可变可转单波片偏振控制器研究

基于PLZT波片的相对相位延迟量可变性和其折射率椭球主光轴的可转性,提出后反馈单个PLZT可变可转波片偏振控制器.采用模拟退火算法进行扰动寻优,仿真结果显示这种控制器是有效的：能将任意输入偏振态转换为稳定的线偏振光而其光强达到总光强的98%以上,在控制过程中相移能在限定范围内变化,避免了由复位重置可能引起的波动.     

Dynamic arbitrary waveform shaping in a continuous fiber

We present a low-loss dynamic waveform shaping technique for high-repetition-rate signals by independent phase and amplitude control of spectral lines in a continuous fiber. Our system employs uniform fiber Bragg gratings to separate the spectral lines and provides independent amplitude and phase control for each line via an in-line polarization controller and an in-line fiber stretcher, respectively. Several distinct waveforms are experimentally demonstrated by manipulating five spectral lines with a spectral resolution of 0.12 nm and a temporal resolution of 17 ps. Better temporal resolution can be achieved by increasing the bandwidth through additional spectral lines.     

Performance of a wavelength-tunable erbium-doped fiber laser using a Sagnac interferometer

We experimentally demonstrate a wavelength-tunable erbium-doped fiber laser that is composed of a ring cavity and a single-mode fiber Sagnac interferometer in a new and simple arrangement. We find that the fiber laser output wavelength is tunable by adjusting the filter effect of the Sagnac fiber loop through a fiber polarization controller set there. The quasi-single-wavelength continuously tunable laser outputs could be achieved within some wavelength range. The multi-wavelength laser outputs could also be observed under some appropriate settings of the polarization controller. A theoretical demonstration of the wavelength tunability about the transmission-type Sagnac loop filter has also been achieved using the Jones calculus theory.     

可变波片构造等效线性可转波片的研究

利用四元数理论分析了可变延迟波片,并依此由可变延迟波片组合构造了等效可转线性半波片和四分之一波片.提出由可变延迟波片按可转波片控制算法设计偏振控制器,以避免可变延迟波片偏振控制器所需的复位重置过程.仿真结果显示,按此构想得到的四波片控制器,能把任意偏振态转换为固定线偏振输出,其光强波动小于1%,相移范围不超过2π,控制过程不需要附加复位操作,其相移变化平缓.     

An intensity-modulation direct-detection radio-over-fiber link with a tunable transfer function

An intensity-modulation direct-detection (IMDD) radio-over-fiber link with a tunable transfer function is presented. It utilizes a bias drift free intensity modulator based on a Sagnac fiber loop interferometer containing an optical phase modulator. By adjusting the polarization controller in the interferometer, the transfer function of the whole system can be tuned. The present method is simple and easy to implement.     

Generation of radially polarized light beams of high quality using a step-index optical fiber

We present an experimental setup to generate radially polarized beams without using high-cost optical elements. In the setup a four-segment polarization converter is used in front of the fiber to produce a pseudo radially polarized beam. A traditional step-index fiber which supports only LP₀₁ and LP₁₁ modes is then used as a mode-cleaning device. A commercial mechanical fiber-squeezer polarization controller is applied to produce adequate pressure and twist onto the fiber. The four-segment polarization converter and the fiber squeezer polarization controller are adjusted by turns for improving the beam quality in intensity and polarization. Additionally, several methods of characterizing the polarization properties of radially polarized beams are reviewed. One of the latest methods is applied for characterizing the polarization properties of the radially polarized beams produced by using our technique. The results show the highquality of the obtained beams.     

Broadly tunable dual-wavelength erbium-doped ring fiber laser based on a high-birefringence fiber loop mirror

A broadly tunable dual-wavelength erbium-doped ring fiber laser based on a high-birefringence fiber loop mirror (HiBi-FLM) and a polarization controller is demonstrated experimentally. The measured transmission spectrum of HiBi-FLM covers a wide range from 1525 to 1575 nm. The wavelength of proposed laser can be flexibly tunable during this range of ∼50 nm by adjusting the polarization controller. In addition, the spacing of two wavelengths is adjustable by changing the length of HiBi fiber. The dual-wavelength lasers with the HiBi fiber length of 1 and 2 m are experimentally demonstrated and compared. The experimental results show that the proposed laser can stably operate on two wavelengths simultaneously at room temperature, and the output peak power variation is about 0.5 dB during 40 min.     

全光纤量子通信系统中的高速偏振控制方案

偏振控制在光通信中是至关重要的技术, 关系着通信系统的稳定性和误码率. 本文提出一种基于双向Sagnac环工作方式的全光纤高速偏振控制方案, 通过调节环中一个光纤电光相位调制器的相位差而精确控制光场偏振方向, 并且实现了单个端口输出各种偏振态, 无需后续耦合操作. 相位控制精度为10^-3 rad, 最大消光比可达30 dB, 工作速率可达2 GHz. 由于本方案的精度、调制速度和稳定性都很高, 并采用了器件简单、成本低廉的全光纤光路, 易于集成, 在量子保密通信等光通信领域中有很好的应用前景. 关键词： 光纤偏振控制器 Sagnac环 量子通信     

Spectral polarimetry with a differential group delay bias

We show that the addition of a polarization controller and bias differential group delay to a spectral polarimeter increases the amount of polarization information that can be extracted from a Stokes spectrum measurement. We use this biased spectral polarimetry on 40-Gbit/s signals to measure the polarization mode dispersion of the optical fiber through which they propagate. Our measurements do not require any control of the polarization at the fiber input. Averaging measurements from several settings of the polarization controller yields improved accuracy, and, after data rejection is applied, both the accuracy and the number of valid data points is increased when using several measurements.     

Switchable Multi-Wavelength Erbium-Doped Fiber Lasers based on a Mach-Zehnder Interferometer Using a Twin-Core Fiber

A switchable multi-wavelength erbium-doped fiber ring laser based on a compact in-fiber Mach-Zehnder interferometer comb filter at room temperature is presented. The comb filter is formed by splicing a section of twin-core fiber between two single mode fibers. By adjusting the states of the polarization controller appropriately, the laser can be made to operate in stable single-, dual- and three-wavelength lasing states. The operation principle is based on spectral hole burning induced by the saturated effect and polarization hole burning.     

Tunable single- and dual-wavelength erbium-doped fiber laser based on Sagnac filter with a high-birefringence photonic crystal fiber

In this paper, we observed and experimentally investigated a high-performance single- and dual-wavelength erbium-doped fiber ring laser based on a Sagnac filter which contains a section of high-birefringence photonic crystal fiber (HB-PCF) and a polarization controller. Incorporation of the high-birefringence photonic crystal fiber can suppress multimode oscillation, improve power stability and increase the optical signal-to-noise ratio (SNR). Wavelength tunable was achieved by using a polarization controller in the Sagnac filter. Highly stable single-, dual-wavelength oscillations are tunable within a wavelength range from 1550 to 1562 nm and SNR as high as 57 dB with narrow line width about 0.011 nm, is experimentally demonstrated.     

Spatio-spectral dynamics of soliton pulsation with breathing behavior in the anomalous dispersion fiber laser

We have numerically and experimentally observed the soliton pulsation with obvious breathing behavior in the anomalous fiber laser mode-locked by a nonlinear polarization rotation technique. The numerical study of the soliton pulsation with breathing behavior was analyzed through the split-step Fourier method at first, and it was found that the phase difference caused by the polarization controller would affect the breathing characteristics. Then, taking advantage of the dispersive Fourier transform technique, we confirmed the breathing characteristic of soliton pulsation in the same fiber laser as the simulation model experimentally. These results complement the research on the breathing characteristic of soliton pulsation.     

A tunable comb filter using single-mode/multimode/polarization-maintaining-fiber-based Sagnac fiber loop

A novel tunable comb filter composed of a single-mode/multimode/polarization-maintaining-fiber-based Sagnac fiber loop is proposed and experimentally demonstrated. The filter tunability is achieved by rotating the polarization controller. The spectral shift is dependent on rotation direction and the position of the polarization controller. In addition, the adjustable range achieved by rotating the half-wave-plate polarization controller is twice higher than that of the quarter-wave-plate one.     

Tunable Fiber Ring Laser Employing a Sagnac Interferometric Filter

A tunable erbium-doped fiber ring laser employing an all -polarization- maintaining fiber loop filter with certain birefringence is proposed and demonstrated. The lasing frequencies can be selected by properly adjusting the polarization controller in the cavity.     

Switchable multi-wavelength fiber ring laser based on a compact in-fiber Mach-Zehnder interferometer with photonic crystal fiber

Switchable multi-wavelength fiber ring laser with an in-fiber Mach-Zehnder interferometer incorporated into the ring cavity serving as wavelength-selective filter at room temperature is demonstrated. The filter is formed by splicing a section of few-mode photonic crystal fiber (PCF) and two segments of single mode fiber (SMF) with the air-holes on the both sides of PCF intentionally collapsed in the vicinity of the splices. By adjusting the states of the polarization controller (PC) appropriately, the laser can be switched among the stable single-, dual- and triple-wavelength lasing operations by exploiting polarization hole burning (PHB) effect.     

All optical microwave photonic filters with a round-trip configuration

We propose novel photonic microwave multi-tap filters using a section of Hi-Bi fiber in a round-trip configuration, together with their application in a 20 km single mode fiber (SMF) radio-over-fiber (RoF) link. We demonstrate for the first time that the effect of chromatic dispersion in these multi-tap filters can be reduced in an RoF link when a linearly chirped fiber Bragg grating (FBG) is adopted. This result can be used to combat radio frequency power fading in an RoF link. The configurations are free from optical coherent interference and phase noise. Measured results show 3-tap filters with notch rejections greater than 35 dB and suppression of the level of secondary sidelobes by adjusting a polarization controller. PACS 42.81.-I; 42.81.Gs; 07.50.Qx     

An interferometric structure with a dual-resonance long period grating for strain sensing

Spectral characteristics and amplitude tunability of a long period grating with a dual- resonance inside fiber loop mirror are studied in terms of applied stress caused by elongation. Inserting the polarization controller between grating and part of polarization maintaining fiber in the loop structure enables tuning of resonance and interferometric peaks. The maximum sensitivity of demonstrated sensor is of 1.943?dB/mε for the range of 1.1–4.4 mε. Combination of these two optical components allows to measure strain in a wider range comparing with sensors based on standard long period grating.     

Tunable fiber ring laser employing a Sagnac interferometric filter

A tunable erbium-doped fiber ring laser employing an all-polarization-maintaining fiber loop filter is proposed and demonstrated. The lasing frequencies can be selected by properly adjusting the polarization controller in the cavity.     

Polarization controlled multiwavelength switchable erbium-doped fiber laser based on high birefringence few-mode fiber loop mirror

A multiwavelength switchable erbium-doped fiber laser with linear cavity is proposed and experimentally demonstrated. It is based on a fiber loop mirror incorporating a piece of high birefringence few-mode fiber and polarization controller. Due to dependence of its reflection properties on the polarization controllers, the fiber laser can operate in the random combination of three wavelengths by only adjusting the polarization controllers in the linear cavity. The wavelengths involved in the switching operation are determined by the merged Sagnac and intermodal interferences elicited in the fiber loop mirror. The optical signal to noise extinction ratio of every oscillation line is higher than 40 dB and power fluctuation less than 0.5 dB.     

Wavelength switchable all-fiber comb filter using a dual-pass Mach-Zehnder interferometer and its application in multiwavelength laser

A novel wavelength switchable all-fiber comb filter based on a dual-pass Mach-Zehnder (M-Z) interferometer is proposed and demonstrated. The proposed filter consists of a rotatable polarizer and a standard dual-pass M-Z interferometer composed of two 3-dB fiber couplers with a polarization controller (PC) in one arm. When the PC is properly set, the wavelength switchable operation is achieved by adjusting the polarization state of the input light. Theoretical calculation is verified by the experimental results. As applications, the proposed comb filter is incorporated into a fiber ring laser to generate wavelength switchable multiwavelength lasing.