Splices / Termination


Fiber Splices and Temporary Termination

  • Temporary Fiber Terminator
  • Reusable Splices Preloaded with Index Matching Gel
  • Index Matching Gel Available Separately
  • One-Time-Use Splice Protector Sleeves

Bare Fiber Terminator



  • Temporary Fiber Termination
  • Mechanically Holds the Fiber and Connector in Place without Epoxy
  • Reusable Design
  • Compatible with the Thorlabs Fiber Connectors Listed Below

For applications where a temporary fiber termination is desired, our BFTU Bare Fiber Terminator is the solution. The bare fiber terminator is designed to hold fibers in standard connectors (sold separately). The back of the connector is held in place using a 2-56 setscrew, while the fiber is secured with a spring-loaded, button-actuated clamp (see photo to the right).

The BFTU accepts ferrules up to Ø0.158" (Ø4 mm) and fibers up to Ø0.03" (Ø0.7 mm). It is reusable and can be easily cleaned out if the fiber breaks inside the connector by using WC100 clean out wires.

Incompatible Connectors
Connector Type Product Number
SMA 10850A, 11040A, 11050A, 11275A, 11580A
FC/PC 30080D1, 301255D1, 30xxxC, 30140E1, 30126G2-xxx, 30126G2
FC/APC 30080K1, 30128A3, 30126A9
SC/PC 30500A1, 30126G1, 30126H1
Compatible Connectors
Connector Type Product Number
SMA 10125A, 10140A, 10230A, 10250A, 10260A, 10270A, 10340A, 10410A, 10440A, 10450A, 10510A, 10610A, 10640A, 10670A, 10770A
FC/PC 30128C3, 30126C3, 30126C9
FC/APC 30126A9, 30126A3
ST®/PC 10140G1, 10127C, 30126B1
LC®/PC 30126L9


Mechanical Fiber-to-Fiber Splices



  • Fast Splicing of Fibers
  • Self-Gripping Clamshell Design
  • Accepts Fibers with Cladding Between Ø125 and Ø140 µm
  • 2 Mechanical Splices per Package

Thorlabs' TS126 reusable, mechanical fiber-to-fiber splices are designed for splicing two single mode or multimode fibers with cladding sizes between Ø125 µm and Ø140 µm. The fiber channels in the gray clamshell casing (see the photo to the above right) are divided into two sections with different diameters. The section closest to the yellow fiber splice tube is Ø250 µm to accomodate the fiber coating, while the outer sections are Ø900 µm. Each splice comes preloaded with index matching gel, guaranteeing an average splicing loss of 0.2 dB. Additional index matching gel (G608N3 available below) can be applied to the ends of the fibers before inserting them into the yellow splice tube to improve performance when reusing the splice.

Our mechanical fiber-to-fiber splices hold fiber with a self-gripping clamshell design. They are easy to use, providing a quick solution when performing emergency fiber optic splicing. The yellow splice tube can be used alone for a compact package or with the gray clamshell clamp installed for greater stability. For permanent usage, an adhesive (e.g., Super Glue or epoxy) can be injected into the two small through holes in the bottom section of the clamp to achieve a pull strength of 1.5 lbs.


Fiber Splice Assembly

Required Materials

Before beginning a fiber splice, be sure to have the required materials available. This includes the Reusable Fiber-to-Fiber Splice (Item # TS126). Additional needed materials include a fiber stripper, fiber scribe (S90R), 99% pure hospital-grade isopropanol, and Kimwipes (KW32). Fibers compatible with this splice unit have cladding sizes between 125 µm and 140 µm. Therefore, depending on the cladding size, one of these fiber fiber strippers will be needed: T06S13, T08S13, or T08S40. Please visit the links above for additional information about these tools.


Step 1. Strip, clean, and cleave the two fibers to be spliced. Approximately 14 mm of stripped fiber should be present on each end after cleaving. Complete, step-by-step instructions on how to properly cleave a fiber are found in the Guide to Connectorization and Polishing of Optical Fibers, which is available.

Step 2. Separate the gray plastic "clamshell" pieces from the yellow fiber tube (see Figure 1).

Step 3. Insert one fiber into the small hole at the end of the yellow fiber tube (see Figure 2). When the fiber is securely inside the splice channel, it will start to resist movement.

Step 4. Insert the other fiber into the opposite side of the yellow fiber tube. Couple a light source into one of the fibers and attach the other fiber to a power meter. As the fiber tips approach each other, the transmitted power level will rise until it reaches a maximum as the fiber tips touch (average splicing losses are ~0.2 dB). It may be necessary to gently rotate the fibers to achieve lowest losses. Do not continue to press the fibers together, as this could either break the fibers or result in scratches on the end faces that reduce signal strength.

Step 5. (Optional) Reassemble the gray clamshell pieces for mechanical stability (see Figure 3). Make sure that the fiber is placed into the grove of the clamshell piece as it exits the yellow tube. For a permanent splice and added stability, inject epoxy into the two holes of the larger gray plastic piece.


Index Matching Gel



Index Matching Gel

Thorlabs G608N3 is a crystal clear, gel-like, optical coupling compound intended to reduce signal attenuation in wave guide assemblies at connections.  The presence of air at the junction of two optical fibers causes significant signal refraction due to the large differential optical impedance that exists between air and the signal-carrying wave guides.  The optical coupling compound G608N3 has been formulated with the requisite optical properties of clarity, purity, and refractive index to minimize signal losses while allowing pliable mechanical connections between rigid parts. Unlike a rigid optical epoxy, this pliable gel is viscoelastic and can take up the differential thermal expansion of precision optical parts without inducing excessive stresses or delamination.

In many devices, these materials serve an additional function: they help seal out ambient dust or fluids from sensitive optical components. This gel is formulated to be ultraclean, non-yellowing, and unaffected by x-ray, ultraviolet or sunlight exposure. It has extremely low outgassing and volatility characteristics and is free from light-absorbing microscopic particulates. This optical product is a chemically stable, non-toxic, synthetic material with wide temperature serviceability and is suitable for designs with high reliability and long service life. Each syringe comes with 3 cc of index matching gel.

This index matching gel can also be used to eliminate possible air gaps between fibers when mating connectors using a mating sleeve.

Refractive Index 402 nm 1.4995
589.3 nm 1.4646
980 nm 1.4462
1550 nm 1.4378
Refractive Index Temperature Coefficient (25 °C to 60 °C) -3.5 x 10-4 per °C
Refractive Index vs. Wavelength (Cauchy Fit) 1.4338 + 10520 λ-2
Optical Absorption (450 - 750 nm) <0.003% per µm
Apparent Viscosity (25 °C) 10,600 poises
Oil Separation (24 hrs at 100 °C) 0.2%
Evaporation (24 hrs at 100 °C) 1.0%
Specific Gravity (25 °C) 1.06
Thermal Coefficient of Expansion 0.0006 cc/cc/°C
Microscopic Particulate Contamination 10 - 34 µm  
≥35 µm 0 Particles/cc


Splice Protector Sleeves



  • Fits Fiber Outer Diameter up to 900 µm
  • Available in Either 40 mm or 60 mm Lengths
  • Ø3.2 mm After Shrinking
  • Sold in Packs of 25

Thorlabs’ Splice Protector Sleeves are designed to protect splices in fibers with an outer diameter up to 900 µm. These fusion splice protector sleeves are an economic solution that offers reliable and solid protection for splice joints. An outer shrink tube holds the tube through which the fiber is threaded as well as the strength member, a solid steed rod that provides rigid support for the splice joint. This design not only provides a replacement for the original fiber cable jacket, but also provides excellent rigidity around the splice joint, preventing the spliced area from bending or flexing.

To use, thread the fiber through the inner fiber tube of the sleeve. Position the sleeve so that the splice joint is in the middle. The sleeve must then be heated causing the outer shrink tube to contract to Ø3.2 mm. Proper heating is required to ensure an accurate fit and function of the splice protector sleeve. The image to the left illustrates the effects of proper and improper heating on these sleeves. The top image shows normal heating; here the shrink tube is uniform across the splice, providing permanent and rigid protection. The middle image shows excessive heating; here the shrink tube shows evidence of blemishes and melts in the tubing. The bottom image shows insufficient heating; here the shrink tube is not uniform across the splice, resulting in loose or poor protection for the splice joint. A fiber splicer can be used to ensure proper heating of the sleeve (refer to the operation manual of your splicer for correct heating settings). The image to the right shows a properly heated splice protector sleeve in a fiber splicer

Sleeve Length 40 mm 60 mm
Stainless Steel Rod Length 35 mm 55 mm
Inner/Outer Tube Material Ethylene-Vinyl Acetate
Dimension after Shrinking Ø3.2 mm × 40 mm Ø3.2 mm × 60 mm

Each splice protector sleeve is composed of an outer shrink tube, an inner tube, and a stainless steel rod to provide rigid support for the splice joint.



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