Quick answer. A fibre optic transceiver works by converting electrical signals from network equipment into modulated light signals, which it then sends through a fibre optic cable to a matching transceiver at the other end of the cable. This second transceiver then converts the modulated light back into electric signals.
Fibre optic transceivers, also known as optical transceivers, form a key component of all fibre optic networks. In this article, we take a look at how they work and what benefits they bring to transferring data.
What is a fibre optic transceiver?
A fibre optic transceiver, or optical transceiver, is a device used in fibre optic communications to transmit and receive data through fibre optic cables. Each transceiver is split into two parts, a transmitter which is used to transmit the signals, and a receiver which is used to receive the signals. It’s these two parts, the transmitter and receiver, that give the transceiver its name.
How does a fibre optic transceiver work?
Transceivers work by sending modulated light pulses transmitted by a diode through a fibre optic cable. The most common transceivers require two separate fibre optic cables, one to transmit the data one way and the other for the signal from the opposite direction. They are unable to send and receive a signal through the same fibre optic cable at the same time as this can cause signal interference.
It is possible to get multi-directional transceivers, such as the Cisco SFP-10g-bxd-i, which allows data to be sent in both directions using the same cable at the same time. Multi-directional transceivers do this by modulating the light transmitted at different wavelengths meaning they can transmit and receive signals that don’t interfere with each other as they pass through the cable.
Many modern fibre optic transceivers are now hot-pluggable, meaning they are easy to integrate into existing networks and can be used instantly with minimal setup.
As previously mentioned, there are two main parts of the optical transceiver, the transmitter and receiver. They operate by converting electric signals to light, which is then sent through the fibre optic cable itself to transmit the data over distances. Here we give a quick overview of the role each one plays.
The transmitter
Held within the transmitter is a laser diode or LED which emits either infrared or visible light. When the transmitter receives an electrical signal, it modulates the light emitted from the diode into either amplitude modulation (AM) or frequency modulation (FM). This modulated light is then sent through the fibre optic cable at high speed towards the transceiver at the other end of the cable. Depending on the distance the transmission needs to be sent, will determine whether an LED or laser diode is used to transmit the light signal. LEDs are really only useful for short range transmissions, whereas laser diodes are preferable over longer distances.
Most laser-based diodes utilise three main types of lasers. Fabry Perot (FP) lasers are used for high speed, medium range transmissions. Distributed Feedback (DFB) lasers are used for long range, very high speed transmissions and Vertical-Cavity Surface-Emitting (VCSEL) lasers are used for medium range, high speed transmissions.
The receiver
Held within the transceiver is the receiver. The receiver has a photodiode or photodetector depending on the type of light source the transmitter sends. The receiver converts the optical signal into an electrical current. This current is then amplified and converted back into a digital signal, which is then relayed as required.
Fibre optic cable
Fibre optic cable consists of a microscopic glass core, which is surrounded by cladding. The purpose of the cladding is to ensure the light signal doesn’t ‘escape’ and continues to travel down the optic cable. The size of the actual optic core itself can be miniscule, with a width of no more than 9 micrometres. For comparison, a human hair is approximately 70 micrometres wide.
The type of cable used will vary based on its requirements. Most fibre optic cables can be categorised into two different modes, each having specific uses. There are cost and application benefits to both of them, so it’s important to decide which best suits the requirements of the network.
- Single mode fibre – As its name suggests, single mode fibre is designed to carry one form of light transmission, the transverse form. This type of cable is also the smallest, with a core width of approximately 9 micrometres. By utilising only one mode of light transmission, combined with a narrow optic core, this fibre mode is ideal to transmit data over a long distance, whilst maintaining a high bandwidth signal and minimal degradation.
- Multimode fibre – This mode is designed to transmit multiple different wavelengths at the same time. It has a wider cable diameter of up to 100 micrometres. Due to the way the multi types of light are transmitted down the cable, it is more susceptible to signal degradation due to the modal dispersion effect. Because of the risk of increased modal dispersion with multimode fibre, it is best suited for shorter transmission distances.
It’s important to note that the different modes of cable are not compatible with each other. As each has different core widths and operates on different light wavelengths, mixing the two will cause significant performance issues.
Why are fibre optic transceivers useful?
There are several benefits to using fibre optic transceivers over traditional copper. In many cases, they are more efficient and often safer, and more secure than copper. Here we list some of the key benefits of using fibre.
Lack of signal degradation
One of the key advantages of a fibre optic transceiver is that they’re able to transmit data over a considerable distance without losing signal integrity. In traditional telecommunications, copper cables were used with the signal being sent using electricity. Over distance, this signal could degrade, causing the final data to become corrupted. Because the light used in fibre optics travels considerably faster than electricity, it is capable of travelling over a longer distance, whilst experiencing a lesser degree of signal degradation.
Fibre is not susceptible to EM interference
Electromagnetic interference (EMI) is a considerable challenge when using traditional copper wiring to transmit and receive signals. The performance of copper is particularly prone to interference from environmental EM radiation, and unfortunately, there is an abundance of this in the modern world. Whether it be from your mobile phone or microwave, there are hundreds of sources of EMI that can corrupt a signal running through a copper wire. With fibre cables this isn’t a problem because the light signals sent via optic cables cannot be affected by EMI radiation.
Fibre is more secure
With fibre optical cable, the fibre core is enclosed making it impossible to ‘tap’ a fibre cable. The only way to access the signal being sent via a fibre cable is to access the optical interface connection at either end of the cable. Unlike a copper cable, where the cable itself can be accessed. This makes fibre a more secure connection, which is preferable if sensitive data is being sent.
They reduce the risk of sparks
In certain environments, fire hazards are a considerable concern. With traditional copper wiring, data is transmitted through the use of an electrical signal, meaning there is the possibility of sparks being created if the electrical cable becomes damaged. With a fibre cable that only carries light rather than electricity, you are reducing the possibility of sparks in the event that a cable experiences a fault. Overall this makes fibre optics a safer method of data transmission in high fire-risk environments.
What is the distance of a fibre optic transceiver?
In most cases, single-mode fibre optic cables can transmit data to a distance of approximately 40 km (24 miles). Usually, a multi-core fibre cable can only do the same to approximately 550m. However, there are several different factors that can have an effect on this, including the type of cable being used, the wavelength of the signal being transmitted, the optical power level of the signal being sent and the sensitivity of the receiver. It is possible to increase this distance through the use of amplifiers across a fibre optic network.
How to know which fibre optic transceiver to choose?
This really depends on the type of networking solution you are trying to establish. As we’ve mentioned there are various types of transceivers and different types of optic cables to support them. At TXO we have a large range of transceivers available to purchase, both OEM-originals (from brands such as Alcatel, Ciena and Huawei), and OEM-compatible optical transceivers.
If you need help and information on which transceiver is the best option for your network, get in contact with us today and we can provide you with expert advice on what to choose.
