CN110221445A - Circular polarization orphan generation device and multi-photon micro imaging system - Google Patents

Abstract

The invention relates to a circularly polarized soliton generating device and a multiphoton microscopic imaging system. The circularly polarized soliton generating device includes a pump laser, a first quarter-wave plate, a first focusing lens and an optical fiber located on the same optical path. Wherein, the linearly polarized light generated by the pump laser is transformed into circularly polarized light after passing through the first quarter-wave plate, the circularly polarized light is coupled into the optical fiber after passing through the focusing lens, and the circularly polarized light is transformed into circularly polarized solitons. Through the first quarter-wave plate, the linearly polarized light becomes circularly polarized light, and then the circularly polarized light becomes circularly polarized soliton after passing through the optical fiber. Experiments have proved that under the same conditions, the energy of circularly polarized solitons is 1.56 times that of linearly polarized solitons, enabling multi-photon signals to travel farther in the brain, enabling humans to further explore the deep tissues of the brain, and then unlock The mystery of the brain.

Description

Circularly Polarized Soliton Generator and Multiphoton Microscopic Imaging System

technical field

The invention relates to the technical field of optical imaging, in particular to a circularly polarized soliton generating device and a multiphoton microscopic imaging system.

Background technique

Optical solitons (Solitons, Solitons in optical fibers) refer to light pulses that keep their shape unchanged after long-distance transmission. A beam of light pulses contains many different frequency components. Different frequencies have different propagation speeds in the medium. Therefore, the light pulses will be dispersed in the optical fiber, making the pulse width wider. However, when a very narrow monochromatic light pulse with high intensity is incident into the fiber, the Kerr effect will occur, that is, the refractive index of the medium changes with the light intensity, which leads to self-phase modulation in the light pulse, making the pulse front The resulting phase change causes the frequency to decrease, and the phase change produced by the trailing edge of the pulse causes the frequency to increase, so the leading edge of the pulse propagates slower than its trailing edge, thereby narrowing the pulse width. When the pulse has an appropriate amplitude, the above two effects can be exactly offset, and the pulse can be transmitted in the fiber with a stable waveform, that is, an optical soliton is formed, also known as a fundamental optical soliton. If the pulse amplitude continues to increase, the narrowing effect will exceed the broadening effect, and high-order optical solitons will be formed, and the pulse shape transmitted in the fiber will change continuously, first compressed and narrowed, and then split, and the pulse is periodic at a specific distance restored.

Optical solitons are formed by the combined action of two of the most fundamental physical phenomena in optical fibers, namely, group velocity dispersion (GVD) and self-phase modulation (SPM).

When the optical pulse is transmitted in the optical fiber, there is always a certain frequency range. In the linear approximation, the optical pulse is often expressed as a superposition of a series of simple harmonics within a certain range. Since the phase velocity of each harmonic component is different, the transmission of the optical pulse envelope is usually represented by the group velocity vg=dω/dβ (β is the wave number of the light wave, and ω is the carrier frequency). It can be seen from this formula that the group velocity changes with the frequency, and the components of different frequencies in the optical pulse will propagate at different speeds, resulting in the dispersion of the pulse. This phenomenon is called group velocity dispersion (GVD ). The research results show that λd=1310nm is zero dispersion wavelength, λ>λd is called anomalous dispersion region, and λ<λd is called normal dispersion region. The transmission characteristics of light pulses in the normal and anomalous dispersion regions are different. In the anomalous dispersion region, the high frequency component (blue shift) and the lower frequency component (red shift) of the light pulse travel faster, while in the normal dispersion region, the situation is just the opposite. . Due to the different transmission conditions, the group velocity dispersion effect is different, which finally leads to the broadening of the optical pulse.

The self-phase modulation effect is the phase shift caused by the light wave itself when it is transmitted in the optical fiber. It originates from the nonlinear effect between the refractive index n of the optical fiber and the electric field intensity I—the Kerr effect, namely: n=n0+n2I. In the above formula, n=1.45 is the linear refractive index, and n2=6.1×1023V/m is the nonlinear refractive index coefficient. It can be seen from the above formula that the phase velocities of pulse components with different intensities are different, so that different phase shifts will occur during the transmission of optical pulses, resulting in changes in the pulse spectrum. For example, the analysis of Gaussian pulses shows that self-phase modulation will lead to a red shift in the spectrum of the front edge of the pulse, and a blue shift of the spectrum of the rear edge of the pulse. The analysis of pulses with other shapes has similar results. In addition, relative to the anomalous dispersion region of group velocity dispersion (GVD), the high-frequency (blue-shifted) component of the pulse moves faster than the low-frequency (red-shifted) component, and the pulse front spectrum caused by the self-phase modulation (SPM) effect The red shift slows down the movement speed of the pulse front and accelerates the movement speed of the pulse trail due to the blue shift of the spectrum, and then narrows the pulse, which corresponds to the pulse broadening trend of the group velocity dispersion in the anomalous dispersion region. Therefore, when these two effects are quantitatively balanced, the light pulse remains unchanged and becomes a light soliton, that is, an optical soliton. Therefore, the formation mechanism of optical solitons is the precise balance of group velocity dispersion and self-phase modulation effects in the anomalous dispersion region in optical fibers.

In 1986, Mitschke and Mollenauer discovered the nonlinear optical effect of soliton self-frequency shift (SSFS) in optical fibers [1]: when ultrashort optical solitons propagate in anomalous dispersion fibers, they will experience continuous wavelength shift to long wavelength. The wavelength-tunable optical soliton can be generated by the soliton self-frequency shifting technology. The optical soliton has the following characteristics: ultra-short pulse width (tens of femtoseconds to sub-picoseconds), excellent pulse quality, and broadband wavelength tunability sex. These characteristics make it an ideal light source choice for multiphoton microscopy (MPM).

Multiphoton microscopy is a nonlinear optical imaging technique, especially suitable for deep tissue imaging in vivo. Multiphoton microscopy has been widely used in various modalities in biology, physiology, and medical research.

Multiphoton signals are limited by the energy of optical solitons in the brain, making multiphoton signals decay exponentially with the absorption and scattering of brain tissue during the propagation of multiphoton signals in brain tissue. In the prior art, due to the low energy of the optical solitons generated by the multiphoton microscopic imaging system, the existing multiphoton microscopic imaging system can only study the shallow tissue of the brain, so it is impossible to further study the deep tissue of the brain. Thus limiting the further exploration of the deep layers of the brain.

Contents of the invention

The main purpose of the present invention is to provide a circularly polarized soliton generating device and a multi-photon microscopic imaging system, aiming at solving the technical problem of low energy of optical solitons generated in the prior art.

In order to solve the problems of the technologies described above, the technical solution provided by the invention is:

A circularly polarized soliton generating device, comprising a pump laser located on the same optical path, a first quarter wave plate, a first focusing lens, and an optical fiber, wherein the linearly polarized light generated by the pump laser passes through the first quarter wave plate One of the wave plates is converted into circularly polarized light, the circularly polarized light is coupled into the optical fiber after passing through the focusing lens, and the circularly polarized light is converted into circularly polarized solitons after passing through the optical fiber.

Wherein, the circularly polarized soliton generating device also includes a first collimating lens and a long-wave pass filter, wherein the circularly polarized solitons are scattered after passing through the collimating lens, and the scattered circularly polarized solitons pass through the long-wave pass filter The light sheet is filtered.

Wherein, the optical fiber is a rod-shaped photonic crystal optical fiber.

A multiphoton microscopic imaging system, comprising a second quarter-wave plate, a flat-field focusing lens, a dichroic mirror, an objective lens, a photomultiplier tube and the circularly polarized soliton generation described in any one of claims 1-3 device; wherein, the circularly polarized soliton generated by the circularly polarized soliton generating device is transformed into a linearly polarized soliton after passing through the second quarter-wave plate, and the linearly polarized soliton passes through the flat-field focusing lens and the dichroic The mirror is coupled into the objective lens, and is focused on the object to be detected through the objective lens to generate a signal. After the signal is scattered, it passes through the objective lens and the dichroic mirror in turn, and the dichroic mirror couples the signal to the photomultiplier inside the tube and imaged through the photomultiplier tube.

Wherein, the multiphoton microscopic imaging system further includes a first reflector, and the first reflector is located between the second quarter-wave plate and the f-field focusing lens.

Wherein, the multiphoton microscopic imaging system further includes a barrel lens, and the barrel lens is located between the f-field focusing lens and the dichroic mirror.

Wherein, the multiphoton microscopic imaging system further includes a second reflector, and the second reflector is located between the barrel lens and the dichroic mirror.

The circularly polarized soliton generating device and the multiphoton microscopic imaging system described above convert linearly polarized light into circularly polarized light through the first quarter-wave plate, and then convert the circularly polarized light into circularly polarized solitons after passing through an optical fiber. Experiments have proved that under the same conditions, the energy of circularly polarized solitons is 1.56 times that of linearly polarized solitons, enabling multiphoton signals to travel farther in the brain, enabling humans to further explore the deep tissues of the brain, and then unlock The mystery of the brain.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained according to these drawings without creative work.

Fig. 1 is a schematic diagram of a circularly polarized soliton generating device according to an embodiment of the present invention.

Fig. 2 is an energy contrast diagram of circularly polarized solitons and linearly polarized solitons passing through a long-pass filter according to an embodiment of the present invention.

FIG. 3( a ) is a graph showing the relationship between the normalized pump power of linearly polarized light passing through the first quarter-wave plate and the rotation angle of the polarizer according to an embodiment of the present invention.

Fig. 3(b) is a graph showing the relationship between the normalized pump power of circularly polarized light passing through a collimating lens and the rotation angle of a polarizer according to an embodiment of the present invention.

FIG. 4 is a schematic diagram of a multiphoton microscopic imaging system according to an embodiment of the present invention.

10. Multiphoton microscopic imaging system; 1. Circularly polarized soliton generating device; 11. Pump laser; 12. First quarter wave plate; 13. First focusing lens; 14. Optical fiber; 15. First quasi Straight lens; 16, long-wave pass filter; 2, second quarter-wave plate; 3, flat-field focusing lens; 31, scanning mirror; 32, scanning lens; 4, dichroic mirror; 5, objective lens; 6. Photomultiplier tube; 7. First reflector; 8. Tube lens; 9. Second reflector.

specific embodiment

In order to make the purpose, features and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described The embodiments are only some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts belong to the protection scope of the present invention.

Fig. 1 is a schematic diagram of a circularly polarized soliton generating device according to an embodiment of the present invention.

As can be seen from the figure, the circularly polarized soliton generating device 1 can have a pump laser 11, a first quarter-wave plate 12, a first focusing lens 13, and an optical fiber 14 on the same optical path, wherein the pump laser The linearly polarized light generated by 11 passes through the first quarter-wave plate 12 and is transformed into circularly polarized light. The circularly polarized light is coupled into the optical fiber 14 after passing through the focusing lens, and the circularly polarized light is transformed into circularly polarized solitons after passing through the optical fiber 14 .

In this embodiment, the linearly polarized light is transformed into circularly polarized light through the first quarter-wave plate 12 , and then the circularly polarized light is transformed into circularly polarized solitons after passing through the optical fiber 14 . Experiments have proved that under the same conditions, the energy of circularly polarized solitons is 1.56 times that of linearly polarized solitons, enabling multiphoton signals to travel farther in the brain, enabling humans to further explore the deep tissues of the brain, and then unlock The mystery of the brain.

The following theoretically proves that the energy of the circularly polarized soliton is 1.56 times that of the linearly polarized soliton, and the propagation formula of the linearly polarized soliton in the optical fiber 14 is:

Among them, i represents the imaginary unit, Represents the differential sign, z represents the transmission distance, Ax represents the linearly polarized pulse envelope, _β2 represents the group velocity dispersion, T represents time, and γ represents the nonlinear coefficient.

The propagation formula of the circularly polarized soliton in the optical fiber 14 is:

Among them, A+ represents the right-handed circularly polarized soliton envelope, and the formula (2) is also applicable to the left-handed polarized soliton impulse (A+ is replaced by A-).

A new nonlinear coefficient γ'=2/3γ can be defined by formula (1) and formula (2), so that the two are consistent. Formula (2) can be converted into the energy of circularly polarized solitons, and the formula is as follows:

Among them, En ₊ represents the energy of circularly polarized solitons, and En _x represents the energy of linearly polarized solitons.

It can be seen from the formula (3) that the energy of a circularly polarized soliton is 1.5 times that of a linearly polarized soliton.

The following experiment proves that the energy of circularly polarized solitons is 1.56 times that of linearly polarized solitons. In this embodiment, the pump laser 11 used in the experiment is (FLCPA-02CSZU, Calmar), and its output laser is linearly polarized light with a wavelength of 1550nm. The width is 500fs and the repetition rate is 1MHz. As shown in FIG. 2 , under the same conditions, the energy ratio of circularly polarized solitons and linearly polarized solitons after passing through the long-pass filter 16 is about 1.56, which is consistent with the theoretical value of 1.5.

The following experiment proves that the linearly polarized light generated by the pump laser 11 is transformed into circularly polarized light after passing through the first quarter-wave plate 12 . A polarizer and a power meter are arranged behind the first quarter-wave plate 12, the polarizer is rotated, and the power after the polarizer is rotated is measured by the power meter. In theory, the power of each angle of circularly polarized light is equal; however, in reality, there will be a certain error in the power of each angle of circularly polarized light. As shown in Figure 3(a), the abscissa is the angle, and the ordinate is the normalized power, where the normalized power means that dividing the power of each angle by the maximum power is the normalized power of the angle, for example , Now measure ten power values at 0-360 degrees, the power measured at 60 degrees is 23.5mw, and the maximum power is 24.5mw, then the normalized power at 60 degrees is 23.5/24.5. In theory, the extinction ratio of circularly polarized light is 1, but in practice, the extinction ratio of circularly polarized light is close to 1, where the extinction ratio represents the ratio of the minimum power to the maximum power of circularly polarized light at different angles. Finally, the experimentally measured extinction ratio ERpump=1.06, it can be seen that the linearly polarized light generated by the pump laser 11 is transformed into circularly polarized light after passing through the first quarter-wave plate 12 .

The following experiment proves that circularly polarized light becomes a circularly polarized soliton after passing through the optical fiber 14. In this embodiment, a polarizer and a power meter are arranged behind the first collimating lens 15, the polarizer is rotated, and the polarizer is measured by a power meter after the rotation power. As shown in Fig. 3(b), the abscissa is the angle, and the ordinate is the normalized power. Finally, the extinction ratio ERpump=1.03 measured in the experiment shows that the circularly polarized light becomes circularly polarized solitons after passing through the optical fiber 14 .

In the illustrated embodiment, the circularly polarized soliton generating device 1 also includes a first collimator lens 15 and a long-wave pass filter 16, wherein the circularly polarized solitons are scattered after passing through the collimating lens, and the scattered circularly polarized solitons are passed through the long-wavelength filter. Filter through filter 16. Circularly polarized solitons other than specific wavelengths can be filtered by the long-pass filter 16 . In this embodiment, the wavelength of circularly polarized solitons that the long-pass filter 16 allows to pass is 1617 nm.

In this embodiment, the optical fiber 14 is a rod-shaped photonic crystal fiber. It can be understood that, in an optional embodiment, the optical fiber 14 may also be a high-order mode optical fiber, a large mode field optical fiber or a hollow core optical fiber.

FIG. 4 is a schematic diagram of a multiphoton microscopic imaging system according to an embodiment of the present invention.

As can be seen from the figure, the multiphoton microscopic imaging system 10 can have a second quarter-wave plate 2, a flat field focusing lens 3, a dichroic mirror 4, an objective lens 5, a photomultiplier tube 6 and claim 1 Circularly polarized soliton generating device 1 according to any one of 3; wherein, the circularly polarized soliton generated by circularly polarized soliton generating device 1 is transformed into linearly polarized soliton after passing through the second quarter-wave plate 2, and the linearly polarized soliton is focused through flat field The lens 3 and the dichroic mirror 4 are coupled into the objective lens 5, and are focused on the object to be detected through the objective lens 5 to generate a signal. Coupled into the photomultiplier tube 6, and imaged through the photomultiplier tube 6.

In the illustrated embodiment, the multiphoton microscopic imaging system 10 further includes a first mirror 7 , and the first mirror 7 is located between the second quarter-wave plate 2 and the flat-field focusing lens 3 .

In the illustrated embodiment, the multiphoton microscopy imaging system 10 further includes a lens tube lens 8 , and the lens tube lens 8 is located between the f-field focusing lens 3 and the dichroic mirror 4 .

In the illustrated embodiment, the multiphoton microscopy imaging system 10 further includes a second mirror 9 , and the second mirror 9 is located between the lens tube lens 8 and the dichroic mirror 4 . The dichroic mirror 4 can transmit long-wavelength solitons and reflect short-wavelength solitons. In this embodiment, the dichroic mirror 4 can transmit optical solitons with a wavelength of 1617nm and reflect optical solitons with a wavelength of 716nm.

In this embodiment, the flat-field focusing lens 3 includes an X-axis and Y-axis scanning mirror 31 and a scanning lens 32 .

work process:

The linearly polarized light generated by the pump laser 11 passes through the first quarter-wave plate and becomes circularly polarized. The circularly polarized light is coupled into the rod-shaped photonic crystal fiber 14 after passing through the focusing lens. The circularly polarized light becomes circularly polarized after passing through the rod-shaped photonic crystal fiber 14. Solitons, circularly polarized solitons diffuse after passing through the collimating lens, and the diffused circularly polarized solitons are filtered by the long-pass filter 16, and the filtered circularly polarized solitons pass through the second quarter-wave plate 2 to become linearly polarized solitons , the linearly polarized solitons are reflected by the first reflector 7, and the reflected linearly polarized solitons are diffused after passing through the flat-field focusing lens 3 and the lens barrel lens 8, and the diffused linearly polarized solitons are reflected by the second reflector 9 to emit The final linearly polarized soliton is coupled into the objective lens 5 through the dichroic mirror 4, and the linearly polarized soliton is focused on the fluorescent dye of the object to be tested through the objective lens 5, and causes the fluorescent dye to produce a nonlinear effect (the fluorescent molecule absorbs three photons and jumps to Excited state, the excited state changes to the ground state and emits a photon), thereby generating a fluorescent signal, the fluorescent signal passes through the objective lens 5 and the dichroic mirror 4 in sequence after being scattered, and the dichroic mirror 4 couples the fluorescent signal to the photomultiplier tube 6 , and finally, through the photomultiplier tube 6 for imaging.

The above is a description of a circularly polarized soliton generating device and a multiphoton microscopic imaging system provided by the present invention. For those skilled in the art, based on the ideas of the embodiments of the present invention, there will be some differences in specific embodiments and application ranges. Changes, in summary, the contents of this specification should not be construed as limiting the present invention.

Claims (7)

1. a kind of circular polarization orphan generation device, which is characterized in that including be located at same optical path on pump laser, the one or four / mono- wave plate, the first condenser lens and optical fiber, wherein the line polarisation that the pump laser generates by the one or four/ It is changed into rotatory polarization after one wave plate, rotatory polarization is coupled in the optical fiber after the condenser lens, described in rotatory polarization process It is changed into circular polarization orphan after optical fiber.

2. circular polarization orphan generation device according to claim 1, which is characterized in that the circular polarization orphan generation device It further include the first collimation lens and long wave pass filter, wherein circular polarization orphan scatters after the collimation lens, dissipates Circular polarization orphan after penetrating is filtered by the long wave pass filter.

3. circular polarization orphan generation device according to claim 1, which is characterized in that the optical fiber is rodlike photonic crystal Optical fiber.

4. a kind of multi-photon micro imaging system, which is characterized in that including the second quarter-wave plate, f-theta lens, two To Look mirror, object lens, photomultiplier tube and the described in any item circular polarization orphan generation devices of claim 1-3；Wherein, described The circular polarization orphan that circular polarization orphan's generation device generates is changed into linear polarization orphan after second quarter-wave plate, Linear polarization orphan is coupled in object lens after the f-theta lens and dichroscope, and is focused on by object lens to be detected Generate signal on object, signal scatter after successively by the object lens and the dichroscope, the dichroscope is by signal It is coupled in the photomultiplier tube, and is imaged by the photomultiplier tube.

5. multi-photon micro imaging system according to claim 4, which is characterized in that the multi-photon micro imaging system Further include the first reflecting mirror, first reflecting mirror be located at second quarter-wave plate and the f-theta lens it Between.

6. multi-photon micro imaging system according to claim 4, which is characterized in that the multi-photon micro imaging system It further include tube lens, the tube lens are between the f-theta lens and the dichroscope.

7. multi-photon micro imaging system according to claim 6, which is characterized in that the multi-photon micro imaging system It further include the second reflecting mirror, second reflecting mirror is between the tube lens and the dichroscope.