Optical modulators

• US 10,135,542 B2
• Filed: 02/10/2017
• Issued: 11/20/2018
• Est. Priority Date: 12/15/2016
• Status: Active Grant

• Current Assignee: Rockley Photonics Limited
• Original Assignee: Rockley Photonics Limited
• Inventors: Nagra, Amit Singh, Abediasl, Hooman, Poon, Joyce Kai See, Yong, Zheng
• Primary Examiner(s): Liu, Li
• Application Number:
  US15/430,314
• Publication Number:
  US 20170155452A1
• Time in Patent Office: 648 Days
• Field of Search: None
• CPC Class Codes: G02F 1/0121 Operation of devices; Circuit arrangements, not otherwise provided for in this subclass
• CPC Class Codes: G02F 1/0147 based on thermo-optic effects G02F1/132 takes precedence
• CPC Class Codes: G02F 1/015 based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction G02F1/03 takes precedence
• CPC Class Codes: G02F 1/0157 using electro-absorption effects, e.g. Franz-Keldysh [FK] effect or quantum confined stark effect [QCSE]
• CPC Class Codes: G02F 1/025 in an optical waveguide structure G02F1/017, G02F1/2257 take precedence
• CPC Class Codes: G02F 2201/063 ridge; rib; strip loaded
• CPC Class Codes: G02F 2201/16 series; tandem
• CPC Class Codes: H04B 10/524 Pulse modulation
• CPC Class Codes: H04B 10/541 Digital intensity or amplitude modulation

Abstract

An optoelectronic device. The optoelectronic device operable to provide a PAM-N modulated output, the device comprising: M optical modulators, M being an integer greater than 1, the M optical modulators being arranged in a cascade, the device being configured to operate in N distinct transmittance states, as a PAM-N modulator, wherein, in each transmittance state of the N distinct transmittance states, each of the M optical modulators has applied to it a respective control voltage equal to one of: a first voltage or a second voltage.

Claims

1. An optoelectronic device operable to provide a PAM-N modulated output, the device comprising:

M optical modulators, M being an integer greater than 1, the M optical modulators being arranged in a cascade,

the device being configured to operate in N distinct transmittance states, as a PAM-N modulator,

wherein, in each transmittance state of the N distinct transmittance states, each of the M optical modulators has applied to it a respective control voltage equal to one of;

a first voltage or

a second voltage,

the optoelectronic device further comprising an intermediate waveguide composed of a first material, disposed between a first optical modulator of the M optical modulators and a second optical modulator of the M optical modulators, and operable to convey electromagnetic waves from the first optical modulator to the second optical modulator,

wherein;

the first optical modulator is an electro-absorption modulator comprising a waveguide ridge composed of a second material different from the first material, the waveguide ridge of the first optical modulator having a doped sidewall, a boundary surface between the intermediate waveguide and the waveguide ridge of the first optical modulator being at an angle, different from 90 degrees, relative to a longitudinal direction of the first optical modulator; and

the second optical modulator is an electro-absorption modulator comprising a waveguide ridge composed of the second material, a boundary surface between the intermediate waveguide and the waveguide ridge of the second optical modulator being at an angle, different from 90 degrees, relative to a longitudinal direction of the second optical modulator.

2. The device of claim 1, wherein M=N−

1.

3. The device of claim 1, wherein:

N=4;

M=3;

the first voltage is between 0 V and 0.2 V; and

the second voltage is between 1.8 V and 2.0 V.

4. The device of claim 1, wherein an optical modulator of the M optical modulators is an electro-absorption modulator.

5. The optoelectronic device of claim 1, further comprising an intermediate waveguide, disposed between a first optical modulator of the M optical modulators and a second optical modulator of the M optical modulators, and operable to convey electromagnetic waves from the first optical modulator to the second optical modulator.

6. The optoelectronic device of claim 5, wherein a first interface between the first optical modulator and the intermediate waveguide is at a first angle relative to a guiding direction of the intermediate waveguide, and a second interface between the second optical modulator and the intermediate waveguide is at an opposite angle to the first angle, wherein the first angle is not a right angle and the opposite angle is not a right angle.

7. The optoelectronic device of claim 1, wherein the M optical modulators are optically active regions of a ridge waveguide.

8. The optoelectronic device of claim 1, wherein:

the optoelectronic device has a first transmittance in a first transmittance state of the N distinct transmittance states;

the optoelectronic device has a second transmittance in a second transmittance state of the N distinct transmittance states; and

the first transmittance is one half of the second transmittance.

9. The optoelectronic device of claim 1, further comprising a heater, such that the M optical modulators are tuneable with respect to wavelength.

10. The optoelectronic device of claim 1, wherein:

in a first transmittance state of the N distinct transmittance states, all of the M optical modulators have applied to them a control voltage equal to the first voltage; and

in a second transmittance state of the N distinct transmittance states, all of the M optical modulators have applied to them a control voltage equal to the second voltage.

11. The optoelectronic device of claim 1, wherein M=2.

12. An optoelectronic device operable to provide a PAM-N modulated output, the device comprising:

M optical modulators, M being an integer greater than 1, the M optical modulators being arranged in a cascade,

the device being configured to operate in N distinct transmittance states, as a PAM-N modulator,

wherein, in each transmittance state of the N distinct transmittance states, each of the M optical modulators has applied to it a respective control voltage equal to one of k different control voltages, wherein k is an integer greater than 1 and less than N,

the optoelectronic device further comprising an intermediate waveguide composed of a first material, disposed between a first optical modulator of the M optical modulators and a second optical modulator of the M optical modulators, and operable to convey electromagnetic waves from the first optical modulator to the second optical modulator,

wherein;

the first optical modulator is an electro-absorption modulator comprising a waveguide ridge composed of a second material different from the first material, the waveguide ridge of the first optical modulator having a doped sidewall, a boundary surface between the intermediate waveguide and the waveguide ridge of the first optical modulator being at an angle, different from 90 degrees, relative to a longitudinal direction of the first optical modulator; and

the second optical modulator is an electro-absorption modulator comprising a waveguide ridge composed of the second material, a boundary surface between the intermediate waveguide and the waveguide ridge of the second optical modulator being at an angle, different from 90 degrees, relative to a longitudinal direction of the second optical modulator.

13. The optoelectronic device of claim 12, wherein the M optical modulators are electro-absorption modulators.

14. The optoelectronic device of claim 12, wherein:

N=4;

M=2; and

k=3.

15. The optoelectronic device of claim 14, wherein:

in a first transmittance state of the 4 distinct transmittance states;

a first optical modulator of the 2 optical modulators has maximum transmittance; and

a second optical modulator of the 2 optical modulators has maximum transmittance;

in a second transmittance state of the 4 distinct transmittance states;

the first optical modulator has a first transmittance, the first transmittance being less than maximum transmittance; and

the second optical modulator has maximum transmittance;

in a third transmittance state of the 4 distinct transmittance states;

the first optical modulator has maximum transmittance; and

the second optical modulator has a second transmittance, the second transmittance being less than the first transmittance; and

in a fourth transmittance state of the 4 distinct transmittance states;

the first optical modulator has a third transmittance, the third transmittance being less than the first transmittance; and

the second optical modulator has the second transmittance.

16. The optoelectronic device of claim 12, further comprising an intermediate waveguide, disposed between a first optical modulator of the M optical modulators and a second optical modulator of the M optical modulators and operable to convey electromagnetic waves from the first optical modulator to the second optical modulator.

17. The optoelectronic device of claim 16, wherein a first interface between the first optical modulator and the intermediate waveguide is at a first angle relative to a guiding direction of the intermediate waveguide, and a second interface between the second optical modulator and the intermediate waveguide is at an opposite angle to the first angle, wherein the first angle is not a right angle and the opposite angle is not a right angle.

18. The optoelectronic device of claim 12, wherein a first optical modulator of the M optical modulators and a second optical modulator of the M optical modulators are optically active regions of a ridge waveguide.

19. The optoelectronic device of claim 12, wherein:

the optoelectronic device has a first transmittance in a first transmittance state of the N distinct transmittance states;

the optoelectronic device has a second transmittance in a second transmittance state of the N distinct transmittance states; and

the first transmittance is one half of the second transmittance.

20. The optoelectronic device of claim 12, further comprising a heater, such that an optical modulator of the M optical modulators is tuneable with respect to wavelength.

21. The optoelectronic device of claim 12, wherein:

in a first transmittance state of the N distinct transmittance states, all of the M optical modulators have applied to them a control voltage equal to a first voltage; and

in a second transmittance state of the N distinct transmittance states, all of the M optical modulators have applied to them a control voltage equal to a second voltage.

22. The optoelectronic device of claim 12, wherein M is greater than or equal to Log₂(N).