Self-pulsation dynamics in narrow stripe semiconductor lasers

In this paper, we address the physical origin of self-pulsation in narrow stripe edge emitting semiconductor lasers. We present both experimental time-averaged polarization-resolved near-field measurements performed with a charged-coupled device camera and picosecond time resolved near-field measurements performed with a streak camera. These results demonstrate dynamic spatial-hole burning during pulse formation and evolution. We conclude from these experimental results that the dominant process which drives the self-pulsation in this type of laser diode is carrier induced effective refractive index change induced by the spatial-hole burning.     

Characteristics of a semiconductor laser with external feedback

The theoretical analysis of the compound cavity of a semiconductor laser with external optical feedback is conducted. For large optical feedback, the output power from the laser and its oscillation frequency differ from those for small optical feedback. From the rate equations of the compound cavity, the conditions of the laser oscillation are derived in the presence of large optical feedback The dependencies of the output power and the laser oscillation frequency on the external-cavity length are investigated. Some new results involving laser oscillation depending on the external-cavity length are presented. The experimental results are compared with theoretical predictions. The dependence of the laser oscillation on the external-cavity length is qualitatively explained in the present model     

The dependence of the output of an external-cavity laser on therelative phases of inputs from five gain elements

Five diode lasers that each have one facet antireflection (AR) coated are fiber coupled into an external-cavity and operated as a coherent ensemble. The external-cavity laser output power and spectrum are functions of the relative phases of the inputs from the optical fibers. The phases can be adjusted for an optimum single-mode spectrum simultaneous with maximum output power. In this case, the residual reflections from the AR-coated facets are also properly phased. Dephasing reduces the output power and tunes the wavelength through a series of discrete, lower-power maxima. These maxima occur at wavelengths for which the fiber inputs to the cavity are again in phase but the reflections from the AR-coated facets are not in phase     

Bistability in grating-tuned external-cavity semiconductor lasers

Bistability has been observed in the tuning characteristic and power versus current relation of a 1.3 μm grating-tuned external-cavity semiconductor laser. Tuning-direction reversal, current variations, and feedback interruption can change the output power and threshold current at a given wavelength. These effects are shown theoretically to be due to the coupling of the semiconductor gain and index of refraction. From measurements of the semiconductor chip facet reflectivity, solitary laser diode mode spectrum, and tuning curve in the presence of external feedback, the analysis yields values for the external feedback strength, semiconductor modal loss, and linewidth enhancement factor. Using an InGaAsP double-channel-planar-buried-heterostructure laser diode with a 4 percent reflectivity antireflection-coated facet inside an external cavity consisting of a 0.60 numerical aperture lens and a 1200 line/mm diffraction grating, we found 22 percent external feedback, 60 cm^-1modal loss, and a linewidth enhancement factoralpha = -7.1.     

High-power 980-nm ridge waveguide laser diodes including an asymmetrically expanded optical field normal to the active layer

We propose a new ridge waveguide laser diode (LD) which supports an asymmetrically expanded optical field normal to the active layer in order to increase the maximum kink-free output power and reduce the aspect ratio of output beams. The dependence of maximum kink-free output power on facet reflectivity was analyzed from the viewpoint of the total optical power in the cavity. It was clarified that the maximum kink-free output power is influenced by the facet reflectivity which affects the refractive index changes of the ridge region via the total optical power in the cavity. More than 600 mW of maximum kink-free output power and an aspect ratio of less than 2.5 were achieved in experiments with 980-nm ridge waveguide LDs by means of this proposed new structure.     

Dynamic properties of optically switched bistable semiconductorlasers

The dynamic properties of optically switched semiconductor lasers biased from below-to-above threshold are presented theoretically. An analytic expression for the carrier density in the active region of a laser with respect to time is given to discuss the switching-off time. The numerical results show that the switching-on time and the switching-off time are governed by different mechanisms. They are related to the laser parameters for the free-running laser. They also depend on the optical power and the time duration of the input optical pulse and the frequency detuning between the frequency of the free-running laser and that of the input optical pulse. A small frequency detuning is desired to reduce both the switching-on and switching-off times. However, there is an optimal detuning to maximize the energy of the output optical pulse. On the other hand, for fixed detuning and injection power, a larger bias current results in a shorter switching-off time, but a lower bias current results in a shorter switching-on time     

A theoretical analysis of optical clock extraction using aself-pulsating laser diode

The potential for using inexpensive compact disc laser diodes as optical clock extraction elements in transparent networks has led to an increase in research into the dynamics of self-pulsating laser diodes. We use a rate-equation model to simulate the synchronization of the self-pulsating laser output pulses to a periodic optical signal, In particular, we investigate the time it takes for the laser to synchronize to the input signal and also, the time taken for the laser to unlock when the signal is removed. The effect of varying the power of the optical signal and the detuning of the input signal frequency relative to the laser's self-pulsation frequency are determined. Our results enable us to identify important issues which need to be addressed when a self-pulsating laser diode is used in a clock extraction subsystem, In particular, we find that the signal frequency and laser free-running frequency must be as close as possibility to minimize errors. Also, the higher the signal power the quicker the laser synchronizes to the signal, although we find that if the power becomes too large the laser can no longer lock, which would cause a significant increase in detection errors     

Low-noise 650-nm-band AlGaInP visible laser diodes with a highlydoped saturable absorbing layer

Stable self-sustained pulsating and low-noise 650-nm-band AlGaInP visible laser diodes were demonstrated by adopting a novel structure, which has a highly doped saturable absorbing (SA) layer. Short carrier lifetime, which is indispensable for self-pulsation, was realized by applying high doping concentration to the p-type SA layer. 500-μm-long devices with 51%/51% coated facets were fabricated, resulting in the threshold current of 75 mA at 20°C. The temporal output power was measured at the average output power of 5 mW and the stable self-pulsation was observed up to an ambient temperature of 60°C. Therefore, the relative intensity noise (RIN) was kept about -140 dB/Hz in temperature ranging from 20°C to 60°C. Since the refractive index difference could be kept large and the optical mode could be confined effectively, the astigmatism in this work was below 3 μm at 5 mW against dc injection current. The lasers operated over 1350 h under the average output power of 5 mW at 60°C     

Bistability and optical switching in a polarization-bistable laserdiode

Dependences of the polarization-bistable condition on the coefficients of linear and nonlinear gains of a laser diode are analyzed, including S-shaped and pitchfork types of bistability, in the optical output versus injection current characteristics. Moreover, the steady-state and dynamic characteristics of the optical output for optical input are investigated, taking account of a detuning of incident optical beam from the cavity resonant frequency of a polarization-bistable laser diode, TE-TM polarization switching is shown to be attained in the optical output of the polarization-bistable laser diode in a very fast switching time less than a nanosecond by the application of TE and TM optical input pulses     

Nanosecond Switching and Wavelength Tuning of External-Cavity Laser Diode Using a Reflective Electroabsorption Modulator

We present a novel technique for ultrafast on-off switching and wavelength tuning of an external-cavity laser diode (ECLD) using an intracavity reflective electroabsorption modulator array as the end mirror. on-off and wavelength switching of the ECLD are based upon the electrically induced control of the modulator's reflectivity yielding a modulation of the cavity losses and hence a modulation of the lasing threshold. We experimentally demonstrate on-off switching of selected wavelengths with a contrast in excess of 40 dB. Ultrafast modulation in the nanosecond-regime has been achieved which is close to the fundamental physical speed limit of the ECLD.     

A dual-wavelength erbium-doped fiber laser with widely tunable wavelength spacing

A stable dual-wavelength erbium-doped fiber laser （EDFL） with tunable wavelength spacing and equalized output power is proposed and experimentally demonstrated. The fiber laser uses two fiber Fabry-Perot tunable filters （FFP- TFs） as the wavelength filter. The main cavity is divided into two sub-cavities with imbalance cavity losses through a 30/70 optical coupler. The tunable wavelength spacing can be achieved by changing the center wavelength of the filters and the equalized dual-wavelength output power can be achieved by properly controlling the variable optical attenuator （VOA） inserted in the lower-loss cavity.     

An open-resonator model for the analysis of a short external-cavitylaser diode and its application to the optical disk head

Based on the open resonator theory, a model of a complex coupling coefficient suitable for the analysis of an ultrashort external-cavity laser diode is presented. It is shown that the effective reflectivity of the short external-cavity laser diode calculated by using this model is a function of the size of the laser-emitting area and is significantly influenced by the phase-modification factor as well as by the amplitude-reduction factor of the complex coupling coefficient. The calculated output power characteristics show good qualitative agreement with experimental observation. The necessary condition that the optical disk head using an external-cavity laser diode does not fail to detect the recorded signal for a broad range of flying height is also derived     

A 780 nm high-power and highly reliable laser diode with a longcavity and a thin tapered-thickness active layer

Conventional AlGaAs laser diodes with uniform thickness active layers of various cavity lengths are investigated. It is recognized that the extension of the cavity length is effective in the improvement of the maximum output power, the temperature characteristics, and the operating life in high-temperature conditions. A 780-nm, high-power laser diode having a 350-μm-long cavity with a thin tapered-thickness active layer was fabricated. The optical power density near the mirror facets, the thermal resistance, the current density, and the carrier density were reduced by this structure. The laser emitted over 100 mW of CW (continuous-wave) output power at temperatures up to 80°C. A maximum output power level of 160 mW was achieved at room temperature. The fundamental transverse mode was confirmed at least up to 120 mW     

Experimental demonstration of uncompressed 4K video transmission over directly modulated distributed feedback laser-based terahertz wireless link

We demonstrate the transmission of uncompressed 4K videos over the photonics-based terahertz (THz) wireless link using a directly modulated distributed feedback laser diode (DFB-LD). For optical heterodyne mixing and data modulation, a DFB-LD was employed and directly modulated with a 5.94-Gb/s non-return-to-zero signal, which is related to a 6G-serial digital interface standard to support ultra-high-definition video resolution. We derived the optimal frequency of the THz carrier by varying the wavelength difference between DFB-LD output and Tunable LD output in the THz signal transmitter to obtain the best transmission performances of the uncompressed 4K video signals. Furthermore, we exploited the negative laser-to-filter detuning for the adiabatic chirp management of the DFB-LD by the intentional discrepancy between the center wavelength of the optical band-pass filter and the output wavelength of the DFB-LD. With the help of the abovementioned methods, we successfully transmitted uncompressed 4K video signals over the 2.3-m wireless transmission distance without black frames induced by time synchronization error.     

Vertical external-cavity surface-emitting laser for dual-wavelength generation

We report an optically pumped vertical external-cavity surface-emitting laser that is designed for emission at two wavelengths simultaneously. Single transverse mode continuous-wave (CW) operation is demonstrated at the wavelengths of 984 and 1042 nm. The device produces a CW optical power of 140 mW for the 984-nm component and 115 mW for the 1042-nm component, exhibiting over 10% efficiency. At a high pump power, self-pulsation of the components appeared on top of the CW-mode components. The maximum total output of 1 W was obtained at the pump power of 9 W.     

Wavelength Selector External Cavity Laser Diode by Fiber Switch

A Fabry–Perot laser diode coupled to a single-mode fiber Bragg grating has the ability to emit a single longitudinal mode. In this paper a wavelength selector source based on a mechanical fiber switch used to change the Bragg grating in front of the laser diode is investigated. The external laser wavelength is changed. Critical coupling exists between the two fiber ends of the switch, which leads to the creation of a parasitic cavity inside the laser cavity. The aim of this work is to optimize the coupling ends of a single-mode fiber switch with respect to coupling efficiency and afterward measure the laser output power variation and spectrum to check their optical feedback characteristics on the relative intensity noise. Typical emission performance is a power of −2.5 dBm with a SMSR of 43 dB and a RIN of −146 dB/Hz.     

Longitudinal mode-switching dynamics in a dual external-cavitylaser diode [optical neural network]

We study the potential speed of an optical neural network that uses the longitudinal cavity modes of an external-cavity laser diode as neurons. For this purpose, we used a laser diode coupled to two external cavities, each corresponding to one longitudinal cavity mode. The process of longitudinal mode switching is investigated for the case of intracavity optical modulation. In this experiment, the feedback for the mode in one cavity is modulated, and the length of the other cavity can be controlled. Three limitations are imposed on the switching speed. A number of external-cavity round trips are needed to switch from one mode to the other. It is observed that, depending on the amount of optical feedback in both cavities, between 7 and 21 round trips are needed. When the experimental results for varying cavity length are extrapolated to zero cavity length, a residual delay of a few nanoseconds remains. It is believed that this delay is due to a change in carrier density, needed to switch from one mode to another. Modified rate equations are used to model our experiments. The results of numerical simulations are in good agreement with the experimental results and predict the residual delay. The model also predicts a turn-on delay that is related to relaxation oscillations and imposes a third limitation on the operation speed of our optical neural network. Implications of our findings on the potential operation speed of the optical neural network are discussed and suggestions are made for optimization     

双波长光纤光栅外腔半导体激光器中波长转换

提出了基于双波长光纤光栅外腔半导体激光器增益饱和效应的全光波长转换方案，特点是可将输入信号同时转换到激光器的2个波长上。在静态波长转换实验中，观察到了1554.8nm输入信号对激光器1531.5nm与1549.4nm波长输出功率的增益饱和作用。表明可实现输入信号到激光器的两个波长的同时转换。     

Frequency stabilization in FBG external cavity semiconductor laser based on acetylene absorption method

A frequency-stabilized 1.53 μm FBG external-cavity semiconductor laser by using acetylene absorption is presented and its basic principles are introduced. Graded refractive index fiber and pigtailed fiber are used in the absorption air chamber to enhance the coupling stability. The impact of the background power is eliminated by using the third-harmonic mode-locking technique. A lock-in amplifier is utilized to ensure that the output laser wavelength is locked at the C2H2 absorption line of 1530.37 nm. The frequency stability reaches 10^-8 within 24 h.     

LD泵浦6.8W连续Nd:YVO4/LBO 671nm红光激光器

报道了一种光纤耦合半导体激光二极管(LD)阵列端面抽运Nd∶YVO4晶体,腔内Ⅰ类临界相位匹配LBO(LiB3O5)晶体倍频,实现波长为671nm的全固态红光激光器瓦级连续输出的理论分析和实验结果.采用短三镜折叠腔结构,通过对激光晶体热效应的考虑,估算其热透镜焦距,用计算机优化设计选取合适谐振腔参数,在26W的注入泵浦功率下,获得了连续输出6.8W、波长为671nm的红光基模稳定输出,光-光转化效率达到26%.