@article{Strenge-2022,
   author = {Strenge, P.;Lange, B.;Grill,C.;Danicke,V.;Theisen-Kunde, D.;Hagel, C.;Spahr-Hess, S.;;Bonsanto, Matteo M.;Handels, H.; and Huber, R.;Brinkmann, R.},
   title = {Differentiation of different stages of brain tumor infiltration using optical coherence tomography: Comparison of two systems and histology},
   journal = {Frontiers in Oncology},
Keywords = {AG-Huber_FDML, AG-Huber_OCT, brain, tumor, glioblastoma multiforme, OCT, neural network, attenuation (absorption)
coefficient, optical coherence tomography},
   DOI = {https://doi.org/10.3389/fonc.2022.896060},
   url = {https://www.frontiersin.org/articles/10.3389/fonc.2022.896060/full},
   year = {2022},
   type = {Journal Article}
}

@article{Grill2022,
  doi = {10.1038/s42005-022-00960-w},
  year = {2022},
  publisher = {Springer Science and Business Media {LLC}},
  volume = {{5}},
  number = {{1}},
  author = {C. Grill, T. Bl\"{o}mker, M. Schmidt, D. Kastner, T. Pfeiffer, J.P. Kolb, W. Draxinger, S. Karpf, C. Jirauschek and R. Huber},
  title = {Towards phase-stabilized Fourier domain mode-locked frequency combs},
  journal = {{Communications Physics}},
keywords={AG-Huber_FDML, FDML, Fourier domain mode locking, phase, frequency comb, coherence, beating}
}

@article{Strenge2022,
   author = {Strenge, P;Lange, B;Grill, C;Draxinger, W;Danicke, V;Theisen-Kunde, D;Hagel, C;Spahr-Hess, S;Bonsanto, Matteo M.;Huber, R;Handels, H and Brinkmann, R},
   title = {Registration of histological brain images onto optical coherence tomography images based on shape information},
keywords = {brain, glioblastoma multiforme, shape, OCT, optical coherence tomography, AG-Huber_OCT,},
   journal = {Physics in Medicine & Biology},
   ISSN = {0031-9155},
   url = {http://iopscience.iop.org/article/10.1088/1361-6560/ac6d9d},
   year = {2022},
   type = {Journal Article}
}

@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{Deen2022,
   author = {Deen, A D;Van Beusekom, H M. M.;Pfeiffer, T;Stam, M;Kleijn, D De;Wentzel, J;Huber, R;Van Der Steen, A F. W.;Soest, G Van and Wang, T},
   title = {Spectroscopic thermo-elastic optical coherence tomography for tissue characterization},
   journal = {BioOptExpr},
keywords = {AG-Huber, Endoscopic imaging, Image processing, Image quality, Imaging techniques, Optical imaging, Tissue characterization},
   volume = {13(3)},
   pages = {1430-1446},
   DOI = {10.1364/BOE.447911},
    year = {2022},
   type = {Journal Article}
}

@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.},
}

@article{Yashin-2022,
   author = {Yashin, K;Bonsanto, M M;Achkasova, K;Zolotova, A;Wael, Al-M;Kiseleva, E;Moiseev, A;Medyanik, I;Kravets, L;Huber, R;Brinkmann, R and Gladkova, N},
   title = {OCT-Guided Surgery for Gliomas: Current Concept and Future Perspectives},
   journal = {Diagnostics},
   volume = {12},
   number = {2},
   pages = {335},
   ISSN = {2075-4418},
keywords = {AG-Huber; optical coherence tomography; brain imaging; neurosurgical guidance; brain tumor; minimally invasive theranostics; intraoperative imaging},
   url = {https://www.mdpi.com/2075-4418/12/2/335},
   year = {2022},
   type = {Journal Article}
}

@inproceedings{Strenge:21,
author = {P. Strenge, B. Lange, C. Grill, W. Draxinger, V. Danicke, D. Theisen-Kunde, H. Handels, M. M. Bonsanto, C. Hagel, R. Huber and R. Brinkmann},
journal = {European Conferences on Biomedical Optics 2021 (ECBO)},
keywords = {AG-Huber_OCT; Absorption coefficient; Attenuation coefficient; Fourier domain mode locking; Multiple scattering; Optical coherence tomography; Spectral domain optical coherence tomography},
pages = {EW1C.7},
publisher = {Optical Society of America},
title = {Comparison of two optical coherence tomography systems to identify human brain tumor},
year = {2021},
url = {https://doi.org/10.1117/12.2616044},
abstract = {The identification of ex vivo brain tumor tissue was investigated with two different optical coherence tomography systems exploiting two optical parameters. The optical parameters were calculated from semantically labelled OCT B-scans.},
}

@inproceedings{Gob:21,
author = {Madita G\"{o}b and Sazgar Burhan and Wolfgang Draxinger and Jan Philip Kolb and Robert Huber},
booktitle = {European Conferences on Biomedical Optics 2021 (ECBO)},
journal = {European Conferences on Biomedical Optics 2021 (ECBO)},
keywords = {AG-Huber_OCT;Fourier domain mode locking; Image processing; Image quality; Optical coherence tomography; Temporal resolution; Three dimensional imaging},
pages = {EW3C.4},
publisher = {Optical Society of America},
title = {Towards densely sampled ultra-large area multi-MHz-OCT for in vivo skin measurements beyond 1 cm$^2$/sec},
year = {2021},
url = {http://www.osapublishing.org/abstract.cfm?URI=ECBO-2021-EW3C.4},
abstract = {We demonstrate a 3.3 MHz A-scan rate OCT for rapid scanning of large areas of human skin. The mosaicking performance and different OCT imaging modalities including intervolume speckle contrast are evaluated.},
}

@inproceedings{Detrez:21,
author = {N. Detrez, K. Rewerts, M. Matthiae, S. Buschschlueter, M.M. Bonsanto, D. Theisen-Kunde and R. Brinkmann},
journal = {European Conferences on Biomedical Optics 2021 (ECBO)},
keywords = {AG-Huber_OCT},
pages = {EW4A.10},
publisher = {Optical Society of America},
title = {Flow Controlled Air Puff Generator Towards In Situ Brain Tumor Detection Based on MHz Optical Coherence Elastography},
year = {2021},
url = {https://doi.org/10.1117/12.2615022},
abstract = {A precision air puff excitation system for MHz Optical Coherence Elastography in neurosurgery was developed. It enables non-contact soft-tissue excitation down to {\textmu}N, with direct, noncontact force determination via gas flow measurement.},
}

@inproceedings{Rewerts2021ECBO,
author = {K. Rewerts, M. Matthiae, N. Detrez, S. Buschschlueter, M.M. Bonsanto, R. Huber and R. Brinkmann},
journal = {European Conferences on Biomedical Optics 2021 (ECBO)},
keywords = {AG-Huber_OCT},
pages = {ETh3A.3},
publisher = {Optical Society of America},
title = {Phase-Sensitive Optical Coherence Elastography with a 3.2 MHz FDML-Laser Using Focused Air-Puff Tissue Indentation},
year = {2021},
url = {http://www.osapublishing.org/abstract.cfm?URI=ECBO-2021-ETh3A.3},
abstract = {Tumor discrimination from healthy tissue is often performed by haptically probing tissue elasticity. We demonstrate non-contact elastography using air-puff excitation and tissue indentation measurement by phase-sensitive OCT with a 3.2 MHz FDML-laser.},
}

@article{Hakert2021,
   author = {H. Hakert, M. Eibl, M. Tillich, R.Pries, G. Hüttmann, R. Brinkmann, B. Wollenberg, K-L. Bruchhage, S. Karpf and R. Huber},
   title = {Time-encoded stimulated Raman scattering microscopy of tumorous human pharynx tissue in the fingerprint region from 1500–1800  cm-1},
   journal = {Optics Letters},
   volume = {46(14)},
   number = {14},
   pages = {3456-3459},
keywords = {AG-Huber_NL, Clinical applications, Master oscillator power amplifiers, Optical coherence tomography, Raman scattering, Stimulated Raman scattering, Stimulated scattering},
   DOI = {https://doi.org/10.1364/OL.424726},
   year = {2021},
   type = {Journal Article}
}

@article{PenateMedina2021,
   author = {Peñate Medina, T;Kolb, J P;Hüttmann, G;Huber, R;Peñate Medina, O;Ha, L;Ulloa, P;Larsen, N;Ferrari, A;Rafecas, M;Ellrichmann, M;Pravdivtseva, M S.;Anikeeva, M;Humbert, J;Both, M;Hundt, J E. and Hövener, J-B},
   title = {Imaging Inflammation - From Whole Body Imaging to Cellular Resolution},
   journal = {Frontiers in immunology},
keywords = {AG-Huber, MRI, PET, SPECT, optical imaging, Optical coherence tomography (OCT), precision medicine, Two-Photon microscopy (TPM), hyperpolarization},
   volume = {12},
   pages = {692222-692222},
   ISSN = {1664-3224},
   DOI = {10.3389/fimmu.2021.692222},
   url = {https://pubmed.ncbi.nlm.nih.gov/34248987
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8264453/},
   year = {2021},
   type = {Journal Article}
}

@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{Gottschall2021,
   author = {T. Gottschall, T. Meyer-Zedler, M. Schmitt, R. Huber, J. Popp, A. Tünnermann and J. Limpert},
   title = {Ultra-compact tunable fiber laser for coherent anti-Stokes Raman imaging},
   journal = {JRS},
  keywords = { AG-Huber_NL, coherent anti-Stokes Raman scattering microscopy, four-wave mixing, nonlinear
microscopy, ultrafast laser},
   ISSN = {0377-0486},   
   url = {https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/abs/10.1002/jrs.6171},
   year = {2021},
   type = {Journal Article}
}

@inproceedings{Strenge2021A,
author = {P. Strenge, B. Lange, C. Grill, W. Draxinger, V. Danicke, D. Theisen-Kunde, H. Handels, M. Bonsanto, C. Hagel, R. Huber and R. Brinkmann},
title = {{Characterization of brain tumor tissue with 1310 nm optical coherence tomography}},
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},
pages = {74 -- 80},
abstract = {The separation of tumorous brain tissue and healthy brain tissue is still a big challenge in the field of neurosurgery, especially when it comes to the detection of different infiltration grades of glioblastoma multiforme at the tumor border. On the basis of a recently created labelled OCT dataset of ex vivo glioblastoma multiforme tumor samples the detection of brain tumor tissue and the identification of zones with varying degrees of infiltration of tumor cells was investigated. The identification was based on the optical properties, which were extracted by an exponential fit function. The results showed that a separation of tumorous tissue and healthy white matter based on these optical properties is possible. A support vector machine was trained on the optical properties to separate tumor from healthy white matter tissue, which achieved a sensitivity of 91% and a specificity of 76% on an independent training dataset.},
keywords = {AG-Huber_OCT, optical coherence tomography, OCT, glioblastoma multiforme, MHz-OCT, brain imaging, tumor, neurosurgery},
year = {2021},
URL = {hhttps://doi.org/10.1117/12.2578409}
}

@inproceedings{Strenge2021,
author = {P. Strenge, B. Lange, C. Grill, W. Draxinger, V. Danicke, D. Theisen-Kunde, H. Handels, C. Hagel, M. Bonsanto, R. Huber and R. Brinkmann},
title = {{Creating a depth-resolved OCT-dataset for supervised classification based on ex vivo human brain samples}},
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},
pages = {66 -- 73},
abstract = {Optical coherence tomography (OCT) has the potential to become an additional imaging modality for surgical guidance in the field of neurosurgery, especially when it comes to the detection of different infiltration grades of glioblastoma multiforme at the tumor border. Interpretation of the images, however, is still a big challenge. A method to create a labeled OCT dataset based on ex vivo brain samples is introduced. The tissue samples were embedded in an agarose mold giving them a distinctive shape before images were acquired with two OCT systems (spectral domain (SD) and swept source (SS) OCT) and histological sections were created and segmented by a neuropathologist. Based on the given shape, the corresponding OCT images for each histological image can be determined. The transfer of the labels from the histological images onto the OCT images was done with a non-affine image registration approach based on the tissue shape. It was demonstrated that finding OCT images of a tissue sample corresponding to segmented histological images without any color or laser marking is possible. It was also shown that the set labels can be transferred onto OCT images. The accuracy of method is 26 ± 11 pixel, which translates to 192 ± 75 μm for the SS-OCT and 94 ± 43 μm for the SD-OCT. The dataset consists of several hundred labeled OCT images, which can be used to train a classification algorithm.},
keywords = {AG-Huber_OCT, optical coherence tomography, OCT, image registration, glioblastoma multiforme, MHz-OCT, brain imaging, tumor, neurosurgery},
year = {2021},
URL = {https://doi.org/10.1117/12.2578391}
}

@inproceedings{Grill2021,
author = {C. Grill, T. Blömker, M. Schmidt, D. Kastner, T. Pfeiffer, J.P. Kolb, W. Draxinger, S. Karpf, C. Jirauschek and R. Huber},
title = {{A detailed analysis of the coherence and field properties of an FDML laser by time resolved beat signal measurements}},
volume = {11665},
booktitle = {Fiber Lasers XVIII: Technology and Systems},
editor = {Michalis N. Zervas},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {242 -- 247},
keywords = {AG-Huber_FDML, Fourier domain mode locking, FDML laser, laser beating , tunable laser, optical coherence tomography, OCT},
year = {2021},
URL = {hhttps://doi.org/10.1117/12.2578293}
}

@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}
}

@Conference{Lamminger2021,
  author    = {P. Lamminger, M. Loop, J. Klee, D. Weng, J.P. Kolb, M. Strauch, S. Karpf and R. Huber},
  booktitle = {Multimodal Biomedical Imaging XVI},
  title     = {Combination of two-photon microscopy and optical coherence tomography with fully fiber-based lasers for future endoscopic setups},
  year      = {2021},
  publisher = {SPIE},
  doi       = {10.1117/12.2578679},
  keywords  = {AG-Huber_NL, AG-Huber_OCT},
}

@inproceedings{RN5318,
   author = {Strauch, M;Kolb, J P;Draxinger, W;Popp, A-K;Wacker, M;Merg, N;Hundt, J;Karpf, S and Huber, R},
   title = {Sectioning-free virtual H&E histology with fiber-based two-photon microscopy},
   booktitle = {SPIE BiOS},
   publisher = {SPIE},
   volume = {11648},
Year = {2021},
   DOI = {https://doi.org/10.1117/12.2578334},
   url = {https://doi.org/10.1117/12.2578334},
   type = {Conference Proceedings}
}

@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}
}