Low Vertical Divergence Research Articles

Low Divergence Angle Output in Tunnel Junction Cascade Laser With in-Phase Mode Operation

In this study, we report a novel laser with in-phase super-mode coupled double emitter cascaded by tunnel junction. By incorporating a mode expansion layer on the P-type side of the upper emitter to suppress other high-order modes, pure in-phase fundamental mode operation demonstrated via far-field measurements and simulations is realized in the fast-axis direction with a slope efficiency of 2.08 W/A driven by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$100~\mu \text{s}$ </tex-math></inline-formula> , 100Hz quasi-continuous wave (QCW) bias current. More importantly, the only central peak of emitted in-phase mode has a low vertical far-field divergence angle of 12.69° due to the coupled design of the two adjacent emitters. The novel mode coupling structure has obvious benefits for the practical application of tunnel junction lasers in LIDAR detection areas.

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.

Emitting direction tunable slotted laser array for Lidar applications

In this work, a new type of emitting direction tunable slotted laser array for Lidar applications is proposed. By designing the structure of periodic slots, the laser array can achieve tunable emitting direction in a wide range with low vertical divergence angle. The laser array can be directly used as Lidar emitting chip without complex beam reshaping, coupling or mechanically moving parts, which makes it has the advantages of good stability, system simplification and low cost compared with other Lidars. Experimentally, an 11-channel laser array of C band with periodic slots at the output end is fabricated based on AlGaInAs/InP material system. As the slot period changes from 8μm to 18μm, the inclined angles of emission from 66.6° to 20.25° with all the vertical divergence angles less than 3.5° are obtained, and the minimum vertical divergence angle is even 1.3°. Typical optical power is 13.5 mW under 600 mA continuous injection.

Near-diffraction-limited Bragg reflection waveguide lasers.

We report a near-diffraction-limited tapered Bragg reflection waveguide laser (BRL) with a 10μm ridge width, which is significantly larger than the conventional design. The large mode expansion in the vertical waveguide enables a scalable increase in the ridge width for single lateral mode operation. The role of the taper angle in the performance of tapered BRLs with the intrinsic characteristics of a thick vertical waveguide was investigated. The results indicate that the BRL with a taper angle of 3° shows the best far-field performance. An extremely low vertical divergence angle of 14.5° and a lateral divergence as low as 2.8° for 95% power inclusion were realized. A continuous-wave power exceeding 1W was demonstrated. Over the entire operating current range, the vertical beam is almost unchanged with an excellent beam quality (M2) of about 1.3. Lateral beam width increases slightly at higher currents due to the increasing contribution of side lobes, but it still remains nearly diffraction-limited with a lateral M2 of less than 2. Narrow beam divergence and high beam quality of the lasers allow simple and inexpensive collimation and coupling.

Inclined emitting slotted single-mode laser with 1.7° vertical divergence angle for PIC applications.

In this Letter, a new type of single-mode slotted laser used for an on-chip light source in photonic integrated circuits is proposed. An inclined light beam with a low vertical divergence angle can be directly coupled into the surface grating of the silicon to form an integrated light source. Experimentally, a III-V laser with a 54.6° inclined angle and a vertical divergence angle of 1.7° is achieved by introducing a kind of specially distributed microstructure. The side mode suppression ratio is better than 45dB, and the continuous wave output power reaches 6.5mW at room temperature. We report the inclined emitting microstructured single-mode laser with a low divergence angle for the first time, to the best of our knowledge.

2-W High-Efficiency Ridge-Waveguide Lasers With Single Transverse Mode and Low Vertical Divergence

We report recent developments on 980-nm single-transverse-mode ridge-waveguide (RW) lasers with high efficiency and low-vertical divergence. RW lasers fabricated with 7- $\mu \text{m}$ -wide ridge and 3-mm-long cavity achieve 2-W optical power, 59% maximum power conversion efficiency, as well as a beam divergence of 7.2° in lateral and 10.3° in vertical under 1.5-A injection current. The lateral beam quality factors M2 are below 1.7 up to 2-W output power.

Efficient 600-W-Laser Bars for Long-Pulse Pump Applications at 940 and 975 nm

We report the first demonstration of 1.2 J-emission into long pulses ( $\ge 2$ ms) from passively cooled laser bars. These efficient high-fill-factor bars were developed for long-pulse pumping of Yb:CaF2-laser media at a power level of 600 W. The spatial brightness inferred (23 MW/cm $^{2}{\times } \text {sr}$ ) exceeds the state of the art. The bars are based on an extreme-double-asymmetric and an extremely-low-vertical-divergence epitaxial design for pumping at 940 and 975 nm, respectively. While the first design is optimized for high power-conversion efficiency $\eta _{\mathrm{ E}} > 60$ % (at 600 W), the latter exhibits low vertical divergence to enable low-loss external spectral stabilization at the zero-phonon line of Yb:CaF2 $(\eta _{\mathrm{ E}} = 50$ % at 600 W). The higher $\eta _{\mathrm{ E}}$ at 940 nm and lower thermal resistance due to its vertical structure improve the lateral farfield, increasing the brightness by nearly 50% over the 975 nm-structure. We varied the lateral layout comprising 186, 400, and 1200 $\mu \text{m}$ -stripes at 70% fill-factor. The smaller stripes revealed the highest brightness, while the degree of polarization increases by 5% using wider stripes.

High-Power Ultralow Divergence Edge-Emitting Diode Laser With Circular Beam

A recognized drawback of edge-emitting diode lasers is their high divergence and elliptical beam shape since the first diode laser was demonstrated. In this paper, we demonstrated the ultranarrow circular beam emission from the broad area diode laser based on a modified Bragg-like waveguide. The low vertical divergence of 9.8° with 95% power content and 4.91° with the full-width at half-maximum was realized in the devices with 150 μm stripe width. The maximum output power was 4.2 W under quasi-continuous-wave operation and presently limited by thermal rollover. The detailed design principle was presented and it was found that reducing the refractive index and thickness of the defect layer was able to improve the vertical divergence and achieve the stable circular beam emission by controlling the lateral current distribution using the deep stripe. The packaged device with 90 μm stripe width demonstrated a maximum continuous wave power of 4.6 W at 10 °C. A direct fiber coupling efficiency of 90.6% had been achieved with a common fiber of 105 μm core diameter.

High-power low-divergence 1060 nm photonic crystal laser diodes based on quantum dots

GaAs-based photonic band crystal diode lasers with low vertical divergence and high output power have been designed and realised with a quantum dot active area at a wavelength of 1060 nm. Broad area lasers with 100 µm stripe width show low transparency current densities of 129 Acm−2 and high differential efficiency of 70 %. Devices of 1 mm length deliver up to 17.7 W pulsed output power and 2.6 W continuous-wave output power is demonstrated for 2 mm-long devices. The maximum output power is presently limited by catastrophic degradation in the pulsed case and by thermal rollover in the continuous-wave case. The full width half maximum vertical divergence of the fundamental mode of the devices is reduced to 13°, being nearly independent of driving current.

High-power high-efficiency 1150-nm quantum-well laser

Edge emitting diode lasers with highly strained InGaAs quantum wells and GaAs waveguide layers emitting at 1150 nm were investigated focusing on the impact of the waveguide design on the laser performance. Using a thick GaAs waveguide layer broad area devices with low vertical divergence of 20/spl deg/ FWHM and reliable operation at a power level of 80-mW//spl mu/m stripe width were demonstrated.

Design of AlGaInP visible lasers with a low vertical divergence angle

AlGaInP visible lasers with depressed index cladding layers are studied theoretically and experimentally. Using the above low-refractive-index layer, we can significantly improve the characteristics of the transverse beam divergence. According to our experimental results, the transverse beam divergence can be reduced from 41.4° to 26.2°. These values also agree well with our theoretical calculations. In addition, we have optimized this structure theoretically. With a proper choice of structure parameters, we can design an AlGaInP laser diode with a transverse divergence angle as narrow as 8° while maintaining a low threshold current density.

High-power low-divergence semiconductor lasers for GaAs-based 980-nm and InP-based 1550-nm applications

High-power diode lasers with low-vertical divergence and high-fiber coupling efficiency were developed for GaAs-based 980-nm pump lasers and InP-based 1550-nm Fabry-Perot and distributed-feedback (DFB) lasers. Narrow divergence at 980 nm was made possible by a large optical-mode waveguide design, with full-width at half-maximum (FWHM) far-field angles of 11.7/spl deg//spl times/17.8/spl deg/ and coupling efficiency of 80% into a cleaved single-mode fiber (SMF). A vertical taper processing technique was developed for InP-based laser structures. Fabry-Perot lasers produced over 90-mW output power, 17/spl deg//spl times/16/spl deg/ FWHM beam divergence angles, and 63% coupling efficiency into a lensed SMF. The vertical taper was successfully integrated in 1550-nm DFB lasers, and over 80 mW single-mode output power with beam divergence angles of 12/spl deg//spl times/14/spl deg/ was obtained.

Small angle scattering setting at LURE: Description and results

A device has been assembled on the X-Ray beam line of D.C.I. (Orsay) which permits to record small angle scattering diagrams and/or large angle diffraction patterns. Experiments are made with a monochromatic beam provided by a germanium crystal whose curvature is adjustable to focus at 2 m from the monochromator. Scattering data are collected with a wire chamber. The experiments which have been yet performed at LURE use three of the characteristics of the Synchroton radiation: the low vertical divergence of the beam, the high intensity, and the fact that the wavelength can be easily changed. On the basis of preliminary results it will be discussed about the improvement of the resolution in the small angle scattering curves and the possibility of studying kinetics.