Wavelength-tunable organic semiconductor lasers based on elastic distributed feedback gratings

Wavelength-tunable organic semiconductor lasers based on mechanically stretchable polydimethylsiloxane (PDMS) gratings were developed. The intrinsic stretchability of PDMS was explored to modulate the period of the distributed feedback gratings for fine tuning the lasing wavelength. Notably, elastic lasers based on three typical light-emitting molecules show com-parable lasing threshold values analogous to rigid devices and a continuous wavelength tunability of about 10 nm by mechanic-al stretching. In addition, the stretchability provides a simple solution for dynamically tuning the lasing wavelength in a spec-tral range that is challenging to achieve for inorganic counterparts. Our work has provided a simple and efficient method of fab-ricating tunable organic lasers that depend on stretchable distributed feedback gratings, demonstrating a significant step in the advancement of flexible organic optoelectronic devices.

Numerical Simulation of External-Cavity Distributed Feedback Semiconductor Laser

We propose a theoretical model to describe external-cavity distributed feedback semiconductor lasers and investigate the impact of the number of external feedback points on linewidth and side-mode suppression ratio through numerical simulation. The simulation results demonstrate that the linewidth of external-cavity semiconductor lasers can be reduced by increasing the external cavity length and feedback ratio, and adding more external feedback points can further narrow the linewidth and enhance the side mode suppression ratio. This research provides insight into the external cavity distributed feedback mechanism and can guide the design of high-performance external cavity semiconductor lasers. .

Chaos generation by a hybrid integrated chaotic semiconductor laser

We design a hybrid integrated chaotic semiconductor laser with short-cavity optical feedback. It can be assembled in a commercial butterfly shell with just three micro-lenses. One of them is coated by a transflective film to provide the optical feedback for chaos generation while insuring regular laser transmission. We prove the feasibility of the chaos generation in this compact structure and provide critical external parameters for the fabrication by theoretical simulations. Rather than the usual changeless internal parameters used in previous simulation research, we extract the real parameters of the chip by experiment. Moreover, the maps of the largest Lyapunov exponent with varying bias current and feedback intensity Kap demonstrate the dynamic characteristics under different external-cavity conditions. Each laser chip has its own optimal external cavity length（L） and feedback intensity（Kap） to generate chaos because of the different internal parameters. We have acquired two ranges of optimal parameters（L = 4 mm, 0.12 〈 Kap 〈 0.2 and L = 5 mm, 0.07 〈 Kap 〈 0.12） for two different chips.

Tunable and broadband microwave frequency combs based on a semiconductor laser with incoherent optical feedback

Based on a semiconductor laser （SL） with incoherent optical feedback, a novel all-optical scheme for generating tunable and broadband microwave frequency combs （MFCs） is proposed and investigated numerically. The results show that, under suitable operation parameters, the SL with incoherent optical feedback can be driven to operate at a regular pulsing state, and the generated MFCs have bandwidths broader than 40 GHz within a 10 dB amplitude variation. For a fixed bias current, the line spacing （or repetition frequency） of the MFCs can be easily tuned by varying the feedback delay time and the feedback strength, and the tuning range of the line spacing increases with the increase in the bias current. The linewidth of the MFCs is sensitive to the variation of the feedback delay time and the feedback strength, and a linewidth of tens of KHz can be achieved through finely adjusting the feedback delay time and the feedback strength. In addition, mappings of amplitude variation, repetition frequency, and linewidth of MFCs in the parameter space of the feedback delay time and the feedback strength are presented.

Chaos synchronization in injection-locked semiconductor lasers with optical feedback

Based on the rate equations, we have investigated three types of chaos synchronizations in injection-locked semiconductor lasers with optical feedback. Numerical simulation shows that the synchronization can be realized by the symmetric or asymmetric laser systems. Also, the influence of parameter mismatches on chaos synchronization is investigated, and the results imply that these two lasers can achieve good synchronization, with smaller tolerance of parameter mismatch existing.

Flexible control of semiconductor laser with frequency tunable modulation transfer spectroscopy

We introduce a new method of simultaneously implementing frequency stabilization and frequency shift for semiconductor lasers. We name this method the frequency tunable modulation transfer spectroscopy （FTMTS）. To realize a stable output of 780 nm semiconductor laser, an FTMTS optical heterodyne frequency stabilization system is constructed. Before entering into the frequency stabilization system, the probe laser passes through an acousto-optical modulator （AOM） twice in advance to achieve tunable frequency while keeping the light path stable. According to the experimental results, the frequency changes from 120 MHz to 190 MHz after the double-pass AOM, and the intensity of laser entering into the system is greatly changed, but there is almost no change in the error signal of the FTMTS spectrum. Using this signal to lock the laser frequency, we can ensure that the frequency of the laser changes with the amount of AOM shift. Therefore, the magneto-optical trap （MOT）-molasses process can be implemented smoothly.

Waveguide external cavity narrow linewidth semiconductor lasers

Narrow linewidth light source is a prerequisite for high-performance coherent optical communication and sensing.Waveguide-based external cavity narrow linewidth semiconductor lasers(WEC-NLSLs)have become a competitive and attractive candidate for many coherent applications due to their small size,volume,low energy consumption,low cost and the ability to integrate with other optical components.In this paper,we present an overview of WEC-NLSLs from their required technologies to the state-of-the-art progress.Moreover,we highlight the common problems occurring to current WEC-NLSLs and show the possible approaches to resolving the issues.Finally,we present the possible development directions for the next phase and hope this review will be beneficial to the advancements of WEC-NLSLs.

Graded doping low internal loss 1060-nm InGaAs/AlGaAs quantum well semiconductor lasers

Internal loss is a key internal parameter for high power 1060-nm InGaAs/A1GaAs semiconductor laser. In this paper, we discuss the origin of internal loss of 1060-nm InGaAs/GaAs quantum welt （QW） AIGaAs separate confinement het- erostructure semiconductor laser, and the method to reduce internal loss. By light doping the n-cladding layer, and stepwise doping the p-cladding layer combined with the expanded waveguide layer, a broad area laser with internal loss of 1/cm is designed and fabricated. Ridge waveguide laser with an output power of 350 mW is obtained. The threshold current and slope efficiency near the threshold current are 20 mA and 0.8 W/A, respectively.

Research on quantum well intermixing of 680 nm AlGaInP/GaInP semiconductor lasers induced by composited Si-Si_(3)N_(4) dielectric layer

The optical catastrophic damage that usually occurs at the cavity surface of semiconductor lasers has become the main bottleneck affecting the improvement of laser output power and long-term reliability.To improve the output power of 680 nm AlGaInP/GaInP quantum well red semiconductor lasers,Si-Si_(3)N_(4)composited dielectric layers are used to induce its quantum wells to be intermixed at the cavity surface to make a non-absorption window.Si with a thickness of 100 nm and Si_(3)N_(4)with a thickness of 100 nm were grown on the surface of the epitaxial wafer by magnetron sputtering and PECVD as diffusion source and driving source,respectively.Compared with traditional Si impurity induced quantum well intermixing,this paper realizes the blue shift of 54.8 nm in the nonabsorbent window region at a lower annealing temperature of 600 ℃ and annealing time of 10 min.Under this annealing condition,the wavelength of the gain luminescence region basically does not shift to short wavelength,and the surface morphology of the whole epitaxial wafer remains fine after annealing.The application of this process condition can reduce the difficulty of production and save cost,which provides an effective method for upcoming fabrication.

Polarization switching and synchronization of mutually coupled vertical-cavity surface-emitting semiconductor lasers

Polarization switching （PS） dynamics and synchronization performances of two mutually coupled vertical-cavity surface-emitting lasers （VCSELs） are studied theoretically in this paper. A group of dimensionless rate equations is derived to describe our model. While analysing the PS characteristics, we focus on the effects of coupling rate and frequency detuning regarding different mutual injection types. The results indicate that the x-mode injection defers the occurrence of PS, while the y-mode injection leads the PS to occur at a lower current. Strong enough polarization-selective injection can suppress the PS. Moreover, if frequency detuning is considered, the effects of polarization-selective mutual injection will be weakened. To evaluate the synchronization performance, the correlation coefficients and output dynamics of VCSELs with both pure mode and mixed mode polarizations are given. It is found that performance of complete synchronization is sensitive to the frequency mismatch but it is little affected by mixed mode polarizations, which is opposite to the case of injection-locking synchronization.

Influences of semiconductor laser on fibre-optic distributed disturbance sensor based on Mach-Zehnder interferometer

This paper investigates the influences of a semiconductor laser with narrow linewidth on a fibre-optic distributed disturbance sensor based on Mach-Zehnder interferometer. It establishes an effective numerical model to describe the noises and linewidth of a semiconductor laser, taking into account their correlations. Simulation shows that frequency noise has great influences on location errors and their relationship is numerically investigated. Accordingly, there is need to determine the linewidth of the laser less than a threshold and obtain the least location errors. Furthermore, experiments are performed by a sensor prototype using three semiconductor lasers with different linewidths, respectively, with polarization maintaining optical fibres and couplers to eliminate the polarization induced noises and fading. The agreement of simulation with experimental results means that the proposed numerical model can make a comprehensive description of the noise behaviour of a semiconductor laser. The conclusion is useful for choosing a laser source for fibre-optic distributed disturbance sensor to achieve optimized location accuracy. What is more, the proposed numerical model can be widely used for analysing influences of semiconductor lasers on other sensing, communication and optical signal processing systems.

Analysis of the time domain characteristics of tapered semiconductor lasers

We use traveling wave coupling theory to investigate the time domain characteristics of tapered semiconductor lasers with DBR gratings.We analyze the influence of the length of second order gratings on the power and spectrum of output light,and optimizing the length of gratings,in order to reduce the mode competition effect in the device,and obtain the high power output light wave with good longitudinal mode characteristics.

Synchronization and bidirectional communication without delay line using strong mutually coupled semiconductor lasers

This paper numerically demonstrates synchronization and bidirectional communication without delay line by using two semiconductor lasers with strong mutual injection in a face-to-face configuration. These results show that both of the two lasers＇ outputs synchronize with their input chaotic carriers. In addition, simulations demonstrate that this kind of synchronization can be used to realize bidirectional communications without delay line. Further studies indicate that within a small deviation in message amplitudes of two sides （±6%）, the message can be extracted with signal-noise-ratio more than 10 dB; and the signal-noise-ratio is extremely sensitive to the message rates mismatch of two sides, which may be used as a key of bidirectional communication.

A 40-GHz Colliding Pulse Mode-Locked Semiconductor Laser

A monolithically active-passive integrated colliding pulse mode-locked semiconductor laser is demonstrated in the InGaAsP//InP material system. The device is mode locked at the second harmonic passive mode-locking regime with a wide mode-locking range. Pulse trains with the repetition rate of 40 GHz, 3-dB rf line width of 25 kHz, the pulse width of 2.5 ps, and a nearly transform-limited time-bandwidth product of 0.53 are obtained.

Square microcavity semiconductor lasers

Square microcavities, which support whispering-gallery modes with total internal reflections, can be employed as high-quality laser resonators for fabricating compact, low-threshold semiconductor lasers. In this paper, we review the recent progress of square microcavity semiconductor lasers. The characteristics of confined optical modes in the square microcavities are introduced briefly. Based on the mode properties of the square microcavities, dual-mode lasers with tunable wavelength intervals are realized for generating microwave signals. Furthermore, deformed square microcavity lasers with the sidewalls replaced by circular sides are proposed and experimentally demonstrated to enhance the mode confinement and increase the dual-mode interval to the THz range. In order to further reduce the device size, metal-confined wavelength-scale square cavity lasers are also demonstrated.

High power semiconductor laser array with single-mode emission

The semiconductor laser array with single-mode emission is presented in this paper.The 6-μm-wide ridge waveguides(RWGs)are fabricated to select the lateral mode.Thus the fundamental mode of laser array can be obtained by the RWGs.And the maximum output power of single-mode emission can reach 36 W at an injection current of 43 A,after that,a kink will appear.The slow axis(SA)far-field divergence angle of the unit is 13.65.The beam quality factor M;of the units determined by the second-order moment(SOM)method,is 1.2.This single-mode emission laser array can be used for laser processing.

Multi-target ranging using an optical reservoir computing approach in the laterally coupled semiconductor lasers with self-feedback

We utilize three parallel reservoir computers using semiconductor lasers with optical feedback and light injection to model radar probe signals with delays.Three radar probe signals are generated by driving lasers constructed by a threeelement laser array with self-feedback.The response lasers are implemented also by a three-element lase array with both delay-time feedback and optical injection,which are utilized as nonlinear nodes to realize the reservoirs.We show that each delayed radar probe signal can be predicted well and to synchronize with its corresponding trained reservoir,even when parameter mismatches exist between the response laser array and the driving laser array.Based on this,the three synchronous probe signals are utilized for ranging to three targets,respectively,using Hilbert transform.It is demonstrated that the relative errors for ranging can be very small and less than 0.6%.Our findings show that optical reservoir computing provides an effective way for applications of target ranging.

Impulse Spatial-Temporal Domains in Semiconductor Laser with Feedback

An initial value boundary problem for system of diffusion equations with delay arguments and dynamic nonlinear boundary conditions is considered. The problem describes evolution of the carrier density and the radiation density in the semiconductor laser or laser diodes with “memory” and with feedback. It is shown that the boundary problem can be reduced to a system of difference equations with continuous time. For large times, solutions of these equations tend to piecewise constant asymptotic periodic wave functions which represent chain of shock waves with finite or infinite points of discontinuities on a period. Applications to the optical systems with linear media and nonlinear surface optical properties with feedback have been done. The results are compared with the experiment.

High Wall-Plug Efficiency 1060 nm High Power Semiconductor Laser

By analyzing the factors which affect the wall-plug efficiency of semiconductor Laser Diodes (LDs), a high efficiency 1060 nm LD was designed, including active region, waveguide layers, and cladding layers. The simulation result shows that the component of In in InGaAs in the active region cannot be too small, otherwise the thickness of InGaAs active layer will exceed the critical thickness, meanwhile the asymmetric large optical cavity can decrease the cavity loss effectively. The epitaxial structure was grown by MOCVD, experimental results of varying cavity length showed that the internal quantum efficiency reached 98.57%, and the cavity loss was only 0.273 cm?1. Devices with 4 mm-cavity-length and 100 μm-strip-width were fabricated, 47.4% wall-plug efficiency was reached under QCW pulse condition at room temperature, and the peak wavelength was 1059.4 nm.

Frequency Sweep Linearization for Semiconductor Laser Using a Feedback Loop Based on Amplitude-Frequency Response

A scheme of frequency sweep linearization of semiconductor lasers using a feed-back loop based on amplitude-frequency response is demonstrated in this paper. The beat frequency signal is obtained by self-heterodyne detection. The frequency changes are converted to the envelope of beat frequency signal after amplitude-frequency response. The active frequency sweep linearization is realized by feeding envelope deviations back to the drive currents of the lasers by a feedback loop. A simulation model is built to verify this scheme by Simulink. This scheme does not need high-performance, expensive lasers, complex linearization or tedious post-processing processes, which are of great significance for related applications.