Spectroscopic Principle of An Optical Splitter

Fiber splitter or fiber optic splitter is one of the most important passive devices in the fiber network, an optical fiber having a plurality of inputs and a plurality of output terminals tandem device, commonly used in M × N to indicate a splitter M inputs and N outputs. The optical splitter used in the CATV system, are generally 1 × 2, 1 × 3, and composed of them 1 x N optical splitter. Just the same with the coaxial cable transmission system, in a optical network system, an optic signal of a optical network system also needs to coupled to the branch distribution, which require a important fiber optic passive component - the optical splitter.
Optical splitter can be divided into two types according to the spectroscopic principle: Fused Biconical Taper (FBT) and Planar Lightwave Circuit (PLC). FBT splitter is to side fuse two or more fiber together. While the PLC splitter is a micro-optical components product, which adapt of the lithography, forming an optical waveguide in the medium or on a semiconductor substrate. Basically the two type of fiber splitter share the similar spectroscopic principle. Both of them are coupled to each other by changing the optical fiber between the evanescent field (the degree of coupling, the coupling length) as well as to change the radius of the optical slender to achieve different size branching amount. On the contrary, things that combining multiple optical signals or vice versa into one single can be called Fiber synthesizer.
FTB Coupler
The working principle of FTB method is to fuse two or more optical fiber that without coating layer together by melting them under a high temperature environment, stretching the both sides to form a double cone zonespecial waveguide structured. Different spectral radios can be obtained by controlling the length of the fiber torsion angle and stretched. Finally, pull the cone on the quartz substrate with a curable adhesive curing and insert into a stainless brass. That’s how an FTB coupler formed.
There are some disadvantages of this method. Due to the coefficient of thermal expansion of the curing adhesive with a quartz substrate, the stainless steel tube inconsistencies, the degree of thermal expansion and contraction will be inconsistent when the ambient temperature changes. This is likely to cause damages to the optical splitter, which would become worse if in the wild. This is also the main reason that this fiber optic splitter is easy to get damaged. However, due to the making method of the FBT Coupler is simple, inexpensive, easy to connect to external fiber as a whole, and resistance in for-mechanical vibration and temperature changes, and other advantages, it has become the mainstream manufacturing technology in current the market.
PLC Splitter
The PLC splitter adopted semiconductor production process like photolithography, etching, developing technology and more. Waveguide array is located on the upper surface of the chips, the shunt function is integrated on the chip, which is implemented 1:1 branching on a chip. Then then coupled the multi-channel optical fiber array in the input terminal and output terminal of the chip, respectively, and last encapsulating.
Comparing with FTB coupler, PLC splitter shares some obvious advantages: meeting transmission needs of different wavelengths, compact structure, small size, uniform spectroscopic etc. At the same time, the main drawback of the PLC splitter is the complicated production process while the chip monopoly by several companies, as well as the cost disadvantages versus the FBT splitters.