Optical transmitter-receiver

• US 6,459,519 B1
• Filed: 04/08/1998
• Issued: 10/01/2002
• Est. Priority Date: 04/09/1997
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Sasai, Hiroyuki, Utsumi, Kuniaki, Maeda, Kazuki
• Primary Examiner(s): Pascal, Leslie
• Assistant Examiner(s): SINGH, DALZID E
• Application Number:
  US09/056,611
• Time in Patent Office: 1,637 Days
• Field of Search: 359/180, 359/181, 359/188, 359/145
• US Class Current: 398/183
• CPC Class Codes: H04B 10/505 using external modulation
• CPC Class Codes: H04B 10/5051 using a series, i.e. cascade, combination of modulators
• CPC Class Codes: H04B 10/572 Wavelength control

Abstract

A modulated electrical signal Smod produced upon amplitude-modulating a subcarrier having a high frequency (for example, a millimeter-wave band) by a baseband signal SBB to be transmitted and a main carrier MC outputted from a light source are inputted to an external optical modulating portion in an optical transmitter. The external optical modulating portion amplitude-modulates the main carrier MC by the modulated electrical signal Smod, to output a double-modulated optical signal OSdmod to an optical filter portion. The optical filter portion passes only a component of one of sidebands included in the double-modulated optical signal OSdmod, and outputs the component to an optical fiber as an optical signal OS. An optical/electrical converting portion in an optical receiver optical/electrical-converts the optical signal OS transmitted through the optical fiber, to directly obtain a baseband signal SBB. Consequently, the optical receiver is constructed simply and at low cost without requiring a wideband optical/electrical converting element for optical/electrical-converting a high-frequency electrical signal and a high-frequency electrical component (a frequency converter, a demodulator, a semirigid cable or a waveguide) which is very high in cost or is difficult to process.

Claims

1. An optical transmitter-receiver in which an optical transmitter and at least one optical receiver are interconnected for optical transmission, comprising:

a double-modulating portion for double-modulating a main carrier, which is unmodulated light having a predetermined optical frequency, by an externally provided subcarrier modulated by an electrical signal to be transmitted, to produce and output a double-modulated optical signal,

an optical spectrum of said double-modulated optical signal produced from said double-modulating portion including a component of said main carrier at said predetermined optical frequency and further including components of an upper sideband and a lower sideband at frequencies spaced by the frequency of said subcarrier apart from the predetermined optical frequency;

an optical filter portion for passing an optical signal including the component of either one of said upper sideband and said lower sideband in said double-modulated optical signal inputted from said double-modulating portion; and

a first optical-electrical converting portion for converting said optical signal inputted from said optical filter portion into said electrical signal to be transmitted,

said optical transmitter comprising at least said double-modulating portion, said optical receiver comprising at least said first optical-electrical converting portion, and said optical filter portion being included in either one of the optical transmitter and the optical receiver.

2. The optical transmitter-receiver according to claim 1, wherein said double-modulating portion comprises:

a light source for outputting said main carrier; and

an external optical modulating portion for amplitude-modulating, using an external optical modulation, said main carrier inputted from said light source by a subcarrier amplitude-modulated by an externally provided electrical signal to be transmitted.

3. The optical transmitter-receiver according to claim 1, wherein the subcarrier amplitude-modulated by said electrical signal to be transmitted is a signal externally provided through wireless transmission, and said optical transmitter-receiver further comprises

an antenna portion receiving said signal through wireless transmission for supply to said double-modulating portion.

4. The optical transmitter-receiver according to claim 3, wherein said electrical signal to be transmitted is a multichannel signal frequency-multiplexed, and said subcarrier amplitude-modulated by said multichannel signal is received by said antenna portion.

5. The optical transmitter-receiver according to claim 3, wherein

said electrical signal to be transmitted is digital information, and

said subcarrier is OOK (on-off keying)-modulated by said digital information is received by said antenna portion.

6. The optical transmitter-receiver according to claim 1, wherein said double-modulating portion comprises:

a light source for outputting said main carrier;

a first external optical modulating portion for amplitude-modulating said main carrier inputted from said light source by said subcarrier externally provided to generate a modulated optical signal; and

a second external optical modulating portion for amplitude-modulating said modulated optical signal inputted from said first external optical modulating portion by said electrical signal to be transmitted that is externally provided.

7. The optical transmitter-receiver according to claim 1, wherein said double-modulating portion comprises:

a mode locked light source for generating and outputting a modulated optical signal by being mode-locked with said subcarrier externally provided; and

an external optical modulating portion for generating said double-modulated optical signal by amplitude-modulating said modulated optical signal received from said mode locked light source by said electrical signal to be transmitted that is externally provided.

8. The optical transmitter-receiver according to claim 1, further comprising:

an optical branching portion for branching the optical signal inputted from said optical filter portion into a first optical signal and a second optical signal, and outputting the first and second optical signals;

said first optical-electrical converting portion converting said first optical signal inputted from said optical branching portion into said electrical signal to be transmitted,

a second optical-electrical converting portion for outputting as a detecting signal an electrical signal obtained by converting said second optical signal inputted from said optical branching portion; and

a wavelength control portion for detecting the average values of detected signals inputted from said second optical-electrical converting portion at predetermined time intervals, and controlling a wavelength of the double-modulated optical signal outputted from said double-modulating portion on the basis of the maximum value of the detected average values.

9. The optical transmitter-receiver according to claim 1, wherein

said optical transmitter is connected to a first optical receiver and a second optical receiver for optical transmission,

said optical transmitter further comprises:

a local oscillating portion for outputting a subcarrier having a predetermined frequency to said double-modulating portion;

said double-modulating portion double-modulates the main carrier, which is unmodulated light having a predetermined optical frequency, by an externally provided electrical signal to be transmitted and said subcarrier inputted from said local oscillating portion, to produce and output a double-modulated optical signal,

said optical filter portion divides said double-modulated optical signal inputted from said double-modulating portion into a first optical signal including the component of either one of said upper sideband and said lower sideband and a second optical signal including the component of said main carrier and the component of the other one of said upper sideband and said lower sideband, to output the first optical signal and the second optical signal,

said first optical receiver converts, through optical-electrical conversion by said first optical-electrical converting portion included therein, said first optical signal transmitted from said optical filter portion into said electrical signal to be transmitted, and

said second optical receiver converts, through optical-electrical conversion by a second optical-electrical converting portion included therein, said second optical signal transmitted from said optical filter portion into said subcarrier modulated by said electrical signal to be transmitted.

10. The optical transmitter-receiver according to claim 9, wherein said double-modulating portion comprises:

an electrical modulating portion for amplitude-modulating said subcarrier inputted from said local oscillating portion by said externally provided electrical signal to be transmitted, to produce and output a modulated electrical signal;

a light source for outputting said main carrier which is unmodulated light having a predetermined optical frequency; and

an external optical modulating portion for amplitude-modulating said main carrier inputted from said light source by said modulated electrical signal inputted from said electrical modulating portion, to produce said double-modulated optical signal.

11. The optical transmitter-receiver according to claim 10, wherein

said electrical signal to be transmitted carries digital information, and

said electrical modulating portion OOK (on-off keying)-modulates said subcarrier by said digital information.

12. The optical transmitter-receiver according to claim 9, wherein said double-modulating portion comprises:

a light source for outputting said main carrier, which is unmodulated light having a predetermined optical frequency;

a first external optical modulating portion for amplitude-modulating said main carrier inputted from said light source by said subcarrier inputted from said local oscillating portion, to produce and output a modulated optical signal, and

a second external optical modulating portion for amplitude-modulating said modulated optical signal inputted from said first external optical modulating portion by said externally provided electrical signal to be transmitted, to produce said double-modulated optical signal.

13. The optical transmitter-receiver according to claim 9, wherein said double-modulating portion comprises:

a light source for outputting said main carrier, which is unmodulated light having a predetermined optical frequency;

a first external optical modulating portion for amplitude-modulating said main carrier inputted from said light source by said externally provided electrical signal to be transmitted, to produce and output a modulated optical signal; and

a second external optical modulating portion for amplitude-modulating said modulated optical signal inputted from said first external optical modulating portion by said subcarrier inputted from said location oscillating portion, to produce said double-modulated optical signal.

14. The optical transmitter-receiver according to claim 9, wherein said optical filter portion comprises

an optical circulator portion for outputting said double-modulated optical signal inputted from said double-modulating portion as it is;

and

an optical fiber grating portion for reflecting the component of either one of said upper sideband and said lower sideband in said double-modulated optical signal inputted from said optical circulator portion, to produce and output said first optical signal to said optical circulator portion, and passing the component of said main carrier and the component of the other one of said upper sideband and said lower sideband, to produce and output said second optical signal to the second optical-electrical converting portion of said second optical receiver, wherein

said optical circulator portion further outputs said first optical signal inputted from said optical fiber grating portion as it is to the first optical-electrical converting portion of said first optical receiver.

15. The optical transmitter-receiver according to claim 9, wherein said second optical receiver comprises an antenna portion for radiating to space the subcarrier that is modulated by said electrical signal to be transmitted which is obtained through optical-electrical conversion by the second optical-electrical converting portion.

16. The optical transmitter-receiver according to claim 9, wherein said electrical signal to be transmitted is an electrical signal to be transmitted which is digital information converted from analog information.

17. The optical transmitter-receiver according to claim 9, wherein said electrical signal to be transmitted is obtained by modulating, by analog information or digital information, a carrier having an intermediate frequency lower than that of the subcarrier outputted from said local oscillating portion.

18. The optical transmitter-receiver according to claim 9, wherein said electrical signal to be transmitted is obtained by multiplexing, through a predetermined multiplexing technique, a plurality of electrical signals each obtained by modulating a carrier having an intermediate frequency by analog information or digital information.

19. The optical transmitter-receiver according to claim 18, wherein said predetermined multiplexing technique is a frequency division multiplexing access, a time division multiplexing access or a code division multiplexing access.