CN109814282B - Rod-shaped photonic crystal fiber-based soliton synthesis method and device - Google Patents
Rod-shaped photonic crystal fiber-based soliton synthesis method and device Download PDFInfo
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Abstract
The invention is suitable for the technical field of optics, and provides a rod-shaped photonic crystal fiber-based soliton synthesis method and a rod-shaped photonic crystal fiber-based soliton synthesis device, wherein the method comprises the following steps: the method comprises the steps of separating a preset pump pulse into two linear polarization pump pulses with orthogonal polarization states, enabling the two linear polarization pump pulses to be independently transmitted in a rod-shaped photonic crystal fiber, and generating a horizontal polarization soliton and a vertical polarization soliton; the horizontal polarization solitons and the vertical polarization solitons have delay when being output to the rod-shaped photonic crystal fiber; and then, the wavelengths of the horizontal polarization solitons and the vertical polarization solitons are the same, and after the horizontal polarization solitons and the vertical polarization solitons are separated, opposite delay is introduced into the vertical polarization solitons, so that the horizontal polarization solitons and the vertical polarization solitons are overlapped in time to synthesize target solitons with double soliton energy. The invention can improve the soliton single pulse energy generated based on the rod-shaped photonic crystal fiber, so that the energy requirement of excitation light with the wave band of 1700nm can be met.
Description
Technical Field
The invention relates to the technical field of optics, in particular to a rod-shaped photonic crystal fiber-based soliton synthesis method and device.
Background
Multiphoton microscopy, which is based on nonlinear optical techniques and includes different imaging modalities such as two-photon, three-photon, and four-photon fluorescence, second, third, and fourth harmonics, etc., has a wide range of applications in biology, physiology, and medicine. The main advantage of multiphoton imaging is that three-photon fluorescence microscopy can achieve the greatest imaging depth among numerous imaging modalities, especially in vivo animal models, based on penetration capability on deep tissues.
Three-photon fluorescence microscopy of deep tissues requires femtosecond pulse excitation with repetition frequency at megahertz level to satisfy the requirements for two conditions of three-photon signal level and excitation light average power. There are generally two choices in the excitation wavelength, 1300nm and 1700nm windows, respectively. Theoretical calculations show that the attenuation of excitation light in the two wavelength bands of the 1300nm and 1700nm windows through biological tissue is smaller compared to the 800nm window, and has been demonstrated in brain imaging experiments in live mice. The three-photon microscopic imaging excited by a 1300nm window corresponds to a mature green fluorescent protein product, and can be used for functional imaging of hippocampus in the brain of a mouse. In contrast, excitation light in the 1700nm band is attenuated less than 1300nm when transmitted through biological tissue, and thus deeper deep brain structure imaging, such as cerebral vascular imaging, can be achieved.
At a given repetition rate, the fluorescence signal intensity depends on the single pulse energy of the excitation light. For all the deep brain imaging of the three-photon living mouse with the window of 1700nm demonstrated at present, a high-energy 1550nm laser rod-shaped photonic crystal fiber is used, solitons generated by a soliton self-frequency shift effect are used as an excitation light source, and the technical device for generating the solitons by using the rod-shaped photonic crystal fiber is simple, good in stability and suitable for generating the high-energy 1700nm solitons.
However, the currently commercialized rod-shaped photonic crystal fiber has a core diameter of about 100 μm, and can generate a maximum soliton single pulse energy of about 110nJ, and the imaging depth of three-photon microscopic imaging is limited by this energy limit. Although the output soliton energy can be increased by increasing the core diameter of the rod-shaped photonic crystal fiber, the energy limit cannot be broken through. Due to the coupling efficiency, the above method has reached the optical damage threshold of the rod-shaped photonic crystal fiber, and therefore, a technology needs to be developed to break through the current soliton energy limitation and be applied to the rod-shaped photonic crystal fiber which is currently commercialized or may have a larger mode field area in the future.
Disclosure of Invention
The invention mainly aims to provide a soliton synthesis method and a device based on a rod-shaped photonic crystal fiber, and aims to solve the problem that in the prior art, the single pulse energy of soliton generated by the rod-shaped photonic crystal fiber cannot meet the energy requirement of excitation light with a 1700nm waveband, so that the three-photon fluorescence microscopic imaging of deep tissues cannot realize deeper brain structure imaging.
In order to achieve the above object, a first aspect of embodiments of the present invention provides a rod-shaped photonic crystal fiber-based soliton synthesis method, including:
separating a preset pump pulse into two linear polarization pump pulses with orthogonal polarization states, so that the two linear polarization pump pulses with orthogonal polarization states are independently transmitted in the rod-shaped photonic crystal fiber and respectively generate a horizontal polarization soliton and a vertical polarization soliton;
wherein the horizontal polarization solitons and the vertical polarization solitons have delay when being output to the rod-shaped photonic crystal fiber;
in the rod-shaped photonic crystal fiber, adjusting the energy of the two linearly polarized pump pulses with orthogonal polarization states so that the wavelengths of the horizontally polarized solitons and the vertically polarized solitons are the same;
after the horizontal polarization solitons and the vertical polarization solitons are separated at the output end of the rod-shaped photonic crystal fiber, opposite delay is introduced into the vertical polarization solitons, and meanwhile, the optical path of the vertical polarization solitons is adjusted at the input end of the rod-shaped photonic crystal fiber, so that the horizontal polarization solitons and the vertical polarization solitons are overlapped in time to synthesize target solitons with double soliton energy.
In combination with the first aspect of the present invention, in a second embodiment of the first aspect of the present invention, the splitting the preset pump pulse into two linearly polarized pump pulses with orthogonal polarization states, so that the two linearly polarized pump pulses with orthogonal polarization states are transmitted in the rod-shaped photonic crystal fiber and generate a horizontally polarized soliton and a vertically polarized soliton, respectively, includes:
generating the preset pumping pulse with a preset pulse width and a preset repetition frequency by a femtosecond laser;
the pump pulses are separated into two linearly polarized pump pulses with orthogonal polarization states using a half-wave plate, a first polarization separation means.
With reference to the first aspect of the present invention, in a third embodiment of the first aspect of the present invention, after the horizontal polarization solitons and the vertical polarization solitons are separated at the output end of the rod-shaped photonic crystal fiber, the opposite delay is introduced into the vertical polarization solitons, and at the same time, the optical path of the vertical polarization solitons is adjusted at the input end of the rod-shaped photonic crystal fiber, so that the horizontal polarization solitons and the vertical polarization solitons are temporally overlapped to synthesize a target solitons having double soliton energy, including:
combining the horizontal polarization solitons and the vertical polarization solitons at the output end of the rod-shaped photonic crystal fiber through a second polarization separation device;
introducing opposite said delays in said vertically polarized solitons at the output end of said rod-shaped photonic crystal fiber by a second polarization splitting means;
adjusting the optical path of the vertical polarization solitons at the input end of the rod-shaped photonic crystal fiber through a three-dimensional displacement rotating platform and a first polarization separation device;
judging whether the horizontal polarization solitons and the vertical polarization solitons are overlapped or not at the output end of the rod-shaped photonic crystal fiber through the two-photon current of the silicon detector;
and when the output time of the horizontal polarization solitons and the output time of the vertical polarization solitons at the output end of the rod-shaped photonic crystal fiber are coincident, synthesizing the horizontal polarization solitons and the vertical polarization solitons into target solitons.
With reference to the first aspect of the present invention, in a fourth embodiment of the first aspect of the present invention, after separating the horizontally polarized solitons and the vertically polarized solitons at the output end of the rod-shaped photonic crystal fiber, the method further includes, before adjusting the optical path of the vertically polarized solitons at the input end of the rod-shaped photonic crystal fiber so that the horizontally polarized solitons and the vertically polarized solitons overlap each other in time to synthesize a target soliton having double soliton energy, the method further including:
and filtering the horizontal polarization solitons and the vertical polarization solitons through a long-wave pass filter with preset transmission wavelength.
The invention provides a soliton synthesis device based on a rod-shaped photonic crystal fiber, which comprises: the device comprises a femtosecond laser, a half-wave plate, a rod-shaped photonic crystal fiber, a first polarization separation device, a second polarization separation device and a collimating lens group;
the femtosecond laser, the half-wave plate, the first polarization separation device, the rod-shaped photonic crystal fiber and the second polarization separation device are sequentially connected, and the collimating lens groups are respectively arranged at the input end and the output end of the rod-shaped photonic crystal fiber;
the femtosecond laser is used for outputting preset pumping pulses with preset pulse width and preset repetition frequency;
the half-wave plate and the first polarization separation device are used for separating a preset pump pulse into two linear polarization pump pulses with orthogonal polarization states, so that the two linear polarization pump pulses with orthogonal polarization states are independently transmitted in the rod-shaped photonic crystal fiber and respectively generate a horizontal polarization soliton and a vertical polarization soliton;
the first polarization separation device is internally provided with a three-dimensional displacement rotating platform which is used for adjusting the optical path of the vertical polarization soliton;
the rod-shaped photonic crystal fiber is used for coupling the two linear polarization pump pulses with the orthogonal polarization states so that the two linear polarization pump pulses with the orthogonal polarization states can be independently transmitted in the rod-shaped photonic crystal fiber;
the rod-shaped photonic crystal fiber also adjusts the energy of the two linear polarization pump pulses with orthogonal polarization states so as to enable the wavelengths of the horizontal polarization solitons and the vertical polarization solitons to be the same;
the second polarization separation device is configured to introduce the opposite delay into the vertical polarization soliton after separating the horizontal polarization soliton and the vertical polarization soliton at the output end of the rod-shaped photonic crystal fiber, so that the horizontal polarization soliton and the vertical polarization soliton are temporally overlapped to synthesize a target soliton with double soliton energy;
the collimating lens group is used for collimating the horizontal polarization solitons and the vertical polarization solitons at the input end and the output end of the rod-shaped photonic crystal fiber.
In a first embodiment of the second aspect of the present invention in combination with the second aspect of the present invention, the first polarization separation device and the second polarization separation device each include a pair of polarization beam splitting cubes and a pair of silver mirrors.
With reference to the first embodiment of the second aspect of the present invention, in a second embodiment of the second aspect of the present invention, a three-dimensional displacement rotary stage is provided in the first polarization separation device;
the first polarization separation device is converted into the second polarization separation device through the three-dimensional displacement rotating table.
With reference to the second aspect of the present invention, in a third embodiment of the second aspect of the present invention, a long-wave filter is disposed at an output end of the rod-shaped photonic crystal fiber;
the long wave filter is used for filtering the horizontal polarization solitons and the vertical polarization solitons.
The embodiment of the invention provides a soliton synthesis method based on a rod-shaped photonic crystal fiber, which comprises the steps of taking a preset pump pulse as a basic pulse signal, separating the preset pump pulse to obtain two linear polarization pump pulses with orthogonal polarization states, independently transmitting the two linear polarization pump pulses with the orthogonal polarization states in the rod-shaped photonic crystal fiber, respectively generating a horizontal polarization soliton and a vertical polarization soliton, then adjusting the energy of the two linear polarization pump pulses with the orthogonal polarization states to enable the wavelengths of the horizontal polarization soliton and the vertical polarization soliton to be the same, introducing opposite delay into the vertical polarization soliton after separating the horizontal polarization soliton and the vertical polarization soliton with the same wavelength at the output end of the rod-shaped photonic crystal fiber, adjusting the optical path of the vertical polarization soliton at the input end of the rod-shaped photonic crystal fiber, and supplementing the delay error, the horizontal polarization solitons and the vertical polarization solitons can be coincided in time to finally synthesize target solitons with double soliton energy, and the soliton energy output by the rod-shaped photonic crystal fiber is improved under the condition that the diameter of a fiber core of the rod-shaped photonic crystal fiber is not increased, so that the soliton single pulse energy generated by the rod-shaped photonic crystal fiber can meet the energy requirement of excitation light of a 1700nm wave band, and the deep brain structure imaging can be realized by three-photon fluorescence microscopic imaging of deep tissues.
Drawings
Fig. 1 is a schematic flow chart illustrating an implementation of a soliton synthesis method based on a rod-shaped photonic crystal fiber according to an embodiment of the present invention;
FIG. 2 is a detailed flowchart illustrating the step S104 in FIG. 1;
FIG. 3 is a schematic diagram of a soliton synthesis process provided in one embodiment of the present invention;
fig. 4 is a graph of soliton spectra generated by a soliton synthesis method based on a rod-shaped photonic crystal fiber according to a first embodiment of the present invention;
fig. 5 is a graph showing soliton interference autocorrelation data of solitons generated by a soliton synthesis method based on a rod-shaped photonic crystal fiber according to an embodiment of the present invention;
fig. 6 is a schematic structural diagram of a composition of a soliton synthesis apparatus based on a rod-shaped photonic crystal fiber according to a second embodiment of the present invention.
The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.
Detailed Description
It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
Suffixes such as "module", "part", or "unit" used to denote elements are used herein only for the convenience of description of the present invention, and have no specific meaning in themselves. Thus, "module" and "component" may be used in a mixture.
In the following description, the serial numbers of the embodiments of the invention are merely for description and do not represent the merits of the embodiments.
Example one
As shown in fig. 1, an embodiment of the present invention provides a rod-shaped photonic crystal fiber-based soliton synthesis method, wherein soliton energy output by a rod-shaped optical fiber is increased by synthesizing polarized solitons, and the synthesized soliton energy is twice of the original single-path soliton energy, so as to meet a high-energy light source requirement for deep brain imaging in a 1700nm window. The soliton synthesis method based on the rod-shaped photonic crystal fiber comprises the following steps:
s101, separating a preset pump pulse into two linear polarization pump pulses with orthogonal polarization states, so that the two linear polarization pump pulses with orthogonal polarization states are independently transmitted in the rod-shaped photonic crystal fiber and respectively generate a horizontal polarization soliton and a vertical polarization soliton.
In the step S101, the horizontally polarized solitons and the vertically polarized solitons have a delay when being output to the rod-shaped photonic crystal fiber.
The horizontal polarization solitons and the vertical polarization solitons are two linear polarization pump pulses with orthogonal polarization states, so that the horizontal polarization solitons and the vertical polarization solitons are perpendicular to each other and staggered in time, and have time delay when being output to the rod-shaped photonic crystal fiber.
In the above step S101, the polarization states of the horizontal polarization soliton and the vertical polarization soliton are the same.
The rod-shaped photonic crystal fiber is not designed with a polarization maintaining structure, namely, the fiber does not have a fast axis and a slow axis, so that a two-color soliton generation technology which only needs to adjust the polarization state cannot be applied to the rod-shaped photonic crystal fiber. However, due to the output design of the rod-shaped photonic crystal fiber, the polarization state of the pump pulse is completely reserved in the rod-shaped photonic crystal fiber, and the polarization state of the output pulse is consistent no matter what linear polarization angle is input, so that the preset pump pulse is separated to form two linear polarization pump pulses with orthogonal polarization states, and the polarization states of the corresponding horizontal polarization solitons and the vertical polarization solitons are the same.
In an embodiment of the present invention, the predetermined pump pulse is a linearly polarized pump pulse.
The preset pumping pulse refers to femtosecond pulse excitation with the repetition frequency lower than megahertz or megahertz level so as to meet the three-photon fluorescence microscopic imaging of deep tissues.
In an embodiment, the step S101 may include:
generating the preset pumping pulse with a preset pulse width and a preset repetition frequency by a femtosecond laser;
the pump pulse is split into two linearly polarized pump pulses with delays and orthogonal polarization states using a half-wave plate, a first polarization splitting means.
And S102, in the rod-shaped photonic crystal fiber, adjusting the energy of the linear polarization pump pulses with the two orthogonal polarization states so as to enable the wavelengths of the horizontal polarization solitons and the vertical polarization solitons to be the same.
In the above step S102, the wavelengths of the horizontal polarization solitons and the vertical polarization solitons are adjusted to be the same, so that the frequencies of the horizontal polarization solitons and the vertical polarization solitons are the same.
S103, after the horizontal polarization solitons and the vertical polarization solitons are separated at the output end of the rod-shaped photonic crystal fiber, opposite delays are introduced into the vertical polarization solitons, and meanwhile, the optical path of the vertical polarization solitons is adjusted at the input end of the rod-shaped photonic crystal fiber, so that the horizontal polarization solitons and the vertical polarization solitons are overlapped in time to synthesize target solitons with double soliton energy.
In step S103, since the horizontal polarization soliton and the vertical polarization soliton cannot be temporally overlapped by introducing a delay only to the vertical polarization soliton, it is necessary to adjust the angle at which the vertical polarization soliton is input to the rod-shaped photonic crystal fiber, thereby reducing an error.
In the above step S103, the horizontal polarization soliton and the vertical polarization soliton are temporally coincident.
In an embodiment, the step S103 may include:
and S1031, combining the horizontal polarization solitons and the vertical polarization solitons at the output end of the rod-shaped photonic crystal fiber through a second polarization separation device.
S1032, introducing opposite delay into the vertical polarization solitons through a second polarization separation device at the output end of the rod-shaped photonic crystal fiber.
In the above steps S1031 and S1032, the second polarization separation means has the same composition as the first polarization separation means, but is disposed at an angle of 90 °, thereby introducing a retardation opposite to that before.
In specific application, if the horizontal polarization solitons are transmitted to the output end of the rod-shaped photonic crystal fiber before the vertical polarization solitons, the delay is reduced in the vertical polarization solitons through the second polarization separation device, so that the speed of the vertical polarization solitons is increased. If the vertical polarization solitons are transmitted to the output end of the rod-shaped photonic crystal fiber earlier than the horizontal polarization solitons, the delay is increased in the vertical polarization solitons through the second polarization separation device, but the speed of the vertical polarization solitons is reduced.
S1033, adjusting the optical path of the vertical polarization soliton at the input end of the rod-shaped photonic crystal fiber through a three-dimensional displacement rotating platform and a first polarization separation device.
In step S1033, adjusting the optical path length of the vertical polarization soliton may also reduce or increase the retardation to compensate for the error of introducing the opposite retardation into the vertical polarization soliton in step S1032.
S1034, judging whether the horizontal polarization solitons and the vertical polarization solitons are overlapped or not at the output end of the rod-shaped photonic crystal fiber through the two-photon current of the silicon detector.
In the step S1034, the time coincidence between the horizontally polarized solitons and the vertically polarized solitons can be determined by the two-photon current of the silicon detector, and the principle is as follows:
an analyzer is arranged in front of the silicon detector, and the angle of the analyzer is adjusted to ensure that the synthesized solitons passing through the analyzer have the maximum transmittance, so that the energy of the solitons in the vertical polarization state and the horizontal polarization state which are transmitted becomes half of the original energy because the polarization state and the analyzer form 45 degrees respectively.
And S1035, when the output time of the horizontal polarization soliton and the output time of the vertical polarization soliton at the output end of the rod-shaped photonic crystal fiber coincide, synthesizing the horizontal polarization soliton and the vertical polarization soliton into a target soliton.
In step S1035, if it is determined that the time of the soliton is overlapped by the two-photon current of the silicon detector, the polarization states of the horizontal polarization soliton and the vertical polarization soliton at this time are orthogonal and have the same wavelength, pulse width, and pulse energy, and when the time is overlapped again, the horizontal polarization soliton and the vertical polarization soliton converge to a new pulse, that is, the target soliton.
In a specific application, the target soliton is linearly polarized, the polarization state is rotated by 45 degrees compared with the optical axis of the polarization-maintaining fiber, and the energy of the synthesized soliton is doubled, and the calculation formula is as follows:
Es＝As 2＝A⊥ 2+A// 2＝E⊥+E//＝2E//；
above Es、E⊥And E∥Respectively representing the energy of the synthesized target solitons, the energy of the vertical polarization solitons and the energy of the horizontal polarization solitons, wherein the vertical polarization solitons and the horizontal polarization solitons can be respectively horizontal polarization solitons and vertical polarization solitons or respectively vertical polarization solitons and horizontal polarization solitons, and As、A⊥And A∥Respectively representing the corresponding electric field intensity, and constant terms are omitted from the formula.
In an embodiment, before the step S104, the method may further include:
and filtering the horizontal polarization solitons and the vertical polarization solitons through a long-wave pass filter with preset transmission wavelength.
In a particular application, the residual pulses may be filtered out using a long-wave pass filter.
In the embodiment of the invention, the residual 1550nm pulse is filtered out through a 1575nm long-wave pass filter in a normal incidence mode, so that two solitons with the same wavelength are output.
As shown in fig. 3, the embodiment of the present invention further provides a schematic diagram of a soliton synthesis process.
Fig. 3 a is a schematic diagram of a preset pump pulse being split into two linearly polarized pump pulses with orthogonal polarization states before being input into a rod-shaped photonic crystal fiber, where P is the preset pump pulse, P1 is the horizontally linearly polarized pump pulse, P2 is the vertically linearly polarized pump pulse, and D is delay; the b diagram in fig. 3 is a schematic diagram of two linear polarization pump pulses with orthogonal polarization states at the output of the rod-shaped photonic crystal fiber, wherein P1 is a horizontally polarized soliton, P2 is a vertically polarized soliton, and D is a delay; the diagram c in fig. 3 is a schematic diagram of the horizontal polarization solitons and the vertical polarization solitons coinciding in time after opposite delays are introduced into the vertical polarization solitons, wherein p' is a target solitons synthesized after the horizontal polarization solitons and the vertical polarization solitons coincide in time.
The soliton synthesis method based on the rod-shaped photonic crystal fiber provided by the embodiment of the invention is characterized in that preset pump pulses are used as basic pulse signals and are subjected to separation processing to obtain two linear polarization pump pulses with orthogonal polarization states, so that the two linear polarization pump pulses with the orthogonal polarization states are independently transmitted in the rod-shaped photonic crystal fiber and respectively generate horizontal polarization solitons and vertical polarization solitons, then the energy of the two linear polarization pump pulses with the orthogonal polarization states is adjusted to enable the wavelengths of the horizontal polarization solitons and the vertical polarization solitons to be the same, after the horizontal polarization solitons and the vertical polarization solitons with the same wavelength are separated at the output end of the rod-shaped photonic crystal fiber, opposite delay is introduced into the vertical polarization solitons, and meanwhile, the optical path of the vertical polarization solitons is adjusted at the input end of the rod-shaped photonic crystal fiber to supplement the delay error, the horizontal polarization solitons and the vertical polarization solitons can be coincided in time to finally synthesize target solitons with double soliton energy, and the soliton energy output by the rod-shaped photonic crystal fiber is improved under the condition that the diameter of a fiber core of the rod-shaped photonic crystal fiber is not increased, so that the soliton single pulse energy generated by the rod-shaped photonic crystal fiber can meet the energy requirement of excitation light of a 1700nm wave band, and the deep brain structure imaging can be realized by three-photon fluorescence microscopic imaging of deep tissues.
Example two
The embodiment of the invention characterizes the soliton generated in the first embodiment. Under the condition of the maximum output power of the laser, horizontal polarization solitons and vertical polarization solitons with the wavelength of 1613nm are generated simultaneously.
In the embodiment of the present invention, it is assumed that in the first embodiment, a linearly polarized pump pulse with a pulse width of 500fs and a repetition frequency of 1MHz is used as a preset pump pulse; a rod-shaped photonic crystal fiber with the length of 44cm and the fiber core diameter of 100 mu m is used as a transmission fiber of a horizontal polarization soliton and a vertical polarization soliton, a 1575nm long-wave pass filter is used, and after residual 1550nm pulses are filtered out in a normal incidence mode, the horizontal polarization soliton and the vertical polarization soliton are obtained through separation.
Fig. 4 shows the spectral measurement data, in which the lines with different gray levels respectively represent the soliton spectra after horizontal polarization, vertical polarization and polarization synthesis, the horizontal axis represents the wavelength, and the vertical axis represents the pulse signal, and it can be seen that the spectra of the two solitons with orthogonal polarization states are completely consistent.
Fig. 5 shows the result of the interference autocorrelation measurement, from top to bottom, which is the horizontal polarization soliton, the vertical polarization soliton and the synthetic soliton, respectively, and the horizontal axis represents the delay and the vertical axis represents the pulse signal. After deconvolution of hyperbolic secant (sech2) intensity distribution, the measurement results of soliton pulse widths of horizontal polarization and vertical polarization are 82.6fs and 83.3fs respectively, the measurement results of power are 75mW and 76mW respectively, and single pulse energy is 75nJ and 76nJ respectively under the repetition frequency of 1 MHz. The measurement result shows that the two solitons with orthogonal polarization states have basically the same spectrum and very close pulse width and power parameters, and a foundation is laid for soliton synthesis.
It is then necessary to achieve horizontal polarization by fine tuning of the time delay between pump pulsesThe solitons and vertically polarized solitons coincide in time. The time coincidence of the solitons can be judged by the two-photon current of the silicon detector, wherein the two-photon current I generated on the silicon detector2pProportional to the square of the pulse energy E, the formula is:
I2p,⊥＝(E⊥/2)2＝E2 ⊥/4；
I2p,//＝(E///2)2＝E2 ///4；
thus, I2p,⊥＝I2p,∥。
Wherein, I2p,⊥And I2p,∥The two-photon currents generated by the vertical polarization solitons and the horizontal polarization solitons on the silicon detector respectively ignore constant terms in the calculation.
When the horizontal polarization solitons and the vertical polarization solitons are superposed in time, the two-photon current generated by the synthesized solitons on the silicon detector becomes:
I2p,s＝(2E⊥)2＝(2E//)2＝16I2p,⊥＝16I2p,//；
that is, after the horizontal and vertical polarization solitons are temporally superimposed, the two-photon current generated on the silicon detector after passing through the analyzer is 16 times the current generated by the horizontal or vertical polarization solitons.
As shown in the spectral measurement data shown in fig. 4 and the interference autocorrelation data shown in fig. 5, it can be known that in the above inspection manner, the solitons of horizontal polarization and vertical polarization are temporally superimposed, and are substantially consistent with the solitons of vertical or horizontal polarization, and the power of the solitons after synthesis is 151mW, which is exactly the sum of the powers of the two orthogonal polarization solitons. Consistent with expectations, the pulse width of the synthetic soliton was 83.7fs, essentially the same as the two solitons of orthogonal polarization.
With the combination of the first embodiment, the power obtained by temporally superimposing the horizontal polarization solitons and the vertical polarization solitons, that is, the power of the synthesized target solitons, can be obtained as the sum of the powers of the two linear polarization pump pulses with orthogonal polarization states; the pulse width of the synthesized target solitons is the same as the pulse widths of the horizontal polarization solitons and the vertical polarization solitons.
EXAMPLE III
As shown in fig. 6, an embodiment of the present invention provides a soliton synthesis apparatus 60 based on a rod-shaped photonic crystal fiber, including: a femtosecond laser 61, a half-wave plate 62, a rod-shaped photonic crystal fiber 54, a first polarization separation device 63, a second polarization separation device 65 and a collimating lens group 66;
the femtosecond laser 61, the half-wave plate 62, the first polarization separation device 63, the rod-shaped photonic crystal fiber 64 and the second polarization separation device 65 are sequentially connected, and the collimating lens group 66 is respectively arranged at the input end and the output end of the rod-shaped photonic crystal fiber 64;
a femtosecond laser 61 for outputting a preset pumping pulse with a preset pulse width and a preset repetition frequency;
the half-wave plate 62 and the first polarization separation device 63 are used for separating the preset pump pulse into two linear polarization pump pulses with orthogonal polarization states, so that the two linear polarization pump pulses with orthogonal polarization states are independently transmitted in the rod-shaped photonic crystal fiber and respectively generate a horizontal polarization soliton and a vertical polarization soliton;
the first polarization separation device is internally provided with a three-dimensional displacement rotating platform which is used for adjusting the angle of the vertical polarization soliton input rod-shaped photonic crystal fiber;
a rod-shaped photonic crystal fiber 64 for coupling the two linearly polarized pump pulses with orthogonal polarization states such that the two linearly polarized pump pulses with orthogonal polarization states are independently transmitted therein;
the rod-shaped photonic crystal fiber 64 also adjusts the energy of the two linear polarization pump pulses with orthogonal polarization states, so that the wavelengths of the horizontal polarization solitons and the vertical polarization solitons are the same;
the second polarization separation device 65 is used for introducing opposite delay into the vertical polarization solitons after the horizontal polarization solitons and the vertical polarization solitons are separated at the output end of the rod-shaped photonic crystal fiber, so that the horizontal polarization solitons and the vertical polarization solitons are overlapped in time to synthesize target solitons with double soliton energy;
and the collimating lens group 66 is used for collimating the horizontal polarization solitons and the vertical polarization solitons at the input end and the output end of the rod-shaped photonic crystal fiber.
In an embodiment of the present invention, the first polarization separation device and the second polarization separation device each include a pair of polarization beam splitting cubes and a pair of silver mirrors.
In the embodiment of the invention, a three-dimensional displacement rotating platform is arranged in the first polarization separation device; the first polarization separation device is converted into a second polarization separation device through a three-dimensional displacement rotating platform.
In the embodiment of the invention, the output end of the rod-shaped photonic crystal fiber is provided with a long-wave filter; the long wave filter is used for filtering the horizontal polarization solitons and the vertical polarization solitons.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the foregoing embodiments illustrate the present invention in detail, those of ordinary skill in the art will understand that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present invention, and are intended to be included within the scope of the present invention.
Claims (7)
1. A soliton synthesis method based on a rod-shaped photonic crystal fiber is characterized by comprising the following steps:
separating a preset pump pulse into two linear polarization pump pulses with orthogonal polarization states, so that the two linear polarization pump pulses with orthogonal polarization states are independently transmitted in the rod-shaped photonic crystal fiber and respectively generate a horizontal polarization soliton and a vertical polarization soliton;
wherein the horizontal polarization solitons and the vertical polarization solitons have delay when being output to the rod-shaped photonic crystal fiber;
in the rod-shaped photonic crystal fiber, adjusting the energy of the two linearly polarized pump pulses with orthogonal polarization states so that the wavelengths of the horizontally polarized solitons and the vertically polarized solitons are the same;
combining the horizontal polarization solitons and the vertical polarization solitons at the output end of the rod-shaped photonic crystal fiber through a second polarization separation device;
introducing opposite said delays in said vertically polarized solitons at the output end of said rod-shaped photonic crystal fiber by a second polarization splitting means;
adjusting the optical path of the vertical polarization solitons at the input end of the rod-shaped photonic crystal fiber through a three-dimensional displacement rotating platform and a first polarization separation device;
judging whether the horizontal polarization solitons and the vertical polarization solitons are overlapped or not at the output end of the rod-shaped photonic crystal fiber through the two-photon current of the silicon detector;
and when the output time of the horizontal polarization solitons and the output time of the vertical polarization solitons at the output end of the rod-shaped photonic crystal fiber are coincident, synthesizing the horizontal polarization solitons and the vertical polarization solitons into target solitons.
2. The soliton synthesis method based on the rod-shaped photonic crystal fiber according to claim 1, wherein the preset pump pulse is a linearly polarized pump pulse.
3. The rod-shaped photonic crystal fiber-based soliton synthesis method according to claim 1, wherein the splitting of the preset pump pulse into two orthogonal polarization state linear polarized pump pulses to enable the two orthogonal polarization state linear polarized pump pulses to propagate in the rod-shaped photonic crystal fiber and generate a horizontally polarized soliton and a vertically polarized soliton respectively comprises: generating the preset pumping pulse with a preset pulse width and a preset repetition frequency by a femtosecond laser;
the pump pulses are separated into two linearly polarized pump pulses with orthogonal polarization states using a half-wave plate, a first polarization separation means.
4. The rod-shaped photonic crystal fiber-based soliton synthesis method of claim 1, wherein after separating the horizontally polarized solitons and the vertically polarized solitons at the output end of the rod-shaped photonic crystal fiber, the opposite delay is introduced into the vertically polarized solitons, and simultaneously, at the input end of the rod-shaped photonic crystal fiber, the optical path of the vertically polarized solitons is adjusted so that the horizontally polarized solitons and the vertically polarized solitons coincide in time, before synthesizing a target soliton with double soliton energy, further comprising: and filtering the horizontal polarization solitons and the vertical polarization solitons through a long-wave pass filter with preset transmission wavelength.
5. A soliton synthesizer based on a rod-shaped photonic crystal fiber is characterized by comprising: the device comprises a femtosecond laser, a half-wave plate, a rod-shaped photonic crystal fiber, a first polarization separation device, a second polarization separation device and a collimating lens group;
the femtosecond laser, the half-wave plate, the first polarization separation device, the rod-shaped photonic crystal fiber and the second polarization separation device are sequentially connected, and the collimating lens groups are respectively arranged at the input end and the output end of the rod-shaped photonic crystal fiber;
the femtosecond laser is used for outputting preset pumping pulses with preset pulse width and preset repetition frequency;
the half-wave plate and the first polarization separation device are used for separating a preset pump pulse into two linear polarization pump pulses with orthogonal polarization states, so that the two linear polarization pump pulses with orthogonal polarization states are independently transmitted in the rod-shaped photonic crystal fiber and respectively generate a horizontal polarization soliton and a vertical polarization soliton; wherein the horizontal polarization solitons and the vertical polarization solitons have delay when being output to the rod-shaped photonic crystal fiber;
the first polarization separation device is internally provided with a three-dimensional displacement rotating platform which is used for adjusting the optical path of the vertical polarization soliton;
the rod-shaped photonic crystal fiber is used for coupling the two linear polarization pump pulses with the orthogonal polarization states so that the two linear polarization pump pulses with the orthogonal polarization states are independently transmitted in the rod-shaped photonic crystal fiber;
the rod-shaped photonic crystal fiber also adjusts the energy of the two linear polarization pump pulses with orthogonal polarization states so as to enable the wavelengths of the horizontal polarization solitons and the vertical polarization solitons to be the same;
the second polarization separation device is used for combining the horizontal polarization solitons and the vertical polarization solitons at the output end of the rod-shaped photonic crystal fiber through the second polarization separation device; introducing opposite said delays in said vertically polarized solitons at the output end of said rod-shaped photonic crystal fiber by a second polarization splitting means; adjusting the optical path of the vertical polarization solitons at the input end of the rod-shaped photonic crystal fiber through a three-dimensional displacement rotating platform and a first polarization separation device; judging whether the horizontal polarization solitons and the vertical polarization solitons are overlapped or not at the output end of the rod-shaped photonic crystal fiber through the two-photon current of the silicon detector; when the output time of the horizontal polarization solitons and the output time of the vertical polarization solitons at the output end of the rod-shaped photonic crystal fiber are coincident, the horizontal polarization solitons and the vertical polarization solitons are synthesized into target solitons;
the collimating lens group is used for collimating the horizontal polarization solitons and the vertical polarization solitons at the input end and the output end of the rod-shaped photonic crystal fiber.
6. The rod-shaped photonic crystal fiber based soliton synthesis apparatus according to claim 5, wherein the first polarization separation means and the second polarization separation means each comprise a pair of polarization beam splitting cubes and a pair of silver mirrors.
7. The soliton synthesizer based on rod-shaped photonic crystal fiber as claimed in claim 5, wherein the rod-shaped photonic crystal fiber has a long wave filter at its output end;
the long wave filter is used for filtering the horizontal polarization solitons and the vertical polarization solitons.
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| US9841557B2 (en) * | 2013-07-10 | 2017-12-12 | Nkt Photonics A/S | Microstructured optical fiber, supercontinuum light source comprising microstructured optical fiber and use of such light source |
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| US5111322A (en) * | 1991-04-04 | 1992-05-05 | At&T Bell Laboratories | Polarization multiplexing device with solitons and method using same |
| CN104201549A (en) * | 2014-07-24 | 2014-12-10 | 深圳大学 | Wavelength space adjustable double-color soliton pulse light source system |
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