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We report a new method of generating continuous-wave (cw) radiation, Q-Switched as well as mode-locked laser pulses from a single linear fiber laser cavity. The three operating modes can be selected by the electric signal that is applied to an intracavity liquid crystal (LC) transducer cell. In addition, this is the first demonstration of using an LC modulator as an active mode-locking device in a fiber laser oscillator to date. In the proof-of-principle experiments presented here, the Q-Switched laser pulses with a duration of 1.3 $ {\mu }\text{s}$ , a maximum energy of 2.7 $ {\mu }\text{J}$ , and a peak power of 1.93 W were generated at low repetition rates ranging from 0.2 to 6 kHz. In mode-locked operation, pulse trains with repetition rates as high as 944.5 kHz and a shorter duration of 65 ns were achieved. Finally, a slight modification of the LC cell allows for a direct comparison between amplitude modulation (AM) and frequency modulation (FM) mode-locking.

We demonstrate operation of a mid-infrared dysprosium-doped fiber laser with emission at 3388 nm, representing the longest wavelength yet achieved from this class of laser, to the best of our knowledge. Oscillation far removed from the D y 3 + gain peak around 3 µm is achieved through the design of a high feedback optical cavity employing a directly inscribed fiber Bragg grating as the output coupler. Laser performance is characterized by a slope efficiency with respect to injected pump power of 38% and maximum output power of 134 mW, an improvement of at least three orders of magnitude over prior attempts at long wavelength D y 3 + fiber laser operation. This wavelength coincides with a maximum in the absorption coefficient of PMMA, which we exploit for preliminary demonstration of the utility of this source in polymer processing.

We present our work towards a 3.5 µm Er3+:ZBLAN femto-second laser inscribed waveguide laser. The waveguide was made by extruding bulk ZBLAN glass into a slab for the first time, to the best of our knowledge. The slab was then cut and polished with multiple concentric-ring waveguides of 28 – 36 µm core diameter written into the glass along its long axis resulting with a 125 mm long waveguides embedded within a glass rectangle of 7×10×125 mm. The waveguide structures are pumped by two single mode pump sources at 976 nm and 1973 nm employing the dual-wavelength pumping method for obtaining 3.5 µm operation. Numerical analysis of the system will be presented as well as our latest experimental results.

First demonstrated over four decades ago, fiber gratings, and in particular fiber Bragg gratings (FBGs), have become indispensable and ubiquitous components within fiber laser cavities as well as optical communication networks and sensor systems. Because of their overwhelming use, the bulk of published work to date has concentrated on fibers that are composed of silica-based glasses, yet those become virtually opaque at wavelengths above 2 μm, i.e., in the technically increasingly important mid-infrared part of the electromagnetic spectrum. Soft glass fluoride fibers on the other hand, in particular those composed of ZBLAN (abbreviation for ZrF4-BaF2-LaF3-AlF3-NaF), offer low-loss transmission out to wavelengths of up to almost 4 μm. However, while fiber manufacturing itself has now reached a high level of maturity, with passive fiber attenuation levels as low as 1 dB/km becoming commercially available, grating fabrication in these fibers remains challenging, and research into suitable inscription techniques is still a very active and ongoing scientific field. This review aims to provide an overview of work that has been done in this area to date with an emphasis on femtosecond-laser based fabrication methods.

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.

ToF-SIMS is a sensitive technique for interrogating chemical composition at or near the surface of a material, with an emphasis on detecting elements present in extremely low quantities. Here, it was utilized to determine changes in element distribution at a muscovite surface caused by a single 150 fs laser pulse at 800 nm. Muscovite is a mineral with the standard chemical formula KAl2 (Si3Al) O10(OH)2. As a natural mineral, the composition varies. Several ions were studied including aluminium (Al), potassium (K), sodium (Na), and silicon (Si). The laser-irradiated surface area is microscopic - a few microns in diameter. To achieve spatial resolution of the ions within the laser treated region, a ∼100 nm wide ion beam is used. The laser material interaction produces a non-flat surface morphology that changes as the laser pulse fluence increases. Thus, ToF-SIMS is influenced by the ion beam shadowing effect. After the implications of artefacts linked to this are taken into account, there is a finding of net enrichment of sodium and potassium due to the laser irradiation. ToF-SIMS also shows differences in the elemental makeup of nanoparticulates ejected from the laser treated region and redeposited on the surrounding surface. With careful consideration of surface morphological changes, this study shows that ToF-SIMS can be employed in laser materials processing studies to investigate changes in elemental distribution.

Ultrafast laser pulse processing is an important tool used to modify the structural and morphological properties of a target material. Muscovite, a naturally occurring nano-layered mineral, is a material that has exhibited a complex systematic variation in the topography of laser processed sites as a function of the fluence of a single 150 fs, 800 nm laser pulse. These sites include depressed craters; raised bumps; bumps in craters, both with and without rims; and ultimately the onset of what would be identified as standard ablation. A means of quantifying the sequence of observed topographies of these micron sized modifications; which have height features ranging from a few, to a few hundred, nanometers; is required. We present the quantification of the sub-cubic-micrometer laser-modified-volumes in muscovite using full 3-D profiles obtained from optical surface profilometry. This includes quantifying modification volumes above and below the original surface plane separately. This gives information about redistribution of material. The net volume change indicates whether there is a net or apparent volume increase due to rarefraction, delamination, or cavitation, or a net volume removal. Thus, the volumetric analysis in combination with the morphological knowledge of the modified sites emerges as a potential indicator of the likely physical phenomena at play. This is illustrated by the volumetric analysis reported here-in for muscovite, exposed to single pulses in the fluence range 1.5–7 J/cm2. The OSP technique is commonly used to characterize surface roughness, and, morphology of processed surfaces, including laser processed surfaces. But, to our knowledge, this is the first time a detailed micro-volume analysis has been reported in a laser processing context. This can be applied universally to different laser processed materials, especially when multiple physical processes are at play. The resolution of the measurements is limited by the lateral and vertical resolution specifications of the OSP instrument.

We report two excited-state absorption free near-infrared pump wavelengths (0.8 and 0.9 μm) for dysprosium-doped mid-infrared fibre lasers. High power diodes are available at these wavelengths, which opens up the opportunity for a diode-pumped system.

We report the direct femtosecond laser inscription of high reflective fibre Bragg gratings into the core of InF3 fibres. These results pave the way to the development of all-fibre mid-infrared lasers above 4 µm.

We have modified an asynchronous cross-correlation technique for measuring the duration of low energy ultrafast ultraviolet pulses using an auxiliary probe laser, extending its capability to sub-100 fs pulses that are not necessarily stable.

We report the first wavelength stabilized all-fibre ultrafast mid-infrared laser using MXene as a novel saturable absorber. This all-integrated pulsed laser is a promising tool for a broad range of applications in the mid-infrared regime.

Muscovite, a dielectric, shows a qualitatively different response to irradiation with a single ~150fs laser pulse at 515 nm as compared to 800 nm. Pulse fluences up to 7J/cm2 are studied. © 2020 The Author(s)

We report the direct generation of sub-100 fs ultraviolet pulses from a synchronously-pumped mode-locked Ce:LiCAF laser. Dispersion-tuning around 290 nm via cavity length is also demonstrated, when setup for longer pulses. © 2020 The Authors

A systematic parameter study into the inscription of optical waveguides into the mid-infrared compatible fluorophosphate glass N-FK58 is presented. Results show that the fabrication of structures with high numerical aperture is feasible in this material.

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 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.

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 research into the fabrication of different types of gratings into optical fibres that are transparent at mid-infrared wavelengths. In particular, we focus on direct femtosecond laser inscription of fibre-Bragg gratings with parallel as well as with tilted grating planes into zirconium and indium fluoride fibres. It is shown that post-annealing of the gratings can lead to an increase or decrease in reflectivity depending on the fabrication method and that even a relatively low concentration of rare-earth ions that are present in active fibres can have a big influence on the inscription process.Further, the feasibility investigating the physical mechanisms that underpin the induced refractive index modulation by utilising argon-beam cross-sectional polishing of the inscribed fibres followed by spatially resolved Raman microscopy and electron probe microanalysis, is discussed.

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 report on the feasibility of MXene and platinum diselenide (PtSe2) as novel saturable absorbers for the development of wavelength stabilized passively mode-locked mid-infrared fibre laser systems. After evaluating the performance of individual absorbers in a test cavity, we demonstrate a linear all-fibre laser cavity that utilizes a high reflective chirped fibre Bragg grating for wavelength selective feedback. The observed mode-locked pulse train from this Er3+:ZBLAN fibre laser has a 37 MHz repetition rate with an average power of 603 mW and a spectral width of 721 pm. Our results show that MXene and PtSe2 are promising nonlinear materials for all-integrated ultrafast fibre laser cavities for the important mid-infrared spectral region.

Muscovite, a nanolayered transparent crystalline dielectric, is shown to respond like a polymer upon irradiation with a single 190 fs duration laser pulse, at a wavelength of 515 nm, for a range of fluences (1.4–6.4 J/cm2). Laser-pulse-modified sites were characterized using field emission scanning electron microscopy (FESEM). Cavitation and bubbling are observed in the laser processed region similar to previous observations in poly-methyl-methacrylate (PMMA). The diameter of these sites is consistent with the standard model commonly applied in laser ablation studies. These polymer-like results at 515 nm are in contrast to the response of muscovite exposed to a 150-fs single laser pulse at 800 nm for a similar range of fluences. Where a diverse range of topologies was observed as the fluence was increased. Additionally, we also report an absorption band edge at ~4 eV (for the muscovite sheet used in the study). This is lower than the previously reported band gap energy value of 7.8 eV. We propose that the differences observed at the two wavelengths are primarily due to either 2 or 3 photons being required for nonlinear photoionization and the impact of the mineral water content of muscovite (4.7 wt%).

Current active Q-switching is mainly generated by acousto-optical modulators (AOMs) or electro-optical modulators (EOMs). However, EOMs make the setup bulky, while AOMs require the radiofrequency (RF) signal and water-cooling. We present a novel approach to active Q-switching of an integrated waveguide chip laser by utilizing a deformed helix ferroelectric liquid crystal cell (6mm × 6mm) with a thickness of 2 mm. This device can be directly integrated onto the Ytterbium-doped waveguide chip and controlled by the electrical signal. In experiments, with an electrical signal with a pulse duration of 2 μs and a magnitude from 10 V to 84 V, the Q-switched lasers can be observed at a repetition rate ranging from 0.1 kHz to 20 kHz. The shortest pulse duration and the maximum slope efficiency is 38 ns and 22% respectively. This novel integrated and low-cost laser source is a promising tool for a broad range of applications such as gas sensing and LIDAR.

We report on the fabrication of, to the best of our knowledge, the first highly reflective fiber Bragg gratings for the 4 µm wavelength range. A second-order grating with a coupling coefficient ( κ ) of 230 m − 1 , losses < 0.25 d B / c m , and a bandwidth of approximately 3 nm was inscribed into the core of a passive indium fluoride ( I n F 3 ) fiber using a femtosecond (fs) laser. Thermal annealing of this grating at a temperature of 150°C for 90 min resulted in the enhancement of κ to 275 m − 1 . Further, we show that I n F 3 fibers respond very differently to irradiation with fs laser pulses as compared to ZBLAN fibers and that this difference manifests itself in a significantly larger process window for inscription and in the formation of a more complex refractive index profile that is believed to be caused by the larger nonlinearity of I n F 3 . This Letter paves the way to the development of new wavelength stabilized all-fiber mid-infrared lasers beyond 4 µm.

Ultrafast, femtosecond laser pulse interaction with dielectric materials has shown them to have significantly higher laser fluence threshold requirements, as compared to metals and semiconductors, for laser material modification, such as laser ablation. Examples of dielectrics are crystalline materials such as quartz and sapphire, and amorphous glasses. The interaction between femtosecond laser pulses, at a wavelength with negligible linear absorption, and a dielectric has been found to be weak, and multiple pulse irradiation is therefore typically used in order to see significant and quantifiable effects. In this study the dielectric is the crystalline, layered, natural mineral muscovite, a mica with formula KAl_2 (Si_3 Al) O_10 (OH)_2. Muscovite, newly cleaved, is used in a wide range of technological and scientific applications including as an insulating material in electronics and as an ultra-flat and ultra-clean substrate. A single, ~800 nm wavelength, ~6 micron spotsize, ~150 fs laser pulse is found to lead to a systematic range of laser modification topologies, as a function of the fluence of the single laser pulse, including bulk removal of material. The fs laser pulse/material interaction is greater than expected for a standard dielectric at a given fluence. Optical surface profiling and FESEM are used to characterise the topologies. Contrasting the results of the two techniques supports the use of optical surface profiling to characterise the material modification despite its limitations in lateral resolution as compared to FESEM. The interlayer mineral water content of natural muscovite is proposed as the primary reason that mica behaves differently to a standard dielectric when irradiated with a single 800 nm fs laser pulse.

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.

Rare-earth-doped fiber lasers are emerging as promising high-power mid-infrared sources for the 2.6-3.0 {\mu}m and 3.3-3.8 {\mu}m regions based on erbium and holmium ions. The intermediate wavelength range, however, remains vastly underserved, despite prospects for important manufacturing and defense applications. Here, we demonstrate the potential of dysprosium-doped fiber to solve this problem, with a simple in-band pumped grating-stabilized linear cavity generating up to 1.06 W at 3.15 {\mu}m. A slope efficiency of 73% with respect to launched power (77% relative to absorbed power) is achieved: the highest value for any mid-infrared fiber laser to date, to the best of our knowledge. Opportunities for further power and efficiency scaling are also discussed.

A miniaturized deformed helix ferroelectric liquid crystal transducer cell was used in combination with a femtosecond laser inscribed active waveguide to realize a compact actively Q-switched laser source. The liquid crystal cell was controlled by a low-voltage frequency generator and laser pulse durations below 40 ns were demonstrated at repetition rates ranging from 0.1 kHz to 20 kHz and a maximum slope efficiency of up to 22%. This novel, integrated and low-cost laser source is a promising tool for a broad range of applications such as trace gas sensing, LIDAR, and nonlinear optics. To the best of our knowledge, this is the first demonstration of an actively Q-switched glass waveguide laser that has a user-variable repetition rate and can be fully integrated.

We report the femtosecond laser inscription of a 45◦ tilted fibre Bragg grating (TFBG) into ZBLAN fibre. Integrating this TFBG into a mid-IR fibre laser cavity resulted in 20.5 dB output polarization extinction ratio.

We demonstrate a novel all-fiber laser system with an integrated liquid crystal transducer cell that can electronically be switched between continuous-wave, mode-locked (achieved by both, amplitude and phase modulation) or q-switched operation.

We demonstrate the fabrication of aperiodic fiber Bragg gratings (AFBGs) for their application as filter elements. Direct inscription was performed by focusing ultrashort laser pulses with an oil-immersion objective into the fiber core and utilizing the line-by-line technique for flexible period adaptation. The AFBGs inscribed allow for the suppression of 10 lines in a single grating and are in excellent agreement with simulations based on the specific design. Applications in astronomy for the suppression of hydroxyl emission lines are discussed.

We demonstrate an optimized in-band-pumped dysprosium fiber laser with 73% slope efficiency and 1.1 W output at 3.15 μm: the first watt-level fiber source in the 3.0–3.4 μm region and highest ever efficiency mid-IR fiber laser.

We demonstrate the generation of 70-fs pulses (∼7 optical-cycles) from a mid-infrared mode-locked Ho:ZBLAN fiber laser using nonlinear compression with step-index chalcogenide fiber. Experiments are supported by numerical modelling, confirming the scalability of this approach.

We report the fabrication of fiber Bragg gratings (FBGs) in passive as well as doped fibers utilizing the femtosecond laser line-by-line technique. Narrow-linewidth linear gratings as well as broadband chirped gratings were inscribed into silica- and fluoride-glass optical fibers. Polarization-dependent characteristics of non-tilted and of 45°-tilted gratings are analyzed and the possibility of direct inscription into coated (i.e. non-stripped) fibers is demonstrated.

Output pulses from an ultrafast holmium-praseodymium co-doped fiber ring laser are spectrally broadened in different highly nonlinear chalcogenide fibers. Moderate levels of broadening are achieved in step-index fibers and the effect is utilized for nonlinear pulse compression. Much larger broadening factors can be observed in suspended-core fibers and polymer-protected robust all-chalcogenide microwires. Under optimized conditions, an ultra-broadband supercontinuum spanning from 2 – 12 μm is generated.

We propose and demonstrate a simple route to few-optical-cycle pulse generation from a mid-infrared fiber laser through nonlinear compression of pulses from a holmium-doped fiber oscillator using a short length of chalcogenide fiber and a grating pair. Pulses from the oscillator with 265-fs duration at 2.86 {\mu}m are spectrally broadened through self-phase modulation in step-index As2S3 fiber to 141-nm bandwidth and then re-compressed to 70 fs (7.3 optical cycles). These are the shortest pulses from a mid-infrared fiber system to date, and we note that our system is compact, robust, and uses only commercially available components. The scalability of this approach is also discussed, supported by numerical modeling., Comment: Published in Optics Letters

We report on our research into fluoride fiber-based 3 µm class laser sources. Using holmium as the gain medium, record-high peak power levels are achieved in mode-locked laser systems that emit ultrashort pulses in the water vapor transmission window around 2.9 µm. Highly nonlinear and dispersion-engineered hybrid chalcogenide-polymer microwires are utilized to extend the frequency range of those sources further into the mid-infrared. In addition, dysprosium- doped fibers are employed to demonstrate continuous-wave lasers that are tunable between 3 and 3.5 µm.

We have recently experimentally demonstrated that a novel liquid crystal-based photonic transducer for sensing systems could be utilized as an active Q-switch in a miniaturised and integrated waveguide laser system. In this paper, we now present a comprehensive numerical modelling study of this novel laser architecture by deriving a set of equations that accurately describe the temporal optical response of the liquid crystal cell as a function of applied voltage and by combining this theoretical model with laser-rate equations. We validate the accuracy of this model by comparing the results with previously obtained data and find them in excellent agreement. This enables us to predict that under realistic conditions and moderate pump power levels of 500 mW, the laser system should be capable of generating peak power levels in excess of 1.1 kW with pulse widths of about 20 ns, corresponding to pulse energies > 20 μJ. We believe that such a low-cost and ultra-compact laser source could find applications ranging from trace gas sensing and LIDAR to material processing.

We demonstrate record performance in a mid-IR ultrafast fiber laser by using holmium instead of erbium as the active gain medium. The 2.9 μm laser emits 180 fs pulses with 37 kW peak power.

We demonstrate a holmium-doped fluoride fiber laser that emits 37 kW peak power pulses with 180 fs pulse durations at 3 µm. The 100 nm redshift of holmium gain relative to erbium allows for minimal interaction with atmospheric water absorption resulting in a significant increase in performance for 3 µm class ultrafast fiber lasers.

We demonstrate supercontinuum spanning from 2.2 to 4.6 µm in a dispersion-engineered, As2Se3 microwire using a mode-locked holmium fiber laser operating at 2.9 µm. The output spectrum is > 50 times broader than the input laser spectrum.

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.

Mode-locked integrated mid-IR waveguide chip lasers with ultra-short pulse duration and high peak power are of great interest for a large range of applications like trace-gas spectroscopy and early-cancer detection. As those lasers are automatically embedded within a small block of doped glass, they are inherently robust and immune to environmental fluctuations. In this paper we investigate the suitability of various novel nanomaterials for the realisation of saturable absorbers for passive mode locking of femtosecond laser-written mid-infrared waveguide lasers. We compare and characterise saturable absorbers based on carbon nanotubes, graphene, topological insulators, transition metal dichalcogenides as well as black phosphorus and analyse their performance in a thulium-doped waveguide laser operating around 2 micron.

We compare and contrast novel techniques for the fabrication of chirped broadband fiber Bragg gratings by ultrafast laser inscription. These methods enable the inscription of gratings with flexible period profiles and thus tailored reflection and dispersion characteristics in non-photosensitive optical fibers. Up to 19.5 cm long chirped gratings with a spectral bandwidth of up to 30 nm were fabricated and the grating dispersion was characterized. A maximum group delay of almost 2 ns was obtained for linearly chirped gratings with either normal or anomalous group velocity dispersion, demonstrating the potential for using these gratings for dispersion compensation. Coupling to cladding modes was reduced by careful design of the inscribed modification features.

In the two decades since the first extra-solar planet was discovered, the detection and characterization of extra-solar planets has become one of the key endeavours in all of modern science. Recently, direct detection techniques such as interferometry or coronagraphy have received growing attention because they reveal the population of exoplanets inaccessible to Doppler or transit techniques, and moreover they allow the faint signal from the planet itself to be investigated. Next-generation stellar interferometers are increasingly incorporating photonic technologies due to the increase in fidelity of the data generated. Here, we report the design, construction and commissioning of a new high-contrast imager, the integrated pupil-remapping interferometer, an instrument we expect will find application in the detection of young faint companions in the nearest star-forming regions. The laboratory characterization of the instrument demonstrated high-visibility fringes on all interferometer baselines in addition to stable closure phase signals. We also report the first successful on-sky experiments with the prototype instrument at the 3.9-m Anglo-Australian Telescope. Performance metrics recovered were consistent with ideal device behaviour after accounting for expected levels of decoherence and signal loss from the uncompensated seeing. The prospect of complete Fourier coverage coupled with the current performance metrics means that this photonically enhanced instrument is well positioned to contribute to the science of high-contrast companions.

We report the direct femtosecond laser inscription of type-I fiber Bragg gratings (FBGs) into the core of soft-glass ZBLAN fibers. We investigate and compare various fabrication methods such as single pass (line by line), double pass, and stacking (plane by plane) to create the highest reflectivity FBGs (99.98%) for mid-infrared (mid-IR) applications. In addition, we experimentally demonstrate how the parameters that influence the coupling coefficient, i.e., refractive index modulation and overlap factor, can be controlled in these gratings to specifically tailor the FBG properties. The performance of the direct-written type-I gratings after 6 h of annealing is further analyzed, and the reflectivity increases by approximately 10 dB. To the best of our knowledge, this is the first demonstration of temperature-stable mid-IR FBGs with highest coupling coefficient (464 m−1) and lowest loss (