In an ordinary single mode fiber extreme care is taken to assure that the optical pulse is transmitted with the least possible distortion of the signal to enable the best possible performance of an optical fiber span. Sometimes, however, distortion is a good thing.
OFS has developed highly non-linear fiber (HNLF) to have a high degree of non-linear performance. “Simply put, HNFL is designed to enhance non-linear effects that cause the spectrum to broaden while light is guided,” explains Finn Birkedahl, Sales & Marketing Manager, OFS Denmark.
To accomplish this, HNLF has a reduced core size and an increased refractive index of the core resulting in a very small modefield. This small modefield has the effect of increasing the energy density to a point where the refractive index changes depending on the intensity of the light in the fiber.
OFS uses conventional optical fiber technology to achieve a very high delta index between the core and cladding, low loss, and a small effective area. The span of the continuum generated is related to the wavelength of the laser light and the dispersion properties of the HNLF.
“These dispersion properties can be precisely controlled to allow generation at different wavelength spans to meet the requirements of varied applications,” says Birkedahl.
OFS HNLF has many applications, as it combines high non-linearity with a numerically small dispersion, and it has been used in experiments covering a wide range of applications:
• Pulse compression
• Optical regeneration
• High-speed optical switching
• Super continuum generation
• Parametric amplification
• Optical sampling
• Non-linear optical loop mirror optical time domain de-multiplexing
• Wavelength conversion
Supercontinuum generation – with light sources covering the 1,000 – 2,000 nm wavelength range – presents many new opportunities.
For example, OFS Labs has developed two new categories of broadband supercontinuum sources: one pumped with continuous wave (CW) lasers, and one pumped with pulsed lasers. These all-fiber, portable devices can be customized to generate the broad wavelength spectrum and the power level required by the application. Light from either a Pulsed Erbium Fiber Laser or a CW Raman Fiber Laser is used to pump a span of OFS highly non-linear fiber.
The interaction of the laser light with the specialty fiber triggers non-linear optical effects that broaden the narrow spectrum of the laser by 100 times or more. The supercontinuum output exhibits a broad continuous spectrum, and many of the characteristics of laser light. Power levels of the supercontinuum are dependent upon the laser type used.
Other applications involving HNLF include high speed (160+ Gb/s) optical communications systems, now being researched in laboratories. Applications are also being studied in microscopy and fundamental metrology.
“At OFS we are supporting the research in many areas by manufacturing and supplying HNLF with a wide range of parameters that are optimized for specific applications to a wide range of institutions throughout the world,” says Birkedahl.
More on highly non-linear fibers can be found in
OFS white papers.
