# US 8,532,498 B2 · Secure orthogonal frequency multiplexed optical communications

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- Number: US 8,532,498 B2
- Document ID: US8532498B2
- Status: Granted
- Kind: B2
- Application number: 13/070,719
- Filed: 2011-03-24
- Published: 2011-07-14
- Granted: 2013-09-10
- Earliest claimed: 2008-02-08
- Assignees: CeLight, Inc.
- Applicants: Isaac Shpantzer
- Inventors: Isaac Shpantzer
- Web page: https://patentgrep.com/patent/US8532498B2

## CPC

- H04B 10/60: Receivers
- H04B 10/11: Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
- H04B 10/548: Phase or frequency modulation
- 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 10/63: Homodyne {, i.e. coherent receivers where the local oscillator is locked in frequency and phase to the carrier signal}
- H04B 10/64: Heterodyne {, i.e. coherent receivers where, after the opto-electronic conversion, an electrical signal at an intermediate frequency [IF] is obtained}
- H04J 14/0227: {Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation}
- H04J 14/0257: {Wavelength assignment algorithms}
- H04J 14/0298: {with sub-carrier multiplexing [SCM]}
- H04L 9/0858: {Details about key distillation or coding, e.g. reconciliation, error correction, privacy amplification, polarisation coding or phase coding}
- H04L 27/0008: {arrangements for allowing a transmitter or receiver to use more than one type of modulation (negotiating modulation type for two-way transmission paths H04L5/1453)}
- H04L 27/2604: {Multiresolution systems (by means of multiresolution subcarriers H04L27/183, H04L27/3488)}
- H04L 27/2637: {with direct modulation of individual subcarriers}
- H04L 27/2697: {in combination with other modulation techniques}
- G02F 1/212: {Mach-Zehnder type}
- H04J 14/06: Polarisation multiplex systems
- H04B: TRANSMISSION
- 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)
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- 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

The invention provides a system and method for secure communication that involve encoding and transmitting an optical orthogonal frequency division multiplexed (OFDM) signal. Each subcarrier of an optical carrier in OFDM transmission is modulated with data individually, and a variety of data format are used, such as QPSK, OOK, QAM, etc. The data format of each subcarrier may change in time according to a predetermined pattern. An optical receiver uncovers the data transmitted via an optical link. It is based on a coherent optical receiver and a digital signal processing (DSP) unit. A key to the data mapping and change is transmitted via the same optical link or by a separate channel. In one embodiment, the key is transmitted using quantum encryption technique. Besides subcarrier modulation encoding, the system may provide additional layers of security: optical carrier frequency hopping and polarization scrambling.

## Claims

### Claim 1

A system for secure data transmission via optical link, comprising: an optical transmitter for orthogonal frequency division multiplexed (OFDM) communications, wherein each channel carrier has multiple subcarriers, each subcarrier being individually encoded with data and a data encoding format is different for different subcarriers; the transmitter is sending data to an optical receiver; an output electrical signal from the optical receiver is processed in a digital signal processing (DSP) unit to recover data from each subcarrier, wherein for security purposes the data encoding format of each subcarriers changes in time according to a pattern.

### Claim 2 (depends on 1)

The system of claim 1, wherein the encoding formats of the subcarriers are stored in a DSP unit memory.

### Claim 3 (depends on 1)

The system of claim 1, wherein a key for the subcarrier encoding change is transmitted from the transmitter to the receiver via a separate key channel.

### Claim 4 (depends on 3)

The system of claim 3, wherein the key channel implements quantum encryption for transmission of the key sequence.

### Claim 5 (depends on 1)

The system of claim 1, wherein the encoding format change occurs independently in each subcarrier.

### Claim 6 (depends on 1)

The system of claim 1 adapted to operate with data transmission using an optical beam having two polarization states.

### Claim 7 (depends on 1)

The system of claim 1, wherein the data encoding format is selected from PSK formats, QAM or OOK formats and mixture of thereof.

### Claim 8

A system for secure data transmission via optical link, comprising: an optical transmitter for orthogonal frequency division multiplexed (OFDM) communications, wherein each channel carrier has multiple subcarriers, each subcarrier being individually encoded with data and a data encoding format is different for different subcarriers; the transmitter is sending data to an optical receiver; an output electrical signal from the optical receiver is processed in a digital signal processing (DSP) unit to recover data from each subcarrier, wherein the optical receiver configured to receive an encoded OFDM signal and to mix it with a signal from a local oscillator, and wherein the optical carrier changes its polarization state according to a sequence of polarization change keys, and the local oscillator has a polarization state corresponding to the polarization state of the incoming carrier.

### Claim 9 (depends on 8)

The system of claim 8, wherein the optical receiver performs homodyne or heterodyne mixture of the encoded OFDM with the local oscillator signal.

### Claim 10 (depends on 8)

The system of claim 8, wherein the local oscillator is a separate device from a source device generating the encoded signal.

### Claim 11 (depends on 8)

The system of claim 8, wherein the optical receiver consists of two 90-degrees optical hybrids, one for H-polarization light and one for V polarization light and is adapted for operation with the optical signal of two polarization states.

### Claim 12

A system for secure data transmission via optical link, comprising: an optical transmitter for orthogonal frequency division multiplexed (OFDM) communications, wherein each channel carrier has multiple subcarriers, each subcarrier being individually encoded with data and a data encoding format is different for different subcarriers; the transmitter is sending data to an optical receiver; an output electrical signal from the optical receiver is processed in a digital signal processing (DSP) unit to recover data from each subcarrier, wherein the optical receiver configured to receive an encoded OFDM signal and to mix it with a signal from a local oscillator, further comprising means for changing the carrier wavelength according to a sequence of wavelength change keys, and the local oscillator has a wavelength corresponding to the wavelength of the incoming carrier.

### Claim 13 (depends on 12)

The system of claim 12, wherein the optical carrier changes its polarization state according to a sequence of polarization change keys, and the local oscillator has a polarization state corresponding to the polarization state of the incoming carrier.

### Claim 14 (depends on 1)

The system of claim 1, wherein the optical link is a fiber or a free space link.

### Claim 15

A method of optical secure communication, comprising: transmitting data using an optical carrier from a transmitter to an optical receiver, the optical carrier has N subcarriers, N>1, the subcarriers forming an orthogonal frequency division multiplexed (OFDM) optical signal; each subcarrier being individually encoded with data and a data encoding format is different for different subcarriers; receiving the OFDM encoded signal using the optical receiver, where it is mixed with a signal from a local oscillator; an output electrical signal from the optical receiver is processed in a digital signal processing (DSP) unit to recover data from each subcarrier, wherein for security purposes the data encoding format of each subcarriers changes in time according to a key pattern.

### Claim 16 (depends on 15)

The system of claim 15, wherein a key for the subcarrier encoding change is transmitted from the transmitter to the receiver via a separate key channel.

### Claim 17 (depends on 16)

The system of claim 16, wherein the key channel implements a quantum encryption for transmission of the key sequence.