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All-fiber modulators for laser applications
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.ORCID iD: 0000-0003-3933-4406
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The objective of this thesis was to explore the usefulness of all-fiber modulators for laser applications. The modulators were all based on refractive index change achieved in the core of the studied fiber- components, exploiting either the elasto-optic effect or the electro-optic effect. This was realized with the aid of electrodes inside the fiber cladding close to the core that provided either thermal stress in the core, or an electric field across the core. The electrodes consisted of low melting-point alloys, such as BiSn and AuSn, which were pushed into the hole-fiber, in the liquid state, which then solidified to form solid electrodes filling the entire hole.

Together with an analyzer such as a polarizer or an interferometer the achieved refractive index modulation in the core could then be translated into an amplitude modulation of the guided light, which was subsequently utilized for switching fiber-lasers to generate cavity dumped, Q-switched, or mode-locked pulses. The fast rise/fall-time of a few nanoseconds for the elasto-optic devices was due to the fast thermal expansion of the electrodes. The maximum repetition rate, however, was limited to a few tens of kHz, due to the slow thermal processes for dissipation of the applied energy. The electro-optic fiber components, which displayed similar rise/fall-times on the other hand, showed a much higher cut-off frequency of 16 MHz.

The electro-optic, all-fiber switch was also employed to select single pulses at 1 MHz repetition rate out of a 7 MHz train of pulses. Additionally, simulations using the finite element method were performed in order to gain insight and to explain the underlying processes of the observed response of a long-period grating written in a 2-hole fiber with electrodes, when applying HV-pulses to one of these.

The thesis shows that the studied fiber-components show great potential of becoming complementary devices with high damage threshold for all-fiber laser applications in the future. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , vii, 77 p.
Series
Trita-FYS, ISSN 0280-316X ; 2012:86
Keyword [en]
All-fiber, fiber optics, modulation, q-switching, mode-locking
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-105863ISBN: 978-91-7501-574-3 (print)OAI: oai:DiVA.org:kth-105863DiVA: diva2:572616
Public defence
2012-12-18, FD5, Albanova, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20121129

Available from: 2012-11-29 Created: 2012-11-28 Last updated: 2015-03-30Bibliographically approved
List of papers
1. All-fiber cavity dumping
Open this publication in new window or tab >>All-fiber cavity dumping
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2009 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 17, no 20, 17596-17602 p.Article in journal (Refereed) Published
Abstract [en]

Cavity dumping of an all-fiber laser system is demonstrated. The active element is a pulse-picker with nanosecond rise time consisting of a microstructured fiber with electrically driven internal electrodes. The device is used for intracavity polarization rotation and dumping through a polarization splitter. The optical flux is removed from the cavity within one roundtrip and most of the amplified spontaneous emission, spiking and relaxation oscillation that follow during the gain recovery phase of the laser are blocked from the output signal.

Keyword
optical-fiber, laser, modulator, dynamics, pulses
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-18808 (URN)10.1364/OE.17.017596 (DOI)000270295300038 ()19907544 (PubMedID)2-s2.0-70349654119 (Scopus ID)
Note
QC 20100525 QC 20111122Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Actively Q-switched all-fiber laser with an electrically controlled microstructured fiber
Open this publication in new window or tab >>Actively Q-switched all-fiber laser with an electrically controlled microstructured fiber
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2010 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 18, no 11, 11052-11057 p.Article in journal (Refereed) Published
Abstract [en]

Actively Q-switching of an all-fiber laser system is demonstrated. The active element is a polarization switch with nanosecond risetime based on a microstructured fiber with electrically driven internal electrodes. Optical feedback between two 100% reflectors is inhibited until a nanosecond current pulse Q-switches the laser. After a short optical pulse develops several roundtrips later, the fiber switch is turned off, removing the short optical pulse from the cavity through a polarization splitter. Pulses of 50 W peak power and similar to 12 ns duration are obtained with 400 mW pump power at 100 Hz. (C) 2010 Optical Society of America

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-27319 (URN)000278512300015 ()2-s2.0-77952821636 (Scopus ID)
Note
QC 20101209Available from: 2010-12-09 Created: 2010-12-09 Last updated: 2017-12-11Bibliographically approved
3. Dynamics of long-period gratings tuned with internal fiber electrodes
Open this publication in new window or tab >>Dynamics of long-period gratings tuned with internal fiber electrodes
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2011 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 36, no 5, 633-635 p.Article in journal (Refereed) Published
Abstract [en]

The physics of electrically switched long-period grating in a twin-hole fiber with internal electrodes is studied. Dynamic measurements for the two polarizations show how the grating spectra shift in time due to the mechanical stress and heat transfer in the core and the cladding.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-31605 (URN)10.1364/OL.36.000633 (DOI)000287912500013 ()2-s2.0-79952336688 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note
QC 20110325Available from: 2011-03-25 Created: 2011-03-21 Last updated: 2017-12-11Bibliographically approved
4. Pulse selection at 1 MHz with electrooptic fiber switch
Open this publication in new window or tab >>Pulse selection at 1 MHz with electrooptic fiber switch
2012 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 20, no 9, 9465-9470 p.Article in journal (Refereed) Published
Abstract [en]

Two 78-cm long electrooptic fibers with nonlinear coefficient. chi((2)) similar to 0.26 pm/V are used in a Sagnac loop for pulse selection at up to 1 MHz repetition rate. Laser pulses of 1.5 mu m wavelength arriving at every 140 ns are selected with an extinction ratio as high as -30 dB. The arrangement is entirely based on silica fiber.

Keyword
Modulation, Microstructured fibers
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-93691 (URN)10.1364/OE.20.009465 (DOI)000303989300015 ()2-s2.0-84861117821 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note
QC 20120612Available from: 2012-04-23 Created: 2012-04-23 Last updated: 2017-12-07Bibliographically approved
5. Soliton generation from an actively mode-locked fiber laser incorporating an electro-optic fiber modulator
Open this publication in new window or tab >>Soliton generation from an actively mode-locked fiber laser incorporating an electro-optic fiber modulator
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2012 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 20, no 3, 2905-2910 p.Article in journal (Refereed) Published
Abstract [en]

This work demonstrates an actively mode-locked fiber laser operating in soliton regime and employing an all-fiber electro-optic modulator. Nonlinear polarization rotation is utilized for femtosecond pulse generation. Stable operation of the all-fiber ring laser is readily achieved at a fundamental repetition rate of 2.6 MHz and produces 460 fs pulses with a spectral bandwidth of 5.3 nm.

Keyword
All fiber, Electro-optic modulators, Femtosecond pulse generation, Fs pulse, Nonlinear polarization rotation, Repetition rate, Soliton generation, Spectral bandwidth, Stable operation
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-91025 (URN)10.1364/OE.20.002905 (DOI)000300499500097 ()22330528 (PubMedID)2-s2.0-84856417174 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation
Note
QC 20120319Available from: 2012-03-06 Created: 2012-03-06 Last updated: 2017-12-07Bibliographically approved

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