基于半导体光放大器瞬态交叉相位调制效应的高速反相和同相波长转换的研究

采用半导体光放大器(SOA)中的瞬态交叉相位调制效应是实现高速全光信号处理的有效途径.利用SOA和带宽为0.4 nm的窄带滤波器同时实现了重复频率为10 GHz、脉冲宽度为10 ps的同相和反相全光波长转换.当滤波器的中心波长相对于探测光载波波长蓝移0.25 nm或者红移0.05 nm时，得到反相波长转换；当滤波器的中心波长相对于探测光波长蓝移0.29 nm或者红移0.25 nm时，得到同相的波长转换.同时用数值模拟了从同相到反相波长转换的极性演化过程，理论分析和实验结果基本相符. 关键词： 半导体光放大器 波长转换 瞬态交叉相位调制     

Theoretical Study of SOA-Based Wavelength Conversion with NRZ and RZ Format at 40 Gb/s

We theoretically discuss 40 Gb/s semiconductor optical amplifier （SOA）-based wavelength conversion （WC） using a detuning optical bandpass Jilter based on ultrafast dynamic characteristics of SOA. Both the inverted and noninverted WCs are obtained by shifting the filter central wavelength with respect to the probe wavelength when input data signal is in return-to-zero （RZ） format. However, we can obtain format conversion from nonreturn- to-zero （NRZ） to pseudo-return-to-zero （PRZ） and inverted WC when the input signal is in NRZ format.     

Analysis of tunable codirectional vertical couplers with liquid crystal overlays for integrated dye lasers

We propose a guided-wave dye laser using a grating-assisted codirectional vertical coupler as an intracavity tunable filter. A liquid crystal overlay is designed to attain a phase-matching wavelength shift in the vertical coupler and a tunable range of over 60 nm is calculated at a center wavelength of 590 nm with a coupling efficiency of more than –1 dB. The tunable range is limited by the coupling length mismatch rather than by the refractive index variation in the liquid crystal overlay. Sidelobe level in the filter response is increased when the phase-matching wavelength is shifted to the long-wavelength side; nevertheless, the weighted coupling keeps the sidelobe-suppression ratio at more than 30 dB over a spectral span of 100 nm.     

Optimization of Brillouin pump wavelength location on tunable multiwavelength BEFL

Optimization of Brillouin pump (BP) wavelength location on tunable multiwavelength Brillouin-erbium fiber laser (BEFL) with BP pre-amplified technique is experimentally investigated. The tunable multiwavelength BEFL is achieved by utilization a tunable band-pass filter in a laser cavity. The optimum BP power and BP wavelength location within the filter bandwidth is determined in order to obtain the maximum stable output channels. Optimum distance of launching the BP wavelength is found at 0.80 nm shorter from the center wavelength of the filter bandwidth. 15 stable output channels are achieved from the tunable fiber laser system within the optimum range of BP power which is found to be between 5.2 to 5.7 dBm.     

Dual-Wavelength Erbium-Doped Fibre Ring Laser by Cascading Tunable Bandpass Filter with Bandstop Filter

A novel fibre ring laser is proposed and successfully demonstrated. By cascading a tunable bandpass filter with a bandstop filter to construct the desired narrow dual-transmission-peak spectrum, and employing a segment of unpumped erbium-doped fibre as a saturable absorber, a stable fibre ring laser is achieved at room temperature. The proposed laser can operate in dual-wavelength with the wavelength spacing of 0.48 nm and the extinction ratio more than 50 dB or switch between the two wavelengths by adjusting a polarization controller. The stability is investigated experimentally and explained theoretically.     

Tunable and switchable all-fiber comb filter using a PBS-based two-stage cascaded Mach-Zehnder interferometer

We propose and demonstrate a novel tunable and switchable all-fiber comb filter by employing a polarization beam splitter (PBS)-based two-stage cascaded Mach-Zehnder (M-Z) interferometer. The proposed comb filter consists of a rotatable polarizer, a fiber PBS, a non-3-dB coupler and a 3-dB coupler. By simply adjusting the polarization state of the input light, the dual-function of channel spacing tunable and wavelength switchable (interleaving) operations can be efficiently obtained. The theoretical analysis is verified by the experimental results. A comb filter with both the channel spacing tunable from 0.18 nm to 0.36 nm and the wavelength switchable functions is experimentally demonstrated.     

基于半导体光放大器交叉偏振调制效应实现正、反相波长变换

利用琼斯矩阵，对基于半导体光放大器中的交叉偏振调制效应实现全光波长变换进行了理论分析.结果表明，利用这种机制可以实现同相与反相波长变换.在实验上同时实现了10Gb/s归零信号的正相与反相波长变换，输出消光比分别达到了6.9 dB和8.1 dB.     

A reconfigurable multiwavelength fiber laser with switchable wavelength channels and tunable wavelength spacing

We report the experimental demonstration of a reconfigurable multiwavelength fiber laser source with switchable wavelength channels and tunable wavelength spacing by spectrum slicing a broadband light source using a tunable comb filter. The tunable comb filter is based on a thermally-induced linearly-chirped fiber Bragg grating (LCFBG). As an example to demonstrate the effectiveness of the method, two wavelength channels with various wavelength spacings and eight wavelength channels with ∼1.6 nm wavelength spacing were experimentally demonstrated. All the wavelength channels have rejection ratios of greater than 20 dB, and very small 3-dB linewidths of ∼10 pm. The multiwavelength optical source has such unique advantages as simple all-fiber structure, switchable wavelength channels, tunable wavelength spacing, very narrow linewidths, and stable room-temperature operation.     

A new type of small size acousto-optic tunable filter with super narrow optical linewidth

The new concept of the creation of an acousto-optic tunable filter (AOTF) with super-resolution and small size is discussed. The advantage of the device is based on the use of a novel type of multi reflector beam expander that produces a highly collimated optical beam (angular spread about 100 ppm), tilted with a change in optical wavelength. The proposed AOTF, 1 cm in length, can have an optical linewidth about 0.1 nm and up to 400 tunable channels at a wavelength of 1540 nm. It can be utilized as a tunable filter for dense wavelength-division multiplexing (DWDM) in fiber optic networks and as a small-sized tunable optical spectrometer, for example, in sensors of gases, liquids and solids. The acousto-optic tunable filter can be developed by known technology developed for the creation of integrated optics and microelectronics devices. Received: 28 April 2001 / Revised version: 22 August 2001 / Published online: 2 November 2001     

A mid-infrared tunable filter in a semiconductor-dielectric photonic crystal containing doped semiconductor defect

In this work, we theoretically analyze tunable filtering properties in a semiconductor-dielectric photonic crystal (SDPC) containing doped semiconductor defect in the mid-infrared frequency region. We consider two possible configurations of filter structures, the symmetric and asymmetric ones. With a defect of the doped n-type semiconductor, n-Si, the resonant transmission peak can be tuned by varying the doping concentration, that is, the peak wavelength will be shifted to the position of lower wavelength for both structures. Additionally, by increasing the defect thickness, it is also possible to have a filter with multiple resonant peaks, leading to a multichannel filter. The results provide another type of tunable filter in the defective SDPC that could be of technical use for semiconductor applications in optical electronics.     

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.     

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.     

Thermally switchable and discretely tunable comb filter with a linearly chirped fiber Bragg grating

We propose and experimentally demonstrate a novel switchable and discretely tunable comb filter based on a thermally induced linearly chirped fiber Bragg grating. Experimentally we achieved a thermally induced optical bandpass filter that has eight switchable passband peaks with peak separations of 1.6 and 3.2 nm, a very narrow bandwidth (as small as 10 pm) of each peak, a tunable range of 16.5 nm, and a greater than 25 dB rejection ratio. Two spectral peaks separated by only 0.8 nm were also obtained with this comb filter. This filter provides the unique advantages of an all-fiber structure, switchable spectral peaks, independent tuning of the center wavelength and wavelength spacing of the spectral peaks, low polarization sensitivity, simple structure, ease of fabrication, and low cost.     

Transmission characteristics of Mach–Zehnder interferometer comb filter based on thermal operation

We propose and experimentally demonstrate switchable and tunable transmission characteristics of a Mach–Zehnder interferometer comb filter based on thermal operation. Its temperature characteristics are investigated to reveal a shift in the peak wavelength position from 0.003 to 0.004 nm/°C and a tunable range of wavelength spacing of 0.76–0.90 nm for maximum and minimum effective lengths, respectively. This configuration provides the unique advantages of an all-fiber structure, tunable wavelength spacing, switchable spectral peaks, independent tuning of the center wavelength and wavelength spacing of the spectral peaks, and low polarization sensitivity. It is relatively simple to fabricate and expected to have applications in temperature fiber optic sensors and multiwavelength fiber laser sources.     

Tunable microwave photonic filter based on chirped fiber gratings working with a single optical carrier at constant wavelength

This paper presents a tunable transversal filter working with a single optical carrier at constant wavelength. The filter consists of a set of chirped gratings whose time delay is tuned with respect to the emission wavelength of a fiber laser by a piezoelectric actuator; extra lengths of fiber are inserted in the filter arms in order to avoid interferences between signals reflected in different gratings. Two and three taps filters are experimentally demonstrated, the filters transfer function is electronically tuned within the free spectral range.     

Wavelength Tuning of Double-Cavity Micromachined Filter with Electrical and Thermal Actuations

We demonstrate double-cavity micromachined tunable filters with electrical actuations for both blue and red wavelength tuning. Electrical actuations for both shifts can be achieved by combining electrostatic and electro-thermal actuations below and above the breakdown voltage of p-n junctions in the micromachined cantilevers. The measured tuning range with the actuation is 8 nm for both tuning sides and the micromachined filter with a cantilever length of 80 μm exhibits a switching time of less than 115 μs for both turn-on and turn-off states. We also present the theoretical and measured temperature dependence of fabricated micromachined filters at various cantilever lengths, which experimentally gives us a temperature dependence of 0.14 nm/K for a cantilever length of 100 μm.     

Tunable wavelength filtr in extrinsic fabry-perot of optical fiber

Characteristics of a tunable wavelength filter in extrinsic Fabry-Perot of optical fiber are studied both theoretically and experimentally in this paper. Using a slabby PZT-51, a tuning range of over 10nm is achieved by changing the distance between two fiber end faces. We chose a SLED to provide incident light into the filter and achieved a filter with narrow passband(subnanometer bandwidth). The basic characteristics of the filter, as well as the special properties of its output spectrum, are discussed and analyzed.     

Tunable high energy giant chirped passively mode-locked Yb-doped fiber laser

A tunable, low-repetition rate, all-normal-dispersion Yb-doped fiber laser (YDFL) that is passively mode locked based on a phase shifted long period fiber grating (PS-LPFG) is demonstrated and proposed. The mode-locking mechanism of the laser is based on nonlinear polarization evolution (NPE). Using a PS-LPFG as the spectral filter in the laser cavity, the mode-locked output wavelength can be tuned continuously and smoothly over a spectral range of 10 nm, which is the first time implementation of a tunable giant chirped pulse with all-fiber format bandpass filter in YDFL. The maximum output pulse energy is 38.9 nJ at the repetition rate of 2.499 MHz.     

Dual-wavelength Brillouin ring-cavity fiber laser with tunable channel spacing

We experimentally demonstrate a dual-wavelength Brillouin fiber laser configured a pre-amplified Brillouin pump and FBG filter in a ring-cavity. The Brillouin laser can generate 21 Brillouin Stokes with 0.084 nm spacing, the first-Stoke has a peak power of 2.19 dBm. By adjusting the TLS wavelength and FBG’s reflection wavelength from circulating in the ring-cavity, the generated output dual-wavelength is stabile and the channel spacing is tunable, the widest and narrowest channel spacing obtained is approximately 1.12 nm (139 GHz) and 0.084 nm (10.5 GHz).     

向列相液晶染料可调谐激光器的研究

对向列相液晶染料的可调谐激光器进行了光学特性研究. 以650 nm为中 心波长设计了SiO₂和TiO₂多层膜的一维光子晶体, 以激光染料与向列相液晶的混合物作为增益介质层, 制备了波长可调谐激光器.用Nd: YAG倍频脉冲激光器输出的532 nm激光抽运所制备的激光器样品得出如下光学特性: 激光发射波长随温度调谐范围为605.5---639.8 nm, 达到34.3 nm, 随电压调谐范围为634.5---619.5 nm, 达到15 nm. 发射激光每脉冲的阈值能量为12.3 μJ, 激光线宽小于1 nm.