Self-mixing particulate matter sensors using VCSELs with extrinsic photodiodes
Aspects of the subject technology relate to an apparatus for self-mixing particulate-matter sensing using a vertical-cavity surface-emitting laser (VCSEL) with extrinsic photodiodes. The apparatus includes a dual-emitting light source disposed on a first chip and to generate a first light beam and a second light beam. The first light beam illuminates a particulate matter (PM), and a light detector extrinsic to the first chip measures the second light beam and variations of the second light beam and generates a self-mixing signal. The variations of the second light beam are caused by a back-scattered light resulting from back-scattering of the first light beam from the PM. The light detector is coupled to the dual-emitting light source. The direction of the second light beam is opposite to the direction of the first light beam, and the second light beam is directed to a sensitive area of the light detector.
1. An apparatus comprising:
a dual-emitting light source disposed on a first chip and configured to generate a first light beam and a second light beam, the first light beam being configured to illuminate a particulate matter (PM); and
a light detector extrinsic to the first chip and configured to measure the second light beam and variations of the second light beam and to generate a self-mixing signal, wherein:
the dual-emitting light source comprises a vertical-cavity surface-emitting laser (VCSEL),
the light detector comprises a photodiode (PD) positioned on a second chip that includes a VCSEL structure and surrounds the VCSEL on the first chip,
the variations of the second light beam are caused by a back-scattered light resulting from back-scattering of the first light beam from the PM,
the light detector is coupled to the dual-emitting light source,
a direction of the second light beam is opposite to the direction of the first light beam, and
the second light beam is directed from the dual-emitting light source to the light detector through an optically transparent layer that is electrically and thermally conductive and is attached to the light detector.
2. The apparatus of claim 1 , wherein the optically transparent layer is disposed in between the VCSEL and the light detector.
3. The apparatus of claim 2 , wherein an electrical contact layer of the VCSEL is electrically isolated from the PD via the optically transparent layer.
4. The apparatus of claim 3 , wherein a second laser power associated with the second light beam is equal or more than a first laser power associated with the first light beam.
5. The apparatus of claim 1 , wherein the back-scattered light is configured to recouple into a resonant cavity of the dual-emitting light source and to cause the variations of the second light beam.
6. An apparatus for PM sensing, the apparatus comprising:
a light source disposed on a first chip and configured to generate a first light beam to illuminate a particulate matter (PM);
a light detector extrinsic to the light source; and
a beam splitter configured to split the first light beam to generate a second light beam directed to the light detector,
wherein:
the light source comprises a vertical-cavity surface-emitting laser (VCSEL),
the light detector comprises a photodiode (PD) positioned on a second chip that includes a VCSEL structure, and
the PD is configured to measure the second light beam and variations of the second light beam resulting from a back-scattered light created due to back scattering of the first light beam from the PM and to generate a self-mixing signal.
7. The apparatus of claim 6 , wherein the VCSEL structure is configured to surround the VCSEL on the first chip.
8. The apparatus of claim 7 , wherein the VCSEL structure surrounding the VCSEL is structurally similar to the VCSEL and is isolated from the VCSEL using a trench isolation region and is reverse biased.
9. The apparatus of claim 8 , further comprising an optical element configured to:
focus a portion of the first light beam transmitted through the beam splitter to a sensing volume for sensing the PM, and
direct the back-scattered light through the beam splitter to the VCSEL.
10. The apparatus of claim 9 , wherein the beam splitter comprises on of a wedge-shaped beam splitter with a wedge angle within 6-8 degrees or a diffraction grating having 0 th order and ±1 st order diffractions aligned to locations of the VCSEL and the PD, respectively.
11. The apparatus of claim 10 , wherein the wedge-shaped beam splitter is further configured to focus a portion of the first light beam transmitted through the wedge-shaped beam splitter to a sensing volume for sensing the PM.
12. The apparatus of claim 10 , further comprising an optical element configured to:
focus a portion of the first light beam transmitted through the wedge-shaped beam splitter to a sensing volume for sensing the PM, and
direct the back-scattered light through the beam splitter to the VCSEL.
13. The apparatus of claim 6 , further comprising an electrical insulation layer and an optical band-pass filter disposed between the light source and the PD.
14. The apparatus of claim 6 , further comprising: an electrical insulation layer disposed between the light source and the PD, and an optical band-pass filter implemented over the beam splitter and configured to remove ambient light.
15. An electronic device comprising:
a processor; and
a particulate matter sensing device comprising:
a dual-emitting vertical-cavity surface-emitting laser (VCSEL) disposed on a first chip and configured to generate a first light beam and a second light beam, the first light beam being configured to illuminate a particulate matter (PM); and
a photodiode (PD) extrinsic to the first chip
and is configured to measure the second light beam and variations of the second light beam and to generate a self-mixing signal,
wherein:
the PD is disposed on a second chip underneath the VCSEL,
the variations of the second light beam are caused by recoupling into a resonant cavity of the dual-emitting VCSEL by a back-scattered light,
the back-scattered light results from back-scattering of the first light beam from the PM,
the PD is coupled to the dual-emitting VCSEL,
a direction of the second light beam is opposite to the direction of the first light beam, and
the second light beam is directed from the dual-emitting VCSEL to PD through an optically transparent layer that is electrically and thermally conductive and is attached to the PD.
16. The electronic device of claim 15 , wherein the optically transparent layer is disposed in between the VCSEL and the PD, and wherein the second light beam is configured to reach a sensitive area of the PD through the optically transparent layer.
17. The apparatus of claim 15 , further comprising an electrical insulation layer and an optical band-pass filter disposed between the light source and the PD.
18. The apparatus of claim 15 , further comprising:
an electrical insulation layer disposed between the light source and the PD, and
an optical band-pass filter implemented over the beam splitter and configured to remove ambient light.