Chunfeng He

Vertical-external-cavity surface-emitting lasers operating at different wavelength: design, numerical simulation, and characteristics

We describe design, numerical simulation and characteristics of high-power optical pumped VECSELs at different wavelength (980nm, and 1300nm). The device design realizes the integrating diode-pumped lasers with vertical-cavity surface-emitting laser structure, drawing on the advantages of both. With periodical gain element structure, optical pumped VECSEL is scalable to watt level output. The characteristics such as threshold condition and output power are calculated theoretically. An optimum number of quantum wells and external mirror reflectivity are obtained from the calculation results, and the thermal characteristic is also considered. Finally the calculation results also predict high output power in this kind of device structure.

Temperature characteristics of several familiar diode lasers with broad area

Temperature characteristics of several familiar high power diode lasers with broad area, whose wavelength was separately 808 nm, 810 nm, 940 nm and 980 nm, were analyzed. In order to see the effect the change of the quantum well structure on the characteristic temperatures, different structures were attempted. For the 808 nm structure, we tried different barrier thicknesses. For the 810 nm structure, different cavity lengths were attempted. And we studied the 940 nm and 980 nm also. In this paper, the widths of these devices were all 100 μm. Characteristic temperatures of these devices were calculated. The appropriate structure was available for different application.

Vertical-external-cavity surface-emitting lasers: numerical simulation, and characterization

Firstly, the vertical external-cavity surface-emiting lasers (VECSELs) device structure and model was given, and the output characteristic was simple calculated. Then, in experiment, the VECSELs were grown, bonded on to the heat sink, and optically pumped by high-power 808nm diode laser array with fiber output module, the light emission spectra were measured. Finally, The thermal characteristic of the VECSELs was investigated by changing the temperature of the substrate.

Temperature characteristics of high power vertical cavity surface emitting lasers

By using oxidation confinement technology high power vertical-cavity surface-emitting lasers are fabricated in experiment. The electrical and optical performance characteristics such as threshold current, efficiency, emission wavelength, and output power are measured under continuous wave (CW) condition at room temperature. The maximum output power is up to watt regime at wavelength of about 980nm. The temperature characteristics of the device are investigated experimentally in detail. The variation in lasing threshold current with temperature is studied. The characteristic temperature T0 of the device is derived, and the value is about 211K. Such a high characteristic temperature T0 of threshold current can lead to good temperature sensitivity of the device. At the same time, the lasing spectrum characteristics with temperature are also measured. The wavelength shift with temperature is just about 0.06nm/K. From the measured results, it is shown that the device can still operate at high temperature condition.

The spectral feature analysis of semiconductor thin disk laser

The semiconductor thin disk laser is a new type of semiconductor laser. This work gives the basic operation function of semiconductor disk laser, and analyses the heat effect by the experimentally measured photoluminescence spectrum of the laser chip at different pump power and different temperature. We can see that: with increasing pump power, the thermal effects of the gain material becomes seriously and causes the saturation of carrier lifetime, so the electron-hole pair created in the absorbtion layer have no enough time to rate to one of the wells, and the non-radiative recombination happens in the barrier. When the thermal effects becomes stronger, the chip will not lasing. This phenomenon is from the smaller energy offset between barrier and quantum well. We optimize the original structure design and experimental technology. A non-absorbing AlGaAs layer who is transparent to the pumping and laser wavelength is added to confine the carriers in the quantum wells. At the same time a DBR with double reflecting band is induced to improve the absorbing efficiency of the pumping light. The single QW is replaced by the three narrow QWs, This three QWs structure can add the quantum state of QW, increase the recombination probability of carriers in the QWs and reduce the heat effect. The chemical etch equipment is also improved to control the surface unevenness to be within 50 nm.

High power vertical cavity surface-emitting laser with high reliability

High-power vertical-cavity surface-emitting lasers with InGaAs/GaAs quantum well active gain region are investigated. By using AlAs oxidation technology, the devices have been fabricated in experiment, and the characteristics of the device are carried out at room temperature. The 300μm-diameter VCSELs have the maximum room temperature continuous wave (CW) optical output power of about 1.1W, and the threshold current of the device is about 0.46A. The life test of the device is carried out in constant current mode. The life test of 300-μm diameter lasers shows that the average lifetime is about 1800h at 80°C. The device degradation mechanism is also discussed in detail.

High Power Diode Pumped Vertical Externalcavity Surface-emitting Lasers (VECSELS)

We describe the theoretical analysis and calculations of the 980 nm high-power diode-pumped vertical external cavity surface emitting laser (VECSEL). The VECSEL with active region of InGaAs/GaAsP/AlGaAs system can be operated near 500 mW in a single transverse mode.

High-power VCSELs single devices and 2-D arrays

The high power bottom-emitting vertical-cavity surface-emitting lasers (VCSELs) and laser arrays emitting at 980 nm are reported. Extensive investigations on size scaling behavior of thermal properties of single devices show limits of attainable output characteristics. The maximum continuous wave (CW) output power at room temperature of single devices with aperture size up to 500 μm is as high as 1.95 W. The key characteristics such as maximum output power, wavelength and thermal resistance are discussed. The bottom-emitting arrays of 16 elements and 200 μm aperture size of individual elements show output power of CW 1.35 W at room temperature. The far-field angle is below 17° for all driving current, which is very favorable for focusing or collimating optics.

Theoretical analysis of 980nm high power vertical external-cavity surface-emitting semiconductor laser (VECSEL)

By using bottom-emitting structure, we will develop laser diode (LD) pumped 980 nm VECSEL with active region of InGaAs/GaAsP/AlGaAs system. Because the thickness of barrier layer and absorption layer exceed that of quantum well, single well approximation model (KP method) can be used to calculate the band structure of VECSEL. The Schrodinger equation of finite deep potential well can be adopted to calculate the energy level structures of electron, heavy and light holes. According to the transition selection rule, we theoretically obtained the emitting wavelength of VECSEL and calculated quasi-Femi energy of valence band and conduction band based on the analysis of energy level structure of electron and holes. By analyzing the gain of strained quantum wells, we calculated the gain of VECSEL using transition matrix elements of electron, heavy and light holes. We give out the threshold gain, output power and other characteristic parameters. We will study the configuration of VECSEL and pumping scheme. We designed external cavity mirror, active region and bottom-emitting structure. A LD-pumped vertical external cavity surface-emitting laser whose output power is greater than 1.0 W can be predicted.

980-nm high power vertical external-cavity surface-emitting semiconductor lasers (VECSEL)

We describe the design, fabrication, and calculation characteristics of the 980nm high-power diode-pumped vertical external-cavity surface-emitting laser(VECSEL).From our calculation, the VECSEL with active region of InGaAs/GaAsP/AlGaAs system can operate near 1w in a single transverse mode.