Georg Bruederl

True Green Laser Diodes at 524 nm with 50 mW Continuous Wave Output Power on c-Plane GaN

We pushed direct green laser diodes towards longer wavelengths at 524–532 nm based on improvements of epitaxial design and material quality on c-plane GaN substrate. Mounted ridge laser diodes show significant performance improvement in cw operation. For 524 nm laser, wall plug efficiency up to 2.3% at 50 mW optical output power is achieved. In pulse mode operation we demonstrate broad-area test lasers with an emission wavelength of 531.7 nm. Nonpolar and polar substrates are compared with respect to indium content in InGaN quantum wells. The limiting factors for achieving longer wavelengths and better performance of green lasers are discussed from this viewpoint.

Recent results of blue and green InGaN laser diodes for laser projection

Mobile laser projection is of great commercial interest. Today, a key parameter in embedded mobile applications is the optical output power and the wall plug efficiency of blue and green lasers. We report on improvements of the performance of true blue riedge waveguide InGaN lasers at 452nm with cw-output power up to 800mW in overstress and mono mode operation up to 500mW in a temperatures range of 20°C to 80°C. We succeeded in high and almost temperature independent wall plug efficiencies >20% at stable output power levels from 200 to 500mW in cw-operation. Due to several improvements of our blue laser diodes we now estimate life times is in the order of 40khrs for 80mW output power in cw-operation at 40°C. Additional overstress degradation tests at power levels up to 200mW show a strong dependency of lifetime with output power. Furthermore, we present pioneering results on true green InGaN laser diodes on c-plane GaN-substrates. The technological challenge is to achieve In-rich InGaN-quantum wells with sufficiently high material quality for lasing. We investigated the competing recombination processes below laser threshold like nonradiative defect recombination by electro-optical measurements, such confirming that low defect densities are essential for stimulated emission. A model for alloy fluctuations in In-rich InGaN-MQWs based on spectral and time resolved photoluminescence measurements yields potential fluctuations in the order of E0=57meV for our blue laser diodes. To get a closer insight into the physics of direct green InGaN-Laser we investigated the inhomogeneous broadening of experimentally measured gain curves via Hakki-Paoli-measurements in comparison to calculated gain spectra based on microscopic theory showing the importance of strong LO-phonon coupling in this material system. Investigations of current dependent gain measurements and calculations yield a factor of 2 higher inhomogeneous broadening for our green lasers than for our blue laser diodes on c-plane GaN. Based on the improvements of the material quality and design we demonstrate true green InGaN-Laser in cw-operation at 522nm with more than 80mW output power on c-plane GaN. The combination of low laser threshold ~60-80mA, high slope efficiency ~0.65W/A and low operating voltage 6.9-6.4V of our green monomode RWG-Laser results in a high wall plug efficiency of 5-6% in a temperature range of 20-60°C.

GaInN laser diodes from 440 to 530nm: a performance study on single-mode and multi-mode R&D designs

The range of applications of blue and green lasers is increasing from year to year. Driving factors are costs and performance. On one hand we study the characteristics of low power R&D c-plane laser structures with improved Gaussian vertical and horizontal beam profile: We present new best values for efficiencies of single mode green lasers of 10.8% at 517nm and new long wavelength data at 532nm with efficiency of 6.5%. Furthermore, we present a new R&D design of a blue single mode laser diode with a very low threshold of 8.5mA. On the other hand, recent R&D results on broad area multi-mode power designs are shown: Efficiencies of 43% at 4W optical output power are achieved. Lifetime tests as long as 10000h are presented. High reliability is reached by a new facet design.

47.3: Invited Paper: Recent Progress in Direct Green Lasers for Mobile Image Projectors

We report on direct green lasers based on nitride semiconductors that are suitable for mobile projection applications. The TO38 packaged lasers achieved in continuous wave operation at 522nm wavelength more than 80mW optical power. The wall plug efficiency reached 5∼6% depending on operating temperature. The good performance of the lasers was possible due to the low threshold currents in range of 60∼80mA and large slope efficiency ∼0.65W/A. The optical beam properties are also shown.

10.7 Gb/s WDM transmission over 100-m SI-POF with discrete multitone

We report the record capacity of 10.7 Gb/s over 100-m step-index polymer optical fiber (SI-POF) with 1-mm core diameter over six WDM channels in visible wavelength range.

Blue and green nitride based laser diodes for projection

Summary form only given. Two fields for laser projection have attended big interest since several years due to the potential of high volume markets. One is the mobile projection; ideally a projection unit embedded in a mobile phone. For customer acceptance a reasonable price and high brightness of such a device are crucial. Mobile pico projectors need a brightness of 15 to 20 lumens. While red and blue laser with sufficient output power are available, direct green single mode laser with the necessary power are still under development. We report R&D results of single mode green laser with output power up to 200mW. This demonstrates that long term operation of green laser at 80mW to 100mW output power is realistic. The second field is the business projection with brightness up to several thousands of lumens. The concept here is to use blue high power laser as blue light source and also for the green light by conversion technology. The challenge is to reduce the cost of the light engine which is strongly dominated by the output power of the laser. We report R&D results of blue high power laser with an output power up to 3 watt.

An industry perspective on the optimization of InGaN lasers and LEDs via modeling

In this paper, we illustrate the role of modeling in the development of commercial nitride-based lasers and LEDs. Aside from optimizing device performance, joint analysis of simulations and experimental results can shed light into the intrinsic properties of the InGaN/GaN material system.