Continuous wave supercontinuum generation

We demonstrate a novel multiwavelength light source around the 1.7-μm region based on continuous-wave (CW) supercontinuum (SC) generation for the deeper imaging of low-water-absorption sample with a spectrally sampled optical coherence tomography (OCT) system. This self-regulated Gaussian spectrum of CW SC source has an extremely smooth flat width with more than 210-nm full-width at half-maximum bandwidth centered at the 1.7-μm region, a high output power of 500 mW, and a low temporal instability with less than 0.1 dB for an hour. In order to improve the OCT signal sensitivity without increasing the optical illumination power, a multiwavelength light source based on this CW SC was implemented by using a tunable fiber Sagnac comb filter. When it was applied to the spectrally sampled OCT imaging, the multiwavelength light source enabled a dynamic range improvement, compared to conventional continuous spectral light source with the same average optical power.

The supercontinum generation has been achieved mainly by two different approaches, namely, with femtosecond intense pulses or using a continuous wave laser or larger pulses centered on the anomalous dispersion region. In order to improve temporal coherence, it has been suggested the introduction of a pulse seed or the propagation of both a large pulse pump and a small weaker continuous wave to control the soliton fission. Here we propose supercontinuum generation using a hybrid input, we pump with a continuous laser and copropagate a picosecond signal. We compare the bandwidth of the supercontinuum using only the continuous pump or the hybrid setup. Simulations of the generalized Schrodinger equation, using an adequate input-noise model to reproduce the spectrum of the continuous signal, are performed in order to investigate the supercontinuum generation in the optical communication window under different dispersion regimes.

Supercontinuum generation in a highly nonlinear, dispersion-shifted fiber at 1550 nm is discussed. Spectrum generation under both pulsed and continuous-wave conditions is considered. With a few meters of highly nonlinear, dispersion-shifted fiber and a femtosecond erbium fiber laser, an octave-spanning supercontinuum is demonstrated. Kilometer lengths of nonlinear fiber pumped by a continuous-wave Raman fiber laser are shown to generate a continuum with a bandwidth greater than 247 nm. A nonlinear Schrodinger-equation model is used to investigate the effect of varying the dispersion on the pulsed continuum and noise effects in the continuous-wave continuum.

Temperature effects on supercontinuum generation using a continuous-wave Raman fiber laser

The control of temporal noise of the pump could add an additional degree of freedom to manipulate the spectrum of continuous-wave (CW) pumped SC generation. In this paper, we experimentally tailor the CW-pumped supercontinuum (SC) generation in a cascaded Raman random fiber laser (CRRFL) based on a 1 µm pump with tunable temporal dynamics. The pump is based on a spectrally filtered ytterbium-doped random fiber laser (YRFL) seed laser, which can be amplified to a 10 W level with the tunable temporal noise. By increasing the detuning between the wavelength of a filter and the central wavelength of a YRFL, the temporal noise of the pump can be gradually increased, and we experimentally demonstrate the larger temporal noise of the pump can significantly enhance the spectral performance of SC generation in terms of spectral bandwidth and flatness. As a result, we realize the enhanced SC generation in a CRRFL with a more than doubled -10 dB bandwidth in a 50-km-long single-mode fiber by optimizing the temporal dynamics of the pump. We also demonstrate the enhanced output power of the spectral-optimized SC generation to 1.27 W with a shorter cavity length. We anticipate the combination of a tunable temporal noise ytterbium-doped pump and CRRFL could provide a new route to realize high-power, ultra-broadband, and smooth SC generation in a simple fiber cavity.

Modulation instability of a continuous infrared wave leading to red-shifting solitons and blue-shifting dispersive waves and then subsequent soliton trapping is shown to enable the generation of blue solitary waves in optical fibers. The physical mechanism is described in the context of continuous wave supercontinuum generation leading to a spectrum which spans the visible and near infrared within practical experimental conditions.

We have obtained spectral broadening by pumping a nonmicrostructured highly nonlinear fiber with a continuous wave signal from a Raman fiber laser. The experiment was simulated using a generalized Schrodinger equation containing the actual Raman response of the fiber as calculated from the experimental Raman gain. A different input-noise model, that reproduces well the power spectral density of the laser, was used and compared with others previously proposed. (C) 2013 Optical Society of America

Supercontinuum (SC) generation in nonlinear photonic crystal fibers (NLF) using continuous-wave (CW) fiber lasers for pumping has been studied before[1,2]. The advantages of CW-SC are high spectral smoothness, high spectral power density, simplicity of the system, and lower noise than the more common picosecond-pumped SC. The cost of these features is increased nonlinear fiber lengths due to less efficient nonlinear processes at the lower power levels. Especially, the generation of light in the visible wavelength range has been a challenge. This has previously been tackled by increasing the nonlinearity of the fiber, zero dispersion shifting along the fiber length, and using 200 m of NLF[1], or alternatively using extremely high powers of 100's of Watts[2].

The noise properties of supercontinuum (SC) sources are of importance in many applications. This intensity noise of the SC arises from nonlinear amplification of the input-pulse shot noise and the spontaneous Raman scattering down the fiber [1]. Low noise femtosecond SC generation (SCG) has previously been demonstrated [2]. However, in commercial SC sources, the SC is generated by pumping with picosecond to nanosecond pulses and the SCG is thus initiated by modulation instability (MI). Therefore, the SC is characterized by low coherence and high shot-to-shot fluctuations, in particular at the spectral edges [3-5]. However, the influence of the noise properties when pumping in the normal dispersion regime has so far not been investigated for long pulse pumping. In this work we have measured and compared the relative intensity noise (RIN) properties of long-pulse MI initiated SCG in three different regimes: (i) all-normal SCG, (ii) normal-pumped SCG where higher-order Raman lines occur in the anomalous dispersion regime, and (iii) anomalous-pumped SCG. We show that the noise properties for the three regimes are similar: when increasing the input pump power, the intensity noise will continuously decrease for a given wavelength, and for a given input power the intensity noise will be lowest at the pump wavelength and increase when moving towards the spectral edge [6].

We propose a novel technique to convert any high-power, continuous-wave, Ytterbium fiber laser into a supercontinuum source using standard telecom fiber. We demonstrate an octave-spanning supercontinuum(880nm to >1900nm) with power >34W and ~44% conversion efficiency.

We report the first observation of supercontinuum (SC) generation in single semiconductor nanoribbons (NRs). By launching a continuous wave (CW) 532-nm pump light along a 200-μm-length CdS NR for waveguiding excitation, SC generation is realized with a threshold down to sub-milliwatt level, which is ~3 orders lower compared with previous CW-pumped SC generated in glass fibers. The low threshold is benefitted from the favorable material properties and waveguide geometries including high Raman gains, strong light confinement, more optical guided modes and phonon modes. Our work paves the way to low-threshold nanoscale SC sources and may find widespread applications ranging from spectroscopic analysis and biological imaging to material research.

In this study, the use of a continuous-wave (CW) supercontinuum (SC) seeded by an erbium-doped fiber's amplified spontaneous emission (ASE) for optical-coherence tomography imaging is experimentally demonstrated. It was shown, by taking an in-depth image of a human tooth sample, that due to the smooth, flat spectrum and long-term stability of the proposed CW SC, it can be readily applied to the spectral-domain optical-coherence tomography system. The relative-intensity noise level and spectral bandwidth of the CW SC are also experimentally analyzed as a function of the ASE beam power.

Modulation instability induced supercontinuum generation in liquid core suspended photonic crystal fiber with cubic-quintic nonlinearities

Role of higher order dispersion on instability criterion of saturable fiber system with Non-Kerr Nonlinearities

Modulation instabilities in twin-core fibers with self-steepening effects