Vertical-cavity surface-emitting laser with liquid crystal overlay

Abstract

We perform a theoretical study of the spectral and polarization threshold characteristics of Vertical-Cavity Surface-Emitting Lasers with Liquid Crystal overlay (LC-VCSEL) in three different configurations of the LC cell. Our model predicts the possibility of selecting between two orthogonal directions of linear polarization (LP) of the fundamental mode (x or y LP) by choosing appropriate LC length. It further predicts very strong polarization discrimination with LP mode threshold gain difference as large as several times the threshold gain of the lasing mode. We also numerically demonstrate an active control of light polarization by electro-optically tuning the LC director and show that either polarization switching between x and y LP modes or continuous change of the LP direction would be possible. Finally, we numerically demonstrate that LC-VCSEL would be capable of efficient wavelength tuning.

Hybrid VCSEL: liquid crystal systems

“…1c) we apply an electric field to the LC along the direction of light emission(E LC Oz). 24,30 The planar alignment of the nematic LC molecules close to the glass boundaries (the longer axis of the LC molecules along Oy axis) is achieved by a photoalignment layer. An electric field E LC applied to the LC cell will turn the LC director (the averaged direction of the longer axis of the LC molecules) at an angle θ, which depends on the distance to the anchoring boundary.…”

“…24 In Fig. 5 (a) we show the LC-VCSEL polarization resolved resonant wavelength (a,c) and threshold gain (b,d) as a function of the angle θ for the case of LC cell with a metal mirror and for two LC lengths: (a,b) L LC = 5.1µm and (c,d) L LC = 50.2µm.…”

“…[21][22][23] Here, we consider the case when the extremely-short external-cavity is filled in with a LC thus forming a laser with a LC overlay (LC-VCSEL). 24 In such a hybrid system, the normal VCSEL Figure 1. Hybryd LC-VCSEL systems: (a) coupled-cavity LC-VCSEL system; (b) cholesteric LC-VCSEL and (c) intracavity LC-VCSEL system.…”

“…Such devices can be independently biased using separate electrical contacts for the VCSEL and the LC cell and potentially offer extended functionality than common VCSELs. 24 From another side, cholesteric Liquid Crystals (CLC), when doped with dye molecules and optically pumped, can provide efficient and tunable lasing due to the existence of a band gap for circularly polarized (CP) light with the same handedness as the CLC helix. 25,26 The optical feedback necessary for lasing is realized by the CLC band gap for CP light with the same handedness as the CLC helix.…”

“…24 In order to obtain maximum efficiency and widest wavelength region of tuning, the light confinement factor in the LC should be as large as…”