Tunable polarisation-maintaining filter based on liquid crystal photonic bandgap fibre

A tunable and polarisation-maintaining all-in-fibre filter based on a liquid crystal photonic bandgap fibre is demonstrated. Its polarisation extinction ratio reaches 14 dB at 1550 nm wavelength. Its spectral tunability range spans over 250 nm in the temperature range 30?708C. The measured transmission spectrum is compared with that obtained through finite element simulations.     

Tunable photonic crystal coupled-cavity laser

We report the development of a tunable photonic crystal coupled-cavity laser diode based on InP. The laser consists of two photonic crystal channel waveguides that are coupled through a photonic crystal mirror segment in /spl Gamma/-M direction. The cavity lengths define the respective mode spacings in the cavities. The tuning characteristics of the device are compared with results obtained from a transfer matrix model. Quasi-continuous tuning is achieved in a 29.6-nm window with 36 wavelength division multiplexing channels spaced 0.8 nm apart (ITU grid). The simplicity of fabrication and promising output characteristics should make this tunable laser design an interesting source for monolithic integration into highly integrated photonic circuits.     

温度对铁电液晶电调谐滤波特性影响的研究

在改变外加电场实现铁电液晶电调谐滤波中,由于铁电液晶的螺距和自发极化强度对温度变化很敏感,从而为铁电液晶电调谐滤波器的应用和准确度的提高带来了困难。从铁电液晶的螺距和自发极化强度与温度的关系出发,讨论了温度对铁电液晶双折射的影响,给出了铁电液晶电调谐滤波器的透射率随温度变化的关系式,并进行了数值计算。结果表明,温度升高时,透射率和带宽增大,透射峰波长向短波长方向移动,温度变化对铁电液晶电调滤波特性的影响远小于电场变化的影响。     

1.2- to 2.2-$mu$m Tunable Raman Soliton Source Based on a Cr : Forsterite Laser and a Photonic-Crystal Fiber

A 1.2- to 2.2-mum tunable femtosecond light source based on the soliton-self-frequency-shift effect of high-power Cr: forsterite laser pulses propagating inside a highly nonlinear photonic crystal fiber is reported. The demonstrated soliton self-frequency shift is higher than 42% of the pump laser frequency, corresponding to a record 910-nm wavelength tuning range. Due to the advantages of simplicity, easy tunability, high-temperature stability, and low cost of this new femtosecond light source, it accordingly, could be widely applicable for many applications.     

Liquid crystal applications in photonics

We developed new optical switches based on nematic and ferroelectric liquid crystal (LC) cells for photonics applications. Certain new LC switches based on the effect of total internal reflection in nematic LC and deformed helix ferroelectric effect ferroelectric LC with very fast response time were developed. Fast bistable optical switches of the light polarization based on ferroelectric liquid crystal cells were proposed. The switches are characterized by 100 us switching time and 26 dB crosstalk at the wavelength of 632.8 nm and bistable, i.e., required zero power consumption in the switch state.High frequency hysteretic free electrically controlled 0-2π phase modulation of light has been proposed using a very short helix pitch (less than 400 nm) deformed helix ferroelectric liquid crystal. The electrically controlled 0-2π hysteretic free phase modulation was achieved at the driving voltage frequency up to 4 kHz and the voltage amplitude of 32 V. The application of fast V-shaped deformed helix ferroelectric ferroelectric LC (DHF-FLC) for new active-matrix liquid crystal display (LCD) and optical data processing devices is envisaged.Photoalignment technology can be very useful for the new generation of liquid crystal devices as well as in new photovoltaic, optoelectronic and photonic devices based on highly ordered thin organic layers. We have investigated the LC photoalignment in superthin tubes, which are basic elements of switchable photonic crystal/liquid crystal structures and obtained the order parameter comparable with usual homogeneous nematic LC cells. We studied LC alignment on silicon surfaces with submicrometer-sized straight and curved waveguide profiles. The liquid crystal cladding refractive index was then varied according to the applied voltage, and subsequently the microresonator resonance wavelengths were tuned. Based on our initial measurements, the free spectral range (FSR) wavelength shift within the range of 20 nm was obtained, which is comparable with a thermooptic effect. The new voltagecontrollable Si-based add drop filters are envisaged based on this principle.     

基于铁电液晶电控双折射的调谐滤波器的研究

将铁电液晶作为缺陷层引入一维光子晶体中,基于液晶的电控双折射,形成快速窄带调谐滤波器.用传输矩阵法研究了铁电液晶缺陷光子晶体的可调谐滤波特性,计算了电场对滤波器透射峰的位置、强度、个数和带宽的影响,结果表明该滤波器呈现良好的滤波功能.     

Tunable,Gap‐State Lasing in Switchable Directions for Opal Photonic Crystals

A photonic crystal laser that is tunable throughout the visible in three‐dimensionally switchable directions is demonstrated. This photo‐pumped laser utilizes a dye‐infiltrated, single‐crystal SiO₂ opal having incomplete bandgaps. Our results support a gap‐state‐enhanced distributed feedback mechanism for lasing. Three different types of wavelength tunability are demonstrated, each applicable over a different frequency range and involving either single or multiple bandgaps. The many independent laser cavities that exist in one photonic crystal are demonstrated by simultaneously obtaining lasing in various colors and directions from an opal crystal. The observation of characteristic laser emission lines provides a new spectroscopy for characterizing intra‐gap photonic states, which may be useful for developing the photonic crystal analogues of electronic circuitry.     

液晶光子晶体光纤电场传感的模式特性

光子晶体光纤(PCF)的导光特性可通过改变空气孔的结构参数(孔径、间距和排列方式)、材料填充等方法进行调节。由于自身具有电可调性,液晶作为PCF的填充材料具有很大的研究价值,可以用于制作电可调PCF。利用有限元法分析了液晶(E7)填充的光子晶体光纤的基模有效折射率、有效模场面积等参量随占空比、外电场的变化关系,得到了不同占空比下基模的截止电压和一定电压下基模的截止波长。结果表明光子晶体光纤的电压可调范围随占空比增大而增大;占空比一定时,电压越大,波长可调范围越小。这种液晶填充的光子晶体光纤可以应用于电场传感等领域。     

Polarization sensitive performance of one dimensional photonic crystal filters with a liquid crystal layer

A tunable photonic crystal (PC) filter is proposed with the twisted nematic (TN) liquid crystal (LC) as a defect layer. The polarization sensitive performance and the eigenmodes are analyzed. The results show that there are two kinds of transmission modes, namely o and e, when the voltage is low. The different modes can be selected by rotating the filter axially. The e mode shifts toward the shorter wavelength side as the applied voltage increases. Then the peaks of two modes merge into each other and the polarization sensitive performance disappears. The photonic band gap is insensitive to the voltage. The tunable range of the filter is 53 nm.     

级联光子晶体Mach-Zehnder干涉仪的可调谐滤波特性

基于液晶的电控双折射特性和光子晶体自准直特性,在二维光子晶体引入复合缺陷提出一种可调谐Mach-Zehnder 干涉(MZI)滤波器结构,应用液晶系统的自由能理论,推导了外加电压与液晶有效折射率的关系,并结合MZI 相位调制原理和光子晶体等效折射率理论,得到液晶的电控双折射特性与MZI 滤波器的输出光谱间的数学关系,运用时域有限差分法(FDTD)对滤波器的输出进行仿真模拟,并根据仿真结果对结构进行一级级联的优化设计。结果表明:通过控制外加电压的大小可以改变输出端的透射波长,达到可调谐滤波的效果,并且一级级联后的滤波效果比级联前有很大的改善,滤波的半波带宽从20 nm 减小为7 nm,可调谐范围从15 nm 增大为40 nm,因此可以通过进一步级联的方式使滤波器结构更加的优化,以便运用到光波分复用系统中。     

一维液晶缺陷光子晶体温度传感器的研究

将向列相液晶作为缺陷层引入一维光子晶体中,利用液晶折射率对温度变化敏感特性,设计了一维液晶缺陷光子晶体温度传感器。用传输矩阵法研究了传感器的温度特性,并用Matlab编程进行了模拟计算。结果表明,当温度升高时,液晶排列沿平行介质表面的传感器,缺陷峰波长向长波长方向漂移,缺陷模透射峰的宽度减小;而液晶排列沿介质表面法向的传感器,缺陷峰波长则向短波长方向漂移,缺陷模透射峰的宽度增大;传感器的温度灵敏度大于普通材料缺陷的光子晶体,与液晶材料和温度有关,温度接近液晶相变点而增大迅速;传感器缺陷峰波长的漂移与温度成非线性关系。设计了温度传感器探头结构和实验测量系统,测量结果与理论计算值符合。     

新型光子晶体调谐滤波器的研究

提出了一种在光子晶体中引入液晶缺陷层的光子晶体调谐滤波器.用传输矩阵法给出了含液晶层时光子晶体的光谱透过率公式,对电压和液晶材料参数对调谐滤波器透射谱的影响进行了数值计算.结果表明,改变电压时光子晶体滤波器的透射峰波长和带宽作周期性变化,在适当电压作用下光子晶体具有多通道滤波功能,而液晶的厚度和固有双折射的改变几乎不能实现光子晶体滤波器的调谐作用.     

一种新型可调谐光子晶体滤波器的理论研究

建立了可调谐光子晶体滤波器的设计标准,作为设计的依据.通过数值计算和理论分析,得出了一维掺杂光子晶体的缺陷模随杂质光学厚度L和光子晶体折射率n2的变化特征.设计出的可调谐一维光子晶体滤波器在理论上能很好地满足设计标准,滤波通道的半高宽(FWHM)可调范围在1～4 nm间,波长λ可调范围达300 nm,透射率峰值大于0.95.     

平板型光子晶体液晶微谐振腔的温度特性

在二维光子晶体薄板的中心空气孔中填充厚度与光波长相当的液晶材料,形成平板型光子晶体液晶微谐振腔结构。用时域有限差分法研究了液晶微谐振腔的温度特性,并用Matlab编程进行了数值计算。计算结果表明,由于液晶折射率是温度的函数以及微腔对光波传输的约束,当温度升高时微谐振腔的透射峰波长向长波长方向移动,透射峰半高宽度减小,品质因子增大,谐振波长和品质因子随填充因子与平板厚度的变化曲线向增大方向移动,接近液晶相变点时微腔的温度特性变化更迅速。平板型光子晶体液晶微谐振腔的温度特性,为可调光子晶体器件的设计提供了理论基础。     

基于光子晶体光纤放大系统的皮秒方波产生

在光子晶体光纤飞秒激光放大系统中,利用液晶空间光调制器的调制特性,实现了对超短激光脉冲实时、可控的脉冲振幅整形,分析了大线性啁啾方波脉冲在放大过程中的频域和时域形状随泵浦功率的变化规律,在此基础上,通过液晶空间光调制器对主放大器前的脉冲频谱形状进行了预先调整,放大后获得了中心波长为1 031 nm,光谱宽度为13 nm,脉宽为15 ps的方波脉冲,证实了采用光谱优化后的飞秒脉冲作种子,可以较好地克服光子晶体光纤放大器增益不均引起的频谱形状的变化。     

液晶光子晶体可调自准直特性研究

液晶材料光子晶体由于具有可调谐性而得到了广泛的研究,但目前的研究主要集中在可调的光子带隙特性上。详细研究了液晶光子晶体的可调自准直特性。使用平面波展开法分析了液晶旋转角对光子晶体自准直频率的影响,并使用时域有限差分法对光在液晶光子晶体中的传输进行了仿真。结果表明,通过控制液晶旋转角,可以对光子晶体自准直频率进行调节,从而满足不同频率自准直的需要。     

Compact Design of an Electrically Tunable and Rotatable Polarizer Based on a Liquid Crystal Photonic Bandgap Fiber

In this letter, a compact electrically controlled broadband liquid crystal (LC) photonic bandgap fiber polarizer is designed and fabricated. A good fiber coupling quality between two single-mode fibers and one 10-mm-long LC-filled photonic crystal fiber is obtained and protected by using SU-8 fiber fixing structures during the device assembly. The total insertion loss of this all-in-fiber device is 2.7 dB. An electrically tunable polarization extinction ratio of 21.3 dB is achieved with 45deg rotatable transmission axis as well as switched on and off in the wavelength range of 1300-1600 nm.     

Tunable edge-emitting microlaser on photonic crystal slab

A tunable edge-emitting microlaser is realised by a chirped line-defect photonic crystal waveguide. A tunable range of 57 nm is obtained experimentally.     

Digitally tunable wavelength filter and laser

A novel nonmechanical, digitally tunable, polarization insensitive and optically transparent wavelength filter using holograms electro-optically written on a ferroelectric liquid crystal (FLC) spatial light modulator (SLM) has been constructed and operated to tune to discrete wavelengths spaced by 1.3 nm. The filter has been incorporated in a ring laser which is tunable over a range of 38.5 nm across the erbium window, giving output powers of 10 mW. Both wavelength filter and tunable laser are suitable for wavelength division multiplexing (WDM) applications.     

异质结构光子晶体微腔实现多通道可调谐滤波

为解决WDM系统中多信道同时滤波问题,设计并研究了缺陷对一种异质结构光子晶体多通道滤波器的调制机制,结果表明:在光子晶体环形滤波通道中引入点缺陷形成复合缺陷,可克服光子晶体环形腔结构的多模特性,实现单通道内的单纵模滤波;对于各个通道,复合缺陷中点缺陷的折射率对输出端透射谐振波长具有调谐作用,且对各通道的可调谐滤波作用彼此独立,随着点缺陷折射率的增大,输出的谐振波长出现红移现象。所设计的异质结构结构光子晶体对WDM系统实现多信道滤波功能提供理论和设计参考。