Numerical analysis of optical feedback phenomenon and intensity noise of fibre‐grating semiconductor lasers

This paper demonstrates numerical analysis of the dynamics and intensity noise of fibre‐grating semiconductor lasers (FGSLs). The induced phenomenon of strong optical feedback (OFB) is analysed. The simulations are based on an improved time‐delay rate equations model of a single‐mode laser that takes into account the multiple round‐trips of the lasing field in the fibre cavity. The analyses are performed in terms of the temporal trajectory of the laser intensity, bifurcation diagram and relative intensity noise (RIN). We explore influence of the fibre‐cavity length on the dynamics and RIN. The results show that when the fibre cavity is short, the regime of strong OFB is characterized by either continuous‐wave (CW) operation or periodic pulsation. The pulsation frequency is locked at the frequency separation of either the compound‐cavity modes or the external fibre‐cavity modes. The corresponding RIN level is close to or higher than the level of the solitary laser depending on pulse symmetry. When the fibre cavity is long, the laser exhibits unstable dynamics over wider range of OFB. Moreover, the strong‐OFB pulsation becomes beating quasi‐periodic at the relaxation oscillation frequency and the fibre‐cavity mode‐separation frequency. Copyright © 2007 John Wiley & Sons, Ltd.     

Numerical modeling of the route‐to‐chaos of semiconductor lasers under optical feedback and its dependence on the external‐cavity length

This paper investigates numerically influence of the external‐cavity length on the type of the route‐to‐chaos of semiconductor lasers under external optical feedback. The study is based on numerical solution of a time‐delay model of rate equations, and the solutions are employed to construct bifurcation diagrams and to examine the Fourier frequency spectrum of the laser output. The ratio of the relaxation frequency to the external‐cavity resonance frequency is employed to measure the influence of the length of the external cavity. The route‐to‐chaos is period doubling when this frequency ratio is less than unity. The route is sub‐harmonic when the frequency ratio increases up to 2.25. When the frequency ratio increases further, the transition to chaos becomes quasi‐periodic characterized by the compound‐cavity frequency and the relaxation frequency as well as their difference. Copyright © 2009 John Wiley & Sons, Ltd.     

Microring-Resonator-Based Widely Tunable Lasers

We describe widely tunable lasers incorporating microring resonators. By using a double-ring-resonator-coupled filter, a wide wavelength tuning range is achieved with a low tuning current. A double-ring-resonator-coupled tunable laser has series-connected microring resonators in the laser cavity. A tuning range of 50 nm is achieved with injection current of less than 5.2 mA. This low injection current reduces the frequency drift caused by thermal transients to less than 5 GHz. We also describe an integrated filtered feedback tunable laser consisting of a Fabry–Perot (FP) laser and integrated filtered feedback sections. In this device, the filter section is removed from the laser cavity. The device exhibits a 24-nm tuning range with a side-mode suppression ratio of 50 dB. The frequency drift is less than 1 GHz because the longitudinal mode of the laser is mainly determined by the FP laser section. We have also developed a filter-free widely tunable wavelength converter by monolithically integrating a tunable laser and a wavelength converter based on a semiconductor optical amplifier. Wavelength conversion for a 10-Gb/s nonreturn-to-zero signal is also demonstrated, tunable over a 40-nm range.      

Stability of injection-locked CW-emitting external-cavity semiconductor lasers

We analyze the stability of phase-locked emission modes of a semiconductor laser subject to both optical feedback and continuous-wave optical injection. We consider a large external cavity and examine the case of weak injection and feedback rates. We find that injection increases the number of excitable resonances in the external cavity and that phase-locked antimodes may bifurcate into a regime of stable bounded phase oscillations. The period of these oscillations is typically on the order of twice the round-trip time.     

Numerical modeling of the output and operations of semiconductor lasers subject to strong optical feedback and its dependence on the linewidth‐enhancement factor

Influence of the linewidth‐enhancement factor on the output and operations of InGaAs/InP pumping lasers emitting at a wavelength of 980 nm under strong optical feedback is investigated numerically. The investigations are performed based on intensive numerical integration of an improved time‐delay rate equations of semiconductor lasers over wide ranges of the linewidth‐enhancement factor and optical feedback strength. The results show that the semiconductor laser operates under strong optical feedback in continuous wave and pulsation at small values of the linewidth‐enhancement factor. Under large values of the linewidth‐enhancement factor, the laser happens to exhibit chaos and pulsation. We predict that semiconductor laser subjected to strong optical feedback exhibits much more stable pulsing operation under higher values of the linewidth‐enhancement factor, which indicates that the laser is locked at the external cavity frequency. Copyright © 2010 John Wiley & Sons, Ltd.     

Nonlinear Dynamics of Semiconductor Lasers Under Repetitive Optical Pulse Injection

In this paper, nonlinear dynamics of semiconductor lasers under repetitive optical pulse injection are studied numerically. Different dynamical states, including pulsation and oscillation states, are found by varying the intensity and the repetition rate of the injection pulses. The laser is found to enter the chaotic pulsation (CP) states and chaotic oscillation (CO) states through individual period-doubling routes. Mapping and corresponding Lyapunov exponents of these dynamical states are plotted and examined in the parameter space. Moreover, the bandwidths of the chaos states found are investigated, where the bandwidths of the CP states observed at the strong injection regime are two to four times broader than the bandwidths of the CO states found at the weak injection regime. In this paper, frequency-locked states with different winding numbers, the ratio of the oscillation frequency, and the repetition frequency of the injection pulses are also studied. Both the cases for repetition frequency above and below the relaxation oscillation frequency are examined. The winding numbers of the frequency-locked states reveal a Devil's staircase structure, where a Farey tree showing the relations between the neighboring states is constructed.      

Low-frequency fluctuations in vertical-cavity surface-emitting lasers with polarization selective feedback: experiment and theory

We present theory and measurements on a vertical-cavity surface-emitting laser (VCSEL) biased close to its solitary threshold and subject to polarization selective external optical feedback. The system shows low-frequency fluctuations (LFF) in the selected polarization mode (PM). Below solitary laser threshold, the orthogonal PM remains silent, while it only responds after a dropout event in the main mode above threshold. Our calculations show good agreement with the measurements and identify a type of synchronization between the low-frequency dynamics of the two PMs.     

Tunable narrow-linewidth photonic microwave generation using semiconductor laser dynamics

Generation of a broadly tunable narrow-linewidth microwave subcarrier on an optical wave by exploiting the nonlinear dynamics of a semiconductor laser through a proper combination of optical injection and optoelectronic feedback is experimentally demonstrated. The microwave frequency is generated by the period-one oscillation of an optically injected semiconductor laser. It is tuned in the range from 10 to 23 GHz by varying the optical injection strength, and its linewidth can be narrowed by optoelectronic feedback alone. The linewidth is reduced from the range of 40-120 MHz without stabilization by three orders of magnitude to the range of 10-160 kHz with stabilization through optoelectronic feedback alone. The effect of a small microwave modulation is also investigated. It reduces the linewidth to below the 1-kHz resolution limit of our instrument.     

Low‐noise blue light generation of intracavity frequency‐doubled LD‐pumped Cr:LiSAF laser by single‐mode method

We have demonstrated the production of low‐noise blue SHG (Second Harmonic Generation) light by single‐mode oscillation in an intracavity frequency‐doubled laser diode (LD)‐pumped Cr‐doped LiSrAlF₆ (Cr:LiSAF) solid‐state laser. The SHG crystal was LiB₃O₅ (LBO). A birefringent filter and an etalon plate were used for the single‐mode Cr:LiSAF laser oscillation wave. A maximum blue SHG output power of 32 mW was obtained by using a 1‐mm‐thick birefringent filter and an etalon plate 200 μm thick with 20% reflectivity. The oscillation wavelength varied by 0.24 pm/hPa in response to changes in atmospheric pressure. A long‐term stability of 300 hours was obtained with the cavity enclosed in a barostat. © 2001 Scripta Technica, Electr Eng Jpn, 138(1): 49–55, 2002     

High-power mode-locked external cavity semiconductor laser usinginverse bow-tie semiconductor optical amplifiers

This paper presents experimental results of using an inverse bow-tie gain guided semiconductor optical amplifier (SOA) as the optical gain element in a high-power external cavity semiconductor laser. An average output power of 700 mW is demonstrated in continuous-wave (CW) operation while 400 mW of average power is obtained in both passive and hybrid mode-locked operation, with subsequent optical amplification in an identical SOA. The mode-locked laser operates at a repetition rate of 1.062 GHz, owing to the interplay between the gain and saturable absorber dynamics. Optical pulses are generated with a temporal duration of 5 ps, which implies a pulse energy of 376 pJ, and a peak power of 60 W. Further reduction of the optical pulsewidth to 1.3 ps is also achieved by using dispersion compensation techniques. These results show the promise of novel SOA devices for use as gain elements in external cavity semiconductor lasers. The generated output pulse characteristics from mode-locked operation is sufficient for use in novel three-dimensional data storage applications, and in large-scale commercial printing and marking applications     

椭圆聚焦型无极紫外固化灯研究与设计

利用蒙特卡洛分析法和有限积分法,设计一种椭圆聚焦型无极紫外固化灯。首先利用光学仿真软件分析了椭圆柱型谐振腔对非理想圆柱光源的光线利用率和光斑宽度两者之间的影响,选择合适的放大倍率和离心率;再通过电磁场仿真软件分析了谐振腔的电磁共振模式及频率,确定最佳电磁共振条件下谐振腔的开口深度;最后根据波导耦合原则,设计谐振腔与波导的耦合方式。经实验测试,无极紫外固化灯的发射光谱与所用无极紫外放电灯管的理论光谱相一致,并且测得的紫外光功率分布也与光学仿真的结果符合。     

Frequency control characteristics of a single-frequency fiber laserwith an external light injection

Characteristics of a single-frequency erbium-doped fiber laser (EDFL) controlled by an external light source is investigated. The frequency control is achieved by cooperatively induced spatial hole-burning (SHB) formed by the interference between the lasing light and the external light. We evaluate the frequency stability of several cavity designs of the fiber laser and the frequency control characteristics in detail. Tunable operation as wide as 30 nm wavelength range with a good frequency stability is also demonstrated     

Tuning range extension by active mode-locking of external cavity laser including a linearly chirped fiber Bragg grating

We demonstrate electrical wavelength tuning by mode locking of an external cavity laser (ECL) with linearly chirped fiber Bragg grating (LCFBG). The configuration consists of a laser chip providing the gain coupled to an LCFBG with a large chip rate of 10 or 55 nm/cm providing the counter-reaction for laser oscillation. The laser chirp is electrically modulated by a sinusoidal signal in such a way that the ECL is mode locked. By changing the modulation frequency, a wavelength tuning range of 27 nm is achieved with the 10 nm/cm LCFBG, and a partial tuning range over 41 nm is demonstrated with the 55-nm/cm LCFBG. The output pulse stream at a specific mode-locking frequency and a corresponding wavelength is obtained for both positively and negatively chirped grating. A time bandwidth product reduction is measured in the case of negatively chirp grating when compared with positively chirp grating. A simple general law between the laser parameters is given (locking frequency, tuning range, and FBG chirp value). The parameters for a 40-nm tunable source modulated at 10 GHz are given. This simple tuning mechanism is very well adapted for a structure that requires accurate wavelength monitoring.     

Highly External Optical Feedback-Tolerant 1.49-$mu$ m Single-Mode Lasers With Partially Corrugated Gratings

An InGaAsP single-mode laser diode (LD) highly tolerant to optical feedback was realized utilizing a partially corrugated grating with a window-mirror structure. The length and the coupling coefficient of the grating were properly chosen to enable moderate output power, low feedback sensitivity, and a side mode suppression ratio of 40 dB simultaneously. Under −16 dB external optical feedback, the relative intensity noise (RIN) was improved by 10 dB compared with that of a conventional DFB LD. The RIN was maintained at less than −120 dB/Hz under strong external optical feedback as high as −10 dB. These results show that the fabricated lasers are potentially useful for isolator-free optical modules.      

Modeling of noise and distortion associated with ultra‐high‐speed modulation of VCSEL with slow‐light feedback

This paper presents numerical modeling on the noise properties and signal distortion associated with millimeter‐frequency modulation of vertical‐cavity surface‐emitting laser (VCSEL) under with a transverse‐coupled cavity. The study is based on a time‐delay rate equation model that takes into account the multiple round trips in the feedback cavity and the optical loss and phase delay in each round trip. Strong slow‐light feedback is found to boost the modulation bandwidth to frequencies approaching 70 GHz and induce resonance modulation due to photon–photon resonance (PPR) over passbands centered on frequencies reaching 90 GHz. We show that the relative intensity noise of the VCSEL with resonance modulation is enhanced when the noise frequency approaches the corresponding PPR frequency VCSEL. The same effect applies for the VCSEL with extended carrier‐photon resonance (CPR) at the CPR frequency. The low‐frequency part is characterized by flat (white) noise of level nearly equal to −140 dB/Hz. The second‐harmonic distortion (2HD) values are smaller than −10 dB under small‐signal modulation and increase to lower than −5 dB when the modulation index becomes 0.3. Copyright © 2015 John Wiley & Sons, Ltd.     

Analysis of a Spatial-Filtering Passive Fiber Laser Beam Combining System

In this paper, a formulation of the cavity mode structure, loss, and beam quality of a ring-cavity fiber laser beam combining apparatus is developed, which shows that the resonator is rigorously single mode. The passive phasing property is clearly understood on the basis of the theory, and conditions are specified for a cavity that permits the attainment of optimum phasing conditions. An important result is that reduction of over-all cavity loss must be achieved at the price of reduction of maximum array size, although mitigated by the property that this loss occurs in the low-power feedback leg. Application of the analysis to specific examples gives the dependence of cavity loss and Strehl ratio on fiber and cavity properties.     

High-yield external optical feedback resistant partially corrugatedwaveguide laser diodes

This paper clarifies high yield external optical feedback resistant characteristics in partially corrugated waveguide laser diodes (PC-LD's), compared to conventional distributed feedback laser diodes (DFB-LD's). Based on a novel large single dynamic analysis by combining the transient mirror loss (total net threshold gain) fluctuation with the van der Pol equations in single-mode LD's, the feedback effect of mirror loss on the external optical feedback resistance in single-mode LD's was found for the first time. Theoretical analysis predicted that in the PC-LD's, relatively stable transient mirror loss suppresses the positive feedback effect of mirror loss, as well as the optical output fluctuations under the external optical feedback. Experimental results show that the increase of the relative intensity noise in 70% PC-LD's could be suppressed to lower than -120 dB/Hz and the minimum RIN was as low as -126 dB/Hz with the external optical feedback of -20 dB     

Passive optical limiting of picosecond-nanosecond laser pulsesusing highly nonlinear organic liquid cored fiber array

We present a detailed account of theoretical and experimental studies of nonlinear molecular photonic processes accompanying the propagation of short intense laser pulses through an organic liquid cored fiber array. The theory takes into account two-photon absorption, excited state absorption, and dynamical evolution of the molecular energy level populations and the laser intensity. The coupled dynamical equations for the molecular energy-level populations and laser intensity are solved numerically using experimentally observed molecular and optical parameters. Experimentally obtained optical limiting results are analyzed along with nonlinear absorption and pump-probe studies of other nonlinear optical processes occurring in the fiber core. It is found that in the nanosecond time regime, besides excited state and two-photon absorption, thermal and density effects also contribute significantly to the optical limiting performance of the constituent fiber     

基于电感电压反馈和输入整形技术的LC滤波器混合阻尼控制

电流型PWM整流器采用LC环节来滤除谐波及帮助器件换流,LC型滤波器呈二阶特性,存在谐振尖峰,且电容阻尼较小,在控制系统存在扰动的情况下,容易引起电流波形畸变和振荡。提出了一种采用输入整形技术和电感电压反馈结合的控制策略,输入整形技术能够有效地抑制小阻尼系统的振荡,电感电压反馈控制能够在外部干扰抑制网侧电流波形畸变。结合两者的优点,可有效地解决电流型脉宽调制整流器网侧电流振荡和畸变。仿真验证了所提出的控制策略能够有效减少电流畸变,增加系统的稳定性,并具有一定工程实用性。     

Frequency response of strain-compensated InGaAsN-GaAsP-GaAs SQW lasers

We investigate the below and above threshold frequency response of InGaAsN lasers with different nitrogen content. This is accomplished through detailed analysis of the small signal modulation response of the laser diodes using a comprehensive model based on rate equations and that incorporates the effect of parasitics. For below threshold conditions the model is instrumental in separating the contributions from the parasitics (more severe at low bias) and carrier recombination (predominant at higher bias) to the measured carrier lifetime. It is found that the addition of nitrogen reduces the recombination lifetime, mainly as a result of a four-fold increase in monomolecular recombination which predominates even near threshold. For bias above threshold the analysis compares electrical versus optical modulation frequency responses and concludes that resonance frequency and damping extracted from the electrical modulation responses are significantly influenced by the device parasitics. Instead, it is shown that optical modulation traces allow extraction of a relaxation frequency that is shaped only by the stimulated processes in the laser active region. Even in this case, the damping is found to be affected by the parasitics. When compared with nitrogen free lasers, a reduction in the resonance frequency is observed, while the damping is not altered. The former arises from a factor of /spl sim/2.5 decrease in the combined effect of the differential gain and carrier transport parameters. The latter reflects the more significant contribution of the parasitics to the damping.