Hollow-core photonic crystal fiber gas cell and method for preparing the same

Abstract

A hollow-core photonic crystal fiber gas cell and method for preparing the same. The hollow-core photonic crystal fiber gas cell comprises a single-mode fiber, a fiber splicing protection sleeve, a hollow-core photonic crystal fiber, and a photoelectric detector. One end of the single-mode fiber is fusion spliced with one end of the hollow-core photonic crystal fiber to form a fusion splice and seal one end of the hollow-core photonic crystal fiber gas cell. The fiber splicing protection sleeve covers and protects the fusion splice. The other end of the hollow-core photonic crystal fiber is processed into an output end by fusion sealing, and the surface of the output end faces, but is not parallel to, a detection surface of the photoelectric detector.

Claims

1. A hollow-core photonic crystal fiber gas cell, comprising a single-mode fiber having two ends, a fiber splicing protection sleeve, a hollow-core photonic crystal fiber having two ends, and a photoelectric detector having a detection surface, wherein one end of the single-mode fiber is fused with one end of the hollow-core photonic crystal fiber to form a fusion splice and the end of a sealed hollow-core photonic crystal fiber gas cell; the fiber splicing protection sleeve covers and protects the fusion splice; the other end of the hollow-core photonic crystal fiber gas cell is processed into an output end in by fusion sealing, and an end surface of the output end faces, but is not parallel to, the detection surface of the photoelectric detector.

2. A method for preparing the hollow-core photonic crystal fiber gas cell as described in claim 1, comprising processing one end of the single-mode fiber by fusion splicing to form a fusion splice and sealing the end of the hollow-core photonic crystal fiber gas cell air-tight, covering and protecting the fusion splice with the fiber splicing protection sleeve, placing the hollow-core photonic crystal fiber and the single-mode fiber spliced thereto in a vacuum chamber, filling the vacuum chamber and the hollow-core of the hollow-core photonic crystal fiber with gas, causing the other end of the hollow-core photonic crystal fiber to be collapsed by fusing in the gas chamber and sealing the gas in the hollow-core, treating the collapsed end of the hollow-core photonic crystal fiber, and fixing the output end of the hollow-core photonic crystal fiber and the photodetector on a base plate, wherein the collapsed end of the hollow-core photonic crystal fiber is treated by passing a signal light into the other end of the single-mode fiber and receiving a transmitted light from the collapsed end, detecting the transmitted light by the photodetector, and recording the detected signal; and matching the detecting signal to requirements of the system by cutting, polishing, or coating the collapsed end of the hollow-core photonic crystal fiber, and the after machining collapsed end forms the output end of the hollow-core photonic crystal fiber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the structure of the hollow-core photonic crystal fiber gas cell of the present invention.

(2) FIG. 2 shows the processing of the collapsed end of the hollow-core photonic crystal fiber in the present invention.

(3) FIG. 3 shows the output end of the hollow-core photonic crystal fiber in the first embodiment of the present invention.

(4) FIG. 4 shows the output end of the hollow-core photonic crystal fiber in the second embodiment of the present invention.

(5) FIG. 5 shows the output end of the hollow-core photonic crystal fiber in the third embodiment of the present invention.

(6) FIG. 6 shows comparison of the transmission spectrum of the present invention and that of a common hollow-core photonic crystal fiber gas cell in the prior art: FIG. 6(a) shows the structure of the gas cell of the prior art and corresponding transmission spectrum; FIG. 6(b) shows the structure of the gas cell of the present invention and corresponding transmission spectrum.

(7) These drawings are for illustration only and are not drawn in proportion. Accordingly, same components are marked with same reference numbers.

DETAILED DESCRIPTION OF THE INVENTION AND EMBODIMENTS

(8) The present invention is further described in details, but the description does not serve to limit the scope of the invention.

(9) As shown in FIG. 1, the hollow-core photonic crystal fiber gas cell of the present invention comprises a single-mode fiber 103, a optic fiber splicing protection sleeve 105, a hollow-core photonic crystal fiber 111, and a photoelectric detector 121. One end of the single-mode fiber 103 is fused with one end of the hollow-core photonic crystal fiber 111 so that a fusion splice 107 is formed and one end of a sealed hollow-core photonic crystal fiber gas cell is formed. The fiber splicing protection sleeve 105 protects the fusion splice 107 in a covering manner. The hollow-core photonic crystal fiber gas cell is characterized in that the other end of the hollow-core photonic crystal fiber 111 is processed into an output end 115 in a fusion sealing manner. An output end surface faces, but is not parallel to, a detection surface of the photoelectric detector 121.

(10) The method for making the hollow-core photonic crystal fiber gas cell is characterized in the following steps:

(11) 1) One end of the single-mode fiber 103 is fusion spliced with one end of the hollow-core photonic crystal fiber 111 so that a fusion splice 107 is formed and the end of the hollow-core photonic crystal fiber gas cell is sealed air-tight. The fiber splicing protection sleeve 105 protects the fusion splice 107 in a covering manner.

(12) 2) The hollow-core photonic crystal fiber 111 and the single-mode fiber 103 that it has been spliced to are placed in the vacuum chamber, where the hollow-core 113 of the hollow-core photonic crystal fiber is filled with gas.

(13) 3) After being filled with gas, the free end of the hollow-core photonic crystal fiber 111 is collapsed by fusing in the gas chamber so that the gas is sealed in the hollow-core 113.

(14) 4) The collapsed end of the hollow-core photonic crystal fiber 111 is processed by following steps: (i) The signal light 101 comes into the free end of the single-mode fiber 103, then the transmitted light 117 comes out of the collapsed end of the hollow-core photonic crystal fiber 111 and is detected by the photodetector 121; and the detecting signal 123 from the photodetector 121 is recorded by instrument. (ii) The collapsed end of the hollow-core photonic crystal fiber 111 is polished, cut, coated with membrane, in order to make the detecting signal 123 to meet the requirements of the system. The after machining collapsed end is the output end 115 of the hollow-core photonic crystal fiber 111.

(15) 5) The device comprises the output end 115 of the hollow-core photonic crystal fiber 111 and the photodetector 121 are fixed on a base plate.

(16) FIG. 2 shows the treatment effects of the output end of the hollow-core photonic crystal fiber. The left side of the Figure shows untreated hollow-core photonic crystal fiber having an open core 201. The right side of the Figure shows the hollow-core photonic crystal fiber after heat treatment process 205 on the output end 203. It shows that the output end 115 of the hollow-core photonic crystal fiber has been sealed with optic fiber layer coverage and collapsed to seal, and the hollow-core 113 of the hollow-core photonic crystal fiber forms a seal cavity, while the output end 115 forms a complete surface which may be further processed.

(17) The heat treatment process 205 as shown in FIG. 2 uses a CO.sub.2 laser or fusion splicer to heat. The end of hollow-core photonic crystal fiber is collapsed to form a non-planarity inside surface which prevents the Fabry-Prot fringes that may be caused by the refection and scattered light 207, and the transmission spectrum noise is decreased as well.

(18) FIG. 3 shows a first embodiment of the hollow-core photonic crystal fiber gas cell of the present invention. The figure partially shows the output end 115 of the hollow-core photonic crystal fiber 111. In the embodiment, the output end 115 has been polished to form a surface 301 with a particular shape that may focus the transmission light 117 to be parallel. The surface 301 has also treated with an anti-reflective 303 coating.

(19) FIG. 4 shows a second embodiment of the hollow-core photonic crystal fiber gas cell of the present invention. The figure illustrates the output end 115 of the hollow-core photonic crystal fiber 111. In the embodiment, the output end 115 has been cut in a slant angle to form a tilted surface 401, which reduces reflection light from the surface of output end 115, and further reduces background oscillations caused by the Fabry-Prot fringes in the transmission spectrum.

(20) FIG. 5 shows a third embodiment of the hollow-core photonic crystal fiber gas cell of the present invention. The Figure partially shows the output end 115 of the hollow-core photonic crystal fiber 111 and a focusing lens 501. In the embodiment, the output end 115 has been cut at an angle on the surface to form a tilted surface 401 and then the tilted surface 401 is coated with an anti-reflective coating 503. The focusing lens 501 is fixed between the output end 115 and the photodetector 121.

(21) In these three embodiments, the anti-reflective coating is optional on the surface of the output end after being cut or polished. The anti-reflective coating may further reduce the Fresnel reflection and eliminates the Fabry-Prot fringes while increase the complexity of processing.

(22) FIG. 6(a) shows the structure of the hollow-core photonic crystal fiber gas cell and the measured transmission spectra. The upper portion of FIG. 6(a) shows the structure of a conventional hollow-core photonic crystal fiber gas cell whose front and rear end surfaces are fusion spliced as flat ends with two optical fibers to form the gas cell; the lower portion of the FIG. 6(a) shows its transmission spectrum with obvious oscillations by the Fabry-Prot fringes. FIG. 6(b) shows an embodiment of the hollow-core photonic crystal fiber gas cell and the measured transmission spectrum of the present invention. The upper portion of FIG. 6(b) shows the structure of the hollow-core photonic crystal fiber gas cell; the lower portion of the figure shows measured transmission spectrum with oscillations being eliminated.

(23) The hollow-core photonic crystal fiber gas cell effectively alleviates the background noise of the transmitted light of the existing hollow-core photonic crystal fiber gas cells and has the characteristics of being small in size, light in weight, and high in stability.

(24) Various embodiments have been described above. Although the invention has been described with reference to these specific embodiments, the descriptions are intended to be illustrative of the invention and are not intended to be limiting. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined in the appended claims.