Mr. Nicholas W. Melena Profile

Nicholas W. Melena

Sr. Optical Engineer at Compound Photonics

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Proceedings Article | 28 March 2021 Presentation + Paper

Pixel size requirements for AR/MR

Nicholas Melena, Joshua Wiersma

Proceedings Volume 11765, 1176505 (2021) https://doi.org/10.1117/12.2584168

KEYWORDS: Waveguides, Imaging systems, Image resolution, Projection systems, Multiplexing, Liquid crystal on silicon

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For conventional projection displays, the sizes of the microdisplay and imaging lens aperture stop typically limit the optical throughput or étendue of the system. However, for AR/MR projection systems using diffractive pupil-replicating waveguide combiners, we examine how re-interaction with the in-coupler grating at one FOV extreme and pupil replication sparsity at the other FOV extreme severely restrict the optical throughput. Diffractive waveguides are the most commonly used AR/MR combiner technology due to their low cost, attractive form factor, and large achievable FOV. Nevertheless, we show that current and anticipated diffractive combiners only support étendues up to approximately 6.2 mm²sr, equivalent to no larger than a 0.34” display operating at f/2. At this display diagonal, maintaining 60 PPD for retinal resolution over a 50°-diagonal FOV requires a 3-μm pixel pitch. Future combiners with larger FOVs and higher resolutions will require even smaller pixels. Additionally, we find that optical engine volume varies quadratically with pixel pitch. Finally, we illustrate how the push for small pixels will intensify as the dominant array-based microdisplay technology used in AR/MR devices transitions from LCoS to inorganic microLED (micro-iLED). The emissive nature of micro-iLED displays offers exceptional potential power savings for sparse AR/MR content. Nonetheless, the broad angular emission and spatially multiplexed color subpixels of many proposed micro-iLED architectures further strain the bandwidth of the limited waveguide throughput. We demonstrate how CP Display has anticipated the requirement of 3-μm and smaller pixels in architecting its IntelliPix™ display platform.

Proceedings Article | 7 September 2013 Paper

Advanced surface metrology for meter-class optics

M. Valente, B. Lewis, N. Melena, M. Smith, J. Burge, C. Zhao

Proceedings Volume 8838, 88380F (2013) https://doi.org/10.1117/12.2035141

KEYWORDS: Surface finishing, Aspheric lenses, Interferometry, Computer generated holography, Mirrors, Calibration, Optical testing, Optics manufacturing, Spatial resolution, Optical scanning systems

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Refinements in computer controlled optical surfacing allow efficient grinding and polishing of meterclass optics to accuracy limited only by the surface metrology. We present a categorization of metrology methods and their implementation for meter-class optical components. Interferometry with computer generated holograms provides nanometer accuracy for full surface measurements of a wide range of convex and concave aspheric surfaces. For measuring off-axis and freeform aspheric surfaces, the holograms include features that provide references for alignment. Very high spatial resolution is achieved with subaperture interferometric measurements which can be stitched together to provide a full-aperture map. Scanning systems complement the capabilities of interferometry by achieving larger dynamic range and providing independent corroboration. Optical coordinate measurement machines (CMMs) provide non-contact measurements of surfaces in their ground state to guide figuring, as well as highly accurate measurements of finished optics. Scanning systems for measuring flat mirrors provide excellent resolution and absolute accuracy. The performance and practical issues for this full array of measurement techniques are presented to show the relative strengths of each method.

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