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.
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.
Ulrich Steegmueller, Michael Kuehnelt, Heiko Unold, Thomas Schwarz, Michael Schmitt, Karsten Auen, Roland Schulz, Christoph Walter, Ines Pietzonka, Stefan Illek, Hans Lindberg, Alvaro Gomez-Iglesias, Michael Furitsch, Christian Lauer, Uwe Strauss, Thomas Hoefer
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.
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
than 0.5cm3.
We present the design and characteristics of an optically pumped vertical external cavity surface emitting laser emitting near 1550 nm. The InP-based laser was grown by Metalorganic vapor-phase epitaxy including an InGaAsP gain element and an InP/InGaAsP mirror. The gain element comprises 20 strain compensated quantum wells on top of a distributed Bragg reflector. As an external mirror we used a concave spherical mirror, which also provides the outcoupling of light. Gain is achieved by optical pumping with a high power, 1250 nm fiber Raman laser focused on the gain chip. Essential for achieving high output power is to reduce the temperature of the gain material and this is accomplished by bonding an intra-cavity silicon heat spreader to the surface of the gain element. The maximum output power is 260 mW at multi transverse mode operation and 230 mW at single transverse mode operation with a near Gaussian beam profile (M2=1.22) at 240 K. At room temperature the output power was limited to 12 mW. The maximum output power greatly depends on the operating temperature and studies of pump induced thermal effects show that thermal lensing imposes limitations on the attainable power.
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