The field of mid-infrared fiber photonics has seen significant progress in recent years [1]. In virtually all molecules, transitions involving changes in both vibrational and rotational states can be excited by illumination with light at midinfrared wavelengths from ~ 2 – 15 Μm, giving rise to a plethora of application in environmental sensing, defense, and medicine, to only name a few. However, for most applications, compact and monolithic laser sources without bulky and sensitive free-space optical components are needed. While in-fiber components in mid-infrared compatible soft-glass fibers [2,3] as well as fiber endcaps [4] for long-term stable operation have both been demonstrated, little work to date has focused on the fabrication of fiber-pigtailed optical chips that could offer additional functionalities. The femtosecond laser direct-write technique is a highly versatile method that enables the inscription of tailored three-dimensional photonic circuits into bulk glasses [5]. Here we summaries our recent progress into the fabrication of linear and nonlinear waveguide chips for the realization of all fiber mid-infrared sources.
In a recent report, the National Academies of Science, Engineering, and Medicine (NASEM) recommends that “the United States should start a national program of accompanying research and technology leading to the construction of a compact pilot plant that produces electricity from fusion at the lowest possible capital cost.” It is generally acknowledged that a decarbonization of the world’s energy system is unavoidable to combat climate change. While an exothermic chemical reaction such as the combustion of fossil fuels produces an energy of <1 eV per molecule, a nuclear fusion reaction is an attractive alternative as it releases 10 million times more energy. To date, considerable effort has been devoted to research involving the fusion between the nuclei of the two heavy isotopes of hydrogen: deuterium (D) and tritium (T). However, the main roadblock for the adoption of this technology is the need to heat the fuel to temperatures in the order of 50 million Kelvin and to keep it stable under extreme pressure conditions. Recent results show that this difficulty can be overcome by utilizing the nonthermal radiation pressure that can be generated via chirped-pulse amplifier laser systems and can trigger the fusion of hydrogen and boron-11 nuclei, producing clean energy in the form of kinetic alpha particles, thus sidestepping nuclear radiation problems due to the aneutronic nature of the process.
Mid-infrared (mid-IR) fiber lasers that are based on dysprosium (Dy) as the active laser ion provide emission in the wavelength range between 2.6–3.4 μm and can thus bridge the spectral gap between holmium (Ho) and erbium (Er) based mid-IR lasers. Another distinct feature is the wide choice of pump wavelengths (1.1 μm, 1.3 μm, 1.7 μm, and 2.8 μm) that can be used. To date, pump wavelengths shorter than 1.1 μm have not been reported and all demonstrated pump wavelengths apart from in-band pumping suffer from pump excited state absorption (ESA). In this paper, we report new excitation wavelengths, 0.8 μm and 0.9 μm, for Dy-doped mid-IR fiber lasers. We have measured 18.5% and 23.7% slope efficiency (relative to launched pump power) for 0.8 μm and 0.9 μm pumping wavelengths, respectively. By comparing the residual pump power of experimental and numerical simulation data of a 0.5 m Dy-doped fiber, we have found that these new excitation wavelengths are free from pump ESA. Moreover, the high power laser diodes are commercially available at these new excitation wavelengths; therefore, the realization of a diode-pumped Dy-doped mid-infrared fiber laser might become feasible in the near future.
Muscovite is a naturally occurring crystalline mineral, a mica, with a unique layered structure with planes of low cleavage energy spaced by ~1.3 nm in the crystal structure. It is a dielectric insulator. Freshly cleaved muscovite surfaces are extremely flat, clean and used in many technical applications of the material. Previous laser ablation study of mica using ultraviolet, nanosecond duration pulses, led to a poor finish at the process sites (K. Rubahn et.al., J. Appl. Phys. 86(5), 2847, 1999). Interest in laser processing of the material, other than CO2 laser cutting of mica sheets, was subsequently, and not surprisingly, curtailed. Here-in we report the morphologies of the laser processed site affected by a single, ~150 fs duration, 800nm wavelength, 6 micron spotsize laser pulse focussed on the surface of a mica substrate. A systematic sequence of the morphology as the fluence of the single pulse is increased is obtained. Optical surface profiling and field emission secondary electron microsocopy are used to characterise the site morphology. Time of flight secondary ion mass specroscopy has been used to map the redistribution of key elements at the process site. Muscovite emerges as a fascinating material in its response to a femtosecond laser pulse. Useful marking without creation of debris beyond the footprint of the laser spotsize is achieved at a flunece as low as 2.4 J/cm2. There is evidence of plasticity and cavitation within the sequence of morphologies found.
The next-generation gravitational wave detectors aim to enhance our understanding of extreme phenomena in the Universe. The high-frequency sensitivity of these detectors will be maximized by injecting squeezed vacuum states into the detector. However, the performance advantages offered by squeezed state injection can be easily degraded by losses in the system. A significant source of loss is the mode mismatch between optical cavities within the interferometer. To overcome this issue, new actuators are required that can produce a highly spherical wavefront change, with minimal higher order aberrations, whist adding low phase noise to the incident beam.
We present a compact design for a 1064 nm Q-Switched waveguide laser based on a liquid crystal transducer. Directly integrating the input-coupling mirror on the chip and utilising a Grin lens to also integrate the modulator optics enables a miniaturised setup. The preliminary experimental results have demonstrated that the Q-switched laser pulses with a pulse width of 45 ns and average output power of 4.5 mW can be achieved with a pump power of 350 mW, when an electrical signal with a repetition rate of 5 kHz, a peak-to-peak voltage of 30 V and a duration of 4 µs is applied. This work was supported by the Office of Naval Research Global (N62909-18-1-2147).
We demonstrate the first stable mode-locking from an Er3+ doped fluoride fibre laser cavity using various novel two-dimensional saturable absorber materials such as PtSe2 and MXene operating near 2.8 μm wavelength to the best of our knowledge. The linear cavity includes a high reflective chirped fibre Bragg grating to provide wavelength stability. The observed mode-locked pulse train has a 30 MHz repetition rate and an average power of 223 mW. Our results demonstrate the feasibility of using the novel two-dimensional nanomaterials such as PtSe2 and MXene into the fibre laser cavity for the application in mid-infrared wavelength regime.
We report on the latest development of our photonics-based brain-machine interface. This work done in collaboration between UNSW and Macquarie University – and supported by the US Office of Naval Research – directly addresses the long-term DARPA challenge of producing implantable chips with 1 million neural connections. To the best of our knowledge, no technology has demonstrated the potential so far to scale up to such a massive number of channels.
The development of new, compact mid-infrared light sources is critical to enable biomedical sensing applications in resource-limited environments. Here, we review progress in fiber-based mid-IR sources, which are ideally suited for clinical environments due to their compact size and waveguide format. We first discuss recent developments in mid-IR supercontinuum sources, which exploit nonlinear optic phenomena in highly nonlinear materials (pumped by ultrashort pulse lasers) to generate broadband spectra. An emerging alternative approach is then presented, based on broadly tunable mid-IR fiber lasers, using the promising dysprosium ion to achieve orders of magnitude higher spectral power density than typical supercontinua. By employing an acousto-optic tunable filter for wavelength tuning, an electronically controlled swept-wavelength mid-IR fiber laser is developed, which is applied for absorption spectroscopy of ammonia (NH3), an important biomarker, with 0.3 nm resolution and 40 ms acquisition time.
We demonstrate the direct inscription of aperiodic fiber Bragg gratings (AFBGs) for their use as in-fiber filter elements. The modifications are induced by focusing ultrashort laser pulses with an oil-immersion objective into the fiber core. We apply an advanced point-by-point inscription technique for flexible period adaptation. The fabricated AFBGs are targeted on the suppression of 10 lines in a single grating and simulations based on the specific design show excellent agreement. Furthermore, we discuss the application in astronomy as filters for the suppression of OH emission lines.
We demonstrate a passively mode-locked holmium-praseodymium co-doped ring fiber laser that produces an estimated 950 fs pulsewidth and peak power of 4.3 kW at a pulse repetition rate of 74 MHz. The measured center wavelength was 2.86 µm which overlaps more strongly with liquid water whilst better avoiding atmospheric water vapor which overlaps more strongly with previously reported ultrafast Er3+ fiber lasers operating at 2.8. Thus the present system should display better long term stability compared to the Er3+-based system and at the same time, be a more practical tool for interaction with biological tissues.
The laser was constructed using a 1.2 m long double-clad fluoride fiber doped with Ho3+ and Pr3+ ions and arranged into a unidirectional ring resonator that was resistant to instabilities associated with back reflections. Two semiconductor 1150 nm laser diodes with the maximum combined output of 7.5 W were used to pump the fiber. Mode-locking was achieved using the combination of two techniques: sub-picosecond pulses were produced by nonlinear polarization evolution after longer pulses were initially obtained using an in-cavity GaAs saturable absorber having a modulation depth of 90% and a relaxation time of 10 ps. A standard arrangement employing two waveplates and an optical isolator was introduced into the resonator to carry out nonlinear polarization rotation. The average power of the mode-locked laser reached 350 mW after the 50% outcoupling mirror. The RF signal-to-noise ratio reached 67 dB for the first peak at the resolution bandwidth of 10 kHz.
Tightly focused femtosecond laser pulses can be used to alter the refractive index of virtually all optical glasses. As the
laser-induced modification is spatially limited to the focal volume of the writing beam, this technique enables the
fabrication of fully three-dimensional photonic structures and devices that are automatically embedded within the host
material. While it is well understood that the laser-material interaction process is initiated by nonlinear, typically
multiphoton absorption, the actual mechanism that results in an increase or sometimes decrease of the refractive index of
the glass strongly depends on the composition of the material and the process parameters and is still subject to scientific
studies.
In this paper, we present an overview of our recent work aimed at uncovering the physical and chemical processes that
contribute to the observed material modification. Raman microscopy and electron microprobe analysis was used to study
the induced modifications that occur within the glass matrix and the influence of atomic species migration forced by the
femtosecond laser writing beam. In particular, we concentrate on borosilicate, heavy metal fluoride and phosphate glasses.
We believe that our results represent an important step towards the development of engineered glass types that are ideally
suited for the fabrication of photonic devices via the femtosecond laser direct write technique.
Since the discovery, that a tightly focused femtosecond laser beam can induce a highly localized and permanent refractive index change in a wide range of dielectrics, ultrafast laser inscription has found applications in many elds due to its unique 3D and rapid prototyping capabilities. These ultrafast laser inscribed waveguide devices are compact and lightweight as well as inherently robust since the waveguides are embedded within the bulk material. In this presentation we will review our current understanding of ultrafast laser - glass lattice interactions and its application to the fabrication of inherently stable, compact waveguide lasers and astronomical 3D integrated photonic circuits.
We report laser-written chip lasers with potential to be a platform planar technology versatile enough to cover the visible through to the mid-infrared spectral region. By femtosecond laser direct-writing a thulium doped fluoride based glass host (ZBLAN), we have demonstrated a 151% quantum efficiency λ=1.9 μm laser with a close to diffraction limited beam quality (M2~ 1.12 ± 0.08) with 225 nm of continuous tunability in a device that can be rapidly fabricated by singlestep optical processing. The 9 mm long planar chip developed for concept demonstration contains fifteen large modearea waveguides that can operate in semi-monolithic or external cavity laser configurations. This chip laser has achieved the highest quantum efficiency from a planar glass waveguide laser. The depressed cladding geometry supports the largest fundamental modes reported for a rare-earth doped waveguide laser thereby favouring high peak-power operation which is demonstrated by achieving 1.9 kW peak-power pulses when Q-switched.
High contrast imaging techniques such as aperture masking interferometry allow for the detection of faint companions
such as substellar companions by utilizing light from the planet itself. This allows access to study a larger population of
planetary companions as compared to the transit technique where only systems viewed edge on can be studied, for
example. However, aperture masking has several shortcomings including, low throughputs, limited Fourier coverage,
and leakage of residual atmospheric noise due to phase corrugations across each sub-apertures. These limitations can be
overcome by remapping the pupil with single-mode waveguides. We present an integrated pupil remapping
interferometer, known as Dragonfly, that aims to do just that. We discuss the progress we have made over the past year
in developing a stable and robust instrument and elucidate challenges and the innovative solutions that were applied.
Finally we discuss improvements to the instrument that will enable future scientific endeavors and outline the expected
performance limitations.
In this publication we present the results of a detailed study into directly written multimode waveguides for astronomical
applications. We show that waveguides up to 100 ìm across can be inscribed with the cumulative heating form of this
technique. The waveguides have 2 concentric guiding regions which are elliptical; a core that has an average ellipticity
of 1.1±0.1 and an outer cladding with an ellipticity of 0.15±0.03. It was demonstrated that the ellipticity of the
waveguides could be reduced by creating "structured" waveguides which consist of several waveguides stacked together.
The 7 mm long waveguides demonstrated insertion losses at 800 nm as low as 39% when light was launched and
collected by a standard multimode fibre (50 ìm core diameter and numerical aperture of 0.12), which is representative of
the fibres currently used on astronomical installations. More importantly, we show for the first time that structured
waveguides designed to have outer cladding regions which match the dimensions of the core of the launch and collection
fibers, have lower insertion losses than structured waveguides designed to have matching core dimensions. It is believed
that by moving to longer wavelengths of operation and exploring other structuring and beam shaping techniques it may
be possible to reduce the losses even further and make these waveguides of practical use for astronomy.
We report on direct inscription of type-II waveguides in bulk titanium-doped sapphire with an ultrafast chirpedpulse
oscillator. Ti3+:Sapphire is of particular interest due to its large emission bandwidth which enables a
broadband tunability and generation of ultra-short pulses. However, its lasing threshold is high and powerful
high brightness pump sources are required. The fabrication of a waveguide in Ti3+:Sapphire could thus enable
the fabrication of low-threshold tunable lasers and broadband fluorescence sources. The latter are of interest for
optical coherence tomography where the obtainable resolution scales with the bandwidth of the light source.
The fabricated waveguides are formed in-between two laser induced damage regions. This technique has been
applied to other crystalline materials (e.g. LiNbO3) but not in Ti3+:Sapphire, yet. The size of the structural
changed regions is strongly dependent on the writing laser polarization. These damage regions of changed
structure cause a stress-field inside the crystalline lattice which consequently increases the refractive index to
form a waveguide. The written structures exhibit a strong birefringence and two waveguides that support
orthogonal polarized modes are formed between each pair of damage lines. Linearly polarized light parallel to
the crystal's surface is guided between the two damage regions while a waveguide for the orthogonal polarization
is formed underneath.
The propagation properties of the waveguides are characterized by their near-field profiles and insertion losses
with respect to the writing parameters. Further the fluorescence output power is measured and the emission
spectra of the waveguides are compared to the bulk material.
In this paper we demonstrate a simple temperature and strain discriminating sensor based on a single fibre Bragg grating
inscribed by a femtosecond laser via the point-by-point technique. These gratings exhibit strong and extensive cladding
mode structures and by simultaneously monitoring both the Bragg wavelength and a cladding mode spaced by ~ 40 nm
from the Bragg peak, as a function of both temperature and strain, it is possible to distinguish between the two effects
and potentially obtain and increased sensitivity over prior reports for similar systems. In preliminary experiments the two
parameters were determined with an accuracy of 1°C and 40 με respectively. Due to the close spectral separation of the
two peaks that were monitored, quick and simultaneously measurements of the two parameters was possible, allowing
for real time measurements of the temperature and strain and making the device practical for use in various applications.
We show evidence of rapid photo-erasure of ultra stable Type-II fibre Bragg gratings written with a femtosecond laser
into the active medium when employed as high reflectors in >1kW medium power Yb3+-doped Q-switched fibre laser
cavities.
A well-known side-effect from fibre Bragg grating UV-fabrication is short wavelength attenuation, where irradiation
with laser light, usually in the UV, generates both defect-induced absorption and scattering. These losses are especially
problematic for high power optical fibre lasers operating at shorter wavelengths where resonant assisted coupling into the
glass matrix through the rare earth ions can take place (e.g. Yb3+). In this, work we present a study of the relative
magnitude of short wavelength attenuation in gratings written by the point-by-point method using a Ti-sapphire
femtosecond laser operating at 800 nm. Such gratings are very stable and have been used as the feedback elements in
fibre lasers with powers exceeding 100 W. We show that the scattering properties responsible for the attenuation are
analogous to those associated with type II gratings written with UV lasers.
We report on the development of a compact, all fibre laser source operating at 1 μm with a linearly polarized (extinction ratio > 20 dB) and very narrow linewidth (12 pm) output. The unique cavity design included a fibre Bragg grating high reflector and output coupler, inscribed via the point-by-point method directly into the active core. A single splice within the cavity between the fibre incorporating the high reflector and the output coupler permitted re-orientation of the stressors at an angle of 90 degrees to each other, which produced a single lasing polarisation. This simple technique removed the need for a more complicated and expensive polarization controller.
Chalcogenide glass based optical waveguides offer many attractive properties in all-optical signal processing because of the large Kerr nonlinearity (up to 420 × silica glass), the associated intrinsic response time of less than 100 fs and low two-photon absorption. These properties together with the convenience of a fiber format allow us to achieve all-optical signal processing at low peak power and in a very compact form. In this talk, a number of non-linear processing tasks will be demonstrated including all-optical regeneration, wavelength conversion and femtosecond pedestal-free pulse compression. In all-optical regeneration, we generate a near step-like power transfer function using only 2.8 m of fiber. Wavelength conversion is demonstrated over a range of 10 nm using 1 m of fiber with 7 ps pulses, peak power of 2.1 W, and 1.4 dB additional penalty. Finally, we will show efficient compression of low-power 6 ps pulses to 420 fs around 1550 nm in a compact all-fiber scheme.
These applications show chalcogenide glass fibers are very promising candidate materials for nonlinear all-optic signal processing.
We report on the generation of sub-30fs pulses from a mirror-dispersion-controlled (MDC) Ti:sapphire oscillator, containing a multiple-pass Herriott-cell for increasing the cavity length. Using that scheme, repetition rates down to some few MHz could be achieved. To avoid multiple pulsing instabilities, we operate the laser in a regime of slight positive group-delay dispersion (GDD) over a very broad wavelength range. This results in the formation of strongly chirped light pulses, reducing the otherwise very high peak-intensity inside the laser crystal, which would limit the maximum output energy. We have investigated the spectral phase associated with these pulses with the help of the well known SPIDER-technique, and, based on the results, have constructed an optimized compressor.
When pumped with the full 10 W of a frequency-doubled Nd:YVO4 laser (Coherent Verdi V10), output energies well above 200 nJ could be obtained. As no signs of instabilities were observed, we believe, that our approach is scaleable to even higher energies if more powerful pump lasers are used. Thanks to the excellent beam profile, high-resolution micromachining of various materials, including transparent dielectrica could be demonstrated.
Results on sub-micrometer surface modification of transparent materials will be presented.
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