A liquid-core photonic crystal fiber and a supercontinuum generator

Abstract

This utility model relates to the field of crystal fiber technology, and discloses a liquid-core photonic crystal fiber and a supercontinuum generator, including a core, a cladding, pores, and a protective layer. The cladding is disposed between the core and the protective layer, and pores are provided within the cladding. The pores include several circumferentially arranged elliptical pore layers and several circumferentially arranged circular pore layers. The elliptical pore layers are disposed inside the circular pore layers. There is one elliptical pore layer, and it is hexagonal in shape. There are three circular pore layers, and they are regular hexagonal in shape. By designing elliptical pores, the symmetry of the circular pores is disrupted, resulting in birefringence characteristics. This also solves the problem that optical fibers cannot generate supercontinuum in longer wavelength bands. The first layer, designed as elliptical pores, gives the entire fiber excellent optical constraint and nonlinear characteristics, increasing design freedom. Its perfect match with the cladding optimizes the fiber's performance.

Description

Technical Field

[0001] This utility model relates to the field of crystal fiber technology, specifically to a liquid-core photonic crystal fiber and a supercontinuum generator. Background Technology

[0002] The supercontinuum is a spectral broadening phenomenon caused by the interaction of light pulses with nonlinear optical effects during propagation in a group velocity-dispersive medium. Supercontinuum possesses excellent properties such as wide bandwidth, high spatial coherence, and strong output. Particularly covering the mid-infrared region, its high spectral density and brightness have led to its widespread application in telecommunications, optical coherence tomography, and optical metrology.

[0003] Liquid-core fiber, as a structure in supercontinuum generators, possesses many excellent properties, but it also has some drawbacks. The main disadvantage of these fibers is their requirement for high peak power input, typically tens of kilowatts. Therefore, a better structure must be designed to enable liquid-core photonic crystal fibers to generate mid-infrared supercontinuum spectra using low peak power input. Utility Model Content

[0004] The purpose of this invention is to provide a liquid-core photonic crystal fiber and a supercontinuum generator to enhance nonlinear effects, reduce the effective film area of ​​the fiber, and thus increase the bandwidth of the supercontinuum.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a liquid-core photonic crystal fiber, comprising a core, a cladding, pores, and a protective layer, wherein a cladding is disposed between the core and the protective layer, and pores are disposed within the cladding, wherein the pores comprise several circumferentially arranged elliptical pore layers and several circumferentially arranged circular pore layers.

[0006] Preferably, the elliptical pore layer is disposed inside the circular pore layer.

[0007] Preferably, the elliptical pore layer has one layer, and the elliptical pore layer is hexagonal in shape.

[0008] Preferably, the elliptical pore layer includes a plurality of elliptical pores, wherein the major axis a of the elliptical pores is 1.2 μm and the minor axis b is 0.7 μm.

[0009] Preferably, the circular pore layer has three layers, and the circular pore layer is arranged in a regular hexagonal shape.

[0010] Preferably, the circular pore layer includes a plurality of circular pores, and the diameter d1 of the circular pores is 1.0 μm.

[0011] Preferably, the core diameter d2 is 1.2 μm; the set distance Λ2 between the core and the first layer of elliptical pores is configured to be 1.8 μm.

[0012] Preferably, the spacing Λ1 between the elliptical pore layer and the circular pore layer, as well as the spacing Λ1 between the circular pore layers, is 2 μm.

[0013] Preferably, the core material is liquid ethylene glycol, and the cladding material is arsenic trisulfide.

[0014] This utility model also provides the following technical solution: a supercontinuum generator, comprising a liquid core photonic crystal fiber and a mid-infrared light source connected to the liquid core photonic crystal fiber, wherein the mid-infrared light source is used to provide mid-infrared light in a set 4400nm-4600nm band, and the length of the liquid core photonic crystal fiber is 4mm.

[0015] An optical isolation coupler, a tunable grating, and a beam splitter are also provided between the liquid-core photonic crystal fiber and the mid-infrared light source.

[0016] Compared with the prior art, the beneficial effects of this utility model are:

[0017] By designing elliptical pores, the symmetry of circular pores was disrupted, resulting in birefringence. This also solved the problem that optical fibers cannot generate supercontinuum in longer wavelength bands.

[0018] By designing the first layer of pores as circumferentially elliptical shapes, the entire optical fiber exhibits excellent optical confinement and nonlinear characteristics. This pore design perfectly matches the cladding, optimizing the fiber's performance. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the cross-sectional structure of the photonic crystal fiber of this invention.

[0020] Figure 2 This is a schematic diagram of the photonic crystal fiber and supercontinuum generator of this utility model.

[0021] Figure 3 The dispersion curve of the photonic crystal fiber of this invention is shown.

[0022] Figure 4 The effective film area curve of the photonic crystal fiber of this invention is shown.

[0023] Figure 5 The curve shows the nonlinear coefficient of the photonic crystal fiber of this invention.

[0024] Figure 6 This is the confinement loss curve of the photonic crystal fiber of this invention.

[0025] Figure 7The effective refractive index curve of the photonic crystal fiber of this invention is shown.

[0026] Figure 8 The supercontinuum intensity curves obtained by the supercontinuum generator of the photonic crystal fiber of this invention are shown.

[0027] 1. Core; 2. Cladding; 3. Pores; 31. Elliptical pore layer; 32. Circular pore layer; 4. Protective layer. Detailed Implementation

[0028] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0029] Please see Figure 1 This utility model provides a technical solution: a liquid-core photonic crystal fiber, comprising a core 1, a cladding 2, pores 3, and a protective layer 4. The cladding 2 is disposed between the core 1 and the protective layer 4, and the cladding 2 is provided with pores 3. The pores 3 include several circumferentially arranged elliptical pore layers 31 and several circumferentially arranged circular pore layers 32. The different arrangements of pores 3 are used to solve the problem that current optical fibers cannot generate supercontinuum in longer wavelength bands.

[0030] The elliptical pore layer 31 is disposed inside the circular pore layer 32. The elliptical pore layer 31 has one layer and is hexagonal in shape. The elliptical pore layer 31 includes a plurality of elliptical pores, with a major axis a of 1.2 μm and a minor axis b of 0.7 μm. The elliptical pores generate birefringence by disrupting the symmetry of the circular pores, and they also achieve polarization maintenance; therefore, the first layer of pores is designed as elliptical pores. These pores possess excellent optical constraint and nonlinear characteristics, increasing design freedom. Simultaneously, they perfectly match the cladding, optimizing the performance of the optical fiber.

[0031] The circular pore layer 32 has three layers and is arranged in a regular hexagonal shape. The circular pore layer 32 includes a plurality of circular pores, with the outer circular pore layer 32 having a greater number of circular pores than the inner circular pore layer 32. The diameter d1 of the circular pores is 1.0 μm.

[0032] The diameter d2 of the fiber core 1 is 1.2 μm; the set distance Λ2 between the fiber core 1 and the first layer of elliptical pores is 1.8 μm. The spacing Λ1 between the elliptical pore layer 31 and the circular pore layer 32, as well as the spacing Λ1 between the circular pore layers 32, is 2 μm.

[0033] The fiber core 1 is made of liquid ethylene glycol, and the cladding 2 is made of arsenic trisulfide. Both materials exhibit high nonlinear coefficients at room temperature and pressure. Furthermore, the elliptical and circular pores enhance the nonlinear effect, reducing the effective film area of ​​the optical fiber and thus increasing the bandwidth of the supercontinuum. Arsenic trisulfide and liquid ethylene glycol promote nonlinear effects such as self-phase modulation in the mid-infrared band, controlling the dispersion flat region between 4300 nm and 4700 nm, thereby achieving supercontinuum broadening in the mid-infrared band. Additionally, liquid ethylene glycol can intelligently adjust the supercontinuum broadening band through temperature changes, enabling the utilization of multiple bands in the generator.

[0034] This invention also provides a supercontinuum generator, comprising a liquid-core photonic crystal fiber and a mid-infrared light source connected to the liquid-core photonic crystal fiber. The mid-infrared light source can be a laser pump source. The mid-infrared light source is used to provide mid-infrared light in the set wavelength range of 4400nm-4600nm. The length of the liquid-core photonic crystal fiber is 4mm, at which length the constraint loss of the fiber is very small when generating the supercontinuum. After the mid-infrared light source is input into the photonic crystal fiber, a supercontinuum is generated due to nonlinear effects (such as four-wave mixing, self-phase modulation, soliton breaking, etc.), and the supercontinuum broadens as the light source propagates in the fiber.

[0035] An optical isolation coupler, a tunable grating, and a beam splitter are also provided between the liquid-core photonic crystal fiber and the mid-infrared light source. These optical devices prevent the infrared light source from feeding back to the mid-infrared light source and ensure unidirectional transmission of the infrared light source. From a transmission characteristic perspective, supercontinuum spectral emission devices generally need to ensure stable transmission of the optical signal along a single direction, which is crucial for maintaining spectral continuity and stability. These optical devices effectively prevent the back propagation of the optical signal, ensuring that the spectral signal always transmits along the predetermined direction, thereby avoiding signal attenuation, degradation, and mutual interference caused by back propagation, and providing a reliable guarantee for the stable operation of the supercontinuum spectral emission device.

[0036] Please see Figure 2In this embodiment, the mid-infrared light source is designated as a, the photonic crystal fiber as b, and the output spectrum c is a supercontinuum spectrum. d and e are the spectra of the input and output spectra, respectively, with time on the horizontal axis and spectral intensity on the vertical axis. The spectra demonstrate the broadening effect of the laser in the photonic crystal fiber b. f is a cross-sectional view of the beginning and end of the input and output light sources in the photonic crystal fiber. The wavelength dispersive spectrometer g is a precision instrument that utilizes the differences in the refraction or diffraction characteristics of light of different wavelengths in a medium to achieve spectral analysis.

[0037] A wavelength dispersive spectrometer g generates a characteristic spectrum in a photonic crystal fiber b through an excitation source. The light is then separated into different wavelengths by a crystal dispersive element according to Bragg's law. The signals are converted into electrical signals by a detection system, and then processed to present a spectral image. By optimizing its parameters, the desired supercontinuum spectral range and characteristics can be achieved.

[0038] In this embodiment, the supercontinuum spectroscopy generator connects the infrared light source a in the laser pump source to the photonic crystal fiber b, thereby inputting the optical signal into the designed photonic crystal fiber b. After transmission and evolution, the supercontinuum spectrum generated is finally received by the wavelength dispersive spectrometer g. The photonic crystal fiber b has an all-fiber confinement loss of 10⁻⁶ nm in the wavelength range of 4400 nm to 4600 nm. -9 The difference is on the order of dB / m and negligible, and two zero-dispersion points were obtained at 4487 nm and 4575 nm in the mid-infrared region. At a wavelength of 4000 nm, the nonlinear coefficient of photonic crystal fiber A was calculated to be 3276 W. -1 km -1 Meanwhile, for an input pulse with a peak power of 6kW and a length of 4mm, the photonic crystal fiber b generated a supercontinuum spectrum with a bandwidth of 4800nm.

[0039] Figure 3 This is the dispersion curve of the photonic crystal fiber based on this embodiment. Dispersion represents the rate at which the refractive index of the photonic crystal fiber changes with wavelength. The flat region of dispersion is generally distributed in the wavelength range of 4400 nm to 4600 nm, and two zero-dispersion points appear at 4487 nm and 4575 nm. It is waveguide dispersion (D... w ) and material dispersion (D m The sum of ) is analyzed by the following formula:

[0040]

[0041] Where n eff It is the effective refractive index, Re(n) eff ) is the real part of the effective refractive index, c is the speed of light in a vacuum, and λ is the wavelength of light. It is the second-order partial derivative of the real part of the effective refractive index with respect to the wavelength.

[0042] Figure 4 This is the effective mode area curve of the photonic crystal fiber based on this embodiment. As the wavelength increases, the mode confinement from core 1 decreases, leading to an increase in the effective mode area. At the pump source center wavelength of 4500 nm, the effective mode area of ​​the PCF reaches 24.8 μm. 2 The nonlinear coefficient is 3276W. -1 km -1 The effective mode area is defined as the transverse area occupied by the fundamental mode propagating along the fiber axis, characterizing the degree of electromagnetic field confinement in the magnetic core. Effective mode area A eff The area can be obtained using the following effective model area analysis formula:

[0043]

[0044] Where E is the transverse electric field amplitude, obtained by solving the eigenvalue problem of Maxwell's equations.

[0045] Figure 5 This is the nonlinear coefficient curve of the photonic crystal fiber based on this embodiment. The nonlinear coefficient is an indicator of the nonlinear effect of an optical fiber, and it is closely related to the effective mode area of ​​the fiber. Increasing the wavelength leads to a decrease in core mode constraint and an increase in the effective mode area. This observation demonstrates that the inverse relationship between the effective mode area and nonlinearity is consistent. The As2S3 photonic crystal fiber has a very high nonlinear coefficient of 3276 W at the center wavelength. -1 km -1 .

[0046] Figure 6 This is the confinement loss curve of the photonic crystal fiber based on this embodiment. The photonic crystal fiber exhibits very low confinement loss in the range of 4400nm to 6200nm, at 10. -9 On the order of dB / m. When light passes through an optical fiber with a finite lattice structure, all modes are susceptible to leakage. The confinement loss is the loss of leaked modes, and its extent can be characterized by the parameter CL, which can be calculated from the following confinement loss analysis formula:

[0047]

[0048] Where k0 represents the free space wavenumber, derived from... It can be concluded that;

[0049] Figure 7This is the effective refractive index curve of the photonic crystal fiber based on this embodiment. As the wavelength increases, the effective refractive index of the PCF decreases approximately linearly. The decrease in effective refractive index is due to the increase in the inner ring chalcogenide arsenic trisulfide and the significant influence of the innermost elliptical cavitation on the fundamental conductivity of the photonic crystal fiber. At the center wavelength of 4500 nm, the effective refractive index of the designed fiber is 1.151.

[0050] Figure 8 The supercontinuum intensity curve is obtained based on the supercontinuum generator of photonic crystal fiber in this embodiment. The peak power of the infrared light source in the set band is 6kW. The pulse width of the infrared light source in the set band is 300fs, and the input pulse with the center wavelength of the infrared light source in the set band is 4500nm. The maximum spectrum (considered above -40dB) from the corresponding spectrum of 1500nm to 6300nm is achieved in an optical fiber of 4mm in length, thereby achieving an ultra-wideband spectral intensity of 4800nm.

Claims

1. A liquid-core photonic crystal fiber, comprising a core (1), a cladding (2), pores (3), and a protective layer (4), wherein the cladding (2) is disposed between the core (1) and the protective layer (4), and pores (3) are provided within the cladding (2), characterized in that: The pores (3) include several layers of circumferentially arranged elliptical pore layers (31) and several layers of circumferentially arranged circular pore layers (32).

2. The liquid-core photonic crystal fiber according to claim 1, characterized in that: The elliptical pore layer (31) is disposed inside the circular pore layer (32).

3. The liquid-core photonic crystal fiber according to claim 1, characterized in that: The elliptical pore layer (31) has one layer and is hexagonal in shape.

4. The liquid-core photonic crystal fiber according to claim 3, characterized in that: The elliptical pore layer (31) includes a plurality of elliptical pores, wherein the major axis a of the elliptical pores is 1.2 μm and the minor axis b is 0.7 μm.

5. The liquid-core photonic crystal fiber according to claim 1, characterized in that: The circular pore layer (32) has 3 layers, and the circular pore layer (32) is arranged in a regular hexagon.

6. The liquid-core photonic crystal fiber according to claim 5, characterized in that: The circular pore layer (32) includes a plurality of circular pores, the diameter d1 of which is 1.0 μm.

7. The liquid-core photonic crystal fiber according to claim 1, characterized in that: The diameter d2 of the fiber core (1) is 1.2 μm; the set distance Λ2 between the fiber core (1) and the first layer of elliptical pores is configured to be 1.8 μm.

8. The liquid-core photonic crystal fiber according to claim 1, characterized in that: The spacing between the elliptical pore layer (31) and the circular pore layer (32), as well as the spacing between the circular pore layers (32) themselves, is Λ1, both of which are 2μm.

9. The liquid-core photonic crystal fiber according to claim 1, characterized in that: The core (1) is made of liquid ethylene glycol, and the cladding (2) is made of arsenic trisulfide.

10. A supercontinuum generator, comprising a liquid-core photonic crystal fiber as described in any one of claims 1-9 and a mid-infrared light source connected to the liquid-core photonic crystal fiber, characterized in that: The mid-infrared light source is used to provide mid-infrared light in the set 4400nm-4600nm band, and the length of the liquid core photonic crystal fiber is 4mm; An optical isolation coupler, a tunable grating, and a beam splitter are also provided between the liquid-core photonic crystal fiber and the mid-infrared light source.

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