Internal Frequency Modulation Research Articles

Studies on Charge Carrier Transport in an Injection Laser with Frequency Modulation of the Optical Radiation

One of the promising approaches to solve the problem of increasing the efficiency for interelement connections consists in the use of integrated optical switching systems, whose main elements represent injection lasers with functionally integrated optical radiation modulators. Injection lasers make it possible to modulate the laser radiation by subpicosecond controlling pulses at a constant pumping current, as well as making it possible to implement the sources and modulators of optical radiation in a united AIIIBV nanoheterostructure with second-type heterojunctions. This work is devoted to the studies concerning the transport of charge carriers within a functionally integrated modulator laser with internal frequency modulation of the generated optical radiation using a proposed two-dimensional diffusion-drift model and a numerical simulation technique. The results of the numerical simulation of charge carrier transport in a modulator laser when the pumping current is switched on, as well as under pulsed variation of the controlling voltage, take the structural features, the transport effects, the mechanisms of stimulated and spontaneous radiative recombination, and the photon lifetime into account. It is shown that the maximum modulation frequency of laser radiation is determined by the subpicosecond time of the controlled spatial relocation of the charge-carrier density maxima in the quantum zones of the modulator laser, as well as by the photon lifetime in the laser resonator, and corresponds to the terahertz range. To increase the maximum modulation frequency, it is necessary to reduce the photon lifetime in the active zone of the modulator laser to values lower than 3 ps by changing the resonator’s parameters in a corresponding manner. The proposed model and the method of numerical simulation make it possible to optimize the parameters of a functionally integrated modulator laser, and to provide the required relationships between the maximum modulation frequency of the optical radiation, the modulation coefficient, and the density of the threshold pumping current.

Loss of sleep spindle frequency deceleration in Obstructive Sleep Apnea

ObjectiveSleep spindles have been suggested as surrogates of thalamo-cortical activity. Internal frequency modulation within a spindle’s time frame has been demonstrated in healthy subjects, showing that spindles tend to decelerate their frequency before termination. We investigated internal frequency modulation of slow and fast spindles according to Obstructive Sleep Apnea (OSA) severity and brain topography. MethodsSeven non-OSA subjects and 21 patients with OSA contributed with 30min of Non-REM sleep stage 2, subjected to a Matching pursuit procedure with Gabor chirplet functions for automatic detection of sleep spindles and quantification of sleep spindle internal frequency modulation (chirp rate). ResultsModerate OSA patients showed an inferior percentage of slow spindles with deceleration when compared to Mild and Non-OSA groups in frontal and parietal regions. In parietal regions, the percentage of slow spindles with deceleration was negatively correlated with global apnea-hypopnea index (rs=−0.519, p=0.005). DiscussionLoss of physiological sleep spindle deceleration may either represent a disruption of thalamo-cortical loops generating spindle oscillations or some compensatory mechanism, an interesting venue for future research in the context of cognitive dysfunction in OSA. SignificanceQuantification of internal frequency modulation (chirp rate) is proposed as a promising approach to advance description of sleep spindle dynamics in brain pathology.

Design of an internal FM radio antenna for mobile handsets with an arrow-shaped patch

This article describes the design, fabrication, and measurement of an internal FM radio ferrite sheet flexible antenna using an arrow-shaped patch to enhance passive gain performance for mobile handsets.To obtain sufficient passive gain performance ≥–20 dBi, an arrow-shaped patch is inserted in the antenna radiator and monopole type wire is used. The measured result of the fabricated antenna provides passive gain performance (15.6–13.5 dBi) from 86 to 108 MHz with the frequency modulation (FM) bandwidth from 83.20 to 123.72 MHz (≤voltage standing wave ratio (VSWR) 6:1). Also, a good radiation pattern is achieved within the FM bandwidth (86–108 MHz) range. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26180

Determining the time–frequency parameters of low-power bright picosecond optical pulses by using the interferometric technique

We present an approach to the characterization of low-power bright picosecond optical pulses with an internal frequency modulation simultaneously in both time and frequency domains in practically much used case of the Gaussian shape. This approach exploits the Wigner time–frequency distribution, which can be found for these bright pulses by using a novel interferometric technique under our proposal. Then, the simplest two-beam scanning Michelson interferometer is selected for shaping the field-strength auto-correlation function of low-power picosecond pulse trains. We are proposing and considering in principle the key features of a new experimental technique for accurate and reliable measurements of the train-average width as well as the value and sign of the frequency chirp of pulses in high-repetition-rate trains. This technique is founded on an ingenious algorithm for the advanced metrology, assumes using a specially designed supplementary semiconductor cell, and suggests carrying out a pair of additional measures with exploiting this semiconductor cell. Such a procedure makes possible constructing the Wigner distribution and describing the above-listed time–frequency parameters of low-power bright picosecond optical pulses. In the appendix, we follow one of possible avenues for deriving the joint Wigner time–frequency distribution via choosing the Weil's correspondence between classical functions and operators.

휴대 단말기용 내장형 FM 라디오 안테나의 설계

이 논문은 휴대 단말기의 내장형 FM(Frequency Modulation) 라디오 안테나의 설계에 관하여 기술하고 있다. 설계 안테나의 동작 주파수에서의 임피던스를 조절하기 위해서 집중 정수 소자인 R과 L칩 소자를 사용하였다. 안테나 후면의 패치와 스터브는 설계 안테나의 정확한 공진 주파수치 조절과 소형화를 위해 추가하였다. 제작된 안테나의 크기, 측정된 반사 손실, 임피던스, 대역폭, 이득은 각각 <TEX>$40{\times}70{\times}1$</TEX> mm, 99 MHz에서 -23 dB, <TEX>$55-j7{\Omega}$</TEX>, -10 dB 이하 22 MHz(<TEX>$88{\sim}110$</TEX> MHz), -15 dBi이고, 시뮬레이션 결과와 잘 일치하였다. 특히 제작된 안테나의 측정 이득은 설계 주파수 대역 내에서 기존의 이어폰 안테나의 이득과 유사한 값을 보였다. 측정된 방사 패턴도 계산된 무지향성 패턴과 잘 일치하였다. This paper describes a design of internal frequency modulation(FM) radio antenna fur mobile terminal. In order to control of impedance at an operating frequency of the designed antenna, the lumped constant elements of R and L chip components are used. Patch and stubs located at antenna backside are added to control an exact resonance frequency and miniaturization. A fabricated antenna sire, the measured return loss, impedance, bandwidth, and gain are <TEX>$40{\times}70{\times}1$</TEX> mm, -23 dB at 99 MHz, <TEX>$55-j7{\Omega}$</TEX>, 22 MHz(<TEX>$88{\sim}110$</TEX> MHz) below -10 dB, and -15 dBi, respectively. These measured results show a good agreement with simulated results. Especially, the measured gain of fabricated antenna is similar with value of a conventional ear-phone antenna in the designed frequency band. The measured radiation pattern agrees well with the calculated omni-directional pattern.

Experimental observation of spectral oscillations in frequency modulation laser operation.

The experimental observation of transient coherent oscillations in the optical frequency spectrum of an Er-Yb solid-state laser with internal frequency modulation (FM) is reported. These oscillations, which arise in the presence of a slight detuning between the modulation frequency and the cavity axial mode separation, are transiently observed when the modulator is switched on and appear as a damped breathing of laser spectral width superimposed to the relaxation oscillation dynamics of the laser intensity. The experimental results are in good agreement with the theoretical predictions which take into account both the fast dynamics of spectral oscillations and the slow dynamics of relaxation oscillations for the codoped Er-Yb laser system.

Spectral oscillations in a frequency-modulation laser operation.

We show the existence of coherent oscillations in the optical frequency spectrum of a laser with internal frequency modulation. These oscillations arise in presence of a slight detuning between the modulation frequency and the cavity axial mode separation and are analogous to collective oscillation modes of a chain of weakly coupled pendula with resonance frequencies slightly varying along the chain. Although spectral oscillations are damped due to the finite gain bandwidth of the laser cavity, they can be observed in the transient dynamics during switch-on of the modulator, or can be resonantly excited by an external forcing.

Stabilization of a CO 2 pump laser using external CH 3OH stark-cell modulation

In order to stabilize the 118.8 μm CH 3OH laser output, frequency stabilization of the CW 9P(36) CO 2 laser pump is carried out using external CH 3OH Stark-cell modulation without internal frequency modulation. The CO 2 laser output power around the CH 3OH absorption center is stabilized to within ±1.0% for 60 min. The frequency stability of the CO 2 laser is estimated to be within ±1.4 MHz for 60 min, assuming the output fluctuation to be caused by this frequency fluctuation. As a result of the CO 2 pump laser stabilization, an output power stability of about ± 1.0% for 30 min is obtained for the 118.8 μm CH 3OH laser.

On the Physical Dynamics of Laser Mode Sweeping in a Fabry-Perot Resonator of Varying Optical Length

We present in this paper a basic analysis of the physical mechanism underlying the internal frequency modulation of a laser oscillator which is caused by a variation of the optical path length of its Fabry-Perot resonator. It is shown how adiabatic variations of the optical resonator length are continuously converted into frequency variations of the electromagnetic field energy trapped between the resonator mirrors by a rapid succession of small Doppler shifts, thus complying with the general principle of adiabatic invariance in oscillatory systems.

Single mode CO&amp;lt;inf&amp;gt;2&amp;lt;/inf&amp;gt;laser frequency modulation up to 350 MHz

Experiments on internal frequency modulation (FM) of a CO 2 laser showed no limitation of FM by the linewidth. However, distortions in the form of strong enhancement of sideband amplitude arise for frequencies equal to the cavity resonant frequencies, most pronounced if the modulator is positioned near a cavity mirror.