External Cavity Semiconductor Laser Research Articles

Recent Progresses on Hybrid Lithium Niobate External Cavity Semiconductor Lasers.

Thin film lithium niobate (TFLN) has become a promising material platform for large scale photonic integrated circuits (PICs). As an indispensable component in PICs, on-chip electrically tunable narrow-linewidth lasers have attracted widespread attention in recent years due to their significant applications in high-speed optical communication, coherent detection, precision metrology, laser cooling, coherent transmission systems, light detection and ranging (LiDAR). However, research on electrically driven, high-power, and narrow-linewidth laser sources on TFLN platforms is still in its infancy. This review summarizes the recent progress on the narrow-linewidth compact laser sources boosted by hybrid TFLN/III-V semiconductor integration techniques, which will offer an alternative solution for on-chip high performance lasers for the future TFLN PIC industry and cutting-edge sciences. The review begins with a brief introduction of the current status of compact external cavity semiconductor lasers (ECSLs) and recently developed TFLN photonics. The following section presents various ECSLs based on TFLN photonic chips with different photonic structures to construct external cavity for on-chip optical feedback. Some conclusions and future perspectives are provided.

The Effect of Lens Focal Length on the Output Characteristics of 1.55 μm Tunable External-Cavity Semiconductor Lasers

The Effect of Lens Focal Length on the Output Characteristics of 1.55 μm Tunable External-Cavity Semiconductor Lasers

Dual-wavelength channel GHz repetition rate mode-locked VECSEL cavities sourced from a common gain medium.

Mode-locked vertical external cavity semiconductor lasers are a unique class of nonlinear dynamical systems driven far from equilibrium. We present a novel, to the best of our knowledge, experimental result, supported by rigorous microscopic simulations, of two coexisting mode-locked V-cavity configurations sourced by a common gain medium and operating as independent channels at angle controlled separated wavelengths. Microscopic simulations support pulses coincident on the common gain chip extracting photons from a nearby pair of coexisting kinetic holes burned in the carrier distributions.

Linear polarization and narrow-linewidth external-cavity semiconductor laser based on birefringent Bragg grating optical feedback

We demonstrate an external-cavity semiconductor laser (ECSL) with linear polarization and a narrow linewidth. A birefringent Bragg grating prepared by a femtosecond laser point-by-point technique in a polarization-maintaining fiber (PMF) is used to provide external-cavity feedback, and its polarization-dependent characteristics enable selection of the main polarization mode and linewidth narrowing of the ridge waveguide emission gain chip (GC). This compact and robust ECSL achieves an output power of > 60 mW and a polarization extinction ratio (PER) of > 30 dB. We simulate and calculate the linewidth and injection current, while a Lorentz linewidth of 2.58 kHz is obtained based on delayed self-heterodyne beat frequency measurement. This flexible and cost-effective solution allows realization of a compact ECSL with linear polarization and a narrow linewidth.

Impact of α-factor, combined optical phase and gain saturation on the onset of chaos of short external cavity semiconductor lasers

Influences of line-width enhancement factor (α-Factor), combined optical phase (COP), and gain saturation (GS) on the onset of chaos (route to chaos (RTC)) of the short external cavity (EC) semiconductor lasers (LDs) are numerically investigated. The bifurcation diagrams (BDs), output photon number time variations, corresponding phase portraits, and fast Fourier transforms (FFT) are presented to examine the RTC of the laser in terms of GS, COP, and α-Factor. Calculated results displayed that variation of the α-Factor leads to RTC considerable modifications and these changes are positive by including the GS. The COP variation moves the optical feedback (OFB) intensity to higher values and causes fluctuations in the RTC of the LD with and without including the GS. The LD RTC is specified for four separate regions, oscillations with one frequency (PO), oscillations with two frequencies (PD), oscillations with three frequencies (3P), and oscillations with four frequencies (4P), in terms of GS, COP, and α-Factor. As the LD operation state moves from continuous wave (CW) to PO, PD, or chaos operation state the OFB intensity decreases / increases through α-Factor / GS increasing and fluctuates with increasing the COP within one period (0–2π). The results presented here can be useful in designing stable LD and directing chirp in integrated devices through COP and α-Factor changing.

Narrow-linewidth external cavity semiconductor laser based on permanent index modulated grating optical feedback for radiation resistance

Narrow-linewidth external cavity semiconductor laser based on permanent index modulated grating optical feedback for radiation resistance

Numerical simulation of linewidth compression dynamics of external-cavity semiconductor laser

We theoretically simulate the linewidth compression dynamics of the semiconductor laser with a single external-cavity feedback. The evolution time from the periodic oscillation state to the equilibrium state is calculated by tracking the change of the intrinsic linewidth. The influences of the external-cavity length and feedback level are also explored. The linewidth evolution time of the external-cavity semiconductor laser can be extended with longer external cavity length and higher feedback level. Simultaneously, the intrinsic linewidth can be compressed while the side mode suppression ratio will be decreased. The simulation work show that the dynamic linewidth compression can be obtained by single external-cavity feedback, and nevertheless it is difficult to achieve the single-frequency output, which can instruct the design of the dynamical parameter tuning of the external-cavity semiconductor laser.

Forecasting the chaotic dynamics of external cavity semiconductor lasers.

Chaotic time series prediction has been paid intense attention in recent years due to its important applications. Herein, we present a single-node photonic reservoir computing approach to forecasting the chaotic behavior of external cavity semiconductor lasers using only observed data. In the reservoir, we employ a semiconductor laser with delay as the sole nonlinear physical node. By investigating the effect of the reservoir meta-parameters on the prediction performance, we numerically demonstrate that there exists an optimal meta-parameter space for forecasting optical-feedback-induced chaos. Simulation results demonstrate that using our method, the upcoming chaotic time series can be continuously predicted for a time period in excess of 2 ns with a normalized mean squared error lower than 0.1. This proposed method only utilizes simple nonlinear semiconductor lasers and thus offers a hardware-friendly approach for complex chaos prediction. In addition, this work may provide a roadmap for the meta-parameter selection of a delay-based photonic reservoir to obtain optimal prediction performance.

Wide-range external-cavity tunable semiconductor laser with mode-hopping free

Wide-range external-cavity tunable semiconductor laser with mode-hopping free

Optimal design for reducing diffraction loss of Littman-Metcalf grating external cavity semiconductor laser

Optimal design for reducing diffraction loss of Littman-Metcalf grating external cavity semiconductor laser

Research Progress of Wide Tunable Bragg Grating External Cavity Semiconductor Lasers.

In this paper, we review the progress of wide tunable Bragg grating external cavity semiconductor lasers (BG-ECSLs). We concentrate on BG-ECSLs based on the wide tunable range for multicomponent detection. Wide tunable BG-ECSLs have many important applications, such as wavelength-division multiplexing (WDM) systems, coherent optical communications, gas detection and atom cooling. Wide tunability, narrow linewidth and a high side-mode suppression ratio BG-ECSLs have attracted much attention for their merits. In this paper, three main structures for achieving widely tunable, narrow linewidth, high side-mode suppression ratio BG-ECSLs are reviewed and compared in detail, such as the volume Bragg grating (VBG) structure, fiber Bragg grating (FBG) structure and waveguide Bragg grating (WBG) structure of ECSLs. The advantages and disadvantages of different structures of BG-ECSLs are analyzed. The results show that WBG-ECSLs are a potential way to realize the integration, small size, wide tuning range, stable spectral output and high side-mode suppression ratio laser output. Therefore, the use of WBG as optical feedback elements is still the mainstream direction of BG-ECSLs, and BG-ECSLs offer a further new option for multicomponent detection and multi-atoms cooling.

Reservoir computing based on an external-cavity semiconductor laser with optical feedback modulation.

We numerically and experimentally investigate reservoir computing based on a single semiconductor laser with optical feedback modulation. In this scheme, an input signal is injected into a semiconductor laser via intensity or phase modulation of the optical feedback signal. We perform a chaotic time-series prediction task using the reservoir and compare the performances of intensity and phase modulation schemes. Our results indicate that the feedback signal of the phase modulation scheme outperforms that of the intensity modulation scheme. Further, we investigate the performance dependence of reservoir computing on parameter values and observe that the prediction error improves for large injection currents, unlike the results in a semiconductor laser with an optical injection input. The physical origin of the superior performance of the phase modulation scheme is analyzed using external cavity modes obtained from steady-state analysis in the phase space. The analysis indicates that high-dimensional mapping can be achieved from the input signal to the trajectory of the response laser output by using phase modulation of the feedback signal.

Tunable Chaotic External-Cavity Semiconductor Laser With Time-Delay Signature Suppression Including a Broadband Chirped FBG

A wavelength tunable chaotic external cavity semiconductor laser (ECSL) composed by a distributed-feedback laser diode (DFB-LD) and a broadband chirped fiber Bragg grating (CFBG), is proposed and experimentally demonstrated for generating tunable chaos signals with time delay signature (TDS) suppression. The experimental results show that by using a CFBG with a 3-dB reflection bandwidth of approximately 30 nm and a low dispersion of approximately 1.25 ps/nm, the chaotic ECSL can be tuned over a wide wavelength range, and the generated chaos possesses a low TDS of about 0.04. With the increase of the bias current of the DFB-LD, the chaotic ECSL is tuned towards long-wavelength direction, the effective bandwidth of the chaotic signal is extended, and the TDS of the chaotic signal remains effectively suppressed. To highlight the advantages of the proposed scheme, relevant experiments for the DFB-LD under fiber mirror feedback and fiber Bragg grating feedback are also performed and compared.

Security-Enhanced Chaotic Optical Communication Based on External Temporal Self-Feedback Hardware Encryption and Decryption

Chaotic optical communication based on conventional external cavity semiconductor laser is a very promising solution for physical layer secure communication. However, the intrinsic time delay signature (TDS) associated with the external cavity length and the potential direct linear filtering (DLF) or synchronization utilization attack greatly threaten the system security. In this work, we propose and numerically demonstrate a novel scheme for TDS suppression and security enhancement of chaotic optical communication based on external temporal self-feedback hardware encryption and decryption. In this scheme, the confidential chaotic modulated signal is temporally scrambled in the time domain by two optical dispersion components and an electro-optic self-feedback phase modulation loop between them, which simultaneously conceal the TDS and enhance the security against malicious attacks. Proof-of-principle demonstration for a security enhanced chaotic optical communication system with error free transmission is successfully achieved. The proposed scheme may provide a promising way for pure-hardware based physical secure chaotic optical communication systems.

Research on Narrow Linewidth External Cavity Semiconductor Lasers

Narrow linewidth external cavity semiconductor lasers (NLECSLs) have many important applications, such as spectroscopy, metrology, biomedicine, holography, space laser communication, laser lidar and coherent detection, etc. Due to their high coherence, low phase-frequency noise, high monochromaticity and wide wavelength tuning potential, NLECSLs have attracted much attention for their merits. In this paper, three main device structures for achieving NLECSLs are reviewed and compared in detail, such as free space bulk diffraction grating external cavity structure, waveguide external cavity structure and confocal Fabry–Perot cavity structure of NLECSLs. The Littrow structure and Littman structure of NLECSLs are introduced from the free space bulk diffraction grating external cavity structure of NLECSLs. The fiber Bragg grating external cavity structure and silicon based waveguide external cavity structure of NLECSLs are introduced from the waveguide external cavity structure of NLECSLs. The results show that the confocal Fabry–Perot cavity structure of NLECSLs is a potential way to realize a lower than tens Hz narrow linewidth laser output.

Nonlinear reflectivity of AlGaInP SESAMs for mode locking in the red spectral range.

Mode-locked vertical external-cavity semiconductor lasers (VECSELs) are a wavelength-versatile laser that relies on a semiconductor saturable absorber mirror (SESAM) to initiate pulsed emission while simultaneously significantly influencing the pulse's properties. A SESAM can be characterized using a nonlinear reflectivity setup, realized here in the red spectral range around 660 nm and achieving a moderate peak-to-peak variation of 0.17%. We use our home-built mode-locked VECSEL to reach a high maximum fluence up to 430 µJ/cm2 with strongly chirped 7.5 ps pulses. This allows the first-of-its-kind characterization of GaInP quantum well SESAMs, thereby revealing saturation fluences of 38 µJ/cm2 and 34 µJ/cm2 with modulation depths of 5% and 10.3% for SESAMs comprising one or two active quantum wells, respectively. For all structures, a nonsaturable loss of 2.8% is found and attributed to scattering loss.

Wavelength stabilization and spectra narrowing of a 405 nm external-cavity semiconductor laser based on a volume Bragg grating.

We introduce a 405 nm external-cavity semiconductor laser using a volume Bragg grating (VBG) as the feedback element. By decreasing the length of the external cavity and reducing the wavelength difference between the output wavelength of the laser diode during free running and Bragg wavelength of the VBG, the emission wavelength of the semiconductor laser is stably locked at 405.1 nm with a spectral linewidth of 0.08 nm. The output power reaches 292 mW, and the wavelength drift with temperature reduces to 0.0006 nm/°C. These results are helping for the spectroscopy applications of a blue-violet laser diode. In contrast to traditional external-cavity semiconductor lasers, this laser is less expensive and more compact, in addition to having a narrow linewidth and good wavelength stability. These advantages would facilitate the development of associated areas of research, including optical data storage, laser display, and laser medicine.

Research on Silicon-Substrate-Integrated Widely Tunable, Narrow Linewidth External Cavity Lasers

Widely tunable, narrow linewidth external cavity lasers on silicon substrates have many important applications, such as white-light interferometry, wavelength division multiplexing systems, coherent optical communication, and optical fiber sensor technology. Wide tuning range, high laser output power, single mode, stable spectral output, and high side-mode suppression ratio external cavity lasers have attracted much attention for their merits. In this paper, two main device-integrated structures for achieving widely tunable, narrow linewidth external cavity lasers on silicon substrates are reviewed and compared in detail, such as MRR-integrated structure and MRR-and-MZI-integrated structure of external cavity semiconductor lasers. Then, the chip-integrated structures are briefly introduced from the integration mode, such as monolithic integrated, heterogeneous integrated, and hybrid integrated. Results show that the silicon-substrate-integrated external cavity lasers are a potential way to realize a wide tuning range, high power, single mode, stable spectral output, and high side-mode suppression ratio laser output.

Multi-Wavelength Terahertz Parametric Generator Using a Seed Laser Based on Four-Wave Mixing

In this study, we developed a multi-wavelength terahertz-wave parametric generator that operates with only one injection seeding laser. Tunable lasers used as an injection seeder must be single-frequency oscillators, and conventional multi-wavelength terahertz-wave parametric generator requires basically the same number of lasers as the number of wavelengths. In order to solve this problem, we developed a new external cavity semiconductor laser that incorporates a DMD in its wavelength-selective mechanism. In this process, stable multi-wavelength oscillation from a single laser was made possible by efficiently causing four-wave mixing. This seed laser can be applied to practical real-time terahertz spectroscopy by arbitrarily switching the desired wavelength to be generated and the interval between multiple wavelengths.

Semiconductor Laser-Based Multi-Channel Wideband Chaos Generation Using Optoelectronic Hybrid Feedback and Parallel Filtering

We propose and experimentally demonstrate a novel multi-channel chaos generation scheme, which can simultaneously produce multiple chaotic signals with wideband spectrum and suppressed time-delay signature (TDS). In this scheme, we introduce an external self-phase-modulated feedback (ESPMF) to improve the optical bandwidth of the initial chaos generated by a conventional external-cavity semiconductor laser (ECSL), then optical tunable filters (OTFs) are utilized to simultaneously extract three-channel chaotic outputs. The experimental results show that the proposed scheme has three main advantages. Firstly, it can simultaneously generate multiple chaotic outputs with different central wavelengths and low correlations. Secondly, the bandwidth of original ECSL-based chaos can be improved by several times, and the undesired TDS characteristics in the original chaos can be completely suppressed to an indistinguishable level (lower than 0.02). Thirdly, the bandwidths of these chaotic outputs are flexible and can be adjusted within a wide range of 20 GHz by controlling the filter bandwidths. In addition, we demonstrate an application of the proposed chaos generation scheme in random bit generation (RBG), and multi-channel high-speed random bit sequences with a total generation rate over Tb/s and NIST verified randomness are simultaneously obtained.