Patent ID: 11956014
Assignee: UNIVERSITA' DEGLI STUDI DI MILANO
Field: Telecommunications (Electrical engineering)
Classification: CPC H  G | IPC G  H

Claim 20:
21. A system for performing a telecommunication of modulated signals according to any known modulation technique and grouped by means of multiplexing in the orbital angular momentum variable, comprising:
means for generating an electromagnetic beam, configured to:
generate a first electromagnetic radiation beam (F1) characterized by a first orbital angular momentum (L1), and generate at least one second electromagnetic radiation beam (F2) characterized by at least one respective second orbital angular momentum (L2), wherein both the first electromagnetic radiation beam (F1) and the at least one second electromagnetic radiation beam (F2) have respective spectra in the same first frequency band, and furthermore have respective radii of curvature substantially coinciding with a first beam radius-of-curvature value;
generate a reference electromagnetic radiation beam (F0), characterized by a second orbital angular momentum (L0), a second spectrum in a second frequency band which is distinct from said first frequency band, and a second beam radius of curvature having a value substantially coinciding with said first beam radius-of-curvature value;

modulation means, configured to:
modulate a first piece of information to be transmitted, represented by a first modulation function a(t), on the first electromagnetic radiation beam (F1), by means of any amplitude and/or phase and/or frequency modulation technique, to obtain a first modulated beam (Fm1);
modulate at least one second piece of information to be transmitted, represented by a second modulation function b(t), on the at least one second electromagnetic radiation beam (F2), by means of any amplitude and/or phase and/or frequency modulation technique, to obtain a second modulated beam (Fm2);

beam combination and/or superposition means, configured to superimpose and/or combine said reference beam (F0), first modulated beam (Fm1) and second modulated beam (Fm2) to generate a composite electromagnetic radiation beam (Q1), consisting of the superposition of the reference beam (F0) and a main beam, in turn consisting of the superposition of said first modulated beam (Fm1) and at least one second modulated beam (Fm2);
transmission means, configured to transmit said generated composite electromagnetic radiation beam (Q1);
means for receiving the composite electromagnetic radiation beam, comprising:
first beam detection means, located in a first position, configured to generate a first composite beam electrical signal (D1), representative of the electric and/or magnetic field and/or of the intensity of the electromagnetic radiation of the composite beam in said first position;
second beam detection means, located in a second position, which are different with respect to said first position, configured to generate a second composite beam electrical signal (D2), representative of the electric and/or magnetic field and/or of the intensity of the electromagnetic radiation of the composite beam in said second position;
first frequency discrimination means, configured to perform a frequency discrimination of said first composite beam electrical signal (D1) with reference to said first frequency band and second frequency band to obtain, respectively, a first main beam electrical signal (P1), representative of the electric and/or magnetic field and/or of the intensity due to the main beam in said first position, and a first reference beam electrical signal (R1), representative of the electric and/or magnetic field and/or of the intensity due to the reference beam in said first position;
second frequency discrimination means, configured to perform a frequency discrimination of said second composite beam electrical signal with reference to said first frequency band and second frequency band to obtain, respectively, a second main beam electrical signal (P2), representative of the electric and/or magnetic field and/or of the intensity due to the main beam in said second position, and a second reference beam electrical signal (R2), representative of the electric and/or magnetic field and/or of the intensity due to the reference beam in said second position;

phase determination means, configured to:
determine the phase of the first main beam electrical signal (P1) and the phase of the second main beam electrical signal (P2);
determine the phase of the first reference beam electrical signal (R1) and the phase of the second reference beam electrical signal (R2);
determine a first phase difference value (ΔPab) corresponding to the difference between the phase of the first main beam electrical signal (P1) and the phase of the second main beam electrical signal (P2), said first phase difference value (ΔPab) being dependent on the values taken by the first modulation function a(t) and the second modulation function b(t);
determine a second phase difference value (ΔR) corresponding to the difference between the phase of the first reference beam electrical signal (R1) and the phase of the second reference beam electrical signal (R2);
subtract the second phase difference value (ΔR), divided by a wave number k′, from the first phase difference value (ΔPab), to obtain a difference value (Q2=ΔPab/k−ΔR/k′), said difference value (Q2=ΔPab/k−ΔR/k′) being representative of a combination of values taken by the first modulation function a(t) and the second modulation function b(t), while being independent of positional inclination conditions between said first detector and second detector and independent of phase variations due to disturbances suffered by the transmitted composite beam before reception,
where the first wave number k is the wave number corresponding to the main beam, defined as k=2π/λ, λ being the wavelength of said main beam belonging to the first frequency band, and where the second wave number k′ is the wave number corresponding to the reference beam, defined as k′=2π/λ′, λ′ being the wavelength of said reference beam belonging to the second frequency band;

processing means, configured to demultiplex and demodulate the information modulated on each of the first modulated beam (Fm1) and the at least one second modulated beam (Fm2), based on said determined difference value (Q2=ΔPab/k−ΔR/k′).