Research ArticleMATERIALS SCIENCE

Wavelength-tunable and shape-reconfigurable photonic capsule resonators containing cholesteric liquid crystals

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Science Advances  22 Jun 2018:
Vol. 4, no. 6, eaat8276
DOI: 10.1126/sciadv.aat8276
  • Fig. 1 Air-stable CLC capsule resonators.

    (A) Schematic of a photonic capsule resonator composed of a dye-dissolved CLC core, an inner alignment layer, and an outer elastic shell. (B and C) Photograph and optical microscopy (OM) image of dried CLC capsules taken in reflection mode without polarization. The capsules maintain their spherical shape and radially aligned helical axes in the air, which results in photonic cross-communication. The inset of (C) is a cross-polarized OM image in transmission mode, which shows small and large fourfold patterns at the center. (D) Reflectance spectrum (right y axis) of CLC capsules in the air and lasing spectrum (left y axis) in the LWE on the CLC capsules. We obtained the reflectance spectrum by subtracting the spectrum taken at 60°C (isotropic state) from the measured one to exclude the influence of the dye absorption. The inset shows a lasing on the capsules. (E) Series of the emission spectra on the capsules in the air at various pumped energies. The inset shows an emission intensity as a function of the pumped energy, which has a threshold value of 0.98 μJ per pulse.

  • Fig. 2 Wavelength tuning with temperature.

    (A) Series of OM images of a CLC capsule taken at denoted temperatures. The stop band of CLC blue-shifts along with temperature. (B and C) Reflectance spectra (right y axis) of dye-free CLC film and lasing spectra (left y axis) from the capsules containing dye-dissolved CLC, where we used the same concentration of chiral dopants in the film and capsule. Lasing occurs in the SWE in the range of 18° to 21.5°C and occurs in the LWE in the range of 22° to 34°C. (D) Wavelengths of LWE, SWE, and lasing emission as a function of temperature, where a spontaneous emission spectrum of the dye is shown in the right panel and represented with a color gradient in the main panel. (E) Threshold energy (left y axis) for lasing on the CLC capsule in LWE (red circles) and SWE (blue triangles) as a function of wavelength. The temperature is also denoted. The spontaneous emission spectrum of the dye (right y axis) is shown for a comparison.

  • Fig. 3 Control of lasing direction and intensity.

    (A) Side view of the CLC capsule compressed by a pair of two plates. An FR of the deformed capsule is defined as FR = 1 − H/D. (B) Side-view OM images of a CLC capsule immediately after the deformation taken in transmission mode without polarization (top) and with cross-polarization (bottom). (C) Top-view OM images of a CLC capsule taken in reflection mode, showing the expansion of flattened area responsible for strong reflection at stop band, where FR is varied in the range of 0 to 0.56. The insets are corresponding schematics. (D) Output intensity of lasing emission as a function of the pumped energy, where we used CLC capsules with five different FRs in (C). (E) Output intensity relative to the input energy on the flattened area of capsules (left x axis) for a pumped energy of 1.4 μJ per pulse, where we normalized the value by that of a spherical capsule (FR = 0). We also included the FWHM of emission spectra above the threshold energy (right y axis).

  • Fig. 4 Shape-reconfigurable capsule resonators.

    (A and B) OM images of CLC capsules inserted in polygonal holes taken in reflection mode without polarization (A) and with cross-polarization (B). The insets of (A) show a shape of polygonal holes, and the insets of (B) are schematics for planar alignment of CLC (dotted lines) and line defects (solid lines). (C) Series of the emission spectra from the capsule confined in the square hole at various pumped energies. The inset shows a threshold behavior of the emission, where the threshold value is 0.98 μJ per pulse. (D) Threshold energy (red circles; left y axis) and FWHM of laser spectra (blue circles; right y axis) for the capsules confined in the triangular, square, pentagonal, and hexagonal holes. Insets show lasing from the shape-transformed capsules.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/6/eaat8276/DC1

    section S1. Microfluidic production of triple-emulsion drops

    section S2. Photonic cross-communication in CLC capsule array

    section S3. Optical setup for measurement of emission from CLC capsules

    section S4. Temperature dependence of photonic stop-band of CLC solution

    section S5. Competition between SWE and LWE

    section S6. Temperature-dependent threshold energy

    section S7. Input energy on the flattened area of deformed capsule

    section S8. Enhancement of lasing intensity and reduction of FWHM during incubation

    fig. S1. Preparation of triple-emulsion drops using a capillary microfluidic device.

    fig. S2. Photonic cross-communication.

    fig. S3. Optical setup for emission measurement from capsules.

    fig. S4. Tuning of photonic stop band with temperature.

    fig. S5. Competition between SWE and LWE for lasing.

    fig. S6. Temperature-dependent threshold energy.

    fig. S7. Input energy on the flattened area of deformed capsule.

    fig. S8. Enhancement of laser quality over incubation.

    movie S1. Spontaneous healing of oily streak in deformed capsule.

  • Supplementary Materials

    This PDF file includes:

    • section S1. Microfluidic production of triple-emulsion drops
    • section S2. Photonic cross-communication in CLC capsule array
    • section S3. Optical setup for measurement of emission from CLC capsules
    • section S4. Temperature dependence of photonic stop-band of CLC solution
    • section S5. Competition between SWE and LWE
    • section S6. Temperature-dependent threshold energy
    • section S7. Input energy on the flattened area of deformed capsule
    • section S8. Enhancement of lasing intensity and reduction of FWHM during incubation
    • fig. S1. Preparation of triple-emulsion drops using a capillary microfluidic device.
    • fig. S2. Photonic cross-communication.
    • fig. S3. Optical setup for emission measurement from capsules.
    • fig. S4. Tuning of photonic stop band with temperature.
    • fig. S5. Competition between SWE and LWE for lasing.
    • fig. S6. Temperature-dependent threshold energy.
    • fig. S7. Input energy on the flattened area of deformed capsule.
    • fig. S8. Enhancement of laser quality over incubation.

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mp4 format). Spontaneous healing of oily streak in deformed capsule.

    Files in this Data Supplement:

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