Waveguide heater
An optical waveguide structure. In some embodiments, the optical waveguide structure includes a semiconductor waveguide having a waveguide ridge, and a heater. The waveguide ridge may have a varying dopant concentration across its cross-section. The heater may include a first contact and a second contact, and the waveguide structure may include a conductive path from the first contact to the second contact, the conductive path extending through a doped portion of the waveguide ridge.
1. An optical waveguide structure, comprising:
a semiconductor waveguide having a waveguide ridge, and
a heater,
the waveguide ridge having a varying dopant concentration across its cross-section and a doped portion extending across an optical core of the waveguide ridge,
the heater comprising a first contact and a second contact,
the waveguide structure comprising a conductive path from the first contact to the second contact, the conductive path extending through the doped portion of the waveguide ridge,
wherein the conductive path is such that, when a potential difference is provided between the first and second contacts, a current flows through the optical core of the waveguide ridge.
2. The optical waveguide structure of claim 1 , wherein the first contact and the second contact are on opposite sides of the waveguide ridge.
3. The optical waveguide structure of claim 1 , wherein the optical waveguide structure has a conductivity distribution such that the potential difference between the first contact and the second contact results in a current, between the first contact and the second contact, at least half of which flows through the waveguide ridge.
4. The optical waveguide structure of claim 3 , wherein the current is, at a point within the waveguide ridge, in a direction that is within 45 degrees of a direction perpendicular to the waveguide ridge.
5. The optical waveguide structure of claim 1 , wherein:
the waveguide ridge has a top surface; and
a doping concentration within the waveguide ridge at a first depth, from the top surface, is at least 10% greater than a doping concentration within the waveguide ridge at a second depth, from the top surface, the second depth being greater than the first depth.
6. The optical waveguide structure of claim 1 , wherein the waveguide ridge has a first sidewall and a second sidewall, and a doping concentration, at a point midway between the first sidewall and the second sidewall, between 5e16/cm 3 and 5e17/cm 3 .
7. The optical waveguide structure of claim 1 , wherein the waveguide structure is configured to have, in steady state operation with a voltage of 3 V between the first contact and the second contact, a temperature that is uniform to within 30 degrees C. within a waveguide of the waveguide structure.
8. The optical waveguide structure of claim 1 , wherein, in steady state operation with a voltage of 3 V between the first contact and the second contact, the minimum temperature within the semiconductor waveguide is at least 20 degrees greater than in steady state operation with no current flowing through the heater.
9. The optical waveguide structure of claim 1 , wherein a waveguide of the waveguide structure has an optical insertion loss of less than 1 dB per millimeter.
10. The optical waveguide structure of claim 1 , wherein the waveguide structure comprises a grating having a temperature-dependent reflectivity peak.
11. A distributed Bragg reflector laser, comprising the waveguide structure of claim 10 .
12. The optical waveguide structure of claim 10 , wherein:
in steady state operation, with a voltage of 0 V between the first contact and the second contact, the reflectivity peak is at a first wavelength,
in steady state operation, with a voltage of 3 V between the first contact and the second contact, the reflectivity peak is at a second wavelength, and
the second wavelength is greater than the first wavelength by at least 0.1 nm.
13. The optical waveguide structure of claim 12 , wherein the power dissipated in the heater, with a voltage of 3 V between the first contact and the second contact, is less than 1 W.
14. The optical waveguide structure of claim 1 , comprising a rib waveguide.
15. The optical waveguide structure of claim 1 , comprising a strip waveguide.
16. The optical waveguide structure of claim 1 , wherein the waveguide ridge has a width greater than 2 microns.
17. The optical waveguide structure of claim 1 , wherein:
the waveguide structure is on a silicon on insulator chip, comprising:
a substrate,
a buried oxide layer on the substrate, and
a device layer on the buried oxide layer; and
the waveguide structure comprises a trench, in the device layer, between the semiconductor waveguide and the first contact, a thickness of the device layer at a bottom of the trench being less than 1 micron.
18. The optical waveguide structure of claim 1 , wherein a time constant of the waveguide structure, relating current flow through the heater to temperature of a waveguide of the waveguide structure, is less than 20 microseconds.
19. The optical waveguide structure of claim 1 , further comprising a diode connected in series with the heater.
20. The optical waveguide structure of claim 1 , wherein the heater comprises a first heater and a second heater, connected in parallel.
21. The optical waveguide structure of claim 1 , wherein the heater comprises a first heater and a second heater, connected in series.