A tunable dual-wavelength erbium-doped fiber ring laser using a self-seeded Fabry-Perot laser diode

A tunable dual-wavelength erbium-doped fiber ring laser using a self-seeded Fabry-Perot laser diode (FP-LD) is proposed and demonstrated. By adding an FP-LD incorporated with a tunable bandpass filter within the ring cavity, the fiber laser can lase two wavelengths simultaneously because of the self-seeded mechanism. This dual-wavelength output exhibits a good performance having the optical side-mode suppression ratio over 31 dB. The wavelength-tuning range of this tunable dual-wavelength fiber laser can be up to 9 nm.     

二维空频域光码分多址编解码方法

以哈达玛(Hadamard)矩阵为基础,给出一种二维空间相位码的编码方法,分析它的各种性能,并用这种二维空间相位码作为用户的地址码,构成一种新的空间-相位码分多址系统,使光码分多址编解码在空频域内进行,由于对空频域内的信息只作相位调制,大大提高了光传递效率。     

Three-dimensional encoding/two-dimensional decoding of medical data

We propose a fully three-dimensional (3-D) wavelet-based coding system featuring 3-D encoding/two-dimensional (2-D) decoding functionalities. A fully 3-D transform is combined with context adaptive arithmetic coding; 2-D decoding is enabled by encoding every 2-D subband image independently. The system allows a finely graded up to lossless quality scalability on any 2-D image of the dataset. Fast access to 2-D images is obtained by decoding only the corresponding information thus avoiding the reconstruction of the entire volume. The performance has been evaluated on a set of volumetric data and compared to that provided by other 3-D as well as 2-D coding systems. Results show a substantial improvement in coding efficiency (up to 33%) on volumes featuring good correlation properties along the z axis. Even though we did not address the complexity issue, we expect a decoding time of the order of one second/image after optimization. In summary, the proposed 3-D/2-D multidimensional layered zero coding system provides the improvement in compression efficiency attainable with 3-D systems without sacrificing the effectiveness in accessing the single images characteristic of 2-D ones.     

Differential absorption measurement by use of self-seeded gain-switched Fabry-Perot laser diode

Differential absorption measurement for acetylene has been carried out by the use of a self-seeded, gain-switched Fabry-Perot (FP) laser diode. During the measurement, the two wavelengths from the laser output can be conveniently selected by switching the repetition frequency The system has flexible wavelength tunability, larger sensitivity than those based on DFBs, and high potential for multipoint, multiple gas sensing.     

Optimized operation of self-seeded gain-switched laser diode forelectrically wavelength-tunable singlemode pulses

A gain-switched Fabry-Perot laser diode at 1.3 μm was self-seeded at different electrical bias and optical feedback rates. With a strong feedback, a comparatively large tuning range and a high sidemode suppression ratio were obtained but multimode emission might occur around the center of the range. Similar phenomenon was observed at a weaker feedback when the electrical bias was sufficiently large. The degradation in tunability was attributed to a broadening of the optical pulses, resulting in temporal overlapping of different longitudinal modes. Our optimized feedback of 2.5% and 3.1 mA bias provided a tuning range of 23.5 nm with a sidemode suppression ratio >10 dB     

Effective generation of tunable single- and multiwavelength optical pulses from a Fabry-Perot laser diode

A tunable pulse source capable of both single- and multiwavelength oscillations has been developed by self-injection seeding of a laser diode. A side-mode-suppression ratio (SMSR) of about 20 dB has been obtained in the outputs. The key element in our setup is a wavelength multiplying stage consisting simply of 50/50 beam splitters, a diffraction grating, and a mirror. The maximum number of available wavelengths increases rapidly with the beam splitters. Our scheme can be adopted for use in high-speed wavelength switching.     

Dynamics of single-mode formation in self-seeded Fabry-Perot laserdiodes

We obtain single-mode picosecond pulses with a tuning range of more than 40 nm by self-seeding of a standard gain-switched Fabry-Perot laser diode. The switch-on behavior is investigated experimentally and numerically for the first time. Stable single-mode operation is reached after ⩽5 round-trips, which shows the potential for extremely fast wavelength tuning     

A dual-function mixed-signal circuit for LDPC encoding/decoding

We present a low power, dual-function encode/decode circuit for a class of reversible low-density parity-check codes. The circuit offers a small silicon footprint, by operating as an analog decoder and reusing resources to switch into a digital encode mode. In order to achieve this behaviour from a single circuit we have developed mode-switching gates. These logic gates are able to switch between analog (soft) and digital (hard) computation. Only a small overhead in circuit area is required to transform the analog decoder into a full codec. The encode operation can be performed two orders of magnitude faster than the decode operation, making the circuit suitable for full-duplex applications. The low power and small area of the circuit make it an attractive option for battery powered wireless devices. Circuit simulations indicate a decoding latency of with negligible SNR loss with respect to digital sum-product decoders.     

A self-seeded reflective SOA-based optical network unit for optical beat interference robust WDM/SCM-PON link

We have proposed and experimentally demonstrated a novel optical source configuration that uses a self-seeded reflective semiconductor optical amplifier (RSOA) as an optical network unit (ONU) in a wavelength division multiplexed/subcarrier multiplexing (SCM)-passive optical network (PON). A fiber Bragg grating (FBG) was used to obtain a single longitudinal mode of the RSOA. The proposed ONU configuration is simple, cost-effective, and effective regardless of wavelength allocation. Additionally, it would be robust for optical beat interference (OBI) noise. As the ONU is composed only of an RSOA and FBG, the self-seeded RSOA, due to the strong self-injection caused by the reflection of the FBG, has a broad optical spectrum. A self-homodyne apparatus method was performed in order to demonstrate the robustness of the self-seeded RSOA in OBI. To confirm the validity of the proposed scheme, a 16-quadrature amplitude modulation transmission experiment was performed in a 10-, 20-km optical access link with an SCM frequency of 1 GHz. An error vector magnitude of less than 4% for 2 Msps was successfully obtained through the transmission experiment.     

液晶电视用作图像编/解码实时光学相关滤波器

文章介绍了一种一维光学相关器,在其傅里叶平面内,将液晶电视（ Ｌ Ｃ Ｔ Ｖ） 编码成单极二元纯位相滤波器用于图像实时编码或解码。给出了初步光学实验结果     

一种新的二维OCDMA编解码方案

介绍了一种在哈达玛(Hadamard)矩阵基础上构造二维空间相位码的方法，分析它的各种性能，找到了在空频域内仅对信息相位编解码时所需要的二维光正交码，给出二维空频域光码分多址编解码的方案。     

Multi-dimensional encoding and decoding for high capacity optical communication using OCDMA

Photonic Network Communications - This paper describes a novel multi-dimensional OCDMA coding technique with the objective of enhancing capacity of the optical communication network. In order to...     

Phase encoding and decoding of short pulses at 10 Gb/s usingsuperstructured fiber Bragg gratings

A 7-chip, 160-Gchip/s phase-shift keyed code is assigned to short pulses after reflection from a superstructured fiber Bragg grating. The code is then recognized by a second grating, which is nominally identical to the encoder grating. Such an encoding/decoding action is required in code-division multiple-access systems and packet-switched networks     

光编解码系统实验研究

对光编解码系统进行了实验研究,数据速率2.5Gb/s,主动锁模光纤激光器提供247fs的超短光脉冲作为码片源,码片速率>640Gb/S,采用光正交码(码长511)和时域光编解码,实验结果显示,此系统具有好的光编解码性能,为OCDMA系统提供了有效、实用的技术方案,并展示出光明的应用前景.     

Block encoding and decoding for the optical PPM channel (Corresp.)

Pulse position modulation (PPM) is a popular signaling format in pulsed optical communication links. PPM encoding is extended to include block pulse encoding over multiple PPM frames. Maximum likelihood decoding operations associated with this encoding are developed for both shot-noise limited and thermal-noise limited optical receiver models. Both ideal (Poisson) and avalanche photodetectors are considered, and it is shown that optimal block decoders involve combinations of linear and quadratic operations. Error probability bounds are presented, showing the relative improvement in detectability that appears possible by resorting to block encoding over multiple frames.     

Self-seeding of Fabry-Perot laser diode for generating wavelength-tunable chirp-compensated single-mode pulses with high-sidemode suppression ratio

We report an effective technique for generating wavelength-tunable chirp-compensated single-mode pulses with a high sidemode suppression ratio (SMSR) based on self-seeding a Fabry-Perot laser diode. This technique relies on the use of a tunable linearly-chirped fiber Bragg grating to provide wavelength-selective feedback, output filtering, and chirp compensation. With this technique, we have generated chirp-compensated picosecond pulses with a SMSR higher than 40 dB over a tuning range of 11.5 nm.     

Effects of message encoding and decoding on synchronized chaotic optical communications

Chaotic optical communication at 2.5 Gb/s is experimentally investigated using three major encoding and decoding schemes, namely chaos shift keying (CSK), chaos masking (CMS), and additive chaos modulation (ACM). The effects of message encoding and decoding on the chaotic dynamics, the chaos synchronization, and the chaotic communication performance are compared among the three schemes. In the schemes of CSK and ACM, it is found that a small amount of message injected into the chaotic dynamics can increase the complexity of the chaotic state dramatically. In the CMS scheme, the chaotic dynamics are found not to be influenced by the encoded message. The synchronization quality deteriorates dramatically with an increase in the message strength in CSK and CMS. The ACM scheme is found to have the best synchronization quality among the three schemes when there is an encoded message. Message recovery is demonstrated for each of the three schemes. The ACM scheme is found to have the best communication performance.     

Time-resolved chirp evaluations of Gbit/s NRZ and gain-switched DFB laser pulses using narrowband Fabry-Perot spectrometer

A compact, easy-to-use, low-cost spectrometer for solving the chirped spectrum of DFB lasers is demonstrated using narrowband Fabry-Perot etalons with resolutions comparable to grating spectrometers. Time-resolved chirp measurements of Gbit/s NRZ and gain-switched DFB laser pulses are presented.<>     

二维激光告警光学系统设计

由于现有单激光告警系统只能实现来袭激光一维的方位和波长等信息,提出了一种单激光告警系统同时测得二维方位信息和波长信息的新方法,该方法的光学系统主要由遮光罩、光栅、透镜组和面阵CCD组成,通过对来袭激光经过光栅后的一级和零级衍射光斑位置的判决,得到来袭激光二维方位和波长信息。通过理论分析说明了该方法的原理,并推导得出二维方位角和波长的测量公式,根据要求推导确定了光学元件参数,并通过实验验证了其可行性。实验结果显示波长分辨率小于10 nm,角度分辨率小于1x方向视场角为30,y方向视场角为15。     

Digital signal processors for decoding/encoding color TV signals

A set of video signal processor VLSIs has been developed using 2-/spl mu/m p-well CMOS technology. These VLSIs perform bidirectional transformation between NTSC (National Television System Committee) composite video signals and component video signals, both of which contain luminance signals and two kinds of color signals. A special circuit configuration is used for the line memory, and an automatic layout program for uniformly structured circuits is developed for the layout design of the digital filters. A design effort of only 12 man-months, which includes logic, circuit, and layout design, is required for each VLSI using CAD systems. These VLSIs have proved effective in reducing the cost of video signal transmission systems.