研究目的
Investigating the loss mechanisms, particularly lateral radiation losses, in tunable vertical-cavity surface-emitting lasers (VCSELs) to understand and mitigate performance degradation at tuning range edges.
研究成果
The paper identifies lateral radiation losses as a significant cause of threshold gain increase in tunable VCSELs, particularly at tuning range edges. Using Poynting vector analysis and VELM simulations, it demonstrates that these losses are due to diffraction in the air-gap and not abrupt dielectric profiles. Three countermeasures (curved top mirrors, cavity-lensed approach, diffractive optical element lens) are proposed and shown to reduce threshold gain and improve efficiency, with lens-based solutions being most effective. This provides deeper insight into scattering losses and offers practical design improvements for tunable VCSELs.
研究不足
The study is based on simulations using the VELM code, which may have inherent approximations. The VCSEL structure assumes lossless dielectric layers except where specified, and real-world fabrication challenges (e.g., non-radiative losses from etching) are not fully addressed. The solutions proposed (curved mirrors, lenses) require technological feasibility, which might not be trivial to implement.
1：Experimental Design and Method Selection:
The study uses a 3-D vectorial electromagnetic simulator called VELM (VCSEL ELectroMagnetic) to simulate tunable VCSELs. It employs coupled-mode theory and a generalized transmission matrix formalism to solve Maxwell's equations in cylindrical coordinates. A novel approach based on the Poynting vector analysis is used to quantify power flux and identify loss mechanisms.
2：Sample Selection and Data Sources:
The VCSEL structure is based on a bottom-emitting design with a Si/SiO2 top DBR, a EuTe/PbxEu1?xTe bottom DBR, and a PbySr1?ySe cavity with quantum wells. Simulations are performed for various air-gap widths (wag) to cover a free spectral range.
3：List of Experimental Equipment and Materials:
The simulations are computational; no physical equipment is used. Materials include Si, SiO2, EuTe, PbxEu1?xTe, PbySr1?ySe, and quantum wells.
4：Experimental Procedures and Operational Workflow:
Simulations involve varying the air-gap width, computing electromagnetic fields, analyzing Poynting vector components (Sz and Sρ), and calculating longitudinal power flux Pz(z). Different VCSEL designs (e.g., with curved mirrors or lenses) are simulated to compare performance.
5：Data Analysis Methods:
Data analysis includes plotting threshold gain vs. air-gap, Poynting vector maps, eigenvector components vs. transverse wavenumber, and efficiency calculations. Statistical techniques are not specified; analysis is based on simulation outputs.
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