# US 5,708,734 A · Polarisation-independent optical device

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- Number: US 5,708,734 A
- Document ID: US5708734A
- Status: Granted
- Kind: A
- Application number: 08/667,619
- Filed: 1996-06-21
- Granted: 1998-01-13
- Earliest claimed: 1995-07-07
- Assignees: Koninklijke PTT Nederland N.V.
- Inventors: Johannes Jacobus Gerardus Maria Van Der Tol
- Web page: https://patentgrep.com/patent/US5708734A

## CPC

- G02F 1/0353: {involving an electro-optic TE-TM mode conversion}
- G02F 1/225: in an optical waveguide structure
- G02F 2203/06: Polarisation independent
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS

## Abstract

A polarisation-independent optical device for influencing the phase of an optical signal includes, in a light conductor (11), two identical adjustable phase shifters (14, 15), between which there is placed a polarisation converter (16). Optical signal components (I) entering at the input (12) of the light conductor as TE and TM polarisation modes, leave the light conductor at an output (13) as TM and TE polarisation modes having the same phase differences with respect to the signal components at the input. By way of simultaneous control of the phase shifters (14, 15) having a same modulation voltage V, there is obtained a polarisation-independent phase modulator. By including such a phase modulator in a branch of an MZ interferometer and placing, in the other branch, an identical polarisation converter, there may be realised a polarisation-independent switch or an intensity modulator.

## Claims

### Claim 1

Optical device for polarisation-independently influencing an optical signal, which device comprises:
a channel-shaped waveguide section in which optical signals propagate having signal components according to a first and a second, mutually orthogonal polarisation mode,
first phase-shifting means, operative in a first subsection of the channel-shaped waveguide section, for generating first variable phase shifts in signal components propagating in the first subsection,
second phase-shifting means, operative in a second subsection of the channel-shaped waveguide section, for generating second variable phase shifts in signal components propagating in the second subsection, and
a polarisation converter, included in the channel-shaped waveguide section between the first and the second subsection, for converting signal components propagating in the first and in the second polarisation mode into signal components propagating in the second and in the first polarisation mode, respectively, wherein the first and the second phase-shifting means are coupled, and the first and the second phase shifts are equal, at least substantially, for equal polarisation modes.

### Claim 2 (depends on 1)

Optical device according to claim 1, wherein the device additionally comprises:
a wave-guiding input section for incoming optical signals,
a Mach-Zehnder interferometer connecting thereto, provided with two waveguide branches moving away from one another to outside their mutual interaction distance and subsequently coming together again, over which the incoming signals are equally distributed and propagate therein having signal components according to first and second, mutually orthogonal polarisation modes, with the channel-shaped waveguide section being part of a first of the two waveguide branches,
a further polarisation converter of a type equal to the former polarisaton converter, which further polarisation converter is included in a second of the two waveguide branches of the MZ interferometer, and
a wave-guiding output section connecting to the MZ interferometer.

### Claim 3 (depends on 2)

Device according to claim 2, wherein the device further comprises third and fourth coupled phase-shifting means of a same type as the first and second phase-shifting means, respectively, which third and fourth phase-shifting means are operative in a first and a second subsection, respectively, of the second waveguide branch on either side of the further polarisation converter, with the third and fourth phase shifts being inversely equal to the first and the second phase shifts, respectively.

### Claim 4 (depends on 1)

Device according to claim 1, wherein the polarisation converters are passive converters.

### Claim 5 (depends on 2)

Device according to claim 2, wherein the input section and the output section are Y junctions.

### Claim 6 (depends on 2)

Device according to claim 2, wherein the input section and the output section are 3 dB couplers.

### Claim 7 (depends on 2)

Device according to claim 2, wherein the input section is a Y junction and the output section is a 3 dB coupler.

### Claim 8 (depends on 2)

Device according to claim 2, wherein the waveguide branches are monomodal waveguides and that at least one polarisation converter of the polarisation converter and the further polarisation converter is a 100% TE.rarw..fwdarw.TM converter known per se, based on a monomodal waveguide having a periodic geometrical structure.

### Claim 9 (depends on 3)

Device according to claim 3, wherein the polarisation converters are passive converters.

### Claim 10 (depends on 9)

Device according to claim 9, wherein the input section and the output section are Y junctions.

### Claim 11 (depends on 10)

Device according to claim 10, wherein the input section and the output section are 3 dB couplers.

### Claim 12 (depends on 10)

Device according to claim 10, wherein the input section is a Y junction and the output section is a 3 dB coupler.

### Claim 13 (depends on 10)

Device according to claim 10, wherein the waveguide branches are monomodal waveguides and that at least one polarisation converter of the polarisation converter and the further polarisation converter is a 100% TE.rarw..fwdarw.TM converter known per se, based on a monomodal waveguide having a periodic geometrical structure.

### Claim 14 (depends on 2)

Device according to claim 2, wherein the polarisation converters are passive converters.

### Claim 15 (depends on 3)

Device according to claim 3, wherein the input section and the output section are Y junctions.

### Claim 16 (depends on 3)

Device according to claim 3, wherein the input section and the output section are 3 dB couplers.

### Claim 17 (depends on 3)

Device according to claim 3, wherein the input section is a Y junction and the output section is a 3 dB coupler.

### Claim 18 (depends on 3)

Device according to claim 3, wherein the waveguide branches are monomodal waveguides and that at least one polarisation converter of the polarisation converter and the further polarisation converter is a 100% TE.rarw..fwdarw.TM converter known per se, based on a monomodal waveguide having a periodic geometrical structure.