Simon Lotz

@article{Lotz:24,
author = {Simon Lotz and Madita G\"{o}b and Sven B\"{o}ttger and Linh Ha-Wissel and Jennifer Hundt and Floris Ernst and Robert Huber},
journal = {Biomed. Opt. Express},
keywords = {Angiography; Biomedical imaging; In vivo imaging; Machine vision; Point clouds; Spectral domain optical coherence tomography},
number = {6},
pages = {3993--4009},
publisher = {Optica Publishing Group},
title = {Large area robotically assisted optical coherence tomography (LARA-OCT)},
volume = {15},
month = {Jun},
year = {2024},
url = {https://opg.optica.org/boe/abstract.cfm?URI=boe-15-6-3993},
doi = {10.1364/BOE.525524},
abstract = {We demonstrate large-area robotically assisted optical coherence tomography (LARA-OCT), utilizing a seven-degree-of-freedom robotic arm in conjunction with a 3.3\&\#x2005;MHz swept-source OCT to raster scan samples of arbitrary shape. By combining multiple fields of view (FOV), LARA-OCT can probe a much larger area than conventional OCT. Also, nonplanar and curved surfaces like skin on arms and legs can be probed. The lenses in the LARA-OCT scanner with their normal FOV can have fewer aberrations and less complex optics compared to a single wide field design. This may be especially critical for high resolution scans. We directly use our fast MHz-OCT for tracking and stitching, making additional machine vision systems like cameras, positioning, tracking or navigation devices obsolete. This also eliminates the need for complex coordinate system registration between OCT and the machine vision system. We implemented a real time probe-to-surface control that maintains the probe alignment orthogonal to the sample by only using surface information from the OCT images. We present OCT data sets with volume sizes of 140\&\#x2009;\&\#x00D7;\&\#x2009;170\&\#x2009;\&\#x00D7;\&\#x2009;20 mm3, captured in 2.5 minutes.},
}

@article{RN5474,
   author = {Schulte, Berenice;Göb, Madita;Singh, Awanish Pratap;Lotz, Simon;Draxinger, Wolfgang;Heimke, Marvin;pieper, Mario;Heinze, Tillmann;Wedel, Thilo;Rahlves, Maik;Huber, Robert and Ellrichmann, Mark},
   title = {High-resolution rectoscopy using MHz optical coherence tomography: a step towards real time 3D endoscopy},
   journal = {Scientific Reports},
   volume = {14},
   number = {1},
   pages = {4672},
   ISSN = {2045-2322},
   DOI = {10.1038/s41598-024-55338-5},
   url = {https://doi.org/10.1038/s41598-024-55338-5},
   year = {2024},
   type = {Journal Article}
}

@Article{Schulte2024,
author={Schulte, B.; Burhan, S.; Singh, A. P.; Draxinger, W.; Lotz, S.; Heimke, M.; Heinze, T.; Wedel, T.; Rahlves, M.; Huber, R.; Ellrichmann, M.},
title={Hochaufl{\"o}sende Rektoskopie mittels dual-mode MHz optischer Koh{\"a}renztomographie -- ein Schritt zur real time 3D Endoskopie},
journal={Z Gastroenterol},
year={2024},
month={Sep},
day={26},
publisher={Georg Thieme Verlag KG},
volume={62},
number={09},
pages={KV 355},
issn={0044-2771},
doi={10.1055/s-0044-1790019},
url={http://www.thieme-connect.com/products/ejournals/abstract/10.1055/s-0044-1790019},
url={https://doi.org/10.1055/s-0044-1790019},
language={DE}
}

@article{Klufts:23,
author = {Marie Klufts and Alejandro Martinez Jimenez and Simon Lotz and Muhammad Asim Bashir and Tom Pfeiffer and Alexander Mlynek and Wolfgang Wieser and Alexander Chamorovskiy and Adrian Bradu and Adrian Podoleanu and Robert Huber},
journal = {Biomed. Opt. Express},
keywords = {Analog to digital converters; Laser beams; Laser imaging; Laser modes; Point spread function; Vertical cavity surface emitting lasers},
number = {12},
pages = {6493--6508},
publisher = {Optica Publishing Group},
title = {828 kHz retinal imaging with an 840\&\#x2005;nm Fourier domain mode locked laser},
volume = {14},
month = {Dec},
year = {2023},
url = {https://opg.optica.org/boe/abstract.cfm?URI=boe-14-12-6493},
abstract = {This paper presents a Fourier domain mode locked (FDML) laser centered around 840 nm. It features a bidirectional sweep repetition rate of 828 kHz and a spectral bandwidth of 40 nm. An axial resolution of ∼9.9 µm in water and a 1.4 cm sensitivity roll-off are achieved. Utilizing a complex master-slave (CMS) recalibration method and due to a sufficiently high sensitivity of 84.6 dB, retinal layers of the human eye in-vivo can be resolved during optical coherence tomography (OCT) examination. The developed FDML laser enables acquisition rates of 3D-volumes with a size of 200 × 100 × 256 voxels in under 100 milliseconds. Detailed information on the FDML implementation, its challenging design tasks, and OCT images obtained with the laser are presented in this paper.},
}

@inproceedings{10.1117/12.2670950,
author = {Madita G{\"o}b and Simon Lotz and Linh Ha-Wissel and Sazgar Burhan and Sven B{\"o}ttger and Floris Ernst and Jennifer Hundt and Robert Huber},
title = {{Advances in large area robotically assisted OCT (LARA-OCT): towards drive-by continuous motion imaging}},
volume = {12632},
booktitle = {Optical Coherence Imaging Techniques and Imaging in Scattering Media V},
editor = {Benjamin J. Vakoc and Maciej Wojtkowski and Yoshiaki Yasuno},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {126321N},
abstract = {Optical coherence tomography is a powerful imaging technique to visualize and localize depth-dependent tissue structure to differentiate between healthy and pathological conditions. However, conventional OCT systems are only capable of detecting small areas. To overcome this limitation, we have developed a large area robotically assisted OCT (LARA-OCT) system for automatic acquisition of large OCT images. Using mosaic pattern acquisition and subsequent stitching, we previously demonstrated initial in vivo OCT skin images beyond 10 cm². To improve acquisition speed and reduce dead times, we here demonstrate and analyze LARA-OCT with a new drive-by continuous motion imaging protocol.},
keywords = {Optical Coherence Tomography, Fourier Domain Mode Locking, Robotically Assisted Imaging Systems, Three-dimensional image acquisition, Large Area Scanning, Skin Imaging, OCT, FDML},
year = {2023},
doi = {10.1117/12.2670950},
URL = {https://doi.org/10.1117/12.2670950}
}

@INPROCEEDINGS{10232019,
  author={Klufts, M. and Lotz, S. and Bashir, M. A. and Pfeiffer, T. and Mlynek, A. and Wieser, W. and Chamorovskiy, A. and Shidlovski, V. and Podoleanu, A. and Huber, R.},
  booktitle={2023 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)}, 
  title={Dual Amplification 850 nm FDML Laser}, 
  year={2023},
  volume={},
  number={},
  pages={1-1},
  doi={10.1109/CLEO/Europe-EQEC57999.2023.10232019}}

@INPROCEEDINGS{10232141,
  author={Lamminger, Philipp and Hakert, Hubertus and Lotz, Simon and Kolb, Jan Philip and Kutscher, Tonio and Karpf, Sebastian and Huber, Robert},
  booktitle={2023 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)}, 
  title={Four-Wave Mixing Fast Wavelength Sweeping FDML Laser with kW Peak Power at 900 nm and 1300 nm}, 
  year={2023},
  volume={},
  number={},
  pages={1-1},
  doi={10.1109/CLEO/Europe-EQEC57999.2023.10232141}}

@INPROCEEDINGS{10231419,
  author={Lotz, Simon and Göb, Madita and Draxinger, Wolfgang and Dick, Anneli and Huber, Robert},
  booktitle={2023 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)}, 
  title={13.4 MHz FDML Laser for Intra-Surgical Optical Coherence Tomography}, 
  year={2023},
  volume={},
  number={},
  pages={1-1},
  doi={10.1109/CLEO/Europe-EQEC57999.2023.10231419}}

@INPROCEEDINGS{10232661,
  author={Bashir, M. A. and Lotz, S. and Kluftsa, M. and Jirauschek, C. and Huberab, R.},
  booktitle={2023 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)}, 
  title={1190 nm FDML laser: Challenges and Strategies}, 
  year={2023},
  volume={},
  number={},
  pages={1-1},
  doi={10.1109/CLEO/Europe-EQEC57999.2023.10232661}}

@article{Lamminger:23,
author = {Philipp Lamminger and Hubertus Hakert and Simon Lotz and Jan Philip Kolb and Tonio Kutscher and Sebastian Karpf and Robert Huber},
journal = {Opt. Lett.},
keywords = {Green fluorescent protein; Laser beam combining; Laser crystals; Laser imaging; Optical amplifiers; Photonic crystal lasers},
number = {14},
pages = {3713--3716},
publisher = {Optica Publishing Group},
title = {Four-wave mixing seeded by a rapid wavelength-sweeping FDML laser for nonlinear imaging at 900 nm and 1300 nm},
volume = {48},
month = {Jul},
year = {2023},
url = {https://opg.optica.org/ol/abstract.cfm?URI=ol-48-14-3713},
doi = {10.1364/OL.488181},
abstract = {Four-wave mixing (FWM) enables the generation and amplification of light in spectral regions where suitable fiber gain media are unavailable. The 1300 nm and 900 nm regions are of especially high interest for time-encoded (TICO) stimulated Raman scattering microscopy and spectro-temporal laser imaging by diffracted excitation (SLIDE) two-photon microscopy. We present a new, to the best of our knowledge, FWM setup where we shift the power of a home-built fully fiber-based master oscillator power amplifier (MOPA) at 1064 nm to the 1300-nm region of a rapidly wavelength-sweeping Fourier domain mode-locked (FDML) laser in a photonic crystal fiber (PCF) creating pulses in the 900-nm region. The resulting 900-nm light can be wavelength swept over 54 nm and has up to 2.5 kW (0.2 {\textmu}J) peak power and a narrow instantaneous spectral linewidth of 70 pm. The arbitrary pulse patterns of the MOPA and the fast wavelength tuning of the FDML laser (419 kHz) allow it to rapidly tune the FWM light enabling new and faster TICO-Raman microscopy, SLIDE imaging, and other applications.},
}

@inproceedings{10.1117/12.2649646,
author = {M. Klufts and S. Lotz and M. A. Bashir and T. Pfeiffer and A. Mlynek and W. Wieser and A. Chamorovskiy and V. Shidlovski and R. Huber},
title = {{850 nm FDML: performance and challenges}},
volume = {12367},
booktitle = {Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXVII},
editor = {Joseph A. Izatt and James G. Fujimoto},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {1236705},
abstract = {We demonstrate a Fourier domain mode locked (FDML) laser centered around 850 nm with a sweeping range of 50 nm, a fundamental repetition rate of 2×416 kHz and an output power of 2 mW. A new cavity design using three chirped Fiber Bragg gratings is required to overcome sweeping limitations caused by high dispersion. Other solutions to address challenges such as high loss and high polarization mode dispersion will be discussed along with performance. A main application of this laser will be retinal imaging, but it might also be applicable for TiCo-Raman and SLIDE microscopy. },
keywords = {Swept source, FDML, Laser, Ophthalmic imaging, OCT, 800 nm, retinal imaging, light sources},
year = {2023},
doi = {10.1117/12.2649646},
URL = {https://doi.org/10.1117/12.2649646}
}

@inproceedings{10.1117/12.2649663,
author = {Philipp Lamminger and Hubertus Hakert and Simon Lotz and Jan Philip Kolb and Tonio Kutscher and Sebastian Karpf and Robert Huber},
title = {{900 nm swept source FDML laser with kW peak power}},
volume = {12400},
booktitle = {Fiber Lasers XX: Technology and Systems},
editor = {V.  R. Supradeepa},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {124001I},
abstract = {A wavelength agile 900 nm 2.5 kW peak power fiber laser is created by four-wave mixing (FWM) in a photonic crystal fiber (PCF), while amplifying a 1300 nm Fourier-domain mode-locked (FDML) laser. The FWM process is pumped by a home-built 1064 nm master oscillator power amplifier (MOPA) laser and seeded by a home-built 1300 nm FDML laser, generating high power pulses at wavelengths, where amplification by active fiber media is difficult. The 900 nm pulses have a spectral linewidth of 70 pm, are tunable over 54 nm and have electronic pulse-to-pulse tuning capability. These pulses can be used for nonlinear imaging like two-photon or coherent anti-Stokes Raman microscopy (CARS) microscopy including spectro-temporal laser imaging by diffracted excitation (SLIDE) and time-encoded (Tico) stimulated Raman microscopy.},
keywords = {Fourier domain mode locking,  FDML, Raman, two photon microscopy, SLIDE, 900 nm, fiber laser, photonic crystal fiber, swept source},
year = {2023},
doi = {10.1117/12.2649663},
URL = {https://doi.org/10.1117/12.2649663}
}

@inproceedings{10.1117/12.2652884,
author = {M. A. Bashir and S. Lotz and M. Klufts and I. Krestnikov and C. Jirauschek and R. Huber},
title = {{1190 nm Fourier domain mode locked (FDML) laser for optical coherence tomography (OCT)}},
volume = {12367},
booktitle = {Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXVII},
editor = {Joseph A. Izatt and James G. Fujimoto},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {1236707},
abstract = {We demonstrate a Fourier domain mode locked (FDML) laser centered at 1190 nm with 2×410 kHz sweep repetition rate, a sweeping range of 100 nm and 2.5 mW output power. The laser is based on a quantum dot-semiconductor optical amplifier with small linewidth enhancement factor. The laser could be used as a probe laser in stimulated Raman scattering microscopy and it may be attractive for optical coherence tomography due to low water absorption and the spectral signature of lipids around 1200nm. Moreover, it is ideal to close the gap between FDML lasers at 1064 nm and 1300 nm. Combining these three lasers can enable ultrawideband sweeping to improve the axial OCT resolution down to 2 μm. },
keywords = {FDML, Swept source, laser, SS-OCT, OCT, Tunable lasers},
year = {2023},
doi = {10.1117/12.2652884},
URL = {https://doi.org/10.1117/12.2652884}
}

@inproceedings{10.1117/12.2652616,
author = {Madita G{\"o}b and Simon Lotz and Linh Ha-Wissel and Sazgar Burhan and Sven B{\"o}ttger and Floris Ernst and Jennifer Hundt and Robert Huber},
title = {{Large area robotically assisted optical coherence tomography (LARA-OCT) for skin imaging with MHz-OCT surface tracking}},
volume = {12367},
booktitle = {Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXVII},
editor = {Joseph A. Izatt and James G. Fujimoto},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {123670C},
abstract = {Optical coherence tomography (OCT) is a powerful imaging technique to non-invasively differentiate between healthy skin and pathological conditions. Unfortunately, commercially available OCT-systems are typically slow and not capable of scanning large areas at reasonable speed. Since skin lesions may extend over several square centimeters, potential inflammatory infiltrates remain undetected. Here, we present large area robotically assisted OCT (LARA-OCT) for skin imaging. Therefor a collaborative robot is combined with an existing, home-built 3.3 MHz-OCT-system and for surface tracking an online probe-to-surface control is implemented which is solely based on the OCT surface signal. It features a combined surface-distance and surface-orientation closed-loop control algorithm, which enables automatic positioning and alignment of the probe across the target while imaging. This allows to acquire coherent OCT images of skin areas beyond 10 cm<sup>2</sup>. },
keywords = {Optical Coherence Tomography, Fourier Domain Mode Locking, Robotically Assisted Imaging Systems, Three-dimensional image acquisition, Large Area Scanning, Skin Imaging , OCT, FDML},
year = {2023},
doi = {10.1117/12.2652616},
URL = {https://doi.org/10.1117/12.2652616}
}

@inproceedings{10.1117/12.2612171,
author = {Madita G{\"o}b and Sazgar Burhan and Simon Lotz and Robert Huber},
title = {{Towards ultra-large area vascular contrast skin imaging using multi-MHz-OCT}},
volume = {11948},
booktitle = {Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXVI},
editor = {Joseph A. Izatt and James G. Fujimoto},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {1194807},
abstract = {We demonstrate ultra-large field of view OCT scanning using standard optics, a X-Y-galvanometer scanner and a synchronously driven motorized XYZ-positioning stage. The integration of a movable stage into our self-built 3.3 MHz- OCT system allows acquiring coherent ultra-large area images, fully leveraging the high speed potential of our system. For fast OCT-angiography, one galvanometer axis scanner is driven in a repetitive sawtooth pattern, fully synchronized to the movement of the linear stage, to obtain multiple measurements at each position. This technique requires exact synchronization, precise repositioning, and uniform movements with low tolerances to ensure a minimum revisitation error. We analyze error and performance of our setup and demonstrate angiographic imaging.},
keywords = {Optical Coherence Tomography, Fourier Domain Mode Locking, FDML, Optical Coherence Angiography, OCTA, Medical optics and biotechnology, Medical imaging, Three-dimensional image acquisition, Scanners, Microscopy},
year = {2022},
doi = {10.1117/12.2612171},
URL = {https://doi.org/10.1117/12.2612171}
}

@inproceedings{10.1117/12.2608773,
author = {M. Klufts and S. Lotz and M. Bashir and S. Karpf and R. Huber},
title = {{Ultra-high-accuracy chromatic dispersion measurement in optical fibers}},
volume = {11997},
booktitle = {Optical Components and Materials XIX},
editor = {Shibin Jiang and Michel J. F. Digonnet},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {119970L},
abstract = {The chromatic dispersion in optical fibers is a key property for applications where a broadband light source is used and the timing of each individual wavelength is crucial. Counteracting the timing offset introduced by the fiber is a challenge in many applications especially in mode locked lasers. The dispersion parameters need to be measured with high precision. The length of the fiber, the temperature, and the used wavelength will highly impact the amount of dispersion and the accuracy of the measurement. We developed an ultra-high-accuracy dispersion measurement setup at 1080 ± 50 nm considering all the parameters that may influence the measurement. It is based on a home-built wavelength tunable laser where the output is modulated by an electro-optical modulator connected to a 24 GSamples/s arbitrary waveform generator to a complex pattern consisting of pulses and a 4 GHz sine wave. After passing through the fiber the signal is measured with an 80 GSamples/s real time oscilloscope. The fiber’s temperature is controlled to allow for reproducible measurements over several days and we achieve timing measurement accuracies down to ~200 fs. We also present the performance of the setup at ~850 nm. We will discuss and quantify all effects which can negatively impact the system accuracy and we will report on more cost-effective options using lower performance equipment.},
keywords = {Dispersion measurement, Chromatic dispersion, fiber dispersion measurement, optical component characterization, tunable laser, FDML},
year = {2022},
doi = {10.1117/12.2608773},
URL = {https://doi.org/10.1117/12.2608773}
}

@article{Gob:22,
author = {Madita G\"{o}b and Tom Pfeiffer and Wolfgang Draxinger and Simon Lotz and Jan Philip Kolb and Robert Huber},
journal = {Biomed. Opt. Express},
keywords = {High speed imaging; Image processing; Image quality; In vivo imaging; Range imaging; Vertical cavity surface emitting lasers},
number = {2},
pages = {713--727},
publisher = {Optica Publishing Group},
title = {Continuous spectral zooming for in vivo live 4D-OCT with MHz A-scan rates and long coherence},
volume = {13},
month = {Feb},
year = {2022},
url = {https://opg.optica.org/boe/abstract.cfm?URI=boe-13-2-713},
doi = {10.1364/BOE.448353},
abstract = {We present continuous three-dimensional spectral zooming in live 4D-OCT using a home-built FDML based OCT system with 3.28 MHz A-scan rate. Improved coherence characteristics of the FDML laser allow for imaging ranges up to 10 cm. For the axial spectral zoom feature, we switch between high resolution and long imaging range by adjusting the sweep range of our laser. We present a new imaging setup allowing for synchronized adjustments of the imaging range and lateral field of view during live OCT imaging. For this, a novel inline recalibration algorithm was implemented that enables numerical k-linearization of the raw OCT fringes for every frame instead of every volume. This is realized by acquiring recalibration data within the dead time of the raster scan at the turning points of the fast axis scanner. We demonstrate in vivo OCT images of fingers and hands at different resolution modes and show real three-dimensional zooming during live 4D-OCT. A three-dimensional spectral zooming feature for live 4D-OCT is expected to be a useful tool for a wide range of biomedical, scientific and research applications, especially in OCT guided surgery.},
}

@INPROCEEDINGS{9542126,
  author={Grill, Christin and Lotz, Simon and Blömker, Torben and Schmidt, Mark and Draxinger, Wolfgang and Kolb, Jan Philip and Jirauschek, Christian and Huber, Robert},
  booktitle={2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)}, 
  title={Superposition of two independent FDML lasers}, 
  year={2021},
  volume={},
  number={},
  pages={1-1},
  abstract={Fourier domain mode locking (FDML) is a laser operating regime, which was developed in 2005 [1] . The output of this laser is a train of optical wavelength sweeps, equivalent to extremely chirped pulses with an optical bandwidth of up to 25 THz and frequency tuning rates of >10 19 Hz/s. This laser type was developed for optical coherence tomography [2] , but found recently more and more applications like LiDAR [3] , Raman microscopy [4] or two-photon microscopy [5] . The laser’s coherence properties are relevant for a better understanding of the FDML laser itself and its applications. Because of the wide sweep range and high tuning rate, the laser linewidth cannot be measured with an RF spectrometer. Superposition with a narrowband continuous wave laser only yields phase information for small fractions of the sweep [6] . However, beat signal measurements between two independent FDML lasers with equal sweep range and direction can give information about the complete sweep.},
  keywords={},
  doi={10.1109/CLEO/Europe-EQEC52157.2021.9542126},
  ISSN={},
  month={June}
}

@inproceedings{Pfeiffer2021,
author = {T. Pfeiffer, T. Klein, A. Mlynek, W. Wieser, S. Lotz, C. Grill and R. Huber},
title = {{High finesse tunable Fabry-Perot filters in Fourier-domain modelocked lasers}},
volume = {11630},
booktitle = {Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXV},
editor = {Joseph A. Izatt and James G. Fujimoto},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
abstract = {We demonstrate that the coherence roll-off and dynamic range of OCT systems using Fourier-domain mode-locked (FDML) lasers can be significantly improved by a fiber Fabry-Perot tunable filter (FFP-TF) with a finesse of more than 3000, a more than fivefold improvement over previous designs. In contrast to previous work, standard resampling using a pre-acquired signal (as in SD-OCT) with no k-clocking is sufficient for 20 nm and 100 nm sweep range, significantly reducing the system complexity. 3D-OCT imaging at 20 cm imaging range is demonstrated.},
keywords = {AG-Huber_FDML, AG-Huber_OCT, optical coherence tomography, FDML laser, swept source laser, high finesse, Fabry-Perot, MHz-OCT, OCT, tunable laser},
year = {2021},
URL = {hhttps://doi.org/10.1117/12.2583501}
}

@article{Lotz2021,
   author = {S. Lotz, C. Grill, M. Göb, W. Draxinger, J.P. Kolb and R. Huber},
   title = {Cavity length control for Fourier domain mode locked (FDML) lasers with µm precision},
   journal = {Biomedical Optics Express},
   volume = {12(5)},
   keywords={AG-Huber_FDML},
   pages = {2604-2616},
   url = {https://doi.org/10.1364/BOE.422898},
   year = {2021},
   type = {Journal Article}
}

@Article{Schmidt2021,
  author   = {M. Schmidt, C. Grill, S. Lotz, T. Pfeiffer, R. Hubert and C. Jirauschek},
  journal  = {Applied Physics B},
  title    = {Intensity pattern types in broadband Fourier domain mode-locked (FDML) lasers operating beyond the ultra-stable regime},
  year     = {2021},
  issn     = {1432-0649},
  number   = {5},
  pages    = {60},
  volume   = {127},
keywords={AG-Huber_FDML},
  abstract = {We report on the formation of various intensity pattern types in detuned Fourier domain mode-locked (FDML) lasers and identify the corresponding operating conditions. Such patterns are a result of the complex laser dynamics and serve as an ideal tool for the study of the underlying physical processes as well as for model verification. By numerical simulation we deduce that the formation of patterns is related to the spectral position of the instantaneous laser lineshape with respect to the transmission window of the swept bandpass filter. The spectral properties of the lineshape are determined by a long-term accumulation of phase-offsets, resulting in rapid high-amplitude intensity fluctuations in the time domain due to the narrow intra-cavity bandpass filter and the fast response time of the semiconductor optical amplifier gain medium. Furthermore, we present the distribution of the duration of dips in the intensity trace by running the laser in the regime in which dominantly dips form, and give insight into their evolution over a large number of roundtrips.},
  doi      = {10.1007/s00340-021-07600-1},
  refid    = {Schmidt2021},
}

@inproceedings{LotzLASE2021,
author = {S. Lotz, C. Grill, M. Göb, W. Draxinger, J. P. Kolb and R. Huber},
title = {{Characterization of the dynamics of an FDML laser during closed-loop cavity length control}},
volume = {11665},
booktitle = {Fiber Lasers XVIII: Technology and Systems},
editor = {Michalis N. Zervas},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {236 -- 241},
abstract = {In Fourier domain mode locked (FDML) lasers, extremely precise and stable matching of the filter tuning period and light circulation time in the cavity is essential for ultra-low noise operation. During the operation of FDML lasers, the ultra-low noise mode can be lost due to temperature drifts of the already temperature stabilized cavity resulting in increased intensity noise. Until now, the filter frequency is continuously regulated to match the changing light circulation time. However, this causes the filter frequency to constantly change by a few mHz and leads to synchronization issues in cases where a fixed filter frequency is desired. We present an actively cavity length controlled FDML laser and a robust and high precision feedback loop algorithm for maintaining ultra-low noise operation. Instead of adapting the filter frequency, the cavity length is adjusted by a motorized free space beam path to match the fixed filter frequency. The closed-loop system achieves a stability of ~0.18 mHz at a sweep repetition rate of ~418 kHz which corresponds to a ratio of 4×10<sup>-10</sup>. We investigate the coherence properties during the active cavity length adjustments and observe no noise increase compared to fixed cavity length. The cavity length control is fully functional and for the first time, offers the possibility to operate an FDML laser in sweet spot mode at a fixed frequency or phase locked to an external clock. This opens new possibilities for system integration of FDML lasers.},
keywords = {AG-Huber_FDML, FDML, Fourier domain mode locking, laser beating, tunable laser, optical coherence tomography, OCT},
year = {2021},
URL = {hhttps://doi.org/10.1117/12.2578514}
}

@inproceedings{Grill2020,
author = {C. {Grill}, S. {Lotz}, T. {Blömker}, D. {Kastner}, T. {Pfeiffer}, S. {Karpf}, M. {Schmidt}, W. {Draxinger}, C. 
 {Jirauschek} and R. {Huber}},
title = {{Beating of two FDML lasers in real time}},
volume = {11260},
booktitle = {Fiber Lasers XVII: Technology and Systems},
editor = {Liang Dong},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {132 -- 138},
keywords = {AG-Huber_FDML, FDML laser, fiber lasers, beat signal, OCT, Optical Coherence Tomography, Fourier domain mode locking},
year = {2020},
doi = {10.1117/12.2545794},

}