Many different mode-locking techniques have been realized in the past [1, 2], but mainly focused on increasing the spectral bandwidth to achieve ultra-short coherent light pulses with well below picosecond duration. In contrast, no mode-locked laser scheme has managed to generate Fourier-limited nanosecond long pulses, which feature narrow spectral bandwidths (~MHz regime) instrumental to applications in spectroscopy, efficient excitation of molecules, sensing, and quantum optics. The related limitations are mainly caused by the adverse operation timescales of saturable absorbers, as well as by the low strength of the nonlinear effects typically reachable through nanosecond pulses with manageable energies

Chu, Sai T.

Hansson, Tobias

Kues, Michael

Kues, Michael (michael.kues@emt.inrs.ca)

Little, Brent E.

Morandotti, Roberto

Moss, David J.

Reimer, Christian

Roztocki, Piotr

Viktorov, Evgeny A.

Wetzel, Benjamin

English

Enlighten: Publications

 
 
 
 
Kues, M., Reimer, C., Wetzel, B., Roztocki, P., Little, B. E., Chu, S. T., 
Hansson, T., Viktorov, E. A., Moss, D. J. and Morandotti, R. (2017) A 
Passively Mode-locked Nanosecond Laser with an Ultra-narrow Spectral 
Width. In: Conference on Lasers and Electro-Optics Europe & European 
Quantum Electronics Conference (CLEO/Europe-EQEC 2017), Munich, 
Germany, 25-29 Jun 2017, ISBN 9781509067367 (doi:10.1109/CLEOE-
EQEC.2017.8086991) 
 
This is the author’s final accepted version. 
 
There may be differences between this version and the published version. 
You are advised to consult the publisher’s version if you wish to cite from 
it. 
 
 
 
 
http://eprints.gla.ac.uk/158414/ 
     
 
 
 
 
 
 
Deposited on: 06 March 2018 
 
 
 
 
 
 
 
 
 
 
 
 
Enlighten – Research publications by members of the University of Glasgow 
http://eprints.gla.ac.uk 
 A Passively Mode-locked Nanosecond Laser With An Ultra-narrow 
Spectral Width 
Michael Kues,1,2* Christian Reimer,1 Benjamin Wetzel,1,3 Piotr Roztocki,1 Brent E. Little,4 Sai T. Chu,5  
Tobias Hansson,1 Evgeny A. Viktorov,6 David J. Moss,1,7 and Roberto Morandotti1 
1INRS-EMT, 1650 Boulevard Lionel-Boulet, Varennes, Québec J3X 1S2, Canada. 
2School of Engineering, University of Glasgow, Rankine Building, Oakfield Avenue, Glasgow G12 8LT, UK. 
3School of Mathematical and Physical Sciences, University of Sussex, Sussex House, Falmer, Brighton BN1 9RH, UK. 
4Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Science, Xi'an, China. 
5City University of Hong Kong, Department of Physics and Materials Science, Tat Chee Avenue, Hong Kong, China. 
6National Research University of Information Technologies, Mechanics and Optics, St. Petersburg, Russia. 
7Center for Micro-Photonics, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia. 
*michael.kues@emt.inrs.ca 
 
Many different mode-locking techniques have been realized in the past [1,2], but mainly focused on 
increasing the spectral bandwidth to achieve ultra-short coherent light pulses with well below picosecond 
duration. In contrast, no mode-locked laser scheme has managed to generate Fourier-limited nanosecond long 
pulses, which feature narrow spectral bandwidths (~MHz regime) instrumental to applications in spectroscopy, 
efficient excitation of molecules, sensing, and quantum optics. The related limitations are mainly caused by the 
adverse operation timescales of saturable absorbers, as well as by the low strength of the nonlinear effects 
typically reachable through nanosecond pulses with manageable energies. 
Here, we demonstrate a technique for passive mode-locking based on an integrated nonlinear microring 
resonator embedded in a nonlinear amplifying loop mirror (NALM) architecture, acting as an artificial saturable 
absorber (Fig. 1a). Using this new approach, we realize the first Fourier-transform-limited nanosecond mode-
locked laser pulses [3]. Specifically, the high-Q integrated microring resonator simultaneously limits the 
spectral bandwidth of the oscillating laser field, while increases the nonlinear interactions through field cavity 
enhancement, ultimately resulting in the appropriate nonlinear phase shift for nanosecond mode-locking by the 
NALM. The laser characteristics are summarized in Fig. 1b-e. The laser produced optical pulses in the 
nanosecond regime (4.3 ns in duration), with an overall spectral bandwidth of 104.9 MHz—more than two 
orders of magnitude smaller than previous realizations. The very narrow bandwidth of the laser made it possible 
to fully characterize its spectral properties in the radiofrequency domain using a beating technique exploiting a 
continuous wave laser in combination with widely available GHz-bandwidth optoelectronic components. In 
turn, this characterization reveals the strong coherence of the generated pulse train. 
 
Fig. 1:  a) Experimental setup of the mode-locked laser. b) Real-time time trace of 44 pulses, with RMS noise below 2.3%. c) Temporal 
profile of the emitted pulses (10 pulses superimposed) with a 4.31 ns FWHM Gaussian pulse fit (blue solid line) and a low FWHM jitter of 
0.13 ns. d) Radiofrequency spectrum of the mode-locked laser beating with a CW laser. Lower frequency part (intensity FT): clear and 
narrow peaks at the repetition rate of the laser (9.565 MHz). High frequency part (beat note): related to the optical spectrum of the mode-
locked laser. e) Optical spectrum of the laser, retrieved with a high-resolution optical spectrum analyzer (dashed green line) and from the 
beat note (red crosses). The blue line corresponds to the spectrum of the fitted pulse (Fig. 1c) with an additional temporal phase induced by 
the Kerr nonlinearity.   
The compact architecture, and modest requirements in terms of power, readily allow for stable and portable 
operation, while opening up a route towards the full integration of the laser system. Together with the possibility 
to resolve the full laser spectrum in the RF domain, such characteristics can pave the way towards novel sensing 
and spectroscopy implementations. From a fundamental perspective, the low and tractable number of modes (11 
within the spectral FWHM), may enable further studies of both nonlinear mode coupling and complex mode-
locking regimes. 
References  
[1] E. P. Ippen, “Principles of passive mode locking,” Appl. Phys. B 58, 159–170 (1994). 
[2] U. Keller, “Recent developments in compact ultrafast lasers,” Nature 424, 831–838 (2003).  
[3] M. Kues et al., “Passively mode-locked laser with an ultra-narrow spectral width,” Nature Photonics, 10.1038/nphoton.2016.271 (2017). 
  
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A Passively Mode-locked Nanosecond Laser with an Ultra-narrow Spectral Width

Enlighten

    Kues, M., Reimer, C., Wetzel, B., Roztocki, P., Little, B. E., Chu, S. T., Hansson, T., Viktorov, E. A., Moss, D. J. and Morandotti, R. (2017) A Passively Mode-locked Nanosecond Laser with an Ultra-narrow Spectral Width. In: Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC 2017), Munich, Germany, 25-29 Jun 2017, ISBN 9781509067367 (doi:10.1109/CLEOE-EQEC.2017.8086991)  This is the author’s final accepted version.  There may be differences between this version and the published version. You are advised to consult the publisher’s version if you wish to cite from it.     http://eprints.gla.ac.uk/158414/            Deposited on: 06 March 2018             Enlighten – Research publications by members of the University of Glasgow http://eprints.gla.ac.uk  A Passively Mode-locked Nanosecond Laser With An Ultra-narrow Spectral Width Michael Kues,1,2* Christian Reimer,1 Benjamin Wetzel,1,3 Piotr Roztocki,1 Brent E. Little,4 Sai T. Chu,5  Tobias Hansson,1 Evgeny A. Viktorov,6 David J. Moss,1,7 and Roberto Morandotti1 1INRS-EMT, 1650 Boulevard Lionel-Boulet, Varennes, Québec J3X 1S2, Canada. 2School of Engineering, University of Glasgow, Rankine Building, Oakfield Avenue, Glasgow G12 8LT, UK. 3School of Mathematical and Physical Sciences, University of Sussex, Sussex House, Falmer, Brighton BN1 9RH, UK. 4Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Science, Xi'an, China. 5City University of Hong Kong, Department of Physics and Materials Science, Tat Chee Avenue, Hong Kong, China. 6National Research University of Information Technologies, Mechanics and Optics, St. Petersburg, Russia. 7Center for Micro-Photonics, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia. *michael.kues@emt.inrs.ca  Many different mode-locking techniques have been realized in the past [1,2], but mainly focused on increasing the spectral bandwidth to achieve ultra-short coherent light pulses with well below picosecond duration. In contrast, no mode-locked laser scheme has managed to generate Fourier-limited nanosecond long pulses, which feature narrow spectral bandwidths (~MHz regime) instrumental to applications in spectroscopy, efficient excitation of molecules, sensing, and quantum optics. The related limitations are mainly caused by the adverse operation timescales of saturable absorbers, as well as by the low strength of the nonlinear effects typically reachable through nanosecond pulses with manageable energies. Here, we demonstrate a technique for passive mode-locking based on an integrated nonlinear microring resonator embedded in a nonlinear amplifying loop mirror (NALM) architecture, acting as an artificial saturable absorber (Fig. 1a). Using this new approach, we realize the first Fourier-transform-limited nanosecond mode-locked laser pulses [3]. Specifically, the high-Q integrated microring resonator simultaneously limits the spectral bandwidth of the oscillating laser field, while increases the nonlinear interactions through field cavity enhancement, ultimately resulting in the appropriate nonlinear phase shift for nanosecond mode-locking by the NALM. The laser characteristics are summarized in Fig. 1b-e. The laser produced optical pulses in the nanosecond regime (4.3 ns in duration), with an overall spectral bandwidth of 104.9 MHz—more than two orders of magnitude smaller than previous realizations. The very narrow bandwidth of the laser made it possible to fully characterize its spectral properties in the radiofrequency domain using a beating technique exploiting a continuous wave laser in combination with widely available GHz-bandwidth optoelectronic components. In turn, this characterization reveals the strong coherence of the generated pulse train.  Fig. 1:  a) Experimental setup of the mode-locked laser. b) Real-time time trace of 44 pulses, with RMS noise below 2.3%. c) Temporal profile of the emitted pulses (10 pulses superimposed) with a 4.31 ns FWHM Gaussian pulse fit (blue solid line) and a low FWHM jitter of 0.13 ns. d) Radiofrequency spectrum of the mode-locked laser beating with a CW laser. Lower frequency part (intensity FT): clear and narrow peaks at the repetition rate of the laser (9.565 MHz). High frequency part (beat note): related to the optical spectrum of the mode-locked laser. e) Optical spectrum of the laser, retrieved with a high-resolution optical spectrum analyzer (dashed green line) and from the beat note (red crosses). The blue line corresponds to the spectrum of the fitted pulse (Fig. 1c) with an additional temporal phase induced by the Kerr nonlinearity.   The compact architecture, and modest requirements in terms of power, readily allow for stable and portable operation, while opening up a route towards the full integration of the laser system. Together with the possibility to resolve the full laser spectrum in the RF domain, such characteristics can pave the way towards novel sensing and spectroscopy implementations. From a fundamental perspective, the low and tractable number of modes (11 within the spectral FWHM), may enable further studies of both nonlinear mode coupling and complex mode-locking regimes. References  [1] E. P. Ippen, “Principles of passive mode locking,” Appl. Phys. B 58, 159–170 (1994). [2] U. Keller, “Recent developments in compact ultrafast lasers,” Nature 424, 831–838 (2003).  [3] M. Kues et al., “Passively mode-locked laser with an ultra-narrow spectral width,” Nature Photonics, 10.1038/nphoton.2016.271 (2017).   Time (ns)0 2000 4000 6000Norm. intensity00.51Time (ns)-10 -5 0 5 1000.51 Norm. intensityFWHM4.31 nsb) c)FWHM jitter±0.13 nsRMS 2.23%d)Frequency (MHz)0 500 1600Norm. Intensity 00.51Beat note Intensity FTFrequency (MHz)1200 1400 1600 180000.51Norm. Intensitye)OSABeat note fita)

Michael Kues

Christian Reimer

Benjamin Wetzel

Piotr Roztocki

Brent E. Little

Sai T. Chu

Tobias Hansson

Evgeny A. Viktorov

David J. Moss

Roberto Morandotti

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A passively mode-locked nanosecond laser with an ultra-narrow spectral width

Institutional Repository of Xi'an Institute of Optics and Precision Mechanics, CAS

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A Passively Mode-locked Nanosecond Laser with an Ultra-narrow Spectral Width

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