MOEMS variable optical attenuator with improved dynamic characteristics based on robust design

The design and preliminary data of a novel microoptoelectromechanical systems variable optical attenuator (VOA) driven by a pair of V-beam electrothermal actuators is described. This VOA deploys a face-to-face arranged pair of 45/spl deg/ tilted mirrors in front of two coaxially aligned lensed fibers to form retro-reflection planar light path for attenuation. The initial insertion loss is 0.7 dB at 1550 nm and the maximum dynamic range of attenuation is 50 dB, respectively. The polarization-dependent loss is measured as 0.15 dB at 20-dB attenuation. The dynamic attenuation deviation is less than /spl plusmn/0.36 dB at 20-dB attenuation with respect to 20-G shock of periodical mechanical vibration at 1 K Hz, in which it complies with requirements of the Telcordia GR1221 regulations.     

Variable optical attenuator based on ion-exchange technology in glass

A thermooptic variable optical attenuator (VOA) based on the Mach-Zehnder interferometer principle was fabricated in glass by an ion-exchange technique. The thermooptical effect was reached via heating electrodes on the side of the Mach-Zehnder arms. The insertion loss of the device was 1 dB, the dynamic range was 38 dB, maximal power consumption was 138 mW, and the polarization-dependent loss (PDL) was 0.2 dB/0.6 dB at 10 dB/20-dB attenuations, respectively.     

A MEMS VOA Using Electrothermal Actuators

A comprehensive study of electrothermally driven microelectromechanical system (MEMS) variable optical attenuator (VOA) devices using an H-shaped structure is presented in this paper. Based on its unique structural design, a retroreflection-type VOA of smaller footprint is realized. The repeatability and stability of the static and transient characteristics of attenuation behavior at various ambient temperatures are characterized. The fluctuation of attenuation curves under the same driving voltage at the same ambient temperatures is less than plusmn0.1 dB. Again, comparing the attenuation curves measured at 25 degC to 75 degC and at 25 degC to 12.5 degC, the deviation of attenuation under the same driving voltage is within the 0.6-dB range. Within the 40-dB attenuation range, the measured switching time from nonattenuation state to a particular attenuation state or between two attenuation states is less than 10 ms. This electrothermally actuated MEMS VOA also demonstrates the state-of-the-art dynamic attenuation stability that complies with the Telecordia GR1221 regulations, where the dynamic fluctuation of attenuation at 20 dB is less than plusmn0.36 dB under a vibration testing condition of 20 G periodical shocks with frequency from 20 Hz to 2 kHz     

Tapered, resonant DBR transmission filters

Wavelength-tunable optical filters, in the form of resonant distributed Bragg reflector laser filters, have been fabricated and evaluated. The devices are specially designed as transmission filters and have a novel structure, using low coupling strength in the grating and an up-tapered active section, in order to improve the crosstalk performance and the saturation properties. Fabricated devices have 6-8-dB dynamic range and would give less than 1-dB crosstalk penalty in four-channel systems at 13-dB chip gain. System experiments with two 2-Gb/s channels are reported     

A fiber connectorized MEMS variable optical attenuator

A voltage-controlled moving-mirror microelectro-mechanical systems variable optical attenuator is described that has less than 1-dB fiber-to-fiber insertion loss at 1550-nm wavelength and greater than 50-dB dynamic range. The device was configured with a simple feedback circuit to operate as an optical power regulator capable of stabilizing the output power to within 0.26 dB for a 12-dB input power excursion     

Retro-Axial VOA Using Parabolic Mirror Pair

This letter presents a design of a microelectromechanical systems variable optical attenuator (VOA) that employs a pair of parabolic mirrors as the retro-reflector, which has obtained a linear relationship over a 62-dB range between the attenuation (in decibels) and the mirror rotation angle (in degrees). The insertion loss measures 0.6 dB thanks to the three-dimentional optical coupling design. The linearity comes from the simultaneous shift and defocus of the laser beam. Compared with the conventional coaxial and cross-axial VOAs, such retro-axial design has the two fibers arranged on the same side and thus facilitates the use of standard packaging formats     

全光纤热光型可变光衰减器

根据光纤包层中的倏逝场机制,将具有热光效应的聚合物材料直接覆盖在侧边抛磨光纤上,进行了全光纤热光型可变光衰减器(VOA)的研究.根据理论分析,确定了在侧边抛磨光纤的抛磨区上覆盖材料的折射率与纤芯中光衰减量之间的关系,为选择适当折射率的热光材料提供依据.设计适当的侧边抛磨区,利用先进的轮式侧边抛磨技术,制备了侧边抛磨光纤,以达到最佳可变光衰减效果.采用螺绕电极和优化封装,制作出性能优良的全光纤热光型可变光衰减器.性能测试表明,器件插入损耗小于0.1 dB,衰减范围为0~80 dB,偏振相关损耗小于0.02 dB,背向反射大于70 dB.该方法制作的全光纤热光型可变光衰减器具有可用电驱动调控、可靠性高等优点.     

Suppression of cladding mode coupling loss in fiber Bragg gratings

We have demonstrated, for the first time, the suppression of cladding mode coupling loss to ~0.1 dB in 30-dB fiber Bragg gratings for both nonhydrogenated and hydrogenated fibers. These fibers have also been optimized to give 0.04-dB average splice loss to SMF-28 fiber. The suppression of cladding mode coupling is achieved by accurately characterizing and controlling the photosensitive profile. This low level of cladding mode coupling loss has opened up a new range of broadband applications, previously restricted by the limited free spectral range of fiber Bragg gratings     

Enhancement of clock component in a nonreturn-to-zero signal through beating process

For optical clock recovery of nonreturn-to-zero (NRZ) signals of more than 40 Gb/s, we propose and experimentally demonstrate a simple clock recovery scheme through beating process between the carrier frequency component and one of the clock frequency components in modulated NRZ signals. The proposed scheme consists of a circulator, a variable optical attenuator (VOA), and two fiber Bragg grating (FBG) filters. With FBG filters and a VOA, the proposed scheme can equalize the amplitudes of two extracted frequency components for a maximum clock-to-noise ratio (CNR). Through this scheme, we have squared the adjustment range of the VOA and achieved an enhanced CNR of more than 15 dB before the receiver in experiment. Bit error rate (BER) curves for back-to-back and 80 km transmissions showed that BERs of less than 10⁻¹¹ can be obtained without error floors for both cases. We expect that the proposed scheme can operate as an efficient clock extraction system for high-speed optical communications.     

光可变衰减器的研究进展

光可变衰减器(VOA)作为波分复用(WDM)网络中关键的功率管理器件,能够实现信道均衡和自动增益控制功能.微电机械系统(MEMS)型和热光型VOA以其衰减范围宽、功耗低、体积小、易于集成等优点成为研究重点,热光特性极佳的聚合物材料则成为最引人注目的热光材料.文章对已有的VOA器件作了概括分类,介绍了各种MEMS型VOA,还从热光材料的角度,总结了聚合物材料的研究成果,对已见报道的基于聚合物的各种热光型VOA进行了重点的描述和分析.最后给出了VOA的两种网络实例.     

Optical amplifier with 27 dB dynamic range in a coherenttransmission system

For applications of optical amplifiers it is important to know the range of amplifier input powers that cause no or negligible system performance degradation. This dynamic range sets limits on information capacity and amplifier cascadability. A 27-dB dynamic range was measured for a traveling-wave optical amplifier with 10-dB fiber-to-fiber and 0.8-dB gain ripple. The device was used in a 150-Mb/s coherent transmission system. The result, the widest dynamic range reported to date, indicates the suitability of the optical amplifier for coherent photonic networks and systems     

Smart dynamic wavelength equalizer based on an integrated planaroptical circuit for use in the 1550-nm region

A microprocessor-controlled dynamic wavelength equalizer is presented. Th subsystem is based on an integrated optical circuit made in silica and covers a large portion of the usable region of the electromagnetic spectrum for optical fiber transmission (1530-1565 nm). The chip is connected in a software-controlled feedback loop, and with its dynamic range of ~7 dB for each channel, the system is capable of flattening the spectral response of an erbium-doped fiber amplifier to within 0.35-dB peak-to-peak. Insertion loss equals ~8 dB     

High Dynamic Range Variable Fiber-Optical Attenuator Using Digital Micromirrors and Opto-Fluidics

To the best of the authors knowledge, proposed is the first variable fiber-optical attenuator (VFOA) using a digital micromirror device (DMD) and an opto-fluidic electronically controlled variable focus lens (ECVFL). The hybrid VFOA uses individually controllable two-state micromirrors of the DMD and the variable focal length capability of the ECVFL to control the amount of light coupled between two fiber ports leading to a high dynamic range VFOA. The demonstrated VFOA at 1545 nm has a 63.5-dB dynamic range, $≪$0.1-dB resolution, 0.2-dB polarization-dependent loss, 4.9-dB optical loss, and $≪$ 100-ms switching time. Applications for the proposed VFOA include use in test and measurement systems.      

Wideband planar lightwave circuit type variable optical attenuator using phase-generating coupler

A novel wideband planar lightwave circuit type variable optical attenuator (VOA) that incorporates a phase-generating coupler is proposed. The proposed VOA was fabricated on a 1.5%-/spl Delta/ silica-based waveguide, and obtained a low insertion loss of less than 1.2 dB and a low wavelength dependent loss of less than 0.8 dB at attenuation levels of 0 to 25 dB over the C- and L-band wavelength range.     

Asymmetric Tuning Schemes of MEMS Dual-Shutter VOA

A dual-shutter MEMS variable optical attenuator (VOA) is designed for advanced tuning functions such as linear attenuation relationship and simultaneous coarse and fine tunings. The mechanism behind is to take advantage of the additional shutter to render one more degree of freedom for attenuation adjustment. Although dual-shutter VOAs with asymmetric functionalities have been reported before, these intrinsic capabilities owing to asymmetry have not been extensively investigated. In experiment, the fabricated VOA device has demonstrated a linear tuning over a 20-dB range with respect to the driving voltage of one shutter, and it has also realized simultaneously coarse tuning (2.5 dB/V) and fine tuning (0.1 dB/V) by the two shutters. Ideally, the tuning can start from any available working point, linear to any controlling parameter, at any slope of linearity, and with any tuning resolution. Theoretical attenuation model has also been developed to provide a roadmap for the VOA design and choice of working point. An interesting finding is that over a certain range the linear attenuation can be obtained by moving a fixed aperture rather than by reducing the aperture size, which greatly relaxes the difficulty of shutter position control. The measured results match well with the theoretical data, implying the possibility of developing a look-up table to locate the shutter positions quickly. The dual-shutter VOA accomplishes these features without the need of high-precision control systems and therefore gives a structure-based rather than a control-system-based solution, clearly advantageous over the previously developed VOAs.     

Variable optical attenuator for large-scale integration

A polymer thermooptic variable optical attenuator (VOA) was designed and demonstrated for dense waveguide device integration. The waveguide bend design is compatible with photolithography fabrication techniques and operates by controlling waveguide bend radiation loss. The design optimizes the compromise between integration capability, integration cost, and attenuation efficiency. For a 5 mm bend length, optical attenuation of >40 dB has been achieved with an applied electrical power of 250 mW. The fiber-to-fiber insertion loss was 1.5 dB for a 20-mm total waveguide length. The design's compact size makes it practical for both VOA arrays and dense integrated optical circuits     

Design and nonlinearity compensation of Fabry-Perot type tunable optical filters for dynamic strain sensing systems

The collected spectrum of the fiber Bragg grating （FBG） and the loss of the detected optical power are discussed with respect to the 3-dB bandwidth of a Fabry-Perot （F-P） type tunable optical filter （TOF）, respectively. And the optimized parameters of the TOF are obtained consequently. It is demonstrated that the relationship between the transmission wave- length of the TOF and its drive voltage is nonlinear. A new method to compensate the nonlinearity of the TOF is proposed. The linear sweeping of the transmission wavelength of the TOF is achieved through modifying the drive voltage using interpolation algorithm. It is observed that the average error and the maximum error of the transmission wavelength are reduced sharply under linear fit. The dynamic strain sensing is realized by use of a reference FBG and moving averaging algorithm in this system.     

High-linearity 208-MS/s photonic analog-to-digital converter using1-to-4 optical time-division demultiplexers

This letter describes a demonstration of a photonic analog-to-digital converter operating at 208 MS/s and utilizing phase-encoded optical sampling to achieve an 87-dB two-tone third-order intermodulation-free dynamic range. A pair of LiNbO₃ 1-to-4 optical time-division demultiplexers with >35-dB channel extinction distribute the 30-ps sampling pulses to an array of photonic integrate-and-reset circuits followed by 12-b 52-MS/s electronic quantizers. Interleaving spurs due to temporal crosstalk currently limit the overall spur-free dynamic range to 65 dB     

Performance optimization of an InP-based widely tunable all-optical wavelength converter operating at 40 Gb/s

We report on the design and performance optimization of a quantum-well active region-based semiconductor optical amplifier Mach-Zehnder interferometer wavelength converter monolithically integrated with a widely tunable sampled-grating distributed Bragg reflector laser, operating differentially at 40 Gb/s. The device is fabricated using an offset quantum-well platform, requiring a single regrowth. We show error-free operation, with a less than 3-dB power penalty at the optimal differential delay, and open eyes across a 25-nm output tuning range.     

Optical Phase Noise Extraction and Amplification Technique Through Four-Wave Mixing and its Application to Optical Phase Noise Monitoring in (D)PSK Systems

We propose and experimentally demonstrate an optical phase noise extraction and amplification (OPNEA) technique for phase-shift keying (PSK) signals. It could effectively extract and amplify the phase noise carried in the incoming PSK signals. By applying this OPNEA technique to optical phase-noise (PN) monitoring, a 13-dB monitoring dynamic range and a 0.2-dB/degree monitoring sensitivity were achieved. The monitoring performance is effectively improved compared with an optical PN direct-monitoring scheme based on a Mach–Zehnder interferometer.