Free space optical communication link with diversity

• US 6,731,878 B1
• Filed: 08/17/2000
• Issued: 05/04/2004
• Est. Priority Date: 08/17/2000
• Status: Expired due to Term

• Current Assignee: AT&T Corporation (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Miller, Robert R., Britz, David M., Dodley, Jeevan Prakash
• Primary Examiner(s): NEGASH, KINFE MICHAEL
• Application Number:
  US09/640,576
• Time in Patent Office: 1,356 Days
• Field of Search: 398/96, 398/91, 398/79, 398/118, 398/130, 398/102, 398/115, 398/161, 250/227.12
• US Class Current: 398/96
• CPC Class Codes: H04B 10/1121 One-way transmission
• CPC Class Codes: H04B 10/1125 using a single common optical path
• CPC Class Codes: H04J 14/02 Wavelength-division multiplex systems

Abstract

A free space communication system includes first and second terminals, and the first terminal includes a transmitter to transmit an input signal. The transmitter has plural laser sources, at least one optical delay line and a telescope. Each laser source modulates the input signal onto a wavelength that is distinct from a wavelength of each other laser source. The plural laser sources include a first laser source and at least one other laser source, and the at least one optical delay line is coupled to a respective output of the at least one other laser source. The telescope projects an output of the first laser source and an output of each of the at least one optical delay line toward the second terminal. Alternatively, a free space communication system includes first and second terminals, and the first terminal includes a transmitter to transmit an input signal. The transmitter has at least one electrical delay line, plural laser sources and a telescope. The at least one electrical delay line delays the input signal. The plural laser sources include a first laser source and at least one other laser source, the first laser source modulates the input signal onto a first wavelength, and each of the at least one other laser source modulates an output of a corresponding electrical delay line onto a wavelength that is distinct from the first wavelength. The telescope projects an output of each of the plural laser sources toward the second terminal.

Claims

1. A free space optical system comprising first and second terminals, the first terminal including a transmitter to transmit an input signal, the transmitter having:

a plurality of lasers sources, each laser source of said plurality modulating the input signal onto a wavelength that is distinct from a wavelength onto which each other laser source modulates the input signal, said plurality including a first laser source and at least one other laser source;

at least one optical delay line coupled to a respective output of the at least one other laser source; and

a telescope that projects an output of the first laser source and an output of each of the at least one optical delay line toward the second terminal.

2. The free space optical system of claim 1, wherein:

the at least one other laser source includes a second laser source; and

an optical delay line coupled to the second laser source delays any optical signal passing therethrough by a predetermined time delay.

3. The free space optical system of claim 1, wherein:

the at least one other laser source includes a second laser source;

the first laser source of the transmitter produces a first optical signal at a first wavelength;

the second laser source of the transmitter produces a second optical signal at a second wavelength;

an optical delay line coupled to the second laser source delays the second optical signal by a predetermined time delay;

the second terminal includes a receiver;

the receiver includes a telescope and a wavelength separator coupled to the telescope, the wavelength separator providing a first received signal at the first wavelength and a second received signal at the second wavelength; and

the receiver further includes an optical delay line coupled to the wavelength separator to provide a delayed received signal delayed with respect to the first received signal by the predetermined time delay.

4. The free space optical system of claim 1, wherein:

the at least one other laser source includes a second laser source;

the first laser source of the transmitter produces a first optical signal at a first wavelength;

the second laser source of the transmitter produces a second optical signal at a second wavelength;

an optical delay line coupled to the second laser source delays the second optical signal by a predetermined time delay;

the second terminal includes a receiver;

the receiver includes a telescope and a wavelength separator coupled to the telescope, the wavelength separator providing a first received signal at the first wavelength and a second received signal at the second wavelength;

the receiver further includes a first optical to electrical converter coupled to the first received signal;

the receiver further includes a second optical to electrical converter coupled to the second received signal; and

the receiver further includes an electrical delay line coupled to the first optical to electrical converter.

5. A free space optical system comprising first and second terminals, the first terminal including a transmitter to transmit an input signal, the transmitter having:

at least one electrical delay line coupled to delay the input signal;

a plurality of laser sources that include a first laser source and at least one other laser source, the first laser source modulating the input signal onto a first wavelength, and the at least one other laser source modulating an output of a corresponding one of said at least one electrical delay line onto a wavelength that is distinct from the first wavelength; and

a telescope that projects an output of each of the plural laser sources toward the second terminal.

6. The free space optical system of claim 5, wherein the at least one delay line includes a first delay line to delay the input signal by a predetermined time delay.

7. The free space optical system of claim 5, wherein:

the at least one other laser source includes a second laser source;

the first laser source of the transmitter produces a first optical signal at the first wavelength;

the second laser source of the transmitter produces a second optical signal at a second wavelength;

an electrical delay line coupled to the second laser source delays an output of the second laser source by a predetermined time delay;

the second terminal includes a receiver;

the receiver includes a telescope and a wavelength separator coupled to the telescope, the wavelength separator providing a first received signal at the first wavelength and a second received signal at the second wavelength;

the receiver further includes a first optical to electrical converter coupled to the first received signal;

the receiver further includes a second optical to electrical converter coupled to the second received signal; and

the receiver further includes an electrical delay line coupled to the first optical to electrical converter.

8. The free space optical system of claim 5, wherein:

the at least one other laser source includes a second laser source;

the first laser source of the transmitter produces a first optical signal at the first wavelength;

the second laser source of the transmitter produces a second optical signal at a second wavelength;

an optical delay line coupled to the second laser source delays the second optical signal by a predetermined time delay;

the second terminal includes a receiver;

the receiver includes a telescope and a wavelength separator coupled to the telescope, the wavelength separator providing a first received signal at the first wavelength and a second received signal at the second wavelength; and

the receiver further includes an optical delay line coupled to the wavelength separator to provide a delayed received signal delayed with respect to the first received signal by the predetermined time delay.

9. A free space optical system comprising first and second terminals, the first terminal including a transmitter having:

an electrical converter to convert a serial bitstream into a plurality of parallel blocks of data;

an FEC encoder, bit interleaver and laser source for each parallel block of data, each laser source modulating the interleaved FEC encoded parallel block of data on a wavelength distinct from a wavelength of each other laser source; and

an optical combiner to combine an optical signal from each laser source.

10. The free space optical system of claim 9, wherein the transmitter further includes a multiplexer to combine plural input signals into the serial bitstream.

11. The free space optical system of claim 9, further comprising a telescope that projects an output of the combiner toward the second terminal.

12. The free space optical system of claim 9, wherein:

the plural laser sources for each respective block including a first laser source and at least one other laser source;

the transmitter further includes at least one optical delay line coupled between a respective output of the at least one other laser source and the optical combiner; and

the transmitter further includes a telescope that projects an output of the first laser source and an output of each of the at least one optical delay line toward the second terminal.