Measurement of a laser pulse repetition frequency using upconversion

1 . An apparatus, comprising:

a silicon-based image sensor that has i) a pixel array with one or more pixels and ii) an upconversion layer of crystals on at least one of a front side and a backside of the silicon-based image sensor, and

a pulse repetition frequency decoder configured to cooperate with the upconversion layer of crystals to decode a pulse repetition frequency of a laser flash captured by one or more of the pixels of the silicon-based image sensor, wherein the pulse repetition frequency decoder is configured to use a known frame rate of the silicon-based image sensor and a decay time of an upconverting emission from the upconversion layer of crystals to decode the pulse repetition frequency of the laser flash.

2 . The apparatus of claim 1 , wherein the pulse repetition frequency decoder is configured to use an area under an emission curve that provides a photon signal at a first time period that spans from a first frame read post capture of the laser flash until one or more frame reads later, when electrons, in crystals with a dopant in the upconversion layer of crystals, have decayed from a higher energy state than their ground energy state down to the ground energy state to determine the pulse repetition frequency of the laser flash.

3 . The apparatus of claim 1 , wherein the upconversion layer of crystals has a dopant selected to absorb incident electromagnetic radiation at a first range of wavelengths and to emit electromagnetic radiation at a second range of wavelengths that is within a wavelength range that the silicon-based image sensor is able to detect, wherein the dopant comprises a rare-earth element.

4 . The apparatus of claim 1 , wherein the pulse repetition frequency decoder is located on a chip containing the silicon-based image sensor that has the pixel array.

5 . The apparatus of claim 1 , wherein the pulse repetition frequency decoder is located in a camera in an imaging pipeline located off a chip that contains the silicon-based image sensor that has the pixel array.

6 . The apparatus of claim 1 , wherein the pixel array with the one or more pixels on the silicon-based image sensor is configured to detect light wavelengths in one or more of ultraviolet (UV) light, visible light, and near-infrared (NIR) light, and

wherein the upconversion layer has a plurality of crystals intermixed with a dopant that is configured to convert short wave infrared (SWIR) light to the light wavelengths of the UV light, the visible light, or the NIR light.

7 . The apparatus of claim 1 , wherein the pulse repetition frequency decoder is configured to use the decoded pulse repetition frequency to determine an identity of a laser that produced the laser flash captured by one or more of the pixels by comparing the pulse repetition frequency to known codes of lasers.

8 . The apparatus of claim 1 , wherein the upconversion layer of crystals is located on the backside of the silicon-based image sensor.

9 . The apparatus of claim 1 , wherein the upconversion layer of crystals is located on the front side of the silicon-based image sensor.

10 . The apparatus of claim 1 , wherein the silicon-based image sensor that has i) the pixel array with one or more pixels and ii) the upconversion layer of crystals, and the pulse repetition frequency decoder are configured to cooperate with a second image sensor, wherein pixels in the second image sensor are configured to receive light in all wavelengths of an image frame, and wherein light in all wavelengths of an image frame will be incident on the upconversion layer of crystals, wherein some of the light incident on the upconversion layer of crystals in a first wavelength will be absorbed and converted by the upconversion layer of crystals into a second wavelength, which is different than the first wavelength, and then the light in the second wavelength is transmitted to the one or more pixels in the silicon-based image sensor.

11 . A method for imaging, comprising:

providing a silicon-based image sensor that has i) a pixel array with one or more pixels and ii) an upconversion layer of crystals on at least one of a front side and a backside of the silicon-based image sensor;

providing a pulse repetition frequency decoder to cooperate with the upconversion layer of crystals to decode a pulse repetition frequency of a laser flash captured by one or more of the pixels of the silicon-based image sensor; and

providing the pulse repetition frequency decoder to use a known frame rate of the silicon-based image sensor and a decay time of an upconverting emission from the upconversion layer of crystals to decode the pulse repetition frequency of the laser flash.

12 . The method of claim 11 , further comprising:

providing the pulse repetition frequency decoder to use an area under an emission curve that provides a photon signal at a first time period that spans from a first frame read post capture of the laser flash until one or more frame reads later, when electrons, in crystals with a dopant in the upconversion layer of crystals, have decayed from a higher energy state than their ground energy state down to the ground energy state in order to determine the pulse repetition frequency of the laser flash.

13 . The method of claim 11 , further comprising:

providing the upconversion layer of crystals with a dopant selected to absorb incident electromagnetic radiation at a first range of wavelengths and to emit electromagnetic radiation at a second range of wavelengths that is within a wavelength range that the silicon-based image sensor is able to detect, wherein the dopant comprises a rare-earth element.

14 . The method of claim 11 , further comprising:

providing the pulse repetition frequency decoder that is located on a chip containing the silicon-based image sensor that has the pixel array.

15 . The method of claim 11 , further comprising:

providing the pulse repetition frequency decoder that is located in a camera in an imaging pipeline located off a chip that contains the silicon-based image sensor that has the pixel array.

16 . The method of claim 11 , further comprising:

providing the pixel array with the one or more pixels on the silicon-based image sensor to detect light wavelengths in one or more of ultraviolet (UV) light, visible light, and near-infrared (NIR) light, and

providing the upconversion layer that has a plurality of crystals intermixed with a dopant that is configured to convert short wave infrared (SWIR) light to the light wavelengths of the UV light, the visible light, or the NIR light.

17 . The method of claim 11 , further comprising:

providing the decoded pulse repetition frequency to determine an identity of a laser that produced the laser flash captured by one or more of the pixels by comparing the pulse repetition frequency to known codes of lasers.

18 . The method of claim 11 , wherein the upconversion layer of crystals is located on the backside of the silicon-based image sensor.

19 . The method of claim 11 , wherein the upconversion layer of crystals is located on the front side of the silicon-based image sensor.

20 . The method of claim 11 , further comprising:

providing the silicon-based image sensor that has i) the pixel array with one or more pixels and ii) the upconversion layer of crystals, and the pulse repetition frequency decoder to cooperate with a second image sensor, wherein pixels in the second image sensor are configured to receive light in all wavelengths of an image frame, and wherein light in all wavelengths of an image frame will be incident on the upconversion layer of crystals, wherein some of the light incident on the upconversion layer of crystals in a first wavelength will be absorbed and converted by the upconversion layer of crystals into a second wavelength, which is different than the first wavelength, and then the light in the second wavelength is transmitted to the one or more pixels in the silicon-based image sensor.