5748
The commonly used optical modules of Ethernet switches are SFP, GBIC, XFP and XENPAK.

The full name of their English is:
SFP:Small Form-factor Pluggabletransceiver, small package can be plugged transceiver.
GBIC:GigaBit Interface Converter, Gigabit Ethernet interface converter.
XFP: 10-Gigabit small Form-factorPluggable transceiver Gigabit Ethernet interface.
Small package pluggable transceiver
XENPAK: 10 Gigabit EtherNet TransceiverPAcKage, 10 Gigabit Ethernet interface transceiver package.

Fiber optic connector

The optical fiber connector is composed of optical fiber and plug at both ends of the optical fiber, and the plug is composed of a pin and a peripheral locking structure. According to different locking mechanisms, optical fiber connectors can be divided into FC, SC, LC, ST and KTRJ types.

The FC connector adopts screw locking mechanism. It is an optical fiber movable connector which was invented earlier and used most.
SC is a rectangular joint developed by NTT. It can be directly inserted without threaded connection. Compared with FC connector, it has small operation space and easy to use. Low-end Ethernet products are very common.

LC is a type of Mini type SC connector developed by LUCENT. It has a smaller volume and is widely used in the system. It is a direction for the future development of optical fiber active connectors. Low-end Ethernet products are very common.

The ST connector is developed by AT&T company, with the clamp locking mechanism, the main parameter index is equivalent to the FC and SC connector, but it is not widely used in the company. It is usually used in the connection of multimode devices and is more used when docking with other manufacturers.

KTRJ inserting needle is plastic, through the steel needle positioning, with the increase of the number of inserting, each face will wear and tear, the long-term stability is not as good as the ceramic pin connector.

Optical fiber knowledge

Optical fibers are conductors that transmit light waves. Optical fiber can be divided into single-mode fiber and multi-mode optical fiber from the mode of optical transmission.

In single-mode optical fiber, there is only one basic mode of light transmission, that is to say, light travels only along the inner core of optical fiber. Because the mode dispersion completely avoids the wide transmission bandwidth of single-mode fiber, it is suitable for high-speed and long distance optical fiber communication.

There are many modes of optical transmission in multimode fiber. Due to dispersion or aberration, the transmission performance is poor, the frequency band is narrow, the transmission rate is small, and the distance is short.

Characteristic parameters of optical fiber

The structure of optical fiber is fabricated by prefabricated quartz fiber rod. The outer diameter of multimode fiber and single-mode optical fiber used for communication is 125 m.

This is divided into two regions: the core and cladding (Core) (Cladding layer). The core diameter of the single mode fiber is 8~10 mu m, and the core diameter of the multimode fiber has two standard specifications. The core diameter is 62.5 u m (American Standard) and 50 mu m (European standard).

The specification of interface fiber has such a description: 62.5 mu m/125 m multimode optical fiber, of which 62.5 m is the core diameter of optical fiber, and 125 m refers to the outer diameter of optical fiber.

The wavelength of single mode fiber is 1310nm or 1550 nm.

The optical wavelengths of the multimode fiber are 850 nm.

From the color, we can distinguish single-mode fiber and multi-mode optical fiber. The external body of single-mode fiber is yellow, and the outer body of multimode optical fiber is orange.

Gigabit port auto negotiation
Can two gigabit optical port auto negotiation mode in the work of compulsory and. Support 1000M 802.3 gigabit optical access rate specification, support full duplex (Full) and half duplex (Half) two duplex mode.

The most fundamental difference between self negotiation and coercion is that they send a different bit stream when they re establish a physical link. The self negotiation mode sends a /C/ code, that is, the configuration (Configuration) code stream, and the mandatory mode sends a /I/ code, that is, the idle stream.

Since the negotiation process of gigabit optical access

First, both ends are set as self negotiation
Both sides send /C/ bitstreams to each other. If the 3 same /C/ codes are received continuously and the received bit stream is matched with the work mode of the end, then a /C/ code with Ack response is returned to the other. After receiving the Ack information at the end, the two can be interconnected and the port is UP state.

Two, one side is set up for self negotiation, one end is mandatory.
The /C/ code stream is sent from the negotiable side, and the /I/ code stream is sent by the coercive end. The mandatory end can not provide the negotiation information to the end and the Ack reply to the end. Therefore, the DOWN is self negotiated. But the mandatory terminal itself can identify the /C/ code, and think that the port is the port matching itself, so the UP port is directly set up.

Three, both ends are set as mandatory mode
The two sides send /I/ bitstreams to each other. After receiving the /I/ bitstream at one end, they think that the ports are matching ports to themselves, and the UP ports are directly set up.

How does fiber work?
The optical fiber for communication is made up of thin glass fiber coated with plastic protective layer. The glass fiber is essentially composed of two parts: the core diameter is 9 to 62.5 m, and the outer diameter is 125 m, the low refractive index glass material. Though there are some other kinds of optical fiber according to the materials and sizes, the most common ones are mentioned here. Light is transmitted in the "full internal reflection" mode in the core of the fiber, that is, after the light enters one end of the fiber, it reflects back and forth between the core layer and the cladding interface, and then transfers to the other end of the fiber. The core diameter is 62.5 m, and the outer diameter of the cladding is 125 m. The optical fiber is called 62.5/125 m light.

What is the difference between a multimode and a single mode fiber?
It can transmit hundreds of thousands of modes of optical fiber, called multi-mode (MM) fiber. According to the radial distribution of refractive index in core and cladding, it can also be divided into step multimode fiber and gradual multimode fiber. Almost all the multimode optical fibers are 50/125, m or 62.5/125 m, and the bandwidth (optical fiber).
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