Femtosecond laser-based 3D printing has strongly improved the field of photonics, enabling the fabrication of complex optical components. In this study, we present the development and characterization of a bulk Bragg grating sensor created using the FEMTOprint system, which integrates a femtosecond laser for high-precision structuring. The latter enables the direct writing of waveguides with Bragg gratings within a transparent substrate. This unique manufacturing process grants control over the waveguide's geometry, grating period, and refractive index modulation, resulting in sensor capable of extraordinary sensitivity. We conducted a characterization of the waveguide with a Bragg grating sensor to assess its performance. Our results demonstrate remarkable sensitivity to environmental parameters, with a temperature sensitivity of 10.51 pm/°C and a mechanical strain sensitivity of 1.22 pm/με. These characteristics make the sensor ideal for a wide range of applications, including temperature monitoring and structural health assessment. The innovative combination of femtosecond laser printing and Bragg grating technology offers a new dimension to the design and application of optical sensors. Our research not only highlights the unique capabilities of these sensors but also opens up exciting prospects for future developments and interdisciplinary collaborations.
Femtosecond laser pulses are more and more spread for the micro/nano-machining of various materials. They were successfully used for the manufacturing of Bragg gratings in optical fibres through the implementation of the so-called point-by-point, line-by-line and plane-by-plane processes. In this work, we report the use of such laser for Bragg grating manufacturing in pure fused silica planar substrates. In particular, we rely on the commercial system called Femtoprint. This machine has efficiently produced Bragg gratings from bulk silica following several steps. First of all, a waveguide was imprinted in the glass substrate by tight control of the laser pulses and path. Then, an access point was created at one edge of the substrate so that a standard optical fibre can be easily connected with the engraved waveguide for light injection and collection. This was again done with femtosecond laser pulses and a subsequent etching with KOH was performed to create the required open spaces in the substrate. Finally, a Bragg grating was imprinted within the waveguide thanks to a third femtosecond laser process. The reflected amplitude spectrum of the grating was characterized using a dedicated interrogator and the obtained experimental results will be presented in this paper.
Femtosecond laser pulses are increasingly utilized for the micro/nano-machining of a wide range of materials. They have been effectively employed in the production of fiber Bragg gratings (FBGs) through the implementation of point-by-point, line-by-line, and plane-by-plane processes. This study reports on the use of such lasers for the manufacture of Bragg gratings in pure fused silica planar substrates. In particular, the commercial system known as FEMTOprint was employed. This machine enabled the efficient production of Bragg gratings from bulk silica through several steps. Initially, a waveguide was engraved into the glass substrate through precise control of laser pulses and paths. Subsequently, an access point was created at one edge of the substrate to facilitate the easy connection of a standard optical fiber for light injection and collection. This was accomplished through the use of femtosecond laser pulses, followed by an etching process utilizing KOH to selectively ablate some material and create the necessary open spaces in the substrate. Finally, a third femtosecond laser process was utilized to inscribe a Bragg grating within the waveguide. The reflected amplitude spectrum of the grating was characterized with an FBG interrogator, and the obtained experimental results will be presented in this paper.
Femtosecond laser pulses are more and more spread for the micro/nano-machining of various materials. Bragg gratings are known to be good written within optical fibers using the point-by-point or line-by-line technique. The objective of our work is to produce Bragg grating sensors within planar glass substrates. To this aim, the synthesis of an optical waveguide in a glass substrate is a key parameter. Among the physical techniques that are available one of them is the utilization of a femtosecond laser. In this paper, we report our achievements obtained with the so-called Femtoprint machine, a commercial device created to engineer materials. We show the parameters that were used to produce waveguides in planar substrates. We show the characterization set-up that was implemented and report the first experimental results that were obtained.
KEYWORDS: Talc, Mirrors, Space telescopes, Actuators, Telescopes, Segmented mirrors, Solid modeling, Transducers, Control systems, James Webb Space Telescope
Thin aperture light collector (TALC) is the next generation of telescopes for space exploration. TALC consists of deployable annular segmented mirrors supported on a central mast with the help of cables. The dynamic stability of the telescope is of immense importance in order to make sure that the telescope is pointing in the right direction during the observation period. We present a control strategy for the dynamic stabilization of the segmented TALC structure using active rods. The active rods consist of collocated pairs of piezoelectric stack actuators and sensors. Decentralized integral force feedback is proposed to enhance the dynamic stability of the TALC. The effectiveness of the strategy is demonstrated on a 1/10th scaled mock-up model of the TALC. For numerical investigation, finite element analysis of the TALC is carried out and a reduced order model is extracted using the Craig–Bampton method. This reduced order model is then used for the design and numerical validation of the controller. Experiments are conducted on the mock-up model of the TALC to evaluate the performance of the proposed strategy. It is found that the proposed strategy is quite effective for dynamic stabilization of TALC. It is found to reduce both steady state and transient responses of the TALC.
KEYWORDS: Space telescopes, Mirrors, Telescopes, Active optics, Space telescopes, Telescopes, Active optics, Talc, Carbon, Astronomy, Manufacturing, Nickel, Optics manufacturing
Astronomy is driven by the quest for higher sensitivity and improved angular resolution in order to detect fainter or smaller objects. The far-infrared to submillimeter domain is a unique probe of the cold and obscured Universe, harboring for instance the precious signatures of key elements such as water. Space observations are mandatory given the blocking effect of our atmosphere. However the methods we have relied on so far to develop increasingly larger telescopes are now reaching a hard limit, with the JWST illustrating this in more than one way (e.g. it will be launched by one of the most powerful rocket, it requires the largest existing facility on Earth to be qualified). With the Thinned Aperture Light Collector (TALC) project, a concept of a deployable 20 m annular telescope, we propose to break out of this deadlock by developing novel technologies for space telescopes, which are disruptive in three aspects:
• An innovative deployable mirror whose topology, based on stacking rather than folding, leads to an optimum ratio of collecting area over volume, and creates a telescope with an eight times larger collecting area and three times higher angular resolution compared to JWST from the same pre-deployed volume;
• An ultra-light weight segmented primary mirror, based on electrodeposited Nickel, Composite and Honeycomb stacks, built with a replica process to control costs and mitigate the industrial risks;
• An active optics control layer based on piezo-electric layers incorporated into the mirror rear shell allowing control of the shape by internal stress rather than by reaction on a structure.
We present in this paper the roadmap we have built to bring these three disruptive technologies to technology readiness level 3. We will achieve this goal through design and realization of representative elements: segments of mirrors for optical quality verification, active optics implemented on representative mirror stacks to characterize the shape correction capabilities, and mechanical models for validation of the deployment concept. Accompanying these developments, a strong system activity will ensure that the ultimate goal of having an integrated system can be met, especially in terms of (a) scalability toward a larger structure, and (b) verification philosophy.
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