I. Hassiaoui

Very compact external cavity diffraction-coupled tapered laser diodes.

To maintain the same beam quality as that of a single emitter and to be close to diffraction limit, we have combined a phase corrected array, emitting at lambda = 975 nm, coherently using the Talbot effect. First, to improve the beam quality of the array, a phase correcting system was added. The FWHM divergences of the array (which is approximately the same as that of the single emitter since the emitters within the array are not optically coupled to each other) were reduced from 34 degrees to 0.17 degrees in the fast axis and from 3.5 degrees to 0.7 degrees in the slow axis at 6 A. Then, to be close to the diffraction limit, we have combined this corrected array coherently using the Talbot effect. We have obtained a quasi-monolobe slow axis far field profile for the in-phase mode with a central peak divergence of only 0.27 degrees at 1.5 A, 315 mW under cw operation, and of only 0.20 degrees at 2.5 A, 787 mW under pulsed operation. To our knowledge, this is the first demonstration of coherent coupling of a corrected tapered laser diode array in an external Talbot cavity.

High-power, low-divergence, linear array of quasi-diffraction-limited beams supplied by tapered diodes

We describe for the first time to our knowledge the performance for a linear array of tapered laser diodes with both fast- and slow-axis collimation using a microlens for fast-axis collimation and a laser-written phase plate for slow-axis collimation and correction of the residual fast-axis errors from lens aberrations, thermal lensing, astigmatism, pointing errors, and other wavefront distortions. The phase plate leads to M(2) factor reductions of 1.5 for the lensed array following the fast axis and 2.6 for the whole bar following the slow axis.

In-phase coherent coupling of tapered lasers in an external Talbot cavity

Tapered lasers offer both high-power, together with good beam quality. They contain a ridge waveguide, which acts as a modal filter, and a tapered section of increasing width, which provides high power. Our lasers are based on Al-free active region and the material structure, which was grown by Metallorganic Chemical Vapor Deposition, has very low internal losses of 0.5 cm-1, a very low transparency current density of 86 A/cm2, a high internal quantum efficiency of 86%, and a high characteristic temperature T0 of 171 K. Based on these good results, we have realised fully index-guided single emitters (IG1) with a narrow output width of a few tens of microns, a narrow taper angle of less than 1°, which deliver a maximum power of 1 W CW, together with a good beam quality parameter M2&sgr;&sgr; =3 at &lgr;=915nm. In order to obtain higher power, we have realized an array of N=6 fully index-guided tapered diode lasers. They deliver a maximum output power of 4W CW. The emitters of the free-running array are not optically coupled to each other, as a consequence, the array has a highly beam quality parameter M2 which is at least equal to N times the single emitter one. In order to improve beam quality of diode arrays, several approaches have been investigated to combine them coherently such as evanescent coupling [1], intracavity spatial filtering [2, 3, 4], or a combining technique using a binary phase grating [5] and also the Talbot effect. For the Talbot effect, both monolithic [6] as well as external Talbot cavity [7] configurations have been demonstrated. The Talbot effect refers to a diffraction phenomenon and consists of a reproduction of the field of an illuminated periodic object at certain distances away from the object plane. These distances are multiples of the Talbot distance ZT=2d2/&lgr;, where d is the spatial periodicity of the object and &lgr; the wavelength. It was studied for many kinds of lasers such as CO2 lasers [8] or semiconductor lasers [9]. Particular interest was placed on semiconductor lasers because of their small size and high efficiency. Here, we demonstrate for the first time the coherent operation of an array of tapered diode lasers placed in an external Talbot cavity. The in phase supermode is selected by tilting the reflecting mirror. The divergence of the central peak is 0.4° FWHM.

Coherent Coupling of Tapered Laser diodes in an External Talbot Cavity

We demonstrate the first operation of a tapered laser diode array in an external Talbot cavity. The in-phase supermode is selected by tilting the reflected wave. The divergence of the central peak is 0.4deg FWHM.

High-power diode lasers with an aluminium-free active region at 915 nm

We have developed high-power lasers, which are based on an Al-free active region at 915 nm. The laser structure has very low internal losses of 0.5 cm-1, a very low transparency current density of 86 A/cm2, and a high internal quantum efficiency of 86%. Based on these good results, we have realised narrow-aperture, index-guided tapered lasers which deliver 1 W CW with and M2 beam quality factor of 3.0 using both the 1/e2 and standard-deviation methods. We have also fabricated index-guided tapered lasers with a Clarinet shape, which deliver 0.65 W CW with an M2 beam quality factor of less than 1.5 at 1/e2, and less than 2.5 using the standard deviation method.

Diffraction coupling of tapered laser diodes in an external Talbot cavity

We demonstrate the in-phase coherent coupling of a tapered laser diode array in an external Talbot cavity. The divergence of the central peak is 0.27deg FWHM at 3.1 A with an output power of 931 mW CW.

External cavity phase-locked semiconductor tapered lasers

This work relates to combining a phase corrected array of tapered laser diodes, emitting at λ = 975 nm, coherently using the Talbot effect. Diffractive coupling of semiconductor lasers by use of the Talbot effect provides a means for coherent beam addition of multiple elements in laser diode arrays and makes possible a very compact external cavity. We have used, in this work, fully index guided tapered laser diodes. They contain a ridge waveguide, which acts as a modal filter, and a tapered section of increasing width, which provides high power. We have realized arrays of several emitters (N=10), which are not optically coupled to each other. First, to improve the beam quality of the array, a phase correcting micro system, achieving collimation in the fast axis, correction of the wave front tilts in both directions and also a slow axis collimation, was added. The FWHM divergences of the array were reduced from 34° to 0.17° in the fast-axis and from 3.5° to 0.7° in the slow-axis at 6A, 3.7 W. Then, to be close to diffraction limit, we have combined this corrected array coherently using the Talbot effect. We have obtained quasi-monolobe slow axis far field profile for the in phase mode with a central peak divergence of only 0.27° at 1.5 A, 315 mW under CW operation and of only 0.20° at 2.5 A, 787 mW under pulsed operation.

Diffraction coupling of semiconductor tapered lasers in a very compact external Talbot cavity

This work relates to combining a phase corrected array of tapered laser diodes, emitting at λ = 975 nm, coherently using the Talbot effect. Diffractive coupling of semiconductor lasers by use of the Talbot effect provides a means for coherent beam addition of multiple elements in laser diode arrays and makes possible a very compact external cavity. We have used, in this work, fully index guided tapered laser diodes. They contain a ridge waveguide, which acts as a modal filter, and a tapered section of increasing width, which provides high power. We have realized arrays of several emitters (N=10), which are not optically coupled to each other. First, to improve the beam quality of the array, a phase correcting micro system, achieving collimation in the fast axis, correction of the wave front tilts in both directions and also a slow axis collimation, was added. The FWHM divergences of the array were reduced from 34 ° to 0.17 ° in the fast-axis and from 3.5 ° to 0.7 ° in the slow-axis at 6A, 3.7 W. Then, to be close to diffraction limit, we have combined this corrected array coherently using the Talbot effect. We have obtained quasi-monolobe slow axis far field profile for the in phase mode with a central peak divergence of only 0.27 ° at 1.5 A, 315 mW under CW operation and of only 0.20 ° at 2.5 A, 787 mW under pulsed operation.

High-power, high-brightness, index-guided tapered lasers, comparison between CW and pulsed operation

Index-guided tapered lasers at 975 nm deliver 1 W CW, with a low M² of 1.6 at 1/e², which is a record for such a device, no measurable astigmatism, and a narrow far-field angle of 6.8deg FWHM.

High-power high-brightness tapered lasers with an Al-free active region at 915 nm

We have developed high power and high brightness tapered lasers based on an Al-free active region at 915 nm. The material structure, which was grown by MOCVD (Metallorganic Chemical Vapor Deposition), has very low internal losses of 0.5 cm-1, a very low transparency current density of 86 A/cm2, a high internal quantum efficiency of 86%, and a high characteristic temperature T0 of 171 K. Based on these good results, we have realised index-guided tapered lasers (IG1) with a narrow output width of a few tens of microns, a narrow taper angle of less than 1o, which deliver 1 W CW, together with an M2 beam quality parameter of 3.0, and a divergence angle in the slow axis of 6o FWHM and 10.2o at 1/e2. We have also realised a small array of six IG1 lasers, which delivers 4 W CW, together with a divergence angle of 5.6o FWHM and 10.2o at 1/e2. Clarinet lasers were also fabricated. These devices were recently proposed to achieve high brightness together with a very narrow divergence angle, which is stable with current. These index-guided tapered lasers have also a narrow output width, but a larger taper angle of 2o. The Clarinet lasers at 915 nm deliver 0.65 W CW, together with an M2 beam quality factor of less than 1.5 at 1/e2, and a very narrow divergence angle of 2.6o FWHM, and 4.8o at 1/e2.