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Highly Nonlinear Fiber (HNLF) for NIR Supercontinuum Generation
The HN1550 Highly Nonlinear Fiber (HNLF) can be used for nonlinear spectral broadening of femtosecond pulses around 1550 nm. For more information about this application, please see the Spectral Broadening tab.
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Thorlabs' HN1550 Highly Nonlinear Fiber has a flat dispersion (zero-dispersion slope) compared to standard SM fiber (SMF-28 Fiber).
Thorlabs' HN1550 Highly Nonlinear Fiber (HNLF) is a single mode fiber designed for applications that require a large nonlinear coefficient as well as near-zero dispersion around 1550 nm (C & L bands). A primary application for this fiber is in nonlinear spectral broadening of femtosecond pulses in the 1550 nm band through self-phase modulation. This spectral broadening process can be used to generate broadband light sources (supercontinuum generation) and compressed pulses. Additionally, the combination of a high nonlinear coefficient and near-zero dispersion make the fiber ideal for four-wave mixing processes in this wavelength region.
The nonlinear coefficient of our HNLF is approximately 10 times higher than that of standard single mode fiber at this wavelength (SMF-28). This fiber provides near-zero normal dispersion and a flat (near-zero) dispersion slope. A typical dispersion plot for the fiber is available in the specification table.
This fiber is designed with a small mode-field diameter in order to enhance its nonlinearity. Therefore, splice recipe optimization or a bridge fiber should be used in order to minimize coupling losses between the standard single mode fiber and the HNLF. Thorlabs can provide this highly nonlinear fiber with single mode fiber spliced to one or both ends. Please contact Tech Support to request a quote on splice services for this fiber.
Spectral Broadening and Pulse Compression
One application for the HN1550 highly nonlinear fiber (HNLF) is spectral broadening of femtosecond pulses. The examples of spectral broadening in this fiber provided below can be used as a reference for designing systems or experiments. Please note that all simulations are made with the assumption that the input pulses are transform-limited sech2 shaped pulses, and the indicated power levels are after coupling into the HNLF fiber. The simulation results are not guaranteed and should only be used as guidelines for designing experiments; see the specifications table in the Overview tab for guaranteed performance.
Figures 1 through 3 show the spectral broadening of a 200 fs pulse at 100 MHz repetition rate and at three different average power levels, when sent into a 1 m long HNLF fiber. The spectral broadening can be used to generate broadband (supercontinuum) light sources.
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Figure 1: Simulated normalized output spectra from 1 m long HNLF fiber seeded with 100 MHz, 200 fs pulses at 20 mW average power.
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Figure 2: Simulated normalized output spectra from 1 m long HNLF fiber seeded with 100 MHz, 200 fs pulses at 40 mW average power.
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Figure 3: Simulated normalized output spectra from 1 m long HNLF fiber seeded with 100 MHz, 200 fs pulses at 80 mW average power.
The diagram and plots below show how nonlinear broadening can be utilized for compressing pulses in time. In the example shown here, a 100 fs pulse at 100 MHz repetition rate and 100 mW average power is sent into a 10 cm long HN1550 fiber. Figures 4 and 5 show the pulse normalized spectrum and its temporal intensity profile before entering the HN1550, respectively. Because the dispersion of the HNLF is normal, the pulses after broadening accumulate a negative chirp and can, therefore, be compressed in a medium with anomalous dispersion. By collimating the beam at the output of the HN1550 fiber and sending the pulses into 20 mm long bulk fused silica (anomalous dispersion, with negligible nonlinearity), the pulses are compressed in time to a pulse width (FWHM) less than 20 fs. Figures 6 and 7 show the output pulse normalized spectrum and temporal intensity profile, respectively. Please note that by compensating higher-order dispersions, a cleaner temporal profile can be achieved. Additionally, higher compression factors can be achieved by additional spectral broadening of higher intensity pulses.
Figures 4 - 7: Input spectrum (normalized) and temporal intensity profile for a pulse sent through a 10 cm long HN1550 fiber. Output spectrum (normalized) and temporal intensity profile for a pulse after propagating through the fiber and compression in 20 mm of bulk fused silica. The input pulse has a 100 fs pulse width, 100 MHz repetition rate, and 100 mW average power.