Diode laser à cavité verticale émettant par la surface

Résumé

thumb|350px|right|Schéma d'une structure VCSEL simple Une diode laser à cavité verticale émettant par la surface, ou VCSEL [v'ɪxl] (pour l'anglais vertical-cavity surface-emitting laser) est un type de diode laser à semi-conducteur émettant un rayon laser perpendiculairement à la surface, contrairement aux lasers conventionnels à semi-conducteur émettant par la tranche. Les diodes VCSEL présentent de nombreux avantages sur les lasers émettant par la tranche, en particulier en ce qui concerne le procédé de fabrication :

les semi-conducteurs émettant par la tranche ne peuvent pas être testés au cours du processus de fabrication puisqu'il faut découper la galette puis monter la partie ainsi découpée, de sorte que si en définitive la diode ne fonctionne pas, par exemple à cause d'un mauvais contact ou des matériaux défectueux, le temps et les matériaux mis en œuvre pour la fabrication sont gâchés ; à l'inverse, dans le cas des VCSEL, on peut tester la galette en cours de fabrication et

Source officielle

https://fr.wikipedia.org/wiki/Diode_laser_%C3%A0_cavit%C3%A9_verticale_%C3%A9mettant_par_la_surface

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Air-suspended TiO2-based HCG reflectors for visible spectral range

Ehsan Hashemi, Georg Rossbach

For GaN-based microcavity light emitters, such as vertical-cavity surface-emitting lasers (VCSELs) and resonantcavity light emitting diodes (RCLEDs) in the blue-green wavelength regime, achieving a high reflectivity wide bandwidth feedback mirror is truly challenging. The material properties of the III-nitride alloys are hardly compatible with the conventional distributed Bragg reflectors (DBRs) and the newly proposed high-contrast gratings (HCGs). Alternatively, at least for the top outcoupling mirror, dielectric materials offer more suitable material combinations not only for the DBRs but also for the HCGs. HCGs may offer advantages such as transverse mode and polarization control, a broader reflectivity spectrum than epitaxially grown DBRs, and the possibility to set the resonance wavelength after epitaxial growth by the grating parameters. In this work we have realized an air-suspended TiO2 grating with the help of a SiO2 sacrificial layer. The deposition processes for the dielectric layers were fine-tuned to minimize the residual stress. To achieve an accurate control of the grating duty cycle, a newly developed lift-off process, using hydrogen silesquioxan (HSQ) and sacrificial polymethyl-methacrylate (PMMA) resists, was applied to deposit the hard mask, providing sub-10 nm resolution. The finally obtained TiO2/air HCGs were characterized in a micro-reflectance measurement setup. A peak power reflectivity in excess of 95% was achieved for TM polarization at the center wavelength of 435 nm, with a reflectivity stopband width of about 80 nm (FWHM). The measured HCG reflectance spectra were compared to corresponding simulations obtained from rigorous coupled-wave analysis and very good agreement was found.

Spie-Int Soc Optical Engineering2015

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TiO2 membrane high-contrast grating reflectors for vertical-cavity light-emitters in the visible wavelength regime

Ehsan Hashemi, Georg Rossbach

In this work, the authors describe a novel route to achieve a high reflectivity, wide bandwidth feedback mirror for GaN-based vertical-cavity light emitters; using air-suspended high contrast gratings in TiO2, with SiO2 as a sacrificial layer. The TiO2 film deposition and the etching processes are developed to yield grating bars without bending, and with near-ideal rectangular cross-sections. Measured optical reflectivity spectra of the fabricated high contrast gratings show very good agreement with simulations, with a high reflectivity of >95% over a 25 nm wavelength span centered around 435 nm for the transverse-magnetic polarization. (C) 2015 American Vacuum Society.

A V S Amer Inst Physics2015

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Phase shifted microcavities

Ross Stanley

An optically-active multi-layer dielectric structure comprises an optically active zone between two mirrors forming a Fabry-Perot microcavity. The optically active zone comprises an optically active material of wavelength lambda centred in a layer of high refractory index medium of optical thickness less than lambda/2 surrounded by two layers of low refractory index medium each of optical thickness less than &lambda/4,the combined optical thickness of said three layers making up the optically active zone being less than or equal to 3lambda/4. This structure behaves like a lambda/2 high index cavity except that there is a maximum of the optical field in the centre of the cavity instead of the usual node. This phase-shifted structure is useful for planar light emitting devices, vertical cavity lasers, and photo-detectors.

2004

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