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.
Highlights
Photobiomodulation, known as low-level light therapy (LLLT), was first demonstrated to aid hair growth in mice in 19681,2
The optimal dose of light is important in LLLT because of the biphasic dose response or the Arndt-Schulz curve, which states that the therapeutic effect depends on the light dose[27,28,29,30]
Since liquid crystals (LCs) are superior in the modulation of light amplitude and optical phase, versatile photonic devices have been designed based on LC materials, such as attenuators, lenses, waveplates, gratings, polarization rotators and color filters[32,33,34,35,36,37,38,39,40,41,42,43]
Summary
Light passing through the electrically tunable color filter turns out to be green as θ1 = θ2 = 135° (defined as the on-state for both of the phase retarders) because the green polarized light reaches maximal transmittance. The transmittance of the FLC phase retarder under crossed-polarizers as a function of applied voltage was tested in a previous study[44]. The measured lens power for the LC lens ranges from +2 Diopter to −2.5 Diopter (i.e., focal length from −40 cm to +50 cm)
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