Femtosecond fiber lasers together with nonlinear fibers are compact, reliable, all-fiber supercontinuum sources. Maintaining an all-fiber configuration, however, necessitates pulse compression in an optical fiber, which can lead to nonlinearities for subhundred femtosecond, nanojoule pulses. In this work we show that using large-mode-area fibers for pulse compression mitigates the nonlinearity, resulting in compressed pulses with significantly reduced satellite pulses. Consequently, supercontinua generated with these pulses are shown to have as much as a 10 dB increase in coherence fringe contrast. By using a hybrid highly nonlinear fiber-photonic crystal fiber, the continuum can be extended to visible wavelengths while still maintaining high coherence.

Supercontinuum extending to visible wavelengths is generated in a hybrid silica nonlinear fiber pumped at 1560 nm by a femtosecond, erbium-doped fiber laser. The hybrid nonlinear fiber consists of a short length of highly nonlinear, germano-silicate fiber (HNLF) spliced to a length of photonic crystal fiber (PCF). A 2 cm length of HNLF provides an initial stage of continuum generation due to higher-order soliton compression and dispersive wave generation before launching into the PCF. The visible radiation is generated in the fundamental mode of the PCF.

We have built and tested an interferometric fiber-optic gyroscope made with photonic crystal fiber. This paper reports the test results and examines the advantages of photonic crystal fiber for this type of gyroscope.

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Visible supercontinuum in the fundamental mode is generated in a silica hybrid nonlinear fiber using a femtosecond, erbium-doped fiber laser pump. The nonlinear fiber consists of highly nonlinear, germano-silicate fiber (HNLF) fusion spliced to a photonic crystal fiber (PCF). 2007 Optical Society of AmericaOCIS codes: (060.4370) Nonlinear optics, fibers; (060.5530) Pulse propagation and solitonsSupercontinuum generation produced by propagation of femtosecond pulses in nonlinear fibers has revolutionized the field of frequency metrology [1,2]. Photonic crystal fibers (PCF) with small effective areas can have anomalous dispersion at short wavelengths and are suitable for continuum generation with Ti:Sapphire pulses at 800 nm [3]. In another common configuration, highly nonlinear, germano-silicate fibers with low dispersion and dispersion slope at 1550 nm can generate octave spanning spectra when pumped by an Er-doped fiber laser [4,5].Supercontinua generated from femtosecond erbium-doped fiber lasers in conjunction with HNLF do not extend much below 850 nm in wavelength, even when using high energy pulses [6,7]. However, in frequency metrology experiments, optical frequency references are often at visible wavelengths, and consequently frequency doubling is employed to compare these references to infrared combs [8]. Therefore the ability to extend fiber laser combs to shorter wavelengths could potentially allow direct comparison of the comb to visible frequency references without additional nonlinear optics.Visible radiation from nonlinear PCFs has been demonstrated with a 1550 nm pump, however the visible light is produced in a variety of higher-order-modes [9,10]. In addition, extremely broad supercontinuum extending to visible wavelengths has been demonstrated in soft glass photonic crystal fibers using a femtosecond pulses at 1550 nm [11], but fusion splicing these fibers is difficult, as is maintaining a bulk-optic launch into such small core fibers for extended periods of time. In another approach, Bragg gratings in nonlinear fibers have been shown to produce light at wavelengths shorter than the edge of the continuum that can be obtained from the nonlinear fiber alone, but the short wavelength light is only generated over a narrow (<1 nm bandwidth) wavelength range 12 .Splicing together nonlinear fibers with different dispersion parameters or effective areas (Aeff) can beneficially impact the supercontinuum's characteristics. For example, creating a dispersion-decreasing, highly nonlinear fiber can broaden and flatten the supercontinuum [4], whereas concatenating anomalous and normal dispersion HNLFs can generate octave spanning supercontinuum with reduced relative intensity noise [13]. In another experiment, mico-managing the dispersion of PCFs on a short length scale using tapering, led to noise reduction in the supercontinuum [14]. Tapering photonic crystal fibers to alter the dispersion properties along the length of the fiber has also been shown to extend the short wavelength edge of the supercontinuum ...