Electro-absorption modulator
View Patent ↗Embodiments of the invention provide an electro-absorption modulator including an optical waveguide and a microwave waveguide. The microwave waveguide is electromagnetically coupled to the optical waveguide. The optical waveguide includes a quantum well region and a substantially sinusoidal structure. The waveguide mode of the optical waveguide is responsive to the substantially sinusoidal structure.
1. An electro-absorption modulator, comprising:
an optical waveguide, comprising:
a quantum well region, and
a substantially sinusoidal structure coupled to said quantum well region,
said optical waveguide having a waveguide mode responsive to said substantially sinusoidal structure; and
a microwave waveguide electromagnetically coupled to said optical waveguide,
wherein said substantially sinusoidal structure has a periodicity that provides velocity matching between the group velocity of an optical signal propagating through said optical waveguide and the phase velocity of a microwave signal propagating along said microwave waveguide.
2. The electro-absorption modulator according to claim 1 , wherein:
said optical waveguide additionally comprises:
a first cladding layer having a sinusoidal surface relief, said sinusoidal surface relief having a first periodicity; and
a second cladding layer;
said quantum well region comprises a single quantum well structure between said cladding layers, said quantum well structure constituting said substantially sinusoidal structure and comprising a sinusoidal quantum well layer having a periodicity substantially equal to said first periodicity between sinusoidal barrier layers having a periodicity substantially equal to said first periodicity; and
said microwave waveguide comprises:
a first electrode extending alongside said first cladding layer; and
a second electrode over said second cladding layer.
3. The electro-absorption modulator according to claim 1 , wherein:
said optical waveguide additionally comprises:
a first cladding layer; and
a second cladding layer;
said quantum well region comprises a multiple quantum well structure between said first cladding layer and said second cladding layer, said multiple quantum well structure constituting said substantially sinusoidal structure; and
said microwave waveguide comprises:
a first electrode extending along a first side of said first cladding layer; and
a second electrode over said second cladding layer.
4. The electro-absorption modulator according to claim 3 , wherein:
said first cladding layer has a sinusoidal surface relief, said sinusoidal surface relief having a first periodicity; and
said multiple quantum well structure comprises sinusoidal quantum well layers having a periodicity substantially equal to said first periodicity interleaved with sinusoidal barrier layers having a periodicity substantially equal to said first periodicity.
5. The electro-absorption modulator according to claim 3 , wherein said microwave waveguide further comprises a third electrode extending along a second side of said first cladding layer.
6. The electro-absorption modulator according to claim 2 , wherein said first cladding layer is lightly doped with a first impurity.
7. The electro-absorption modulator according to claim 6 , further comprising:
a substrate upon which said first cladding layer is located; and
a first contact layer heavily doped with said first impurity located in a portion of said substrate below said first cladding layer.
8. The electro-absorption modulator according to claim 2 , wherein said second cladding layer is lightly doped with a second impurity.
9. The electro-absorption modulator according to claim 8 , further comprising a second contact layer heavily doped with said second impurity atop said second cladding layer.
10. The electro-absorption modulator according to claim 1 , wherein:
said optical waveguide additionally comprises:
a first cladding layer; and
a second cladding layer having a substantially sinusoidal surface relief extending in said direction of propagation of said optical signal, said substantially sinusoidal surface relief constituting said sinusoidal structure; said quantum well region is located between said cladding layers; and said microwave waveguide comprises:
a first electrode extending alongside said first cladding layer; and
a second electrode over said second cladding layer.
11. A method of velocity matching in an electro-absorption modulator, said method comprising:
providing an optical waveguide comprising a quantum well structure, a sinusoidal structure coupled to said quantum well structure and extending in a direction of propagation of an optical signal through said optical waveguide, and a microwave waveguide extending alongside said optical waveguide and electromagnetically coupled thereto;
determining an operating mode of said optical waveguide;
determining a phase velocity of a microwave signal propagating through said microwave waveguide; and
selecting the periodicity of said sinusoidal structure such that said operating mode is displaced from a photonic bandgap by a displacement that sets a group velocity of said optical signal substantially equal to said phase velocity of said microwave signal.
12. The method of claim 11 , wherein said selecting comprises:
using a dispersion curve in which a set of energies of said optical signal is plotted against a set of wave numbers and in which a photonic bandgap exists wherever a forward and a backward propagating state of equal energy are separated by 2π/L, where L quantifies the periodicity of said sinusoidal structure; and
selecting said periodicity to set said operating mode to a point on said dispersion curve where said group velocity of said optical signal matches said phase velocity of said microwave signal.
13. A method of fabricating an electro-absorption modulator, the method comprising:
forming an optical waveguide by a process, comprising:
forming a first cladding layer over a substrate;
forming a quantum well region over said first cladding layer;
forming a second cladding layer over said quantum well region;
forming a substantially sinusoidal structure on top of said second cladding layer coupled to said quantum well region and extending in a direction of propagation of an optical signal through said quantum well region,
said optical waveguide having waveguide mode responsive to said substantially sinusoidal structure;
patterning said first cladding layer, said quantum well region and said second cladding layer to define a ridge structure;
forming a first electrode along a first side of said ridge structure; and forming a second electrode over said ridge structure.
14. The method according to claim 13 , wherein said forming said quantum well region comprises forming conformal quantum well layers interleaved with three or more conformal barrier layers over said first cladding layer.
15. The method according to claim 13 , wherein said forming said quantum well region comprises forming a conformal quantum well layer between two conformal barrier layers over said first cladding layer.
16. The method according to claim 13 , additionally comprising lightly doping said first cladding layer with a first type of impurity.
17. The method according to claim 16 , additionally comprising heavily doping a portion of said substrate adjacent said first cladding layer with said first type of impurity to form a first contact region.
18. The method according to claim 13 , additionally comprising lightly doping said second cladding layer with a second type of impurity.
19. The method according to claim 18 , additionally comprising heavily doping a portion of said second cladding layer remote from said quantum well region with said second type of impurity to form a second contact region.
20. The method according to claim 13 , further comprising forming a third electrode along a second side of said ridge structure.
21. The method according to claim 13 , wherein said forming said substantially sinusoidal structure comprises:
forming a sinusoidal relief on top of said first cladding layer extending in said direction of propagation of said optical signal;
conformally forming said quantum well region over said first cladding layer; and
conformally forming said second cladding layer over said quantum well region.
22. The method according to claim 21 , wherein said forming said quantum well region comprises forming conformal quantum well layers interleaved with three or more conformal barrier layers.
23. The method according to claim 21 , wherein said forming said quantum well region comprises forming a conformal quantum well layers between two conformal barrier layers.