System for optical imaging comprising matched spectral filters
Systems, methods and devices are for optical imaging are described. A system includes a light source and a light detection unit. The light source includes a light-emitting device and a first spectral filter opposite the light emitting device. The first spectral filter includes at least one dielectric filter and has a first angular dependence of a transmission passband. The light source further includes at least one reflector adjacent side surfaces of the light emitting device. The light detection unit includes an optical sensor and a second spectral filter opposite the optical sensor. The second spatial filter has a second angular dependence of a transmission passband that is matched to the first angular dependence.
1. A system comprising:
a light source comprising:
a light-emitting device configured to generate light having a wavelength range, and
a first spectral filter configured to receive the light generated by the light-emitting device, the first spectral filter having a first transmission passband with characteristics that include a shift towards smaller wavelengths with increasing incidence angle of the light impinging thereon and with a transmission passband that is narrow compared to the wavelength range of the light; and
a light detection unit comprising:
a second spectral filter configured to receive light from the light source that has been reflected by an object, the second spectral filter having a second transmission passband with characteristics that match the characteristics of the first spectral filter; and
an optical sensor configured to receive light that has passed through the second spectral filter.
2. The system of claim 1 , wherein the light-emitting device comprises a light-emitting diode (LED).
3. The system of claim 1 , wherein at least one of the first and second transmission passband has a full width at half maximum (FWHM) of at most about 50 nm.
4. The system of claim 1 , wherein an exit surface of the light-emitting device from which the light generated by the light-emitting device exits the light-emitting device and an entrance surface of the light detection unit at which the light from the light source that has been reflected by the object enters the light detection unit are substantially parallel.
5. The system of claim 4 , wherein the light source is adjacent the light detection unit.
6. The system of claim 1 , wherein the first and second spectral filter each have dual transmission passbands with a first dual transmission passband in a visible light range and a second dual transmission passband in a near infrared (NIR) range.
7. The system of claim 6 , wherein the first dual transmission passband has a wider bandwidth than the second dual transmission passband in each of the first and second spectral filter.
8. The system of claim 6 , wherein the first and second dual transmission passbands have different angular dependencies in each of the first and second spectral filter.
9. The system of claim 8 , wherein the first dual transmission passband has a smaller angular shift than the second dual transmission passband.
10. A camera comprising:
a light source comprising:
a light-emitting device configured to generate light having a wavelength range,
a first spectral filter configured to receive the light generated by the light-emitting device, the first spectral filter having a first transmission passband with characteristics that include a shift towards smaller wavelengths with increasing incidence angle of the light impinging thereon and having a full width at half maximum (FWHM) that is narrow compared to the wavelength range of the light, and
side surfaces that extend between the light emitting device and the first spectral filter and are reflective to the light having the wavelength range; and
a light detection unit adjacent the light detection unit, the light detection unit comprising:
a second spectral filter configured to receive light from the light source that has been reflected by an object, the second spectral filter having a second transmission passband with characteristics that match the characteristics of the first spectral filter; and
an optical sensor configured to receive light that has passed through the second spectral filter.
11. The camera of claim 10 , further comprising a processor configured to receive signals from the light detection unit, the signals corresponding to the light received by the optical sensor, the light including the light from the light source that has been reflected by the object and ambient light, the processor configured to perform ambient light image subtraction.
12. The camera of claim 10 , wherein at least one of the first and second transmission passband has a full width at half maximum (FWHM) of at most about 50 nm.
13. The camera of claim 10 , wherein an exit surface of the light-emitting device from which the light generated by the light-emitting device exits the light-emitting device and an entrance surface of the light detection unit at which the light from the light source that has been reflected by the object enters the light detection unit are substantially parallel.
14. The camera of claim 10 , wherein the first and second spectral filter each have dual transmission passbands with a first dual transmission passband in a visible light range and a second dual transmission passband in a near infrared (NIR) range.
15. The camera of claim 14 , wherein the first dual transmission passband has a wider bandwidth than the second dual transmission passband in each of the first and second spectral filter.
16. The camera of claim 14 , wherein the first and second dual transmission passbands have different angular dependencies in each of the first and second spectral filter.
17. The camera of claim 16 , wherein the first dual transmission passband has a smaller angular shift than the second dual transmission passband.
18. The camera of claim 10 , wherein the light-emitting device is disposed on a substrate and a reflective coating is disposed on the substrate between the light-emitting device and the side surfaces, the reflective coating configured to reflect the light generated by the light-emitting device.
19. The camera of claim 18 , wherein the side surfaces extend non-perpendicularly between the substrate and the first spectral filter.
20. A method of operating a lighting system, the method comprising:
generating light having a wavelength range;
filtering the light using a first spectral filter having a first transmission passband that shifts towards smaller wavelengths with increasing incidence angle of the light and a full width at half maximum (FWHM) that is narrow compared to the wavelength range of the light; and
detecting, by an optical sensor, the light after reflection by an object and filtering by a second spectral filter having a second transmission passband with matching shift and FWHM characteristics as the first spectral filter.
21. The method of claim 20 , further comprising performing ambient light image subtraction to subtract the detected light from ambient light detected by the optical sensor.
22. The method of claim 20 , wherein:
the first and second spectral filter each have dual transmission passbands with a first dual transmission passband in a visible light range and a second dual transmission passband in a near infrared (NIR) range, and
the first dual transmission passband has a smaller angular shift than the second dual transmission passband.