Ben King

A general theory for the intrinsic (Lorentzian) linewidth of photonic-crystal surface-emitting lasers (PCSELs) is presented. The effect of spontaneous emission is modeled by a classical Langevin force entering the equation for the slowly varying waves. The solution of the coupled-wave equations, describing the propagation of four basic waves within the plane of the photonic crystal, is expanded in terms of the solutions of the associated spectral problem, i.e. the laser modes. Expressions are given for photon number, rate of spontaneous emission into the laser mode, Petermann factor and effective Henry factor entering the general formula for the linewidth. The theoretical framework is applied to the calculation of the linewidth-power product of air-hole and all-semiconductor PCSELs. For output powers in the Watt range, intrinsic linewidths in the kHz range are obtained in agreement with recent experimental results.

Current progress in the scaling of continuous wave optical output power and conversion efficiency of broad-area GaAs-based edge emitters, broad-area lasers (BALs), operating in the 900…1000 nm wavelength range is presented. Device research and engineering efforts have ensured that BALs remain the most efficient of all light sources, so that in the past 10 years, power conversion efficiency at 20 W continuous wave (CW) output power from BA lasers with a 90…100 μm wide stripe has increased 1.5-fold to 57% (via epitaxial layer design developments), whilst peak CW power per single emitter has increased around 3-fold to 70 W (via scaling of device size), with further scaling underway, for example via use of multi-junction designs. However, the peak achievable CW power conversion efficiency and CW specific output power (defined here as peak output power from a 100 μm stripe diode lasers with a single p-n junction) has changed remarkably little, remaining around 70% and 25 W, respectively, for the past decade. Fortunately, research to understand the limits to peak efficiency and specific output power has also shown progress. Specifically, recent studies indicate that spatial non-uniformity in optical field and temperature play a major role in limiting both power and conversion efficiency. Technological efforts motivated by these discoveries to flatten lateral and longitudinal temperature profiles have successfully increased both power and efficiency. In addition, epitaxial layer designs with very high modal gain successfully reduce threshold current and increase slope at 25°C to values comparable to those observed at 200 K, offering a path toward the 80% conversion efficiency range currently seen only at these cryogenic temperatures. Overall, whilst operating efficiency and power continue to scale rapidly, a technological path for increased specific power and peak efficiency is also emerging.

We present single emitter laser diodes with high optical output power ( P _out ), conversion efficiency (η _E ), and lateral beam quality in quasi-continuous-wave (QCW) and continuous-wave (CW) operations enabled by using very wide stripe width (ranging from 400 to 1500 µm) and laterally structured p-side contact to prevent higher order and unwanted ring modes. We show that the maximum QCW P _out increases for wider stripe and P _out of ~ 290 W (limited by facet failure) is obtained at η _E = 60% for 1500 µm stripes using 500 µs pulse width and 10 Hz repetition-rate at a heatsink temperature of T _HS = 25 °C. In contrast, the maximum CW P _out of 71 W (limited by the available cooling of the test set-up) at η _E = 59% is obtained for 1000 µm stripes, with lateral-beam-parameter-product ( BPP _Lat. ) < 75 mm∙mrad, which is suitable for coupling into 1 mm core 0.15 NA fiber.

Quantum dot-based epitaxially regrown photonic crystal surface emitting lasers are demonstrated at room temperature. The GaAs-based devices, which are monolithically integrated on the same wafer, exhibit ground state lasing at ∼1230 nm and excited state lasing at ∼1140 nm with threshold current densities of 0.69 and 1.05 kA/cm2, respectively.

Buried-regrown-implant-structure (BRIS) technology combines two-step epitaxial regrowth with an intermediate ion implantation step in order to realise a buried current aperture close to the active region of a laser diode. In this paper we carry out a systematic performance comparison demonstrating the benefit of BRIS technology in single emitter broad-area lasers (BALs). We investigate stripe width W = 100 μ m and resonator length L = 4 mm single emitter lasers emitting at wavelength λ = 915 nm, comparing the performance of BRIS devices with different implantation depths with reference devices with only contact layer implantation. We show that using BRIS technology we achieve a continuous wave output power of 20 W at 57% efficiency, with a peak efficiency of 68%, and maintain a lateral brightness of 3.4 mm · mrad up to 19 W, improved over the reference devices due to reduced lateral current spreading in the BRIS devices. Further, we show results of ongoing aging experiments, which has shown no device degradation up to 5000 hours from BRIS devices.

We discuss algorithms and numerical challenges in constructing and resolving spectral problems for photonic crystal surface-emitting lasers (PCSELs) with photonic crystal layers and large (up to several tens of mm ² ) emission areas. We show that finite difference schemes created using coarse numerical meshes provide sufficient accuracy for several major (lowest-threshold) modes of particular device designs. Our technique is applied to the example of large-area all-semiconductor PCSELs, showing how it can be used to optimize device performance.

This paper analyzes 2D photonic crystal surface-emitting laser diodes with void-containing and all-semiconductor structures by comparing their simulated mode distribution, band structure, and coupling coefficients. A photonic crystal design with a square lattice and circle atoms is considered.

We report the engineering of air voids embedded in GaAs-based photonic crystal surface-emitting lasers realized by metalorganic vapor-phase epitaxy regrowth. Two distinct void geometries are obtained by modifying the photonic crystal grating profile within the reactor prior to regrowth. The mechanism of void formation is inferred from scanning transmission electron microscopy analysis, with the evolution of the growth front illustrated though the use of an AlAs/GaAs superlattice structure. Competition between rapid lateral growth of the (100) surface and slow diffusion across higher index planes is exploited in order to increase the void volume, leading to an order of magnitude reduction in threshold current and an increase in output power through an increase in the associated grating coupling strength.

A key benefit of photonic crystal surface emitting lasers (PCSELs) is the ability to increase output power through scaling the emission area while maintaining high quality single mode emission, allowing them to close the brightness gap which exists between semiconductor lasers and gas and fiber lasers. However, there are practical limits to the size, and hence power, of an individual PCSEL device, and there are trade-offs between single-mode stability and parasitic in-plane losses with increasing device size. In this paper, we discuss 2D coherent arrays as an approach to area and coherent power scaling of PCSELs. We demonstrate in two and three element PCSEL arrays an increase in the differential efficiency of the system due to a reduction in in-plane loss.