200×200 µm2 structured light source.

Abstract

3D structured illumination is important in high-speed 3D metrology where beam patterns are roughly categorized into multi-dot and fringe patterns. For example, large-scale multi-dot patterns are utilized for facial recognition in an iPhone X on the basis of an active stereo method, while fringe patterns are utilized in Grey code patterns or fringe projection profilometry including Fourier transform profilometry and the phase shifting profilometry, which is suitable for high-resolution measurement. Among these applications, the light sources include a combination of vertical-cavity surface-emitting lasers (VCSELs) and diffractive optical elements (DOEs), a projector, and so on. Recently, we demonstrated static arbitrary two-dimensional beam patterns without a zero-order beam from needle-tip sized integrable spatial-phase-modulating surface-emitting lasers (iPMSELs). Due to their compactness (they are one order of magnitude smaller than DOE), surface-emitting device, lack of zero-order beam, and ease of switching the beam patterns electrically, iPMSELs will be suitable as an ultra-compact light source for 3D metrology that not only downsizes the conventional light source but also contributes to 3D inspections in narrow spaces such as dental and endoscope examinations. In this context, we have examined two beam patterns (multi-dot and fringe) both without a zero-order beam by using the iPMSELs. In the former, we have demonstrated projection of large-scale dot patterns of more than 10,000 points, which is the same order of magnitude as points in a practical device from a 200×200-µm2 emitter. Since the emitter has approximately 1 mega scattering points, this structure enables 1-mega-pixel images in the wavenumber space, which are comparable to the images of a typical projector emitting several-mega-pixel images from several tens of centimeters. In the latter, we successfully shifted the fringe patterns, which is vital to applying the phase shifting profilometry, despite the superposition of the conjugate ±1st order beam patterns.