Figure 6: Design of a stopband optical filter based on photon’s OAM.
From: Synthetic-lattice enabled all-optical devices based on orbital angular momentum of light
(a) Spectrum band of the device in Fig. 2 with three marked frequencies ωA=ω0, ωB≃ω0−1.1κ and ωC≃ω0−1.8κ. The corresponding group velocities are vg(ωA)=2κ, vg(ωB)=1.65κ and vg(ωC)=0.9κ. (b) The filter function 
of the device in Fig. 2 when its maximum absorption frequency is designed to be ωA, ωB and ωC, respectively. A maximum absorption frequency closer to the band edge results in a steeper skirt slope but poorer in-band rejection ratio. (c) A two-cavity design with their maximum absorption frequencies chosen to be ωC and ωB, respectively. (d) The filter function for the design in c. (b,d) 
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