How To Select the Right Optical Fiber for Your Application?

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.

Boot	Color	Product Code	Fiber Type	Best Efficiency
	Gray	-XSR	UV-VIS XSR Solarization Resistant	180 – 800 nm
	Gray	-SR	UV/SR-VIS High OH content	200 – 1100 nm
	Blue	-UV-VIS	UV-VIS High OH content	300 – 1100 nm
	Red	-VIS-NIR	VIS-NIR Low OH content	400 – 2100 nm

Band Colors

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

Band	Color	Fiber Core Size
	Purple	8 μm
	Blue	50 μm
	Green	100 μm
	Yellow	200 μm
	Gray	300 μm
	Red	400 μm
	Orange	500 μm
	Brown	600 μm
	Clear	1000 μm

Jacketing

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.

Jacket	Description	Outer Diameter	Chemical Resistance	Steam Sterilizable	Temperature Limit	Mechanical Tolerance	Maximum Length
PVC monocoil	PVC covering stainless steel monocoil; OEM applications only	3.4 mm	Poor	No	70°C	Good	6 m
PVDF zip tube	Best for budget-conscious applications; standard in lab-grade assemblies	3.8 mm	Poor	No	100°C	Good	50 m
PVDF zip tube (large OD)	Best for budget-conscious applications; larger in diameter than jacket #2	5.0 mm	Poor	No	100°C	Good	50 m
Silicone Monocoil	High-end jacketing; standard in premium-grade assemblies (silicone covering stainless steel monocoil)	5.6 mm	Good	Yes	250°C	Good	20 m
Stainless-steel BX	OEM applications only; optional polyolefin heatshrink overcoat	5.0 mm	Good	Yes	250°C	Poor	4 m
Stainless-steel fully interlocked BX	Excellent stainless steel jacketing; supports longer lengths of fiber; optional polyolefin heatshrink overcoat	7.0 mm	Good	Yes	250°C	Excellent	40 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

Band	Fiber Core Size	Fiber Types	Cladding Thickness	Buffer Material	Buffer Thickness	Maximum OD	Operating Temperature (fiber core)	LTBR	STBR
	50 ± 5 μm	VIS/NIR, UV/VIS	35 ± 0.5 µm	polyimide	17 ± 5 µm	155 µm	-65 to 300 °C	4 cm	2 cm
	100 ± 3 μm	VIS/NIR, UV/VIS	12 ± 5 µm	polyimide	17 ± 3 µm	155 µm	-65 to 300 °C	4 cm	2 cm
	200 ± 4 μm	VIS/NIR, UV/VIS, SR	10 ± 4 µm	polyimide	10 ± 5 µm	243 µm	-65 to 300 °C	8 cm	4 cm
	300 ± 6 μm	SR	15 ± 7 µm	polyimide	20 ± 10 µm	380 µm	-65 to 300 °C	12 cm	6 cm
	400 ± 8 μm	VIS/NIR, UV/VIS, SR	20 ± 3 µm	polyimide	20 ± 7 µm	487 µm	-65 to 300 °C	16 cm	8 cm
	500 ± 10 µm	VIS/NIR, UV/VIS	25 ± 3 µm	polyimide	20 ± 10 µm	600 µm	-65 to 300 °C	20 cm	10 cm
	600 ± 10 μm	VIS/NIR, UV/VIS, SR	30 ± 3 µm	polyimide	25 ± 10 µm	720 µm	-65 to 300 °C	24 cm	12 cm
	1000 ± 3 µm	VIS/NIR	50 ± 3 µm	acrylate	50 ± 40 µm	1120 µm	-50 to 85 °C	30 cm	15 cm
	1000 ± 20 µm	UV/VIS	25 ± 3 µm	acrylate	50 ± 40 µm	1065 µm	-50 to 85 °C	30 cm	15 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

Band	Fiber Core Size	Fiber Types	Cladding OD	Buffer Materials	Primary Buffer OD	Maximum OD	Operating Temperature (fiber core)	LTBR	STBR
	113 ± 6 μm (115 μm nominal)	XSR	125 ± 6 µm	aluminum, polymer	150 µm	230 µm	-50 to 80 °C	4 cm	2 cm
	230 ± 12 μm	XSR	250 ± 13 µm	aluminum, polymer	300 µm	380 ± 20 µm	-50 to 80 °C	4 cm	2 cm
	455 ± 22 μm	XSR	500 ± 25 µm	aluminum, silicone, nylon	580 µm	1300 ± 100 µm	-50 to 80 °C	8 cm	4 cm
	600 ± 30 μm	XSR	660 ± 33 µm	aluminum, silicone, nylon	800 µm	1700 ± 200 µm	-50 to 80 °C	24 cm	12 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

Band	Fiber Core Size	Fiber Types	Cladding OD	Buffer Material	Buffer OD	Operating Temperature (fiber core)	LTBR	STBR
	8.2 ± 0.2 μm	Single mode	125 ± 7 µm	dual acrylate	245 ± 5 µm	-60 to 85 °C	4 cm	2 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 θ_max 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 θ_max of 12.7° (full angle is ~25^o). 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 Type	Numerical Aperture	Full Angle
Single mode	0.14	16.1°
VIS/NIR	0.22	25.4°
UV/VIS	0.22	25.4°
SR	0.22	25.4°
XSR	0.22	25.4°

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.