What is optical splitter, PLC splitter, FBT splitter?

What is optical splitter

Optical fiber splitter is to split an optical fiber signal into two or more optical signal outputs by a determined ratio, which is an important device in access FTTH networks. For example, a 1x4 optical splitter distributes the optical signal in one optical fiber to four optical fibers in a certain proportion. Unlike the WDM (wavelength division multiplexer), the demultiplexer divides the optical signals of different wavelengths into corresponding wavelength channels, while the optical splitter divides the entire optical signal into multiple channels for transmission.

The work principle of optical splitter

The optical signal transmitted in the single-mode fiber cannot be completely concentrated in the core, and a small amount of light can propagate close to the fiber cladding. If the cores of the two fibers are close enough, the mode field of light traveling in one fiber can enter the other, and the optical signal is redistributed in the two fibers.

Types of optical splitter (PLC splitter VS FBT Splitter)

Optical splitters can be divided into planar waveguide (PLC) optical splitters and fused tapered (FBT) optical splitters according to the principle; according to the port type, it can be divided into: X-type (2×2) coupler, Y-type (1×2) couplers, star-type (N×N, N>2) couplers, tree-type (1×N, N>2) couplers, etc.; or divided into evenly or unevenly by splitting ratio; or divided by single mode(1310nm) and multimode(850nm).

What is FBT splitter

The FBT optical splitter is produced by using the traditional tapered coupler process. Two or more optical fibers that have been removed from the coating are bundled together, and then heated and melted at a high temperature on the tapered machine, and stretched to both sides at the same time. Monitor the change of splitting ratio in real time, and stop stretching once the splitting ratio is ok. One end of the optical fiber (the rest is cut off) is used as the input end, and the other end is used as the multi-channel output end. Different light splitting ratios can be obtained by controlling the twisted angle and stretched length of the fiber. Finally, the tapered area is solidified on the quartz substrate with curing glue and inserted into the stainless copper tube. That is process how FBT made.

How does plc splitter work

PLC (Planar Lightwave Circuit) optical splitter is an integrated waveguide optical power distribution device based on quartz substrate, which is manufactured by semiconductor technology (lithography, corrosion, development, etc.). The PLC splitter realizes the splitting of optical signals from one optical fiber to multiple optical fibers, and the optical energy is evenly distributed. The optical waveguide array is located on the upper surface of the chip, and the branching function is integrated on the chip; the multi-channel optical fiber arrays at the input end and the output end are respectively coupled at both ends of the chip and packaged.

?What is the difference between FBT and PLC splitter

The main advantages of the FBT optical splitter are easy material getting, low cost and easy production. The splitting ratio can be monitored in real time as required, and unequal splitters can be made. The disadvantage is: the mature tapering process can only draw less than 1:4 at a time. Therefore, when the splitting ratio is greater than 1:8, the FBT optical splitter needs more than 7 1x2 connection packages, which is prone to errors and failures. FBT splitter only supports three wavelengths: 850nm, 1310nm, 1550nm, which makes it impossible to work on other wavelengths.

The product features of the PLC splitter are: Loss is not sensitive to the wavelength, it can meet the transmission requirement of different wavelengths(1260~1650nm); Light can be evenly divided and equally distributed to the users; Compact structure; High branching channels, up to 64CH; Low cost, higher channels, lower cost. The disadvantage is that the cost is higher than that of the fused tapered splitter, especially in the low channel splitter. The manufacturing process of the device is complicated, and the chips mainly rely on imports.

Structure of plc splitter

The PLC optical splitter consists of three parts, an optical splitter chip and two fiber arrays coupled at both ends. These three components must be precisely aligned, and their design and assembly are critical to the stability of the PLC splitter. The chip is manufactured using semiconductor technology to grow a layer of splitting waveguide on a quartz substrate. The chip has one input port and N output port waveguides. Then, input and output fiber arrays are coupled to both ends of the chip, and the package is sealed to form an optical splitter with one input and N output ports.

PLC splitter chips & splitting ratios

The term “PLC splitter chip” refers to the individual chips obtained by cutting and polishing the PLC splitter wafer into Bar strips. These chips have a high yield and reliable quality. According to QYresearch data, the global market size of PLC splitter chips was 173 million in 2021 and is expected to reach 322 million by 2028, with a compound annual growth rate of 15.5%. China is the largest producer of PLC splitter chips in the world, accounting for approximately 85% of the market share, followed by South Korea. In terms of product type, 1xN is the largest sub-segment market, with a market share of over 60%. The biggest application market is the FTTX and PON systems. In the China market, FTTR has entered the scaling deployment phase. In overseas markets, according to the report of Fiber Online, the United States is in the upsurge of FTTH deployment, which will reach its peak in 2024-2026 and last for the entire decade. FTTH construction in Europe is also in full swing. According to Omdia’s forecast, the global PON equipment market will exceed $18 billion by 2027.

PLC splitter chips can be designed as 1×N and 2×N, and N is generally a multiple of 2, such as 1x2, 1x4, 1x8, 1x16, 1x32, 1x64; and non-equally divided, such as 1×3, 1×5, 1×9, etc. With the rise of demand for FTTR (Fiber to the Room), splitters with non-uniform splitting ratio will be more widely used, and the process will be more difficult. The PLC optical splitter chip has the advantages of low cost, high reliability, high flexibility, and scalability, and is especially suitable for various application scenarios such as transmission system, network integration, broadband access, optical fiber communication and multimedia services.

?Fiber Array（FA）

A Fiber Array (FA) is an array composed of a bundle of optical fibers or an optical fiber ribbon that is installed on a V-groove substrate with a specific interval. The FA is primarily composed of a V-groove baseplate, a cover plate, optical fibers, and glue. The FA is an important component of the PLC splitter, and it significantly reduces the loss caused by the alignment of optical waveguide devices and optical coupling.

The Fiber Array mainly relies on a precisely etched V-groove to achieve positioning. The V-groove requires a special cutting process to achieve precise fiber positioning. The stripped fiber portion, without the fiber coating, is placed in the V-groove. This process requires ultra-precision machining technology to accurately position the fiber core in the V-groove to reduce connection loss. The fiber array is then formed by pressing it with a pressurizer and fixing it with adhesive, and the end face is optically polished. The substrate material will affect the optical properties of the fiber array. Therefore, materials with small thermal expansion coefficients are used to ensure that the fiber array has no stress, high reliability, and no fiber displacement at high temperatures. Glass and silicon are commonly used materials, and there are also ceramics, conductive substrates, and plastic substrates.

?Polarization Maintaining (PM) fiber optic PLC splitter

A polarization-maintaining PLC splitter mainly achieves the uniform distribution of input signal while maintaining the polarization state unchanged. It uses a single-channel polarization-maintaining fiber array as the input end and a multi-channel polarization-maintaining fiber array as the output end. The polarization of the linearly polarized light wave emitted into the fiber remains unchanged during propagation, and there is little or no power cross-coupling between polarization modes, thus achieving polarization-maintaining coupling and signal splitting. Typically, PANDA polarization-maintaining fiber is used. PM PLC splitters are mainly used in special applications that require polarization maintenance, such as fiber optic sensing systems or coherent communication.

Types of PLC splitter

The types of PLC splitters mainly depend on their packaging, which can be classified into bare fiber optical splitter, blockless PLC splitter, ABS box PLC splitter, LGX PLC splitter, plug-in PLC splitter, and rack-mount PLC splitter.

The bare fiber optical splitter has bare fibers at all ends and is mainly used in situations where disassembly is rare, such as cable connector boxes, fiber optic distribution panels, etc.

The blockless PLC splitter is a mini-steel tube packaged splitter that can be either with or without fiber tails. Connectors typically include SC, LC, FC, and ST. It can be installed in fiber optic splice closures, module boxes, and distribution boxes.

ABS boxed PLC splitter is currently the most widely used type for operators. The ABS packaging is compact, versatile, and flexible in application.

LGX PLC splitter is packaged in a small metal box that can be installed in a 19-inch 1U/2U/3U panel. Input and output tails can be connected to the ODF panel adapter, saving time. It is compact, plug-and-play design, and can be easily installed in fiber optic distribution boxes, ODF frames, fiber optic terminal boxes, and cable junction boxes.

Plug-in PLC splitter is installed in a plug-in box with connector types such as SC/FC/LC. It is mainly used in FTTH access mode corridor or outdoor splitting points and is usually installed in wall-mounted FTTH boxes. Commonly used 1X4, 8, 16, 32 and 2X8, 16, 32 PLC splitters are used as plug-ins for installation in customer-specific chassis, especially in corridor boxes.

Rack-mount PLC splitter is designed for standard 19" cabinet installation to meet the high-density cabling requirements of data centers or server rooms. It is commonly packaged in a metal box that provides good protection for the PLC splitter device. It has various adapter installation interfaces such as SC, LC, FC, or ST connectors and is widely used in FTTX projects, cable TV systems, and data communication centers.

?Key parameters of PLC splitter

The indicators that affect the performance of PLC splitters generally include the following:

Insertion Loss (IL): It refers to the reduction value of the optical signal at a specified output port relative to the total input optical signal of the PLC splitter at the working wavelength. Simply put, it is the dB value of the light loss of each output relative to the input. Generally, the smaller the insertion loss value, the better the performance of the splitter.

Return Loss (RL): It refers to the ratio in dB of the reflected light (scattered light that continuously propagates to the input end) to the input light at the fiber optic connection point. The larger the return loss, the better, in order to reduce the impact of reflected light on the light source and the system.

Directivity: It refers to the ratio of the output optical power of the non-injected light on the same side to the injected optical power (measured wavelength) of the PLC splitter when it is working properly.

Polarization Dependent Loss (PDL): It refers to the maximum change in output optical power of the PLC splitter at each output port when the polarization state of the transmitted optical signal changes from fully polarized.

Isolation: It refers to the ability of an optical path of a fiber optic splitter to isolate the optical signal from other optical paths.

PLC splitter for FTTX and PON networks

A PON system can enable FTTx and provide a solution for the "last mile" of the access network. A typical PON system consists of an Optical Line Terminal (OLT), an Optical Distribution Network (ODN), and Optical Network Units/Terminals (ONUs/ONTs).

?The optical splitter is the most important passive optical device in the ODN equipment and allows multiple users to share a PON interface in FTTx. The split construction in PON networks includes primary and secondary splitting. Primary splitting has the advantages of high flexibility and low operating costs and is mainly used in densely populated urban areas. Secondary splitting has lower initial investment and can be used in areas with scattered users. There are two principles for splitter settings: first, try to use primary splitting, and second, the splitting level should not exceed secondary splitting.

The first-level method refers to the distribution of optical splitters in fiber distribution boxes, with a single optical fiber directly connected to the OLT at the central office end, and the other end connected to multiple ONT fibers at the user end through multi-fiber cables. First-level splitting can only connect to one splitter, generally using splitter with a larger number of splitting, such as 1:32 or 1:64. Second-level splitting typically uses a 1:8 or 1:16 splitter at the first-level splitting location, and a 1:4 or 1:8 splitter at the second-level splitting point.

?With fiber broadband entering the era of Gigabit, FTTR (Fiber to the Room) has become an important driver for the growth of home broadband services, and the demand for non-uniform optical splitters will increase as FTTR grows. Currently, all three major operators in China have launched commercial FTTR packages in their provinces, with rapid development in this field. According to securities industry calculations, the demand for PLC optical splitter chips for FTTR is tens of times that of FTTH/B.

About HYC

HYC Co.,Ltd（HYC）is a national Hi-tech optoelectronics company engaged in R&D, manufacture and marketing of fiber optical products. Providing professional product and service for fiber connectivity, WDM, PLC splitter, Micro-optics and optical subassemblies for high-speed transceivers. HYC products and solutions widely applied in 4G/5G, Data Center and Cloud Computing industry etc.