Ultra-long distance wavelength-division-multiplexed solitontransmission using inhomogeneously broadened fiber amplifiers

The use of inhomogeneously broadened amplifiers for wavelength-division-multiplexed (WDM) optical soliton transmission is proposed. Dynamic gain equalization can be achieved through saturation, by adjustment of the time-averaged intensity of control lasers tuned between the WDM channels. The authors investigate numerically an example in which seven WDM channels at 2 Gb/s each are equalized using parameter values reasonable for germanosilicate core erbium-doped fibers     

Temperature dependence of the gain of lasers based on quantum-dot arrays with an inhomogeneously broadened density of states

A model making it possible to describe analytically the temperature dependence of the optical gain and threshold current density in lasers based on quantum-dot arrays characterized by inhomogeneous broadening of the density of states is proposed. At high temperatures the dependence obtained is universal, i.e., it is determined exclusively by the broadening of the density of states, not by its specific form. Fiz. Tekh. Poluprovodn. 33, 1395–1400 (November 1999)     

Gain nonlinearities due to carrier density dependent dispersion insemiconductor lasers

Semiconductor-field interaction is analyzed by using a semiclassical density-matrix approach. Using an exact elimination procedure for the dipole moments, corrections to the standard rate equation are obtained and shown to result in gain nonlinearities. The gain nonlinearities are due to carrier-density-dependent dispersion at the lasing frequency. Using available measured data of the frequency dependence of the carrier-induced refractive index change, gain compression coefficients in agreement with experimental values are obtained     

应用前景广阔的紫光二极管激光器

受繁荣的发光二极管市场的影响，GaN基二极管激光器最近又开拓出新的应用领域。光存储市场正引领新一代写入器/播放器的发展方向，一种新的存储格式面临两家竞争对手，一种被称之为Blu-ray磁盘格式是由10家大型企业联合体提出并在最近实现标准化处理；另一种存储格式被称之为AOD格式，它是由日本东芝公司和电气公司联合提出。这     

On injection locking of homogeneously broadened lasers

The dynamic rate equations are obtained from a semiclassical analysis for a homogeneously broadened laser operating in two modes with an externally injected signal. The time-dependent behavior of two competing modes can be described by three-coupled first-order nonlinear equations which relate the inversion density and the photon density of the two modes. Considerations regarding injection locking are presented.     

Homogeneously broadened CW lasers with uniform distributed loss

The exact equations relating the CW output power to the parameters of a homogeneously broadened laser with distributed loss and its cavity are analytically intractable. In their place, simple approximate expressions are derived which permit convenient evaluation of the laser parameters from output power measurements in cavities with variable coupling, and conversely, of the maximum available oscillator power from small-signal gain and absorption-loss measurements. The approximate solutions have negligible error for lossy standing-wave lasers and are but slightly less accurate for lossy traveling-wave ring lasers.     

Effect of photon lifetime on absorptive bistability in inhomogeneously pumped lasers

The letter comments on the validity of assuming a constant photon lifetime in the photon conservation equation under steady-state conditions for inhomogeneously pumped lasers. An expression for photon lifetime is derived which depends on device geometry and the levels of photon fluxes in the device. The effect of this on the I/L characteristics is given.     

Application of spectral-hole burning in the inhomogeneously broadened gain of self-assembled quantum dots to a multiwavelength-channel nonlinear optical device

A nonlinear device capable of handling multiple wavelength channels simultaneously by using spectral-hole burning in the inhomogeneous broadening of the gain in self-assembled quantum dots is proposed. The multichannel property of this device stems from the localized absorption or gain change at the pump wavelength within the inhomogeneously broadened gain spectrum. The spectral width of the modulation and its time evolution was also evaluated. The result indicates the applicability of this device to multichannel operation.     

Optimum output efficiency of homogeneously broadened lasers with constant loss

The exact solution of a laser power extraction model is analyzed that relates the extraction efficiency with the laser parameters such as output coupling, small-signal gain, absorption loss, and laser cavity length. The model assumes a stable optical resonator and a homogeneously broadened gain medium. Optimum output coupling and resulting maximum extraction efficiency are determined for a range of values of the small-signal gain and absorption loss per pass. A relation is derived that allows determination of the intrinsic laser parameters from output power measurements when output mirrors are utilized with three different reflectances.     

Fading in lightwave systems due to polarization-mode dispersion

System fading caused by polarization-mode dispersion is investigated at 1.7 Gb/s using highly-birefringent, dispersion-shifted fiber at 1.55 μm. The observed fading, which is manifested by random fluctuations of the bit error rate for a fixed receiver power, is observed to depend on the environmental conditions of the fiber, with the time constant for fading varying from minutes to hours depending on the rate of change of the ambient temperature. The mean dispersion penalty inferred from the observed fluctuations in the bit error rate is consistent with a square-law dependence on the polarization-mode dispersion for small penalties     

Transverse switching due to Hopf bifurcation in semiconductor lasers

A new method for investigating the spatial and temporal stability of semiconductor lasers is presented, which represents the first application of Hopf bifurcation theory to semiconductor lasers. Unlike the classical Hurwitz approach, whose applicability is restricted to a small number of piecewise homogeneous regions at most, details of the spatial distributions of carrier and photon densities can now be included with modest additional computational effort. The actual stability analysis involves solving no more than a 5 × 5 real eigenvalue problem once the steady-state distributions are known. This feature is particularly important where spatial variations play a fundamental role, Numerical results are presented to illustrate the application of the algorithm to oscillations and to nonlinear light-current characteristics in standard stripe-geometry lasers. The further application of the technique to the analysis of optical bistability and high-speed optical switching is discussed.     

Off-Axial mode selection in solid-state lasers due to nonuniformities

It is shown that the nonuniformity of excitation produced in circular cross-section solid-state lasers due to the focusing of pump power leads to a coupling of certain modes and reduction in their threshold of oscillation. These modes correspond in plane-wave representation to simple closed paths in the cavity. The off-axial radiation observed in the form of rings by Collins and Giordmaine and others is explained on the basis of the theory.     

CO激光器的光栅色散腔选支

本文报导在GO激光器中采用光栅色散腔进行了实验比较,提高了波长的分辨力。     

Absolute instabilities in lasers with host-induced nonlinearitiesand dispersion

We analyze the occurrence of absolute instabilities in lasers that contain a dispersive host material with third-order nonlinearities. Starting from the Maxwell-Bloch equations, we derive general multimode equations to distinguish between convective and absolute instabilities. We find that both self-phase modulation and intensity-dependent absorption can dramatically affect the absolute stability of such lasers. In particular, the self-pulsing threshold (the so-called second laser threshold) can occur at few times the first laser threshold even in good-cavity lasers for which no self-pulsing occurs in the absence of intensity-dependent absorption     

Linewidth rebroadening in semiconductor lasers due to lateral spatial holeburning

The linewidth of semiconductor lasers is calculated taking into account a transversely inhomogeneous carrier distribution within the active region which gives an additional contribution to laser linewidth if the material linewidth enhancement factor is carrier density-dependent. For the first time it is theoretically shown that lateral spatial holeburning causes linewidth rebroadening in BH DFB lasers at high output power.<>     

Nonlinear gain suppression in semiconductor lasers due to carrier heating

A simple model is presented for carrier heating in semiconductor lasers from which the temperature dynamics of the electron and hole distributions can be calculated. Analytical expressions for two new contributions to the nonlinear gain coefficient, in are derived, which reflect carrier heating due to stimulated emission and free carrier absorption. In typical cases, carrier heating and spectral holeburning are found to give comparable contributions to nonlinear gain suppression. The results are in good agreement with recent measurements on InGaAsP laser diodes.<>     

Stability of self-pulsing due to Hopf bifurcation in semiconductor lasers

A formulation is given of the stability criterion for oscillations arising at Hopf bifurcations in semiconductor lasers. A second-order perturbation expansion is utilized to provide nonlinear rate equations for the laser. The rate equations contain terms whose second-order partial derivatives are required in the definition of stability parameters. Using these parameters, a simple statement of the stability criterion is possible. Numerical calculations are included, using typical device parameters, and show the existence of both stable and unstable Hopf oscillations.     

Linewidth rebroadening in DFB lasers due to weak side modes

A new mechanism for linewidth rebroadening in distributed feedback (DFB) lasers is proposed. It is shown that mode partitioning between the main mode and a weak side mode in conjunction with the difference in longitudinal distributions can lead to strong rebroadening even for side mode suppression ratios (SMRs) larger than 30 dB. An analytical expression for the new linewidth contribution is derived. The contribution increases with the third power of the photon number in the dominant side mode. This agrees with experiments on DFB lasers when one generally observes a strong increase in linewidth where the SMSR decreases below 30 dB. This work and the reported experimental results clearly show that linewidths increase if the side mode suppression goes down. However, it seems that in some DFB lasers rebroadening can occur without any decrease in SMSR, so that other mechanisms need to be considered.<>