Range selective frequency-modulated digital holography with temporal-heterodyning

Abstract

We present a novel approach for on-axis range selective phase shifting digital holographic imaging using a Timeof-flight (TOF) camera and temporal heterodyning (TH). The modulated arrayed detection of a TOF camera allows for integration of holograms at a selected range using chirped frequency modulated continuous wave (FMCW) techniques. The achieved range resolution is significantly better than the optical system's depth of field. Each pixel of the TOF camera is equipped with a photonic mixing device (PMD) that facilitates gated integration with an internal reference frequency. Our innovative technique leverages the unique capabilities of a TOF camera where the required four phase shifted images, used in phase shifting digital holography (DH) reconstruction, are recorded by changing the phase shift of the TOF camera's internal modulation frequency. The heterodyne method of recording the phase shifted holograms also filters out any background light not at the internal modulation frequency of the TOF camera. Our range selective TH FMCW DH system successfully performs imaging for both image and Fresnel holograms for target distances of approximately 80 centimeters and 95 centimeters. In this experiment we used a 2.39 GHz FMCW chirp bandwidth, which resulted in an achieved range resolution of 6.3 cm. The performance of range selectivity is further analyzed by computing extinction percentages, which quantify the amount of light removed from unselected targets. In all recording geometries, we achieved extinction percentages of over 96%.