G. Trankle

Ferdinand-Braun-Institut, Berlin, Land Berlin, Germany

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Publications (127)133.94 Total impact

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    ABSTRACT: GaAs-based narrow-stripe broad-area lasers with integrated surface gratings are shown to operate with high power and efficiency, low beam parameter product (BPP), and narrow spectra. These distributed feedback lasers are constructed using a surface-etched, 80th-order grating, leading to spectral width $Deltalambda_{95%}<0.7~{rm nm}$ (95% power) and wavelength ${sim}{rm970}~{rm nm}$. Optical output powers $({>}{rm 6}~{rm W})$ and power conversion efficiencies $({>}{50%})$ comparable with devices without grating are enabled by a small coupling coefficient, $kappa{rm L}{sim}{0.3}$, consistent with coupled mode theory calculations. The lasers were constructed with a stripe width of 30 $mu{rm m}$, enabling BPP ${<}{rm 1.8}~{rm mm}$ mrad up to 6-W output power, improved over devices without gratings, that show BPP ${>}{rm 2.2}~{rm mm}$ mrad. We attribute the improvement to spatial filtering of higher order lateral modes by the narrow surface grating. Such devices are attractive sources for use in spectral beam combination systems for material processing.
    IEEE Photonics Technology Letters 04/2014; 26(8):829-832. · 2.04 Impact Factor
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    ABSTRACT: A dual-wavelength master oscillator (MO) power amplifier (PA) diode-laser system emitting at 785 nm suitable for shifted excitation Raman difference spectroscopy is presented. The laser system consists of a distributed Bragg reflector Y-branch diode laser as a dual-wavelength MO and a ridge waveguide PA. The system reaches an optical output power of more than 750 mW at 25 $^{circ}{rm C}$ . Optical spectra show wavelength stabilized single mode emission at 784.60 and 785.22 nm over the whole power range with a spectral width ${leq}{10}~{rm pm}~(leq 0.5~{rm cm}^{-1})$ and a spectral distance of 0.62 nm $(leq 10.1~{rm cm}^{-1})$ .
    IEEE Photonics Technology Letters 01/2014; 26(11):1120-1123. · 2.04 Impact Factor
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    ABSTRACT: GaAs-based broad-area diode lasers are needed with improved lateral beam parameter product (BPPlat) at high power. An experimental study of the factors limiting BPPlat is therefore presented, using extreme double-asymmetric (EDAS) vertical structures emitting at 910 nm. Continuous wave, pulsed and polarization-resolved measurements are presented and compared to thermal simulation. The importance of thermal and packaging-induced effects is determined by comparing junction -up and -down devices. Process factors are clarified by comparing diodes with and without index-guiding trenches. We show that in all cases studied, BPPlat is limited by a non-thermal BPP ground-level and a thermal BPP, which depends linearly on self-heating. Measurements as a function of pulse width confirm that self-heating rather than bias-level dominates. Diodes without trenches show low BPP ground-level, and a thermal BPP which depends strongly on mounting, due to changes in the temperature profile. The additional lateral guiding in diodes with trenches strongly increases the BPP ground-level, but optically isolates the stripe from the device edges, suppressing the influence of the thermal profile, leading to a BPP-slope that is low and independent of mounting. Trenches are also shown to initiate strain fields that cause parasitic TM-polarized emission with large BPPlat, whose influence on total BPPlat remains small, provided the overall polarization purity is >95%.
    Journal of Applied Physics 01/2014; 116(6):063103-063103-14. · 2.21 Impact Factor
  • IEEE Journal of Selected Topics in Quantum Electronics 01/2014; 20(1):1-1. · 4.08 Impact Factor
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    ABSTRACT: First results on epitaxial-side (epi-down) mounting of terahertz quantum-cascade lasers (QCLs) on sapphire submounts using indium solder are presented. The single-plasmon ridge waveguide lasers emit in the range 3.1–3.3 THz. An epi-down mounting scheme for stressless assembly is realized, which provides enhanced heat dissipation at the corresponding operating temperature and high stability against thermal cycling. The thermal conductance of the devices is improved by 30%, and the maximum continuous-wave operating temperature is increased by 10 K for epi-down mounted lasers achieving output power levels ${>}{rm 3}~{rm mW}$ at 55 K.
    IEEE Photonics Technology Letters 01/2013; 25(16):1570-1573. · 2.04 Impact Factor
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    ABSTRACT: The threshold current density of narrow (1.5 μm) ridge waveguide (In,Al)GaN based laser diodes is found to strongly depend on the ridge etch depth. By solving the complex-value two-dimensional waveguide equation, it is shown that, for shallow-ridge devices with a small built-in index step, the dependence of the modal gain on the material gain is strongly influenced by antiguiding effects. Taking into account the lateral extension of the material gain beyond the ridge as well as the optical mode absorption in the unpumped regions of the quantum wells, the observed differences in the threshold current density can be reproduced by simulations.
    Journal of Applied Physics 01/2013; 114(11):113102-113102-9. · 2.21 Impact Factor
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    ABSTRACT: We review high power semiconductor laser development at the Ferdinand-Braun-Institut, focusing on studies to improve material quality, design development for peak performance in standard structures and the development of novel device concepts for new applications.
    Photonics Conference (IPC), 2013 IEEE; 01/2013
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    ABSTRACT: A high output power and a good beam quality are required for the application of diode lasers for direct material processing. One possible way to increase the output power while keeping the beam quality almost constant is spectral beam combining. The required stabilization of the emission wavelengths of the single emitters can be achieved by the monolithic integration of Bragg gratings into the chips, which is a promising way to reduce fabrication costs in comparison to the utilization of volume Bragg gratings. A DFB laser with a stripe width of 30 µm is presented, which reached a side mode suppression ratio of 50 dB and an output power of 5.5 W. Aspects of the simulation and the fabrication of the Bragg gratings will be discussed.
    High Power Diode Lasers and Systems Conference (HPD), 2013; 01/2013
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    ABSTRACT: We report on the design and characterization of terahertz detection devices using field-effect transistors and on-chip broadband antennas. Experimental results from measurements on high-electron-mobility transistors fabricated with a AlGaN/GaN heterostructure are presented. Physical device parameters are extracted. The measured samples exhibit good noise-equivalent power (NEP) values at 0.6 THz of down to ~ 125 pW/√Hz. The responsivity is maximized by gate width. The best NEP value is found for the narrowest devices.
    Microwave Integrated Circuits Conference (EuMIC), 2013 European; 01/2013
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    ABSTRACT: Extremely large epitaxial waveguides with thickness ${\rm t}_{{\rm WG}}=8.6~\mu{\rm m}$ enable diode lasers with very narrow vertical divergence angle. We demonstrate that when such designs are processed in ridge waveguide laser format, there is substantial interaction between the vertical and lateral waveguiding mechanisms. For very narrow stripes with width ${\rm w}\ll{\rm t}_{{\rm WG}}$ , such interaction leads to lasing operation in the second-order mode in the vertical direction. For the case of an optimal stripe width ${\rm w}{\sim}{\rm t}_{{\rm WG}}$, single fundamental mode operation is achieved, with peak kink-free optical output power of 1.3 W and beam divergence angles (vertical, lateral) of $9^{\circ}\times6^{\circ}$ at full-width at half-maximum and $17^{\circ}\times 13^{\circ}$ with 95% power content. The maximum brightness is $90~{\rm MW}\times{\rm cm}^{-2}{\rm sr}^{-1}$ for 95% power content.
    IEEE Journal of Quantum Electronics 01/2012; 48(5):568-575. · 2.11 Impact Factor
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    ABSTRACT: This paper reports results on a transferred-substrate InP heterojunction bipolar-transistor technology for high-frequency power stages. The basic building block is a 2-finger transistor with fT and fmax values of 376 GHz and 385 GHz, respectively, at an emitter size of 0.8 × 5 μm2. The transistors demonstrate more than 7 dB of gain at 96 GHz with good power densities of better than 3.7 mW/μm2. For a 4-finger transistor, fT and fmax reduce to 302/325 GHz while doubling the power. W-band amplifiers based on a single 2-finger transistor have reached a saturated output power of 14.8 dBm at 77 GHz with more than 10 dB return loss on input and output. The results confirm that the transistors are suitable for compact circuit design with minimum inter-stage matching.
    Microwave Integrated Circuits Conference (EuMIC), 2012 7th European; 01/2012
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    ABSTRACT: Reliability tests for wavelength-stabilized compact diode laser systems emitting at 671 nm are presented. The devices were mounted on microoptical benches with the dimensions of 13 mm $\times\,$4 mm. Reflecting Bragg gratings were used for wavelength stabilization and emission width narrowing. The reliability tests were performed at 25$^{\circ}{\rm C}$ and at an output power up to 10 mW per micrometer stripe width of the gain medium. Reliable operation could be demonstrated over a test time up to 14500 h at an output power up to 1.0 W. Environmental tests using random vibrations with acceleration up to 29 g were performed without deterioration of the devices.
    IEEE Transactions on Components, Packaging, and Manufacturing Technology 01/2012; 2(1). · 1.26 Impact Factor
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    ABSTRACT: GaN-based heterostructure lateral Schottky barrier diodes (SBDs) grown on $n$-SiC substrate are investigated in this letter. These SBDs own very low onset voltage $V_{F} = \hbox{0.43}\ \hbox{V}$, high reverse blocking $V_{\rm BR} > \hbox{1000}\ \hbox{V}$, very low capacitive charge of 0.213 nC/A, and a very fast recovery time of 10 ps. These unique qualities are achieved by combining lateral topology, GaN:C back-barrier epitaxial structure, fully recessed Schottky anode $(\phi_{B} = \hbox{0.43}\ \hbox{eV})$, and slanted anode field plate in a robust and innovative process. Diode operation at elevated temperature up to 200 $^{\circ}\hbox{C}$ was also characterized.
    IEEE Electron Device Letters 01/2012; 33(3):357-359. · 2.79 Impact Factor
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    ABSTRACT: In the development process towards an integration of laser systems into compact modules many key points can be simulated. Yet, a reliable and stable testing environment is needed for a deeper understanding of the system. We present the micro optical bench (MiOB) as an advanced platform for the hybrid micro integration of active and passive optical elements. The modular yet robust design enables the precise mounting of those elements with an accuracy of better than 1 μm. By examples of second harmonic generation, master oscillator power amplifier and external cavity diode laser modules a wide range of applications are addressed. Each module is used to highlight different aspects of the MiOB. Examples are the thermal design of the MiOB that allows the precise heating of selected components without influencing others, the robustness that can withstand different mechanical tests, and the overall stiffness that allows the high precision mounting of volume holographic Bragg gratings.
    Electronic Components and Technology Conference (ECTC), 2012 IEEE 62nd; 01/2012
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    ABSTRACT: This paper reports results on a transferred-substrate InP heterojunction bipolar-transistor technology for high-frequency power stages. The basic building block is a 2-finger transistor with fT and fmax values of 376 GHz and 385 GHz, respectively, at an emitter size of 0.8 × 5 μm2. The transistors demonstrate more than 7 dB of gain at 96 GHz with good power densities of better than 3.7 mW/μm2. For a 4-finger transistor, fT and fmax reduce to 302/325 GHz while doubling the power. W-band amplifiers based on a single 2-finger transistor have reached a saturated output power of 14.8 dBm at 77 GHz with more than 10 dB return loss on input and output. The results confirm that the transistors are suitable for compact circuit design with minimum inter-stage matching.
    Microwave Conference (EuMC), 2012 42nd European; 01/2012
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    ABSTRACT: In this letter, we demonstrate how the coupling efficiency of a tapered diode laser (TPL) into a single-mode fiber under specified conditions can be predicted from measured Wigner distribution functions (WDFs). The WDFs were measured with a simple setup similar to the method of measuring the beam propagation ratio $M^{2}$ as specified in the ISO standard 11146. We used the measured WDFs to predict the coupling efficiencies of the beam into a single-mode fiber by using a predefined and well-known optical system. We then realized the fiber coupling and compared the measured coupling efficiencies to the predicted values. For this comparison we used the beam of a distributed Bragg reflector TPL which emits a fairly complex and structured beam. The predictions fitted the experimental result with relative deviations below 10%.
    IEEE Photonics Technology Letters 01/2012; 24(14):1248-1250. · 2.04 Impact Factor
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    ABSTRACT: We present a micro-integrated master-oscillator-power-amplifier diode laser system with more than 1W output power at 780.2 nm and narrow linewidth emission. The laser is designed for Rubidium Bose-Einstein condensate experiments in space.
    Lasers and Electro-Optics (CLEO), 2012 Conference on; 01/2012
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    ABSTRACT: A truncated tapered semiconductor amplifier in a master oscillator-power amplifier configuration is shown to deliver 56W output power at 970nm under quasi-cw conditions, with reasonable beam quality M2(1/e2)=21. Narrow spectral width (42pm) operation is confirmed.
    IEEE Photonics Conf. 10/2011;
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    ABSTRACT: We present a micro-integrated, high power, narrow linewidth extended cavity diode laser (ECDL) for precision quantum optics experiments at 780 nm onboard a sounding rocket. Although micro-integrated ECDL is based on a Littrow configuration, it features an excellent mechanical stability because any moveable parts were omitted. It provides an overall tuneability of 40 GHz and a continuous tuneability of 4 GHz. We have demonstrated a maximum output power of more than 120 mW, an intrinsic linewidth of approximately 3.6 kHz full-width- at-half-maximum (FWHM) at an output power of 62 mW and less than 50 kHz FWHM short term (10 µs) linewidth including technical noise. An upgraded version will provide an overall tuneability of 100 GHz and continous tuneability in excess of 20 GHz.
    01/2011;
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    ABSTRACT: The authors present a micro-integrated MOPA concept (footprint: 10 x 50 mm2) which uses a micro-isolator to suppress optical feedback. The oscillator is optimized for narrow linewidth operation and consists of a distributed Bragg reflector laser with a length of 4 mm (cavity: 3 mm, grating 1 mm). The reflectivity of the grating is estimated to be 60% and the front facet reflectivity is 30%. The amplifier consists of a 2 mm long ridge-waveguide pre-amplifier section and a 2 mm long tapered section.
    01/2011;