CW Operation of a Tunable 1550-nm VCSEL Integrating Liquid-Crystal Microcells

Abstract

Laser (VCSEL) with a liquid crystal (LC) microcell monolithi-2 cally integrated on its surface for spectral tuning is investigated. 3 Unlike tunable VCSELs integrating a movable membrane, here 4 the physical length of the cavity remains unchanged and only the 5 voltage applied on the LC ensures a refractive index modification 6 for a particular polarization emitted by the VCSEL. This tunable 7 VCSEL operates in CW at room temperature and exhibits 8 more than 23 nm wavelength tuning around 1.55 µm at a 9 maximum applied voltage of 20 V. The measured laser threshold 10 around 6.5 mW is still comparable to VCSEL without 11 LC microcell, a clear indication that the optical losses related 12 the LC are very low. On the other hand, for this first optically 13 pumped device, the lasing characteristics suggest that the LC 14 birefringence is lower than expected. To assess this hypothesis, 15 thermo-optical simulations have been conducted.

Anisotropic Transverse Confinement Design for Electrically Pumped 850 nm VCSELs Tuned by an Intra Cavity Liquid-Crystal Cell

“…The use of a single SU-8 nanograting for LC alignment and of polymer-based walls to define the LC microcells made indeed the fabrication of first efficient tunable optical devices possible, like passive Fabry-Pérot filters [17], tunable III-V photodiodes (with electrodes and microreliefs) [18]. More recently, optically-pumped 1.55 µm VCSELs [14] were demonstrated within our technology, displaying a continuous tuning of about 23.5 nm in CW.…”

“…A thin SU-8 layer, a negative photoresist, is deposited on the surface of this mirror and a 200 nm-period polymer grating that will serve for LC alignment is fabricated by nanoimprint lithography (NIL) in the SU-8 layer (grating depth 48 nm, duty cycle 50%) [17]. The process used here is similar to the one reported by the authors for the fabrication of optically-pumped LC tunable VCSELs [14]. The cells are collectively assembled by thermal sealing under pressure of the (glass/ITO/DBR/grating) stack placed upside down above the PermiNex walls.…”

“…Experimental data are available for VCSELs, overlayed by an LC reservoir [8], [9], [10], which is very different compared to an intracavity tunable device. Hitherto two different approaches have been proposed: wafer fusion [11], [12] and hybrid approach [13], [14], both lacking experimental demonstration of an electrically driven device.…”

“…To guide the experimental work and make it more effective, we design here an electrically-driven 850 nm LC-VCSEL. It is based on the same tunable section adopted in the successful device reported in [14], which solves issues directly related to our hybrid technology. At the same time, we investigate the relevant transverse effects and the issues related to electrical injection in the 850 nm half-VCSEL.…”

33 nm wavelength tuning of a 1550 nm VCSEL in CW operation based on the liquid crystal micro-cells technology

“…We have already developed this technology by fabricating LC micro-cells, and we have been able to realize and demonstrate passive optical filtering, and wavelength selective tunable integrated photodetector with large tuning range as high as 100-150 nm [3], [4]. More recently, we demonstrated for the first time CW operation of a tunable VCSEL integrating this LC micro-cell concept, presenting however a lower than expected 23.5 nm tuning range, and suffering from polarization instabilities [5].…”