Modulation transfer characteristics of injection-locked diode lasers

In this paper, we investigate modulation transfer in an injection-locked diode laser when the master laser frequency or intensity is modulated. The modulation transfer properties of injection-locked diode lasers are shown to depend on frequency detuning between the master and slave lasers. This observation is of practical importance, since the laser frequencies are typically prone to ambient conditions. Also conversion of the master laser frequency modulation to slave laser intensity modulation is shown to be of importance if large frequency modulation amplitudes and small intensity modulation amplitudes of the master laser are used. On the other hand, the injection-locking technique is proved to be an effective way to suppress spurious intensity modulation in certain operational conditions.     

Mutual injection locking and coherent combining of three individual fiber lasers

Mutual injection locking and coherent combining of three individual erbium-doped fiber lasers are reported. Theoretical model of the three fiber lasers under mutual injection is also analyzed. Under free running state, the far field beam profile is a simple intensity superposition as three incoherent beams. Under mutual injection locking, interference lobes with high contrast ratio are obtained in the far field of three fiber lasers, which shows that the three fiber lasers have good interference characteristic under mutual injection. The experimental results are in good agreement with the theoretical results. According to this method, we can also realize coherent beam combining in more fiber lasers.     

Tuning ranges of an injection-locked excimer laser

The advantages and the practical limitations of injection locking are discussed. Experimental results for a system working in the regime between ideal injection locking and regenerative amplification are presented.     

Photonic microwave generation and transmission using direct modulation of stably injection-locked semiconductor lasers

Direct modulation of a semiconductor laser subject to stable injection locking is capable of generating microwave subcarriers that are broadly frequency-tunable, more than 4 times its free-running relaxation resonance frequency, and are highly sideband-asymmetric, more than 22 dB. The latter characteristic makes the laser system particularly attractive for radio-over-fiber applications. Therefore, such modulation sideband asymmetry, its underlying mechanism, and its effect on chromatic dispersion-induced microwave power variation are extensively studied, in particular, over a broad range of injection conditions. Mappings showing integrated and global understandings of the modulation sideband asymmetry together with the modulation frequency enhancement are obtained accordingly. Interestingly, it is found that the microwave frequency can be tuned over a broad range while keeping a similar level of modulation sideband asymmetry and vice versa, either of which is achieved by simply changing the injection condition. This, therefore, considerably adds the flexibility and re-configurability to the laser system. The cavity resonance shift due to injection locking is responsible for not only the enhanced modulation frequency but also the modulation sideband asymmetry, where a modification in its previous interpretation is obtained for explanation. The modified modulation characteristics are strong functions of the linewidth enhancement factor, making it possible to choose lasers with proper values of the factor for different photonic microwave characteristics.     

Numerical study of converting beat-note signals of dual-frequency lasers to optical frequency combs by optical injection locking of semiconductor lasers

The optical injection locking of semiconductor lasers to dual-frequency lasers is studied by numerical simulations. The beat-note signals can be effectively transformed to optical frequency combs due to the effective four wave-mixing in the active semiconductor gain medium. The low-noise Gaussian-like pulse can be obtained by locking the relaxation oscillation and compensating the gain asymmetry. The simulations suggest that pulse trains of width below 30 ps and repetition rate in GHz frequency can be generated simply by the optical injection locking of semiconductor lasers. Since the optical injection locking can broaden the spectrum and amplify the optical power simultaneously, it can be a good initial stage for generating optical frequency combs from dual-frequency lasers by multi-stage of spectral broadening in nonlinear waveguides.     

两个半导体激光器交叉注入的理论分析

 提出了一个复杂非线性动力学系统－交叉注入锁定半导体激光系统。针对其中最简单的两激光系统,导出了描述它的方程组,解析求解了它们具有相同自由振荡频率时的定态解。结果表明,在相同耦合条件下,锁定的频率范围比主-从方式扩大了大约一倍。从结果可以看出,即使是这种特殊系统,在锁定后频率也可能会改变。     

An injection-locked erbium-doped fibre ring laser

The effects of injection-locked on an erbium-doped fibre laser based on a ring configuration have been demonstrated. A comparison between experimental results and theoretical prediction in the locking range is made with consistent results in a small wavelength range of about 15 nm. Frequency stabilisation was obtained by applying this approach, ensuring stable output power of the fibre laser system.     

两个半导体激光器交叉注入的理论分析

提出了一个复杂非线性动力学系统－交叉注入锁定半导体激光系统。针对其中最简单的两激光系统,导出了描述它的方程组,解析求解了它们具有相同自由振荡频率时的定态解。结果表明,在相同耦合条件下,锁定的频率范围比主-从方式扩大了大约一倍。从结果可以看出,即使是这种特殊系统,在锁定后频率也可能会改变。     

注入噪声对光纤激光器锁模启动的影响

 从掺镱光纤激光器腔内的激光场出发,讨论了掺镱光纤激光器腔内的噪声信号对锁模启动的影响,并针对我们设计的8字腔超短脉冲光纤激光器进行了研究。通过对激光器腔内锁模过程的分析发现：在泵浦功率为214.75 mW时,自行研制的8字形腔掺Yb³⁺光纤激光器在未注入噪声信号时,输出端在30～50 s内获得稳定的锁模脉冲激光输出;在腔内注入脉宽30 ns,频率10 kHz,平均功率0.2 mW的脉冲噪声后,输出端在1~2 s内获得同样稳定的锁模脉冲激光输出。实验结果表明,注入激光器谐振腔内一定的噪声信号,可加速锁模的启动。     

Periodic locking of chaos in semiconductor lasers with optical feedback

We show how a chaotic system can be locked to emit a periodic waveform belonging to its chaotic attractor. We numerically demonstrate our idea in a system composed of a semiconductor laser driven to chaos by optical feedback from an external cavity. The clue is the injection of an appropriate periodic signal that modulates the phase and amplitude of the intra-cavity radiation, a chaotic analogy of conventional mode-locking. The result is a time process that manifests a chaotic signature embedded in a long-scale periodic train.     

Wideband optical comb generation using an injection-locked feedback loop

This paper presents a novel circuit for wideband optical comb generation which will be useful in DWDM applications. The injection-locked feedback loop broadens the bandwidth of the optical comb. The injection-locked laser diodes perform amplification, bandpass filtering as well as laser RIN suppression. Several hundred GHz bandwidth optical comb can be generated by this circuit within a reasonable power envelope.     

A simple heterodyne frequency offset locking system for pulsed lasers

As a new approach the heterodyne frequency offset locking system which is applicable to a broad range of pulsed lasers is described. A 100 MHz wide-band and all-digital frequency discriminating technique is presented and an offset locking loop in which the frequency discriminator works accordingly is designed. The result of the experiment on offset locking between a CW CO₂ laser and an electro-optically Q-switched CO₂ laser with an optical pulse width 300 ns and its repetition rate 20 kHz showed that the beat frequency stability was kept within ±2 MHz.     

利用全光纤耦合环实现三路光纤激光器的相位锁定

利用三个2×2的光纤耦合器按一定规则联接成一个全光纤耦合环,该耦合环将三个独立的掺铒光纤激光器连成一个锁相阵列. 由于耦合环的引入,锁相阵列的整体损耗减小,且三个单元激光器之间可以进行有效的能量相互注入耦合,进而实现阵列的锁相输出. 实验中观察到的远场干涉图样和锁相前后的输出光谱均表明三路光纤激光器实现了相位锁定,当三路抽运源的功率均为100 mW时,获得了92 mW的稳定相干输出. 关键词： 光纤激光器 相干合成 光纤耦合器 相位锁定     

再生锁模激光系统的定态输出及其稳定性

将准孤子解代入再生锁模激光系统的主方程，推导出脉冲参量的三个自治微分方程. 求解了无啁啾和有啁啾两种情况下系统的定态解，并分析了其稳定性. 研究表明，系统的定态输出随系统的调制深度或调制频率、群速色散或自相位调制等参量值的变化而变化. 因此，通过调制系统的参量可以控制激光系统的定态输出. 关键词： 再生锁模激光系统 线性稳定性分析 罗斯-霍维茨判据 定态输出及其稳定性     

Open loop synchronization of semiconductor lasers with periodical injection

In this paper, the influence of fluctuation amplitude and frequency of the injection field on the dynamics and synchronization of semiconductor lasers are studied numerically. The fluctuation amplitude and frequency of the injection field are controlled by external modulation of the master laser. In the simulation, we use a modified correlation coefficient named similarity index to evaluate the synchronization performance. The results show that frequency and fluctuation amplitude of the injection field play important roles on the dynamics and synchronization quality of the system. Large fluctuation amplitude and moderate fluctuation frequency of the injection field will contribute to the synchronization of the two lasers. The results can also be extended to the analysis of chaotic signals.     

32路光纤激光相干阵列的相位锁定

报道了32路光纤激光相干阵列的相位锁定实验研究。搭建了32路光纤激光相干阵列实验系统,基于现场可编程逻辑阵列（FPGA）设计制作了高速高精度相位控制器。当相位控制器执行随机并行梯度下降（SPGD）算法对各路激光的相位进行锁定时,相干阵列输出的激光功率与不进行相位锁定时相比提高了约26倍。     

Long-exposure far-field properties of the array of mutually-injected fiber lasers

In this paper, the long-exposure far-field properties of the array of mutually-injected fiber lasers are studied to understand the effect of the multiple phase-locked states on coherent beam combining of the array. It is found that the long-exposure far-field will degenerate into the superposition of the intensities of the elementary lasers when all the phase-locked states of the array are exported with the same probability. It means that the interference pattern will be greatly weakened in the long-exposure far-field because of the export of multiple phase-locked states of the array. This result implies that the multiple phase-locked states of the array go against coherent beam combining of the array, and only some of these phase-locked states should be exported. Then, the effects of the high-order phase-locked states on the far-field are discussed. The result suggests that only the in-phase state should be exported (i.e., all the other phase-locked states should be suppressed) in order to realize high-efficiency (> 80%) coherent beam combining when the number of the elementary lasers of the array is smaller than 19.     

Determine locking range of coherently combined fiber lasers joined by fiber couplers

When the wavelength difference of two fiber lasers, sharing a common reflection mirror with the aid of an optical coupler, is tuned to fall into a certain range, the array lasers can be locked to generate coherent radiation with a wavelength somewhere between the two constituent field wavelengths. Based on the fact that the laser should oscillate at the wavelength with the lowest losses and the band widths of the reflection curves of the laser tuning elements are finite, the locking range of the laser array has been quantified. For the tuning element (i.e., fiber gratings) selected in this work, the calculations show that the locking range is mainly dependent on the coupling coefficients of the gratings which ever is smaller.     

Analysis of mode-locked internally frequency doubled broad-band continuous wave lasers

Closed-form analysis of pulse evolution in the transient regime in an actively modelocked internally frequency doubled broad-band continuous wave laser is presented. The analysis enables investigation of the effect of nonlinear crystal inside the laser cavity on mode-locked pulse parameters at the fundamental frequency. It is shown that the presence of internal second harmonic crystal broadens the fundamental mode-locked pulse while accelerating the approach of the system to steady-state. The dependence of pulse parameters on the bandwidth of the tuning element, modulation depth of the active mode-locker and conversion efficiency of the frequency doubler is presented in detailed graphical form.     

Analysis of linewidth and extinction ratio in directly modulated lasers for performance optimization in 10 Gbit/s CWDM systems

Direct Modulation Lasers (DMLs) have attracted increased attention during the past few years because of their intrinsic simplicity and cost-effectiveness, especially when applied to WDM metro and access networks. However, the output power waveform from a directly modulated laser is not an exact replica of the modulation current and its instantaneous optical frequency varies with time depending on the changes in optical power and the extinction ratio (ER) (an effect also known as frequency chirp). In this work, using an Optical Communication System Design Software, we have studied a directly modulated WDM 10 Gb/s system which transmission performance depends strongly on DML characteristics; simulation results have provided supplementary details about the effects of DML type (adiabatic or transient chirp dominated) as well as the effects of the optical output power. These details can provide useful design guidelines for constructing a WDM metro network.