阅读说明：本技术 一种可调谐太赫兹光纤偏振分束器 (Tunable terahertz optical fiber polarization beam splitter ) 是由 田凤军 王宝库 白若兰 李立 史金辉 张建中 于 2019-09-10 设计创作，主要内容包括：本发明提供的是一种可调谐太赫兹光纤偏振分束器。包括两个介质条、一个介质包层管、两个椭圆纤芯和一个空气包层,两个介质条对称固定于介质包层内壁,两个椭圆纤芯通过两个介质条悬挂于介质包层管中央处,空气包层充满介质包层管,介质条和介质包层管的介质材料是TOPAS聚合物,在所述聚合物光纤径向上施加压力使其发生径向形变,通过调节压力来改变聚合物光纤的径向形变量,控制两个椭圆纤芯间距。本发明将太赫兹偏振分束器集成在一根光纤内,具有实时可调谐功能。可实现超短光纤长度、宽工作带宽、低传输损耗,解决传统偏振分束器大体积、窄带宽、单一工作频率等不足。(The invention provides a tunable terahertz optical fiber polarization beam splitter. The optical fiber comprises two dielectric strips, a dielectric cladding pipe, two elliptical fiber cores and an air cladding, wherein the two dielectric strips are symmetrically fixed on the inner wall of the dielectric cladding, the two elliptical fiber cores are suspended in the center of the dielectric cladding pipe through the two dielectric strips, the air cladding is filled in the dielectric cladding pipe, the dielectric materials of the dielectric strips and the dielectric cladding pipe are TOPAS polymers, pressure is applied to the polymer optical fiber in the radial direction to enable the polymer optical fiber to deform in the radial direction, the radial deformation amount of the polymer optical fiber is changed by adjusting the pressure, and the distance between the two elliptical fiber cores is controlled. The terahertz polarization beam splitter is integrated in one optical fiber, and has a real-time tunable function. The ultra-short optical fiber length, wide working bandwidth and low transmission loss can be realized, and the defects of large volume, narrow bandwidth, single working frequency and the like of the traditional polarization beam splitter are overcome.)

1. A tunable terahertz optical fiber polarization beam splitter comprises two dielectric strips, a dielectric cladding tube, two elliptical fiber cores and an air cladding, and is characterized in that: the two dielectric strips are symmetrically fixed on the inner wall of the dielectric cladding, the two elliptical fiber cores are suspended at the center of the dielectric cladding pipe through the two dielectric strips, the air cladding is filled in the dielectric cladding pipe, the dielectric materials of the dielectric strips and the dielectric cladding pipe are TOPAS polymers, pressure is applied to the polymer optical fiber in the radial direction to enable the polymer optical fiber to deform in the radial direction, the radial deformation amount of the polymer optical fiber is changed by adjusting the pressure, and the distance between the two elliptical fiber cores is controlled.

2. The tunable terahertz fiber polarization beam splitter of claim 1, wherein: two elliptical air holes are introduced into each elliptical fiber core.

3. the tunable terahertz fiber polarization beam splitter of claim 1 or 2, wherein: the two dielectric strips are in a bent shape and are not parallel to each other.

4. The tunable terahertz fiber polarization beam splitter of claim 1 or 2, wherein: the two elliptical core spacings maintain a weak coupling distance.

5. the tunable terahertz fiber polarization beam splitter of claim 3, wherein: the two elliptical core spacings maintain a weak coupling distance.

6. The tunable terahertz fiber polarization beam splitter of claim 1 or 2, wherein: the pressure is a pair of pressures with equal magnitude and opposite directions.

7. The tunable terahertz fiber polarization beam splitter of claim 3, wherein: the pressure is a pair of pressures with equal magnitude and opposite directions.

8. The tunable terahertz fiber polarization beam splitter of claim 4, wherein: the pressure is a pair of pressures with equal magnitude and opposite directions.

9. The tunable terahertz fiber polarization beam splitter of claim 5, wherein: the pressure is a pair of pressures with equal magnitude and opposite directions.

Technical Field

The invention relates to a terahertz device, in particular to a terahertz optical fiber polarization beam splitter.

Background

Terahertz waves (THz) refer to electromagnetic waves having a frequency of 0.1 to 10THz (wavelength of 0.03 to 3mm), and a wavelength band thereof is located between microwave and far infrared wavelength bands. The terahertz wave covers various rotation and vibration frequencies including condensed substances and biomacromolecules and characteristic spectral lines of a large amount of interstellar dust, so that the terahertz wave is very suitable for identifying the structure and the type of substances. Meanwhile, the photon energy of the terahertz wave is lower and is several orders of magnitude lower than that of X-rays, so that the photoionization of biological tissues can not be caused, and the terahertz wave can be applied to biological living body detection. In addition, terahertz can penetrate through non-metal and non-polar substances (such as materials of cloth, ceramics, paper, plastics and the like), and non-contact and non-destructive quality and safety inspection can be performed on the object by utilizing the characteristic. The deep development of the terahertz technology provides new requirements for integration and miniaturization of a terahertz system, and the development of a functional device capable of controlling terahertz waves is also a basic requirement for terahertz application, and particularly along with the development of terahertz communication, the terahertz communication device has more urgent requirements for various terahertz functional devices capable of realizing information processing. Due to the high absorption loss of most materials to terahertz waves, the design of terahertz functional devices needs to consider two points: transmission loss and operating bandwidth. The polymer has low absorption loss in a terahertz waveband and the flexible design of the microstructure optical fiber thereof, and the microstructure polymer optical fiber is a necessary choice for terahertz low-transmission-loss functional devices. The polarization beam splitter is an indispensable component in a terahertz system, and the main function is to realize the separation of two orthogonal polarization states.

A low-loss suspended core terahertz fiber and its application in a polarization beam splitter are disclosed in the documents "Yuanfeng Zhu, Mingyang Chen, Hua Wang, Hongbing Yao, Yongkang Zhang, Jichang Yang, Design and Analysis of a low-loss suspended core terahertz fiber and its application to polarization beam splitters," IEEE Photonics Journal, vol.5, No.6,7101410, Dec.2013 ", which comprises 6 rectangular dielectric rods and an outer large-diameter hollow polymer tube, wherein the orthogonal region of the rectangular dielectric rods is a core and the other regions are cladding. The separation length of the polarization beam splitter at the center frequency of 1THz is 3.36cm, the transmission loss is 0.89dB, and the bandwidth lower than-20 dB is 0.032 THz. However, when the fiber polarization beam splitter applies pressure, the fiber core distance change is weak, and the fiber polarization beam splitter is not suitable for being made into a tunable polarization beam splitter by applying pressure. Terahertz polarization beam splitters based on double elliptical core polymer fibers are proposed in the literature "hongzhihi Chen, Guofeng Yan, Erik Fersberg, and Sailing He, Terahertz polarization split base on dual-elliptical-core polymer fiber, Applied Optics, vol.55, No.23, pp.6236-6242, aug.102016", which comprise two identical elliptical cores, two parallel thin-walled, outer large diameter hollow polymer tubes. The polarization beam splitter has a separation length of 1.43cm at a center frequency of 0.6THz, a transmission loss of 0.4dB, extinction ratios of-18 dB and-19 dB, and a bandwidth of 0.02 THz.

The two polarization beam splitters have narrow working bandwidths, long separation lengths and high transmission loss, and do not have the function of implementing tuning.

Disclosure of Invention

The invention aims to provide a tunable terahertz optical fiber polarization beam splitter which is integrated in an optical fiber, wide in bandwidth and low in loss.

The purpose of the invention is realized as follows: the optical fiber comprises two dielectric strips, a dielectric cladding pipe, two elliptical fiber cores and an air cladding, wherein the two dielectric strips are symmetrically fixed on the inner wall of the dielectric cladding, the two elliptical fiber cores are suspended in the center of the dielectric cladding pipe through the two dielectric strips, the air cladding is filled in the dielectric cladding pipe, the dielectric materials of the dielectric strips and the dielectric cladding pipe are TOPAS polymers, pressure is applied to the polymer optical fiber in the radial direction to enable the polymer optical fiber to deform in the radial direction, the radial deformation amount of the polymer optical fiber is changed by adjusting the pressure, and the distance between the two elliptical fiber cores is controlled.

The present invention may further comprise:

1. Two elliptical air holes are introduced into each elliptical fiber core.

2. The two dielectric strips are in a bent shape and are not parallel to each other.

3. the two elliptical core spacings maintain a weak coupling distance.

4. The pressure is a pair of pressures with equal magnitude and opposite directions.

the invention provides a tunable terahertz optical fiber polarization beam splitter, which realizes in-fiber integration, wide bandwidth and low loss by introducing an elliptical air hole and radial pressure tuning. The invention achieves the following beneficial effects:

The terahertz polarization beam splitter is integrated in one optical fiber, and has a real-time tunable function. The ultra-short optical fiber length, wide working bandwidth and low transmission loss can be realized, and the defects of large volume, narrow bandwidth, single working frequency and the like of the traditional polarization beam splitter are overcome.

Drawings

Fig. 1(a) -fig. 1 (b): the invention discloses a cross section view of a tunable terahertz optical fiber polarization beam splitter;

FIG. 2: FIG. 1 is a graph of normalized transmission power versus transmission distance in the core A of a polarization beam splitter;

FIG. 3: FIG. 1 is a graph showing the extinction ratio with frequency for a polarizing beam splitter having a length of 0.865 cm;

FIG. 4: FIG. 1 is a graph showing the variation of operating frequency with core pitch for a polarizing beam splitter length of 0.865 cm.

Detailed Description

The invention is described in more detail below by way of example.

With reference to fig. 1(a) -1 (b), the tunable terahertz fiber polarization beam splitter of the present invention includes two dielectric strips 1, a dielectric cladding tube 2, two elliptical cores 3, and an air cladding 4. The optical fiber dielectric material is TOPAS polymer. And applying pressure in the radial direction of the polymer optical fiber to enable the polymer optical fiber to deform in the radial direction, changing the radial deformation amount of the polymer optical fiber by adjusting the pressure, further controlling the distance between the two fiber cores, and expanding the tunable working frequency range to 0.9-1 THz.

The two dielectric strips are symmetrically fixed on the inner wall of the dielectric cladding, are in bent shapes and are not parallel to each other, and the bending function of the dielectric strips is to increase the distance displacement of the fiber cores when the polymer optical fiber is subjected to pressure tuning.

Two elliptical air holes 5 are introduced into the fiber core to improve the birefringence of the fiber core and reduce the transmission loss, and the fiber core is suspended in the center of a dielectric cladding tube through two dielectric strips, and the distance between the two fiber cores keeps a weak coupling distance.

the core has a major axis of 140 μm and a minor axis of 70 μm, and the distance between the two cores is 100 μm.

The semiaxis of the ellipse air hole is 54 μm, and the semiaxis of the ellipse air hole is 14.5 μm.

The dielectric strip had a length of 3.4mm and a width of 20 μm.

The hollow inner radius of the medium cladding is 2mm, and the wall thickness is 300 mu m.

The optical fiber medium material is TOPAS polymer, and the effective refractive index is 1.5258.

The pressure is a pair of equal and opposite forces, but not limited to this, and any method of radially deforming the polymer optical fiber and changing the core pitch, such as changing the pressure of each internal part, may be used. The magnitude of the pressure is F.

According to the tunable terahertz optical fiber polarization beam splitter disclosed by the invention, the structural asymmetry is enhanced by introducing the two elliptical air holes into each fiber core, so that the birefringence is improved, the absorption loss is reduced, the coupling length difference between the x polarization state and the y polarization state of a fundamental mode can be increased, and the separation length of orthogonal polarized light is reduced.

When the applied pressure is zero, as shown in FIG. 1(a), there are two high birefringent cores with the same structure and symmetrical positions, and both the parallel and perpendicular polarization states are completely coupled between the two cores, but their coupling lengths are different. Thus, by selecting an appropriate transmission length, separation of the two orthogonal polarization states can be easily achieved. The coupling length L of the invention in the x-polarization direction and the y-polarization direction of 1THz can be obtained by adopting a beam propagation method_xAnd L_yRespectively 0.294cm and 0.420 cm. As can be seen from fig. 2, a polarizing beam splitter having a transmission length L of 0.865cm can be prepared. And f is 1THz, y polarized light is completely output from the fiber core A, x polarized light is coupled into the fiber core B and is output, and the two light rays are completely separated. The transmission losses of the polarization beam splitter in the x polarization direction and the y polarization direction are respectively 0.08dB and 0.13dB, the extinction ratios are respectively-20.8 dB and-20.2 dB, and the bandwidth with the extinction ratio smaller than-10 dB can reach 0.03 THz.