What is Optical Transceiver: A Beginner Guide (2024)

Initial Published: April 28, 2017

What is an Optical Transceiver?
Optical Transceivers Types
Structure of An Optical Transceiver
Optical Transceiver Applications
The Main Parameters of Optical Transceiver
FAQs

What is an Optical Transceiver?

An optical transceiver, also known as a fiber optic transceiver or optical module, is a small packaged device that uses fiber optic technology to transmit and receive data.

‘Transceiver’ combines the words’ transmitter’ and ‘receiver’. In other words, the optical transceiver usually comprises an optical transmitter and an optical receiver that are combined and share common circuitry or a single housing.

The optical transceiver is an essential part of optical network equipment. It has electronic components to condition and encode/decode data into light pulses and then send them to the other end as electrical signals.

To send data as light, it uses a light source, such as VSCEL, FP, DFB, and EML laser, which is controlled by the electronic parts, and to receive light pulses, such as Pin or APD, it uses a photodiode semiconductor.

Figure 1: Optical transceiver decomposition diagram

Optical Transceivers Types

Optical transceivers are classified into various types based on different methods to meet diversified requirements. But in most cases, we classify them based on form factors.

Classified by Transceiver Form Factors

By different form factors, they are classified as below types:

1×9 Transceivers: Like its name “1×9”, the most noticeable feature is one prominent row of 9 pins. Most manufacturers have stopped using 1×9 transceivers and chose more popular types like SFP or SFP+.
GBIC Transceivers: short for Gigabit Interface Converter, they are a hot-pluggable form factor, but due to their considerable size, they can now only be found on ancient switches or devices.
SFF Transceivers are short for small form factor. They usually have 2×5 or 2×7 pins but are smaller than the 1×9 transceiver. Note that SFF doesn’t support hot pluggable.
SFP (mini-GBIC) Transceivers: short for small form pluggable, the most successful form factor to date. Therefore, it is the most popular type in the transceiver industry. Most of the later transceivers are developed based on them and upgraded with higher speed and compact form variants.
SFP+ Transceivers: These enhanced SFPs support higher speeds, such as 8G and 10G. In most cases, users may call them 10G SFP+.
XFP Transceivers: This stands for 10-gigabit small form factor pluggable, and “X” in this word stands for 10G. It was only briefly famous before being quickly replaced by SFP+ because of its drawbacks, such as significant form factor and high power consumption.
SFP28 Transceivers: This is an upgraded version of SFP+ that supports 25G to 28Gbps speed. It is mainly used in 25G Ethernet CPRI and data centers.
QSFP Transceivers: Short for quad small form pluggable, they provide a 4-lane signal for a combined speed of 40Gbps.
QSFP28 Transceivers: Building on the QSFP design, these transceivers can support 4x25G or 4x28G speeds, making them versatile and powerful tools in modern data center applications.CFP Transceivers: Defined in CFP MSA, this transceiver supports 40G/100G speed and is 82 mm × 13.6 mm × 144.8 mm.
CFP2 Transceivers: Similar to CFP, but provide a smaller size of 41.5 mm × 12.4 mm × 107.5 mm and lower power consumption.
CFP4 Transceivers: CFP4 is released based on CFP2 for higher density and lower power consumption; the standard size is 21.5 mm × 9.5 mm × 92 mm.
CFP8 Transceivers
CXP Module: CXP is 120 Gb/s 12x Small Form-factor Pluggable; by supporting 12x10G lanes, it reaches a total speed of 120Gbps.
CSFP Transceivers: These are compact, small-form-factor pluggable devices that feature two BOSAs in the SFP size and provide double bandwidth capacity at some port density.
QSFP56 Transceivers
QSFP-DD Transceivers
OSFP Transceivers
CDFP Transceivers
X2 Transceivers
XENPAK Transceivers
XPAK Transceivers
SFP56 Transceivers
SFP56-DD Transceivers
Mini SFP Transceivers
COBO (Consortium for On-Board Optics)

Many transceiver form factors are available, but many require updates over time. For instance, most manufacturers have stopped supplying switches with Xpak, X2, and XENPAK ports instead of the more commonly used SFP+ and QSFP ports. Consequently, finding a supplier that still offers these transceivers can be challenging.

Indeed, some form factors are still in use, even though manufacturers may give them little attention. One example is the 1×9 SIP package, which is still used as the fiber I/O interface in some industrial Ethernet switches and media converters. That is probably why regular end customers may not be aware of them.

As our dependence on the internet grows, so does the need for reliable, high-speed connections. It has led to a significant increase in fiber cabling, which relies on high-speed optical transceivers. As a result, newer Form factors like SFP+, QSFP+, QSFP28, and QSFP-DD are gaining popularity and dominating the market.

Classified by Transceiver Transmission Rates

The transmission rate is the number of bits transmitted per second. The unit of measure for transmission rate is Mbps (Megabits per second) or Gbps (Gigabits per second).

Depending on transmission rates, fiber optic transceivers are classified into the following types:

0.5Mbps
2Mbps
10Mbps
52Mbps
84Mbps
100Mbps (155Mbps)
622Mbps
1Gbps (1.25Gbps)
2G/4G/8G/16G/32G Fibre Channel
2.5Gbps
3Gbps
6Gbps

10Gbps
25Gbps
40Gbps
50Gbps
56Gbps
100Gbps
120Gbps
200Gbps
400Gbps
800Gbps
1.6Tbps

Further Reading

Classified by Fiber Mode Types

Optical fibers are divided into: single mode fiber (SMF) and multi-mode fiber (MMF). As a result, optical transceivers are also classed as single mode and multi-mode transceivers to handle different optical fibers.

Single mode transceivers typically have transmission distances ranging from 10km to 160km. They operate on a typical center wavelength of 1310nm, 1490nm, or 1550nm over single mode fiber. Therefore, it is suitable for long-distance or large-capacity transmission.

Multi-mode transceivers are utilized for shorter transmission distances ranging from 0.5km to 2km. They operate on a typical center wavelength of 850nm over multimode fiber, which makes them suitable for low-cost, short-distance transmission.

Classified by transceiver applications

There are many different transceivers for various applications. By different applications, they are classified into the following.

SONET/SDH
FE/GE/10G/40G/100G/400G Ethernet
Broadcast Video
CPRI and LTE
Fibre Channel
PON
CWDM/DWDM

Structure of An Optical Transceiver

Take the most popular SFP/SFP+ as an example; the optical transceiver comprises the below parts. The other QSFP-DD, QSFP28, XFP, QSFP, CFP, CFP2, and GBIC transceivers have similar structures.

1	Latch
2	Optical Receiver
3	Optical Transmitter
4	Transceiver Shell
5	Label
6	Dust Plug
7	Spring

Table 1: A typical transceiver structure

Optical Transceiver Applications

Fiber Optic Transceiver is widely found in wired networking applications such as Ethernet, Fibre Channel, SONET/SDH/ONT, CPRI, FTTx, and InfiniBand. The platform includes Ethernet switches, routers, firewalls, network interface cards, and fiber media converters.

Storage interface cards, called HBAs or Fibre Channel storage switches, use fiber optic transceivers at speeds such as 2Gb, 4Gb, 8Gb, and 16Gb.

The Main Parameters of Optical Transceiver

• Data Rate: the number of bits transmitted per second.

• Transmission distance: the maximum distance over which optical signals can transmit. Optical signals sent from different types of sources can be transmitted over different distances due to the negative effects of optical fibers, such as dispersion and attenuation. Select optical modules and fibers when connecting optical interfaces based on the maximum signal transmission distance.

• Central wavelength: central wavelength represents the wave band for optical signal transmission. Currently, there are mainly three central wavelengths for standard fiber transceiver modules: 850 nm, 1310 nm, and 1550 nm, respectively, representing three wavebands.

• Optical Transmit power: The output optical power of an optical transceiver when it works properly. When two optical transceivers are connected, the transmit optical power of one end must be within the range of received optical power on the other end.

• Receiving sensitivity: the power at which the receiver of a fiber optic transceiver can receive optical signals within a range of bit error rate (BER = 10^-12), in dBm.

• Fiber mode: The mode of optical fibers is defined based on core diameters and features of optical fibers. Optical fibers are classified into single-mode (SMF) and multi-mode fibers (MMF). The multi-mode fibers have large core diameters and can transport light in multiple modes. However, the inter-mode dispersion is greater, so they are used to transmit optical signals over short distances. Single-mode fibers (SMF) have a small core size and can transmit light in only one mode with a small dispersion, so they can transmit optical signals for long-reach communication distances.

• Connector Type: The interface on an optic transceiver to accommodate a fiber. The commonly used connector types are LC connector (applicable to QSFP, SFP, SFP+, SFF, and XFP transceivers), SC connector (applicable to BIDI SFP, GBIC, X2, XENPAK, and 1×9 transceivers), ST and FC connector (applicable to 1×9 transceivers), and MPO connector (applicable to QSFP+, SR4, and CXP modules).

• Extinction ratio: the Minimum ratio of the average optical power with signals transmitted against the average optical power without signals transmitted in complete modulation mode. The extinction ratio indicates the capability of an optical module to identify signal 0 and signal 1. This parameter is a quality indicator for fiber optic transceivers.

• Eye diagram: an oscilloscope display in which a digital signal from a receiver is repetitively sampled and applied to the vertical input. At the same time, the data rate is used to trigger the horizontal sweep.

FAQs

Q: How to clean optical transceivers?

A dirty transceiver optical interface will lower the power and degrade the optical signal. So, cleaning the transceiver is crucial. For the field engineer, use the fiber optical cleaner tool per the steps below.

Check the transceiver connector end face using an end face checker.
Use the one-click fiber cleaner and insert it into the transmitter side.
Click the button to vibrate quickly and remove dirt from the end face.

Q: Can I use Single mode with a Multimode transceiver?

You can not. Because the single-mode transceiver usually uses a 1310nm or 1550nm laser, whereas the multimode module typically uses an 850nm laser. The generic transceiver can not work with different wavelengths.

Q: What is the optical transceiver HS code?

The most widely used HS code for most US customers is 8517.62.0090, but others may use different codes. Check with the local customs for details.

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Optical Transceiver