Polarization control and mode optimization of 850 nm multi-mode VCSELs using surface grating

Abstract

To control the polarization of 850 nm multi-mode oxide-confined vertical-cavity surface-emitting lasers (VCSELs), monolithically integrated surface gratings are investigated. VCSELs with different grating parameters are simulated by the rigorous coupled-wave analysis (RCWA) method. Optical field intensity of two polarization orientations with different grating periods and duty cycles is obtained. The mode characteristics of VCSELs with different grating parameters are achieved by FDTD method. 850 nm surface grating VCSELs are fabricated and characterized, a maximum orthogonal polarization suppression ratio (OPSR) of 20.7 dB is observed. Meanwhile, VCSEL’s output mode characteristics are improved by integrating the surface grating. Application of integrated surface grating technique to achieve dynamically polarization-stable multi-mode VCSELs which enable polarization division multiplexed data transmission, the data throughput over a given link can be doubled.

Negative Capacitance Phenomenon and Origin in Alkali Niobate Film with Self‐Assembled Lattice Faults

“…For KNN ceramics, E a calculated is around 0.7 eV and 1.2 eV for single‐ and double‐charged oxygen vacancies ($$V_O^\centerdot $$ and $\[V_O^{\centerdot \centerdot }\]$), respectively. [ 45 ] Hence, by comparison, the E a of 0.72 eV obtained in this work lies close to the E a of ionic conduction caused by the migration of $$V_O^\centerdot $$. However, based on our analysis, the observed conduction mechanism cannot be attributed to such ionic conduction for the following reasons.…”

“…However, based on our analysis, the observed conduction mechanism cannot be attributed to such ionic conduction for the following reasons. Firstly, the V O − based ionic conduction is a high‐temperature phenomena which usually initiates at temperatures as high as 300–350 °C, [ 45 ] while the observed conduction mechanism in this case initiated at a substantially lower temperature of 200 °C (Figure 5b). Secondly, the obtained magnitude of conductivity at 200 °C is too high to be associated with ionic conduction observed in both KNN ceramics [ 42 ] and thin films.…”

Low Threshold Current and Polarization-Stabilized 795 nm Vertical-Cavity Surface-Emitting Lasers

“…Among these polarization control technologies for VCSELs, the surface grating is the most promising one because of its advantages of monolithic integration, compatibility with standard VCSELs manufacturing processes, and high polarization stability. So far, most of the surface grating VCSELs have been focused on 850 nm or 894.6 nm VCSELs in data communication or cesium atomic clock, where the grating period, grating depth, and duty cycle typically are 600 nm, 60 nm, and 0.5, respectively [ 19 , 24 , 25 ]. However, 795 nm VCSELs have attracted more attention because of their applicability for rubidium atomic clocks, which provide a stable time and frequency reference for a variety of applications such as mobile and wired telecommunication infrastructure, broadcasting products, defense applications, calibration equipment and scientific instrumentation [ 26 ].…”

Diverse Defects in Alkali Niobate Thin Films: Understanding at Atomic Scales and Their Implications on Properties

“…[ 7,9 ] However, the highly volatile nature of alkali metals during high‐temperature processing makes it highly challenging to control the composition which makes KNN quite vulnerable to the formation of various defects and impurities even with the slight off‐stoichiometry. [ 10 ] The commonly reported issues in KNN thin films include comparatively lower piezoelectric and dielectric constant, high‐leakage current, and low fatigue resistance. [ 7,11 ] Based on the previous reports, the inferior electrical and electromechanical properties of KNN‐based thin films are attributed to the formation of oxygen vacancies and secondary phases which are also present in bulk electroceramics.…”