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1650 nm 1x2 Single Mode Fused Fiber Optic Couplers / Taps
Use for Splitting Signals
99:1 Coupler with FC/APC Connectors
50:50 Coupler with FC/PC Connectors
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Each coupler is engraved with the Item #, serial number, and key specifications for easy identification. 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.
Thorlabs' Single Mode 1x2 Fiber Optic Couplers, also known as taps, have a flat spectral response across the entire specified range. Wideband couplers that can be used at 1650 nm are featured below. These couplers are available with a ±100 nm bandwidth and a coupling ratio of 50:50, 75:25, 90:10, or 99:1.
1x2 couplers are manufactured using the same process as our 2x2 fiber optic couplers, but 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).
Thorlabs provides an individual test data sheet with each coupler that includes coupling data and performance graphs. These graphs show data within the designed bandwidth and also extend outside of the specified bandwidth, covering the entire wavelength range where the coupling ratio meets the specified tolerance. A sample data sheet for our 1650 nm wideband couplers can be viewed here.
These couplers are offered from stock with 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. Custom coupler configurations with other wavelengths, fiber types, coupling ratios, or port configurations are also available. If a custom connector configuration is needed, one-day turnaround is possible for small orders if the order is placed before 12 PM EST. Please contact Tech Support with inquiries.
Our complete selection of 1x2 SM couplers is outlined in the table to the right and on the SM Coupler Guide tab. Thorlabs also offers fiber optic couplers for 1650 nm in a 2x2 configuration; they can be found here.
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 wavelength division multiplexers (WDMs). The ports on our 1x2 couplers are configured as shown in the schematic below.
Excess loss in dB is determined by the ratio of the total input power to the total output power:
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.
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:
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).
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:
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 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
Then, the insertion loss in dB can be calculated as follows:
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A graphical representation of the coupling ratio calculation.
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.
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.
Fiber Coupler Testing and Verification Procedure
During Thorlabs' coupling manufacturing process, the coupling ratio and bandwidth of each coupler is monitored as the two branches are fused together. This ensures that each coupler meets the stated specifications over the bandwidth. Each coupler is shipped with an individualized data sheet providing a summary of the results of these tests. Click for a sample data sheet for our 1650 nm couplers here.
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.
The spectrum of the source through the fiber and switch is measured using the OSA and zeroed.
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.
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.
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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.
Our 1x2 and 2x2 Single Mode Coupler offerings are outlined in the graphs below. Click on the colored bars to visit the web presentation for each coupler.