Apparatus, systems, and methods for waveguide-coupled resonant photon detection

Patent metadata

Field	Value
Publication number	US-9939586-B2
Application number	US-201715419694-A
Country	US
Kind code	B2
Filing date	Jan 30, 2017
Priority date	Jan 28, 2016
Publication date	Apr 10, 2018
Grant date	Apr 10, 2018

Abstract

A photodetector includes a germanium layer evanescently coupled to a ring resonator. The ring resonator increases the interaction length between light guided by the ring resonator and the germanium layer without increasing the size of the photodetector, thereby keeping the photodetector's dark current at a low level. The germanium layer absorbs the guided light and converts the absorbed light into electrical signals for detection. The increased interaction length in the resonator allows efficient transfer of light from the resonator to the germanium layer via evanescently coupling. In addition, the internal and external quality factors (Q) of the ring resonator can be matched to achieve (nearly) full absorption of light in the germanium with high quantum efficiency.

First claim

The invention claimed is:

1. An apparatus comprising:
a resonator to guide light, the resonator having an internal quality factor (Q);
a germanium layer, evanescently coupled to the resonator, to absorb at least a portion of the light guided by the resonator, the germanium layer having an external quality factor substantially equal to the internal Q of the ring resonator, a first side, and a second side opposite the first side;
a first electrode disposed on the first side of the germanium layer; and
a second electrode, disposed on the second side of the germanium layer, to apply a bias voltage on the germanium layer.

2. The apparatus of claim 1 , wherein the resonator comprises a ring resonator and the germanium layer comprises a germanium arcuate member at least partially concentric with the ring resonator.

3. The apparatus of claim 2 , wherein germanium arcuate member comprises a germanium ring substantially concentric with the ring resonator.

4. The apparatus of claim 3 , wherein a distance between an outer edge of the ring resonator and an outer edge of the germanium ring is about 0.1 μm to about 2 μm.

5. The apparatus of claim 3 , further comprising:
an input waveguide, evanescently coupled to the ring resonator, to couple the light into the ring resonator.

6. The apparatus of claim 5 , wherein the input waveguide and the ring resonator define a gap with a width of about 50 nm to about 250 nm.

7. The apparatus of claim 5 , wherein the input waveguide has an external Q substantially equal to the internal Q of the ring resonator.

8. The apparatus of claim 3 , further comprising:
a heater, operably coupled to the ring resonator, to change a resonant wavelength of the ring resonator.

9. The apparatus of claim 1 , wherein the resonator has a resonant wavelength greater than 1.5 μm.

10. The apparatus of claim 1 , wherein the germanium layer has a thickness of about 0.01 μm to about 1 μm.

11. The apparatus of claim 1 , further comprising:
an output waveguide, evanescently coupled to the resonator, to couple another portion of the light out of the resonator.

12. The apparatus of claim 1 , wherein the resonator is a first resonator, the germanium layer is a first germanium layer, and the apparatus further comprises:
a second resonator, in optical communication with the first resonator, to guide the light not absorbed by the first germanium layer; and
a second germanium layer, evanescently coupled to the second resonator, to absorb the light guided in the second resonator.

13. The apparatus of claim 12 , wherein the first resonator has a first resonant wavelength and the second resonator has a second resonant wavelength different from the first resonant wavelength.

14. The apparatus of claim 1 , wherein the germanium layer has a detection responsivity greater than 1 A/W at a wavelength greater than 1500 nm.

15. The apparatus of claim 1 , wherein the germanium layer has a detection bandwidth greater than 30 GHz at a wavelength greater than 1500 nm.

16. The apparatus of claim 1 , further comprising:
a voltage source, in electrical communication with the first electrode and the second electrode, to apply the bias voltage, the bias voltage being within a range of about 0.2 V to about 15 V.

17. An apparatus comprising:
a ring resonator to guide light;
a germanium ring, substantially concentric with and evanescently coupled to the ring resonator, to absorb at least a portion of the light guided by the ring resonator, the germanium ring having a first side and a second side opposite the first side;
a first electrode disposed on the first side of the germanium ring; and
a second electrode, disposed on the second side of the germanium ring, to apply a bias voltage on the germanium ring,
wherein the ring resonator has a first mean diameter and the germanium ring has a second mean diameter less than the first mean diameter.

18. An apparatus comprising:
a resonator to guide light;
a germanium layer, evanescently coupled to the resonator, to absorb at least a portion of the light guided by the resonator, the germanium layer having a first side and a second side opposite the first side;
a first electrode disposed on the first side of the germanium layer; and
a second electrode, disposed on the second side of the germanium layer, to apply a bias voltage on the germanium layer,
wherein the first electrode comprises doped germanium, the resonator comprises silicon, and the second electrode comprises doped silicon.

19. A method of detecting light, comprising:
applying a bias voltage on a germanium layer having an external quality factor (Q);
guiding the light in a resonator evanescently coupled to the germanium layer so as to cause the germanium layer to absorb at least a portion of the light guided by the resonator, the germanium layer converting the at least a portion of the light into an electrical signal and the resonator having an internal Q substantially equal to the external Q of the germanium layer; and
detecting the electrical signal.

20. The method of claim 19 , wherein guiding the light comprises guiding the light in a ring resonator evanescently coupled to a germanium ring substantially concentric with the ring resonator.

21. The method of claim 20 , further comprising:
coupling the light into the ring resonator via an input waveguide evanescently coupled to the ring resonator, the input waveguide and the ring resonator separated by a gap of about 50 nm to about 250 nm.

22. The method of claim 20 , further comprising:
changing a temperature of the ring resonator so as to change a resonant wavelength of the ring resonator.

23. The method of claim 20 , further comprising:
coupling the light not absorbed by the germanium layer out of the ring resonator.

24. The method of claim 19 , wherein the resonator is a first resonator, the germanium layer is a first germanium layer, and further comprising:
coupling the light not absorbed by the germanium layer out of the first resonator and into a second resonator evanescently coupled to a second germanium layer so as to cause the second germanium layer to absorb at least a portion of the light guided by the second resonator.

25. The method of claim 24 , wherein coupling the light beam into the second resonator comprises coupling the light beam into the second resonator having a second resonant wavelength different from a first resonant wavelength of the first resonator.

26. A semiconductor photodetector, comprising:
a ring resonator to guide light at a wavelength greater than about 1500 nm, the ring resonator having an internal quality factor and an external quality factor approximately equal to the internal quality factor;
an input waveguide, disposed about 50 nm to about 250 nm away from the ring resonator, to couple the light into the ring resonator;
a germanium arcuate member, evanescently coupled to the ring resonator and substantially concentric with the ring resonator, to absorb at least a portion of the light guided in the ring resonator, the ring resonator having an outer edge disposed about 1 μm to about 2 μm away from an outer edge of the germanium arcuate member; and
a pair of electrodes, in electrical communication with the germanium arcuate member, to apply a bias voltage to the germanium arcuate member.

Assignees

• Timurdogan Erman
• Watts Michael R
• Su Zhan
• Hosseini Ehsan Shah
• Sun Jie
• Massachusetts Inst Technology

Inventors

• Timurdogan Erman
• Watts Michael R
• Su Zhan
• Hosseini Ehsan Shah
• Sun Jie

Classifications

• G02B2006/12123

  Diode · CPC title

• H01L31/1055

  Electricity · mapped topic

• G02B6/29395

  configurable, e.g. tunable or reconfigurable (switching G02B6/35) · CPC title

• H01L31/105

  Electricity · mapped topic

• H01L31/035281

  Electricity · mapped topic