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US-20260126585-A1 - SPOT SIZE CONVERTER INCLUDING A TWO-DIMENSIONAL BI-ANISOTROPIC SUBWAVELENGTH GRATING STRUCTURE

US20260126585A1US 20260126585 A1US20260126585 A1US 20260126585A1US-20260126585-A1

Abstract

In some implementations, a photonic integrated circuit (PIC) may include a spot size converter (SSC). The SSC may include a tapered waveguide having a length along a first direction and a width along a second direction. The first direction may be parallel to a direction of propagation and the second direction may be perpendicular to the direction of propagation. The SSC may include a two-dimensional (2D) bi-anisotropic subwavelength grating (SWG) structure. A portion of the 2D bi-anisotropic SWG structure may surround a portion of the tapered waveguide in the second direction and along the first direction.

Inventors

  • Md Borhan Mia
  • Kenneth A. McGreer

Assignees

  • LUMENTUM OPERATIONS LLC

Dates

Publication Date
20260507
Application Date
20241223

Claims (20)

  1. 1 . A photonic integrated circuit (PIC) comprising a spot size converter (SSC), the SSC comprising: a tapered waveguide having a length along a first direction and a width along a second direction, wherein the first direction is parallel to a direction of propagation and the second direction is perpendicular to the direction of propagation; and a two-dimensional (2D) bi-anisotropic subwavelength grating (SWG) structure, wherein a portion of the 2D bi-anisotropic SWG structure surrounds a portion of the tapered waveguide in the second direction and along the first direction.
  2. 2 . The PIC of claim 1 , wherein a periodicity of grating elements of the 2D bi-anisotropic SWG structure along the first direction is different from a periodicity of the grating elements of the 2D bi-anisotropic SWG structure along the second direction.
  3. 3 . The PIC of claim 1 , wherein a periodicity of grating elements of the 2D bi-anisotropic SWG structure along the first direction matches a periodicity of the grating elements of the 2D bi-anisotropic SWG structure along the second direction.
  4. 4 . The PIC of claim 1 , wherein a filling fraction of the grating elements of the 2D bi-anisotropic SWG structure along the first direction is different from a filling fraction of the grating elements of the 2D bi-anisotropic SWG structure along the second direction.
  5. 5 . The PIC of claim 1 , wherein a filling fraction of the grating elements of the 2D bi-anisotropic SWG structure along the first direction matches a filling fraction of the grating elements of the 2D bi-anisotropic SWG structure along the second direction.
  6. 6 . The PIC of claim 1 , wherein one or more of the grating elements of the 2D bi-anisotropic SWG structure have a rectangular shape, an elliptical shape, or a trapezoidal shape.
  7. 7 . The PIC of claim 1 , wherein a dimension of the grating elements is based on a wavelength range associated with the SSC.
  8. 8 . The PIC of claim 1 , wherein the grating elements of the 2D bi-anisotropic SWG structure are symmetrically distributed along the tapered waveguide and extend along the first direction.
  9. 9 . The PIC of claim 1 , wherein a dielectric constant of the bi-anisotropic SWG structure along the first direction is different from a dielectric constant of the bi-anisotropic SWG structure along the second direction.
  10. 10 . The PIC of claim 1 , wherein a dielectric constant of the bi-anisotropic SWG structure along a third direction is different from the dielectric constant of the bi-anisotropic SWG structure along the first direction and the dielectric constant of the bi-anisotropic SWG structure along the second direction.
  11. 11 . The PIC of claim 1 , wherein a height of the grating elements of the 2D bi-anisotropic SWG structure is different than a height of the tapered waveguide.
  12. 12 . The PIC of claim 1 , wherein a height of the grating elements of the 2D bi-anisotropic SWG structure matches a height of the tapered waveguide.
  13. 13 . The PIC of claim 1 , wherein the tapered waveguide comprises at least one of silicon or silicon nitride.
  14. 14 . The PIC of claim 1 , wherein the tapered waveguide is a segmented waveguide.
  15. 15 . The PIC of claim 1 , wherein the 2D bi-anisotropic SWG structure comprises silicon grating elements surrounded by one or more of silica, an index matching fluid, or air.
  16. 16 . The PIC of claim 1 , wherein the 2D bi-anisotropic SWG structure comprises silicon nitride grating elements surround by one or more of silica, an index matching fluid, or air.
  17. 17 . The PIC of claim 1 , wherein the periodicity of the grating elements of the 2D bi-anisotropic SWG structure along the first direction and the periodicity of the grating elements of the 2D bi-anisotropic SWG structure along the second direction are less than approximately λ/n, where λ is an operational wavelength associated with the SSC and n is a refractive index of the 2D bi-anisotropic SWG structure.
  18. 18 . The PIC of claim 1 , wherein the grating elements of the 2D bi-anisotropic SWG structure are oriented at 90° with respect to the direction of propagation.
  19. 19 . The PIC of claim 1 , wherein the grating elements of the 2D bi-anisotropic SWG structure are oriented at an arbitrary angle with respect to the direction of propagation.
  20. 20 . The PIC of claim 1 , wherein the grating elements of the 2D bi-anisotropic SWG structure are arranged in a Gaussian pattern, a linear pattern, an apodized pattern, or a parabolic pattern with respect to a plane defined by the first direction and the second direction.

Description

CROSS-REFERENCE TO RELATED APPLICATION This patent application claims priority to U.S. Provisional Application No. 63/717,650, filed on Nov. 7, 2024, and entitled “MODE SIZE CONVERTER INCLUDING SUBWAVELENGTH GRATING METAMATERIALS.” The disclosure of the prior application is considered part of and is incorporated by reference into this patent application. TECHNICAL FIELD The present disclosure relates generally to a spot size converter (SSC) and to an SSC including a two-dimensional (2D) bi-anisotropic subwavelength grating (SWG) structure. BACKGROUND An SSC is an optical device that can be used to enable fiber-to-chip coupling by matching a mode field diameter (also referred to as a spot size) of an optical fiber to a mode size of a photonic waveguide on an integrated chip. The mode field diameter of a standard single-mode optical fiber (e.g., in a range from approximately 8 micrometers (μm) to approximately 10 μm at a 1550 nanometer (nm) wavelength) is significantly larger than the mode size in a waveguide on a photonic chip (e.g., in a range from approximately 0.5 μm to approximately 2 μm). Without an SSC, there would be a significant mismatch between the field distributions of the fiber and waveguide modes, leading to poor coupling efficiency and higher insertion loss. An SSC serves to reduce this mismatch, which improves power transfer between the fiber and the waveguide. The improved mode matching provided by the SSC can also reduce back reflection, which would otherwise degrade performance of an optical system. SUMMARY In some implementations, a photonic integrated circuit (PIC) comprising an SSC includes a tapered waveguide having a length along a first direction and a width along a second direction, wherein the first direction is parallel to a direction of propagation and the second direction is perpendicular to the direction of propagation; and a 2D bi-anisotropic SWG structure, wherein a portion of the 2D bi-anisotropic SWG structure surrounds a portion of the tapered waveguide in the second direction and along the first direction. In some implementations, a PIC comprising an SSC includes a first section comprising a first portion of a tapered waveguide; a second section comprising a second portion of the tapered waveguide and a first portion of a bi-anisotropic SWG structure comprising a plurality of grating elements, wherein the second portion of the bi-anisotropic SWG structure surrounds the second portion of the tapered waveguide along a length of the second section; and a third section comprising a second portion of the bi-anisotropic SWG structure. In some implementations, a PIC comprising an SSC includes a waveguide having a length along a first direction and a width along a second direction that is perpendicular to the first direction; and a 2D bi-anisotropic SWG structure around a portion of the tapered waveguide along the first direction, wherein a dielectric constant of the bi-anisotropic SWG structure with respect to the first direction is different from a dielectric constant of the bi-anisotropic SWG structure with respect to the second direction, and wherein the dielectric constant of the bi-anisotropic SWG structure with respect to a third direction is different from the dielectric constant of the bi-anisotropic SWG structure with respect to the first direction and the dielectric constant of the bi-anisotropic SWG structure with respect to the second direction. BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A-1B are diagrams illustrating example implementations of an SSC including a 2D bi-anisotropic SWG structure described herein. FIG. 2 is a diagram illustrating grating elements of a 2D bi-anisotropic SWG structure described herein distributed along a direction of propagation based on a Gaussian distribution. FIGS. 3-6 are diagrams illustrating simulation results associated with various example implementations of an SSC including a 2D bi-anisotropic SWG structure described herein. FIGS. 7-12 are diagrams illustrating simulation results illustrating effects of different parametric variations associated with an SSC including a 2D bi-anisotropic SWG structure described herein. FIGS. 13-14 are diagrams illustrating simulation results illustrating insertion loss and PDL associated with an SSC including a 2D bi-anisotropic SWG structure described herein. DETAILED DESCRIPTION The following detailed description of example implementations refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. Please note that references herein to letter-designated optical bands (e.g. O-band, C-band, L-band, or the like) refer to the International Telecommunication Unit (ITU) optical bands in the near infrared. Fiber-to-chip coupling is a challenge with respect to the development of silicon photonics-based devices, which are integral to increasing efficiency of optical communication systems. Two conventional techniques for interfacing a sta