In an interview with SIL co-chair ROBERT STEELE, SoraaLaser’s PAUL RUDY describes the future of SSL and applications that will be advanced by evolving laser light sources.
The dramatic developments in LED technology have clearly had an enormous impact on the lighting industry. However, light source technology evolution is far from complete, and continuing technology development will be key to the future of lighting. At the upcoming Strategies in Light 2017 (SIL; February 28-March 2, Anaheim, CA) conference, in the track entitled “Technology Innovation to Support Market Growth,” a session will be devoted to the topic “Light Source Evolution and the Future of Lighting.” The lead speaker in this session will be Paul Rudy, PhD, co-founder and SVP of business development at SoraaLaser, whose presentation is entitled “Laser Light Sources for Specialty Illumination Applications.” Rudy has worked in the field of photonics for 20 years and has extensive general management, technical product marketing, and product management experience. Prior to SoraaLaser, Rudy worked as director of marketing at Coherent, the world’s largest commercial laser manufacturer, specifically commercializing laser devices based on gallium arsenide (GaAs).
Recently, SIL co-chair Bob Steele interviewed Paul Rudy regarding the subject of laser-based light sources.
Bob Steele: InGaN [indium gallium nitride] diode lasers have been around for a long time, and are widely used in consumer electronics products such as Blu-ray players. Why are they only now being considered for lighting?
Paul Rudy: In recent years, a more advanced type of visible laser diode technology has been developed, largely at UC Santa Barbara, based on a material known as semipolar GaN. The use of semipolar GaN results in the elimination of internal electrostatic fields, and maximum overlap between electrons and holes. Diode lasers based on this material have a 3-5X higher gain compared to more conventional c-plane InGaN laser diodes. This high gain, along with design freedom such as aluminum-free structures, enables higher power and higher efficiency InGaN lasers. From the applications perspective, high-power blue lasers have seen increasing use in the area of projection displays, which has driven production volumes in the industry, along with advancements in efficiency and cost.
Steele: What kind of performance is achieved with this approach?
Rudy: Wall plug efficiencies of up to 40% have recently been reported, up from 15% in 2005. Optical power outputs of 6W have also been reported. The main thing to realize here is that, unlike InGaN LEDs, these diode lasers do not suffer from “droop” (the roll-off of efficiency at higher drive currents). Therefore, high wall plug efficiencies can be achieved at high power outputs, and additional advances are expected.
Strategies in Light, co-located with The LED Show and Lightspace California, will deliver a full spectrum of illuminating industry speakers, workshops, and exhibits. View the full conference program and find additional details in the pre-conference brochure.
Steele: How is a blue-emitting InGaN diode laser used to create white light?
Rudy: Just as in the case with using a blue LED as a pump source for creating white light, a phosphor is required. There are several options for pumping the phosphor, including transmissive (the white light emission is in the same direction as the pump beam) and reflective (the white light emission is at an angle relative to the pump beam). Also remote pumping, in which optical fiber is used to direct the laser light to the phosphor, is possible. This is the approach used by European automobile manufacturers to develop laser-based headlamps. We at SoraaLaser have developed a white light module using a reflective approach in which the diode laser pumps a small phosphor chip, which emits up to 500 lm of white light from a 300-μm spot. This approach is shown in the figure.
White light being generated by laser light sources.
Steele: What are the advantages of laser sources compared to LEDs for producing white light?
Rudy: As noted above, these laser-pumped phosphor light sources do not suffer from droop, so high conversion efficiencies at high optical pump power are achieved. Laser-based white light sources have very high luminance values (1000 cd/mm2) relative to LEDs, so hundreds of lumens can be emitted within a small beam angle (1–2°), allowing for a high degree of optical control using very small optical elements. The laser-based sources can also enable a convergence of projection display with miniaturized luminaires for projection illumination applications.
Steele: What applications do you envision for laser-based sources?
Rudy: Clearly, laser-based sources are not suitable for all lighting applications, such as broad area illumination. However, we are exploring a number of applications in which such sources are highly advantageous. These include micro-spotlights and micro-luminaires for directional applications in architecture and entertainment, and fiber-delivered, high-lumen ultracompact outdoor lights for roadways and stadiums. We are also exploring applications such as Li-Fi systems with very high data rate capacity relative to Wi-Fi and LED Li-Fi.
Steele: When do you expect laser-based light sources to be commercialized for general lighting applications (as noted above, they are already being used in car headlamps)?
Rudy: In the past 3 years, laser-based displays have emerged to consume substantial volumes of laser-based light sources. Specialty lighting and automotive lighting are now adopting this exciting technology, and will drive a new additional wave of volumes in the coming three years. Beyond that, development is already ongoing to integrate dynamic laser light sources into advanced general lighting applications such as smart lighting, Li-Fi, and IoT [Internet of Things].
BOB STEELEis conference co-chair for Strategies in Light (strategiesinlight.com).