Gain Mirror Research Articles

Efficient and widely tunable mid-infrared sources using GaAs and AlGaAs integrated platforms for second-order frequency conversion

Integrated coherent mid-infrared (mid-IR) sources are crucial for spectroscopy and quantum frequency conversion (QFC) to facilitate scalable fiber-based application of single photons. Direct mid-IR emission with broad tunability poses fundamental challenges from the gain media and mirror components. This paper presents a characterization of a second-order nonlinear platform. It showcases a mid-IR parametric coherent source with a continuous tuning range exceeding 230 nm centered around 2425 nm, achieved through difference-frequency generation (DFG). The nonlinear coefficient d14 of gallium arsenide (GaAs) and aluminum gallium arsenide (AlGaAs) on insulator is experimentally determined via second-harmonic generation (SHG) in waveguides of various lengths, and the tolerance of the process is investigated. These materials are explored for their high conversion efficiency, utilizing monolithic epitaxial quantum dots and integrated waveguides for QFC. The results demonstrate efficient and tunable mid-IR emission suitable for compact, scalable quantum emitters, with applications in environmental and health monitoring.

Spatiotemporally reconfigurable light in degenerate laser cavities

We show that a III-V semiconductor vertical external-cavity surface-emitting laser (VECSEL) can be engineered to generate light with a customizable spatiotemporal structure. Temporal control is achieved through the emission of temporal localized structures (TLSs), a particular mode-locking regime that allows individual addressing of the pulses traveling back and forth in the cavity. The spatial profile control relies on a degenerate external cavity, and it is implemented due to an absorptive mask deposited onto the gain mirror that limits the positive net gain within two circular spots in the transverse section of the VECSEL. We show that each spot emits spatially uncorrelated TLSs. Hence, the spatiotemporal structure of the light emitted can be shaped by individually addressing the pulses emitted by each spot. Because the maximum number of pulses circulating in the cavity and the number of positive net-gain spots in the VECSEL can be increased straightforwardly, this result is a proof of concept of a laser platform capable of handling light states of scalable complexity. We discuss applications to three-dimensional all-optical buffers and to multiplexing of frequency combs that share the same laser cavity.

Ultrashort cavity length effects on the performance of GaInP multiple-quantum-well laser diode

The cavity length of a semiconductor laser plays a key role in its operation and dynamic behaviour. Moreover, downsizing the quantum well (QW) laser chip is required for specific applications, such as hard disk drives (HDDs). Therefore, it is vital to study laser operation at various cavity lengths in micro-scale dimensions. Here, the operation of a GaInP/GaAs multiple-quantum-well laser with different short cavity lengths (i.e., 200, 300, 400, and 500 µm) at room temperature is demonstrated. The threshold current (Ith), differential efficiency, emission spectra, and near-field profile images are all experimentally reported in this study. Likewise, the modal gain threshold and mirror facet coating effects on the operation of the samples are also discussed. The Ith decreases with the increase of cavity length, whereas emission spectra exhibited a redshift by about 3 nm when the laser length rises from 200 to 500 µm. The near-field images showed a reduction in profile width when the laser length is shorter, which is attributed to a reduction of the spreading current along the laser stripe. The short cavity of the 200 µm sample showed high efficiency, low spreading current, and fast carrier dynamic but a slightly high Ith which can be reduced by coating its facets. This could be a promising small-footprint candidate laser chip for next-generation HDDs and for downsizing photonic applications.

High output power, single mode, and TEM00 operation of a multiple gain chip VECSEL using a twisted-mode configuration.

A vertical external cavity surface emitting laser (VECSEL) has been developed for a sodium guide star application. Stable single frequency operation with 21 W of output power near 1178 nm with multiple gain elements while lasing in the TEM00 mode has been achieved. Higher output power results in multimode lasing. For the sodium guide star application, the 1178 nm can be frequency doubled to 589 nm. The power scaling approach used involves using multiple gain mirrors in a folded standing wave cavity. This is the first demonstration of a high power single frequency VECSEL using a twisted-mode configuration and multiple gain mirrors located at the cavity folds.

VECSEL systems for quantum information processing with trapped beryllium ions

We demonstrate two systems based on vertical-external-cavity surface-emitting lasers (VECSELs) for producing ultraviolet laser light at wavelengths of 235 and 313 nm. The systems are suitable for quantum information processing with trapped beryllium ions. Each system consists of a compact, single-frequency, continuous-wave VECSEL producing high-power near-infrared light, tunable over tens of nanometers. One system generates 2.4 W at 940 nm, using a gain mirror based on GaInAs/GaAs quantum wells, which is converted to 54 mW of 235 nm light for photoionization of neutral beryllium atoms. The other system uses a gain mirror based on GaInNAs/GaAs quantum wells, enabling wavelength extension above 1200 nm with manageable strain in the GaAs lattice. This system generates 1.6 W at 1252 nm, which is converted to 41 mW of 313 nm light that is used to laser cool trapped 9Be+ ions and quantum state preparation and detection. The 313 nm system is also suitable for implementing high-fidelity quantum gates.

Theory of Dronized Laser Source for Next Generation of Optical Wireless Power Transmission

A theory of dronized laser resonator source which can be applied effectively to achieve an efficient remote wireless optical power transmission (WOPT) for the next 6G mobile communications, internet of things (IoT) devices, and continuous flying unmanned aerial vehicles (UAV) is proposed. The proposed laser resonator composes mainly of mirrors and a gain element that can be carried individually by drones to form a relatively long cavity. The airborne components can be assembled according to a specified formation flight of drones to configure a flying laser cavity that exposes its output towards the corresponding target. The stability of the proposed device is theoretically analyzed in terms of main important intracavity parameters, such as length, g-geometrical parameters, and radius of curvature of mirrors. Accordingly, the performance of the confocal symmetric laser resonator is determined in terms of mode size, beam waist size, and beam divergence angle of the fundamental mode in presence of refractive power variation. Simulation results have shown that a stable operation over a wide range of refractive power of confocal long laser resonator can be obtained when the value of curvature of mirror approaches resonator length. In addition, an acceptable fundamental mode size at gain element and mirrors is obtained with an expected efficient gain medium excitation and low diffraction loss.

Remember Me Gone by Stacy Stokes

Reviewed by: Remember Me Gone by Stacy Stokes Kate Quealy-Gainer, Editor Stokes , Stacy Remember Me Gone . Viking , 2022 [ 368 p] Trade ed. ISBN 9780593327661 $17.99 E-book ed. ISBN 9780593327678 $10.99 Reviewed from digital galleys R Gr. 7-10 Tumble Tree, Texas, is a small rundown town only surviving because of one thing: the Memory House, where Lucy's dad helps people with their sadness by taking away their memories. Lucy has supposedly inherited the ability to manipulate memories like the generations before her, but her gift isn't manifesting quite like the rest of her family, and she's worried she won't be able to take over the family business. Meanwhile, the town's shady mayor is acting even shadier, forcing her dad to go to the local mines in the middle of the night, and she continues to feel a strange connection to the mayor's nephew Marco, whom she barely knows. It's clear early on that Lucy's memory has been tampered with, and so the reliability of her narration is quickly thrown into doubt, leaving readers to intuit clues from what might otherwise be casual interactions with other characters. From his first appearance, the mayor is the obvious bad guy, but the extent of his villainy is breathtaking—and surprisingly familiar. The material he's forcing people to mine might be magical, but his violent methods of control and focus on personal gain and profit mirror real world corporate organizations uncomfortably well, and the book approaches the idea of happiness at any cost on multiple provocative levels. The resolution is murky on the details, especially when it comes to the nature of Lucy's powers, but the magical realism elements and vividly described setting will sweep readers into Tumble Tree, and few will forget the strange town and its intriguing, resilient residents. Copyright © 2022 The Board of Trustees of the University of Illinois

High-Power 760 nm VECSEL Based on Quantum Dot Gain Mirror

We report high-power second-harmonic generation of 760 nm laser light from optically-pumped vertical-external-cavity surface-emitting laser based on quantum dot active medium. The laser generates ~1.2 W in fundamental transverse mode with fixed linear polarization. The emission wavelength can be continuously tuned from 738 to 778 nm by using an intra cavity birefringent filter for fundamental radiation without readjustment of phase-matching angle of the nonlinear crystal. The result constitutes a viable alternative for applications requiring broadly tunable high brightness lasers in the 700-800 nm range.

Single crystal diamond gain mirrors for high performance vertical external cavity surface emitting lasers

We report on the design, fabrication and optical performance of gain mirrors in single crystal diamond substrates for vertical external cavity surface emitting lasers (VECSELs). VECSELs have gained attention recently due to their potential for high emission power in single mode with low beam divergence, yet their maximum output power remains typically limited due to thermal roll-over resulting from insufficient heat dissipation. In order to increase the heat transfer, we exploit the excellent thermal conductivity of single crystal diamond, which is assembled in direct contact with the active structure. The optical cavity is hereby defined by an output coupler and a high reflection grating structure etched into the diamond surface. We here present the design and microfabrication of a diffraction grating that was optimized to reflect light into the 0th order, therefore combining the role of a gain mirror and a heatsink at the same time. Our process involved metal mask deposition onto the diamond surface, e-beam lithography and reactive ion etching. Characterization showed reflection above 95% at a center wavelength of 1550 nm, potentially allowing the integration of the diamond mirror into a vertical external cavity surface emitting laser.

Orthogonally polarized frequency combs in a mode-locked VECSEL

We introduce a spin–flip model for a vertical-external-cavity surface-emitting laser (VECSEL) with a saturable absorber. We demonstrate the possibility, due to the spin–flip dynamics, to generate two orthogonally linearly polarized frequency combs in the mode-locked regime. The two combs are shifted in wavelength due to the birefringence in the VECSEL gain and/or saturable absorption mirror. We show that the polarization degree of freedom may also lead to several pulses being generated per roundtrip in the two orthogonal linear polarizations and to more complicated dynamics with both linear polarizations excited.

Flip-Chip Wafer-Fused OP-VECSELs Emitting 3.65 W at the 1.55-μm Waveband

Optically pumped vertical external cavity surface emitting lasers (VECSELs) based on flip-chip gain mirrors emitting at the 1.55 μm wavelength range are reported. The gain mirrors employ wafer-fused InAlGaAs/InP quantum well heterostructures and GaAs/AlAs distributed Bragg reflectors fixed on a diamond heat-sink substrate in a flip-chip geometry, incorporated in a V-cavity configuration. A maximum output power of 3.65 W was achieved for a heatsink temperature of 11°C and employing a 2.2% output coupler. The laser exhibited circular beam profiles for the full emission power range. This demonstration represents more than five-fold increase of the output power compared to the state-of-the-art flip-chip VECSELs previously reported at the 1.55 μm wavelength range. It opens new perspectives for developing practical VECSEL-based laser systems operating at a wavelength range widely used in many applications.

Narrow-linewidth operation of folded 1178nm VECSEL with twisted-mode cavity.

A vertical external-cavity surface-emitting laser (VECSEL) with a twisted-mode configuration is demonstrated. This architecture is particularly advantageous for power scaling of single-frequency VECSELs employing multiple gain mirrors in folded cavities. In such a configuration, some of the gain mirrors are inherently at the fold, and the lasing spectrum becomes unstable. This is caused by four waves interfering, destabilizing the standing wave pattern at the quantum wells. We show that the lasing spectrum can be narrowed by employing a twisted-mode configuration, which stabilizes the standing-wave pattern at the gain mirror. Furthermore, single-frequency output of more than 10 W at 1178 nm is demonstrated for a VECSEL employing two gain mirrors in a standing-wave cavity. In comparison, the output power for operation with one gain mirror only was 7.4 W when operating in single frequency. The choice of wavelength for the work reported in this paper is motivated by the opportunity to demonstrate compact VECSEL-based guide star lasers for adaptive optics via frequency doubling to the sodium D2 resonance at 589 nm.

72‐W vertical‐external‐cavity surface‐emitting laser with 1180‐nm emission for laser guide star adaptive optics

We report a high-power optically-pumped vertical-external-cavity surface-emitting laser emitting at around 1180 nm. The free-running laser produced 72 W of output power at a heatsink temperature of 0°C and 53 W near room temperature (20°C). The GaAs-based gain mirror was bonded to a 2-mm-thick diamond attached to a TEC-cooled copper mount in order to enable efficient heat extraction for high-power operation. Moreover, the spectrum of the laser was narrowed down to 0.06 nm by employing a combination of a birefringent filter and an etalon inside the cavity which yielded a maximum of 19 W at a heatsink temperature of 20°C. The demonstration opens a new perspective for the realisation of sodium laser guide star adaptive optics employing frequency doubling of 1180 nm radiation.

33 W continuous output power semiconductor disk laser emitting at 1275 nm.

We demonstrate a semiconductor disk laser emitting at 1275nm, employing a wafer fused AlInGaAs/InP-AlAs/GaAs gain mirror. A built-in Au-reflector was used to reflect the pump light not absorbed in a single pass through the gain chip active region. The laser exhibited an output power of 33 W for a pump spot with a diameter of 0.86 mm, an output coupler of 2.5%, and a heat-sink temperature of -5°C. When the temperature of the heat-sink was increased to 15 °C, the maximum output power reached a value of ~24 W. The study reveals that the wafer fused gain mirrors have a high optical quality and good uniformity enabling scaling of the maximum emitted power with the diameter of the pump spot, i.e. at least up to the 1 mm diameter.

Monolithic GaInNAsSb/GaAs VECSEL Operating at 1550 nm

The first monolithic GaAs-based vertical-external-cavity surface-emitting laser (VECSEL) operating at 1550 nm is reported. The VECSEL operation is based on a gain mirror which was grown in a single growth run by plasma-assisted molecular beam epitaxy. The gain mirror comprised eight GaInNAsSb/GaAs quantum wells with a photoluminescence peak at 1505 nm and an AlAs/GaAs distributed Bragg reflector ensuring high reflectivity. The VECSEL chip was pumped with an 808-nm diode laser that had a large quantum defect in respect to the lasing wavelength. An output power of 80 mW in continuous wave mode and 210 mW in pulsed pump mode are demonstrated close to room temperature.

Highly coherent modeless broadband semiconductor laser.

We report on the highly coherent modeless broadband continuous wave operation of a semiconductor vertical-external-cavity-surface-emitting laser. The laser design is based on a frequency-shifted-feedback scheme provided by an acousto-optic frequency shifter inserted in a linear or a ring traveling wave cavity. The gain mirror is a GaAs-based multiple quantum well structure providing large gain at 1.07 μm. This laser exhibits a coherent optical spectrum over 1.27 nm (330 GHz) bandwidth, with 70 mW output power and a high beam quality. The light polarization is linear (>30 dB extinction ratio). The laser dynamics exhibits a low intensity noise close to class A regime, with a ∼1.5 MHz cutoff frequency. The frequency noise spectral density shows a first-order low-pass like shape (130 kHz cutoff) leading to a Gaussian shape for homodyne interferometric signals. The measured beat width is ≃54 kHz and the coherence time of ∼19 μs. No nonlinear effects are observed, showing dynamics very close to theory.

615 nm GaInNAs VECSEL with output power above 10 W.

A high-power optically-pumped vertical-external-cavity surface-emitting laser (VECSEL) generating 10.5 W of cw output power at 615 nm is reported. The gain mirror incorporated 10 GaInNAs quantum wells and was designed to have an emission peak in the 1230 nm range. The fundamental emission was frequency doubled to the red spectral range by using an intra-cavity nonlinear LBO crystal. The maximum optical-to-optical conversion efficiency was 17.5%. The VECSEL was also operated in pulsed mode by directly modulating the pump laser to produce light pulses with duration of ~1.5 µs. The maximum peak power for pulsed operation (pump limited) was 13.8 W. This corresponded to an optical-to-optical conversion efficiency of 20.4%.

8.5 W VECSEL output at 1270 nm with conversion efficiency of 59%.

We report on 1270 nm vertical-external-cavity surface-emitting lasers (VECSELs) with up to 59% conversion efficiency and maximum output power of 8.5 W (pump limited), at 5°C heat sink temperature. These VECSELs comprised wafer-fused gain mirrors in the flip-chip (thin-disk) heat dissipation scheme. The reflected pump light from the gain mirror surface was found to depend considerably on temperature and pump power.

High performance wafer-fused semiconductor disk lasers emitting in the 1300 nm waveband

We report for the first time on the performance of 1300 nm waveband semiconductor disc lasers (SDLs) with wafer fused gain mirrors that implement intracavity diamond and flip-chip heat dissipation schemes based on the same gain material. With a new type of gain mirror structure, maximum output power values reach 7.1 W with intracavity diamond gain mirrors and 5.6 W with flip-chip gain mirrors, using a pump spot diameter of 300 µm, exhibiting a beam quality factor M(2)< 1.25 in the full operation range. These results confirm previously published theoretical modeling of these types of SDLs.

1180 nm VECSEL with output power beyond 20 W

The highest power result for an optically-pumped single-chip vertical external-cavity surface-emitting laser with emission near 1180 nm is reported. The gain mirror was grown by molecular beam epitaxy and incorporated a strain compensated GaInAs/GaAs/GaAsP active region. An intra-cavity diamond heat spreader was attached to the gain mirror for thermal management. In free-running operation, the laser emitted more than 20 W at a mount temperature of about 12 °C. The output spectrum was centred between 1165–1190 nm depending on the mount temperature and pump power. By using an intra-cavity birefringent filter, the full width at half-maximum linewidth could be narrowed to ≤1 nm and at the same time achieved approximately 14 W of output power near 1178 nm. Moreover, the lasing wavelength could be tuned over more than 40 nm.