Fig. 1. Concept of (a) an OAM-multiplexed optical network with OAM-multiplexed optical connections and OAM-based reconfigurable optical networking functions: (b) charge shift, (c) charge exchange, and (d) charge-selective manipulation [3,18].

Fig. 2. Concept of OAM channel add/drop multiplexing [19].

Fig. 3. Experimental results: (a1)–(a6) intensity profiles of multiplexed OAM beams for each step of adding/dropping the OAM +2 channel; BER curves for (b1) added/dropped channels and (b2) pass-through channels. B2B, back-to-back; BER, bit error rate; conv., conversion; MUX, multiplex; OSNR, optical signal-to-noise ratio [19].

Fig. 4. Functional block diagram of the 2×2 OAM-based switch. Switching is performed with the help of mode downconversion, programmable beam steering, and mode upconversion stages [20].

Fig. 5. BERs for modes appearing at output port A for different switch configurations: (a) channels from input port A, (b) channels from input port B, (c) channels from input port A while switch was in “bar” state. FEC: forward error correction [20].

Fig. 6. Procedures of the conversion (a) from a polarization-multiplexed signal to an OAM-multiplexed signal, (b) from an OAM-multiplexed signal to a polarization-multiplexed signal. MUX, multiplexing [21].

Fig. 7. Schematic view of conversion (a) from OAM +2 on x-pol and y-pol to OAM +3 and OAM +6 on x-pol, and (b) from OAM +1 and OAM +6 on x-pol to OAM +1 on x-pol and y-pol [21].

Fig. 8. (a) Concept of channel hopping in the spatial domain using OAM modes; one period of the received waveforms for channel ℓ=+1 at hopping rates of (b1) 10 and (b2) 50 MHz; recovered 100  Gbit/s QPSK constellations for channel ℓ=+1 during the (b3) data period and (b4) hopping transition time at 50 MHz hopping rate (2 ns guard time). Mode set ℓ=−3, −1, +1, +3 is used [22].

Fig. 9. (a) Concept of the multicasting function in an OAM multiplexing system, (b) the OAM power spectrum before and after multicasting [23].