# US 7,609,935 B2 · Optical vector modulator

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- Number: US 7,609,935 B2
- Document ID: US7609935B2
- Status: Granted
- Kind: B2
- Application number: 11/690,240
- Filed: 2007-03-23
- Published: 2008-09-25
- Granted: 2009-10-27
- Earliest claimed: 2007-03-23
- Assignees: BBN Technologies Corp.
- Inventors: Jerry D. Burchfiel
- Web page: https://patentgrep.com/patent/US7609935B2

## CPC

- H04B 10/505: {using external modulation}
- H04B: TRANSMISSION

## Abstract

An optical vector modulator includes an information generator that generates a plurality of N-bit streams at an output where each of the plurality of N-bit streams represents a desired modulation point in a signaling constellation. A memory look-up table having an N-bit address input retrieves a first and a second stored value that corresponds to the N-bit address input, where each of the first and the second stored value represent a respective one of a first and a second modulation vector of a desired modulation point in the signaling constellation. A first and a second digital-to-analog converter generates first and second analog signals, respectively, that correspond to respective ones of the first and second modulation vectors of the desired modulation points in the signaling constellation. A dual-drive interferometric modulator modulates the first and the second analog signals on the optical beam to obtain the desired modulation points in the signaling constellation.

## Claims

### Claim 1

An optical vector modulator comprising:
a) an information generator that generates a plurality of N-bit streams at an output, each of the plurality of N-bit streams representing a desired modulation point in a signaling constellation;
b) a memory look-up table having an N-bit address input that is electrically connected to the output of the information generator, the memory look-up table retrieving a first and a second stored values at a first and a second outputs that corresponds to the N-bit address input, each of the first and the second stored values representing a respective one of a first and a second modulation vectors of a desired modulation point in the signaling constellation;
c) a first and a second digital-to-analog converters each having an input that is coupled to a respective one of the first and the second outputs of the memory look-up table, the first and the second digital-to-analog converters generating first and second analog signals, respectively, at an output that corresponds to respective ones of the first and second modulation vectors of the desired modulation points in the signaling constellation; and
d) a dual-drive interferometric modulator having an optical input that is coupled to an output of an optical source, and a first and a second electrical modulation input that is coupled to a respective output of the first and second digital-to-analog converters, the modulator modulating the first and the second analog signals on the optical beam to obtain the desired modulation points in the signaling constellation.

### Claim 2 (depends on 1)

The optical vector modulator of claim 1 wherein the first modulation vector comprises a phase equal to θ1=θ(P)−cos−1(r(P)) and the second modulation vector comprises a phase equal to θ2=θ(P)+cos−1(r(P)).

### Claim 3 (depends on 2)

The optical vector modulator of claim 2 where an amplitude of the first modulation vector is substantially equal to an amplitude of the second modulation vector.

### Claim 4 (depends on 1)

The optical vector modulator of claim 1 wherein the memory look-up table store 2n values.

### Claim 5 (depends on 1)

The optical vector modulator of claim 1 wherein the dual-drive interferometric modulator comprises a dual-drive mach-Zehnder interferometric modulator.

### Claim 6 (depends on 1)

The optical vector modulator of claim 1 wherein the first and the second stored values are chosen to at least partially compensate for non-linear effects introduced during modulation.

### Claim 7 (depends on 1)

The optical vector modulator of claim 1 wherein the first and the second stored values are chosen to at least partially velocity match the first and second analog signals to the optical beam.

### Claim 8 (depends on 1)

The optical vector modulator of claim 1 wherein the desired modulation point in the signaling constellation comprises a QAM modulation point.

### Claim 9 (depends on 1)

The optical vector modulator of claim 1 wherein the memory look-up table and at least one of the first and second digital-to-analog converters comprise a single device.

### Claim 10

A method of optical vector modulation comprising:
a) generating a plurality of N-bit streams, each of the plurality of N-bit streams representing a desired modulation point in a signaling constellation;
b) retrieving a first and a second stored values for each of the N-bit streams, each of the first and the second stored values representing a first and a second modulation vectors of a desired modulation point in the signaling constellation;
c) generating first and second analog signals from respective ones of each of the first and the second stored values representing the first and the second modulation vectors of the desired modulation points; and
d) modulating an optical beam with the first and the second analog signals that represent the first and the second modulation vectors to generate the desired modulation points in the signaling constellation.

### Claim 11 (depends on 10)

The method of claim 10 wherein the first modulation vector comprises a phase equal to θ1=θ(P)−cos−1(r(P)) and the second modulation vector comprises a phase equal to θ2=θ(P)+cos−1(r(P)).

### Claim 12 (depends on 10)

The method of claim 10 wherein the retrieving the first and second stored values comprises retrieving one of 2n possible digital symbol values.

### Claim 13 (depends on 10)

The method of claim 10 wherein at least one of the first and the second stored values is chosen to approximately velocity match the first and second analog signals to the optical beam.

### Claim 14 (depends on 10)

The method of claim 10 wherein at least one of the first and the second stored values is chosen to reduce non-linear effects introduced during modulation.

### Claim 15 (depends on 10)

The method of claim 10 wherein the desired modulation points in the modulation constellation comprise QAM modulation points.

### Claim 16 (depends on 10)

The method of claim 10 further comprising adjusting a bias of a modulator modulating the optical beam to reduce non-linear effects introduced during modulation.

### Claim 17

A method of optical modulation comprising:
a) generating a first analog signal having an amplitude and a phase that corresponds to a first modulation vector of a desired modulation point within a signaling constellation;
b) generating a second analog signal having an amplitude and a phase that corresponds to a second modulation vector of a desired modulation point within a signaling constellation;
c) modulating an optical beam with the first and second analog signals, the modulated optical beam having a desired modulation point in the signaling constellation that is defined by the first and second modulation vectors.

### Claim 18 (depends on 17)

The method of claim 17 wherein the first modulation vector comprises a phase equal to θ1=θ(P)−cos−1(r(P)) and the second modulation vector comprises a phase equal to θ2=θ(P)+cos−1(r(P)).

### Claim 19 (depends on 17)

The method of claim 17 wherein the generating the first and second analog signals comprises retrieving predetermined analog signals stored in a look-up table.

### Claim 20 (depends on 17)

The method of claim 17 wherein the predetermined analog signals stored in a look-up table correspond to particular N-bit streams.

### Claim 21 (depends on 17)

The method of claim 17 wherein the amplitude and phase of at least one of the first and the second analog signals is chosen to approximately velocity match the first and second analog signals to the optical beam.

### Claim 22 (depends on 17)

The method of claim 17 wherein the amplitude and phase of at least one of the first and the second analog signals is chosen to reduce non-linear effects introduced during modulation.

### Claim 23 (depends on 17)

The method of claim 17 wherein the desired modulation point in the modulation constellation comprises QAM modulation points.

### Claim 24 (depends on 17)

The method of claim 17 further comprising adjusting a bias of a modulator modulating the optical beam to reduce non-linear effects introduced during modulation.

### Claim 25 (depends on 17)

The method of claim 17 wherein the amplitude of the first and second modulation vectors are substantially the same.