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.
In this contribution the relevant technological aspects of LED-based lamps for solid state lighting are discussed. In
addition to general energy efficiency considerations improvements in LED chip technology and white light generation
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.
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.
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.
Among enabling key components for mobile laser projection, the green laser plays an outstanding role: We present green
laser modules based on frequency doubled optically pumped semiconductor disk lasers. In these lasers with twofold
conversion, from 808nm over 1060nm to 530nm, active semiconductor components and second harmonic generation
have to be carefully optimized to realize good efficiency at moderate output powers. The concept was developed not
only to meet power and efficiency targets, but also to provide simple operation and control by pump diode current. The
latest concept targets green output powers of more than 50mW at wall plug efficiencies >7%, limiting total electrical
power consumption to less than 1W. Consequent use of micro optical components allows for a package volume of less
High power diode lasers convince by their very efficient conversion of electrical into optical energy. Besides high efficiencies and record absolute power levels, reliability in all possible operation modes and cost become increasingly important. We present diode laser bars in the 940nm range with wall plug efficiencies of about 65% at an emission power of 100W and with excellent reliability. The test had been performed on a stack with 5 bars at an output power of 100W per 1cm bar and after about 4000hrs test time, lifetimes of more than 40 000hour were estimated. The efficiency of these bars was at the beginning and at the end of this test about 65%. Operation modes between cw operation and q-cw (200μsec pulses) were evaluated and it will be shown, that pulses in the range of 1Hz are the hardest conditions, which can cause catastrophic failures. Using submounts with matched thermal expansion coefficient, this failure was prevented and lifetimes similar to cw-operation were reached. In order to reduce costs of laser power, we developed a laser package that offers high power at good reliability and provides a collimated beam for about 5$/W, as a cost target in mass production conditions. This was achieved by using packaging concepts that were developed for high power semiconductor devices. These results will further enhance the applicability of diode lasers in industrial application.
We demonstrate 0.7W cw output power at 520nm from an intracavity frequency doubled optically pumped semiconductor disk laser at room temperature. High beam quality and optical conversion efficiency of 10% has been achieved.