Francois Parent

Fabrication of ultrafast laser written low-loss waveguides in flexible As₂S₃ chalcogenide glass tape.

As2S3 glass has a unique combination of optical properties, such as wide transparency in the infrared region and a high nonlinear coefficient. Recently, intense research has been conducted to improve photonic devices using thin materials. In this Letter, highly uniform rectangular single-index and 2 dB/m loss step-index optical tapes have been drawn by the crucible technique. Low-loss (<0.15  dB/cm) single-mode waveguides in chalcogenide glass tapes have been fabricated using femtosecond laser writing. Optical backscatter reflectometry has been used to study the origin of the optical losses. A detailed study of the laser writing process in thin glass is also presented to facilitate a repeatable waveguide inscription recipe.

Enhancement of accuracy in shape sensing of surgical needles using optical frequency domain reflectometry in optical fibers

We demonstrate a novel approach to enhance the precision of surgical needle shape tracking based on distributed strain sensing using optical frequency domain reflectometry (OFDR). The precision enhancement is provided by using optical fibers with high scattering properties. Shape tracking of surgical tools using strain sensing properties of optical fibers has seen increased attention in recent years. Most of the investigations made in this field use fiber Bragg gratings (FBG), which can be used as discrete or quasi-distributed strain sensors. By using a truly distributed sensing approach (OFDR), preliminary results show that the attainable accuracy is comparable to accuracies reported in the literature using FBG sensors for tracking applications (~1mm). We propose a technique that enhanced our accuracy by 47% using UV exposed fibers, which have higher light scattering compared to un-exposed standard single mode fibers. Improving the experimental setup will enhance the accuracy provided by shape tracking using OFDR and will contribute significantly to clinical applications.

Toward the integration of optical sensors in smartphone screens using femtosecond laser writing

We demonstrate a new type of sensor incorporated directly into Corning Gorilla glass, an ultraresistant glass widely used in the screen of popular devices such as smartphones, tablets, and smart watches. Although physical space is limited in portable devices, the screens have been so far neglected in regard to functionalization. Our proof-of-concept shows a new niche for photonics device development, in which the screen becomes an active component integrated into the device. The sensor itself is a near-surface waveguide, sensitive to refractive index changes, enabling the analysis of liquids directly on the screen of a smartphone, without the need for any add-ons, thus opening this part of the device to advanced functionalization. The primary function of the screen is unaffected, since the sensor and waveguide are effectively invisible to the naked eye. We fabricated a waveguide just below the glass surface, directly written without any surface preparation, in which the change in refractive index on the surface-air interface changes the light guidance, thus the transmission of light. This work reports on sensor fabrication, using a femtosecond pulsed laser, and the light-interaction model of the beam propagating at the surface is discussed and compared with experimental measurement for refractive indexes in the range 1.3-1.7. A new and improved model, including input and output reflections due to the effective mode index change, is also proposed and yields a better match with our experimental measurements and also with previous measurements reported in the literature.

UV Exposed Optical Fibers with Frequency Domain Reflectometry for Device Tracking in Intra-arterial Procedures

Shape tracking of medical devices using strain sensing properties in optical fibers has seen increased attention in recent years. In this paper, we propose a novel guidance system for intra-arterial procedures using a distributed strain sensing device based on optical frequency domain reflectometry (OFDR) to track the shape of a catheter. Tracking enhancement is provided by exposing a fiber triplet to a focused ultraviolet beam, producing high scattering properties. Contrary to typical quasi-distributed strain sensors, we propose a truly distributed strain sensing approach, which allows to reconstruct a fiber triplet in real-time. A 3D roadmap of the hepatic anatomy integrated with a 4D MR imaging sequence allows to navigate the catheter within the pre-interventional anatomy, and map the blood flow velocities in the arterial tree. We employed Riemannian anisotropic heat kernels to map the sensed data to the pre-interventional model. Experiments in synthetic phantoms and an in vivo model are presented. Results show that the tracking accuracy is suitable for interventional tracking applications, with a mean 3D shape reconstruction errors of 1.6 +/- 0.3 mm. This study demonstrates the promising potential of MR-compatible UV-exposed OFDR optical fibers for non-ionizing device guidance in intra-arterial procedures.

3D shape tracking of minimally invasive medical instruments using optical frequency domain reflectometry

We propose here a new alternative to provide real-time device tracking during minimally invasive interventions using a truly-distributed strain sensor based on optical frequency domain reflectometry (OFDR) in optical fibers. The guidance of minimally invasive medical instruments such as needles or catheters (ex. by adding a piezoelectric coating) has been the focus of extensive research in the past decades. Real-time tracking of instruments in medical interventions facilitates image guidance and helps the user to reach a pre-localized target more precisely. Image-guided systems using ultrasound imaging and shape sensors based on fiber Bragg gratings (FBG)-embedded optical fibers can provide retroactive feedback to the user in order to reach the targeted areas with even more precision. However, ultrasound imaging with electro-magnetic tracking cannot be used in the magnetic resonance imaging (MRI) suite, while shape sensors based on FBG embedded in optical fibers provides discrete values of the instrument position, which requires approximations to be made to evaluate its global shape. This is why a truly-distributed strain sensor based on OFDR could enhance the tracking accuracy. In both cases, since the strain is proportional to the radius of curvature of the fiber, a strain sensor can provide the three-dimensional shape of medical instruments by simply inserting fibers inside the devices. To faithfully follow the shape of the needle in the tracking frame, 3 fibers glued in a specific geometry are used, providing 3 degrees of freedom along the fiber. Near real-time tracking of medical instruments is thus obtained offering clear advantages for clinical monitoring in remotely controlled catheter or needle guidance. We present results demonstrating the promising aspects of this approach as well the limitations of using the OFDR technique.

Enhancement of Rayleigh scatter in optical fiber by simple UV treatment: an order of magnitude increase in distributed sensing sensitivity

Rayleigh scatter in optical fiber communication systems has long been considered a nuisance as a loss mechanism, although applications have used such scatter to probe the fiber for faults and propagation loss using time domain reflectometry (OTDR). It is however only with the development of Frequency domain reflectometry (OFDR) and coherent-phase OTDR that Rayleigh scatter has been probed to its deepest and can now be used to measure strain and temperature along a fiber, leading to the first distributed sensing applications. However, Rayleigh scatter remains very weak giving rise to very small signals which limits the technique for sensing. We show here a new technique to significantly enhance the Rayleigh scatter signal by at least two orders of magnitude, in a standard optical fiber with simple UV exposure of the core. A study of various exposures with different types of fibers has been conducted and a phenomenological description developed. We demonstrate that such an increase in signal can enhance the temperature and strain sensitivity by an order of magnitude for distributed sensing with an OFDR technique. Such improved performance can lead to temperature/strain RMS noise levels of 6 mK and 50 nε for 1 cm spatial resolution in UV exposed SMF-28, compared to the typical noise level of 100 mK for the same spatial resolution in the similar unexposed fiber.

Calibration of a needle tracking device with fiber Bragg grating sensors

Accurate needle placement is essential in percutaneous procedures such as radiofrequency ablation (RFA) of liver tumors. Use of real-time navigation of an interventional needle can improve targeting accuracy and yield precise measurements of the needle tip inside the body. An emerging technology based on Fiber Bragg Grating (FBG) sensors has demonstrated the potential of estimating shapes at high frequencies (up to 20 kHz), fast enough for real-time applications. In this paper, we present a calibration procedure for this novel needle tracking technology using strain measurements obtained from fiber Bragg gratings (FBGs). Three glass fibers equipped with two FBGs each were incorporated into a 19G needle. The 3D needle shape is reconstructed based on a polynomial fitting of strain measurements obtained from the fibers. The real-time information provided by the needle tip position and shape allows tracking of the needle deflections during tissue insertion. An experimental setup was designed to yield a calibration that is insensitive to ambient temperature fluctuations and robust to slight external disturbances. We compare the shape of the 3D reconstructed needle to measurements obtained from camera images, as well as assess needle tip tracking accuracy on a ground-truth phantom. Initial results show that the tracking errors for the needle tip are under 1mm, while 3D shape deflections are minimal near the needle tip. The accuracy is appropriate for applications such as RFA of liver tumors.

PLENARY empowering cell phones with photonics

The last frontier in the development of the personal data accessories is the integration of photonics into the display glass. This paper reports on the integration of photonic functions directly into the display glass, allowing novel devices to be implemented, enhancing the functionality for the user.