Tunable all-optical isolator based on space self-phase modulation effect

Abstract

The invention discloses a tunable all-optical isolator based on a space self-phase modulation effect. The tunable all-optical isolator sequentially comprises a laser, a beam splitter, a reflector I, an attenuator, a focusing lens I, an adjustable optical power attenuator, a nonlinear sample A, a nonlinear sample B, a focusing lens II, an optical detector and a reflector II from left to right. An optical isolator designed based on the spatial self-phase modulation effect often adopts two materials with different nonlinear optical thresholds, and whether the self-diffraction effect can be excited or not is directly influenced by the sequence of light beams passing through the combined materials. According to a traditional optical isolator designed based on the spatial self-phase modulation effect, the self-diffraction phenomenon can only be observed in the forward direction, namely, a signal light beam sequentially passes through two materials with low nonlinear optical threshold values and high nonlinear optical threshold values and cannot be observed in the reverse direction, and the function is relatively fixed. According to the invention, on the basis of an original isolator, a beam of control light which is in opposite paraxial propagation with the signal light is introduced, so that the self-diffraction phenomenon can be controllably adjusted when the signal light passes through a material in the reverse direction, and the functions of the isolator are enriched.

Description

Technical Field

[0001] The invention relates to an all-optical device based on nonlinear optical effect, belonging to the technical field of nonlinear optics. Background Art

[0002] In recent years, the spatial self-phase modulation effect has been widely used in the characterization of the nonlinear refractive index and nonlinear polarizability coefficients of low-dimensional nanomaterials [Y.Liao, C.Song, Y.Xiang, and X.Dai, "Recent advances in spatial self-phase modulation with 2D materials and its applications," Ann.Phys.(Berlin), 532(12), 2000322(2020)]. When using the spatial self-phase modulation effect to characterize the nonlinear optical coefficients of a material, it is only necessary to count the number of self-diffraction rings excited in the material under different light intensities. This method is simple to operate, requires simple equipment, and the phenomenon is intuitive and obvious, so it is favored by many researchers. In addition, all-optical devices designed based on the spatial self-phase modulation effect, such as optical switches [Y.Shan, Z.Li, B.Ruan, J.Zhu, Y.Xiang and X.Dai, "Two-dimensional Bi2S3-based all-optical photonic devices with strong nonlinearitydue to spatial self-phase modulation," Nanophotonics 8(12), 2225-2234(2019)], optical logic gates [L.Wu, Y.Zhang, X.Yuan, F.Zhang, W.Huang, D.Ma, J.Zhao, Y.Wang, Y.Ge, H.Huang, N.Xu, J.Kang, Y.Xiang, Y.Zhang, J.Li, H.Zhang, "1D@0D hybrid dimensional heterojunction-based photonics logical gate and isolator,”Appl.Mater.Today19,100589(2020)] and all-optical diodes [Y.Pan,C.Wang,Z.Lyu,and T.Chen,“Nonlinearity-induced asymmetric diffraction in a hybrid A / B structure with two azo-containing materials,”Appl.Phys.Lett.118,011108(2021)] have also been proposed.

[0003] All-optical diodes designed based on the spatial self-phase modulation effect are usually realized with the help of two materials with different nonlinear optical properties. Generally, the two selected materials have optical nonlinear thresholds and light absorption characteristics that differ greatly. When the two materials are arranged in the optical path, if the focused light beam passes through the material with low nonlinear optical threshold and small light absorption in turn, and then passes through the material with high nonlinear optical threshold and strong light absorption, then the self-diffraction ring phenomenon can generally be observed at the output end, and the propagation direction of the light beam through the material is called the forward direction; conversely, if the light beam first passes through the material with high nonlinear optical threshold and strong light absorption, and then passes through the material with low nonlinear optical threshold, then the self-diffraction ring phenomenon cannot be observed, and the propagation direction of the light beam is called the reverse direction. This self-diffraction ring phenomenon that can be observed in one direction is quite similar to the function of the diode in the circuit system, so this device is also called an all-optical diode. The reported all-optical diode devices have basically similar structures, and the optical isolation function they realize is also relatively simple. Improving the structure of all-optical devices and realizing richer optical nonlinear regulation functions are of great significance to the future development of all-optical devices. Summary of the invention

[0004] Technical issues:

[0005] In order to solve the above problems, the present invention proposes a tunable all-optical isolator based on the spatial self-phase modulation effect. Based on the spatial self-phase modulation effect and optical control technology, the present invention firstly optically characterizes the nonlinear optical material and obtains the third-order nonlinear polarizability of the material; secondly, through the optical control technology, the control light beam controls the signal light. When the signal light propagates in the reverse direction through the nonlinear sample, the control light beam propagating in the opposite direction can regulate the self-diffraction phenomenon in the signal light, thereby realizing the tunable operation of the optical isolation function. With the help of optical control technology, the present invention greatly improves the functional diversity of all-optical devices, which has important reference significance for the design and development of all-optical devices in the future.

[0006] Technical solution:

[0007] In order to realize the above functions, the technical solution adopted by the present invention is as follows: a tunable all-optical isolator based on the spatial self-phase modulation effect, wherein the device is composed of a laser, a beam splitter, a reflector I, an attenuator, a focusing lens I, an adjustable optical power attenuator, a nonlinear sample A, a nonlinear sample B, a focusing lens II, a light detector and a reflector II from left to right. The lateral light intensity distribution of the laser output beam used should be a fundamental mode Gaussian beam or a near-Gaussian beam, and its output wavelength and light intensity conditions should satisfy the conditions for stimulating the spatial self-phase modulation effect of nonlinear materials. The nonlinear optical material used is a two-dimensional material dispersion liquid, which has obvious spatial self-diffraction phenomenon under the irradiation of the light source used, and the minimum light power threshold corresponding to the spatial self-phase modulation effect stimulated by different materials is significantly different. The device is simple in device, clear in theory, and controllable in function, which is significantly improved compared with existing devices.

[0008] The exemplary light source selected in the present invention (hereinafter the same) is an infrared continuous light laser with a wavelength of 975 nm.

[0009] The beam splitter selected in the present invention is a beam splitter with a transmission-reflection light intensity ratio of 1:1.

[0010] The reflector I and reflector II selected in the present invention are silver-plated reflectors, which only change the propagation direction of the light beam but do not change the lateral distribution of the light intensity.

[0011] The attenuator and the adjustable optical power attenuator selected in the present invention are both neutral density attenuation sheets, wherein the attenuation ratio of the adjustable optical power attenuator is adjustable.

[0012] The focusing lens I and the focusing lens II selected in the present invention are both positive lenses with a focal length of 150 mm, and are used for focusing the signal light beam and the control light beam respectively.

[0013] The nonlinear samples selected in the present invention are dispersions of MXene nanosheet materials made in different solvents, wherein the dispersion made in PC solvent has a low nonlinear optical threshold, recorded as material B, and the dispersion made in water solvent has a high nonlinear optical threshold, recorded as material A.

[0014] The optical detector selected by the present invention is a light screen or a beam quality analyzer, which is used to detect the lateral light intensity distribution of the signal light after passing through the sample.

[0015] The present invention proposes a tunable all-optical isolator based on the spatial self-phase modulation effect, which realizes the function that the self-diffraction phenomenon can be observed when the signal light beam propagates in the forward direction, and the self-diffraction phenomenon can be tuned when it propagates in the reverse direction. The specific operation method is as follows:

[0016] Step 1: Press Figure 1Build an optical path system, use a light screen to block and control the light in the reflected light path of the beam splitter, place different nonlinear materials separately near the focus of focusing lens I, change the optical power output by the laser, count the number of diffraction rings excited in the material under different optical powers, complete the third-order polarizability characterization of different materials, and obtain the third-order polarizability coefficient of the material.

[0017] Step 2: Based on the characterization results of step 1, place the combined material at the focal plane of focusing lens I, where material B with a low nonlinear threshold is in front and material A with a high nonlinear threshold is in the back. The signal light propagates in the forward direction, and the intensity distribution of the signal light on the photodetector is observed and recorded.

[0018] Step 3: Exchange the order of materials A and B, and observe and record the intensity distribution of the signal light on the light detector when the signal light propagates through the sample in the reverse direction.

[0019] Step 4: Remove the light shield in the control light, and observe and record the intensity distribution of the signal light on the light detector.

[0020] Step 5: Turn the adjustable optical power attenuator to increase the intensity of the control light and observe the changes in the intensity distribution of the signal light on the optical detector.

[0021] To optimize the light isolation effect, we tested and compared the nonlinear polarizability of dispersions of MXene nanosheets in various solvents, such as Figure 2 As shown, it is found that the dispersion in water solvent has the smallest nonlinear polarizability and the dispersion in PC solvent has the largest nonlinear polarizability. Therefore, we selected these two solvents as the research objects to design a controllable optical isolator. According to the above steps, the third-order nonlinear polarizabilities are 0.23×10 -5 esu(MXene / H 2 O) and 1.67×10 -5 esu(MXene / PC).

[0022] To explain the different optical performances of MXene nanosheets in different solvents, we tested the optical absorption coefficients of different solvent dispersions at 975 nm, such as Figure 3 The solid line in the figure is the double regression curve fitted according to the measured data. Figure 3The square data points in the middle are the third-order nonlinear coefficients of MXene nanosheets in different solvents, and the dotted lines are the corresponding double regression fitting curves. It is well known that the self-diffraction ringing phenomenon is caused by the photo-induced reorientation effect [Y.Wu, Q.Wu, F.Sun, C.Cheng, S.Meng, and J.Zhao, "Emergence of electron coherence and two-color all-optical switching in MoS2 based on spatial self-phase modulation," Proc.Natl.Acad.Sci.USA112(38), 11800-11805(2015)]. In the ringing process, the existence of Brownian motion will hinder the reorientation process of the material, and the Brownian motion will increase with the increase of local light absorption. In other words, the process of self-diffraction ringing is a competition process between the photo-induced reorientation force and the Brownian force. Under low light intensity conditions, Brownian motion is dominant and no self-diffraction ringing phenomenon is observed; as the irradiation light intensity increases, the photo-induced reorientation effect becomes dominant and the diffraction ring gradually forms. For the same nanosheet material, stronger solvent background absorption will promote the enhancement of Brownian motion, thereby suppressing the photoinduced reorientation effect. Therefore, a dispersion with strong absorption will instead excite a smaller third-order polarizability, and the two are inversely correlated, such as Figure 3 In addition, we call the light intensity corresponding to the formation of the first diffraction ring the nonlinear optical threshold of the material. The nonlinear optical thresholds of 0.01 mg / mL MXene nanosheets in water solvent and PC solvent are 6.63 W / cm 2 (MXene / H 2 O) and 0.97W / cm 2 (MXene / PC). Based on the differences in nonlinear thresholds in different solvents, we designed a system composed of MXene / PC and MXene / H 2 Controllable optical isolator made of O dispersion.

[0023] We arranged these two dispersions in the optical path. Within a certain optical power range, when the signal light propagates through the mixed sample in the forward direction, it first passes through the MXene / PC dispersion and then passes through the MXene / H 2 O dispersion, the self-diffraction ring can be observed normally at the signal light output end; otherwise, the self-diffraction ring cannot be observed, realizing the function of light isolation. In addition, in order to optimize the effect of the optical isolator, we increased the concentration of MXene in the water solvent. After multiple tests and comparisons, the concentrations of MXene samples in PC solvent and water solvent were finally selected to be 0.01mg / mL and 0.05mg / mL, respectively.

[0024] Beneficial effects:

[0025] Compared with the existing optical isolation solution, we have improved the original isolator optical path, such as Figure 1 As shown. When the signal light passes through the sample in the reverse direction, the self-diffraction effect cannot be observed at the output end of the signal light. We introduce a beam of control light in the opposite direction of the signal light transmission, and the optical power of the control light can be continuously adjusted. Through diffraction elements, such as focusing lenses, reflectors, etc., the signal light and the control light are made confocal in the sample. When observing the output light distribution of the reverse-propagating signal light, adjusting the optical power of the control light can make it possible to observe the self-diffraction pattern of the signal light that could not be observed originally. And the number of self-diffraction rings is controlled by the control light. In theory, the presence and intensity of the self-diffraction signal of the signal light (that is, the number of diffraction rings) can be arbitrarily changed. The device realizes the forward observable and reverse tunable functions of the self-diffraction signal. On the basis of completely reproducing the traditional optical isolator designed based on the spatial self-phase modulation effect, the device adds the tunable function of the reverse self-diffraction signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A diagram of a tunable all-optical isolator device based on spatial self-phase modulation effect provided by the present invention,

[0027] Figure 2 The nonlinear polarizability of the dispersion of MXene nanosheets in various solvents, from low to high solvents are water, alcohol, NMP, DMSO and PC.

[0028] Figure 3 The light absorption coefficient and nonlinear polarizability of MXene dispersions in different solvents. The circular data points and solid lines correspond to light absorption, and the square data points and dotted lines correspond to nonlinear polarization.

[0029] Figure 4 is the outgoing light intensity distribution when the signal light propagates in the forward direction through the combined sample,

[0030] Figure 5 is the intensity distribution of the outgoing light when the signal light propagates in the reverse direction through the combined sample,

[0031] Figure 6 To control the growth curve of the number of self-diffraction rings in the signal light when the light is enhanced.

[0032] Among them: 1-laser, 2-beam splitter, 3-reflector I, 4-attenuator, 5-focusing lens I, 6-adjustable optical power attenuator, 7-nonlinear sample A, 8-nonlinear sample B, 9-focusing lens II, 10-photodetector and 11-reflector II. DETAILED DESCRIPTION

[0033] The following is a detailed description of the results of optically characterizing MXene nanosheet materials, designing optical isolation, and increasing adjustable functions using the spatial self-phase modulation effect, in conjunction with the accompanying drawings and specific implementation methods.

[0034] Example 1: See Figure 1 , a tunable all-optical isolator based on the spatial self-phase modulation effect, the device is composed of a laser, a beam splitter, a reflector I, an attenuator, a focusing lens I, an adjustable optical power attenuator, a nonlinear sample A, a nonlinear sample B, a focusing lens II, a light detector and a reflector II from left to right. When characterizing the third-order polarizability of a nonlinear sample, a light shielding screen is set in front of the reflector I to retain only the signal light path. A single nonlinear sample is placed near the focal plane of the focusing lens I. The output power of the laser is adjusted to observe the number of self-diffraction rings behind the sample. The functional relationship between the incident light intensity and the number of diffraction rings is statistically fitted, and the third-order polarizability of the sample is calculated according to the formula. The specific operations are as follows:

[0035] Step 1: Press Figure 1 Build the experimental optical path;

[0036] Step 2: Set a light shield in front of reflector I to keep only the signal light path, and load the dispersion sample on a 1×1×3.5cm 3 The quartz cuvette is placed near the focal plane of focusing lens Ⅰ;

[0037] Step 3: Adjust the laser output power to the minimum, and then gradually increase the laser output power until a self-diffraction ring appears on the detector;

[0038] Step 4: Count the number of rings and the optical power before the sample;

[0039] Step 5: Continue to increase the laser output optical power;

[0040] Step 6: Repeat steps 4-5 multiple times to obtain experimental data of incident light intensity and number of diffraction rings;

[0041] Step 7: According to the statistical results of steps 4-6, fit and calculate the third-order polarizability coefficient of the sample;

[0042] Step 8: Change the sample and repeat steps 3-7.

[0043] In this case, we used a 976nm infrared laser light source to characterize the third-order polarizability coefficients of MXene nanosheet dispersions in different solvents. The results are shown in Figure 2. Figure 2 shown.

[0044] Example 2: Based on the characterization results of Example 1, MXene / PC and MXene / H 2O dispersion is a composite material, the composite material is placed near the focal plane of lens 1, the appropriate optical power is set, and the light intensity distribution on the light detector is observed.

[0045] The specific operations are as follows:

[0046] Step 1: Based on Example 1, set the optical power of the signal light to 12.3 W / cm 2 MXene / PC dispersion and MXene / H 2 O dispersions are placed in Figure 1 At the sample position, the signal light propagates through the MXene / PC dispersion and MXene / H 2 O dispersion;

[0047] Step 2: Observe the outgoing light intensity distribution on the light detector. The result is as follows: Figure 4 As shown;

[0048] Step 3: Replace MXene / PC dispersion and MXene / H 2 O dispersion position, so that the signal light passes through the combined sample in the reverse direction;

[0049] Step 4: Observe the outgoing light intensity distribution on the detector. The result is as follows: Figure 5 shown.

[0050] It can be seen that the combined sample realizes the optical isolation function, that is, the signal light can excite the self-diffraction pattern along the forward direction but not in the reverse direction.

[0051] Application Example 1:

[0052] On the basis of Example 2, we introduce control light along the opposite propagation direction of the signal light, keep the optical power of the signal light unchanged, adjust the optical power of the control light, and observe the self-diffraction phenomenon in the signal light. The specific steps are as follows:

[0053] Step 1: Based on Example 2, the signal light is kept passing through the sample in the reverse order, that is, passing through the MXene / H 2 O dispersion then passes through MXene / PC dispersion;

[0054] Step 2: Turn the adjustable optical attenuator to the maximum attenuation position, remove the light shielding screen in front of the reflector I, and introduce the control light beam;

[0055] Step 3: Observe the intensity distribution of the signal light on the light detector;

[0056] Step 4: Turn the variable optical attenuator to increase the intensity of the control light, repeat the previous step, and count the number of diffraction rings in the signal light under different optical powers of the control light, such as Figure 6 shown.

[0057] It can be seen that the self-diffraction phenomenon in the signal light can be controlled by changing the intensity of the control light without changing the optical power of the signal light, and the number of diffraction rings increases linearly with the increase of the control light intensity.

[0058] It should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any combination or equivalent transformation made on the basis of the above embodiments belongs to the protection scope of the present invention.

Claims

1. A tunable all-optical isolator based on spatial self-phase modulation effect, characterized in that: The device comprises, from left to right, a laser, a beam splitter, a reflector I, an attenuator, a focusing lens I, an adjustable optical power attenuator, a nonlinear sample A, a nonlinear sample B, a focusing lens II, a light detector and a reflector II.

2. The tunable all-optical isolator based on spatial self-phase modulation effect according to claim 1, characterized in that: The lateral distribution of the intensity of the laser output beam is a Gaussian or nearly Gaussian incident field, which can stimulate the spatial self-phase modulation effect of the material.

3. The tunable all-optical isolator based on spatial self-phase modulation effect according to claim 2, characterized in that: The beam splitter can separate the incident fundamental mode Gaussian beam into two sub-beams propagating in two orthogonal directions, and the transmitted beam is a signal beam, and the reflected beam is a control beam.

4. The tunable all-optical isolator based on spatial self-phase modulation effect according to claim 3, characterized in that: The reflector I and reflector II are plane reflectors.

5. The tunable all-optical isolator based on spatial self-phase modulation effect according to claim 4, characterized in that: The attenuator is a neutral density attenuation sheet with a fixed attenuation ratio.

6. The tunable all-optical isolator based on spatial self-phase modulation effect according to claim 5, characterized in that: The adjustable optical power attenuator is a neutral density attenuator with an adjustable attenuation ratio.

7. The tunable all-optical isolator based on spatial self-phase modulation effect according to claim 6, characterized in that: The focusing lens I and the focusing lens II are positive lenses with a focal length of 150 mm, and the focal points of the two focusing lenses coincide with each other.

8. The tunable all-optical isolator based on spatial self-phase modulation effect according to claim 7, characterized in that: The nonlinear samples are two low-dimensional nanomaterial dispersions with different nonlinear optical thresholds, from left to right: material A, which has a higher nonlinear threshold and cannot be stimulated by signal light to self-diffract under low-power conditions, and material B, which has a lower nonlinear threshold and can be stimulated by controlled light to self-diffract.

9. The tunable all-optical isolator based on spatial self-phase modulation effect according to claim 8, characterized in that: The optical detector is a beam quality analyzer or an optical white screen, which can receive and detect the lateral light intensity distribution of the laser beam.

10. The tunable all-optical isolator based on spatial self-phase modulation effect according to claim 8, characterized in that: The implementation method is as follows: Step 1: Build the optical path system, set a light screen between the beam splitter and the reflector I to block the control light, place different nonlinear materials separately near the focus of the focusing lens I, change the optical power output by the laser, count the number of diffraction rings excited in the material under different optical powers, complete the third-order polarizability characterization of different materials, and obtain the third-order polarizability coefficient of the material. Step 2: Based on the characterization results of step 1, place the combined material at the focal plane of focusing lens I, where material B with a low nonlinear threshold is in front and material A with a high nonlinear threshold is in the back. The signal light propagates in the forward direction and the intensity distribution of the signal light on the photodetector is observed. Step 3: Change the order of materials A and B, observe and record the intensity distribution of the signal light on the light detector, Step 4: Remove the light shield in the control light, observe and record the intensity distribution of the signal light on the light detector, Step 5: Turn the adjustable optical power attenuator to increase the intensity of the control light, and observe and record the changes in the intensity distribution of the signal light on the optical detector.

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