G. Trankle

Ferdinand-Braun-Institut, Berlín, Berlin, Germany

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Publications (165)181.16 Total impact

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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 08/2014; 116(6):063103-063103-14. DOI:10.1063/1.4892567 · 2.19 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 06/2014; 26(11):1120-1123. DOI:10.1109/LPT.2014.2314140 · 2.18 Impact Factor
  • IEEE Journal of Selected Topics in Quantum Electronics 01/2014; 20(1):1-1. DOI:10.1109/JSTQE.2013.2289943 · 3.47 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 09/2013; 114(11):113102-113102-9. DOI:10.1063/1.4821064 · 2.19 Impact Factor
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    ABSTRACT: We discuss two different implementations of field-effect-transistor based detectors (TeraFETs) optimised for imaging above 1 terahertz (THz). (i) Resonant-antenna-coupled MOSFET rectifiers have been fabricated using CMOS technology and (ii) broad-band devices by exploting GaN/AlGaN high-electron-mobilitiy transistors. Both technologies are scalable to large detector arrays and allow realisation of sensitive detectors deep in the THz frequency range.
    2013 6th UK, Europe, China Millimeter Waves and THz Technology Workshop (UCMMT); 09/2013
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    ABSTRACT: form only given. High-power diode lasers capable of generating spectrally stable and nearly diffraction-limited optical pulses in the nanosecond range can be used in a variety of applications including free-space communications, metrology, material processing and frequency doubling. Especially nanosecond laser systems emitting more than 10 W optical peak power are of potential interest for differential absorption light detection and ranging of atmospheric species (DIAL). Due to the pressure broadening of the absorption lines a spectral line width below 0.01 nm together with excellent wavelength stability is necessary. MOPA systems where a distributed Bragg reflector (DBR), a distributed feedback (DFB), or an external cavity diode laser (ECDL) acting as master oscillator (MO) and a tapered amplifier as power amplifier (PA) have promising characteristics. They combine the narrow spectral line width and the wavelength stability of the MOs with high output power of the PA.In this work a hybrid ns-MOPA system comprising a 1064 nm DFB laser operated in CW mode as a master oscillator (MO) and a multi-section power amplifier for pulse generation and amplification will be presented (see Fig. 1). The power amplifier is based on an InGaAs triple quantum well embedded in asymmetric AlGaAs based super large optical cavity with a narrow vertical divergence of about 15° (FWHM). The total length is 6 mm. The facets of the amplifier were both anti-reflection coated with a reflectivity R <; 5x10-4. The device was mounted p-side up on a C-mount and operated at a heat sink temperature of 25°C. The amplifier consists of three ridge-waveguide (RW) sections and one tapered section. The three RW sections are in total 2 mm long and have a ridge with a width of 5 μm. One RW section is driven pulsed to modulate the transparency [1] with a pulse width Pulse <; 4 ns and gate optical pulses from the CW input signal. The other two RW sections have a length- of 500 μm each and were operated near transparency to avoid unwanted feedback effects. The tapered section is also excited with current pulses to decrease the ASE between the generated optical pulses. Current pulses up to 20 A with a width of 6 ns and a repetition frequency of 800 kHz are applied. Fig. 2 shows the temporal shape of the generated optical pulses at a delay time of 3 ns between amplifier pulse and gate pulse at 13.5 A pulse peak current. The optical pulse has a pulse width of 3 ns and a pronounced plateau with a power amplitude of 12.5 W. The rise and fall times are 0.4 ns and 0.7 ns, respectively. ASE is only generated at the beginning and the end of the amplifier pulse and is <; 5%. Dependent on the length of the pulses optical peak powers up to 16 W were observed. In best cases the ASE power amounts are less than 1 % in comparison to the laser power. The dependence of the pulse shape and the ASE on the delay time Delay between the pulses injected into the RW and tapered sections and the physics behind them will be discussed in detail at the conference. The peak wavelength of = 1063.075 nm and the measured spectral line width (FWHM) of 10 pm given by the resolution limit of the spectrometer coincide for the DFB laser and the MOPA. The DFB laser has a side mode suppression ration (SMSR) of 52 dB whereas the SMSR of the MOPA is deteriorated to 42 dB indicating the ASE contribution. In Fig. 3 a spectral map in the amplifier current range between 3 A and 15 A is shown. A stable wavelength in the pulse peak power range up to 16 W is reached. In comparison to monolithic lasers no variation of the emission wavelength and linewidth of the laser emission occur with increasing pulse power, which allows the application of the system for the measurements of absorption lines of molecular species under atmospheric conditions. No saturation of the output power was observed, so a further increase of the output power seems to be possible with current pul
    2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC; 05/2013
  • ECS Transactions 03/2013; 52(1):979-989. DOI:10.1149/05201.0979ecst
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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: 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 07/2012; 24(14):1248-1250. DOI:10.1109/LPT.2012.2199746 · 2.18 Impact Factor
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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 05/2012; 48(5):568-575. DOI:10.1109/JQE.2012.2184526 · 2.11 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 03/2012; 33(3):357-359. DOI:10.1109/LED.2011.2179281 · 3.02 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: 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). DOI:10.1109/TCPMT.2011.2171342 · 1.24 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: 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 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: 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.
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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.

Publication Stats

1k Citations
181.16 Total Impact Points


  • 1997–2013
    • Ferdinand-Braun-Institut
      • Department of Optoelectronics
      Berlín, Berlin, Germany
  • 2009
    • Technische Universität Berlin
      • Department of solid state Physics
      Berlin, Land Berlin, Germany
  • 2007–2008
    • Ruhr-Universität Bochum
      Bochum, North Rhine-Westphalia, Germany
  • 1994–1998
    • Ludwig-Maximilian-University of Munich
      • Center for Nanoscience (CeNS)
      München, Bavaria, Germany
  • 1992–1998
    • Technische Universität München
      • Walter Schottky Institut (WSI)
      München, Bavaria, Germany
  • 1996
    • Fraunhofer Institute for Applied Solid State Physics IAF
      Freiburg, Baden-Württemberg, Germany
  • 1995
    • Universitätsklinikum Erlangen
      Erlangen, Bavaria, Germany