Abstract
We shape fs optical pulses and deliver them in a single spatial mode to the input of a multimode fiber. The pulse is shaped in time such that at the output of the multimode fiber an ultrashort pulse appears at a predefined focus. Our result shows how to raster scan an ultrashort pulse at the output of a stiff piece of square-core step-index multimode fiber and in this way show the potential for making a nonlinear fluorescent image of the scene behind the fiber, while the connection to the multimode fiber can be established via a thin and flexible single-mode fiber. The experimental results match our numerical simulation well.
Highlights
All-optical imaging via multimode fibers (MMF) has the potential to become the method of choice for imaging in confined spaces, combining the smallest access diameter with the highest NA [1,2]
Several nonlinear optical imaging techniques through a single MMF probe have been demonstrated including two-photon excitation microscopy [25,26], 3D microfabrication based on two-photon polymerization [27], and coherent anti-Stokes Raman scattering (CARS) microscopy [28]
Inverting one of the responses and using that as the input pulse shape results in a transform-limited pulse in either spot A or B, depending on which response was inverted. This enables making a short pulse at a particular spot at the output facet, even though the input pulse is still in a single spatial mode
Summary
All-optical imaging via multimode fibers (MMF) has the potential to become the method of choice for imaging in confined spaces, combining the smallest access diameter with the highest NA [1,2]. Several nonlinear optical imaging techniques through a single MMF probe have been demonstrated including two-photon excitation microscopy [25,26], 3D microfabrication based on two-photon polymerization [27], and coherent anti-Stokes Raman scattering (CARS) microscopy [28] All these methods of nonlinear imaging require spatial-domain wavefront shaping and control over many spatial modes on the MMF input. Our system allows control over the position of a nonlinearly focused beam in space on the MMF output facet by shaping an input pulse in a single spatial mode in time. Controlling only a temporal shape on the single-mode input allows us to avoid the spatial control over the MMF input This way of light control at the MMF output can help to avoid the perturbation sensitivity of MMF-based imaging probes. To the best of our knowledge, this paper is the first to experimentally demonstrate grid scanning an ultrashort pulse over the output facet of a stiff piece of the MMF by temporally re-shaping the single-mode input pulse using nonlinear optical feedback
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