Basical Information About Fiber Coupler
Definition of Optical CouplerFiber couplers are special optical fiber devices with one or several input fibers for distributing optical signals into two or more output fibers or from free space into a fiber.
Fiber optic coupler has input and output configurations defined as M x N. M is the number of input ports. N is the number of output ports and is always equal to or greater than M. For example, following is a 2x2 fiber coupler.
2*2 fiber coupler
Common Types of Fiber Optic Couplers
Typical types of fiber optical couplers include fiber splitters, fiber combiners.
Fiber optic splitters take one input optical signal and supply two outputs. Also described as either Y-couplers or T-couplers. The difference between Y-couplers and T-couplers is the power distribution, the former Y-couplers have equal power distribution and the two output signal each receive half. While the power distribution of T-couplers is uneven. This is the specifications of splitting ratio, will mentioned in the follow.
fiber splitter
While, Fiber optic combiners receive two input signals and provide a single output. The output signal is typically comprised of multiple wavelengths, due to the amount of interference that occurs when attempting to combine two signals that share the same wavelength.
fiber combiner
What Factors do We Consider When buying Optical Fiber Coupler?
When buying optical couplers, we always consider the fiber optic cable, the coupler type, signal wavelength, number of inputs and outputs, as well as insertion loss, splitting ratio, and polarization dependent loss (PDL).
-Wavelength
Most fiber couplers work only in a limited range of wavelength (a limited bandwidth), since the coupling strength is wavelength-dependent (and often also polarization-dependent). This is a typical property of those couplers where the coupling occurs over a certain length. Fiber optic couplers transmit light waves from the far visible region, red (630nm), to the near infrared region (1700nm). Within this region specific frequency bands are used as to avoid absorption bands within the carrier medium, the optical fiber. Wavelength choices for fiber optic couplers include 633 nm, 830 nm, 1060 nm, 1300 nm, and 1550 nm.
-Splitting Ratio
The splitting ratio is the distribution of power among the output fibers of a optic coupler, it is also referred to as the coupling ratio. A splitting ratio of 50/50 means that there is an equal distribution of optical power; a 60/40 ratio means 60% of the power is transmitted to a primary output and 40% to the secondary output.
-Insertion Loss
In particular, it is not possible to combine two or more inputs of the same optical frequency into a single-polarization output without significant excess losses, except if the optical phases of the input beams are precisely adjusted and stabilized. That means that the two inputs to be combined would have to be mutually coherent. The degree to which the signal has been depleted is described as insertion loss, which is the undesired attenuation of the signal measured in decibels (dB).
-Polarization Dependent Loss (PDL)
Polarization dependent loss is a measure of the peak-to-peak difference in Transmission of an optical component or system with respect to all possible states of polarization. It is the ratio of the maximum and the minimum transmission of an optical coupler with respect to all polarization states. The polarization dependence of the transmission properties of optical components has many sources.
Spoke for so long, you still don't know where to use the optical couplers. For example, in a cable TV system, the powerful signal from one transmitter is sent in to a fiber splitter, which distributes the power over a large number of output fibers for different customers. You may come up with other examples, in general, people benefit a lot in common life from fiber couplers.