Roland Schulz

Visible lasers for mobile projection

Visible laser sources are attracting considerable interest to enable ultra-small, embedded laser scanning projection devices. We report recent progress on the development of red, green and blue semiconductor based laser sources. Red and blue colours are achieved by edge-emitting laserdiodes, whereas green uses frequency doubled optically pumped semiconductor lasers. Green lasers turned-out to be on the critical path for the technical and commercial success of laser displays. Because all current approaches are based on frequency doubling, the green source is the major contributor of cost, size and power consumption. Important parameters like size, efficiency, output power, beam quality, and modulation bandwidth are discussed.

Progress in ultra-compact green frequency doubled optically pumped surface emitting lasers

Compact, stable and efficient green lasers are of great interest for many applications like mobile video projection, sensing, distance measurement and instrumentation. Those applications require medium values of output power in the 50mW range, good wall-plug efficiency above 5 % and stable operation over a wide temperature range. In this paper we present latest results from experimental investigations on ultra-compact green intracavity frequency doubled optically pumped semiconductor InGaAs disk lasers. The green laser setup has been limited to a few micro optical and semiconductor components built on a silicon backplane and fits within an envelope of less than 0.4 cc. An optical frequency looking scheme in order to fix the fundamental wavelength over varying operating conditions like changing output power and ambient temperature has been applied. The cavity has been optimized for fast modulation response and high efficiency using quasi-phase matching non-linear material. Recent data from cw and high-frequency characterization is presented.

Recent advances in VECSELs for laser projection applications

Laser projectors integrated in portable devices offer a new platform for media display but put strong demands on the laser sources in terms of efficiency, modulation band width, operating temperature range and device cost. Osram Opto Semiconductors has developed and produces synthetic green lasers for projection applications on which the latest results are reported. Based on vertical external cavity surface emitting laser (VECSEL) technology and second harmonic generation an output power of >75mW has been achieved. The maximum output power is to a large extent limited by the high thermal resistance of the monolithic VECSEL chip used. To overcome the thermal limitations a new thinfilm VECSEL chip design is proposed where the epitaxial layers are transferred to a silicon carrier and processed on wafer level, thus significantly lowering the thermal resistance and improving the maximum output power.

High-performance at low cost: the challenge manufacturing frequency doubled green semiconductor lasers for mass markets

Laser projection arising as a new application in the consumer market has been the driving force for OSRAM Opto Semiconductors to develop a frequency doubled semiconductor laser and the production technology necessary to make the complexity of an advanced laser system affordable. Optically pumped frequency doubled semiconductor lasers provide an ideal platform to serve the laser projection application. Based on this scalable technology, we developed a 50 mW green laser comprising all the properties that can be expected from a high performance laser: Excellent beam quality and low noise, high speed modulation, good efficiency and long life time. More than that, the package is very compact (<0.4 cm3) and may be operated passively cooled at up to 60°C. Managing lasing wavelength and controlling phase matching conditions have been major design considerations. We will describe the key characteristics of the green laser, and will also present results from reliability testing and production monitoring.

3.5: Late-News Paper: RGB Laser for Mobile Projection Devices

Recent advances in small form factor lasers for mobile projection devices are discussed. Based on semiconductor solutions, efficient and very compact full color laser modules are realized, suitable both for imager and scanning beam type laser projection systems.

IR lasers optimised for high-temperature operation in frequency-doubled green module for mobile laser projection

The above presented data of a green laser module regarding output power of 100mW based on an 850nm pump laser, 1060nm VECSEL and intra-cavity second-harmonic generation prove an excellent performance of the whole module with the overall WPE of as high as 10% at 40°C. It is the highest value of all cutting edge technologies enabling green lasing achieved up to date with capability of high-speed modulation in MHz range. Reliability and WPE of a pump die at high temperatures are of crucial importance for this kind of device. We demonstrate reliable operation up to 90°C junction temperature of the pumping IR laser diode at current density of 1.4kA/cm2, which is also used as a single emitter delivering 0.5–1W output power after being mounted in TO-can under the same junction temperature and current load.