Phase-sensitive Amplifier Research Articles

Phase sensitive amplification in a periodically poled gradient lithium niobate waveguide

The article presents a phase sensitive amplifier based on cascaded second harmonic generation and difference frequency generation in a waveguide in the gradient periodically poled lithium niobate. The influence of the composition gradient in periodically poled lithium niobate on phase and spectral dependence of amplification factor is described. The increase of 35% is shown in spectral range of the gradient amplifier in comparison with the gradientless one in the range of 1.55 μm. The dependence of amplification factor of the optical signal from the propagation direction in the waveguide channel in gradient PPLN is also presented.

Phase detection through four-wave mixing in an optical fiber

A scheme for detecting the phase of an incoming optical signal is systematically optimized and demonstrated experimentally. It makes use of four-wave mixing in a highly nonlinear fiber but differs from a phase-sensitive amplifier by its focus on phase detection, rather than on phase-dependent noise reduction. This experimental setup combines the signal with its phase-conjugated idler at the same frequency, before sending the combination to a photodetector. Experimental results show that the ratio of maximum and minimum currents can exceed 1000 even at a relatively low pump power of 10 mW. The proposed scheme may be useful for detecting the signal phase in coherent communication systems without the need of heterodyne detection.

Characterization of quantum squeezing generated from the phase-sensitive and phase-insensitive amplifiers in the ultra-low average input photon number regime.

We give the general expressions of intensity-difference squeezing (IDS) generated from two types of optical parametric amplifiers [i.e. phase-sensitive amplifier (PSA) and phase-insensitive amplifier (PIA)] based on the four-wave mixing process, which clearly shows the IDS transition between the ultra-low average input photon number regime and the ultra-high average input photon number regime. We find that both the IDS of the PSA and the IDS of the PIA get enhanced with the decrease of the average input photon number especially in the ultra-low average input photon number regime. This result is substantially different from the result in the ultra-high average input photon number regime where the IDS does not vary with the average input photon number. Moreover, under the same intensity gain, we find that the optimal IDS of the PSA is better than the IDS of the PIA in the ultra-low average input photon number regime. Our theoretical work predicts the presence of strong quantum correlation in the ultra-low average input photon number regime, which may have potential applications for probing photon-sensitive biological samples.

Modulation format dependence on transmission reach in phase-sensitively amplified fiber links.

We quantify the maximum transmission reach for phase-insensitive amplifier (PIA) and phase-sensitive amplifier (PSA) links with different modulation formats and show that the maximum transmission reach increase (MTRI) when using PSAs compared to PIAs is enhanced for higher-order modulation formats. The higher-order modulation formats are more susceptible to smaller phase rotations from nonlinearities, and PSAs are efficient in mitigating these smaller phase distortions. Numerical simulations were performed for single- and multi-span PIA and PSA links with single and multiple wavelength channels. We obtain a significant enhancement in the MTRI with PSAs compared to PIAs when using higher-order modulation formats for both the single- and multi-channel systems in single- and multi-span links. We verify the enhancement with a single-span, single-channel system experiment. We also demonstrate, for the first time, a 64-QAM modulation format fiber transmission in phase-sensitively amplified link, with a 13.3-dB maximum allowable span loss increase compared to a phase-insensitively amplified link.

PPLN-Based Low-Noise Phase Sensitive Amplification Using an Optical Phase-Locked Pump

PPLN-Based Low-Noise Phase Sensitive Amplification Using an Optical Phase-Locked Pump

Accurate Estimation of Chromatic Dispersion for Non-Degenerate Phase-Sensitive Amplification

A phase-sensitive amplifier (PSA) has the potential of low-noise optical amplification and nonlinear phase noise mitigation. For PSA operation, the chromatic dispersion (CD) that causes gain ripple must be compensated before amplification. We propose an accurate CD estimation method for non-degenerate PSAs (ND-PSAs). We experimentally demonstrated its effectiveness by using periodically poled LiNbO3 waveguides as amplification mediums. We first modified the conventional formula for the gain spectrum under residual CD conditions to be applicable to ND-PSAs by considering phase locking. We then experimentally described the effect of passband narrowing due to the gain ripple on the signal quality using a probabilistically shaped 64QAM signal. Furthermore, we applied the modified formula to CD estimation and compensation. As a result, accurate CD estimation on the sub-ps/nm order and gain-flattened spectrum over 3.5 THz were demonstrated with our method. We also propose a method for estimating residual CD from the gain variation among wavelength division multiplexing (WDM) channels. The possibility of adaptive compensation for CD was shown by carrying out WDM amplification.

One photon-per-bit receiver using near-noiseless phase-sensitive amplification

Space communication for deep-space missions, inter-satellite data transfer and Earth monitoring requires high-speed data connectivity. The reach is fundamentally dictated by the available transmission power, the aperture size, and the receiver sensitivity. A transition from radio-frequency links to optical links is now seriously being considered, as this greatly reduces the channel loss caused by diffraction. A widely studied approach uses power-efficient formats along with nanowire-based photon-counting receivers cooled to a few Kelvins operating at speeds below 1 Gb/s. However, to achieve the multi-Gb/s data rates that will be required in the future, systems relying on pre-amplified receivers together with advanced signal generation and processing techniques from fibre communications are also considered. The sensitivity of such systems is largely determined by the noise figure (NF) of the pre-amplifier, which is theoretically 3 dB for almost all amplifiers. Phase-sensitive optical amplifiers (PSAs) with their uniquely low NF of 0 dB promise to provide the best possible sensitivity for Gb/s-rate long-haul free-space links. Here, we demonstrate a novel approach using a PSA-based receiver in a free-space transmission experiment with an unprecedented bit-error-free, black-box sensitivity of 1 photon-per-information-bit (PPB) at an information rate of 10.5 Gb/s. The system adopts a simple modulation format (quadrature-phase-shift keying, QPSK), standard digital signal processing for signal recovery and forward-error correction and is straightforwardly scalable to higher data rates.

OSNR and dispersion tolerance of FWM based optical carrier recovery scheme

In this paper we demonstrate the Optical signal-to-noise ratio (OSNR) and Dispersion characteristics of Four-Wave Mixing (FWM) based optical carrier recovery scheme for a 10-Gb/s nonreturn-to-zero binary phase-shift-keyed input. The performance was evaluated by measuring the linewidth of the recovered carrier against different OSNR and accumulated dispersion values and recording the eye diagrams. The system characterization will enable new avenues of using the FWM based carrier recovery system in phase-sensitive amplification and heterodyne detection.

Investigation of the noise figure in a degenerate dual-pump phase-sensitive amplifier using a multi-wave model

A semi-classical seven-wave model is developed to investigate the noise performances of a degenerate dual-pump phase-sensitive amplifier. This approach takes into account the transfer to the signal, through multiple four-wave mixing processes, of the vacuum fluctuations injected into high-order waves. This effect leads to a degradation of the noise figure of the amplifier with respect to the 0 dB value predicted by the usual three-wave model. However, it is proved that a careful choice of the fiber dispersion allows us to use high-order waves to enhance the signal gain without degrading the noise figure above 1 dB.

Fluorescence-detected Fourier transform electronic spectroscopy by phase-tagged photon counting.

Fluorescence-detected Fourier transform (FT) spectroscopy is a technique in which the relative paths of an optical interferometer are controlled to excite a material sample, and the ensuing fluorescence is detected as a function of the interferometer path delay and relative phase. A common approach to enhance the signal-to-noise ratio in these experiments is to apply a continuous phase sweep to the relative optical path, and to detect the resulting modulated fluorescence using a phase-sensitive lock-in amplifier. In many important situations, the fluorescence signal is too weak to be measured using a lock-in amplifier, so that photon counting techniques are preferred. Here we introduce an approach to low-signal fluorescence-detected FT spectroscopy, in which individual photon counts are assigned to a modulated interferometer phase ('phase-tagged photon counting,' or PTPC), and the resulting data are processed to construct optical spectra. We studied the fluorescence signals of a molecular sample excited resonantly by a pulsed coherent laser over a range of photon flux and visibility levels. We compare the performance of PTPC to standard lock-in detection methods and establish the range of signal parameters over which meaningful measurements can be carried out. We find that PTPC generally outperforms the lock-in detection method, with the dominant source of measurement uncertainty being associated with the statistics of the finite number of samples of the photon detection rate.

Observation of binary phase states of time-multiplexed degenerate optical parametric oscillator pulses generated using a nonlinear fiber Sagnac loop.

We generated time-multiplexed degenerate optical parametric oscillator (DOPO) pulses using a nonlinear fiber Sagnac loop as a phase-sensitive amplifier (PSA), where the pump and amplified light in pump-signal-idler degenerate four-wave mixing can be spatially separated. By placing the PSA in a fiber cavity, we successfully generated more than 5000 time-multiplexed DOPO pulses. We confirmed the bifurcation of pulse phases to 0 or π relative to the pump phase, which makes them useful for representing Ising spins in an Ising model solver based on coherent optical oscillator networks. We also confirmed inherent randomness of the DOPO phases using the National Institute of Standards and Technology random number test.

Phase-sensitive optomechanical amplifier for quantum noise reduction in laser interferometers

The sensitivity of future gravitational wave interferometers is expected to be limited through-out the detection band by quantum vacuum fluctuations, which can be reduced by quantum non-demolition methods such as squeezed vacuum injection. However, optical losses in the readout chainseverely limit the effectiveness of such schemes. We propose an optomechanical device to be installedat the output of the detector that mitigates the effect of readout loss, thus allowing the detector tobetter exploit quantum noise evasion schemes.

Investigation of analog signal distortion introduced by a fiber phase sensitive amplifier

We numerically simulate the distortion of an analog signal carried in a microwave photonics link containing a phase sensitive amplifier (PSA), focusing mainly on amplitude modulation format. The numerical model is validated by comparison with experimental measurements. By using the well-known two-tone test, we compare the situations in which a standard intensity modulator is used with the one where a perfectly linear modulator would be employed. We also investigate the role of gain saturation in the nonlinearity of the PSA. Finally, we establish the conditions in which the signal nonlinearity introduced by the PSA itself can be extremely small.

Enhanced analog-optical link performance with noiseless phase-sensitive fiber optical parametric amplifiers.

In this paper, we investigate the enhancement of analog optical link performance with noiseless phase-sensitive fiber optical parametric amplifiers. The influence of different noise sources in the link impacts the quality of analog optical signals, especially with low optical signal power, which has not been investigated before. Theoretically, the increase in signal-to-noise ratio and spurious-free dynamic range can be up to ∼6 dB and ∼4 dB, respectively, if the noise figure of optical pre-amplifier drops 3 dB when the received optical power is less than -65 dBm. In addition, experiments based on a 1.3 dB-noise-figure phase-sensitive fiber optical parametric amplifier and conventional optical pre-amplifiers are implemented, and the measured results agree with the theoretical expectations. This illustrates that noiseless phase-sensitive optical amplification may pave the way to long-haul distribution of analog optical signals and find applications in microwave-photonic systems.

Phase-sensitive amplification via multi-phase-matched four-wave mixing.

Phase-sensitive nonlinear gain processes have been implemented as noise-reduced optical amplifiers, which have the potential to achieve signal-to-noise ratios beyond the classical limit. We experimentally demonstrate a novel phase-sensitive four-wave mixing amplification process in a single atomic vapor cell with only two input frequencies and two input vacuum modes. The amount of phase sensitivity depends on the power ratio between the inserted probes as well as on the input frequency of the probes. We find that, for certain phase values, the intensity noise of an output mode is lower than that of its phase-insensitive counterpart.

Quantum dense metrology by an SU(2)-in-SU(1,1) nested interferometer

With the help of quantum entanglement, quantum dense metrology (QDM) is a technique that can make joint estimates of two conjugate quantities such as phase and amplitude modulations of an optical field, with an accuracy beating the standard quantum limit simultaneously. SU(1,1) interferometers (SUIs) can realize QDM with detection loss tolerance but is limited in absolute sensitivity. Here, we present a QDM scheme with a linear or SU(2) interferometer nested inside an SUI. By using a degenerate SUI and controlling the phase angle of the phase-sensitive amplifiers in the SUI, we can achieve the optimum quantum enhancement in the measurement precision of an arbitrary mixture of phase and amplitude modulation.

One-Pump Phase Sensitive Fiber Optical Parametric Amplifier With Dual-Core Fiber

The gain performance of one pump phase sensitive fiber optical parametric amplifier (PS-FOPA) in the dual-core fiber is numerically investigated without pump depleting. The effects of the core coupling coefficient(C), the pump wavelength and the initial signal phase on the gain of PS-FOPA are analyzed in detail. It shows that, the signal gain is greatly affected by different core coupling coefficients, and a flatter gain is achieved with suitable C value. Also, when the pump wavelength is greater than the zero-dispersion wavelength (ZDW), both the peak gain and gain bandwidth decrease with the increase of C, but the trend is opposite in case of the pump wavelength less than the ZDW. Additionally, the flatter and broader gain spectra are obtained by adjusting the initial signal phase in core 2. This simulation provides a detail analysis for the dual-core PS-FOPA, which is significant for the all optical fiber amplifier systems.

Topological framework for directional amplification in driven-dissipative cavity arrays

Directional amplification, in which signals are selectively amplified depending on their propagation direction, has attracted much attention as key resource for applications, including quantum information processing. Recently, several, physically very different, directional amplifiers have been proposed and realized in the lab. In this work, we present a unifying framework based on topology to understand non-reciprocity and directional amplification in driven-dissipative cavity arrays. Specifically, we unveil a one-to-one correspondence between a non-zero topological invariant defined on the spectrum of the dynamic matrix and regimes of directional amplification, in which the end-to-end gain grows exponentially with the number of cavities. We compute analytically the scattering matrix, the gain and reverse gain, showing their explicit dependence on the value of the topological invariant. Parameter regimes achieving directional amplification can be elegantly obtained from a topological ‘phase diagram’, which provides a guiding principle for the design of both phase-preserving and phase-sensitive multimode directional amplifiers.

Noise evolution with the phase-sensitive gain in a hybrid fiber phase-sensitive amplifier

We investigate the noise evolution of a hybrid fiber phase-sensitive amplifier (PSA) with an erbium-doped fiber amplifier (EDFA) as a function of the phase-sensitive gain. The noise performance of the hybrid amplifier with a large overall gain of 45.6 dB is experimentally evaluated in optical and electrical domains. The experimental results are in good agreement with theory, showing that significant improvement of the overall noise figure (NF) of the hybrid amplifier occurs in a low PSA gain region. A combined NF below 3 dB has been obtained in the hybrid amplifier with a PSA gain of 9 dB, which is 1.1 dB better than a conventional EDFA with an equivalent overall gain.

Measuring continuous-variable quantum entanglement with parametric-amplifier-assisted homodyne detection

Traditional method for measuring continuous-variable quantum entanglement relies on balanced homodyne detections, which are sensitive to vacuum quantum noise coupled in through losses resulted from many factors such as detector's quantum efficiency and mode mismatching between detected field and local oscillator. In this paper, we propose and analyze a new measurement method, which is realized by assisting the balanced homodyne detections with a high gain phase sensitive parametric amplifier. The employment of the high gain parametric amplifier helps to tackle the vacuum quantum noise originated from detection losses. Moreover, because the high gain parametric amplifier can couple two fields of different types in a phase sensitive manner, the proposed scheme can be used to reveal quantum entanglement between two fields of different types by using only one balanced homodyne detection. Furthermore, detailed analysis shows that in the multi-mode case, the proposed scheme is also advantageous over the traditional method. Such a new measurement method should find wide applications in quantum information and quantum metrology involving measurement of continuous variables.