Short Cavity Research Articles

Performance evaluation of ∼2.1 μm microchip laser operation in Ho3+ doped germanate glass

An in-band pumped continuous wave (CW) ∼2.1 μm microchip laser is presented for the first time based on a short cavity Ho3+ doped germanate glass (GeO2-PbO-Ga2O3–Na2O: GPGN). A 1.94 μm, 5 W Tm3+ fiber laser was employed for the excitation of the Ho3+ ions. A 19% laser slope efficiency was achieved in a simple, unoptimized plane parallel Fabry-Perot cavity configuration. A positive thermal lens was estimated in the laser cavity with a sensitivity factor of S ∼31 m−1W−1 and an optical path distortion value exceeding 6 μm. The laser results along with the analysis of the thermal lens indicate that with improved thermal management and an optimized cavity configuration GPGN is a promising gain medium for microchip laser operation around 2.1 μm.

High-Power, High-Beam-Quality, Long-Pulse-Width 532 nm Laser Based on a 4f Optical System

In response to the demand for high-power, long-pulse-width 532 nm lasers in the medical and industrial processing fields, this paper explains how the laser cavity of a high-power Nd:YAG 532 nm laser can be extended while maintaining the laser’s q-parameter by using a 4f optical system. The results show that at a repetition rate of 10 kHz, the extended cavity achieved a maximum average power of 112 W. Compared with the short cavity, the power was not significantly reduced. The pulse width was extended from 56 ns to 85 ns, and its broadening ratio reached 46.5%. The laser maintained good beam quality during high-power operation.

Compact widely tunable laser integrated on an indium phosphide membrane platform

We present the design, fabrication, and characterization results of a compact, widely tunable laser realized on an indium phosphide membrane-on-silicon (IMOS) platform. The laser features a compact Mach–Zehnder interferometric structure as the wavelength-selective intracavity filter with a footprint of 0.13 mm2. The filter design is optimized to ensure narrow filter transmission and high side-mode-to-main-mode-ratio, enabling single-mode operation for the laser. The high optical confinement on the IMOS platform can support tight waveguide bends. Leveraging this, the laser achieves a short cavity length, further enhancing the single-mode operation. Measurement results indicate a threshold current of 29 mA and a maximum on-chip output power of approximately 3.6 dBm and wall plug efficiency of 1.8%. The side-mode suppression ratio ranges from 30 to 44 dB, with a tuning range spanning 40 nm, from 1555 to 1595 nm. A complete tuning lookup table is generated via an automated setup incorporating a stochastic search algorithm.

Vertical InGaN Light-Emitting Diode with Hybrid Distributed Bragg Reflectors.

A vertical-type InGaN light-emitting diode with a resonant cavity was demonstrated with a 9 μm aperture size and a short cavity formed by hybrid distributed Bragg reflectors (DBRs). The approach involved designing epitaxial structures and utilizing an electrochemical etching process to convert heavily doped n-type gallium nitride (n+-GaN) layers into porous GaN layers as a porous-GaN DBR structure. Thirteen pairs of the conductive porous-GaN:Si/GaN:Si DBR structure provided a vertical current path in a vertical-type light-emitting diodes (LED) structure. The LED epitaxial layers were separated from sapphire for membrane-type LED structures through a laser lift-off process. During the free-standing membrane fabrication process, the dielectric DBR deposited on ITO/p-GaN:Mg layers was inverted from top to bottom, thereby establishing the concept of higher reflectivity for the bottom DBR compared to the porous-GaN DBR. The physical cavity length was reduced from about 2.3 μm for the LED membrane to 0.74 μm for the membrane-type LED with the embedded porous-GaN DBR structure. The divergent angles and line width of EL emission light were reduced from 124°/31.7 nm to 44°/3.3 nm due to the resonant cavity effect. The membrane-type LED structures with hybrid DBRs consisted of small divergent angles, narrow line width, and vertical current injection properties that have potential for directional emission light sources and vertical-cavity surface-emitting diode laser applications.

Frequency‐Division Multiplexing Continuous Variable Quantum Dense Coding with Broadband Entanglement

AbstractQuantum dense coding (QDC) provides great potential for high‐capacity quantum communication. However, it is highly demanded for practical applications to realize high‐capacity QDC with multiple coded information. Here, a high‐capacity QDC with multiple streams is reported in different channels simultaneously through frequency‐division multiplexing (FDM). The broadband entangled state is generated from a pair of degenerate optic al parametric amplifiers with short cavity lengths. Based on the resultant broadband entanglement, multiple pieces of information coded using binary phase shift keying (BPSK) are transferred with the FDM method. As an experimental demonstration, four pieces of information composed of pseudo‐random numbers are transmitted at a rate of 4 Mbit s–1 using BPSK encoding. The decoded bit error rate reaches , which is an average 35‐fold improvement compared with the classical scheme. Furthermore, it is possible to make full use of sideband resource for four different information by using orthogonal FDM. This scheme can be extended to more different information by directly increasing the FDM sideband subchannels, and opens an avenue to construct high‐capacity quantum communication, while minimizing the cost of quantum resource.

Tunable Diode Laser with a Short Tandem External Cavity

Tunable Diode Laser with a Short Tandem External Cavity

Demonstration of Watt Level 375 nm Short Cavity Laser Diode With Etched Facets

Demonstration of Watt Level 375 nm Short Cavity Laser Diode With Etched Facets

Single-frequency orbital angular momentum switchable modes from a microchip laser.

We demonstrate the direct generation of single-frequency switchable orbital angular momentum (OAM) modes in a 1 µm wavelength range using a Nd:YVO4 microchip laser. The 808 nm laser diode pump beam is shaped into annular through an axicon associated with a lens. By adjusting the diameter and power of the annular pump beam, various OAM modes with different mode volumes can oscillate inside the Nd:YVO4 microchip. Moreover, a single-frequency output is also available due to the short cavity of the microchip. In the proof-of-principle experiment, single-frequency twofold multiplexed OAM modes | ± 1> and | ± 2> are generated, with experimentally measured fidelity higher than 96%. This work presents a compact and versatile single-frequency OAM source and will inspire multiple advanced scenarios ranging from classical to quantum photonics.

High-speed GaN-based laser diode with modulation bandwidth exceeding 5 GHz for 20 Gbps visible light communication

Visible light communication (VLC) based on laser diodes demonstrates great potential for high data rate maritime, terrestrial, and aerial wireless data links. Here, we design and fabricate high-speed blue laser diodes (LDs) grown on c-plane gallium nitride (GaN) substrate. This was achieved through active region design and miniaturization toward a narrow ridge waveguide, short cavity length, and single longitudinal mode Fabry–Perot laser diode. The fabricated mini-LD has a low threshold current of 31 mA and slope efficiency of 1.02 W/A. A record modulation bandwidth of 5.9 GHz (−3 dB) was measured from the mini-LD. Using the developed mini-LD as a transmitter, the VLC link exhibits a high data transmission rate of 20.06 Gbps adopting the bit and power loading discrete multitone (DMT) modulation technique. The corresponding bit error rate is 0.003, satisfying the forward error correction standard. The demonstrated GaN-based mini-LD has significantly enhanced data transmission rates, paving the path for energy-efficient VLC systems and integrated photonics in the visible regime.

Quantum Cascade Surface Emitting Lasers

AbstractA low‐cost single frequency laser, emitting in the mid‐infrared spectral region and dissipating minimal electrical power, is a key ingredient for the next generation of portable gas sensors for high‐volume applications involving chemical sensing of important greenhouse and pollutant gases. Herein, a Quantum Cascade Surface Emitting Laser (QCSEL) is proposed, which is implemented as a short linear cavity with high reflectivity coated end‐mirrors to suppress any edge emission and employs a buried semiconductor diffraction grating to extract the light from the surface. By wafer‐level testing, the cavity length scaling is investigated, mirror reflectivities larger than 0.9 are extracted, and a pulsed threshold power dissipation of 237 mW for an emission wavelength near 7.5 µm is achieved. Finally, single‐mode emission with a side‐mode suppression ratio larger than 33 dB is demonstrated for a 248 µm short cavity, which is mounted with the epitaxial layer up and operated in continuous wave at 20 .

High brightness widely tunable, hundred picosecond mid-IR MgO:PPLN optical parametric oscillator with short cavity

A high brightness hundred picosecond (ps) mid-infrared tunable optical parametric oscillator (OPO) based on MgO doped periodically poled lithium niobate (MgO: PPLN) was demonstrated. The pumping source was provided by a cascade amplified microchip laser at 10 kHz with pulse width of 466 ps. The idler wavelength tuning from 2.8 to 4.3 μm was achieved by the combination of period and temperature tuning. The maximum idler average output power was 262 mW at 2.8 μm with a pulse duration of 252 ps, corresponding to 6.7% conversion efficiency. The average beam quality factor was measured to be M 2 = 2.46, resulting in a brightness value of 0.55 MW sr cm−2. Pulse width of 209 ps at 4.3 μm, which was the shortest pulse width from a short cavity OPO to our best knowledge.

Hybrid parallel photonic reservoir computing with accelerated data processing speed

Reservoir computing is a bio-inspired approach especially suited for processing time-dependent information. In this work, we propose a hybrid reservoir computing scheme based on parallel photonic time-delay reservoirs with optical injection. The state of virtual nodes are evaluated from the combination of temporal outputs of parallel lasers. It is demonstrated that our proposed hybrid scheme enables photonic reservoir computer with shortened time interval θ and less virtual nodes number N, which could break through the limitation of short external cavity length in miniaturization of reservoir computing with photonic integrated circuits. The computational efficiency of photonic reservoir is numerically evaluated by chaotic time-series prediction task and memory capacity test. State-of-the-art speed performances reach 20 GSa/s with prediction error rate below 0.01. Our scheme bridges the areas of photonic integrated circuits and photonic information processing.

The passive Q-switched and Q-switched mode-locked Nd: GYAP laser based on a novel Bi2O3 saturable absorber

With a newly fabricated Bi2O3 saturable absorber, the passive Q-switched and Q-switched mode-locked laser operations were experimentally demonstrated on a novel Nd: GYAP (Nd: Gd0.1Y0.9AlO3) disordered crystal. For the Q-switched operation, a 358 ns pulse was achieved with a short cavity laser, and a maximum output power of 0.203 W with a slope efficiency of 3.1% was realized. For the Q-switched mode-locked operation, the laser of a maximum output power of 0.264 W and a spectrum of 1.062 nm (FWHM) was also achieved on a 1.78 m Z-folded cavity. The mode-locked pulse has a calculated pulse width of sub-1000 ps and a repetition rate of 90.09 MHz. The research results will open up applications of 2D Bi2O3 saturable absorber and the Nd: GYAP crystal in the field of ultrafast lasers.

A mini broadband cavity enhanced absorption spectrometer for nitrogen dioxide measurement on the unmanned aerial vehicle platform

We developed a small size and light weight analyzer based on the broadband cavity enhanced absorption spectroscopy for measuring nitrogen dioxide (NO2) with high spatial-temporal resolution and high accuracy. The instrument utilizes a LED centered at 450 nm, a short optical cavity, and a spectrometer to determine the extinction coefficients span 435–465 nm, allowing us to retrieve the mixing ratio of NO2 by absorption cross-section. The measurement precision (1σ) for NO2 is 98 ppt in 2 s under laboratory conditions. The uncertainty is estimated at 6% mainly attributed to cross-section and the mirror reflectivity. Good consistency was achieved by comparing with commercial chemiluminescence detector and cavity attenuation phase shift spectrometer (CAPS) (both R2 = 0.99). We further mounted the instrument on an unmanned aerial vehicle (UAV), and maintained the UAV flight at the height of 20 m, the comparative measurement with a CAPS set in a neighbor building with the same sampling height showed a good correlation (R2 = 0.97), which confirmed the instrumental feasibility and stability on the UAV platform. At last, we present a successful NO2 vertical measurement test, the good performance indicates this portable technique has great potential for vertical measurement. In particular, the mini-CEAS technique can further extend to measure the vertical profiles of other trace gas species (such as nitrous acid) with strong optical structural absorptions, which would largely promote the understanding of atmospheric chemistry on a vertical scale.

Смена режимов генерации в эрбиевых волоконных лазерах

Operation features of the erbium fiber lasers with short cavities near two phase transitions have been established experimentally for the first time. The power-law behavior of the system parameters in the vicinity of the critical point in a wide range of pump power values was revealed. The parameters and operation regimes dependence on the cavity length and pump power, namely the switching from pulsed to CW operation, was investigated. The pulse duration and frequency dependencies with varying cavity length have been investigated, which made it possible to experimentally establish the universal dependence of these parameters on the lasing power for passively Q-switched erbium fiber lasers. The critical indices for pulsed operation of the erbium fiber lasers are determined weakly depending on the cavity parameters. The results of the study can be used for designing high-coherent fiber laser sources.

CW and Pulsed Generation of Short Cavity Yb-doped Phosphosilicate Fiber Laser

CW and Pulsed Generation of Short Cavity Yb-doped Phosphosilicate Fiber Laser

Influence of Reynolds number and rotational number on the features of a transitional flow in short Taylor-Couette cavity

The paper reports on the DNS results of the flow in co- and counter-rotating coaxial cylinders of aspect ratios Γ = H/(R2 − R1) between 3.8 and 4.05, and radius ratio η = R1/R2 = 0.5, with the end-walls rotating with the angular velocity of the inner cylinder Ω1. The computations are performed for a wide range of rotational number RΩ = (1 − η)(Re1 + Re2)/(ηRe2 − Re1), from − 1.069 to 0.0, which includes both the linearly unstable flows and the Rayleigh stable flows. The considered Reynolds numbers of the inner cylinder Re1 = Ω1R1(R2 − R1)/ν are up to 3000 (Re2 = Ω2R2(R2 − R1)/ν). The obtained flow structures appearing at various stages of the laminar-turbulent transition and the radial profiles of statistical parameters are discussed in the light of the data published by other authors. The critical bifurcation lines are determined as functions of the inner and outer cylinder Reynolds numbers. Many interesting phenomena have been found.

Guided mode resonances for angular and spectral filtering

The development of devices based on compact waveguides is a rapidly evolving field. A unique variation of such devices is the Fano-like resonance dielectric spectral and spatial filtre, made from a dielectric conformal thin film on a surface relief grating. It can be used in a normal (or oblique) angle-of-incidence configuration. This device facilitates directional selectivity, which is useful for transverse-mode cleaning in short optical cavities. It can also be enhanced by using leaky-mode effects to produce even sharper spectral features. However, a perfect spatial filtre should be as invariant as possible in the spectral and enhanced angular domains. Here, we solved the inverse design problem to produce such an effect. Numerically, we tuned the surface profile of the substrate grating, assuming a conformal layer on top. This resulted in trapezoidal relief patterns followed by narrow flat-top angular features. The combination of leaky mode effect and enhanced device topology will enable efficient and useful devices with a bandwidth of 50 nm and even more in the future.

Efficient continuous-wave Nd:YVO4/KGW intracavity Raman laser

We demonstrate an efficient Nd:YVO4/KGW intracavity Raman laser in continuous-wave (CW) scheme. With a V-shaped fundamental laser cavity and a short Stokes cavity in it, the oscillating beam sizes are designed to alleviate the thermal effect and to enhance the Raman gain for efficient CW operation. The output power of CW Stokes wave at 1177 nm reached 9.33 W under an incident laser diode pump power of 36.65 W, with corresponding optical efficiency being 25.5%. To the best of our knowledge, these are the highest Stokes output power and conversion efficiency of CW intracavity Raman lasers.

Features of Single-Mode Emission in 7.5–8.0 μm Range Quantum-Cascade Lasers with a Short Cavity Length

Features of Single-Mode Emission in 7.5–8.0 μm Range Quantum-Cascade Lasers with a Short Cavity Length