The Introduction of Common Optical Modules

The continuous expansion and rate improvement of the transmission capacity of communication network trunk has made optical fiber communication the main means of modern information networks. In today's optical communications networks, wide area network (WAN), metropolitan area network (MAN), local area network (LAN) and so on make a demand of the optical transceiver module which is one of the core optoelectronic devices because of the increasing types, which leads to the high demand and the increasingly high degree of complexity at an alarming pace. A sharp increase in optical transceiver modules leads to its diversity, so we need to improve the related technologies to meet the needs of this application.

What Is Optical Transceiver Module

The optical transceiver module is composed of the optoelectronic devices, functional circuits and optical interfaces and other components. The optoelectronic devices include the transmission and reception parts. The emitting portion is inputting a certain rate of signals. After processed by the internal driver chip, the semiconductor laser (LD) or a light emitting diode (LED) will emit a modulated optical signal in corresponding rate. In it's interior part, it has the light automatic power control circuit, which makes the optical signal power output stable. Receiving portion is the inputting a certain rate of the optical signal. After processed by a light detecting diode module, it will be transformed into an electrical signal. After the output of the preamplifier corresponding rate, the electrical signal will be typically PECL level. In the meanwhile, the input optical power will output an alarm signal when it's less than a certain value.

The Classification of Optical Transceiver Modules

According to the rate point there are 100Base (megabytes), 1000Base (Gigabit), and 10GE which are used in Ethernet. 155M, 622M, 2.5G, and 10G are used in SDH .

According to package points: 1×9, SFF, SFP, GBIC, XENPAK, XFP. Various packages shown in figure1-6.

1×9
It’s the welding type optical module, generally no higher than Gigabit speed. It mostly uses SC Interface.

SFF
SFF is welding small package optical modules. It’s generally no higher than Gigabit speed, mostly using the LC interfaces. Small package optical modules use advanced precision optics and integrated circuit technology. The size is only half of the ordinary duplex SC (1X9) fiber optic transceiver module, but in the same space it can be increased to double the number of ports of light. It can also increase the line port density, and lower system cost of per port. Moreover, because a small package SFF modules use the copper network similar MT-RJ interface, and the size is the same with common computer network, which is conducive to the existing copper-based network equipment's transition to higher speed fiber-optic network to meet the rapid growth of network bandwidth.

GBIC
GBIC is hot swappable gigabit interface of optical module and it uses SC interface. Giga bitrate interface converter is the abbreviation of GBIC. GBIC is an interface device that converts the gigabit optical signals to electrical signals. GBIC is designed for hot-swappable. GBIC is an international standard interchangeable products. Because of the flexibility of the GBIC Gigabit switch interface design, it accounts for a large market share.

SFP
SFP (as the picture below) package is the hot-plug small package module. Its highest data rates can reach up to 4G and it uses the LC interfaces. The module volume of SFP is half less than the GBIC, but SFP can be configured more than double ports on the same panel. SFP is the abbreviation of small-form-pluggable, which can be simply understood as an upgrade version of the GBIC. Other features of SFP and GBIC modules are basically the same. Some switch vendors call the SFP module as small GBIC (MINI-GBIC).

XENPAK
XENPAK is applied for gigabit Ethernet interfaces, using SC interface.

XFP
XFP 10G optical module in package can be used in gigabit Ethernet, SONET, and other systems. It uses LC interface

More Understanding of GBIC, SFP, SFP+, XFP

The first thing to know is GBIC (Giga Bitrate Interface Converter). It is a generic, low-cost Gigabit Ethernet stacking modules providing high-speed connectivity between Cisco switches, not only creating a stack of high-density port, but also achieving the server or Gigabit backbone connection for fast Ethernet to Gigabit Ethernet transition. GBIC module is divided into two categories, one is common cascade of GBIC module, the second is dedicated stacking GBIC module.

Secondly, small form factor pluggable (SFP) transceivers are optical modules, which can be simply understood as upgraded versions of GBIC. Compared with GBIC, the module volume of SFP module is reduced by half. SFP module can configure more than double the number of ports on the same panel. Since the SFP module is functionally consistent with GBIC, therefore, some switch vendors call it as small GBIC (Mini -GBIC). Because SFP can be directly inserted in the circuit board, it saves space and time in the package.

Gigabit network currently often uses the SFP + modules. SFP is small form-factor pluggable. The difference is that one is used in gigabit networks and the other supports the gigabit and fast. SFP+ is the latest pluggable fiber optic module for 10Gbps Ethernet and 8.5Gbps fiber channel (fiber channel) system.

SFP+ has a more compact package than the X2 and XFP form factor, and the power consumption is less than 1W. It also provides the mounting density higher than the current 10Gbps devices. A more novel design has made SFP+ have the same volume with the standard of SFP (Small Form Factor Pluggable) industry, and the latter for data rates is up to 4Gbps.

As the well-known XFP, it is 10 gigabit small form factor pluggable gigabit Ethernet optical transceiver module. XFP is a serial module for 10GbE field, and it is the optical module for next generation. But as to the ongoing discussions about whether directly use 10G or transmitted to 4G first and the introduction of 4G network standards and products, XFP seems to have taken some blows.

Difference Between SFP+, SFP and XFP

10G module has developed from 300Pin, XENPAK, X2, XFP, and ultimately realized 10G transmission signal of the same size as SFP, which is the SFP+. With its advantages of compact and low cost, SFP has met the equipment needs of high-density optical modules. From 2002 to 2010, it has replaced XFP and become the mainstream of 10G market.

Advantages of SFP+ optical module

1, SFP+ has a more compact package than the X2 and XFP form factor. And the size is the same as SFP.

2, It can be connected directly with the same type of XFP, X2, XENPAK.

3, The cost is lower than XFP, X2, XENPAK.

Differences between SFP+ and SFP

1, SFP and SFP+ are the same size.

2, SFP protocol specification: IEEE802.3, SFF-8472.

Difference between SFP + and XFP

1, SFP+ and XFP are both 10G fiber optical modules, and they can be communicated with other types of 10G modules.

2, SFP+ is smaller than the XFP from the size.

3, Because of the smaller volume of SFP+, it can transmit the signal modulation function, serial/deserializer, MAC, clock and data recovery (CDR), as well as electronic dispersion compensation (EDC) function to the motherboard card from the module.

4, XFP complies the XFP MSA agreement;