Bit-loaded quadrature amplitude modulation-orthogonal frequency division multiplexing (QAM-OFDM) encoding and photonic-crystal-engineered multi-mode vertical-cavity surface-emitting lasers (MM-VCSELs) transmission performance are analyzed. Two different surface photonic-crystal designs are used to configure the core and cladding regions of MM-VCSELs, producing continuous-wave and digital-encoding outputs. These outputs are combined with the end-face-flattened OM5 multi-mode fiber (MMF) for 100 m short-reach transmission. The photonic-crystal (PhC) structure exhibits a spatial mode-filtering ability, supporting few or single-mode outputs from the MM-VCSEL. This helps reduce the modal dispersion during OM5-MMF transmission of the encoded data. Comparing the original MM-VCSEL with two different surface-photonic-crystal-configured MM-VCSELs, the allowable bit-loaded QAM-OFDM data rate can be increased from 60.7 (for the VCSEL without the PhC structure) to 85/65 Gbit/s (for the PhC VCSELs with 2-layer PhC structures in the cladding layer and the ones with a 1-layer PhC structure in the core layer and 2-layer PhC structures in the cladding layer, respectively) under back-to-back (BtB) encoding and enable the 100 m OM5-MMF transmission to increase from 58.5 (for the VCSEL without the PhC structure) to 81.2/64.6 Gbit/s (for the PhC VCSELs with 2-layer PhC structures in the cladding layer and the ones with a 1-layer PhC structure in the core layer and 2-layer PhC structures in the cladding layer), respectively. Furthermore, by comparing the 7°-titled and 0°-normalized vertical coupling conditions, it can be observed that the purely normalized vertical coupling can collect more output power, resulting in an improved signal-to-noise ratio. This significantly increases the allowable error-free data rate from 85 to 98.9 Gbit/s in the BtB case and from 81.2 Gbit/s to 95.3 Gbit/s in the 100 m OM5-MMF case. Full article

A vertical-cavity surface-emitting laser (VCSEL) is easily made into a two-dimensional array to improve its output power. However, if the near-field complex amplitude output cannot be stabilized in the lowest supermode generated by the fundamental transverse mode, the spot cannot converge on the center normal of the far-field array geometry, and the energy will be diverged. The external cavity is prepared for the VCSEL array, and the output of the array can be stabilized in the lowest order supermode generated by the fundamental transverse mode by supermode control through diffraction coupling. In this study, the parallel-coupled model for the 2-dimensional VCSEL array based on Fresnel diffraction integration was established and used to numerically calculate and analyze the influence on the supermodes’ thresholds of different array distributions, array elements’ transverse modes and duty ratios versus the length of the external cavity. The simulation results show that the square array provides a wider range of external cavity control length ($0.2d^2/\lambda$ and approximately $0.9 \mathrm{to} 1.0d^2/\lambda$). The lowest supermode of the fundamental transverse mode can be outputted. For the regular hexagonal array with the length of the external cavity of $0.15d^2/\lambda$ and $0.6d^2/\lambda$. The results have important reference significance for the design of an external cavity VCSEL array, which can control the supermode and obtain VCSEL coherent array beams with high power and near diffraction limits. Full article

The degradation process of Vertical-cavity Surface-emitting lasers with high speed and a central wavelength at 850 nm is investigated via constant-current accelerated aging experiments. Degradation of the photoelectric performances under different operating conditions are characterized by optical output power, and forward and reverse bias current–voltage. The 1/f noise characteristics and formation mechanism are discussed in terms of the experimental results of low frequency noise below threshold current. The main composition of low frequency noise before and after aging, the bias current dependence and the origin of the noise are analyzed emphatically. The correlation between the degradation suggests that the loss of photoelectric performance and the fluctuation of low frequency noise characteristic can be attributed to the contagion of defects towards the active region of Vertical-cavity Surface-emitting lasers. Furthermore, the results of failure analysis confirmed the conclusion that the contagion of defects occurred towards the active region of the samples after aging. Full article

In this work, the architecture of a high-power InAlGaP/InGaP vertical-cavity surface-emitting laser (VCSEL) with an emission wavelength of 680 nm was studied. The design of quantum well, including the well thickness, indium composition, and barrier aluminum composition targeting the emission wavelength, was elaborately optimized. Moreover, the influences of leakage current, temperature dependence of optical gain, and resonance mode gain to threshold current under different barrier aluminum compositions were investigated. Lastly, the temperature characteristics of InAlGaP/InGaP VCSEL with substrate removal have also been calculated with 24% and 40.6% improvement in thermal resistance and operating current range, respectively. It holds great promise for high-power red VCSEL application. Full article

Directly modulated 850-nm multimode vertical-cavity surface-emitting lasers (MM-VCSELs) with different oxide apertures and transmission microstrip lengths are compared on the transmission performance of the non-return-to-zero on-off keying (NRZ-OOK) and four-level pulse amplitude modulation (PAM-4) data formats. In this work, intrinsic and extrinsic responses of the MM-VCSEL are also discussed concurrently. By tuning the length of the transmission microstrip in VCSEL, the low reflection coefficient and the enhanced 3-dB modulation bandwidth are achieved. The inductance of the transmission microstrip in the series connection with the capacitance in the active region is optimized to reduce the power loss induced by imaginary impedance. The different oxide aperture sizes for MM-VCSEL are also studied to control the capacitance and photon density. More importantly, the 3-dB modulation bandwidth, impedance matching, slope efficiency, relative intensity noise (RIN), and mode partition noise (MPN) for the MM-VCSEL with various designs are discussed to determine the best device with the high-speed transmission capability. The optimal MM-VCSEL with a diameter of 7 µm oxide aperture and a length of 25 µm transmission microstrip successfully demonstrates 50-Gbit/s OOK and 84-Gbit/s PAM4 after using the pre-emphasis technique for future data-center applications. Full article