Journal: Light, Science & Applications

Article Title: Multimodal nonlinear endomicroscopic imaging probe using a double-core double-clad fiber and focus-combining micro-optical concept

doi: 10.1038/s41377-021-00648-w

Figure Lengend Snippet: a microscopic image of the front facet of the manufactured DCDC fiber consisting of two single-mode cores made of pure silica separated by 24 µm and 4.8 µm (core 1, cut-off wavelength 836 nm) and 6.3 µm (core 2, cut-off wavelength 970 nm) in diameter for guiding pump and Stokes laser at 795 and 1030 nm, respectively, and a fluorine-doped inner cladding of 60 µm diameter and a pure silica double-clad of 125 µm diameter for signal collection, coated with a fluorine-doped polymer of 230 µm diameter ( n = 1.363 at 852 nm) ( b ) fiber attenuation of the two cores and the outer cladding. The attenuation per km fiber length of core 1 is 11 dB at 795 nm, of core 2 8.5 dB at 1030 nm, and the one of the outer cladding 185 dB at 400 nm and 7.5 dB at 700 nm. Maxima in transmission loss correspond to the modal cut-off of the individual cores. c Refractive index Δn of the fiber relative to fluorine-doped pure silica measured in 2D at 633 nm. d Cross-sections of the refractive index profiles at the red and green lines indicated in ( c ). The deviation from the step refractive index profile for the green graph is an artefact resulting from the reconstruction algorithm. The grey area marks the region of the polymer coating of n = 1.363, which was removed for the measurement

Article Snippet: The DCDC fiber is scanned by a piezo tube resonant scanner in a spiral pattern at 1240 Hz resonance frequency. b Spot diagrams for the on-axis and off-axis field positions for pump (795 nm, purple) and Stokes laser (1030 nm, blue), the black circle shows the Airy disk (Airy radius 0.883 μm @ 795 nm) in the high NA object plane (NA = 0.55), simulated in ZEMAX. c Strehl ratio as a function of the field height in the object plane for both, pump and Stokes wavelengths.

Techniques: Polymer, Transmission Assay, Refractive Index

Journal: Light, Science & Applications

Article Title: Multimodal nonlinear endomicroscopic imaging probe using a double-core double-clad fiber and focus-combining micro-optical concept

doi: 10.1038/s41377-021-00648-w

Figure Lengend Snippet: a Photo of the endomicroscopic fiber probe and laser coupling unit. A picture of the stainless steel shielded probe head of 2.4 mm diameter and a length of 39 mm is shown in the upper right corner in comparison with the size of one Euro cent coin. The optical fiber and the four connection cables of the piezo-scanner are guided in a 1 mm tube, which is enclosed in a sealed medical-grade endoscopic tube of 4.5 mm in diameter. b The fiber laser (AFS, Germany) is collimated by the lens L1 ( f = 3 mm), filtered from FWM at the CARS wavelength by F1 (750 nm long pass). The laser power is adjusted using a 1050 nm short pass dichroic mirror (DC1). A linear diffractive grating G of 39.4 μm grating period and lens L3 ( f = 4 mm) couple pump and Stokes-wavelengths into the two different cores. Sample signals are guided back through the DCDC fiber and detected by the PMT detector after deflection at the dichroic mirror DC2. The bandpass filter F2 is selecting the non-linear signal of interest (CARS/SHG/TPEF) and the lens L2 focusing the signals onto the PMT

Article Snippet: The DCDC fiber is scanned by a piezo tube resonant scanner in a spiral pattern at 1240 Hz resonance frequency. b Spot diagrams for the on-axis and off-axis field positions for pump (795 nm, purple) and Stokes laser (1030 nm, blue), the black circle shows the Airy disk (Airy radius 0.883 μm @ 795 nm) in the high NA object plane (NA = 0.55), simulated in ZEMAX. c Strehl ratio as a function of the field height in the object plane for both, pump and Stokes wavelengths.

Techniques: Comparison

Journal: Light, Science & Applications

Article Title: Multimodal nonlinear endomicroscopic imaging probe using a double-core double-clad fiber and focus-combining micro-optical concept

doi: 10.1038/s41377-021-00648-w

Figure Lengend Snippet: a Design scheme of the endomicroscopic objective consisting of a resonant piezo-scanner guided DCDC fiber, GRIN lens of 2.0 mm diameter, linear diffractive grating for combining pump and Stokes beam and front optics consisting of a refractive doublet and two singlet lenses, providing a numerical aperture of 0.55 at a working distance of 30 µm in water. The DCDC fiber is scanned by a piezo tube resonant scanner in a spiral pattern at 1240 Hz resonance frequency. b Spot diagrams for the on-axis and off-axis field positions for pump (795 nm, purple) and Stokes laser (1030 nm, blue), the black circle shows the Airy disk (Airy radius 0.883 µm @ 795 nm) in the high NA object plane (NA = 0.55), simulated in ZEMAX. c Strehl ratio as a function of the field height in the object plane for both, pump and Stokes wavelengths. The dashed line corresponds to a Strehl ratio of 0.8 indicating a diffraction-limited performance in the object plane. d Ray tracing spot diagrams in the DCDC fiber image are shown for the first two diffraction orders of the relevant signal wavelengths of 647 nm (CARS @ 2850 cm −1 ), 515 nm (SHG from Stokes laser @ 1030 nm), and 550 nm (TPEF, spectral range 525.5–630.5 nm). The objective design allows to cover the ray bundles of both diffraction orders for all three signals by the two diameters, 60 and 125 µm, of the collection cladding of the fiber (yellow and blue circle), assuming ideal point sources with NA = 0.55 as origins in the object plane. The percentage values given are calculated diffraction efficiencies of an ideal blazed grating profile with a Blaze wavelength of 927 nm, which is optimized for the pump and Stokes laser

Article Snippet: The DCDC fiber is scanned by a piezo tube resonant scanner in a spiral pattern at 1240 Hz resonance frequency. b Spot diagrams for the on-axis and off-axis field positions for pump (795 nm, purple) and Stokes laser (1030 nm, blue), the black circle shows the Airy disk (Airy radius 0.883 μm @ 795 nm) in the high NA object plane (NA = 0.55), simulated in ZEMAX. c Strehl ratio as a function of the field height in the object plane for both, pump and Stokes wavelengths.

Techniques: