Squeezing in the degenerate parametric oscillator

Squeezing of the intracavity field in a degenerate parametric oscillator is calculated above threshold neglecting pump depletion. Arbitrary squeezing is in principle obtainable. We conclude that above threshold squeezing in the steady-state parametric oscillator is limited primarily by pump depletion rather than degradation by vacuum fluctuations at the mirrors. The squeezing predicted by the present calculation should be observable in an oscillator operated in a transient or pulsed mode     

Self-phase-locked degenerate femtosecond optical parametric oscillator

We demonstrated a stable degenerate synchronously pumped femtosecond optical parametric oscillator (SPOPO) as a divide-by-2 subharmonic generator. The SPOPO exhibited passive all-optical self-phase-locking between the pump and signal/idler and thus required no external electronic feedback to produce the phase-locked subharmonic. We employed a type I phase-matched, 1-mm-long, periodically poled MgO:LiNbO3 crystal as the nonlinear gain element and an 80 MHz mode-locked Ti:sapphire laser with 180 fs pulses tuned at 775 nm as the pump. The SPOPO generated transform-limited 70 fs phase-locked output pulses centered at 1550 nm. The self-phase-locking operation was confirmed by separate beat-note measurement techniques with respect to the pump laser and with respect to an external cw laser.     

Dynamics of a degenerate parametric oscillator in a squeezed reservoir

Dynamics of a cavity mode which, in addition to interacting to an outside field with squeezed fluctuations, is simultaneously submitted to linear and parametric amplification processes is discussed in the Markovian approximation. The master equation for a density matrix of the cavity field is solved analytically in the Heisenberg picture. Long time asymptotic properties of the cavity mode are studied in the whole range of the evolution parameters and the corresponding decoherence effects are reported. It is also shown that in an appropriate regime of the evolution parameters there exists a unique steady state such that all initial density matrices evolve towards it. This allows engineering cavity states with desired properties.     

Pulsed degenerate optical parametric oscillator based on a nonlinear-fiber Sagnac interferometer

We report operation of an all-fiber degenerate optical parametric oscillator that employs a nonlinear-fiber Sagnac interferometer as a parametric amplifier. Synchronous pumping with 3.9-ps pulses at 1544 nm yields 0.83-ps output pulses. The wide bandwidth of the fiber parametric amplifier causes the oscillator to act as a pulse compressor. The output signal pulses exhibit improved spectral symmetry and a reduced time-bandwidth product compared with the pump pulses. Currently, the net group-velocity dispersion in the passive section of the fiber cavity limits the signal-pulse bandwidth and hence the minimum-obtainable pulse width. This experiment suggests the possibility of frequency conversion by operation of a similar pulsed parametric oscillator away from degeneracy.     

Entanglement of states and quantum distributions in pulsed optical parametric oscillator

The time-domain properties of Einstein-Podolsky-Rosen (EPR) entangled states of light are studied by means of analysis of both the Wigner functions and variance of quadrature amplitudes of generated modes. As a source of EPR states a non-degenerate optical parametric oscillator is considered driven by a sequence of laser pulses with a Gaussian time envelope.     

简并光学参量振荡器混沌反控制

提出一种实现简并光学参量振荡器混沌反控制的方法，用正弦信号调制简并光学参量振荡器的基模衰减率，使简并光学参量振荡器从定态输出转化为混沌态.数值模拟结果表明，选择不同的调制幅度和调制角频率，只要满足系统的最大李雅谱诺夫指数大于零，即可实现不同的混沌轨道重构.通过比较最大李雅谱诺夫指数λ_max随调制幅度和调制角频率变化曲线， 指出系统从周期态调制到混沌态比从无亚谐波输出的定态调制到混沌态更容易，有更宽的调制幅度和调制角频率选择范围. 关键词： 简并光学参量振荡器 混沌反控制 调制     

Broadband radiation of a degenerate optical parametric oscillator operating above threshold in information applications

Information applications of the essentially multimode (in time) radiation of a degenerate optical parametric oscillator operating above the oscillation threshold, such as protocols of quantum parallel dense coding and multimode quantum teleportation, have been considered. The stream of Shannon mutual information as a function of the spectral width of Alice’s signal and the spectral fidelity of transmission of a multimode quantum signal are evaluated from the estimates of the achievable radiation squeezing that occurs as the oscillation threshold is approached. The advantages of the multimode scheme over the single-mode scheme are discussed.     

Phase-separation dynamics of circular domain walls in the degenerate optical parametric oscillator

We study the dynamics of the formation of circular domain walls, which are large-intensity structures, in a degenerate optical parametric oscillator. We show that the mean-field and the propagation models predict the same increase in the domain size proportional to t(1/3) .     

简并光学参量振荡器混沌相同步与反相同步

从广泛意义上研究了简并光学参量振荡器的混沌同步. 数值结果表明, 当最大条件李指数小于零时, 处于混沌态的两个简并光学参量振荡器通过单向耦合可以实现相同步或反相同步. 当两个简并光学参量振荡器同时实现正耦合或负耦合时为相同步, 当其中一个为正耦合而另一个为负耦合时实现反相同步.     

Entanglement of a degenerate system in adiabatic process

Entanglement evolution of a degenerate system is studied. It is found that an entangled state becomes unentangled under an adiabatic variation of the system, and vice versa. The amount of entanglement varies with different adiabatic paths. It is concluded that the entanglement of complete set of eigenstates of a system at thermal equilibrium is independent on perturbations, but the entanglement of partial eigenstates may change with adiabatic perturbations. This can help us to control entanglement properties and is very useful in the quantum computations.     

Entanglement and sudden death of two two-level atoms interacting with a cavity field in presence of degenerate parametric amplifier

In the presence of degenerate two-photon transitions the problem of the interaction between two two-level atoms and a single-mode is considered. Near resonance case, a closed form of the analytic solution for the wave function is obtained. The entanglement between an atom and field in the interacting system is studied by using the change in atomic and field entropies. The relationship between entropy changes and concurrence entanglement is discussed. Our results show that the behavior of the entropy change in agreement with the behavior of the concurrence to measure the entanglement between two subsystem structures.     

Entanglement in cascaded-crystal parametric down-conversion

We use spontaneous parametric down-conversion in a cascade of crystals, driven by a single monochromatic cw pump laser, to study the interference of entangled photon pairs. By changing the distance between the crystals, the observed quantum interference pattern varies continuously from that associated with a longer single crystal to that associated with independent emissions from two distinct crystals. Postselection via spectral filtering suppresses this phenomenon. These findings are expected to advance the field of quantum-state engineering.     

Threshold and linewidth of a mirrorless parametric oscillator

We analyze the above-threshold behavior of a mirrorless parametric oscillator based on resonantly enhanced four-wave mixing in a dense atomic vapor. It is shown that, in the ideal limit, an arbitrary small flux of pump photons is sufficient to reach the oscillator threshold. We demonstrate that, due to the large group velocity delays associated with electromagnetically induced transparency, an extremely narrow oscillator linewidth is possible, making a narrow-band source of nonclassical radiation feasible.     

Dynamics of a parametric exciton-polariton oscillator in a microcavity

We study the dynamics of parametric oscillations of polaritons in a microcavity that consists of a periodic conversion of a pair of pump polaritons into polaritons of signal and idle modes and vice versa. The period and amplitude of oscillations considerably depend on the initial polariton density, the initial phase difference, and the resonance detuning. We show that there is a possibility of phase controlling the polariton dynamics in the microcavity.     

Production of squeezed states in a degenerate parametric amplifier

An analysis of the degenerate parametric amplifier including the quantisation of pump and signal modes is presented. It is shown that the fluctuations in one quadrature of the signal mode may be reduced at most by a factor of two. This is in contradistinction to analyses where the pump field is treated classically which overestimate the reduction in fluctuations possible.     

Continuous-wave, singly resonant, intracavity parametric oscillator

Performance characteristics of a continuous-wave intracavity optical parametric oscillator are described by use of an experimental arrangement comprising a KTP singly resonant oscillator located within a Ti:sapphire laser cavity and analyzed by use of a steady-state model. Internal and external powers, circulating fields, tuning ranges, spectral bandwidths, and amplitude-stability levels are measured and discussed. The nonresonant idler tunes from 2.53 to 2.87 microm, delivers a maximum output power of approximately 0.4W and displays long-term amplitude-stable operation. The total downconverted power approaches the optimum power coupled out of the Ti:sapphire laser in the absence of frequency conversion.     

Compact, high-pulse-energy, picosecond optical parametric oscillator

We report a high-energy optical parametric oscillator (OPO) synchronously pumped by a 7.19 MHz, Yb:fiber-amplified, picosecond, gain-switched laser diode. The 42-m-long ring cavity maintains a compact design through the use of an intracavity optical fiber. The periodically poled MgO-doped LiNbO(3) OPO provides output pulse energies as high as 0.49 μJ at 1.5 μm (signal) and 0.19 μJ at 3.6 μm (idler). Tunability from 1.5 to 1.7 μm and from 2.9 to 3.6 μm is demonstrated, and typical M(2) values of 1.5 × 1.3 and 2.8 × 1.9 are measured for the signal and idler, respectively, at high power.     

Photoacoustic measurement of N2O concentrations in ambient air with a pulsed optical parametric oscillator

Photoacoustic spectroscopy, in combination with a pulsed grazing-incidence optical parametric oscillator (GIOPO), was used for sensitive detection of nitrous oxide (N₂O) in ambient air. The ν₁+ν₃ combination band of N₂O was excited with the idler beam of the GIOPO in the 2.76 μm–2.91 μm spectral region, where CO₂ and water-absorption lines are also present. Three chemical filters filled with KOH, CaCl₂, and P₂O₅ were used to reduce the CO₂ and water concentrations to the level of several parts per billion (10⁹) by volume (ppbv). Photoacoustic spectra containing several absorption lines were recorded and the concentration was determined by an integral evaluation method and a fast Fourier transform evaluation method. The photoacoustic signal was calibrated by a standard mixture of 50.6 parts per million by volume (ppmv) of N₂O in synthetic air. Values of 311±5 ppbv, 314±5 ppbv, and 316±5 ppbv were found for three ambient samples collected at nearby roads. PACS 42.62.Fi; 42.65.Yj; 07.07.Df; 42.68.Ca     

30-fs, cavity-dumped optical parametric oscillator

We demonstrate cavity dumping of a synchronously pumped optical parametric oscillator (OPO). The OPO delivers 30-fs pulses with energies as high as 13 nJ at up to 400-kHz repetition rates. The OPO's tunability ranges from 570 to 600 nm and is limited by the resonator mirror coatings. The time jitter between pulses of a Ti:sapphire laser and the cavity-dumped OPO pulses is smaller than 30 fs, permitting multicolor time-resolved spectroscopic experiments.     

Compact, actively Q-switched optical parametric oscillator

An ultracompact, actively Q -switched optical parametric oscillator (OPO) has been realized that is only 30 mm in length, based on a semimonolithic microchip laser, a quadrupole deflector, and a monolithic periodically poled lithium niobate crystal. The OPO threshold was 550 mW when Nd:YAG was used as the gain material and 590 mW for Nd:Y VO(4), giving signal pulses of as much as 8.7 muJ in energy with Nd:YAG at 1 kHz and 5.9-mu;J pulses with Nd:Y VO(4) at 5 kHz, for 1.2- and 2-W laser diode pumping, respectively. The output was single frequency and could be tuned over the range 1540-3440 nm.