Femtosecond laser written (FLW) reconfigurable photonic integrated circuits are attracting large attention from many applications thanks to their unique features. However, in these devices the frequency response of thermo-optic phase shifters is currently limited to the Hz range, hindering the diffusion of FLW circuits in different fields. Here, we present a thermally-reconfigurable Mach-Zehnder interferometer inscribed just a few micrometers below the surface of a fused silica substrate. The interferometer design, purposely optimized by finite element simulations, allows for switching time lower than 200 μs, phase modulation of the optical signal at kHz frequency and limited impact on the power dissipation.
We present a way to exploit 3D resonant mechanical micro-structures, embedded in glass substrates, to achieve optical signals switching at MHz frequency. These structures are realised by means of femtosecond laser pulses: combining direct waveguide writing and laser-assisted etching in hydrofluoric acid of the 3D microstructure. The mechanical oscillation of the resonator induces periodical refractive index modifications, due to localised stress, across the waveguide region, thus modulating the phase of the propagating optical signal.
In this work we present a microscope on chip based on Light Sheet Fluorescence Microscopy, capable to automatically perform 3D and dual-color imaging of specimens diluted in a liquid suspension. A microfluidic channel is used for automatic sample delivery, while integrated optical components such as optical waveguides and lenses are used to illuminate the sample flowing in the channel. The device is fabricated by femtosecond laser micromachining in a glass substrate. Benefiting from the versatility of the fabrication technique we present two prototypes that have been optimized for different samples such as single cells and Drosophila embryos.
Lab on a Chip devices are compact and portable chips mainly constituted by a network of microfluidic channels. They aim at substituting bulk laboratory instrumentations, with the advantages of increasing the automation and the sensitivity of the analysis, reducing the costs and opening the possibility of performing measurements at the Point of Care. Among different Lab on Chips, optofluidic ones have the advantages of optical investigation, but the integration of optical and microfluidic components in a single substrate is very challenging from a technological point of view. A recent fabrication technique, known as femtosecond laser micromachining (FLM), has proven to be ideal for the realization of these devices, allowing the fabrication of the whole device in a single irradiation step. Here, we will present a platelet counter and a microscope on chip, that fully take advantage from the versatility of FLM. To succeed in these works a fundamental aspect to address is the capability to control the sample positioning in the microfluidic channel. A single particle per time should pass in the detection region to avoid the overlooking of specimen. Moreover, a precise control of the sample orientation and position in the channel cross section is needed for imaging. The 3D capabilities of FLM have been fundamental in the realization of advanced fluidic layouts capable of sample manipulation with no need of any additional external field. We have successfully proven red blood cells and platelets counting, as well as single cells, cellular spheroids and drosophila embryos 3D imaging.
Integrated modulators of optical phase or intensity are essential elements to reconfigure dynamically the operation of a complex waveguide circuit, or to achieve convenient optical switching within a fiber network. Thermo-optic effects are commonly exploited to achieve dynamic phase modulation in glass-based devices, since nonlinear optical effects are weak in such substrates. Thermo-optic modulators rely on electric resistive heaters patterned on top of the waveguides: they are reliable and easy to fabricate, but they suffer from slow response, dictated by the thermal diffusion dynamics. On the other hand, optically-coupled microstructures in glass, driven at their mechanical resonances, may provide interesting possibilities to achieve modulation of the optical signals in the kilohertz range and higher. In this work, we demonstrate integrated-optics intensity modulators based on micro-cantilevers with resonant oscillation frequencies in the tens-of-kilohertz range. The mechanical structures are realized in alumino-borosilicate glass substrate by water-assisted femtosecond-laser ablation. With the same femtosecond laser an optical waveguide is inscribed within the oscillating beam; a waveguide also continues in the substrate beyond the cantilever's tip. Since the entire device, with all its optical and mechanical parts, is realized in a single fabrication process, relative alignment is guaranteed. If the cantilever is at rest, light propagating in the internal waveguide yields maximum coupling to the remaining part of the waveguide. When the device is excited at resonance by means of a piezo-electric actuator, the cantilever oscillation produces periodical variations of the coupling efficiency, with an observed contrast higher than 10 dB.
Drosophila Melanogaster is a sample of high biological interest that is being widely used as biological model, due to the relatively short life cycle, short genome and ease in culturing. In this work we present a microscope on chip capable of processing Drosophila embryos to obtain three dimensional fluorescent images at high throughput. This device, based on light sheet microscopy, uses a plane of light intercepting the sample channel to optically and noninvasively section the embryos while flowing. This permits to automatically acquire for each sample the stack of images necessary for the subsequent 3D reconstruction with no need of any manual sample positioning and alignment. The whole chip is fabricated in a glass substrate by femtosecond laser micromachining. The device has been optimized for the specific morphology of the sample. Indeed, the highly elliptical shape of the embryos (about 100 x 500 μm2) might affect the image quality degrading both the vertical and the axial resolution of the system. To overcome this issue, we have first optimized the layout of the fluidic channel to precisely control the sample orientation by means of hydrodynamic forces. Thereafter, we have optimized the properties of the optical circuit, to realize two opposite light sheets impinging on the sample, perfectly overlapped, with a high signal to noise ratio. With these actions, we have been able to obtain high quality Drosophila reconstruction.
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