Backward Optical Parametric Oscillator Research Articles

Theoretical study of diode pumped intracavity backward optical parametric oscillator based on periodically poled lithium niobate

Theoretical study of diode pumped intracavity backward optical parametric oscillator based on periodically poled lithium niobate

Theoretical Investigation of Backward Optical Parametric Oscillator Pumped by Vortex Beams

Nonlinear generation and manipulation of vortex beams have emerged as a research hot topic in recent years. During nonlinear frequency conversions, orbital angular momentum will transfer from the fundamental wave to harmonic waves. In this work, we study theoretically the backward optical parametric oscillator pumped by vortex beams. The orbital angular momentum conservation law has been disclosed for the counter propagation nonlinear process. In addition, the oscillation threshold and the conversion efficiency have been investigated in detail. Our results will be helpful for the experimental demonstration of backward optical parametric oscillator pumped by vortex beams.

Backward optical parametric oscillator threshold and linewidth studies

We carry out a theoretical investigation of the backward interaction optical parametric oscillator (OPO), in which one of the generated waves is counterpropagating with respect to the pump. We derive simple, self-consistent analytical formulas for the continuous-wave and pulsed regimes. While consistent with previous works on the continuous-wave regime, our study enables us to extend the analysis to the pulsed regime. In particular, we derive simple expressions of the oscillation build-up time, pulsed threshold, and efficiency, for the first time, to our knowledge. We also investigate the peculiar spectral features of the backward OPO when pumped with a narrow-linewidth pulsed radiation, in particular, the absence of tolerance to phase mismatch and the natural ability to emit two waves with a Fourier-transform-limited spectrum. A comparison with the conventional forward OPO is also carried out to emphasize the unique properties of the backward OPO.

Tunable Backward Terahertz-wave Parametric Oscillation

Backward optical parametric oscillation has attracted attention for cavityless spectral narrowband generation based on perfect photon conversion. Few demonstrations have shown its potential from the aspect of nonlinear photonics; therefore, the mechanisms of momentum conservation among interacting light waves have been concealed by the restricted configuration under the phase-matching condition of periodically poled structures. Here, we unveil a tunable mechanism in the terahertz region by active control of the phase-matching condition. The tunability of backward terahertz-wave parametric oscillation is investigated using a quasi-collinear phase-matching model and its frequency range from the sub-terahertz to terahertz region is identified. Transform-limited terahertz-wave pulse is achieved simply by installing a device on the pump propagating line with no cavity. Moreover, the cascading terahertz-wave generation enhances the photon conversion efficiency, thus making nonlinear optics and its applications more promising. The results highlight new capabilities for using modern ferroelectric materials and encourage further research on nonlinear optics.

Backward three-wave optical solitons

Backward symbiotic solitary waves in quadratic media with absorption losses are generated through the nonlinear non-degenerate three-wave interaction. We study these solitary waves in the particular case of a doubly backward quasi-phase matching configuration. The same mechanism responsible for nanosecond solitary wave morphogenesis in the c.w. pumped Brillouin-fiber-ring laser may act for picosecond pulse generation in a quadratic c.w. pumped optical parametric oscillator (OPO). The resonant condition is automatically satisfied in stimulated Brillouin backscattering when the fiber-ring laser contains a large number of longitudinal modes beneath the gain curve. However, in order to achieve quasi-phase matching between the three optical waves in the Χ(2) medium, a nonlinear susceptibility inversion grating of sub-µm period is required. Such a quadratic medium supports solitary waves that result from energy exchanges between dispersionless waves of different velocities. We show, by a stability analysis of the non-degenerate backward OPO in the QPM decay interaction between a c.w. pump and backward signal and idler waves that the inhomogeneous stationary solution exhibits a Hopf bifurcation with a single control parameter. Above OPO threshold, the nonlinear dynamics yields self-structuration of a backward symbiotic solitary wave, which is stable for a finite temporal walk-off (i.e. different group velocities) between signal and idler waves. We also study the dynamics of singly backward mirrorless OPO’s (BMOPO’s) pumped by an incoherent field, in line with the recent experimental demonstration of this OPO configuration. We show that this system is characterized, as a general rule, by the generation of a highly coherent backward field, despite the high degree of incoherence of the pump field. This remarkable property finds its origin in two distinct phase-locking mechanisms that originate respectively in the convection and the dispersion properties of the fields. In both cases we show that the incoherence of the pump is transferred to the co-moving field, which thus allows the backward field to evolve towards a highly coherent state. We propose realistic experimental conditions that may be implemented with currently available technology and in which backward coherent wave generation from incoherent excitation may be observed and studied.

Generation of mid-infrared wavelengths larger than 40 μm in a mirrorless counterpropagating configuration

We report that mid-infrared wavelengths larger than 4.0 μm are efficiently generated in a periodically poled lithium niobate as a counterpropagating backward optical parametric oscillator. In comparison with the forward optical parametric oscillator, the backward configuration does not require a cavity mirror to establish laser oscillations. Also, the changing curves of the threshold intensity with and without the idler absorption for beyond 4.0 μm generation are quite different. Whether the idler absorption is considered or not, the conversion efficiency of both the signal and the idler will always increase with the pump intensity above the threshold. However, as the idler absorption cannot be neglected, the signal becomes larger than that without the idler absorption, while the idler gets smaller, and the threshold intensity is lower than that in forward QPM optical parametric generation without a cavity mirror only when the idler wavelength is less than 5.6 μm. The design that is presented offers practical mid-infrared generation with a low pump threshold.

Temporal walk-off for self-structuration of three-wave solitons in CW-pumped backward optical parametric oscillators

Stability analysis of the non-degenerate backward optical parametric oscillator in quasi-phase-matching decay interaction, between a CW-pump and counter-propagating signal and idler waves, proves that inhomogeneous stationary solutions exhibit a Hopf bifurcation, in contrast with the degenerate configuration. More importantly, we show that this Hopf instability gives rise to the generation of a backward three-wave soliton whose stable self-similar symbiotic structure is ensured by the group-velocity delay, or temporal walk-off, between the signal and the idler waves.

Unconditional temporal instability and self-pulse structuration in the phase-matched degenerate backward optical parametric oscillator

Stability analysis of the degenerate backward optical parametric oscillator in the phase-matching decay interaction, between a CW-pump and a sub-harmonic counter-propagating signal, proves that the inhomogeneous stationary solutions are always temporally unstable whatever the cavity length and pump power above threshold. The nonlinear dynamics exhibits self-pulse structuration of the backward signal with unlimited amplification and compression. Above a critical pulse steepening, dispersion saturates this singular behavior leading to strongly modulated solitary structures.

Second-order nonlinear optical materials for efficient generation and amplification of temporally-coherent and narrow-linewidth terahertz waves

We have considered forward and backward optical parametric oscillation and amplification, and difference-frequency generation for efficiently generating and amplifying terahertz waves in several second-order nonlinear optical materials. We have used a single crystal of CdSe as an example. We have also investigated GaSe, periodically-poled LiNbO3 and LiTaO3, and diffusion-bonded-stacked GaAs and GaP plates. The advantage of using birefringence in CdSe and GaSe is tunability of the output terahertz frequency. Furthermore, both CdSe and GaSe can be used to achieve the backward parametric oscillation without any cavity. On the other hand, in periodically-poled LiNbO3 and LiTaO3, one can take advantage of large diagonal elements of second-order nonlinear susceptibility tensor. In the diffusion-bonded-stacked GaAs and GaP plates, quasi-phase matching can be achieved by alternatively rotating the plates. We have shown that it is feasible to achieve forward optical parametric oscillation in the THz domain using these plates. The advantage of using coherent parametric processes is possibility of efficiently generating and amplifying temporally-coherent and narrow-linewidth terahertz waves. Compared with a noncollinear configuration, by using the parallel wave propagation configurations, the conversion efficiency can be higher because of longer effective interaction length among all the waves.

Generation of tunable coherent far-infrared waves based on backward optical parametric oscillation in gallium selenide

We show that it is possible to use backward optical parametric oscillation in GaSe to obtain tunable output in the 13–20-μm range with the minimum threshold intensity as low as a few 108 W/cm2. We may be able to use this configuration to achieve large amplification factors for a coherent weak beam in the far-infrared region. It is also possible to generate coherent far-infrared waves in the presence of pump and signal waves.