A fiber optic splitter, also known as an optical splitter, is a passive optical device used in FTTH (Fiber to the Home) systems to split a single optical fiber signal into two or more output optical signals according to a predetermined ratio. For example, a 1x4 optical splitter distributes the optical signal from one fiber to four fibers in a specific ratio. Unlike the wavelength division multiplexer (WDM) in a WDM system, which separates optical signals of different wavelengths into corresponding wavelength channels, an optical splitter distributes the entire optical signal across multiple channels for transmission.
Working Principle of an Optical Splitter
When transmitting optical signals in a single-mode fiber, the energy of the light is not entirely concentrated in the fiber core; a small amount propagates through the cladding near the core. In other words, if the cores of two fibers are close enough, the mode field of the light propagating in one fiber can enter the other, allowing the optical signal to be re-enhanced in both fibers. New allocation.
Types of Optical Splitters
Optical splitters can be classified into two types according to their operating principle: planar waveguide (PLC) optical splitters and fused biconical tapered (FBT) optical splitters; according to their port configuration, they can be classified into: X-type (2x2) couplers, Y-type (1x2) couplers, star (NxN, N>2) couplers, tree (1xN, N>2) couplers, etc.; according to their splitting ratio, they can be classified into non-uniform splitting and uniform splitting; another classification method is based on single-mode (1310nm) and multi-mode (850nm).
FBT Fused Biconical Tapered Optical Splitter
FBT optical splitter... The circuit is manufactured using a traditional tapered coupler process. Two or more optical fibers, with their coating removed, are bundled together and then melted at high temperature on a tapering machine while being stretched to both sides. The splitting ratio is monitored in real time. Once the desired splitting ratio is achieved, the melting and stretching process ends. One end retains one fiber (the rest are cut off) as the input, while the other end serves as a multi-output terminal. Different splitting ratios can be obtained by controlling the angle of fiber twist and the length of stretching. Finally, the tapered section is cured with adhesive onto a quartz substrate and inserted into a stainless steel tube.
PLC Plane Wave PLC (Planar Lightwave Circuit) optical splitters are integrated waveguide optical power distribution devices based on quartz substrates, fabricated using semiconductor processes (photolithography, etching, development, etc.). PLC splitters split optical signals from a single optical fiber into multiple optical fibers, achieving uniform distribution of optical energy. The optical waveguide array is located on the upper surface of the chip, integrating the splitting function onto the chip; then, multi-channel fiber arrays are coupled to the input and output ends at both ends of the chip and encapsulated.
FBT VS The main advantages of PLC FBT tapered splitters are simple raw material usage, relatively low cost, and less demanding equipment and process requirements. The splitting ratio can be monitored in real-time as needed, allowing for the fabrication of unequal splitters. The disadvantages are: currently, mature tapering technology can only produce splitters up to 1x4. For devices larger than 1x4, multiple 1x2 units are connected together and then packaged in a splitter housing. FBT splitters only support three wavelengths: 850nm, 1310nm, and 1550nm, making them incompatible with other wavelengths.
The product characteristics of PLC splitters are: loss is insensitive to optical wavelength, meeting the transmission requirements of different wavelengths (1260~1650nm); uniform splitting, distributing signals equally to users; compact structure and small size; single unit... The device has a high number of splitter channels, reaching over 64: higher cost per channel, and the more channels, the more significant the cost advantage. The disadvantage is its higher cost compared to fused biconical tapered splitters, especially in low-channel splitters.
Structure of PLC Optical Splitter
The PLC optical splitter consists of three parts: an optical splitter chip and fiber optic arrays coupled at both ends. These three components must be precisely aligned; their design and assembly play a crucial role in the stability of the PLC splitter. The chip uses semiconductor technology to grow a splitter waveguide on a quartz substrate. The chip has one input and N output waveguides. Then, input and output fiber optic arrays are coupled to both ends of the chip, and a casing is installed to form an optical splitter with one input and N outputs.
PLC Splitter chips can be designed as 1xN and 2xN, where N is usually a multiple of 2, such as 1x2, 1x4, 1x8, 1x16, 1x32, 1x64; and non-uniformly distributed splitters, such as 1x3, 1x5, 1x9, etc. With the rise in demand for FTTR (Fiber to the Room), the application of non-uniformly distributed power splitters will become increasingly widespread, and the manufacturing process will become more challenging. PLC optical splitter chips have advantages such as low cost, high reliability, high flexibility, and scalability, making them particularly suitable for various application scenarios such as transmission systems, network integration, broadband access, fiber optic communication, and multimedia services.
Polarization-Maintaining PLC Splitter The polarization-maintaining PLC splitter mainly realizes... While maintaining the polarization state, the input power is uniformly split, using a single-channel polarization-maintaining fiber array as the input and a multi-channel polarization-maintaining fiber array as the output. The polarization of the linear polarimetric wave emitted into the fiber remains unchanged during propagation, and there is little or no cross-coupling between polarization modes, thus achieving polarization-maintaining coupling and beam splitting. Typically, PANDA fiber is used. PLC optical splitters are mainly used in special applications requiring polarization maintenance, such as fiber optic sensing systems or coherent communication.
Key Performance Indicators of PLC Optical Splitters
The performance indicators affecting optical splitters generally include:
Insertion Loss Insertion Loss (IL): Insertion loss refers to the reduction in optical power at a specified output port relative to the total input optical power at the operating wavelength of a PLC splitter. Simply put, it's the dB loss of each output relative to the input. Generally, the lower the insertion loss, the better the splitter's performance.
Return Loss: Return loss refers to the ratio in decibels of the reflected light (scattered light continuously transmitted to the input) to the input light at the fiber optic connection. Higher return loss is better to reduce the impact of reflected light on the light source and system.
Directivity: Directivity refers to the ratio of the output optical power at the non-injection light end to the injection light power (measured wavelength) on the same side of the PLC splitter during normal operation.
Polarization Dependent Loss: Polarization dependent loss refers to the maximum change in output optical power at each output port of the PLC splitter when the polarization state of the transmitted optical signal changes across the entire polarization state.
Isolation: Isolation refers to the ability of a fiber optic splitter to isolate optical signals in other optical paths from a given optical path.