Ridge Lasers Research Articles

Comment on 'Posterior to the ridge laser in zone 2 stage 3 retinopathy of prematurity with plus disease: Efficacy and safety'.

Comment on 'Posterior to the ridge laser in zone 2 stage 3 retinopathy of prematurity with plus disease: Efficacy and safety'.

Coupled terahertz quantum cascade wire lasers

We present mutual optical coupling in terahertz (THz) quantum cascade wire laser arrays that are flip-chip bonded to a dielectric substrate. The mounting substrate is patterned for individual electrical contacting of each wire laser of the array. The resulting sandwich-like structure supports wire laser modes with a significant part propagating outside the cavity and mediates the long range coupling. The evanescent field part of the modes couples to the adjoining ridge, which, in turn, leads to mutual optical injection-locking between them. We demonstrate this effect for both geometrically similar and dissimilar wire lasers when biased in pulsed operation with temporally overlapping bias pulses. Finite element simulations confirm our measurement results. By applying time-shifted bias pulses to individual array elements, a controllable optical injection seeding of the wire cavity is achieved. We observe intensity modification of the laser modes with changing bias pulse overlap as a result of the injection locking. By choosing both the physical spacing of the laser ridges and the intensity of the seeding laser correctly, the relative intensities of the favored lasing modes are enhanced up to 95 percent. Understanding the coupling in THz wire laser arrays is important for future device improvements in terms of higher continuous-wave operating temperatures through better thermal dissipation, and higher output power and an improved far field due to controlled coupling of their modes.

Phase-locked single-mode terahertz quantum cascade lasers array

We demonstrated a scheme of phase-locked terahertz quantum cascade lasers (THz QCLs) array, with a single-mode pulse power of 108 mW at 13 K. The device utilizes a Talbot cavity to achieve phase locking among five ridge lasers with first-order buried distributed feedback (DFB) grating, resulting in nearly five times amplification of the single-mode power. Due to the optimum length of Talbot cavity depends on wavelength, the combination of Talbot cavity with the DFB grating leads to better power amplification than the combination with multimode Fabry−Perot (F−P) cavities. The Talbot cavity facet reflects light back to the ridge array direction and achieves self-imaging in the array, enabling phase-locked operation of ridges. We set the spacing between adjacent elements to be 220 μm, much larger than the free-space wavelength, ensuring the operation of the fundamental supermode throughout the laser's dynamic range and obtaining a high-brightness far-field distribution. This scheme provides a new approach for enhancing the single-mode power of THz QCLs.

Fundamental spatial mode high power 808 nm double trench wide ridge waveguide laser

—Lasers operating at a wavelength of 808 nm, with watt-level output power and high beam quality in the fundamental spatial mode, have garnered significant attention due to their potential applications across various fields. Transverse optical confinement in double trench ridge waveguide lasers is determined by the width of the ridge and the refractive index difference between the ridge and trench. In this study, we have designed and fabricated a wide ridge laser operating at 808 nm with high power output and stable fundamental spatial mode based on this principle. The fundamental spatial mode operation was successfully achieved with an 8 μm ridge waveguide laser, producing an impressive output power of 1.3 W. The device exhibits a stable far-field as the current was increased from 0.3 A to 1.8 A. The laser's output power exhibits a 14% reduction with an increase in temperature of 80 °C, demonstrating a decrease rate of only 1.25 mW/°C and a wavelength variation rate of 0.22 nm/°C, indicating low sensitivity to temperature changes.

Supersymmetric quantum cascade laser array

Electrically injected supersymmetric (SUSY) quantum cascade laser (QCL) array of the wavelength at around 13.4 μm has been demonstrated. By applying SUSY transformations to the main array with five laser elements, a lossy superpartner array with four laser elements is constructed. As a result, except for the fundamental supermode, which is confined in the main array, other high order supermodes penetrating into the superpartner array are suppressed. By selectively pumping the main array, the fabricated SUSY QCL array can emit light with a near-diffraction-limited (D.L.) beam over the whole dynamic range, with the full-width half-maximum up to 11.7° in the lateral direction and the output peak power up to 406 mW in pulsed operation at room temperature, which is 3.6 times the power of a single ridge laser of the same laser length. Furthermore, the far field tuning through the mode switching of fundamental and high order supermodes is realized experimentally, by electrically adjusting the gain and loss in the superpartner array, which agrees well with the designs. The electrically far field tunability has great potential to find applications in beam steering.

Continuous-wave GaAs/AlGaAs quantum cascade laser at 5.7 THz.

Design strategies for improving terahertz (THz) quantum cascade lasers (QCLs) in the 5-6 THz range are investigated numerically and experimentally, with the goal of overcoming the degradation in performance that occurs as the laser frequency approaches the Reststrahlen band. Two designs aimed at 5.4 THz were selected: one optimized for lower power dissipation and one optimized for better temperature performance. The active regions exhibited broadband gain, with the strongest modes lasing in the 5.3-5.6 THz range, but with other various modes observed ranging from 4.76 to 6.03 THz. Pulsed and continuous-wave (cw) operation is observed up to temperatures of 117 K and 68 K, respectively. In cw mode, the ridge laser has modes up to 5.71 THz - the highest reported frequency for a THz QCL in cw mode. The waveguide loss associated with the doped contact layers and metallization is identified as a critical limitation to performance above 5 THz.

Posterior to the ridge laser in zone 2 stage 3 retinopathy of prematurity with plus disease: Efficacy and safety.

This study aimed to ascertain the efficacy and safety of an additional posterior to the ridge laser for treatable zone 2 stage 3 retinopathy of prematurity (ROP). This study was a retrospective chart review of infants undergoing laser treatment for ROP at a single center from March 2014 to March 2022. The chart review specifically searched for infants treated for zone 2 stage 3 ROP with plus disease, where additional posterior to the ridge laser was performed. Seventy-eight eyes of 45 infants met the inclusion criterion. The mean birth weight and gestational age were 1166.09 ± 329.66 gm and 29 ± 2 weeks, respectively. Group 1 comprised 52 eyes treated for high-risk prethreshold stage 3 ROP, while group 2 comprised 26 eyes treated for threshold ROP. 532-nm frequency-doubled Nd:YAG laser (Nidek, Japan) was used in all eyes. Apart from the standard laser to the avascular retina, an additional three rows of laser were applied posterior to the ridge in all eyes during the primary laser sitting (except in two eyes where it was performed as a rescue treatment 2 weeks after the first sitting). No complications were observed during or immediately after the laser procedure. A favorable outcome was achieved in 98.07% of eyes with prethreshold ROP and 76.92% of eyes with threshold ROP. Overall, a favorable outcome was achieved in 71 (91.02%) of the 78 eyes. Posterior to the ridge laser performed in the primary sitting along with the standard laser for treatable stage 3 ROP in zone 2 is safe and effective. Further prospective studies are needed to study this underutilized approach.

Sustainable production of bread wheat using laser land levelling and sowing methods as potent regulators of carbon sequestration, fuel consumption and water use in the arid environment of Bahawalpur, Pakistan

AbstractExcessive use of water in wheat is associated with high fuel consumption and the emission of carbon dioxide into the environment. This study was conducted with the objectives to decrease water use and the associated fuel consumption and carbon dioxide emissions and to improve the productivity of wheat on a sustainable basis using LASER levelling and sowing methods as potent modulators of these adversities. The experiment was conducted in the research area of the Agronomic Research Station Bahawalpur over 3 years using a split‐plot experimental design and four replications. Treatments contained LASER levelling in the main plot (L0 = no LASER levelling, L1 = LASER levelling) and sowing methods in split plots (S1 = broadcast, S2 = ridge sowing and S3 = drill sowing). Less water use, fuel consumption and emission of carbon dioxide were quantified under ‘LASER levelling’ and under ‘ridge sowing’ compared to other treatments. Regarding wheat crop productivity, the same treatment combination (LASER levelling and ridge sowing) resulted in more fertile tillers, grains per spike, 1000‐grain weight and grain yield. Therefore, we concluded that ‘LASER levelling’ and ‘ridge sowing’ have the potential to reduce the cost involved and environmental pollution (by reducing fuel consumption) and improve water use efficiency, grain yield and yield components of wheat compared to other treatments. Moreover, strong negative associations of water use, fuel consumption and carbon dioxide emissions with the grain yield of wheat were recorded.

High-power density, single plasmon, terahertz quantum cascade lasers via transverse mode control

Terahertz (THz) quantum cascade lasers (QCLs) have been shown to emit peak powers greater than 1 W from a single facet in a single plasmon geometry. However, this is typically achieved by increasing the laser ridge width, resulting in higher-order transverse modes, limiting the achievable power density. Here, we control and fully suppress these modes through thin metallic side-absorbers, showing laser action solely on the fundamental transverse mode operation without sacrificing high THz peak powers. This leads to enhanced power densities and electric fields of up to 1.8 kW/cm2 and 1.17 kV/cm, respectively, opening up the possibility of applying THz QCLs as pump sources for investigations of nonlinear THz physical phenomena.

Phase-locked terahertz quantum cascade laser array integrated with a Talbot cavity.

Increasing the power of a quantum cascade laser by widening laser ridges will lead to the degradation of the beam quality because of the operation of high-order transverse modes. We report on a phase-locked array scheme of terahertz quantum cascade laser (THz QCL) utilizing Talbot effect. By adjusting the absorbing boundary width of each ridge in the array, stable operation of the fundamental supermode is realized. A five-element array shows 4 times power amplification than that of a single ridge device. Due to the large power amplification efficiency, stable mode selection, and simple fabricating process, the phase-locked array scheme is very promising to further improve the performance of THz QCL.

Reliable InAs quantum dot lasers grown on patterned Si (001) substrate with embedded hollow structures assisted thermal stress relaxation

Direct epitaxial growth of III–V quantum dot (QD) lasers on Si (001) substrates is recognized as a promising and low-cost method for realizing high-performance on-chip light sources in silicon photonic integrated circuits (PICs). Recently, the CMOS-compatible patterned Si (001) substrates with sawtooth structures have been widely implemented to suppress the lattice mismatch induced defects and antiphase boundaries for heteroepitaxial growth of high-quality III–V materials on Si. Considerable progresses have been made on high-performance 1300 nm InAs/GaAs QD lasers on Si (001). Here, we report a thermal stress-relaxed (111)-faceted silicon hollow structures by homoepitaxial method for reliable InAs/GaAs QD lasers growing on Si (001) substrates. Both simulation analysis and experimental results indicate that the voids buried below the sawtooth structures can release about 9% of the accumulative thermal stress of the III–V/Si system during the cooling process. Furthermore, electrically pumped InAs/GaAs QD narrow ridge lasers are grown and fabricated on the specially designed Si (001) platforms with a maximum operation temperature up to 90 °C under continuous-wave operation mode. Additionally, an extrapolated lifetime of over 5300 h is calculated from the reliability test at 65 °C. These results lead toward high-yield, scalable, and reliable III–V lasers on Si (001) substrates for PICs.

Independent Control of Mode Selection and Power Extraction in Terahertz Semiconductor Lasers

Mode selection and power extraction are the core of single-mode semiconductor lasers, but generally, they restrict each other. A large gain area with high radiation efficiency is necessary for high output power but will induce more competitive modes and increase the threshold gain of the desired mode. Here, we demonstrate a novel laser cavity─an active distributed Bragg reflector (ADBR) and a grating coupler (GC) are monolithically integrated into a laser ridge─enabling independent control of mode selection and power extraction. The ADBR features a reflection peak with an extremely narrow bandwidth that releases the constraint on the cavity length, while the GC provides a controllable high radiation efficiency. The concept is implemented onto terahertz quantum cascade lasers, exhibiting robust single-mode emission with high output power and high operating temperature. Given the universality of the ADBR and GC, our concept can be utilized in different material systems at different wavelengths.

Ultra-low threshold lasing through phase front engineering via a metallic circular aperture

Semiconductor lasers with extremely low threshold power require a combination of small volume active region with high-quality-factor cavities. For ridge lasers with highly reflective coatings, an ultra-low threshold demands significantly suppressing the diffraction loss at the facets of the laser. Here, we demonstrate that introducing a subwavelength aperture in the metallic highly reflective coating of a laser can correct the phase front, thereby counter-intuitively enhancing both its modal reflectivity and transmissivity at the same time. Theoretical and experimental results manifest a decreasing in the mirror loss by over 40% and an increasing in the transmissivity by 104. Implementing this method on a small-cavity quantum cascade laser, room-temperature continuous-wave lasing operation at 4.5 μm wavelength with an electrical consumption power of only 143 mW is achieved. Our work suggests possibilities for future portable applications and can be implemented in a broad range of optoelectronic systems.

Thin THz QCL active regions for improved continuous-wave operating temperature

We compare the performance of 10 and 5 μm thick metal–metal waveguide terahertz quantum-cascade laser ridges operating around 2.7 THz and based on a 4-well phonon depopulation active region design. Thanks to reduced heat dissipation and lower thermal resistance, the 5 μm thick material shows an 18 K increase in continuous wave operating temperature compared to the 10 μm material, despite a lower maximum pulsed-mode operating temperature and a larger input power density. A maximum continuous wave operating temperature of 129 K is achieved using the 5 μm thick material and a 15 μm wide ridge waveguide, which lased up to 155 K in the pulsed mode. The use of thin active regions is likely to become increasingly important to address the increasing input power density of emerging 2- and 3-well active region designs that show the highest pulsed operating temperatures.

Approaches to tuning the exceptional point of PT-symmetric double ridge stripe lasers.

Electrically injected Parity-time (PT)-symmetric double ridge stripe semiconductor lasers lasing at 980 nm range are designed and measured. The spontaneous PT-symmetric breaking point or exceptional point (EP) of the laser is tuned below or above the lasing threshold by means of varying the coupling constant or the mirror loss. The linewidth of the optical spectrum of the PT-symmetric laser is narrowed, compared with that of traditional single ridge (SR) laser and double ridge (DR) laser. Furthermore, the far field pattern of the PT-symmetric laser with EP below the lasing threshold is compared with that of the PT-symmetric laser with EP above the lasing threshold experimentally. It is found that when the laser start to lase, the former is single-lobed while the latter is double-lobed. when the current continues to increase, the former develops into double lobe directly while the latter first develops into single lobe and then double lobe again.

Spatially resolved self-heating and thermal impedance of laser diodes using CCD-TR imaging

The spatial distribution of the surface temperature of single and multi-section slotted semiconductor laser diodes with surface gratings is investigated experimentally with CCD-thermoreflectance imaging. The lasers are single frequency devices, operating at approximately 1550 nm. High resolution temperature maps of the laser ridge are obtained, with spatial resolution near 1 µm. The temperature profile in the direction lateral to the ridge is presented and a rapid decay in temperature away from the ridge is observed. Acquisition of the temperature maps takes about 8 minutes, with three maps required for a 400 µm device. The ridge temperature rise is shown to be linear with the power consumed by the diode. The temperature profile along the laser ridge is shown to be uniform within a section of the multi-section laser. The thermal impedance of the single section slotted laser and the various sections of the multi-section slotted laser were determined. It was found that the thermal impedance ridge length product (ZthL) was 40 ± 6 ° C µm/mW for all section lengths. Between sections a rapid decay is also observed.

19-element vertical cavity surface emitting laser arrays with inter-vertical cavity surface emitting laser ridge connectors

We achieve record concurrent combinations of bandwidth (18 GHz), optical output power (150 mW), and wall plug efficiency (30%) with a unique arrangement of 19-element, electrically parallel 980 nm vertical cavity surface emitting laser (VCSEL) arrays. We use a new two-dimensional, quasi honeycomb geometry with inter-VCSEL ridge connectors—made nonconducting by selective thermal oxidation—to improve heat dissipation and facilitate a single top surface anode contact. Via on-wafer probing we perform static and dynamic measurements over the wide temperature range of 23 °C to 85 °C and extract, report, and discuss key array figures-of-merit.

Monolithic InP Quantum Dot Mode-Locked Lasers Emitting at 730 nm

This letter reports on InP/GaInP quantum dot mode-locked lasers emitting in the 730 nm wavelength region, extending the spectral range of previously reported monolithic mode-locked edge-emitting lasers. Modal gain and absorption measurements were used to identify a relatively broad spectrum which is utilised to support passive mode-locking in a monolithically integrated two-section ridge laser. The conditions for mode-locking were explored by varying the current to the gain section and reverse bias to the absorber section. For a total cavity length of 3 mm, the shortest pulse train observed was 6 ps in duration with a repetition rate of 12.55 GHz.

InAs/GaAs quantum dot narrow ridge lasers epitaxially grown on SOI substrates for silicon photonic integration.

Monolithic integration of III-V laser sources on standard silicon-on-insulator (SOI) substrate has been recognized as an enabling technology for realizing Si-based photonic integration circuits (PICs). The Si-based ridge lasers employing III-V quantum dot (QD) materials are gaining significant momentum as it allows massive-scalable, streamlined fabrication of Si photonic integrated chips to be made cost effectively. Here, we present the successful fabrication of InAs/GaAs QD ridge lasers monolithically grown on {111}-faceted SOI hollow substrates. The as-cleaved Fabry-Perot (FP) narrow ridge laser is achieved with a relatively low threshold current of 50 mA at room temperature under pulse current operation. The maximum working temperature achieved is up to 80 oC. The promising lasing characteristics of such SOI-based InAs/GaAs QD ridge lasers with low threshold current and small footprint provide a viable route towards large-scale, low-cost integration of laser sources on SOI platform for silicon photonic integration purpose.

Quantum Transmission Line Modeling and Experimental Investigation of the Output Characteristics of a Terahertz Quantum Cascade Laser

We describe a new approach to modeling the optoelectronic properties of a terahertz-frequency quantum cascade laser (THz QCL) based on a quantum transmission line modelling (Q-TLM) method. Parallel quantum cascade transmission line modeling units are employed to describe the dynamic optical processes in a nine-well THz QCL in both the time and frequency domains. The model is used to simulate the current–power characteristics of a QCL device and good agreement is found with experimental measurements, including an accurate prediction of the threshold current and emitted power. It is also confirmed that the Q-TLM model can accurately predict the Stark-induced blue shift of the emission spectrum of the THz QCL with increasing injection current. Furthermore, we establish the new Q-TLM model to describe the properties of a THz QCL device incorporating a photonic lattice patterned on the laser ridge, by linking the transmission line structure to each scattering module. The predicted effects of the lattice structure on the steady-state emission spectra of the THz QCL, including the side-mode suppression, are found to be in good agreement with experimental results. Our Q-TLM modeling approach is a promising tool for the future design of THz QCLs and analysis of their temporal and spectral behaviors.