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This paper presents the use of oblique illumination in self-referencing digital holographic microscopy (SR-DHM) to separate the interfering beams and enhance the resolution. SR-DHM is a compact and vibration-immune quantitative phase microscopy technique in which the interference of the object beam with part of itself forms the digital hologram. However, one drawback with SR-DHM is that both interfering beams contain object information that may overlap and hinder proper reconstruction. This study shows that using oblique illumination in off-axis DHM configurations separates the two interfering beams' spectra in the Fourier space, which can be used in SR-DHM to separate the overlapping beams' information without any restriction on the sample or the Field of View (FoV). The technique's capability is first shown in lateral shearing SR-DHM using a glass plate in which the object beams reflected from the front and back surfaces of a thick glass plate interfere and form the hologram. Using oblique illumination in this setup removes the redundant information from the FoV and improves the resolution twice. On the other hand, the technique is applied in SR-DHM using Lloyd's mirror, in which part of the object beam reflected from the Lloyd's mirror interferes with the part that arrives straightly at the camera plane. By tuning the fringe density in this setup using the illumination angle, we show that the interfering beams can be separated and the two simultaneous holograms can be recorded and reconstructed without overlapping information. This feature can be used for single-shot 1D resolution enhancement without overlapping information. The samples used in our validation experiments are a USAF test target and a 1D phase grating.
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