The optical modules commonly used in Ethernet switches are SFP, GBIC, XFP, and XENPAK.

The optical modules commonly used in Ethernet switches are SFP, GBIC, XFP, and XENPAK.

Their full English name:

SFP: Small Form-factor Pluggabletransceiver, small package pluggable transceiver

GBIC: GigaBit Interface Converter, Gigabit Ethernet Interface Converter

XFP: 10-Gigabit small Form-factorPluggable transceiver 10 Gigabit Ethernet interface

Small package pluggable transceiver

XENPAK: 10 Gigabit EtherNet Transceiver PAcKage 10 Gigabit Ethernet Interface Transceiver Collection Package

The fiber optic connector consists of a fiber and a plug at both ends of the fiber. The plug consists of a pin and a peripheral locking structure. According to different locking mechanisms, fiber connectors can be classified into FC type, SC type, LC type, ST type and KTRJ type.

The FC connector adopts a thread locking mechanism and is an optical fiber movable connector which is the earliest and most used invention.

SC is a rectangular joint developed by NTT. It can be directly inserted and removed without thread connection. Compared with FC connector, it has small operation space and is easy to use. Low-end Ethernet products are very common.

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

The ST connector is developed by AT&T. It uses a bayonet locking mechanism. The main parameters are equivalent to FC and SC connectors, but they are not common in the company. They are usually used in multimode devices to connect with other manufacturers. Use more when docking.

KTRJ's pins are made of plastic. Through the positioning of the steel pins, the mating surfaces will wear out as the number of insertions and removals increases. The long-term stability is not as good as the ceramic pin connectors.

An optical fiber is a conductor that transmits light waves. Optical fiber can be divided into single mode fiber and multimode fiber from the mode of optical transmission.

In single-mode fibers, optical transmission has only one fundamental mode, which means that light is transmitted only along the inner core of the fiber. Since the mode dispersion is completely avoided, the single-mode fiber has a wide transmission band and is suitable for high-speed, long-distance fiber communication.

In multimode fiber, there are multiple modes of optical transmission. Due to dispersion or aberration, the transmission performance of such an optical fiber is poor, the frequency band is narrow, the transmission rate is small, and the distance is short.

The fiber structure is prefabricated by a quartz fiber rod, and the multimode fiber and the single mode fiber for communication have an outer diameter of 125 μm.

The slimming is divided into two areas: the core and the Cladding layer. The single-mode fiber core has a core diameter of 8~10μm. The multimode fiber core diameter has two standard specifications, and the core diameter is 62.5μm (US standard) and 50μm (European standard).

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

Single mode fibers use a wavelength of 1310 nm or 1550 nm.

Multimode fibers use a wavelength of 850 nm.

Single mode fiber and multimode fiber can be distinguished in color. The outer body of the single-mode fiber is yellow, and the outer body of the multimode fiber is orange-red.

Gigabit optical ports can work in both forced and auto-negotiated modes. In the 802.3 specification, the Gigabit optical port supports only 1000M speed and supports full-duplex (Full) and half-duplex (Half) duplex modes.

The most fundamental difference between auto-negotiation and coercion is that the code stream sent when the two establish a physical link is different. The auto-negotiation mode sends the /C/code, which is the configuration (ConfiguraTIon) code stream, and the forced mode sends / I / code, which is the idle stream.

First, both ends are set to auto-negotiation mode

The two parties send each other /C/code stream. If three identical /C/codes are received consecutively and the received code stream matches the working mode of the local end, the other party returns a /C/ code with an Ack response. After receiving the Ack information, the peer considers that the two can communicate with each other and set the port to the UP state.

Second, one end is set to auto-negotiation, one end is set to mandatory

The auto-negotiation end sends a /C/stream, and the forced end sends the /I/stream. The forcing end cannot provide the peer with the negotiation information of the local end, and cannot return the Ack response to the peer. Therefore, the auto-negotiation terminal DOWN. However, the mandatory terminal itself can recognize the /C/code, and considers that the peer end is a port that matches itself, so directly set the local port to the UP state.

Third, both ends are set to mandatory mode

The two sides send each other/I/streams. After receiving the /I/stream, the peer considers that the peer is a port that matches itself and directly sets the local port to the UP state.

The optical fiber for communication consists of a thin, hair-like glass filament covered with a plastic protective layer. The glass filament consists essentially of two parts: a core diameter of 9 to 62.5 μm, and a low refractive index glass material having a diameter of 125 μm. Although there are some other types of fibers depending on the materials used and the different sizes, the most common ones are mentioned here. Light is transmitted in the "total internal reflection" mode of the core portion of the optical fiber, that is, after the light enters one end of the optical fiber, it is reflected back and forth between the core layer and the cladding interface, and then transmitted to the other end of the optical fiber. An optical fiber having a core diameter of 62.5 μm and a cladding outer diameter of 125 μm is referred to as 62.5/125 μm light.

Multimode:

Fibers that can propagate hundreds to thousands of modes are called multimode (MM) fibers. According to the radial distribution of the refractive index in the core and the cladding, it can be further divided into step multimode fiber and gradual multimode fiber. Almost all multimode fibers are 50/125 μm or 62.5/125 μm in size, and the bandwidth (the amount of information transmitted by the fiber) is usually 200 MHz to 2 GHz. Multimode optical transceivers can carry up to 5 kilometers of transmission through multimode fiber. A light emitting diode or a laser is used as a light source.

Single mode:

A fiber that can only propagate one mode is called a single mode fiber. The standard single mode (SM) fiber refractive index profile is similar to the step fiber, except that the core diameter is much smaller than the multimode fiber.

Single mode fiber has a size of 9-10/125 μm and has an infinite bandwidth and lower loss characteristics than multimode fiber. Single-mode optical transceivers are often used for long-distance transmission, sometimes reaching 150 to 200 kilometers. LEDs with narrower LD or spectral lines are used as the light source.

Differences and connections:

Single-mode devices typically operate on both single-mode fibers and multimode fibers, while multimode devices are limited to operation on multimode fibers.

This depends on the wavelength of the transmitted light and the type of fiber used.

When the 850 nm wavelength is used for multimode fiber: 3.0 dB/km

When the 1310nm wavelength is used for multimode fiber: 1.0dB/km

When the 1310nm wavelength is used for single mode fiber: 0.4dB/km

When the 1550 nm wavelength is used for single mode fiber: 0.2 dB/km

GBIC is an abbreviation of Giga Bitrate Interface Converter, which is an interface device for converting gigabit electrical signals into optical signals. The GBIC can be designed for hot swapping. GBIC is an interchangeable product that meets international standards. Gigabit switches designed with GBIC interface have a large market share in the market due to flexible interchangeability.

SFP is an abbreviation of SMALL FORM PLUGGABLE, which can be simply understood as an upgraded version of GBIC. The SFP module is half the size of the GBIC module and can be configured with more than double the number of ports on the same panel. The other functions of the SFP module are basically the same as the GBIC. Some switch manufacturers call the SFP module a miniaturized GBIC (MINI-GBIC).

Future optical modules must support hot swap, that is, the module can be connected or disconnected from the device without powering off. Since the optical module is hot-swappable, the network administrator can upgrade and expand the system without shutting down the network. Users will not have any effect. Hot plugging also simplifies overall maintenance and enables end users to better manage their transceiver modules. At the same time, due to this hot-swap performance, the module enables network managers to plan the total cost of transmission and reception, link distance, and all network topologies based on network upgrade requirements without having to replace the system board. The hot-swappable optical modules currently have GBIC and SFP. Since the SFP and SFF are similar in size, they can be directly inserted into the circuit board, which saves space and time on the package, and has a wide application range. Its future development is worth looking forward to, and may even threaten the SFF market.