Method and device for endless phase shifting of an optical signal

Patent metadata

Field	Value
Publication number	US-11476948-B2
Application number	US-202017005393-A
Country	US
Kind code	B2
Filing date	Aug 28, 2020
Priority date	Aug 30, 2019
Publication date	Oct 18, 2022
Grant date	Oct 18, 2022

Abstract

An optical endless phase shifting device includes a Mach-Zehnder structure operated in push-pull configuration and that creates a differential phase shift. The first stage outputs combined signals which are phase shifted by a phase shift of zero or π in the second stage by phase shifters provided in both arms of the second stage or in a first arm only. These additionally phase-shifted signals are combined to at least one output signal. A control device controls the phase shifters such that endless shifting capability is provided by switching one of the phase shifters or the single phase shifter of the second stage to the respective other value when the differential phase shift reaches a given range of the differential phase shift of [0;π/2] in the configuration with two phase shifters in the second stage or [0;π/2] in the configuration with only one phase shifters in the second stage.

First claim

The invention claimed is:

1. An optical endless phase shifting device for shifting an optical input signal by a desired phase shift comprising a first and a second stage,
(a) the first stage comprising a Mach-Zehnder structure comprising a passive optical splitter device configured to receive, at an input port, an optical input signal (S in ) and to split the input signal into a first and a second partial signal, each of which is fed, from a dedicated output port of the splitter device, to a first and a second branch of the first stage that connects the respective output port of the splitter device to a dedicated input port of a passive optical combiner device, the combiner device being configured to output a first combined signal (S sin ) at a first output port and a second combined signal (S sin ) at a second output port, each of the first and second branches of the first stage comprising a controllable optical phase shifter, wherein the phase shifter in the first branch is configured to shift the phase of the first partial signal by a positive predetermined phase shift (+φ) and wherein the phase shifter in the second branch is configured to shift the phase of the second partial signal by a negative predetermined phase shift (−φ), and
(b) the second stage comprising a passive optical combiner device having a first input port connecting a first branch of the second stage to the first output port of the first stage combiner device and a second input port connecting a second branch of the second stage to the second output port of the first stage combiner device, the first branch or the first and second branches of the second stage comprising a controllable optical phase shifter, the combiner device being configured to output, at at least one output port, an optical output signal (S out,1 , S out,2 ), which corresponds to the optical input signal (S in ) that is phase shifted by a desired phase shift (φ tot ),
(c) wherein the optical phase shifters in the first branch or the first and second branches of the second stage are configured to be switchable between a first value of zero and a second value of π for a phase shift created by the respective optical phase shifter, and
(d) wherein the first stage optical phase shifters are controllable in such a way
(i) that they create a predetermined phase shift (+φ, −φ) having an absolute value within a range from 0 to π/2 in case an optical phase shifter is provided in both branches of the second stage, or
(ii) that they create a predetermined phase shift (+φ, −φ) having an absolute value within a range from 0 to π in case an optical phase shifter is provided in only the first branch of the second stage.

2. The optical endless phase shifting device according to claim 1 , wherein the optical splitter device is configured to output a first and a second optical output signal, wherein the electrical fields of the first and second optical output signals have essentially the same absolute value but are phase shifted by π/2.

3. The optical endless phase shifting device according to claim 2 , wherein the optical splitter device is an optical 1×2 coupler.

4. The optical endless phase shifting device according to claim 3 , wherein the optical 1×2 coupler comprises an optical 1×2 fiber coupler or an optical integrated 1×2 coupler.

5. The optical endless phase shifting device according to claim 1 , wherein the optical combiner device of the first stage is configured to create:
(a) the first combined signal (S sin ) by adding the electrical field of the optical signal that is fed to the first input port and the electrical field of the optical signal that is fed to the second input port shifted by π/2, and
(b) the second combined signal (S cos ) by adding the electrical field of the optical signal that is fed to the second input port and the electrical field of the optical signal that is fed to the first input port phase-shifted by π/2.

6. The optical endless phase shifting device according to claim 5 , wherein the optical combiner device is an optical 1×2 coupler.

7. The optical endless phase shifting device according to claim 6 , wherein the optical 1×2 coupler comprises an optical 1×2 fiber coupler or an optical integrated 1×2 coupler.

8. The optical endless phase shifting device according to claim 1 , wherein the optical combiner device of the second stage is configured to create the at least one output signal (S out,1 , S out,2 )
(a) by adding the electrical field of the optical signal that is fed to the first input port and the electrical field of the optical signal that is fed to the second input port phase-shifted by π/2, and/or
(b) by adding the electrical field of the optical signal that is fed to the second input port and the electrical field of the optical signal that is fed to the first input port shifted by π/2.

9. The optical endless phase shifting device according to claim 1 , wherein the first stage combiner device is configured to create, at the first and second output port, the first and second combined signals (S sin , S cos ) in such a way that they can be described by
E sin =j·E in ·sin(φ) and

E cos =j·E in ·cos(φ)

wherein E in , E sin and E cos designate complex field amplitudes of the optical input signal (S in ), the first combined signal and the second combined signal (S sin , S cos ), respectively, and φ designates the absolute value of the predetermined phase shift.

10. The optical endless phase shifting device according to claim 9 , wherein the second stage combiner device is configured to create, at the at least one output port, the at least one optical output signal (S out,1 , S out,2 ) in such a way that it can be described by:

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Assignees

• Adva Optical Networking Se

Inventors

• Eiselt Michael

Classifications

• G02F1/212

  Mach-Zehnder type · CPC title

• G02B6/2935

  Mach-Zehnder configuration, i.e. comprising separate splitting and combining means · CPC title

• H04B10/6165 Primary

  Estimation of the phase of the received optical signal, phase error estimation or phase error correction · CPC title

• G02F1/01 Primary

  for the control of the intensity, phase, polarisation or colour  (G02F1/29, G02F1/35 take precedence) · CPC title