# US 2007/0110362 A1 · Coherent optical detector and coherent communication system and method

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- Number: US 2007/0110362 A1
- Document ID: US20070110362A1
- Status: Published application
- Kind: A1
- Application number: 11/610,964
- Filed: 2006-12-14
- Published: 2007-05-17
- Earliest claimed: 2001-09-26
- Assignees: CeLight, Inc.
- Inventors: Isaac Shpantzer; Arkady Kaplan; Aviv Salamon; Yaakov Achiam; Jacob Khurgin; Michael Tseytin; Pak Cho; Arthur Greenblatt; Christopher Kerr; Geothrey Harston
- Web page: https://patentgrep.com/patent/US20070110362A1

## CPC

- H04B 10/50: Transmitters
- G02B 6/12004: {Combinations of two or more optical elements}
- G02B 6/12007: {forming wavelength selective elements, e.g. multiplexer, demultiplexer}
- H04B 10/60: Receivers
- H04B 10/61: Coherent receivers
- H04B 10/613: {including phase diversity, e.g., having in-phase and quadrature branches, as in QPSK coherent receivers}
- H04B 10/614: {comprising one or more polarization beam splitters, e.g. polarization multiplexed [PolMux] X-PSK coherent receivers, polarization diversity heterodyne coherent receivers (H04J14/06 takes precedence)}
- H04B 10/6162: {Compensation of polarization related effects, e.g., PMD, PDL}
- H04B 10/63: Homodyne {, i.e. coherent receivers where the local oscillator is locked in frequency and phase to the carrier signal}
- H04J 14/005: {Optical Code Multiplex}
- G02B 2006/12147: {Coupler}
- H04B: TRANSMISSION
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S)

## Abstract

An optical device is provided with first and second inputs. A first coupler coupled is coupled to the first input and produces at least a first and second output. A second coupler is coupled to the second input and produces at least a first and second output. A third coupler is coupled to the first output of the first coupler and to the first output of the second coupler. A fourth coupler is coupled to the second output of the first coupler and to the second output of the second coupler. First and second crossing waveguides are provided with an angle selected to minimize crosstalk and losses between the first and second cross waveguides. The first crossing waveguide connects one of the first or second outputs from the first coupler with an input of the fourth coupler. The second crossing waveguide connects one of the first or second outputs from the second coupler with an input of the third coupler. A first phase shifter is coupled to the first and second waveguides. The first and second waveguides connect one of the outputs of the first or second coupler and one of the inputs of the third or fourth couplers. The first, second, third and fourth couplers, the two crossing waveguides and the phase shifter are each formed as part of a single planar chip made of an electro-optical material.

## Claims

### Claim 1

An monolithically integrated optical device for receiving and demodulating of an incoming quadrature modulated optical signal having one polarization and transmitted via optical path; the device having a first and a second inputs, comprising:
a first adjustable coupler connected to the first input and producing at least a first and second output;
a second adjustable coupler connected to the second input and producing at least a first and second output;
a third adjustable coupler connected to the first output of the first coupler and to the first output of the second coupler;
a fourth adjustable coupler connected to the second output of the first coupler and to the second output of the second coupler;
electrodes providing said tuning of the first, second, third, and fourth couplers;
first and second crossing waveguides with an angle selected to minimize crosstalk and losses between the first and second cross waveguides,
the first crossing waveguide connecting one of the first or second outputs from the first coupler with an input of the fourth coupler,
the second crossing waveguide connecting one of the first or second outputs from the second coupler with an input of the third coupler;
a first phase shifter coupled to the first and second waveguides,
the first and second waveguides connecting one of the outputs of the first or second coupler and one of the inputs of the third or fourth couplers,
a first, a second, a third and a fourth photodiodes converting optical signal into a first, a second, a third and a fourth electrical signals;
the first, second, third and fourth electrical signals being processed to obtain an in-phase and an in-quadrature signals and to recover quadrature modulated data embedded in the incoming quadrature modulated optical signal having one polarization;
wherein the first, second, third and fourth couplers, the two crossing waveguides and the phase shifter are each formed as part of a single planar chip made of an electro-optical material.

### Claim 2 (depends on 1)

The optical device of claim 1, wherein the optical device is a free-space optical link device.

### Claim 3 (depends on 1)

The optical device of claim 1, wherein the optical device is an optical pointing device.

### Claim 4 (depends on 1)

The optical device of claim 1, wherein the optical device is a tracking device.

### Claim 5 (depends on 1)

The optical device of claim 1, wherein the chip is a single piece of crystal.

### Claim 6 (depends on 1)

The optical device of claim 1, wherein the chip is made of LiNbO3 or LiTaO3

### Claim 7 (depends on 1)

The optical device of claim 1, wherein the chip is made of LiNbO3 or LiTaO3 cut at X, or Y, or Z planes.

### Claim 8 (depends on 1)

The optical device of claim 1, wherein the first coupler is a Y-junctions.

### Claim 9 (depends on 1)

The optical device of claim 1, wherein the second coupler is a Y-junctions.

### Claim 10 (depends on 1)

The optical device of claim 1, further comprising: a second phase shifter coupled to the first and second waveguides, the first and second waveguides connecting one of the outputs of the first or second coupler and one of the inputs of the third or fourth coupler.

### Claim 11 (depends on 1)

The optical device of claim 1, wherein the first, second, third and fourth couplers are 3-dB devices.

### Claim 12 (depends on 1)

The optical device of claim 1, wherein the chip is a two-layer structure.

### Claim 13 (depends on 1)

The optical device of claim 1, wherein an output power splitting ratio from the first, second, third and fourth couplers is independently adjustable.

### Claim 14 (depends on 1)

The optical device of claim 1, further comprising: first, second, third and fourth biased electrodes. is coupled to the first, second, third and fourth couplers respectively.

### Claim 15 (depends on 1)

The optical device of claim 1, wherein the first biased electrode is coupled to the first coupler, the second biased electrode is coupled to the second coupler, the third biased electrode is coupled to the third coupler, and the fourth biased electrode is coupled to the fourth coupler.

### Claim 16 (depends on 15)

The optical device of claim 15, wherein the first, second, third and fourth couplers, the first and second crossing waveguides are formed in a first layer, and the first, second, third fourth biased electrodes and the first and second phase shifters are formed in an adjacent second layer.

### Claim 17 (depends on 14)

The optical device of claim 14, wherein the each of the first, second, third and fourth couplers have electrode geometries with alternating polarity.

### Claim 18 (depends on 17)

The optical device of claim 17, wherein the first, second, third and fourth electrodes are split into an even integer number of sections to provide voltages that have a reversed polarity at each section.

### Claim 19 (depends on 14)

The optical device of claim 14, wherein each of the first, second, third and fourth electrodes are push-pull electrodes.

### Claim 20 (depends on 1)

The optical device of claim 1, wherein each of the first, second, third and fourth electrodes are configured to optimize a splitting operating point of the first, second, third and fourth couplers.

### Claim 21 (depends on 20)

The optical device of claim 20, wherein each of the first, second, third and fourth electrodes optimize the splitting operating point by splitting an output power ratio of the first, second, third and fourth couplers.

### Claim 22 (depends on 1)

The optical device of claim 1, wherein the first phase shifter is adjustable.

### Claim 23 (depends on 1)

The optical device of claim 1, further comprising: a second phase shifter.

### Claim 24 (depends on 23)

The optical device of claim 23, wherein the second phase shifter is adjustable.

### Claim 25 (depends on 14)

The optical device of claim 14, wherein the first phase shifter includes a phase-shifting electrode.

### Claim 26 (depends on 23)

The optical device of claim 23, wherein the second phase shifter includes a phase-shifting electrode.

### Claim 27 (depends on 1)

The optical device of claim 1, wherein the electro-optical material is a ferroelectric material.

### Claim 28 (depends on 27)

The optical device of claim 27, wherein the ferroelectric material is selected from LiNbO3 and LiTaO3.

### Claim 29 (depends on 1)

The optical device of claim 1, wherein the electro-optical material is a semiconductor material.

### Claim 30 (depends on 29)

The optical device of claim 29, wherein the semiconductor material is selected from Si and InP.

### Claim 31 (depends on 1)

The optical device of claim 1, wherein the optical device is made utilizing indifussed metal technology.

### Claim 32 (depends on 1)

The optical device of claim 1, includes the optical device is made utilized protonic-exchange technology.

### Claim 33 (depends on 1)

The optical device of claim 1, wherein the optical device is made utilizing etching technology.

### Claim 34 (depends on 1)

The optical device of claim 1, wherein the optical device is made utilizing milling technology.

### Claim 35 (depends on 1)

The optical device of claim 1, wherein the optical device is made utilizing CVD technology.

### Claim 36 (depends on 1)

The optical device of claim 1, further comprising: a substrate.

### Claim 37 (depends on 36)

The optical device of claim 36, wherein the substrate is coated with a buffer layer.

### Claim 38 (depends on 37)

The optical device of claim 37, wherein the buffer layer is silicon dioxide.

### Claim at position 39

39-93. (canceled)

### Claim 94 (depends on 1)

The optical device of claim 1, further comprising:
a first analog-to-digital converter and
a digital signal processing unit, wherein the digital processing unit performs calibration of the optical device.

### Claim 95 (depends on 10)

The optical device of claim 10, further comprising:
a first analog-to-digital converter and
a digital signal processing unit, wherein the digital processing unit performs calibration of the optical device.
a second analog-to-digital converter.

### Claim 96 (depends on 95)

The optical device of claim 95, wherein the digital signal processing unit is adapted to control the first coupler, the second coupler, the third coupler, the fourth coupler, the first phase shifter, and the second phase shifter.

### Claim 97

A method of the optical device calibration, comprising:
an initialization of the fourth coupler, the third coupler, the first coupler, and the second coupler, and
an on-line tracking of the fourth coupler, the third coupler, the first coupler, and the second coupler.

### Claim 98 (depends on 97)

The method of claim 97, wherein the initialization of the third coupler comprises
an adjustment of a control signal to the first coupler to maximize the variance of I electrical output signal,
an adjustment of a control signal to the second coupler to maximize the variance of I electrical output signal,
an adjustment of a control signal to the third coupler to maximize the variance of I electrical output signal.

### Claim 99 (depends on 97)

The method of claim 97, wherein the initialization of the fourth coupler comprises
an adjustment of the control signal to the first coupler to maximize the variance of Q electrical output signal,
an adjustment of the control signal to the second coupler to maximize the variance of Q electrical output signal,
an adjustment of the control signal to the third coupler to maximize the variance of Q electrical output signal.

### Claim 100 (depends on 97)

The method of claim 97, wherein the initialization of the first and the second coupler comprises
an adjustment of the control signal to the first coupler and the control signal to the second coupler to maximize the sum of two variances of I electrical output signal, while maintaining the variance of I electrical output signal equal to the variance of the Q electrical output signal.

### Claim 101 (depends on 97)

The method of claim 97, wherein the on-line tracking of the fourth coupler, the third coupler, the first coupler, and the second coupler comprises
an adjustment of the control signal to the third coupler to maximize the variance of I electrical output signal;
an adjustment of the control signal to the fourth coupler to maximize the variance of Q electrical output signal;
an adjustment of the control signal to the first coupler and the control signal to the second coupler so that the variance of I electrical output signal is equal to the variance of Q electrical output signal, while maximizing the sum of two variances of I and Q electrical output signals.

### Claim 102

A method of the optical device calibration, comprising:
an initialization of the first and the second phase shifters, and
an on-line tracking of the of the first and the second phase shifters.

### Claim 103 (depends on 102)

A method of claim 102, wherein the initialization of the first and the second phase shifters comprises:
an adjustment of a control line to control the first phase shifter and a control line to control the second phase shifter at the same time to cancel the covariance of I and Q electrical output signals, while minimizing the expected output signal value E{((v1−E{v1})2−(v2−E{v2})2)2}, where v1 is the measured sampled set at I output, v2 is the measured sampled set at the Q output.

### Claim 104 (depends on 102)

A method of claim 102, wherein the on-line tracking of the first and the second phase shifters comprises:
an adjustment of a control line to control the first phase shifter and a control line to control the second phase shifter at the same time to cancel the covariance of I and Q electrical output signals, while minimizing the expected output signal value E{((v1−E{v1})2−(v2−E{v2})2)2}, where v1 is the measured sampled set at I output, v2 is the measured sampled set at the Q output.