An optical system via liquid crystal photonic devices for photobiomodulation

Abstract

Photobiomodulation or low-level light therapy (LLLT) has extensive applications based on light-induced effects in biological systems. Photobiomodulation remains controversial because of a poorly understood biochemical mechanism limited by the well-known biphasic dose response or Arndt-Schulz curve. The Arndt-Schulz curve states that an optimal dose of light is a key factor for realizing a therapeutic effect. In this report, we demonstrate a tunable optical system for photobiomodulation to aid physicians in overcoming the constraints of light due to biphasic dose response. The tunable optical system is based on a white light-emitting diode and four liquid crystal (LC) photonic devices: three LC phase retarders, and one LC lens. The output light of the tunable optical system exhibits electrical tunability for the wavelength, energy density and beam size. The operating principle is introduced, and the experimental results are presented. The proposed concept can be further extended to other electrically tunable photonic devices for different clinical purposes for photobiomodulation.

Figure 1

Four parts of a tunable optical system for LLLT.

Figure 2

(a) The structure of the proposed optical system for portable LLLT. (b) Detailed beam propagation in lens L₃ and the LC lens.

Figure 3

(a) Calculated transmissive spectrum of the optical system for the electrically tunable color filter only. (b) Calculated transmissive spectrum for the bandwidth suppressor only. By combining (a) and (b), (c), (d), and (e) Illustrate the transmissive spectra for the blue mode, green mode and red mode with the bandwidth suppressor, respectively. The parameters used are: Δn = 0.17, d₁ = 2.65 μm and d₂ = 3.82 μm, Γ_LC is set as 6.46π/λ radians.

Figure 4

The structure of phase retarder 1 and phase retarder 2 using an FLC, (a) when the FLC phase retarder is subject to an applied voltage of −10 V and (b) +10 V. (c) The structure of phase retarder 3 using nematic LC when the voltage is switched off. (d) The phase retardation of phase retarder 3 as a function of applied voltage.

Figure 5

(a) The structure of the LC lens. (b) The voltage-dependent lens power of the LC lens. Red squares represent the lens power at different V₁ for V₂ = 10 V_rms and f = 4.2 kHz. Blue diamonds represent the lens power at different V₂ for V₁ = 30 V_rms and f = 800 Hz. The LC lens is (c) a positive lens when V₁ > V₂ and (d) a negative lens when V₂ > V₁.

Figure 6

Experimental results showing the normalized transmission spectra for (a) the electrically tunable color filter without a bandwidth suppressor and (b) the electrically tunable color filter with a bandwidth suppressor.

Figure 7

Light intensity spectra for (a) LED light source, (b) electrically tunable color filter and (c) electrically tunable color filter with bandwidth suppressor.

Figure 8

(a) Beam spots at different lens power for the LC lens at different modes. (b) Irradiance as a function of beam diameter at different modes. The theoretical curves are obtained based on Eqs (5) and (10).