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Power Scaling of Highly Compact Single-Frequency Yb-Doped Fiber Amplifiers
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. (Physical Electronics and Photonics)ORCID iD: 0000-0002-4681-0514
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Both scientific interests and industrial applications have stimulated the advance of single-frequency laser technology. The high spatial and temporal coherence of this technology has facilitated many applications such as gravitational wave detection, high-precision fiber sensors, high-resolution spectroscopy, holography, and nonlinear optical conversion. However, this is currently achieved through large footprint lasers with limited portability and mobility. Therefore, there is a need to reduce the size of these lasers into a compact format. Power performance of hundreds of watts in the near-infrared spectrum and tens of watts in the visible and UV spectra for continuous (CW) operation mode and pulse energies up to several tens of mJ in pulsed operation mode are needed. 

An amplification structure for single-frequency lasers that meets these requirements is the master oscillator power amplifier (MOPA). However, compactness imposes several constraints on the MOPA design. The main challenge is the limited output power of the single-frequency fiber MOPA due to the onset of stimulated Brillouin scattering (SBS) in the amplifier fiber. SBS arises from the interaction of acoustic phonons with the propagating signal wave and is converted into a frequency-shifted, backward-propagating wave. SBS is manifested through high-intensity pulses propagating in the backward direction, which can be very harmful for optical components and the seed laser itself. Hence, the suppression of SBS is crucial to the power optimization of the MOPA. This thesis therefore focuses on investigating different SBS suppression techniques that fit a compact MOPA design. More specifically, this is implemented by studying the efficiency of the strain distribution technique applied to the amplifier fiber and the use of custom and commercial highly Yb- doped fibers both in CW and pulse operating MOPAs. Using highly Yb-doped fibers presents challenges with respect to the composition of the fiber material and in high- power operation that can have undesirable degradational effects, such as photodarkening and thermal load generation, and these have been investigated and discussed in this thesis. 

As a result of the different mitigation approaches, output power approaching 100 W in CW mode operation and pulse energies near mJ in pulse mode operation are demonstrated in only one amplification stage, showing the feasibility of a MOPA design with high performance and a small footprint. This may facilitate many applications in the visible and UV spectral ranges that require mobility and portability. 

Abstract [sv]

Både vetenskapliga intressen och industriella tillämpningar har stimulerat utvecklingen inom singelfrekvens laserteknologi. Den höga rumsliga- och tidsmässiga koherensen hos dessa  lasrar har underlättat många tillämpningar såsom gravitationsvågdetektering, fibersensorer med hög precision, högupplöst spektroskopi, holografi och ickelinjär optisk konvertering. Detta uppnås för närvarande genom användande av relativt stora lasrar med en begränsad portabilitet och rörlighet. Det finns därför ett behov av att göra dessa lasrar mer kompakta. Samtidigt efterfrågas en förbättrad effektprestanda på hundratals Watt i det nära infraröda spektrala området och tiotals Watt i det synliga- och ultravioletta området för kontinuerligt (CW) driftläge samt pulsenergier upp till flera tiotals mJ i pulsat driftläge.

En typ av förstärkare för singelfrekvenslasrar som uppfyller dessa kravär så kallade master oscillator effektförstärkare (MOPA). En kompakt design sätter dock flera begränsningar på dessa förstärkare. Huvudutmaningen är uppkomsten av stimulerad Brillouin spridning (SBS)  i förstärkarfibern som begränsar uteffekten. SBS uppstår genom en växelverkan mellan akustiska fononer och signalvågen som omvandlas till en utbredningsvåg som är frekvensförskjuten och bakåt-propagerande. Dessa bakåt-propagerande vågor kan skada optiska komponenter i förstärkaren och i själva signal lasern. Därför är en minskning av SBS avgörnade för en effektiv effektoptimering av förstärkaren. Denna avhandling fokuserar på att undersöka olika tekniker för att minska SBS som dessutom passar för en kompakt MOPA-design. Mer specifikt implementeras detta genom att studera effektiviteten av en distribuerad töjning som tillämpas på förstärkarfibern samt användningen av särskilt anpassade- och kommersiella Yb-dopade fibrer både för kontinuerliga och pulsstyrda förstärkare. Att använda Yb-dopade fibrer med hög Yb-koncentration innebär stora utmaningar med avseende på fibermaterialets sammansättning, som kan medföra en negativ inverkan på förstärkarens prestanda i form av inducerade optiska förluster (s.k. photodarkening), försämrad strålkvalite' och generering av termiska förluster. Dessa har undersökts och diskuteras i denna avhandling.

Som ett resultat av de olika  begränsningsmetoderna, demonstreras förstärkare med en uteffekt som närmar sig 100 W i CW driftläge och pulsenergier nära mJ-området i pulsat läge med användade av endast ett förstärkarssteg. Detta visar genomförbar-heten av en MOPA-design med hög prestanda och ett kompakt format. Detta kan underlätta användningen för många tillämpningar inom det synliga och ultravioletta spektrala området som ståller krav på en ökad mobilitet och portabilitet.

Place, publisher, year, edition, pages
Sundsvall, Sweden: Mid Sweden University , 2022. , p. 62
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 363
Keywords [en]
single-frequency, fiber amplifier, Yb-doped fibers, stimulated Brillouin scattering, compact lasers, thermal load, SHG, MOPA
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:miun:diva-44060ISBN: 978-91-89341-45-6 (electronic)OAI: oai:DiVA.org:miun-44060DiVA, id: diva2:1629201
Public defence
2022-02-15, C312, Holmgatan 10, Sundsvall, 09:30 (English)
Opponent
Supervisors
Available from: 2022-01-17 Created: 2022-01-17 Last updated: 2022-01-17Bibliographically approved
List of papers
1. Compact nanosecond pulsed single stage Yb-doped fiber amplifier
Open this publication in new window or tab >>Compact nanosecond pulsed single stage Yb-doped fiber amplifier
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2014 (English)In: Proceedings of SPIE - The International Society for Optical Engineering, 2014, p. Art. no. 895910-Conference paper, Published paper (Refereed)
Abstract [en]

In this work we present a compact, nanosecond pulsed, single frequency, single stage Yb-doped fiber amplifier by using an overall fiber core diameter of 20 μm. The key component is a custom made, compact, ultra-low noise, single frequency ring-cavity solid state laser (SSL) at 1064 nm used as a master oscillator. The SSL can be designed to provide nanosecond pulses with pulse energies in the sub-mJ range. Our ultimate goal is to develop a compact linearly polarized, single frequency, nanosecond pulsed laser source in an all-fiber format. Short (less than 1m), highly Yb-doped fibers have been used in order to suppress non-linear effects. © 2014 SPIE.

Keywords
Fiber amplifier, MOPA, Pulsed, Single frequency, Solid state laser, Stimulated Brillouin Scattering
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-22101 (URN)10.1117/12.2040799 (DOI)000335902300030 ()2-s2.0-84900795880 (Scopus ID)STC (Local ID)9780819498724 (ISBN)STC (Archive number)STC (OAI)
Conference
Solid State Lasers XXIII: Technology and Devices; San Francisco, CA; United States; 2 February 2014 through 4 February 2014; Code 104995
Note

CODEN: PSISD

Available from: 2014-06-09 Created: 2014-06-05 Last updated: 2022-01-17Bibliographically approved
2. Single-frequency, pulsed Yb3+-doped multicomponent phosphate power fiber amplifier
Open this publication in new window or tab >>Single-frequency, pulsed Yb3+-doped multicomponent phosphate power fiber amplifier
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2020 (English)In: Journal of Optics, ISSN 2040-8978, E-ISSN 2040-8986, Vol. 22, no 11, article id 115606Article in journal (Refereed) Published
Abstract [en]

High-power, single-frequency, pulsed fiber amplifiers are required in light detection and ranging, coherent laser detection, and remote sensing applications to reach long range within a short acquisition time. However, the power-scaling of these amplifiers is limited by nonlinearities generated in the optical fibers, in particular by stimulated Brillouin scattering (SBS). In this regard, the use of multicomponent phosphate glasses maximizes the energy extraction and minimizes nonlinearities. Here, we present the development of a single-stage, hybrid, pulsed fiber amplifier using a custom-made multicomponent Yb-doped phosphate fiber. The performance of the phosphate fiber was compared to a commercial Yb-doped silica fiber. While the latter showed SBS limitation at nearly 6.5 kW for 40 cm length, the maximum achieved output peak power for the multicomponent Yb-doped phosphate fiber was 11.7 kW for 9 ns pulses using only 20 cm with no sign of SBS.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2020
Keywords
single-frequency, Yb-doped phosphate fiber, high-power, single-stage master-oscillator power fiber amplifier
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:miun:diva-40239 (URN)10.1088/2040-8986/abbb5f (DOI)000577218400001 ()2-s2.0-85094980408 (Scopus ID)
Available from: 2020-10-19 Created: 2020-10-19 Last updated: 2022-04-04Bibliographically approved
3. A compact, single-frequency, high-power, SBS-free, Yb-doped single-stage fiber amplifier
Open this publication in new window or tab >>A compact, single-frequency, high-power, SBS-free, Yb-doped single-stage fiber amplifier
2019 (English)In: Proceedings of SPIE - The International Society for Optical Engineering / [ed] W. Andrew Clarkson and Ramesh K. Shori, SPIE - International Society for Optical Engineering, 2019, Vol. 10896, p. 6pp-, article id 1089618Conference paper, Published paper (Refereed)
Abstract [en]

Interest in compact, single-frequency fiber amplifier has increased within many scientific and industrial applications. The main challenge is the onset of nonlinear effects, which limit their power scaling. Here we demonstrate a compact, high-power, single-frequency, polarization-maintaining, continous-wave fiber amplifier using only one amplification stage. We developed the fiber amplifier using a master oscillator fiber amplifier architecture, where a low-noise, single-frequency, solid-state laser operating at 1064 nm was used as a seed source. We evaluated the amplifier's performance by using several state-of-the-art, small-core, Ytterbium (yb)-doped fibers, as well as an in-house-made, highly Yb-doped fiber. An output power of 82 W was achieved with no sign of stimulated Brillouin scattering. A good beam quality and a polarization extinction ratio (PER) of > 25 dB were achieved. The compact fiber amplifier can be a competitive alternative to multi stage designed fiber amplifiers.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2019
Keywords
Single-frequency laser, Ytterbium-doped fiber amplifier, stimulated Brillouin scattering, high-power fiber amplifier, compact fiber amplifier
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:miun:diva-36042 (URN)10.1117/12.2511049 (DOI)000483062600028 ()2-s2.0-85068317380 (Scopus ID)9781510624344 (ISBN)9781510624351 (ISBN)
Conference
Solid State Lasers XXVIII: Technology and Devices 2019, San Francisco, California, United States, 5-7 February, 2019
Available from: 2019-04-25 Created: 2019-04-25 Last updated: 2022-11-07Bibliographically approved
4. Compact single-frequency mopa using a silica fiber highly doped with yb3+
Open this publication in new window or tab >>Compact single-frequency mopa using a silica fiber highly doped with yb3+
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2021 (English)In: Applied Sciences, E-ISSN 2076-3417, Vol. 11, no 21, article id 9951Article in journal (Refereed) Published
Abstract [en]

We report on a single-frequency fiber master oscillator power amplifier utilizing a polarization-maintaining step-index fiber with an Al/Ce/F core-glass composition doped with a very high Yb concentration (0.25 at.%). This design made it possible to use a very short fiber (~1 m) and to coil it in a tight radius (4 cm in the amplifier, while 2 cm gave similarly negligible bending loss) so that the packaged system is one of the most compact reported to date (~0.6 L). The use of a short fiber increased the threshold for stimulated Brillouin scattering well above 100 W while maintaining near-ideal beam quality. The fiber was pumped with a diode-pumped solid-state laser and cooled passively by spooling it on a grooved aluminum mandrel. The amplifier produced a strongly linearly polarized output at 1064 nm in the fundamental mode (M2 ≤ 1.2) with a 150 kHz linewidth and a power of 81.5 W for 107 W of launched pump power. No deleterious effects from the elevated thermal load were observed. The residual photodarkening loss resulting from the high Yb concentration, found to be small (~0.7 dB/m inferred at 1064 nm) with accelerated aging, reduced the output power by only ~20% after 150 h of operation. 

Keywords
Compact fiber amplifier, Fiber amplifier, Photodarkening, Single frequency, Yb-doped fibers
National Category
Physical Sciences
Identifiers
urn:nbn:se:miun:diva-43639 (URN)10.3390/app11219951 (DOI)000723186800001 ()2-s2.0-85118276487 (Scopus ID)
Available from: 2021-11-09 Created: 2021-11-09 Last updated: 2022-01-17
5. Predictive comparison of anti-Stokes fluorescence cooling in oxide and non-oxide fiber hosts doped with Er3+, Pr3+, or Yb3+
Open this publication in new window or tab >>Predictive comparison of anti-Stokes fluorescence cooling in oxide and non-oxide fiber hosts doped with Er3+, Pr3+, or Yb3+
2019 (English)In: Proceedings of SPIE - The International Society for Optical Engineering: Photonic Heat Engines: Science and Applications, SPIE - International Society for Optical Engineering, 2019, Vol. 10936, article id 109360JConference paper, Published paper (Refereed)
Abstract [en]

A comprehensive study was performed to quantify anti-Stokes-fluorescence (ASF) cooling in fibers of various host compositions (telluride, fluorozirconates, fluorophosphates, phosphates, and chalcogenides) doped with Yb3+ or Er3+. Published expressions were used to calculate the maximum heat that can be extracted per unit length and time from a single-mode fiber in the limit of negligible absorptive loss, and the associated cooling efficiency. These expressions consider host- and ion-dependent parameters, namely the absorption and emission cross-section spectra, the radiative and nonradiative lifetimes, and the critical concentration for quenching. Using these expressions with published values for these parameters, the maximum extractable heat was calculated for a large-mode-area fiber (NA = 0.05) doped with either Yb3+ or Er3+ in a variety of hosts. The results show that for a given ion, the maximum heat that can be extracted depends strongly on the host due to the strong dependence of quenching on host composition. In contrast, the cooling efficiency (ratio of extracted heat to pump power absorbed) depends very weakly on the host. The cooling efficiency is also almost twice as high for Er3+ (average of 3.8%) than for Yb3+ (average of 2.2%) due to the larger gap between the pump and mean fluorescence energy in Er3+. Of the limited number of materials for which a full set of data was found in the literature, the highest extractable heat for Yb3+ is in phosphate (-51.5 mW/m), and for Er3+ is in chalcogenide (-10.3 mW/m). This work provides a simple methodology to evaluate the quantitative cooling performance of these and other rare-earth ions in any amorphous host, a procedure that should guide researchers in the selection of optimum materials for ASF cooling of fibers.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2019
Keywords
Laser cooling, anti-Stokes fluorescence, rare-earth-doped fibers, Yb-doped fibers, Er-doped fibers, Yb-doped silica fibers, phosphate fibers
National Category
Other Physics Topics
Identifiers
urn:nbn:se:miun:diva-35797 (URN)10.1117/12.2510859 (DOI)000468075900009 ()2-s2.0-85065625035 (Scopus ID)
Conference
SPIE OPTO, SPIE Photonics West, San Francisco, California, United States, 3-4 February, 2019
Available from: 2019-03-16 Created: 2019-03-16 Last updated: 2022-01-17Bibliographically approved
6. Quasi‐cw pumping of a single‐frequency fiber amplifier for efficient shg in ppln crystals with reduced thermal load
Open this publication in new window or tab >>Quasi‐cw pumping of a single‐frequency fiber amplifier for efficient shg in ppln crystals with reduced thermal load
2022 (English)In: Applied Sciences, E-ISSN 2076-3417, Vol. 12, no 1, article id 285Article in journal (Refereed) Published
Abstract [en]

Single‐frequency lasers are essential for high‐resolution spectroscopy and sensing applications as they combine high‐frequency stability with low noise and high output power stability. For many of these applications, there is increasing interest in power‐scaling single‐frequency sources, both in the near‐infrared and visible spectral range. We report the second‐harmonic generation of 670 μJ at 532 nm of a single‐frequency fiber amplifier signal operating in the quasi‐continuous‐wave mode in a 10‐mm periodically poled Mg‐doped lithium niobate (MgO:PPLN) crystal, while increasing compactness. To the best of our knowledge, this is the highest pulse energy generated in this crystal, which may find applications in the visible and UV such as remote Raman spectroscopy. 

Keywords
Compact, PPLN crystal, Quasi‐CW, SBS, SHG, Single‐frequency, Thermal load
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:miun:diva-44042 (URN)10.3390/app12010285 (DOI)000742440900001 ()2-s2.0-85121988364 (Scopus ID)
Available from: 2022-01-11 Created: 2022-01-11 Last updated: 2022-01-21

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Balliu, Enkeleda

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