Spacing-tunable multi-wavelength fiber laser based on cascaded four-wave mixing in highly nonlinear photonic-crystal fiber

A multi-wavelength fiber laser based on the cascaded four-wave mixing in highly-nonlinear photonic-crystal fiber is proposed and investigated. The cascade operation is initiated by two strong pump waves boosted by multi-mode pumping erbium/ytterbium co-doped double-cladding fiber amplification technique. A segment of highly-nonlinear near-zero-dispersion-flattened photonic crystal fiber is employed to induce highly efficient cascaded four-wave mixing. The wavelength spacing can be continuously tunable by stretching the fiber Bragg grating. Experimental results show that multiple wavelengths with a high optical side-mode suppression-ratio of >30 dB are achieved. Furthermore, the proposed multi-wavelength fiber laser exhibits an excellent stability at room temperature.     

Enhanced four-wave mixing in a high-finesse highly nonlinear fiber Fabry-Perot resonator

We have achieved a four-wave mixing process in a high-finesse highly nonlinear fiber Fabry-Perot resonator, where the amplified signal and idler were enhanced in transmission by 6 dB and 10 dB respectively comparing with those in a single fiber. We used a 6 m long low-loss Fabry-Perot resonator with two high-reflectivity fiber Bragg gratings written directly into a highly nonlinear fiber provided by Sumitomo Electric Inc., where the minimised intracavity loss resulted in the finesse in excess of 100. The resonator length was locked for 30 min by means of a modified Pound-Drever-Hall technique. The maximum intracavity power was increased by 14.3 dB by increasing the stimulated Brillouin scattering threshold with periodic phase modulation by a pseudo-random bit sequence, with length matching that of the cavity.     

Phase-matched four-wave mixing of isolated waveguide modes of high-intensity femtosecond pulses in a hollow photonic-crystal fiber

Hollow-core photonic-crystal fibers with a special dispersion profile are shown to allow phase-matched nonlinear optical interactions of isolated air-guided modes of high-intensity femtosecond laser pulses confined in the hollow fiber core. We present theoretical and experimental studies of the four-wave mixing of fundamental and second-harmonic pulses of a Cr:forsterite laser with an initial pulse duration of about 50 fs and an intensity on the order of 10¹⁴ W/cm² in waveguide modes of a hollow photonic-crystal fiber with a core diameter of about 13μm.     

Light trapping in a fiber grating defect by four-wave mixing

We propose the use of nonlinear four-wave mixing as a means of trapping light in a defect state in a nonuniform fiber grating. The amount of energy deposited is estimated by use of an approach similar to Fermi's "golden rule" and is approximately 30 fJ for realistic grating parameters and a pulsed pump of 100-ps width.     

Multi-wavelength erbium-doped fiber laser using four-wave mixing effect in doped fiber

We demonstrate a multi-wavelength erbium-doped fiber laser (EDFL) using erbium gain and four-wave mixing (FWM) effect in a piece of erbium-doped fiber (EDF) with high erbium ion concentration. The EDF has a pump absorption rate of 24.6 dB/m at 979 nm and is bi-directionally pumped by 980-nm laser diodes. FWM effect redistributes the energy of different oscillating lines and causes multi-wavelength operation. The laser generates more than 22 lines of optical comb with a line spacing of approximately 0.10 nm at the 1569-nm region using only 1.5-m-long EDF.     

Terahertz-wave generation by surface-emitted four-wave mixing in optical fiber

We propose a novel terahertz-wave source through the four-wave mixing effect in a conventional single-mode optical fiber pumped by a dual-wavelength laser whose difference frequency lies in the terahertz range. Surface-emitted geometry is employed to decrease absorption loss. A detailed derivation of the terahertz-wave power expression is presented using the coupled-wave theory. This is a promising way for realizing a reasonable narrow-band terahertz-wave source.     

Reduced threshold of a stimulated four-wave mixing process in an optical fiber

The possibility for all-optical control of the effective parametric Stokes gain was demonstrated in an optical fiber. For the first time the threshold reduction induced by the interference of two different four-wave mixing processes which share a common Stokes wave was used as a control mechanism.     

Nondegenerate four-wave mixing in a birefringent optical fiber pumped by a dye laser

An efficient nondegenerate four-wave-mixing process in a highly birefringent optical fiber pumped by a dye laser is reported. The output beam from a dye laser (at ~610 nm) was found to mix with the accompanying superfluorescent light (from 575 to 600 nm) in a birefringent fiber to generate a distinct frequency-shifted beam, which could be Stokes or anti-Stokes radiation, depending on which mode of the fiber was excited. The frequency shift was comparable with that observed in the well-known pump-divided degenerate process, as confirmed by the theory.     

Self-induced phase matching in stimulated four-wave mixing in a nonbirefringent single-mode optical fiber

Self-induced phase matching in stimulated four-wave mixing in a nonbirefringent single-mode optical fiber has been observed. It is shown that in a nonbirefringent single-mode fiber the phase matching that is necessary for stimulated four-wave mixing can be accomplished with a combination of self-phase modulation and cross-phase modulation induced by a pump-laser pulse.     

Optical parametric oscillator based on four-wave mixing in microstructure fiber

We demonstrate, for the first time to our knowledge, optical parametric oscillation based on four-wave mixing in microstructure fiber. The measured wavelength-tunability range of the device (40 nm) and the threshold-pump peak power (34.4 W) are in good agreement with the theory of four-wave mixing in optical fibers. The ellipticity of the fiber's polarization modes allows the device to be implemented in a relatively simple Fabry-Perot configuration. Spectral peaks that are due to cascaded-mixing processes are easily observed in our setup, which may provide a way to extend the tunability range of existing high-power lasers.     

Phase-matching analysis of four-wave mixing induced by modulation instability in a single-mode fiber

Four-wave mixing induced by modulation instability in a single-mode fiber is analyzed from the phase-matching point of view. For the two-channel transmission, a method is proposed to select the four-wave-mixing-induced sidebands, which is based on the proper use of a continuous-wave and a pulse as light sources. We find that a mass of sidebands are generated in the modulation instability resonance region, and the power of the sideband increases with not only the peak power of the pump pulse but also the continuous-wave power which acts as a seed. The research will provide guidance for fiber communication and sensing systems using wavelength division multiplexing technology.     

Quantum noise generated by four-wave mixing process within a fiber ring resonator

We have analyzed the dissipative effect of the entangled photons generated by a nonlinear optical ring resonator from a non-degenerate four-wave mixing (FWM) process. The system and reservoir Hamiltonian are established in the interaction picture. To eliminate the reservoir operators, the Markov approximation is used and result them in a Linblad form in the master equation. Consequently, the positive P representation can recast this equation to the Fokker-Planck equation, and then the stochastic differential equations i.e., the entangled photon state equation of motion for photons propagating in the fiber, are obtained and easy to analyze numerically. Results obtained have shown that the entangled strength measurement depends on three main factors; first the nonlinear susceptibility of the third harmonic generation, second the damping rate that represents loss of energy from the system to the reservoir, and final the diffusion of fluctuations in the reservoir into the entangled photon modes.     

Enhanced nondegenerate four-wave mixing owing to electromagnetically induced transparency in a spectral hole-burning crystal

We have demonstrated electromagnetically induced transparency (EIT) in an inhomogeneously broadened spectral hole-burning system of Pr(3+)-doped Y(2)SiO(5) at 6 K. We have also shown enhancement of four-wave mixing under conditions of reduced absorption. This demonstration opens the possibilities of pursuing EIT applications such as high-resolution optical image processing and optical data storage in solids.     

Visible supercontinuum generation controlled by intermodal four-wave mixing in microstructured fiber

We present an experimental and numerical study of supercontinuum generation extended in the visible part of the spectrum by using a selective optical coupling of the pump wave in the largely anomalous dispersion regime. The broadband frequency generation is induced by an initial four-wave mixing process that converts the pump wave at 1064 nm into 831 nm anti-Stokes and 1478 nm Stokes wavelengths. Phase matching is ensured on such a large frequency shift thanks to a microstructured multimodal fiber with a specific design. Continuum generation is therefore enhanced around the two generated sidebands.     

Tunable dual-wavelength fiber laser based on an opto-VLSI processor and four-wave mixing in a photonic crystal fiber

A stable wavelength and wavelength spacing tunable dual-wavelength fiber laser based on an Opto-very-large-scale-integration (Opto-VLSI) processor and four-wave mixing (FWM) in a high-nonlinear photonic crystal fiber is experimentally demonstrated. The results show that the line width of the tunable dual-wavelength fiber laser is 0.02 nm, and the wavelength spacing can be tuned from 0.8 nm to 4 nm with a 0.15 nm step. Under the influence of the FWM, the uniformity is below 0.6 dB and the measured side mode suppression ratio (SMSR) is above 45 dB.     

Spatiotemporal mode-locked multimode fiber laser with dissipative four-wave mixing effect

The high degree of freedom and novel nonlinear phenomena of multimode fiber are attracting attention. In this work, we demonstrate a spatiotemporal mode-locked multimode fiber laser, which relies on microfiber knot resonance (MKR) via dissipative four-wave-mixing (DFMW) to achieve high-repetition-rate pulses. Apart from that, DFMW mode locking with switchable central wavelengths can also be obtained. It was further found that high pulse energy induced nonlinear effect of the dominant mode-locking mechanism transforming from DFMW to nonlinear Kerr beam cleaning effect (NL-KBC). The experimental results are valuable for further comprehending the dynamic characteristics of spatiotemporal mode-locked multimode fiber lasers, facilitating them much more accessible for applications.     

Broadband wavelength converter based on four-wave mixing in a highly nonlinear photonic crystal fiber

We demonstrate a 10 Gbit/s nonreturn-to-zero wavelength converter based on four-wave mixing in a 20 m highly nonlinear photonic crystal fiber. The tunable wavelength conversion bandwidth (3 dB) is about 100 nm. The conversion efficiency is -16 dB when the pump power is 22.5 dBm. Phase modulation was not used to suppress the stimulated Brillouin scattering; thus the linewidth of the converted wavelength remained very narrow. The eye diagrams show that there is no additional noise during wavelength conversion. The measured power penalty at a 10(-9) bit-error-rate level is about 0.7 dB.     

Multi-wavelength bismuth-based erbium-doped fiber laser based on four-wave mixing effect in photonic crystal fiber

A stable multi-wavelength erbium-doped fiber laser based on four-wave mixing (FWM) in a photonic crystal fiber (PCF) is demonstrated in this paper. The phase matching condition for four-wave mixing in the photonic crystal fiber has been enhanced using a seed signal and a polarisation controller to control the states of polarisation in the ring laser cavity. At a maximum pump power of 1480 nm, 5 lines are observed with nearly 2.15 nm spacing between the lines, and with a signal to noise ratio of more than 20 dB. The number of channels and wavelength spacing can be controlled by varying the output coupler ratio.     

Phase-sensitive four-wave mixing and Raman suppression in a microstructure fiber with dual laser pumps

On coupling two phase-coherent frequency-conjugate laser pulses into a microstructure fiber, we observe phase-sensitive photon generation via four-wave mixing, and suppression of Raman emission at the middle frequency.     

Four-wave mixing in hollow photonic-crystal fibers

A radical enhancement of four-wave mixing in hollow-core photonic-crystal fibers is experimentally demonstrated. An enhancement ratio of about 800 relative to the regime of tight focusing is achieved for the four-wave mixing process 3ω=2ω+2ω?2ω, where ω and 2ω are the frequencies of fundamental radiation and the second harmonic of picosecond Nd:YAG laser pulses.