Non-reciprocal polarization rotator integrated with metasurface

Abstract

The non-reciprocal polarization rotator comprises: a chip housing having an empty space region formed in a trench shape in the central portion thereof; a non-reciprocal polarization rotation module mounted in the space region to perform a non-reciprocal polarization rotation function; a first waveguide formed such that an end thereof is in contact with the space region on one side surface of the chip housing; and a second waveguide formed such that an end thereof is in contact with the space region on the other side surface of the chip housing, wherein the non-reciprocal polarization rotation module comprises: a metasurface for optical coupling having a metasurface formed in a direction of the first waveguide and performing collimating and focusing functions on a transmitted light beam; a metasurface wave plate having a metasurface formed in a direction of the second waveguide and performing polarization rotation, collimating, and focusing functions on the transmitted light beam; and a magneto-optic film mounted between the metasurface for optical coupling and the metasurface wave plate, and maintaining polarization rotation of the transmitted light beam and the same magnetic field direction on both sides.

Description

Metasurface-Integrated Nonreciprocal Polarization Rotators

[0001] The present invention relates to an irreversible polarization rotator with an integrated metasurface.

[0002] Recently, optical and optical communication systems are demanding increasingly higher data transmission rates and integration. In particular, the Photonic Integrated Circuit (hereinafter referred to as "PIC") is a key technology that meets these demands (see Non-Patent Literature 1). PICs provide miniaturization and energy efficiency, and because they can integrate optical components such as lasers, modulators, and detectors onto a single chip, they have established themselves as a core component of next-generation optical communication and optical computing systems (see Non-Patent Literatures 1 and 2). However, one of the critical issues that degrades the stability and performance of these PICs is interference caused by the reflection and scattering of optical signals. In particular, if light reflected from a laser source re-enters the device, it can cause signal distortion, increased noise, and damage to the laser (see Non-Patent Literatures 3 to 7). To solve these problems, an irreversible polarization rotator that enables asymmetric optical path control is essential.

[0003] Conventional irreversible polarization rotators have mostly relied on bulk Faraday rotators. While this method is optically effective, it is difficult to integrate into miniaturized PICs due to their large volume (see Non-Patent Literatures 8–10). Furthermore, bulk devices are unsuitable for large-scale production as they require a separate assembly step in the integrated fabrication process (see Non-Patent Literatures 8–13).

[0004] To achieve irreversible polarization rotation characteristics on the chip, structures in which most magneto-optical materials are deposited on top of waveguides have been attempted (see Non-patent Literature 11, 12, 14, 15). However, there are limitations in that the process is complex and a magnetic field must be continuously applied through the introduction of additional electrodes.

[0005] Metasurfaces (hereinafter referred to as 'MS'), which are ultrathin optical components containing artificial meta-atom arrays, can significantly enhance the interaction between photons and matter by carefully designing the geometric structure, arrangement, and materials of the meta-atoms, and can realize ultra-small polarizers by combining these. As such, optical devices utilizing MS have been studied, including beam deflectors capable of controlling beam polarization or focusing (see Patent Documents 1 and 2) and half-wave plate metasurfaces capable of controlling polarization and focusing (see Patent Document 3 and Non-Patent Document 16).

[0006] [Prior Art Literature]

[0007] [Patent Literature]

[0008] (1) Korean Registered Patent Publication No. 10-2603484 (Dielectric metasurface doublet device enabling enhanced beam steering by polarization control)

[0009] (2) Korean Registered Patent Publication No. 10-2143535 (Two-function metasurface capable of bias or focusing adjustment)

[0010] (3) Korean Registered Patent Publication No. 10-2262913 (half-wave plate metasurface capable of polarization and focusing control, metalens and method for manufacturing the same)

[0011] [Non-patent literature]

[0012] [1] T. L. Koch and U. Koren, “Semiconductor photonic integrated circuits,” IEEE J. Quantum Electron. 27(3), 641-653 (1991).

[0013] [2] N. L. Kazanskiy, M. A. Butt, and S. N. Khonina, “Optical Computing: Status and Perspectives,” Nanomaterials, 12(13), 2171 (2022).

[0014] [3] I. A. Williamson, M. Minkov, A. Dutt et al. “Integrated Nonreciprocal Photonic Devices with Dynamic Modulation,” Proc. IEEE, 108(10), 1759-1784 (2020).

[0015] [4] Y. Shoji and T. Mizumoto,“Magneto-optical non-reciprocal devices in silicon photonics,” Sci. Technol. Adv. Mater., 15, 014602 (2014).

[0016] [5] R. W. Tkach and A. R. Chraplyvy, “Regimes of Feedback Effects in 1.5㎛ Distributed Feedback Lasers,” J. Lightwave Technol. 4(11), 1655-1661 (1986).

[0017] [6] A. Sabharwal, P. Schniter, D. Guo et al., “In-Band Full-Duplex Wireless: Challenges and Opportunities,” IEEE J. Sel. Areas Commun., 32(9), 1637-1652 (2014).

[0018] [7] K. Petermann, “External Optical Feedback Phenomena in Semiconductor Lasers,” IEEE J. Sel. Top. Quantum Electron, 1(2), 480-489 (1995).

[0019] [8] N. Shirasaki and K. Asama “Compact optical isolator for fibers using birefringent wedges,” Appl. Opt. 21(23), 4296-4299 (1982).

[0020] [9] K. W. Chang and W. V. Sorin, “Polarization independent isolator using spatial walkoff polarizers,” IEEE Photonics Technol.Lett.1(3), 68-70 (1989).

[0021]

[0010] Y. Fujii,“High-isolation polarization-independent optical circulator,” J. Lightwave Technol., 9(10), 1238-1243 (1991).

[0022]

[0011] R. Takei, K. Yoshida, and T. Mizumoto,“Effects of Wafer Precleaning and Plasma Irradiation to Wafer Surfaces on Plasma-Assisted Surface-Activated Direct Bonding,” Jpn. J. Appl. Phys., 49, 086204 (2010).

[0023]

[0012] Y. Shoji, R. Takei, and T. Mizumoto,“Direct Wafer Bonding and Its Application to Waveguide Optical Isolators.” Materials, 5(5), 985-1004 (2012).

[0024]

[0013] K. Srinivasan and B. Stadler,“Magneto-optical materials and designs for integrated TE- and TM-mode planar waveguide isolators: a review,” Opt. Mater. Express, 8(11), 3307-3318 (2018).

[0025]

[0014] P. Pintus, D. Huang, P. A. Morton et al., “Broadband TE Optical Isolators and Circulators in Silicon Photonics Through Ce:YIG Bonding.” J. Lightwave Technol., 37(5), 1463-1473 (2019).

[0026]

[0015] D. Huang, P. Pintus, and J. E. Bowers,“Towards heterogeneous integration of optical isolators and circulators with lasers on silicon,” Opt. Mater. Express, 8(9), 2471-2483 (2018).

[0027]

[0016] Song Gao, Chul-Soon Park, Sang-Shin Lee and Duk-Yong Choi, “Dielectric metasurfaces for simultaneously realizing polarization rotation and wavefront shaping of visible light,” Nanoscale, 2019,11.4083.

[0028] The objective of the present invention is to provide an irreversible polarization rotator integrated with a metasurface having irreversible polarization rotation characteristics, wherein the output light maintains the same TE0 mode as the input light in the forward direction, and a polarization mode (TM0) orthogonal to the input light (TE0) is output in the reflection direction.

[0029] Another objective of the present invention is to provide an irreversible polarizer integrated with a metasurface having the characteristic of being able to distinguish and sense reflected light from input light simply and compactly by utilizing the converted polarization mode characteristics of reflected light at the input end during the input and output of a light beam through a single microchip.

[0030] The present invention is not limited to the purposes mentioned above, and other unmentioned purposes will be clearly understood from the description below.

[0031] According to one aspect of the present invention, an irreversible polarization rotator comprises: a chip housing having a trench-shaped empty space region formed in the center; an irreversible polarization rotator module mounted in the space region to perform an irreversible polarization rotator function; a first waveguide formed on one side of the chip housing such that its end contacts the space region; and a second waveguide formed on the other side of the chip housing such that its end contacts the space region. The irreversible polarization rotator module comprises: a metasurface for optical coupling formed in the direction of the first waveguide and performing collimating and focusing functions for a transmitted light beam; a metasurface waveplate formed in the direction of the second waveguide and performing polarization rotation, collimating, and focusing functions for a transmitted light beam; and a magneto-optical film mounted between the metasurface for optical coupling and the metasurface waveplate, which maintains the polarization rotation of the transmitted light beam and the same magnetic field direction in both directions.

[0032] Additionally, the chip housing comprises a base substrate formed of silicon (Si); a silicon dioxide embedded oxide layer formed of SiO2 on the base substrate; a Si waveguide formed of silicon (Si) material in the center of the upper portion of the silicon dioxide embedded oxide layer; and a silicon dioxide cladding layer covering the periphery and upper portion of the waveguide; wherein the waveguide is characterized as being the first waveguide or the second waveguide.

[0033] In addition, the above Si waveguide is formed with a thickness of 0.22 μm and a width of 500 nm, and the above silicon dioxide cladding layer is formed up to 2.2 μm above the Si waveguide.

[0034] In addition, the optical coupling metasurface is characterized by performing the function of converting a forward beam incident on the focal point of the optical coupling metasurface into a parallel beam, and performing the function of focusing a beam incident as a reverse parallel beam onto the focal point of the optical coupling metasurface and outputting it.

[0035] In addition, the metasurface wave plate is characterized by performing the function of rotating a parallel beam incident in the forward direction to -45° polarization to focus it at the focal point of the metasurface wave plate and outputting it, and also rotating a divergent beam incident in the reverse direction to +45° polarization and converting it into a parallel beam to output it.

[0036] In addition, the magneto-optical film is characterized by performing the function of outputting a forward beam rotated by +45° and also outputting a reverse beam incident in the reverse direction rotated by +45°.

[0037] In addition, the input beam of TE0 mode input in the forward direction is diverged from the end of the first waveguide and converted into a parallel beam through the optical coupling metasurface; the converted parallel beam passes through the magneto-optical film, where its polarization is rotated by +45°, and passes through the metasurface wave plate, where its polarization is rotated by -45°; at the same time, the transmitted beam is focused and output to the second waveguide, wherein the output beam maintains the same TE0 mode as the input beam; and the input beam of TE0 mode input in the reverse direction is diverged from the end of the second waveguide, passes through the metasurface wave plate, and is converted into a parallel beam with a polarization rotated by +45°, and passes through the magneto-optical film, where it is additionally rotated by +45° to be converted into TM0 mode, and then the converted TM0 mode beam passes through the optical coupling metasurface, where it is focused and output to the first waveguide, so that the beam input in the reverse direction is the input light (TE0) and It is characterized by outputting an orthogonal TM0 mode.

[0038] In addition, the first waveguide is characterized by having a tapered structure with a length of 100 μm at the end portion from a 500 nm uniform width waveguide, and the tapered structure is characterized by being formed such that the end portion decreases to 150 nm over the width of the waveguide from 500 nm to 100 μm.

[0039] In addition, the second waveguide is characterized by being formed with an inversely taper waveguide portion extending from 150 nm to 100 μm to 500 nm and a uniformly wide waveguide portion formed with a uniform width of 500 nm.

[0040] In addition, each metaatom forming the optical coupling metasurface is formed with an a-Si:H rectangular prism structure on a silicon dioxide substrate with a thickness of 0.5 μm, the height (h) of the metaatom is 930 nm, and the interval period (Λ) between each metaatom is 800 nm. The optical coupling metasurface is characterized by having eight metaatoms of different widths and heights selected and arranged as metaatom unit cell groups at intervals of π / 4 to provide 2π phase control, wherein the metaatoms are selected and arranged as metaatom unit cell groups such that the phase values ​​calculated by the following mathematical formula 1 are evenly distributed from 0 to 2π.

[0041] [Mathematical Formula 1]

[0042]

[0043] In addition, each metaatom forming the metasurface wave plate is formed on a silicon dioxide substrate with a thickness of 0.5 μm in the shape of an a-Si:H rectangular prism tilted at 22.5° from the x-axis, the height (h) of the metaatom is 930 nm, the spacing period (Λ) between each metaatom is 800 nm, and the metasurface of the metasurface wave plate is characterized by having eight metaatoms of different widths and heights selected and arranged as metaatom unit cell groups at intervals of π / 4 to provide 2π phase control.

[0044] Unlike conventional bulk-type irreversible polarization rotators, the irreversible polarization rotator with an integrated metasurface according to one embodiment of the present invention can be implemented within a single chip based on a silicon waveguide, thereby significantly improving integration density.

[0045] According to one embodiment of the present invention, the optical coupling metasurface (210, MS) designed has a transmission efficiency of 76%. In addition, the metasurface wave plate (230, MWP) has a transmittance of 74% and a polarization rotation efficiency of 98.6%.

[0046] An irreversible polarization rotator integrated with a metasurface according to one embodiment of the present invention has an irreversible polarization rotation characteristic by the characteristic that in the forward direction, the output light maintains the same TE0 mode as the input light, and in the reflection direction, a polarization mode (TM0) orthogonal to the input light (TE0) is output.

[0047] An irreversible polarization rotator integrated with a metasurface according to one embodiment of the present invention has the effect of distinguishing reflected light from input light and sensing it simply and compactly by utilizing the converted polarization mode characteristics of reflected light at the input end during the input and output of a light beam through a single microchip. In addition, irreversible polarization rotation characteristics can be realized without an external magnetic field through a residual magnetized magneto-optical film.

[0048] An irreversible polarization rotator with an integrated metasurface according to one embodiment of the present invention can have a transmitting and receiving unit configured as an integrated unit, and thus can be applied to the implementation of a fixed-type single-wavelength beam scanner.

[0049] FIG. 1 is a schematic diagram illustrating the operating structure of an irreversible polarization rotator integrated with a metasurface according to one embodiment of the present invention.

[0050] FIG. 2 illustrates a cross-sectional view of a chip housing including a first waveguide or a second waveguide element according to one embodiment of the present invention.

[0051] FIG. 3 is a diagram illustrating the irreversible rotation characteristics of an irreversible polarization rotator integrated with a metasurface according to one embodiment of the present invention.

[0052] FIG. 4 illustrates the cross-sectional structure of an irreversible polarization rotator with an integrated metasurface according to one embodiment of the present invention.

[0053] Figure 5 shows a cross-sectional design of a silicon waveguide device and the effective refractive index characteristics of each mode according to the width of the silicon waveguide.

[0054] FIG. 6 illustrates the structure of a tapered waveguide and the electric field characteristics of a beam propagating along the tapered waveguide according to one embodiment of the present invention.

[0055] FIG. 7 is a schematic diagram illustrating the structure of a metasurface (210) for optical coupling according to one embodiment of the present invention.

[0056] FIG. 8 illustrates a schematic diagram of a metaatom of a metasurface (210, MS) for optical coupling in an irreversible polarization rotator according to one embodiment of the present invention.

[0057] FIG. 9 illustrates the results of calculating the transmittance and phase of x-polarized light according to the size of the metaatom at a wavelength of 1550 nm according to one embodiment of the present invention.

[0058] FIG. 10 illustrates the phase distribution of a metasurface (210, MS) for optical coupling and the arrangement pattern structure of metaatoms arranged on the metasurface (210, MS) for optical coupling according to one embodiment of the present invention.

[0059] FIG. 11 illustrates the focusing performance characteristics of a parallel beam passing through a metasurface (210, MS) for optical coupling according to one embodiment of the present invention.

[0060] FIG. 12 illustrates a schematic diagram of a metasurface wave plate (230, MWP) according to one embodiment of the present invention.

[0061] FIG. 13 is a diagram illustrating the operating principle of a metasurface wave plate (230, MWP) according to one embodiment of the present invention.

[0062] FIG. 14 illustrates a schematic diagram of a metaatom of a metasurface wave plate (230, MWP) according to one embodiment of the present invention.

[0063] FIG. 15 illustrates an example of calculating the phase difference between the fast axis and the slow axis according to the width and height of the metaatom in a metasurface wave plate (230, MWP).

[0064] FIG. 16 illustrates the x-component transmittance and phase calculation results for 45° polarized light according to the width and height of each metaatom when a light beam of 1550 nm wavelength is transmitted through a metasurface wave plate (230, MWP) according to one embodiment of the present invention.

[0065] FIG. 17 shows the phase distribution of a metasurface wave plate (230, MWP) and the arrangement pattern structure of a metatom according to one embodiment of the present invention.

[0066] FIG. 18 illustrates the characteristics of focusing and half-wave plate performance after a parallel beam polarized at 45° passes through a metasurface wave plate (230, MWP) according to one embodiment of the present invention.

[0067] FIG. 19 shows the polarization change characteristics of a beam passing through an MWP according to the polarization of a beam incident on a metasurface wave plate (230, MWP) according to one embodiment of the present invention.

[0068] [Explanation of the symbol]

[0069] 100: Chip housing

[0070] 101: Base board

[0071] 102: Silicon dioxide landfill oxide layer

[0072] 103: Silicon dioxide cladding layer

[0073] 110: First waveguide

[0074] 120: Second wave path

[0075] 200: Irreversible polarization rotation module

[0076] 210: Metasurface for optical coupling

[0077] 220: Magneto-optical film

[0078] 230: Metasurface wave plate

[0079] The terms used in this application are used merely to describe specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0080] In this application, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0081] Additionally, terms such as “…part,” “…unit,” “module,” and “device” described in the specification refer to a unit that processes at least one function or operation, and this may be implemented in hardware, software, or a combination of hardware and software.

[0082] In addition, terms such as "first," "second," etc., may be used when describing the components of the embodiments of the present invention. These terms are intended merely to distinguish the component from other components, and the essence, order, or sequence of the component is not limited by such terms. Where it is stated that a component is "connected," "combined," or "connected" to another component, it should be understood that while the component may be directly connected, combined, or connected to the other component, another component may also be "connected," "combined," or "connected" between the component and the other component.

[0083] The following describes in detail an irreversible polarization rotator integrated with a metasurface according to an embodiment of the present invention.

[0084] In one embodiment of the present invention, an irreversible polarization rotator is implemented by inserting a metasurface (MS) and a magneto-optical film (MOF) into a silicon waveguide device. Unlike conventional bulk irreversible polarization rotators, the irreversible polarization rotator with an integrated metasurface according to one embodiment of the present invention can be implemented within a single chip based on a silicon waveguide, thereby significantly improving integration density. Furthermore, irreversible polarization rotation characteristics can be achieved without an external magnetic field through the residual magnetized magneto-optical film.

[0085] FIG. 1 is a schematic diagram illustrating the operating structure of an irreversible polarization rotator integrated with a metasurface according to one embodiment of the present invention.

[0086] Referring to FIG. 1, an irreversible polarization rotator with an integrated metasurface according to one embodiment of the present invention comprises a chip housing (100) having a trench-shaped empty space region formed in the center;

[0087] An irreversible polarization rotation module (200) mounted in the above spatial region and performing an irreversible polarization rotation function; a first waveguide (110) formed such that its end contacts the above spatial region on one side of the chip housing (100); and

[0088] It includes a second waveguide (120) formed such that its end contacts the space area on the other side of the chip housing (100).

[0089] According to one embodiment of the present invention, the spatial region is formed between the end of the first waveguide (110) and the end of the second waveguide (120).

[0090] The above-described irreversible polarization rotation module (200) is formed in a vertical plate shape with respect to the optical path leading to the first waveguide (110) and the second waveguide (120) of the chip housing (100), and includes a metasurface for optical coupling (210) with a metasurface formed in the direction of the first waveguide (110), a metasurface wave plate (230) formed in a vertical plate shape with respect to the optical path of the chip housing (100) with a metasurface formed in the direction of the second waveguide (120), and a magneto-optical film (220) mounted between the metasurface for optical coupling (210) and the metasurface wave plate (230).

[0091] In the present invention, the direction of the beam from the first waveguide (110) to the second waveguide (120) is described as the forward direction or transmission direction, and the direction of the beam from the second waveguide (120) to the first waveguide (110) is described as the backward direction or reflection direction. Additionally, the direction is described as the (+) direction when the light beam rotates counterclockwise, and the (-) direction when it rotates clockwise.

[0092] The above-mentioned optical coupling metasurface (210, Metasurface, hereinafter referred to as “MS”) performs collimating (converting to a parallel beam) and focusing (focusing) functions of a transmitted light beam to improve optical coupling efficiency, and is formed such that the end of the first waveguide (110) has a focal length (first focus) of the optical coupling metasurface (210).

[0093] A meta-surface waveplate (230, MWP: Meta-Waveplate, hereinafter referred to as “MWP”) performs polarization rotation, collimating, and focusing functions of a transmitted light beam so as to simultaneously improve optical coupling efficiency and act as a half-waveplate, and is formed such that the end of the second waveguide (120) has a focal length (second focal point) of the meta-surface waveplate (230).

[0094] A magneto-optical film (220, Magneto-Optic Film, hereinafter referred to as “MOF”) utilizes the Faraday effect to perform the function of rotating the polarization of a transmitted light beam and maintaining the same direction of the magnetic field in both directions.

[0095] A metasurface (210) for optical coupling according to one embodiment of the present invention is characterized by performing the function of converting a forward beam incident from a first focal point into a parallel beam, and also performing the function of focusing a beam incident as a reverse parallel beam at the first focal point of the metasurface (210) and outputting it.

[0096] A magneto-optical film (220) according to one embodiment of the present invention outputs a transmitted forward beam rotated by +45°. In addition, it performs the function of outputting a reverse beam incident in the reverse direction rotated by +45°.

[0097] A metasurface wave plate (230) according to one embodiment of the present invention is characterized by rotating a parallel beam incident in the forward direction to -45° polarization and focusing it to the focal point of the metasurface wave plate (230) for output, and is also characterized by performing the function of rotating a divergent beam incident in the reverse direction to +45° polarization and converting it into a parallel beam for output.

[0098] According to one embodiment of the present invention, the first waveguide (110) is formed with an equal width waveguide portion formed with an equal width of 500 nm and a tapered waveguide portion with a terminal portion extending over 100 μm and a terminal portion extending to 150 nm to improve coupling efficiency between the irreversible polarization rotation module (200) and the waveguide. Additionally, the second waveguide (120) is formed with an inverse tapered waveguide portion extending from 150 nm to 500 nm over 100 μm and a equal width waveguide portion formed with an equal width of 500 nm.

[0099] FIG. 2 illustrates a cross-sectional view of a chip housing including a first waveguide or a second waveguide element according to one embodiment of the present invention.

[0100] Referring to FIG. 2, a chip housing (100) including a silicon waveguide element according to one embodiment of the present invention comprises a base substrate (101) formed of silicon (Si), and SiO2 on the base substrate (101). It includes a formed silicon dioxide buried oxide layer (102, BOX: Buried Oxide) and a Si waveguide (110 or 120) formed in the upper center of the silicon dioxide buried oxide layer (102), and a silicon dioxide cladding layer (103) covering the upper part of the silicon dioxide buried oxide layer (102) excluding the upper part of the Si waveguide (110 or 120) and the Si waveguide (110 or 120).

[0101] For example, the waveguides forming the first waveguide (110) and the second waveguide (120) in the chip housing (100) are formed with a Si material at the upper center of the silicon dioxide-filled oxide layer (102), and the surrounding and upper parts are covered with a silicon dioxide cladding layer (103).

[0102] According to one embodiment of the present invention, the base substrate (101) has a thickness of ~725 μm, the silicon dioxide embedded oxide layer (102) has a thickness of 2 μm, the Si waveguide (110 or 120) has a thickness of 0.22 μm and a width of 500 nm, and the silicon dioxide cladding layer (103) is formed up to 2.2 μm above the waveguide.

[0103] A Si waveguide according to one embodiment of the present invention can be fabricated by patterning it with a thickness of 0.22 μm and a width of 500 nm using 100 keV electron beam lithography.

[0104] FIG. 3 is a diagram illustrating the irreversible rotation characteristics of an irreversible polarization rotator integrated with a metasurface according to one embodiment of the present invention.

[0105] Referring to FIG. 3, in the forward direction, the input TE0 mode is emitted from the end of the first waveguide (110) and then converted into a parallel beam through the optical coupling metasurface (210). The converted parallel beam passes through a permanently magnetized magneto-optical film (220), where its polarization is rotated by +45°, and then passes through a metasurface wave plate (230), where its polarization is rotated by -45°, and at the same time, the beam is focused at a second focal point and coupled to the second waveguide (120). As a result, in the forward direction, the output light maintains the same TE0 mode as the input light.

[0106] In the backward direction, the beam emitted from the output second waveguide (120) passes through the metasurface wave plate (230) and is converted into a parallel beam, and the polarization is rotated by +45°. Subsequently, when passing through the magneto-optical film (220), unlike the transmission direction, the polarization is additionally rotated by +45° in the same direction and converted into a TM0 mode. Then, the converted TM0 mode beam passes through the optical coupling metasurface, is focused at the first focal point, and is output to the first waveguide (110). Accordingly, the irreversible polarization rotator integrated with the metasurface according to one embodiment of the present invention has an irreversible polarization rotation characteristic due to the feature that a mode (TM0) different from the input light (TE0) is output in the backward direction.

[0107] Accordingly, the irreversible polarization rotator integrated with a metasurface according to one embodiment of the present invention has the effect of distinguishing reflected light from input light and sensing it simply and compactly by utilizing the converted polarization mode characteristics of the reflected light at the input end during the input and output of a light beam through a single microchip. In addition, an irreversible polarization rotation function can be implemented without an external magnetic field through a permanently magnetized magneto-optical film.

[0108] FIG. 4 illustrates the cross-sectional structure of an irreversible polarization rotator with an integrated metasurface according to one embodiment of the present invention.

[0109] Figure 4 (a) is a plan view, and Figure 4 (b) is a front view.

[0110] Referring to FIG. 4, an irreversible polarization rotator according to one embodiment of the present invention is formed with a structure through which a light beam passes through a first waveguide (110), a metasurface for optical coupling (210, MS), a magneto-optical film (220, MOF), a metasurface wave plate (230, MWP), and an output second waveguide (120).

[0111] Figure 5 shows a cross-sectional design of a silicon waveguide device and the effective refractive index characteristics of each mode according to the width of the silicon waveguide.

[0112] FIG. 5(a) is a cross-sectional design view of a silicon waveguide device according to one embodiment of the present invention, and FIG. 5(b) shows the effective refractive index of each mode according to the width of the silicon waveguide.

[0113] Referring to FIG. 5, as the width of the silicon waveguide increases, the number of higher-order modes that can exist in the waveguide increases. This leads to changes in mode characteristics, such as a decrease in effective refractive index, an increase in inter-mode dispersion characteristics, and boundary scattering loss. In one embodiment of the present invention, the width of the Si waveguide was designed to be 500 nm to maintain single-mode propagation and suppress higher-order modes based on simulation results.

[0114] FIG. 6 illustrates the structure of a tapered waveguide and the electric field characteristics of a beam propagating along the tapered waveguide according to one embodiment of the present invention.

[0115] FIG. 6(a) illustrates a plan view of a tapered waveguide according to an embodiment of the present invention. FIG. 6(b) illustrates the electric field distribution of a beam propagating along the tapered waveguide of FIG. 6(a). FIG. 6(c)-(m) illustrate cross-sectional mode profiles at different locations of the tapered waveguide of FIG. 6(a).

[0116] Referring to FIG. 6, the tapered waveguides of the first waveguide (110) and the second waveguide (120) designed according to one embodiment of the present invention are characterized in that the equal width waveguide section is formed with a waveguide width of 500 nm, and the tapered section introduces a tapered structure with a length of 100 μm at the end portion to increase the mode field diameter (MFD) of the waveguide, thereby reducing the waveguide width from 500 nm to 150 nm from the equal width waveguide.

[0117] As shown in Fig. 6, when the mode field diameter (MFD) increases, the sensitivity to angular and positional errors during optical coupling decreases, which lowers the difficulty of alignment and improves coupling stability. This increases optical coupling efficiency and improves overall stability. In addition, reducing the waveguide width has the effect of suppressing the propagation of higher-order modes, thereby contributing to maintaining single-mode propagation.

[0118] [Metasurface for Optical Coupling]

[0119] FIG. 7 is a schematic diagram illustrating the structure of a metasurface (210) for optical coupling according to one embodiment of the present invention.

[0120] Referring to FIG. 7, in an irreversible polarization rotator according to one embodiment of the present invention, the optical coupling metasurface (210, MS) serves to convert a divergent beam radiated from the end of the first waveguide (110) into a parallel beam. The optical coupling metasurface (210, MS) according to one embodiment of the present invention is designed with a structure in which rectangular pillars (212) of metaatoms made of hydrogenated amorphous silicon (a-Si:H) are arranged on a transparent SiO2 substrate (211), and the phase of light at each position is precisely controlled by adjusting the horizontal and vertical dimensions of the rectangular pillars of the metaatoms.

[0121] According to one embodiment of the present invention, a metasurface (210, MS) for optical coupling is formed in a circular shape with a diameter of 150 μm or more according to a set periodic interval, such that the metasurface faces the first waveguide (110) at a distance of 100 μm corresponding to the focal length from the end of the first waveguide (110).

[0122] FIG. 8 illustrates a schematic diagram of a metaatom of a metasurface (210, MS) for optical coupling in an irreversible polarization rotator according to one embodiment of the present invention.

[0123] Referring to FIG. 8, a metaatom designed according to one embodiment of the present invention has an a-Si:H rectangular prism structure (212) formed on a silicon dioxide (SiO2) substrate with a thickness of 0.5 μm. The height (h) of the metaatom is 930 nm, and the spacing period Λ between each metaatom is designed to be 800 nm. Based on the 1550 nm wavelength band, the refractive indices of SiO2, a-Si:H, and space air are 1.44, 3.42, and 1.00, respectively. When light passes through the optical coupling metasurface (210, MS), the phase of the light is controlled according to the horizontal and vertical dimensions (w1, w2) of the metaatom and the difference in refractive index. Through this, a desired phase value can be realized.

[0124] FIG. 9 illustrates the results of calculating the transmittance and phase of x-polarized light according to the size of the metaatom at a wavelength of 1550 nm according to one embodiment of the present invention.

[0125] As shown in Fig. 9, transmittance and phase were calculated by varying the size of the metatom from 100 nm to 550 nm in 5 nm increments using ANSYS Lumerical FDTD simulation. The size and arrangement of the metatom were designed to implement the phase at each position, and in particular, the size of the metatom was optimized to consider fabrication feasibility while maintaining the continuity of the phase distribution.

[0126] In one embodiment of the present invention, eight metaatoms are selected and arranged as a metaatom unit cell group at π / 4 intervals to provide 2π phase control. From FIG. 9, it can be seen that the transmittance of each metaatom at a wavelength of 1550 nm is 85% or higher, and that a gradual π / 4 phase shift has been achieved.

[0127] Table 1 shows the specifications of the metaatom of the optical coupling metasurface (210, MS) according to one embodiment of the present invention.

[0128] ParameterSymbolValueWavelengthλ1550 nmPitch of the meta-atomΛ800 nmThickness of the meta-atomh930 nmDimensions of the meta-atomw1150~505 nmw2145~530 nmRefractive index(@ λ=1550 nm)n a-si:H 3.42n siO2 1.44n air 1

[0129] Table 2 shows the width, height, and characteristics of each metaatom of the metaatom unit cell group in a metasurface (210, MS) for optical coupling according to one embodiment of the present invention.

[0130] UC#w1[nm]w2[nm]T Ex [au]Φ Ex [rad.]SimulatedTarget11504750.900.15022153950.910.770.7932404050.911.481.5742605300.8 72.442.3654801450.823.243.1463752250.903.803.9374102500.874.834.7185052600.875.365.50

[0131] According to one embodiment of the present invention, the proposed optical coupling metasurface (210, MS) is designed with a focal length of 100 μm to generate a parallel beam with a diameter of 150 μm as shown in FIG. 7.

[0132] According to one embodiment of the present invention, the phase distribution of the proposed optical coupling metasurface (210, MS) is calculated by the following function.

[0133] [Mathematical Formula 1]

[0134]

[0135] Here, x and y are the position coordinates of the metatom, f is the focal length, and λ is the wavelength of light.

[0136] The calculated phase values ​​are designed and arranged into metaatom unit cell groups so that they are evenly distributed from 0 to 2π.

[0137] FIG. 10 illustrates the phase distribution of a metasurface (210, MS) for optical coupling and the arrangement pattern structure of metaatoms arranged on the metasurface (210, MS) for optical coupling according to one embodiment of the present invention.

[0138] Figure 10(a) shows the result of calculating the phase distribution of MS, and Figure 10(b) shows the layout of the array structure of the arranged metatoms.

[0139] A metasurface (210, MS) for optical coupling according to one embodiment of the present invention is quantized with the phase values ​​of the meta-atom unit cell groups of eight designed meta-atoms and has a phase distribution as shown in FIG. 10(a), and the layout of the MS structure arranged with meta-atoms corresponding to the phase values ​​at each position is as shown in FIG. 10(b).

[0140] FIG. 11 illustrates the focusing performance characteristics of a parallel beam passing through a metasurface (210, MS) for optical coupling according to one embodiment of the present invention.

[0141] Figure 11(a) shows the x-component electric field strength, Figure 11(b) shows the cross-sectional beam profile at a focal length of 100 μm, and Figure 11(c) shows the y-component electric field strength.

[0142] The performance of the optical coupling metasurface (210, MS) designed according to one embodiment of the present invention was verified through 3D FDTD simulation. As a result of the simulation, it was confirmed that after an x-polarized parallel beam with a diameter of 150 μm at a wavelength of 1550 nm passed through the optical coupling metasurface (210, MS), only the x-component beam was focused at a focal length of 100 μm as shown in FIG. 11(a) and (b), and the y-component beam was not present as shown in FIG. 11(c).

[0143] In addition, the transmission efficiency of the optical coupling metasurface (210, MS) designed according to one embodiment of the present invention is 76%.

[0144] [Magneto-Optical Film (MOF)]

[0145] In an irreversible polarization rotator according to one embodiment of the present invention, the magneto-optical film (220, MOF) plays a key role in the irreversible polarization rotator module (200) and is a major component that implements irreversible polarization rotation characteristics. The magneto-optical film (220, MOF) rotates the polarization of light using the Faraday effect and, unlike a general half-wave plate, provides irreversible characteristics because it maintains the same magnetic field directionality in the transmission and reception directions.

[0146] The Faraday effect is a phenomenon in which the direction of polarization rotates according to the direction of the magnetic field when light passes through a magneto-optical material; this angle of rotation is determined by the relative direction of the magnetic field to the direction of light propagation. The formula for the angle of polarization rotation is as follows:

[0147] [Mathematical Formula 2]

[0148]

[0149] Here, θ Fθ is the polarization rotation angle, V is the Verde constant, B is the magnetic field strength, and L is the thickness of the magneto-optical material. In one embodiment of the present invention, the magneto-optical film (220, MOF) applied is permanently magnetized and provides a stable polarization rotation angle through its inherent magnetization characteristics even without an external magnetic field.

[0150] The magneto-optical film (220, MOF) material applied in one embodiment of the present invention is bismuth-doped rare-earth iron garnet (BIG) from Coherent, USA. BIG provides sufficient polarization rotation even at a small thickness due to its high Verde constant (~3000 rad / T / m), which is very advantageous for integrated optical devices. The product name used is “FLL Garnet - Low Loss Faraday Rotator” from Coherent, USA. The thickness of the magneto-optical film used in one embodiment of the present invention is 430 μm, and the refractive index is 2.356 in the 1550 nm wavelength band.

[0151] BIG-based magneto-optical films provide 45° polarization rotation by maintaining a stable magnetization state even in environments without external magnetic fields through their residual magnetic properties. This reduces energy consumption and enables design simplification in small optical systems. In addition, they exhibit high optical transmittance (over 95%) and low loss characteristics in the 1550 nm wavelength band, acting as an essential component by maximizing the efficiency of irreversible polarization rotators.

[0152] PropertiesFLL garnetTemperature Coefficient; dθ / dT (deg / ℃)-0.065Wavelength Dispersion; dθ / dλ (deg / nm)-0.07 @1550 nmThermal Expansivity; α(°C) -1 )11.0 x 10 -6 Refractive Index; n2.356 @1550 nmCurie Temperature; Tc (℃)270Specific Faraday Rotation; θ / t (deg / nm)-105 @1550 nmThickness for 45 degrees; t (㎛)~430 @1550 nmSaturating Field; Hs(Oersted)≤1000 for 11 x 11 mm

[0153] Table 3 shows the specifications of the “FLL Garnet - Low Loss Faraday Rotator” from Coherent, USA, which was used as a magneto-optical film in one embodiment of the present invention.

[0154] [Meta-Waveplate (230, MWP)]

[0155] FIG. 12 illustrates a schematic diagram of a metasurface wave plate (230, MWP) according to one embodiment of the present invention.

[0156] According to one embodiment of the present invention, the proposed metasurface waveplate (230, MWP) simultaneously performs the function of a metasurface and the role of a half-waveplate.

[0157] As shown in FIG. 12, the wave plate (230, MWP) focuses a parallel beam with a diameter of 150 μm onto a focal length of 100 μm to improve the optical coupling efficiency with the output second waveguide. In addition, it controls the polarization of the light and plays a key role in the irreversible polarization rotator.

[0158] FIG. 13 is a diagram illustrating the operating principle of a metasurface wave plate (230, MWP) according to one embodiment of the present invention.

[0159] The Jones matrix of the half-wave plate, which is the main role of the metasurface wave plate (230, MWP) according to one embodiment of the present invention, is as follows.

[0160] [Mathematical Formula 3]

[0161]

[0162] At this time, if the half-wave plate is rotated by a specific angle θ, it is combined with the rotation matrix R(θ) and expressed as the following mathematical equation 4.

[0163] [Mathematical Formula 4]

[0164]

[0165]

[0166] Input polarization J with a specific angle α in When this exists, output polarization (J out The Jones matrix of ) is equal to the following mathematical equation 5.

[0167] [Mathematical Formula 5]

[0168]

[0169] Therefore, the output polarization is rotated by twice the angle formed by the input polarization and the fast axis of the half-wave plate. That is, as shown in FIG. 13, the angle of the output polarization is the value obtained by subtracting the angle of the input polarization from twice the angle at which the half-wave plate is rotated.

[0170] FIG. 14 illustrates a schematic diagram of a metaatom of a metasurface wave plate (230, MWP) according to one embodiment of the present invention.

[0171] Referring to FIG. 14, the metaatoms of the metasurface wave plate (230, MWP) according to one embodiment of the present invention are designed with a structure in which rectangular metaatom prisms made of hydrogenated amorphous silicon (a-Si:H) are arranged on a transparent SiO2 substrate at intervals of lattice period (Λ) in a shape tilted at 22.5° from the x-axis, and the phase of light at each position is precisely controlled by adjusting the horizontal and vertical dimensions of the rectangular prisms. The metasurface wave plate (230, MWP) according to one embodiment of the present invention is formed in a circular shape with a diameter of 150 μm or more, such that the metasurface faces the second wave guide (120) at a distance of 100 μm from the inverse taper end of the second wave guide (120).

[0172] A metaatom designed according to one embodiment of the present invention is formed as an a-Si:H rectangular prism (232) structure tilted at 22.5° from the x-axis on a silicon dioxide (SiO2) substrate (231) with a thickness of 0.5 μm.

[0173] Table 4 shows the specifications of the metaatoms of a metasurface wave plate (230, MWP) according to one embodiment of the present invention. Referring to Table 4, the height h of the rectangular prism of the metaatom is 930 nm, and the spacing period Λ between each metaatom is designed to be 800 nm.

[0174] ParameterSymbolValueWavelengthλ1550 nmPitch of the meta-atomΛ800 nmThickness of the meta-atomh930 nmDimensions of the meta-atomw1150~505 nmw2145~530 nmRefractive index(@ λ=1550 nm)n a-si:H 3.42n siO2 1.44n air 1

[0175] Each metaatom of the metasurface wave plate (230, MWP) acts as a half-wave plate, and to control the polarization of light, the tilted angle of the metaatom is determined to be 22.5° from the x-axis as shown in FIG. 14. According to Equation 5 described above, if the polarization direction of the input light and the fast-axis of the metaatom differ by 22.5°, the polarization of the input light is rotated by 45°.

[0176] As previously explained, the metasurface wave plate (230, MWP) is designed to focus a parallel beam with a diameter of 150 μm to a focal length of 100 μm (second focal point) in order to perform the same focusing and collimating functions as the optical coupling metasurface (210, MS).

[0177] In addition, to enable the MWP to operate as a half-wave plate, the rotation angle of the metatom was determined to be 22.5°, and the design was made such that the phase difference between the metatom's fast axis and slow axis is π. The phase difference of the metatom is calculated using the following mathematical equation 6.

[0178] [Mathematical Formula 6]

[0179]

[0180]

[0181] Here, n eff_TE0 , n eff_TM0 θ represents the effective refractive index of the metaatom for the TE0 and TM0 modes, respectively, λ represents the wavelength of light, and h represents the height of the rectangular prism of the metaatom.

[0182] FIG. 15 illustrates an example of calculating the phase difference between the fast axis and the slow axis according to the width and height of the metaatom in a metasurface wave plate (230, MWP).

[0183] By calculating the difference in the effective refractive index of the metaatom for the TE0 and TM0 modes and substituting it into Equation 7 below as shown in Fig. 15, the phase difference between the fast axis and the slow axis of the metaatom can be derived.

[0184] [Mathematical Formula 7]

[0185]

[0186] Table 5 shows the width, height, and phase change characteristics of each metaatom in the metaatom unit cell group in the metasurface wave plate (230, MWP) according to one embodiment of the present invention.

[0187] UC#w1[nm]w2[nm]T Ex [au]Φ Ex[rad.]SimulatedTarget11504750.850022153950.930.740.7932404050.861.501.5742605300.90 2.212.3654801450.943.223.1463752250.983.803.9374102500.934.564.7185052600.875.365.50

[0188] Referring to Table 5, in one embodiment of the present invention, a metasurface wave plate (230, MWP) is configured such that eight metaatoms of different sizes are selected and arranged as metaatom unit cell groups at intervals of π / 4 to provide 2π phase control.

[0189] FIG. 16 illustrates the x-component transmittance and phase calculation results for 45° polarized light according to the width and height of each metaatom when a light beam of 1550 nm wavelength is transmitted through a metasurface wave plate (230, MWP) according to one embodiment of the present invention.

[0190] In one embodiment of the present invention, the transmittance and phase of eight metaatoms were verified using FDTD simulation as shown in FIG. 16. To verify the performance of the half-wave plate, the rotation angle of the metaatoms was set to 22.5° and the polarization direction of the light to 45°, and the transmittance and phase for the x-component were checked. As a result of the simulation, the eight metaatoms exhibited a transmittance of over 85% at a wavelength of 1550 nm, and the phase of each metaatom gradually shifted by π / 4. In addition, the phase difference between the fast axis and the slow axis had an average error of approximately ±0.04π from the target value of π, indicating that the design objective was satisfied.

[0191] FIG. 17 shows the phase distribution of a metasurface wave plate (230, MWP) and the arrangement pattern structure of a metatom according to one embodiment of the present invention.

[0192] Referring to FIG. 17, a metasurface wave plate (230, MWP) according to one embodiment of the present invention is quantized with the phase values ​​of eight designed metaatoms to have a phase distribution as shown in FIG. 17(a), and the layout of the metasurface wave plate (230, MWP) structure arranged with metaatoms corresponding to the phase values ​​of each position is shown as in FIG. 17(b).

[0193] According to one embodiment of the present invention, the metaatom of the metasurface wave plate (230, MWP) is designed to have the same size as the optical coupling metasurface (210, MS) described above, and the phase distribution of the entire structure is also the same, so it is characterized by having the same focusing function. In the case of the metasurface wave plate (230, MWP), by rotating the angle of the metaatom to 22.5°, it is further characterized by simultaneously performing the role of a half-wave plate that has a 45° polarization rotation effect for x-polarized light.

[0194] That is, the metasurface wave plate (230, MWP) is characterized in that each metaatom is arranged in the same size and pattern as the optical coupling metasurface (210, MS), except that the rectangular prisms of each metaatom are formed at an angle of 22.5° from the x-axis.

[0195] FIG. 18 illustrates the characteristics of focusing and half-wave plate performance after a parallel beam polarized by 45° rotated passes through a metasurface wave plate (230, MWP) according to one embodiment of the present invention.

[0196] Figure 18(a) shows the x-component and Figure 18(b) shows the y-component electric field intensity and the cross-sectional beam profile at a focal length of 100 μm.

[0197] FIG. 18 shows the transmittance and polarization rotation efficiency calculated through 3D FDTD simulation of the designed metasurface waveplate (230, MWP). As a result of the simulation, it was confirmed that after a parallel beam polarized at 45° with a diameter of 150 μm at a wavelength of 1550 nm passed through the metasurface waveplate (230, MWP), only x-polarized light was focused at a focal length of 100 μm (second focal point) as shown in FIG. 18(a), and y-polarized light had a negligible intensity compared to x-polarized light as shown in FIG. 18(b).

[0198] FIG. 19 shows the polarization change characteristics of a beam passing through an MWP according to the polarization of a beam incident on a metasurface wave plate (230, MWP) according to one embodiment of the present invention.

[0199] Referring to FIG. 19, the transmittance of the designed metasurface wave plate (230, MWP) is 74%, and the polarization rotation efficiency is calculated to be 98.6%.

[0200] In one embodiment of the present invention, to verify the results of calculating polarization rotation efficiency, a vector arrow was added to the cross-sectional beam profile at the focal length (second focal point) as shown in FIG. 19 to confirm the polarization direction. Referring to FIG. 19, it was confirmed that when x-polarized light is incident, the polarization rotates 45° after passing through the MWP, and when 45° polarized light is incident, the polarization rotates -45° after passing through the MWP to become x-polarized light, thereby performing the function of a half-wave plate.

[0201] Unlike conventional bulk-type irreversible polarization rotators, the irreversible polarization rotator with an integrated metasurface according to one embodiment of the present invention can be implemented within a single chip based on a silicon waveguide, thereby significantly improving integration density.

[0202] According to one embodiment of the present invention, the optical coupling metasurface (210, MS) designed has a transmission efficiency of 76%. In addition, the metasurface wave plate (230, MWP) has a transmittance of 74% and a polarization rotation efficiency of 98.6%.

[0203] An irreversible polarization rotator with a metasurface integrated according to one embodiment of the present invention has an irreversible polarization rotation characteristic by the characteristic that in the forward direction, the output light maintains the same TE0 mode as the input light, and in the reflection direction, a polarization mode (TM0) orthogonal to the input light (TE0) is output.

[0204] An irreversible polarization rotator integrated with a metasurface according to one embodiment of the present invention has the effect of distinguishing reflected light from input light and sensing it simply and compactly by utilizing the converted polarization mode characteristics of reflected light at the input end during the input and output of a light beam through a single microchip. In addition, irreversible polarization rotation characteristics can be realized without an external magnetic field through a permanently magnetized magneto-optical film.

Claims

1. In an irreversible polarization rotator, The above irreversible polarization rotator is, A chip housing having a trench-shaped empty space region formed in the center, an irreversible polarization rotation module mounted in the space region to perform an irreversible polarization rotation function, a first waveguide formed so that its end contacts the space region on one side of the chip housing, and a second waveguide formed so that its end contacts the space region on the other side of the chip housing. The above irreversible polarization rotation module is, A metasurface for optical coupling formed in the direction of a first waveguide and performing collimating and focusing functions of a transmitted light beam; A metasurface wave plate that forms a metasurface in the direction of a second waveguide and performs polarization rotation, collimating, and focusing functions of a transmitted light beam; and An irreversible polarization rotator with an integrated metasurface, characterized by including: a magneto-optical film mounted between the optical coupling metasurface and the metasurface wave plate, which maintains the polarization rotation of the transmitted light beam and the same magnetic field direction in both directions.

2. In Paragraph 1, The above chip housing is a base substrate formed of silicon (Si); A silicon dioxide embedded oxide layer formed of SiO2 on the above base substrate; A Si waveguide formed of silicon (Si) material in the upper center of the silicon dioxide-filled oxide layer; and A silicon dioxide cladding layer covering the periphery and top of the waveguide; comprising, An irreversible polarization rotator with an integrated metasurface, characterized in that the above waveguide is the above first waveguide or second waveguide.

3. In Paragraph 2, An irreversible polarization rotator with an integrated metasurface, characterized in that the above Si waveguide is formed with a thickness of 0.22 μm and a width of 500 nm, and the above silicon dioxide cladding layer is formed up to 2.2 μm above the Si waveguide.

4. In Paragraph 1, An irreversible polarization rotator with an integrated metasurface, characterized in that the above-mentioned optical coupling metasurface performs the function of converting a forward beam incident by diverging from the focal point of the above-mentioned optical coupling metasurface into a parallel beam, and performs the function of focusing a beam incident as a reverse parallel beam at the focal point of the above-mentioned optical coupling metasurface and outputting it.

5. In Paragraph 4, An irreversible polarization rotator with an integrated metasurface, characterized in that the metasurface wave plate rotates a parallel beam incident in the forward direction to -45° polarization and focuses it to the focal point of the metasurface wave plate for output, and also rotates a divergent beam incident in the reverse direction to +45° polarization and converts it into a parallel beam for output.

6. In Paragraph 5, An irreversible polarization rotator with an integrated metasurface, characterized in that the magneto-optical film outputs a forward beam rotated by +45° and also outputs a reverse beam incident in the reverse direction rotated by +45°.

7. In Paragraph 1, The input beam of the TE0 mode input in the forward direction is diverged from the end of the first waveguide and converted into a parallel beam through the optical coupling metasurface, and the converted parallel beam is polarized by +45° while passing through the magneto-optical film and polarized by -45° while passing through the metasurface wave plate, and the transmitted beam is focused and output to the second waveguide, wherein the output beam maintains the same TE0 mode as the input beam. An irreversible polarization rotator with an integrated metasurface, characterized in that an input beam of TE0 mode input in the reverse direction is diverged from the end of the second waveguide, passes through the metasurface waveplate to be converted into a parallel beam and then converted into polarization rotated by +45°, passes through the magneto-optical film and is further rotated by +45° to be converted into TM0 mode, and then the converted TM0 mode beam passes through the optical coupling metasurface, is focused, and outputs to the first waveguide, so that the beam input in the reverse direction outputs a TM0 mode that is orthogonal to the input light (TE0).

8. In Paragraph 1, An irreversible polarization rotator with an integrated metasurface, wherein the first waveguide is characterized by having a tapered structure with a terminal length of 10 μm from a 500 nm uniform width waveguide, and the tapered structure is formed such that the end portion decreases to 150 nm over the width of the waveguide from 500 nm to 10 μm.

9. In Paragraph 1, An irreversible polarization rotator with an integrated metasurface, characterized in that the second waveguide is formed with an end portion extending from 150 nm to 500 nm over a length of 10 μm and a portion formed with an equal width of 500 nm.

10. In Paragraph 1, Each metaatom forming the above-mentioned optical coupling metasurface has an a-Si:H rectangular prism structure formed on a silicon dioxide substrate with a thickness of 0.5 μm, the height (h) of the metaatom is 930 nm, and the spacing period (Λ) between each metaatom is 800 nm. The above-mentioned optical coupling metasurface is configured such that eight metatoms of different widths and heights are selected and arranged as metatom unit cell groups at π / 4 intervals to provide 2π phase control, An irreversible polarization rotator with an integrated metasurface, characterized by being selected and arranged into metaatom unit cell groups such that the phase values ​​calculated by the following mathematical formula 1 are evenly distributed from 0 to 2π. [Mathematical Formula 1] 11. In Paragraph 10, Each metaatom forming the above metasurface wave plate is formed on a silicon dioxide substrate with a thickness of 0.5 μm in the shape of an a-Si:H rectangular prism tilted at 22.5° from the x-axis, the height (h) of the metaatom is 930 nm, and the spacing period (Λ) between each metaatom is 800 nm. An irreversible polarizing rotator integrated with a metasurface, characterized in that the metasurface of the above metasurface wave plate is configured such that eight metatoms with different horizontal and vertical sizes are selected and arranged as metatom unit cell groups at intervals of π / 4 to provide 2π phase control.

Images