Polarization-stable vertical-cavity surface-emitting lasers with inverted grating relief for use in microscale atomic clocks

Abstract

Vertical-cavity surface-emitting lasers (VCSELs) with single-mode, single-polarization emission at a wavelength of 894.6 nm have become attractive light sources for miniaturized Cs-based atomic clocks. So far, VCSELs used for these applications are single-mode because of small active diameters which has the drawbacks of increased ohmic resistance and reduced lifetime. By employing surface grating reliefs, enhanced fundamental-mode emission as well as polarization-stable laser oscillation are achieved. VCSELs with 5 μm active diameter show side-mode suppression ratios of 20 dB even at currents close to thermal roll-over with orthogonal polarization suppression ratios better than 20 dB at elevated ambient temperatures up to 100 °C.

Fabrication and Characterization of Low-Threshold Single Fundamental Mode VCSELs With Dielectric DBR Mirror

“…8 Single-mode VCSELs have been widely employed in data center research [21], [22]. However, for many applications, the VCSELs are required not only to be single-mode, but also to be polarization-stable for high system performance [23], [24]. Unfortunately, VCSELs inherently have an unstable and hardly predictable polarization due to cylindrical symmetry and isotropic gain.…”

“…Unfortunately, VCSELs inherently have an unstable and hardly predictable polarization due to cylindrical symmetry and isotropic gain. This increases the relative intensity noise of VCSELs and limits their use in polarization-sensitive applications [23], [24]. Typical methods used to control the polarization of VCSELs include introducing a polarization-dependent gain by an oriented substrate [25], an asymmetric resonator [26], or introducing polarization-dependent mirror loss by surface grating [27], [28].…”

Metrological characterization of custom-designed 8946 nm VCSELs for miniature atomic clocks

“…The polarization of inverted grating VCSELs with optimum design is always orthogonal to the grating lines [10], resulting in an opposite sign of the OPSR in Fig. 7 compared to Fig.…”

“…2 (a), which shows the VCSEL chip with 300 × 300 μm 2 size. In addition, this chip design applies the so-called inverted grating relief [10] by which favorable single-mode and polarization-stable laser emission is achieved. The surface grating is etched in an extra topmost GaAs quarter-wave antiphase layer.…”

Reduced Dimensionality Multiphysics Model for Efficient VCSEL Optimization

“…In [11] we performed a parameter calibration that allowed us to achieve very good agreement between numerical and experimental results of all the observable macroscopic relevant quantities, such as current-voltage (I-V) and light-current (L-I) characteristics and optical modal features (wavelength red-shift and side-mode suppression ratio). The main goal was to extend the agreement from room temperature to higher temperatures, up to 110 • C, which is of the highest importance in applications like miniaturized atomic Cs-clocks [12,13] or datacenters [2,14]. As a matter of fact, many hyperscale datacenter operators need to adopt high-speed connections to handle data traffic in environments reaching temperatures of 85 • C [15].…”