An all-fiber spectrometer based on photonic crystal fiber and hollow-core fiber cascade structure

Abstract

The application discloses a kind of all-fiber spectrometer based on photonic crystal fiber and coreless fiber cascade structure, including polarization maintaining fiber, cascade fiber, CCD and computer connected in turn, the cascade fiber is photonic crystal fiber and coreless fiber cascade fiber structure;Spectrum to be measured successively through polarization maintaining fiber and cascade fiber, the speckle pattern formed is detected by CCD and transmitted to computer, and computer is inverted by reconstruction algorithm to spectrum to be measured, realizes spectrum measurement.The application uses the above structure of all-fiber spectrometer based on photonic crystal fiber and coreless fiber cascade structure, by staggered splicing coreless fiber and photonic crystal fiber, the symmetry of core structure is destroyed, the number of mode excitation is increased, the randomness of speckle is enhanced, while guaranteeing the miniaturization of spectrometer system, improve spectral resolution, to significantly shorten fiber length, realize the miniaturization and portability of spectrometer.

Description

Technical Field

[0001] This invention relates to a spectral measurement instrument technology, and more particularly to an all-fiber spectrometer based on a cascaded structure of photonic crystal fiber and coreless fiber. Background Technology

[0002] Spectroscopic analysis technology has important applications in environmental monitoring, food and drug testing, agriculture, and biomedicine. However, traditional benchtop spectrometers typically rely on a combination of large dispersive optics, long optical paths, detector arrays, and movable parts, resulting in drawbacks such as large size, heavy weight, poor stability, high cost, and demanding operating environment requirements. This makes them unsuitable for meeting the evolving demands for on-site and rapid spectroscopic analysis. Therefore, the development of lightweight, highly integrated, and stable miniature spectrometers has become a current research hotspot. Summary of the Invention

[0003] The purpose of this invention is to provide an all-fiber spectrometer based on a cascaded structure of photonic crystal fiber and coreless fiber. Since intermodal interference occurs in the cascaded structure of coreless fiber and photonic crystal fiber, this invention increases the number of excitation modes by misaligning the coreless fiber and photonic crystal fiber, thereby improving speckle decorrelation. Then, a CCD imaging device is used to detect the speckle, and high-resolution spectral measurements are achieved through spectral reconstruction calculations. This spectrometer has advantages such as miniaturization, portability, ultra-high resolution, and ease of on-site testing.

[0004] To achieve the above objectives, the present invention provides an all-fiber spectrometer based on a cascaded structure of photonic crystal fiber and coreless fiber, comprising a polarization-maintaining fiber, a cascaded fiber, a CCD and a computer connected in sequence, wherein the cascaded fiber is a cascaded fiber structure of photonic crystal fiber and coreless fiber.

[0005] The spectrum to be measured passes through polarization-maintaining fiber and cascaded fiber in sequence. The resulting speckle pattern is detected by CCD and transmitted to computer. Computer then uses a reconstruction algorithm to reconstruct the spectrum to be measured, thus realizing spectral measurement.

[0006] Preferably, the cascaded optical fiber is composed of coreless optical fiber and photonic crystal fiber spliced ​​together alternately multiple times.

[0007] Preferably, the number of segments spliced ​​in the photonic crystal fiber is 5 to 50, and the length of each segment of the photonic crystal fiber is 50 μm to 800 μm.

[0008] Preferably, the spacing between the coreless optical fiber and the photonic crystal fiber is 50 μm-1000 μm.

[0009] Preferably, the coreless optical fiber and the photonic crystal optical fiber are fused together face-to-face.

[0010] Preferably, the coreless optical fiber and the photonic crystal fiber are spliced ​​in a staggered manner.

[0011] Preferably, the lateral offset distance between the coreless optical fiber and the photonic crystal fiber is 5μm-80μm.

[0012] Preferably, the photonic crystal fiber is a photonic bandgap type, a total internal reflection type, or an all-solid-state multi-core fiber.

[0013] Preferably, the polarization-maintaining fiber has a length of not less than 1m.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] 1. By repeatedly splicing coreless optical fibers and photonic crystal fibers in an alternating, staggered manner, the number of excitation modes in the coreless fiber is increased, enhancing the interference effect and improving speckle decorrelation, resulting in ultra-high spectral resolution. Compared with traditional speckle speckle spectrometers based on multimode fibers, the spectrometer described above can improve spectral resolution by approximately 60 times for the same fiber length.

[0016] 2. It can significantly shorten the fiber optic length, thereby miniaturizing the fiber optic spectrometer and making it suitable for on-site testing.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the present invention;

[0019] Figure 2 This is a schematic diagram of the misaligned cascaded structure of photonic crystal fiber and coreless fiber of the present invention;

[0020] Figure 3 This is a schematic diagram of the cascaded structure of photonic crystal fiber and coreless fiber of the present invention;

[0021] Figure 4 This is a sample image of the all-solid-state photonic crystal fiber of the present invention;

[0022] Figure 5 This is a graph of the correlation function of the speckle intensity spectrum measured in the experiment according to the present invention;

[0023] Figure 6 This is a speckle intensity spectrum correlation function graph obtained by the present invention using a conventional multimode fiber of the same length;

[0024] Figure 7 These are reconstructed spectra of some narrow spectral lines at different wavelengths according to the present invention;

[0025] Figure 8This is the reconstructed spectrum of two narrow spectral lines with a wavelength interval of only 10 pm, as described in this invention.

[0026] Among them: 1. Polarization-maintaining fiber; 2. Cascaded fiber; 3. CCD; 4. Computer; 5. Photonic crystal fiber; 6. Coreless fiber. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings. It should be noted that this embodiment is based on the present technical solution and provides detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to this embodiment.

[0028] Figure 1 This is a schematic diagram of the structure of the present invention, as shown below. Figure 1 As shown, the structure of the present invention includes a polarization-maintaining fiber 1, a cascaded fiber 2, a CCD (charge-coupled device) 3, and a computer 4 connected in sequence. The cascaded fiber 2 is a cascaded fiber structure of a photonic crystal fiber 5 and a coreless fiber 6. The spectrum to be measured passes through the polarization-maintaining fiber 1 and the cascaded fiber 2 in sequence, and the resulting speckle pattern is detected by the CCD 3 and transmitted to the computer 4. The computer 4 uses a reconstruction algorithm to invert the spectrum to be measured, thereby realizing spectral measurement.

[0029] Preferably, the cascaded optical fiber 2 is composed of coreless optical fiber 6 and photonic crystal fiber 5 alternately spliced ​​together multiple times. Preferably, the number of segments splicing the photonic crystal fiber 5 is 5-50 segments, and the length of each segment of the photonic crystal fiber 5 is 50μm-800μm. Preferably, the spacing between the coreless optical fiber 6 and the photonic crystal fiber 5 is 50μm-1000μm.

[0030] Preferably, the coreless optical fiber 6 and the photonic crystal fiber 5 are fused together directly opposite each other. Alternatively, the coreless optical fiber 6 and the photonic crystal fiber 5 are fused together with a staggered arrangement. In the staggered fusion, the lateral offset distance between the coreless optical fiber 6 and the photonic crystal fiber 5 is 5μm-80μm.

[0031] Preferably, the photonic crystal fiber 5 is a photonic bandgap type, a total internal reflection type, or an all-solid-state multi-core fiber.

[0032] Preferably, the polarization-maintaining fiber 1 has a length of not less than 1m.

[0033] The working principle of a speckle detection spectrometer: A scattering element scatters light of different wavelengths at varying proportions onto different detection units. The detection information from each unit constructs a set of light intensity signals, i.e., speckles. Since there is a one-to-one correspondence between the incident light wavelength and the speckles, wavelength information can be obtained by identifying the speckles. Essentially, it utilizes the scattering element to establish a one-to-many mapping relationship between the frequency and spatial domains. When the input light has multiple wavelengths, the output image is a superposition of speckles generated by each monochromatic wavelength. A reconstruction algorithm is used to identify the speckles and calculate their corresponding weights to obtain the intensity information of each wavelength of the incident light, thereby reconstructing the spectrum.

[0034] Example:

[0035] Figure 2 This is a schematic diagram of the misaligned cascaded structure of photonic crystal fiber and coreless fiber of the present invention, as shown below. Figure 2 As shown, firstly, a photonic crystal fiber and a coreless fiber are spliced ​​using a fiber optic fusion splicer with a lateral misalignment of 10 μm. Then, under a microscope, the photonic crystal fiber is cut 100 μm from the splice point, and the end face is spliced ​​again with the coreless fiber with a lateral misalignment of 10 μm, in the opposite direction to the previous splice. Repeating this process yields a cascaded structure of 10 segments of photonic crystal fiber and a coreless fiber.

[0036] Figure 3 This is a schematic diagram of the cascaded structure of photonic crystal fiber and coreless fiber of the present invention, as shown below. Figure 3 As shown, coreless fiber and photonic crystal fiber are fused together face-to-face. The spectrum to be measured is input from a 1.5m long polarization-maintaining fiber, injected through a connector into the cascaded structure of the photonic crystal fiber and coreless fiber, and speckle pattern is generated at the output end. The speckle image is acquired using a CCD, transmitted to a computer, and spectral reconstruction is performed to achieve spectral measurement.

[0037] Figure 4 This is a sample image of the all-solid-state photonic crystal fiber of the present invention; Figure 5 This is a graph of the correlation function of the speckle intensity spectrum measured in the experiment according to the present invention; Figure 6 This is a speckle intensity spectrum correlation function plot obtained by the present invention using a conventional multimode fiber of the same length. Figure 7 These are reconstructed spectra of some narrow spectral lines at different wavelengths, as shown in the present invention. Figures 4-7 As shown, a series of narrow spectral lines were reconstructed by truncated singular value decomposition over a working bandwidth of 1550-1565 nm. The reconstructed spectra include both calibrated and uncalibrated wavelengths.

[0038] Figure 8 This is the reconstructed spectrum of two narrow spectral lines with a wavelength interval of only 10 pm, as described in this invention. Figure 8As shown, a speckle pattern to be tested is obtained by weighted superposition of two speckle patterns with a wavelength 10 pm apart, and then the speckle pattern to be tested is inverted.

[0039] The workflow of this embodiment is as follows: First, the transmission matrix is ​​calibrated. After the monochromatic light generated by the tunable laser source passes through the spectrometer system, the corresponding speckle pattern detected by the CCD is recorded in the computer.

[0040] Next, the speckle pattern to be measured is acquired. Since light signals of different wavelengths propagate independently, the speckle pattern generated by the spectrum to be measured is a linear combination of the speckle patterns generated by each wavelength component. Therefore, in system testing, the speckle pattern to be measured can be indirectly generated by weighted superposition of speckle patterns generated by monochromatic light (in actual measurement, the speckle pattern to be measured is directly generated by the light source).

[0041] Finally, the most widely used truncated singular value decomposition reconstruction algorithm is used to recover the spectrum to be measured.

[0042] Therefore, the all-fiber spectrometer based on the above-mentioned structure of photonic crystal fiber and coreless fiber cascade structure of the present invention can improve the spectral resolution by 60 times compared with the traditional speckle spectrometer based on multimode fiber, under the same fiber length.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An all-fiber spectrometer based on a cascaded structure of photonic crystal fiber and coreless fiber, characterized in that: It includes a polarization-maintaining fiber, a cascaded fiber, a CCD and a computer connected in sequence, wherein the cascaded fiber is a cascaded fiber structure of photonic crystal fiber and coreless fiber. The spectrum to be measured passes through polarization-maintaining fiber and cascaded fiber in sequence. The resulting speckle pattern is detected by CCD and transmitted to computer. Computer then uses reconstruction algorithm to reconstruct the spectrum to be measured, thus realizing spectral measurement. The cascaded optical fiber is composed of coreless optical fiber and photonic crystal fiber spliced ​​together repeatedly.

2. The all-fiber spectrometer based on a cascaded structure of photonic crystal fiber and coreless fiber according to claim 1, characterized in that: The number of segments spliced ​​in the photonic crystal fiber is 5 to 50, and the length of each segment of the photonic crystal fiber is 50 μm to 800 μm.

3. The all-fiber spectrometer based on a cascaded structure of photonic crystal fiber and coreless fiber according to claim 2, characterized in that: The spacing between the coreless optical fiber and the photonic crystal fiber is 50μm-1000μm.

4. The all-fiber spectrometer based on a cascaded structure of photonic crystal fiber and coreless fiber according to claim 1, characterized in that: The coreless optical fiber and the photonic crystal optical fiber are fused together face-to-face.

5. The all-fiber spectrometer based on a cascaded structure of photonic crystal fiber and coreless fiber according to claim 1, characterized in that: The coreless optical fiber is fused to the photonic crystal fiber in a staggered manner.

6. The all-fiber spectrometer based on a cascaded structure of photonic crystal fiber and coreless fiber according to claim 5, characterized in that: The lateral offset distance between the coreless optical fiber and the photonic crystal fiber is 5μm-80μm.

7. The all-fiber spectrometer based on a cascaded structure of photonic crystal fiber and coreless fiber according to claim 1, characterized in that: The photonic crystal fiber is a photonic bandgap type, a total internal reflection type, or an all-solid-state multi-core fiber.

8. The all-fiber spectrometer based on the cascaded structure of photonic crystal fiber and coreless fiber according to claim 1, characterized in that: The polarization-maintaining fiber is not less than 1m in length.

Images