Polarization-independent tunable wavelength-selective filter usinga liquid crystal

The authors demonstrate a polarization-independent liquid crystal Fabry-Perot interferometer. An input light beam was split into two orthogonal polarized beams by a polarization beam splitter and prism and the polarization of one beam was rotated 90° by a half-wave plate. These two beams were filtered through different points of the filter and recombined. Two transmission peaks corresponding to these beams usually appeared. However, there were some regions where the two beams were superimposed. At these regions, the filter had a tuning range of over 50 nm with a band pass of 0.4-0.5 nm and a low fiber-to-fiber loss of 3 dB. At the regions where two peaks appeared, the two peaks could be superimposed by applying different voltages     

Micro-opto-mechanical 2×2 switch for single-mode fibers basedon plasma-etched silicon mirror and electrostatic actuation

This paper reports on a new optical 2×2 switch for single-mode fibers. The switching principle is based on a vertical micro-mirror which can be moved into the optical path to switch light between two pairs of fibers. The micromirror switch is designed for by-pass applications. When power is turned off the mirror spring back into its rest position and brings the switch into its bar state. This operation is very reliable, since the moving parts do not get into contact. Fabrication is based on the silicon micromachining technology, which allows to integrate the switching mirror, its electrostatic actuator and the alignment grooves for the fibers on the same chip. The mechanical switching principle brings with it a number of optical advantages such as a high crosstalk attenuation above 50 dB and wavelength and polarization insensitivity. At a wavelength of 1310 nm a minimum insertion loss of 0.6 dB was measured in the bar state, i.e. when the mirror is out of the optical path. In the cross state the light is reflected on the gold coated micro-mirror which has a reflectivity of about 80%. The insertion loss of the bar state was thus higher and a minimum value of 1.6 dB could be obtained. The switching time was well below 1 ms     

Tunable liquid-crystal Fabry-Perot interferometer filter forwavelength-division multiplexing communication systems

We explain how to obtain the bandwidth and tunable range required for wavelength-division multiplexing communication systems and how to design tunable liquid-crystal Fabry-Perot interferometer filters. The main factors determining the performance are liquid-crystal loss, mirror loss, surface roughness, and parallelism, as well as mirror reflectivity and cavity gap. Experimental results closely agree with the designed performance. Temperature dependence, response time, acceptable input power, and reliability are investigated. Pigtailed polarization-independent filter modules with a Peltier controller are made and are shown to have low polarization dependence (<0.3 dB), low driving voltage (<15 V), and compact size, as well as a narrow bandwidth (0.3 nm), high finesse of 189, and large tunable range (50 nm)     

Micromechanical fiber-optic attenuator with 3 μs response

Optomechanical fiber-optic attenuators are bulky and slow. The mechanical antireflection switch (MARS) modulator offers a high-speed alternative for applications including dynamic gain control in fiber amplifiers. This paper describes a compact electrically controlled variable attenuator using a micromechanical device where electrostatic deflection of a silicon nitride quarter-wave dielectric layer suspended over a silicon substrate creates a variable reflectivity mirror. This device is packaged with two fibers in one ceramic ferrule placed in contact with a gradient index (GRIN) collimation lens, so that the input light reflects from the modulator in the collimated beam plane and couples into the output fiber. Using a 300 μm diameter MARS attenuator and a 500 μm diameter collimation lens, the total insertion loss at 1550 nm was 3.0 dB with no applied voltage, increasing to 31 dB at 35.2 V. The polarization dependent loss was less than 0.06 dB. Full attenuation with more than 100 mW input power produced no damage. The response time was 2.8 μs to move from maximum to minimum transmission and 1.1 μs to return to maximum transmission     

A Low-Loss Branching Filter for Broad Widely Spaced Bandwidths (Short Papers)

A waveguide filter which separates the 4-GHz band the combined 4-, 6-, and 11-GHz common-carrier bands with a loss of only 0.05 dB is described. The input is limited to a single polarization, but dual polarizations can be accommodated by using two such filters in combination with a polarization coupler. The filter also has low insertion losses at 6 and 11 GHz: 0.1 dB and 0.06 dB, respectively, a good return loss, 32 dB, and a short length, 2 1/2 ft. Additionally, it has high power-handling capability, good isolation properties, and good mode purity.     

InAlGaAs bulk micromachined tunable Fabry–Pérot filter for dense WDM systems

In this work we report on micromechanically tunable Fabry–Pérot filter concepts for wavelength division multiplexing (WDM) systems. The optical resonator is designed for a cavity length around 30 μm in order to increase the filter selectivity while relaxing the demands on the required mirror reflectance. The introduction of micromechanical actuators, utilizing electrothermal and electrostatic principles, allows wavelength tuning of the filter over a range of more than 40 nm in the 1.55 μm wavelength regime. The movable Bragg mirror, designed as suspended membrane and fabricated with an InP bulk-micromachining technology, consists of a molecular beam epitaxy-grown InAlGaAs quarter-wavelength multilayer stack. The influence of micromechanical actuation and the effect of intrinsic mechanical stress on the mirror deformation has been investigated systematically to optimize the optical filter performance. Filter losses induced by the light absorption within the epitaxial Bragg mirror have been minimized using a highly doped InGaAs/InAlAs composition. Furthermore, low-loss Fabry–Pérot filters have been fabricated using InAlGaAs/InAlAs Bragg mirrors. The measured full-width at half-maximum (FWHM) is 0.24 nm and a filter insertion loss of 2.8 dB has been observed. The FWHM is kept below 0.35 nm over an entire tuning range of 40 nm for an actuation power of 1.3 mW. The bulk-micromachining technology presented here is open for the future development of WDM components, e.g. tunable receivers or laser diodes.     

27-dB gain unidirectional 1300-nm polarization-insensitive multiplequantum well laser amplifier module

An unidirectional polarization-insensitive multiple quantum well laser amplifier module for the 1300-nm window with a record high gain of 27 dB and a 3-dB saturation output power of 13 dBm is demonstrated. The module gain has a 3-dB width exceeding 60 nm and shows a typical polarization sensitivity and gain ripple as low as 0.3 dB. To provide immunity for backscattered or reflected light, polarization independent optical isolators were inserted in the input and output coupling optics of the package. A practical optical amplifier module for the 1300-nm window is very desirable, because most of the presently installed fiber has its zero dispersion wavelength around 1310 mm, while much of the older fiber often only can be operated around this wavelength     

Demonstration of the MEMS Digital Micromirror Device-Based Broadband Reconfigurable Optical Add–Drop Filter for Dense Wavelength-Division-Multiplexing Systems

For the first time, an optimized optical add-drop filter (OADF) for dense wavelength-division-multiplexing systems is demonstrated using the Texas Instruments microelectro-mechanical-system Digital Micromirror Device (DMDtrade). This OADF features a polarization-insensitive fault-tolerant broadband operation, low loss, and the ability to selectively add/drop with high-wavelength-resolution multiple channels in the C telecommunications band. The proof-of-concept OADF designed for the C-band demonstrates low insertion loss, 0.15-dB polarization dependent loss, 3-dB wavelength resolution of 0.4 nm, and an average crosstalk of better than 30 dB. With the use of a reference mirror, the OADF becomes a multiwavelength 2 times 2 routing switch     

A non-polarization short-wave-pass thin film edge filter

Multilayer dielectric thin film edge filter has serious polarization sensitivity under oblique incidence. The cutoff-bands of the s-polarization and p-polarization light in conventional edge filter will separate obviously under 45° oblique inci- dence, which limits its application. Based on the two chosen materials TiO2 and SiO2, a novel stack structure is pro- posed to design the non-polarization short-wave-pass thin film edge filter. By using the （4H 4L 4H） as the matching layers, the polarization separation at 3 dB transmittance for the thin film edge filter cutoff-band is less than 1 nm at the incident angle of 45°. In this way, the non-polarization short-wave-pass edge filter is easily designed and fabricated.     

A computer controlled narrow bandpass optical tunable filter usinga Fourier diffraction grating in the range of 1.3-1.55 μm

A novel tunable filter using a Fourier grating is studied and discussed. It consists of a Fourier grating, a collimator lens, single-mode fibers, and a computer controlled rotary actuator. It has very low polarization dependence of less than 0.3 dB, an insertion loss of less than 3 dB, and a narrow bandwidth of 1.5 nm. Wavelength selection was realized by rotating the grating, which was controlled by a computer. The device is able to select the light at the desired wavelength from more than 100 WDM optical data streams with 2 nm spacing in the range of 1.3-1.55 μm     

A design of a tunable hybrid Solc filter for 40-Gbps DWDM optical systems

In this paper, a contribution for enhancing the performance of a hybrid tunable Solc filter for 40-Gbps DWDM systems is presented. By using liquid crystal cells with variable birefringence, we have achieved a wavelength tuning of 33 ITU channels, for a 100-GHz frequency spacing, from 1564.69 to 1530.32 nm via a 10-stage hybrid Solc filter. The designed device presents a tuning step of 0.1 nm by applying a voltage difference of 0.2 V. The optical cancelling technique is used to make a 3-dB bandwidth tuning between 0.31 and 1.4 nm. The channel’s bandwidth is adjusted for different kinds of 40-Gbps modulated channels spectra. The 10-stage hybrid Solc filter provides theoretically an insertion loss of 4.6 dB, by using polarizers and birefringent plates characterized by high anti-reflection coatings, while its crosstalk approximates 14 dB. The proposed filter provides very low polarization-dependent loss through the incorporation of a polarization beam splitter and a polarization beam combiner.     

Optical frequency conversion device with asymmetric κ-DBRstructure

An optical-frequency conversion device is fabricated, using monolithically integrated distributed Bragg reflector (DBR) mirrors with different coupling coefficients at the outer sides of the active and the saturable absorber regions. The input-end DBR mirror has a higher coupling coefficient than that of the output-end DBR mirror. The converted light is reflected by the input-end DBR mirror and is emitted only from the output end of the device. This device successfully performs optical frequency conversion when the input TM-polarized light has a wavelength within the wavelength range for which the reflection of the input-end DBR mirror is fairly high for TE-polarized light. The ratio of the converted-light output power for TE-polarized light from the input end to that from the output end is less than -30 dB     

Polarisation independent tunable liquid-crystal Fabry-Perotinterferometer filter module with double-pass configuration

A novel tunable liquid-crystal Fabry-Perot interferometer (LC-FPI) filter module with a Faraday rotator and double-pass configuration has been fabricated. The filter module has a 3 dB bandwidth of ~0.4 nm, a 20 dB bandwidth of 1.5 nm, and a polarisation dependent loss (PDL) <0.8 dB over a tuning range of 56 nm. More than 49 dB isolation from the output port to the input port has been achieved     

Polarization-independent integrated optical, acoustically tunabledouble-stage wavelength filter in LiNbO3

We report a polarization-independent integrated acousto-optical double-stage wavelength filter in X-cut, Y-propagating LiNbO₃. The device consists of a combination of four acousto-optical mode converters, a TE- and a TM-pass polarizer, and two polarization splitters; their specific design and properties are discussed. The filter has a bandwidth of 1.4 nm and a tuning range of 76 nm around λ1.55 μm. Maximum filter transmission is achieved with a RF drive power of only 80 mW; it excites via a single unidirectional transducer a guided surface acoustic wave driving the four polarization converters of both stages. Fiber-to-fiber insertion loss is 4.6 dB for TM- and 4.8 dB for TE-polarized waves. Multiwavelength filtering has been demonstrated     

用双折射晶体制做偏振无关分束器

以光波在双折射晶体中传播的相位延迟理论为依据,本文提出一种新型的单片式偏振无关分束器,即通过合理选择晶体的厚度和光轴的取向,可以使透、反射光的分束比不受入射光偏振形态的影响,文中给出了器件设计的一般理论,对晶体石英器件的测量表明,当入射偏光方位角变化时,其分束比的起伏小于0.2dB.     

MEMS可调谐平顶窄带光学滤波器

设计了一种基于MEMS技术的可调谐光学滤波器,它通过光栅将输入的宽带光信号色散展开,以一个MEMS扭镜选择将对应滤波器通带的光信号反射至输出端,从而实现光学滤波和波长调谐功能。滤波器的输入端采用单模光纤,输出端采用多模或者少模光纤,可以实现窄带且平顶的通带特性。经过参数优化,仿真分析得结果显示,采用多模/少摸光纤输出的两种滤波器,其0.5 dB和25 dB带宽分别为0.95 nm/0.29 nm和1.39 nm/0.69 nm,分别满足100 GHz和50 GHz信道间隔的DWDM系统要求。由于输出端采用多模或者少摸光纤,从该滤波器输出的光信号不能继续在单模光纤中传输,只能由光探测器接收,因此该滤波器一般应用于全光网络节点中的下载端口。     

Tunable wavelength filter using nano-sized droplets of liquidcrystal

An electrically tunable optical filter has been developed that uses a polymer containing fine droplets of nematic liquid crystal as the active cavity in a Fabry-Perot interferometer (FPI). This FPI filter, whose finesse was 62, had a free spectral range of 37 nm in the 1.55-μm range with a full-width at half maximum of 0.6 nm and a transmission loss of 2.4 dB. The polarization dependent loss was smaller than 0.17 dB. The transmitted peak wavelength decreased with an electric field. This resulted in a tuning range of 10 nm at 300 V. The switching time was about 370 μs     

三个传输零点的三阶LTCC Ka-band 窄带滤波器

本文介绍了一种基于LTCC（低温共烧陶瓷）技术的Ka 波段三阶窄带滤波器,中心频率35.78GHz,带宽0.8GHz（2.24%）,带内插损小于0.1dB（未考虑介质和金属损耗）。并且在输入输出端口、各枝节之间引入交调耦合分量,在带外形成三个传输零点,带外抑制EM 仿真结果为：>20dB@f>36.9GHz,>30dB@f<34.9GHz。此滤波器可用于毫米波收发 组件中,对镜频信号和杂波进行抑制。     

基于NPR效应及NOLM的多波长SOA光纤激光器

为了获得具有超窄波长间隔的稳定多波长输出,设 计并实验验证了一种基于非线性偏振旋转(NPR)效应及NOLM的多波长SOA光纤激光器。利用 SOA的NPR效应,将SOA与其他偏振器件组合引起强度相关损耗(IDL)效应,从而抑制SOA均 匀加宽线宽内的模式竞争,实现稳定的多波长输出。Lyot-sagnac滤波器作为波长选择器件 ,选用71 m长保偏光纤(PMF)得到超窄波长间隔。另外NOLM作为功率 均衡器进一步抑制了模式竞争效应并且实现了功率均衡,提高了边模抑制比(SMSR)。通过调 节偏振控制器(PCs),最终在室温下实现了稳定且功率均衡的多波长输出,10 dB带宽内输出的波长数量为184,波长间隔为0.08 nm,SMSR高达22 dB。该激光器可作为DWDM光通信系统 中的光源。     

Video camera system using liquid-crystal polarizing filter toreduce reflected light

We have been developed a video camera system using an electrically-controllable liquid crystal polarizing filter for television program production, which can quickly reduce undesirable reflected light from a window pane or watery surface, by automatically judging the polarization state of incident light from the change in video signal intensity. More than 80% of linearly-polarized incident light is removable by this method for all incident polarization angles. The time required for detecting and reducing reflected light is approximately 0.3s in our system. The drastic reduction of polarized light reflected from glass and watery surfaces was demonstrated, and object images obscured by bright reflected light were clearly captured in an instant