Slow light waveguide

Patent metadata

Field	Value
Publication number	US-9733499-B1
Application number	US-201715434469-A
Country	US
Kind code	B1
Filing date	Feb 16, 2017
Priority date	Mar 17, 2016
Publication date	Aug 15, 2017
Grant date	Aug 15, 2017

Abstract

This slow light waveguide includes an initial region which extends, along an optical axis, from a start starting from which the width of a central waveguide begins to continuously decrease up to an end beyond which the width of the central waveguide no longer decreases up to the end of a slowing section, this initial region overlapping a broadening region where the length of lateral teeth continuously increases, a final region which extends, along the optical axis, from a start starting from which the width of the central waveguide begins to continuously increase up to an end beyond which the width of the central waveguide no longer increases, this final region overlapping a narrowing region where the length of the lateral teeth continuously decreases.

First claim

The invention claimed is:

1. A slow light waveguide designed to slow the propagation of an optical signal that it said waveguide is guiding, said waveguide comprising:
a substrate which extends essentially in a plane referred to as “substrate plane”,
an optical axis tangent at any point to the direction of propagation of the optical signal inside of the slow light waveguide, said optical axis extending in a plane parallel to the substrate plane,
a slowing section designed to slow the propagation of the optical signal, said section comprising lateral teeth disposed symmetrically on either side of the optical axis with a regular pitch p along the optical axis from the start of said slowing section up to its end, each lateral tooth extending continuously in a direction of extension parallel to the substrate plane, from a proximal end up to a distal end which constitutes the part of the lateral tooth furthest from the optical axis and each lateral tooth comprising a point of intersection between its direction of extension and the optical axis, the length of each lateral tooth being equal to the shortest distance between the optical axis and its distal end,
a central waveguide which extends along the optical axis and which comprises, on either side of the optical axis, lateral sidewalls, the width of the central waveguide, inside of the slowing section, only being defined between two immediately consecutive lateral teeth and taken equal to the shortest distance, measured in a transverse direction parallel to the substrate plane and perpendicular to the optical axis, between the lateral sidewalls of the central waveguide situated on either side of the optical axis and between these consecutive lateral teeth,
a broadening region extending along the optical axis, over a distance greater than d min from a start, coinciding with the start of the slowing section, up to an end situated inside of the slowing section, the distance d min being a distance equal to the greater of the wavelength λ of the optical signal and of 5p, where p is the pitch between the lateral teeth, the length of the lateral teeth situated inside of the broadening region continuously increasing going from the start up to the end of said broadening region, the distal ends of all the lateral teeth situated on the same side of the optical axis inside of said broadening region being all situated on a curve getting continuously further from the optical axis, the length of the lateral tooth situated just after the end of the broadening region being equal to or less than the length of the last lateral tooth situated inside of said broadening region,
a narrowing region which extends along the optical axis over a distance greater than d min from a start, situated inside of the slowing section, up to an end coinciding with the end of the slowing section, the length of the lateral teeth situated inside of the narrowing region, continuously decreasing going from the start up to the end of said narrowing region, the distal ends of all the lateral teeth situated on the same side of the optical axis inside of said narrowing region being all situated on a curve getting continuously closer to the optical axis, the length of the lateral tooth situated just before the start of the narrowing region being equal to or less than the length of the first lateral tooth situated inside of said narrowing region,
wherein the slow light waveguide also comprises:
an initial region which extends, along the optical axis, over a distance greater than d min , from a start starting from which the width of the central waveguide begins to continuously decrease up to an end beyond which the width of the central waveguide no longer decreases up to the end of the slowing section, said initial region overlapping the broadening region over a non-zero distance greater than d min ,
a final region which extends, along the optical axis, over a distance greater than d min , from a start starting from which the width of the central waveguide begins to continuously increase up to an end beyond which the width of the central waveguide no longer increases, said final region overlapping the narrowing region over a non-zero distance greater than d min .

2. The waveguide according to claim 1 , wherein the length of the slowing section between its start and its end is greater than 15 μm or 50 μm.

3. The waveguide according to claim 1 , wherein the angle between the direction of extension of each lateral tooth and the optical axis is in the range between 85° and 95°.

4. The waveguide according to claim 1 , wherein the slow light waveguide comprises an intermediate region which extends along the optical axis over a distance greater than d min from a start coinciding with the end of the broadening region up to an end coinciding with the start of the narrowing region, the length of the teeth inside of said intermediate region being constant.

5. The waveguide according to claim 1 , wherein the slow light waveguide comprises a central region which extends along the optical axis over a distance greater than d min from a start coinciding with the end of the initial region up to an end coinciding with the start of the final region, the width of the central waveguide inside of said central region being constant.

6. The waveguide according to claim 1 , wherein the end of the broadening region coincides with the start of the narrowing region and the end of the initial region coincides with the start of the final region.

7. The waveguide according to claim 1 , wherein the width of the central waveguide is twice as big at the start of the initial region than at the end of said initial region, and the width of the central waveguide is half as big as at the start of the final region than at the end of the final region.

8. The waveguide according to claim 1 , wherein the ratio S1/S2 is in the range between 0.25 and 0.75, where:
S1 is the surface area of the orthogonal projection of the slowing section on the substrate plane, and
S2 is the surface area of the smallest convex envelope which totally contains the orthogonal projection of the slowing section.

9. The waveguide according to claim 1 , wherein:
the pitch p is strictly less than λ/n eff , where λ is the wavelength of the optical signal and n eff is the effective index of propagation of the optical signal propagating within said slow light waveguide,
the direction of extension of each lateral tooth forms a constant angle with the optical axis,
the lateral sidewalls of the central waveguide are disposed symmetrically on either side of the optical axis.

10. The waveguide according to claim 1 , wherein:
the slow light waveguide comprises a heater designed to heat the central waveguide to a desired temperature in response to an electrical control signal, and
a control circuit designed to generate the electrical control signal which allows the central waveguide to be maintained at a temperature where the group index n g of the fundamental TE mode of the optical signal which is propagating in the central waveguide is greater than or equal to eight.

11. A semiconductor modulator of the phase or of the amplitude of an optical signal, said modulator comprising:
a slow light waveguide, and
a controllable device designed to make the density of the free charge carriers inside of the slow light waveguide vary in response to an electrical control signal for modulating the phase or the amplitude of the optical signal,
wherein the slow light waveguide is according to claim 1 .

12. The semiconductor modulator according to claim 11 , wherein the central waveguide comprises at least one PN or PIN junction and the modulator comprises

Assignees

• Commissariat Energie Atomique
• Commissariat à l'Energie Atomique et aux Energies Alternatives

Inventors

• Ben Bakir Badhise
• Hassan Karim

Classifications

• G02B6/124

  Geodesic lenses or integrated gratings · CPC title

• G02F1/025 Primary

  in an optical waveguide structure (G02F1/017, {G02F1/2257} take precedence) · CPC title

• G02B6/1228

  Tapered waveguides, e.g. integrated spot-size transformers (for coupling with fibres G02B6/305) · CPC title

• G02F2203/07

  Polarisation dependent · CPC title

• G02F1/0147

  based on thermo-optic effects (G02F1/132 takes precedence) · CPC title