An optical method for dynamically controlling the propagation direction of spin waves

Abstract

The present invention relates to the field of spintronic technologies, and discloses an optical method for dynamically regulating the propagation direction of spin waves. Based on the excitation of spin waves by an ultrashort laser pulse, a liquid crystal spatial light modulator is used to dynamically shape the excitation light field, modulate the amplitude and phase of the excitation light field, obtain an arbitrarily controllable pulsed excitation light field distribution on the surface of a magnetic medium, and further generate a desired instantaneous spin wave source field, thereby realizing the dynamic regulation of the propagation direction of spin waves. This method can be controlled by a computer and has the advantages of flexibility, real-time performance, programmability, etc.

Description

Technical Field

[0001] The present invention relates to the field of spintronic technologies, and particularly to an optical method for dynamically regulating the propagation direction of spin waves. Background Art

[0002] As the feature size of semiconductor manufacturing processes continues to decrease, the thermal effect during the carrier transport process has become a direct constraint on the performance improvement of semiconductor integrated circuits. Problems such as energy consumption, heat dissipation, and quantum effects limit the further development of traditional semiconductor technologies. Spintronic technologies that utilize the spin properties of electrons can overcome the above problems and are one of the development directions of future information technologies. As an important branch of them, magnon spintronic technologies aim to use spin waves as information carriers to achieve high-speed information transmission and computing processing, and are a hot topic in frontier research.

[0003] Regarding the propagation properties of spin waves, there is currently a lack of flexible and effective regulation means. Once the excitation conditions (including antennas, electrodes, laser sources, magnetic fields, etc.) are determined, it is difficult to directly change the propagation properties of spin waves. The regulation of spin wave propagation is associated with its excitation method. For the currently widely used spin wave excitation methods based on microwave fields or spin transfer torques, once the antenna or electrode is fabricated and the magnetic field direction is fixed, it is difficult to directly change the propagation properties of spin waves. Another type of excitation method is to use ultrashort pulsed lasers to excite spin waves, including methods based on optically induced equivalent anisotropic field pulses (also known as thermal excitation) and transient inverse Faraday giant magnetic pulses (also known as non-thermal excitation). Optical excitation is a non-contact local excitation, and it is easy to obtain a point excitation source with a micron or even sub-micron scale. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides an optical method for dynamically regulating the propagation direction of spin waves. This method is based on the spin wave excitation method using ultrashort laser pulses, and uses a liquid crystal spatial light modulator to dynamically shape the excitation light field. It can be controlled by a computer to obtain an arbitrarily controllable pulsed excitation light field distribution on the surface of a magnetic medium, and then generate the required instantaneous spin wave source field to achieve real-time dynamic regulation of the propagation direction of spin waves.

[0005] To achieve the above dynamic regulation of the propagation direction of spin waves, the present invention provides the following technical solution: An optical method for dynamically regulating the propagation direction of spin waves, comprising the following steps:

[0006] S1. Use ultrashort laser pulses to excite spin waves, and use a liquid crystal spatial light modulator to dynamically shape the pulsed excitation light field;

[0007] S2. Use a liquid crystal spatial light modulator to modulate the amplitude and phase of the excitation light field, and be controlled by a computer according to the target light field distribution to obtain an arbitrarily controllable pulsed excitation light field distribution on the surface of a magnetic medium;

[0008] S3. Generate the required instantaneous spin-wave source field by exciting the optical field with modulation pulses, and then control the propagation direction of the spin wave.

[0009] Preferably, in step S2, the pulse-excited optical field output by modulation can be measured and analyzed, and the phase distribution on the liquid crystal spatial light modulator can be adjusted through calculation and feedback, so as to obtain the required target pulse-excited optical field.

[0010] Preferably, in step S2, basic phase retrieval algorithms can be used for pre-calculation. For example, using the GS algorithm, from the known incident pulse optical field distribution (usually a Gaussian optical field) and the pre-given pulse-excited optical field distribution, through multiple iterations of Fourier transform and its inverse transform, the output optical field tends to be consistent with the pre-given target optical field, that is, the required phase distribution on the liquid crystal spatial light modulator is obtained. Store this distribution result in the computer for calling in actual applications.

[0011] Preferably, in step S2, deep learning algorithms can be used. Taking the phase distribution on the liquid crystal spatial light modulator as the input quantity and the measured output optical field as the output quantity, an optimization model can be obtained through sample training, so as to quickly calculate the phase distribution on the liquid crystal spatial light modulator for any target optical field in actual applications. The actual time-space distribution of spin wave propagation can also be measured to correct the target output optical field and even the phase distribution on the liquid crystal spatial light modulator.

[0012] Preferably, in step S3, the modulation pulse-excited optical field can generate the required instantaneous spin-wave source field for both thermal excitation and non-thermal excitation methods, and can be used to control the surface magnetostatic spin wave and the bulk magnetostatic spin wave mode.

[0013] Preferably, in step S3, the distribution h(k) of the spin-wave source field (for the thermal excitation method, it is the optically induced equivalent anisotropic magnetic field pulse, and for the non-thermal excitation method, it is the giant magnetic field pulse generated by the inverse Faraday effect) in the wave vector space is proportional to the Fourier transform of the excitation optical field intensity distribution |E(r)| 2 as Figure 1 shown. Taking the pulse-excited optical field with an elliptical Gaussian distribution as an example, correspondingly h(k) also shows an elliptical Gaussian distribution. The wave numbers of the spin waves excited thereby will also have a similar two-dimensional distribution. If the major axis of the ellipse in the k space is much larger than the minor axis length, the spin wave will be mainly restricted to propagate along the major axis direction, that is, the spin-wave energy flow mainly transmits along the y-axis direction. Therefore, by changing the anisotropy of the pulse-excited optical field distribution, the propagation direction of the spin wave can be controlled.

[0014] Preferably, in step S3, as Figure 2As shown in the figure, the pulsed excitation light field is modulated into a linear light field and a dot array light field by a liquid crystal spatial light modulator. The linear light field corresponds to a strongly anisotropic h(k), so that better spin wave propagation directivity can be obtained. The dot array light field corresponds to multiple spin wave source fields, and good propagation directivity is obtained through the spin wave interference effect. In addition, if the pulsed excitation light field is modulated into a "petal-shaped" distribution, it can assist in realizing the control of multi-channel transmission in specific situations.

[0015] The above optical method for dynamically regulating the propagation direction of spin waves, the overall method process is as Figure 3 shown.

[0016] Compared with the prior art, the present invention provides an optical method for dynamically regulating the propagation direction of spin waves, which has the following beneficial effects:

[0017] 1. The optical method for dynamically regulating the propagation direction of spin waves can be controlled by a computer to obtain an arbitrarily controllable pulsed excitation light field distribution on the surface of the magnetic medium, so that flexible, real-time, and programmable regulation of the spin wave propagation direction can be realized.

[0018] 2. This method is applicable to thermal excitation or non-thermal excitation methods, and can be used for the regulation of various propagation modes such as magnetostatic surface spin waves and bulk magnetostatic spin waves. Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the relationship between the excitation light field and the spin wave source field of the present invention;

[0020] Figure 2 It is a schematic design diagram of the modulated excitation light field of the present invention;

[0021] Figure 3 It is a schematic diagram of the method process of the present invention;

[0022] Figure 4 It is a schematic diagram of the optical path system principle of a preferred embodiment of the present invention. Detailed Embodiments

[0023] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0024] In a preferred embodiment, the principle of the optical path system of the present invention is as Figure 4As shown, the system functions include the optical excitation, regulation, and measurement of spin waves. A femtosecond pulsed laser is used as the light source. The linearly polarized femtosecond laser beam is split by a beam splitter into a stronger excitation light and a weaker probe light. The optical delay line can control the optical path difference between the excitation light pulse and the probe light pulse to achieve time-resolved measurement. After passing through a half-wave plate, the excitation light is modulated by a reflective liquid crystal spatial light modulator for its optical field. The role of the quarter-wave plate is to convert the excitation optical field into a circularly polarized pulse for the case of non-thermal excitation. The modulated pulsed excitation optical field is focused and incident on the sample to generate the required instantaneous spin wave source field, thereby exciting spin waves and regulating the propagation direction of spin waves.

[0025] A small part of the modulated excitation light is separated by the beam splitter and enters the CMOS camera to measure the modulated optical field. As described above, the GS algorithm can be used. From the known incident optical field distribution and the pre-given optical field distribution (such as Figure 2 the designed optical field shown), through multiple iterations of Fourier transform and its inverse transform, the modulated output optical field is made to tend to be consistent with the pre-given target optical field. And the required phase distribution result on the liquid crystal spatial light modulator can be stored in the computer for quick call in practical applications. The deep learning algorithm can also be used. Taking the phase distribution on the liquid crystal spatial light modulator as the input quantity and the measured pulsed output optical field as the output quantity, an optimized model is obtained through sample training, so as to quickly calculate the phase distribution on the liquid crystal spatial light modulator for any target optical field in practical applications. The actual time-space distribution of spin wave propagation can also be measured to correct the target output optical field and even the phase distribution on the liquid crystal spatial light modulator. The probe light passes through several fixed mirrors and a precision electronically controlled rotating mirror and then is incident on the sample. After being reflected by the sample, it enters the magneto-optical Kerr detection system. The spin polarization information of the detection point is obtained by measuring the magneto-optical Kerr effect. The role of the electronically controlled rotating mirror is to enable the probe light to achieve high-precision two-dimensional angular scanning to achieve spatial-resolved measurement on the sample surface. Here, the electronically controlled rotating mirror can also be replaced by other modules or devices that can achieve spatial-resolved detection on the sample surface. The role of the magneto-optical Kerr detection system is to achieve magneto-optical polarization rotation angle or dichroic measurement. The typical composition includes but is not limited to an optical balance bridge and a phase-locked detector. Through time-space resolved magneto-optical measurement, the time-space distribution information of spin wave propagation can be obtained to verify the regulation effect, and then the target output optical field and even the phase distribution on the liquid crystal spatial light modulator can be finely adjusted and corrected.

[0026] The propagation direction of spin waves is regulated by utilizing the anisotropy of the amplitude distribution of the pulsed excitation light field. The pulsed excitation light field is modulated into a linear light field and a point array light field by a liquid crystal spatial light modulator. The linear light field corresponds to the strongly anisotropic h(k), thereby enabling better spin wave propagation directivity. The point array light field corresponds to multiple spin wave source fields, and good propagation directivity is obtained through the spin wave interference effect. In addition, if the pulsed excitation light field is modulated into a "lobed" distribution, it can assist in realizing the control of multiplex transmission in specific scenarios.

[0027] The above-mentioned optical delay line, liquid crystal spatial light modulator, CMOS camera, precision electronically controlled rotating mirror, and magneto-optical Kerr detection system are all connected to a computer for unified control. By changing the phase distribution of the liquid crystal spatial light modulator, the pulsed excitation light field can be dynamically shaped and modulated, and further, the dynamic regulation of the propagation direction of the optically excited spin waves can be achieved. To effectively excite spin waves, an appropriate external magnetic field is generally applied to the magnetic thin film sample. The excited spin wave modes are related to factors such as the magnetic structure of the sample, the magnitude and direction of the external field, Figure 4 The direction of the medium magnetic field is only for example.

[0028] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An optical method for dynamically regulating the propagation direction of spin waves, characterized in that, the method uses the spin wave excitation method of ultra - short laser pulses, and a liquid crystal spatial light modulator is used to dynamically shape the excitation light field, so as to realize real - time dynamic regulation of the propagation direction of spin waves on the magnetic medium. The method includes the following steps: S1. Use ultra - short laser pulses to excite spin waves, and use a liquid crystal spatial light modulator to dynamically shape the pulse excitation light field; S2. The liquid crystal spatial light modulator modulates the amplitude and phase of the excitation light field, which is controlled by a computer according to the target light field distribution, so as to obtain an arbitrarily controllable excitation light field distribution on the magnetic medium surface; S3. Generate the required instantaneous spin wave source field from the modulated pulse excitation light field, and then regulate the propagation direction of the spin wave.

2. An optical method for dynamically regulating the propagation direction of spin waves according to claim 1, characterized in that, in step S2, the pulse excitation light field output by modulation is measured and analyzed, and the phase distribution on the liquid crystal spatial light modulator is adjusted by calculation feedback, so as to obtain the required target pulse excitation light field.

3. An optical method for dynamically regulating the propagation direction of spin waves according to claim 2, characterized in that, step S2 further includes pre - calculating using a basic phase retrieval algorithm, and making the output pulse excitation light field tend to be consistent with the pre - given target light field distribution through repeated iteration, that is, obtaining the required phase distribution on the liquid crystal spatial light modulator, and storing this distribution result in the computer for calling during use.

4. An optical method for dynamically regulating the propagation direction of spin waves according to claim 2, characterized in that , step S2 further includes using a deep learning algorithm, taking the phase distribution on the liquid crystal spatial light modulator as the input quantity and the measured pulse excitation light field as the output quantity, obtaining an optimized model through sample training, so as to quickly calculate the phase distribution on the liquid crystal spatial light modulator for any target light field, and realize flexible and rapid modulation of the pulse excitation light field.

5. An optical method for dynamically regulating the propagation direction of spin waves according to claim 1, characterized in that, in step S3, the modulated pulse excitation light field can generate the required instantaneous spin wave source field for both thermal excitation and non - thermal excitation methods, and can be used for the regulation of magnetostatic surface spin waves and bulk magnetostatic spin wave modes.

6. An optical method for dynamically regulating the propagation direction of spin waves according to claim 1, characterized in that, in step S3, the excitation light field is modulated into a linear light field and a dot - array light field by a liquid crystal spatial light modulator to excite the corresponding spin wave source field, and good spin wave propagation directivity is regulated and obtained. The excitation light field is modulated into a lobed light field by a liquid crystal spatial light modulator to assist in realizing the control of multiplex transmission.

7. An optical method for dynamically regulating the propagation direction of spin waves according to claim 1, characterized in that, in step S3, by measuring the actual time - space distribution of the spin wave propagation, the target light field distribution and the phase distribution on the liquid crystal spatial light modulator are corrected by feedback.

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