By laney | 06 August 2025 | 0 Comments
FBT Splitter
An FBT (Fused Biconical Taper) Splitter is a fundamental type of passive optical component used extensively in fiber optic communication networks to split an incoming optical signal into two or more outgoing signals. It's one of the two main technologies for manufacturing fiber splitters, the other being PLC (Planar Lightwave Circuit).
1.Core Principle (Based on Evanescent Wave Coupling):
Two or more optical fibers are precisely twisted together, heated (using a burner or electric heater), and stretched (tapered) while fused.
As the fibers are fused and tapered, their cores come very close together within the coupling region.
Light traveling in the core of one fiber extends slightly beyond its core into the cladding (this is the "evanescent wave").
In the fused region, the evanescent wave of one fiber overlaps with the core of the adjacent fiber. This allows light energy to couple from one core into the other.
The split ratio (e.g., 50:50, 70:30, 90:10) is primarily determined by the length of the fused coupling region and the degree of tapering during the manufacturing process.
2.Configuration (Number of Inputs/Outputs):
1x2 Splitter: Most fundamental type. Splits one input signal into two output signals. Can be equal (50:50) or unequal (e.g., 10:90, 5:95).
1x4 Splitter: Splits one input signal into four output signals. Often made by cascading three 1x2 splitters inside the package.
1x8 Splitter: Splits one input signal into eight output signals. Made by cascading multiple 1x2 splitters (e.g., one 1x2 feeding two 1x4s, or three 1x2 stages). Less common than PLC for this count due to size/loss.
1xN Splitter (N=16, 32, etc.): Technically possible by cascading, but highly impractical and uncommon for FBT technology. PLC splitters are vastly superior for these higher split counts due to compact size and lower loss.
2x2 Splitter: Has two inputs and two outputs. Can function bidirectionally. Common configurations include 50:50 (coupler) or specific unequal splits. Often used for signal combining or redundancy.
3.Operating Wavelength:
Single Window: Optimized for one specific wavelength band (e.g., 1310nm or 1550nm). Less common now.
Dual Window: Optimized for two wavelengths simultaneously (e.g., 1310nm & 1550nm). Very common for basic PON applications.
Triple Window (Wideband): Optimized for three wavelengths simultaneously (e.g., 1310nm, 1490nm, & 1550nm). Essential for modern PON systems (GPON, EPON, XGS-PON) carrying downstream video (1550nm), downstream data (1490nm), and upstream data (1310nm). A major advantage of FBT over some early PLC designs.
CWDM (Coarse Wavelength Division Multiplexing): Designed to split specific CWDM channel wavelengths (e.g., 1470nm, 1490nm, 1510nm, etc.) with minimal loss at those channels. More specialized.
4.Packaging:
Bare Fiber (No Connectors): Just the fused splitter module with unprotected fiber pigtails. Requires splicing into the network. Cheapest but needs protection.
Blockless / Mini Module: The fused splitter is embedded in a small, robust tube (often stainless steel filled with silicone) with short pigtails emerging. Compact and rugged for tight spaces like splice closures.
ABS Box Module: The splitter module is housed in a plastic (ABS) box. Input/Output fibers are terminated with connectors (e.g., SC/APC, LC/UPC) mounted on the box front panel. Provides easy plug-and-play connectivity. Common for FTTH distribution points (ODP, FDH) or lab use.
Rack Mount Chassis: Multiple splitter modules (usually ABS boxes or blockless modules on trays) are mounted inside a metal chassis designed for 19" equipment racks. Used in Central Offices (COs) or Headends for high-density splitting.
LGX Box Module: Similar to ABS box but designed to fit into standard LGX compatible chassis for modular deployment in panels or racks.
5.Key Considerations When Choosing an FBT Splitter Type:
Network Architecture: What split counts are needed? (FBT best for 1x2, 1x4, 2x2; PLC better for 1x8+).
Power Budget: Does the design require equal splitting, or is an unequal split needed for specific branches? (Unequal is an FBT strength).
Wavelengths Used: Is it a simple dual-window (1310/1550) application, or does it require triple window (1310/1490/1550) for modern PON?
Deployment Environment: Compact tube for closures? ABS box for distribution points? Rack chassis for CO?
Connectivity: Splicing (bare/mini-module) or connectors (ABS box)?
Summary Table of Common FBT Splitter Types:
6.Manufacturing Process:
Alignment: Two or more bare optical fibers (typically standard single-mode fiber - SMF) are stripped of their coatings and aligned parallel to each other.
Fusing & Tapering: The aligned section is heated while being stretched simultaneously. This creates a fused, elongated, and tapered region where the cores are brought close enough for coupling to occur.
Control: The process is carefully monitored and controlled to achieve the desired coupling ratio and minimize excess loss.
7.Typical Applications:
Passive Optical Networks (PONs): Like GPON, EPON, XG-PON (especially for lower splits or specific branch points).
Fiber-to-the-Home (FTTH): Distributing signals to multiple subscribers.
Local Area Networks (LANs) / Data Centers: Signal distribution.
Cable Television (CATV): Distributing video signals over fiber.
Test & Measurement: Signal monitoring or splitting for testing.
Sensors: Distributing light to multiple sensing points.
8.Advantages vs. PLC Splitters:
Lower cost (especially for low splits & unequal ratios).
Can handle multiple specific wavelengths effectively.
Simpler manufacturing for low splits/unequal ratios.
Disadvantages vs. PLC Splitters:
Higher temperature sensitivity.
Larger physical size for high split counts.
Higher and less uniform insertion loss across outputs for high splits.
Higher PDL.
Wavelength sensitivity can be more pronounced.
More difficult to achieve high uniformity across splits and wavelengths compared to PLC.
In Summary:
An FBT splitter is a cost-effective, widely used fiber optic component created by physically fusing and tapering optical fibers together. It splits light based on evanescent wave coupling within the fused region. It excels in applications requiring low split counts (especially 1x2), unequal splits, or where cost is a primary driver, but has limitations in size, temperature stability, and uniformity for higher split counts compared to PLC technology.
1.Core Principle (Based on Evanescent Wave Coupling):
Two or more optical fibers are precisely twisted together, heated (using a burner or electric heater), and stretched (tapered) while fused.
As the fibers are fused and tapered, their cores come very close together within the coupling region.
Light traveling in the core of one fiber extends slightly beyond its core into the cladding (this is the "evanescent wave").
In the fused region, the evanescent wave of one fiber overlaps with the core of the adjacent fiber. This allows light energy to couple from one core into the other.
The split ratio (e.g., 50:50, 70:30, 90:10) is primarily determined by the length of the fused coupling region and the degree of tapering during the manufacturing process.
2.Configuration (Number of Inputs/Outputs):
1x2 Splitter: Most fundamental type. Splits one input signal into two output signals. Can be equal (50:50) or unequal (e.g., 10:90, 5:95).
1x4 Splitter: Splits one input signal into four output signals. Often made by cascading three 1x2 splitters inside the package.
1x8 Splitter: Splits one input signal into eight output signals. Made by cascading multiple 1x2 splitters (e.g., one 1x2 feeding two 1x4s, or three 1x2 stages). Less common than PLC for this count due to size/loss.
1xN Splitter (N=16, 32, etc.): Technically possible by cascading, but highly impractical and uncommon for FBT technology. PLC splitters are vastly superior for these higher split counts due to compact size and lower loss.
2x2 Splitter: Has two inputs and two outputs. Can function bidirectionally. Common configurations include 50:50 (coupler) or specific unequal splits. Often used for signal combining or redundancy.
3.Operating Wavelength:
Single Window: Optimized for one specific wavelength band (e.g., 1310nm or 1550nm). Less common now.
Dual Window: Optimized for two wavelengths simultaneously (e.g., 1310nm & 1550nm). Very common for basic PON applications.
Triple Window (Wideband): Optimized for three wavelengths simultaneously (e.g., 1310nm, 1490nm, & 1550nm). Essential for modern PON systems (GPON, EPON, XGS-PON) carrying downstream video (1550nm), downstream data (1490nm), and upstream data (1310nm). A major advantage of FBT over some early PLC designs.
CWDM (Coarse Wavelength Division Multiplexing): Designed to split specific CWDM channel wavelengths (e.g., 1470nm, 1490nm, 1510nm, etc.) with minimal loss at those channels. More specialized.
4.Packaging:
Bare Fiber (No Connectors): Just the fused splitter module with unprotected fiber pigtails. Requires splicing into the network. Cheapest but needs protection.
Blockless / Mini Module: The fused splitter is embedded in a small, robust tube (often stainless steel filled with silicone) with short pigtails emerging. Compact and rugged for tight spaces like splice closures.
ABS Box Module: The splitter module is housed in a plastic (ABS) box. Input/Output fibers are terminated with connectors (e.g., SC/APC, LC/UPC) mounted on the box front panel. Provides easy plug-and-play connectivity. Common for FTTH distribution points (ODP, FDH) or lab use.
Rack Mount Chassis: Multiple splitter modules (usually ABS boxes or blockless modules on trays) are mounted inside a metal chassis designed for 19" equipment racks. Used in Central Offices (COs) or Headends for high-density splitting.
LGX Box Module: Similar to ABS box but designed to fit into standard LGX compatible chassis for modular deployment in panels or racks.
5.Key Considerations When Choosing an FBT Splitter Type:
Network Architecture: What split counts are needed? (FBT best for 1x2, 1x4, 2x2; PLC better for 1x8+).
Power Budget: Does the design require equal splitting, or is an unequal split needed for specific branches? (Unequal is an FBT strength).
Wavelengths Used: Is it a simple dual-window (1310/1550) application, or does it require triple window (1310/1490/1550) for modern PON?
Deployment Environment: Compact tube for closures? ABS box for distribution points? Rack chassis for CO?
Connectivity: Splicing (bare/mini-module) or connectors (ABS box)?
Summary Table of Common FBT Splitter Types:
| Feature | Common Options | Notes |
| Config | 1x2, 1x4, 2x2 | 1x8+ possible but impractical; PLC preferred. 2x2 useful for combining/redundancy. |
| Split Ratio | Equal: 50:50 (1x2), 25:25:25:25 (1x4) Unequal: 5:95, 10:90, 20:80, 30:70, 40:60 (1x2) |
FBT excels at custom unequal splits. |
| Wavelength | Dual Window (1310/1550nm), Triple Window (1310/1490/1550nm), CWDM | Triple window essential for modern PON. CWDM for specific channel splitting. |
| Packaging | Bare Fiber, Blockless/Mini Module, ABS Box (with connectors), LGX Box, Rack Mount | Blockless for closures; ABS/LGX for plug & play; Rack for central offices. Bare for splicing. |
6.Manufacturing Process:
Alignment: Two or more bare optical fibers (typically standard single-mode fiber - SMF) are stripped of their coatings and aligned parallel to each other.
Fusing & Tapering: The aligned section is heated while being stretched simultaneously. This creates a fused, elongated, and tapered region where the cores are brought close enough for coupling to occur.
Control: The process is carefully monitored and controlled to achieve the desired coupling ratio and minimize excess loss.
7.Typical Applications:
Passive Optical Networks (PONs): Like GPON, EPON, XG-PON (especially for lower splits or specific branch points).
Fiber-to-the-Home (FTTH): Distributing signals to multiple subscribers.
Local Area Networks (LANs) / Data Centers: Signal distribution.
Cable Television (CATV): Distributing video signals over fiber.
Test & Measurement: Signal monitoring or splitting for testing.
Sensors: Distributing light to multiple sensing points.
8.Advantages vs. PLC Splitters:
Lower cost (especially for low splits & unequal ratios).
Can handle multiple specific wavelengths effectively.
Simpler manufacturing for low splits/unequal ratios.
Disadvantages vs. PLC Splitters:
Higher temperature sensitivity.
Larger physical size for high split counts.
Higher and less uniform insertion loss across outputs for high splits.
Higher PDL.
Wavelength sensitivity can be more pronounced.
More difficult to achieve high uniformity across splits and wavelengths compared to PLC.
In Summary:
An FBT splitter is a cost-effective, widely used fiber optic component created by physically fusing and tapering optical fibers together. It splits light based on evanescent wave coupling within the fused region. It excels in applications requiring low split counts (especially 1x2), unequal splits, or where cost is a primary driver, but has limitations in size, temperature stability, and uniformity for higher split counts compared to PLC technology.
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