We numerically investigate the output characteristics of dissipative solitons (DSs) in a thulium-doped fiber ring laser mode-locked by a semiconductor saturable absorber mirror (SESAM). It is shown that DSs could be formed with the SESAM acting as a mode-locker and a filtering-equivalent component. The pump power, together with the net-cavity dispersion, determines the properties of the generated DSs. The numerical results qualitatively match with previously reported experimental observations. The pulse compression of the generated DSs is numerically demonstrated by using a segment of single-mode fiber with anomalous dispersion as an external pulse compressor. The corresponding compressed pulses have a minimum duration of 450 fs.
Based on Wheeler's transformation of multilayer microstrip line, velocity and impedance matching have been analyzed for polymer electro-optic (EO) modulator. Due to the advantages of polymer materials, velocity-matching and impedance-matching can be simultaneously achieved by optimized design for multilayer microstrip electrode. A modified modulator structure has been introduced with a compensation layer placed on the electrode to adjust the microwave index and characteristic impedance. The optimal thicknesses of electrode and compensation layer, and optimal width of electrode can make the EO modulator achieve both velocity matching and impedance matching.
We present a landslide monitoring approach using a high-resolution distributed fiber stress sensor based on polarizationsensitive
optical frequency reflectometry (P-OFDR) technology. The sensing system consists of a polarizationmaintaining
(PM) fiber and an OFDR with a high spatial resolution. The PM fiber is used as a distributed sensing
element. The OFDR is used to measure the polarization mode coupling loss in PM fiber causing by the external pressure
along the PM fiber. With the advantages of frequency domain technique and coherent detection, the sensing system can
achieve high spatial resolution, high sensitivity and large dynamic range. By monitoring the mechanical property
distribution and variations in the landslide body, the occurrence of the landslides can be predicted accurately. We
demonstrate an early landslide warning system based on polarization-sensitive distributed fiber stress sensor, which has a
spatial resolution of 5cm, dynamic range of about 70dB and theoretical measuring range of 10km. The warning system is
also investigated experimentally in the field trial.
The authors propose a new compound cavity model with optical feedback for study the nonlinear dynamic behavior of VCSEL. The results show that system can be controlled to its fixed point, periodic orbits by using modulation parameters. In addition, the stable range be obtained and indicate the introduction of external reflectivity enhances chaotic characteristics. As increase of the external mirror reflectivity the CW state become unstable and the output power exhibit single period oscillation, higher order bifurcation, eventually leading to chaos.
We have developed a rigorous phenomenological model for analyzing Yb3+/Er3+-codoped phosphate waveguide lasers. The model is based on time-dependent laser rate equations for an Yb3+/Er3+-codoped laser host with multiple energy levels. We have used the model to predict the characteristics of waveguide lasers pumped by a 980-nm source. We also define and discuss the waveguide laser intensity distributions, host parameters, doping profiles, and the laser cavity design parameters. Solutions for the laser signal power, pump power, and populations of ion energy levels as functions of space and time are obtained for waveguide lasers.
In this letter, extending the normal OrCAD Pspice into electro-optical system of FLC, we construct an equivalent circuit model based on this principle; formulate the operation of the OASLM. Especially, we also show that the OASLM gray scale is realized not by FLC multidomain switching, but by uniform director rotation between bistable states. At the same time, the method could realize the dynamic switch simulation, memory characteristics and give the relation of memory threshold and critical pulse square, and show that this theory agrees with various experimental photographed trace results.
The availability of integrated optical sources in glass is expected greatly to enhance optical signal processign in glass substrates. In this paper, we report the design, fabrication and characterization of waveguide lasers in Er3+/Yb3+-codoped phosphate glass substrates. Waveguides were fabricated in a commercially avilable phosphate glass. The glass was codoped with 1.65wtpercent Er2O3 and 20wt percent Yb2O5. Waveguides were formed by K+-Na+ exchange through channel apertures etched in 150nm thick AL mask layer. Yb3+ is commonly used as a sensitizer in Er3+ lasers because it has a much larger absorption cross section near 980nm than Er3+, and it efficiently transfers its excited state eneryg to the upper level of the Er3+ 1535nm transition. The parameters that affect lasing characteristics of waveguide lasers are discussed in the light of equations for the lasing threshold and slope efficiency. Design parameters for low-threshold waveguide lasers with high slope efficiencies are described, and methods are given for substrates, waveguides and lasers cavities.
This paper proposed electrical model is based on the elastic continuum theory applied to the ferroelectric liquid crystal (FELC), which gives a good description for the simulated switching and memory behavior by the different time order and driving waveforms. Optical transmission dependence onthe complex voltage waveforms and the rotational viscosity and spontaneous polarization of cell is obtained as a function of director profile. The model agree to 10 percent experimental results, over an applied voltage of 1.0 to 20 volt. The electrical model of real FELC displays may contribute to the design and development of optimized devices.
It is well known that when the laser is turned on by increasing the device current from its initial value Jo to the above-threshold value J greater than Jth, stimulated recombination is delayed by td, the time during which the carrier population rises to its threshold value. On the besis ofthe rate equations for quantum well VCSEL, a closed expression describing the time evolution of the carrier density within the turn-on period of a VCSEL has been derived for the case that the Auger effect is considered with a term proportional to the cube ofthe carrier density. The theoretic results are
simulated with Simulink of MATLAB software. As a result, an explicit analytical expression for the turn-on delay of the VCSEL has also been deduced. Since the turn-on delay is an important parameter of a semiconductor laser, intensified studies on this parameter have been carried out in the past years.
Based on analytical continuation of the round-trip condition, in contrast to existing rate equations. Threshold current density, slope efficiency, and threshold gain of cascade VCSEL as a function of number of active regions for the different size-dependent paramenters such as the cavity of length and thickness of each active region are discussed as applications. The results showed behavior of an almost linear increase in slope efficiency and a reduction in threshold
current density with the number of stages.
The model is written using Pspice8.0 soft, such that it can be directly integrated with the normal Pspice components used to simulate drive circuitry. The equivalent circuit model is based on a set of rate equations of vertical-cavity surface- emitting lasers (VCSEL's). To confirm that our model is valid, we present samples simulations that demonstrate its ability to replicate typical dc, small-signal, temperature-dependent light-current curves, transient operation, and modulation responses. Characteristics of the extracted quantum well models are discussed in detail. The predictive capability of the extracted models is demonstrated by good agreement between modeled and measured transient response pulse shapes.
In this paper, a scheme of all-optical wavelength conversion based on fiber semiconductor ring lasers has been suggested. The analyses on this wavelength converter have also been given by using rate equations. Some properties such as extinction ratio and the conversion wavelength range are discussed.
In this paper, our main goal was to simulate vertical cavity surface emitting lasers (VCSEL) characteristics, including the threshold current, transient phenomena, and modulation operation. The simulation results of transient response and the phase diagram of the carrier and photon are given. We have got the relation of spontaneous emission factor, current and aperture size on threshold, turn-on delay, relaxation oscillations frequency, and output power. Furthermore, it is found that the threshold current, light current curves, transient phenomena, and modulation operation of a VCSEL are determined by size-dependent.
Wavelength dependence and finite band width of reflectivity at the AR-coated facet have been taken into account to study the oscillation wavelength and threshold carrier density of one- fact antireflection semiconductor lasers. Analytic expressions for both the upper bound of the threshold carrier density and oscillation wavelength have been derived. Analysis shows the deviation between the wavelength of the AR-coated facet minimum reflectivity an that of the gain peak is a key parameter to reduce the Fabry-Perot oscillations.