Development of Short-wave Infrared Fibre Lasers
Development of Short-wave Infrared Fibre Lasers
Although Thulium and erbium doped fibre lasers are common,
and used in a wide array of applications, there are methods of operation which
are not well matured. In this work, the operation of laser sources utilising
both dopants in power scalable architectures is investigated to explore their potential.
To mitigate the impact on device efficiency caused by long
device lengths in Er-doped fibre lasers (EDFLs), brightness enhancement of
few-moded fibres through bend loss is investigated in chapter 3. By careful
design of the fibre to compromise between core to cladding area ratio and modal
content, it is found that inducing bend loss is an effective way to achieve
diffraction limited beam quality in large mode area (LMA) fibres.
In chapter 4 it is discussed how EDFLs compare against
competing sources in the 1500 - 1600 nm wavelength band. In particular, how
power-scaling differs between Yb sensitised Er-doped sources, and Er-only
devices. The impact of pair-induced-quenching (PIQ) and long device lengths is
modelled to arrive at optimal device parameters, which are then utilised in a
real device. In a cladding pumped configuration, 104 W of singlemode output
power is demonstrated with slope efficiencies of 24% (30%) with respect to
launched (absorbed) pump power. Furthermore, the linearity of the observed
slope efficiency and good thermal properties of the device lend themselves to
further power scaling by increasing the available pump power and further
optimisation of the fibre design.
In chapter 5, the difficulty in operating Tm-doped fibre
lasers (TDFLs) around 1700 nm is discussed, and the relevant fibre design
parameters modelled. Through the use of in-band core-pumping with the EDFL
presented in chapter 4, and an ultra-low dopant concentration Tm-doped fibre
(TDF), a TDFL which displays 47 W of output power at 1726 nm is presented. The
tuning capabilities of this pump and fibre combination are also explored; A
maximum tuning range of 371 nm (1654-2025 nm), and 360 nm above 1 W, is
presented, an improvement of 44% over that previously reported for similar
fibre compositions.
The commercial options for pumping Er:YAG in the 1532 nm
band are explored in chapter 6. Accessing the narrow absorption line at 1532 nm
requires a pump source such as an Er/Yb fibre laser. By comparing the relative
performance of two commercial fibres, it is shown that their composition;
primarily the ratio of erbium to ytterbium, has a significant impact on their
performance limits. With the higher ratio of erbium to ytterbium displaying
much higher spectral purity. In a simple linear configuration a maximum output
power of 15 W is achieved with an efficiency of 42% with a spectral purity of
99.3%.
Aluminium beam dumps are frequently used to terminate high
power beams where needed. It is often taken for granted that these dumps are
not perfect absorbers, particularly as a black anodised coating may lead one to
intuitively think otherwise. In v chapter 7, a simple and reliable method for
determining the total reflectivity of a material is developed and used to
characterise a variety of aluminium coatings. Several coatings are tested, all
of which appear black and are thus assumed to absorb in the visible region.
Reflectivity is determined by measuring the amount of energy deposited into a
known mass of aluminium through calorimetry and calculating the transmission of
a known beam power. A number of coatings tested displayed reflectivity below
20% at 975 nm, 1580 nm, and 2090 nm. However, it is found that a number of
these coatings display a very low damage threshold. In particular, powder
coated samples which are polymer-based. Only one of the coatings tested in this
work is shown to withstand suitable beam powers, with an approximate damage
threshold at 975 nm of 1470 W cm−2 . Though thoughtful beam dump design may not
preclude coatings with a lower damage threshold.
University of Southampton
Burns, Mark, David
7f7ca346-f31a-46cf-a848-acb4bcae18b9
Burns, Mark, David
7f7ca346-f31a-46cf-a848-acb4bcae18b9
Shardlow, Peter
9ca17301-8ae7-4307-8bb9-371df461520c
Clarkson, W.A.
3b060f63-a303-4fa5-ad50-95f166df1ba2
Burns, Mark, David
(2021)
Development of Short-wave Infrared Fibre Lasers.
Zepler Institute for Photonics and Nanoelectronics, Doctoral Thesis, 164pp.
Record type:
Thesis
(Doctoral)
Abstract
Although Thulium and erbium doped fibre lasers are common,
and used in a wide array of applications, there are methods of operation which
are not well matured. In this work, the operation of laser sources utilising
both dopants in power scalable architectures is investigated to explore their potential.
To mitigate the impact on device efficiency caused by long
device lengths in Er-doped fibre lasers (EDFLs), brightness enhancement of
few-moded fibres through bend loss is investigated in chapter 3. By careful
design of the fibre to compromise between core to cladding area ratio and modal
content, it is found that inducing bend loss is an effective way to achieve
diffraction limited beam quality in large mode area (LMA) fibres.
In chapter 4 it is discussed how EDFLs compare against
competing sources in the 1500 - 1600 nm wavelength band. In particular, how
power-scaling differs between Yb sensitised Er-doped sources, and Er-only
devices. The impact of pair-induced-quenching (PIQ) and long device lengths is
modelled to arrive at optimal device parameters, which are then utilised in a
real device. In a cladding pumped configuration, 104 W of singlemode output
power is demonstrated with slope efficiencies of 24% (30%) with respect to
launched (absorbed) pump power. Furthermore, the linearity of the observed
slope efficiency and good thermal properties of the device lend themselves to
further power scaling by increasing the available pump power and further
optimisation of the fibre design.
In chapter 5, the difficulty in operating Tm-doped fibre
lasers (TDFLs) around 1700 nm is discussed, and the relevant fibre design
parameters modelled. Through the use of in-band core-pumping with the EDFL
presented in chapter 4, and an ultra-low dopant concentration Tm-doped fibre
(TDF), a TDFL which displays 47 W of output power at 1726 nm is presented. The
tuning capabilities of this pump and fibre combination are also explored; A
maximum tuning range of 371 nm (1654-2025 nm), and 360 nm above 1 W, is
presented, an improvement of 44% over that previously reported for similar
fibre compositions.
The commercial options for pumping Er:YAG in the 1532 nm
band are explored in chapter 6. Accessing the narrow absorption line at 1532 nm
requires a pump source such as an Er/Yb fibre laser. By comparing the relative
performance of two commercial fibres, it is shown that their composition;
primarily the ratio of erbium to ytterbium, has a significant impact on their
performance limits. With the higher ratio of erbium to ytterbium displaying
much higher spectral purity. In a simple linear configuration a maximum output
power of 15 W is achieved with an efficiency of 42% with a spectral purity of
99.3%.
Aluminium beam dumps are frequently used to terminate high
power beams where needed. It is often taken for granted that these dumps are
not perfect absorbers, particularly as a black anodised coating may lead one to
intuitively think otherwise. In v chapter 7, a simple and reliable method for
determining the total reflectivity of a material is developed and used to
characterise a variety of aluminium coatings. Several coatings are tested, all
of which appear black and are thus assumed to absorb in the visible region.
Reflectivity is determined by measuring the amount of energy deposited into a
known mass of aluminium through calorimetry and calculating the transmission of
a known beam power. A number of coatings tested displayed reflectivity below
20% at 975 nm, 1580 nm, and 2090 nm. However, it is found that a number of
these coatings display a very low damage threshold. In particular, powder
coated samples which are polymer-based. Only one of the coatings tested in this
work is shown to withstand suitable beam powers, with an approximate damage
threshold at 975 nm of 1470 W cm−2 . Though thoughtful beam dump design may not
preclude coatings with a lower damage threshold.
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Development of Short-wave Infrared Fibre Lasers MD Burns
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Submitted date: 21 September 2021
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Local EPrints ID: 455722
URI: http://eprints.soton.ac.uk/id/eprint/455722
PURE UUID: 7c317007-6afe-44b5-80dc-072453c421e8
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Date deposited: 31 Mar 2022 16:37
Last modified: 18 Mar 2024 03:21
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Mark, David Burns
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