A miniaturized fiber-coupled terahertz endoscope system

Abstract

In this study, we have designed, fabricated, and characterized a miniaturized optical fiber-coupled terahertz (THz) endoscope system. The endoscopic system utilized a photoconductive generator and detector driven by a mode-locked Ti:sapphire laser. In reflection mode, the endoscope showed a high signal-to-noise ratio and a wide frequency spectrum similar to the conventional THz time-domain spectroscopic system. The cross section of the endoscope including generator and detector head is (2 x 4 mm) x 6 mm, which is small enough to be inserted into a human body. For a feasibility test, the endoscopic system was used to measure reflective THz signals from the side wall of the mouth, tongue, and palm skin as well as from water for comparison. The absorption and refractive index of the side wall of the mouth and tongue were similar to those of water but those of the palm skin were less than water.

Single-channel prototype terahertz endoscopic system

“…A recently developed fiber guided THz endoscopic system used two channels to measure the reflected signals from the specimen, and relied on optical fibers for pulse propagation. 7 Here, the optical fiber is connected with a photo-conductive antenna and is necessarily operated under high voltage which is undesirable for in vivo applications. Another study based on antiresonant hollow-core waveguides used a polymer tube for the transmission; since the radiation is not confined inside the bent tube, it limits the guiding capability and possesses high bending losses.…”

Terahertz spectroscopic imaging and properties of gastrointestinal tract in a rat model

“…3(c) and 3(d), the THz signals reflected from the analysis points of these organs are almost same. Because reflected THz signals contain amplitude and phase information about the samples, the refractive index and absorption coefficient could be calculated by referencing the THz signal reflected from the interface between quartz and metal [26]. The calculated refractive indices and absorption coefficients are shown in Figs.…”

Terahertz otoscope and potential for diagnosing otitis media

“…The total optical path is as follows: i) THz waves are generated from lateral photo-Dember currents in a forward direction from a semiconductor (Tx) [18], ii) THz waves are collimated by a hemispherical silicon lens and pass through a silicon splitter with 1/2-inch diameter and 3-mm thickness, iii) THz waves are reflected from indium tin oxide (ITO) glass that enables both optical and THz diagnostics since it is transparent in optical regime and is metallic in THz regime [19], iv) THz waves pass through an ear speculum with a 5-mm diameter hole and are reflected back from the tympanic membrane, v) reflected THz waves go back to a photoconductive antenna receiver (Rx) after reflecting from the ITO glass, silicon splitter, and metal plate. Tx and Rx are driven by femto-second laser pulses with optical fibers as we previously described [10]. The most important consideration during THz otoscope development was the silicon lens for THz collimation.…”

“…Terahertz (THz) electromagnetic waves are highly sensitive to biomolecules and water; they have been applied to many biomedical applications [7][8][9][10][11][12] including diagnosing various types of cancer [13][14][15][16][17]. The fundamental reason for the use of THz waves in cancer diagnosis is that they sensitively interact with water molecules.…”