Synchronously Pumped Optical Parametric Oscillators Research Articles

Noncritical generation of nonclassical frequency combs via spontaneous rotational symmetry breaking

Synchronously pumped optical parametric oscillators (SPOPOs) are optical cavities containing a nonlinear crystal capable of down-converting a frequency comb to lower frequencies. These have received a lot of attention lately, because their intrinsic multimode nature makes them compact sources of quantum correlated light with promising applications in modern quantum information technologies. In this work we show that SPOPOs are also capable of accessing the challenging but interesting regime where spontaneous symmetry breaking plays a crucial role in the quantum properties of the emitted light, difficult to access with any other nonlinear optical cavity. Apart from opening the possibility of studying experimentally this elusive regime of dissipative phase transitions, our predictions will have a practical impact, since we show that spontaneous symmetry breaking provides a specific spatiotemporal mode with perfect squeezing for any value of the system parameters, turning SPOPOs into robust sources of highly nonclassical light above threshold.

Reduced models and design principles for half-harmonic generation in synchronously pumped optical parametric oscillators

We develop reduced models that describe half-harmonic generation in a synchronously-pumped optical parametric oscillator above threshold, where nonlinearity, dispersion, and group-velocity mismatch are all relevant. These models are based on (1) an eigenmode expansion for low pump powers, (2) a simulton-like sech-pulse ansatz for intermediate powers, and (3) dispersionless box-shaped pulses for high powers. Analytic formulas for pulse compression, degenerate vs. nondegenerate operation, and stability are derived and compared to numerical and experimental results.

Characteristics of optical parametric oscillators synchronously pumped by second harmonic of femtosecond Yb:KGW laser

We present experimental data and numerical simulation results obtained during investigation of synchronously pumped optical parametric oscillators (SPOPOs) pumped by second harmonic (515nm) of femtosecond Yb:KGW laser. We used two different nonlinear media for parametric generation – lithium triborate (LBO) and beta barium borate (BBO) in slightly different experimental setups. Maximum parametric light conversion efficiency from pump power to signal power was more than 25% whereas the largest achieved signal wave tuning ranges were from 670nm to 1030nm for BBO SPOPO and from 780nm to 940nm for LBO SPOPO. We also used intracavity group delay dispersion (GDD) compensation to achieve shorter signal pulses and investigated changes of various SPOPO output characteristics when changing net cavity GDD.

Yb-Fiber-Laser-Pumped Ultrafast Frequency Conversion Sources From the Mid-Infrared to the Ultraviolet

We describe the development of versatile, practical, and high-power ultrafast optical sources based on second-order nonlinear frequency conversion in bulk materials pumped by the mode-locked Yb-fiber laser at 1064 nm, and covering spectral regions from the near- to mid-infrared (mid-IR) to the visible and ultraviolet (UV). By exploiting synchronously-pumped optical parametric oscillators (SPOPOs) based on quasi-phase-matched nonlinear materials of MgO:PPLN and MgO:sPPLT, in combination with internal and external single-pass harmonic generation in birefringent crystals of BiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> and β-BaB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , we have generated tunable picosecond pulses in spectral regions from above ~4 μm in the mid-IR, into the visible, and down to 317 nm in the UV. The demonstrated sources can deliver average output powers of up to 11.7 W in the near- to mid-IR, 3.5 W in the visible, and 30 mW in the UV, in picosecond pulses at ~80 MHz repetition rate, with high passive stability, excellent output characteristics, and the potential for further power scaling with increased fiber laser pump power. The described sources represent an effective approach for the extension of fiber laser technology across the entire wavelength range from the UV to mid-IR spectrum, and ultimately the THz spectral range.

Optical damage studies of mercury thiogallate nonlinear crystals for use in 1-μm pumped optical parametric oscillators

We investigated optical damage (surface and bulk) in one of the most promising wide bandgap nonoxide nonlinear crystals, HgGa2S4, that can be used in ∼1-μm pumped optical parametric oscillators (OPOs) and synchronously pumped OPOs (SPOPOs) for generation of idler pulses above 4 μm without two-photon absorption losses at the pump wave- length. The optical damage has been characterized at the pump wave- length for different repetition rates using uncoated and antireflection- coated (mainly with a single layer for pump and signal wavelengths) sam- ples. HgGa2S4 is the most successful nonlinear crystal (both in terms of output energy and average power) for such OPOs, but optical damage inside the OPO has a lower threshold and represents at present the prin- cipal limitation for the achievable output. It is related to peak pulse and not to average intensity, and bulk damage in the form of scattering centers occurs before surface damage. Such bulk damage formation is faster at higher repetition rates. Lower repetition rates increase the lifetime of the crystal but do not solve the problem. The safe pump fluence in extrac- avity measurements is <1 J∕cm 2 , which corresponds to ∼100 MW∕cm 2 for the 8-ns pulse duration (both values peak on-axis). In the OPO, how- ever, peak on-axis fluence should not exceed 0.3 J∕cm 2 limited by the formation of bulk scattering centers in orange-phase HgGa2S4. In the nanosecond OPO regime, the damage resistivity of Cd-doped HgGa2S4 is higher and that of the almost colorless CdGa2S4 is roughly two times higher, but the latter has no sufficient birefringence for phase-matching. In SPOPOs operating in the ∼100 MHz regime, the dam- age limitations are related both to the peak pulse and the average inten- sities, but here HgGa2S4 seems the best nonoxide candidate to obtain first steady-state operation with Yb-based mode-locked laser pump sources. © 2013 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10

Dual‐wavelength optical parametric oscillator using antiresonant ring interferometer

AbstractA novel technique for coupling of two resonant optical cavities using an antiresonant ring (ARR) interferometer is reported. By deploying two synchronously‐pumped femtosecond optical parametric oscillators (OPOs), it is shown that the use of an ARR can provide an intracavity common path for the two oscillating fields, but without gain coupling between the two nonlinear media. The new technique permits the generation of two signal (idler) wavelengths, which can be independently and arbitrarily varied across the OPO tuning range. The absence of gain coupling also enables unrestricted and uninterrupted tuning through wavelength degeneracy at any arbitrary point within the OPO tuning range. It is shown that signal wavelength pairs tunable across 1500–1580 nm, corresponding to a frequency separation from ∼ 10 THz down to exact degeneracy, can be generated from the coupled OPOs, limited only by the reflectivity of the available mirrors.

A time/frequency quantum analysis of the light generated by synchronously pumped optical parametric oscillators

We present in this paper a general model for determining the quantum properties of the light generated by a synchronously pumped optical parametric oscillator (SPOPO) operating below threshold. This model considers time and frequency on an equal footing, which allows us to find new quantum properties, related for example to the carrier envelope offset (CEO) phase, and to consider situations that are close to real experiments. We show that, in addition to multimode squeezing in the so-called ‘supermodes’, the system exhibits quadrature entanglement between frequency combs of opposite CEO phases. We have also determined the quantum properties of the individual pulses and their quantum correlations with the neighboring pulses. Finally, we determine the quantum Cramer–Rao limit for an ultra-short time delay measurement using a given number of pulses generated by the SPOPO.

Synchronized retroreflection-pumped femtosecond optical parametric oscillator

We report a flexible technique for threshold reduction and output power enhancement in synchronously pumped optical parametric oscillators (SPOPOs) based on synchronized retroreflection of the undepleted pump using a collimating system and a delay line, which allows easy and independent adjustment of the spatial and temporal overlap of the retroreflected beam in the nonlinear crystal. The method permits initial synchronization of the forward and retroreflected pump by interferometry, providing threshold reduction before oscillation is initiated. We demonstrate the technique in a femtosecond SPOPO based on BiB3O6, where a threshold reduction of 22% and an output power enhancement of 70% are achieved compared with single-pass pumping, with no detrimental effect on the spectral and temporal characteristics of the output pulses.

Generation and Characterization of Multimode Quantum Frequency Combs

Multimode nonclassical states of light are an essential resource in quantum computation with continuous variables, for example, in cluster state computation. We report in this Letter the first experimental evidence of a multimode nonclassical frequency comb in a femtosecond synchronously pumped optical parametric oscillator. In addition to a global reduction of its quantum intensity fluctuations, the system features quantum correlations between different parts of its frequency spectrum. This allows us to show that the frequency comb is composed of several uncorrelated eigenmodes having specific spectral shapes, two of them at least being squeezed, and to characterize their spectral shapes.

Numerical investigations of parametric transfer in synchronously pumped optical parametric oscillators for indirect mid-infrared pulse shaping

We present numerical investigations of parametric transfer in synchronously pumped optical parametric oscillators (SPOPOs) used for indirect mid-infrared pulse shaping. The introduction of an optical bandpass filter in the resonator results in transfer of intensity and phase profile of the input pump onto the output idler pulse. We investigate the effect of resonator parameters, process nonlinearity, and chromatic dispersion of the nonlinear crystal, on the SPOPO behavior and the transfer fidelity. We show numerically that parametric transfer from a broad-bandwidth pump pulse can be achieved with good fidelity and high efficiency for a broad range of parameters in a periodically poled lithium niobate SPOPO.

Fiber-feedback continuous-wave and synchronously-pumped singly-resonant ring optical parametric oscillators using reverse-proton-exchanged periodically-poled lithium niobate waveguides

We describe guided-wave singly-resonant reverse-proton-exchanged (RPE) periodically-poled lithium niobate (PPLN) waveguide ring optical parametric oscillators (OPOs) in which the feedback was provided via a single-mode fiber pigtailed to the waveguide. Wavelength selection was achieved by means of a fiber Bragg grating inside the feedback loop. The SRO threshold for the synchronously-pumped OPO was below 1 mW of average coupled pump power.