# US 2021/0278566 A1 · Isotropic Filters in Spatial Frequency Domain by a Photonic Crystal Slab > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0278566 A1 - Document ID: US20210278566A1 - Status: Published application - Kind: A1 - Application number: 17/181,318 - Filed: 2021-02-22 - Published: 2021-09-09 - Earliest claimed: 2017-11-14 - Assignees: The Board of Trustees of the Leland Stanford Junior University - Applicants: The Board of Trustees of the Leland Stanford Junior University - Inventors: Cheng Guo; Meng Xiao; Momchil Minkov; Yu Shi; Shanhui Fan - Web page: https://patentgrep.com/patent/US20210278566A1 ## CPC - G02B 1/005: {made of photonic crystals or photonic band gap materials (photonic band-gap structures or photonic lattices in integrated optics G02B6/1225; photonic band-gap structures or photonic lattices in optical fibres G02B6/02295)} - G02B 5/20: Filters (polarising elements G02B5/30) - G02B 5/28: Interference filters - G02B 27/46: Systems using spatial filters - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract An isotropic imaging filter is provided that includes a photonic crystal slab, where the photonic crystal slab includes a square lattice of air through holes, a dielectric constant, a thickness (d), a through hole radius (r), and a lattice constant (a), where the square lattice of air holes are separated according to a value of the lattice constant, where the thickness is configured according to d=M(a), where the through hole radii is configured according to r=N(a), where the thickness and the hole radii are configured to generate isotropic bands of guided resonances of an incident image. ## Claims ### Claim 1 1) A method of making an isotropic imaging filter comprising a photonic crystal slab, comprising: designing a photonic crystal slab having a periodic lattice of air through holes, wherein parameters of a photonic crystal slab design include a dielectric constant, a thickness, a through hole radius and a lattice constant, wherein the periodic lattice of air holes are separated according to a value of the lattice constant, wherein the thickness and the hole radius are configured such that the photonic crystal slab generates isotropic bands of guided resonances; and making a photonic crystal slab according to the photonic crystal slab design. ### Claim 2 (depends on 1) 2) The method of claim 1, wherein the guided resonances are selected from the group consisting of an isotropic high-pass filter guided resonance, an isotropic low-pass filter guided resonance, an isotropic band-reject filter guided resonance, and an isotropic band-pass filter guided resonance. ### Claim 3 (depends on 2) 3) The method of claim 2, wherein isotropic low-pass filtering and isotropic band-pass filtering are obtained in reflection. ### Claim 4 (depends on 2) 4) The method of claim 2, wherein isotropic high-pass filtering and isotropic band-reject filtering are obtained in transmission. ### Claim 5 (depends on 1) 5) The method of claim 1, wherein the photonic crystal slab comprises a dielectric material. ### Claim 6 (depends on 1) 6) The method of claim 1, further comprising disposing a uniform dielectric slab proximal to the photonic crystal slab, wherein a thickness of the uniform dielectric slab and an air gap between the uniform dielectric slab and the photonic crystal slab are configured to set a background transmission to unity. ### Claim 7 (depends on 1) 7) The method of claim 1, wherein the hole radius is 0.5 the lattice constant. ### Claim 8 8) A method of making an isotropic image filter comprising a photonic crystal slab, comprising: designing a photonic crystal slab having a periodic lattice of air through holes, wherein parameters of a photonic crystal slab design include a dielectric constant, a thickness, a through hole radius and a lattice constant; wherein the periodic lattice of air holes are separated according to a value of the lattice constant; wherein the thickness and the hole radius are configured such that the photonic crystal slab generates isotropic guided resonances; and making a photonic crystal slab according to the photonic crystal slab design. ### Claim 9 (depends on 8) 9) The method of claim 8, wherein the guided resonances are selected from the group consisting of an isotropic high-pass filter guided resonance, an isotropic low-pass filter guided resonance, an isotropic band-reject filter guided resonance, and an isotropic band-pass filter guided resonance. ### Claim 10 (depends on 9) 10) The method of claim 9, wherein isotropic low-pass filtering and isotropic band-pass filtering are obtained in reflection. ### Claim 11 (depends on 9) 11) The method of claim 9, wherein isotropic high-pass filtering and isotropic band-reject filtering are obtained in transmission. ### Claim 12 (depends on 8) 12) The method of claim 8, wherein the photonic crystal slab comprises a dielectric material. ### Claim 13 (depends on 8) 13) The method of claim 8, further comprising disposing a uniform dielectric slab proximal to the photonic crystal slab, wherein a thickness of the uniform dielectric slab and an air gap between the uniform dielectric slab and the photonic crystal slab are configured to set a background transmission to unity. ### Claim 14 (depends on 8) 14) The method of claim 8, wherein the hole radius is 0.5 the lattice constant. ### Claim 15 15) A method of making an isotropic image filter comprising a photonic crystal slab, comprising: designing a photonic crystal slab having a periodic lattice of air through holes, wherein parameters of the photonic crystal slab include a dielectric constant, a thickness, a through hole radius and a lattice constant; wherein the periodic lattice of air holes are separated according to a value of the lattice constant; wherein the thickness and the hole radius are configured such that the photonic crystal slab generates isotropic image filtering; and making a photonic crystal slab according to the photonic crystal slab design. ### Claim 16 (depends on 15) 16) The method of claim 15, wherein the isotropic image filtering is selected from the group consisting of isotropic high-pass filtering, isotropic low-pass filtering, isotropic band-reject filtering, and isotropic band-pass filtering. ### Claim 17 (depends on 16) 17) The method of claim 16, wherein the isotropic low-pass filtering and the isotropic band-pass filtering are obtained in reflection. ### Claim 18 (depends on 16) 18) The method of claim 16, wherein the isotropic high-pass filtering and the isotropic band-reject filtering are obtained in transmission. ### Claim 19 (depends on 15) 19) The method of claim 15, wherein the photonic crystal slab comprises a dielectric material. ### Claim 20 (depends on 15) 20) The method of claim 15, further comprising disposing a uniform dielectric slab proximal to the photonic crystal slab, wherein a thickness of the uniform dielectric slab and an air gap between the uniform dielectric slab and the photonic crystal slab are configured to set a background transmission to unity. ### Claim 21 (depends on 15) 21) The method of claim 15, wherein the hole radius is 0.5 the lattice constant.