On-line phase shifting digital holography requires recording of multiple holograms. In this paper, we describe a real time 3-D object recognition system using single exposure on-line digital holography. In contrast to 3-D object recognition employing conventional phase shifting scheme which requires multiple exposures, this method requires only one single digital hologram to be synthesized and used to recognize 3-D objects. A benefit of the proposed 3-D recognition method is enhanced practicality of digital holography for 3-D recognition in terms of its simplicity and more robustness to external scene parameters such as moving targets and environmental noise factors. We show experimentally, that the single exposure on-line digital holography based 3-D object recognition method is capable of providing 3-D object recognition. The experimental results are compared with that of the on-line phase shifting digital holographic based 3D recognition.
In-line digital holography using a quarter wave plate and averaging technique is described in this paper. In-line digital holographic scheme inherently suffers from DC and conjugate object image noise terms. This problem can be overcome by using phase shifting technique which usually requires four digital holograms. However, it requires four successive holograms, which makes it less robust in relatively poor environment than one-shot off axis scheme. This study is on two-exposure method employing only a quarter wave plate which can produce 90 degree phase difference between two successive holograms. The two-exposure method can provide conjugate-free reconstruction capability. Also, the DC terms can be minimized by applying averaging technique for object DC term. Detail explanation on how to reduce the DC term noise and how the intensity level of reference and object wave can affect the reconstructed image quality is discussed. Although the reconstructed image quality has a little undesired background noise compared with the conventional four frame method, it has a benefit in the sense that it requires only two holograms for eliminating the DC and the conjugate terms. The numerically reconstructed results show the feasibility of the two-exposure method and it may be capable of providing more robust approach in on-axis scheme.
This paper describes a newly designed multipoint process monitoring system based on an acousto-optic tunable filter. In order to prove the feasibility of the suggested multipoint monitoring system for use in the NIR spectral region, some experiments were carried out in the visible range. The multipoint process monitoring system consists of an AOTF device for wavelength selecting, a CCD imaging sensor, and a specially designed in-line type of optical fiber probe. Unlike an FTS (Fourier Transform Spectrometry) based monitoring system, an AOTF has no moving parts, and it can be rapidly tuned to any wavelength in its operating range within microseconds. Thus, the AOTF is advantageous in terms of faster spectral imaging capability and rigidity required for industrial monitoring environment. Also, Fourier Transform Spectrometry experiments were conducted for comparison with the AOTF based monitoring system. In the current feasibility evaluation, an enhanced optical fiber probe with 3 monitoring points was used. However, the number of monitoring points can be easily expanded to dozens more points as required.