Piezoelectric fiber optic phase modulator with a reduced level of spurious polarization modulation

It is experimentally demonstrated that a tenfold decrease in the level of spurious polarization modulation can be achieved in a fiber optic phase modulator comprising two fiber sections featuring the polarization mode conversion, arranged on the same piezoelement.     

Multifrequency erbium-doped fiber laser operating at room temperature

A method to realize room-temperature operation of a multifrequency Er-doped fiber laser with low-frequency shift feedback placed within a linear laser cavity is theoretically proposed and experimentally demonstrated. Simultaneous multiwavelength lasing with 0.5 nm wavelength spacing is experimentally demonstrated by applying a sinusoidal signal of 10 kHz to a fiber phase modulator inserted within the linear cavity to prevent single wavelength steady-state oscillation. In the linear cavity, an all-polarization-maintaining fiber Sagnac loop is used as a periodic filter, and a single-mode fiber loop with a polarization controller is used as a partial reflector and also as an output port.     

Recirculation fiber loop interferometer with a Faraday reflector

A new optical scheme of the recirculation fiber loop interferometer with a Faraday reflector and a broadband radiation source is suggested. It is experimentally established that this scheme provides for a more than tenfold decrease in the instrument zero response caused by a spurious polarization modulation in the phase modulator. Factors leading to additional shifts in the instrument zero response are revealed.     

High peak-power single-frequency pulses using multiple stage, large core phosphate fibers and preshaped pulses

We have developed a monolithic high power pulsed fiber laser in a master oscillator power amplifier (MOPA) configuration, which is capable of reaching 0.38 mJ pulse energy and 128 kW peak power for 3 ns pulses at ~1550 nm while maintaining transform-limited linewidth. The fiber laser pulse seed was achieved by directly modulating a CW single-frequency fiber laser using an electro-optic modulator. We used an arbitrary waveform generator to preshape the fiber laser pulses before amplification to avoid pulse steepening and dynamic gain saturation. Single-mode, polarization maintaining highly Er/Yb codoped large core phosphate fibers were used in the power amplifier stages to scale the transform-limited fiber laser pulses, avoiding any nonlinearities.     

Fiber-optic polarization and phase modulator utilizing transparent piezofilm with indium tin oxide electrodes

A highly efficient optical polarization and phase modulator formed by the placement of a thin transparent piezofilm with indium tin oxide electrodes directly in the path of the output from an optical fiber is presented. Various configurations that differ in the clamping conditions, utilization of epoxy, and optical arrangement are presented. For a film thickness of 63.9 μm, a linear phase-shifting coefficient of 0.131 rad/voltage peak (Vp) at 2 kHz and of 0.508 rad/Vp at 7.4 kHz is demonstrated. An intrinsic birefringence of 0.0328 between the directions along the stretch and its perpendicular in the plane of the film has been measured. The polarization modulation coefficient was determined to be 0.323 rad/Vp at 8.423 kHz, corresponding to a half-wave voltage of 8.353 Vp. Applications of the device involving concurrent spatiotemporal polarization and phase modulation are indicated.     

Finite-Element Analysis of Lossy TE-TM modes in Metal-Clad Optical Waveguides

Finite-element analysis employing the scalar and vector H-field formulations and with the aid of the perturbation technique is used to calculate the TE-TM complex propagation characteristics of integrated optical devices in gallium arsenide, lithium niobate, and silica fiber, incorporating a lossy metal cladding. The propagation and attenuation properties of several types of metal-clad planar optical waveguide, which exhibit surface-plasmon properties for the TM polarization, are reviewed, and the modal loss caused by the metal cladding in a titanium-diffused lithium niobate electro-optic directional coupler modulator, an indium gallium arsenide phosphide-based TE-TM optical polarizer, and a submicron metal-clad silica fiber suitable for near-field optical scanning microscopy is calculated.     

Longitudinal vibrations of a silica fiber segment characterized using a fiber Bragg grating

A modulator assembly that excites longitudinal vibrations in a short (19 cm) silica fiber segment is described. A physical model of the modulator assembly is used to theoretically predict the behavior of longitudinal vibrations in the fiber segment. The longitudinal vibrations are experimentally characterized using an intrinsic fiber Bragg grating. Experimental results are compared to theoretical predictions.     

M－Z型铌酸锂高速调制器

报道了采用行波电极结构的偏振型和与偏振无关型Ｔｉ：ＬｉＮｂＯ３高速强度调制器，其中与偏振无关的高速强度调制器是首次研制成功。     

Optimization of the spatial light modulation with twisted nematic liquid crystals by a genetic algorithm

An optimization technique determining the configuration of optical components in a spatial light modulator is proposed. We study a spatial light modulator composed of a twisted nematic liquid crystal, a polarization state generator, and a polarization state detector. To obtain the desired phase and amplitude modulations, four parameters of the polarization state generator and detector should be optimized. A genetic algorithm is applied in searching the configurations suitable to a given twisted nematic liquid crystal. By embodying the proposed technique, the evolution of the designed cost functions is proved.     

Quantum cryptography with perfect multiphoton entanglement

Multiphoton entanglement in the same polarization has been shown theoretically to be obtainable by type-I spontaneous parametric downconversion (SPDC), which can generate bright pulses more easily than type-II SPDC. A new quantum cryptographic protocol utilizing polarization pairs with the detected type-I entangled multiphotons is proposed as quantum key distribution. We calculate the information capacity versus photon number corresponding to polarization after considering the transmission loss inside the optical fiber, the detector efficiency, and intercept-resend attacks at the level of channel error. The result compares favorably with all other schemes employing entanglement.     

Efficient linearly polarized ytterbium-doped fiber laser at 1120 nm

We report a 20 W linearly polarized, spectrally clean Yb-doped fiber laser at 1120 nm with an optical conversion efficiency of 54%. An excellent polarization extinction ratio of more than 23 dB is obtained using fiber Bragg gratings (FBGs) polarization selection technique at all power levels. The results reveal that a Yb-doped fiber laser at 1120 nm could be a promising replacement compared to Raman fiber lasers.     

Optimized half-wave voltage and insertion loss in a strip-loaded waveguide electro-optic polymer modulator

A strip-loaded waveguide, electro-optic modulator was designed and analyzed in terms of single mode conditions, optical loss due to the metal electrodes, modulation efficiency, and mode size. Two designs were compared: Design 1 optimized the half-wave voltage (V(π)=1.1 V) with a nearly symmetric waveguide by maximizing modulation efficiency and minimizing the overall thickness of the waveguide; Design 2 optimized the insertion loss by reducing coupling loss by 4.6 dB via a strongly asymmetric waveguide that maximizes the overall mode size to most efficiently overlap with a single mode fiber. Design 2 also has a favorable half-wave voltage (V(π)=1.75 V). Some general guidelines in the selection of cladding layers in a detailed design of a poled-polymer electro-optic modulator incorporating a strip-loaded waveguide structure are suggested.     

Use of wavefront encoding in optical interconnects and fiber switches for cross talk mitigation

A technique of cross talk mitigation developed for liquid crystal on silicon spatial light modulator based optical interconnects and fiber switches is demonstrated. By purposefully introducing an appropriate aberration into the system, it is possible to reduce the worst-case cross talk by over 10 dB compared to conventional Fourier-transform-based designs. Tests at a wavelength of 674 nm validate this approach, and show that there is no noticeable reduction in diffraction efficiency. A 27% spot increase in beam diameter is observed, which is predicted to reduce at longer datacom and telecom wavelengths.     

Photonic microwave frequency conversion scheme with flexible phase shift

In this paper, a single, flexible and stable optical frequency conversion scheme with tunable phase shift is proposed. It mainly consists of a dual-parallel binary phase shift keying (DP-BPSK) modulator and a polarization modulator (PolM). Properly setting the values of two DC bias points in the DP-BPSK modulator, the frequency conversion ability can be achieved. Meanwhile, the phase shift can also be realized by controlling the DC voltage that drives the PolM or tuning the polarization controller (PC3). The simulation results show that a 20?GHz RF signal can be converted into a 10?GHz IF signal with the conversion efficiency of ?4.45?dB and a full 0° to 360° phase shift. It should be noted that the system performs well against different non-ideal factors such as extinction ratio, DC drifting or different LO and RF amplitudes. In addition, spurious free dynamic range of 82.14 dB·Hz^2/3 is achieved and it can be greatly improved if a better extinction ratio is available.     

An economical piezoelectric phase modulator for fiber optic sensors

A homemade piezoelectric phase modulator for interfero-metric fiber optic sensors was fabricated using piezoelectric buzzers as strain elements. Six piezoelectric elements were embedded between the two halves of a bakelite cylinder split along its axis and secured tightly together again to form a cylinder. Single-mode optical fiber was then wound around the cylinder to complete the unit. Up to a frequency of 500 Hz, the phase shift produced by the modulator is linearly proportional to the amplitude of the applied voltage. The sensitivity of the phase modulator is about 3.6 rad/V and has a dynamic range of 1,000 rad, which is sufficient for most phase modulation purposes.     

2.07μm光纤激光在弱湍流条件下的传输特性研究

本文报道了一种2.07μm波段可调谐主动锁模光纤激光并在室内模拟大气湍流条件下进行传输特性研究。增益介质为1.5 m长的掺钬光纤,主动锁模通过LiNbO3强度调制器在腔内引入周期强度调制实现。腔内引入非线性偏振旋转效应实现波长2058.4nm^2078.6nm可调谐。实验获得了稳定的基频锁模脉冲和10阶,24阶,48阶谐波锁模脉冲,对应频谱信噪比为66.79 dB、61.37 dB、54.82 dB和49.66 dB。锁模脉冲经过数字调制后在实验室内大气湍流模拟池中进行传输,分别获得了?T为70℃,140℃和210℃时三种湍流强度和背对背条件下的眼图;与背对背条件相比,在?T=210℃时光信噪比降低了9.14 dB。     

Coding and decoding in a point-to-point communication using the polarization of the light beam

A new technique for coding and decoding of optical signals through the use of polarization is described. In this technique the concept of coding is translated to polarization. In other words, coding is done in such a way that each code represents a unique polarization. This is done by implementing a binary pattern on a spatial light modulator in such a way that the reflected light has the required polarization. Decoding is done by the detection of the received beam's polarization. By linking the concept of coding to polarization we can use each of these concepts in measuring the other one, attaining some gains. In this paper the construction of a simple point-to-point communication where coding and decoding is done through polarization will be discussed.     

Polarization-independent optical fiber modulator by use of polymer-dispersed liquid crystals

Ultrasmall light modulators have been made by sandwiching a polymer-dispersed liquid crystal (PDLC) between two ferrules with optical fibers. The device can modulate light independent of the state of polarization, because the PDLC becomes transparent or opaque when either sufficient or no voltage is applied to the film. The PDLC was prepared by mixing and annealing a prepolymer and nematic liquid crystal with large anisotropy. An optical fiber modulator with a 30-mum thick PDLC film had an extinction ratio of 8:1-33:1, an insertion loss of 1.3 dB, and rise and decay times of 4 ms at a wavelength of 1.3 mum.     

Configuration to improve second-harmonic-generation conversion efficiency

The dependence of second-harmonic-generation (SHG) conversion efficiency on the intercrystal phase shift between two nonlinear crystals is analyzed with heuristic theory, and a novel scheme for SHG with two cascaded nonlinear crystals and a polarization modulator is proposed. More than 30 W output power is obtained experimentally at 532 nm with 70% external doubling efficiency. To the best of our knowledge, this is the highest conversion efficiency obtained with LiB3O5 crystal external frequency doubling. This scheme provides a simple and effective method for improving second-harmonic conversion efficiency.     

Accurate polarization measurements with a dual photoelastic modulator

Measurements of the polarization effects in multimirror experiments by using a dual photoelastic modulator are described. The effect of single and multiple mirrors in polarization measurements in two and three dimensions is discussed, and experimental results show how symmetrical placement of mirrors in three-dimensional geometry can eliminate changes in the polarization. Calibration procedures for a dual photoelastic modulator and potential error sources such as misalignment of analyzer, signal dc offset, and neglect of aperture size are presented. Mirror-surface evolution and how it can disturb the polarization measurement are also addressed.