Phase-sensitive Gain Research Articles

A CMOS Noise-Squeezing Amplifier

Noise squeezing occurs through phase-sensitive gain implemented by a parametric process in a nonlinear LC resonator. This process enhances the sensitivity for one quadrature component of an input signal at the expense of degrading the sensitivity for the other quadrature. We demonstrate an 8.75-GHz parametric resonant amplifier in a 0.13-μm CMOS process, which provides gain of 21 dB and 12 dB for the two quadrature components. This 9-dB gain difference results in a 2.5-dB sensitivity improvement for one quadrature, while it degrades the other quadrature sensitivity by 6.4 dB. The amplifier bandwidth is around 800 MHz and draws 36 mA from a 1.2-V supply.

Phase sensitive amplification in a highly nonlinear lead-silicate fiber

We experimentally demonstrate phase-sensitive amplification in a highly nonlinear and low-dispersion lead-silicate W-type fiber. A phase-sensitive gain variation of 6 dB was observed in a 1.56-m sample of the fiber for a total input pump power of 27.7 dBm.

Large Phase Sensitive Gain in Periodically Poled Lithium–Niobate With High Pump Power

We investigate phase-sensitive operation at telecommunication wavelengths in periodically-poled lithium-niobate waveguides, measuring a record phase-dependent dynamic range of 14.5 dB with 5-dB phase-sensitive gain, compared to phase-insensitive operation. We also highlight limitations arising at high pump powers from green light emission and thermal instability which limits performance compared with an ideal theoretical model.

Third-order dispersion drastically changes parametric gain in optical fiber systems

We demonstrate that the third-order dispersion drastically changes the phase-sensitive parametric gain in cw-pumped fiber systems. We analytically calculate the phase-sensitive gain as a function of the frequency for amplification of two weak monochromatic fields with spectral components symmetric with respect to the pump field. In the absence of the third-order dispersion, the phase-sensitive gain is symmetric with respect to the frequency. When the third-order dispersion is present, the gain has an asymmetric shape. This asymmetry has its origin in the phase-sensitive nature of the parametric gain.

Wide Bandwidth Experimental Study of Nondegenerate Phase-Sensitive Amplifiers in Single- and Dual-Pump Configurations

We experimentally demonstrate nondegenerate phase-sensitive amplification of a 40-Gb/s differential phase-shift-keying data signal in both single- and double-pumped parametric configurations. Careful optimization of the system has allowed a uniform phase-sensitive gain and attenuation to be achieved over at least 20 nm of bandwidth.

Detailed characterization of a fiber-optic parametric amplifier in phase-sensitive and phase-insensitive operation

We experimentally demonstrate a single-pumped, non-degenerate phase-sensitive parametric amplifier with a precise control of phase and amplitude of the in-going waves and investigate in detail its gain, attenuation and saturation properties in comparison with operation in phase insensitive amplifier (PIA) mode. We experimentally observe the variation of the gain and attenuation as a function of the relative phase, pump power and the signal-idler power ratio. The phase sensitive gain spectrum is studied over a 24 nm symmetrical bandwidth and we achieve a maximum phase sensitive amplification (PSA) gain of 33 dB. A departure from the theoretical maximum attenuation as the gain increases is observed and explained.

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-Regenerative Wavelength Conversion for BPSK and DPSK Signals

Phase-regenerative wavelength conversion is demonstrated experimentally. The simultaneous combination of two nonlinear optical processes, phase conjugation and frequency conversion (Bragg scattering), produces phase-sensitive gain at two new idler wavelengths in addition to the original signal wavelength. This single-stage approach does not require phase-locking of the tunable pump. At maximum pump depletion, amplitude and phase regeneration occur simultaneously.

Demonstration of phase-regeneration of DPSK signals based on phase-sensitive amplification

Amplification and simultaneous phase regeneration of DPSK signals is demonstrated using a phase-sensitive amplifier. Phase-sensitive gain is achieved in a Sagnac fiber interferometer comprised of nonpolarization maintaining, highly nonlinear fiber operating in the un-depleted pump regime. Both the pump and signal are RZ-DPSK pulse trains. The amplifier is capable of producing greater than 13 dB of phase-sensitive gain for an average pumping power of 100 mW, and easily reduces the BER of the regenerated DPSK signal by two orders of magnitude compared to the un-regenerated signal, corresponding to a negative power penalty of 2 dB. Careful optimization of the regenerator reveals much stronger BER Improvement.

Gain characteristics of a frequency nondegenerate phase-sensitive fiber-optic parametric amplifier with phase self-stabilized input

We experimentally demonstrate, for the first time to our knowledge, a phase-sensitive amplifier based on frequency nondegenerate parametric amplification in optical fiber, where the input signal-idler pair is prepared all-optically. Using two fiber-optic parametric amplifier sections separated by a fiber-based wavelength-dependent phase shifter, we observe and investigate phase-sensitive gain profile in the 1550 nm region both experimentally and theoretically. The realized scheme automatically generates gain-defining phase that is environmentally stable, making it advantageous for building phase-sensitive transmission links.

Phase and amplitude control of the inversionless gain in a microwave-driven ?-type atomic system

In order to achieve the phase-sensitive probe gain without population inversion, we investigate a three-level Λ-type atomic system driven by a coherent field and a microwave field. It is shown that, by modulating the relative phase of applied fields, we can obtain quite high inversionless gain at different probe detunings and change the gain behavior of the probe correspondingly. We find that amplitudes of the coherent field and the microwave field are also important factors that can result in different gain behavior of the probe. Here, we use the microwave field to induce the quantum coherence between the two ground levels, which is necessary for phase-sensitive effects, since it can result in the interference between two different transition channels.

In-line optical phase-sensitive amplifier with pump light source controlled by optical phase-lock loop

This paper describes an in-line optical phase-sensitive amplifier (PSA) with a pump laser whose optical phase is locked to that of a randomly modulated signal by using an optical phase-lock loop (OPLL). The OPLL is designed with the capability of optical phase locking at an arbitrary relative phase. Experimental evaluation is presented of the OPLL employing a newly developed external cavity semiconductor ring laser with a spectrum linewidth of less than 20 kHz. Employing this pump laser with the OPLL in conjunction with a 4.4-km long nonlinear fiber Sagnac interferometer (NFSI) yields optical phase-sensitive gain of up to 11 dB. A randomly modulated signal is successfully amplified and confirmed offering a clear eye-opening.

Mechanical parametric amplification in piezoresistive gallium arsenide microcantilevers

Preamplification of mechanical signals in external force detection systems can improve overall sensitivity in a case where sensitivity is limited by secondary detection noise. We report experimental data on degenerate and nondegenerate mechanical parametric amplification in GaAs piezoresistive atomic force microscopy cantilevers due to an inherent mechanical nonlinearity. The mechanical nonlinearity is estimated to be a result of curvature at the cantilever base. Characteristics of parametric amplification such as phase sensitive gain, small signal gain, gain saturation, and self-oscillation have been studied. A small signal phase sensitive gain of 19.5 dB was observed for the degenerate parametric amplifier.

Amplitude noise suppression using a high gain phasesensitive amplifier as a limiting amplifier

A phase sensitive gain of 23 dB is achieved using a pulse excited nonlinear loop mirror with a 3 km zero dispersion optical fibre. It is shown that the phase sensitive amplifier (PSA) behaves as a limiting amplifier in the high input signal power region. The suppression of amplitude fluctuation in the input signal is also demonstrated using the PSA as a limiting amplifier.

A phase sensitive SIS mixer to circumvent the quantum limit

A conventional superconductor-insulator-superconductor (SIS) mixer, that is pumped by a single-frequency local oscillator (LO) functions as a phase-insensitive linear amplifier and may achieve a noise level near the quantum limit of one-half photon added noise per unit bandwidth. A phase-sensitive linear amplifier may have less noise than this quantum limit. To overcome the quantum noise limit with an SIS mixer, a two-LO technique which makes the mixer's gain dependent upon the phase of the incoming signal was used. The phase sensitive gain of this two-LO mixer is experimentally demonstrated. The gain variation from maximum to minimum is more than 20 dB. Theoretical predictions of the noise of the two-LO mixer are presented.

Observation of parametric amplification and deamplification in a Josephson parametric amplifier.

We present the results of an experimental effort to generate squeezed microwave radiation using the phase-sensitive gain of a Josephson parametric amplifier. To facilitate the interpretation of the experimental results, we first present a discussion of the theory of microwave squeezing via Josephson parametric amplifiers. This is followed by a detailed description of the device fabricated for our experiment. Experimental results are then presented for the device used in both the doubly degenerate or four-photon mode and for the degenerate or three-photon mode. We have observed parametric deamplification of signals by more than 8 dB. We have demonstrated squeezing of 4.2-K thermal noise. When operated at 0.1 K, the amplifier exhibits an excess noise of 0.28 K when referred to the input. This is smaller than the vacuum fluctuation noise level \ensuremath{\Elzxh}\ensuremath{\omega}/2k=0.47 K. The amplifier is thus quieter than a linear phase-insensitive amplifier in principle can be.

Gain as an optical diagnostic in the ENEA free-electron laser

A brief summary is given of the collaborative project between ENEA and Heriot-Watt University on the Italian ENEA free-electron laser (FEL). The importance of optical diagnostics is discussed, and an outline of the physical process of gain in a FEL is given, with special reference to phase sensitive coherent gain measurement.