The effect of chirping-induced pulse shaping on the performance of11 Gbit/s lightwave systems

The influence of laser chirping, fiber chromatic dispersion, and receiver filtering on the shape of the pulses in 11 Gb/s lightwave transmission systems is discussed. Both the NRZ and RZ encoding formats are considered as well as positive and negative dispersion. The results quantify the sensitivity of the system performance to the receiver decision time, the maximum permissible deviation of the laser wavelength from the fiber zero dispersion wavelength, and the improvement in transmission performance offered by pulse compression arising from negative dispersion     

Chirping-induced waveform distortion in 2.4-Gb/s lightwavetransmission systems

The performance of high-speed lightwave transmission systems operating in the 1.55-μm-wavelength region with conventional single-mode optical fiber can be influenced by the dynamic wavelength chirping exhibited by directly modulated semiconductor lasers. In a recent paper (1989), the authors presented the first detailed analysis of the bit error ratio performance of lightwave systems influenced by chirping-induced waveform distortion. Here, additional numerical results which address the performance implications of the waveform distortion by considering the dependence of the receiver sensitivity on the decision time and decision threshold, the eye pattern, and bit error rate ratio pattern are presented. It is shown that the response of the linear receiver filter can influence the dependence of the receiver sensitivity on the decision time     

Effects of intermodulation distortions due to the joint action ofdynamic chirping and “dispersive” transmission of SCMoptical signals

The effect of the joint action of the AM-FM conversion due to chirping in a semiconductor laser and the chromatic dispersion of the optical fiber has been so far analyzed in the case of static chirping in hybrid multichannel AM/QAM optical fiber transmission systems, based on subcarrier-multiplexing (SCM) technique. The static approach is not exhaustive in the case of channeling covering the whole bandwidth, that is ≈1 GHz, for which the dynamic chirping must be considered, as well. In this letter, analytical expressions of the power spectral density of the intermodulation distortions due to “dispersive” transmission of chirped intensity-modulated signals are calculated, considering both the static and the dynamic effects. As a consequence of this analysis, an accurate method for the determination of the small-signal photon decay rate Γ_P of the semiconductor laser is proposed, which is based on electrical measurements of the second-order intermodulation products     

单量子阱激光器小信号调制时的啁啾噪声

量子阱激光器具有良好的小信号调制频率响应 ,能作为高速光通信光源采用直接调制方式进行信号传输。与普通半导体激光器一样 ,直接调制将引起啁啾 ,从而影响光纤通信系统的性能。文中对小信号调制下单量子阱激光器的啁啾特性进行了研究和分析。得出了啁啾幅度和啁啾相位与调制频率的关系。对考虑与不考虑啁啾两种情况下 ,光脉冲在常规光纤中传输时的色散特性进行了模拟分析 ,发现了啁啾对系统的高阶色散有较大影响     

Effects of carrier transport on injection efficiency and wavelengthchirping in quantum-well lasers

Using the steady-state solution to the carrier transport rate equation model for the quantum-well laser that they had previously proposed, the authors derive analytic expressions for the laser internal efficiency, carrier injection efficiency, and wavelength chirping under current modulation and show that the various carrier transport times can have a significant effect on these quantities. They present experimental data and theoretical calculations that clearly demonstrate that, as in the case of device optimization for high-speed operation, one has to minimize the transport time across the optical and current confinement regions and maximize the escape time out of the quantum-well active region in order to maximize the internal and the injection efficiencies and minimize the wavelength chirping     

Theoretical study of frequency chirping and extinction ratio ofwavelength-converted optical signals by XGM and XPM using SOA's

We develop a complete large-signal dynamic model of semiconductor optical amplifier (SOA)-based wavelength converters using cross-gain modulation (XGM) and cross-phase modulation (XPM). The large-signal dynamic model has been implemented using the modified transfer matrix method (TMM). This model takes into account longitudinal variations of carrier-induced refractive index, n-parameter, internal reflection, photon density, and amplified spontaneous emission noise at each small section. Therefore, we can accurately estimate frequency chirping, optical pulse patterns, and the extinction ratio as well as the dynamic characteristics of SOA's. Frequency chirping and the extinction ratio have been calculated for various parameters such as signal power and wavelength, CW power and wavelength, and facet reflectivity. Modulation bandwidth, defined by the 3-dB drop as the eye opening ratio (EOR) is investigated with current density, confinement factor, and cavity length     

A new approach to an optical attenuator for a time compressionmultiplex system using a laser diode as both transmitter and receiver

A novel method of constructing an optical attenuator for a time compression multiplex system with a laser transceiver is proposed and investigated. The main purpose is to achieve wide dynamic range in a receiver. The transceiver consists of a laser diode backed by a photodiode. At average power levels, the laser diode is the main photodetector. At higher than average levels, the laser diode acts as an optical attenuator for the photodiode. The laser diode is called the laser attenuator (LATT). Basic properties of the proposed LATT, such as wavelength and polarization dependence, are clarified. The LATT is confirmed to have an optical dynamic range of over 37 dB     

Ultra-long-range OTDR in single-mode fibres at 1.3 ?m

A single-mode optical time-domain reflectometer (OTDR) operating at a wavelength of 1.3 ?m with a dynamic range in excess of 26 dB one way is reported. The equipment incorporates a semiconductor laser source and a new low-noise optical receiver design utilising a PIN diode detector and a transimpedance amplifier.     

窄带干涉滤波器与YAG调Q倍频激光器的匹配

在机载激光探测海底地貌系统中,窄带干涉滤光片与YAG调Q倍频激光器中心波长的匹配非常重要。介绍了一种滤波器与中心波长匹配的方法。利用这种方法,得到了机载激光测深的实验结果。     

Generation and cancellation of second-order harmonic distortion inanalog optical systems by interferometric FM-AM conversion

The generation of strong harmonic distortion from interferometric FM-AM conversion in analog lightwave systems is demonstrated both theoretically and experimentally. The effect results from the combined effects of wavelength chirping of the laser coupled with the nonlinear transmission characteristics of a dispersive element in the optical beam path. It is shown that reflections as small as 2-10^-4 will result in second-order distortion as large as -65 dBc. The effect can also be used to cancel any laser- or detector-induced harmonic distortion. In one example, the -36 dBc second-order distortion in a distributed-feedback (DFB) laser is improved to better than -70 dBc     

Generation of wavelength tunable gain-switched pulses from FP MQW lasers with external injection seeding

High-repetition rate (20 GHz), wavelength tunable (40 nm) optical pulses have been generated by gain switching of 1.55-/spl mu/m Fabry-Perot (FP) multiple-quantum-well (MQW) lasers using continuous-wave (CW) light injection for longitudinal mode selection. After fiber compression, a pulse duration shorter than 5.8 ps was obtained over the entire wavelength tuning range. The pulsewidth, chirping characteristics and side-mode suppression ratio were investigated as functions of the seeding power and wavelength. In addition, we report on the observation of chaos and period doubling for a gain-switched laser without injection seeding, and show that irregular behavior can be suppressed by injection seeding of the laser.     

Picosecond optical pulse compression from gain-switched 1.3 ?m distributed-feedback laser diode through highly dispersive single-mode fibre

The first demonstration to compress the linearly chirped optical pulses from a gain-switched distributed-feedback laser diode (DFB-LD) is described at 1.3 ?m wavelength. By travelling through a highly dispersive single-mode fibre with 48 ps/nm normal dispersion, a 26 ps (FWHM) pulse having red-shift frequency chirping of 85 GHz (FWHM) is compressed to 8.3 ps with the time-bandwidth product of 0.71.     

High-speed intensity modulation of 1.5 μm DBR lasers withwavelength tuning

Intensity modulation characteristics of a 1.5-μm butt-jointed DBR (distributed-Bragg-reflector) laser with wavelength tuning were studied. A 3-dB modulation bandwidth of 9 GHz and a high relaxation oscillation frequency of more than 10 GHz were obtained for the DBR laser. These characteristics were not affected by changing the lasing wavelength. The chirping width of the DBR laser is lower than that of the distributed feedback (DFB) laser. A clear eye opening and low chirping characteristics were obtained under 5-Gb/s nonreturn to zero (NRZ) pseudorandom modulation with a sufficient extinction ratio     

基于半导体光放大器交叉增益调制的全光波长变换器啁啾特性分析

本文分析了基于半导体光放大器，交叉增益调制机理的全光波长变换器转换信号啁啾随探测光功率的增加而减小的原因，给出了设计最佳全光波长变换器的方法。     

利用SOA交叉增益调制实现2.5 Gbit/s非归零码的全光波长变换

采用半导体光放大器 (SOA)的交叉增益调制进行了 2 5Gbit/s的非归零码光脉冲的波长变换。向下波长变换间距大于 2 0nm ,向上波长变换间距大于 10nm。对变换信号测量了接收机入纤功率和误码率的关系。实验中采用同向变换的方式 ,信号光中心波长固定 ,探测光采用外腔半导体激光器 ,中心波长连续可调。对变换信号进行了至少 1h的测量 ,误码为零。为其在波分复用(WDM)网络中的应用奠定了基础。     

Erbium-doped fiber amplifier second-order distortion in analog links and electronic compensation

The authors study the second-order distortion when an erbium-doped fiber amplifier (EDFA) is used to amplify the analog optical AM cable TV (CATV) multiple carrier signal from a directly modulated distributed feedback (DFB) semiconductor laser. Experimentally, it was seen that this second order distortion depends critically on the gain of the EDFA fiber amplifier. The authors attribute this distortion to the interaction between the frequency chirping of the DFB laser and the variable gain with wavelength of the amplifier. The authors describe an electronic predistorter that compensates the nonlinearity produced by the DFB-laser-EDFA combination. As a result, the high power advantage of the EDFA can be fully realized in spite of the potential for second-order distortion in the system.<>     

Static and dynamic characteristics analysis of all-opticalwavelength conversion using directionally coupled semiconductor opticalamplifiers

We analyze the wavelength-converting operation of directionally coupled semiconductor optical amplifiers (DCSOA's) with respect to their static and dynamic characteristics. A complete dynamic DCSOA model based on the modified time-dependent transfer-matrix method is developed. This model accurately considers longitudinal variations of carrier and photon densities, gain, refractive index, coupling coefficients, and lateral optical fields. The extinction ratio, modulation bandwidth, and frequency chirping of DCSOA-based wavelength converters are investigated. For most characteristics, the DCSOA scheme has advantages over cross-gain modulation. Furthermore, by optimizing the injection current into the DCSOA, even better performance can be attained     

Analysis of semiconductor intersectional waveguide opticalswitch-modulator

Transmission and reflection characteristics and wavelength chirping of a guided mode in a semiconductor intersectional optical switch-modulator are analyzed by considering the electric field-induced refractive index variation along with the absorption loss variation. The refractive index and absorption ratio, α¯_p, is shown to determine the performance of the switch-modulator. A transmission port is suitable for a modulation with a high extinction ratio, low insertion loss, and small wavelength chirping. The insertion loss at the reflection port depends heavily on α¯_p. A low insertion loss and high extinction ratio intersectional optical switch is possible when -α¯_p is higher than 10, which can be realized with a quantum box structure     

A 10-Gb/s Monolithically Integrated Filterless InGaAsP/InP Widely Tunable Wavelength Converter With Conversion Gain

In this paper, we present the details of a monolithically integrated filterless wavelength converter based on photocurrent-driven technology. The device consists of an integrated tunable laser transmitter and an optical receiver. The transmitter includes a sampled-grating distributed-Bragg-reflector laser, an electroabsorption modulator, and a semiconductor optical amplifier. The optical receiver employs two semiconductor optical amplifiers and a quantum-well p-i-n photodetector. The wavelength converter is characterized at 10 Gb/s over a variety of bias conditions at various input-power levels in various digital-system experiments. Bit-error-rate measurements at 10 Gb/s over an output tuning range of 32 nm between 1531 and 1563 nm show power penalties less than 1 dB. Similar experiments over an input wavelength range of 25 nm from 1535 to 1560 nm show a power penalty less than 2.5 dB. For a wavelength conversion from 1548 nm to a range of output wavelengths between 1531 and 1563 nm, the facet-to-facet gain ranges from 9 to 13 dB, neglecting fiber coupling losses.     

Linewidth-insensitive coherent AM optical links: design,performance, and potential applications

The use of coherent detection in analog optical links offers several advantages over direct detection: improved receiver sensitivity, inherent frequency translation, and the ability to utilize angle modulation and separate wavelength division multiplexed (WDM) signals. In this paper, we investigate an externally modulated coherent AM optical link. We study the dynamic range of the coherent AM link, considering receiver noise, laser phase noise, laser relative intensity noise (RIN), and system nonlinearities. With proper selection of the receiver's IF bandwidth, the coherent AM link can be made insensitive to the laser linewidth. For optical powers less than 5 mW, RIN of less than -160 dB/Hz reduces the spurious-free dynamic range (SFDR) by less than 3 db with the use of a balanced receiver. The external modulator nonlinearity is the dominant nonideal effect; it reduces the SFDR by 5-19 dB from the theoretical limit for 100% modulation index. We compare the performance of the coherent AM link with that of a conventional direct detection link for two applications: point-to-point links and distribution networks. When the received optical power is less than 1 mW, the coherent link can provide higher SFDR than the direct detection link. Thus, coherent links are well-suited for long distance point-to-point links and FM video distribution systems