The wide range of applications in biophotonics, television or projectors, spectroscopy and lithography made the
vertical external cavity surface-emitting lasers an important category of power scalable lasers. The possibility of
bandgap engineering, inserting frequency selective and converting elements into the external laser cavity and laser
emission in the fundamental Gaussian mode leads to ongoing growth of the area of applications for tunable laser
sources. We present an intra cavity frequency-doubled VECSEL with emission wavelength around 330 nm and a
maximum tuning range of more than 7nm with output powers exeeding 100mW. Frequency doubling is realized
with an anti-reflection coated beta barium borate crystal, while a birefringent filter, placed inside the laser cavity
under Brewster's angle, is used for frequency tuning. The fundamental laser, pumped by a 532nm Nd:YAG laser
under an angle of 50° normal to the surface, is realized by a multi quantum well structure consisting of 20
compressively strained GaInP quantum wells in an AlxGa1-xInP separate confinement heterostructure and it
emits around 660 nm. The VECSEL-chip with its n-λ cavity is completed by a 55 λ/4 pairs Al0.50Ga0.50As/AlAs
distributed Bragg reflector. Next to the optical properties of the device, we show results of different arrangements
of the quantum wells, namely five times four and ten times two packages.
We present a non-resonantly pumped red-emitting vertical external cavity surface-emitting laser system based
on a multi-quantum-well structure with 20 compressively-strained GaInP quantum wells for an operation wavelength
between 645-675 nm. Five quantum well packages with four quantum wells are placed in a separate
confinement heterostructure in a resonant periodic gain design in quaternary AlGaInP barriers and cladding layers,
respectively. The 3 λ cavity is fabricated on a 55 λ/4 pairs Al0.50Ga0.50As/AlAs distributed Bragg reflector.
By bonding an intra-cavity diamond heatspreader to the chip, continuous-wave operation exceeding 700mW
output power at a wavelength of 662 nm with a low threshold power of 0.8W was achieved. A thermal resistance
value of R1 = 5K/W and R2 = 7K/W could be determined for our setup at operation heatsink temperatures
of Ths = -28°C and Ths = 16°C, respectively. Measurements of the slope efficiency within a v-type cavity with
different outcoupling mirror reflectivities lead to a cavity round-trip transmission factor of Tloss = 98.6% and an
absorption efficiency of ηabs = 17.6%. Using a birefringent filter in a folded cavity, a maximum tuning range
of 22 nm at a center wavelength of 667 nm could be shown. With this method wavelengths below 650 nm were
observed. Utilizing a non-linear crystal for intra-cavity frequency doubling in this cavity geometry, coherent
emission down to 322 nm could be detected. In the UV spectral range, a maximum tuning range of 10 nm could
be measured at a center wavelength of 330 nm, so we could match the HeCd laser line at 325 nm.
We demonstrate electrically pumped single-photon emission in the visible spectral range from InP quantum dots
embedded in a resonant cavity LED device structure. The electroluminescence from a single QD can be observed
up to 120 K. Our devices can also be operated using pulsed electrical excitation. The successful injection of
carriers is verified by time-correlated photon counting experiments and the pulsed signature in second-order
In this paper we discuss the problems of the AlGaInP material system and its consequences for the laser applications in vertical-cavity surface-emitting lasers (VCSEL). The epitaxial and technological solutions to overcome at least parts of the inherent problems were presented. Measured power-current curves of 660nm AlGaInP-based oxide-confined VCSEL are compared with calculated data by a cylindrical heat dissipation model to improve heat removal out of the device. Pulsed lasing operation of a 670nm VCSEL at +120°C heat sink temperature is demonstrated, where we exceeded 0.5mW and at +160°C still 25μW output power were achieved. We also studied the modulation bandwidth of our devices and achieved 4GHz and calculations lead to a maximum possible intrinsic -3dB frequency of 25GHz.
This contribution drafts the problems of the AlGaInP material system and its consequences for the laser applications in vertical-cavity surface-emitting lasers (VCSEL). The epitaxial and technological solutions to overcome at least parts of the inherent problems were discussed. Calculated data by a cylindrical heat dissipation model were compared with measured power-current curves of 660nm oxide-confined VCSEL to improve the heat removal out of the device. At high temperatures pulsed operation of a 670nm VCSEL is demonstrated, where we could exceeded 0.5mW at +120°C and at +160°C still 25µW optical output power were achieved.
This talk focuses on the high frequency characteristics of red VCSELs. After a short description of important fabrication issues the modulation behaviour of GaInP surface emitting lasers is discussed on the basis of the laser rate equations. The influence of the geometric dimensions of the laser structure and of the operating conditions is investigated. From the S-parameter analysis a modulation coefficient of 3 GHz/(mA)1/2 for VCSELs with a 7 µm aperture and a differential gain of 1.15•10-16 cm2 are deduced. A more detailed analysis reveals, that the modulation behaviour of red VCSELs nearly solely depends on their photon density inside the quantum wells as expected from the rate equations. These results imply that for a certain range of geometries diffusion and diffraction have a second order influence on the high frequency characteristics of red VCSELs. The K-factor analysis indicates very short carrier transfer and relaxation times around 5 ps and a maximum frequency of 25 GHz. Large signal modulation issues such as the properties of the eye diagram are also addressed. From the device characteristics it is concluded that the GaInP-VCSEL is suitable for data communication applications. Low cost fabrication makes the red VCSEL an attractive candidate for both automotive and high-speed data communication.
Vertical cavity surface emitting lasers (VCSEL) in the GaInP/AlGaInP material system have experienced a rapid development in their short history. In general lasers from that material system are suitable for a huge number of applications beginning with TV lasers and high power lasers for edge emitters, continuing with optical data storage, medical applications as well as data communication in cars, air planes, offices and between computers as application field for VCSELs. Especially automotive applications show the highest requirements on a laser with respect to operation temperature and power. In this talk we draw out the problems of the material system AlGaInP and its implications for laser applications. We discuss the epitaxial and technological solutions to overcome at least a part of these inherent problems. We will discuss the possible power that we can expect from VCSELs emitting in the range between 650 nm to 670 nm. We got from our lasers 5 mW, CW @ RT, 670nm and 2.5mW, CW@RT, 650 nm. We emphasize the role of doping, Bragg mirror grading, suitable detuning of cavity mode and gain, and optimisation of the contact layer and control of the oxide aperture in the VCSEL structure to get improved operation characteristics at higher temperatures. From the analysis of high frequency measurements, we could evaluate modulation bandwidths between 4 GHz and 10 GHz. The application of polyimide as a dielectric isolation material shows the potential to obtain modulation bandwidths beyond 10 GHz. For the intrinsic modulation bandwidth we get a value of 25 GHz, which is near the value edge emitters show. A more detailed discussion on photon lifetimes and carrier transport times will be given in the talk. Red light emitting VCSELS driven with short current pulses showed laser emission up to + 160°C case temperature. Thus, a CW operation up to +120°C can be expected after further improvement of power generation (decrease of series resistance) and heat spreading (optimized contacts and mounting). From these characteristics we can conclude that AlGaInP-surface emitting lasers have a real potential as low cost lasers for automotive applications as we all as data communication applications up to 10 GHz.