# US 5,703,975 A · Interferometric switch

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- Number: US 5,703,975 A
- Document ID: US5703975A
- Status: Granted
- Kind: A
- Application number: 08/672,188
- Filed: 1996-06-27
- Granted: 1997-12-30
- Earliest claimed: 1995-06-09
- Assignees: Corning Incorporated
- Inventors: William J. Miller; Daniel A. Nolan
- Web page: https://patentgrep.com/patent/US5703975A

## CPC

- G02F 1/3517: {using an interferometer}
- G02F 1/3136: {of interferometric switch type}
- G02B 6/2835: {formed or shaped by thermal treatment, e.g. couplers}
- G02B 6/29352: {in a light guide}
- G02B 2006/12145: {Switch}
- G02F 1/3131: {in optical fibres}
- 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
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A compact monolithic interferometric switch such as a Mach-Zehnder switch is formed such that one of the waveguide paths between the input and output couplers contains a material having exhibits a resonant nonlinearity, whereby its refractive index changes when pump power propagates through it. Each of the waveguide paths has a different propagation constant whereby signal light is subjected to a different delay in each path when no pump power is propagating through the rare nonlinear path. An input signal applied to the input of the switch appears at a first output terminal when the pump power does not propagate through the nonlinear path, and it appears at a second output terminal when the pump power is applied to the nonlinear path. Switching occurs at relatively low levels of pump power.

## Claims

### Claim 1

A monolithic Mach-Zehnder switch comprising
input coupler means for splitting an input signal into N equal signal components, where N>1,
combining means for combining said N components, said combining means having at least first and second output terminals,
N optical waveguide paths connecting said N signal components to said combining means, at least one of said waveguide paths containing a material having a resonant nonlinearity, whereby the refractive index of the path changes when pump power propagates through it, said input coupler means and said combining means being free from said material, and
a matrix glass body, said input coupler means, said combining means and said optical waveguide paths being in thermal contact with said body.

### Claim 2 (depends on 1)

A monolithic Mach-Zehnder switch in accordance with claim 1 wherein there is a difference .DELTA..beta. between the propagation constants of said waveguide paths such that each of said N waveguide paths subjects the light propagating therethrough to a delay that is different from the delay experienced by light propagating through each of the other waveguide paths when no pump power is propagating through said at least one waveguide path.

### Claim 3 (depends on 2)

A monolithic Mach-Zehnder switch in accordance with claim 2 wherein .DELTA..beta. is equal to or greater than 0.003.

### Claim 4 (depends on 1)

A monolithic Mach-Zehnder switch in accordance with claim 1 wherein the length of said matrix glass body is no greater than 15 cm.

### Claim 5 (depends on 1)

A monolithic Mach-Zehnder switch in accordance with claim 1 wherein said paths are optical fibers, and wherein said fibers, said input coupler means and said combining means are surrounded by an elongated body of said matrix glass.

### Claim 6 (depends on 5)

A monolithic Mach-Zehnder switch in accordance with claim 5 wherein said input coupler means and said combining means are regions in said body wherein the diameter of said body and the diameters of said fibers are smaller than the diameters thereof in said phase shift region.

### Claim 7 (depends on 1)

A monolithic Mach-Zehnder switch in accordance with claim 1 wherein said matrix glass body comprises a planar substrate, said paths, said input coupler means and said combining means being located at the surface of said substrate.

### Claim 8 (depends on 1)

A monolithic Mach-Zehnder switch in accordance with claim 1 wherein said material having a resonant nonlinearity is a rare earth.

### Claim 9

A monolithic Mach-Zehnder switch comprising
an elongated body of matrix glass,
first and second optical fibers extending longitudinally through said body,
a phase shift region in said body,
two spaced coupler regions in said body at opposite ends of said phase shift region, the diameter of said body and the diameters of said fibers being smaller in said coupler regions than in said phase shift region,
at least that portion of said first fiber that is in said phase shift region containing a material having a resonant nonlinearity, whereby the refractive index of said first fiber changes when pump power propagates through it, said fibers having different propagation constants in said phase shift region in the absence of pump power propagating through said first fiber so that said first fiber subjects the light propagating therethrough to a delay that is different from the delay experienced by light propagating through said second fiber.

### Claim 10 (depends on 9)

A monolithic Mach-Zehnder switch in accordance with claim 9 wherein said material having a resonant nonlinearity is a rare earth.

### Claim 11

An interferometric switch comprising first and second optical couplers and first and second optical paths extending between said couplers, and means defining a first input port connected to said first coupler and a first output port connected to said second coupler, said paths having optical path lengths L1 and L2, respectively, between said couplers, at least one of said paths being a nonlinear path including a material having a resonant nonlinearity such that the refractive index of said material and the optical path length of the nonlinear path changes when optical pumping power propagates through such path, said path lengths L1 and L2 being different from one another in the absence of said optical pumping power.

### Claim 12 (depends on 11)

A switch as claimed in claim 11 having a zero-power transfer function relating the proportion of light supplied through said first input port which appears at said first output port to wavelength in the absence of said optical pumping power, said transfer function including a peak at a first wavelength at which substantially all of the light appears at said first output port and a valley at a second wavelength at which substantially none of the light appears at said first output port said first and second wavelengths have a difference .DELTA..lambda. therebetween of about 10 nm or less.

### Claim 13 (depends on 12)

A switch as claimed in claim 12 wherein said first and second wavelengths have a difference .DELTA..lambda. therebetween about 6 nm or less.

### Claim 14 (depends on 13)

A switch as claimed in claim 13 wherein .DELTA..lambda. is between about 1 nm and about 6 nm.

### Claim 15 (depends on 11)

A switch as claimed in claim 11 further comprising a second output port connected to said second coupler.

### Claim 16 (depends on 11)

A device as claimed in claim 11 wherein said first and second optical paths are constituted by first and second fibers, said first and second fibers extending through said couplers.

### Claim 17 (depends on 16)

A device as claimed in claim 16 wherein portions of said fibers extend beyond said couplers and constitute said ports.

### Claim 18 (depends on 11)

A device as claimed in claim 11 wherein said paths and couplers are formed as a monolithic unit.

### Claim 19

An interferometric switch comprising at least three optical couplers and a plurality of optical paths extending between said couplers in groups so that said couplers are connected to one another in series by said groups of fibers, each such group including at least two said paths in parallel with one another, one of said couplers being an input coupler at one end of said series, another one of said couplers at an opposite end of said series being an output coupler, the device further including means defining a signal input port connected to said input coupler and a first output port connected to said output coupler, each said path having an optical path length between said couplers, at least one of said paths being a nonlinear path including a material having a resonant nonlinearity such that the refractive index of said material and the path length of the nonlinear path changes when optical power propagates through such path, said path lengths of the paths in at least one said group being different from one another in the absence of said optical pumping power, said device having a zero-power transfer function relating the proportion of light supplied through said first input port which appears at said first output port to wavelength in the absence of said optical pumping power, said zero-power transfer function including a peak at a first wavelength at which substantially all of the light appears at said first output port and a valley at a second wavelength at which substantially none of the light appears at said first output port.

### Claim 20 (depends on 19)

A switch as claimed in claim 19 wherein each said group includes at least one nonlinear path having said nonlinear material.

### Claim 21 (depends on 20)

A switch as claimed in claim 20 wherein said couplers are adapted to direct light in a signal wavelengths band including said first and second wavelength through all of said paths and to direct light in a pumping wavelength band outside said signal wavelength band only along said nonlinear paths, said nonlinear material being responsive to pumping radiation in said pumping wavelength band to alter its index of refraction.

### Claim 22 (depends on 21)

A switch as claimed in claim 21 wherein said nonlinear paths are directly connected with one another at each of a plurality of said couplers to form a continuous nonlinear path array extending through a plurality of said couplers, the switch further comprising a pumping input port directly connected to said nonlinear path array, said couplers being effective to couple light in said signal wavelength band between paths but substantially ineffective to couple light at a pumping wavelength outside of said signal wavelength band between paths, whereby pumping light at said pumping wavelength applied to said pumping input port will propagate through only said nonlinear path array.

### Claim 23 (depends on 22)

A switch as claimed in claim 22 wherein said paths are constituted by optical fibers, said nonlinear path array being constituted by a first continuous fiber extending through said plural couplers.

### Claim 24 (depends on 23)

A switch as claimed in claim 23 wherein said first continuous fiber includes a plurality of spaced-apart nonlinear sections incorporating said nonlinear material and a plurality of linear sections free of said nonlinear material, said linear sections extending through said couplers.

### Claim 25 (depends on 24)

A switch as claimed in claim 24 further comprising a second continuous fiber extending through a plurality of said couplers, said second continuous fiber constituting a second path array including paths in each of a plurality of said groups.

### Claim 26 (depends on 25)

A switch as claimed in claim 25 wherein all of said paths are constituted by said first and second continuous fibers.

### Claim 27 (depends on 23)

A switch as claimed in claim 23 further comprising a monolithic glass body surrounding said fibers, each said coupler being an overclad tapered coupler including narrowed portions of said fibers and said body.

### Claim 28 (depends on 22)

A switch as claimed in claim 22 wherein each said group of paths includes a linear path having optical propagation properties substantially insensitive to pumping power, the linear paths of each said group being directly connected to one another and constituting a linear path array.

### Claim 29 (depends on 22)

A switch as claimed in claim 22 wherein said first and second wavelengths have a difference .DELTA..lambda. therebetween of about 10 nm or less.

### Claim 30 (depends on 22)

A switch as claimed in claim 22 wherein said first and second wavelengths have a difference .DELTA..lambda. therebetween about 6 nm or less.

### Claim 31 (depends on 30)

A switch as claimed in claim 30 wherein .DELTA..lambda. is between about 1 nm and about 6 nm.

### Claim 32 (depends on 28)

A switch as claimed in claim 28 further comprising a second output port connected to said output coupler.

### Claim 33 (depends on 32)

A switch as claimed in claim 32 wherein each said group consists of one said nonlinear path and one second path, each said coupler other than said output coupler being adapted to split light arriving at such coupler substantially equally between the paths extending to the next coupler, said output coupler being adapted to couple light arriving at said coupler unequally to said first and second output ports.