Nowadays, distorted grating has been widely used for wavefront curvature sensing, multifocal imaging in microscopy, and 3D nanoparticle tracking. However, similar to conventional gratings, the diffractive energy of this distorted grating is actually focused at several low diffraction orders and the high orders are too weak to detect in practice (usually only the 0th and the_1st orders are detectable for amplitude-only distorted gratings). Moreover, the energy distribution among those several low diffraction orders is also not uniform, and the 0th order usually occupies the most diffractive energy. Therefore, it is impossible to achieve both large axial imaging range and high axial resolution in real time.

Researchers at Laboratory of Information Optics and Optoelectronics Techniques——Shanghai Institute of Optics and Fines Mechanics (SIOM/China) introduce the Dammann phase-encoding method into original distorted gratings and propose a modified distorted grating, called a distorted Dammann grating (DDG), to realize multiplane imaging of several tens of layers within the object field onto a single image plane. This property implies that the DDG makes it possible to achieve simultaneously high axial resolving power and large axial imaging range without scanning. This DDG should be of high interest for its potential applications in real-time three-dimensional optical imaging and tracking. [Optics Letters, Vol. 38, Issue 4, pp. 474-476 (2013)]

They experimentally demonstrated the multiplane imaging of 7 × 7 equal-distance layers within the object field onto a single camera plane .In fact, a much larger number of object layers could also be achieved, such as 21 × 21 or even 64 × 64, if only the pupil aperture of the focusing system is large enough (which indicates a large Debye focusing region).Further, in this case, a CCD camera with a large-enough detection area is also desired to capture images of so many object layers. Therefore, the DDG opens up the possibility to achieve high axial resolution and large axial imaging range without scanning, and this real-time 3D optical imaging should be of high interest for its applications in various areas, such as in vivo cellbiological microscopy and real-time nanoparticle tracking.Recently, a 3D Dammann array of focus spots was demonstrated that could be used for 3D parallel optical manipulation . The DDG presented here also provides an interesting solution for monitoring this 3D parallel optical manipulation.