Figure 6 shows the filtered holograms obtained by filtering four holograms, which arerecorded using the off-axis DHM in Fig. 1. In our configuration, the wavelength of the coherent laser source is 666 nm. The magnification factor for microscope is 40 × /0.75NA.The angle θ between the object wave and the reference wave that are incident on the detector is about 3.26 degrees. We use these filtered holograms with the size of 1024 × 1024 pixels for numerical simulations to verify the feasibility of the proposed scheme. A set of four BPMs is applied to four encrypted holograms to obtain a single multiplexed image, which are shown in Fig. 7.We calculate the correlation coefficient (CC) between the decrypted hologram and theoriginal hologram to objectively evaluate the correlation between two holograms, which is defined aswhere cov(D, O) is the cross covariance between the decrypted hologram and the original hologram, and σ(D) and σ(O) are the standard deviations for both holograms.In the decryption process, we first extract the four encrypted holograms from themultiplexed image by applying the same BPMs that were used in the phase encoding andmultiplexing process. Then, we can restore four original holograms by applying the RPM2s to those encrypted holograms in Fourier domain and then inverse Fourier transforming those images, respectively. In our simulations, we can successfully restore four holograms using correct BPMs and correct RPMs, as shown in Figs. 8(a)-8(d), where the CC values are 1.Figures 8(e)-8(h) shows four holograms decrypted using the correct RPMs but the wrong BPMs. Their CC values were 0.001645, 0.001097, −0.0008185, and 0.0005702, respectively.These values are so small that there is no way to find out any information about the holograms.Next, we first encrypt 16 holograms, which are shown in Fig. 9, separately by using DRPE and divide them into four groups of four encrypted holograms. We can phase encode and superimpose them by separately applying different four sets of four BPMs, and then obtain four multiplexed images, as shown in Fig. 10. For example, Figs. 10(a) and 10(e) arethe amplitude and phase distributions of the multiplexed image from group I, which is shown in Figs. 9(a)-9(d). This multiplexed image is obtained by phase encoding and superimposing four encrypted holograms of group I by applying the first set of four BPMs.