Intracavity Four-wave Mixing Research Articles

Toward new frontiers for terahertz quantum cascade laser frequency combs

AbstractBroadband, quantum-engineered, quantum cascade lasers (QCLs) are the most powerful chip-scale sources of optical frequency combs (FCs) across the mid-infrared and the terahertz (THz) frequency range. The inherently short intersubband upper state lifetime spontaneously allows mode proliferation, with large quantum efficiencies, as a result of the intracavity four-wave mixing. QCLs can be easily integrated with external elements or engineered for intracavity embedding of nonlinear optical components and can inherently operate as quantum detectors, providing an intriguing technological platform for on-chip quantum investigations at the nanoscale. The research field of THz FCs is extremely vibrant and promises major impacts in several application domains crossing dual-comb spectroscopy, hyperspectral imaging, time-domain nanoimaging, quantum science and technology, metrology and nonlinear optics in a miniaturized and compact architecture. Here, we discuss the fundamental physical properties and the technological performances of THz QCL FCs, highlighting the future perspectives of this frontier research field.

Demonstration of Phase Correlation Between the Spectral Lines of a Broadband Fiber Laser

The spectrally broadened output of an erbium-doped fiber laser generated by intra-cavity four-wave mixing is passed through a demultiplexer yielding multiple narrow-linewidth spectral sources. These spectral lines are tested for their phase correlation by providing two such spectral lines simultaneously as input to the fiber-optic Mach–Zehnder-based interferometer, and studying the interference. Significant phase correlation is obtained which is not limited by the wavelength separation between the spectral lines. Comparison with the results from two standard narrow-linewidth lasers as well as two broadband non-laser sources aid in the interpretation of the spectral visibility data.

Resonant intracavity four-wave mixing in a composite atom–cavity system

We experimentally study intracavity four-wave mixing (FWM) using Λ-type, three-level electromagnetically induced transparency (EIT) atoms confined in an optical ring cavity. The original dark-state peak disappears accompanying the generation of intracavity FWM when the coupling light is changed from traveling-wave to standing wave. Additionally, this FWM signal is on resonance with the optical cavity only when the coupling laser is detuned from the atomic resonance center, where the absorption is drastically reduced for both the probe and FWM fields. At last, we do theoretically analysis for the susceptibility of this composite atom–cavity system.

Spectral broadening due to intra-cavity four-wave mixing at low pump powers in erbium-doped fiber ring laser

In this paper, we present the experimental results of multi-pump-induced four-wave mixing (FWM) in erbium-doped fiber ring laser (EDFRL) in the wavelength range of 1560–1600 nm. The required multiple pumps are generated within the ring cavity by an appropriate choice of the wavelength range of operation with a suitable length of erbium-doped fiber. By introducing the optical nonlinearity with specialty fibers such as the highly nonlinear fiber (HNLF) and dispersion shifted fiber (DSF), FWM processes occurring in the laser are studied at low powers of the pump laser at 980 nm. The prevalent FWM theory is improved to interpret the two-pump and four-pump-induced side band generation in the first- and second-orders, after including the effect of phase mismatch at the wavelengths used in the experiments.

Tunable Terahertz Beat Signal Generation From an InAs/InP Quantum-Dot Mode-Locked Laser Combined With External-Cavity

Tunable terahertz beat signal generation is demonstrated by using a C-band InAs/InP quantum-dot (QD) mode-locked laser combined with external cavity of two fiber Bragg gratings (FBGs), where one of the FBGs is tunable in wavelength. Beat signals with ultra-high repetition rates quasi-continuously from 1 to 2.21 THz are observed between the two modes, which are phase-correlated due to intracavity four-wave mixing effect in the QD waveguide.

Continuous-Wave Multifrequency Laser Emission Generated Through Stimulated Raman Scattering and Four-Wave Raman Mixing in an Optical Cavity

The frequency of a continuous-wave laser was converted via high-order stimulated Raman scattering and four-wave Raman mixing in a high-finesse optical cavity. The threshold for the generation of a Stokes beam was determined by the Raman gain coefficient and the loss in the cavity. The intracavity power of the second-order Stokes beam increased with an increase in pump power, whereas the power of the first-order Stokes beam stayed constant. The output power of the anti-Stokes beam was low when there was a phase mismatch between the pump and the first-order Stokes beam. The anti-Stokes beam, however, was enhanced by decreasing the pressure of the Raman active medium. This suggests that the dispersion can be used to improve the efficiency of the intracavity four-wave Raman mixing.

Correlated Photon-Pair Source for Secured $C$-Band Quantum Communications

We have experimentally investigated and shown evidence of correlated photon-pair generation based on coupled intracavity four-wave mixing (FWM) in a dual-wavelength erbium-doped fiber ring laser operating in the fiber-optic communication <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> -band regime. In the coupled FWM process, the pump photons are both involved in the absorption and stimulated emission, which generate signal and idler wavelengths simultaneously. The correlation experiment was performed with various photon count levels in the order of hundreds of photons/s at each channel. The photon number of channel was less than 0.1/pulse and the maximum coincidence to single counts ratio was approximately 12% with a Gaussian profile in the accumulated counts.

Four-wave mixing in intra-cavity dual-wavelength fibre ring laser

An intra-cavity four-wave mixing (FWM) in a dual-wavelength erbium-doped fibre ring laser has been demonstrated where a 100 m-long dispersion-shifted fibre has been introduced as a nonlinear medium to pronounce the FWM effect in a 1550 nm window. The laser operates in the gain switched (pulse) mode for effectively achieving high power and increasing the intermodulation effect in the ring cavity. This scheme provides a simple and efficient way of archieving a dual-wavelength source for various optical systems.

Phase-Matched Raman-Resonant Four-Wave Mixing in a Dispersion-Compensated High-Finesse Optical Cavity

A highly efficient intracavity four-wave mixing in a Raman-active medium pumped by a continuous-wave laser is first demonstrated. Managing the intracavity dispersion to satisfy the phase matching in a high-finesse cavity substantially enhances the anti-Stokes emission. This process is observed in a region far beyond small signal approximation, indicating the generation of phase-locked sidebands arising from molecular modulation. This points to a novel approach of an optical modulator and mode-locked laser operating at a frequency of more than 10 THz.

Frequency up-conversion of coherent images by intracavity nondegenerate four-wave mixing

This work presents theoretical and experimental studies of the processes of light field transformations upon frequency-nondegenerate fourwave mixing (NFWM) in a nonlinear Fabry-Perot interferometer (FPI). The principal aims are the development of a theory for intracavity four-wave mixing in complex molecular media in conditions of scattering from dynamic gratings and resonator feedback; determination of a mechanism of light field transformations in dynamic holograms, and also by nonlinear interferometers; working out and introduction of novel nonlinear-optical methods to control the characteristics of light beams. High diffraction efficiency (up to 13.5%) with simultaneous infrared-to-visible frequency conversion of coherent images has been experimentally obtained by intracavity NFWM.

Determining the coefficient of transverse turbulent diffusion in a flow of the active medium of a CO2 laser with fast axial gas circulation

A method for determining the coefficient of transverse turbulent diffusion in a flow of the active medium of a CO2 laser with fast axial gas circulation is described. The method is based on the phase conjugation during degenerate intracavity four-wave mixing.

Complete characterization of a self-mode-locked Ti:sapphire laser in the vicinity of zero group-delay dispersion by frequency-resolved optical gating

The intensity and the phase of ultrashort pulses from a self-mode-locked Ti:sapphire laser operating in the vicinity of zero group-delay dispersion (GDD) have been completely characterized by the technique of frequency-resolved optical gating (FROG). For small values of negative GDD, the appearance of a dispersive wave in the pulse spectrum is manifested in the measured FROG trace, and pulse retrieval directly shows its association with a broad leading-edge pedestal. For positive GDD, we confirm previous experimental observations of picosecond pulses with large positive chirp and report a new operating regime in which the output pulses are of picosecond duration but are intensity modulated at 20 THz. The physical origin of this modulation is discussed by analogy with similar effects observed during pulse propagation in optical fibers, and the experimental results are compared with a model of intracavity four-wave mixing about the cavity zero GDD wavelength.

Nonlinear optical properties of the active medium in intracavity phase conjugation of the radiation of a pulsed electron-beam-controlled discharge CO2 laser. II. Theoretical analysis

Numerical simulation is used as the basis of an analysis of nonlinear optical properties of the active medium in intracavity four-wave mixing of the radiation of a pulsed electron-beam-controlled discharge CO2 laser on saturated-gain and refractive-index diffraction gratings. The reflection coefficient of the phase-conjugated signal is determined for various cavity Q-factors, specific input energies, and pressures of the laser-active mixture. A comparison is made of the theoretical and experimental results. It is found that the rate of formation of amplitude gratings is governed primarily by the initial population inversion and by the intensities of the interacting waves. It is shown that transient phase gratings make the dominant contribution to the phase-conjugate reflection coefficient at high pressures of the mixture.

Squeezing in intracavity four-wave mixing with non-degenerate pumps

The authors present a quantum analysis of four-wave mixing in a non-resonant nonlinear medium inside a cavity which is driven by two driving fields. In this process a nonlinear medium couples two pump modes with a signal mode of the frequency equal to the half-sum of the two pump field frequencies. Three types of stable steady-state solutions of the deterministic problem, describing three regimes of oscillation, are found: one below threshold and two different above-threshold regimes. The spectra of fluctuations of the quadrature-phase amplitudes for all three modes are calculated. It is found that in the above-threshold regime each of three modes may display a squeezed noise reduction. Below threshold a squeezing is realized for the central mode.

Comparison of external and intracavity four-wave mixing of cw infrared radiation

A comparative study was made of external and intracavity four-wave mixing of cw infrared radiation in toluene. The intracavity mixing efficiency was found to be almost four times less than that of mixing outside the resonator cavity. The quality of the intracavity phase conjugation process deteriorated when the pump wave intensity exceeded 30 W/cm2 .

Correction of optical path differences using phase conjugation in single-mode diode lasers

Intracavity four-wave mixing in single-mode diode lasers operating above threshold is shown to phase conjugate optical path differences. This capability, in conjunction with observed conjugate reflectivities in excess of 10(4), makes diode-laser conjugators an attractive and potentially monolithically integratable conjugator technology for semiconductor optoelectronics.

Quantum-noise reduction in intracavity four-wave mixing.

We present a simple quantum model for intracavity four-wave mixing above threshold. A reduction of quantum noise below the shot-noise level is predicted not only for the intensity difference of the signal and idler beams, but for the signal and idler intensity sum and also for the individual signal and idler intensities. The noise spectrum for the signal and idler phase variables is also calculated.

Coherent coupling of CW laser oscillators using intracavity four-wave mixing

A theoretical study of frequency locking laser oscillators using an intracavity four-wave interaction is discussed. An experimental demonstration that successfully locked two CW dye lasers using this concept was performed, along with intracavity four-wave mixing studies, with sodium vapor serving as the nonlinear (mixing) element.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Coupled cw dye lasers using intracavity four-wave mixing

An experimental investigation of laser-oscillator frequency locking by a four-wave interaction was conducted. An experiment was performed that successfully demonstrated the locking of two cw dye lasers using this concept with Na vapor serving as the nonlinear (coupling) medium.

Squeezing by parametric oscillation and intracavity four-wave mixing

We present a unified quantum analysis of parametric oscillators and intracavity four-wave mixers. The squeezing spectra below and above threshold for the degenerate cases are compared. Similarities between the systems are discussed and the optimum operating regimes identified.