Large Optical Cavity Research Articles

Design of photonic crystals for nanokelvin-resolution thermometry

High-resolution thermometry is key for the development of calorimeters, bolometers, and high-stability light sources, as well as for probing dissipation and transport in microelectronics and quantum devices. Achieving nanokelvin-level temperature resolution at room temperature requires using large optical cavities, which are unsuitable for microscale integration. Here we computationally design a one-dimensional photonic crystal Band Edge Thermometer that achieves significant temperature sensitivity by combining: (i) the abrupt variation in optical properties of a direct bandgap semiconductor at the band edge, and (ii) a large quality factor in a resonant photonic structure. Two devices are designed which are constructed from GaAs/AlAs and GaN/AlN multilayer structures. The optimal sensor design features an extremely large thermoreflectance coefficient of 60.6 K−1 and a thermal time constant of 1.1 µs, with a sensor thickness of only 6.7 µm. The projected thermometry noise floor is 84 nK.Hz-½ for the GaAs/AlAs sensor and 35 nK.Hz-½ for the GaN/AlN sensor. The designed sensor architecture is expected to enable a broad range of applications in microcalorimetry and bolometry where a high temperature resolution combined with microscale sensor footprint is required.

High-power 940 nm DFB laser diode with large optical cavity.

High-power laser diodes with a stable wavelength and narrow linewidth are crucial for many applications. In this study, we introduce a first-order distributed feedback (DFB) grating into an asymmetric large-cavity laser diode operating around 940 nm. This design maintains high output power and offers a wide temperature locking range. The nearly sinusoidal shape first-order grating is fabricated by ultraviolet (UV) nanoimprint lithography, inductively coupled plasma (ICP) dry etching, and wet polishing. At a heat sink temperature of 25°C, the DFB laser diode, with a 200 µm stripe width and 4 mm cavity length, achieves a maximum output power of 24.8 W and a full width at half maximum (FWHM) of 0.4 nm under continuous-wave (CW) conditions. The maximum slope efficiency is calculated to be 1.04 W/A. At an output power of 10.7 W, the device reaches a peak wall-plug efficiency of 56%. Under quasi-continuous operation at 20 A, the laser output spectrum remains locked to the DFB grating over a temperature range from -10°C to 110°C, with a temperature coefficient of 0.062 nm/°C.

Progress of Edge-Emitting Diode Lasers Based on Coupled-Waveguide Concept.

Semiconductor lasers have developed rapidly with the steady growth of the global laser market. The use of semiconductor laser diodes is currently considered to be the most advanced option for achieving the optimal combination of efficiency, energy consumption, and cost parameters of high-power solid-state and fiber lasers. In this work, an approach for optical mode engineering in planar waveguides is investigated. The approach referred to as Coupled Large Optical Cavity (CLOC) is based on the resonant optical coupling between waveguides and allows the selection of high-order modes. The state-of-art of the CLOC operation is reviewed and discussed. We apply the CLOC concept in our waveguide design strategy. The results in both numerical simulation and experiment show that the CLOC approach can be considered a simple and cost-efficient solution for improving diode laser performance.

A self-locking Rydberg atom electric field sensor

A crucial step toward enabling real-world applications for quantum sensing devices such as Rydberg atom electric field sensors is reducing their size, weight, power, and cost (SWaP-C) requirements without significantly reducing performance. Laser frequency stabilization is a key part of many quantum sensing devices and, when used for exciting non-ground state atomic transitions, is currently limited to techniques that require either large SWaP-C optical cavities and electronics or use significant optical power solely for frequency stabilization. Here, we describe a laser frequency stabilization technique for exciting non-ground state atomic transitions that solves these challenges and requires only a small amount of additional electronics. We describe the operation, capabilities, and limitations of this frequency stabilization technique and quantitatively characterize its performance. We show experimentally that Rydberg electric field sensors using this technique are capable of data collection while sacrificing only 0.1% of available bandwidth for frequency stabilization of noise up to 900 Hz.

Semiconductor laser design with an asymmetric large optical cavity waveguide and a bulk active layer near p-cladding for efficient high-power red light emission

A semiconductor laser design for efficient, high power, high brightness red light emission is proposed, using a large optical cavity asymmetric waveguide and a bulk active layer (AL) positioned very close to the p-cladding. The low threshold carrier density associated with the broad AL, as well as the proximity of the AL to the p-cladding, ensure that the electron leakage current, the major detrimental factor in red lasers, stays modest in a broad range of excitation levels. This in turn promises high-power, efficient operation.

Improvement of thermal resistance in InGaAs/GaAs/AlGaAs microdisk lasers bonded onto silicon

Epi-side down bonding on a silicon substrate of AlGaAs/GaAs microdisk lasers is presented. A heterostructure with coupled large optical cavities enables location of an InGaAs quantum dot active region at a distance of ∼1 µm from the heterostructure surface. The thermal resistance was reduced to 0.2 and 0.1 K mW−1 for disks of 30 and 50 µm in diameter, respectively. The maximum continuous-wave power limited by the thermal rollover is more than doubled after bonding.

High efficiency of spectral beam combining by using large optical cavity lasers

High efficiency of spectral beam combining by using large optical cavity lasers

High efficiency of spectral beam combining by using large optical cavity lasers

High efficiency of spectral beam combining by using large optical cavity lasers

High Power 980-nm Broad-Area Lasers with Distributed Bragg Reflection Grating

High-power and highly stable 980 nm semiconductor lasers are widely used in fiber laser pumping and instrumentation applications. We report on a distributed Bragg reflector (DBR) semiconductor laser manufactured on the waveguide structure of an asymmetric large optical cavity. Wavelength stabilization is achieved using a 500-µm-long DBR with a sixth-order Bragg grating, which is fabricated using a combination of electron beam lithography and inductively coupled plasma etching. When the device injection current is 22 A, the output power ranges up to 16 W, the slope efficiency is 0.73 W/A, and a spectral linewidth of 1.4 nm is achieved.

783 nm wavelength stabilized DBR tapered diode lasers with a 7 W output power.

Wavelength stabilized distributed Bragg reflector (DBR) tapered diode lasers at 783 nm will be presented. The devices are based on GaAsP single quantum wells embedded in a large optical cavity leading to a vertical far field angle of about 29° (full width at half maximum). The 3-inch (7.62 cm) wafers are grown using metalorganic vapor phase epitaxy. In a full wafer process, 4 mm long DBR tapered lasers are manufactured. The devices consist of a 500 µm long 10th order surface DBR grating that acts as rear side mirror. After that, a 1 mm long ridge waveguide section is realized for lateral confinement, which is connected to a 2.5 mm long flared section having a full taper angle of 6°. At an injection current of 8 A, a maximum output power of about 7 W is measured. At output powers up to 6 W, the measured emission width limited by the resolution of the spectrometer is smaller than 19 pm. Measured at 1/e2 level at this output power, the lateral beam waist width is 11.5 µm, the lateral far field angle 12.5°, and the lateral beam parameter M2 2.5. The respective parameters measured using the second moments are 31 µm, 15.2°, and 8.3. 70% of the emitted power is originated from the central lobe.

Monolithic Integrated Semiconductor Optical Amplifier With Broad Spectrum, High Power, and Small Linewidth Expansion

Semiconductor optical amplifiers (SOAs) offer direct electrical injection, power consumption, integration, and anti-radiation advantages over optical fiber amplifiers. However, saturation output power and gain bandwidth have been limited in traditional structure SOAs. We demonstrate a monolithic integrated SOA with broad spectrum, high power, high gain, and small spectral linewidth expansion. The device adopts a two-stage amplified large optical cavity structure, and a lower optical field confinement factor is obtained by adjusting the thickness of the waveguide layer. The lower optical field confinement factor is conducive to improving the coupling efficiency and the maximum output power. Our device, fabricated only by standard i-line lithography with micron-scale precision, obtains excellent and stable performance. When the input power is set to 1 mW, the output power is 419 mW with a gain of 26.23 dB. When the input power is set to 25 mW at 25 °C, the output power increases to 600 mW with a gain of 13.8 dB. The corresponding gain bandwidth of 3 dB measures at least 70 nm. The spectral linewidth after the SOA is 1.15 times wider than that of the seed laser.

Design of 1178 nm diode laser with step waveguide layers for reduced voltage and low vertical divergence

A 1178 nm diode laser with step waveguide layers (SWGLs) into the optical cavity is designed for frequency doubling. It is found that the mode field of the fundamental mode can be modulated easily for this kind of diode laser. A strong confinement for the fundamental mode can also be achieved by adopting a low Al content in the optical cavity. Diode lasers with SWGLs can deliver a high output power. Compared with diode lasers based on the conventional large optical cavity, the low Al content results in a reduced voltage, which is helpful to improve the electro-optical conversion efficiency. Based on an asymmetric large optical cavity with SWGLs, a beam divergence of 15.5° in the vertical direction is obtained for the designed diode laser.

Effect of carrier localization on performance of coupled large optical cavity diode lasers

Results are presented on a comparative study of InGaAs/GaAs/AlGaAs coupled large optical cavity (CLOC) laser heterostructures emitting at either 1.03 or 0.98 μm. The smaller energy of carrier localization in the active region of the latter structure leads to stronger carrier leakage out of the quantum well that in its turn results in a higher internal optical loss, higher threshold current density and more pronounced temperature sensitivity. In continuous wave regime, the maximal output power of 8 W in the 0.98-μm lasers is found to be limited by the thermal rollover, whereas in the longer wavelength laser it is 10.8 W being limited by the catastrophic optical mirror damage.

Reducing of thermal resistance of edge-emitting lasers based on coupled waveguides

We present a study on minimization of thermal resistance of edge-emitting diode lasers by placing the active region closer to the laser surface. We demonstrate that using coupled large optical cavity (CLOC) approach one can reduce the thickness of the p-cladding down to 0.5 μm due to the strong mode localization in a broad active waveguide (1.35 μm) coupled to a passive optical cavity. Also, the advanced laser design allowed us to put the active region closer to the cladding in comparison with conventional broad waveguide lasers. As a result, a record-low thermal resistance of 2 K/W for 3 mm device directly mounted on a copper heatsink in combination with a low optical internal loss of 0.4 cm−1 where demonstrated.

Improved 808-nm High-Power Laser Performance With Single-Mode Operation (Vertical Direction) in Large Optical Cavity Waveguide

We present a detailed study of the effect of large optical cavity (LOC) waveguide design on the laser's kink performance and it was found that a multimode waveguide in the epi growth direction could lead to the occurrence of the power kink in the light–current ( L–I ) curve, and the occurrence of the power kink was accompanied with the broadening of the beam divergence in the wafer growth direction. In order to eliminate the kink issue that is associated with the lasing of the higher-order modes, a new type of waveguide, which is called higher-order-mode tunneling waveguide, was proposed in our design. The new type of waveguide can strongly promote the leakage of higher-order modes, and in this way, the LOC waveguide becomes single-moded. Test of the fabricated devices based on the new design showed that the devices indeed exhibited perfect L–I linearity without kinks.

High-power high-brightness 980 nm lasers with >50% wall-plug efficiency based on asymmetric super large optical cavity.

High-power high-brightness super large optical cavity laser diodes with an optimized epitaxial structure are investigated at the wavelength of 980 nm range. The thicknesses of P- and N-waveguides are prudently chosen based on a systematic consideration about mode characteristics and vertical far-field divergences. Broad area laser diodes show a high internal quantum efficiency of 98% and a low internal optical loss of 0.58 cm-1. The ridge-waveguide laser with 7 μm ridge and 3 mm cavity yields 1.9 W single spatial mode output with far-field divergence angles of 6.8° in lateral and 11.5° in vertical at full width at half maximum under 2 A CW operating current. The corresponding M2 values are 1.77 and 1.47 for lateral and vertical, respectively, and the corresponding brightness is 76.8 MW‧cm-2‧sr-1. The far-field divergence angles with 95% power content are in the range of 24.7° to 26.1° across the whole measured range.

Edge-emitting lasers based on coupled large optical cavity with high beam stability

In this paper we present a study on temperature and current stability of far-field patterns of lasers based on the coupled large optical cavity (CLOC) concept. Previously it has been shown that the CLOC structures allows effective suppressing of high-order mode lasing in broadened waveguides. For the first time we report on transverse single-mode emission from the CLOC lasers with 4.8 μm thick waveguide. Using broadened waveguide allowed us to reduce the divergence of the far-field patterns down to 14° in continuous-wave (CW) regime. Far-field patterns proved to be insensitive to current and temperature changes.

Investigation of lasers based on coupled waveguides by near-field scanning optical microscopy

We have investigated near field intensity distributions of InGaAs/GaAs/AlGaAs lasers possessing broadened waveguides based on coupled large optical cavity structures (CLOC) by scanning near-field optical microscopy (SNOM). The concept allows effective suppressing of the transverse high-order mode lasing. The obtained results can be considered to be the direct proof of pure transverse single-mode emission of the CLOC lasers.

Transverse mode tailoring in diode lasers based on coupled large optical cavities

The key principles of transverse mode engineering in edge-emitting lasers with broadened waveguides based on coupled large optical cavity (CLOC) structures are presented. The CLOC laser design is shown to be an effective approach for reducing the optical loss, broadening the waveguide, and lowering the beam divergence. Having simulated the sensitivity of the CLOC design to variations in layer thicknesses and compositions we have shown its high robustness. Advanced versions of the CLOC laser structures having two extra passive waveguides have been treated and shown to effectively eliminate several transverse modes. We have considered an application of the CLOC concept for waveguides with shifted active regions aimed at reducing laser thermal and electric resistances.

Large dynamic range optical cavity based sensor using a low cost three-laser system.

An optical cavity based biosensor using a differential detection method has been proposed to provide a novel approach to point-of-care diagnostics. A two-laser based optical cavity based sensor system is designed and experimentally demonstrated. While the calculated differential value of the two-laser system shows larger responsivity compared to individual wavelengths, the dynamic range of the system is rather small. Because of that, it turned out its fabrication tolerance is also small based on the simulation. We employed a three-laser system and redesigned the optical cavity to increase the dynamic range and improve the fabrication tolerance. In this presentation, we report the measurement results of the three-laser system for the first time. This system increases the dynamic range threefold by a chaining action. Because of this large dynamic range, this three-laser system is anticipated to have a larger fabrication tolerance.