Monolithic power monitor and wavelength detector
View Patent ↗Monolithic single and/or dual detector structures are fabricated on the emitting surface of a VCSEL and/or on a lens or glass substrate configured to be positioned along the axis of emission of an optical light source. Each monolithic detector structure includes one or two PIN detectors fabricated from amorphous silicon germanium with carbon doping or amorphous germanium with hydrogen doping. The monolithic detectors may additionally include various metallization layers, buffer layers, and/or anti-reflective coatings. The monolithic detectors can be grown on 1550 NM VCSELs used in optical transmitters, including lasers with managed chirp and TOSA modules, to reduce power and real estate requirements of the optical transmitters, enabling the optical transmitters to be implemented in long-reach SFP+ transceivers.
1. An optical transmitter incorporating monolithic detector structures for power and wavelength monitoring, the transmitter comprising:
an optical light source configured to emit light in an optical wavelength range through an emitting surface, the optical light source being coupled to a first thermoelectric cooler configured to control the temperature of the optical light source, wherein a change in the temperature of the optical light source results in a change in the wavelength of light emitted by the optical light source;
a first monolithic detector structure coupled to the emitting surface of the optical light source and being positioned along the emission axis of the optical light source and configured to detect optical output power of light emitted by the optical light source;
a periodic structure positioned along the emission axis of the optical light source following the first monolithic detector structure, the periodic structure being attuned to a particular wavelength within the optical wavelength range such that the periodic structure is substantially transmissive for light of the particular wavelength and variably less transmissive for light of different wavelengths outside of the optical wavelength range; and
a second monolithic detector structure positioned along the emission axis of the optical light source following the periodic structure and configured to detect the wavelength of light emitted by the optical light source.
2. The optical transmitter of claim 1 , wherein the periodic structure is included within an optical spectrum reshaper coupled to a second thermoelectric cooler configured to control the temperature of the optical spectrum reshaper, wherein a change in the temperature of the optical spectrum reshaper results in a change of the bandpass of the optical spectrum reshaper and the particular wavelength to which the periodic structure is attuned.
3. The optical transmitter of claim 1 , wherein the second monolithic detector structure is coupled to
an optical lens following the optical spectrum reshaper.
4. The optical transmitter of claim 1 , wherein the optical light source comprises a vertical cavity surface emitting laser and wherein the first monolithic detector structure is fabricated on the emitting surface of the vertical cavity surface emitting laser along the axis of light emission, wherein a buffer layer is located between the emitting surface and first monolithic detector,
the first monolithic detector comprising:
a first metallization layer on the buffer layer;
a PIN layer or junction on the first metallization layer; and
a second metallization layer on the PIN layer or junction; and
the second monolithic detector comprising:
a first metallization layer on the optical lens or on an a buffer layer between the optical lens and first metallization layer;
a PIN layer or junction on the first metallization layer; and
a second metallization layer on the PIN layer or junction.
5. The optical transmitter of claim 4 , wherein the optical transmitter is implemented in an SFP+ form factor optical transceiver that includes a transmit CDR chip for electrical signal equalization.
6. The optical transmitter of claim 1 , further comprising an optical lens disposed between the optical light source and the periodic structure, wherein the axis of light emission of the optical light source passes through the optical lens.
7. The optical transmitter of claim 6 , wherein the optical light source comprises a vertical cavity surface emitting laser or a distributed feedback laser and wherein the optical wavelength range is between 1520 nanometers and 1570 nanometers.
8. The optical transmitter of claim 1 , wherein the first and second monolithic detector structures include one or more of: amorphous silicon germanium with carbon doping, and amorphous germanium with hydrogen doping.
9. The optical transmitter of claim 1 , wherein photocurrents generated by the first and second monolithic detector structures are used in a feedback loop to determine and adjust an emission wavelength of the light emitted by the optical light source.
10. The optical transmitter of claim 1 , further comprising a lookup table or calibration file indicative of the wavelength of light emitted by the optical light source depending on a ratio of photocurrents generated by the first and second monolithic detector structures.
11. An optical transmitter incorporating monolithic detector structures for power and wavelength monitoring, the transmitter comprising:
an optical light source configured to emit light in an optical wavelength range through an emitting surface, the optical light source being coupled to a first thermoelectric cooler configured to control the temperature of the optical light source, wherein a change in the temperature of the optical light source results in a change in the wavelength of light emitted by the optical light source;
a first optical lens positioned long the emission axis of the optical light source so that light emission from the emitting surface passes through the optical lens;
a first monolithic detector structure located on a surface of the first optical lens by being grown thereon and being positioned along the emission axis of the optical light source and configured to detect optical output power of light emitted by the optical light source;
a periodic structure positioned along the emission axis of the optical light source following the first monolithic detector structure, the periodic structure being attuned to a particular wavelength within the optical wavelength range such that the periodic structure is substantially transmissive for light of the particular wavelength and variably less transmissive for light of different wavelengths outside of the optical wavelength range; and
a second monolithic detector structure positioned along the emission axis of the optical light source following the periodic structure and configured to detect the wavelength of light emitted by the optical light source.
12. The optical transmitter of claim 11 , wherein the periodic structure is included within an optical spectrum reshaper coupled to a second thermoelectric cooler configured to control the temperature of the optical spectrum reshaper, wherein a change in the temperature of the optical spectrum reshaper results in a change of the bandpass of the optical spectrum reshaper and the particular wavelength to which the periodic structure is attuned.
13. The optical transmitter of claim 11 , wherein the second monolithic detector structure is coupled to a second optical lens following the optical spectrum reshaper.
14. The optical transmitter of claim 13 , wherein the optical light source comprises a vertical cavity surface emitting laser,
the first monolithic detector comprising:
a first metallization layer on the first optical lens or on an a buffer layer between the first optical lens and first metallization layer;
a PIN layer or junction on the first metallization layer; and
a second metallization layer on the PIN layer or junction; and
the second monolithic detector comprising:
a first metallization layer on the second optical lens or on an a buffer layer between the second optical lens and first metallization layer;
a PIN layer or junction on the first metallization layer; and
a second metallization layer on the PIN layer or junction.
15. The optical transmitter of claim 14 , wherein the optical transmitter is implemented in an SFP+ form factor optical transceiver that includes a transmit CDR chip for electrical signal equalization.
16. The optical transmitter of claim 11 , further comprising an optical lens disposed between the optical light source and the periodic structure, wherein the axis of light emission of the optical light source passes through the optical lens and wherein the first monolithic detector structure is fabricated on an output surface of the optical lens along the axis of light emission.
17. The optical transmitter of claim 16 , wherein the optical light source comprises a vertical cavity surface emitting laser or a distributed feedback laser and wherein the optical wavelength range is between 1520 nanometers and 1570 nanometers.
18. The optical transmitter of claim 11 , wherein the first and second monolithic detector structures include one or more of: amorphous silicon germanium with carbon doping, and amorphous germanium with hydrogen doping.
19. The optical transmitter of claim 11 , wherein photocurrents generated by the first and second monolithic detector structures are used in a feedback loop to determine and adjust an emission wavelength of the light emitted by the optical light source.
20. The optical transmitter of claim 11 , further comprising a lookup table or calibration file indicative of the wavelength of light emitted by the optical light source depending on a ratio of photocurrents generated by the first and second monolithic detector structures.