Fabrication of a Novel Tellurite Hollow Core Optical Fiber and

Supercontinuum Light Propagation in Its Hollow Core

Tong Hoang Tuan, Nobuhiko Nishiharaguchi, Takenobu Suzuki and Yasutake Ohishi

Research Center for Advanced Photon Technology, Toyota Technological Institute,

2-12-1 Hisakata, Tempaku, Nagoya, 468-8511, Japan

Keywords: Hollow Core Fiber, Photonic Crystal Fiber, Microstructured Optical Fiber, Fiber Fabrication and

Characterization.

Abstract: For the first time, we experimentally demonstrated the fabrication of a tellurite HC-PCF which has a large

hexagonal hollow core in the center. The tellurite glass was developed by our group based on TeO

, ZnO,

O and Bi

oxides. The fiber was successfully obtained by using rotational casting and rod in tube

methods. A supercontinuum light source from 500 nm to more than 1500 nm was launched into the hollow

core of the fiber. The result shows that the light beam can be coupled and propagated in the hollow core by

the fundamental mode.

1 INTRODUCTION

After the first practical demonstration of single-

mode hollow-core fiber in 1999 (Cregan, 1999),

hollow-core photonic crystal fibers (HC-PCFs) has

attracted huge interest of scientists and researchers

due to their unique optical properties which are not

possible to obtain by using conventional solid-core

optical fibers. In general, a HC-PCF consists of a

central hollow core surrounded by an array of

hollow channels formed in the cladding running

along the entire length of the fiber (Cubillas, 2017).

Because the hollow-core region has low refractive

index than that of the surrounding photonic crystal

cladding, light is confined to the central hollow-core

by photonic bandgap or anti-resonant reflection

mechanisms which are different from the total

internal reflection in solid-core fibers (Poli, 2007).

Thus, HC-PCFs have the potential to overcome

some of the fundamental limitations of solid fibers

(Poletti, 2013).

HC-PCFs exhibit a number of intriguing optical

properties including ultra-low optical nonlinearity,

excellent power handling capabilities, high damage

threshold, low latency and ultra-low losses at both

conventional wavelengths around 1550 nm and

longer wavelengths in the mid-IR region where

conventional solid silica fibers effectively cease to

transmit light (Poletti, 2013). In addition, they have

low sensitivity to macro-bending (Hansen, 2004)

and even for small bending diameter value (Poli,

2007).

The air-guiding properties of HC-PCFs offer

significant advantages for the delivery of pulsed

laser beams with high optical power and energies.

They are needed in diverse applications ranging

from industrial materials processing to biology and

medicine such as laser marking, machining and

welding, laser-Doppler velocimetry, multi-photon

microscopy, treatment of various skin conditions and

laser surgery (Poli, 2007; Poletti, 2013).

Recently, it has been demonstrated that a gas-

filled HC-PCF can provide high conversion

efficiency and signals detectable down to the deep-

UV range (200 nm) (Joly, 2011) or even to the

vacuum-UV range (less than 200 nm) (Mak, 2013).

The ability to quickly adjust the gas species and gas

pressure inside the fiber core results in a new degree

of freedom for the control of the nonlinearity and the

group velocity dispersion (GVD) which cannot be

easily accessed by conventional optical fibers. These

gas-filled HC-PCFs can offer broadband

transmission from the deep UV range to the near-IR

range which is a unique light source for metrology

and spectroscopy (Travers, 2011) and gas sensing

such as ammonia (Cubillas, 2008), methane

(Cubillas, 2009) and carbon-dioxide (Nwaboh,

2013).

246

Tuan, T., Nishiharaguchi, N., Suzuki, T. and Ohishi, Y.

Fabrication of a Novel Tellurite Hollow Core Optical Fiber and Supercontinuum Light Propagation in Its Hollow Core.

DOI: 10.5220/0006892302460250

In Proceedings of the 15th International Joint Conference on e-Business and Telecommunications (ICETE 2018) - Volume 1: DCNET, ICE-B, OPTICS, SIGMAP and WINSYS, pages 246-250

ISBN: 978-989-758-319-3

Another important feature of HC-PCFs is that

their excellent guidance properties are preserved

even when both core and cladding channels are

filled with liquid, provided that the liquid index n

less than the index of the glass n

(Birks, 2004; Cox,

2006). These liquid-filled HC-PCFs are favourable

for chemical sensors and efficient micro-reactors for

photochemistry and catalysis applications (Cubillas,

2013; Schmidt, 2013). However, most of HC-PCFs

are based on fused silica material (Poletti, 2013)

which limits the choice of liquids because their

refractive indices must be less than that of silica (n

= 1.45 at 600 nm) to preserve the benefits of single-

mode guidance. To overcome this issue glasses with

higher refractive index are highly required.

Moreover, another key difference between HC-PCFs

and solid fibers is that the minimum loss

transmission window of HC-PCFs is shifted from

1.55 µm to the spectral region around 1.9–2.1 μm

(Lyngso, 2009) and the low loss transmission range

can be extended to the mid-IR region (Wheeler,

2013). In order to take advantages of this low loss

spectral range, glasses with broader transmission

spectrum than that of silica are necessary.

Among several non-silica glasses, tellurite

glasses can be considered as promising candidates as

they exhibit not only wide transmission regions from

0.35 to 6 µm, but also large refractive index (n

2.0 up to 3000 nm), high nonlinearity, high thermal

stability and good corrosion resistance (Mori, 2008).

In this work, we demonstrated for the first time the

fabrication of tellurite HC-PCF and the propagation

of a supercontinuum light source in its central

hollow core. By controlling the coupling conditions,

a fundamental mode can be transmitted.

2 FIBER FABRICATION

A tellurite glass composed of TeO

, ZnO, Li

O and

(TZLB) was developed by our group aiming

at their high thermal and mechanical stability. These

two properties are very necessary for the fiber

fabrication process because the hollow core fiber has

a complex structure of micro-scale air holes. This

microstructure is easily to be deformed or damaged

by residual stresses and cracks which are caused by

the unstable thermal and mechanical properties of

the host glass.

An UV/VIS/NIR spectrometer (Perkin Elmer,

Lambda 900) and an FT-IR spectrometer (Perkin

Elmer, Spectrum 100) were used to measure

transmission spectrum of the TZLB glass. The

thickness of glass sample was about 1 mm. The

transmission spectrum is shown in Fig. 1 with a

broad transmission range covering from about 0.4

μm up to 6.0 µm.

Figure 1: Transmission spectrum of the TZLB glass.

The refractive index of the TZLB glass was

measured at different wavelengths from 0.5 to 4.6

μm by using a glass prism and the minimum

deviation method. The uncertainness of the

measurement is as low as ±10

-4

. The measured

refractive indices were fitted to the Sellmeier

equation and were plotted in Fig. 2.

Figure 2: Wavelength-dependent refractive index of the

TZLB glass.

In this work, the tellurite HC-PCF was

successfully fabricated based on the rotational

casting and rod in tube methods. The commercial

pure reagents (99.99%) were used as raw materials.

The fiber was constructed with a large hexagonal

hollow core in the center which was surrounded by a

microstructure of smaller air holes in the cladding. A

schematic diagram which illustrates the fiber

fabrication process was shown in Fig. 3.

012345678

100

Transmission (%)

Wavelength (

12345678

1.6

1.7

1.8

1.9

2.0

2.1

2.2

2.3

2.4

Refractive index

Wavelength (

Fabrication of a Novel Tellurite Hollow Core Optical Fiber and Supercontinuum Light Propagation in Its Hollow Core

247

Figure 3: Schematic and experimental images of the

fabrication of a TZLB HC-PCF.

At first, a cylindrical TZLB tube was prepared

by using rotational casting method. The outer

diameter of this tube was 12 mm and its wall was

controlled to be as thin as 1 mm. An elongation

process was carried out to reduce the outer diameter

from 12 mm to 1.7 mm and the product was called

as TZLB capillary tube. Each of them was 15 cm

long. A set of 6 capillary tubes was used to form a

hexagonal close-packed structure by stacking them

together. In order to form the large hollow core in

the final fiber, the central capillary tube was absent.

This hexagonal structure of TZLB capillary tubes

was inserted into the second cylindrical TZLB jacket

tube and was elongated to obtain a preform whose

outer diameter was 3 mm. Finally, the preform was

inserted into the third cylindrical TZLB jacket tube

and was drawing into fiber whose diameter was

about 160 μm. The cross-sectional image of the fiber

was taken by an optical microscope and was shown

in Fig. 3.

3 MODE CONFINEMENT

PROPERTIES

Figure 4: Experimental setup to investigate the

characteristic of light propagation in the tellurite HC-PCF.

An experimental setup shown in Fig. 4 was used to

study the mode confinement of the light beam

propagated in the fabricated tellurite HC-PCF. A

supercontinuum light source generated in a step-

index silica fiber was launched into a 7-cm-long

tellurite HC-PCF. The image of the propagated

mode at the output facet of the tellurite HC-PCF was

captured by a near-infrared CCD camera (Thorlabs-

DC1240C). Figure 5 shows the images of different

modes which were able to propagate in the tellurite

HC-PCF. By controlling the coupling conditions, a

fundamental mode was successfully coupled into the

fiber. The captured images of the propagated modes

are consistent with those can be obtained from our

numerical calculation as shown in Fig. 6.

Camera

Pulsed

Laser

Silica fiber

SC Light

(

)

Filter

Objective

lens

Telluri te

HC-PCF

Lens

7cm

1.5μm

OPTICS 2018 - International Conference on Optical Communication Systems

248

Figure 5: Images of different modes which were able to

propagate in the tellurite HC-PCF.

Figure 6: Calculated results of modes which can be

confined in a tellurite HC-PCF.

4 CONCLUSIONS

For the first time, we experimentally demonstrated

the fabrication of a tellurite HC-PCF which has a

large hexagonal hollow core in the center. A

supercontinuum light source from 500 nm to more

than 1500 nm was launched into the fiber. The result

shows that the light beam can be coupled and

propagated in the hollow core with the fundamental

mode. With the advantages of using tellurite glass

such as high refractive index and broad transmission

spectrum, it is expected that tellurite HC-PCF will

be a good candidate for many interesting

applications which are not possible to obtain by

using silica-based HC-PCFs.

ACKNOWLEDGEMENTS

This work was supported by the JSPS KAKENHI

Grant Number 15H02250 and by JSPS KAKENHI

Grant Number 17K14671.

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