## 1 Introduction  
Functional micro-optics components (FMOCs) are typically used in the modulation of optical wave fields, digital holographic interferometry, and the measurement of phase or intensity in 3D specimens. The surface of these devices exhibits varying features and diverse combinations of microstructures, which can be used to modulate optical parameters such as phase, amplitude, and polarization. A wide variety of miniature optical instruments, based on FMOCs, has been developed in recent years. For example, micro-lens arrays have been used to measure the slope of wave fronts in Hartmann sensors, a challenging application of phase imaging with FMOCs. Digital holographic microscopy (DHM), a relatively new technique, can measure the amplitude and phase distribution of an objective wave field used to modulate sample data. DHM offers the advantages of full field, noninvasive, high precision, and high-speed imaging. As a result, it has been widely used for micro-lens measurement [1; 2], microstructure measurements [3; 4; 5; 6], particle tracking [7; 8; 9], biological imaging [10; 11; 12], and material engineering [13; 14].  
Conventional DHM systems are based on a Michelson and Mach-Zehnder interferometer. In these configurations, the object and reference beams pass through separated light paths. The primary disadvantage of this approach is the disturbance caused by mechanical vibrations in either of the interferometric arms, which reduces the long-term stability of the device. Novel optical configurations implementing parallel glass plates [11; 15], cube beam splitters [16; 17; 18], or a Sagnac framework [19; 20] have been introduced to resolve problems with instability. This configuration, in which both interference beams propagate together, is referred to as common-path DHM. Common-path techniques can be divided into two broad categories: in-line and off-axis imaging. In-line holography faces the inevitable problem of a conjugate image and zeroth-order wave being superimposed on the object image, making phase reconstruction difficult. The precision of off-axis holography is reduced by the spectral selection window, which restricts the bandwidth of the frequency spectrum. Phase-shifting digital holography was proposed to resolve this issue [21; 22; 23; 24; 25; 26]. In this process, a phase-shifting device, such as flat mirror mounted to a piezoelectric transducer (PZT), is introduced in the reference arm to shift the phase between the two interference beams. This allows for the recording of multiple phase-shifted holograms, but only the object image can be reconstructed using a phase-shifting technique. A PZT-actuated flat mirror is easily introduced in a Michelson or Mach-Zehnder interferometry configuration; however, this requires mechanical movement with high-positioning precision. Wavelength-tuning technology [27; 28; 29; 30] can realize phase shifting without mechanical movement when an interference cavity remains constant, [PERSON] et al. [29] established a 300 mm aperture Fizeau interferometer based on wavelength-tuning technology with repeatability precision of 0.3 nm RMS, and a 610 mm aperture interferometer was developed with residual error of 0.56 nm RMS by the Zygo Corporation [30].  
This study introduces a novel wavelength-tuning methodology for the quantitative phase imaging of functional micro-optics components in common-path digital holographic microscopy. With this approach, system errors can be reduced and phase measurement precision can be improved by eliminating mechanical components from the phase-shifting steps. Experimental results demonstrated the proposed technique to be a powerful new tool for DHM imaging.