Laser beam wavelength determination algorithm using a digital micromirror device

Abstract

An approach for wavelength characterization whereby dynamic Fresnel zone plate (FZP) patterns are written to a digital micromirror device (DMD) and used to focus incoming light onto a camera is proposed. The incoming wavelength is then assessed by scanning the focal length. Rectangular basis Zernike modes are implemented to match the rectangular geometry of the DMD, we believe for the first time. A procedure is developed to correct for inherent aberrations of the optical system by adjusting the Zernike mode amplitudes, thus improving focal spot quality. The aberration corrected FZPs are used to assess the focusing conditions needed for four lasers of different visible wavelengths ranging from blue (405 nm) to near infrared (760 nm). The system is able to produce focused beams with a width of twice the diffraction limit and achieve a wavelength resolution of 3 nm. The operational wavelength of the system is ultimately limited by the spectral bandwidth of the detector.

Spatial channel multiplexing emulation with a 21-channel multiplane plane light converter

“…The DMD has tilting mirrors which reflect light away from the optical axis which adds aberrationsmost notably astigmatismto the diffracted wavefront. These additional aberrations can be at least partially corrected using the same Zernike mode structures as are used for distorting the wavefront in accordance with [10]. Thus a set of fixed correcting Zernike modes is added to the fixed focussing and the varying turbulence distortion to produce the final sequence of turbulence emulation frames.…”

Spatial Mode Division Multiplexing of Free-Space Optical Communications Using a Pair of Multiplane Light Converters and a Micromirror Array for Turbulence Emulation

“…The DMD has tilting mirrors that reflect light away from the optical axis which adds aberrations-most notably astigmatism-to the diffracted wavefront. These additional aberrations can be at least partially corrected using the same Zernike mode structures as the ones used for distorting the wavefront in accordance with [23]. Thus, a set of fixed correcting Zernike modes is added to the fixed focussing and the varying turbulence distortion to produce the final sequence of turbulence emulation frames.…”