Optical Fiber Technical Information

Fiber Attenuation

To achieve the best system performance, it is important to choose optical fibers that transmit well over your full wavelength range of interest. This will minimize the amount of light lost through fiber coupling, and reduce attenuation of some wavelengths over others. When working in the ultraviolet portion of the spectrum, particularly below 300 nm, it is important to use solarization-resistant fibers, as other fibers will become less transmissive over time at those wavelengths (an effect known as solarization).

Take a look below to find the attenuation spectrum that best suits your application, or contact one of our application engineers for guidance. Keep in mind that 1 dB is equivalent to ~21% of light being lost in transmission.

Fiber Attenuation Graphs.png

Identifying Our Fibers

Our optical fiber and probe assemblies are clearly and cleanly labeled in three ways so that you can always determine the part number, the fiber core diameter, and its wavelength range of best efficiency.


Boot Colors

The assembly’s boot color lets you know the fiber type and the most efficient wavelength range for using your fiber.

 BootColorProduct CodeFiber TypeBest Efficiency
UV_SR_Fiber_boot.pngGray-XSRUV-VIS XSR Solarization Resistant180 – 800 nm
UV_SR_Fiber_Boot2.pngGray-SRUV/SR-VIS High OH content200 – 1100 nm
UV_VIS_Fiber_boot.pngBlue-UV-VISUV-VIS High OH content300 – 1100 nm
VIS_NIR_Fiber_Boot.pngRed-VIS-NIRVIS-NIR Low OH content400 – 2100 nm

Band Colors

The assembly’s color band tells you the the fiber core diameter.

BandColorFiber Core Size
               Purple8 μm
               Blue50 μm
               Green100 μm
               Yellow200 μm
               Gray300 μm
               Red400 μm
               Orange500 μm
               Brown600 μm
               Clear1000 μm


The fiber assembly jacketing is designed to protect the fiber and provide strain relief, but we have options that can do so much more. Tell us about the environment and application in which the fiber assembly will be used and we’ll help you to select the best jacketing material for the assembly.

JacketDescriptionOuter DiameterChemical ResistanceSteam SterilizableTemperature LimitMechanical ToleranceMaximum Length
PVC monocoilPVC covering stainless steel monocoil; OEM applications only3.4 mmPoorNo70°CGood6 m
PVDF zip tubeBest for budget-conscious applications; standard in lab-grade assemblies3.8 mmPoorNo100°CGood50 m
PVDF zip tube (large OD)Best for budget-conscious applications; larger in diameter than jacket #25.0 mmPoorNo100°CGood50 m
Silicone MonocoilHigh-end jacketing; standard in premium-grade assemblies (silicone covering stainless steel monocoil)5.6 mmGoodYes250°CGood20 m
Stainless-steel BXOEM applications only; optional polyolefin heatshrink overcoat5.0 mmGoodYes250°CPoor4 m
Stainless-steel fully interlocked BXExcellent stainless steel jacketing; supports longer lengths of fiber; optional polyolefin heatshrink overcoat7.0 mmGoodYes250°CExcellent40 m

Bend Radius & Mechanical Specifications

Optical fiber works by guiding light down the fiber core due to variations in index of refraction between the core and cladding. A flexible buffer material in one or more layers is then applied to improve flexibility and protect the glass core/cladding. Even with this additional coating, there are still limits on how tightly the fiber can be bent without being prone to microscopic fractures that can lead to breaks.

LTBR (long term bend radius): Observe as a minimum radius allowed for storage conditions.
STBR (short term bend radius): Observe as a minimum radius allowed during use and handling.

Mechanical Specifications: VIS/NIR, UV/VIS, SR fibers

BandFiber Core Size          Fiber TypesCladding ThicknessBuffer MaterialBuffer Thickness  Maximum ODOperating Temperature (fiber core)LTBRSTBR
        50 ± 5 μmVIS/NIR, UV/VIS35 ± 0.5 µmpolyimide17 ± 5 µm155 µm-65 to 300 °C4 cm2 cm
        100 ± 3 μmVIS/NIR, UV/VIS12 ± 5 µmpolyimide17 ± 3 µm155 µm-65 to 300 °C4 cm2 cm
        200 ± 4 μmVIS/NIR, UV/VIS, SR10 ± 4 µmpolyimide10 ± 5 µm243 µm-65 to 300 °C8 cm4 cm
        300 ± 6 μmSR15 ± 7 µmpolyimide20 ± 10 µm380 µm-65 to 300 °C12 cm6 cm
        400 ± 8 μmVIS/NIR, UV/VIS, SR20 ± 3 µmpolyimide20 ± 7 µm487 µm-65 to 300 °C16 cm8 cm
        500 ± 10 µmVIS/NIR, UV/VIS25 ± 3 µmpolyimide20 ± 10 µm600 µm-65 to 300 °C20 cm10 cm
        600 ± 10 μmVIS/NIR, UV/VIS, SR30 ± 3 µmpolyimide25 ± 10 µm720 µm-65 to 300 °C24 cm12 cm
        1000 ± 3 µmVIS/NIR50 ± 3 µmacrylate50 ± 40 µm1120 µm-50 to 85 °C30 cm15 cm
        1000  ± 20 µmUV/VIS25 ± 3 µmacrylate50 ± 40 µm1065 µm-50 to 85 °C30 cm15 cm
VIS/NIR is multimode step index fiber with a low OH fused silica core and glass cladding (400 – 2100 nm)
UV/VIS is multimode step index fiber with a high OH fused silica core and glass cladding (300 – 1100 nm)
SR is multimode step index fiber with a high OH fused silica core and glass cladding (200 – 1100 nm)

Mechanical Specfications: XSR Fibers

BandFiber Core SizeFiber TypesCladding ODBuffer MaterialsPrimary Buffer ODMaximum ODOperating Temperature (fiber core)LTBRSTBR
        113 ± 6 μm (115 μm nominal)XSR125 ± 6 µmaluminum, polymer150 µm230 µm-50 to 80 °C4 cm2 cm
        230 ± 12 μmXSR250 ± 13 µmaluminum, polymer300 µm380 ± 20 µm-50 to 80 °C4 cm2 cm
        455 ± 22 μmXSR500 ± 25 µmaluminum, silicone, nylon580 µm1300 ± 100 µm-50 to 80 °C8 cm4 cm
        600 ± 30 μmXSR660 ± 33 µmaluminum, silicone, nylon800 µm1700 ± 200 µm-50 to 80 °C24 cm12 cm
XSR is multimode step index fiber with a high OH fused silica core and fluorine-doped silica cladding (180 – 900 nm)

Mechanical Specifications: Single mode fibers

BandFiber Core SizeFiber TypesCladding ODBuffer MaterialBuffer ODOperating Temperature (fiber core)LTBRSTBR
        8.2 ± 0.2 μmSingle mode125 ± 7 µmdual acrylate245 ± 5 µm-60 to 85 °C4 cm2 cm
Single mode fiber is Corning SMF-28e+ fiber optimized for telecom use (1260 – 1700 nm)
Single-mode performance ceases below the cutoff wavelength of λc = 1260 nm

Numerical Aperture

Optical fibers are designed to transmit light from one end of the fiber to the other with minimal loss of energy. The principle of operation in an optical fiber is total internal reflection. When light passes from one material to another, its direction is changed. According to Snell’s Law, the new angle of the light ray can be predicted from the refractive indices of the two materials. When the angle is perpendicular (90º) to the interface, transmission into the second material is maximum and reflection is minimum. Reflection increases as the angle gets closer to parallel to the interface. At the critical angle and below the critical angle, transmission is 0% and reflection is 100% (see figure below).


Snell’s Law can be formulated to predict critical angle and also the launch or exit angle θmax from the index of refraction of the core (n1) and cladding (n2) materials. The angle also depends on the refractive index of the media (n).


The left side of equation is called the numerical aperture (NA), and determines the range of angles at which the fiber can accept or emit light.

Most Ocean Optics fibers have a numerical aperture of 0.22 (see table below). If the fiber is in a vacuum or air, this translates into an acceptance angle θmax of 12.7° (full angle is ~25o). When light is directed at the end of an optical fiber all the light rays or trajectories that are within the ±12.7° cone are propagated down the length of the fiber by total internal reflection. All the rays that exceed that angle pass through the cladding and are lost. At the other end of the fiber, light exits in a cone that is ±12.7°.

There are many types of fibers available, with a variety of numerical apertures.  While a fiber with a larger numerical aperture will collect more light than a fiber with a smaller numerical aperture, it is important to look at both ends of the system to ensure that light exiting at a higher angle can be used. In optical sensing, one end is gathering light from an experiment and the other is directing light to a detector. Any light that does not reach the detector will be wasted.

Fiber TypeNumerical ApertureFull Angle
Single mode0.1416.1°

Solarization Effects

Ultraviolet radiation below 300 nm degrades transmission in silica fibers, resulting in solarization (increased light absorption in the fiber that occurs over time and impacts data). For applications below 300 nm, we recommend solarization-resistant assemblies.

XSR Fibers for High Transparency and Durability

Xtreme solarization-resistant (XSR) optical fiber and probe assemblies for spectroscopy are manufactured using a proprietary process for enhanced UV transmission (signal will transmit to 180 nm) and remarkable resistance to UV degradation, making it ideal for deep-UV applications (<300 nm). Ocean Optics is the only spectroscopy manufacturer to offer XSR Fiber.