We demonstrate that diode laser self-mixing interferometry can be exploited to instantaneously measure the ablation front displacement and the laser ablation rate during ultrafast microdrilling of metals. The proof of concept was obtained using a 50-μm-thick stainless steel plate as the target, a 120 ps/110 kHz microchip fiber laser as the machining source, and an 823 nm diode laser with an integrated photodiode as the probe. The time dependence of the hole penetration depth was measured with a 0.41 µm resolution.
Temporal cavity solitons are optical pulses that propagate indefinitely in nonlinear resonators [1][2][3]. They are currently attracting a lot of attention, both for their many potential applications and for their connection to other fields of science. Cavity solitons are phase locked to a driving laser. This is what distinguishes them from laser dissipative solitons [4] and the main reason why they are excellent candidates for precision applications such as optical atomic clocks [5]. To date, the focus has been on driving Kerr solitons close to their carrier frequency, in which case a single stable localised solution exists for fixed parameters [1]. Here we experimentally demonstrate, for the first time, Kerr cavity solitons excitation around twice their carrier frequency. In that configuration, called parametric driving, two solitons of opposite phase may coexist [6]. We use a fibre resonator that incorporates a quadratically nonlinear section and excite stable solitons by scanning the driving frequency. Our experimental results are in excellent agreement with a seminal amplitude equation [7], highlighting connections to hydrodynamic [8, 9] and mechanical systems [10], amongst others [11]. Furthermore, we experimentally confirm that two different phase-locked solitons may be simultaneously excited and harness this multiplicity to generate a string of random bits, thereby extending the pool of applications of Kerr resonators to random number generators [12] and Ising machines [13].
Conventional thermal poling methods require direct physical contact to internal fiber electrodes. Here, we report an indirect electrostatic induction technique using electrically floating wires inside the fiber combined with external electric fields that can allow for facile poling of complex microstructured fibers (MOFs) of arbitrarily long lengths. In combination with our unique ability to use liquid gallium electrodes, inducing second-order nonlinearities inside otherwise difficult to access multi-core or multi-hole MOFs now becomes entirely feasible and practical. The formation of a permanent second-order nonlinearity is unequivocally demonstrated by realizing quasi-phase-matched frequency doublers using periodic UV erasure methods in the induction-poled fibers. The second-order susceptibility created inside the fiber is driven by the potential difference established between the floating electrodes, which we calculate via numerical simulations.
We report on the development of an all-interferometric optomechatronic sensor for the detection of multi-degrees-of-freedom displacements of a remote target. The prototype system exploits the self-mixing technique and consists only of a laser head, equipped with six laser sources, and a suitably designed reflective target. The feasibility of the system was validated experimentally for both single or multi-degrees-of-freedom measurements, thus demonstrating a simple and inexpensive alternative to costly and bulky existing systems.
Since their first demonstration some 25 years ago, thermally poled silica fibers have been used to realize device functions such as electro-optic modulation, switching, polarization entangled photons and optical frequency conversion with a number of advantages over bulk free-space components. We have recently developed an innovative induction poling technique that could allow for the development of complex microstructured fiber geometries for highly efficient χ (2) based device applications. In order to systematically implement these more advanced poled fiber designs, we report here the development of comprehensive numerical models of the induction poling mechanism itself via 2D simulations of ion migration and space-charge region formation using finite element analysis. © 2016 Optical Society of America OCIS codes : (190.4370) Nonlinear optics, fibers; (230.4320) Nonlinear optical devices; (190.2620) Harmonic generation and mixing; (230.1150) All-optical devices; (000.4430) Numerical approximation and analysis.The development of thermal poling, a technique to generate effective second order nonlinearities in silica optical fibers [1], has found widespread applications in parametric frequency conversion [2], electro-optic modulation, switching [3] and polarization-entangled photon pair generation [4]. During thermal poling, the optical fiber is heated in order to increase the mobility of the impurity charge carriers (typically Na + , Li + , K + ), while a high voltage is applied for a certain time between two electrodes embedded into the fiber [5]. The static electric field due to the application of the high voltage causes the impurity charges to drift from regions at high potential towards regions at lower potential creating a space charge region located near the anode. When the sample is cooled down whilst the voltage is still applied, an electric field is frozen into the depleted region and an effective nonlinear susceptibility ( ) is induced into the sample due to a process of third order nonlinear optical rectification. The early issues mainly related to the high risk of breakdown between the two electrodes (typically separated by a few tens of microns) were addressed by Margulis et al. [6], who demonstrated that it is possible to induce a value of ( ) higher than the one obtained in the conventional case[5] by means of a poling configuration in which the two embedded electrodes are both connected to the same positive potential of the anode. The method for "charging" optical fibers has been recently further developed by De Lucia et al. [7], who discovered that it is possible to create a space charge region using electrostatic induction between an external inductor and the floating electrodes embedded inside a fused silica twin-hole fiber. As this novel technique avoids any physical contact to the internally embedded electrodes, it automatically lifts a number of restrictions on the use of microstructured optical fibers for poling where the multiple contacting of individual electrodes becomes a prohibit...
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