Generation of quadrature-squeezed light during the propagation of a light wave in a birefringent fiber

It is shown that generation of quadrature-squeezed states of a vector electromagnetic field in which quantum fluctuations in one of the quadrature components are smaller than in the coherent state can occur in cubically nonlinear media (birefringent fibers) with efficient energy transfer between the polarization modes of the field. It is shown that for certain distributions of the initial total power between modes, light with suppressed quantum fluctuations in both polarization modes of the vector field is formed at the fiber exit. The optimal conditions for obtaining quadrature-squeezed light are determined. New analytical expressions are obtained for the degree of squeezing in the two polarization modes in the case when there is no energy transfer between the polarization components of the field propagating in the fiber (eigenmodes of two-wave mixing).     

Monomode fiber modulators: Frequency and polarization state control

Two experimental fiber components are described that exploit the properties of highly birefringent monomode optical fiber. In the first the generation of a traveling ultrasonic flexure wave on the fiber produces a frequency shift on the input optical signal. In the second a variable axial tension modulates the differential phase retardance between the two guided polarization eigenmodes to produce an arbitrary output polarization state from a linear input state (or vice versa) without loss of optical power.     

Monomode fiber modulators: Frequency and polarization state control

Two experimental fiber components are described that exploit the properties of highly birefringent monomode optical fiber. In the first the generation of a traveling ultrasonic flexure wave on the fiber produces a frequency shift on the input optical signal. In the second a variable axial tension modulates the differential phase retardance between the two guided polarization eigenmodes to produce an arbitrary output polarization state from a linear input state (or vice versa) without loss of optical power.     

Evolution of first-order sidebands from multiple FWM processes in HiBi optical fibers

The generation of two idler waves inside a high birefringent (HiBi) optical fiber through three four-wave mixing (FWM) processes is studied theoretically. The coupled-equations for the field amplitudes are derived and analytically solved, in the co-polarized and orthogonal polarization schemes. The obtained solutions take into account the delayed Raman response of the medium. The polarization sensitivity of the generation of the idler waves is analyzed. Results show that the stimulated Raman scattering does not change the efficiency of the idler wave generation in the co-polarized scheme, whereas in the orthogonal polarization scheme that nonlinear process decreases the efficiency of the four-wave mixing processes. Results also show that this set of multiple four-wave mixing processes is physically quite different from the typical single or dual pump four-wave mixing configurations. Findings show that the power transfer from the pumps to the idler fields can lead to a monotonous growth, or a periodic evolution of the sidebands along the fiber. Results show that the process efficiency varies greatly with the angle between the two pump polarizations.     

Experimental evidence for Raman-induced limits to efficient squeezing in optical fibers

We report new experiments on polarization squeezing using ultrashort photonic pulses in a single pass of a birefringent fiber. We measure what is to our knowledge a record squeezing of -6.8+/-0.3 dB in optical fibers, which when corrected for linear losses is -10.4+/-0.8 dB. The measured polarization squeezing as a function of optical pulse energy, which spans a wide range from 3.5-178.8 pJ, shows a very good agreement with the quantum simulations, and for the first time we see the proof experimentally that Raman effects limit and reduce squeezing at high pulse energy.     

基于量子增强型光纤马赫-曾德尔干涉仪的低频信号测量

利用低频光通信波段真空压缩态光场可实现基于光纤的量子精密测量.本文利用简并光学参量振荡器实验制备出1550 nm低频真空压缩态光场.在分析频段10—500 kHz范围内压缩态光场的压缩度均达3 dB.用实验制备的1550 nm真空压缩态光场填补光纤马赫-曾德尔干涉仪的真空通道,实现了量子增强型光纤马赫-曾德尔干涉仪,完成了突破标准量子极限的相位调制频率为500 kHz的低频信号测量.与光纤马赫-曾德尔干涉仪相比,测量信噪比提高了2 dB.     

双模激发压缩真空态的维格纳函数

利用纠缠态表象下的维格纳(Wigner)算符,构造了双模激发压缩真空态的维格纳函数,并根据该函数在相空间ρ-γ中随参量m,n和r的变化关系,讨论了双模激发压缩真空态的量子干涉特性和压缩效应。结果表明,对于参量m,n不同的取值,双模激发压缩真空态的量子干涉效应的强弱不同;而对于不同的压缩参量r,双模激发压缩真空态呈现出不同程度的压缩效应。最后,根据双模激发压缩真空态的维格纳函数的边缘分布,阐明了此维格纳函数的物理意义。     

光频率调制法测量动态光栅瞬态反射谱特性

动态光栅的瞬态特性影响了单纵模掺铒光纤激光器的稳定性. 提出一种利用铒离子瞬态效应,通过对写入光施加快速频率调制测量动态光栅瞬态反射谱的新方法. 测量了线性结构动态光栅的瞬态反射谱,研究了注入光功率与端面反射率 对动态光栅响应特性的影响.结果表明, 3 m长的掺铒光纤形成的动态光栅半带宽为30 MHz, 与稳态理论值符合较好.光栅瞬态反射率相对变化随注入光功率增加和端面反射率增加而减小, 在小注入功率或低端面反射率时,最大的反射率相对变化值约为4%. 光栅建立时间随注入光功率增加而减小,当注入光功率大于4倍饱和功率时,建立时间小于1 ms. 使用双波混频过程可解释这一实验规律.     

Generation of a stable low-frequency squeezed vacuum field with periodically poled KTiOPO4 at 1064 nm

We report the generation of a stable continuous-wave low-frequency squeezed vacuum field with a squeezing level of 7.4+/-0.1 dB at 1064 nm, the wavelength at which laser-interferometric gravitational wave (GW) detectors operate, using periodically poled KTiOPO4 (PPKTP) in a subthreshold optical parametric oscillator. The squeezing was observed in a broad band of frequencies above 700 Hz where the sensitivity of the currently operational GW detectors is limited by shot noise. PPKTP has the advantages of higher nonlinearity, smaller pump-induced seed absorption, and wider temperature tuning range than alternative nonlinear materials such as MgO-doped or periodically poled LiNbO3, and is, therefore, an excellent material for generation of squeezed vacuum fields for application to laser interferometers for GW detection.     

Polarization insensitive wavelength multicasting of DPSK signal using four-wave mixing in a birefringent photonic crystal fiber

We demonstrate polarization-insensitive wavelength multicasting of differential phase-shift keying (DPSK) signal based on four-wave mixing (FWM) in a highly nonlinear, birefringent photonic crystal fiber (PCF). The 10-Gbit/s RZ-DPSK input signal is copied to 8 wavelength channels through FWM with three optical pumps. The pump wavelengths are unequally spaced to avoid undesirable crosstalk from pump-to-pump beatings. The dependence of conversion efficiency on input signal polarization is suppressed by exploiting the PCF birefringence together with control of the pump polarizations. All pump polarizations are aligned at 45 degrees to the principal axes of the PCF. Open eyes and error-free results are obtained in all the 8 multicast channels for polarization-scrambled RZ-DPSK input signal.     

Many-body quantum dynamics of polarization squeezing in optical fibers

We report new experiments that test quantum dynamical predictions of polarization squeezing for ultrashort photonic pulses in a birefringent fiber, including all relevant dissipative effects. This exponentially complex many-body problem is solved by means of a stochastic phase-space method. The squeezing is calculated and compared to experimental data, resulting in excellent quantitative agreement. From the simulations, we identify the physical limits to quantum noise reduction in optical fibers. The research represents a significant experimental test of first-principles time-domain quantum dynamics in a one-dimensional interacting Bose gas coupled to dissipative reservoirs.     

Simultaneous experimental generation of vacuum squeezing and bright amplitude squeezing from a frequency doubler

Both vacuum-squeezed and bright amplitude-squeezed states of light are experimentally generated from a frequency doubler with a semimonolithic Fabry-Perot configuration consisting of a type II nonlinear crystal and a concave mirror. Vacuum squeezing of 3.2 +/- 0.1 dB and amplitude squeezing of 1.3 +/- 0.2 dB are obtained simultaneously at a pump power of 8 mW. The two quadrature-squeezed optical fields that are generated are of identical frequency at 1080-nm wavelength and orthogonal polarization. Optimizing the input pump power by 19 mW yields as much as 5.0 +/- 0.2 dB of maximum vacuum squeezing. The advantages of the system are its simplicity and multiple utility.     

压缩真空态中三能级原子的定态共振荧光

本文得到了与压缩白噪声真空库耦合的三能级原子在强相干驱动场作用下的定态共振荧光谱。结果表明谱分布强烈地依赖于库场压缩性及相干驱动场与库场压缩分量之间的位相差。 关键词：     

高双折射光纤环镜改善40 GHz光时钟消光比的研究

时钟信号的好坏在同步、解复用和光判决中起着决定性的作用,双折射光纤环镜具有灵活可调的滤波特性,光时钟信号通过双折射环形镜可以使其消光比得到改善,从而提高时钟信号的质量。为此提出了利用高双折射光纤环形镜提高光时钟信号消光比的方案,数值上模拟了环形镜透射谱随双折射器件偏振延时量(Δt)、偏振控制器快慢轴角度以及偏振控制器所引入光程差的变化而变化的情况,并理论分析了消光比不理想的时钟信号经过环形镜后的光谱形式。用法布里-珀罗滤波器提取的40 GHz时钟信号进行实验,时钟经过环形镜后消光比改善了13 dB,实验结果和理论模拟得到了很好的匹配。     

Polarization entanglement generation at 1.5 μm based on walk-off effect due to fiber birefringence

In this Letter, a linear scheme to generate polarization entanglement at 1.5 μm based on commercial polarization maintained dispersion shifted fiber (PM-DSF) is proposed. The birefringent walk-off effect of the pulsed pump light in the PM-DSF provides an effective way to suppress the vector scattering processes of spontaneous four-wave mixing. A 90 deg offset of fiber polarization axes is introduced at the midpoint of the fiber to realize the quantum superposition of the two correlated photon states generated by the two scalar processes on different fiber polarization axes, leading to polarization entanglement generation. Experiments of the indistinguishable property on single-side and two-photon interference in two nonorthogonal polarization bases are demonstrated. A two-photon interference fringe visibility of 89±3% is achieved without subtracting the background counts, demonstrating its great potential in developing highly a efficient and stable fiber based polarization-entangled quantum light source at the optical communication band.     

Polarization insensitive homodyne detection of optical phase modulation by two-wave mixing in saturable Er-doped fiber

We report linear polarization-insensitive detection of optical phase modulation in an adaptive interferometer based on transient two-wave mixing via dynamic population gratings in saturable Er-doped fiber (EDF). The proposed simple and robust configuration has an all-fiber design based on commercially available elements which makes it promising for applications in optical fiber interferometric sensors and coherent optical communication systems. The experimentally investigated single-mode polarization-maintaining EDF arrangement operated at 1492 nm and demonstrated efficient compensation of the polarization drifts below 100 Hz.     

Analysis of optically amplified mid-infrared parametric generation in AlGaAs waveguides

Based on the recent breakthroughs in oxidized AlGaAs technology, a considerable improvement in IR generation through merging of optical amplification and three-wave mixing is predicted. Amplification of one of the two input fields is shown to strongly relax the phase-matching condition for difference-frequency generation in AlGaAs waveguides. This effect is potentially crucial for the realization of an integrated semiconductor optical parametric oscillator.     

Collective atomic spin squeezing and control

Using a quantum theory for an ensemble of two- or three-level atoms driven by electromagnetic fields in an optical cavity, we show that the various spins associated with the atomic ensemble can be squeezed. Two kinds of squeezing are obtained: on the one hand self-spin squeezing when the input fields are coherent ones and the atomic ensemble exhibits a large non-linearity; on the other hand squeezing transfer when one of the incoming fields is squeezed. Received 14 August 2001 and Received in final form 7 November 2001     

Polarization-sensitive non-3ω third-harmonic generation by femtosecond Cr: Forsterite laser pulses in birefringent microchannel waveguides of photonic-crystal fibers

Femtosecond Cr: forsterite laser pulses coupled into small-diameter birefringent channel waveguides off the central core of a photonic-crystal fiber are shown to generate multiple narrowband spectral peaks within the 380–460 nm wavelength region through multimode-phase-matched third-harmonic generation. Some of these peaks are shifted by tens of terahertz from the tripled frequency of the pump field, dictated by standard energy conservation for third-harmonic generation in monochromatic fields. The spectral contents of the third-harmonic signal generated in such a regime are controlled by changing polarization and the intensity of the input pump field.     

Two-wave mixing in an erbium-doped fiber amplifier for modulation depth enhancement of optically carried microwave signals

We experimentally and theoretically analyze an original method based on two-wave mixing in an erbium-doped fiber amplifier for optical carrier reduction of microwave signals. 75% optical carrier attenuation has been observed, and a 10 dB modulation depth increase of the microwave signal is experimentally demonstrated. Moreover, calculated results are in good agreement with measurements and predict that up to 80% carrier attenuation is easily possible.