Optical heterodyne processing method of mechanically induced phasefluctuations of guided modes in a birefringent single-mode fiber

A method is described for carrying out statistical processing of the individual phases of all the modes guided in a perturbed birefringent single-mode fiber. The method is based on optical heterodyne detection processes using a signal beam with orthogonal linearly polarized two-frequency components and a local oscillator beam. All the time-varying phases of the guided modes are taken out separately and processed to offer their power spectra and correlation functions from which the phase fluctuations can be evaluated statistically     

高双折射单模光纤温度传感器

1 引言 偏振干涉型光纤温度计的灵敏度介于干涉型和强度型之间。典型的干涉型光纤温度传感器是以光纤耦合器为核心,构成Mach-Zehnder的一类干涉仪,它是以两根光纤分别作为干涉仪的测量臂和参考臂。虽然灵敏度高,但由于外界环境因素对参考臂的干扰极为敏感,以致在一般条件下,难以正常工作。文献[2]则以一根高双折射光纤中正交偏振模HE_(11)对外界因素有不同相移,使这两个模式的光发生干涉,从而能有效地克服外界因素的干扰。本文利用时间相     

High resolution spatial interferometry of guided optical waves

The spatial variation of the phase difference Φ(z) between collinear guided waves is measured interferometrically by scanning a localised perturbation along the guide. Milliradian phase resolution is achieved by the use of a quadrature signal. The method is demonstrated with TE⇔TM coupling in Ti:LiNbO₃. It yields the absolute value and the uniformity of the birefringence Δβ(z)=dΦ/dz     

Degenerate-cross-phase modulation of femtosecond laser pulses in a birefringent single-mode optical fiber

Degenerate-cross-phase modulation has been observed for femtosecond laser pulses propagating through a short birefringent single-mode optical fiber. The difference in the spectral broadening of the two output polarization components of a single laser pulse was attributed to the combination of self-phase modulation and degenerate-cross-phase modulation processes in the optical fiber. Theoretical simulations based on the solutions of the two coupled nonlinear Schrodinger equations are in good agreement with the measured results.     

一种高灵敏度相位调制单模光纤传感器的信号处理系统

报道一种高灵敏度相位调制单模光纤传感器的信号处理系统。简述了系统的传感原理,讨论了辨向检测电路和信号的计算机处理。     

Degree of polarisation in a birefringent single-mode optical fibre

We examine the evolution of the polarisation of a field propagating in a birefringent single-mode optical fibre. The explicit dependence of the degree of polarisation on pulse duration, coherence time of the source and chromatic delay of the fibre is derived.     

Evaluation of phase fluctuations of orthogonal optical eigen modesguided in an axially vibrating birefringent single-mode fiber

An optical heterodyne correlation-processing system is devised to process the phase fluctuations of the orthogonal linearly polarized two-frequency components guided in a length of axially vibrating birefringent single-mode fiber. Two wideband phase demodulators make it possible to take out separately both of the phase fluctuations of the two-frequency components from two generated beat photocurrents. The processing system provides the spectrum, the correlation, and the transfer function, as well as the coherency for the mechanically induced phase fluctuations. The phase-fluctuation characteristics and the system linearity are evaluated in terms of the statistical functions and the parameters obtained     

弱双折射光导纤维内的非线性光传输

光在光纤波导内传输过程中，由于光能量非常集中，光与物质作用距离长，因而会产生一系列的非线性效应。例如人们对受激拉曼散射（SRS）和受激布里渊散射（SBS）作了大量的研究。     

Analysis of the degree of polarization of optical waves in a single-mode optical fiber with random coupling

A single-mode optical fiber model is proposed with discrete mode-coupling centers having random coupling coefficients at regular intervals. The degree of polarization in a single-mode fiber with random-mode coupling does not approach zero with increasing fiber length. Numerical results show that the ensemble average of the degree of polarization approaches a nonzero value the magnitude of which depends on the coupling intensity, the light source spectrum, the fiber birefringence, and the spatial frequency of coupling centers, The theoretical and numerical results clarify the limitation of the perturbation iteration method for long optical fibers.     

Generation of optical phase-conjugate waves and compensation forpulse shape distortion in a single-mode fiber

The generation of optical phase-conjugate waves and the application of optical phase conjugation (OPC) to optical communication systems is described. The method of pulse shape distortion compensation by OPC is outlined including distortion due to both fiber dispersion and the optical Kerr effect. The generation of a forward-going phase-conjugate wave in a third-order nonlinear medium is discussed and that by a nondegenerate forward four-wave mixing in a zero-dispersion single-mode fiber (SMF) is investigated. Suppressing the stimulated Brillouin scattering (SBS) of a pump wave in the fiber prevents saturation of the generation efficiency of the phase-conjugate wave even when the pump power exceeds the SBS threshold. In transmission experiments through a 200-km standard SMF with a 16-Gb/s intensity-modulated signal and a 5-Gb/s continuous-phase FSK (CPFSK) modulated signal, it is shown the applicability of OPC is modulation independent and that OPC effectively compensates for both chromatic dispersion and the optical Kerr effect     

Chromatic dispersion measurement by white-light interferometry on metre-length single-mode optical fibres

Chromatic dispersion near 0.8 ?m in a short (~1 m) single-mode optical fibre is determined by a white-light interferometric technique. In particular, the wavelength-dependent group delay of the fibre is obtained directly from the spectra of the output light from a Mach-Zehnder interferometer illuminated by a GaAlAs LED. Its application in single-mode fibre studies in the 1.3 ?m wavelength region is discussed.     

Fabrication of single-mode chalcogenide optical fiber

Long lengths (>150 m) of single-mode chalcogenide optical fiber were fabricated by a double crucible technique. Single-mode transmission through 10 m of continuous fiber was demonstrated using an F-center laser at 2.7 μm. The optical loss of this fiber was measured by a standard cutback technique using an FTIR spectrometer and also using an F-center laser, A minimum loss of less than 1 dB/m was obtained     

Chromatic dispersion measurement of a single-mode fibre by improved optical heterodyne interferometry

The chromatic dispersion of a single-mode fibre is successfully measured by means of an optical heterodyne detection method with temporal resolution of 0.01 ps. The heterodyne signal is detected at the near end of the fibre of length approximately 1 m using laser diodes operating in the 1.19?1.51 ?m wavelength region.     

Raman amplifier model in single-mode optical fiber

Equations to describe the process of Raman amplification in single-mode optical fiber and Stokes and anti-Stokes spontaneous emission generation with conservation of photon number are derived from first principles. The numerical simulation of Stokes and anti-Stokes spontaneous emission is in good agreement with experimental results. The importance of the sometimes-omitted anti-Stokes spontaneous emission terms in wavelength-division-multiplexed situations for optical signal-to-noise ratio is demonstrated by the simulation of light propagation through transmission fiber with and without Raman amplification.     

Polarization fluctuations in a single-mode optical fiber

Polarization fluctuation characteristics of single-mode optical fiber output are examined theoretically and experimentally. A fiber model for studying these characteristics from the perspective of probability on the Poinare sphere is proposed. The relationship of the degree of polarization fluctuation to time and fiber length is shown theoretically. Measurements of submarine and underground cables and long-haul fibers up to 270 km in length generally support the proposed model     

High-precision characterization of single-mode optical fiber arrays

A precise method of measuring core center dispersion in single-mode fiber arrays is presented. This approach dispenses with the use of high-precision linear translation stages and is based on a direct comparison of the fiber core center position to a simple lithographically patterned template. Combining image recognition and efficient processing algorithm, the fiber-core center positions of fiber arrays can be determined with precision of order of 0.1 /spl mu/m, in both longitudinal and transversal directions. Complementary information about the position of fibers within v-grooves as well as bending of multifiber arrays can be also obtained.     

Fast single-mode characterization of optical fiber by finite-difference time-domain method

Usually, although not always, manufacturers producing optical fiber state that the functioning will be single mode in most cases without specifying the wavelengths to be worked with. A rapid method of light simulation within the optical fibers was developed for a single-mode characterization, which avoids errors and problems in transmitting the signals through the fiber. The method was validated with two optical fibers, in which the intensity patterns are well known in theory, and a rather good fit between the theoretic intensity curves at the endface of the fibers was achieved. In order to characterize the monomodal regime, the method was applied to two optical fibers with different refractive-index profiles, using the finite-difference time-domain (FDTD) for the body of revolution (BOR).     

Operation of a nonlinear optical loop mirror with orthogonally polarized waves in nonpolarization-preserving, single-mode fiber

We demonstrate stable operation of a NOLM using orthogonally polarized control and signal beams in nonpolarization-preserving, single-mode fiber. The NOLM can transcribe data from an optically incoherent input at one wavelength to a coherent output over a range of wavelengths. Operation of the NOLM without tuning for the input bit rate is possible over a range of bit rates from less than 1 Gb/s to more than 50 Gb/s.     

Vibration-induced polarisation modulation of light guided in single-mode optical fibres

The polarisation state of the HE11-mode in a single-mode optical fibre with a fused silica core was varied by mechanical vibrations of the fibre. The accompanying amplitude modulation is suppressed in the experimental arrangement. The influence of the plane of the incident polarisation on the signal modulation is discussed. The measurements were made with both reflecting and nonreflecting fibre endfaces.