Integrated Optical Amplifier Boosts Signal Strength by 23.5 Decibels with Minimal Power

Researchers are continually seeking to improve amplification technologies for optical signals, and integrated optical parametric amplifiers (OPAs) present a compelling alternative to traditional rare-earth doped and semiconductor-based devices. Yung-Cheng Kao, Jiaqi Huang, and Ian Briggs, all from the Chandra Department of Electrical and Computer Engineering at The University of Texas at Austin, alongside Pao-Kang Chen and Linran Fan et al., report a significant advance in this field by demonstrating a highly efficient, net-gain integrated OPA operating in the quantum regime. This work overcomes a key limitation of OPAs, their high power requirements, achieving phase-sensitive gain of 23.5 dB with only 110mW of pump power and no cavity enhancement, representing over a ten-fold improvement in pump efficiency compared to previous integrated devices. The realisation of appreciable net gain, coupled with a broad 120nm bandwidth and confirmed quantum-limited noise performance, establishes this integrated OPA as a crucial step towards practical, high-performance amplifiers for future photonic information processing systems.

Thin-film lithium niobate enables high-efficiency integrated optical parametric amplification

Scientists have developed a highly efficient integrated optical parametric amplifier achieving continuous-wave net gain, representing a substantial advancement in photonic technology. This new device overcomes longstanding limitations in optical amplification, specifically addressing the high power requirements that have hindered the widespread adoption of optical parametric amplifiers.
The research demonstrates a phase-sensitive gain of 23.5 dB using only 110mW of pump power, significantly exceeding the performance of previously fabricated integrated OPAs and eliminating the need for cavity enhancement. This breakthrough is enabled by parametric down-conversion within thin-film lithium niobate waveguides, utilising an adapted poling technique to preserve the coherence essential for nonlinear interactions.

The achieved parametric gain surpasses fibre-chip-fibre losses, resulting in appreciable net gain reaching up to 10 dB. A key feature of this integrated OPA is its broad operational bandwidth, approximately 120nm, encompassing the crucial telecommunication S-, C-, and L-bands. Quantum-limited noise performance has been confirmed through measurements of output field fluctuations falling below the classical limit, validating the amplifier’s exceptional signal fidelity.
Furthermore, researchers have demonstrated that this efficient integrated OPA can enhance the signal-to-noise ratio in noisy optical communications, showcasing its practical utility. This work represents a significant step towards realising ideal optical amplifiers characterised by strong amplification, high efficiency, quantum-limited noise, large bandwidth, and continuous-wave operation.

The integrated OPA leverages thin-film lithium niobate waveguides, providing both strong nonlinear characteristics and tight optical confinement. An adapted poling technique mitigates the impact of nanoscale imperfections, a common limitation in thin-film lithium niobate, thereby maintaining coherence and maximising nonlinear efficiency.

The phase-sensitive gain is governed by the relative phase between pump and signal, with maximum amplification occurring when the two are in phase. Simulations and experimental results confirm a 3 dB bandwidth of approximately 140nm, covering the essential S-, C-, and L-bands for telecommunications. The nonlinear efficiency, enhanced by the adapted poling technique, reaches 4700 ±500 %/W, as verified by second-harmonic generation measurements. Characterisation using both direct power detection and homodyne detection of field amplitude confirms the amplifier’s performance and potential for next-generation photonic information processing systems.

Fabrication and characterisation of a periodically poled lithium niobate optical parametric amplifier

A 14-mm long and 2.2-μm wide thin-film lithium niobate waveguide forms the core of this study’s experimental setup, engineered for amplification near 1550nm with a pump near 775nm. The fabrication process incorporates an adapted poling technique to maintain coherence during nonlinear interactions, addressing limitations inherent in nanoscale fabrication imperfections.

This technique adjusts poling periods based on local thickness variations, recovering ideal phase matching conditions and achieving a nonlinear efficiency of 4700 ±500 %/W, verified through second-harmonic generation spectral analysis. Performance characterization employed two distinct methods: direct power detection and homodyne detection of field amplitude.

In direct power measurement, signal and pump light were coupled into the integrated OPA, with a fiber stretcher scanning the phase between them to induce oscillations in output signal power, enabling gain calculation relative to a reference signal without pump illumination. This process demonstrated a phase-sensitive gain of 23.5 dB with 110mW pump power, exceeding previously reported integrated OPAs and achieving a pump efficiency of up to 15.3 dB/(W·mm).

Further analysis involved homodyne detection, replacing power measurement with quantum-level field quadrature analysis. Scanning the phase of a local oscillator with a fiber stretcher allowed for measurement of output signal light along different quadratures, revealing squeezing and anti-squeezing of classical shot noise using a 2 GS/s oscilloscope.

Statistical distributions of time-domain homodyne measurements, fitted with Gaussian functions, extracted variances to quantify squeezing and anti-squeezing levels as a function of pump power, confirming sub-classical noise performance. The integrated OPA exhibited a 3 dB bandwidth of approximately 120nm, covering the telecommunication S-, C-, and L-bands, and achieved over 10 dB net gain, surpassing fibre-chip-fibre losses.

High-efficiency parametric amplification in thin-film lithium niobate waveguides

Phase-sensitive gain of 23.5 dB was demonstrated using only 110mW of pump power and without cavity enhancement. This achievement represents a significant advancement in integrated optical parametric amplifier technology. Net gain up to 10 dB was observed, coupled with a greater than one order-of-magnitude improvement in pump efficiency.

The research leverages low-loss thin-film lithium niobate waveguides, providing strong χ(2) nonlinearity and tight optical confinement. The adapted poling technique employed mitigates nanoscale inhomogeneities, historically limiting nonlinear efficiency in thin-film lithium niobate waveguides. Nonlinear efficiency, verified by second-harmonic generation spectroscopy, reached 4700 ±500 %/W.

A 14-mm long, 2.2-μm wide TFLN waveguide was designed for amplification near 1550nm with a pump near 775nm. Simulations predict a 3 dB bandwidth of approximately 140nm, covering the telecommunication S-, C-, and L-bands. Direct power measurements and homodyne detection of field amplitude were used to characterise the integrated OPA performance.

Phase scanning revealed the oscillatory behaviour of the signal, with maximum gain achieved when the signal and pump are in phase. Measurements confirm that the integrated OPA exhibits a 3-dB bandwidth exceeding 120nm, enabling broad spectral coverage. Time-domain homodyne measurements demonstrate squeezing and anti-squeezing conditions, indicating noise performance below the classical limit.

Statistical analysis of field quadrature variances reveals reduced noise levels compared to shot noise, with pump-blocked measurements serving as a baseline. Squeezing and anti-squeezing levels were measured as a function of pump power, demonstrating the amplifier’s ability to manipulate quantum noise.

Quantum enhanced amplification in thin-film lithium niobate waveguides

Scientists have demonstrated a highly efficient integrated optical parametric amplifier (OPA) fabricated using thin-film lithium niobate waveguides. This device achieves a phase-sensitive gain of 23.5 dB with a remarkably low pump power of 110mW, representing a greater than tenfold improvement in pump efficiency compared to previous integrated OPAs.

The amplifier operates across a broad bandwidth of approximately 120nm, encompassing the telecommunication S-, C-, and L-bands, and exhibits net gain exceeding 10 dB. This advancement is achieved through the implementation of an adapted poling technique, which preserves the coherence necessary for efficient nonlinear interactions within the lithium niobate material.

Crucially, the OPA’s performance extends into the quantum regime, evidenced by measured output field fluctuations below the classical limit, and it improves signal-to-noise ratios in optical communication systems, reducing bit-error rates significantly. While acknowledging that further improvements in net gain are anticipated with optimized edge-coupler designs, the authors note limitations related to nanoscale fabrication imperfections.

Future research may focus on refining fabrication processes to minimise these imperfections and exploring the potential of this technology in quantum technologies such as quantum metrology and fault-tolerant photonic quantum computing. This work establishes a significant step towards practical, high-performance optical amplifiers with strong amplification, high efficiency, broad bandwidth, and low noise. The simplicity of the single-pass waveguide architecture enhances robustness and reliability, unlocking new possibilities for next-generation photonic information processing and optical communication systems.