Pierre Benech

SWIFTS: a groundbreaking integrated technology for high-performance spectroscopy and optical sensors

SWIFTS, or Stationary-Wave Integrated Fourier Transform Spectrometer, is a new, highly integrated high-resolution spectroscopy technology that represents a major advance in the field. This is the first public presentation on the state-ofthe- art SWIFTS system. SWIFTS combines groundbreaking nanotechnology research, integrated optics, microelectronics and embedded software, resulting in high-resolution spectrometer technology bundled into a single device that is over 100 times more powerful in terms of spectral resolution than existing mini-spectrometers and more than 2,000 times smaller than highend spectrometers offering a similar level of performance. Systems based on this technology can typically achieve a spectral resolution of a few pm / 0.2 cm-1 / 6 GHz, with a good SNR over a bandwidth ranging from several nm to a few hundred nm on a chip measuring a few mm2, opening the way for product development based on the most demanding applications currently performed in research laboratories. The principle behind this patented technology will be explained, as will the technological choices made by Resolution Spectra Systems. We will present the most challenging building blocks of the technology: nano-pattern deposition, hybrid-chip assembly, light collection, calibration and data processing. In order to cater for different applications, the SWIFTS principle can be implemented in numerous configurations: multiple bands, multiplexing, spectro-imaging, integrated bio-sensors, etc. Various results have been obtained with either research setups or new products in the Visible and Near-Infrared, including analysis of tunable, multi-mode and high-stability lasers, Bragg sensor interrogator and high-depth Optical Coherent Tomography.

High-performance high-speed spectrum analysis of laser sources with SWIFTS technology

The ZOOM Spectra spectrometer is the first fully integrated system to benefit from the disruptive SWIFTS technology, providing a high-resolution high-rate solution for the characterization of lasers. It allows for the first time a dynamic real-time view of their behavior. The instrument is an alliance of integrated guided optics, groundbreaking nanotechnologies, microelectronics and advanced software. The device has been designed to be a rapid solution for checking the tuning of a laser, the existence of hopping modes and the correct suppression of a side mode. Their performances are particularly valuable for analysis of custom sources such as Distributed Feedback (DFB) lasers, Vertical Cavity Surface Emitting Lasers (VCSELs), External Cavity Lasers (ECL), or Optical Parametric Oscillator (OPO) sources.

Acousto-optic intensity modulation on glass-integrated optic

An elastic beam of waves in the Megahertz range, generated using a PZT ceramic, crosses one arm of an integrated Mac-Zehnder interferometer realised by ion-exchange in a glass substrate. Elastic waves modify locally the refractive index of glass. A laser beam of 0.83 μm wavelength is injected into the interferometer. For a sine excitation voltage of 7 volts of the piezoelectric transducer, the variation of the optical intensity measured at the interferometer output is greater than 20% of the intensity observed without elastic waves. Refractive index variation of 9.4×10-7 were obtained. The optical intensity observed at the output of the interferometer varies at the frequency of the piezoelectric crystal excitation. A model taking into account the elastic and the optical effects is proposed. This model allows the optimisation of the piezoelectric transducer in order to obtain the maximum of elastic strain at the position of the optical waveguides. The theoretical results obtained with the model are in accordance with the experimental results.

Realization of a NIR Compact Static Fourier Transform Spectrometer in glass integrated optics

The realization and characterization of the leaky loop integrated Fourier transform spectrometer (LLIFTS) in integrated optics are described. The component is compact, costless with no moveable parts. The principle lies on a two-beam interferometer in planar design using a leaky loop waveguide structure. The radiated part leaking from the loop induces an interference pattern at the end of the component. The structure has the advantage of controlling the shape of the interference pattern. Ion exchange technology used here requires only a single lithography step. Measurements have been made in the near infrared domain with wavelength resolution of 11 nm.

Determination of refractive index variation of a glass-integrated optical waveguide by the acousto-optic effect

Ion exchange on a glass substrate is now a well-known technology that enables the realization of optical waveguide devices. In recent years, the hybridization of ion-exchanged glass waveguides has become a promising method for functional integration. In this context, an integrated Mach–Zehnder interferometer (MZI), made by ion exchange on a glass substrate, was used to realize an acousto-optic modulator. Over one arm of the MZI a PZT ceramic driven by a high-voltage signal was glued. The acoustic waves cross the light waveguide and locally modify the refractive index of the glass. The optical intensity observed at the output of the interferometer varies according to the piezoelectric ceramic excitation. This component is used to find the relation between the refractive index change induced and the applied stress. Measurements were made for two linear polarizations: TE and TM. The proposed method was validated on a specific glass substrate and can be directly extended to any kind of glass.

Glass integrated optic Fourier transform spectrometer in the spectral bandwith 700-1000nm: process improvement

A leaky loop Fourier Transform spectrometer is presented in 700-1000nm spectral bandwidth. This integrated optic spectrometer is made without moveable parts. The contrast and the shape of the interferogram created at the end of the component are controlled by the gap evolution between the bend waveguide and the planar waveguide. Glass ion exchange has been chosen to obtain a high fringe contrast. A linear camera set directly at the end of the component allows interferences capture from 780nm to 850nm and the light vertical scattering due to the waveguides surface roughness is used to characterize the optical loop behavior.

Compact static Fourier transform spectrometer in glass integrated optics in the NIR and visible domain

The characterization of a Leaky Loop Integrated Fourier Transform Spectrometer (LLIFTS) in integrated optics is described in the visible and the near infrared spectral domain. The device is realized using ion-exchange technology in a glass substrate. LLIFTS is compact, costless with no moveable parts. Its principle consists in a two beam interferometer in planar design using a leaky loop waveguide structure. The advantage of the design of the LLIFTS structure is to control the shape of the interference pattern in order to measure a high contrast and fringe spacing well sampled by a 2048 pixels camera directly at the output of the component. Spectral resolution of 7nm at 1500nm and 2nm at 633nm are obtained.

Far field scattering by a waveguide-coupled nanowire

We study both experimentally and numerically far-field radiation patterns of single metallic nanowires coupled to weak confined optical waveguides. The radiation pattern resulting from the interaction of the nanowire and the optical mode depends strongly on the mode properties (polarization and wavenumber) and on the antenna properties (material and size). To investigate these phenomena we compare the electric far-field distributions computed with different numerical methods (Greens tensor technique, rigourous coupled wave method, Fourier modal method). We also compare simulated results to experimental measurements obtained over a large spectral domain ranging from 400 nm to 1000 nm. This study should be useful for optimizing nanostructured photonic circuits elements.

Integrated acousto-optic polarization analyzer sensor

Ion-exchange in glass substrate has long been an enabling technology for optical waveguides device manufacturing. Thus, in the last years, hybridization of ion-exchanged glass waveguides components has become a promising method for functional integration. In that context, we propose a Integrated acousto-optic Polarization Analyzer Sensor (IPAS) made by ion-exchange in a glass substrate. The IPAS consists in two Y-junctions that give three different outputs. The first one is simply one output waveguides of the first Y-junction. The two other outputs are the waveguides following the second Y-junction. A piezoelectric plate is placed over the entrance waveguide of the second Y-junction. It creates an artificial anisotropy when it is excited electrically. For each one of the three output signals, a polarizer is inserted between the waveguides end and a photodetector. The IPAS is a compact hybrid realization insensitive to vibrations and easy to realize. It is capable to determine, with adequate signal processing, the polarization state of a light beam. Experimental results are obtained with a single buried straight waveguide made by low birefringence Ag+↔Na+ ion-exchange. The measured polarization state is compared with a commercial polarization analyzer.

A compact SWIFTS spectrograph with a leaky loop structure

This paper deals with a new spectrograph on integrated optics. It is composed of an Y-junction where the two junction arms are guided in a loop structure in order to obtain an interference pattern. The measurement of this intensity distribution gives access to the optical spectrum source after a Inverse Fourier Transform. To measure it, we use the property of the loop composed of a bent waveguide which is a leaky structure. Depending on the radius of the bent waveguide, a part of the light leaks from the waveguide to outside. The radiated power, proportional to the intensity in the waveguide, is coupled into a plan waveguide set near the bent waveguide. Indeed the two structures are separated by a gap which changes along the periphery of the loop. This structure enables both to control the leaking light part and to confine in the plan waveguide the propagation of the radiated field. Thereby, the radiated intensity is measured at a peculiar distance of the loop on a perpendicular plan to the input waveguide. So, the interference pattern measured is magnified by the ratio of the plan waveguide length over the loop radius, allowing to use a commercial photodetectors array to sufficiently sample the interference pattern. The spectrum is finally obtained operating a Discrete Fourier Transform. The device modelization is divided in two parts. The first part describes the coupling between the bent and the plan waveguide modelised by a modal method based on a Fourier series expansion (RCWA) combined with an exponential conformal mapping in order to simulate the electromagnetic field near the loop. The second part describes the Helmholtz-Kirchhoff theorem to simulate the far-electromagnetic field. From the interference pattern modelized, the spectrum of the signal is then calculated. A demonstrator in integrated optics on glass is being developed.