Wearable heads-up display with optical path fault detection

1. A wearable heads-up display, comprising:

at least one photodetector positioned proximate a perimeter of a lightguide to detect a first intensity of a portion of a test light emitted within the wearable heads-up display; and

a laser safety circuit coupled to the at least one photodetector, the laser safety circuit to reduce or shut off a supply of electrical power from a power source to a plurality of laser sources carried within the wearable heads-up display in response to the at least one photodetector indicating that the detected first intensity is below a first threshold.

2. The wearable heads-up display of claim 1 , wherein the plurality of laser sources are visible laser sources, and wherein at least one of the visible laser sources generates the test light.

3. The wearable heads-up display of claim 1 , wherein the plurality of laser sources includes a plurality of visible laser sources and at least one infrared laser source, and wherein the at least one infrared laser source generates the test light.

4. The wearable heads-up display of claim 1 , further comprising a display engine to provide controls that modulate outputs of the plurality of laser sources according to display data, wherein the laser safety circuit is to provide a notification to the display engine in response to the at least one photodetector indicating that the detected first intensity is below the first threshold.

5. The wearable heads-up display of claim 1 , further comprising:

the lightguide, wherein the lightguide has at least one optical path defined therein; and

an in-coupler positioned at an input region of the lightguide to couple light into the input region.

6. The wearable heads-up display of claim 5 , further comprising at least one scan mirror positioned to receive an aggregated beam formed from outputs of the plurality of laser sources and redirect the aggregated beam to the in-coupler.

7. The wearable heads-up display of claim 5 , further comprising an out-coupler positioned at an output region of the lightguide to direct light out of the output region.

8. The wearable heads-up display of claim 7 , wherein the lightguide has a second optical path defined therein, and wherein the second optical path is in optical communication with the input region.

9. The wearable heads-up display of claim 8 , further comprising an exit pupil expander positioned at a fold region of the lightguide that is intermediate between the input region and the output region, the exit pupil expander to redirect at least a portion of light propagating along the second optical path to the at least one optical path.

10. The wearable heads-up display of claim 9 , further comprising a second photodetector positioned proximate to the perimeter of the lightguide to detect a second intensity of a portion of the test light that is emitted from the second optical path.

11. The wearable heads-up display of claim 10 , wherein the laser safety circuit is to reduce or shut off the supply of electrical power from the power source to the plurality of laser sources in response to the second photodetector indicating that the detected second intensity is below a second threshold.

12. The wearable heads-up display of claim 11 , further comprising a display engine to provide controls that modulate outputs of the plurality of laser sources according to display data, wherein the laser safety circuit is to provide a notification to the display engine in response to the at least one photodetector indicating that the detected first intensity is below the first threshold, the second photodetector indicating that the detected second intensity is below the second threshold, or both.

13. A wearable heads-up display, comprising:

a laser module including at least one laser source;

a lightguide having at least one optical path defined therein;

at least one light source to output a test light into the lightguide;

a photodetector positioned proximate to a perimeter of the lightguide to detect an intensity of a portion of the test light emitted from within the lightguide; and

a laser safety circuit coupled to a power source and the photodetector, the laser safety circuit to reduce or shut off a supply of electrical power from the power source to the laser module in response to an output signal from the photodetector indicating that the detected intensity is below a threshold.

14. The wearable heads-up display of claim 13 , wherein the at least one light source is a laser diode or a light emitting diode.

15. The wearable heads-up display of claim 13 , further comprising a support frame having a frame front and at least one temple coupled to the frame front, wherein the frame front carries at least one lens, and wherein the lightguide and in-coupler are integrated with the lens.

16. The wearable heads-up display of claim 15 , wherein the at least one light source and photodetector are embedded in a portion of the frame front circumscribing the at least one lens.

17. A method comprising:

testing a wearable heads-up display for optical path faults, the testing comprising:

generating a test light; and

detecting an intensity of a portion of the test light that is emitted at a perimeter of a lightguide; and

in response to detecting that the intensity is below a threshold, reducing or shutting off a supply of electrical power from a power source to a plurality of laser sources.

18. The method of claim 17 , further comprising projecting one or more display images to a display space within a field of view of the wearable heads-up display, wherein projecting each display image comprises:

forming a display light from a combination of laser light generated by the plurality of laser sources; and

coupling the display light into the lightguide.

19. The method of claim 18 , wherein projecting the one or more display images to the display space within the field of view is interspersed with testing the wearable heads-up display for optical path faults.

20. The method of claim 18 , wherein reducing the supply of electrical power from the power source to the plurality of laser sources comprises limiting the supply of electrical power to the plurality of laser sources such that an optical power density of the display light does not exceed the maximum permissible exposure for a Class 1 laser.