Optical deflection device and LIDAR apparatus
View Patent ↗An optical deflection device that achieve both high beam quality and wide angular range of deflection and compatibility with an optical integration technology of silicon photonics. The optical deflection device is a silicon photonics device including a periodic structure of a refractive index. The optical deflection device includes two configurations, which are (1) a configuration in which an optical propagation part where light propagates is a microstructure formed on silicon, and (2) a configuration in which the microstructure constituting the optical propagation part includes a periodic structure that generates slow light and a periodic structure that radiates light. The microstructure formed on the silicon of (1) makes it possible to employ the optical integration technology of silicon photonics and form the optical deflection device. The two periodic structures of (2) make it possible to form a light beam with high beam quality and a wide angular range of deflection.
1. An optical deflection device that is a silicon photonics device comprising periodic structures of a refractive index, wherein the periodic structures comprise:
a first periodic structure comprising a second refractive index medium at a period a in a first refractive index medium that is a silicon substrate, the second refractive index medium including a refractive index different from that of the first refractive index medium, the first periodic structure constituting an optical waveguide part, and the optical waveguide part including at least one end in a periodic direction as an incident end; and
a second periodic structure comprising the second refractive index medium at a period Λ(a<Λ≤2a) that is longer than the period a of the first periodic structure in the first refractive index medium, the second refractive index medium including a refractive index different from that of the first refractive index medium, the second periodic structure constituting an emission part, and the emission part including a side end in the periodic direction as an emission end, wherein
a position where the second periodic structure is disposed is a peripheral part of an intensity distribution of light propagating through the optical waveguide part composed of the first periodic structure, and
the period a is a=λ/2n (n is an equivalent refractive index of the light propagating through the optical waveguide part composed of the first periodic structure, and λ is a wavelength near a Bragg wavelength), wherein
the optical waveguide part is an air-bridge slow light waveguide comprising an air layer between claddings on the silicon substrate, or a cladding embedded slow light waveguide that is embedded in a cladding.
2. The optical deflection device according to claim 1 , wherein, in the first periodic structure and the second periodic structure, etches of the first periodic structure are larger than etches of the second periodic structure.
3. The optical deflection device according to claim 1 , wherein
the emission part composed of the second periodic structure is a diffraction grating.
4. The optical deflection device according to claim 1 , wherein the slow light waveguide is a photonic crystal waveguide composed of a periodic structure of a photonic crystal.
5. The optical deflection device according to claim 3 , wherein the diffraction grating is formed with recesses and projections periodically provided in a refractive index medium or with a photonic crystal periodic structure.
6. An optical deflection device that is a silicon photonics device comprising periodic structures of a refractive index, wherein the periodic structures comprise:
a first periodic structure comprising a second refractive index medium at a period a in a first refractive index medium that is a silicon substrate, the second refractive index medium including a refractive index different from that of the first refractive index medium, the first periodic structure constituting an optical waveguide part, and the optical waveguide part including at least one end in a periodic direction as an incident end; and
a second periodic structure comprising the second refractive index medium at a period Λ(a<Λ≤2a) that is longer than the period a of the first periodic structure in the first refractive index medium, the second refractive index medium including a refractive index different from that of the first refractive index medium, the second periodic structure constituting a diffraction grating, and the diffraction grating including a side end in the periodic direction as an emission end, wherein
a position where the second periodic structure is disposed is a peripheral part of an intensity distribution of light propagating through the optical waveguide part composed of the first periodic structure,
the period a is a=λ/2n (n is an equivalent refractive index of the light propagating through the optical waveguide part composed of the first periodic structure, and λ is a wavelength near a Bragg wavelength), and
the diffraction grating is any one of
an air-bridge diffraction grating comprising an air layer between air-bridge slow light waveguides or between claddings of an cladding embedded slow light waveguide,
an embedded diffraction grating, in the cladding in which the cladding embedded slow light waveguide is embedded, embedded in an upper part of an upper cladding, in a lower cladding, or a lower cladding, and
a diffraction grating formed on the silicon substrate.
7. The optical deflection device according to claim 4 , wherein
the diffraction gratings are provided on both sides of the photonic crystal waveguide, or
the diffraction grating is provided on an upper surface of the photonic crystal waveguide.
8. The optical deflection device according to claim 4 , wherein in the photonic crystal waveguide, the periodic structure of the photonic crystal is composed of a double periodic structure comprising two kinds of periods, which are a short period and a long period,
the periodic structure for the short period constitutes the slow light waveguide of the first periodic structure, and
the periodic structure for the long period constitutes a diffraction grating of the second periodic structure.
9. The optical deflection device according to claim 1 , wherein the first periodic structure is a one-dimensional photonic crystal waveguide comprising a linear periodic structure or a two-dimensional photonic crystal waveguide comprising a linear defect in a planar periodic structure.
10. The optical deflection device according to claim 1 , further comprising a reflector configured to reflect light emitted from the emission part on a substrate side below the second periodic structure.
11. An optical deflection device that is a silicon photonics device comprising periodic structures of a refractive index, wherein the periodic structures comprise:
a first periodic structure comprising a second refractive index medium at a period a in a first refractive index medium that is a silicon substrate, the second refractive index medium including a refractive index different from that of the first refractive index medium, the first periodic structure constituting an optical waveguide part, and the optical waveguide part including at least one end in a periodic direction as an incident end; and
a second periodic structure comprising the second refractive index medium at a period Λ(a<Λ≤2a) that is longer than the period a of the first periodic structure in the first refractive index medium, the second refractive index medium including a refractive index different from that of the first refractive index medium, the second periodic structure constituting a diffraction grating, and the diffraction grating including a side end in the periodic direction as an emission end, wherein
a position where the second periodic structure is disposed is a peripheral part of an intensity distribution of light propagating through the optical waveguide part composed of the first periodic structure,
the period a is a=λ/2n (n is an equivalent refractive index of the light propagating through the optical waveguide part composed of the first periodic structure, and λ is a wavelength near a Bragg wavelength),
the periodic structure is a planar periodic structure of a photonic crystal comprising circular holes,
the first periodic structure is a two-dimensional photonic crystal waveguide comprising a linear defect in the planar periodic structure, and
the second periodic structure is a double periodic structure in which two types of circular holes with different diameters, which form the first periodic structure, are repeated along the two-dimensional photonic crystal waveguide in the same rows at a period longer than a period at which the circular holes of the first periodic structure are repeated.
12. The optical deflection device according to claim 11 , wherein
the double periodic structure comprises a periodic structure in which large diameter circular holes with large diameters are repeated and a periodic structure in which small diameter circular holes with small diameters are repeated,
when the diameter of a reference circular hole is 2r and a difference between the diameters of the circular holes is 2Δr,
the diameter of the large diameter circular holes is 2(r+Δr), and
the diameter of the small diameter circular holes is 2(r−Δr).
13. A lidar apparatus comprising:
the optical deflection device according to claim 1 ;
a pulse light source configured to emit pulse light to the optical deflection device; and
a photodetector configured to detect light received by the optical deflection device.
14. A lidar apparatus comprising:
the optical deflection device according to claim 6 ;
a pulse light source configured to emit pulse light to the optical deflection device; and
a photodetector configured to detect light received by the optical deflection device.
15. A lidar apparatus comprising:
the optical deflection device according to claim 11 ;
a pulse light source configured to emit pulse light to the optical deflection device; and
a photodetector configured to detect light received by the optical deflection device.
16. The optical deflection device according to claim 6 , wherein, in the first periodic structure and the second periodic structure, etches of the first periodic structure are larger than etches of the second periodic structure.
17. The optical deflection device according to claim 6 , wherein the optical waveguide part is photonic crystal slow light waveguide composed of a periodic structure of a photonic crystal.
18. The optical deflection device according to claim 17 , wherein
in the photonic crystal waveguide, the periodic structure of the photonic crystal is composed of a double periodic structure comprising two kinds of periods, which are a short period and a long period,
the periodic structure for the short period constitutes the slow light waveguide of the first periodic structure, and
the periodic structure for the long period constitutes the diffraction grating of the second periodic structure.
19. The optical deflection device according to claim 6 , wherein the diffraction grating is formed with recesses and projections periodically provided in a refractive index medium or with a photonic crystal periodic structure.
20. The optical deflection device according to claim 6 , wherein
diffraction gratings are provided on both sides of the optical waveguide part, or
the diffraction grating is provided on an upper surface of the optical waveguide part.