Optimizing mirror reflectivity for reducing spontaneous emissions in photodiodes
View Patent ↗An optical structure that reduces the effects of spontaneous emissions from the active region of a laser. An optical structure includes optimizations to reduce the effects of spontaneous emissions. The optical structure includes a VCSEL with top and bottom DBR mirrors and an active region connected to the mirrors. The optical structure further includes a photodiode connected to the VCSEL. One or more optimizations may be included in the optical structure including optically absorbing materials, varying the geometry of the structure to change reflective angles, using optical apertures, changing the reflectivity of one or more mirrors, changing the photodiode to be more impervious to spontaneous emissions, and using ion implants to reduce photoluminescence efficiency.
1. An optical structure comprising:
a VCSEL, the VCSEL comprising:
a top DBR mirror;
an active region coupled to the top DBR mirror, wherein during operation of the VCSEL, the active region is configured to emit photons by stimulated emission and by spontaneous emission; and
a bottom DBR mirror coupled to the active region;
a photodiode coupled to the VCSEL; and
an absorbing material disposed within the optical structure near a local minimum of the electric field of the VCSEL such that the absorbing material will absorb more spontaneous emissions than stimulated emissions.
2. The optical structure of claim 1 , wherein at least one of the top DBR mirror or the bottom DBR mirror is configured to reduce transmission of off-axis emissions at a specific angle.
3. An apparatus comprising:
a VCSEL, the VCSEL comprising:
a top DBR mirror;
an active region coupled to the top DBR mirror; and
a bottom DBR mirror coupled to the active region;
a photodiode coupled to the bottom DBR mirror; and
means within at least one of the top DBR mirror or the bottom DBR mirror for reducing spontaneous emissions received by the photodiode, the means being located near a local minimum of the electric field of the VCSEL.
4. An apparatus according to claim 3 , wherein at least the bottom DBR, active region, and top DBR are above the photodiode.
5. An optical structure as in claim 1 , wherein the absorbing material forms part of a mirror layer within the top DBR mirror or the bottom DBR mirror.
6. An optical structure as in claim 1 , wherein the absorbing material is configured to absorb light at a wavelength near the wavelength of the stimulated emissions.
7. An optical structure as in claim 1 , wherein the absorbing material is configured to absorb light at a wavelength below about 735 nm.
8. An optical structure as in claim 1 , wherein the absorbing material is configured to absorb light at a wavelength below about 800 nm.
9. An optical structure as in claim 1 , wherein the absorbing material is configured to absorb light at a wavelength below about 870 nm.
10. An optical structure as in claim 1 , wherein a dopant concentration in the absorbing material is high relative to other regions of the optical cavity.
11. An optical structure as in claim 10 , wherein the absorbing material forms part of a mirror layer within the top DBR mirror or the bottom DBR mirror and the dopant concentration in the absorbing material is high relative to other mirror layers of the top DBR mirror or the bottom DBR mirror.
12. An optical structure as in claim 1 , wherein the absorbing material includes implanted protons that produce low photoluminescence efficiency in the absorbing material.
13. An optical structure as in claim 1 , wherein the absorbing material includes a III-V semiconductor material comprising aluminum.