Linewidth of SG-DBR laser and its effect on DPSK transmission

In this paper the linewidth of widely tunable SG-DBR lasers has been investigated theoretically and experimentally. We demonstrate experimentally the importance of obtaining low linewidth operation for the application of SG-DBR laser with advanced modulation format transmission. This is achieved by choosing two sets of tuning currents for an SG-DBR laser that give the same wavelength channel and good SMSR, but different linewidths. When the laser is employed in a DPSK system only the operating point (the set of drive currents used to obtain specific output characteristics) that portrays low linewidth achieves error free transmission. This work shows that although calibration of tunable lasers is normally based on achieving sufficient SMSR and output power, it will be important to consider the linewidth parameter as these lasers begin to be used in more spectrally efficient WDM systems employing advanced modulation formats. The simulation results illustrate that the operating points which achieve narrow linewidth are correlated with those that exhibit low threshold current. This finding may be used for calibration of SG-DBR lasers to achieve minimum linewidth at each operating wavelength.     

Static and dynamic analysis of side-mode suppression of widely tunable sampled grating DBR (SG-DBR) lasers

Side-mode suppression is an important issue for widely tunable laser design and applications. In this paper, we have developed a relatively simple algorithm to analyze side-mode suppression of widely tunable sampled grating distributed Bragg reflector (SG-DBR) lasers by using the Transfer Matrix Method (TMM) in combination with multimode rate equations. The dependence of gain spectrum on wavelength is also included in this model, and its effects on tuning characteristics of the devices are investigated for the first time. Static tuning characteristics and dynamic behaviors of wavelength switching are simulated. Results agree well with the experimental results reported.     

Impact of tunable laser wavelength drift in a base-band and sub-carrier multiplexed system

The potential use of very densely spaced wavelengths in FTTx systems to carry modest bit rate broadband connections can be implemented either with conventional base-band (BB) intensity modulation or using sub-carrier multiplexing (SCM) using Radio carriers. Such systems will typically use a long time frame time-sharing system to share a transmitting laser between a number of users. The impact of the adjacent channel interference due to wavelength drift of a tunable laser (TL) in such a system has been characterised for both the BB and SCM approaches. In the experiments described, a laser operating on a fixed wavelength represents the desired channel and an interferer is produced by using a TL that switches periodically between two other channels, one of which is adjacent to the desired channel. Although the TL output is blanked during the main switching transient, some wavelength drift occurs after the end of the blanking period which can cause interference to the adjacent channel. The BER measurements on the desired channel show that SCM is more resistant to this interference, allowing for closer channel spacing. For the TL tested, the BB data shows an error floor >1e?4 while the SCM data gave error free performance with a power penalty of ～1.2 dB at 1e?9 in comparison to the back-to-back case.     

SG-DBR半导体激光器的光谱技术研究

可调谐半导体激光吸收光谱作为一种高灵敏度、高选择性、非侵入的痕量气体实时检测技术,已在大气监测、工业控制等方面得到广泛应用。采用一种新型宽带可调谐的SG-DBR半导体激光器(可调谐范围1 520~1 570 nm)作光源,并通过自编程序对该激光器设定了18个通道,输出波长分别对应CO,CO₂以及H₂O的吸收谱线中心位置,设计和构建了一个基于近红外可调谐半导体激光吸收光谱的多组分气体光谱测量系统,描述了相关的光学系统设置,结合波长调制(wm)的二次谐波技术测量其中14个通道(分别对应CO和CO₂的吸收谱线)的吸收光谱,系统获得的CO和CO₂峰值吸收探测极限能够达到10-5。实验结果验证了SG-DBR激光器在波长调制吸收光谱多组分气体检测领域的可行性。在实际应用过程中使用单个SG-DBR激光器可以实现多组分气体的同时测量,有效降低设备成本和系统复杂性。     

High-density wavelength switching obtained from a tunable multisection laser diode

We describe a method based on multistability in wavelength for obtaining high-density wavelength switching for application to signal routing. The method relies on the use of a 1550-nm wavelength-tunable multielectrode laser diode that is fed back electrically. The system operates as a multistable device that exhibits multiple steady states in wavelength. The device can be used to convert time-multiplexed packets into wavelength-multiplexed signals.     

Static and dynamic routing and wavelength assignment algorithms for future transport networks

In this paper, two static and three dynamic routing algorithms have been proposed and compared to some of the existing algorithms on the basis of blocking probability. The two proposed static routing and wavelength assignment (RWA) algorithms reduce the blocking probability to maximize the utilization of network. For dynamic algorithms, first a model with no weights assignments is presented and then three algorithms are proposed and analysed with weight assignment resulting in reduction of blocking probability. All these algorithms are analysed and compared with four wavelength assignment schemes which are first-fit, random, most used and least used. It is shown that our proposed static algorithms give the best performance for first-fit wavelength assignment and most used wavelength assignment strategies with reduced complexity. For least used wavelength assignment and random wavelength assignment, 1 fixed and 2 alternate routing algorithm gives the lowest blocking probability. For dynamic routing, it has been shown that our proposed algorithm “less weight to maximum empty and nearest” gives the least blocking probability as compared to the other dynamic routing algorithms for random, most used and least used wavelength assignment strategies.     

Delay-constrained anycast routing problem in WDM networks with wavelength conversions

Anycast routing and wavelength assignment problem has been intensively studied in wavelength-division multiplexing (WDM) networks, however, real-time application where packets have explicit expiration deadlines is not taken into consideration. In a WDM network, each link is associated with limited wavelengths available for channel connections. Data transmission over one wavelength to another requires wavelength conversion, which causes a long delay of message transmission. When the network and the set of anycast routing requests are given, the delay-constrained wavelength conversions anycast routing (DWCAR) problem is to find a set of light-paths, one for each source, for anycasting message to one member of the anycast destination group. The objective is to find a minimum number of wavelength conversions with the constraint that the sum of delays along every path must not exceed a given delay-bound. In this paper, we present a Tabu-search based delay-constrained anycast routing algorithm (TSDA) to solve this NP-complete problem, and compare it to a simple K shortest path based anycast algorithm (KSPA). Simulation results show TSDA achieves an average 40–50% improvement in required wavelength conversions.     

Cross-channel interference due to wavelength switching events in wavelength packed switched WDM networks

An important characteristic of tunable lasers, that may affect system performance, is that they can generate light at various wavelengths as they tune between different wavelength channels. These spurious components could cause severe cross-channel interference if the tunable laser is used in a WDM network. In this paper, we investigate the effect of such interfering signals, generated by up to three tunable lasers during a switching event, on the BER of a data channel transmitted on the same wavelength as the spurious components. The results show that it is vital to attenuate the output of tunable lasers during their wavelength transition in order to prevent system performance degradation.     

基于光注入Fabry-Perot半导体激光器实现同步全光分路时钟提取与波长转换

提出了一种利用Fabry-Perot（FP）半导体激光器同步提取波长转换的分路光时钟的新方法,并对该方法进行了数值模拟和实验验证.光注入半导体激光器会产生非线性单周期振荡特性,利用交叉增益调制效应及对单周期振荡的微波锁频效应,可从光时分复用信号中提取出波长转换的分路光时钟.采用一个FP半导体激光器作为全光分路时钟提取及波长转换器,数值模拟实现了从波长为1555 nm、速率为2×20 Gb/s的光时分复用信号中提取出波长转换为1550 nm、重复频率为20 GHz的分路光时钟,实验完成了从波长为155024 nm、重复频率为1236 GHz光脉冲信号中提取出相位噪声为-105 dBc/Hz的波长为154591 nm、重复频率618 GHz的分频光时钟.此外还详细研究了注入光功率、波长失谐、FP激光器偏置电流及纵模选择对光时钟提取的影响,实验结果和数值模拟结果符合.该方法在光时分复用混合波分复用通信系统中实现全光解复用及波长路由有着重要的应用价值. 关键词： 波长转换 时钟提取 光注入 非线性动力学     

Four-wave mixing in dual wavelength fiber laser utilizing SOA for wavelength conversion

In this paper, a novel configuration of a wavelength converter is set forth by utilizing a semiconductor optical amplifier (SOA) as a nonlinear gain medium to generate a four-wave mixing (FWM) effect by using a dual wavelength bi-erbium-doped fiber laser that uses an Arrayed Waveguide Grating (AWG) together with two optical channel selector (OSC) as selective elements to function as a dual wavelength switchable pump power. The four-wave mixing (FWM) is produced with a wavelength detuning of 7 nm from the pump and signal which used is as the converted signal at wavelength 1532.8 nm or 1534.5 nm for transferring data from the input signal at wavelength 1547.0 nm. Thus, even though the conversion efficiency is as low as −43 dB, it is still possible for applications as a wavelength converter.     

Routing and wavelength assignment algorithms for multiclass WDM optical networks

In this paper dynamic routing and wavelength assignment strategies have been proposed for multiclass WDM optical networks. Multiclass optical networks provide multiple classes of services to the subscriber according to the requirement, which in turn increase operational profitability. Each class of service could be characterized by parameters like number of wavelengths, expected call holding time and average arrival rate of request. The proposed strategies have been analyzed and compared with existing strategies on the basis of blocking probabilities for multiclass traffic scenarios. Simulation results on different network topologies demonstrate that the performance of proposed strategies “Fixed shortest/alternate shortest path routing with wavelength reservation (FSASWR)” and “Fixed alternate shortest path routing with least priority wavelength assignment (FASPL)” are much better as compared to existing strategies. Proposed strategies minimize blocking probability of the multiclass network using limited number of wavelengths.     

High-Speed Optical Packet Switch with an Optical Digital-to-Analog Conversion-Type Header Processor

We describe a novel type of an optical packet switch with an optical header processor based on optical signal processing and wavelength routing architecture. It consists of an optical digital-to-analog conversion-type header processor, wavelength selection portion with an electrically tunable laser, a wavelength converter based on a semiconductor optical amplifier (SOA), and wavelength routing by use of an arrayed waveguide grating (AWG), which is called a wavelength label switch (WLS). Wavelength switching of an electrically tunable laser, and wavelength conversion were successfully achieved within a few nanoseconds after recognition of an optical header using a two-bit optical header processor and a FPGA-based wavelength table. High-speed transfer performance of less than a few tens of nanoseconds and BER of less than 10^-10 were verified in the wavelength routing operation among three assigned wavelengths.     

Routing and wavelength assignment in WDM networks with dynamic link weight assignment

We consider the routing and wavelength assignment problem on wavelength division multiplexing networks without wavelength conversion. When the physical network and required connections are given, routing and wavelength assignment (RWA) is the problem to select a suitable path and wavelength among the many possible choices for each connection such that no two paths using the same wavelength pass through the same link. In wavelength division multiplexing (WDM) optical networks, there is need to maximize the number of connections established and to minimize the blocking probability using limited resources. In this paper, we have proposed three dynamic link weight assignment strategies that change the link weight according to the traffic. The performance of the existing trend and the proposed strategies is shown in terms of blocking probability. The simulation results show that all the proposed strategies perform better than the existing trend.     

Digital wavelength switching by thermal and carrier injection effects in V-coupled cavity semiconductor laser

Consecutive wavelength switching characteristics of a simple, compact, and digitally wavelength-switchable laser based on V-coupled cavities are reported. Wavelength switching through thermal and carrier injection effects is examined. Without using band gap engineering for the tuning section, 26- and 9-channel wavelength switching schemes are achieved via thermal and carrier injection effects, respectively. The performances of these two tuning schemes are then compared.     

Low crosstalk monolithic wavelength demultiplexing switch arrays

Wavelength Division Multiplexing (WDM) is a key enabling technology for increasing the transmission capacity of optical fiber communication systems. Recently, a new family of optoelectronic devices, including detectors, switches, and emitters, that is based on resonant cavity enhancement, has emerged. Wavelength selective optoelectronic switching is achieved by placing a photothyristor in an asymmetric Fabry-Perot cavity, which provides a highly selective response at a wavelength determined during device fabrication. These WDM optoelectronic devices haue promising applications in optical COmmunications and optical logic circuits. Results on a N-p-n-p optoelectronic switch with a ten wavelength channel capability are presented.     

Dynamic strain monitoring by wavelength locking between two fiber Bragg gratings fiber sensing system

We demonstrated a fiber sensing system using the method of wavelength locking of two identical fibers Bragg gratings (FBG) to interrogate the wavelength shift by directly measuring the intensity of the reflection from the sensing Bragg grating. The light source of the fiber sensing system is an EDFA fiber ring laser pumped by a 980 nm laser diode and a narrow bandwidth fiber Bragg grating for the filter of the ring laser resonator. The wavelength shift is converted to the intensity deviation of the reflection from the sensing FBG under strain variation, and is able to achieve real-time sensing of the dynamic strain sensing in civil engineering. The characteristics and key factors to maintain stability of the dynamic strain sensing system are discussed.     

Analysis of Doppler-effect on satellite constellations with wavelength division multiplexing architectures

With the development of optical space communications, a global space-based optical backbone network is currently proposed by using broadband laser inter-satellite links （ISLs） which enable routing traffic through the space. Satellite optical networking techniques based on wavelength division multiplexing （WDM） ISLs can transit significantly high data rates signals. In this letter, a new function of wavelength excursion due to Doppler-effect is developed for the ISLs, considering the conception of pointing ahead mechanism. The characteristic of wavelength excursion induced by Doppler-effect is examined in one of low earth orbit （LEO） satellite constellation networks named the next-generation LEO system （NeLS） with WDM ISLs assumed, and the influence on its communications caused by wavelength excursion is analyzed.     

Flat and compact switchable dual wavelength output at 1060 nm from ytterbium doped fiber laser with an AWG as a wavelength selector

A dual-wavelength ytterbium doped fiber laser with a narrowest spacing of 0.53 nm and widest spacing of 12.2 nm at 1064 nm is presented in this paper. An arrayed waveguide grating (AWG) together with an optical channel selector (OCS) have also been incorporated in the proposed setup that works as a switchable mechanism giving 23 different wavelength tunings. Producing an average output power of ?8 dB m and side mode suppression ratio (SMSR) of 59.65 dB, this dual-wavelength fiber laser is quite stable with an output power variance as low as 0.47 dB giving it an advantage due to its switching ability and stable dual-wavelength output powers.     

基于双通构型的和频、差频可变波长路由方案及其应用

提出了双通构型的基于“和频”和“差频”级联二阶非线性效应的可变波长路由方案,通过调节两个抽运源的频率,可以从一个WDM(wavelength division multiplexing)链路中取出任意一个信道,然后将其转换为任意一个波长并插入到另一个WDM链路中去.实现了可调谐波长转换和光波长路由的结合.通过小信号分析,给出了相位匹配情况下,输入信号光在波导中功率变化的表达式和输出转换光功率变化的表达式,并给出了提高系统效率的对两个抽运光功率的优化方案.数值计算表明,只要信道间隔大于02nm(25GHz 关键词： 光波长路由 光波长转换 光交换 PPLN     

Analysis of Doppler-effeet on satellite constellations with wavelength division multiplexing architectures

With the development of optical space communications, a global space-based optical backbone network is currently proposed by using broadband laser inter-satellite links (ISLs) which enable routing traffic through the space. Satellite optical networking techniques based on wavelength division multiplexing (WDM) ISLs can transit significantly high data rates signals. In this letter, a new function of wavelength excursion due to Doppler-effect is developed for the ISLs, considering the conception of pointing ahead mechanism. The characteristic of wavelength excursion induced by Doppler-effect is examined in one of low earth orbit (LEO) satellite constellation networks named the next-generation LEO system (NeLS) with WDM ISLs assumed, and the influence on its communications caused by wavelength excursion is analyzed.