CN106200207A - Pattern Filter method and device for photon-phonon coupling photonic device - Google Patents

Abstract

The invention provides a mode filtering method and device for a photoacoustic coupling photonic device. The mode filtering method includes: performing mode conversion on the Gaussian signal beam to obtain the OAM signal beam; making the OAM signal beam and the Gaussian pumping beam input from both sides of the photoacoustic coupling photonic device respectively, so that the Gaussian pumping beam is in the optical The stimulated Brillouin amplification of the OAM signal beam is carried out in the acoustic coupling photonic device; the mode inverse conversion is performed on the mixed beam of the amplified OAM signal beam and the SBS noise beam output from the photoacoustic coupling photonic device, so that after the mode inverse conversion, The amplified OAM signal beam in the mixed beam becomes an amplified Gaussian signal beam, and the SBS noise beam in the mixed beam becomes an OAM‑SBS noise beam; by spatial filtering, the OAM‑SBS noise beam in the mixed beam is filtered out, To obtain an amplified Gaussian signal beam in the mixed beam. The mode filtering method and device of the invention can be used to remove SBS noise in photoacoustic coupling photonic devices.

Description

Mode filtering method and device for photoacoustic coupling photonic device

technical field

The invention relates to the technical field of photoacoustic coupling, in particular to a mode filtering method and device for photoacoustic coupling photonic devices.

Background technique

Photoacoustic coupling is one of the strongest nonlinear light-matter interactions that occurs in transparent media, and this interaction is called stimulated Brillouin scattering (SBS) when phonons are generated by the optical force parameter. Since the invention of lasers, SBSs have been widely used in the generation of high-energy laser pulses, nonlinear optical microscopy, distributed optical fiber sensing, and light velocity control. Recently, with the development of nanomanufacturing technology, people's ability to control photoacoustic coupling has been further enhanced, and photoacoustic coupling photonic devices such as photoacoustic crystals, integrated silicon waveguides, and nanoweb fibers have emerged one after another. These devices play a huge role in the field of integrated signal processing. However, under the conditions of high-energy pumping and extremely weak signals, the SBS noise generated by the interaction between the pump light field and the incoherent phonons in the medium is unavoidable. How to suppress this noise has always been a difficult problem in photoacoustic coupled photonic devices. question. "High amplification and low noise achieved by a double-stage non-collinear Brillouin amplifier" published in Volume 17, Issue 13 of "Optics Express" in 2009 and "Parametric amplification of Orbital angular momentum beams based on light-acoustic interaction" proposes the use of non-collinear Brillouin amplification structure, using the different propagation directions of the amplified signal light and SBS noise in the bulk medium to spatially separate the signal and noise, so as to reduce noise and improve signal-to-noise ratio the goal of. However, this method is only applicable to bulk media. In micro-integrated photonic devices such as photoacoustic crystals and integrated silicon waveguides, the amplified signal light and SBS noise overlap each other and output in the same direction, which cannot be performed using a non-collinear structure. Spatial separation.

Contents of the invention

A brief overview of the invention is given below in order to provide a basic understanding of some aspects of the invention. It should be understood that this summary is not an exhaustive overview of the invention. It is not intended to identify key or critical parts of the invention nor to delineate the scope of the invention. Its purpose is merely to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.

In view of this, the present invention provides a mode filtering method and device for a photoacoustic coupling photonic device, so as to at least solve the problem that the SBS noise in the photoacoustic coupling photonic device cannot be removed in the prior art.

According to one aspect of the present invention, a mode filtering method for a photoacoustic coupled photonic device is provided. The mode filtering method includes: performing mode conversion on a Gaussian signal beam to obtain an OAM signal beam, wherein the Gaussian signal beam and the Gaussian signal beam are There is a Brillouin frequency shift between the pump beams; the OAM signal beam and the Gaussian pump beam are respectively input from both sides of the photoacoustic coupling photonic device, so that the Gaussian pump beam is opposite in the photoacoustic coupling photonic device. The OAM signal beam is subjected to stimulated Brillouin amplification; the mixed beam of the amplified OAM signal beam and the SBS noise beam output from the photoacoustic coupling photonic device is subjected to mode inverse conversion, so that after the mode inverse conversion, the amplified in the mixed beam The OAM signal beam becomes an amplified Gaussian signal beam, and the SBS noise beam in the mixed beam becomes an OAM-SBS noise beam; through spatial filtering, the OAM-SBS noise beam in the mixed beam is filtered to obtain the Amplified Gaussian signal beam.

Further, in the step of filtering out the OAM-SBS noise beam in the mixed beam, a pinhole spatial filter is used to filter out the OAM-SBS noise beam.

Further, the energy of the Gaussian signal beam is lower than 10 ^-4 J.

Further, the energy of the Gaussian signal beam is in the range of [10 ⁻⁸ J, 10 ⁻¹³ J].

Further, the nonlinear medium in the photoacoustic coupling photonic device is one of the following: photoacoustic crystal, integrated silicon waveguide and optical fiber.

According to another aspect of the present invention, there is also provided a mode filtering device for a photoacoustic coupled photonic device, the mode filtering device includes a first spiral phase converter, a second spiral phase converter, a first quarter-wave plate, the second quarter-wave plate, polarization beam splitter and pinhole spatial filter, wherein the topological charges of the first spiral phase converter and the second spiral phase converter are both l, and l is greater than or equal to 1 Integer; the p-polarized Gaussian signal beam is converted into an OAM signal beam with a topological charge of 1 after passing through the first helical phase converter, and the OAM signal beam is converted into right-handed circularly polarized light after passing through the first quarter-wave plate. Acoustic coupled photonic device; the p-polarized Gaussian pump beam is transmitted through the polarization beam splitter, and then transformed into left-handed circularly polarized light after passing through the second quarter-wave plate and enters the photoacoustic coupled photonic device, wherein the p-polarized Gaussian There is a Brillouin frequency shift between the type signal beam and the p-polarized Gaussian pump beam; the first mixed beam of the amplified OAM signal beam and the SBS noise beam output by the photoacoustic coupling photonic device passes through the second quarter wave After the chip, it is reflected to the second helical phase converter through the polarization beam splitter, and the second helical phase converter outputs the second mixed beam; wherein, the amplified signal beam in the second mixed beam is s-polarized and the topological charge is 0 Gaussian beam, and the SBS noise beam in the second mixed beam is an OAM beam with s-polarization and topological charge 1; after the second mixed beam passes through the pinhole spatial filter, the SBS noise beam in the second mixed beam is filtered by the pinhole The spatial filter filters out, and the amplified Gaussian signal beam in the second mixed beam is output through the pinhole spatial filter.

Further, the first helical phase converter and the second helical phase converter are any one of the following devices: a helical phase plate, a spatial light modulator, a computational holographic grating, and a q-wave plate.

Further, the energy of the p-polarized Gaussian signal beam is in the range of [10 ^-8 J, 10 ^-13 J].

Further, the nonlinear medium in the photoacoustic coupling photonic device is a solid medium, a transparent liquid or a gas medium.

Further, the nonlinear medium in the photoacoustic coupling photonic device is a photoacoustic crystal, an integrated silicon waveguide or an optical fiber.

The mode filtering method and device for photoacoustic coupling photonic devices of the present invention convert the input signal light into a high-order OAM beam, and stimulate Brillouin amplification in a nonlinear medium with the counterpropagating Gaussian pump beam Function, the mixed light of the amplified OAM signal light and the pump’s own SBS noise is restored to the original input signal light mode through OAM mode inversion, and is separated from the transformed SBS noise mode space, and the clean and noise-free light is extracted by spatial filtering. Signal amplifies light.

The mode filtering method and device of the present invention apply mode labels to optical signals and use OAM mode filtering to distinguish and extract extremely weak signal light from strong SBS noise, provide noise-free interaction for photoacoustic coupling photonic devices, and solve existing problems. There is a problem that the SBS noise in the photoacoustic coupling photonic device cannot be removed in the existing technology, and an easy-to-operate and practical filtering technology is provided for the photoacoustic coupling photonic device, which can theoretically achieve zero noise.

For strong signals, since the intensity of SBS noise is much smaller than the amplified light intensity of strong signals, SBS noise can be ignored; for weak signals (such as signals below 10 ^-4 J), especially extremely weak signals (such as signals in the range of [10 ^-8 J, 10 ^-13 J]), the intensity of its amplified light is comparable to the intensity of SBS noise, so the noise cannot be ignored. In micro-integrated photonic devices such as photoacoustic crystals and integrated silicon waveguides, the non-collinear Brillouin amplification structure used in bulk media (ie, liquid media or gas media) cannot be used, and only collinear structures can be used. Therefore, the mode filtering method and device of the present invention can realize the separation of signal and noise under the condition of collinear structure, which cannot be realized in the prior art. It should be noted that the mode filtering method and device of the present invention are not only applicable to micro-integrated photonic devices such as photoacoustic crystals and integrated silicon waveguides, but also applicable to bulk media such as CS ₂ .

These and other advantages of the present invention will be more apparent through the following detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings.

Description of drawings

The present invention can be better understood by referring to the following description given in conjunction with the accompanying drawings, wherein the same or similar reference numerals are used throughout to designate the same or similar parts. The accompanying drawings, together with the following detailed description, are incorporated in and form a part of this specification, and serve to further illustrate preferred embodiments of the invention and explain the principles and advantages of the invention. In the attached picture:

Fig. 1 is a flowchart illustrating an exemplary process of the mode filtering method for a photoacoustic coupled photonic device of the present invention;

Fig. 2 is a structural schematic diagram showing an example of a mode filtering device for a photoacoustic coupling photonic device of the present invention;

Fig. 3 is a schematic diagram showing the waveforms of pump light and signal light in preferred embodiment 1 of the present invention;

Fig. 4 is a schematic diagram showing the mixed light waveform of the amplified OAM signal light and the SBS noise light beam output by the photoacoustic coupling photonic device;

Fig. 5 shows the double-pulse envelope waveform diagram obtained after spatial filtering;

Fig. 6 shows the amplification before (c1-c4) and after (d1-d4) mode filtering when the input signal light energy is 10 ^-4 J, 10 ^-6 J, 10 ^-8 J and 10 ^-10 J respectively Schematic diagram of the signal light and SBS noise mixed light spot.

It will be appreciated by those skilled in the art that elements in the figures are illustrated for simplicity and clarity only and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of the embodiments of the present invention.

detailed description

Exemplary embodiments of the present invention will be described below with reference to the accompanying drawings. In the interest of clarity and conciseness, not all features of an actual implementation are described in this specification. It should be understood, however, that in developing any such practical embodiment, many implementation-specific decisions must be made in order to achieve the developer's specific goals, such as meeting those system and business-related constraints and Restrictions may vary from implementation to implementation. Furthermore, it should also be understood that development work, while potentially complex and time-consuming, would at least be a routine undertaking for those skilled in the art having the benefit of this disclosure.

Here, it should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only the device structure and/or processing steps closely related to the solution according to the present invention are shown in the drawings, and the Other details not relevant to the present invention are described.

An embodiment of the present invention provides a mode filtering method for a photoacoustic coupled photonic device. The mode filtering method includes: performing mode conversion on a Gaussian signal beam to obtain an OAM signal beam, wherein the Gaussian signal beam and the Gaussian pump There is a Brillouin frequency shift between the pump beams; the OAM signal beam and the Gaussian pump beam are respectively input from both sides of the photoacoustic coupling photonic device, so that the Gaussian pump beam can affect the OAM signal in the photoacoustic coupling photonic device. The beam is subjected to stimulated Brillouin amplification; the mixed beam of the amplified OAM signal beam and the SBS noise beam output from the photoacoustic coupling photonic device is subjected to mode inverse conversion, so that after the mode inverse conversion, the amplified OAM signal in the mixed beam The beam becomes an amplified Gaussian signal beam, and the SBS noise beam in the mixed beam becomes an OAM-SBS noise beam; through spatial filtering, the OAM-SBS noise beam in the mixed beam is filtered out to obtain the amplified Gaussian signal beam

An example processing flow 100 of the mode filtering method for a photoacoustic coupled photonic device of the present invention will be described below with reference to FIG. 1 .

As shown in FIG. 1 , after the processing flow 100 starts, step S110 is executed.

In step S110, a Gaussian signal beam is subjected to mode conversion to obtain an OAM signal beam, wherein there is a Brillouin frequency shift between the Gaussian signal beam and the Gaussian pump beam. Then, step S120 is executed.

For example, a Gaussian-type signal beam can be mode transformed using a spiral phase shifter such as a spiral phase plate, a spatial light modulator, a computational holographic grating, and a q-wave plate.

Among them, the OAM signal beam, as the signal beam after mode conversion, will be used for Brillouin amplification with the Gaussian pump beam. The topological charge of the OAM signal beam is l, and l can take the value of [1,10] for example Integer in .

Before the mode conversion, the energy of the input Gaussian signal beam is, for example, a signal beam with an energy lower than 10 ^-4 J, for example, a signal beam with an energy in the range of [10 ^-8 J, 10 ^-13 J].

In step S120, the OAM signal beam and the Gaussian pump beam are respectively input from both sides of the photoacoustic coupling photonic device, so that the Gaussian pump beam stimulates the OAM signal beam in the photoacoustic coupling photonic device. Abyss zooms in. Then, step S130 is executed.

Wherein, the photoacoustic coupling photonic device is, for example, one of the following: photoacoustic crystal, integrated silicon waveguide or optical fiber.

In this way, there are two kinds of nonlinear interactions satisfying phase matching conditions in the nonlinear medium of photoacoustic coupling photonic devices: one is Gaussian pump beam and OAM mode signal light (that is, OAM signal beam) with SBA (stimulated distribution Liouin amplification), the topological charge of the amplified OAM mode signal light (that is, the amplified light of the OAM signal beam, referred to as "amplified signal light") remains unchanged, and is still 1; the second is that the Gaussian pump beam and the photoacoustic coupling photonic device are not The incoherent phonons (or distributed spontaneous noise) in the linear medium interact to form the SBS noise of the pump itself, and the topological charge of the noise is zero. After the above two nonlinear effects, the output light wave is a mixture of amplified signal light with a topological charge of 1 and SBS noise with a topological charge of 0. When the energy of the input signal light is extremely weak, the amplified signal light is completely submerged in the SBS noise , cannot be distinguished.

In step S130, the mode inverse transformation is performed on the mixed light beam of the amplified light beam (that is, "amplified signal light") and the noise light beam (that is, "SBS noise") output from the photoacoustic coupling photonic device, so that after the mode inverse transformation, the mixed The amplified beam in the beam becomes a Gaussian amplified beam (that is, the topological charge is 0), and the noise beam in the mixed beam becomes an OAM noise beam (that is, the topological charge is l, which is a hollow beam with zero central intensity). Then, step S140 is executed.

For example, a spiral phase shifter such as a spiral phase plate, a spatial light modulator, a computational holographic grating, and a q-wave plate can be used to perform mode inversion on the above-mentioned mixed beam. The spiral phase shifter used for mode inversion can be used with the above The helical phase shifter used in this paper for mode shifting the Gaussian signal beam is exactly the same.

In step S140, the OAM-SBS noise beam in the mixed beam is filtered out through spatial filtering (for example, a pinhole spatial filter may be used), so as to obtain a Gaussian amplified beam in the mixed beam. Finish processing.

Orbital angular momentum (OAM) is a degree of freedom of light and matter waves, and its paraxial intrinsic Laguerre-Gaussian (LG) mode forms an infinite-dimensional Hilbert space. Phonons do not have spin angular momentum (SAM), but have OAM by forming a vortex phase. In the following, the working principle of the mode filtering method for photoacoustic coupled photonic devices is illustrated by taking the stimulated Brillouin amplification (SBA) as an example.

In the backward SBA, the strong pump light (frequency ω _p ) and the weak signal light (frequency ω _s ) that has been added with OAM tags propagate oppositely in the nonlinear medium, and the coherent Brillouin frequency is Ω=ω The idle frequency sound wave of _p -ω _s , the phase matching condition is: q(Ω)=k(ω _p )-k(ω _s ), where k(ω) and q(Ω) are the dispersion relations of light wave and sound wave respectively . The momentum conservation required by the phase matching includes SAM and OAM, and the LG mode boson particles can be generated by the vacuum state operator describe, that is, Thus, the total momentum of the SBA interaction is conserved as Can be expressed as:

Formula one:

where a _p , a _s and b _ρ are the annihilation operators of pump light, signal light and phonon respectively; s=±1 and are the spin and angle vector quantum numbers of the LG mode. In addition to SBA, pump light directly interacts with spontaneous incoherent acoustic waves to generate idler Stokes light waves, which is SBS noise similar to ASE, and the corresponding phase matching condition is {k _m }=k(ω _p )-{q _m }, where {q _m } and {k _m } are incoherent phonons and SBS noise, respectively. Considering that there is no OAM in spontaneous phonons, the total momentum conservation generated by SBS noise can be expressed as:

Formula two:

Both the photoacoustic coupling described by formula 1 and formula 2 belong to the SBS process, and the energy is transferred from the pump light to the Stokes light wave and the sound wave. The only difference is that the SBA originates from the input signal light, while the SBS noise originates from the phonon noise. From the momentum conservation relationship in Equation 1 and Equation 2, it can be seen that the OAM degree of freedom provides an interface to distinguish signal light from SBS noise. If the pump light is a Gaussian beam, expressed as |k(ω _p ); s,0〉, the amplified OAM signal light and SBS noise should be and |{k _m };-s,0〉, so that the signal light can be "demultiplexed" from the SBS noise background by mode conversion and spatial filtering.

From the above description, it can be seen that the mode filtering method for photoacoustic coupling photonic devices of the present invention transforms the input signal light into a high-order sub-orbital angular momentum beam, and the counterpropagating Gaussian pump beam is affected by the nonlinear medium. Exciting Brillouin amplification, the amplified OAM signal light and the pump’s own SBS noise mixed light are restored to the original input signal light mode through OAM mode inverse transformation, and are space-separated from the transformed SBS noise mode. After spatial filtering, the extracted Clean and noise-free signal amplification light.

The mode filtering method of the present invention can distinguish and extract extremely weak signal light from strong SBS noise by applying mode labels to optical signals and utilizing orbital angular momentum (OAM) mode filtering, providing noise-free interaction for photoacoustic coupling photonic devices, It solves the problem that the SBS noise in the photoacoustic coupling photonic device cannot be removed in the prior art, and provides a simple and practical filtering technology for the photoacoustic coupling photonic device, which can theoretically achieve zero noise.

For strong signals, since the intensity of SBS noise is much smaller than the amplified light intensity of strong signals, SBS noise can be ignored; for weak signals (such as signals below 10 ^-4 J), especially extremely weak signals (such as signals in the range of [10 ^-8 J, 10 ^-13 J]), the intensity of its amplified light is comparable to the intensity of SBS noise, so the noise cannot be ignored. In micro-integrated photonic devices such as photoacoustic crystals and integrated silicon waveguides, the non-collinear Brillouin amplification structure used in bulk media (ie, liquid media or gas media) cannot be used, and only collinear structures can be used. Therefore, the mode filtering method of the present invention can realize the separation of signal and noise under the condition of collinear structure, which cannot be realized in the prior art. It should be noted that the mode filtering method of the present invention is not only applicable to micro-integrated photonic devices such as photoacoustic crystals and integrated silicon waveguides, but also applicable to bulk media such as CS ₂ .

In addition, an embodiment of the present invention also provides a mode filtering device for a photoacoustic coupling photonic device, the mode filtering device includes a first spiral phase converter, a second spiral phase converter, a first quarter-wave plate , a second quarter-wave plate, a polarization beam splitter and a pinhole spatial filter, wherein the topological charges of the first spiral phase converter and the second spiral phase converter are both l, and l is an integer greater than or equal to 1 ; The p-polarized Gaussian signal beam is converted into an OAM signal beam with a topological charge of 1 after the first helical phase converter, and the OAM signal beam is converted into right-handed circularly polarized light after passing through the first quarter-wave plate and enters the photoacoustic Coupled photonic device; the p-polarized Gaussian pump beam is transmitted through the polarization beam splitter, and then transformed into left-handed circularly polarized light after passing through the second quarter-wave plate and enters the photoacoustic coupling photonic device, wherein the p-polarized Gaussian pump beam There is a Brillouin frequency shift between the signal beam and the p-polarized Gaussian pump beam; the first mixed beam of the amplified OAM signal beam and the SBS noise beam output by the photoacoustic coupling photonic device passes through the second quarter-wave plate Afterwards, it is reflected to the second helical phase converter through the polarization beam splitter, and the second helical phase converter outputs the second mixed beam; wherein, the amplified signal beam in the second mixed beam is Gaussian with s-polarization and a topological charge of 0 type beam, and the SBS noise beam in the second mixed beam is an OAM beam with s polarization and topological charge l; after the second mixed beam passes through the pinhole spatial filter, the noise beam in the second mixed beam is filtered by the pinhole space filter, and the amplified Gaussian signal beam in the second mixed beam is output through a pinhole spatial filter.

An example of the mode filtering device for a photoacoustic coupling photonic device of the present invention is shown below with reference to FIG. 2 . As shown in FIG. 2 , the mode filtering device 200 of the present invention includes a first spiral phase converter 210, a second spiral phase converter 220, a first quarter-wave plate 230, a second quarter-wave plate 240, Polarization beam splitter prism 250 and pinhole spatial filter 260.

The topological charges of the first spiral phase converter 210 and the second spiral phase converter 220 are both l, l is an integer greater than or equal to 1, for example, l is an integer in the range of [1, 10] such as 1, 2, 3, etc. The first helical phase converter 210 and the second helical phase converter 220 may be a helical phase plate, a spatial light modulator, a computational holographic grating, a q-wave plate, and the like.

The p-polarized Gaussian signal beam L _S 1 (equivalent to the Gaussian signal beam mentioned in the mode filtering method described above) is converted into an OAM signal beam L _S with a topological charge of 1 after the first spiral phase converter 210 2 (equivalent to the OAM signal beam mentioned in the mode filtering method described above), the OAM signal beam L _S 2 is transformed into right-handed circularly polarized light L _S 3 after passing through the first quarter-wave plate 230 and enters the photoacoustic Coupled photonic devices (as nonlinear media). Wherein, the nonlinear medium in the photoacoustic coupling photonic device is, for example, one of the following: solid media such as photoacoustic crystals and integrated silicon waveguides, optical fibers, etc., transparent liquid or gas media.

Wherein, the energy of the p-polarized Gaussian signal light beam L _S 1 is, for example, signal light lower than 10 ⁻⁴ J. In one example, the energy of L _S 1 is in the range [10 ⁻⁸ J, 10 ⁻¹³ J].

At the same time, the p-polarized Gaussian pump beam L _P 1 (equivalent to the Gaussian pump beam mentioned in the mode filtering method described above) is transmitted through the polarization beam splitter 250, and then passes through the second quarter-wave After the plate 240, it is converted into left-handed circularly polarized light L _P 2 and enters the photoacoustic coupling photonic device, wherein, there is a relationship between the p-polarized Gaussian signal beam L _S 1 and the p-polarized Gaussian pump beam L _P 1 as a nonlinear Median photoacoustic coupling to photonic devices with matched Brillouin shift.

The amplified light beam L _A 1 (equivalent to the "amplified signal light" mentioned in the mode filtering method described above) and the noise beam L _N 1 (equivalent to The first mixed light beam of the mentioned "SBS noise") passes through the second quarter-wave plate 240, is reflected to the second helical phase converter 220 by the polarization beam splitter prism 250, and is output by the second helical phase converter 220 Second mixed beam. The amplified beam L _A 2 in the second mixed beam is a Gaussian beam with s-polarization and a topological charge of 0, while the noise beam L _N 2 in the second mixed beam is an OAM beam with s-polarization and a topological charge of 1.

Among them, in the first mixed beam output by the photoacoustic coupling photonic device: the topological charge of the amplified beam L _A 1 is 1, and the polarization state is circular polarization; while the topological charge of the noise beam L _N 1 is 0, and the polarization state is circular polarization . The amplified light beam L _A1 becomes s-polarized OAM signal light after passing through the second quarter-wave plate 240, and then reflected by the polarization beam splitter 250, and then becomes s-polarized and topologically charged after passing through the second spiral phase converter 220. is a Gaussian beam of 0 (ie, the amplified beam L _A 2 ). In addition, after the noise beam L _N 1 passes through the second quarter-wave plate 240, the s-polarized SBS noise is reflected by the polarization beam splitter 250, and then becomes s-polarized after passing through the second spiral phase converter 220, and the topological charge is The OAM beam of l (ie the noise beam L _N 2).

In this way, after the second mixed beam passes through the pinhole spatial filter 260, the noise beam L _N 2 in the second mixed beam cannot pass through the pinhole of the pinhole spatial filter 260 because it is a hollow beam, so it is filtered by the pinhole space filter 260; and the amplified light beam L _A 2 in the second mixed light beam can just pass through the pinhole spatial filter 260 and be output.

From the above description, it can be seen that the mode filter device for photoacoustic coupling photonic devices of the present invention converts the input signal light into a high-order sub-orbital angular momentum beam, and the counter-propagating Gaussian pump beam is affected by the nonlinear medium. Exciting Brillouin amplification, the amplified OAM signal light and the pump’s own SBS noise mixed light are restored to the original input signal light mode through OAM mode inverse transformation, and are space-separated from the transformed SBS noise mode. After spatial filtering, the extracted Clean and noise-free signal amplification light.

The mode filtering device of the present invention can distinguish and extract extremely weak signal light from strong SBS noise by applying mode labels to optical signals and using orbital angular momentum (OAM) mode filtering, and provide noise-free interaction for photoacoustic coupling photonic devices, It solves the problem that the SBS noise in the photoacoustic coupling photonic device cannot be removed in the prior art, and provides a simple and practical filtering technology for the photoacoustic coupling photonic device, which can theoretically achieve zero noise.

For strong signals, since the intensity of SBS noise is much smaller than the amplified light intensity of strong signals, SBS noise can be ignored; for weak signals (such as signals below 10 ^-4 J), especially extremely weak signals (such as signals in the range of [10 ^-8 J, 10 ^-13 J]), the intensity of its amplified light is comparable to the intensity of SBS noise, so the noise cannot be ignored. In micro-integrated photonic devices such as photoacoustic crystals and integrated silicon waveguides, the non-collinear Brillouin amplification structure used in bulk media (ie, liquid media or gas media) cannot be used, and only collinear structures can be used. Therefore, the mode filter device of the present invention can realize the separation of signal and noise under the condition of collinear structure, which cannot be realized in the prior art. It should be noted that the mode filtering device of the present invention is not only applicable to micro-integrated photonic devices such as photoacoustic crystals and integrated silicon waveguides, but also applicable to bulk media such as CS ₂ .

Preferred Embodiment 1

In this preferred embodiment, a solid ND:YAG passively Q-switched laser is used to output a single longitudinal mode near-Gaussian pulse with a wavelength of 532nm and a pulse width of 3.5ns after frequency doubling as the pump light (as shown in Figure 3), with a distribution The double-pulse 1.5ns Gaussian beam with Liouin Stokes frequency shift is used as the signal light (as shown in Figure 3), the nonlinear medium uses CS ₂ , and the spiral phase plate is used as the spiral phase converter to realize mode conversion and mode inverse conversion. Charge 1=2.

Fig. 4 is the waveform of the mixed light (i.e. the first mixed light beam) of the amplified light beam L _A 1 and the noise light beam L _N 1 output by the photoacoustic coupling photonic device. It can be seen that the double-pulse signal light (i.e. the amplified light beam L _A 1) has been Submerged in the Gaussian pulse envelope of the SBS noise (i.e. the noise beam L _N 1).

After pinhole spatial filtering, the amplified beam L _A 2 and the noise beam L _N 2 in the second mixed beam are separated, and the double pulse envelope can be clearly distinguished, as shown in FIG. 5 .

Figure 6 shows the amplified signals before mode filtering (c1-c4) and after mode filtering (d1-d4) when the input signal light energy is 10 ^-4 J, 10 ^-6 J, 10 ^-8 J and 10 ^-10 J respectively Mixed light spot with light and SBS noise. It can be seen that with the decrease of signal light energy, the amplified signal light is gradually difficult to distinguish, submerged in SBS noise, and presents a circular Gaussian spot after filtering, which is space-separated from noise.

While the invention has been described in terms of a limited number of embodiments, it will be apparent to a person skilled in the art having the benefit of the above description that other embodiments are conceivable within the scope of the invention thus described. In addition, it should be noted that the language used in the specification has been chosen primarily for the purpose of readability and instruction rather than to explain or define the inventive subject matter. Accordingly, many modifications and alterations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the appended claims. With respect to the scope of the present invention, the disclosure of the present invention is intended to be illustrative rather than restrictive, and the scope of the present invention is defined by the appended claims.

Claims (10)

1. the mode filter method for photoacoustic coupling photonic device, it is characterized in that, described mode filter method comprises: Performing mode conversion on a Gaussian signal beam to obtain an OAM signal beam, wherein there is a Brillouin frequency shift between the Gaussian signal beam and the Gaussian pump beam; Let the OAM signal beam and the Gaussian pumping beam be input from both sides of the photoacoustic coupling photonic device, so that the Gaussian pumping beam is opposite to the OAM signal beam in the photoacoustic coupling photonic device Perform stimulated Brillouin amplification; performing mode inverse conversion on the mixed beam of the amplified OAM signal beam and the SBS noise beam output from the photoacoustic coupling photonic device, so that after the mode inverse conversion, the amplified OAM signal beam in the mixed beam becomes an amplified Gaussian signal beam, and the SBS noise beam in the mixed beam becomes an OAM-SBS noise beam; The OAM-SBS noise beam in the mixed beam is filtered out by spatial filtering, so as to obtain an amplified Gaussian signal beam in the mixed beam. 2. The mode filtering method according to claim 1, wherein, in the step of filtering out the OAM-SBS noise beam in the mixed light beam, a pinhole spatial filter is used to filter out the OAM-SBS noise beam. SBS noise beam. 3. The mode filtering method according to claim 1, characterized in that the energy of the Gaussian signal beam is lower than 10 ^-4 J. 4. The mode filtering method according to claim 4, wherein the energy of the Gaussian signal beam is in the range of [10 ⁻⁸ J, 10 ⁻¹³ J]. 5. The mode filtering method according to claim 1, wherein the nonlinear medium in the photoacoustic coupling photonic device is one of the following: photoacoustic crystals, integrated silicon waveguides, and optical fibers. 6. The mode filtering device for photoacoustic coupling photonic device, it is characterized in that, described mode filtering device comprises the first spiral phase converter, the second spiral phase converter, the first quarter-wave plate, the second four A quarter-wave plate, a polarization beam splitter and a pinhole spatial filter, wherein the topological charges of the first spiral phase converter and the second spiral phase converter are both l, and l is an integer greater than or equal to 1 ; The p-polarized Gaussian signal beam is converted into an OAM signal beam with a topological charge of 1 after passing through the first spiral phase converter, and the OAM signal beam is converted into a right-handed circle after passing through the first quarter-wave plate Polarized light enters the photoacoustic coupling photonic device; After the p-polarized Gaussian pump beam is transmitted through the polarization beam splitter, it is converted into left-handed circularly polarized light after passing through the second quarter-wave plate and enters the photoacoustic coupling photonic device, wherein the p There is a Brillouin frequency shift between the Gaussian signal beam in the polarization state and the Gaussian pump beam in the p-polarization state; The first mixed beam of the amplified OAM signal beam and the SBS noise beam output by the photoacoustic coupling photonic device passes through the second quarter-wave plate, and is reflected to the second helical phase by the polarization beam splitter prism converter, the second spiral phase converter outputs a second mixed beam; wherein, the amplified signal beam in the second mixed beam is a Gaussian beam with s-polarization and a topological charge of 0, and the second The SBS noise beam in the mixed beam is an OAM beam with s-polarization and a topological charge of l; After the second mixed beam passes through the pinhole spatial filter, the SBS noise beam in the second mixed beam is filtered by the pinhole spatial filter, and the amplified Gaussian noise beam in the second mixed beam The type signal beam is output through the pinhole spatial filter. 7. The mode filter device according to claim 6, wherein the first spiral phase converter and the second spiral phase converter are any one of the following devices: Spiral phase plate, spatial light modulator, computational holographic grating, and q-wave plate. 8 . The mode filtering device according to claim 6 , wherein the energy of the p-polarized Gaussian signal beam is in the range of [10 ⁻⁸ J, 10 ⁻¹³ J]. 9. The mode filter device according to claim 6, wherein the nonlinear medium in the photoacoustic coupling photonic device is a solid medium, a transparent liquid or a gas medium. 10. The mode filter device according to claim 9, wherein the nonlinear medium in the photoacoustic coupling photonic device is a photoacoustic crystal, an integrated silicon waveguide or an optical fiber.