By designing sliced phase patterns, Yan et al. demonstrated multiple collinear OAM modes generation with a spatial light modulator (SLM) [
34]. Moreover, they also experimentally demonstrated data-carrying multicasting five and seven OAM channels from a single-input OAM channel. The approach is illustrate in Fig. 2. It has been shown that an angular amplitude aperture of central angle
q with
M-fold rotational symmetry can distribute energy from the input OAM beam of charge
l to multiple OAM beams having equally spaced OAM charge number of {
…,
−kM+ l, …,
−M+ l,
l,
M+ l, …,
kM+ l, … } (
k is an integer). Note that in the first row of Fig. 2, the aperture’s transmission part has a constant phase value
b0, which results in a sin
c2-like OAM charge spectrum, centered at input OAM charge
l. In the second row of Fig. 2, the aperture’s transmission part is complementary to that of the first aperture, and it produces a sin
c2-like OAM charge spectrum centered at
l - 6. In the last row, the sliced phase pattern can be viewed as the superposition of the transmission parts of the above two amplitude-phase apertures. As a result, the output spectrum of the sliced phase pattern is a coherent addition of those two previous output spectra. The parameter
b0 is optimized such that most of the multicasting OAM channels have equalized power except for the two channels at the wings of the spectrum. By using this approach, 7 equally spaced OAM modes are successfully generated. The experimental results are shown in Fig. 3. By using a pattern of more slices, seven OAM channels (
l= 6, 9, 12, 15, 18, 21, 24) are generated in the experiment. The phase pattern consists of three sliced regions, where there are two parameters,
b1 and
b2, to be optimized to equalize the power of the multicasting channels. The intensity patterns of before multicasting OAM mode and after multicasting OAM modes are shown in Fig. 3(a). Figure 3(b) illustrates the power distribution after multicasting.