High-gain optical parametric amplification is an important nonlinear process used both as a source of coherent infrared light and as a source of nonclassical light. In this work, we experimentally demonstrate an approach to optical parametric amplification that enables extremely large parametric gains with low energy requirements. In conventional nonlinear media driven by femtosecond pulses, multiple dispersion orders limit the effective interaction length available for parametric amplification. Here, we use the dispersion engineering available in periodically poled thin-film lithium niobate nanowaveguides to eliminate several dispersion orders at once. The result is a quasi-static process; the large peak intensity associated with a short pump pulse can provide gain to signal photons without undergoing pulse distortion or temporal walk-off. We characterize the parametric gain available in these waveguides using optical parametric generation, where vacuum fluctuations are amplified to macroscopic intensities. In the unsaturated regime, we observe parametric gains as large as 71 dB (118 dB/cm) spanning 1700–2700 nm with pump energies of only 4 pJ. When driven with pulse energies > 10 p J , we observe saturated parametric gains as large as 88 dB ( > 146 d B / c m ). The devices shown here achieve saturated optical parametric generation with orders of magnitude less pulse energy than previous techniques.
High-gain optical parametric amplification is an important nonlinear process used both as a source of coherent infrared light and as a source of nonclassical light. In this work, we experimentally demonstrate an approach to optical parametric amplification that enables extremely large parametric gains with low energy requirements. In conventional nonlinear media driven by femtosecond pulses, multiple dispersion orders limit the effective interaction length available for parametric amplification. Here, we use the dispersion engineering available in periodically poled thin-film lithium niobate nanowaveguides to eliminate several dispersion orders at once. The result is a quasi-static process; the large peak intensity associated with a short pump pulse can provide gain to signal photons without undergoing pulse distortion or temporal walk-off. We characterize the parametric gain available in these waveguides using optical parametric generation, where vacuum fluctuations are amplified to macroscopic intensities. In the unsaturated regime, we observe parametric gains as large as 71 dB (118 dB/cm) spanning 1700–2700 nm with pump energies of only 4 pJ. When driven with pulse energies > 10 p J , we observe saturated parametric gains as large as 88 dB ( > 146 d B / c m ). The devices shown here achieve saturated optical parametric generation with orders of magnitude less pulse energy than previous techniques.
Optical parametric amplifiers (OPAs) are promising to overcome the wavelength coverage and noise limitations in conventional optical amplifiers based on rare-earth doping and semiconductor gain. However, the high power requirement remains a major obstacle to the widespread use of OPAs. Integrated OPAs can in principle improve the pump efficiency with tight mode confinement; however, challenges associated with propagation loss, limited nonlinearity, and susceptibility to nanoscale fabrication imperfections prevent them from competing with conventional bulk and fiber-based OPAs. Here, we demonstrate a highly efficient integrated OPAs with continuous-wave net gain. The pump efficiency is improved by over one order of magnitude. Phase-sensitive gain of 23.5 dB is demonstrated, significantly exceeding previous integrated OPAs, using only 110 mW pump power and no cavity enhancement. This is achieved with parametric down-conversion in thin-film lithium niobate waveguides using the adapted poling technique to maintain the coherence of nonlinear interactions. Moreover, the high parametric gain exceeds fibre-chip-fibre losses, leading to appreciable net gain up to 10 dB. The 3 dB bandwidth is approximately 120 nm, covering telecommunication S-, C-, and Lbands. Quantum-limited noise performance is confirmed through the measurement of output field fluctuation below the classical limit. We further demonstrate that signalto-noise ratio in noisy optical communications can be increased by leveraging this efficient integrated OPA. Our work marks a significant step towards ideal optical amplifiers with strong amplification, high efficiency, quantum-limited noise, large bandwidth, and continuous-wave operation, unlocking new possibilities for next-generation photonic information processing systems.
Although thin-film lithium niobate (TFLN) facilitates efficient signal generation and nonlinear and quantum interactions, the realization of optical parametric amplification (OPA) that can provide simultaneous ultra-broadband and high-gain operation in an integrated chip continues to pose a challenge. Here we demonstrate continuous-wave-pumped OPA in an X-cut MgO-doped, dispersion-engineered, and adaptively-poled TFLN waveguide of 1.6 cm length, achieving a flat-top profile covering a 450 nm-wide optical wavelength window, corresponding to a 3-dB gain bandwidth of about 56 THz. Among reported TFLN platforms, our device exhibits the broadest 3-dB gain bandwidth. The same device can be pumped either directly at visible wavelengths through second-order x(2) interactions or in the telecom band through cascaded x(2) processes, the latter eliminating the need for a high-power visible pump laser. We achieve maximum gains of 8.87 +- 0.39 dB and 10.79 +- 0.43 dB at on-chip pump powers of 74 mW and 170 mW for the direct and cascaded schemes, respectively. We further directly probe OPA gain across the 1650-1900 nm wavelength range, where experimental gain measurements have remained scarce. With a normalized on-chip gain of 1.21 dB per W per mm, our device sets a new benchmark among reported cascaded x(2) nonlinear processes. This work advances the realization of integrated optical parametric amplifiers, offering high efficiency, robust gain, ultra-broadband bandwidth, and continuous-wave operation, thereby enabling new capabilities for next-generation quantum sensing and photonic systems.
Although noiseless optical amplification has been demonstrated in bulk KTP crystals, and is well understood, there have been no observations of noiseless optical amplification in bulk quasi-phase-matched (QPM) systems. That such an amplifier is possible was predicted recently and indeed squeezing has already been observed in QPM waveguides (using KTP and LiNbO3). QPM materials are attractive for use in quantum-optical devices because they give access to certain (large) components of the nonlinear susceptibility tensor that cannot be used in conventional birefringent phase-matching schemes. They also extend the range of materials accessible for use in parametric amplifiers to include some low-birefringence crystals exhibiting large nonlinearities. Even with the technological advantages offered by certain QPM crystals, efforts to find practical applications for optical parametric amplifiers are hampered by the need for enormous pump-field strengths. The obvious solution to the problem of the pump-field requirement is to confine the incident energy to a narrow interaction region thereby increasing the energy density. However, this approach can only be realised at the expense of sacrificing the homogeneity of the parametric interaction between pump and signal waves. This in turn causes vacuum field fluctuations from parasitic modes to be mixed into the signal mode thereby degrading the signal to noise ratio and negating the advantage of using an optical parametric amplifier. In the experiments presented here, optical signals have been amplified with up to 9dB of gain, yet with a noise figure (NF) of only 1.09, as compared to the minimum possible NF of a classical amplifier with the same gain which would equal 1.86. Furthermore, the interaction is achieved with tightly focused incident fields in a sample of bulk QPM lithium niobate. The entire interaction region is only 200µm thick and 2.8mm long. This performance was achieved with the aid of a theoretical model m which the effect of wavefront curvature and mode distortion are treated within a quantised mode framework using a spatial mode basis. Such a simulation permits the fundamental origin of the excess quantum noise to be easily traced to zero-point fluctuations of high-order spatial modes which couple to the signal mode via the parametric interaction. Furthermore the simulation enabled an experimental geometry to be selected in which an optimal compromise is made between wavefront matching bump beam smaller than signal) and pump-homogeneity (pump larger than signal), so that the overall noise figure remains well into the quantum-performance region.
Abstract Optical amplifiers are fundamental to modern photonics, enabling long-distance communications, precision sensing, and quantum information processing. Erbium-doped amplifiers dominate telecommunications but are restricted to specific wavelength bands, while semiconductor amplifiers offer broader coverage but suffer from high noise and nonlinear distortions. Optical parametric amplifiers (OPAs) promise broadband, quantum-limited amplification across arbitrary wavelengths. However, their miniaturization and deployment has been hampered by watt-level power requirements. Here we demonstrate an integrated OPA on thin-film lithium niobate that achieves > 17 dB gain with < 200 mW input power -- an order of magnitude improvement over previous demonstrations. Our second-harmonic-resonant design enhances both pump generation efficiency (95% conversion) and pump power utilization through recirculation, without sacrificing bandwidth. The resonant architecture increases the effective pump power by nearly an order of magnitude compared to conventional single-pass designs, while also multiplexing the signal and pump. We demonstrate flat near-quantum-limited noise performance over 110 nm. Our low-power architecture enables practical on-chip OPAs for next generation quantum and classical photonics.
Thin-film lithium niobate (TFLN) has recently emerged as a promising platform for integrated nonlinear photonics, enabling the use of optical parametric amplifiers (OPAs) for applications in quantum information processing, precision metrology, and ultrafast optical signal processing. However, OPA waveguide designs have not yet achieved the phase-matching conditions for type-0 operation in a single spectro-temporal mode, limiting their use. We optimize the waveguide dimensions, poling pattern, pump wavelength, and pump pulse duration for high spectral purity, a metric for single-mode fidelity. We numerically demonstrate a nanophotonic OPA with a spectral purity of 0.982 in a TFLN waveguide. Through semi-classical simulations, we further demonstrate that in the optical parametric regime, where vacuum fluctuations at the input of the OPA can saturate the gain and deplete the pump, the macroscopic output of such a single-mode OPA can be utilized for an ultra-fast quantum random number generator. These results demonstrate a promising direction for integrated OPAs in a wide range of ultrafast quantum nanophotonics applications.
Hybridized parametric amplification (HPA), a recent method to achieve high-efficiency parametric amplification by suppressing back-conversion with idler second harmonic generation, has been demonstrated so far only by birefringent phase matching. In this work, we demonstrate HPA by quasi-phase matching (QPM) in quasiperiodic-poled lithium niobate. QPM greatly expands the tuning range of HPA, while avoiding the limitations imposed by spatial walkoff of noncollinear beams. Since HPA has two concurrent processes, QPM requires a quasiperiodic grating with longitudinal spatial frequency peaks at both the parametric amplification and idler second harmonic generation phase mismatches. We investigate several grating designs for high-efficiency HPA in the near-infrared range. Quantum efficiencies of 70-80% are possible for devices pumped at 1030 nm, for both femtosecond and picosecond duration regimes. Pulse energies over 1 mJ can be accommodated using a chirped pump. However, devices must be designed carefully around the propagation effects of temporal walk-off and self-phase modulation.