Characterization of Single-Mode Vertical Cavity Surface-Emitting Lasers

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 \u3e 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, a study was conducted 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. First, the operating range of the VCSEL was determined utilizing a Semiconductor Parameter Analyzer to obtain the LIV characteristics. Along with this measurement, spectral data was collected using an Optical Spectrum Analyzer at several key operating points, which allowed the RMS linewidths and SMSRs of the devices to be calculated at these points. The novel beam-profiler setup was used 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

Characterization of Single-Mode Vertical Cavity Surface-Emitting Lasers

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 \u3e 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, a study was conducted 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. First, the operating range of the VCSEL was determined utilizing a Semiconductor Parameter Analyzer to obtain the LIV characteristics. Along with this measurement, spectral data was collected using an Optical Spectrum Analyzer at several key operating points, which allowed the RMS linewidths and SMSRs of the devices to be calculated at these points. The novel beam-profiler setup was used 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

Beam quality study for single mode oxide-confined and photonic crystal VCSELs

A high-quality single mode beam is desirable for the efficient use of lasers as light sources for optical data communications and interconnects. This work shows a parametric study of the beam quality of vertical-cavity surface-emitting lasers (VCSELs). Using a novel vertical setup we calculated the beam quality factor, M2, from beam radius measurements across the operating range of on-wafer devices. The device operating range is determined from the light-current-voltage measurement. We measured spectral content across the operating range to determine the number of operating modes, with single mode devices being of primary interest, and calculate the root-mean-square linewidths and side-mode suppression-ratio to further quantify the beam quality. We characterized the beam quality of VCSEL devices emitting ≈ 850 nm with oxide-confined apertures of the 2.5 and 5 μm and photonic crystal confinement with varying hole etch depths and b/a ratios. Device characterization and beam quality data for each of the studied devices is presented and discussed