Single multimode fiber endoscope

Abstract

Multimode fibers can guide thousands of modes capable of delivering spatial information. Unfortunately, mode dispersion and coupling have so far prevented their use in endoscopic applications. To address this long-lasting challenge, we present a robust scanning fluorescence endoscope. A spatial light modulator shapes the input excitation wavefront to focus light on the distal tip of the fiber and to rapidly scan the focus over the region of interest. A detector array collects the fluorescence emission propagated back from the sample to the proximal tip of the fiber. We demonstrate that proper selection of the multimode fiber is critical for a robust calibration and for high signal-to-background ratio performance. We compare different types of multimode fibers and experimentally show that a focus created through a graded-index fiber can withstand a few millimeters of fiber distal tip translation. The resulting scanning endoscopic microscope images fluorescent samples over a field of view of 80µm with a resolution of 2µm.

Hybrid photoacoustic-fluorescence microendoscopy through a multimode fiber using speckle illumination

“…The fluorescence results described in section 3.B were obtained with a slightly different setup for practical reasons related to samples and material availability in the two different facilities involved in this work. The corresponding experimental setup is described in detail in [22,23], and differs from the setup above in particular by the fact that a continuous laser was used for the experiments. Additionnaly, an EMCCD camera (Andor iXon+) was used to collect fluorescence from the input/proximal tip of the MMF.…”

“…The fluorescence imaging setup used for experiments described in section 3B of the main paper consists of a 532 nm CW Coherent Verdi-G laser which passes through a spatial filter SF and is incident on a TI-DLP Discovery 4100 digital micro-mirror device (DMD). The DMD performs phase modulation on the incident wavefront using off-axis computer generated holography, as described in [22]. The incident wavefront is modulated using 9216 independent input modes and imaged onto the back focal plane of a 20x microscope objective MO1 which then couples it into the fiber.…”

“…Multimode fibers (MMF) are becoming a popular alternative employed to guide light and collect signals thanks to their small footprint as compared to fiber bundles with comparable imaging performances, and thanks to their efficient light collection for fluorescence imaging. Several groups have demonstrated the possibility to perform optical resolution imaging through MMF [12][13][14][15][16][17][18][19][20][21][22][23][24][25], including photoacoustic imaging [26][27][28].…”

“…Moreover, generating focal spots at the distal end requires complete calibration of the fiber complex TM. It is worth noticing that the fiber needs to stay mostly unperturbed during the experiment; otherwise the TM changes, reducing the ability to control the intensity distribution at the distal tip [22]. ing, based on sampling the output plane using the natural output speckle patterns of a stationary MMF.…”

Wave-front shaping for nonlinear light propagation in multimode fibers

“…In fiber lasers, the higher damage threshold of larger fibers is attractive as an alternative for power-limited single-mode fiber lasers and amplifiers 24 . MMF are important for endoscopic nonlinear microscopy and laser surgery, where nonlinear pulse distortions are expected 25 . Recently, control over a variety of spatiotemporal nonlinear dynamics in graded-index (GRIN) MMF has been demonstrated by manually adjusting (laterally shifting) the input beam coupling to the fiber 15,26 .…”