While conventional methods like diamond turning can achieve the necessary precision for manufacturing image slicers, they are often expensive in cost and time, and restrictive in terms of the materials to which they can be readily applied. Ultrafast laser-assisted etching (ULAE) is an emerging manufacturing technology that could potentially be used to manufacture free form reflective optics using fused silica, as it enables μm-level precision shaping of fused silica over several millimetres scales. Here we demonstrate the potential of ULAE for manufacturing fused silica image slicers by fabricating precision 8 × 1mm flat fused silica surfaces using ULAE. The waviness meets the required level for this application, staying below 1 μm. Specifically, we measured S10z = 0.164 μm. The roughness varies with surface inclination; for a flat surface at 0◦ inclination, we measured Sq = 109 nm, while at a 5◦ inclination, it increased to Sq = 204 nm. If combined with a suitable polishing technique to remove the high spatial frequency roughness, we believe this work demonstrates that ULAE provides a new route to manufacture freeform reflective monolithic fused silica optics such as image slicers for groundand space-based applications.
Preventing and managing infections is a key aspect of clinical care. UVC light has well-known germicidal properties, but can also cause DNA mutations in human cells. Recently, reduced mutagenic impact was reported in tissue exposed to deep-UV (DUV) light (180 – 230 nm), which remains bactericidal. For future clinical applications, delivering DUV light onto tissue via optical fibres is of interest. We detail a laser direct-write process for inscribing scattering points in silica optical fibre for efficient side-scattering of transmitted DUV light. We report on the germicidal efficacy of the illuminated fibre for inhibiting bacteria growth, determined by in vitro feasibility assays.
We report the ultrafast laser inscription (ULI) of a 2-telescope integrated optic (IO) beam combiner for K-band interferometry in commercial Infrasil glass. The ULI setup used for this work is based on a 1030 nm femtosecond laser which is paired with a spatial-light-modulator (SLM). The SLM controls the numerical aperture of the focused beam used to write waveguides in the substrate. The optimum ULI parameters were found to inscribe straight single-mode waveguides exhibiting an insertion loss of 1.1 ± 0.1 dB for a 17 mm long chip over the entire K-band. To develop optimal directional couplers, we focused our efforts on investigating the effect of varying the core-to-core separation and the effect of detuning the waveguide parameters in the coupler. By doing so, we have identified fabrication parameters that are suitable for the fabrication of a beam combiner integrating an achromatic 3 dB directional coupler and two photometric taps with a splitting ratio of 80:20. These results demonstrate the capability of the ULI fabrication technique to inscribe efficient achromatic directional couplers in the K-band range. A final fabrication step will involve simple assembly of the beam combiner with input/output fibers in preparation for on-sky testing at the CHARA array planned for July 2022.
Direct imaging instruments have the spatial resolution to resolve exoplanets from their host star. This enables direct characterization of the exoplanets atmosphere, but most direct imaging instruments do not have spectrographs with high enough resolving power for detailed atmospheric characterization. We investigate the use of a single-mode diffraction-limited integral-field unit that is compact and easy to integrate into current and future direct imaging instruments for exoplanet characterization. This achieved by making use of recent progress in photonic manufacturing to create a single-mode fiber-fed image reformatter. The fiber link is created with three-dimensional printed lenses on top of a single-mode multicore fiber that feeds an ultrafast laser inscribed photonic chip that reformats the fiber into a pseudoslit. We then couple it to a first-order spectrograph with a triple stacked volume phase holographic grating for a high efficiency over a large bandwidth. The prototype system has had a successful first-light observing run at the 4.2-m William Herschel Telescope. The measured on-sky resolving power is between 2500 and 3000, depending on the wavelength. With our observations, we show that single-mode integral-field spectroscopy is a viable option for current and future exoplanet imaging instruments.
The Multi-Core Integral-Field Unit (MCIFU) is a new diffraction-limited near-infrared integral-field unit for exoplanet atmosphere characterization with extreme adaptive optics (xAO) instruments. It has been developed as an experimental pathfinder for spectroscopic upgrades for SPHERE+/VLT and other xAO systems. The wavelength range covers 1.0 um to 1.6um at a resolving power around 5000 for 73 points on-sky. The MCIFU uses novel astrophotonic components to make this very compact and robust spectrograph. We performed the first successful on-sky test with CANARY at the 4.2 meter William Herschel Telescope in July 2019, where observed standard stars and several stellar binaries. An improved version of the MCIFU will be used with MagAO-X, the new extreme adaptive optics system at the 6.5 meter Magellan Clay telescope in Chile. We will show and discuss the first-light performance and operations of the MCIFU at CANARY and discuss the integration of the MCIFU with MagAO-X.
The performance of astrophotonic instruments is determined by various factors including the quality of optical surfaces and the precise alignment of components. As instruments become more complex and compact, the manufacture and assembly of components is increasingly challenging. We propose that a laser-based glass microfabrication technique known as ultrafast-laser assisted etching (ULAE) is ideally suited to the manufacture of both existing and novel components for astrophotonic instruments. To demonstrate this potential, we will present ULAE manufactured microlenses with integrated passive alignment features for efficient optical fiber coupling. A full physical and optical characterization of the micro-lenses is given. These components have applications in fiber-fed multi-object spectrographs.
The Multi-Core Integral-Field Unit (MCIFU) is a diffraction-limited near-infrared integral-field spectrograph designed to detect and characterise exoplanets and disks in combination with extreme adaptive optics (xAO) instruments. It has been developed by an extended consortium as an experimental path finder for medium resolution spectroscopic upgrades for xAO systems. To allow it to achieve its goals we manufactured a fibre link system composed of a custom integrated fiber, with 3D printed microlenses and an ultrafast laser inscribed reformatter. Here we detail the specific requirements of the fibre link, from its design parameters, through its manufacture the laboratory performance and discuss upgrades for the future.
We report on the conception and the fabrication of a 3D photonic reformatter of 73 waveguides and its associated opaque mask in a wide collaboration to develop a multi-core fiber-fed integral field spectrograph (MCIFU) centered on the Jband. The reformatter is a 3D structure that light from the input quasi-hexagonal multicore fiber is spread out by rearrangement to avoid individual core spectra overlapping when the light is dispersed. The reformatter is fabricated using ultrafast laser inscription (ULI) in a borosilicate glass of 20 mm length. Using a similar ULI process, a 73-hole mask was fabricated in silica glass that precisely matched the waveguides at the output of the reformatter. The output surface of the mask was coated with a 120 nm layer of chromium to block scattered light generated in the bulk material and enhance the signal-to-noise. All inscribed waveguides, characterized using a stable laser centered at 1310 nm from the multicore fiber to the output mask, present consistent single-mode output behavior with a maximum throughput exceeding 60%. Over the 73 cores, the average throughput was measured at 40%. First observations of the full MCIFU device during on-sky measurements have shown promising results to the potential of this novel fiber integral field unit.
Here we demonstrate the use of an advanced microfabrication technique, known as ultrafast laser inscription (ULI) with chemical etching, optimised for the fabrication of micro-optic systems in fused silica. ULI is a precision laser micromachining tool which relies on the high peak intensities associated with focused femtosecond pulses of light to locally modify the structure of a dielectric material. One manifestation of this modification is that the etch-rate of the modified regions can be increased by up to two orders of magnitude compared to that of pristine material, depending on the specific ULI parameters and the chemical etchant used. This capability means that ULI facilitates the repeatable fabrication of three-dimensional freeform structures in glass with micrometre resolution. Firstly, we present the results of investigations aimed at optimising the fabrication process and show that by controlling the laser polarisation during inscription, an etch-rate selectivity of 100 and a fivefold decrease in surface roughness can be achieved. We then demonstrate the characterisation of a microlens fabricated with optimum inscription parameters, including measurements of the lens surface profile, surface roughness and throughput, before demonstrating that the local surface roughness can be further decreased to below 5 nanometres by post-manufacture flame polishing.
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