Laser Cavity Design Research Articles

Conventional soliton and noise-like pulse emissions at 1.98μm utilizing tungsten trioxide as mode-locker

In this paper, we experimentally demonstrate the dual pulse emissions of conventional soliton (CS) and noise-like pulse (NLP) in thulium-holmium co-doped fiber laser using tungsten trioxide saturable absorber (WO3-SA). The CS pulse delivered 2[Formula: see text]ps width, centered at 1982.8[Formula: see text]nm. Increasing the pump power and alteration of polarization states switched the CS to the NLP regime with 1990.0[Formula: see text]nm central wavelength, 17.2[Formula: see text]nm spectral bandwidth, and 396[Formula: see text]fs spike width riding on top of a wide picosecond pulse pedestal in the time domain. This work suggests the capability of WO3-SA as a pulse initiator for future dual-source ultrashort pulses based on an all-fiber laser cavity design.

Hybrid Laser Cavity Design for Improved Photon Lifetime and Performance

Hybrid Laser Cavity Design for Improved Photon Lifetime and Performance

1178 nm self-Q-switched Raman laser generation enabled by BaTeW2O9 crystal

Multifunctional composite crystals have received great attention as an effective way to simplify the laser cavity. In this work, a self-Q-switched Raman laser operating at 1178 nm is demonstrated by using a multifunctional composite crystal BaTeW2O9 (BTW). An acousto-optic modulator (AOM) with a diffraction efficiency of 74% is designed and fabricated based on the Raman crystal BTW. A 1064 nm pulsed laser with a maximum single pulse energy of 260.6 μJ corresponding to a pulse width of 42 ns is obtained by inserting the BTW AOM into the laser cavity with Nd: YAG as the laser gain medium. Then an 1178 nm self-Q-switched Raman laser with the maximum single pulse energy of 22.8 μJ corresponding to a pulse width of 10 ns is successfully obtained. This work not only provides a competitive multifunctional composite device that can simplify the Raman laser cavity design but also has guiding significance for the design and development of multifunctional composite crystals.

Predicting behavior of photonic crystal fiber lasers using artificial neural networks

Simulating pulse propagation within fiber lasers is a difficult and computationally demanding task, which limits the ability to accurately capture their complex nonlinear dynamics. This paper leverages artificial intelligence (AI) and artificial neural networks (ANN) to predict the output pulse shape parameters for a ring cavity fiber laser, thus avoiding the need for traditional complex numerical calculations and reducing the overall computational cost. This study focuses on a dissipative soliton resonance (DSR) ring cavity fiber laser, incorporating a photonic crystal fiber (PCF) and mode locked by a real saturable absorber. The integration of the PCF into the laser cavity design enhances the control of both dispersion and nonlinearity, allowing for a greater range of output pulse shapes and parameters. The proposed approach demonstrates the effectiveness of artificial neural networks in predicting pulse parameters, and could pave the way for more efficient design and optimization of fiber lasers. The results of the study show that the ANN model can accurately predict the output pulse shape parameters for the DSR ring cavity fiber laser, and thus offers a promising tool for future research in the field.

Multiplexed optical fiber cell temperature sensing system with high sensitivity and accuracy.

A multiplexed fiber laser sensing system for cell temperature is proposed. To the best of the authors' knowledge, this is the first multilongitudinal mode (MLM) optical fiber laser sensor array designed for cell temperature sensing. A two-channel cell temperature sensing system with high sensitivity and real-time sensing capability is achieved. The temperature change of human hepatoellular carcinomas (HepG2) cells under the influence of exogenous chemical aflatoxin B1 (AFB1) can be monitored in real time. A fiber laser cavity consists of a pair of fiber Bragg gratings (FBGs) with matched central wavelengths and a piece of erbium-doped fiber (EDF). The static FBG is utilized for design of fiber laser cavity and laser modes selection. In comparison, the sensing FBG is used for cell temperature sensing. The sensing FBG has a length of 10mm and a diameter of . Beat frequency signals (BFS) are generated by MLM lasers after optical-to-electrical conversion at a photodetector. Frequency change of a BFS is closely related to the reflected wavelength change of the sensing FBG. Through frequency division multiplexing, two fiber laser cavities are designed in the sensing system for two-channel temperature sensing. Frequency shift of a BFS that represents temperature change of cells can be automatically recorded in seconds. A two-channel cell temperature sensing system is designed with high sensitivities of 101.62 and , respectively. The temperature change of HepG2 cells under the influence of exogenous chemical AFB1 is monitored in real time. The proposed system has the advantages of simple structure, high sensitivity, and two-channel sensing capability. Our study provides a simple and effective method to design a fiber laser sensor system without complex demodulation techniques and expensive optical components.

Quantification of dissipative effects in a complex Ginzburg-Landau equation governed laser system by tracing soliton dynamics.

The concept of dissipative solitons has provided new insight into the complex pulse dynamics in mode-locked lasers and stimulated novel laser cavity designs. However, most of these studies are restricted to qualitative regimes, because it is difficult to quantify dissipative effects in a mode-locked laser. Meanwhile, the quantification of dissipative effects is a general problem that can be also encountered in other dissipative systems. In this paper, we demonstrate a method for quantifying dissipative effects in a mode-locked laser based on analyzing the soliton dynamics traced by time-stretch dispersive Fourier transform. As a result, we are able to quantitatively reproduce the evolution of the pulse that seeds mode-locking through simulations and gain a deeper understanding of the whole process. The obtained physical picture of mode-locking allows us to propose a simple method to quantify the energy threshold for mode-locking buildup and the stability of mode-locked states. A parameter is introduced to evaluate mode-locking conditions, which can serve as a criterion for designing mode-locked lasers. This work opens up new possibilities in the diagnosis and improvement of mode-locked lasers and studies of soliton physics.

Long-Distance High-Power Wireless Optical Energy Transmission Based on VECSELs

Wireless charging systems are critical for safely and efficiently recharging mobile electronic devices. Current wireless charging technologies involving inductive coupling, magnetic resonance coupling, and microwave transmission are bulky, require complicated systems, expose users to harmful radiation, and have very short energy transmission distances. Herein, we report on a long-distance optical power transmission system by optimizing the external cavity structure of semiconductor lasers for laser charging applications. An ultra-long stable oscillating laser cavity with a transmission distance of 10 m is designed. The optimal laser cavity design is determined by simulating the structural parameters for stable operation, and an improved laser cavity that produces an output of 2.589 W at a transmission distance of 150 cm is fabricated. The peak power attenuation when the transmission distance increases from 50 to 150 cm is only approximately 6.4%, which proves that this wireless power transfer scheme based on a vertical external cavity surface-emitting laser can be used to realize ultra-long-distance power transmission. The proposed wireless energy transmission scheme based on a VECSEL laser is the first of its kind to report a 1.5 m transmission distance output power that exceeds 2.5 W. Compared with other wireless energy transmission technologies, this simple, compact, and safe long-distance wireless laser energy transmission system is more suitable for indoor charging applications.

Efficient TEM00-mode solar laser using four Nd:YAG rods/four off-axis parabolic mirrors pumping approach

A four-rod/four-TEM00-mode beam off-axis parabolic mirror solar pumping concept is proposed. Four off-axis parabolic mirrors with 10 m2 total collection area were used as the primary solar concentrators to pump four 3.1-mm diameter, 84-mm length neodymium-doped yttrium aluminum garnet (Nd:YAG) rods within four 2V-shaped pump cavities through four secondary fused-silica aspheric concentrators and four rectangular fused-silica light guides, ensuring a good absorbed pump power distribution within each rod and avoiding the serious thermal lensing and thermal stress issues associated with classical single large rod solar lasers. The laser design parameters were optimized using ZEMAX© and LASer Cavity Analysis and Design (LASCAD©) analysis software to maximize the TEM00-mode laser power. 155.29-W TEM00-mode total laser power was numerically calculated, corresponding to 15.5 W / m2 solar laser collection efficiency and 1.72% solar-to-TEM00-mode laser conversion efficiency, respectively. This result represents an improvement of nearly 2 and 1.24 times, in solar laser collection efficiency and solar-to-TEM00-mode laser conversion efficiency, respectively, as compared with the previous experimental records of the TEM00-mode solar laser pumped through the parabolic mirror primary concentrator. It provides also a 1.14 and 1.19 times improvement, as compared to the previous numerical record of the TEM00-mode solar laser pumped by the Fresnel lens primary solar concentrator.

III–V Semiconductor Whispering-Gallery Mode Micro-Cavity Lasers: Advances and Prospects

III-V semiconductor lasers are ubiquitous in modern optoelectronic devices, with applications ranging from telecommunication to general lighting. Among the different kinds of laser cavity designs, whispering-gallery mode (WGM) micro-cavity lasers boast outstanding optical performance due to advantages such as ultra-high Q-factor, compact mode volume, and narrow emission linewidth. Over the past decades, research in III-V WGM micro-cavity lasers has progressed rapidly in various aspects, including the fabrication techniques, emission outcoupling methods, and practical applications. In this paper, a comprehensive review is performed on the advances in these aspects. Although III-V WGM lasers are conventionally fabricated with top-down approaches, recent reports have demonstrated the potential of highly-scalable bottom-up methods in fabricating low-loss WGM lasers. Despite the strong optical confinement in III-V WGM cavities, various techniques have been developed to either outcouple WGM emission into waveguides or direct it into free-space with small beam divergence. Finally, recent developments in different applications of III-V WGM micro-cavity lasers are discussed. Other than serving as integrated photonic components, III-V WGM lasers have also displayed exciting potential in other applications such as label-free sensing and the study of cavity quantum electrodynamics (cQED).

Pulse Shape Estimation in a DSR Fiber Laser Using the Genetic Algorithm

Exploiting the computing power of the genetic algorithm, a numerical study of dissipative soliton resonance (DSR) in a ring laser mode-locked by a real saturable absorber (SA) is conducted. A section of photonic crystal fiber (PCF) is inserted into the laser cavity design to facilitate accurate control of both dispersion and nonlinearity. The influence of the cavity parameters on the evolution of the DSR pulses is systematically analyzed. The genetic algorithm demonstrates that the generation of DSR square pulses depends directly on the PCF dispersion, the PCF nonlinearity, the PCF length, and the modulation depth of the SA. Finally, the sensitivity of the DSR pulse width, peak power and energy to perturbations in a few key design parameters are highlighted.

Direct Generation of 7 W, 360 μJ Multi-Pulse Laser From an Ultra-Compact All-Fiber Gain Switched Tm³+-Doped Double-Clad Fiber Laser

We report on the investigation of multi-pulse Tm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped double clad fiber laser (TDCFL) with an ultra-compact four devices-based all-fiber structure. This multi-pulse is implemented by the long relaxation time of gain-switched process. The number of pulse in a pulse cluster can be tuned from 1 to 8 by changing the pump pulse energy. With laser cavity design (i.e. large laser output coupling ratio and high gain mutual balance), the multi-pulse laser can finally generate an average output power of 7.25 W with corresponding pulse energy of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$362.5~\mu \text{J}$ </tex-math></inline-formula> . The 2017 nm multi-pulse TDCFL has a high laser conversion efficiency of ~30% and the good operation stability with signal to noise ratio (SNR) of 77 dB. The experimental results would be fruitful to the communities interested in all-fiber multi-pulse lasers.

High-Efficiency Mini-Slab Laser Based on Tm-doped Double Tungstate Crystal

We report on highly-efficient room-temperature lasing in 5at.%Tm:KLu(WO4)2 mini-slabs side-pumped by a 35W diode bar. QCW (duty cycle ∼ 14%) output power of 1.47 W at 1908 nm has been demonstrated with optical and slope efficiencies being of 33 and 43% respectively. In our experiments, we used samples of active elements produced in the slabs form with Brewster’s angle cut faces and original laser cavity design.

All-intracavity fourth harmonic generation in a passively mode locked VECSEL for ultrafast UV emission

We demonstrate all-intracavity fourth harmonic generation in an ultrafast passively mode locked vertical external cavity surface emitting laser (VECSEL). This novel laser cavity design utilizes a high Q Z-cavity resonator to buildup the circulating power of the second harmonic for frequency quadrupling the fundamental 1060 nm to 265 nm. The demonstrated UV output has an average power of 525 μW, pulse width of 3 ps, and a repetition rate of 510 MHz. This results in a peak pulse power of 250–300 mW over a 30 min duration without active stabilization equipment.

Inverse design of mode-locked fiber laser by particle swarm optimization algorithm

A wide variety of laser applications, that often require radiation with specific characteristics, and relative flexibility of laser configurations offer a prospect of designing systems with the parameters on demand. The inverse laser design problem is to find the system architecture that provides for the generation of the desired laser output. However, typically, such inverse problems for nonlinear systems are sensitive to the computation of the gradients of a target (fitness) function making direct back propagation approach challenging. We apply here particle swarm optimization algorithm that does not rely on the gradients of the fitness function to the design of a fiber 8-figure laser cavity. This technique allows us to determine the laser cavity architectures tailored to generating on demand pulses with duration in the range of 1.5–105 ps and spectral width in the interval 0.1–20.5 nm. The proposed design optimisation algorithm can be applied to a variety of laser applications, and, more generally, in a range of engineering systems with flexible adjustable configurations and the outputs on demand.

Mode splitting and multiple-wavelength managements of surface plasmon polaritons in coupled cavities

Resonance cavity is a basic element in optics, which has wide applications in optical devices. Coupled cavities (CCs) designed in metal-insulator-metal (MIM) bus waveguide are investigated through the finite difference time domain method and coupled-mode theory. In the CCs, the resonant modes of the surface plasmon polaritons (SPPs) split with the thickness decreasing of the middle baffle. Through the coupled-mode theory analysis, it is found that the phase differences introduced in opposite and positive couplings between two cavities lead to mode splitting. The resonant wavelength of positive coupling mode can be tuned in a large range (about 644 nm) through adjusting the coupling strength, which is quite different from the classical adjustment of the optical path in a single cavity. Based on the resonances of the CCs in the MIM waveguide, more compact devices can be designed to manipulate SPPs propagation. A device is designed to realize flexible multiple-wavelength SPPs routing. The coupling in CC structures can be applied to the design of easy-integrated laser cavities, filters, multiple-wavelength management devices in SPPs circuits, nanosensors, etc.

Fiber-based dynamically tunable Lyot filter for dual-wavelength and tunable single-wavelength mode-locking of fiber lasers.

We propose and demonstrate a novel dynamically tunable fiber-based Lyot filter for the realization of a dual-wavelength mode-locked fiber laser, operating at center wavelengths of 1535 nm and 1564 nm. The same laser cavity can also be operated in a single-wavelength mode-locked regime with a wavelength tuning range of 30 nm, from 1532 nm to 1562 nm. The proposed dynamically tunable Lyot-filter provides a simple setup for laser mode-locking using a single laser cavity design to generate dual-wavelength pulses, with the flexibility to also allow the generation of single-wavelength pulses with a continuously-tunable center wavelength.

Nonastigmatic alexandrite ring laser design with wavelength-tunable single-longitudinal-mode operation

This work presents a study of a fully nonastigmatic design of a single-longitudinal-mode, wavelength-tunable, unidirectional alexandrite ring laser cavity and assessment of its performance compared to more complex laser design requiring astigmatism compensation. A “displaced mode” nonastigmatic laser cavity design eliminating astigmatic cavity elements is developed around an alexandrite crystal end-pumped by a low-brightness, high-power red diode laser pump system. Single-longitudinal-mode, continuous-wave operation is demonstrated with output power of 700 mW with an excellent T E M 00 mode ( M 2 &lt; 1.1 ) across a wide pump power range. Wavelength tuning from 748–773 nm is produced using a birefringent filter plate. The nonastigmatic alexandrite laser design achieves better spatial quality and resilience to maintain T E M 00 operation across wide variation in pump-induced lensing compared to the astigmatic design. To the best of our knowledge, this is the first wavelength-tunable, single-longitudinal-mode operation of a unidirectional alexandrite ring system in a fully nonastigmatic cavity regime.

On quantum-dot lasing at gain peak with linewidth enhancement factor αH = 0

This paper describes an investigation of the linewidth enhancement factor αH in a semiconductor quantum-dot laser. Results are presented for active region parameters and laser configurations important for minimizing αH. In particular, the feasibility of lasing at the gain peak with αH = 0 is explored. The study uses a many-body theory with dephasing effects from carrier scattering treated at the level of quantum-kinetic equations. InAs quantum-dot lasers with different p-modulation doping densities are fabricated and measured to verify the calculated criteria on laser cavity design and epitaxial growth conditions.This paper describes an investigation of the linewidth enhancement factor αH in a semiconductor quantum-dot laser. Results are presented for active region parameters and laser configurations important for minimizing αH. In particular, the feasibility of lasing at the gain peak with αH = 0 is explored. The study uses a many-body theory with dephasing effects from carrier scattering treated at the level of quantum-kinetic equations. InAs quantum-dot lasers with different p-modulation doping densities are fabricated and measured to verify the calculated criteria on laser cavity design and epitaxial growth conditions.

Electronic bandwidth enhancement of directly modulated semiconductor lasers

The theoretical possibility of enhancing the modulation bandwidth of a semiconductor laser using digital signal processing (DSP) and a digital-to-analog converter (DAC) is investigated. Simulation results show the feasibility of modulating a distributed feedback (DFB) laser designed for 2.5-Gb/s operation at modulation speeds reaching 56-Gb/s without injection locking or changing the laser cavity design, and at a power penalty less than 6 dB. The utilization of a 6-bit DAC operating at two samples per symbol, improves the modulation speeds of the DFB laser by a factor of 2.5, at the same power penalty, overcoming the intrinsic limitations imposed by the electron–photon resonance inside the laser cavity.

Route towards extreme optical pulsation in linear cavity ultrafast fibre lasers

Pathways towards the generation of extreme optical pulsation in a chaotic transition regime in a linear fibre laser cavity configuration are presented. In a thulium mode-locked fibre laser, extreme events that can be controllably induced by manipulating the cavity birefringence for pulse energies exceeding the single soliton pulse operating regime are studied in detail for the first time. While a solitonic pulsation structure at the fundamental repetition rate is maintained, additional energy is shed in a chaotic manner, leading to broader spectral generation and shorter pulse durations whose behaviour deviates significantly from a classical statistical distribution. These pulses display markedly different characteristics from any previously reported extreme events in fibre lasers associated with multiple solitons and pulse bunching, thus presenting a novel observation of extreme pulsation. Detailed noise studies indicate that significant enhancement of relaxation oscillations, modulation instability and the interplay with reabsorption mechanisms contribute in this transient chaotic regime. The extreme pulsation generated in a compact fibre laser without any additional nonlinear attractors can provide an attractive platform to accelerate the exploration of the underlying physics of the chaos observed in mode-locked laser systems and can lead to novel fibre laser cavity designs.