Value Of Linewidth Enhancement Factor Research Articles

On the pull-in behavior of optical injection phase-lock loop

This paper presents a detailed study of the pull-in behavior of an optical injection phase-lock loop (OIPLL) neglecting the noise components of the loop. We provide formulas for pull-in voltage and pull-in range of OIPLL in terms of the loop propagation delay, line-width enhancement factor and other parameters of the loop. In addition, we give a compact expression for the frequency pulling time of OIPLL for low injection and high injection level in presence of loop-delay. The effects of loop-delay and optical injection on the pull-in performance of the OIPLL are studied for non-zero values of line-width enhancement factor. Analytical expression of the maximum allowable loop delay is presented to study the deterministic stability of the loop. From the stochastic stability of the loop, we provide formula for the maximum value of the laser line-width to achieve the desired tracking performance. The simulation results are given in partial support of the conclusions of the analysis.

Influence of the linewidth enhancement factor on the characteristics of the random number extracted from the optical feedback semiconductor laser

Random numbers play an important role in many fields, including information security, testing and engineering practice. Especially in information security, generation of secure and reliable random numbers, they have a significant influence on national security, financial stability, trade secrets and personal privacy. Generally, random number generators can be classified as two main types: pseudo random number generators and physical random number generators. Pseudo random numbers with high speed are generated by software algorithms, but the inherent periodicity will cause serious hidden dangers when they are used in information security. Random numbers based on physical entropy sources (such as electronic thermal noise, frequency jitter of oscillator, quantum randomness) can produce reliable random numbers. However, due to the limitation of traditional physical source bandwidth, their generation speeds are at a level of Mbit/s typically, which cannot meet the needs of the current high-speed and largecapacity communication. In 2008, Uchida et al. (2008 Nat. Photon. 2 728) realized the physical random number of 1.7 Gbit/s by using a wideband chaotic laser for the first time. The emergence of wideband physical entropy sources such as chaotic laser greatly promote the rapid development of the physical random number generators. As far as we know, a semiconductor laser can generate wideband chaotic signals under external disturbances such as optical feedback, optical injection or photoelectric feedback. However, compared with the structures of other two lasers, the structure of the optical feedback semiconductor laser is simple and easy to integrate. Therefore, chaotic signals have received great attention to produce high-speed physical random number extracted from the optical feedback semiconductor laser. In the reported schemes, a variety of post-processing methods are used to improve the speed and randomness of random numbers. Besides, optimizing the chaotic entropy source can also improve the performance of random number. So far, the influence of internal parameters on the dynamic characteristics of semiconductor lasers has attracted wide attention. The linewidth enhancement factor is one of the key parameters for a semiconductor laser. The values of linewidth enhancement factor are different, depending on the type of semiconductor laser. The existence of linewidth enhancement factor results in a large number of unstable dynamic characteristics of semiconductor lasers. Therefore, it is of great significance for studying the influence of the linewidth enhancement factor on performance of random numbers. In this paper, we focus on the influence of the linewidth enhancement factor on the randomness of the obtained random numbers. The time delay characteristics and complexity are two important parameters to measure the quality of chaotic signals. The simulation results show that with the increase of the linewidth enhancement factor, the time delay characteristic peak of the chaotic signal from an optical feedback semiconductor laser decreases gradually, meanwhile, the maximum Lyapunov exponent of chaotic signal increases gradually. The randomness of random numbers, generated by the chaotic signal from the optical feedback semiconductor laser under different linewidth enhancement factors, is tested by NIST SP 800-22. The test results show that semiconductor laser with larger linewidth enhancement factor is chosen as a physical entropy source to generate random numbers with high quality.

Linewidth Enhancement Factor and Amplification of Angle-Modulated Optical Signals in Injection-Locked Quantum Cascade Lasers

AbstractThis paper presents a nonlinear analysis of the effect of linewidth enhancement factor (LEF) on the amplification of angle-modulated optical signals in injection-locked mid-infrared (IR) quantum cascade lasers (QCLs). A higher value of LEF tends to conserve the output angle modulation index of the amplified mid-IR signal particularly in the low-modulation frequency region. Further, a higher value of signal injection ratio produces a wider bandwidth of the locked QCL amplifier. The LEF introduces asymmetry in the lockband (LB) of the injection-locked QCL and this asymmetry increases with the increase in the value of LEF. Typically ratio of calculated lower-side LB to upper-side LB for an injection power level of – 20 dB and a LEF of unity is 1.67. The electron relaxation time in the uppermost subband lasing level in a three-level system has a profound effect on the LB asymmetry in a QCL.

Stability of continuous wave solutions of one laser model with large delay

Analysis of a delay differential laser model with large delay is presented. Sufficient conditions for existence of continuous wave solutions are found. It is shown that parameters determining the main part of asymptotics of these solutions lie on a bell-like curve. Sufficient conditions for stability of continuos wave solutions are found. The number of stability regions on bell-like curves is studied. It is proved that more than one region of stability may exist on these curves. It is shown that solutions with the same main part of asymptotics may have different stability properties if we change the value of linewidth enhancement factor. A mechanism for the destabilization of continuous wave solutions is found.

InAs/GaAs量子点激光器的增益和线宽展宽因子

A 500-μm-long cavity laser diode with 5 layers of In As quantum dot was fabricated. The laser materials were grown by gas-source molecular beam epitaxy. For the first time,the linewidth enhancement factor was acquired by gain fitting and weighted wavelength. Gain fitting is an important complement to Hakki-Paoli method,and plays an important role in evaluating whether the gain is saturation. The differential modal gain was evaluated by numerical differentiation of the maximum modal gain. The differential modal gain showed a maximum of 1. 33 cm- 1/ m A at 50 m A,and dropped off to 0. 34 cm- 1/ m A at 57 m A( ≈0. 99Ith). The weighted average wavelength was treated as central wavelength in order to calculate the wavelength movement. It was found that Δλ decreased slowly until closed to zero. The new method avoids the error due to selecting the data points,and the value of linewidth enhancement factor is from 0. 12 to 2. 75.

Role of linewidth enhancement factor on the frequency response of the synchronized quantum cascade laser

This paper presents a closed-form analysis of the synchronized quantum cascade laser (QCL) and studies analytically the effect of linewidth enhancement factor (LEF) on the frequency response of the QCL. The analysis predicts that there can be two types of response curves of the QCL—one like series resonant circuit response and the other like antiresonant circuit response. The linewidth enhancement factor introduces asymmetry in the frequency response of the synchronized QCL. The nature of asymmetry in locked QCL is seen to be different from that reported for interband semiconductor lasers. The asymmetry in series resonant-like response is inclined towards the positive detuning side while that in antiresonant circuit-like response is inclined towards the negative detuning side. The degree of asymmetry in QCL response is not only determined by the LEF but also by the upper subband electron relaxation time and the operating wavelength of the QCL. Although the value of LEF in QCL is smaller than that for interband lasers, calculation shows that the LEF has a profound effect on the response of the locked QCL.

Analysis of the Linewidth-Enhancement Factor of Long-Wavelength Tunnel-Injection Quantum-Dot Lasers

We have studied the linewidth-enhancement factor of 1.3-mum tunnel-injection quantum-dot (QD) lasers utilizing a rate-equation model that takes into account the injection of electrons directly into the QDs from a coupled quantum well, the presence of wetting layer states, and nonequilibrium carrier relaxation in the QDs. In a conventional separate confinement heterostructure QD laser, plasma effects, which result from a large portion of the injected carriers preferably occupying the barrier and wetting layer states, largely determine the values of the linewidth-enhancement factor and lead to a strong dependence of the linewidth-enhancement factor on injection current. In a tunnel-injection QD laser, however, due to the injection of "cold" electrons directly into the lasing states of the QDs, both the values of linewidth-enhancement factor and the dependence on injection current are substantially reduced. The calculated linewidth-enhancement factors of conventional separate confinement heterostructure and tunnel-injection QD lasers are in excellent agreement with reported experimental values. Our analysis elucidates the role of tunnel injection in achieving near-zero alpha-parameter, which would be important in the design of chirp-free high-speed QD lasers

RIN in mode-locked external cavity semiconductor lasers

The relative intensity noise (RIN) of a mode-locked hybrid soliton pulse source (HSPS) utilising a linearly chirped uniform fibre Bragg grating, is investigated, taking into account spontaneous noise, by using coupled-mode equations. It is shown that low noise does not affect the operation of device and therefore transform-limited pulses are generated over a wide tuning range around the fundamental frequency. However, for large values of linewidth enhancement factor, spontaneous coupling factor and gain saturation parameter, transform-limited pulses are not obtained over a wide tuning range because of increasing noise. Hence, the proper mode-locked range reduces. It is also shown that RIN reduction is possible by using linearly chirped uniform gratings as compared to unchirped gratings.

Dynamic characteristics of high-speed In0.4Ga0.6As/GaAs self-organized quantum dot lasers at room temperature

We have measured the room-temperature modulation characteristics of self-organized In0.4Ga0.6As/GaAs quantum dot lasers in which electrons are injected into the dot lasing states by tunneling. A small-signal modulation bandwidth of f−3 dB=22 GHz is measured. Values of differential gain at 288 K of dg/dn≅8.85×10−14 cm2 and gain compression factor ε=7.2×10−16 cm3 are derived from the modulation data. Extremely low values of linewidth enhancement factor α∼1 and chirp <0.6 Å were also measured in the devices.

Reduction of Frequency Chirping in Semiconductor Lasers through Injection Locking

This paper analyzes the reduction of frequency chirp under injection locking of the modulated laser to the CW master laser. A closed-form analytical formula has been presented for chirp suppression. Light has been thrown upon the dependence of chirp reduction on the value of linewidth enhancement factor of the slave laser, master-slave detuning and the optical injection power. Effect of injection locking on the output AM index of the modulated laser has also been explored.