Google Inc.

Pgt Photonics, S.p.a

Pirelli Cavi E Sistemi S.p.a.

Pirelli & C. S. P. A.

Politecnico Do Milano

Politecnico Di Milano

Paolo Martelli

Mario Martinelli

Aldo Righetti

Pierpaolo Boffi

Lucia Marazzi

Silvia Maria Pietralunga

Rocco Siano

Paola Parolari

Angelo Barberis

Alberto Gatto

An optical communication system is disclosed. The optical communication system comprises an optical transmitter and a substantially circular multi-mode optical fiber. The optical transmitter comprises a generator of at least two free space circular vortices and comprises an optical element configured to receive the at least two free space circular vortices and to couple them to an input facet of the optical fiber. The optical fiber is configured to receive at the input facet the at least two free space circular vortices and is configured to generate therefrom at least two corresponding guided circular vortices having respective propagation constants, wherein the values of the propagation constants at a defined frequency are different each other.

Mode multiplexing optical communication system

An optical communication system () comprises at least a transmitter () apt to emit a differential phase shift keying (DPSK) optical signal having a bit-rate equal to R, at least a receiving system () for receiving the differential phase shift keying optical signal; and an optical link () optically connecting the transmitter and the receiving system for transmitting the DPSK optical signal from the transmitter to the receiving system, wherein the receiving system comprises a coherent optical receiving device () apt to coherently receive the propagated DPSK optical signal and to emit at least one electrical signal (I) related to the received DPSK optical signal, and wherein the receiving system further comprises at least one electrical filter () for filtering the at least one electrical signal and having &#x2212;3 dB double-side bandwidth greater than or equal to 0.44 R and lower than or equal to 0.68 R, and at least one squarer () for squaring the at least one filtered electrical signal. A related method for optical communication is also disclosed.

System and method for coherent detection of optical signals

A method of stabilizing the state of polarization of an optical radiation comprises: 1) applying sequentially to the optical radiation a first and a second controllable phase retardation; 2) detecting an optical power of at least a first polarized portion of the optical radiation obtained after step 1; 3) applying sequentially to the optical radiation obtained after step 1 a third and a fourth controllable phase retardation; 4) detecting an optical power of a further polarized portion of the optical radiation obtained after step 3; 5) controlling, responsive to the optical power of said first polarized portion, the second controllable phase retardation so as to maintain the polarization state of the optical radiation obtained after step 1 at a defined great circle r on a Poincare sphere; 6) in case the second controllable phase retardation reaches a first limit value, commuting the first controllable phase retardation between first and second values; 7) controlling, responsive to the optical power of said further polarized portion, the fourth controllable phase retardation so as to maintain the polarization state of the optical radiation obtained after step 3 at a defined state of polarization; 8) in case the fourth controllable phase retardation reaches a second limit value, commuting the third controllable phase retardation between third and fourth values, keeping constant the first controllable phase retardation while the third controllable phase retardation is commuting between said third and fourth values. A polarization stabilizing device based on the method above is also disclosed.

Method and device for polarization of an optical radiation

A device and method for stabilizing the state of polarization of polarization multiplexed optical radiation including an identified channel is disclosed. The device and method comprise providing to the polarization multiplexed optical radiation a first controllable polarization transformation to generate a first transformed optical radiation; detecting a first state of polarization of a first polarized portion with respect to a first polarization parameter; controlling the first controllable polarization transformation so that the first polarization parameter has a predetermined value independent of a polarization state of the polarization multiplexed optical radiation; providing to the first transformed optical radiation a second controllable polarization transformation to generate a second transformed optical radiation; detecting a second state of polarization of a second polarized portion; and controlling the second controllable polarization transformation so that the second state of polarization has a predefined value.

Method and device for stabilizing the state of polarization of a polarization multiplexed optical radiation

A device and method for stabilizing the polarization of polarization multiplexed optical radiation includes an identified channel which is provided with a pilot signal. The device and method are based on providing to the polarization multiplexed optical radiation a controllable polarization transformation; measuring the optical power of a polarized portion of the identified channel downstream the polarization transformation; controlling, responsively to the optical power, the controllable polarization transformation so that the identified channel downstream the polarization transformation has a predefined polarization azimuth; providing to the optical radiation downstream the polarization transformation a further controllable polarization transformation; measuring the optical power of a polarized portion of the identified channel downstream the further controllable polarization transformation; and controlling, responsively to the optical power, the further controllable polarization transformation so that the identified channel downstream the further controllable polarization transformation has a predefined state of polarization.

A polarization stabilizing device and method based on controlling the phase retardations of a pair of variable rotators with an optically interposed quarter-wave plate, with a controller such that the first of the variable rotators has its phase retardation switched between first and second values whenever the phase retardation of the second of the variable rotators reaches an upper or a lower limit. The upper and lower limits of the second rotator and the first and second values of the first rotator are chosen so that discontinuities in the power of the output optical radiation are avoided when the first variable rotator is switched, thereby providing endless polarization stabilization using rotators that themselves may have limited retardation ranges.

Method and device for stabilizing the state of polarization of optical radiation

A polarization stabilizing device and method based on controlling the phase retardation of a pair of variable phase retarders with a controller such that the first of the variable retarders has its phase retardation switched between first and second values whenever the phase retardation of the second of the variable retarders reaches an upper or a lower limit. The upper and lower limits of the second retarder and the first and second values of the first retarder are chosen so that discontinuities in the power of the output optical signal are avoided when the first variable retarder is switched, thereby providing endless polarization stabilization using phase retarders that themselves have only limited retardation ranges.

Polarization stabilization

In an interferometer configuration, a retarder in the form of a half-wave plate () and a phase shifter in the form of a glass plate () are arranged in one arm (). The phase shifter provides an optical path difference between the interferometer arms which needs to be greater than the coherence length of the input light to be polarization stabilized. A polarizer in the form of a linear polarizer () aligned at 45&#xb0; to the half-wave plate is arranged across both interferometer arms (&). Polarization stabilization action is achieved by the retarder in combination with the polarizer. More specifically, for at least one input polarization state, the polarization states in the two interferometer arms are rendered orthogonal by the retarder, the polarizer being aligned to allow only one of the two orthogonal states to be transmitted, the other being absorbed. The device is expected to find application for WDM networks based on broadband sources, such as superluminescent diodes. The device is also expected to be useful for providing a front-end polarization stabilization of the signal supplied to optical elements that are sensitive to the polarization state of their input. Examples of such elements are semiconductor optical amplifiers, integrated optical splitters and electro-optical switches.

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Milan, Italy

Paolo Martelli