THz interferometric imaging using subwavelength plastic fiber based THz endoscopes

Abstract

We demonstrate a new reflective imaging technique using continuous-wave THz fiber-endoscopy, in which the sample is placed behind the output of a THz subwavelength plastic fiber and the Fabry Perot interference is formed therein. 3D THz reflective images with a reasonable SNR as well as high lateral and subwavelength axial resolutions are acquired by moving the sample along the axial (z) direction and by 2D scanning the output end of the subwavelength plastic fiber without any focusing medium. By analyzing the axial-position dependent THz signals backward collected by the subwavelength plastic fiber, the THz reflection amplitudes and phases on the sample surface can be successfully reconstructed.

THz dielectric fiber based imaging: In vivo molecular imaging of water

“…The second is the hollow type, which is essentially an air-core waveguide surrounded by a structured cladding and confines most of the power within the air-core region [2][3][4]. I will also discuss various fiber-delivery and fiber scanning THz imaging systems developed by using the demonstrated simple dielectric THz fibers and waveguides, including fiber-scanning THz transmission [8,9] and reflection [10] endoscopy, fiber-scanning near-field microscopy [ 1 1,12], fiber-delivered THz swept-source radar (equivalent to the THz OCT) [13], and pipe-based near-field in vivo imaging systems. Application on in vivo transmission THz mammography for early breast cancer detection [9,12] and for in vivo noninvasive blood glucose monitoring will also be discussed.…”

Spectral characterization of porous dielectric subwavelength THz fibers fabricated using a microstructured molding technique

“…6 Recent efforts on metallic wires have demonstrated the use of a dual-wire suspended in air waveguide, 8 which supports a more easily excitable TEM mode at the expense of a more complicated waveguide geometry that requires maintaining a constant sub-millimeter distance between the two wires. On the other hand, dielectric subwavelength wires 3,[9][10][11] feature low-loss single-mode regime with a linearly-polarized HE 11 fundamental mode which is very easy to excite with a gaussian-like beam of a THz source. Main disadvantage of the dielectric wires is a relatively high dispersion, and a limited operational bandwidth due to onset of large absorption losses at higher frequencies.…”

“…Moreover, both types of subwavelength fiber feature extremely delocalized modes (as large as several mm in diameter), which are susceptible to high bending loss and strong proximity cross-talk with the environment. In some implementations, strong mode delocalization can be used for a benefit to enable, for example, non-destructive cut-backlike measurements of the fiber propagating losses using evanescent directional coupler technique 10,12 . Another potential benefit of the subwavelength waveguides is in THz optical sensing which rely on strong presence of the modal evanescent fields in the analyte.…”

Subwavelength plastic wire terahertz time-domain spectroscopy

“…Among the merits of the simple THz subwavelength plastic wire ͑THz-SPW͒ include single mode sustentation, a high coupling efficiency, a low propagation loss 6 ͑on the order of 0.01 cm −1 ͒, as well as theoretically low dispersion in the transmission band. 7 THz-SPW has been successfully adopted in directional couplers, 8 endoscopic imaging, 9 and microscopy. 10 To our knowledge, the dispersion feature of THz-SPW has not been experimentally measured or analyzed.…”