THz-fiber waveguide composed of a biocompatible Vaseline core and Teflon holey cladding enabling a centimeter bending radius

Yong Soo Lee; Inhee Maeng; Mingyu Lee; Seokjin Kim; Chul Kang; Daniele Tosi; Soeun Kim; Seung Jae Oh; Kyunghwan Oh

doi:10.1364/PRJ.545598

Photonics Research, Volume. 13, Issue 8, 2306(2025)

THz-fiber waveguide composed of a biocompatible Vaseline core and Teflon holey cladding enabling a centimeter bending radius

Yong Soo Lee^1,2、†, Inhee Maeng^3、†, Mingyu Lee^1,2, Seokjin Kim^1,2, Chul Kang⁴, Daniele Tosi⁵, Soeun Kim^4,7, Seung Jae Oh^3,8, and Kyunghwan Oh^1,6、*

Author Affiliations

¹Department of Physics, Yonsei University, Seoul 03722, Republic of Korea

²Center for Quantum Technology, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea

³YUHS-KRIBB Medical Convergence Research Institute, College of Medicine, Yonsei University, Seoul 03722, Republic of Korea

⁴Integrated Optics Laboratory, Advanced Photonics Research Institute, GIST, Gwangju 61005, Republic of Korea

⁵Department of Electrical and Electronical Engineering, Nazarbayev University, 010000 Astana, Kazakhstan

⁶Department of Physics, School of Sciences and Humanities, Nazarbayev University, 010000 Astana, Kazakhstan

⁷e-mail: sekim@gist.ac.kr

⁸e-mail: issac@yuhs.ac

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Figures & Tables(10)

Fig. 1. Transverse cross-section of the proposed THz fiber composed of Vaseline core and PTFE holey cladding (O.D.: outer diameter, $D$ : air hole diameter, $Λ$ : air hole pitch, $φ$ : azimuth angle referenced to the bending orientation).

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Fig. 2. Spatial distributions of the electric field magnitude of the fundamental mode. (a) Comparison of the proposed fiber with step index solid cladding fiber (SI-SCF) for various bending radii $R = 20$ to 200 mm at the frequency of 0.5 THz. Here, the bending angle $φ = 0 °$ . (b) Change of the fundamental mode’s spatial intensity distribution with the frequency when the bending radius $R = 30 mm$ .

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Fig. 3. Optical properties of the proposed THz fiber: (a) effective mode index and single-mode condition, (b) dispersion, (c) effective material loss, and (d) confinement loss.

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Fig. 4. Fabrication processes of the proposed composite THz fiber.

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Fig. 5. Experimental setup to measure the bending characteristics of the proposed THz fiber. The fiber was mounted on a goniometer, and bending parameters are the radius of curvature $C$ , goniometer angle $θ$ , and bent fiber length $L_{θ}$ . THz pulses passed through the proposed fiber and were detected in the time domain. As the fiber bends, the fiber passes through Holder 2, to make $d_{θ}$ longer than $d_{s}$ . Therefore, $L_{θ}$ decreases with increasing $θ$ . Note that the straight fiber has $L_{s}$ and $d_{s}$ for $θ = 0 °$ .

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Fig. 6. Measurement of THz pulses through the proposed fiber in the time domain: (a) when the fiber was bent horizontally, $φ = 0 °$ and (b) vertically, $φ = 90 °$ .

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Fig. 7. Transmittance of the proposed fiber in the THz frequency domain: (a) transmittance of a straight fiber; (b) transmission ratio of the bent fiber to the straight fiber for various curvatures.

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Table 1. Bending Parameters for the THz Fiber
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Table 1. Bending Parameters for the THz Fiber
Angle, $θ$ $R$ [mm] $C$ [ $m^{- 1}$ ] $L_{θ}$ [mm]
0° – – 46.0
30° 85.8 11.7 44.9
60° 39.8 25.1 41.7
90° 23.0 43.5 36.1
110° 16.1 62.1 30.9

Table 2. Comparison of the Proposed THz Fiber with Prior Reports^a

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Table 2. Comparison of the Proposed THz Fiber with Prior Reports^a

Reference	Fiber Type	Material		Length [cm]	Dispersion [ps/(THz·cm)]
Reference	Fiber Type	Core	Cladding	Length [cm]	Dispersion [ps/(THz·cm)]
[25]	Two-wire waveguide	Air	Air	9.5	4.0^b
[29]	Parallel plate waveguide	Air	Air	1.6	1.5^b
[31]	Porous-core fiber	PTFE	Air	20	1.9^b
[32]	Porous-core fiber	PE + PMMA	Air	33.5	13.9^b
[33]	Porous-core PCF	COC	Holey COC	5	10.5^b
[35]	Photonic crystal fiber	HDPE	Holey HDPE	2	9.0^b
Proposed	Holey cladding fiber	Vaseline	Holey PTFE	9	6.0^b
Proposed	Holey cladding fiber	Vaseline	Holey PTFE	9	6.5^c

Table 3. Comparison of the Proposed THz Fiber with Prior Reports

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Table 3. Comparison of the Proposed THz Fiber with Prior Reports

Reference	Fiber Type	Material		Bending Radius [mm]	Operating Frequency [THz]	Loss [dB/cm]
Reference	Fiber Type	Core	Cladding	Bending Radius [mm]	Operating Frequency [THz]	Loss [dB/cm]
[23]	Metal hollow fiber (tube)	Air	Silver (coated)	150	1.2–1.58	$< 0.08$
[24]	Hollow fiber (tube)	Air	Silver/polypropylene	150	0.3	$< 0.013$
[26]	Hollow fiber (tube)	Air	PMMA	100	0.3–1.0	$< 0.5 {cm}^{- 1}$
[27]	Circular tube lattice fiber	Air	PMMA	100	0.25–1	$< 2$
[31]	Porous-core fiber	PTFE	Air	210	0.2–0.33	$< 0.78$
Proposed	Holey cladding fiber	Vaseline	Holey PTFE	16.1	0.2–0.9	0.18 @0.2 THz 0.22 @0.5 THz

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Yong Soo Lee, Inhee Maeng, Mingyu Lee, Seokjin Kim, Chul Kang, Daniele Tosi, Soeun Kim, Seung Jae Oh, Kyunghwan Oh, "THz-fiber waveguide composed of a biocompatible Vaseline core and Teflon holey cladding enabling a centimeter bending radius," Photonics Res. 13, 2306 (2025)

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