Intensity Modulation Characteristics Research Articles

Dual-mode luminescence light intensity modulation characteristics and optical radiation dependence of stannate photochromic ceramics

Alkaline earth stannate is characterized by good physicochemical stability. It has been applied in the field of optical information storage by coupling photoluminescence intensity modulation and photochromic performance, which has attracted the attention of researchers. The development of alkaline earth stannate ceramics with high light intensity modulation properties and non-destructive reading of optical information is of great research value. In this study, Er3+-doped Ca2SnO4 photochromic ceramics were prepared by high-temperature solid-phase reaction method. Alternating UV light irradiation and thermal stimulation, the ceramics achieve a reversible transition between light and dark gray. Er3+ doping gives the ceramics dual-mode luminescence light intensity modulation performance. When the doping amount of Er3+ is 0.01 mol, there is a maximum down-conversion luminous intensity modulation ratio of 93%, which is higher than most of the same type of photochromic materials. The photochromic behavior is explained using the capture-release model of traps for carriers, and the dual-mode luminescence light-intensity modulation behavior is analyzed through the energy transfer mechanism. The optical radiation response properties were investigated and the optimum light response wavelength is found to be 290 nm, which is related to the optical band gap Eg. And the selection of the optimal light response wavelength can effectively improve the performance of photochromic and light intensity modulation. This study provides a promising strategy for performance enhancement of photochromic materials.

Application of Forced Modulation Function Mathematical Model in the Characteristic Research of Reflective Intensity Fibre Sensors

Abstract In order to discuss the application and mode of the forced modulation function in a sensor, the optical fibre emphasis function was established by referring to the geometric method, the tilt factor and the shape factor of the reflecting surface. These were introduced for the first time, and the corresponding mathematical model was established. The method of numerical simulation is systematically studied and multimode optical fibre parameters (including optical fibre of axial spacing, optical fibre core diameter and numerical aperture) are adopted. The reflective surface inclination and shape factors on the RIM–FOS intensity modulation characteristics are studied according to the obtained light quasi-Gaussian distribution model, establishing a general three-intensity modulation function of fibre optic sensor. The results show that the intensity modulation characteristic of specular reflection is obviously better than that of the diffuse reflection surface, and the peak value of the modulation function is five times that of diffuse reflection. The intensity modulation characteristic decreases with increase in the roughness of the reflection surface. The system can not only complete the RIM–FOS characteristic simulation and characteristic testing functions, but can also start-up the test and not be affected by the ambient light interference and power fluctuation of the light source. The test stability is good with high repeatability.

Optical direct intensity modulation of a 79GHz resonant tunneling diode-photodetector oscillator.

We report on the direct intensity modulation characteristics of a high-speed resonant tunneling diode-photodetector (RTD-PD) with an oscillation frequency of 79 GHz. This work demonstrates both electrical and optical modulation and shows that RTD-PD oscillators can be utilized as versatile optoelectronic/radio interfaces. This is the first demonstration of optical modulation of an RF carrier using integrated RTD-PD oscillators at microwave frequencies.

微纳光纤耦合器光致热引起的全光强度调控特性

微纳光纤耦合器光致热引起的全光强度调控特性

On the laws of attraction at cocktail parties: Babble noise influences the production of number agreement

Theoretical accounts of the language production process have claimed that grammatical encoding steps during the formulation stage happen in a largely automatic fashion, unimpeded by other cognitive processes. By eliciting agreement attraction errors, our study tested the effect of external distractor noise on the generation of subject–verb agreement in spoken language. We modelled noisy environments with three different speech-free sounds with spectral, or both spectral and intensity modulation characteristics of speech. In silence and unmodulated noise, we found evidence for a plural mismatch effect, where a plural local noun attracts agreement away from a singular marked head noun. Under modulated noise the error patterns changed, and the number of errors increased in cases where the head noun of the preamble was marked for plural. In addition, background noise led to a reduction of speech rate and a reduction of utterance latency. Our results indicate that unspecific, speech-free noise can create a secondary task load which exerts an influence on the grammatical encoding stage of sentence formulation. We suggest that additional load leads to a slowing down of processing and subsequent difficulty to access the correct number information of the head noun when trying to retrieve an inflected verb form. Subjects overcome this difficulty by resorting to default singular marking on the verb. The results of this study challenge previous claims about the informational encapsulation of the grammatical encoding stage.

Effect of electric field on the photoluminescence intensity of single CdSe nanocrystals

An investigation of the effect of an applied electric field on the photoluminescence (PL) intensity of single CdSe nanocrystals has revealed a measurable field induced PL modulation for a large fraction of the nanocrystals studied. The field induced intensity modulation characteristics (i.e. modulation sign and depth) were observed to vary from particle to particle, and even for different time periods for the same particle in many cases. Simultaneous intensity and frequency resolved PL measurement show that the PL intensity modulation is in fact due to an electric field effect on the PL quantum yield. The results are consistent with a model in which the energies of surface charge trapping sites are modulated by the applied electric field, causing in turn a modulation of the rates of exciton quenching by these sites. The complex observed field effects can be explained by the superposition of the applied and internal electric fields due to deeply trapped charges on the surface of the nanoparticle.

New fiber-optic attenuator calibration technique using linear intensity modulation characteristics of a laser diode

A new fiber-optic attenuator calibration technique has been developed using linear intensity modulation characteristics of a laser diode. It does not require detector linearity to be known. The uncertainty of attenuation calibration for a typical 10 dB attenuator is 0.020 dB at two standard deviation levels. The resolution of the system is 0.001 dB and the dynamic range is 25 dB in a single step.

Amplitude-modulation characteristics of barrier-reservoir and quantum-well electron-transfer (BRAQWET) modulators

We have studied theoretically and experimentally the intensity-modulation characteristics of GaAs-based light modulators based on the barrier-reservoir and quantum-well electron-transfer (BRAQWET) structure. The transmission-voltage characteristics are nonlinear and follow an inverse exponential relationship which is derived herein. It is also seen that a multiple-period BRAQWET structure is unnecessary and partially ineffective for amplitude modulation and that a one-period BRAQWET structure can give comparable results while providing more versatility for the device design. Al/sub x/Ga/sub 1-x/As-based guided-wave modulators are demonstrated with a 50% modulation index at a drive voltage of 1 V.

Real-time intensity correlation with a synthetic discriminant function filter

Real-time optical intensity correlation with a synthetic discriminant function (SDF) filter has been realized. The computed SDF data are fed into an Epson liquid-crystal television to create the optical reference signal. The intensity modulation characteristics of the Epson liquid-crystal television are therefore investigated in the different modulation modes. The difficulties of generating the SDF filter, which are due to the negative values in the SDF data and to the characteristics of the spatial light modulator, are readily overcome by use of an intensity correlator. Experimental results are presented.

Frequency and intensity modulation characteristics of GaAs lasers in an external cavity

Frequency and intensity modulation characteristics were measured for external cavity GaAs diode lasers as a function of modulation frequency. The data, displayed as a chirp-to-power ratio (CPR), showed at low modulation frequencies a flat response and a 0 degrees or 180 degrees relative phase, depending on laser structure. A model incorporating a carrier-density-dependent imaginary part of the differential gain (Henry alpha factor) is developed to explain the data. The model yields simple scaling of the CPR with injection current and photon lifetime. The agreement between the model and data including scaling is excellent. These results provide strong evidence for transverse spatial hole burning in these lasers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Wavelength tuning characteristics of DFB lasers having twin-guide structures modulated by injection current or electric field

The wavelength tuning and intensity modulation characteristics are presented for three types of twin-guide (TG) lasers entirely fabricated by metalorganic vapour phase epitaxy (MOVPE). A wide continuous tuning range of 5.3 nm is obtained for the tunable twin-guide (TTG) laser. The TTG lasers, however, have the drawbacks of output power reduction and spectral linewidth broadening during tuning. A new type of tunable laser, the complementary twin-active-guide (CTAG) laser, is proposed, and its tuning characteristics are presented for the first time. A wide continuous tuning range over 4 nm is obtained, although the thermal effect is more dominant than carrier effects. The CTAG structure enables suppression of the spectral linewidth broadening induced by the injected carrier recombination shot noise (IRSN) during tuning. The characteristics of the TG lasers modulated by reverse bias are presented, and the possibility of using these TG lasers for wavelength tuning is studied.

High-speed intensity modulation of 1.5 mu m DBR lasers with wavelength tuning

Intensity modulation characteristics of a 1.5- mu m 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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modulation characteristics of tunable DFB/DBR lasers with one or two passive tuning sections

Calculation of the small-signal modulation characteristics of tunable distributed-feedback (DFB) and distributed Bragg reflector (DBR) lasers requires rate equations for the photon number, the phase of the electric field, and the carrier densities. Here, the rate equation for the photon number and phase is derived from an optical transmission-line model. Examples of the frequency- and intensity-modulation characteristics of a phase-tunable DFB laser are presented. The modulation responses exhibit the well-known relaxation resonance if either of the drive currents is modulated, but the possibility of complete removal of the resonance peak together with a perfect cancellation of spurious intensity modulation is also demonstrated. The frequency-modulation response then assumes a simple low-pass character with a cutoff frequency determined by the carrier lifetime in the passive tuning section. The importance of choosing the proper bias conditions is emphasized. >

Nature of wavelength chirping in directly modulated semiconductor lasers

Relations are derived concerning the inherent connection between frequency deviations and the optical power wave-form of a directly modulated semiconductor laser, providing for the first time a quantitative assessment of inherent optical fibre dispersion penalties of directly modulated lasers. The relations also indicate that control of chirp involves only the control of the intensity modulation characteristics and proper current drive of semiconductor lasers. Experimental measurement of FM and IM characteristics of a 1.55 μm DFB laser support the results.

The Linear Electrooptic (Pockels) Effect in Cubic Crystals; Wide Angle Light Intensity Modulation

The wide angle light intensity modulation characteristics of a polarizer-crystal-polarizer window are presented for linear electrooptic (Pockels effect) crystals of cubic symmetry class 43m. Polarizer effects and crystal effects both contribute to a nonuniform intensity distribution over wide angle fields of view. Examples are plotted for normal and oblique viewing and for crossed and parallel polarizers. In general, the transmitted intensity does not vary excessively and is more a function of the polarizers than the crystal.