Widely frequency-tunable amplified feedback lasers for 10-GHz optical pulsation

Monolithic amplified feedback semiconductor lasers are demonstrated as a new solution to 10-GHz optical pulsation, where self-pulsations are generated according to the concept of a single-mode laser with shortly delayed optical feedback. They consist of a loss-coupled distributed feedback section operating as a single-mode laser and an integrated feedback cavity including a phase control, an amplifier, and a transparency section. The pulsation frequency is continuously tunable in the range of 7-11.5 GHz with an extinction ratio above 6.5 dB, which indicates that precise control of a cavity length is not needed.     

基于石墨烯超材料的可调谐电磁诱导透明

提出了一种基于石墨烯超材料的可调谐电磁诱导 透明(EIT)结构,该结构是由长条-半圆环形状的石墨烯层和 介质基底组成。通过频域有限差分法研究了该结构的特性,研究结果表明,由于石墨烯条和 石墨烯半圆环之间发生相互 作用,产生较弱的杂化,从而可以观察到EIT透明窗口。更重要的是,通过控制门电压,改 变石墨烯的费米能级,可以 在较宽的频率范围内实现透明窗口的动态调谐。通过调节石墨烯的费米能级,在透射峰附近 群延迟接近0.4ps。同时还研 究了石墨烯条和半圆环间的距离、圆环的半径、方位角等几何参数对EIT效应的影响,这些 因素的改变对EIT 效应产生 了不同的影响。本文设计的超材料结构可应用于调制器和慢光器件等,对光开关、光存储等 新型器件的设计有重要的指导意义。     

Tunable OTDR Based on Direct Modulation of Self-Injection-Locked RSOA for In-Service Monitoring of WDM-PON

We propose a tunable optical time-domain reflectometer (OTDR) for in-service monitoring of wavelength- division- multiplexing passive optical networks (WDM-PONs). The proposed method uses a reflective semiconductor optical amplifier, which is self-injection-locked by a tunable fiber Bragg grating. The proposed tunable OTDR has a tuning range of 30 nm and a resolution of 50 m. The performance of the proposed scheme is experimentally evaluated to demonstrate the in-service monitoring of WDM-PON.     

Highly Sensitive Mechanoresponsive Smart Windows Driven by Shear Strain

Advanced optical materials with rational designs and tunable light transmission have been drawing increasing interest due to their great potential in energy-efficient buildings and on-demand optical devices. Mechanoresponsive smart windows (SWs) can modulate light transmittance by mechanical actuation, showing high energy efficiency, low cost, and chemical stability. However, current research mainly focuses on tensile strain-responsive SWs that typically require a large strain to achieve optical transparency switching-which causes great inconvenience to practical application and fatigue damage to matrix materials. Herein, a novel shear-responsive SW with high strain sensitivity is fabricated by vertically fixing a Fe₃O₄@SiO₂ nanochains (NCs) array in an elastic polyacrylamide matrix. The flexible SW exhibits optically transparent with all NCs standing vertically to the SW surface at initial relaxation state, which enables a good shielding effect, with NCs tilting along the shearing direction as the strain applied. Critically, a rather small shear displacement (1.5 mm) applied on the surface of SW gives rise to tunable optical states varying from the transparency state of 65% transmittance to the opaque state of 10%. The as-prepared SW with novel tuning modulation, high shear strain sensitivity, and optical angle-dependence holds promising potential in smart windows, optical switches, anti-voyeurism, and etc.     

Design and Simulation of a Narrow Passband Electro-Optical Tunable Filter with Band-pass and Band-rejection Output

An electro-optical tunable filter comprised of two paralleled identical long-period waveguide gratings is proposed in this paper. The filter has one input port and two separate output ports, outputting band-pass and band-rejection light respectively. Using poled electro-optical polymer material to fabricate its waveguide cores enable the filter’s tuning speed to approach nanosecond order. With the aid of long-period waveguide gratings, the tuning range of the filter is Λ times larger than the conventional electro-optical filters. We built up a model to design and simulate the proposed tunable optical filter. We investigate the relationship between the parameters of the long-period waveguide grating and the characteristics of the tunable filter, such as tuning range and FWHM. The simulation results show that the tunable optical filter can realize high-speed tuning in the wavelength range of 1530 nm to 1560 nm, and the FWHM width can reach 0.8 nm. Compared with the conventional optical filters, the results show that a high-speed widely tunable optical filter with narrow pass band can be achieved.     

Optical cross-connect system in broad-band networks: system conceptand demonstrators description

A network robust to future evolution in network topologies or transmission formats and bit rates, which would be achieved by introducing an all-optical transparent layer in the transport network hierarchy is considered. The transparency would permit use of physically common fiber lines and nodes for different transmission hierarchies and/or formats. A transparent network could be achieved by combining photonic switching with electronic switching technology in the network nodes. A combination of wavelength routing and space-division switching in the optical layer would increase the capacity, as well as the flexibility in a network, allowing routing with higher granularity within the optical layer. Two optical cross-connect demonstrators have been set up. One demonstrates protection switching and restoration of traffic in a future transport network, and the other demonstrates routing of subscriber signals to different service switches in a local exchange. Space switches, tunable lasers and filters are the key technologies used to obtain enhanced flexibility     

连续可调光延迟线技术研究

光延迟线在雷达技术、全光信号处理、光通信等领域中有着广泛的用途,但是目前通用的可调光延迟线是增量可调而非连续可调的.连续可调技术大大提高了延迟精度,代表了光延迟线的发展方向.因此介绍了几种连续调谐光信号时延技术,具体分析了它们的实现原理和特点.     

Return-to-zero modulation with electrically continuously tunable duty cycle using single NRZ modulator

Two optical return-to-zero (RZ) modulation techniques are discussed, both based on a single Mach-Zehnder modulator driven by non-return-to-zero (NRZ) electrical signals. Both methods allow for continuously electrically tunable duty cycles and lead to chirped RZ formats. We demonstrate and discuss two RZ transmitter setups that generate optical RZ signals with electrically continuously tunable duty cycle using a single, NRZ-driven Mach-Zehnder modulator.     

可调谐激光器在光通信网络中的应用

可调谐激光器技术的日益成熟,使其在光通信网络中的应用逐渐增加。文中对可调谐激光器研究现状进行了探讨,并详细分析了MEMS可调谐激光器优势特点。同时,文中对可调谐激光器在无源光网络、光突发交换网络和光标记交换网络中的应用进行了重点阐述。并在文章最后对可调谐激光器的技术及在光通信网络中的应用前景进行了预测。     

Dynamically Tunable Laser Phase Noise Characterization and Use in a 10-Gb/s Optical Coherent Transmission System

Commercial dynamically tunable lasers (DTLs) for dense wavelength-division-multiplexing optical networks are integrated devices into a butterfly package. Thus, their dimensions are much smaller than standard external cavity tunable lasers. Despite the reduced size, they present unexpected low phase noise. In this letter, the DTL phase noise is fully characterized for real-time optical coherent communication applications by using a suitable measurement technique based on an optical phase-locked loop. We experimentally demonstrate that DTLs can be used in a 10-Gb/s binary phase-shift-keying coherent optical communication system based on a phase-locking technique and a decision-driven architecture.     

Novel kind of lyot birefringent tunable filters

The Lyot filter is a monocolour birefringent filterwhichis invented by the French physicist Lyot for theresearches of astronomy,especiallyfor observingthe so-lar corona.Becausethe birefringent filter can be designedof the special optical characters such a…     

Extremely fast high-gain and low-current SOA by optical speed-up at transparency

We propose a new configuration for semiconductor optical amplifiers (SOAs), called optical speed-up at transparency (OSAT), which allows to speed up the gain recovery of SOAs and their saturation power without sacrificing the gain, nor increasing the applied current. The proposed configuration is particularly well-suited for high-speed WDM or OTDM applications. It consists of an optical CW-signal injected at the transparency point of the SOA. This setup is potentially integrable on a single chip, and still relatively flexible once the device is realized.     

Diffractive Transmission Grating Tuned by Dielectric Elastomer Actuator

A technology for the implementation of electrically tunable optical elements is presented. We illustrate, on the example of a transmission grating (TG), that dielectric elastomer actuators can be used to continuously adjust the properties of diffractive optical elements. The demonstrated TG operates with high transmission, low optical distortion (93 kW/cm²), is polarization-independent, and achieves a very large tuning range (7.5% grating period compression). Extending the presented technology to other optical elements, including lenses, phase shifters, or intensity filters, is expected to result in a wide range of electrically tunable optical devices.     

Coherently tunable mid-infrared distributed feedback lasers

We propose utilization of quantum interference effects in quantum well structures to tune lasing wavelengths of mid-infrared distributed feedback lasers. The interference effects are generated via interaction of an intense laser field with an n-doped quantum well, causing coherent suppression or enhancement of refractive indexes of the conduction intersubband transitions. We show that these processes allow us to shift lasing wavelength to shorter or longer wavelengths by adjusting the intensity and frequency of the intense laser. This study is done for two types of lasers: 1) an electromagnetically induced distributed feedback intersubband laser formed by embedding a longitudinal corrugation of several periods of the quantum well structure within a waveguide structure and 2) a phase-shifted distributed feedback laser where the quantum well is inserted in the middle of an index grating, forming an active phase shift region. In the former the intense laser field is responsible for generation of optical feedback while shifting the coherently induced stop-band. In the latter, however, this field changes the optical length of the phase shift region, tuning the lasing mode within the stop-band. We show that the amount of the wavelength shift, which can reach 17 nm, is controlled by the intensity of the intense laser. The sign of the tuning process (red or blue shift), however, is decided by the frequency of this field, after proper choice of the corrugation periods. We investigate the optical feedback mechanisms in such coherently tunable lasers and discuss how they are related to an electromagnetically induced transparency process that happens in the conduction intersubband transitions.     

High-speed wavelength tunable liquid crystal filter

We describe the first high-speed, continuously tunable liquid crystal optical filter suitable for wavelength division multiaccess (WDMA) optical networks. The filter utilizes chiral smectic A* electroclinic liquid crystal as the active cavity material in a Fabry-Perot etalon to obtain microsecond switching speed. Using the commercially available BDH764E liquid crystal material, we demonstrate a tunable optical filter with a switching speed of less than 10 μs and a tuning range of approximately 30 nm, when the filter passband is centered at 1.55 μm     

Widely tunable bottom-emitting vertical-cavity SOAs

We present bottom-emitting tunable vertical-cavity semiconductor optical amplifiers (VCSOAs) with an effective wavelength tuning range of >20 nm. These devices utilize a high reflectivity micromechanically tunable Bragg mirror as the back reflector. Compared with our first generation tunable VCSOAs, the bottom-emitting devices exhibit a two-fold increase in the effective tuning range as well as a five-fold reduction in the required tuning voltage.     

可调谐滤波器在DWDM系统中的应用

可调谐滤波器是实现未来全光网络的重要器件,在DWDM系统中有着广泛应用.文章介绍了几种常用的可调谐滤波器的原理、最新研究及其在可重构光分插复用和光传输性能监测中的应用.     

An Automatic Wavelength Control Method of a Tunable Laser for a WDM-PON

We propose a novel automatic wavelength control method of a tunable laser for a wavelength-division-multiplexed passive optical network (WDM-PON). By sending a low-power amplified spontaneous emission light generated from a broadband light source (BLS) to a tunable laser through a wavelength-division multiplexer, we match the wavelength of the tunable laser to a peak transmission wavelength of the multiplexer. The deviation of the wavelength of the tunable laser was less than 0.05 nm from the center of the target channel. We demonstrate up to 10-Gb/s transmission in a WDM-PON by using the proposed method. We also show that system impairments induced by the BLS are negligible.      

Tunable Super-Structured Fiber Bragg Gratings with Perfect Sequences Based on m-Sequence

Recently, a tunable fiber Bragg grating (FBG) was developed by using stress-responsive colloidal crystals. In this paper, we have simulated the application of these nanoparticles into the super-structured fiber Bragg grating (SSFBG) written with perfect sequences derived from a short maximal-length sequence. A tunable SSFBG will be available to overcome the prohibitive temperature variation of the optical codecs. Nevertheless, we presented a method to implement coherent time spreading optical code-division multiple-access (OCDMA) where a unique code (or perfect sequence) can be reused and mixed with different wavelengths to obtain a tunable wavelength-division multiplexing (WDM) system. In order to maximize the binary throughput, we have selected a unique short maximal-length sequence composed of 7 chips that can be tuned with 7 different optical wavelengths. We found thousands of different tunable combinations that presented power contrast ratios (P/C) higher than 12 dB. When a WDM-OCDMA system used 2 different combinations simultaneously, the perfect binary detection with error correction codes was achieved successfully. The tunable SSFBG with colloidal crystals will be a simple and good alternative choice for fiber-to-the-home (FTTH) communications.