Rapid progress in big data technologies results in the need for a drastic increase in wireless data transfer rates. To meet the demand, it is necessary to develop communication systems operating at carrier frequencies in the range 0.1–10 THz (so-called THz band). They can provide data transfer rates of more than 1 Tbps in in-door deployments. However, existing hardware solutions for THz transmitters/receivers usually rely on the use of hollow metallic waveguides, which already suffer from noticeable insertion losses of 0.24-0.31 dB/cm at 110 GHz. And these losses increase even more with further increase of operating frequency. Thus, use of metallic waveguides potentially compromises signal strength and sensitivity, increases design complexity and fabrication costs of a transceiver. One of the potential solutions is to use low-loss fully dielectric wave-guiding structures. In this work, we report on the development of a THz dielectric waveguide made from a high-resistivity Si substrate. A square lattice of openings is fabricated in the substrate via the Bosch process. Transmission and reflection spectra of the fabricated waveguide samples are measured over the frequency range 135–160 GHz. Similar to the simulation forecast, we measure insertion and return losses of 0.04 dB/cm and 20 dB at 150 GHz, respectively, which meet requirements of modern practical applications.
Significance: Water content plays a vital role in the normally functioning visual system; even a minor disruption in the water balance may be harmful. Today, no direct method exists for corneal hydration assessment, while it could be instrumental in early diagnosis and control of a variety of eye diseases. The use of terahertz (THz) radiation, which is highly sensitive to water content, appears to be very promising.
Aim: To find out how THz scanning parameters of corneal tissue measured by an experimental setup, specially developed for in vivo contactless estimations of corneal reflectivity coefficient (RC), are related to pathological changes in the cornea caused by B-band ultraviolet (UVB) exposure.
Approach: The setup was tested on rabbit eyes in vivo. Prior to the course of UVB irradiation and 1, 5, and 30 days after it, a series of examinations of the corneal state was made. At the same time points, corneal hydration was assessed by measuring RC.
Results: The obtained data confirmed the negative impact of UVB irradiation course on the intensity of tear production and on the corneal thickness and optical parameters. A significant (1.8 times) increase in RC on the 5th day after the irradiation course, followed by a slight decrease on the 30th day after it was revealed. The RC increase measured 5 days after the UVB irradiation course generally corresponded to the increase (by a factor of 1.3) of tear production. RC increase occurred with the corneal edema, which was manifested by corneal thickening (by 18.2% in the middle area and 17.6% in corneal periphery) and an increased volume of corneal tissue (by 17.6%).
Conclusions: Our results demonstrate that the proposed approach can be used for in vivo contactless estimation of the reflectivity of rabbit cornea in the THz range and, thereby, of cornea hydration.
An adequate water balance (hydration extent) is one of the basic factors of normal eye function, including its external shells: the cornea and the sclera. Adequate control of corneal and scleral hydration is very important for early diagnosis of a variety of eye diseases, stating indications for and contraindications against keratorefractive surgeries and the choice of contact lens correction solutions. THz systems of creating images in reflected beams are likely to become ideal instruments of noninvasive control of corneal and scleral hydration degrees. This paper reports on the results of a study involving transmittance and reflectance spectra for the cornea and the sclera of rabbit and human eyes, as well as those of the rabbit eye, in the frequency range of 0.13 to 0.32 THz. The dependence of the reflectance coefficient of these tissues on water mass percentage content was determined. The experiments were performed on three corneas, three rabbit scleras, two rabbit eyes, and three human scleras. The preliminary results demonstrate that the proposed technique, based on the use of a continuous THz radiation, may be utilized to create a device for noninvasive control of corneal and scleral hydration, which has clear potential of broad practical application.
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