Photonic Crystal Fibers

Broad selection of photonic crystal fibers available
Ability to fill the core or cladding with gasses or liquids
Low Fresnel reflection from the fiber facets
Fibers are practically bend insensitive to even several turns on sub-centimeter diameter spools

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Overview
Specifications
Ordering
Literature & Downloads

Photonic Crystal Fiber (PCF) can provide characteristics that ordinary optical fiber do not exhibit, such as: single mode operation from the UV to IR with large mode-field diameters, highly nonlinear performance for super continuum generation, numerical aperture (NA) values ranging from very low to about 0.9, optimized dispersion properties, and air core guidance, among others. Applications for photonic crystal fibers include spectroscopy, metrology, biomedicine, imaging, telecommunication, industrial machining, and military, and the list keeps growing as the technology becomes a mainstream. Photonic crystal fibers are generally divided into two main categories: Index Guiding fibers that have a solid core, and Photonic Bandgap or air guiding fibers that have periodic micro-structured elements and a core of low index material (e.g. hollow core). Newport offers F-SM Series Large Mode Area, endlessly single-mode PCFs, F-NL Series Highly Nonlinear PCFs, and F-AIR Series Photonic Bandgap fibers, manufactured by NKT Photonics (formerly Crystal Fibre), the biggest commercial supplier of photonic crystal fibers. Also offered is the SCG-800 and SCG-800-CARS self contained Supercontinuum Generation Fiber Devices.

Please refer to the Fiber Optic Basics Tutorial for more detailed information on the properties of photonic crystal fiber. Newport''s broad photonic crystal fiber selection provides the customers with the highest performance, most widely used fiber products. For adding fiber connectors and protective jackets, please contact Newport technical support.

Fig. 1 - Overview of the various classes of Photonic Crystal Fibers

F-SM Series Large Mode Area PCFs

The F-SM Series PCFs are un-doped silica fibers that use a triangular pattern of air holes to form the cladding. Since the index contrast between the core and the cladding, Δn, is determined only by the geometry of the air holes, it is possible to fabricate fibers with a very small and accurate Δn, and thus obtain very low numerical apertures and very large mode areas. Furthermore, this type of fiber is single-mode over a very broad wavelength range, with a practically constant mode-field diameter (MFD). At short wavelengths, the fibers'' performance is limited by macro-bending losses, which determines the practical wavelength range for applications. The F-SM series of fibers are optimized in order to obtain the largest possible MFD without introducing significant macro-bending losses on typical bending radii of more than 16 cm.

The F-SM Series PCFs are typically used where single-mode, high-power delivery is required without introducing non-linear effects. Furthermore, they are the optimal choice for applications requiring single-mode guidance in a very broad wavelength range, e.g. in sensors, spectroscopy, interferometry or RGB displays.

End face image and weakly transmitted cladding modes profile of Newport''s F-SM series micro-structured fiber using an MBP series imaging device (see Micro-Beam Profiler), with lighting on both the ends of a short piece of the photonic crystal fiber.

Free Space Coupling and Handling

Coupling light into and out of an F-SM fiber is as simple as for standard optical fibers. In a free-space set-up, the optics should match the NA of the fiber and be diffraction limited in order to obtain a low-loss coupling. Since the MFD is practically constant, the NA is proportional to the wavelength, which should be considered in the design of coupling optics for a broad wavelength range. The F-SM Series may also be spliced to standard fibers, making them easy to integrate into existing systems or instruments. Optional beam expansion FC connectors enhance high power capabilities.

F-NL Series Highly Nonlinear PCFs

Highly nonlinear PCFs are designed with a small core to get a high nonlinear coefficient. The air-filled microstructured cladding region of nonlinear photonic crystal fibers lends this fiber type several advantages compared to standard step-index fibers. The high index difference between the silica core and the air-filled microstructure enables tight mode confinement resulting in a low effective area and thereby a high nonlinear coefficient. The air-filled region also results in strong wavelength dependence in the characteristics of the fiber and is responsible for the large wave-guide dispersion possible in such fibers. The wave-guide dispersion can be used to enhance or cancel out the material dispersion in the fiber and the flexibility in terms of dispersion profile is therefore much bigger in PCFs than in standard fibers. Changing the design of the microstructure (hole-sizes, pitch, hole structure) strongly influence the wave-guide dispersion and it is possible to design fibers with zero dispersion wavelength (ZDW) in the visible wavelength range or with flat near-zero dispersion over a large wavelength range. By choosing the dispersion profile carefully, the fibers can be tailored to facilitate different nonlinear processes.

Newport''s F-NL Series nonlinear fibers are designed with relatively small holes to be single-mode at the operation wavelength. This approach has several advantages compared to multimode nonlinear fibers with large air holes. First, the fibers are easier to splice to solid standard fiber due to the lower air-filling fraction. Second, alignment and focusing with free-space coupling is less critical as light focused on the cladding region will not be coupled, unlike in high-air-filling fraction fibers, where light can be guided in the silica "islands" between the large holes. Finally, a long range of applications requires strict single-mode operation.

For Supercontinuum generation using a femtosecond laser, try Newport''s SCG-800 and SCG-800-CARS self contained Supercontinuum Generation Fiber Devices. They consist of nonlinear PCFs contained in a robust, sealed, 25mm metal housing, without the hassle of fiber handling and cleaving.

F-Air Series Air-Guided Fibers

One very exciting feature of the PCF technology is the possibility of realizing fibers that guide light in a hollow (air) core, using the Photonic Bandgap (PBG) effect. The highly periodic structure of air holes in the cladding of the fiber creates a photonic bandgap. This means that light of frequencies within the PBG is not allowed to propagate out through the cladding and may be trapped in the core of the fiber. In contrast to index-guiding fibers, there is no requirement on the refractive index of the core region to be larger than the index of the cladding. An inherent feature of PBG-Guiding is that the fiber only guides light in a limited spectral region. For fibers guiding around 1550nm, a typical bandwidth is ~200nm. Outside this region, the fiber core is anti-guiding. A typical transmission spectrum is shown below.

Typical transmission spectrum for an airguiding fiber

Extreme dispersion properties may be found in the PBG fibers, such as anomalous dispersion values in the thousands of ps/nm/km. Due to a negligible contribution from the core material (air), the total dispersion of PBG fibers is dominated by wave-guide dispersion.

F-SM Series Specifications

	F-SM8	F-SM10	F-SM15	F-SM20	F-SM25	F-SM35
Cladding Diameter (µm)	125 ± 5	125 ± 2	230 ± 5	230 ± 5	268 ± 5	335 ± 5
Coating Diameter (µm)	245 ± 10	240 ± 5	405 ± 10	350 ± 10	410 ± 10	488 ± 10
Buffer Coating Material	Single layer acrylate
Core Diameter (µm)	8.5 ± 0.3	10 ± 1	15 ± 0.5	20 ± 0.4	25.2 ± 0.4	35 ± 0.5
Recommended minimum wavelength (nm)	400	400	450	700	950	1450
Cut-Off Wavelength	None
Mode Field Diameter (µm)	6.0 ± 1.0	7.5 ± 1.0	11.5 ± 1.5	15.0 ± 1.5	19.8 ± 2.0	26.0 ± 2.5
NA	0.059 ± 0.01 @ 450 nm	0.08 ± 0.01 @ 635 nm 0.09 ± 0.01 @ 780 nm 0.10 ± 0.01 @ 980 nm	0.04 @ 532 nm 0.05 @ 780 nm	0.041 ± 0.01 @ 780 nm 0.055 ± 0.01 @ 1064 nm	0.037 ± 0.01 @ 980 nm 0.040 ± 0.01 @ 1064 nm	0.046 ± 0.01 @ 1550 nm
Attenuation	<11 dB/km @ 635⁽¹⁾	<2 dB/km @ 1550 nm <7 dB/km @ 700-1000	<0.03 dB/m @ 532 nm <0.01 dB/m @ 780⁽²⁾	<7 dB/km @ 780⁽²⁾	<3.5 dB/km @ 1064⁽²⁾	<10 dB/km @ 1550⁽²⁾

(1) Measured for a bend radius of 8 cm
(2) Measured for a bend radius of 16 cm

Polarization Maintaining F-SM Series Specifications

	F-SM5-PM	F-SM10-PM	F-SM15-PM
Cladding Diameter (µm)	125 ± 3	230 ± 3	230 ± 5
Coating Diameter (µm)	245 ± 10	350 ± 10	350 ± 10
Buffer Coating Material	Single layer acrylate
Core Diameter (µm)	5.0 ± 0.5	10.0 ± 1.0	15 ± 0.5
Cut-Off Wavelength	None
Mode Field Diameter (µm)	4.2 ± 0.5	8.0± 0.8	12.5 ± 0.5
NA	0.09 ± 0.01 @ 470 nm	0.10 ± 0.05 @ 1060 nm	0.09 ± 0.02 @ 1060 nm
Attenuation	<0.03 dB/m @ 470 nm	<5 dB/km @ 1060 nm	< 15 dB/km @ 1060 nm
Polarization Extinction Ratio (dB)	>25	>20	>20

F-NL Series Specifications

	F-NL-PM-750	F-NL-5/1040
Cladding Diameter (µm)	120 ± 5	125 ± 3
Coating Diameter (µm)	240 ± 10	244 ± 10
Buffer Coating Material	Single layer acylate
Core Diameter (µm)	1.8 ± 0.3	4.8 ± 0.2
Zero Dispersion Wavelength (nm)	750 ± 15 1260 ± 20	1040 ± 10
Attenuation, Maximum (nm)	<50 dB/km @ 780	<3.0 dB/km @ 1040
Cut-Off Wavelength (nm)	<650	<1000
Mode Field Diameter (µm)	1.6 ± 0.3⁽¹⁾	4.0 ± 0.2⁽³⁾
NA	~0.38 ± 0.05 @ 780 nm	0.2 ± 0.05 @ 1060 nm
Nonlinear Coefficient (Wkm)^-1	95⁽¹⁾	11⁽²⁾
Birefringence	>3 x 10^{-4 (1)}	<4 x 10^{-6 (4)}

(1) @ 780 nm
(2) @ 1064 nm
(3) @ 980 nm
(4) @ 1550 nm

F-AIR Series Specifications

	F-AIR-6/800	F-AIR-10/1060	F-AIR-11/1550	F-AIR-20/1550
Material	Pure Silica
Cladding Diameter (µm)	122 ± 5	123	120	115
Coating Diameter (µm)	243 ± 10	220	220	220
Buffer Coating Material	Single layer acrylate
Core Diameter (µm)	6 ± 1	9.7	10.9	20 ± 2
NA	~0.17 @ 780 nm ~0.22 @ 830 nm	-	0.12	0.13 ± 0.03
Attenuation (nm)	<0.4 dB/m @ 760-800	<0.1 dB/m @ 1060	<0.1 dB/m @ 1550	<0.02 dB/m @ 1570