Victor Lambin Iezzi

Demonstration of an ultra-high frequency picosecond pulse generator using an SBS frequency comb and self phase-locking

We propose a method to generate phase-locked pulses in the picosecond regime by using Stimulated Brillouin Scattering (SBS). The phase-locked comb is generated using only long length of fiber and a single frequency CW pump laser. We show that there is a phase relationship between multiple Stokes peaks in a cavity, which directly leads to pulsing without the need to add a mode-locking component. This generates highly coherent pulses in the order of ~10 ps. The repetition frequency, which is very stable is in the order of tens of GHz, is based on the SBS frequency shift and has a linear dependence with temperature (1 MHz/°C). Such a laser could therefore be used in high-speed optical clocks and optical communication system. This system allows the pulses to be generated at any wavelength by simply changing the pump wavelength.

High-sensitivity temperature sensing using higher-order Stokes stimulated Brillouin scattering in optical fiber

In an effort to reduce the cost of sensing systems and make them more compact and flexible, Brillouin scattering has been demonstrated as a useful tool, especially for distributed temperature and strain sensing (DTSS), with a resolution of a few centimeters over several tens of kilometers of fiber. However, sensing is limited by the Brillouin frequency shifts sensitivity to these parameters, which are of the order of ~1.3  MHz/°C and of ~0.05  MHz/με for standard fiber. In this Letter, we demonstrate a new and simple technique for enhancing the sensitivity of sensing by using higher-orders Stokes shifts with stimulated Brillouin scattering (SBS). By this method, we multiply the sensitivity of the sensor by the number of the Stokes order used, enhanced by six-fold, therefore reaching a sensitivity of ~7  MHz/°C, and potentially ~0.30  MHz/με. To do this, we place the test fiber within a cavity to produce a frequency comb. Based on a reference multiorder SBS source for heterodyning, this system should provide a new distributed sensing technology with significantly better resolution at a potentially lower cost than currently available DTSS systems.

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.

Temporal characterization of a multi-wavelength Brillouin–erbium fiber laser

This paper provides the first detailed temporal characterization of a multi-wavelength-Brillouin–erbium fiber laser (MWBEFL) by measuring the optical intensity of the individual frequency channels with high temporal resolution. It is found that the power in each channel is highly unstable due to the excitation of several cavity modes for typical conditions of operation. Also provided is the real-time measurements of the MWBEFL output power for two configurations that were previously reported to emit phase-locked picosecond pulse trains, concluded from their autocorrelation measurements. Real-time measurements reveal a high degree of instability without the formation of a stable pulse train. Finally, we model the MWBEFL using coupled wave equations describing the evolution of the Brillouin pump, Stokes and acoustic waves in the presence of stimulated Brillouin scattering, and the optical Kerr effect. A good qualitative consistency between the simulation and experimental results is evident, in which the interference signal at the output shows strong instability as well as the chaotic behavior due to the dynamics of participating pump and Stokes waves.

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.

Stimulated Brillouin scattering in multi-mode fiber for sensing applications

We present measurements and characterization of stimulated Brillouin scattering (SBS) in multi-mode fiber (MMF) in comparison with single-mode fiber (SMF). As can be expected, the threshold for SBS was measured to be much higher in MMF (105 mW) compared with SMF (15 mW). A difference of 525 MHz was observed in the SBS frequency shift between both types of fibers. An increase in the gain bandwidth, which was measured to be 17 MHz for MMF compared to 8 MHz in SMF and which is due to several modes present in the MMF. Temperature dependence of the frequency shift was also investigated and was shown to be the same (1 MHz/°C) for both types of fibers. Several applications are therefore proposed using SBS in multi-mode fiber.

High sensitivity distributed temperature fiber sensor using stimulated Brillouin scattering

Optical fiber technology has become a very powerful tool for distributed temperature (strain and refractive index) sensing, and can be used to monitor critical infrastructures such as bridges, aircrafts, pipelines, etc. Stimulated Brillouin scattering (SBS) in optical fibers used for distributed sensing utilizing the first Stokes order, is limited to a fixed material property, 1.1 MHz/°C for SMF-28. We demonstrate a distributed higher order Stokes SBS temperature fiber-sensor increasing the achievable sensitivity by several folds to over 4 MHz/°C. The proposed system uses time-gating for distributed sensing. This allows the increase in sensitivity by the order of the Stokes waves generated while maintaining a fairly normal spatial resolution over a few kilometers of sensing length. Increased sensitivity on these types of sensors may allow an earlier detection which could prevent failure of the monitored structure.

3D printed long period gratings for optical fibers

We demonstrate a simple technique for implementing long period grating (LPG) structures by the use of a 3D printer. This Letter shows a way of manipulating the mode coupling within an optical fiber by applying stress through an external 3D printed periodic structure. Different LPG lengths and periods have been studied, as well as the effect of the applied stress on the coupling efficiency from the fundamental mode to cladding modes. The technique is very simple, highly flexible, affordable, and easy to implement without the need of altering the optical fiber. This Letter is part of a growing line of interest in the use of 3D printers for optical applications.

Dynamics of Stokes Waves and Pulses Generated by Stimulated Brillouin Scattering in a Resonator Including Highly Nonlinear Fiber

We experimentally and theoretically investigate the generation of Stokes waves and the dynamics of pulses produced by cascaded stimulated Brillouin scattering (SBS) in a resonator, including a highly nonlinear fiber (HNLF) and an in-cavity erbium-doped fiber amplifier (EDFA) forming a multi-wavelength Brillouin erbium-doped fiber laser system. Using coupled wave equations with the Brillouin pump, Stokes and acoustic waves, propagation in the presence of the SBS and optical Kerr effect, the modeled system simulates the evolution of participating pump and Stokes waves to verify the experimental results. The dependence of the number of generated Stokes waves on EDFA pump and Brillouin pump powers is studied showing that the proper simultaneous change (increase or decrease) of the two pump powers over few hundred of milliwatts (using the power design diagram) results in generating the same number of Stokes waves reaching steady state. Dynamics of the interference signal at the resonator output are also presented for a long HNLF (33 m) showing strong instability due to the existence of a few longitudinal modes within the SBS gain bandwidth with the possibility of random mode hopping. For a short HNLF (3 m), a single longitudinal mode operation is possible and the stability of generated pulses is expected but still depends on the phase relationships per round trip of the participating pump and Stokes waves. A good consistency between simulation and experiment is found.

Distributed temperature and strain sensing with high order stimulated Brillouin scattering

Stimulated Brillouin Scattering (SBS) has been extensively studied over the past few decades due to the many interesting properties and potential applications. Primarily, spontaneous Brillouin scattering (BS) has been used as a temperature and strain sensor enabling long range detection (tens of kilometres) with a relatively good spatial resolution (few meters) [1]. Such distributed temperature or strain sensors (DTSS) are capable of sensing 0.1°C temperature changes or micro-strains over long distances across large areas. However, sensitivity has remained mostly unchanged due to intrinsic properties of BS (1st order Brillouin frequency shift) leading towards a typical sensitivity of respectively ∼1.2 MHz/°C and ∼0.046MHz/με to temperature and strain.