Power monitoring approach for VCSELS and VCSEL arrays
The present disclosure relates to an approach for monitoring the output power of a VCSEL or VCSEL array in a relatively compact, low profile package. A VCSEL device or VCSEL package of the present disclosure may generally be configured with a photodiode for monitoring output power of one or more VCSELs. In some embodiments, one or more VCSEL devices may be arranged over or on a photodetector, such that the photodetector is configured to detect light emitted through a bottom of the VCSEL. In such embodiments, the VCSEL device may have a patterned bottom metal layer and/or an etched substrate to allow light to pass below or behind the VCSEL to the photodiode. In other embodiments, a photodetector may be arranged on a submount adjacent one or more VCSELs, and may be configured to detect light reflected via a diffuser in order to monitor output power.
1. A VCSEL device comprising:
a VCSEL chip, the VCSEL chip having a center point and a top surface, and
a photodiode, the photodiode having a center point, wherein the VCSEL chip and the photodiode arranged on a submount such that the center point of the VCSEL chip is separated from the center point of the photodiode by a first distance;
wherein the VCSEL chip and photodiode are housed in a package, the package having:
a window configured and arranged to allow light emitted from the VCSEL chip to pass through the window;
a spacer arranged between the submount and the window; and
a diffuser arranged on the window and completely covering a surface of the window, the diffuser being arranged at a height of a second distance above the top surface of the VCSEL chip, wherein the second distance is less than the first distance;
wherein light emitted by the VCSEL chip travels in three manners:
a portion of the light is transmitted through the diffuser and through the window;
a portion of the light is repeatedly scattered and reflected along the window for a lateral distance; and
a portion of the light is scattered by the diffuser back into the package and to the photodiode.
2. The VCSEL device of claim 1 , wherein the diffuser is arranged on a portion of the window so as to be laterally offset from a central axis of light emitted from the VCSEL chip.
3. The VCSEL device of claim 1 , wherein the VCSEL chip comprises an array of VCSEL chips.
4. The VCSEL device of claim 1 , wherein the photodiode is arranged on the submount adjacent the VCSEL chip.
5. The VCSEL device of claim 1 , wherein the package has a thickness of less than 3 mm.
6. The VCSEL device of claim 5 , wherein the package has a thickness of less than 2 mm.
7. The VCSEL device of claim 1 , wherein the diffuser is placed on an inside surface of the window.
8. The VCSEL device of claim 1 , wherein the VCSEL chip comprises a discrete VCSEL.
9. The VCSEL device of claim 1 , wherein the center point of the VCSEL chip and the center point of the photodiode are laterally separated by a distance of between approximately 2 mm and approximately 2.12 mm and the diffuser includes a surface and wherein the surface is approximately 0.76 mm above the top surface of the VCSEL chip.
10. The VCSEL device of claim 1 , wherein the second distance is less than half of the first distance.
11. A VCSEL device comprising:
a VCSEL chip, the VCSEL chip having a center point and a top surface, and
a photodiode, the photodiode having a center point, wherein the VCSEL chip and the photodiode arranged on a submount such that the center point of the VCSEL chip is separated from the center point of the photodiode by a first distance; and
wherein the VCSEL chip and photodiode are housed in a package, the package having:
a window configured and arranged to allow light emitted from the VCSEL chip to pass through the window, the window having a first lateral end and a second lateral end;
a spacer arranged between the submount and the window; and
a pseudo-random, non-periodic diffuser provided extending from the first lateral end to the second lateral end, the non-periodic diffuser being arranged at a height of a second distance above the top surface of the VCSEL chip, wherein the second distance is less than the first distance;
wherein light emitted by the VCSEL chip travels in three manners:
a portion of the light propagates is transmitted through the diffuser and through the window;
a first minority portion of the light is repeatedly scattered and reflected within the diffuser parallel to a plane of the window; and
a second minority portion of the light is scattered by the diffuser back into the package and to the photodiode.
12. The VCSEL device of claim 11 , wherein the non-periodic diffuser has a pattern etched thereon.
13. The VCSEL device of claim 11 , wherein the VCSEL chip comprises an array of VCSEL chips.
14. The VCSEL device of claim 11 , wherein the non-periodic diffuser completely covers an inside surface of the window.
15. A VCSEL device comprising:
a VCSEL chip, the VCSEL chip having a center point and a top surface, and
a photodiode, the photodiode having a center point, wherein the VCSEL chip and the photodiode arranged on a submount such that the center point of the VCSEL chip is separated from the center point of the photodiode by a first distance;
wherein the VCSEL chip and photodiode are housed in a package, the package having:
a window configured and arranged to allow light emitted from the VCSEL chip to pass through the window;
a spacer arranged between the submount and the window; and
a diffuser arranged on a surface of the window and extending over a majority of the surface, and being arranged at a height of a second distance above the top surface of the VCSEL chip, wherein the second distance is less than the first distance,
wherein light emitted by the VCSEL chip travels in three manners:
a portion of the light is transmitted through the diffuser and through the window;
a portion of the light is repeatedly scattered and reflected within the diffuser parallel to a plane of the window; and
a portion of the light is scattered by the diffuser back into the package and to the photodiode.
16. The VCSEL device of claim 15 , wherein the diffuser is arranged on the window so as to be aligned with a central axis of light emitted from the VCSEL chip.
17. The VCSEL device of claim 16 , wherein the diffuser comprises a hollow shape with a central opening.
18. The VCSEL device of claim 15 , wherein the diffuser is laterally off set from the VCSEL chip.
19. The VCSEL device of claim 15 , wherein the VCSEL chip comprises an array of VCSEL chips.