Chenliang Chang - Research

My research is mainly focused on the SLM based holographic optical field shaping and display technique, where the computer-generated hologram (mostly the phase-only CGH) is calculated and loaded to the SLM. The CGH aims to shape and modulate the incident light into the desired complex structure optical fields that have specifically designed amplitude, phase and polarization distribution. My research works can be concluded into two major parts:

Structure beam shaping. In this work we study the generation of orbital angular momentum (OAM) beams consisting of phase vortex, and vector beams where the beams have inhomogeneous state of polarization.
Holographic 3D display and projection. In this work we develop variety of algorithms to calculate and encode the phase-only CGH, aiming to solve some existing problems such as the huge data amount, low calculation speed, low display quality with speckle noise, et.al.

Other of my research works also includes optical manipulation of micro-particles using OAM beams and digital holographic microscopy for imaging and measurement of phase type samples.

1. Structure optical field shaping

We generate a type of novel vector beams that the polarization state varies along 3D curve paths, by superposing two orthogonal component in a common path optical system.

Chenliang Chang, et.al, Optics Letters, 42(19), (2017)

We generate a type of complex structure optical field consisting of phase vortex array (lattice) or polarization vortex array (lattice) along arbitrary curvilinear arrangement, by coaxially superposing an inner and outer curve beams with prescribed intensity and phase distributions.

Lin Li, Chenliang Chang*, et.al, Optics Express, 26(8), (2018)

Optical manipulation of micro-particles

The beam modulated by the SLM is tightly focused by the 100x objective of a microscopy, and produce a focused ring with phase vortex around its curve. The generated ring vortex can trap and motivate the particles moving around the ring trajectory induced by the orbital angular momentum.

2. Holographic 3D display and projection, holographic AR display

We develop the method of CGH generation using the non-uniform Fourier transform algorithm (NU-FFT) which can reduce the computation cost by exploring the sampling relations in diffraction calculation

Chenliang Chang, et.al, Applied Optics, 55(28), (2016)
Chenliang Chang, et.al, Optics Express, 22(14), (2014)

In order to remove the speckle noise caused by coherent laser source, it is necessary to simultaneously modulate the amplitude and phase (complex amplitude modulation) of the reconstructed field from phase-only SLM in holographic display. We develop several algorithms, such as double-constraint GS algorithm, double-phase encoding algorithm, to calculate the phase-only CGH. The phase-only CGH can reconstruct both of target amplitude pattern and uniform phase distribution.

Chenliang Chang, et.al, Applied Optics, 54(23), (2015)
Yijun Qi, Chenliang Chang, et.al, Optics Express, 24(26), 2016

We improve the complex modulation reconstruction technique to design a compact lensless holographic projection system which can project a high fidelity color images with reduced speckle noise.

Chenliang Chang, et.al, Optics Express, 25(6), (2017)

Holographic AR display: In the above mentioned experiments, the reconstructed 3D objects or scenes are captured by placing the camera at the screen. Besides, the CGH can also directly displays the created 3D virtual objects/scenes into the human retina when looking through the light beam, which can provide a see-through augmented reality (AR) display based on the specific aligned holographic display system.

Digital holographic microscopy (DHM)

The DHM uses interference of the object wavefront and a reference wavefront to form a hologram that is recorded by the CCD. The phase of the object can be retrieved via the hologram post-processing and reconstruction calculations including phase unwrapping algorithms.