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Review of Optical Transceiver Module Evolution

Optical transceivers are the derivatives of the development of the optical fiber communication industry at a particular stage. A review of its invention background confirms this. As high-speed optical modules evolve towards miniaturization, low power consumption, high speed, long distance, and intelligence, low-speed modules are gradually unable to meet the daily data transmission needs. Data centers and telecommunication operators also have increasingly higher requirements for the transmission speed of optical modules. This article will introduce the background and evolution of optical transceiver modules. 

Background Review

1960 saw the invention of the Laser. In 1962, semiconductors began to be adopted in Laser. The theoretical basis of semiconductor lasers was formed for the first time. However, the electric-to-optical conversion efficiency was extremely low, and the working lifespan was short. 1966 marked the beginning of the theoretical foundation for optical fiber to be used for communications. 1970 to 1980 is the development period of optical fiber manufacturing technology and semiconductor lasers theory and technology. By 1985, optical fiber communication started to be industrialized.

1995 – GBIC (Gigabit Interface Converter)

In 1995, the industrialization of optoelectronic signal converters for fiber optic communication began. These converters transform optical signals into electrical signals and vice versa, which is the essence of optical modules. 

 

What era was 1995? Data traffic began to surge after the Internet entered households, Windows 95 was launched, personal computers became prevalent, and people started sending emails, viewing images online, engaging in personal social chats, community gossip, online shopping, etc. 

 

The interface for optoelectronic signal conversion evolved from a hundred megabit to a gigabit (1G), hence the origin of the name GBIC, which stands for Gigabit Interface Converter.

2000 – SFP (Mini GBIC)

As the industry progressed, there was a desire to support more module connections within the same space. Around 2000, SFP emerged, featuring a smaller form factor than GBIC and single-channel transmitting and single-channel receiving. Despite its compact size, SFP could still achieve 1Gbps signal conversion, making modules even smaller.

 

The introduction of SFP was to realize Gbps conversion, which was high-speed for that era. Later, the data rate of SFP gradually speeds to 2.5Gbps, 10Gbps, 28Gbpas, 56Gbps, and 112Gbps while maintaining the external dimensions of the module.

 


 

Figure 1: The 20 pins of GBIC vs SFP

2001 – Xenpak (10 Gigabit EtherNet Transceiver Package)

Xenpak is a 10G Ethernet transceiver package that is large due to its complex design mechanism. It has many auxiliary designs, such as multichannel and electrical signal designs, which makes it difficult to fit the components with 10G conversion capabilities into this large shell. 

2002 – X2 (Mini Xenpak) 

After that, the 10G module continued to be miniaturized. X2 is the miniaturized design of Xenpak, and XFP is an even smaller structure than X2.

2005 – XFP (10 Gigabit Small Form Factor Pluggable)

The evolution continues for the Xenpak, X2, and XFP lines, alongside advancements for the traditional GBIC and SFP modules. By 2009, an upgraded version of SFP, known as SFP+, emerged capable of handling 10Gbps capacity and slightly smaller than XFP, gradually replacing a portion of the XFP market. 

2013 – 100G CFP, QSFP-xx

As the industry progressed, the second and third generations of miniaturized CFP modules, known as CFP2 and CFP4, respectively, were defined in 2013 and 2014. 

 

Following this trend, after 2014, the QSFP-xx series surged ahead, optimizing bandwidth and boosting bit conversion capacity for 100G, 200G, and 400G data center optical modules while maintaining a similar form factor. Subsequently, the mention of CFP4 modules became increasingly rare within the industry.

After 2017 – 400G Module CFP8, QSFP-DD, OSFP

CFP series was first defined for 100G and coherent transceiver modules. To achieve 400G, the industry’s tradition is to expand the size, so CFP8 returns to an appearance similar to CFP2.

 

QSFP-DD is a derivative of the QSFP series, so its appearance and dimensions are very similar. The Q means Quad (4x), and DD refers to Double Density. 

 

OSFP is a new schematic for 400G optics. The O stands for Octal (8x). OSFP transceiver is bigger than QSFP-DD.

 

Overall, OSFP and QSFP-DD dominate 400G optics while CFP8 gradually loses industry share.

800G Era

QSFP-DD is less used in the 800G era because of its small size and high thermal density. 800GBASE OSFP and OSFP-XD have become popular form factor options. The 1.6T hot-swappable series is mainly OSFP-XD. 

3.2Tbps CPO

From 2021 to 2022, the CPO transceiver module will be standardized for more giant density switches of 3.2Tbps. The size of CPO is small; one reason is the use of silicon photonics technology, while another reason is that many manufacturers choose to integrate lasers and detectors or place the Laser outside (moving it outside the optical module), achieving a larger capacity-to-volume ratio for the entire CPO.

Coherent Transceivers

The age of 2011 to 2012 marked the initiation of the coherent module industry. Early coherent modules were board-based, with a large volume of 300-pin 5×7 inches, barely accommodating components such as modulators, light sources, mixers, balanced detectors, DSP, etc., for coherent communication. The power of 100G coherent modules reached 80W.

 

Later, the size was reduced from 5×7 inches to 4×5 inches. With the miniaturization of semiconductor modulators and semiconductor ICRs, as well as the manufacturing process of DSP, coherent modules gradually evolved towards hot-pluggable CFP and CFP2 modules.

 

To 2022, 400G ZR coherent transceivers have been used in QSFP-DD form factors.

 

Form Factor

Year

Length (mm)

Width (mm)

Note

5’’ x 7’’

2011

177.8

127

100G Coherent 300pins

4’’ x 5’’

2013

127

101.6

Gen 2 100G mini

CFP

2017

144.8

82

hot-swappable

CFP2

2018

107.5

41.5

hot-swappable

QSFP-DD

2022

78.3

18.35

400GZR hot-swappable

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