Device and method for generating ultraviolet supercontinuum light source based on sub-wavelength optical fiber

Abstract

The present invention discloses a device for generating an ultraviolet supercontinuum light source based on a subwavelength optical fiber, comprising: a pump light source, a first optical fiber coupler, and a subwavelength optical fiber sequentially arranged on the same optical path; the subwavelength optical fiber outputs an ultraviolet supercontinuum. The present invention also discloses a method for generating an ultraviolet supercontinuum light source based on a subwavelength optical fiber, comprising: emitting an optical pulse with a non-chirped sech-shaped waveform, a central wavelength of 400 nm, an initial pulse width ranging from 250 to 450 fs, and a pulse peak power of kilowatt level through a pump light source; the optical pulse is incident on the subwavelength optical fiber through the first optical fiber coupler for dispersion and nonlinear effects, and the subwavelength optical fiber outputs an ultraviolet supercontinuum. The present invention can generate an ultraviolet supercontinuum light source, solving the technical problem that it is difficult to extend the supercontinuum to the short wavelength band.

Description

Technical Field

[0001] The present invention relates to a device and method for generating an ultraviolet supercontinuum light source based on a subwavelength optical fiber, belonging to the technical fields of nonlinear optics and fiber laser technology. Background Art

[0002] Supercontinuum light sources have characteristics such as broad spectrum, high brightness, and high coherence, and are widely used in fields such as metrology, biomedical imaging, and astronomy. The ultraviolet supercontinuum covers the short-wavelength band, and its spectrum has biological effects, fluorescence effects, photochemistry, and photoelectric effects, playing an important role in many aspects.

[0003] In the generation of supercontinuum, it is difficult to generate short-wavelength bands below 400 nm using ordinary photonic crystal fibers. The fiber structure, fiber material, and pumping conditions will all affect the dispersion characteristics and nonlinear effects of the optical fiber. The type of fiber structure will affect the dispersion characteristics and nonlinear effects of the optical fiber. Fiber materials have different nonlinear properties, which determine the spectral transmission range, nonlinear coefficient, and dispersion characteristics. The pumping light source and its operating conditions directly affect the wavelength range and output characteristics of the generated supercontinuum.

[0004] In the generation of supercontinuum, there has not yet been an ultraviolet-band supercontinuum below 400 nm, leaving a research gap. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a device and method for generating an ultraviolet supercontinuum light source based on a subwavelength optical fiber, which can generate an ultraviolet supercontinuum light source and solve the technical problem that it is difficult to expand the supercontinuum to the short-wavelength band. To achieve the above purpose, the present invention is implemented by the following technical solutions:

[0006] In the first aspect, the present invention provides a device for generating an ultraviolet supercontinuum light source based on a subwavelength optical fiber, including: a pumping light source, a first fiber coupler, and a subwavelength optical fiber arranged in sequence on the same optical path; the subwavelength optical fiber outputs an ultraviolet supercontinuum.

[0007] In combination with the first aspect, further, a second fiber coupler and a spectrometer are also provided on the optical path. The input end of the second fiber coupler is connected to the subwavelength optical fiber, and the output end of the second fiber coupler is connected to the spectrometer.

[0008] In combination with the first aspect, further, the base material of the subwavelength optical fiber is magnesium fluoride.

[0009] In combination with the first aspect, further, the core radius a of the subwavelength optical fiber is 0.3 μm, the fiber radius b is 2.4 μm, and the corresponding zero-dispersion point of the optical fiber is 424 nm.

[0010] In combination with the first aspect, further, the length of the sub-wavelength optical fiber is 3 cm.

[0011] In combination with the first aspect, further, the excitation source emitted by the pump light source is a chirp-free hyperbolic secant-shaped pulsed light with a central wavelength of 400 nm.

[0012] In combination with the first aspect, further, the peak power of the pulsed light is in the kilowatt range, and the initial pulse width is 250 - 450 fs.

[0013] In combination with the first aspect, preferably, the split-step Fourier method is used to solve the non-linear Schrödinger equation of the optical fiber, considering the dispersion and non-linear effects in the optical fiber, and the structural parameters of the sub-wavelength optical fiber and the parameters of the pump light source are optimized.

[0014] In the second aspect, the present invention also provides a method for generating an ultraviolet supercontinuum light source based on a sub-wavelength optical fiber, including,

[0015] Emitting a chirp-free hyperbolic secant-shaped light pulse with a central wavelength of 400 nm, an initial pulse width range of 250 - 450 fs, and a peak power of the pulsed light in the kilowatt range through a pump light source;

[0016] The light pulse is incident on the sub-wavelength optical fiber through the first fiber coupler for dispersion and non-linear effects, and the sub-wavelength optical fiber outputs an ultraviolet supercontinuum.

[0017] In combination with the second aspect, further, the range of the supercontinuum of the ultraviolet supercontinuum is 245 nm - 1114 nm, the flatness of the output is 0.968, and the average output power is -44.02 dB.

[0018] Compared with the prior art, the beneficial effects achieved by the device and method for generating an ultraviolet supercontinuum light source based on a sub-wavelength optical fiber provided by the embodiments of the present invention include:

[0019] In the present invention, a femtosecond laser, a first fiber coupler, and a sub-wavelength optical fiber are sequentially arranged on the same optical path; the sub-wavelength optical fiber outputs an ultraviolet supercontinuum. The present invention uses a sub-wavelength optical fiber to generate an ultraviolet continuous spectrum. The sub-wavelength optical fiber has good dispersion controllability, high non-linear effects, and strong optical field confinement. The base material of the sub-wavelength optical fiber in the present invention is magnesium fluoride, which is beneficial to moving the dispersion zero point towards the short-wave direction and generating an ultraviolet supercontinuum.

[0020] The present invention can obtain a supercontinuum broadened to the deep ultraviolet. The range of the supercontinuum of the external supercontinuum is 245 nm - 1114 nm, and it has a relatively flat dispersion curve and high output power, solving the technical problem that the supercontinuum is difficult to expand to the short-wave band. The present invention can expand the supercontinuum to the deep ultraviolet band and has broad application value and development prospects in the field of ultraviolet light source requirements. Brief Description of the Drawings

[0021] Figure 1 is a schematic diagram of a device for generating an ultraviolet supercontinuum light source based on a subwavelength optical fiber in Embodiment 1 of the present invention;

[0022] Figure 2 is the cross-section of the subwavelength optical fiber in Embodiment 1 of the present invention;

[0023] Figure 3 is a schematic diagram of the variation of the output spectrum with the fiber length in Embodiment 1 of the present invention;

[0024] Figure 4 is the evolution process of the generation of the supercontinuum spectrum by the pulse width of the pump light source in Embodiment 1 of the present invention;

[0025] Figure 5 is the evolution process of the generation of the supercontinuum spectrum by the peak power of the pump light in Embodiment 1 of the present invention. Detailed Embodiments

[0026] The present invention will be further described below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be used to limit the protection scope of the present invention.

[0027] Embodiment 1:

[0028] As Figure 1 shown, in this embodiment, a device for generating an ultraviolet supercontinuum light source based on a subwavelength optical fiber is provided, and a pump light source, a first fiber coupler, a subwavelength optical fiber, a second fiber coupler, and a spectrometer are sequentially arranged on the same optical path.

[0029] The output end of the pump light source is connected to the input end of the first fiber coupler, and the output end of the first fiber coupler is connected to the subwavelength optical fiber. The laser beam is coupled into the subwavelength optical fiber through the first fiber coupler. Under the action of fiber nonlinearity and dispersion, the spectrum is broadened to generate a wide and flat supercontinuum spectrum that can be extended to the ultraviolet band. The output end of the subwavelength optical fiber is connected to the input end of the second fiber coupler, and the output end of the second fiber coupler is connected to the spectrometer. The supercontinuum spectrum is input into the spectral analyzer through the second fiber coupler and the supercontinuum spectrum is displayed.

[0030] The split-step Fourier method is used to solve the nonlinear Schrödinger equation of the optical fiber, considering the dispersion and nonlinear effects in the optical fiber, and optimizing the structural parameters of the subwavelength optical fiber and the parameters of the pump light source.

[0031] Compared with photonic crystal fibers, the subwavelength optical fiber can achieve a larger core-cladding refractive index difference and a smaller core size. Therefore, it has strong dispersion controllability, nonlinear effects, and optical field confinement, which are all beneficial to the generation of deep ultraviolet supercontinuum spectra, and the structure is relatively simple.

[0032] The structure of the sub-wavelength optical fiber determines the dispersion characteristics of the optical fiber. As Figure 2 described, when the core radius a of the sub-wavelength optical fiber is 0.3 μm and the fiber radius b = 8a = 2.4 μm, the corresponding zero-dispersion wavelength of the optical fiber is 424 nm.

[0033] When selecting the substrate material of the sub-wavelength optical fiber, the transmittance and nonlinear effect in the ultraviolet band should be considered simultaneously. Magnesium fluoride is an important inorganic chemical raw material and optical material, which has high stability, good mechanical properties, etc., and has high transmittance in the ultraviolet band, and its nonlinear refractive index is one order of magnitude larger than that of ordinary silica. Using magnesium fluoride as the substrate material of the sub-wavelength optical fiber will increase the nonlinear coefficient, which is beneficial to the zero-dispersion wavelength moving towards the short-wave direction and generating an ultraviolet supercontinuum spectrum.

[0034] As Figure 3 shown in the schematic diagram of the change of the output spectrum with the fiber length, when the input pulse travels a longer distance in the optical fiber, the phase shift caused by various nonlinear effects during the transmission process increases accordingly, and the components generated by the spectrum become more, and the spectrum is broadened. At the same time, at the short-wave end, due to the simultaneous action of Raman solitons and dispersive waves through the SPM and FWM effects, the flatness of the spectrum at the short-wave end decreases, and obvious oscillation peaks appear. Considering the spectrum broadening, spectrum flatness and relative output power comprehensively, the preferred length of the sub-wavelength optical fiber is 3 cm.

[0035] The pump light source emits a chirp-free sech-squared laser beam with a central wavelength of 250 - 450 nm, an initial pulse width of 250 - 450 fs, and a pulse peak power of kilowatt level as the excitation source. As Figure 4 shown in the evolution process of the generation of the supercontinuum spectrum with the pulse width of the pump light source, when the fiber length and the pump peak power are the same, since the increase in the pulse width makes the second-order dispersion length increase, but the nonlinear length remains unchanged, the number of split solitons increases, resulting in more split peaks in the spectrum. Therefore, as the initial pulse width gradually increases, the pulse broadening range decreases, and the generated spectral width also decreases. Considering the spectrum broadening, spectrum flatness and relative output power comprehensively, the pulse width of the pump light source is selected as 400 fs.

[0036] As Figure 5The above is the evolution process of the peak power of the pump light on the generation of supercontinuum spectrum. As the peak power increases, the soliton order rises, leading to the breakup and fission of high-order solitons with different frequencies, generating soliton radiation with frequency redshift and non-soliton radiation with frequency blueshift. Therefore, the output spectral width increases with the increase of the peak power of the pump pulse. When the peak power increases to a certain extent, the width of the supercontinuum spectrum no longer increases. Considering the spectral broadening, spectral flatness, and relative output power comprehensively, the peak power of the pump light is selected to be 7 KW.

[0037] In this embodiment, when the pump light source emits a laser beam with a central wavelength of 400 nm, an initial pulse width range of 250 - 450 fs, and a pulse peak power in the kilowatt range, it can achieve a spectral bandwidth covering 245 nm - 1114 nm with an average output power of -44.02 dB and has good flatness.

[0038] Through the theoretical research on subwavelength optical fiber, a relatively simple theoretical model is established, based on the nonlinear Schrödinger equation of the optical fiber, considering the combined action of the fiber structure and the pump light. When the transmission distance of the input pulse in the optical fiber becomes longer, the phase shift caused by various nonlinear effects during the transmission process increases accordingly, and the components generated by the spectrum also become more, thus resulting in spectral broadening. Utilizing the mode characteristics and nonlinear characteristics of the subwavelength optical fiber, a wide-spectrum flat supercontinuum spectrum can be achieved, and the spectral range can cover from the ultraviolet region to the near-infrared region, which can meet the application requirements of ultraviolet supercontinuum light sources.

[0039] Example 2:

[0040] A method for generating an ultraviolet supercontinuum spectrum light source based on subwavelength optical fiber is provided in this embodiment, including:

[0041] Emitting a chirp-free hyperbolic secant-shaped optical pulse with a central wavelength of 400 nm, an initial pulse width range of 250 - 450 fs, and a pulse peak power in the kilowatt range through a pump light source;

[0042] The optical pulse is incident on the subwavelength optical fiber through a first optical fiber coupler for dispersion and nonlinear effects, and the subwavelength optical fiber outputs an ultraviolet supercontinuum spectrum.

[0043] Using the method described in this embodiment, the range of the obtained ultraviolet supercontinuum spectrum is 245 nm - 1114 nm, the flatness of the output is 0.968, and the average output power is -44.02 dB.

[0044] The present invention can obtain an ultra - continuous spectrum broadened to the deep ultraviolet range. The range of the ultra - continuous spectrum is from 245 nm to 1114 nm, and it has a relatively flat dispersion curve and a high output power, solving the technical problem that it is difficult to expand the ultra - continuous spectrum to the short - wavelength band. The present invention can expand the ultra - continuous spectrum to the deep ultraviolet band, and has broad application value and development prospects in the field of demand for ultraviolet light sources.

[0045] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above - mentioned embodiments. What is described in the above - mentioned embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. An apparatus for generating an ultraviolet supercontinuum light source based on a sub-wavelength optical fiber, characterized in that, Comprising: A pump light source, a first fiber optic coupler, and a sub-wavelength optical fiber sequentially arranged on the same optical path; The sub-wavelength optical fiber outputs an ultraviolet supercontinuum spectrum; Wherein, the substrate material of the sub-wavelength optical fiber is magnesium fluoride, the core radius a of the sub-wavelength optical fiber is 0.3 um, the fiber radius b is 2.4 um, the corresponding zero-dispersion wavelength of the optical fiber is 424 nm, and the length of the sub-wavelength optical fiber is 3 cm; Wherein, the excitation source emitted by the pump light source is a chirp-free sech-squared pulse with a central wavelength of 400 nm, the pulse peak power of the pulse light is in the kilowatt level, and the initial pulse width is 250 - 450 fs; Wherein, the spectral range of the ultraviolet supercontinuum spectrum is 245 nm - 1114 nm, the output flatness is 0.968, and the average output power is -44.02 dB.

2. The device for generating an ultraviolet supercontinuum light source based on a sub-wavelength optical fiber according to claim 1, characterized in that, A second fiber optic coupler and a spectrometer are further arranged on the optical path, the input end of the second fiber optic coupler is connected to the sub-wavelength optical fiber, and the output end of the second fiber optic coupler is connected to the spectrometer.

3. A method for generating an ultraviolet supercontinuum light source based on a subwavelength optical fiber for the device for generating an ultraviolet supercontinuum light source according to claim 1, characterized in that, Comprising: Emitting a chirp-free sech-squared optical pulse with a central wavelength of 400 nm, an initial pulse width range of 250 - 450 fs, and a pulse peak power in the kilowatt level through a pump light source; The optical pulse is incident on the sub-wavelength optical fiber through the first fiber optic coupler for dispersion and nonlinear effects, and the sub-wavelength optical fiber outputs an ultraviolet supercontinuum spectrum.

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