We report on a conceptual design and feasibility demonstration for a scanned beam endoscope, with advantages over present CCD imaging technology in image resolution and quality, light source power, and package diameter. Theoretical calculations were made by optical modeling and finite element analysis of the performance projected for a design meeting size constraints. To verify the design target of 5 mm for the endoscope diameter, we conducted a design study of the deformation and resolution characteristics of a scan mirror small enough to fit within a 2.5 mm capsule within the endoscope. The results show that performance similar to the test system can be achieved. A functional prototype was then built and tested to validate the theory used. The test system consisted of a photonics module with red (635 nm), green (532 nm) and blue (473 nm) lasers, combined by dichroic mirrors and launched to a single mode fiber. The light emerging from the fiber is formed into a beam and reflected from a commercially available bi-axial MEMS scanner with a 1.56 mm square mirror, and a scan angle of 6 degrees zero to peak mechanical, at a frequency of 19.7 kHz. Scanned beam power from 1 to 3 mw impinges the test object at a range from 10 to 100 mm, and the scattered light is collected by several 3 mm diameter multimode fibers and conducted one-meter to detectors. The detected light was digitized and then reconstructed to form an image of the test object, with 800 by 600 output pixels. Several such images will be presented.
We present the results of an ongoing investigation into the use of directly modulated light emitting diodes and laser diodes as light sources for a retinal scanning display. Devices studied include commercially available single-mode 635 nm laser diodes, custom fabricated red edge-emitting LEDs, custom fabricated gallium nitride-based green and blue edge-emitting LEDs, and commercial LEDs. The diodes were characterized in both DC (light vs. current/voltage), and high frequency (approximately 1 ns rise/fall pulse) regimes, and measured for luminance using a CCD camera in conjunction with a variable image aperture, variable NA light collection system. Results show that edge-emitting LEDs and laser diodes are each suitable for a particular range of display requirements.
Miniature displays based on scanning a low power beam directly onto the viewer's retina can offer high spatial and color resolution and very high luminance.For scanning display systems, the resolution is primarily determined by the product of scan-angle and mirror-size. Once (theta) D is determined based on resolution requirements, it then remains to choose D and (theta) . Once choice of D and (theta) has a big impact in scanner design and many factors need to be taken into account. This paper discuses how D and (theta) should be chosen considering the limitations due to dynamic mirror deformation, stress in flexures, scanner frequency, optomechanical design, size, and cost.