Bengong Hao

Parallel two-step spatial carrier phase-shifting common-path interferometer with a Ronchi grating outside the Fourier plane

A parallel two-step spatial carrier phase-shifting common-path interferometer with a Ronchi grating placed outside the Fourier plane is proposed in this paper for quantitative phase imaging. Two phase-shifted interferograms with spatial carrier can be captured simultaneously using the proposed interferometer. The dc term can be eliminated by subtracting the two phase-shifted interferograms, and the phase of a specimen can be reconstructed through Fourier transform. The validity and stability of the interferometer proposed are experimentally demonstrated via the measurement of a phase plate.

Common-path interferometer with a tri-window

A common-path interferometer is proposed with a tri-window. It is built using a 4f optical system with Ronchi ruling as a spatial filter. The input rectangular aperture is formed by three windows; the central window supports a phase object, and the other two are used for reference beams. Using an appropriate grating period relative to input aperture size, an interferogram containing three patterns can be obtained in the output plane. The object phase can then be reconstructed from the three patterns using just one interferogram. The experiments are carried out to demonstrate the feasibility and reliability of the proposed scheme.

Two-shot common-path phase-shifting interferometer with a four-step algorithm and an unknown phase shift

This paper presents a two-shot common-path phase-shifting interferometer that consists of a 4f optical system with two windows in the input plane and a Ronchi grating in the Fourier plane, and generates two adjacent interferograms using only diffraction orders 0 and +1 and 0 and -1. Four phase-shifted interferograms can be obtained in two shots by modulating two linear polarizers with angle difference of π/4 and translating the grating with only an unknown phase shift. An algorithm similar to the standard four-step algorithm is used to retrieve the phase of a specimen, and it requires no knowledge of the phase shift introduced by translation of the grating. The validity and repeatability of the proposed method is proved through simulations and experiments.

Parallel two-step spatial carrier phase-shifting interferometric phase microscopy with fast phase retrieval

A method of parallel two-step spatial carrier phase-shifting two-window interferometer with fast phase retrieval is applied for microscopic imaging. The method prior captures interferograms offline without any sample only once. As a consequence, the interferograms for a phase sample can be acquired by camera in a single shot, and the phase distribution of the sample can be then reconstructed without phase unwrapping process if the phase variance is less than 2π. This method can eliminate the aberration and noise of the system and phase tilt at the same time, and thus improve the phase retrieval speed. Experiments are demonstrated to prove the validation of the presented method.

Tri-window common-path interferometer for quantifying phase objects

A new method is presented using a tri-window common-path interferometer (TriWCPI) for quantitative phase measurement. The prior method obtains the phase shift introduced by the Ronchi grating and the intensity value of the incident light with interferograms acquired offline without any objects. As a consequence, an improved recovery algorithm is established using the phase shift, the intensity value of the incident light, and the interferograms for a phase object acquired by camera in a single shot. The phase of an object then can be reconstructed from the improved algorithm. Because the calculation of phase shift and intensity value can be performed offline only once after the TriWCPI is built, the real-time ability and stability of the TriWCPI remains in this method. But the method avoids the normalization process and thus improves phase-retrieval precision. Experiments are demonstrated to prove the precision, real-time ability, and stability of the proposed method.

Image edge enhancement for moving objects with a spiral phase filter

A fast image edge enhancement method for moving objects is presented with a spiral phase filter using radial Hilbert transform theory. The spiral phase filter is placed in the Fourier plane of a 4f optical system, and used to process the spectral of objects image to achieve 2-D image edge enhancement of shape-free objects. All the directions of object edge can be enhanced similarly because there is a phase difference π along any diameter direction of the spiral phase filter. The results show that this method has good performance for enhancing the edge of moving objects. The advantages of this method are simple operations, clear edge images, high measurement speed and automatic measurement.

FPGA implementation of a modified hard decision decoding for 2-D TPC

A modified algorithm for two-dimensional TPC decoding is proposed to reduce the wrong frame rate in the (16,11,4)2 Turbo Product Code (TPC) decoding in this paper. It is based on the hard decision decoding, including a chooser and a parallel decoding architecture that one is column-row and the other is row-column. The Monte-Carlo simulation shows that 30% wrong frame is eliminated and the implementation of the decoder for TPC (16,11,4)2 with FPGA has achieved the decoding throughput of 53Mbit/s with 20M clock.

Radius measurement using a parallel two-step spatial carrier phase-shifting common-path interferometer

A curvature radius (CR) measurement method using a parallel two-step spatial carrier phase-shifting common-path interferometer is presented. This interferometer is built on a 4f optical system with two windows in the input plane and a ronchi grating outside the fourier plane. A test lens is placed in front of one of the two windows. The phase of the test lens is retrieved from the two phase shifted interferograms recorded using this interferometer and then the profile can be obtained. The CR of the test lens is thus directly derived from the profile according to their geometrical relations. The theoretical model and experimental setup are established to illustrate this method and the measurement processes. Experiments are constructed to verify the effectiveness of the CR measurement using this interferometer. The results prove that this interferometer is an effective approach for the CR measurement with inherent simplicity, high robustness and accuracy.

Radius measurement using two-windows common-path interferometry with phase grating

A method using two-windows common-path interferometry with phase grating is presented to measure the curvature radius (CR). This interferometry is built using a 4f optical system with binary phase grating implemented by spatial light modulator (SLM) as spatial filter. The input plane is formed by two windows, which are used for the measured lens and reference beam, respectively. In the output plane, an interferogram can be achieved by a proper choice of the windows’ spacing with respect to the grating period. The phase of the lens can be retrieved from the shift phase of composite interferograms achieved by lateral movements of the grating. The curvature radius of the lens is thus directly derived from the phase function. A theoretical model is also established using Fourier transform theory and phase retrieval algorithm to describe the measured process using phase-shifting interferometry. Analyzed results indicate that the method is an effective approach for the radius measurement with inherent simplicity, high robustness and flexibility.