Characterization of Single-Mode Vertical Cavity Surface-Emitting Lasers

Jonathan Burton Dencker

Abstract


A high-quality single-mode beam is desirable for the efficient use of lasers as light sources for optical data communications and interconnects, however there is little data which characterizes operating ranges and near-field beam qualities of Vertical Cavity Surface Emitting Lasers (VCSELs), which has resulted in a lack of analysis of these devices. Measures of beam quality include beam-quality factor (M2), Side-Mode-Suppression-Ratio (SMSR) and RMS linewidth. M2 is a measurement of how closely the beam is to an ideal Gaussian. SMSR is the difference, in dB, between the amplitude of the primary peak and the amplitude of the next highest peak of the output spectrum, with single-mode operation defined by a SMSR > 30 dB. RMS linewidth is a second moment calculation involving the power spectral density, where smaller RMS linewidth indicates higher beam quality.

Utilizing a novel vertical M2 setup in which on-wafer VCSEL M2 can be measured, we conducted a study on the relation between M2, SMSR and RMS linewidth, for various oxide-confined VCSELs of varying aperture sizes and Photonic Crystal (PhC) VCSELs of varying aperture sizes and photonic crystal configurations. We first determined the VCSEL operating range utilizing a Semiconductor Parameter Analyzer to obtain the LIV characteristics.  Along with this measurement, we collected spectral data using an Optical Spectrum Analyzer for several key operating points which allowed us to find RMS linewidths and establish the SMSR of the devices at these points. We then used the novel beam-profiler setup to measure the device’s M2. Initial results show a strong correlation between the measures of beam quality, with increasing SMSR, corresponding to M2 values closer to 1, and single-mode operation characterized by a M2 of less than 1.5.  A strong correlation between RMS linewidth and M2 was also seen, with increasing RMS linewidths corresponding to an increase in M2.


Keywords


VCSEL; single-mode; beam quality; photonic crystal

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