Phase-sensitive Optical Parametric Amplifier Research Articles

Ultralow-noise preamplified optical receiver using conventional single-wavelength transmission

Conventional optical amplifiers that use stimulated emission suffer from the generation of excess noise, thus limiting the performance in many applications. The phase-sensitive optical parametric amplifier, relying on the use of a nonlinear material for amplification, is an exception that can approach a noise figure of 0 dB. Its implementation in optical communication links has, however, been cumbersome due to increased complexity both in the transmitter and the receiver, effectively limiting the use of such amplifiers in practice. Here, we propose and demonstrate an implementation of a transmission system with exceptional performance in terms of receiver sensitivity (0.9 photons per bit) using a standalone ultralow-noise phase-sensitively preamplified receiver and a conventional single-wave optical transmitter. This is a significant simplification compared to previous demonstrations and can transform such amplifiers from a curiosity to practical use for example in deep-space-to-earth communication links.

Independently programmable frequency-multiplexed phase-sensitive optical parametric amplification in the optical telecommunication band.

We experimentally demonstrate programmable multimode phase-sensitive amplification multiplexed in the frequency domain for flexible control of parallelly generated squeezed states. We utilize the unique phase-matching condition of a type-II periodically poled potassium titanyl phosphate (PPKTP) crystal and pulse shaping technique to fully control the frequency-domain parallel generation of squeezed states in the optical telecommunication band. We experimentally verify that the independent programmability of phase-sensitive optical parametric amplification (OPA) for the modes corresponding to different frequency bands can be achieved by shaping the pump laser pulse from optical parametric gain measurements using a coherent probe light generated by a degenerate synchronously pumped optical parametric oscillator.

Multimode optical parametric amplification in the phase-sensitive regime.

Phase-sensitive optical parametric amplification of squeezed states helps to overcome detection loss and noise and thus increases the robustness of sub-shot-noise sensing. Because such techniques, e.g., imaging and spectroscopy, operate with multimode light, multimode amplification is required. Here we find the optimal methods for multimode phase-sensitive amplification and verify them in an experiment where a pumped second-order nonlinear crystal is seeded with a Gaussian coherent beam. Phase-sensitive amplification is obtained by tightly focusing the seed into the crystal, rather than seeding with close-to-plane waves. This suggests that phase-sensitive amplification of sub-shot-noise images should be performed in the near field. A similar recipe can be formulated for the time and frequency, which makes this work relevant for quantum-enhanced spectroscopy.

Analysis of nonlinearity mitigation using phase-sensitive optical parametric amplifiers.

Phase-sensitive optical parametric amplifiers (PSAs) can provide low-noise optical amplification while simultaneously mitigating nonlinear distortions caused by the Kerr effect. However, nonlinearity mitigation using PSAs is affected by link parameters, and imperfect link design results in residual nonlinear distortions. In this paper, we use first-order perturbation theory to describe these residual nonlinear distortions, and develop a way to mitigate them using a modified third-order Volterra nonlinear equalizer (VNLE) in the receiver. Using numerical simulations, we show that our proposed VNLE reduces the residual nonlinear distortions in links using in-line PSAs for several combinations of symbol rates and modulation formats, and can increase the maximum transmission distance by up to 80%. We also perform a proof-of-concept experiment and confirm that our modified VNLE can mitigate the residual nonlinear distortions on a 10-Gbaud 16QAM signal after transmission through a 10×80-km link with in-line PSAs.

Frequency-degenerate phase-sensitive optical parametric amplification based on four-wave mixing in graphene–silicon slot waveguide

The phase-sensitive amplification process of a hybrid graphene–silicon (HyGS) slot waveguide with trilayers of graphene is investigated in this paper. Numerical simulation shows that a relatively high extinction ratio (42 dB) is achieved, because of the ultrahigh nonlinear coefficients, with a waveguide length of only 680 µm. In addition, the graphene layer provides the possibility of modulating the phase status and gain of the output signal. This study is expected to be highly beneficial to applications such as integrated optics and graphene-related active optical devices.

Optimization of a degenerate dual-pump phase-sensitive optical parametric amplifier for all-optical regenerative functionality.

We present a thorough investigation aimed at the optimization of a phase-sensitive optical parametric amplifier capable of simultaneous phase and amplitude regeneration. The regeneration potential, quantified in terms of the phase-sensitive extinction ratio, has been carefully assessed by a scalar model involving high-order waves associated with high-order four-wave mixing processes, going beyond the usual three-wave approach. Additionally, this model permits to unveil the physics involved in the high-order waves assisted regeneration. This permits a multi-dimensional and comprehensive optimization that fully exploits the underlying regenerative capability and expedites the design of a transparent regenerator, showing the potential to act as basic building block in future all-optical processing. We also compare different strategies when such regenerators are configured in concatenation. The approach can be readily applied to virtually any similar applications for different all-optical processing functionalities.

Highly efficient phase-sensitive parametric gain in periodically poled LiNbO3 ridge waveguide.

We have developed a periodically poled LiNbO3 (PPLN) ridge waveguide device and experimentally demonstrated a phase-sensitive optical parametric amplification. The highly efficient net phase-sensitive parametric gain of +18.6 dB is obtained in a cascaded second harmonic generation and difference frequency generation configuration. The phase-sensitive gain is greater by +5.8 dB in comparison with the phase-insensitive gain. We successfully confirmed the phase-sensitive amplification with a high gain in the PPLN ridge waveguide.

Frequency non-degenerate phase-sensitive optical parametric amplification based on four-wave-mixing in width-modulated silicon waveguides.

A width-modulated silicon waveguide is proposed to realize non-degenerate phase sensitive optical parametric amplification. It is found that the relative phase at the input of the phase sensitive amplifier (PSA) θIn-PSA can be tuned by tailoring the width and length of the second segment of the width-modulated silicon waveguide, which will influence the gain in the parametric amplification process. The maximum gain of PSA is larger by 9 dB compared with the phase insensitive amplifier (PIA) gain, and the gain bandwidth of PSA is larger by 35 nm compared with the gain bandwidth of PIA. Our on-chip PSA can find important potential applications in highly integrated optical circuits for optical chip-to-chip communication and computers.

Fundamental eigenmode of traveling-wave phase-sensitive optical parametric amplifier: experimental generation and verification

We investigate experimentally the eigenmodes of a Gaussian-beam-pumped traveling-wave phase-sensitive optical parametric amplifier (PSA). By varying the waist of an input LG(00) signal mode, we show that PSA performance improves with increasing spatial overlap between the input and the theoretically predicted fundamental eigenmode. For optimum waist, we report amplification and deamplification markedly higher than those observed for the traditional case of signal waist=√2× (pump waist). Lastly, we demonstrate the generation and verification of the PSA fundamental eigenmode.

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.

Numerical simulation of ultra-broadband phase-sensitive optical parametric amplification of image

The ultra-broadband phase-sensitive optical parametric amplification and de-amplification of image in a BBO nonlinear crystal with type I phase-matching are theoretically investigated. Amplified images with a gain of 108 and a bandwidth as broad as 420 nm are realized using a 25 GW/cm−2 peak pump-power density with 1.125 ps chirped-pulse duration. The spatial resolution after optical parametric amplification is estimated to be q0 =200 rad/mm (i.e., 31.8 lines/mm), which corresponds to the size of the minimum resolvable feature of the amplified image ~5 μm.

Quantum properties of a spatially-broadband traveling-wave phase-sensitive optical parametric amplifier

We present the quantum theory of a spatially-multimode traveling-wave phase-sensitive optical parametric amplifier (OPA) pumped by a beam with arbitrary spatial profile. By using Green's functions of the classical OPA, we derive the normally-ordered quadrature correlators at the OPA output, which provide complete quantum description of the phase-sensitive OPA and enable determination of its independently-squeezed eigenmodes. Two analytically treatable examples of plane-wave pump and infinite spatial bandwidth of the crystal are discussed in detail.

Assessment of image resolution improvement by phase-sensitive optical parametric amplification

Classical information theory can be used to quantify the resolution performance of optical imaging systems. When an optical parametric amplifier (OPA) operated as a phase-sensitive amplifier (PSA) in the transverse spatial domain is used for point source imaging, the angular resolution improvement can approach the de Broglie resolution (i.e. Heisenberg limit). In this paper, classical information theory is employed to quantify the signal-to-noise ratio (SNR) improvement for both an ideal and a realistic multimode PSA applied to the problem of sub-Rayleigh imaging. When only considering the noise originating from the detector, the SNR improvement is found to scale quadratically as a function of the PSA gain, in the limit of noise power comparable to signal power. Differences in performance of an ideal PSA and a realistic PSA are discussed.

Estimation of the spatial bandwidth of an optical parametric amplifier with plane-wave pump

We analyze the spatial-frequency dependence of the gain of phase-insensitive and phase-sensitive optical parametric amplifiers with plane-wave pumping. We discuss the dependence of their spatial bandwidths on pump power and crystal length, L, and observe that the well-known (k s/L)1/2 approximation of spatial bandwidth is not very accurate (here k s is the signal beam's wavevector magnitude). We derive an alternative approximation that is highly accurate at large gains and moderately accurate at low gains. The differences between the phase-insensitive and phase-sensitive amplifier bandwidths are shown to be insignificant for gains above several dB. Maximum phase-sensitive gain and bandwidth are realized by imposing an optimum phase profile onto the input signal's spatial spectrum, which has nearly parabolic shape with added series of π/2 phase discontinuities at spatial frequencies outside the main bandwidth of the amplifier. We show that, apart from the discontinuities, such a profile can be closely approximated by placing the image plane into the middle of the nonlinear crystal (converging input beam). The phase discontinuities contribute an additional narrow component to the point-spread function of the phase-sensitive amplifier.

Phase-Sensitive Manipulations of a Squeezed Vacuum Field in an Optical Parametric Amplifier inside an Optical Cavity

A squeezed vacuum field can be amplified or deamplified when it is injected, as the signal beam, into a phase-sensitive optical parametric amplifier (OPA) inside an optical cavity. The spectral features of the reflected quantized signal field are controlled by the relative phase between the injected squeezed vacuum field and the pump field for the OPA. The experimental results demonstrate coherent phenomena of OPA in the quantum regime and show phase-sensitive manipulations of quantum fluctuations for quantum information processing.

Absorptive and dispersive properties in the phase-sensitive optical parametric amplification inside a cavity

In this paper we investigate the absorptive and dispersive properties in the phase-sensitive optical parametric amplification inside a cavity. First, we study the single-resonant optical parametric amplifier theoretically and experimentally. In this case, the mode splitting in the transmission spectra and the M shape in the reflection spectra are observed. However, the shape of the phase shift of the reflected field is unchanged. Then, the double-resonant optical parametric amplifier is studied theoretically, in which electromagnetically induced transparency-like effect may be emulated when the cavity linewidth for the harmonic wave is narrower than for the subharmonic field. The narrow transparency window appears in the absorption spectrum and is accompanied by a very steep variation of the dispersive profile.

Coherence Phenomena in the Phase-Sensitive Optical Parametric Amplification inside a Cavity

We theoretically and experimentally demonstrate coherence phenomena in optical parametric amplification inside a cavity. The mode splitting in the transmission spectra of a phase-sensitive optical parametric amplifier is observed. Especially, we show that a very narrow dip and peak, which are the shape of a delta function, appear in the transmission profile. The origin of the coherence phenomenon in this system is the interference between the harmonic pump field and the subharmonic seed field in cooperation with dissipation of the cavity.

Pulse propagation in nonlinear-optical fibers with phase-locked phase-sensitive amplifiers

Recently the use of periodically spaced, phase-sensitive optical parametric amplifiers was proposed for compensating for linear loss in a nonlinear fiber-optic communication line [Opt. Lett. 18, 803 (1993)]. In the previous analysis, in which the stability of a single pulse was investigated, the variation of the amplifier phases was neglected. In a physically realizable line, however, the phase of each amplifier would most likely be locked to the phase of the signal pulse or to the average of the phases of many such pulses. Here an analysis is presented in which the amplifier phase is allowed to vary in response to a signal pulse's optical phase. The analysis shows that the solitonlike signal pulses remain stable even with this additional phase variation.

Improvement of photodetection quantum efficiency by noiseless optical preamplification

We demonstrate experimentally that a phase-sensitive optical parametric amplifier used to amplify the incoming optical signal on a lossy photodiode improves the noise figure of detection. At high parametric gains this noise figure tends to 0 dB corresponding to a detection quantum efficiency approaching 100%. This result contrasts with the performance of preamplification by a classical laserlike amplifier in which the noise figure tends to 3 dB giving a saturation of the detection quantum efficiency at 50%.

Pulse propagation in nonlinear optical fiber lines that employ phase-sensitive parametric amplifiers

Recently we proposed using periodically spaced, phase-sensitive optical parametric amplifiers to balance linear loss in a nonlinear fiber-optic communication line [ Opt. Lett.18, 803 ( 1993)]. We present a detailed analysis of pulse propagation in such a fiber line. Our analysis and numerical simulations show that the length scale over which the pulse evolution occurs is significantly increased beyond a soliton period. This is because of the attenuation of phase variations across the pulse’s profile by the amplifiers. Analytical evidence is presented that indicates that stable pulse evolution occurs on length scales much longer than the soliton period. This is confirmed through extensive numerical simulation, and the region of stable pulse propagation is found. The average evolution of such pulses is governed by a fourth-order nonlinear diffusion equation, which describes the exponential decay of arbitrary initial pulses into stable, steady-state, solitonlike pulses.