Mode and polarisation control in VCSELs using shallow surface structures

Polarization investigation of a tunable high-speed short-wavelength bulk-micromachined MEMS-VCSEL

“…The oxide aperture layer is an aluminum rich AlGaAs layer which is selectively oxidized. 5 The half-VCSEL has a non-resonant design 12 where the optical field has its minimum (node) at the semiconductor-air interface. Additionally the semiconductor-air interface can be covered with a λ/4-thick SiN xcoating to increase the nominal reflectivity from the interface and thus reduce the required threshold gain.…”

“…All these techniques have their advantages and disadvantages. 5 In the device presented here, a half-symmetric resonator, achieved by a curved membrane, in combination with an oxide aperture supports the fundamental mode (Gaussian beam) of the VCSEL and makes the single transversal mode operation of the device possible. This plane concave resonator makes it possible to fit the beam waist of the fundamental mode (by changing the air-gap and the radius of curvature (RoC)) into the oxide aperture and thus be able to use an larger oxide aperture.…”

“…To be able to control the state of polarization, the introduced anisotropy must of course be stronger than the inherent anisotropy of the device. 5 For non-tunable VCSELs some polarization controllling techniques have been reported. For example, gain anisotropy is achieved by epitaxial growth on non-(100) substrate such as GaAs (311)A 7 and GaAs (311)B.…”

“…Other polarization stabilizing techniques are using an asymmetric current injection to introduce both anisotropic gain and cavity losses, 9 introducing anisotropic strain in the VCSEL via etching deep trenches close to the VCSEL aperture along the preferential polarization direction 10 or via using strained T-bars 11 and implementing a surface grating. 5 All these methods have their drawbacks and advantages discussed partly in. 5 In this paper we have used a sub-wavelength grating on the half-VCSEL air interface to select one polarization mode.…”

“…5 All these methods have their drawbacks and advantages discussed partly in. 5 In this paper we have used a sub-wavelength grating on the half-VCSEL air interface to select one polarization mode. A PMSR of about 35 dB has been achieved with this technique.…”