Optimum operation of DFB lasers under chirped pulse transmission

Theoretical calculations together with measurements of the chirping characteristics of DFB lasers have revealed the existence of optimum bias condition for longer transmission distance. Ultimate transmission distances in connection with fibre loss and dispersion are estimated for 1.3 and 1.5 ?m transmission on the basis of experimental device characteristics.     

Polarization characteristics of fiber DFB lasers related to sensingapplications

An experimental and theoretical investigation of how the polarization mode competition and beat frequency of Er-doped fiber distributed-feedback lasers depend on perturbations such as localized transverse forces, back reflections, or changes in pump polarization is reported. Good agreement between the experiments and a comprehensive theoretical model is obtained. Use of a dual-polarization laser as a transverse force sensor with a resolution on the order of 1-100 nN/√Hz above 20 Hz is also discussed     

Continuously distributed phase shifts in chirped DFB lasers usingbent waveguides

The authors have implemented chirped distributed feedback (DFB) grating lasers with phase shifts [λ/8, 2λ/8 and 3λ/8] distributed continuously over various axial distances, using their recently proposed method for producing bent optical waveguides. The singlemode stability of the lasers with distributed phase shifts was found to be considerably higher than for lasers with abrupt phase shifts     

Continuously chirped DFB gratings by specially bent waveguides fortunable lasers

We have implemented and studied a new type of tunable multiple-section semiconductor distributed feedback (DFB) laser using tailored chirped DFB gratings. Arbitrarily and continuously chirped DFB gratings are defined by bent waveguides on homogeneous grating fields with ultrahigh spatial precision. The mathematical bending functions are optimized in this case to provide enlarged wavelength tuning ranges. We present the results of model calculations, the technological device realization and experimental results of the DFB laser characterization e.g. a tuning range of 5.5 nm without wavelength gaps and high side mode suppression ratio     

Performance limitations of high-power DFB fiber lasers

In this letter, we experimentally study several different configurations of high-power single-frequency sources based on distributed-feedback fiber laser (DFB FL). In particular, we have compared two schemes in terms of pumping efficiency, relative intensity noise (RIN) and optical signal-to-noise ratio (OSNR): directly pumped DFB FLs pumped by a high-power fiber-based pump source (stand-alone DFB FL) and a combination of a DFB FL and a power amplifier (amplified DFB FL). At the output powers below 40 mW, a stand-alone DFB FL has the highest OSNR (> 63 dB) and the lowest RIN (< -165 dB/Hz). The net efficiency of a stand-alone DFB FL can be doubled by using an amplified DFB FL at the expense of degraded OSNR and RIN. It is also shown that RIN below -160 dB/Hz and OSNR > 60 dB can be achieved by an amplified DFB with output power greater than 1 W.     

Analysis of multiple wavelength DFB fiber lasers

The behavior of multiwavelength distributed feedback fiber lasers is simulated in a comprehensive numerical model. Multiple fundamental modes can coexist, even though the coupling coefficients of their respective refractive index gratings are not equal, due to induced dynamic gain gratings. We have investigated the effect on the lasing state of variations in coupling strengths, gain parameters, grating Bragg frequency separation, relative phase between the gratings, length of the structure relative to the beat lengths between the gratings, grating center phase-shift errors, and saturation level of the UV-induced refractive index change     

Computer simulation of high-bit-rate optical fiber transmission using single-frequency lasers

Chirp-induced dispersion penalties in high-bit-rate optical fiber transmission are assessed using numerical integration of laser rate equations and a Fourier transform fiber dispersion routine. The roles of the imposed modulation waveform and laser design parameters are evaluated from computer generated eye diagrams and simple analytical observations. Consistent with experiment, we find device dependent optimum laser extinction ratios. In addition, we address the delicate balance between nonlinear chirp-induced dispersion penalties and the speed limitations imposed by linear current filtering on both the laser transmitter and the receiver. These considerations become increasingly important at higher bit rates such as 8 Gbit/s.     

Modeling of polarization-mode competition in fiber DFB lasers

A comprehensive model for steady-state analysis of polarization-mode competition in fiber distributed feedback (DFB) lasers is presented. Effects of polarization-dependent grating nonuniformities, polarization-dependent grating strength, coupling between the linear polarization states due to twist or Faraday rotation, back reflections, cross saturation from serially multiplexed lasers, as well as spatially and polarization-dependent gain hole burning are covered by the model. Regimes of single and dual polarization operation are identified for different types of polarization imperfections in the cavity. The output powers of the individual modes and the magnitudes of the hole-burning mechanisms are also calculated anti discussed     

Dynamic analysis of multiple wavelength DFB fiber lasers

The behavior of multi- and single-wavelength distributed feedback fiber lasers is simulated in a comprehensive dynamic model. The evolution of the spatial distribution of gain, saturation-induced gain gratings, and spontaneous emission is taken into account. Stability and relative intensity noise (RIN) of the different laser types and laser modes are compared, and the effect of varying degree of pump RIN and quenching of spontaneous emission lifetimes is analyzed     

Analysis of DFB semiconductor lasers with external optical feedback

A theoretical analysis of the sensitivity of DFB semiconductor lasers to external optical feedback is presented. Numerical simulations allow the authors to determine the optimum facet reflectivity, for a given κL value, to minimise the sensitivity to external optical feedback     

两段式DFB激光器波长调谐特性分析

利用耦合波方程,对两段式DFB激光器进行理论分析,得出了激光器激射工作时两段载流子浓度和激射波长之间所满足的隐含表达式。作为特例,分析了吸收型器件在两段等长情况下的阈值载流子浓度变化和波长调谐特性。     

Aging characteristics of InGaAsP/InP DFB lasers

Aging tests of InGaAsP/InP DFB lasers with a constant light output of 5 mW/facet and ambient temperatures 25°C and 40°C have been carried out. Up to the present, with an aging time of more than 2000 h for six lasers, appreciable degradations have been observed in their driving currents and spectra. This indicates that the corrugation grating near the active region has little influence on short-term reliability of DFB lasers.     

两段式DFB半导体激光器模式特性研究

利用耦合波方程,在引入平均场的方法后,得到了一种新的关于两段式DFB激光器的模式区分方法。并利用此法,分析了激光器的模式特性和波长调谐特性。计算结果与实验较好地吻合,说明了该方法可以有效地分析两段式DFB激光器的不同模式。     

Fundamental and higher order mode thresholds of DFB fiber lasers

Higher order modes are detrimental for distributed feedback (DFB) fiber lasers. The thresholds of these modes are calculated as functions of gain, loss, and various types of grating defects, like harmonic, linear, quadratic, and random chirp, and discrete phase errors. The higher order modes are particularly enhanced by high gain, quadratic chirp, and discrete phase errors close to the center of the grating     

光纤波片对光纤环形镜线性传输特性的影响

利用单模光纤应力双折射率效应，在线性光纤环形镜中引入在线光纤波片、通过改变光纤波片主轴方向，可以实现对一光纤环形镜率和反射率的实时调节。实验结果与理论分析的相致。     

DFB光纤激光器最佳输出特性研究

采用传输矩阵法,对影响DFB掺铒光纤激光器输出功率的耦合因子、光栅长度进行了研究,数值分析了不同谐振腔损耗下最佳输出功率所对应的最佳光栅长度及耦合因子的变化。结果表明,在设计光纤激光器时,根据光纤光栅的制作损耗,优化光栅长度及耦合因子可以使光纤激光器的输出实现最佳化。这些结论对基于光纤激光器的结构优化具有指导意义。     

Direct optical characterisation of DFB lasers for CPFSK system applications

The authors present a new optical characterisation method for single-frequency lasers that are to be applied in Gbit/s CPFSK systems. They use optical delay-demodulation to allow easy matching of the demodulator delay over a wide range of values. It is shown that for a particular device, when used in a 2.4 Gbit/s CPFSK system, the modulation index must be larger than 1.0 to obtain a bit error rate below 10/sup -11/. With a modulation index of 1.5, bit error rates below 5*10/sup -13/ have been measured.<>     

Theoretical analysis of external optical feedback on DFB semiconductor lasers

The effect of external optical feedback on resonant frequency, threshold gain, and spectral linewidth of distributed feedback (DFB) semiconductor lasers is theoretically analyzed. The analysis applies to any type of laser cavity formed by a corrugated waveguide limited by partially reflecting facets. It is shown that the sensitivity to optical feedback on a facet is closely related to the power emitted through this facet. Numerical results on wavelength selectivity and on sensitivity to optical feedback are given for conventional DFB lasers having an AR-coated facet and for quarter-wave-shifted (QWS) DFB lasers with AR-coatings on both facets. Both laser types are found to be more sensitive to optical feedback on their AR-coated facet than Fabry-Perot lasers for lowkL. On the other hand, QWS-DFB lasers are found to be relatively insensitive to optical feedback for largekL.     

Polarization independent, all-fiber phase conjugation incorporatinginline fiber DFB lasers

We propose and demonstrate a novel technique for optical wavelength conversion and phase conjugation by fiber four-wave mixing using inline fiber distributed-feedback lasers as orthogonally polarized pump sources. This technique features polarization independent operation and a simple all-fiber configuration without the need for externally injected pumps. Polarization dependency as low as 0.5 dB has been achieved using this technique