Learn How to Couple Optic Fiber with LED and Sensors


Fiber optics or optical fiber refers to the medium and the technology associated with the transmission of information as the light pulses along a glass or plastic strand or fiber. The central core to the fiber is surrounded by a cladding and a protective coating. Ones the light is injected into the core it remains trapped into it until emerged from the opposite end; this is because the cladding has a slightly higher index of refraction than the core.

The sensors, illuminators, and toys make use of inexpensive plastic fibers. The environment that requires electrical isolation or protection from the elements uses fiber coupled LED.

Coupling of Optical Fibers to LEDs and Sensors

Although many fiber couplers are available for various LEDs and light sensors one can connect silica and plastic fibers directly to LEDs and sensors. Here are different methods used to produce fiber coupled LED and sensors.

Preparing the Fiber Ends

To obtain the best results use the plastic fiber having flat, smooth and polished ends. To achieve the desirable result place the end of the fiber on the wood surface and slice off a few millimeters by pressing a sharp knife straight down into the fiber. After cutting, press the cut ends against the 200, 400 and 600 grit sandpaper on the flat surface and rotate it across the paper. This will trim the roughened edges of the fiber’s jacket and make the end smooth.
Heat-Shrink Tubing

It is the simplest method to produce fiber coupled LED and sensors. However, the method is not employed practically for the long-term use, especially outdoors but works well for basic experiments and demonstrations with the fiber of 2.2mm. To couple, 5mm LED or sensor it is beneficial to use 6mm or 8mm diameter heat-shrink tubing.

Slide a 1” long tubing over the LED or sensor and heat the tubing with a heat gun until it holds the LED or sensor get fixed tightly into it. Now slip the open end of the fiber into the open end of the tubing and continue heating. The fiber either adheres or moves in and out of the tubing, depending upon the diameter of the tubing. To keep the fiber in the place you can apply some adhesives.

Permanent Direct Connection

To make a coupling stronger, reinforce the fiber into a hole bored into the end of the LED or sensor’s epoxy capsule. Cement the jacketed end of the fiber or remove a section of jacket. An inch of heat-shrink over the function is enough to meet the needful. To make a permanent connection takes a tiny wire and carefully bore the hole above it to make contact with the light-emitting or sensing chip. The hole should be large enough to accept 1mm bare fiber core. To blow away any chips in the hole use the compressed air and make sure that all the connection are undamaged.

Now insert the polished end of the fiber into the hole and secure it with cyanoacrylate or other plastic adhesives. Insert a suitable length of darkening heat-shrink tubing over the LED or sensor and 1” or so of the fiber and warm it to secure the tubing in the place. This will produce the long lasting fiber coupled LED or sensor.


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