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High Performance Fiber Lasers with Spectral, Thermal and Life Time Control
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics. (Laserfysik)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis contains the results of research in the fields of spectral control, efficiency andlifetime of high-power, rare-earth doped fiber lasers, properties which are of greatimportance for scientific and industrial applications. Volume Bragg gratings (VBGs) has forthe first time been used together with fiber lasers and the laser performance in terms ofspectral purity, thermal stability, and tunability was evaluated. It was found that VBGs arean excellent high-contrast spectral filter for many fiber laser designs where bulk optics arenecessary, or for speciality fibers such as photonic crystal fibers or large-mode area fibers. Itis also shown that they work equally well in low power and very high-power configurations,i.e. for fiber lasers ranging three orders of magnitude in output power, from ~100 mW to >100 W. Furthermore, VBGs are shown to work very well as tunable spectral filters,producing a narrow emission linewidth in a compact setup.

Concerning efficiency, it was shown how cryogenic cooling of the fiber gain-mediasubstantially increased the efficiency. The reasons are an increased pump absorption, anincreased gain cross-section, and a decreased threshold. The broad spectral output resultingfrom the low temperatures is shown to be easily mitigated by implementing a VBG as oneof the cavity mirrors. The low operating temperature is also shown to efficiently suppressself-pulsing in the fiber laser, which, if left unchecked, can lead to catastrophic break-downof the fiber end-faces. The increased absorption and suppressed self-pulsing allowed a fiberlength long enough to almost completely absorb the pump, which meant that, for the samepump power, more than 60 % higher output-power was attained.

Finally, the lifetime issue of Yb-doped fiber lasers was addressed. It was found that Cecodopingsubstantially reduced the photodarkening-rate while leaving other fiber parametersessentially unchanged. This is especially important for Yb-doped fiber lasers emitting at 980nm, as the high inversion required make them very susceptible to photodarkening. It wasshown that the output power in Yb-doped fiber lasers degraded quickly when no Cecodopingwas present and, conversely, with the right Yb/Ce-codoping ratio, degradationfreelasing could be achieved for many hours.

The research results obtained in this work could be of great interest to scientists andengineers working with spectroscopy, display systems, non-linear optics to just name a fewexamples.

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , x, 72 p.
Series
Trita-FYS, ISSN 0280-316X ; 2009:65
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-11711ISBN: 978-91-7415-504-4 (print)OAI: oai:DiVA.org:kth-11711DiVA: diva2:279910
Public defence
2009-12-11, Sal FB52, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100721Available from: 2009-12-07 Created: 2009-12-07 Last updated: 2015-03-30Bibliographically approved
List of papers
1. Efficient narrow-linewidth volume-Bragg grating-locked Nd: fiber laser
Open this publication in new window or tab >>Efficient narrow-linewidth volume-Bragg grating-locked Nd: fiber laser
2007 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 15, no 18, 11336-11340 p.Article in journal (Refereed) Published
Abstract [en]

A neodymium doped microstructured large mode area fiber is frequency locked with a volume Bragg grating. This configuration is compared with a conventional fiber laser setup. A high efficiency (51% slope), stable output and a drastically narrowed linewidth (<0.07nm) are achieved.

National Category
Other Engineering and Technologies Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-11705 (URN)10.1364/OE.15.011336 (DOI)000249339800031 ()2-s2.0-34548445086 (Scopus ID)
Note
QC 20100721Available from: 2009-12-07 Created: 2009-12-07 Last updated: 2017-12-12Bibliographically approved
2. Efficient skew-angle cladding-pumped tunable narrow-linewidth Yb-doped fiber laser
Open this publication in new window or tab >>Efficient skew-angle cladding-pumped tunable narrow-linewidth Yb-doped fiber laser
2007 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 32, no 24, 3501-3503 p.Article in journal (Refereed) Published
Abstract [en]

A skew-angle cladding-pumped tunable Yb-doped fiber laser is presented. The laser was tunable over more than 30 nm, from 1022 to 1055 nm, by employing a volume Bragg grating in a retroreflector configuration as one of the cavity delimiters. Output powers in excess of 4.3 W were recorded with a spectral bandwidth of 5 GHz and an M2 value below 1.3 over the whole tuning range.

Keyword
BRAGG GRATINGS; POWER; SPECTRUM; CAVITY; GLASS
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-11706 (URN)10.1364/OL.32.003501 (DOI)000252557500010 ()2-s2.0-40149108968 (Scopus ID)
Note
QC 20100721Available from: 2009-12-07 Created: 2009-12-07 Last updated: 2017-12-12Bibliographically approved
3. Narrow linewidth high output-coupling dual VBG-locked Yb-doped fiber laser
Open this publication in new window or tab >>Narrow linewidth high output-coupling dual VBG-locked Yb-doped fiber laser
2010 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 18, no 5, 4980-4985 p.Article in journal (Refereed) Published
Abstract [en]

Two equal highly reflective volume Bragg gratings (VBGs) were used to lock an Yb-doped fiber laser. By heating one of the VBGs, its center wavelength was shifted and the laser was locked on the overlap between the main peak of one grating and the side-lobe of the other creating a large outcoupling with high spectral selectivity. With this simple arrangement, unidirectional output is achieved with a narrow linewidth (2.5GHz), high efficiency (>70%) and with an output power above 7W.

Keyword
Center wavelength; High efficiency; High output; Narrow-line width; Output power; Side lobes; Spectral selectivity; Volume Bragg gratings; Yb-doped fiber lasers
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-14161 (URN)10.1364/OE.18.004980 (DOI)000275454100061 ()2-s2.0-77749304289 (Scopus ID)
Note
QC 20100721Available from: 2010-07-21 Created: 2010-07-21 Last updated: 2017-12-12Bibliographically approved
4. High-power and wavelength-tunable operation of an Er, Yb fiber laser using a volume Bragg grating
Open this publication in new window or tab >>High-power and wavelength-tunable operation of an Er, Yb fiber laser using a volume Bragg grating
Show others...
2008 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 33, no 11, 1204- p.Article in journal (Refereed) Published
Abstract [en]

Efficient high-power operation of double-clad Er,Yb-doped fiber lasers with fixed-wavelength and wavelength-tunable resonator configurations using volume Bragg gratings for wavelength selection are reported. The fixed-wavelength laser yielded a maximum output power of 103 W at 1552.6 nm with a linewidth of ∼0.4 nm (FWHM) for a launched pump power of 290 W at 976 nm. The wavelength-tunable laser could be tuned from 1528 to 1550 nm with a linewidth of 0.2 nm (FWHM) and with output power in the range 30-38 W for a launched pump power of 120 W. The prospects for further improvement in performance are considered.

Keyword
YB; SPECTRUM; CAVITY; GLASS
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-11707 (URN)10.1364/OL.33.001204 (DOI)000257156900015 ()2-s2.0-45749105867 (Scopus ID)
Note
QC 20100721Available from: 2009-12-07 Created: 2009-12-07 Last updated: 2017-12-12Bibliographically approved
5. High-power linearly-polarized operation of a cladding-pumped Yb fibre laser using a volume Bragg grating for wavelength selection
Open this publication in new window or tab >>High-power linearly-polarized operation of a cladding-pumped Yb fibre laser using a volume Bragg grating for wavelength selection
2008 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 16, no 13, 9507-9512 p.Article in journal (Refereed) Published
Abstract [en]

In this work a volume Bragg grating is used as a wavelength selective element in a high-power cladding-pumped Yb-doped silica fiber laser. The laser produced 138 W of linearly-polarized single-spatial-mode output at 1066 nm with a relatively narrow linewidth of 0.2 nm for similar to 202 W of launched pump power at 976 nm. The beam propagation factor (M-2) for the output beam was determined to be 1.07. Thermal limitations of volume Bragg gratings are discussed in the context of power scaling for fiber lasers.

Keyword
PHOTOTHERMOREFRACTIVE GLASS; SPECTRUM; BEAM
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-11708 (URN)10.1364/OE.16.009507 (DOI)000257563900028 ()2-s2.0-46149112384 (Scopus ID)
Note
QC 20100721Available from: 2009-12-07 Created: 2009-12-07 Last updated: 2017-12-12Bibliographically approved
6. Highly efficient temporally stable narrow linewidth cryogenically cooled Yb-fiber laser
Open this publication in new window or tab >>Highly efficient temporally stable narrow linewidth cryogenically cooled Yb-fiber laser
2009 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 17, no 10, 8433-8438 p.Article in journal (Refereed) Published
Abstract [en]

Cryogenic cooling is an effective way of increasing the efficiency in many solid-state lasers. In fiber lasers however, while the efficiency is increased, a reduced reabsorption in combination with reduced homogeneous broadening tends to broaden the linewidth, yielding a low spectral power density of the laser emission. In this work we lock a cryogenically-cooled Yb-doped fiber laser with a volume Bragg grating to overcome this problem and achieve a temporally stable narrow linewidth highly efficient laser. We extract 11.4-W of output power in spectral window of less than 0.4-nm with 14.5-W of launched pump light.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-11709 (URN)10.1364/OE.17.008433 (DOI)000266381900075 ()2-s2.0-66449133549 (Scopus ID)
Note
QC 20100721Available from: 2009-12-07 Created: 2009-12-07 Last updated: 2017-12-12Bibliographically approved
7. Improved photodarkening resistivity in ytterbium-doped fiber lasers by cerium codoping
Open this publication in new window or tab >>Improved photodarkening resistivity in ytterbium-doped fiber lasers by cerium codoping
2009 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 34, no 8, 1285- p.Article in journal (Refereed) Published
Abstract [en]

We show that the photodarkening resistivity of ytterbium-doped fiber lasers can be greatly improved by cerium codoping. It is suggested that the coexistence of the redox couple Ce3+/Ce4+ in the glass provides means for trapping both hole- and electron-related color centers that are responsible for the induced optical losses in Yb-doped fiber lasers.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-11710 (URN)10.1364/OL.34.001285 (DOI)000265869600050 ()2-s2.0-66349098715 (Scopus ID)
Note
QC 20100721Available from: 2009-12-07 Created: 2009-12-07 Last updated: 2017-12-12Bibliographically approved
8. Degradation-resistant lasing at 980 nm in a Yb/Ce/Al-doped silica fiber
Open this publication in new window or tab >>Degradation-resistant lasing at 980 nm in a Yb/Ce/Al-doped silica fiber
2010 (English)In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 27, no 2, 338-342 p.Article in journal (Refereed) Published
Abstract [en]

In this work we measure how photodarkening affects the optical efficiency for three different Yb/Al-doped silica fibers operating at 980 nm, one of which is codoped with cerium. A volume Bragg grating is used for linewidth control and added rejection of amplified spontaneous emission. Several hours of degradation-resistant operation is obtained with the Ce-codoped fiber, while for the Yb/Al doped fibers a large drop in efficiency is observed within the first hour of operation. Our results show that Yb/Ce/Al-doped fibers could be excellent candidates for high-power 980 nm fiber laser sources.

Keyword
Amplified spontaneous emissions; Co-doped; Doped fiber; Fiber laser source; High-power; Line-width control; Optical efficiency; Photodarkening; Silica fibers; Volume Bragg gratings
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-14163 (URN)10.1364/JOSAB.27.000338 (DOI)000274232500023 ()2-s2.0-76649138580 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20110126Available from: 2010-07-21 Created: 2010-07-21 Last updated: 2017-12-12Bibliographically approved

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