A Faraday deflector

Abstract

The present invention provides a Faraday deflector, comprising a magnetic plasma structural unit, wherein the magnetic plasma structural unit comprises a magneto-optical material layer, a circular metal patch is provided on one side of the magneto-optical material layer, and a notch is provided on the circular metal patch. The Faraday deflector provided by the present invention can achieve a large Faraday rotation deflection angle even with a small size.

Description

Technical Field

[0001] The invention belongs to the field of laser and optoelectronic technology, and in particular, relates to a Faraday deflector. Background Art

[0002] In the optical isolator, the linear polarized light is rotated by the Faraday rotator and the angle of the analyzer is adjusted to achieve a high light intensity when the forward light passes through and a low light intensity when the reverse light passes through, thereby achieving the effect of reverse isolation. Currently, the commonly used Faraday deflector mainly obtains the required Faraday rotation angle by increasing the medium size and enhancing the magnetic field. The magneto-optical effect of the raw materials currently discovered cannot meet the requirements of device production, so most of the current research directions are how to enhance the magneto-optical effect.

[0003] At present, in order to obtain a large Faraday rotation angle under small size and small magnetic field strength, the combination of magneto-optical materials and metals will stimulate the plasmon effect in the metal layer. When encountering a slit during propagation, it will be coupled to the dielectric layer. At the same time, under the internal action of the material spin orbit, the plane where the light wave is located will be deflected. However, the Faraday effect obtained by this structure is not very ideal. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a Faraday deflector which can achieve a larger Faraday rotation deflection angle even with a smaller size.

[0005] To solve the above technical problems, the embodiments of the present invention adopt the following technical solutions:

[0006] An embodiment of the present invention provides a Faraday deflector, including a magnetic plasma structure unit, wherein the magnetic plasma structure unit includes a magneto-optical material layer, a circular metal patch is provided on one side of the magneto-optical material layer, and a notch is provided on the circular metal patch.

[0007] As a further improvement to the embodiment of the present invention, there are two notches, and the two notches are symmetrically arranged.

[0008] As a further improvement to the embodiment of the present invention, the angle range of the notch is 10 to 40°.

[0009] As a further improvement of the embodiment of the present invention, the width of the circular ring of the circular ring metal patch is 50-125 nm.

[0010] As a further improvement of the embodiment of the present invention, the thickness of the annular metal patch is 20 nm.

[0011] As a further improvement of the embodiment of the present invention, the thickness of the magneto-optical material layer is 160-900 nm.

[0012] As a further improvement of the embodiment of the present invention, the material of the magneto-optical material layer is bismuth iron garnet.

[0013] As a further improvement of the embodiment of the present invention, the magnetic plasma structure unit further includes a base layer, and the base layer is arranged on the other side of the magneto-optical material layer; the material of the base layer is gadolinium gallium garnet.

[0014] As a further improvement of the embodiment of the present invention, the thickness of the base layer is 100 nm.

[0015] As a further improvement of the embodiment of the present invention, the thickness of the magnetic plasma structure unit is 280-1020 nm.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0017] The Faraday deflector provided by the present invention uses a combination of magneto-optical material and metal to stimulate a plasma excitation effect in the metal layer, thereby strengthening the magneto-optical properties of the material structure. It can maintain a relatively high Faraday deflection angle and transmittance at a low magnetic field intensity within the mid-infrared wavelength range, while making the spectral range of the high Faraday deflection angle and transmittance wider. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0019] Figure 1 is a schematic structural diagram of a Faraday deflector according to an embodiment of the present invention;

[0020] Figure 2 is a schematic structural diagram of a circular metal patch in an embodiment of the present invention;

[0021] Figure 3 (a) is the electric field energy distribution diagram of the interface between the annular metal patch and the magneto-optical material layer of the Faraday deflector of this embodiment at a light wavelength of 8.3 μm when the width of the annular metal patch is 75 nm. Figure 3 (b) is the electric field energy distribution diagram of the interface between the annular metal patch and the magneto-optical material layer of the Faraday deflector of this embodiment at a light wavelength of 8.3 μm when the width of the annular metal patch is 125 nm. Figure 3 (c) is the electric field energy distribution diagram of the interface between the magneto-optical material layer and the substrate layer of the Faraday deflector of this embodiment at a light wavelength of 8.3 μm when the width of the circular metal patch is 75 nm. Figure 3(d) is the electric field energy distribution diagram of the interface between the magneto-optical material layer and the substrate layer of the Faraday deflector of this embodiment at a light wavelength of 8.3 μm when the width of the circular metal patch is 125 nm.

[0022] The figure includes: 1 magnetic plasma structure unit, 11 annular metal patch, 12 magneto-optical material layer, and 13 base layer. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings.

[0024] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate the same or corresponding components and features.

[0025] At present, the research on Faraday rotation characteristics mostly uses the Faraday enhancement characteristics composed of closed gold gratings, and it is impossible to simultaneously maintain small structural size and weak magnetic field conditions, and the wavelength range is also mainly concentrated in the near-infrared band.

[0026] An embodiment of the present invention provides a Faraday deflector, such as Figure 1 As shown, the magnetic plasma structure unit 1 includes a magneto-optical material layer 12, and a circular metal patch 11 is provided on one side of the magneto-optical material layer 12. Figure 2 As shown, a notch 111 is provided on the annular metal patch 11. Preferably, the Faraday deflector has at least two magnetic plasma structural units 1 distributed in an array.

[0027] In the Faraday deflector of the embodiment of the present invention, the magnetic plasma structural unit 1 includes a magneto-optical material layer 12. Considering that the magneto-optical effect of the material of the existing magneto-optical material layer itself cannot meet the requirements of device production under the condition of a small thickness of the structural unit, a circular metal patch 11 is provided on one side of the magneto-optical material layer 12 in this embodiment. After the magneto-optical material and the metal are combined, a plasmon effect will be excited in the metal layer. At the interface between the circular metal patch 11 and the magneto-optical material layer 12, the collective oscillation of free electrons is caused by the frequency of the incident light being the same as the oscillation frequency of free electrons on the surface of the circular metal patch 11, and propagates at the interface between the circular metal patch 11 and the magneto-optical material layer 12. When the incident light excites the structure of the circular metal patch 11 to resonate, a very strong electric field localization will be generated on the inner side of the notch 111, thereby enhancing the electric field strength inside the magneto-optical material layer 12, thereby achieving the effect of enhancing the magneto-optical effect. The Faraday deflector of the embodiment of the present invention can stabilize the Faraday deflection angle at 45° within the spectral range of 4 to 15 microns, and the maximum transmittance is 0.67.

[0028] The material of the annular metal patch 11 is preferably gold. The material of the magneto-optical material layer 12 is preferably bismuth iron garnet, which has the advantages of low loss and high magneto-optical performance. Considering that bismuth iron garnet is generally produced on a substrate of gadolinium gallium garnet when it is produced, there will be residue when the bismuth iron garnet is peeled off, the magnetic plasma structure unit of this embodiment also includes a base layer 13, which is arranged on the other side of the magneto-optical material layer 12, and the material of the base layer 13 is gadolinium gallium garnet. The thickness of the base layer is 100nm.

[0029] Preferably, the notch 111 of the annular metal patch 11 has two, and the two notches 111 are symmetrically arranged, that is, the center lines of the two notches are the same straight line. The annular metal patch 11 of the present embodiment is symmetrically provided with two notches 111. On the one hand, the middle hole is connected obliquely due to the diagonal opening, and the other two directions are closed to cause the light wave to gather electric field energy. It is more convenient to propagate obliquely compared to the single-angle opening after the light wave is connected to be forced to deflect obliquely, and further increase the Faraday deflection angle. On the other hand, the propagation of light waves is similar to flowing in a medium, and the single-angle opening is equivalent to throttling, which improves the local electric field energy density and enhances the diagonal double opening, which is to dredge the channel, making it more convenient to propagate obliquely, and further improve the inhomogeneity of the electric field energy distribution. If the same side opening angle, there will be a situation of mutual cancellation, and the opposite side opening angle can produce a superposition effect, which improves the Faraday deflection angle.

[0030] Preferably, the angle range of the notch 111 of the annular metal patch 11 is 10 to 40°. The angle of the notch 111 is the angle between the two radii of the annular metal patch on both sides of the notch 111. In this embodiment, the angle of the notch 111 can be selected from 10 to 40°, so that the Faraday deflector can reach a Faraday deflection angle of 45° at a wavelength of 8.3 μm, which meets the angle required by the optical isolator, and the maximum transmittance reaches 0.63.

[0031] Preferably, the width of the circular metal patch is 50-125 nm. In this embodiment, the distance between the outer diameter R and the inner diameter r of the circular metal patch can be selected to be 50-125 nm, so that the Faraday deflection angle of the Faraday deflector can reach 45°, meeting the angle required by the optical isolator, and the maximum transmittance is 0.67. Figure 3It can be seen that the light trapping effect produced by the structure of the circular metal patch 11 will cause the light to be concentrated at the opening, resulting in uneven distribution of the electric field and energy. On the other hand, the magneto-optical material layer 12 also strengthens the Faraday deflection. From Figures (a) and (b), it can be seen that there is a little light at the edge of the circular ring, and a large amount of light is concentrated at the gap 111, that is, the electric field energy is densely distributed at the opening, and the magnetic plasma structure composed of the circular ring structure produces an abnormal light transmission effect and stimulates the surface plasmon effect, which is most obvious at the gap 111, resulting in a huge Faraday effect. Due to the different widths of the circular metal patches, the magneto-optical effect is also different. The specific positions of the brightness distribution in Figures (c) and (d) are consistent with those in (a) and (b), and the magneto-optical effect is slightly weaker.

[0032] Preferably, the thickness of the annular metal patch 11 is 20 nm.

[0033] Preferably, the thickness of the magneto-optical material layer 12 is 160-900 nm. In this embodiment, the thickness of the magneto-optical material layer 12 can be 200-500 nm, so that the Faraday deflection angle can reach 45° under a smaller size, meeting the angle required by the optical isolator, and the maximum transmittance reaches 0.615.

[0034] Preferably, the thickness of the magnetic plasma structure unit 1 is 280-1020 nm. The Faraday deflector of this embodiment has a small size and can also achieve a large Faraday rotation deflection angle.

[0035] A specific example and three comparative examples are provided below.

[0036] Example 1

[0037] The magnetic plasma structure unit includes a circular metal patch, a magneto-optical material layer and a base layer in sequence. Two notches are symmetrically arranged on the circular metal patch, and the notch angle is 20°. The material of the circular metal patch is gold, the material of the magneto-optical material layer is bismuth iron garnet, and the material of the base layer is gadolinium gallium garnet. The thickness of the circular metal patch is 20nm, the width of the circular metal patch is 75nm, the thickness of the magneto-optical material layer is 200nm, and the thickness of the base layer is 100nm.

[0038] Comparative Example 1

[0039] The magnetic plasma structure unit includes a magneto-optical material layer and a substrate layer in sequence. The material of the magneto-optical material layer is bismuth iron garnet, and the material of the substrate layer is gadolinium gallium garnet. The thickness of the magneto-optical material layer is 200nm, and the thickness of the substrate layer is 100nm.

[0040] Comparative Example 2

[0041] The magnetic plasma structure unit includes a circular metal patch, a magneto-optical material layer and a base layer in sequence. The material of the circular metal patch is gold, the material of the magneto-optical material layer is bismuth iron garnet, and the material of the base layer is gadolinium gallium garnet. The thickness of the circular metal patch is 20nm, the width of the circular metal patch is 75nm, the thickness of the magneto-optical material layer is 200nm, and the thickness of the base layer is 100nm.

[0042] Comparative Example 3

[0043] The magnetic plasma structure unit includes a circular metal patch, a magneto-optical material layer and a base layer in sequence. A notch is provided on the circular metal patch, and the notch angle is 20°. The material of the circular metal patch is gold, the material of the magneto-optical material layer is bismuth iron garnet, and the material of the base layer is gadolinium gallium garnet. The thickness of the circular metal patch is 20nm, the width of the circular metal patch is 75nm, the thickness of the magneto-optical material layer is 200nm, and the thickness of the base layer is 100nm.

[0044] The finite difference time domain method is used to simulate and analyze Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3, with x and y set as periodic boundaries and z set as a perfect matching layer. The result comparison table shown in Table 1 is obtained.

[0045] Table 1 Performance comparison of magnetic plasma structural units with different structures

[0046]

[0047] It can be seen from Table 1 that setting a circular metal ring can enhance θ F The value of T is reduced. A notch is set on the circular metal ring, θ F The double opening is optimized, and the FOM is further improved. F An increase of 45.5° results in a 10 increase in FOM.

[0048] When the Faraday deflector of the embodiment of the present invention is applied in an optical isolator, a parallel magnetic field is set along the light propagation direction. The direction of the magnetic field is determined by the magneto-optical rotation characteristics of the magneto-optical crystal. The magneto-optical crystal material is placed in the magnetic field. Polarizers are placed on the front and back sides of the Faraday deflector, and the directions of their light transmission axes are in an angle β relationship with each other. When the incident parallel light passes through the first polarizer, it becomes polarized light, and then passes through the Faraday deflector, and its polarization plane is rotated by θ F , through the second polarizer, the light signal passes smoothly and enters the optical path. When β=θ F When the angle is 45°, there is almost no loss in the intensity of the forward light passing through; the intensity of the transmitted light passing through in the reverse direction is 0, which means that the reverse isolation function is realized.

[0049] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above specific embodiments. The above specific embodiments and the description in the specification are only for further illustrating the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of the present invention to be protected is defined by the claims and their equivalents.

Claims

1. A Faraday deflector, characterized in that: In the spectral range of 4 to 15 microns, the Faraday deflection angle can be stabilized at 45°, and the transmittance is up to 0.67; the magnetic plasma structure unit (1) comprises a magneto-optical material layer (12), one side of the magneto-optical material layer (12) is provided with a circular metal patch (11), and the circular metal patch (11) is provided with a notch (111); there are two notches (111), and the two notches are symmetrically arranged; the two sides of the notch (111) are located on two radii of the circular metal patch, and the angle range of the notch (111) is 10 to 40°; the thickness of the magneto-optical material layer (12) is 200 to 500 nm, and the thickness of the magnetic plasma structure unit (1) is 280 to 1020 nm.

2. The Faraday deflector according to claim 1, characterized in that The circular ring width of the circular ring metal patch (11) is 50 to 125 nm.

3. The Faraday deflector according to claim 1, characterized in that: The thickness of the annular metal patch (11) is 20 nm.

4. The Faraday deflector according to claim 1, characterized in that: The material of the magneto-optical material layer (12) is bismuth iron garnet.

5. The Faraday deflector according to claim 4, characterized in that: The magnetic plasma structure unit (1) further comprises a base layer (13), wherein the base layer (13) is arranged on the other side of the magneto-optical material layer (12); the material of the base layer (13) is gadolinium gallium garnet.

6. The Faraday deflector according to claim 5, characterized in that The thickness of the base layer (13) is 100 nm.

Images