Mingxin Li

Small-sized lithographic single-mode VCSELs with high-power conversion efficiency

Small, single mode VCSELs have been pursued almost since the inception of the device, but have been difficult to realize. Here we present data on lithographic and oxide-free VCSELs as small as 2 μm in diameter that produce single transverse mode powers of 8 mW and have high efficiency. The efficiencies reach 46% power conversion with greater than 73 % slope efficiency, with threshold current as low as 300 μA. Smaller VCSELs of 1 μm diameter produce 37 % power conversion efficiency with greater than 79 % slope efficiency, and single mode power over 5 mW. The keys to the high performance are the lithographic control and oxide elimination that reduce the electrical and thermal resistances.

Record low thermal resistance of mode-confined VCSELs using AlAs/AlGaAs DBRs

The influence of AlAs placed at various locations in oxide and non-oxide mode-confined VCSELs is studied. Experimental results show that removing oxide and introducing AlAs in various locations of the VCSEL DBRs can dramatically reduce the thermal resistance.

50% Power Conversion Efficiency on a Non-Oxide VCSEL

Over 50% power conversion efficiency (PCE) has been reached in an oxide-free VCSEL. VCSELs with very small size (2 μm) have shown high single transverse mode selectivity and good lasing characteristics.

Record single mode laser diode packing density using high uniformity lithographic VCSEL arrays with narrow spectral width

Single mode lithographic VCSELs are shown to be capable of unprecedented dense packing into arrays for high pulse power to improve spectral control and beam quality.

Lithographic VCSEL array multimode and single mode sources for sensing and 3D imaging

Sensing applications along with free space data links can benefit from advanced laser sources that produce novel radiation patterns and tight spectral control for optical filtering. Vertical-cavity surface-emitting lasers (VCSELs) are being developed for these applications. While oxide VCSELs are being produced by most companies, a new type of oxide-free VCSEL is demonstrating many advantages in beam pattern, spectral control, and reliability. These lithographic VCSELs offer increased power density from a given aperture size, and enable dense integration of high efficiency and single mode elements that improve beam pattern. In this paper we present results for lithographic VCSELs and describes integration into military systems for very low cost pulsed applications, as well as continuouswave applications in novel sensing applications. The VCSELs are being developed for U.S. Army for soldier weapon engagement simulation training to improve beam pattern and spectral control. Wavelengths in the 904 nm to 990 nm ranges are being developed with the spectral control designed to eliminate unwanted water absorption bands from the data links. Multiple beams and radiation patterns based on highly compact packages are being investigated for improved target sensing and transmission fidelity in free space data links. These novel features based on the new VCSEL sources are also expected to find applications in 3-D imaging, proximity sensing and motion control, as well as single mode sensors such as atomic clocks and high speed data transmission.

Invited impact of VCSEL scaling on speed and bit energy for high speed interconnects

The lithographic VCSELs are now being developed for high-speed applications. We present a number of features important to increase the VCSEL speed. Thermal properties and reliability for high operating current density are given, and the influence of device scaling. Modeling results are presented showing that oxide-free VCSELs can produce high intrinsic speed due to their ability to generate a greater stimulated emission rate.

Metal cavities as the efficiency killer in nanolasers and spontaneous light sources

The metal influence on light emitters has been studied for more than twenty years in semiconductor light emitters. A critical feature is reliance on the correct electromagnetic boundary conditions to understand and predict the performance of either lasers or spontaneous light emitters for which the metal may influence the emission properties. Here we show that nearly (all) recent studies of metal-coupled lasers or spontaneous light emitters leave out near-field interactions that seriously degrade the emission efficiency.