Tunable microwave photonic notch filter using a dual-wavelength fiber laser with phase modulation

A novel tunable microwave photonic notch filter using a phase-modulated dual-wavelength fiber laser is presented. A stable dual-wavelength erbium-doped fiber laser with a linear cavity is formed by a polarization-maintaining uniform fiber Bragg grating (PM-FBG) and a polarization maintaining linearly chirped fiber Bragg grating (PM-LCFBG), both of which were fabricated on a high-birefringence (Hi-Bi) fiber. It is found that a stable room-temperature dual-wavelength operation can be achieved due to the presence of two reflection peaks arising from the orthogonal states of polarization (SOP) of the PM-FBG. Experimental results show stable dual-wavelength lasing operation with a wavelength separation of ∼0.36 nm and a large optical signal-to-noise ratio (OSNR) of over 40 dB under room temperature. The dual-wavelength fiber laser is combined with a phase modulator and a segment of single-mode fiber (SMF) as a dispersive device to form a tunable microwave photonic notch filter. By stretching the PM-FBG to tune the wavelength separation of the dual-wavelength fiber laser, a tunable microwave photonic notch filter with various free spectral ranges (FSRs) and a rejection ratio greater than 35 dB was developed.     

Holographic grating recorded by He–Ne laser operating at 632.8 nm in polymer film containing push–pull azo dye

Holographic gratings were optically recorded by two beams from a He–Ne laser operating at 632.8 nm in poly (methyl methacrylate) (PMMA) film containing push–pull azo dye. The holographic characteristics of the recorded gratings were dependent on the polarization direction of the recording beams and the relationship between the diffractive signals and the power density of recording beams was investigated. The formation of holographic gratings accompanied by 532 nm (double-frequency of Nd:YAG laser) irradiation was studied in detail. It was found that the effect of 532 nm laser to the holographic grating lay in two aspects. The acceleration effect of 532 nm laser to the formation of holographic grating is predominant when the power density of 532 nm laser is low. While at relatively high power density of 532 nm laser, the erasure is the main factor to the holographic grating. Moreover, the holographic grating was probed by 532 nm laser at low power density and the dependence of the first order diffractive signal on the recording beam power density was also presented.     

Dual-wavelength external cavity laser with a sampled grating formed in a silica PLC waveguide for terahertz beat signal generation

We propose and demonstrate a dual-wavelength external cavity laser (ECL). In our design, a Fabry–Pérot laser diode (FP-LD) is hybrid-integrated with a sampled Bragg grating written in a silica planar lightwave circuit (PLC). The grating selects two laser wavelengths that share the same laser cavity. The dual-wavelength oscillation with a side mode suppression ratio >32 dB has been demonstrated experimentally. Experimental results indicate that the hybrid-integrated dual-wavelength ECL exhibits strong dual-wavelength emission corresponding to beat frequency of 1 THz. Simulations of this system also indicate good mutual coherence of the two modes and stability of the 1 THz beat signal. PACS 42.79.Dj; 42.60.By; 42.55.Px     

利用CCD进行透镜焦平面的定位

设计了由全息光栅和CCD等构建的光电混合处理光路,实现对透镜焦平面的定位.采用反射式光学元件设计记录光路,制作满足特定空间频率的全息光栅,并利用质心法计算得到CCD采集面上光斑的中心坐标.     

Development of narrow-linewidth diode lasers by use of volume holographic transmission gratings

We present two diode laser setups that employ volume holographic transmission gratings to provide optical feedback. The advantage of this kind of grating is high diffraction efficiency and the possibility to place optical elements on both sides of the grating. This allows for advanced external cavities and adjustable feedback efficiency. The first setup is a diode laser in the Littman configuration with the transmission grating replacing the conventional reflection grating. The second setup improves the frequency selectivity by substituting the feedback mirror with a passive resonator. This grating-enhanced external cavity diode laser (GECDL) achieves excellent frequency stability. A prototype of the GECDL setup demonstrates an intrinsic linewidth of 7 kHz and an operation range that covers the full amplification profile of the laser diode.     

Dual-wavelength distributed Bragg reflector semiconductor laser based on composite resonant cavity

We report a monolithic integrated dual-wavelength laser diode based on a distributed Bragg reflector (DBR) composite resonant cavity. The device consists of three sections, a DBR grating section, a passive phase section, and an active gain section. The gain section facet is cleaved to work as a laser cavity mirror. The other laser mirror is the DBR grating, which also functions as a wavelength filter and can control the number of wavelengths involved in the laser action. The reflection bandwidth of the DBR grating is fabricated to have an appropriate value to make the device work at the dual-wavelength lasing state. We adopt the quantum well intermixing (QWI) technique to provide low-absorption loss grating and passive phase section in the fabrication process. By tuning the injection currents on the DBR and the gain sections, the device can generate 0.596 nm-spaced dual-wavelength lasing at room temperature.     

Dual-wavelength distributed Bragg reflector semiconductor laser based on a composite resonant cavity

We report a monolithic integrated dual-wavelength laser diode based on a distributed Bragg reflector (DBR) composite resonant cavity. The device consists of three sections, a DBR grating section, a passive phase section, and an active gain section. The gain section facet is cleaved to work as a laser cavity mirror. The other laser mirror is the DBR grating, which also functions as a wavelength filter and can control the number of wavelengths involved in the laser action. The reflection bandwidth of the DBR grating is fabricated to have an appropriate value to make the device work at the dual-wavelength lasing state. We adopt the quantum well intermixing (QWI) technique to provide low-absorption loss grating and passive phase section in the fabrication process. By tuning the injection currents on the DBR and the gain sections, the device can generate 0.596 nm-spaced dual-wavelength lasing at room temperature.     

Actively mode-locked dual-wavelength fiber laser with close wavelength spacing using a fiber Bragg grating

A simple actively mode-locked fiber ring laser is proposed and successfully demonstrated to generate dual-wavelength picosecond pulses with close wavelength spacing using one Bragg grating in standard single-mode fiber. The proposed laser can be made to operate in stable dual-wavelength at room temperature, due to the birefringence characteristic of the FBG induced by transverse strain. Transverse strain loading on the FBG allows the wavelength spacing to be controlled. Generation of stable dual-wavelength pulses with a pulsewidth of 212–234 ps and a tunable wavelength separation from 0.2 to 0.44 nm at a pulse rate of 1.05 GHz was demonstrated.     

Realization of Stable Narrow Linewidth Dual-Wavelength Lasing in an Erbium-Doped Fibre Laser by Cleaving the Wavelength-Selective Filter Spectrum

We propose and demonstrate a new concept of stable narrow-line-width and close wavelength spacing dualwavelength lasing in an Er-doped fibre ring laser （EDFRL） by cleaving the spectrum with a wavelength-selective component in the EDFRL. A fibre loop mirror （FLM） combining with a polarization controller （PC） acts as the cleaver. The cleaver can produce a fine pectinate spectrum. By adjusting the PC, the fine pectinate spectrum can be so changeable that cleaving the spectrum of a fibre Bragg grating （FBG） into two parts. As a result, we obtain the dual-wavelength fibre lasering with a bandwidth of only 0.03nm and a wavelength spacing of only 0.07nm. Furthermore, the laser can also perform stable switchable single wavelength or stable different-bandwidth dual-wavelength by carefully adjusting the PC at room temperature.     

基于相位采样光栅的双波长光纤激光器

提出一种基于相位采样的分布反馈式双波长光纤激光器,在不同的空间化置同时引入相位和采样周期的突变.通过理论分析,这种结构能够实现谐振腔的分离,使不同波长的光波利用不同空间位置的增益介质,克服增益介质均匀加宽引起的模式竞争,实现双波长激射.采用准分子激光器和均匀相位模板,在掺铒光纤上制作波长差为0.46 nm的舣波长光纤激光器,能够实现舣波长激射.通过实验,对激光器输出功率和光栅强度的关系进行研究,表明输出功率和光栅强度成反比.     

Self-adaptive Nd:YLF holographic laser with selectable wavelength operation

We demonstrate, for the first time to our knowledge, operation of a self-adaptive holographic laser with wavelength selection, which uses Nd:YLF as the gain medium. The holographic laser was self-starting and, by virtue of the temporal dynamics in writing the gain grating, passively Q-switched the cavity to produce pulses with 20–50 ns duration. A pulse energy of 184 mJ was obtained from the system with beams having a TEM₀₀ spatial profile. Single-longitudinal-mode operation was observed with near-transform-limited bandwidth. Received: 30 July 2002 / Revised version: 1 October 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax: +44-20/7594-7744, E-mail: s.y.lam@ic.ac.uk     

A Novel Fabrication Technique of Long Period Fiber Gratings Using a Holographic Optical Element

We develop a new flexible and precise ultraviolet exposure technique to fabricate a long period fiber grating using a computer-generated holographic optical element (HOE). The HOE can generate a striped beam pattern with about a 300 #x03BC;m period from a KrF excimer laser. This method offers (1) ease in varying the grating period and (2) grating period precision. We achieve a grating period within an accuracy of #x00B1;0.04 #x03BC;m. This means that the peak wavelength can be controlled within an accuracy of #x00B1;0.2nm with an operating wavelength of 1.55 #x03BC;m.This paper was originally presented at the 2nd International Conference on Optical Design and Fabrication, ODF2000 which was held on November 15-17, 2000 at the International Conference Center, Tokyo, Waseda University, Japan.     

利用倾斜光纤光栅的可开关双波长光纤激光器

报导了一种在四波混频作用下利用倾斜光纤布拉格光栅进行波长选择的可开关双波长掺铒光纤激光器。通过将倾斜光纤光栅与单模光纤进行横向错位焊接,使光栅的反向LP01和LP11两个模式具有相近的有效反射率,从而可以用来进行激光器的双波长选择。接入腔内的一段高非线性光子晶体光纤引入的四波混频效应克服了模式竞争,使得双波长激光在室温下稳定振荡。腔内起偏器和偏振控制器的联合作用可产生依赖于波长的损耗,以补偿光纤光栅两反射峰峰值的大小差异。基于以上原理,通过调节腔内的偏振态,该激光器实现了室温下稳定的双波长输出,也实现了在两波长之间的转换。两波长激光均有超过45 dB的信噪比,最大的功率波动为0.8 dB     

High power TEA CO2 laser tuned by a holographic grating

Wavelength tuning of a TEA CO₂ laser by means of a holographic grating with sinusoidal profile is reported for the first time. The grating with 136 lines/mm had an optimized efficiency according to the gain of the laser. The laser beam was coupled out through the zeroth grating order.     

高质量全息光栅实验系统研究

基于全息光栅在信息光学及光谱仪中的重要地位,对全息光栅进行了理论分析,提出了一种新的制作高质量全息光栅的实验系统.该实验系统的优点在于:将激光器发出的高斯光束改造成为均匀平面光波,以此平面光波作为光源可以制作出高质量的全息光栅.     

一种单色全息平板波导显示系统的研究

设计了一种由耦出线性全息光栅和耦入体全息光栅组成的单色全息平板波导显示系统。该系统的工作原理是微型显示器发出的单色图像光波信息经过准直透镜后,通过耦入体全息光栅和耦出线性光栅把图像光波信息从平板玻璃的一端耦入,另外一端耦出,最终在出瞳位置进入人眼。介绍了全息光栅的特点,利用耦合波理论与K矢量闭合法理论推导全息光栅的视场角,同时介绍了全息光栅的设计方法,该方法是通过分束镜将激光分为物光波和参考光波,且按照一定的入射角度在全息干板上发生干涉来实现。模拟仿真结果表明:该系统显示视场角为18°×14°,出瞳距离为30 mm,传递函数MTF在30 lp/mm时均在0.3以上,满足目视系统的使用要求,可以应用于新一代头盔显示系统中。     

Tunable dual-wavelength fiber laser based on a polarization-maintaining fiber Bragg grating and a Hi-Bi fiber optical loop mirror

We demonstrate experimentally the operation of a linear cavity dual-wavelength fiber laser using a polarization maintaining fiber Bragg grating (PM-FBG) as an end mirror that defines two closely spaced laser emission lines. The PM-FBG is also used to tune the laser wavelengths. The total tuning range is ∼8 nm. The laser operates in a stable dual-wavelength mode for an appropriate adjustment of the cavity losses for the generated wavelengths. The high birefringence (Hi-Bi) fiber optical loop mirror (FOLM) is used as a tunable spectral filter to adjust the losses. The FOLM adjustment was performed by the temperature control of the Hi-Bi fiber.     

用体全息术对皮秒光脉冲进行二维测量

本文提供一种测量两束相干的ps光脉冲的空间二维时间振幅相关函数的新方法.在此方法中,光脉冲是被记录在一种光致折变的体积全息介质中,而所记录的信息可以通过直接量度在介质中所形成的光栅的空间分布而读出.这种方法可的可行性已为实验证实,它是通过3.5ps倍频锁模Nd:YAG激光测量光致折变晶体LiNbO₃来实现的。     

A novel tunable dual-wavelength external-cavity laser diode array and its applications

We review the principles and characteristics of a novel tunable external-cavity laser diode source. It can operate as either a continuous wave (CW) single-wavelength, a CW dual-wavelength, a single-wavelength mode-locked, or a tunable dual-wavelength mode-locked laser. The gain medium is a commercial laser diode array. The telescopic external cavity consists of a grazing-incidence grating, a lens and a stripe-mirror. The external cavity provides functions of wavelength selection, dispersion compensation and spatial mode control. The characteristics of the laser under CW or mode-locked operation are described. The dual-wavelength laser output exhibits beat note beyond 7 THz. The tunable multi-terahertz beat frequency is characterized by a non-collinear intensity autocorrelation technique. A dual-wavelength interferometer that uses a tunable dual-wavelength laser as the light source is demonstrated. Finally, theoretical analysis is presented, which demonstrates that the dual-wavelength output of the laser is stable if the modes at the two wavelengths correspond to different array lateral modes.     

A novel dual-wavelength fiber Bragg grating and its application in fiber ring laser

A novel method for fabricating dual-wavelength fiber Bragg gratings (FBGs) by using one phase mask is developed. The method is based on a double-exposure technique. Our technique lends itself to writing gratings with controllable reflectivity and separation of two Bragg wavelengths. A grating with two equal transmission peaks of 20.25 dB is obtained by this method and the separation of the two Bragg wavelengths is about 0.8 nm. With the grating, we demonstrate a dual-wavelength erbium-doped fiber ring laser whose interval of the two peaks is 0.8 nm. The laser's peak powers can get 3.1 mW above and have a good stability.