1550 nm 1x2 Polarization-Maintaining Fiber Optic Couplers / Taps


  • Narrowband or Wideband PM Couplers with 1550 nm Center Wavelength
  • 50:50, 75:25, 90:10, or 99:1 Split Ratio
  • 2.0 mm Narrow Key FC/PC or FC/APC Connectors
  • High ≥25 dB Polarization Extinction Ratio (PER) Options

Use for Splitting Signals

PNH1550R2F1

90:10 PM Coupler with FC/PC Connectors and High PER

PN1550R5A1

50:50 PM Coupler with FC/APC Connectors

Related Items


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1x2 PM Coupler Selection Guide
Center Wavelength Bandwidth
480 nm ±15 nm
530 nm ±15 nm
560 nm ±15 nm
635 nm ±15 nm
670 nm ±15 nm
780 nm ±15 nm
850 nm ±15 nm
980 nm ±15 nm
1064 nm ±15 nm
±65 nm
±100 nm
1300 nm ±100 nm
1310 nm ±15 nm
1480 nm ±15 nm
1550 nm ±15 nm
±65 nm
±100 nm

Click for Details

Each coupler is engraved with the Item #, serial number, and key specifications for easy identification. When the white port on the left is used as the input, the coupling ratios listed below correspond to the ratio of the measured output power from the white (signal output) port to the red (tap output) port.
As part of Thorlabs' sustainability efforts, we are transitioning from distributing paper copies of unit-specific test reports with these products to offering them digitally. For devices supported by digital download, test results can be accessed by clicking on the red Docs icon () next to the Item # and entering your device's serial number under "Download Serial Item Data." If your device was provided with a paper copy of the test results and you prefer an electronic version, please contact Tech Support.

PANDA PM Fiber Cross Section

Panda Style Fiber
The connector key is aligned to the slow axis of the fiber.

Features

  • 1550 nm Polarization-Maintaining Fiber Optic Couplers
  • Wideband and Narrowband Options Available
    • ±15 nm Bandwidth for All Split Ratios
    • ±65 nm Bandwidth for 50:50 Couplers
    • ±100 nm Bandwidth for 75:25, 90:10, or 99:1 Couplers
  • 50:50, 75:25, 90:10, or 99:1 Split Ratio
  • Polarization Extinction Ratios (PERs):
    • Narrowband Couplers: ≥20.0 dB (Standard) or ≥25.0 dB
      (High PER)
    • Wideband Couplers: ≥20.0 dB (50:50) or ≥18.0 dB (All Other
      Split Ratios)
  • 2.0 mm Narrow Key FC/PC or FC/APC Connectors
  • 0.8 m Long Fiber Leads with a Tolerance of +0.075 m / -0.0 m
  • Individual Test Report Available for Each Coupler (Click for a Sample Test Report: Narrowband and Wideband)
  • Contact Us for Custom Wavelength, Coupling Ratio, and Connector Options

These 1x2 Polarization-Maintaining (PM) Fiber Couplers are designed for operation at 1550 nm and are available with a 50:50, 75:25, 90:10, or 99:1 coupling ratio. Both narrowband (±15 nm bandwidth) and wideband (±65 nm or ±100 nm bandwidth) couplers are featured below. 1x2 couplers have only one input port for simplified use and cable management. These couplers are ideal for applications where light is split from the input port into two output ports at the specified coupling ratio; unlike WDMs, they are generally not recommended for beam combining applications. The unused port is internally terminated within the coupler housing in a manner that minimizes back reflections (please see the 1x2 Coupler Tutorial tab for details).

PM couplers are manufactured using PANDA fiber, which allows them to maintain a high polarization-extinction-ratio (PER) when light is launched along the slow axis of the fiber. As seen in the diagram to the right, stress rods run parallel to the fiber's core and apply stress that creates birefringence in the fiber's core, allowing polarization-maintaining operation. Typical applications for PM couplers include optical sensors, optical amplifiers, and fiber gyroscopes.

Thorlabs' High Polarization Extinction Ratio (PER) Narrowband Couplers provide a PER of ≥25 dB when measured with connectors while the standard narrowband PM Couplers provide a PER of ≥20 dB when measured with connectors. Our wideband couplers with a 50:50 split ratio have a PER of ≥20 dB, and those with a 75:25, 90:10, or 99:1 split ratio have a PER of ≥18.0 dB. For specific differences between the standard and high PER cables, please refer to the Comparison tab. As with all the couplers on this page, the high PER versions have a specified operating temperature range of -40 °C to 85 °C but the actual PER will vary slightly over the entire range, as shown in the Temperature Cycling Tests section of the PER Measurement tab. Note that within an optical system the achievable PER is always limited by the element with the lowest PER within the system.

All of these 1550 nm couplers have a maximum power handling of 1 W with connectors or bare fiber and a maximum power handling of 5 W when spliced (see the Damage Threshold tab for more details). These couplers undergo extensive individual testing and verification of the PER; details of our testing procedures are provided on the PER Measurement tab. Testing results are available for each coupler; click for a sampe test report of our narrowband or wideband 1550 nm PM couplers.

Custom and OEM Fiber Couplers
Our couplers are produced on-site in our North American manufacturing facilities and our design team is able to deliver custom solutions in as little as three weeks. Custom coupler configurations with other wavelengths, fiber types, coupling ratios, port configurations, alignment axes, or housing options are available, and each custom coupler includes an individualized test report. Please contact Tech Sales for inquiries or to discuss your application.

These couplers are available with 2.0 mm narrow key FC/PC or FC/APC connectors, as outlined in the tables below. Fiber leads are jacketed in Ø900 µm Hytrel®* tubing and the leads are 0.8 m long.

*Hytrel® is a registered trademark of DuPont Polymers, Inc.

Alternative Fiber Coupler & Splitter Options
Double-Clad Couplers Single Mode Couplers Single Mode PLC Splitters Multimode Couplers Polarization-Maintaining Couplers Wavelength Division
Multiplexers (WDM)
2x2 1x2 2x2 1x4 1x8 1x16 1x2 2x2 1x2 2x2
Item #a Description Qty.
Light Source (Not Shown)
S5FC1005P PM Benchtop SLD Source, 1550 nm 1
P1-1550PM-FC-1 Patch Cable, FC/PC, 1550 nm, PM Panda Style, 1 m 1
Linear Polarizer Module
PAF-X-11-PC-Cb FiberPort, FC/PC,
1050 nm - 1620 nm
2
CP08FP(/M) Cage Plates for Mounting FiberPorts 2
LPNIR050-MP2 Linear Polarizer 1
CRM1P(/M) Cage Rotation Mount 1
SM1A6T Adapter with External SM1 Threads and Internal SM05 Threads 1
ER2-P4 2" (50.8 mm) Long Cage Rods, 4 Pack 1
Analyzer Module
PAF-X-11-PC-Cb FiberPort, FC/PC,
1050 nm - 1620 nm
1
CP08FP(/M) Cage Plates for Mounting FiberPorts 1
LPNIR050-MP2 Linear Polarizer 1
CRM1P(/M) Cage Rotation Mount 1
SM1A6T Adapter with External SM1 Threads and Internal SM05 Threads 1
CP33(/M) SM1-Threaded (1.035"-40)
Cage Plate
1
PM122D Digital Power Meter, 700 - 1800 nm 1
ER2-P4 2" (50.8 mm) Long Cage Rods, 4 Pack 1
  • Item list does not include the posts, post holders, clamping forks, breadboard, or fiber component tray shown in the photo to the left.
  • This previous-generation FiberPort is no longer available. A suitable replacement is the PAF2P-11C FiberPort.

Click to Enlarge
Setup to Measure the Extinction Ratio of a
1550 nm PM Coupler

Measurement of Polarization Extinction Ratio (PER)

The polarization extinction ratio (PER) is a measure of how well a polarization-maintaining (PM) fiber or device can prevent cross coupling between the different polarization axes of the fiber. External stress on a fiber from sources such as heating, bending, or pulling can cause the PER to change.

There are two accepted techniques for measuring PER in a fiber coupler. The most common method uses a low-coherence (unpolarized or circularly polarized) broadband light source and measures the extinction ratio with a linear polarizer and power meter. An alternative method uses a narrowband, high-coherence light source and measures the PER with a polarimeter.

Thorlabs uses the power meter method to characterize the extinction ratio performance of the PM fiber couplers sold on this page. An example setup is shown in the image to the right with itemized component list in the table. A broadband light source is input into a linear polarizer module, which allows the user to set the polarization of light entering the input leg of the fiber coupler. The output from one of the legs is sent to the analyzer module, which contains another polarizer and the power meter for measuring the output. Alternatively, the analyzer module can be replaced with an extinction ratio meter.

The PER is measured using the following test procedure:

  • Prepare the fiber end faces of the PM coupler to connect to the measurement setup.
    • For bare fiber ends, strip and cleave the fibers. Use a bare fiber terminator, such as the BFT1, to create a temporary fiber termination.
    • For terminated fiber ends, clean and inspect the connector end faces.
    • Attach a fiber optic light trap to any fiber leads not being measured.
  • Adjust the polarizers in the linear polarizer and analyzer modules sequentially until a minimum power value is measured by the power meter. Record the measured value as Pmin.
  • Rotate the analyzer rotation mount by 90°. Then record the measured value as Pmax.

After Pmin and Pmax are measured, the extinction ratio can be calculated:


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7-hour temperature cycling test performed on a standard PN1550R5A1 PM fiber coupler shows that the PER measured for the white-white and white-red paths remains stable over a wide temperature range.

The White-White Path Follows the Input to Signal Output and the White-Red Path Follows the Input to Tap Output


Temperature Cycling Tests

Traditional PM couplers typically exhibit diminished polarization extinction ratio (PER) performance when used at sub-zero (°C) temperatures due to the contraction of the adhesives that are used to assemble the device. This effect disrupts the polarization state of light within the coupler and leads to a decrease in PER. Soft adhesives can be used to mitigate the impact of cold-temperature operation but can create reliability issues at higher temperatures. At high temperatures, adhesives can soften permanently, which changes the optical properties of the coupler.

Unlike traditional coupler manufacturing, Thorlabs uses a proprietary packaging process and design for our standard PM couplers as well as careful selection of adhesives to enable operation over a very wide temperature range (from -40 °C to 85 °C) without significant changes to PER and other optical specifications.

Wideband Fiber Coupler Testing and Verification Procedure

During Thorlabs' coupling manufacturing process, the coupling ratio and bandwidth of each wideband coupler is monitored as the two branches are fused together. This ensures that each wideband coupler meets the stated specifications over the bandwidth. Each coupler has an individualized test report available, providing a summary of the results of these tests. Sample test reports for our 1550 nm wideband couplers are available.

Step 1

The fiber to create the first branch (Path A) of the coupler is connected to a source on one side and a switch leading to an Optical Spectrum Analyzer (OSA) on the other.


Step 2

The spectrum of the source through the fiber and switch is measured using the OSA and zeroed. 


Step 3

The fiber to form the second branch (Path B) of the coupler is connected to the source and to the second port of the switch leading to the OSA. The spectrum of the source through the fiber and switch is also measured and zeroed.


Step 4

The two fibers are fused on a manufacturing station to create the coupler structure. During the fusing process, the output from both legs of the coupler is monitored on the OSA. Coupler fusing stops once the coupler reaches the desired coupling ratio, excess loss, and insertion loss specifications.

For 1x2 couplers, one of the fiber ends is terminated within the coupler housing. The termination is done in a manner that minimizes back reflections from this output.



Click to Enlarge

Insertion loss (in dB) is the ratio of the input power to the output power from each leg of the coupler as a function of wavelength. It captures both the coupling ratio and the excess loss. The coupling ratio is calculated from the measured insertion loss. Coupling ratio (in %) is the ratio of the optical power from each output port (A and B) to the sum of the total power of both output ports as a function of wavelength. It is not impacted by spectral features such as the water absorption region because both output legs are affected equally. Persistence plots showing the coupling ratio of our wideband couplers can be viewed by clicking on the blue info icons below.

Click to Enlarge

The uniformity is also calculated from the measured insertion loss. Uniformity is the variation (in dB) of the insertion loss over the bandwidth. It is a measure of how evenly the insertion loss is distributed over the spectral range. The uniformity of Path A is the difference between the value of highest insertion loss and the solid red insertion loss curve (in the Insertion Plot above). The uniformity of Path B is the difference between the solid blue insertion loss curve and the value of lowest insertion loss. Persistence plots showing the uniformity of our wideband couplers can be viewed by clicking on the blue info icons below.

1550 nm PM Narrowband Coupler Comparison

The graphs below depict sample data comparing Thorlabs' 1550 nm high polarization extinction ratio (PER) narrowband PM couplers to our standard 1550 nm narrowband PM Couplers. Our high PER couplers are specified to have an extinction ratio of 25 dB or higher at 1550 nm, whereas the standard couplers are only guaranteed to have an extinction ratio of at least 20 dB. 

For more information about the methods used to measure the PER, please refer to the PER Measurement tab.

Definition of 1x2 Fused Fiber Optic Coupler Specifications

This tab provides a brief explanation of how we determine several key specifications for our 1x2 couplers. 1x2 couplers are manufactured using the same process as our 2x2 fiber optic couplers, except the second input port is internally terminated using a proprietary method that minimizes back reflections. For combining light of different wavelengths, Thorlabs offers a line of single mode wavelength division multiplexers (WDMs). The ports on our 1x2 couplers are configured as shown in the schematic below.

1x2 CouplerPicture

 

Excess Loss

Excess loss in dB is determined by the ratio of the total input power to the total output power:

Excess Loss

Pport1 is the input power at port 1 and Pport2+Pport3 is the total output power from Ports 2 and 3. All powers are expressed in mW.

 

Polarization Dependent Loss (PDL)

The polarization dependent loss is defined as the ratio of the maximum and minimum transmissions due to polarization states in couplers. This specification pertains only to couplers not designed for maintaining polarization. PDL is always specified in decibels (dB), and can be calculated with the following equation:

Polarization Dependent Loss Equation

where Pmax is the maximum power able to be transmitted through the coupler when scanning across all possible polarization states. Pmin is the minimum transmission across those same states.

 

Optical Return Loss (ORL) / Directivity

The directivity refers to the fraction of input light that is lost in the internally terminated fiber end within the coupler housing when port 1 is used as the input. It can be calculated in units of dB using the following equation:

Directivity or Return Loss

where Pport1 and Pport1b are the optical powers (in mW) in port 1 and the internally terminated fiber, respectively. This output is the result of back reflection at the junction of the legs of the coupler and represents a loss in the total light output at ports 2 and 3. For a 50:50 coupler, the directivity is equal to the optical return loss (ORL).

 

Insertion Loss

The insertion loss is defined as the ratio of the input power to the output power at one of the output legs of the coupler (signal or tap). Insertion loss is always specified in decibels (dB). It is generally defined using the equation below:

Insertion Loss

where Pin and Pout are the input and output powers (in mW). For our 1x2 couplers, the insertion loss specification is provided for both signal and tap outputs; our specifications always list insertion loss for the signal output first. To define the insertion loss for a specific output (port 2 or port 3), the equation is rewritten as:

Insertion Loss

Insertion Loss

Insertion loss inherently includes both coupling (e.g., light transferred to the other output leg) and excess loss (e.g., light lost from the coupler) effects. The maximum allowed insertion loss for each output, signal and tap, are both specified. Because the insertion loss in each output is correlated to light coupled to the other output, no coupler will ever have the maximum insertion loss in both outputs simultaneously.

Calculating Insertion Loss using Power Expressed in dBm
Insertion loss can also be easily calculated with the power expressed in units of dBm. The equation below shows the relationship between power expressed in mW and dBm:

Conversion

Then, the insertion loss in dB can be calculated as follows:

Insertion Loss

 


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A graphical representation of the coupling ratio calculation.

Coupling Ratio

Insertion loss (in dB) is the ratio of the input power to the output power from each leg of the coupler as a function of wavelength. It captures both the coupling ratio and the excess loss. The coupling ratio is calculated from the measured insertion loss. Coupling ratio (in %) is the ratio of the optical power from each output port (ports 2 and 3) to the sum of the total power of both output ports as a function of wavelength. Path A represents light traveling from port 1 to port 2 while Path B represents light traveling from port 1 to port 3. It is not impacted by spectral features such as the water absorption region because both output legs are affected equally.

 


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A graphical representation of the Uniformity calculation.

Uniformity

The uniformity is also calculated from the measured insertion loss. Uniformity is the variation (in dB) of the insertion loss over the bandwidth. It is a measure of how evenly the insertion loss is distributed over the spectral range. The uniformity of Path A is the difference between the value of highest insertion loss and the solid red insertion loss curve (in the Insertion Plot above). The uniformity of Path B is the difference between the solid blue insertion loss curve and the value of lowest insertion loss.

Laser-Induced Damage in Silica Optical Fibers

The following tutorial details damage mechanisms relevant to unterminated (bare) fiber, terminated optical fiber, and other fiber components from laser light sources. These mechanisms include damage that occurs at the air / glass interface (when free-space coupling or when using connectors) and in the optical fiber itself. A fiber component, such as a bare fiber, patch cable, or fused coupler, may have multiple potential avenues for damage (e.g., connectors, fiber end faces, and the device itself). The maximum power that a fiber can handle will always be limited by the lowest limit of any of these damage mechanisms.

While the damage threshold can be estimated using scaling relations and general rules, absolute damage thresholds in optical fibers are very application dependent and user specific. Users can use this guide to estimate a safe power level that minimizes the risk of damage. Following all appropriate preparation and handling guidelines, users should be able to operate a fiber component up to the specified maximum power level; if no maximum is specified for a component, users should abide by the "practical safe level" described below for safe operation of the component. Factors that can reduce power handling and cause damage to a fiber component include, but are not limited to, misalignment during fiber coupling, contamination of the fiber end face, or imperfections in the fiber itself. For further discussion about an optical fiber’s power handling abilities for a specific application, please contact Thorlabs’ Tech Support.

Power Handling Limitations Imposed by Optical Fiber
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Undamaged Fiber End
Power Handling Limitations Imposed by Optical Fiber
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Damaged Fiber End

Damage at the Air / Glass Interface

There are several potential damage mechanisms that can occur at the air / glass interface. Light is incident on this interface when free-space coupling or when two fibers are mated using optical connectors. High-intensity light can damage the end face leading to reduced power handling and permanent damage to the fiber. For fibers terminated with optical connectors where the connectors are fixed to the fiber ends using epoxy, the heat generated by high-intensity light can burn the epoxy and leave residues on the fiber facet directly in the beam path.

Estimated Optical Power Densities on Air / Glass Interfacea
Type Theoretical Damage Thresholdb Practical Safe Levelc
CW
(Average Power)
~1 MW/cm2 ~250 kW/cm2
10 ns Pulsed
(Peak Power)
~5 GW/cm2 ~1 GW/cm2
  • All values are specified for unterminated (bare), undoped silica fiber and apply for free space coupling into a clean fiber end face.
  • This is an estimated maximum power density that can be incident on a fiber end face without risking damage. Verification of the performance and reliability of fiber components in the system before operating at high power must be done by the user, as it is highly system dependent.
  • This is the estimated safe optical power density that can be incident on a fiber end face without damaging the fiber under most operating conditions.

Damage Mechanisms on the Bare Fiber End Face

Damage mechanisms on a fiber end face can be modeled similarly to bulk optics, and industry-standard damage thresholds for UV Fused Silica substrates can be applied to silica-based fiber. However, unlike bulk optics, the relevant surface areas and beam diameters involved at the air / glass interface of an optical fiber are very small, particularly for coupling into single mode (SM) fiber. therefore, for a given power density, the power incident on the fiber needs to be lower for a smaller beam diameter.

The table to the right lists two thresholds for optical power densities: a theoretical damage threshold and a "practical safe level". In general, the theoretical damage threshold represents the estimated maximum power density that can be incident on the fiber end face without risking damage with very good fiber end face and coupling conditions. The "practical safe level" power density represents minimal risk of fiber damage. Operating a fiber or component beyond the practical safe level is possible, but users must follow the appropriate handling instructions and verify performance at low powers prior to use.

Calculating the Effective Area for Single Mode Fibers
The effective area for single mode (SM) fiber is defined by the mode field diameter (MFD), which is the cross-sectional area through which light propagates in the fiber; this area includes the fiber core and also a portion of the cladding. To achieve good efficiency when coupling into a single mode fiber, the diameter of the input beam must match the MFD of the fiber.

As an example, SM400 single mode fiber has a mode field diameter (MFD) of ~Ø3 µm operating at 400 nm, while the MFD for SMF-28 Ultra single mode fiber operating at 1550 nm is Ø10.5 µm. The effective area for these fibers can be calculated as follows:

SM400 Fiber: Area = Pi x (MFD/2)2 = Pi x (1.5 µm)2 = 7.07 µm= 7.07 x 10-8 cm2

 SMF-28 Ultra Fiber: Area = Pi x (MFD/2)2 = Pi x (5.25 µm)2 = 86.6 µm= 8.66 x 10-7 cm2

To estimate the power level that a fiber facet can handle, the power density is multiplied by the effective area. Please note that this calculation assumes a uniform intensity profile, but most laser beams exhibit a Gaussian-like shape within single mode fiber, resulting in a higher power density at the center of the beam compared to the edges. Therefore, these calculations will slightly overestimate the power corresponding to the damage threshold or the practical safe level. Using the estimated power densities assuming a CW light source, we can determine the corresponding power levels as:

SM400 Fiber: 7.07 x 10-8 cm2 x 1 MW/cm2 = 7.1 x 10-8 MW = 71 mW (Theoretical Damage Threshold)
     7.07 x 10-8 cm2 x 250 kW/cm2 = 1.8 x 10-5 kW = 18 mW (Practical Safe Level)

SMF-28 Ultra Fiber: 8.66 x 10-7 cm2 x 1 MW/cm2 = 8.7 x 10-7 MW = 870 mW (Theoretical Damage Threshold)
           8.66 x 10-7 cm2 x 250 kW/cm2 = 2.1 x 10-4 kW = 210 mW (Practical Safe Level)

Effective Area of Multimode Fibers
The effective area of a multimode (MM) fiber is defined by the core diameter, which is typically far larger than the MFD of an SM fiber. For optimal coupling, Thorlabs recommends focusing a beam to a spot roughly 70 - 80% of the core diameter. The larger effective area of MM fibers lowers the power density on the fiber end face, allowing higher optical powers (typically on the order of kilowatts) to be coupled into multimode fiber without damage.

Damage Mechanisms Related to Ferrule / Connector Termination

Click to Enlarge
Plot showing approximate input power that can be incident on a single mode silica optical fiber with a termination. Each line shows the estimated power level due to a specific damage mechanism. The maximum power handling is limited by the lowest power level from all relevant damage mechanisms (indicated by a solid line).

Fibers terminated with optical connectors have additional power handling considerations. Fiber is typically terminated using epoxy to bond the fiber to a ceramic or steel ferrule. When light is coupled into the fiber through a connector, light that does not enter the core and propagate down the fiber is scattered into the outer layers of the fiber, into the ferrule, and the epoxy used to hold the fiber in the ferrule. If the light is intense enough, it can burn the epoxy, causing it to vaporize and deposit a residue on the face of the connector. This results in localized absorption sites on the fiber end face that reduce coupling efficiency and increase scattering, causing further damage.

For several reasons, epoxy-related damage is dependent on the wavelength. In general, light scatters more strongly at short wavelengths than at longer wavelengths. Misalignment when coupling is also more likely due to the small MFD of short-wavelength SM fiber that also produces more scattered light.

To minimize the risk of burning the epoxy, fiber connectors can be constructed to have an epoxy-free air gap between the optical fiber and ferrule near the fiber end face. Our high-power multimode fiber patch cables use connectors with this design feature.

Determining Power Handling with Multiple Damage Mechanisms

When fiber cables or components have multiple avenues for damage (e.g., fiber patch cables), the maximum power handling is always limited by the lowest damage threshold that is relevant to the fiber component. In general, this represents the highest input power that can be incident on the patch cable end face and not the coupled output power.

As an illustrative example, the graph to the right shows an estimate of the power handling limitations of a single mode fiber patch cable due to damage to the fiber end face and damage via an optical connector. The total input power handling of a terminated fiber at a given wavelength is limited by the lower of the two limitations at any given wavelength (indicated by the solid lines). A single mode fiber operating at around 488 nm is primarily limited by damage to the fiber end face (blue solid line), but fibers operating at 1550 nm are limited by damage to the optical connector (red solid line).

In the case of a multimode fiber, the effective mode area is defined by the core diameter, which is larger than the effective mode area for SM fiber. This results in a lower power density on the fiber end face and allows higher optical powers (on the order of kilowatts) to be coupled into the fiber without damage (not shown in graph). However, the damage limit of the ferrule / connector termination remains unchanged and as a result, the maximum power handling for a multimode fiber is limited by the ferrule and connector termination. 

Please note that these are rough estimates of power levels where damage is very unlikely with proper handling and alignment procedures. It is worth noting that optical fibers are frequently used at power levels above those described here. However, these applications typically require expert users and testing at lower powers first to minimize risk of damage. Even still, optical fiber components should be considered a consumable lab supply if used at high power levels.

Intrinsic Damage Threshold

In addition to damage mechanisms at the air / glass interface, optical fibers also display power handling limitations due to damage mechanisms within the optical fiber itself. These limitations will affect all fiber components as they are intrinsic to the fiber itself. Two categories of damage within the fiber are damage from bend losses and damage from photodarkening. 

Bend Losses
Bend losses occur when a fiber is bent to a point where light traveling in the core is incident on the core/cladding interface at an angle higher than the critical angle, making total internal reflection impossible. Under these circumstances, light escapes the fiber, often in a localized area. The light escaping the fiber typically has a high power density, which burns the fiber coating as well as any surrounding furcation tubing.

A special category of optical fiber, called double-clad fiber, can reduce the risk of bend-loss damage by allowing the fiber’s cladding (2nd layer) to also function as a waveguide in addition to the core. By making the critical angle of the cladding/coating interface higher than the critical angle of the core/clad interface, light that escapes the core is loosely confined within the cladding. It will then leak out over a distance of centimeters or meters instead of at one localized spot within the fiber, minimizing the risk of damage. Thorlabs manufactures and sells 0.22 NA double-clad multimode fiber, which boasts very high, megawatt range power handling.

Photodarkening
A second damage mechanism, called photodarkening or solarization, can occur in fibers used with ultraviolet or short-wavelength visible light, particularly those with germanium-doped cores. Fibers used at these wavelengths will experience increased attenuation over time. The mechanism that causes photodarkening is largely unknown, but several fiber designs have been developed to mitigate it. For example, fibers with a very low hydroxyl ion (OH) content have been found to resist photodarkening and using other dopants, such as fluorine, can also reduce photodarkening.

Even with the above strategies in place, all fibers eventually experience photodarkening when used with UV or short-wavelength light, and thus, fibers used at these wavelengths should be considered consumables.

Preparation and Handling of Optical Fibers

General Cleaning and Operation Guidelines
These general cleaning and operation guidelines are recommended for all fiber optic products. Users should still follow specific guidelines for an individual product as outlined in the support documentation or manual. Damage threshold calculations only apply when all appropriate cleaning and handling procedures are followed.

  1. All light sources should be turned off prior to installing or integrating optical fibers (terminated or bare). This ensures that focused beams of light are not incident on fragile parts of the connector or fiber, which can possibly cause damage.

  2. The power-handling capability of an optical fiber is directly linked to the quality of the fiber/connector end face. Always inspect the fiber end prior to connecting the fiber to an optical system. The fiber end face should be clean and clear of dirt and other contaminants that can cause scattering of coupled light. Bare fiber should be cleaved prior to use and users should inspect the fiber end to ensure a good quality cleave is achieved.

  3. If an optical fiber is to be spliced into the optical system, users should first verify that the splice is of good quality at a low optical power prior to high-power use. Poor splice quality may increase light scattering at the splice interface, which can be a source of fiber damage.

  4. Users should use low power when aligning the system and optimizing coupling; this minimizes exposure of other parts of the fiber (other than the core) to light. Damage from scattered light can occur if a high power beam is focused on the cladding, coating, or connector.

Tips for Using Fiber at Higher Optical Power
Optical fibers and fiber components should generally be operated within safe power level limits, but under ideal conditions (very good optical alignment and very clean optical end faces), the power handling of a fiber component may be increased. Users must verify the performance and stability of a fiber component within their system prior to increasing input or output power and follow all necessary safety and operation instructions. The tips below are useful suggestions when considering increasing optical power in an optical fiber or component.

  1. Splicing a fiber component into a system using a fiber splicer can increase power handling as it minimizes possibility of air/fiber interface damage. Users should follow all appropriate guidelines to prepare and make a high-quality fiber splice. Poor splices can lead to scattering or regions of highly localized heat at the splice interface that can damage the fiber.

  2. After connecting the fiber or component, the system should be tested and aligned using a light source at low power. The system power can be ramped up slowly to the desired output power while periodically verifying all components are properly aligned and that coupling efficiency is not changing with respect to optical launch power.

  3. Bend losses that result from sharply bending a fiber can cause light to leak from the fiber in the stressed area. When operating at high power, the localized heating that can occur when a large amount of light escapes a small localized area (the stressed region) can damage the fiber. Avoid disturbing or accidently bending fibers during operation to minimize bend losses.

  4. Users should always choose the appropriate optical fiber for a given application. For example, large-mode-area fibers are a good alternative to standard single mode fibers in high-power applications as they provide good beam quality with a larger MFD, decreasing the power density on the air/fiber interface.

  5. Step-index silica single mode fibers are normally not used for ultraviolet light or high-peak-power pulsed applications due to the high spatial power densities associated with these applications.


Posted Comments:
Ashik A S  (posted 2021-11-18 05:56:00.113)
Hi, I have a question similar to Sebastian Garcia (previous questioner). I need a PM beam splitter that I could operate for 1530 and 1570. I can see that the PM 2X2 BS that you have is centered at 1550 and has a specified bandwidth of 15 nm. I was wondering how well would it work outside this range? Say for the 1530 or 1570? I would like to know the associated loss (coupling ratio) as we operate slightly off the range specified. Thanks.
YLohia  (posted 2021-11-23 02:04:55.0)
Hello, additional data can be requested by emailing your local Thorlabs Tech Support team (in your case, techsupport.se@thorlabs.com). I have reached out to you directly with the data that was sent to the previous questioner.
Sebastien Garcia  (posted 2020-09-16 11:47:16.437)
Hello, I wonder what happens if I try to use a splitter slightly out of the band (1529nm). I have seen in the tutorial tab that the coupling ratio will change with wavelength. Could you tell me how much ? Will I have more excess loss too? Ideally, I would like to see the data of the transmission (or insertion losses) of each port versus the wavelength. Best Regards, Sébastien
YLohia  (posted 2020-09-17 10:20:37.0)
Hello Sébastien, thank you for contacting Thorlabs. I have reached out to you directly with extended split ratio vs wavelength data. This will not have a noticeable impact on the insertion loss.
gregory.gaeumann  (posted 2018-11-30 14:29:15.863)
Do you also sell 1x2 PM fiber couplers (@1550nm) with "custom coupling"? I'm e.g. looking for a 95:5 split ratio. Thanks for your help.
YLohia  (posted 2018-11-30 09:46:58.0)
Hello, thank you for contacting Thorlabs. Custom item quotes can be requested by emailing techsupport@thorlabs.com. We are reaching out to you directly to discuss the possibility of offering this.
sebastien.sauvage  (posted 2016-11-28 17:21:17.487)
The "1x2 Coupler Tutorial" says "1x2 couplers are not recommended for light combining applications". But what would it change to use it as a light combiner (at the same wavelength)? Is there a (single-wavelength) combiner component somewhere? Thank you for your help.
tfrisch  (posted 2016-11-28 02:44:46.0)
Hello. The largest concern is that the unused arm becomes an output rather than an input, so there is light that is dumped inside the housing. For higher power applications, this can cause damage. I will reach out to you with more details.
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50:50 Fiber Couplers

Thorlabs offers both narrowband and wideband fiber optic couplers. Coupling ratio, insertion loss, excess loss, and uniformity are measured without connectors during the manufacturing process, while PER is measured with connectors. Additional information on the testing process for our wideband couplers can be found on the Coupler Verification tab above. Our wideband couplers are highlighted green in the table below.

Item # Info Center
Wavelength
Bandwidth Coupling 
Ratio(%)
Polarization 
Extinction Ratiob
Insertion Lossa Excess
Lossa
Uniformityc Fiberd,e Terminationf
PNH1550R5F1 info 1550 nm ±15 nm 50:50 ≥25.0 dB / ≥25.0 dB 
(With Connectors)
≤3.5 dB / ≤3.5 dB <0.3 dB (Typ.) - Equivalent to
PM 15-U25D
FC/PC
PNH1550R5A1 info FC/APC
PN1550R5F1 info 1550 nm ±15 nm 50:50 ≥20.0 dB / ≥20.0 dB
(With Connectors)
≤3.5 dB / ≤3.5 dB <0.3 dB (Typ.) - Equivalent to
PM 15-U25D
FC/PC
PN1550R5A1 info FC/APC
PW1550R5F1 info 1550 nm ±65 nm 50:50
(Click for Plot)
≥20.0 dB / ≥20.0 dB
(With Connectors)
≤4.1 dB / ≤4.1 dB ≤0.5 dB (Typ.) ≤1.2 dB
(Click for Plot)
Equivalent to
PM 15-U25D
FC/PC
PW1550R5A1 info FC/APC
  • Values are specified with a slow axis launch at room temperature without connectors and measured at the center wavelength through the white input port, as indicated in the diagram above.
  • Extinction ratio is specified with a slow axis launch at room temperature with connectors and measured at the center wavelength through the white input port, as indicated in the diagram above. See the PER Measurement tab for more information on how extinction ratio is measured.
  • Value is specified at room temperature over the bandwidth without connectors and measured through the white input port as indicated in the diagram above.
  • This coupler can be used with patch cables that incorporate PM1550-XP fiber (click for FC/PC and FC/APC versions).
  • Other fiber types may be available upon request. Please contact Tech Support with inquiries.
  • The connector keys are aligned to the slow axis of the fiber.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
PNH1550R5F1 Support Documentation
PNH1550R5F11x2 PM Coupler, 1550 ± 15 nm, 50:50 Split, ≥25 dB PER, FC/PC Connectors
$882.05
Today
PNH1550R5A1 Support Documentation
PNH1550R5A11x2 PM Coupler, 1550 ± 15 nm, 50:50 Split, ≥25 dB PER, FC/APC Connectors
$930.74
Lead Time
PN1550R5F1 Support Documentation
PN1550R5F11x2 PM Coupler, 1550 ± 15 nm, 50:50 Split, ≥20 dB PER, FC/PC Connectors
$588.02
Today
PN1550R5A1 Support Documentation
PN1550R5A11x2 PM Coupler, 1550 ± 15 nm, 50:50 Split, ≥20 dB PER, FC/APC Connectors
$636.72
Today
PW1550R5F1 Support Documentation
PW1550R5F11x2 Wideband PM Coupler, 1550 ± 65 nm, 50:50 Split, ≥20 dB PER, FC/PC Connectors
$735.03
Today
PW1550R5A1 Support Documentation
PW1550R5A11x2 Wideband PM Coupler, 1550 ± 65 nm, 50:50 Split, ≥20 dB PER, FC/APC Connectors
$783.74
Lead Time
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75:25 Fiber Couplers

Thorlabs offers both narrowband and wideband fiber optic couplers. Coupling ratio, insertion loss, excess loss, and uniformity are measured without connectors during the manufacturing process, while PER is measured with connectors. Additional information on the testing process for our wideband couplers can be found on the Coupler Verification tab above. Our wideband couplers are highlighted green in the table below.

Item # Info Center
Wavelength
Bandwidth Coupling
 Ratio(%)
Polarization
Extinction Ratiob
Insertion Lossa Excess
Lossa
Uniformityc Fiberd,e Terminationf
PNH1550R3F1 info 1550 nm ±15 nm 75:25 ≥25.0 dB / ≥25.0 dB
(With Connectors)
≤1.7 dB / ≤6.6 dB <0.3 dB (Typ.) - Equivalent to
PM 15-U25D
FC/PC
PNH1550R3A1 info FC/APC
PN1550R3F1 info 1550 nm ±15 nm 75:25 ≥20.0 dB / ≥20.0 dB
(With Connectors)
≤1.7 dB / ≤6.6 dB <0.3 dB (Typ.) - Equivalent to
PM 15-U25D
FC/PC
PN1550R3A1 info FC/APC
PW1550R3F1 info 1550 nm ±100 nm 75:25
(Click for Plot)
≥18.0 dB / ≥18.0 dB
(With Connectors)
≤2.0 dB / 7.5 dB ≤0.5 dB (Typ.) ≤1.6 dB
(Click for Plot)
Equivalent to
PM 15-U25D
FC/PC
PW1550R3A1 info FC/APC
  • Values are specified with a slow axis launch at room temperature without connectors and measured at the center wavelength through the white input port, as indicated in the diagram above.
  • Extinction ratio is specified with a slow axis launch at room temperature with connectors and measured at the center wavelength through the white input port, as indicated in the diagram above. See the PER Measurement tab for more information on how extinction ratio is measured.
  • Value is specified at room temperature over the bandwidth without connectors and measured through the white input port as indicated in the diagram above.
  • This coupler can be used with patch cables that incorporate PM1550-XP fiber (click for FC/PC and FC/APC versions).
  • Other fiber types may be available upon request. Please contact Tech Support with inquiries.
  • The connector keys are aligned to the slow axis of the fiber.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
PNH1550R3F1 Support Documentation
PNH1550R3F11x2 PM Coupler, 1550 ± 15 nm, 75:25 Split, ≥25 dB PER, FC/PC Connectors
$882.05
Today
PNH1550R3A1 Support Documentation
PNH1550R3A11x2 PM Coupler, 1550 ± 15 nm, 75:25 Split, ≥25 dB PER, FC/APC Connectors
$930.74
Today
PN1550R3F1 Support Documentation
PN1550R3F11x2 PM Coupler, 1550 ± 15 nm, 75:25 Split, ≥20 dB PER, FC/PC Connectors
$588.02
Today
PN1550R3A1 Support Documentation
PN1550R3A11x2 PM Coupler, 1550 ± 15 nm, 75:25 Split, ≥20 dB PER, FC/APC Connectors
$636.72
Today
PW1550R3F1 Support Documentation
PW1550R3F11x2 Wideband PM Coupler, 1550 ± 100 nm, 75:25 Split, ≥18 dB PER, FC/PC Connectors
$735.03
Today
PW1550R3A1 Support Documentation
PW1550R3A11x2 Wideband PM Coupler, 1550 ± 100 nm, 75:25 Split, ≥18 dB PER, FC/APC Connectors
$783.74
Today
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90:10 Fiber Couplers

Thorlabs offers both narrowband and wideband fiber optic couplers. Coupling ratio, insertion loss, excess loss, and uniformity are measured without connectors during the manufacturing process, while PER is measured with connectors. Additional information on the testing process for our wideband couplers can be found on the Coupler Verification tab above. Our wideband couplers are highlighted green in the table below.

Item # Info Center
Wavelength
Bandwidth Coupling 
Ratio(%)
Polarization
Extinction Ratiob
Insertion Lossa Excess
Lossa
Uniformityc Fiberd,e Terminationf
PNH1550R2F1 info 1550 nm ±15 nm 90:10 ≥25.0 dB / ≥25.0 dB
(With Connectors)
≤0.9 dB / ≤10.9 dB <0.3 dB (Typ.) - Equivalent to
PM 15-U25D
FC/PC
PNH1550R2A1 info FC/APC
PN1550R2F1 info 1550 nm ±15 nm 90:10 ≥20.0 dB / ≥20.0 dB
(With Connectors)
≤0.9 dB / ≤10.9 dB <0.3 dB (Typ.) - Equivalent to
PM 15-U25D
FC/PC
PN1550R2A1 info FC/APC
PW1550R2F1 info 1550 nm ±100 nm 90:10
(Click for Plot)
≥18.0 dB / ≥18.0 dB
(With Connectors)
≤1.1 dB / ≤12.0 dB ≤0.5 dB (Typ.) ≤2.0 dB
(Click for Plot)
Equivalent to
PM 15-U25D
FC/PC
PW1550R2A1 info FC/APC
  • Values are specified with a slow axis launch at room temperature without connectors and measured at the center wavelength through the white input port, as indicated in the diagram above.
  • Extinction ratio is specified with a slow axis launch at room temperature with connectors and measured at the center wavelength through the white input port, as indicated in the diagram above. See the PER Measurement tab for more information on how extinction ratio is measured.
  • Value is specified at room temperature over the bandwidth without connectors and measured through the white input port as indicated in the diagram above.
  • This coupler can be used with patch cables that incorporate PM1550-XP fiber (click for FC/PC and FC/APC versions).
  • Other fiber types may be available upon request. Please contact Tech Support with inquiries.
  • The connector keys are aligned to the slow axis of the fiber.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
PNH1550R2F1 Support Documentation
PNH1550R2F11x2 PM Coupler, 1550 ± 15 nm, 90:10 Split, ≥25 dB PER, FC/PC Connectors
$882.05
Today
PNH1550R2A1 Support Documentation
PNH1550R2A11x2 PM Coupler, 1550 ± 15 nm, 90:10 Split, ≥25 dB PER, FC/APC Connectors
$930.74
3 weeks
PN1550R2F1 Support Documentation
PN1550R2F11x2 PM Coupler, 1550 ± 15 nm, 90:10 Split, ≥20 dB PER, FC/PC Connectors
$588.02
Today
PN1550R2A1 Support Documentation
PN1550R2A11x2 PM Coupler, 1550 ± 15 nm, 90:10 Split, ≥20 dB PER, FC/APC Connectors
$636.72
3 weeks
PW1550R2F1 Support Documentation
PW1550R2F11x2 Wideband PM Coupler, 1550 ± 100 nm, 90:10 Split, ≥18 dB PER, FC/PC Connectors
$735.03
Today
PW1550R2A1 Support Documentation
PW1550R2A11x2 Wideband PM Coupler, 1550 ± 100 nm, 90:10 Split, ≥18 dB PER, FC/APC Connectors
$783.74
3 weeks
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99:1 Fiber Couplers

Thorlabs offers both narrowband and wideband fiber optic couplers. Coupling ratio, insertion loss, excess loss, and uniformity are measured without connectors during the manufacturing process, while PER is measured with connectors. Additional information on the testing process for our wideband couplers can be found on the Coupler Verification tab above. Our wideband couplers are highlighted green in the table below.

Item # Info Center
Wavelength
Bandwidth Coupling 
Ratio(%)
Polarization
Extinction Ratiob
Insertion Lossa Excess
Lossa
Uniformityc Fiberd,e Terminationf
PNH1550R1F1 info 1550 nm ±15 nm 99:1 ≥25.0 dB / ≥25.0 dB
(With Connectors)
≤0.5 dB / ≤24.4 dB <0.3 dB (Typ.) - Equivalent to
PM 15-U25D
FC/PC
PNH1550R1A1 info FC/APC
PN1550R1F1 info 1550 nm ±15 nm 99:1 ≥20.0 dB / ≥20.0 dB
(With Connectors)
≤0.5 dB / ≤24.4 dB <0.3 dB (Typ.) - Equivalent to
PM 15-U25D
FC/PC
PN1550R1A1 info FC/APC
PW1550R1F1 info 1550 nm ±100 nm 99:1
(Click for Plot)
≥18.0 dB / ≥18.0 dB
(With Connectors)
≤0.6 dB / ≤27.5 dB ≤0.5 dB (Typ.) ≤3.0 dB
(Click for Plot)
Equivalent to
PM 15-U25D
FC/PC
PW1550R1A1 info FC/APC
  • Values are specified with a slow axis launch at room temperature without connectors and measured at the center wavelength through the white input port, as indicated in the diagram above.
  • Extinction ratio is specified with a slow axis launch at room temperature with connectors and measured at the center wavelength through the white input port, as indicated in the diagram above. See the PER Measurement tab for more information on how extinction ratio is measured.
  • Value is specified at room temperature over the bandwidth without connectors and measured through the white input port as indicated in the diagram above.
  • This coupler can be used with patch cables that incorporate PM1550-XP fiber (click for FC/PC and FC/APC versions).
  • Other fiber types may be available upon request. Please contact Tech Support with inquiries.
  • The connector keys are aligned to the slow axis of the fiber.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
PNH1550R1F1 Support Documentation
PNH1550R1F11x2 PM Coupler, 1550 ± 15 nm, 99:1 Split, ≥25 dB PER, FC/PC Connectors
$882.05
Today
PNH1550R1A1 Support Documentation
PNH1550R1A11x2 PM Coupler, 1550 ± 15 nm, 99:1 Split, ≥25 dB PER, FC/APC Connectors
$930.74
Lead Time
PN1550R1F1 Support Documentation
PN1550R1F11x2 PM Coupler, 1550 ± 15 nm, 99:1 Split, ≥20 dB PER, FC/PC Connectors
$588.02
Today
PN1550R1A1 Support Documentation
PN1550R1A11x2 PM Coupler, 1550 ± 15 nm, 99:1 Split, ≥20 dB PER, FC/APC Connectors
$636.72
3 weeks
PW1550R1F1 Support Documentation
PW1550R1F11x2 Wideband PM Coupler, 1550 ± 100 nm, 99:1 Split, ≥18 dB PER, FC/PC Connectors
$735.03
Today
PW1550R1A1 Support Documentation
PW1550R1A11x2 Wideband PM Coupler, 1550 ± 100 nm, 99:1 Split, ≥18 dB PER, FC/APC Connectors
$783.74
3 weeks