- Delivery of Ultra-Short High-Power Optical Pulses
- Pulse Compression and Pulse Shaping
- Sensors and Spectroscopy
- Available with Design Wavelengths of 820, 1060, 1550, 1570, or 2025 nm
- 7 or 19-Cell Core Offers Large Continuous Operation Bandwidth
- Small Number of Core Modes and Parasitic Surface Modes
- Zero Dispersion at the Design Wavelength
- Near-Gaussian Fundamental Mode
- Virtually Free of Optical Nonlinearity
- Virtually Immune to Bend Loss
- No Fresnel Reflection from the End-Faces (Modal Index ≈ 1)
Photonic bandgap (hollow core) fibers guide light in a hollow core that is surrounded by a microstructured cladding. Photonic bandgaps can form in materials that have a periodically structured refractive index; in PCFs this is achieved by using a periodic arrangement of air holes in silica. A photonic bandgap in the cladding acts as a virtually loss-free mirror confining light to a core, which does not need to be fabricated from a solid material. 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. Therefore, hollow core PCFs exhibit extremely low nonlinearity, 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. The fiber is protected by a single layer acrylate coating and can be stripped and cleaved like ordinary solid fibers.
As with conventional single mode fibers, the favored mode in hollow-core PFCs has a quasi-Gaussian intensity distribution. Even though hollow core PCFs are intended to be used like other single mode fibers, no currently available low-loss hollow-core PCF is a true single mode waveguide; typically, they support several higher order core modes and, in some cases, additional “surface” modes located at the core cladding boundary. All of these modes have higher loss than the fundamental mode and generally decay rapidly, but their presence needs to be taken into account when designing input and output coupling optics.
Unlike in conventional fiber where material dispersion plays a major role, group velocity dispersion (GVD) in hollow-core PCF is dominated by waveguide dispersion. A plot of dispersion versus wavelength is upward sloping and crosses zero close to the center of the operating wavelength band, for any design wavelength, including those where the dispersion of silica makes it impossible to achieve zero dispersion in conventional fiber.
Hollow core fibers only guide light within the wavelength range covered by the photonic bandgap in the cladding. Outside that range — typically about 10% of the design wavelength - loss increases sharply.