Tools of the trade - Vol 18 - Thorlabs - #899

Passive

Components

that the interaction between light and glass can be surprisingly small. In some types of PCF <1% of the optical power propagates in the glass, greatly reducing the extent to which the bulk properties of the glass determine the properties of the fiber. Hollow core PCF can therefore have

Collimation Packages

Mechanical properties and handling

Despite the presence of the holes, silica PCFs are mechanically remarkably robust. Winding them at 2-3mm radius, for example, does not damage to the internal structure. All Crystal Fibre fibers are proof tested at a strain of 0.25%. The fibers can be cleaved with conventional tools and fusion splicing of PCF to PCF and PCF to solid fiber is possible; however, splicing processes developed for conventional fibers need to be modified to achieve optimal results. To facilitate the integration of PCFs into optical systems Crystal Fibre now offers custom splicing, end face protection and connectorization services (page 894).

The Future

One key objective of research is the reduction of attenuation for both solid and hollow core fibers. While the attenuation of some types of solid core fiber already approaches the theoretical limit set by Rayleigh scattering, the principle limits to loss of hollow core PCFs are still largely unexplored. However, hollow core fibers with <2 dB/km loss are now a reality³, and it is possible that PCFs will ultimately achieve a loss well below that

Optical Switches

ackbox Systems

Connectors/ rermination Tools

ngle-Mode Fiber

are Earth Doped

"Stack"-

020mm to 040mm

Single-Mode: PM

Photonic Crystal Fiber

Itimode Fiber: Graded Index

Multimode Fiber:!

Furnace

1800°C

Step Index

Waveguide Circuits

of the best conventional fibers. This, in combination with the virtual absence of non-linearity, may enable PCFs to be the fiber of choice for long-haul transmission in the future.

Square Lattice Cladding

extremely low non-linearity, high breakdown threshold, zero dispersion at any design wavelength, and negligible interface reflection. Furthermore, it becomes possible to fabricate low-loss fibers from comparatively high-loss materials, extending the range of materials that can be considered for fiber fabrication.

Fabrication

Crystal Fibre's PCFs are fabricated by assembling fused silica capillaries into a preform "stack". A core is embedded by replacing one or more of these capillaries by a solid rod or by a thin-walled tube in the case of hollow core PCFs. The resulting preform is then inserted into a sleeve tube and drawn to fiber. Careful control of the process conditions ensures that the capillaries are transformed into the desired arrangements of holes, despite the fact that the diameter of each hole is reduced several hundred-fold from stack to fiber. During the draw process the holes are filled with dry inert gas to minimize the effects of gaseous contaminants. Capillaries and other key components are manufactured in-house from high-grade fused silica glass, giving Crystal Fibre a high degree of design flexibility and control over material quality. Draw lengths of a few kilometers are typical, but there are no known limits to drawing much longer fiber.

Another interesting area of development are PCFs for short wavelengths, promising to improve the level of power that can be delivered or extending the application of fiber optics further into the ultraviolet. The potential in the UV is still unproven; but, Crystal Fibre offers hollow core fibers covering the entire visible spectrum, including fibers optimized for 532nm. Other wavelengths are available on request. Hollow core technology is also promising for the mid-infrared range, extending the wavelength range that can be covered with silica fibers to beyond 2iim, and in the future, to longer wavelengths using non-silica glasses.

The large number of degrees of freedom in the design of PCFs and the fact that small changes in the waveguide structure can sometimes have a surprisingly large effect on the optical properties of the fiber suggest that the range of fiber designs and applications will continue to grow rapidly. Therefore, if none of our standard products are what you are looking for, Crystal Fibre welcomes requests for custom designed products. Our team of experienced application engineers are happy to explore solutions that meet your particular application requirements. Please contact us to discuss any questions you may have about Photonic Crystal Fiber. ■

1) Birks, T. A., et al., 31 1941-1942 (1995)

2) Cregan, R. F. et al, . Science 285 1537-1539 (1999)

3) B.J.Mangan. et al., OFC2004, Post Deadline Paper

Dispersion

Compensating

PCF

Non-silica PCF (SF6)

Dual Core PCF

Doped Double Clad PCF for Lasers

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Sales: 973-579-7227

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