Advancements in Semiconductor Laser Technology

Lasers have revolutionized many fields starting from the telecommunications, data storage to medical diagnostics and consumer electronics. And among the semiconductor laser technologies, Edge Emitting Lasers (EEL) and Vertical Cavity Surface Emitting Lasers (VCSEL) emerged as critical components due to their unique properties and performance. These lasers generate light through the recombination of electrons and holes in a semiconductor material. EELs are known for their high power and efficiency and they are extensively used in fiber optic communications and laser printing. VCSELs on the other hand are compact and are used for applications like 3D sensing. Traditionally VCSELs have struggled to match the efficiency levels of EELs however a recent breakthrough particularly in multi junction VCSEL, has demonstrated remarkable efficiency improvements which place the VCSELs to surpass EELs in various applications. This article focuses on the basics of these laser technologies and their recent advancements.

EELs are a type of laser where light is emitted from the edge of the semiconductor wafer. This design contrasts with the VCSELs which emit light perpendicular to the wafer surface. EELs are known for their high power output and efficiency which makes them particularly suitable for applications that require long-distance light transmission such as fiber optic communications, laser printing and industrial machining.

EELs consist of an active region where electron hole recombination occurs to produce light. This region is sandwiched between two mirrors forming a resonant optical cavity. The emitted light travels parallel to the plane of the semiconductor layers and exits from the edge of the device. This design allows EELs to achieve high gain and power output which makes them effective for transmitting light over long distances with minimal loss. VCSELs is a type of semiconductor laser that emits light perpendicular to the surface of the semiconductor wafer unlike the EELs which emit light from the edge. VCSELs have gained popularity due to their lower threshold currents and ability to form high density arrays.

VCSELs consist of an active region where electron-hole recombination occurs to produce light. This region is situated between two highly reflective mirrors which forms a vertical resonant optical cavity. The light is emitted perpendicular to the wafer surface which allows for efficient vertical emission and easy integration into arrays.

Recent advancements in VCSEL technology marked a significant milestones in the field of semiconductor lasers. And in particular the development of multi junction VCSEL which led to the improvements in power conversion efficiency (PCE) of the laser. Research conducted by Yao Xiao et al. and team has demonstrated the potential of a multi junction VCSELs to achieve efficiency levels which were previously thought unattainable. This research focuses on cascading multiple active regions within a single VCSEL to enhance gain and reduce threshold current which leads to higher overall efficiency.

The study employed a multi-junction design where several active regions are stacked vertically within the VCSEL. This design increases the volume of the gain region and lowers the threshold current density resulting in higher efficiency. Experimental results from the study revealed that a 15-junction VCSEL achieved a PCE of 74% at room temperature when driven by nanosecond pulses. This efficiency is the highest ever reported for VCSELs and represents a significant leap forward from previous records. Simulations conducted as part of the study indicated that a 20-junction VCSEL could potentially reach a PCE exceeding 88% at room temperature. This suggests that further optimization and refinement of the multi-junction approach could yield even greater efficiencies.

The implications of this research are profound for the future of VCSEL technology. Achieving such high efficiencies places VCSELs as strong competitors to EELs particularly in applications where energy efficiency and power density are critical. The multi junction VCSELs demonstrated in the study shows promise for a wide range of applications and future works may focus on optimizing the fabrication process, reducing thermal management issues and exploring new materials to further enhance performance. Integrating these high-efficiency VCSELs into commercial products could revolutionize industries reliant on laser technology.

Written by Arun Sreeraj

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