Feedback-suppressed optical isolation systems, their isolation methods, and applications

Abstract

A feedback-suppressed optical isolation system, its isolation method, and its application are disclosed. The feedback-suppressed optical isolation system includes a source end, a source end shaping module, a resonant metasurface, a functional optical path, a return interface, a return light decoupling module, and a waste light port. The return light decoupling module is configured to cause parameter mismatch in the return light from the return interface, thus decoupling it from the resonant window of the resonant metasurface. This invention employs a system architecture co-designed with the source end shaping module, the resonant metasurface, the return light decoupling module, and the waste light port. This architecture precisely matches the forward working light to the narrow-band high-Q resonant window of the resonant metasurface for efficient passage, while the return light, due to the conditional offset introduced by the return light decoupling module in the reverse path, cannot satisfy the same resonant window again. This overcomes the limitations of existing optical isolation schemes that rely on magneto-optical materials or external excitation, thereby achieving a completely passive source end feedback suppression function in the optical communication band.

Description

Technical Field

[0001] This invention relates to the field of optical isolation technology, and in particular to a feedback suppression optical isolation system based on a resonant metasurface, its isolation method, and its application. Background Technology

[0002] In optical communication, lidar, external cavity semiconductor lasers, coherent detection modules, and free-space coupling systems, back-reflected light entering the laser source or input waveguide can easily cause problems such as mode switching, frequency jitter, increased noise, phase instability, and output power fluctuations. Therefore, it is usually necessary to set up an optical isolator between the light source and the external optical path.

[0003] Existing optical isolators mostly employ magneto-optical materials combined with Faraday rotation to achieve non-reciprocal polarization rotation, and then combine this with a polarizer to achieve forward transmission and backward blocking. Although this type of solution is mature, it usually faces problems such as large size, poor compatibility with planar processes, and difficulty in miniaturization and high integration into on-chip systems.

[0004] On the other hand, metasurfaces and metasurface gratings have been widely used in recent years for filtering, beam splitting, focusing, spectral analysis, polarization imaging, and angle-selective transmission due to their advantages such as ultrathinness, ease of integration, and ease of designing wavefront and polarization responses. In particular, guided-mode resonant gratings, leaky-mode resonant gratings, and quasi-Bound State in the Continuum (quasi-BIC) resonant metasurfaces can form high-quality factor (Q-factor) resonances in narrow or even extremely narrow wavelength bands, and their resonance center will drift significantly with the incident angle, azimuth angle, polarization state, and surrounding medium environment.

[0005] Existing angle-selective filters, guided-mode resonant filters, and quasi-BIC narrowband structures mostly focus on achieving narrowband filtering, angle sensing, spectral detection, polarization multiplexing, or high-Q resonance enhancement, without fully addressing the application goal of "source-end feedback suppression" in system design. Even those structures with angle sensitivity are often used as ordinary filters without establishing structured asymmetric conditions between the "forward operating state" and the "backward recoupling state." Especially for laser source protection scenarios, relying solely on an ordinary angle filter is usually insufficient because if the reverse return light again meets the same incident conditions, it may still couple back to the source.

[0006] In the process of realizing this invention, the inventors discovered at least the following problems in the prior art: First, traditional magneto-optical isolators are large in size and incompatible with planar processes; Second, existing metasurface isolation schemes rely on high-intensity nonlinear effects or external pump sources, and cannot operate passively in the optical communication band; Third, existing narrowband resonant structures are only used as filters, and have not formed a system-level feedback suppression design of "high forward coupling and low backward recoupling"; Fourth, there is a lack of a complete system scheme that coordinates the design of source beam shaping, resonant metasurface, backlight decoupling, and waste light port.

[0007] In view of this, it is necessary to provide a feedback suppression optical isolation system based on resonant metasurfaces, as well as its isolation method and application, to solve the above-mentioned technical problems. Summary of the Invention

[0008] The present invention aims to solve at least one of the technical problems existing in the prior art by providing a feedback suppression optical isolation system and corresponding optical devices, optical systems and isolation methods to address the shortcomings of existing optical isolation solutions in terms of on-chip integration compatibility, return light source protection and system-level feedback suppression.

[0009] In a first aspect, the present invention provides a feedback suppression type optical isolation system, comprising: a source end configured to output working light; a source end shaping module disposed downstream of the source end, the source end shaping module being used to shape the working light into an incident beam having a set incident angle, a set spectral broadening, a set azimuth angle, and a set polarization state; a resonant metasurface disposed downstream of the source end shaping module, the resonant metasurface being configured to excite surface resonance with an incident beam satisfying a resonance window condition and exit along a positive working path; a functional optical path disposed downstream of the resonant metasurface, configured to transmit the working light passing through the resonant metasurface to a target region; a return interface disposed downstream of the functional optical path; a return decoupling module disposed between the resonant metasurface and the functional optical path, at least one location within the functional optical path; the return decoupling module being configured to cause parameter mismatch in the return light from the return interface to decouple from the resonance window of the resonant metasurface; and a waste light port configured to receive return light that has not been recoupled back to the source end. The resonance window condition is that the set incident angle of the incident beam, its set angular spectrum broadening range, set azimuth angle, and set polarization state all fall within the resonance allowable range of the resonant metasurface.

[0010] In some embodiments, the resonant metasurface is selected from one of the following: a transmission-guided mode resonant metasurface, a reflection-guided mode resonant metasurface, a quasi-continuous domain bound state resonant metasurface, a Fano resonant metasurface, or a leaking mode resonant metasurface.

[0011] In some embodiments, the unit structure of the resonant metasurface is at least one of rectangular pillars, elliptical pillars, double rod structures, cross-shaped structures, slotted structures, or H-shaped structures, and the unit structure is arranged in a rectangular lattice or a hexagonal lattice.

[0012] In some embodiments, the resonant metasurface includes a first resonant metasurface layer, a spacer layer, and a second resonant metasurface layer, wherein the first resonant metasurface layer and the second resonant metasurface layer are configured to simultaneously satisfy the resonant transmission condition at the set incident angle and the set operating wavelength, forming a double-layer cascaded resonant window.

[0013] In some embodiments, the first resonant metasurface layer and the second resonant metasurface layer have different resonant peak positions or different angular response characteristics, so that the returned light cannot simultaneously satisfy the resonant window conditions of the first resonant metasurface layer and the second resonant metasurface layer after propagating through the spacer layer.

[0014] In some implementations, the phase matching of the resonant metasurface satisfies: ;in, The propagation constant of the guided mode or the leakage mode. For free space wavenumber, The refractive index of the incident medium is... Angle of incidence For diffraction orders, The grating period is [value]. The resonance window condition satisfies: ;in To set the operating wavelength, For the angle of incidence Azimuth and polarization state The resonant center wavelength under certain conditions The full width at half maximum (FWHM) of the resonance peak of the resonant metasurface.

[0015] In some implementations, the return light decoupling module is configured such that the angular offset generated by the returned light is greater than or equal to the half-width of the resonant window angle of the resonant metasurface.

[0016] In some embodiments, the source-end shaping module includes at least one of a microlens, a cylindrical lens, a collimating lens, an aperture stop, a fiber collimator, a prism, a wedge, or a coupling lens.

[0017] In some embodiments, the source-end shaping module further includes a polarization control element configured to adjust the polarization state of the working light to the set polarization state.

[0018] In some embodiments, the reflective decoupling module includes at least one of a wedge plate, a tilted reflective interface, a prism reflective surface, a polarization perturbation plate, a phase retardation plate, a non-conjugate imaging optical path, or a spatial bias structure.

[0019] In some embodiments, the return light decoupling module includes a wedge plate disposed between the resonant metasurface and the functional optical path. The wedge plate is configured to deflect the incident light beam to an incident angle that satisfies the resonant window condition in the forward path, and to cause the returned light to reach the resonant metasurface again at an angle deviating from the set incident angle in the reverse path.

[0020] In some embodiments, the waste light port includes at least one of an absorption film layer, an absorption cavity, a bypass waveguide, a tilted scattering port, or a non-working detection surface.

[0021] In some embodiments, the source-end shaping module is configured to adjust the working light to a first polarization state, and the return light decoupling module includes a polarization perturbation element configured to at least partially convert the returned light to a second polarization state different from the first polarization state during reverse propagation.

[0022] In some embodiments, the material of the resonant metasurface is selected from at least one of silicon, titanium dioxide, silicon nitride, or germanium.

[0023] In some implementations, the operating wavelength is set to be within the optical communication band of 1500nm to 1650nm.

[0024] In some implementations, the joint optimization of the quality factor and manufacturing tolerance of the resonant metasurface is configured to satisfy the following: within a preset manufacturing tolerance range, the resonant peak position drift of the resonant metasurface does not exceed half the width of the resonant window condition.

[0025] Secondly, the present invention also provides a feedback suppression type optical isolation method, comprising the following steps: S1: shaping the working light output from the source end into an incident beam having a set incident angle, a set spectral broadening, a set azimuth angle, and a set polarization state through a source end shaping module, so as to satisfy the resonance window condition of the resonant metasurface; S2: allowing the incident beam to enter the functional optical path through the resonant metasurface, wherein the resonant metasurface allows the incident beam to pass through with a transmittance higher than a first preset threshold under the resonance window condition; S3: in the return path from the functional optical path to the resonant metasurface, causing the return light to undergo at least one conditional offset relative to the incident beam of step S1 when it reaches the resonant metasurface again through a return light decoupling module, so that the return light does not satisfy the resonance window condition; and S4: guiding the return light that has not been recoupled back to the source end to the waste light port.

[0026] In some embodiments, the resonant metasurface is a quasi-continuous domain bound state resonant metasurface, which transforms the continuous domain bound state mode into a quasi-continuous domain bound state resonant mode with a finite quality factor by breaking the structural symmetry.

[0027] Thirdly, the present invention also provides an optical device, including the aforementioned feedback suppression type optical isolation system.

[0028] Fourthly, the present invention also provides an optical system, comprising: a light source for emitting the working light; an application optical path; and the feedback suppression type optical isolation system disposed on the optical path between the light source and the application optical path for suppressing return light returning from the application optical path to the light source.

[0029] One of the above technical solutions has the following advantages: This invention adopts a system architecture that collaboratively designs a source-end shaping module, a resonant metasurface, a return light decoupling module, and a waste light port. This invention uses the source-end shaping module to pre-set the incident angle, spectral broadening, azimuth angle, and polarization state of the forward working light, ensuring it meets the resonant allowable window conditions of the resonant metasurface; the forward working light efficiently transmits into the functional optical path within the resonant allowable window. When the return light reaches the resonant metasurface again, it deviates from the resonant allowable window due to shifts in angle, azimuth angle, polarization state, spectral density, or wavefront conditions, and is guided to the waste light port or the return light decoupling path, thereby achieving feedback-suppressed optical isolation.

[0030] Through the coordinated operation of the source-end shaping module and the resonant metasurface, the forward beam is actively shaped to precisely match the narrow-band resonant window of the resonant metasurface, achieving high-efficiency forward transmission. At the same time, the natural sensitivity of the narrow-band resonant window to angle and wavefront provides a physical basis for reverse isolation. It does not rely on magneto-optical materials or external magnetic fields and is compatible with planar photonic integration processes such as silicon-based and silicon nitride-based materials.

[0031] By employing a four-level collaborative architecture consisting of a source-end shaping module, a resonant metasurface, a return light decoupling module, and a waste light port, the narrowband resonant structure is incorporated into a complete system-level feedback suppression link that covers source-end shaping, resonant selective transmission and reflection, active return light decoupling, and waste light management. This results in a quantifiable feedback suppression ratio, fundamentally changing the existing paradigm of treating metasurface resonances merely as local filtering devices. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the overall configuration of a feedback suppression type optical isolation structure according to one embodiment of the present invention.

[0033] Figure 2 This is a schematic diagram illustrating the conditional differences between the forward operating state and the backward recoupling state of an optical isolator according to an embodiment of the present invention.

[0034] Figure 3 The diagram illustrates the structure of the resonant metasurface of the present invention, wherein (a) is a cross-sectional view of the resonant metasurface in one embodiment; (b) and (c) are respectively a top view and a cross-sectional view of the resonant metasurface in one embodiment from the bottom view of the substrate.

[0035] Figure 4 This is a schematic diagram of the angular drift characteristics of the resonance peak intensity as a function of the incident angle in one embodiment of the present invention.

[0036] Figure 5 This is a schematic diagram illustrating the relationship between the return coupling efficiency and the angle deviation in one embodiment of the present invention.

[0037] Figure 6 This is a schematic diagram of the single-layer transmission resonant metasurface feedback suppression structure of Embodiment 1 of the present invention.

[0038] Figure 7 This is a schematic diagram of the forward matching and backward mismatch structure of the prism and wedge plate in Embodiment 2 of the present invention.

[0039] Figure 8 In the diagram, (a) shows a schematic diagram of the double-layer cascaded resonant metasurface structure of Embodiment 3 of the present invention, (b) shows the resonance peak intensity-wavelength curve of the first resonant metasurface layer (first layer), and (c) shows the resonance peak intensity-wavelength curve of the second resonant metasurface layer (second layer).

[0040] Figure 9 In the image, (a) is a schematic diagram of the quasi-BIC high-Q resonance metasurface structure of Embodiment 4 of the present invention; (b) is a schematic diagram of the high-Q resonance spectral line intensity-wavelength curve.

[0041] Figure 10 In the diagram, (a) shows a schematic diagram of the polarization-assisted feedback suppression structure of Embodiment 5 of the present invention, and (b) shows the difference in the response of the resonance peak intensity of the TE polarization state and the TM polarization state as wavelength changes.

[0042] Figure 11 This is a curve showing the change of resonance spectrum intensity with wavelength under structural dimensional disturbances caused by manufacturing tolerances in Embodiment Six of the present invention.

[0043] Figure 12 This is a feedback suppression ratio diagram for Example 6 of the present invention.

[0044] The reference numerals in the attached figures are explained as follows: 1-Source end, 2-Source end shaping module, 21-Prism, 22-Polarization control element, 3-Resonant metasurface, 31-First resonant metasurface layer, 32-Spacer layer, 33-Second resonant metasurface layer, 34-Substrate, 35-Subwavelength grating unit, 36-Protective layer, 37-Antireflection film, 4-Functional optical path, 5-Reflection decoupling module, 51-Wedge plate, 6-Waste light port, 7-Return interface. Detailed Implementation

[0045] The present invention will now be described in detail with reference to the specific embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention, and any structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are included within the scope of protection of the present invention.

[0046] In the various figures of this invention, for ease of illustration, some dimensions of structures or parts may be exaggerated relative to other structures or parts; therefore, only the basic structure of the subject matter of this invention is used to illustrate the invention.

[0047] In the description of this invention, the terms "upstream," "downstream," "forward," "positive," "return," and "reverse" are defined relative to the direction of propagation of the working light. The direction from the source end to the return interface is considered positive, and the direction returning from the return interface is considered reverse. Light propagates from upstream to downstream along the transmission direction. A resonant metasurface refers to an artificial electromagnetic structure layer with a subwavelength structure array capable of exciting surface electromagnetic resonances (including but not limited to guided mode resonances, Fano resonances, quasi-continuous bound state resonances, and surface plasmon resonances).

[0048] Wherein, after the parameter mismatch occurs in the return light through the return light decoupling module, the return light deviates from the resonance window of the resonance metasurface and is reflected or diffracted by the resonance metasurface to the waste light port.

[0049] Please refer to Figure 1 As shown, the present invention provides a feedback suppression type optical isolation system. Its overall configuration includes at least a source end 1, a source end shaping module 2, a resonant metasurface 3, a functional optical path 4, a return light decoupling module 5, a waste light port 6 (non-source end dissipation port), and a return interface 7.

[0050] The working light emitted from source 1 passes through source shaping module 2, and is incident on resonant metasurface 3 at a set angle and set angular spectrum, before entering functional optical path 4. The return light from functional optical path 4 returns to the device after passing through return interface 7, and is guided to waste light port 6 or other non-source path.

[0051] Source 1 is configured to output working light. Source 1 can be a semiconductor laser, a narrow linewidth laser, an external cavity laser, a fiber laser, a light-emitting diode (LED), an on-chip waveguide output, or other active light sources.

[0052] The source-end shaping module 2 is located downstream of the source end and is used to perform angle shaping and / or wavefront shaping on the forward input beam so that the shaped forward beam satisfies the resonance window condition of the resonant metasurface 3.

[0053] The source-end shaping module 2 is configured to shape the working light into an incident beam with a set incident angle, a set spectral broadening, a set azimuth angle, and a set polarization state. The source-end shaping module 2 confines the incident angle center, spectral broadening, polarization state, and wavefront curvature of the forward working light within the allowable window of the resonant metasurface 3.

[0054] Specifically, the source-end shaping module 2 may include at least one of the following: microlens, cylindrical lens, collimating lens, aperture stop, fiber collimator, first prism 21, wedge plate, or coupling lens.

[0055] In some embodiments, the source shaping module 2 further includes a polarization control element 22 (e.g., a polarizer) configured to adjust the polarization state of the working light to a set polarization state that matches the resonant window conditions of the resonant metasurface 3.

[0056] In some implementations, the source-end shaping module 2 is configured to adjust the working light to a first polarization state (e.g., a linearly polarized state with TE or TM polarization). The return light decoupling module 5 includes a polarization perturbation element configured to at least partially convert the returned light to a second polarization state different from the first polarization state during back propagation. Since the resonance window condition of the resonant metasurface 3 depends on both polarization state and the return light polarization state, the change in the return light polarization state makes it more difficult to satisfy the resonance window condition, further enhancing the feedback suppression effect. It is understood that by superimposing a polarization-assisted mechanism, an independent suppression dimension can be added in addition to the angular mismatch.

[0057] The resonant metasurface 3 is located downstream of the source-end shaping module 2. The resonant metasurface 3 is configured such that incident light beams satisfying its resonant window conditions excite surface resonance and exit along the forward working path. That is, forward light beams satisfying the resonant window conditions are efficiently transmitted through the resonant window, while returning light beams that do not satisfy the resonant window conditions are reflected or diffracted by the resonant metasurface and deviate from the main optical path.

[0058] The resonant metasurface 3 can guide the truncated return light to the waste light port 6, safely exporting and dissipating the energy of the return light from the system, avoiding the accumulation of return light energy inside the system or the formation of secondary crosstalk, and improving the thermal stability and system reliability in high-power application scenarios.

[0059] The resonance window condition is defined as the incident angle of the incident beam, its set angular spectrum broadening range, set azimuth angle, and set polarization state all falling within the resonance allowable range of the resonant metasurface 3. The resonant metasurface 3 utilizes its narrow-band high-Q angle sensitivity to exhibit high transmission response only for incident light within a small segment of the angle-wavelength-polarization window.

[0060] Alternatively, the resonant metasurface 3 can be understood as being configured to allow incident light beams meeting the resonant window conditions to pass through with a transmittance higher than a first preset threshold at a set operating wavelength. The first preset threshold can be set according to specific application scenarios, for example, 80% or 90%.

[0061] The resonant metasurface 3 can be one of the following: a transmissive guided-mode resonant metasurface, a reflective guided-mode resonant metasurface, a subwavelength dielectric metasurface, a quasi-BIC resonant metasurface, a free-form metasurface, or a two-dimensional or one-dimensional metasurface grating with leakage mode resonance characteristics.

[0062] The resonant metasurface 3 can be a single-layer, double-layer, or multi-layer cascaded structure.

[0063] The unit structure of the resonant metasurface 3 can be a rectangular pillar, an elliptical pillar, a double rod structure, a cross-shaped structure, a slotted structure, an H-shaped structure, a dumbbell-shaped structure, or other micro / nano structures that can support narrowband resonance and angle-sensitive drift, and are periodically arranged in a rectangular or hexagonal lattice.

[0064] Specifically, different resonance peak positions, bandwidths, polarization responses, and angular drift behaviors can be obtained by adjusting the period Λ, structural height h, width, and symmetry breaking amount.

[0065] like Figure 3 As shown, the resonant metasurface 3 can be an asymmetric double rod, an elliptical cylinder, a rectangular cylinder, a slotted structure, or a quasi-BIC structure with slight symmetry disruption.

[0066] The phase matching of resonant metasurface 3 satisfies: .

[0067] in The propagation constant of the guided mode or the leakage mode. For free space wavenumber, The refractive index of the incident medium is... Angle of incidence For diffraction orders, The period is the grating period.

[0068] The resonance window condition can be further expressed as: .

[0069] in, To set the operating wavelength, For the angle of incidence Azimuth and polarization state The resonant center wavelength under the given conditions, where Δλ is the full width at half maximum (FWHM) of the resonant peak of the resonant metasurface 3.

[0070] The effective feedback power returned to the source can be expressed as: .

[0071] Where T is the transmission efficiency of the returned light after passing through the resonant metasurface under the current conditions. For source end 1, accept function, To return the angular spectrum-polarization distribution of light.

[0072] The material of the resonant metasurface 3 can be selected from at least one of silicon (Si), titanium dioxide (TiO2), silicon nitride (Si3N4), or germanium (Ge).

[0073] Furthermore, the material of the resonant metasurface 3 can be selected from single dielectric materials, composite materials, cladding-core structures, or locally filled structures.

[0074] The choice of materials depends on the operating wavelength. For example, in the optical communication band of 1500nm to 1650nm, silicon and silicon nitride are suitable material choices due to their high refractive index and low absorption characteristics in this band.

[0075] To achieve narrowband resonance, the nanostructure layer of resonant metasurface 3 is a periodic subwavelength structure.

[0076] In the design process, the first consideration is the impact of the cross-sectional shape and periodic arrangement of the nanostructure on narrowband efficiency and resonant position. The cross-sectional shape can be circular, rectangular, double rectangular, or double elliptical, etc. The periodic arrangement can be a rectangular lattice or a hexagonal lattice.

[0077] Under the above conditions, after passing through the resonant metasurface 3, a Lorentz-shaped transmission peak with a peak transmittance of over 99.9% can be formed, and the side lobes are suppressed to a transmittance of less than 1%, meaning that only narrow bands near the working wavelength are transmitted, while other wavelengths are reflected.

[0078] By adjusting the cross-sectional diameter, height, and period of the nanostructure unit, the center wavelength and linewidth can be changed to meet different needs.

[0079] Narrowband Q-factor (high quality factor, Q = λ / FWHM) can be achieved based on quasi-BIC resonant metasurfaces. Bound states in the continuous (BIC), as an optical confinement mechanism with an infinite Q-factor, are highly localized states embedded in the continuous spectrum coexisting with radiative modes. True BICs exist only in ideal mathematical models. When the system deviates slightly from the ideal, BIC modes couple to the extended wave and leak into the Fano resonance with a finite high Q-factor, forming quasi-BIC or metacavity modes.

[0080] There are currently two conventional types of BIC: symmetry-protected BIC and resonant interference BIC.

[0081] Symmetry-protected bipolar induction (BIC) originates from certain modes that cannot be excited due to structural symmetry. By slightly disrupting the structural symmetry, the BIC can be converted into an ultra-sharp Fano resonance, yielding ultra-high Q-factor resonance modes. The Fano resonance originates from asymmetric modes supported by an asymmetric structure, whose electromagnetic field distribution deviates slightly from that of the symmetric mode. The Q-factor can be adjusted by the degree of asymmetry. Based on symmetry-protected BIC, the high-Q resonance can be converted by slightly disrupting the excitation field symmetry through oblique incidence or by introducing structural asymmetry at the Γ point (Gamma point).

[0082] In principle, symmetry-protected BICs may also originate from bound states located at other high-symmetry points (such as X or M points) outside the Γ point, which can then be transferred to the Γ point via band folding. By perturbing multiple unit cells in the lattice, it is possible to fold high-symmetry points below the light cone (bound state) onto the light cone (continuum).

[0083] Interference-based resonant interference BIC, or parameter-tuned BIC, results from destructive interference between different channels. This linewidth loss originates from the destructive interference of anti-cross-coupled resonant modes and is independent of symmetry operations. Adjusting a sufficient number of system parameters can lead to complete elimination of radiation, thus forming a BIC.

[0084] The interference channel can be the resonance of different resonators, the resonance of the same resonator, or even a single resonance.

[0085] When a lossless resonant structure is coupled to a single radiation channel, its reflections reach uniformity near the resonant frequency.

[0086] If two resonators are arranged at a specific frequency or spacing to form a cavity, at that frequency or spacing, the wave accumulates a total phase, resulting in destructive interference between the two resonators, a BIC (Bipolar Interference Channel) is formed. This type of BIC is called Fabry Pérot BIC, and it has been verified in photonic systems. A BIC generated by the interference of two resonators belonging to the same resonator is also known as a Friedrich Wintgen (FW) BIC.

[0087] High-Q resonances are used to enhance light-matter interactions. The high-Q properties of quasi-BIC (bipolar interconductor) structures introduce flexibility in the design and realization of high-Q nanophotonic systems, making them promising for applications in lasers, sensing, and nonlinear fields. Applying BIC to CFBG (conductively coupled plasma photonics) provides new opportunities for exploring traditional laser wavelocking. Therefore, high-Q narrowband reflective CFBG functionality can be realized through quasi-BIC metasurfaces.

[0088] Feedback suppression ratio Defined as: .in This refers to the forward operating optical power. This is the effective feedback power returned to source 1.

[0089] In some embodiments, the resonant metasurface 3 includes a first resonant metasurface layer 31, a spacer layer 32, and a second resonant metasurface layer 33.

[0090] The first resonant metasurface layer 31 and the second resonant metasurface layer 33 are configured to simultaneously satisfy the resonant transmission condition under a set incident angle and a set operating wavelength, forming a double-layer cascaded resonant window.

[0091] The forward working light passes through the first resonant metasurface layer 31 and the second resonant metasurface layer 33 in sequence at a set incident angle. Both layers simultaneously satisfy the resonant transmission conditions near the working wavelength, thus the forward light transmission efficiency is high.

[0092] The returned light, due to changes in wavefront curvature, incident position shift, or azimuth angle after propagation through the spacer layer 32, cannot simultaneously satisfy the resonance window of both layers when it reaches the two-layer structure again, and is thus suppressed by at least one layer or guided to the waste light port 6.

[0093] Specifically, the first resonant metasurface layer 31 and the second resonant metasurface layer 33 are configured to have different resonant peak positions or different angular response characteristics to enhance the suppression effect on the returned light.

[0094] From a structural design perspective, such as Figure 3 As shown, the unit cell type, structural height h, period Λ, and symmetry breaking of the resonant metasurface 3 determine the subsequent peak position, bandwidth, polarization response, and angular drift behavior of the device.

[0095] From the perspective of response characteristics, such as Figure 4 As shown, when the incident angle θ of the resonant metasurface 3 changes, the resonance peak shifts accordingly. The center of the transmission resonance peak shifts for different incident angles θ; when the incident angle θ changes continuously, the center of the transmission resonance peak shifts continuously. The forward working light can be locked at the designed peak position, while the returned light will no longer transmit efficiently if the angular spectrum shifts.

[0096] like Figure 5 As shown, the curve of the normalized point illustrates the change in return (return light) coupling efficiency with angular deviation. When deviating from the design angle, the return coupling efficiency (the relative efficiency of the return light recoupled back to source 1) decreases rapidly with angular deviation. This indicates that the narrowband resonant structure has the characteristic of "high response only to a small angular spectral window".

[0097] Existing technologies typically only use this angle drift and narrow window behavior for filtering, tuning, or angle sensing. This invention further transforms it into an isolator objective of "suppressing effective power returned to source 1".

[0098] The functional optical path 4 is located downstream of the resonant metasurface 3 and is configured to transmit working light passing through the resonant metasurface 3 to the target region. The functional optical path 4 can be a free-space optical path, an optical fiber optical path, a waveguide optical path, or other optical transmission paths.

[0099] The return light decoupling module 5 is disposed between the resonant metasurface 3 and the return interface 7, specifically at least one location between the resonant metasurface 3 and the functional optical path 4, or inside the functional optical path 4. The return light decoupling module 5 is configured to cause parameter mismatch in the return light from the return interface 7 (whether it passes through the functional optical path 4 or not) to decouple from the resonant window of the resonant metasurface 3, fundamentally cutting off the path of the return light back to the light source via the resonant metasurface.

[0100] Unlike existing solutions that rely solely on the angular selectivity of the metasurface without active decoupling, the architecture of this invention, which decouples first and then reflects / diffracts, can stably suppress feedback light pointing towards source 1 under the condition that the source shaping parameters and decoupling parameters are independently controllable. Even if the forward and return light share similar physical paths, the protection of source 1 remains effective.

[0101] It should be noted that the return light decoupling module 5 is configured to cause the return light from the functional optical path 4 to undergo at least one of the following conditional shifts relative to the forward incident beam when it reaches the resonant metasurface 3 again: incident angle shift, azimuth angle shift, wavefront curvature mismatch, or polarization state change, so that the return light does not meet the resonant window conditions.

[0102] The conditional offset introduced by the return light decoupling module 5 may allow the returned light to reach the resonant metasurface 3 again, but it is difficult to simultaneously satisfy the resonant allowable window and the source end 1's acceptance condition, thereby reducing the effective optical power returned to the source end 1.

[0103] The angular offset introduced by the return light decoupling module 5 is configured to be greater than or equal to the half-width of the resonant window angle of the resonant metasurface 3, so as to ensure that the returned light reliably deviates from the resonant window in the angular dimension.

[0104] The reflection decoupling module 5 may include at least one of the following: wedge plate 51, tilted reflective interface, prism reflection surface, polarization perturbation plate, phase delay plate, non-conjugate imaging optical path, aperture stop limiting numerical aperture, or spatial bias structure.

[0105] In one specific embodiment, the return beam decoupling module 5 includes a wedge plate 51 disposed between the resonant metasurface 3 and the functional optical path 4. The wedge plate 51 is configured to deflect the incident beam to an incident angle that satisfies the resonant window condition in the forward path, and to cause the return beam to reach the resonant metasurface 3 again at an angle deviating from the set incident angle in the reverse path. Because the deflection effect of the wedge plate 51 on the beam is different in the forward and reverse propagation (due to the change in the incident sequence at the interface), the incident angle of the return beam when it reaches the resonant metasurface 3 again is different from the set incident angle of the forward working beam, thus naturally producing an angle mismatch.

[0106] Waste light port 6 is configured to receive return light that is not coupled back to source end 1, specifically, to receive return light that is reflected or diffracted by the resonant metasurface because the resonant window condition is not met. Waste light port 6 is located in the optical path of the reflection or diffraction direction of resonant metasurface 3, and is used to receive and dissipate the energy of the return beam reflected or diffracted by resonant metasurface 3.

[0107] The waste light port 6 may include at least one of an absorption film, an absorption cavity, a bypass waveguide, a tilted scattering port, or a non-working detection surface.

[0108] By directing the returned optical energy to the waste optical port 6 instead of the source port 1, system-level management of the returned optical energy is achieved, which is the key difference between this solution and the traditional isolator "blocking" approach.

[0109] This invention precisely matches the forward working light to the narrow-band high-Q resonant window of the resonant metasurface 3 for efficient passage. However, the return light cannot satisfy the same resonant window again in the reverse path due to the conditional offset introduced by the return light decoupling module 5. This overcomes the limitations of existing optical isolation schemes that rely on magneto-optical materials or external excitation, and thus realizes a completely passive source-end feedback suppression function in the optical communication band. It has the advantages of miniaturization, integrability, no need for magneto-optical materials, no need for external pump light source, and no need for high incident light intensity.

[0110] The present invention also provides a feedback suppression type optical isolation method, comprising the following steps.

[0111] S1, the working light output from source 1 is shaped into an incident beam that satisfies the resonance allowable window condition of the resonant metasurface 3 by source shaping module 2.

[0112] Specifically, the working light output from source 1 is shaped into an incident beam with a set incident angle, a set spectral broadening, a set azimuth angle, and a set polarization state, so that it satisfies the resonance window condition of the resonant metasurface 3.

[0113] S2 allows the incident light beam to enter the functional optical path 4 through the resonant metasurface 3. Under resonant window conditions, the resonant metasurface 3 allows the incident light beam to pass through with a transmittance higher than a first preset threshold.

[0114] S3, in the return path, the return light is decoupled by the return light decoupling module 5 so that when the return light reaches the resonant metasurface 3 again, it will produce at least one conditional offset relative to the forward working state, so that the resonant allowable window condition is no longer satisfied.

[0115] S4 directs the return light that has not been recoupled back to source port 1 to waste light port 6.

[0116] The resonant metasurface 3 is a quasi-continuous domain bound state resonant metasurface, which transforms the continuous domain bound state mode into a quasi-continuous domain bound state resonant mode with a finite quality factor by destroying the structural symmetry.

[0117] The present invention also provides an optical device, including the aforementioned feedback suppression type optical isolation system.

[0118] The optical device can be any one of the following: laser packaging module, fiber optic coupling module, free space emission module, external cavity laser system, lidar emission module, or coherent optical communication module.

[0119] The present invention also provides an optical system, including a light source, an application optical path, and any of the above-mentioned feedback suppression type optical isolation systems.

[0120] The light source is used to emit the working light. A feedback suppression optical isolation system is disposed on the optical path between the light source and the application optical path to suppress the return light from the application optical path back to the light source.

[0121] The feedback suppression optical isolation system of the present invention will be described below with reference to specific embodiments.

[0122] Example 1: Single-layer transmission resonant metasurface feedback suppression structure.

[0123] Please refer to Figure 6This embodiment includes a source end 1, a source end shaping module 2, a resonant metasurface 3, a functional optical path 4, a return interface 7, and a waste light port 6.

[0124] Source 1 is a semiconductor laser operating at a center wavelength of 1550nm. Source shaping module 2 includes a collimating lens and an aperture stop, which collimates the divergent beam output by the laser into a nearly parallel beam with an angular spectral broadening of less than 0.5 degrees, and incident it onto the resonant metasurface 3 at a set incident angle theta0 = 10 degrees.

[0125] Resonant metasurface 3 is a single-layer transmission-type guided-mode resonant metasurface, constructed from a silicon nanopillar array arranged in a rectangular lattice on a silicon dioxide substrate. Through optimized design, this grating exhibits a full width at half maximum (FWHM) of the guided-mode resonance peak (Δλ) of approximately 1.5 nm at a working wavelength λ0 = 1550 nm, an incident angle of 10°, an azimuth angle of 0°, and a TE polarization state. The corresponding Q value is approximately 10³³, the angular FWHM is approximately 0.3 degrees, and the forward peak transmittance exceeds 95%.

[0126] The incident beam precisely satisfies the resonance window condition and enters the functional optical path 4 through the resonant metasurface 3 with high transmittance, propagating to the target region. The return light from downstream of the functional optical path 4 is reflected or scattered by the return interface 7 and then propagates in the opposite direction. Due to the non-ideal flatness of the return interface 7 surface, finite aperture truncation, and possible scattering effects, the return light undergoes angular broadening and wavefront distortion during its reverse propagation. When the return light reaches the resonant metasurface 3 again, its angular spectrum center has deviated from the set incident angle theta0 by approximately 0.8°, and the angular spectrum broadening exceeds 1.0°. Since the 0.8° angular offset is greater than the half-width of the resonant metasurface 3 (0.3°), only a very low proportion (less than the set threshold) of the return light can satisfy the resonance window condition again; most of the return light is reflected or scattered by the resonant metasurface 3 to the waste light port 6. The feedback suppression ratio of this embodiment... It reaches approximately 15 dB at the center wavelength of 1550 nm.

[0127] Example 2: Forward matching and backward mismatch example with prism and wedge plate.

[0128] Please refer to Figure 7In this embodiment, based on Embodiment 1, a first prism 21 and a wedge plate 51 are introduced before and after the resonant metasurface 3, respectively. The first prism 21 is positioned between the source-end shaping module 2 and the resonant metasurface 3. The forward working light is deflected by the first prism 21 to the incident angle position corresponding to the resonant window condition of the resonant metasurface 3. The wedge plate 51 is positioned between the resonant metasurface 3 and the functional optical path 4. After the forward working light exits the resonant metasurface 3, it passes through the wedge plate 51 and enters the functional optical path 4. The wedge angle of the wedge plate 51 is 2°, and the deflection angle introduced during forward propagation is within the allowable range (the impact on the throughput efficiency is less than 2%). In the reverse path, the return light returns from the functional optical path 4, first passing through the wedge plate 51 before reaching the resonant metasurface 3. Because the incident interface sequence of the wedge plate 51 is different in the two directions, the deflection angle experienced by the return light during reverse propagation is different from that in the forward direction, with a net angle shift of approximately 4°, which is much larger than the half-width of the angle of the resonant metasurface 3. Therefore, the return light cannot satisfy the resonant window condition again. In addition, an absorption coating may be provided on the edge of the wedge plate 51 or on the cavity wall of the device to receive the deflected return light energy.

[0129] Example 3: Example of a two-layer cascaded resonant metasurface.

[0130] Please refer to Figure 8 In this embodiment, the resonant metasurface 3 adopts a two-layer cascaded architecture, including a first resonant metasurface layer 31, a spacer layer 32, and a second resonant metasurface layer 33 arranged sequentially along the optical path. Both the first and second resonant metasurface layers 31 and 33 are guided-mode resonant metasurfaces, with their resonance peak center wavelengths both located near 1550 nm. However, the center of the resonance peak angle response of the first resonant metasurface layer 31 is located at theta0 = 10°, while the center of the resonance peak angle response of the second resonant metasurface layer 33 is located at theta0 = 10.2°, resulting in a 0.2° angular mismatch. When the forward working light is incident at theta0 = 10°, it first satisfies the resonance window condition of the first resonant metasurface layer 31, passing through the first layer with high transmittance. After propagating through the spacer layer 32, the forward working light reaches the second resonant metasurface layer 33 at an angle of approximately 10.2°, precisely satisfying the resonance window condition of the second resonant metasurface layer 33, and also passing through with high transmittance. The total transmittance of the forward path is the product of the transmittances of the two layers, remaining at a high level (>85%). In the reverse path, the returning light first reaches the second resonant metasurface layer 33 at an angle of approximately 10.2° and is highly transmitted. However, after propagating backward through the spacer layer 32, the angle at which the returning light reaches the first resonant metasurface layer 31 is approximately 10.4°, exceeding the half-width of the angle of the first resonant metasurface layer 31 (approximately 0.3°). Therefore, it is strongly reflected or scattered by the first resonant metasurface layer 31 and ultimately guided to the waste light port 6. This embodiment achieves a higher feedback suppression ratio than the single-layer scheme through a double-layer cascaded angle mismatch design.

[0131] Example 4: Quasi-BIC high-Q resonant metasurface example.

[0132] Please refer to Figure 9 In this embodiment, a quasi-BIC resonant metasurface with slightly disrupted symmetry is used as the resonant metasurface 3. This quasi-BIC metasurface is composed of silicon double-rod structural units arranged in a rectangular lattice. The double-rod structure has a slight width difference (asymmetry of 5%) to disrupt in-plane symmetry. Since the Q factor of the quasi-BIC mode can be tuned by the asymmetry, this embodiment selects an asymmetry of 5%, obtaining an ultra-narrowband resonance with a Q value of approximately 5000, corresponding to a full width at half maximum (FWHM) of the resonance peak, a Δλ of approximately 0.31 nm, and an angular FWHM of approximately 0.06°. The extremely high angular sensitivity means that even a small return light angle shift (>0.1 degrees) can cause a sharp decrease in transmittance. This embodiment achieves a feedback suppression ratio of [missing information - likely a specific value] at a wavelength of 1550 nm. The Q value exceeds 25 dB. Understandably, a higher Q value provides stronger feedback suppression, but it also places more stringent demands on manufacturing tolerances. Therefore, this embodiment is suitable for applications requiring extremely high isolation and strong process control.

[0133] Example 5: Polarization-assisted feedback suppression example.

[0134] Please refer to Figure 10 This embodiment adds a polarization-assisted mechanism to the first embodiment. The source-end shaping module 2 includes a linear polarizer to adjust the working light to a TE linear polarization state. The design of the resonant metasurface 3 ensures its highest resonant transmission efficiency (>95%) in the TE polarization state, while the resonant peak position in the TM polarization state deviates by approximately 3 nm. A quarter-wave plate is used as a polarization perturbation element in the return light decoupling module 5. The forward working light (TE polarization) passes through the resonant metasurface 3 with high transmission and then enters the functional optical path 4 through the quarter-wave plate. The return light passes through the quarter-wave plate again during its reverse propagation. Since passing through the quarter-wave plate twice is equivalent to passing through a half-wave plate, the polarization state of the return light is rotated to TM polarization. When the TM polarized return light reaches the resonant metasurface 3, its resonant peak has deviated by 3 nm, resulting in a significant decrease in transmittance at 1550 nm (<5%), thus effectively suppressing it. This embodiment further reduces the probability of the return light coupling back to the source end through a combined mismatch in both angle and polarization dimensions.

[0135] Example 6: Manufacturability and System Integration Example

[0136] Please refer to Figure 11 and Figure 12This embodiment focuses on the joint optimization of manufacturing tolerance and feedback suppression performance of resonant metasurface 3. The high-Q narrowband scheme is highly sensitive to dimensional consistency, relative size of the two rods, peak position drift, and processing errors. This embodiment establishes a joint analysis model of Q-value, angle sensitivity, and manufacturing tolerance. Specifically, the manufacturing tolerance range is set as linewidth deviation + / -5nm, height deviation + / -10nm, and period deviation + / -2nm. Within this tolerance range, the statistical distribution of resonant peak position drift is analyzed using Monte Carlo simulation, constraining it to the resonant window half-width, within Δλ / 2. The optimized design parameters are: Q-value approximately 2000, Δλ approximately 0.78nm, and angle half-width approximately 0.15°. Within the set manufacturing tolerance range, the probability distribution of resonant peak position drift does not exceed the resonant window half-width within the range of 3-σ, thus achieving a balance between manufacturability and feedback suppression performance.

[0137] like Figure 12 As shown, this embodiment will use the feedback suppression ratio As a system-level evaluation metric, the feedback suppression ratio in this embodiment, after accounting for manufacturing tolerances, is [value missing]. (Note: The original text also mentions a 1550nm communication wavelength, but the context is unclear. It seems to be discussing feedback suppression ratio at a communication wavelength, but the connection to manufacturing tolerances is unclear.) The protection level can reach 18dB to 22dB. This feedback-suppressed optical isolation system can be integrated into distributed feedback (DFB) laser packaging modules, external cavity feedback suppression modules, free-space transmitters, or fiber collimation coupling ends to provide effective feedback protection for laser sources.

[0138] The feedback suppression ratio in this embodiment It achieves a margin of approximately 20dB while meeting the manufacturing tolerance requirements of standard CMOS processes, making it suitable for mass production.

[0139] The resonant metasurface 3 in the above embodiments can be fabricated using CMOS-compatible micro / nano fabrication processes. A typical process includes: forming a metasurface material layer (such as amorphous silicon, polycrystalline silicon, or other high-refractive-index dielectric layer) on a substrate 34 (such as a silicon wafer or glass substrate); defining a nanostructure pattern by electron beam lithography or deep ultraviolet lithography; transferring the pattern to the metasurface material layer by ICP-RIE to form a subwavelength grating unit 35; forming a protective layer 36 on the surface of the subwavelength grating unit 35 as needed, and forming an antireflection film 37 on at least one of the light-incident side and the light-outcident side.

[0140] In one embodiment, the resonant metasurface 3 includes a substrate 34 and a subwavelength grating unit 35 disposed on a surface of the substrate 34. To improve the environmental stability and post-processing reliability of the device, a protective layer 36 can be disposed on the surface of the subwavelength grating unit 35. To reduce interface reflection loss, an antireflection film 37 can be disposed on at least one of the light-incident end side and the light-outcident end side.

[0141] The wedge plate 51 and the first prism 21 can be prepared by precision optical processing, molding or injection molding, and the specific process can be selected according to the material system and packaging form.

[0142] The absorption film layer of the waste light port 6 can be formed by physical vapor deposition (PVD) or coating process to improve the absorption capacity of the waste light port for returned light and reduce secondary reflection.

[0143] Those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium. When the program is executed, it includes the steps of the above method embodiments. The storage medium can be selected from any one of read-only memory (ROM), random access memory (RAM), magnetic disk, or optical disk.

[0144] In the above embodiments, Embodiment 1 verifies the basic principle of the conditional difference between the forward working state and the backward return state of a single-layer transmission resonant metasurface; Embodiment 2 verifies the technical effect of achieving precise forward matching and forced backward mismatch through the combination of prisms and wedge plates; Embodiment 3 verifies that the two-layer cascaded architecture further narrows the window and enhances the suppression capability; Embodiment 4 verifies the ultra-high feedback suppression ratio achieved by the quasi-BIC high-Q scheme; Embodiment 5 verifies the additional suppression dimension of the polarization-assisted mechanism in addition to the angle mismatch; Embodiment 6 verifies the joint optimization of manufacturing tolerance and feedback suppression performance, as well as the system integration scheme.

[0145] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0146] For example, the resonant metasurface 3 is not limited to the guided-mode resonance and quasi-BIC resonance in the above embodiments, but can also be a one-dimensional grating, a two-dimensional grating, a double-period grating, or a free-form metasurface. The resonance mode can be any one of transmission resonance, reflection resonance, guided-mode resonance, leaky-mode resonance, Fano resonance, or quasi-BIC resonance. The unit material can be a single dielectric material, a composite material, a cladding-core structure, or a locally filled structure. The backlight decoupling module 5 can be implemented by wedge plates alone, or by a combination of prisms, polarization elements, defocusing optics, and absorption cavities. The source end 1 can be a semiconductor laser, a narrow-linewidth laser, an external cavity laser, a fiber laser, an LED, an on-chip waveguide output end, or other active light sources. The waste light port 6 can be an absorption film, an absorption cavity, a bypass waveguide, a non-working probe surface, or a tilted scattering port. This device can operate in the visible, near-infrared, short-wave infrared, mid-infrared, or other spectral ranges. This feedback suppression structure can be used in communication transmitters, as well as in optical sensing, imaging optical paths, laser processing, and external cavity coupling scenarios.

[0147] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0148] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A feedback suppression type optical isolation system, characterized in that, include: The source end is configured to output working light; A source-end shaping module is located downstream of the source end. The source-end shaping module is used to shape the working light into an incident beam with a set incident angle, a set angular spectrum broadening, a set azimuth angle, and a set polarization state. A resonant metasurface is located downstream of the source-end shaping module. The resonant metasurface is configured to excite surface resonance with an incident beam that satisfies the resonance window condition and exit along the positive working path. A functional optical path, located downstream of the resonant metasurface, is configured to transmit working light passing through the resonant metasurface to the target region; Return to the interface, located downstream of the aforementioned functional optical path; A reflection decoupling module is disposed between the resonant metasurface and the functional optical path, and at least one location within the functional optical path; The return light decoupling module is configured to cause parameter mismatch in the return light from the return interface to decouple it from the resonance window of the resonant metasurface. The waste light port is configured to receive return light that is not recoupled back to the source. The resonance window condition is that the set incident angle of the incident beam, its set angular spectrum broadening range, set azimuth angle, and set polarization state all fall within the resonance allowable range of the resonant metasurface.

2. The feedback suppression type optical isolation system according to claim 1, characterized in that, The resonant metasurface is selected from one of the following: a transmission-guided mode resonant metasurface, a reflection-guided mode resonant metasurface, a quasi-continuous domain bound state resonant metasurface, a Fano resonant metasurface, or a leaky mode resonant metasurface.

3. The feedback suppression type optical isolation system according to claim 2, characterized in that, The unit structure of the resonant metasurface is at least one of rectangular pillars, elliptical pillars, double rod structures, cross-shaped structures, slotted structures, or H-shaped structures, and the unit structure is arranged in a rectangular lattice or a hexagonal lattice.

4. The feedback suppression optical isolation system according to claim 1, characterized in that, The resonant metasurface includes a first resonant metasurface layer, a spacer layer, and a second resonant metasurface layer. The first and second resonant metasurface layers are configured to simultaneously satisfy the resonant transmission condition at the set incident angle and the set operating wavelength, forming a double-layer cascaded resonant window.

5. The feedback suppression optical isolation system according to claim 4, characterized in that, The first resonant metasurface layer and the second resonant metasurface layer have different resonant peak positions or different angular response characteristics, which makes it impossible for the returned light to simultaneously satisfy the resonant window conditions of the first resonant metasurface layer and the second resonant metasurface layer after propagating through the spacer layer.

6. The feedback suppression type optical isolation system according to claim 1, characterized in that, The phase matching of the resonant metasurface satisfies: in, The propagation constant of the guided mode or the leakage mode. For free space wavenumber, The refractive index of the incident medium is... Angle of incidence For diffraction orders, For the grating period; The resonance window condition satisfies: in To set the operating wavelength, For the angle of incidence Azimuth and polarization state The resonant center wavelength under certain conditions The full width at half maximum (FWHM) of the resonance peak of the resonant metasurface.

7. The feedback suppression type optical isolation system according to claim 1, characterized in that, The return light decoupling module is configured such that the angular offset generated by the returned light is greater than or equal to the half-width of the resonant window angle of the resonant metasurface.

8. The feedback suppression optical isolation system according to claim 1, characterized in that, The source-end shaping module includes at least one of the following: microlens, cylindrical lens, collimating lens, aperture stop, fiber collimator, prism, wedge plate, or coupling lens.

9. The feedback suppression type optical isolation system according to claim 8, characterized in that, The source-end shaping module further includes a polarization control element configured to adjust the polarization state of the working light to the set polarization state.

10. The feedback suppression optical isolation system according to claim 1, characterized in that, The reflection decoupling module includes at least one of the following: wedge plate, tilted reflective interface, prism reflection surface, polarization perturbation plate, phase delay plate, non-conjugate imaging optical path, or spatial bias structure.

11. The feedback suppression optical isolation system according to claim 10, characterized in that, The return light decoupling module includes a wedge plate disposed between the resonant metasurface and the functional optical path. The wedge plate is configured to deflect the incident light beam to an incident angle that satisfies the resonant window condition in the forward path, and to cause the returned light to reach the resonant metasurface again at an angle deviating from the set incident angle in the reverse path.

12. The feedback suppression type optical isolation system according to claim 1, characterized in that, The waste light port includes at least one of an absorption film, an absorption cavity, a bypass waveguide, a tilted scattering port, or a non-working detection surface.

13. The feedback suppression type optical isolation system according to claim 1, characterized in that, The source-end shaping module is configured to adjust the working light to a first polarization state, and the return light decoupling module includes a polarization perturbation element configured to at least partially convert the returned light to a second polarization state different from the first polarization state during reverse propagation.

14. The feedback suppression type optical isolation system according to claim 1, characterized in that, The material of the resonant metasurface is selected from at least one of silicon, titanium dioxide, silicon nitride, or germanium.

15. The feedback suppression optical isolation system according to claim 1, characterized in that, The operating wavelength is set to be within the optical communication band of 1500nm to 1650nm.

16. The feedback suppression optical isolation system according to claim 1, characterized in that, The joint optimization of the quality factor and manufacturing tolerance of the resonant metasurface is configured to satisfy the following: within a preset manufacturing tolerance range, the resonant peak position drift of the resonant metasurface does not exceed half the width of the resonant window condition.

17. A feedback-suppression type optical isolation method, characterized in that, Includes the following steps: S1: The source-end shaping module shapes the working light output from the source end into an incident beam with a set incident angle, set spectral broadening, set azimuth angle and set polarization state, so that it meets the resonance window conditions of the resonant metasurface. S2: The incident light beam enters the functional optical path through the resonant metasurface, and the resonant metasurface allows the incident light beam to pass through with a transmittance higher than a first preset threshold under the resonant window conditions; S3: In the return path from the functional optical path to the resonant metasurface, the return light, upon reaching the resonant metasurface again, undergoes at least one conditional shift relative to the incident beam in step S1 via a return light decoupling module, causing the return light to not satisfy the resonant window condition; and S4: Direct the return light that has not been recoupled back to the source end to the waste light port.

18. The method according to claim 17, characterized in that, The resonant metasurface is a quasi-continuous domain bound state resonant metasurface, which transforms the continuous domain bound state mode into a quasi-continuous domain bound state resonant mode with a finite quality factor by breaking the structural symmetry.

19. An optical device, characterized in that, The feedback-suppressed optical isolation system includes any one of claims 1 to 16.

20. An optical system, characterized in that, include: A light source for emitting the working light; Application optical path; The feedback suppression type optical isolation system as described in any one of claims 1 to 16 is disposed on the optical path between the light source and the application optical path to suppress return light from the application optical path back to the light source.

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