PhD13: Alejandro Martinez Jimenez

Host: University of Kent, Applied Optics Group (AOG)

Secondments: NKT Photonics, CenterVue

PhD Project: NPR laser followed by time stretch

During my PhD, I’ll work in developing ultrafast laser source to be applied on OCT. The nonlinear polarization rotation (NPR) technique developed by Matsas et al, is a powerful tool for the generation of pico-femtosecond pulses. In the other hand, time stretch will be used as akinetic tuning mechanism that enables multi-MHz A-Scans rates. In my project, we develop NPR at different bands of the spectrum and with different repetition rate.

Time stretch on a broadband pulse to make an akinetic swept source has been investigated. For that, a broadband pulse was propagated into a stretching element that presents high dispersion. It is generally a long single mode fiber (SMF), or a chirped fiber Bragg grating (cFBG). The dispersion will induce different delay to each spectral component and split them in time. This produces an akinetic swept source. When designing the stretching element, one need to consider the amount of GVD at the central wavelength, but also the losses and the price of the stretcher. Another crucial parameter is the slope of the dispersion, i.e. higher order dispersion. Indeed, an ideal time stretch would lead to a dispersive Fourier transform, where the spectrum is exactly mapped in time. This can be only achieved if the stretching element
presents only linear dispersion.

Completed workshops, Seminars, and Conferences:

  • Students led conference Optics and Photonics for Scientific Progress #OPSP2021 13th -14th April 2021 – Two days of talks, networking and workshops –online participation
  • International Day of Light Conference, 20th – 21st May, 2021, Organizer: Tampere University, Finland
  • 1st NETLAS Online Event, 01/07/2021  
  • 2nd NETLAS Event: Winter School, DTU, Denmark, 1-4th March 2022, oral presentation “Passive mode-locking lasers using the nonlinear polarization evolution as a saturable absorber
  • University of Kent, 06/05/2022, Journal Club, oral presentation “Relationship between axial resolution and signal-to-noise ratio
  • 25th Congress of the International Commission for Optics (ICO), 05 – 09 Sep 2022, Dresden University of Technology – Germany, Oral presentation “Measuring chromatic dispersion for fiber lasers cavities on mode-locked lasers”
  • 3rd NETLAS event: Autumn School, Technical University of Darmstadt (TUDA), Germany4-7th October 2022, oral presentation “Broadband mode-locked laser at 1030 nm for OCT
  • DOPS2023 Conference, Aarhus Denmark, 03/12/2022, poster presentation “Broadband mode-locked laser at 1030 nm for Optical Coherence Tomography
  • SPIE Photonics West, 28 January – 2 February 2023, oral presentation “MHz Time Stretch Swept Source using a commercial Erbium-doped fiber amplifier” and co-author of the poster presentation “Characterization of SiN/SiO2-based MEMS-VCSEL at 1550 nm for Optical Coherence Tomography” by ESR7 Irene Rodriguez Lamoso
  • Biophotonics for Eye Research summer school 2023, Zaragoza, Spain, oral presentation
  • 3rd NETLAS Event: Autumn School, Technical University of Darmstadt (TUDA), Germany4-7th October 2022, oral presentation 2Broadband mode-locked laser at 1030 nm for OCT
  • 23/03/2023 Visit to the Institute of Ophthalmology, Moorfields Eye Hospital, and the Royal Free Hospital, London, On eye instrumentation for diagnostic and handling patients to be investigated by eye imaging instruments
  • ECBO Biomedical Optics 2023, 25-29/06/2023, Munich, Germany, oral presentation
  • 4th NETLAS event: NETLAS Conference in conjunction with Markus Pessa International Summer School “New Frontiers in Optical Technologies”, Tampere, Finland, August 7 – 11, 2023, oral presentation “Recent swept source OCT developments”
  • Photonics West 2024 – San Francisco, 27 January – 1 February 2024, poster presentation “Using complex master-slave protocol for OCT with bidirectional sweeping laser” and co-author of the oral presentation by ESR4 Esteban Andres Proano Grijalva recruited by Technical Univ. of Denmark “Bidirectional 1310 nm MEMS VCSEL”


  • Alejandro Martínez Jiménez; Sacha Grelet; Veronika Tsatourian; Patrick Bowen Montague; Adrian Bradu and Adrian Podoleanu, “400 Hz volume rate swept-source optical coherence tomography at 1060 nm using a KTN deflector” in IEEE Photonics Technology Letters, VOL. 34, NO. 23, 2022, doi: 10.1109/LPT.2022.3212015
  • S. Grelet, A. Martínez Jiménez, R. D. Engelsholm, P. B. Montague and A. Podoleanu, “40 MHz swept-source optical coherence tomography at 1060 nm using a time-stretch and supercontinuum spectral broadening dynamics,” in IEEE Photonics Journal, VOL. 14, NO. 6 doi: 10.1109/JPHOT.2022.3226820.
  • Marie Klufts, Alejandro Martínez Jiménez, Simon Lotz, Muhammad Asim Bashir, Tom Pfeiffer, Alexander Mlynek, Wolfgang Wieser, Alexander Chamorovskiy, Adrian Bradu, Adrian Podoleanu, and Robert Huber, “828 kHz retinal imaging with an 840 nm Fourier domain mode locked laser,” Biomed. Opt. Express 14, 6493-6508 (2023)
  • I. Rodríguez Lamoso, A. Martínez Jiménez, J. Cesar, S. Preu, A. Podoleanu, “Characterization of SiN/SiO2-based MEMS-VCSEL at 1550 nm for optical coherence tomography,” Proc. SPIE 12367, Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXVII, 1236716 (8 March 2023);
  • A. Martínez Jiménez, M. Spacek, M. Wacker, R. Huber, A. Bradu, A. Podoleanu, “MHz time stretch swept source using a commercial erbium-doped fiber amplifier,” Proc. SPIE 12367, Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXVII, 1236706 (8 March 2023);
  • E. A. Proano Grijalva, A. Martínez Jiménez, A. Bradu, A. Fernandez, B. O. Meyer, A. Jensen, E. Semenova, T. Ansbæk, K. Yvind, A. Podoleanu, “Novel 1.6 MHz swept source for real-time volumetric in-vivo OCT imaging of the human retina,” Proc. SPIE 12367, Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXVII, 1236704 (8 March 2023);
  • Alejandro Martínez Jiménez, Sacha Grelet, Patrick Bowen Montague, Adrian Bradu, Adrian Podoleanu, “Dual ultrahigh speed swept-source and time domain optical coherence tomography system using a time stretch laser and a KTN deflector,” Proc. SPIE 12632, Optical Coherence Imaging Techniques and Imaging in Scattering Media V, 126320B (11 August 2023);


Bachelor’s degree Physical Sciences at the University of Murcia. The following year I started an interuniversity master’s degree in photonics with the participation of the University of Barcelona, Polytechnic of Catalunya, Autonoma of Barcelona (UB, UPC, UAB) and the Institute of Photonic Sciences (ICFO) where I was able to learn from the world top researchers (Prof. Dr Niek Van Hulst, Prof. Dr. María García-Parajo, Prof. Dr. Jens Biegert) in different fields such as non-linear optics, ultrafast, biophotonics.

Master thesis work was on correlations with the HBT interferometer, presenting “Generation of artificial thermal sources and their characterization by intensity interferometry