Traveling-wave Optical Parametric Amplifier Research Articles

A photonic integrated continuous-travelling-wave parametric amplifier.

The ability to amplify optical signals is of pivotal importance across science and technology typically using rare-earth-doped fibres or gain media based on III-V semiconductors. A different physical process to amplify optical signals is to use the Kerr nonlinearity of optical fibres through parametric interactions1,2. Pioneering work demonstrated continuous-wave net-gain travelling-wave parametric amplification in fibres3, enabling, for example, phase-sensitive (that is, noiseless) amplification4, link span increase5, signal regeneration and nonlinear phase noise mitigation6. Despite great progress7-15, allphotonic integrated circuit-based demonstrations of net parametric gain have necessitated pulsed lasers, limiting their practical use. Until now, only bulk micromachined periodically poled lithium niobate (PPLN) waveguide chips have achieved continuous-wave gain16,17, yet their integration with silicon-wafer-based photonic circuits has not been shown. Here we demonstrate a photonic-integrated-circuit-based travelling-wave optical parametric amplifier with net signal gain in the continuous-wave regime. Using ultralow-loss, dispersion-engineered, metre-long, Si3N4 photonic integrated circuits18 on a silicon chip of dimensions 5 × 5 mm2, we achieve a continuous parametric gain of 12 dB that exceeds both the on-chip optical propagation loss and fibre-chip-fibre coupling losses in the telecommunication C band. Our work demonstrates the potential of photonic-integrated-circuit-based parametric amplifiers that have lithographically controlled gain spectrum, compact footprint, resilience to optical feedback and quantum-limited performance, and can operate in the wavelength ranges from visible to mid-infrared and outside conventional rare-earth amplification bands.

Bright squeezed-vacuum source with 1.1 spatial mode.

Bright squeezed vacuum, a macroscopic nonclassical state of light, can be obtained at the output of a strongly pumped nonseeded traveling-wave optical parametric amplifier (OPA). By constructing the OPA of two consecutive crystals separated by a large distance, we make the squeezed vacuum spatially single-mode without a significant decrease in the brightness or squeezing.

Optimization of gain in traveling-wave optical parametric amplifiers by tuning the offset between pump- and signal-waist locations

We present experimental demonstration and modeling of the optimization of a phase-sensitive optical parametric amplifier by tuning the relative position between the pump and signal beam waists along the propagation direction. At the optimum position, the pump beam focuses after the signal beam, and this departure from colocated waists increases with increasing pump power. Such optimization leads to more than 3dB improvement in the measured deamplification response of the amplifier.

Decomposing a pulsed optical parametric amplifier into independent squeezers

We discuss the concept of characteristic squeezing modes applied to a travelling-wave optical parametric amplifier pumped by an ultrashort pulse. The characteristic modes undergo decoupled single-mode squeezing transformations, and therefore they form a useful basis to describe the evolution of the entire multimode system. This provides an elegant and intuitive picture of quantum statistical properties of parametric fluorescence. We analyse the efficiency of detecting quadrature squeezing, and present results of numerical calculations for a realistic nonlinear medium.

Femtosecond Noncollinear Optical Parametric Amplification in the Mid-Infrared Range with 1.25 µm Pumping

We study noncollinear three-wave interaction in a traveling wave optical parametric amplifier operating in the mid-infrared spectral range between 6 and 8 µm using HgGa2S4 and AgGaS2 as nonlinear optical crystals. Calculations reveal that matching of the group velocities in both crystals is possible in a wider spectral (or angular) region for type-I interaction. High-power femtosecond pulses at 1.25 µm from a Cr:forsterite regenerative amplifier are used for pumping the optical parametric amplifier at a repetition rate of 1 kHz. Experimentally we verify the advantages of noncollinear interaction by increasing the conversion efficiency approximately sixfold in the saturation regime as compared to the collinear case. The maximum idler energy measured near 6 µm exceeds 4 µJ and typical pulse durations are about 300 fs.

Sum-frequency generation of femtosecond pulses in CsLiB_6O_10 down to 175 nm

Using a 150-mum-thick CsLiB(6)O(10) crystal, we produced 100-fs, >200-nJ light pulses tunable between 175 and 180 nm by sum-frequency generation at a 1-kHz repetition rate with an all-solid-state laser system mixing the fourth harmonic of a femtosecond Ti:sapphire regenerative amplifier and the idler pulse from a traveling-wave optical parametric amplifier.

Generation of widely tunable harmonic pulses in the UV and VUV from a NIR optical parametric amplifier

We demonstrate the generation of tunable high-order harmonics from the interaction of the signal output of a near-infrared (NIR) traveling-wave optical parametric amplifier (OPA) with the xenon atoms of a pulsed gas jet. By tuning the OPA between 1200 and 1550 nm, we generate widely tunable pulses of ultraviolet radiation up to the ninth harmonic order, around 150 nm. The possibility to cover the VUV region thanks to the full overlap of the tunability ranges of different harmonic orders below 220 nm is also proved.

Laser-diode-seeded single and double stage femtosecond optical parametric amplification in the mid-infrared

Tunable mid-infrared pulses are generated with a MgO:LiNbO3-based traveling-wave optical parametric amplifier in single and double stage operation regime pumped by a 1-kHz Ti:sapphire regenerative amplifier system. For the first time to our knowledge a pulsed laser diode is successfully used in the femtosecond regime as a compact seed source at the signal wavelength where the tunability of the generated idler pulses can be realized by tuning the seed wavelength. Almost transform limited mid-infrared pulses as short as 130 and 160 fs with pulse energies as high as 5 and 15 μJ are produced near 3.5 μm by the single and double stage scheme, respectively. The pulse to pulse fluctuations in both cases do not exceed 2% which corresponds to the stability of the pump source.

Quantum fluctuations in traveling-wave amplification of optical images

We investigate amplification of optical images by means of a traveling-wave optical parametric amplifier. As shown recently for a cavity-based geometry, such a scheme can amplify images without deteriorating their signal-to-noise ratio thus working as a noiseless amplifier. Here we consider a configuration without cavity, which is more realistic for a possible experimental realization. We study in detail the quantum fluctuations of the amplifier and formulate criteria for its noiseless performance. We investigate physical features of noiseless amplification, which take place for both traveling-wave and ring-cavity configurations. We demonstrate how the optimum phase matching of a phase-sensitive wave front of an image (by means of a thin lens or a small displacement of the crystal) can improve the noise performance of the amplifier and bring it to the ultimate value achievable under given physical conditions. We discuss the possibility of using detectors with the area much smaller than the area of the input image elements. We compare our results with those obtained for the ring-cavity configuration.

Laser-diode-seeded operation of a femtosecond optical parametric amplifier with MgO:LiNbO_3 and generation of 5-cycle pulses near 3 μm

A high-power traveling-wave optical parametric amplifier based on MgO:LiNbO3 that is capable of producing extremely short pulses in the 3-µm spectral range when pumped by a femtosecond Ti:sapphire amplifier near 800 nm has been developed. With seeding by 1-ns pulses from a low-power Q-switched microlaser, we demonstrate idler tunability between 3.1 and 3.9 µm at >10-µJ pulse energy and <200-fs pulse duration. The maximum internal conversion efficiency is 40% for a single pass. The extremely high gain factors achieved permit a more compact solution for the seed source, and we also report on successful seeding with a pulsed laser diode in the femtosecond regime, achieving 5-µJ pulse energy and 130-fs pulse duration near 3.5 µm. We have produced nearly transform-limited 50-fs, 2-µJ pulses near 3 µm with a 1-mm-thick MgO:LiNbO3 sample by adding a second pass and employing sub-30-fs pumping.

Traveling-wave optical parametric amplifier: investigation of its phase-sensitive and phase-insensitive gain response

We experimentally investigate the gain response of a frequency-degenerate but polarization-nondegenerate traveling-wave optical parametric amplifier that consists of a type II phase-matched potassium titanyl phosphate crystal pumped by a frequency-doubled Q-switched mode-locked Nd:YAG laser. Both the optical phase-sensitive and phase-insensitive configurations of the parametric amplifier are studied. Experimental results are in excellent agreement with the theory of an optical parametric amplifier when the Gaussian-beam nature of the various fields is taken into account. In the phase-sensitive configuration a gain of >100 (20 dB) could be easily obtained in the amplified quadrature, which is limited only by the available pump power. Because of gain-induced diffraction and phase fluctuations, however, maximum deamplification in the orthogonal quadrature is limited to <0.5(-3 dB).

Two independently tunable and synchronised femtosecond pulses generated in the visible at the repetition rate 40 kHz using optical parametric amplifiers

We report on a 40 kHz repetition rate travelling wave optical parametric amplifier (OPA) system designed for ultrafast spectroscopy. Two independently tunable OPAs seeded from a single white light continuum source each generate 40–75 nJ per pulse over a 480–730 nm spectral range when pumped by 1 μJ, 130 fs, 400 nm pulses derived from a Ti:sapphire regenerative amplifier. After removal of chirp, the cross-correlation between the two OPAs was measured to be 150 fs. Bandwidth was 205 ± 85 cm −1, consistent with the transform limit of the compressed pulses. A single OPA gave up to 280 nJ per pulse signal energy when pumped with 3 μJ per pulse.

Sub-shot-noise microscopy: imaging of faint phase objects with squeezed light

We propose a scheme that uses spatially multimode squeezed light, generated by means of a traveling-wave optical parametric amplifier, with which a faint phase object can be imaged with sensitivity better than the shot-noise limit.

Investigation of Temporal and Spectral Properties of Ultrashort Light Pulses from an Optical Parametric Amplifier

A travelling-wave optical parametric amplifier (OPA) is treated, and basic theoretical results are summarized. An OPA connected to KDP crystals pumped by second harmonic pulses (λ= 0·532 μm, τ ≃ 20 ps) from a Nd: YAG laser was studied. The dependence of temporal and spectral parametric pulse properties on the conversion rate (gain saturation) was investigated. Nearly bandwidth-limited pulses (τ Δ v ˜ 0·6) were obtained at low energy conversion. A pulse reduction to 8 ps was measured in this case. At higher conversion ≳ 10 per cent, the stability of the output energy was higher. However, the pulse quality decreased considerably.