In modern optical communication technology, fiber optic couplers play an indispensable role as an essential optical device. With the increasing demand for high-speed, long-distance communication, fiber optic couplers are increasingly prominent in connecting and distributing optical signals. So, what is a fiber optic coupler, and where is it mainly used? This article will take you into the world of fiber optic couplers.
What is a fiber optic coupler?
A fiber optic coupler is a device used to couple light from one or several input fibers into one or more fibers or from free space into the fiber.
A fiber optic coupler is an essential fiber optic device. It is important to note that a fiber optic coupler has two different meanings:
- A fiber optic device may contain one or more input and output fibers. Light from one input fiber may be present in one or more output fibers, and the power distribution is wavelength—and polarization-dependent.
- It may also be a device that couples light from free space into an optical fiber.
The fiber optic couplers referred to here are of the first type, coupling light between optical fibers. Fiber optic couplers are usually directional couplers, i.e., the light entering the incident port does not return to the input port. Another characteristic quantity is the return loss, which characterizes the magnitude of the reflected light relative to the incident light.
Functions of fiber optic couplers
- connecting two or more optical fibers: a fiber optic coupler can connect signals from two or more optical fibers, allowing the signals to be passed between different optical fibers.
- Signal distribution or merging: it can distribute signals from one fiber to multiple fibers or merge signals from multiple fibers to one fiber.
- Terminal connection for fiber optic connection: a fiber optic coupler can connect two optical fibers with the same connector type.
Limitations of fiber optic couplers
If all the fibers used are single-mode, some physical factors will limit the coupler’s performance. In particular, coupling two or more incident lights of the same frequency into a single-polarized output fiber inevitably involves significant additional losses. Of course, the loss can be eliminated if the phase of the incident beams is precisely adjusted and stabilized.
However, this limitation does not exist for different incident wavelengths, and some couplers can couple two different wavelengths of light together into a single output fiber without significant loss.
A multimode fiber combiner can combine two incoherent light beams without coupling loss, but this reduces the luminosity.
Standard classifications of fiber optic couplers:
According to the different fibers coupled:
- SC fiber optic coupler: When applied to the SC fiber optic interface, it looks very similar to the RJ-45 interface, but the SC interface appears to be flatter. The apparent difference is still inside the contact. If it has 8 thin copper contacts, it is the RJ-45 interface; if it has a copper column, it is the SC fiber optic interface.
- LC fiber optic coupler: This is applied to the LC fiber optic interface, connecting the SFP module connector, which uses an easy-to-operate modular jack (RJ) latch mechanism.
- FC fiber optic coupler: applied to the FC fiber optic interface, the external reinforcement is the use of metal bushings, the fastening method for the screw buckle.
- ST fiber optic coupler: applied to ST fiber optic interface, commonly used in fiber optic distribution frame, the shell is a round, fastening method for the screw buckle.
According to the different shapes:
- Y-coupler: Y-coupler is similar to the letter Y. Y-coupler, also known as an optical splitter coupler. The input signal is split into two output fibers. The distribution ratio can sometimes be precisely controlled to meet the user’s specific application.
- T-Coupler: Unlike the Y-coupler, the T-coupler has an uneven power distribution. The power of one output signal is greater than the power of the other output signal. Popular distribution ratios include 10:90% and 20:80%. This type of optocoupler is usually used in small networks with a low number of ports.
- X-Coupler: The X-coupler performs the functions of a splitter and combiner in a single package. It combines the optical power from the two input fibers and distributes it between the two output fibers. Another name for the X-coupler is the 2 x 2 Coupler.
- Star Coupler: Star couplers typically have multiple input and output port combinations, where optical power is distributed from multiple input ports to various output ports.
- Tree Coupler: A tree coupler is also a multi-port coupler. It shunts optical power from one input fiber to more than two output fibers. Tree couplers can also reversely combine optical signals from more than two input fibers into a single output fiber.
Typical Applications of Fiber Optic Couplers
Some typical applications for fiber optic couplers include:
- In a cable television system, intense signal light from one transmitter is fed into a fiber optic splitter, which distributes the light into many different subscriber output fibers.
- Fiber couplers, such as optical coherence tomography (OCT), can be used in fiber optic interferometers.
- In a fiber laser’s resonant cavity, a dichroic fiber coupler can inject pump light, and another coupler is employed as the output coupler. This technique is usually used without injecting light at the resonant cavity port, especially in fiber ring lasers.
- In fiber amplifiers and lasers, dichroic couplers often inject or eliminate residual pump light from the signal input. In high-power fiber lasers and amplifiers, multimode fiber couplers combine the outputs of several laser diodes and feed them into the inner cladding of the active fiber (double-clad fiber).
Conclusion
This article introduces fiber coupler classification, application, and role. I hope you gain a new understanding of fiber couplers through this article.
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