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Comprehensive Guide to Optical Splitters

What is an Optical Splitter?

An optical splitter is a crucial passive fiber optic device that splits and combines optical signals. It can distribute the optical energy transmitted through a single fiber to two or more fibers in a predetermined ratio or combine the optical energy from multiple fibers into one fiber.

It is widely used in passive optical network systems, such as EPON, GPON, BPON, FTTX, and FTTH, to connect central office and terminal equipment and to achieve the branching and distribution of optical signals.

Types of Optical Splitters

Optical splitters can be categorized by manufacturing process into:

  • planar lightwave circuit splitter (PLC fiber optic splitter)
  • fused biconical taper splitter (FBT fiber optic splitter)

 

They can also be categorized by installation packaging into:

  • cassette type splitter (ABS box optical splitter)
  • micro optical splitter
  • bare optical splitter
  • LGX module optical splitter

FBT Splitter

7233101
Multimode 1X2 ABS Box Fused Type
7233102
1×4 out ABS Box Single Mode Fused Type
7233105
1×3 Steel Tube Single Mode Fused Type

LGX Type PLC Splitter

7233206
1X8 LGX Single Mode PLC Splitter with SC FC Connection
7233208
1×2 LGX Single Mode PLC with SC FC Connection
7233219-1x64-lgx-singlemode-plc-fiber-optic-splitter-sc-upc-type-768x768
1×64 LGX Single Mode PLC Splitter with SC FC Connection

ABS BOX Type PLC Splitter

7233209-1x64-abs-box-singlemode-plc-fiber-optic-splitter-sc-upc-type-768x768
1×64 Single Mode PLC Splitter ABS Box Type
7233212-1x8-abs-box-singlemode-plc-fiber-optic-splitter-sc-upc-type-768x768
1×8 Single Mode PLC Fiber Optic Splitter ABS Box Type
7233214-1x2-singlemode-plc-type-fiber-optic-splitter-sc-upc-connector-abs-box-768x768
1×2 Single Mode PLC Splitter ABS Box Type

MINI TUBE Type PLC Splitter

7233203-1x2-single-mode-blockless-plc-fiber-optic-splitter-768x768
1×2 Single Mode Blockless Types
7233201
1×16 Single Mode Blockless PLC Splitter
7233215
1×64 Single Mode Blockless PLC Splitter

What is a PLC Splitter?

A PLC (Planar Lightwave Circuit) splitter is a type of single-mode splitter that can evenly distribute the optical signal from one input fiber to multiple output fibers. This uniform distribution is critical for maintaining signal quality and transmission efficiency.

Advantages:

  • Insensitive to transmission wavelength, meeting the needs of different wavelengths.
  • Uniform light distribution, ensuring even signal distribution to users.
  • Compact structure, small size, and can be directly installed in various existing junction boxes without requiring special design for installation space.
  • Can support many branching channels, exceeding 32 channels.
  • Low cost for multiple branches, with more significant cost advantages as the number of branches increases.

Disadvantages:

  • Complex manufacturing process with high technical barriers. Currently, the chips are monopolized by a few foreign companies, and few domestic enterprises can mass-produce them.
  • Higher cost compared to FBT splitters, especially in low-channel splitters.

The PLC splitter is based on integrated waveguide technology on a quartz substrate, which helps improve the coupling, branching, and distribution efficiency of optical signals, thereby optimizing the signal transmission and processing. However, it should be noted that although LC fiber elements in PLC splitters play a crucial role, they can also be affected by nonlinear optical phenomena such as FWM (Four-Wave Mixing), which may cause signal distortion and reduce signal quality. Therefore, these factors need to be considered in the design and use of PLC splitters to ensure stable and reliable signal transmission.

What is an FBT Splitter?

An FBT (Fused Biconical Taper) splitter is made by fusing and tapering two or more optical fibers. By changing the evanescent field coupling between the fibers (coupling degree, coupling length) and the fiber core radius, different branching ratios can be achieved. Conversely, multiple optical signals can be combined into one, known as a optical combiner.

The fused biconical taper method involves bundling two or more stripped fibers together, heating them to a high temperature, and stretching them to form a special waveguide structure. By controlling the twisting angle and stretching length of the fibers, different splitting ratios can be obtained. The tapered region is then solidified with curing glue on a quartz substrate and inserted into a stainless copper tube, forming the optical splitter.

Advantages:

  • Mature technology and process with low development costs.
  • Low cost of raw materials, such as quartz substrate, fiber, heat-shrink tube, stainless steel tube, and some glue, with lower equipment and depreciation costs. Low-channel splitters like 1×2 and 1×4 are inexpensive.
  • The splitting ratio can be monitored in real-time, allowing for unequal splitters to be made.

Disadvantages:

  • Sensitive to wavelength, requiring devices to be chosen according to the wavelength, which is a critical flaw for triple-play networks that transmit signals at 1310nm, 1490nm, and 1550nm.
  • Poor uniformity, with 1×4 splitters having a maximum difference of about 1.5dB, and larger differences for 1×8 and above, which can affect overall transmission distance.
  • Insertion loss varies significantly with temperature changes (TDL).
  • Larger volume and weight for multi-channel splitters (e.g., 1×16, 1×32, 2×32), reducing reliability and limiting installation space.

Structure of Optical Splitters

Structure of PLC Splitter

A PLC splitter, based on a planar waveguide type on a quartz substrate, typically comprises the following parts:

  • Splitter Chip: The core component of the PLC splitter, made using semiconductor technology to create a layer of branching waveguides on a quartz substrate. It has one input and multiple outputs for efficient optical signal coupling and distribution.
  • Fiber Array Couplers: These couplers at both ends of the chip transmit optical signals from the input to the output. Precise alignment is necessary to ensure the splitter’s stability and performance.
  • LC Fiber: Some designs may include LC fibers as the input and output fibers, which enhance the splitter’s splitting ratio and polarization fidelity due to their high polarization sensitivity and low loss characteristics.
Structure of PLC Splitter

Structure of FBT Splitter

An FBT splitter is made by removing the coating of two or more optical fibers, fusing them through high-temperature heating, and forming a single device through side fusion. The fused area is then recoated to create a complete optical splitter.

Manufacturing of Optical Splitters

Manufacturing of PLC Splitter

1. Preparation of PLC Chips and Fiber Arrays

Prepare the PLC chip and fiber arrays, the fundamental materials for making PLC splitters.

2. Optical Alignment

Create optical waveguide branching devices on the chip, integrating up to 64 splits on one chip, then couple and encapsulate multi-channel fiber arrays at both ends of the chip.

3. Manufacturing Process

  • Use semiconductor processes (e.g., photolithography, etching, development) to create optical waveguide arrays on the chip’s surface, integrating the branching function on the chip (e.g., 1xN splits).
  • Deposition or sputtering process: Cover the glass substrate with a mask layer, then use photolithography and etching to create a waveguide.
  • Ion exchange and ion implantation processes: These can create low-cost waveguides but have less control over waveguide cross-section shapes. Mainly used for making splitters, with ion implantation being more efficient than ion exchange.
  • Chemical vapor deposition (CVD) and flame hydrolysis deposition (FHD): These processes have better control over waveguide cross-section shapes, enabling finer optical waveguide structures.

4. Post-Processing

  • Curing: Fix the optical waveguide array on the chip to ensure stability and consistency.
  • Encapsulation: Couple and encapsulate multi-channel fiber arrays at both ends of the chip.
  • Testing: Conduct reliability, environmental, and mechanical tests to ensure product quality and performance.

Manufacturing of FBT Splitter

The manufacturing process for FBT splitters includes the following steps:

  • Fiber Preparation: Bundle two or more optical fibers, ensuring they are stripped of their coating.
  • Fused Biconical Taper Process: Place the bundled fibers in a taper machine, heat and fuse them, and monitor the splitting ratio in real-time. Once the desired ratio is achieved, end the fusion process. One fiber end remains as the input, and the other end becomes the multi-output end.
  • Optical Fiber Array Formation: After fusion, the fibers form a special waveguide structure, typically a biconical shape. Controlling the twisting angle and stretching length of the fibers achieves different splitting ratios.
  • Optical Performance Testing: During manufacturing, test the optical splitter’s performance to ensure it meets advanced international standards.
  • Encapsulation and Testing: Finally, encapsulate the splitter and conduct final tests to ensure stability and reliability in practical applications.

In the manufacturing process of FBT splitters, what technologies can improve their performance and reliability?

In the fusion taper process of FBT splitters, precise control of melting temperature and time is a key factor in ensuring the quality of optical fiber. An automated control system can be used to precisely control the melting time to avoid excessive or short melting time, thereby improving melting quality and reducing energy consumption. Real-time monitoring of temperature, flow, pressure and other parameters during the melting process, and PID (proportional-integral-differential) control through a computer to maintain the stability and controllability of the melting process. During the fusion taper process, real-time monitoring of the splitting ratio changes, when the splitting ratio reaches the requirement, the fusion drawing is terminated. Avoid performance fluctuations caused by uneven melting.

Examples of technologies to improve the performance and reliability of FBT splitters:

  • Optimized design

According to the characteristics of FBT splitters, the structure and materials are optimized. Since FBT splitters are made by welding multiple optical fibers together and then carefully stretching and tapering them to a specific diameter, this unique manufacturing technology allows for efficient distribution of optical signals. The operational stability of optical components can be improved by improving the design of optical components, such as increasing the length of the optical microcavity.

  • Surface treatment technology

Advanced surface modification technology is used. For example, some optical coatings are not only easy to apply, but also can significantly change the properties of optical substrates, improving durability and optical transparency. In addition, surface activated bonding technology can also be used to improve bonding efficiency and reduce failure rates, thereby enhancing the overall performance of optical components.

  • Vacuum coating

Vacuum coating technology can form a uniform thin film on the surface of optical parts. This method is carried out by physical evaporation or sputtering. This technology can accurately control the thickness and material of the film, thereby significantly improving the performance and stability of optical components.

  • Optimization of fused taper process

In the manufacturing process of FBT splitters, the fused taper process is a key step. By monitoring the change of the splitting ratio in real time and ending the melt stretching after the requirement is met, the splitting ratio of the optical splitter can be ensured to be accurate, thereby improving its optical performance.

  • Multimode coupler design

For devices above 1×4, higher splitting capacity can be achieved by connecting multiple 1×2 couplers together. This design method can improve the flexibility and reliability of the overall system.

  • Non-axisymmetric optical system design

For non-axisymmetric optical systems, more complex optical design methods such as reverse Bragg diffraction and trapezoidal prisms can be used, which can significantly improve image clarity and MTF (simulated transfer function), thereby improving optical performance.

  • Customized applications

Customized applications for different systems and geometries can provide a potential way to improve multi-band optical performance and design high-density integrated photonic chips.

How to ensure the precise alignment and stability of the optical splitter?

Ensuring the precise alignment and stability of the optical splitter requires a comprehensive consideration of various techniques and processes.

Here are thespdcaficd steps and methods.

  1. Cleaning and preparation

First, the waveguide and fiber must be thoroughly cleaned to remove any dust or contaminants. Then, the waveguide is mounted on the waveguide frame, and one end of the fiber is mounted on the precision adjustment frame at the incident end, and the other end is connected to a light source (such as a 6.328 micron red light source) for observation during the initial debugging of the light.

  1. Machine vision and hybrid automatic alignment algorithm

High-precision alignment can be achieved by combining machine vision technology with hybrid automatic alignment algorithms. This system can ensure that the additional alignment loss of the waveguide device is less than 0.15DB.

These technologies not only improve the alignment accuracy, but also ensure the repeatability of the system.

  1. Precision adjustment frame

Use a precision adjustment frame to fine-tune the position of the waveguide and fiber to ensure that they remain in the best alignment during the coupling process.

  1. Interferometry

Interferometry can be used to verify that the correct alignment has been achieved. Dynamic interferometry can provide real-time system alignment information to ensure stability during the alignment process.

  1. Packaging unit

Packaging units usually include technologies such as UV glue or YAG laser welding, which can ensure the stability and long-term reliability of the waveguide and fiber during the packaging process.

  1. Temperature stability

PLC splitters should have good temperature stability, with wavelength-dependent loss and temperature stability of 0.3dB in the temperature range of -40 to 85°C.

  1. Multi-fiber alignment technology

For polarization-maintaining PLC splitters, precision multi-fiber alignment technology can be used to bond the optical fiber to the PLC circuit chip, which can maintain low insertion loss and high polarization extinction ratio over a wide wavelength range.

How does the optical splitter work?

The basic working principle of the splitter is to use the interference effect of the optical waveguide structure to achieve light splitting. When the incident light is coupled into the optical waveguide, interference occurs in the waveguide, thereby achieving light splitting.

Working principle of FTB splitter

When a single-mode optical fiber transmits an optical signal, the energy of the light is not completely concentrated in the core propagation, and a small amount is propagated through the cladding close to the core. If the cores of the two optical fibers are close enough, the mode field of the light transmitted in one optical fiber can enter the other optical fiber, thereby achieving the redistribution of the optical signal between the two optical fibers.

Working principle of PLC splitter

The working principle of PLC splitter can be summarized as follows:

  • Optical signal input

The optical signal first enters the PLC splitter through one or more input ports.

  • Optical waveguide array

The optical signal propagates in the optical waveguide array on the chip. These waveguides are etched on the substrate with a specific pattern and have low insertion loss and high channel uniformity.

  • Optical energy distribution

The optical waveguide array evenly distributes the optical signal to multiple output ports. This distribution process ensures that the light energy received by each output port is uniform.

  • Fiber coupling

Multi-channel fiber arrays are coupled at both ends of the chip, and the input and output ends are coupled and packaged to transmit the optical signal from the chip to the actual optical fiber.

PLC splitter vs FBT splitter

  1. Splitting ratio

PLCl splitters have a splitting ratio of up to 1:64, while FBTl splitters have a splitting ratio of 1:32. This means that PLC splitters can distribute optical signals to more channels and are suitable for larger-scale networks.

  1. Operating wavelength range

FBT splitters perform well in applications with low to medium port configurations and specific bands, but their performance in high-frequency and high-speed communication systems has certain limitations. FBT splitters usually only support specific wavelengths, such as 850nm, 1310nm, 1490nm, and 1550nm, and the insertion loss of other bands will be large. PLC splitters usually operate in the range of 1260nm to 1650nm, which enables it to handle full-band signal transmission.

In addition, the larger the splitting ratio of the FBT splitter, the higher the failure rate. When the splitting ratio exceeds 1:8, more than 7 1×2 connection packages are required, which not only increases the complexity, but also easily leads to errors and failures. This is an obvious disadvantage for high-speed communication systems that require high reliability.

FBT splitters have the advantage of being cost-effective in single-wavelength or dual-wavelength transmission, but PLCl splitters are more ideal in scenarios such as PON transmission that require future network expansion and monitoring. PLC splitters use waveguide technology to provide a wider range of operating wavelengths and are more suitable for large-scale applications due to their compact size and high reliability.

  1. Reliability and uniformity

PLC splitters have the advantages of low insertion loss, high return loss, and high channel uniformity, and are particularly suitable for connecting central offices and terminal devices in passive optical networks (EPON, BPON, GPON, etc.).

FBT splitters have a relatively simple manufacturing process and low cost, but their splitting uniformity may not be as good as PLC splitters.

  1. Volume and structure

FBT splitters may take up more space due to their manufacturing process, and in some cases may require additional equipment to achieve the same function.

  1. Environmental adaptability

PLC splitters have good environmental adaptability and can work normally under different temperature and humidity conditions.

  1. Technical threshold

The technical threshold of PLCl splitters is relatively high. The manufacturing process of PLC splitters is complex, and photolithography technology is required to form optical waveguides on dielectric or semiconductor substrates to achieve branching.

  1. Cost

FBT splitters are mainly made of steel, heat shrink tubing and other materials. The cost of these materials is not high, and the device manufacturing technology is relatively simple, so the price of FBT splitters is cheaper. In contrast, PLC splitters are produced using semiconductor technology, and their manufacturing process is complex and the chip cost is high, so their cost is relatively high.

However, in small-scale applications, the cost of FBT splitters is low, but in large-scale applications, their cost advantage is not obvious, and they may even be at a disadvantage.

  1. Variability and customization capabilities

The splitting ratio of PLC splitters is evenly distributed, which means that their splitting ratio is usually fixed and not variable. This equal distribution feature makes PLC splitters very suitable for occasions where optical signals need to be accurately and evenly distributed, but customized splitting ratios are not supported. FBT splitters can be customized according to user needs and support a variety of splitting ratios, such as 1:3, 1:7, 1:11, etc. This variability enables the FBT splitter to meet a variety of specific application requirements, such as using a lower splitting ratio in a small-scale network and a higher splitting ratio in a large-scale network.

How to evaluate the performance of optical splitters?

Insertion loss

Insertion loss refers to the loss of optical power caused by the intervention of optical devices in a fiber-optic communication system. This loss is usually measured in decibels (dB). Specifically, insertion loss is a measure of the optical loss between two fixed points in a fiber-optic link. The smaller the insertion loss, the better the performance of the optical splitter. Insertion loss is also affected by the splitting ratio.

In an optical splitter, the input optical signal is divided into multiple output optical signals, and the energy distribution ratio of each output optical signal is limited. This means that the energy of each output optical signal is less than the energy of the input optical signal, so the splitting ratio loss is also a loss. The higher the splitting ratio, the greater the proportion of the output optical power of the path to the total output optical power, but correspondingly, the insertion loss will also increase because more optical power is allocated to a single path.

In addition, insertion loss is also directly related to the support capacity of the optical fiber link, that is, the application capacity that the optical fiber link can support.

Directivity

The directivity of an optical splitter refers to the ratio of the output optical power at the non-injected light end to the injected optical power (measured wavelength) on the same side. This parameter directly affects the performance of the optical splitter in the fiber optic communication system.

In a fiber-to-the-home (FTTH) network, an optical splitter needs to distribute optical signals from a central site to multiple users. Highly directional optical splitters can ensure that optical signals maintain high energy during transmission, thereby improving the coverage and signal quality of the system. This is essential for achieving efficient optical signal distribution.

In long-distance transmission systems, optical splitters also need to have high directivity to ensure that optical signals are not affected by excessive attenuation during long-distance transmission, thereby maintaining signal stability and reliability.

In addition, the application of optical splitters in data center networks also requires high directivity, because data centers usually require high-density and high-efficiency optical signal distribution. Highly directional optical splitters can effectively reduce the loss of optical signals during the distribution process, thereby improving the performance of the overall network.

Uniformity

Uniformity refers to the consistency of the insertion loss of the optical splitter between different output ports. The difference between the maximum insertion loss and the minimum insertion loss is the uniformity of the splitter insertion loss.

Polarization Dependent Loss (PDL)

PDL refers to the difference in loss of optical signals of different polarization states for the optical splitter. Quickly measure the PDL index of the device and analyze its influencing factors.

Return Loss

Return loss refers to the optical power loss caused by internal reflection of the optical splitter. The return loss is usually determined by connecting the input end of the optical splitter to the light source and then measuring the optical power of the output port.

Working Bandwidth

The working bandwidth refers to the range of optical wavelengths in which the optical splitter can work effectively. Generally speaking, the wider the working bandwidth, the wider the applicability of the optical splitter.

Isolation

Isolation refers to the ability of the optical splitter to isolate the optical power between different output ports. In practical applications, it is best to choose an optical splitter with an isolation of more than 40dB to avoid affecting the performance of the entire network.

Environmental and mechanical properties

Factors such as vibration, shock, humidity, high temperature, low temperature, high and low temperature cycles, etc., which will affect the long-term stability and reliability of the optical splitter.

How to calculate splitter loss in optical fiber?

The insertion loss of the optical splitter can be calculated by the formula:

Ai=-10 Log10  ∑ (Pouti/Pin)

Ai refers to the insertion loss of the ith output port. Pouti is the optical power of the ith output port. Pin is the optical power value of the input port.

This formula shows that the insertion loss is the logarithm of theratio of the input optical power to the output optical power. Specifically, the greater the insertion loss, the greater the reduction in output optical power relative to the input optical power. This relationship is very important in the design and application of optical splitters because it directly affects the performance and stability of the system.

In addition, the insertion loss is also affected by the splitting ratio. The splitting ratio is defined as the ratio of the output optical power of a certain channel to the sum of all output optical powers, that is:

Ki=Pouti/∑ Pout

Ki is the splitting ratio of the i-th output port.

Another commonly used estimation method is to calculate based on the power of the splitting ratio.

The splitters have specifications such as 1:2, 1:4, 1:8, 1:16, 1:32, 1:64, etc. We can estimate the loss of these splitters accordingly. The loss is n*3+1, where n is the power of 2 of the splitting ratio.

For example, the loss of a 1:2 splitter is 1*3+1=4dB. The loss of a 1:16 splitter is 4*3+1=13dB. The ratio below 1:16 is more accurate. The larger the splitting ratio, the greater the error of this measurement method.

Optical Splitter Loss

To calculate the loss of optical splitter, the following losses need to be considered and accumulated.

1. Loss of the device itself, such as the loss caused by scattering, absorption, etc. of the optical signal when passing through the optical splitter.

2. Insertion loss. The optical splitter is usually connected to other optical devices or equipment through optical fiber. These connection interfaces will introduce insertion loss of the optical signal.

3. Splitting ratio loss.

For example, when the loss of the optical splitter itself is 0.5dB, the interface loss is 0.2dB, and the splitting ratio loss is 1dB, the total loss is 0.5dB+0.2dB+ldB=1.7dB.

It should be noted that the loss of the optical splitter may be affected by some factors, such as the wavelength of the optical signal, temperature, and the working state of the optical splitter. Therefore, in practical applications, it is necessary to select a suitable optical splitter according to the specific system requirements, and calculate and optimize the loss according to the actual situation.

The total loss of an optical link can be calculated by the following formula:

A=aL-10 Log10 k+Ac+Af

A is the total loss of the optical link

aL is the attenuation of the optical fiber to the transmitted light

k is the attenuation coefficient related to the link length

Ac and Af are the insertion loss and additional loss of the connector and joint respectively

The total loss of an optical link is a comprehensive indicator that reflects the attenuation of the optical signal intensity along the entire transmission path from the light source to the receiver, which is crucial to ensuring the performance and reliability of the optical fiber communication system.

Stephen Xie

Stephen Xie

Hello, I'm Stephen Xie, a sales representative at Hello Signal. I specialize in Passive Optical Components and Cabinet & Racks. I can recommend the most suitable products at competitive prices, ensuring worry-free service. Feel free to contact me with any questions.

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