Walter Margulis

A high sensitivity reconfigurable temperature sensor is presented. The sensor is a random laser driven by current pulses, injected into a semiconductor optical amplifier connected to a standard single-mode optical fiber. The pulses repetition rate defines the position of the addressed fiber section whereas the pulse duration defines its length. The wavelength selectivity of the backscattered light defines the random lasing wavelength, which acts as a temperature dependent fingerprint for the optical fiber. Temperature shifts of $0.028 { ^{\circ }C}$ with 50cm spatial resolution are demonstrated.

Spectral measurements of the Rayleigh backscattered light in a single-mode fiber are performed for a white input source. The measured spectrum of the backscattered light from a 45 cm-long fiber exhibits a jagged intensity profile that is highly wavelength-dependent. Spectra from different fiber types were compared with model predictions based on small fluctuations of the fiber refractive index on a centimeter scale, generating interference fluctuations on the spectrum of the backscattered light. The agreement between the statistics of measured data and model simulations confirms the ergodic nature of the phenomenon and supports that optical interference is behind the wavelength-selective nature of Rayleigh backscattering in single mode fibers. Experimental results clearly demonstrate that white light becomes colored when backscattered in a single mode fiber.

Random lasers are usually thought of as being light sources of poor coherence and broad spectrum. As such, interference is expected to take place only over short coherence lengths. In this work, a random fiber laser is used to generate mode-locked pulses that are transform limited, and therefore coherent, over an adjustable length that can reach several meters. The laser is also a phase-OTDR with an open-ended fiber spool that can be probed as a distributed sensor. Temperature resolution in the millikelvin range with a few centimeters spatial resolution can be achieved.

Ever since the mid-1960’s, locking the phases of modes enabled the generation of laser pulses of duration limited only by the uncertainty principle, opening the field of ultrafast science. In contrast to conventional lasers, mode spacing in random lasers is ill-defined because optical feedback comes from scattering centres at random positions, making it hard to use mode locking in transform limited pulse generation. Here the generation of sub-nanosecond transform-limited pulses from a mode-locked random fibre laser is reported. Rayleigh backscattering from decimetre-long sections of telecom fibre serves as laser feedback, providing narrow spectral selectivity to the Fourier limit. The laser is adjustable in pulse duration (0.34–20 ns), repetition rate (0.714–1.22 MHz) and can be temperature tuned. The high spectral-efficiency pulses are applied in distributed temperature sensing with 9.0 cm and 3.3 × 10⁻³ K resolution, exemplifying how the results can drive advances in the fields of spectroscopy, telecommunications, and sensing.

A fiber probe traps single micrometer-particles by fluid suction into a hollow microstructure and enables optical identification by the fluorescence light collected in a fiber core. The probe finds applications in life-science and environmental monitoring.

We propose and experimentally demonstrate a spatially tunable phase-OTDR based distributed microphone for listening to the sound of multiple machines. The distributed acoustic sensing capability, allied with the real-time spatial tuning, enables listening to a drill and to a cooling water system pump placed in two different sections along a single optical fiber, one at a time. The recorded acoustic waveform profile of both machines agreed with their operating cycles. Moreover, the sounds generated by both engines are successfully distinguished with the proposed method even when both machines are operating simultaneously.

By solving the two-dimensional Poisson equation for fibers with circular internal electrodes, we show that the parallelplate approximation incurs significant error in the determination of the electric field applied to the fiber core. This also affects the value of χ ⁽³⁾ measured in electro-optical fibers. The exact solution of Poisson's equation is used to solve the field applied to the core of a photonic crystal fiber, where the many holes screen the field. A universal curve is derived to allow using the simplifying parallel plate approximation and correcting for the error in symmetric fibers with round holes.

We study the creation and erasure of the linear electrooptical effect in silicate fibers by optical poling. Carriers are released by exposure to green light and displaced with simultaneous application of an internal dc field. The second order nonlinear coefficient induced grows with poling bias. The field recorded (~10⁸ V/m) is comparable to that obtained through classical thermal poling of fibers. In the regime studied here, the second-order nonlinearity induced (~0.06 pm/V) is limited by the field applied during poling (1.2 × 10⁸ V/m). Optical erasure with high-power green light alone is very efficient. The dynamics of the writing and erasing process is discussed, and the two dimensional (2D) field distribution across the fiber is simulated.

The integration of a microspherical whispering gallery mode (WGM) resonator inside a microstructured optical fiber taper is demonstrated. Preliminary WGM spectra of this in-fiber resonator in transmission mode are presented and discussed.