Optical transmitter-receiver

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 S BB to be transmitted and a main carrier MC outputted from a light source 110 are inputted to an external optical modulating portion 120 in an optical transmitter 101 . The external optical modulating portion 120 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 130 . The optical filter portion 130 passes only a component of one of sidebands included in the double-modulated optical signal OSdmod, and outputs the component to an optical fiber 140 as an optical signal OS. An optical/electrical converting portion 150 in an optical receiver 102 optical/electrical-converts the optical signal OS transmitted through the optical fiber 140 , to directly obtain a baseband signal S BB . Consequently, the optical receiver 102 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.

What is claimed is:  
     
         1 . An optical transmitter-receiver in which an optical transmitter and an optical receiver are interconnected such that optical transmission is possible, comprising: 
 a double-modulating portion, to which a subcarrier modulated by an electrical signal to be transmitted is inputted from outside, for double-modulating a main carrier, which is unmodulated light having a predetermined optical frequency, by the inputted subcarrier, to produce and output a double-modulated optical signal,    an optical spectrum of said double-modulated optical signal inputted 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    an optical/electrical converting portion for optical/electrical-converting said optical signal inputted from said optical filter portion, to obtain said electrical signal to be transmitted,    said optical transmitter comprising at least said double-modulating portion, said optical receiver comprising at least said 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 semiconductor laser diode for outputting said main carrier, and    at least one external optical modulating portion for amplitude-modulating said main carrier inputted from said semiconductor laser diode by a subcarrier amplitude-modulated by an electrical signal to be transmitted which is inputted from outside using an external optical modulation.    
     
     
         3 . The optical transmitter-receiver according to  claim 2 , wherein the subcarrier amplitude-modulated by said electrical signal to be transmitted is a signal transmitted from outside, further comprising 
 an antenna portion receiving said signal transmitted for supplying the signal 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 modulated by said multichannel signal is inputted into said double-modulating portion from outside.    
     
     
         5 . The optical transmitter-receiver according to  claim 3 , wherein 
 said electrical signal to be transmitted is digital information, and    said subcarrier OOK (on-off keying)-modulated by said digital information is inputted into said double-modulating portion from outside.    
     
     
         6 . An optical transmitter-receiver in which an optical transmitter and an optical receiver are interconnected such that optical transmission is possible, comprising: 
 a double-modulating portion, to which a subcarrier modulated by an electrical signal to be transmitted is inputted from outside, for double-modulating a main carrier, which is unmodulated light having a predetermined optical frequency, by the inputted subcarrier, to produce and output a double-modulated optical signal,    an optical spectrum of said double-modulated optical signal inputted 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    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;    a first optical/electrical converting portion for optical/electrical-converting said first optical signal inputted from said optical branching portion, to obtain said electrical signal to be transmitted;    a second optical/electrical converting portion for outputting as a detecting signal an electrical signal obtained by optical/electrical-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 the 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,    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.    
     
     
         7 . An optical transmitter-receiver in which an optical transmitter and first and second optical receivers are interconnected such that optical transmission is possible, wherein 
 said optical transmitter comprises    a local oscillating portion for outputting a subcarrier having a predetermine frequency,    a double-modulating portion for double-modulating a main carrier which is unmodulated light having a predetermined optical frequency by an electrical signal to be transmitted which is inputted from outside and said subcarrier inputted from said local oscillating portion, to produce and output a double-modulated optical signal,    a spectrum of said double-modulated optical signal outputted 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, and    an optical filter portion for dividing 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 the upper sideband and the lower sideband, to output the first optical signal and the second optical signal,    said first optical receiver optical/electrical-converts said first optical signal transmitted from said optical transmitter, to obtain said electrical signal to be transmitted, and    said second optical receiver optical/electrical-converts said second optical signal transmitted from said optical transmitter, to obtain said subcarrier that is modulated by said electrical signal to be transmitted.    
     
     
         8 . The optical transmitter-receiver according to  claim 7 , wherein 
 said double-modulating portion comprises 
 an electrical modulating portion for amplitude-modulating said subcarrier inputted from said local oscillating portion by said electrical signal to be transmitted which is inputted from outside, 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.  
   
     
     
         9 . The optical transmitter-receiver according to  claim 8 , wherein 
 said electrical signal to be transmitted is digital information, and    said electrical modulating portion OOK (on-off keying)-modulates said subcarrier by said digital information.    
     
     
         10 . The optical transmitter-receiver according to  claim 7 , 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 electrical signal to be transmitted which is inputted from outside, to produce said double-modulated optical signal.    
     
     
         11 . The optical transmitter-receiver according to  claim 7 , 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 electrical signal to be transmitted which is inputted from outside, 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 local oscillating portion, to produce said double-modulated optical signal.  
   
     
     
         12 . The optical transmitter-receiver according to  claim 7 , 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 said first optical signal and output the produced first optical signal to said optical circulator portion, and passing the component of said main carrier and the component of the other one of the upper sideband and the lower sideband, to produce and output said second optical signal to said second optical receiver,  
 said optical circulator portion further outputting said first optical signal inputted from said optical fiber grating portion as it is to said first optical receiver.  
   
     
     
         13 . The optical transmitter-receiver according to  claim 7 , wherein said second optical receiver comprises an antenna portion for radiating to a space the subcarrier that is modulated by said electrical signal to be transmitted which is obtained by the optical/electrical conversion.  
     
     
         14 . The optical transmitter-receiver according to  claim 7 , wherein 
 said electrical signal to be transmitted is an electrical signal to be transmitted which is converted analog information into digital information.    
     
     
         15 . The optical transmitter-receiver according to  claim 7 , wherein 
 said electrical signal to be transmitted is a carrier modulated by an analog information and digital information, the frequency of said carrier is an intermediate frequency lower than that of the subcarrier outputted from said local oscillating portion.    
     
     
         16 . The optical transmitter-receiver according to  claim 7 , wherein 
 said electrical signal to be transmitted is obtained by multiplexing a plurality of electrical signals that have the intermediate frequency and are modulated by analog information or digital information using a predetermined multiplexing technique, respectively.    
     
     
         17 . The optical transmitter-receiver according to  claim 16 , wherein 
 said predetermined multiplexing technique is a frequency division multiplexing access, a time division multiplexing access or a code division multiplexing access.    
     
     
         18 . An optical transmitter-receiver in which an optical transmitter and first and second optical receivers are interconnected such that optical transmission is possible, wherein 
 said optical transmitter comprises 
 a local oscillating portion for outputting a subcarrier having a predetermine frequency,  
 a double-modulating portion for double-modulating a main carrier which is unmodulated light having a predetermined optical frequency by an electrical signal to be transmitted which is inputted from outside and by said subcarrier inputted from said local oscillating portion, to produce and output a double-modulated optical signal, and  
 an optical branching portion for branching said double-modulated optical signal inputted from said double-modulating portion, and outputting double-modulated optical signals obtained by the branching,  
 said first optical receiver comprises a low-pass filter portion for passing a component included in a low frequency band of an electrical signal obtained by optical/electrical-converting said double-modulated optical signal transmitted from said optical transmitter, to output said electrical signal to be transmitted, and  
 said second optical receiver comprises a high-pass filter portion for passing a component included in a high frequency band of an electrical signal obtained by optical/electrical-converting said double-modulated optical signal transmitted from said optical transmitter, to output said subcarrier that is modulated by said electrical signal to be transmitted.  
   
     
     
         19 . The optical transmitter-receiver according to  claim 18 , wherein 
 said double-modulating portion comprises 
 an electrical modulating portion for amplitude-modulating said subcarrier inputted from said local oscillating portion by said electrical signal to be transmitted which is inputted from outside, 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 outputted from said light source by said modulated electrical signal inputted from said electrical modulating portion, to produce said double-modulated optical signal.  
   
     
     
         20 . The optical transmitter-receiver according to  claim 19 , wherein 
 said electrical signal to be transmitted is digital information, and    said electrical modulating portion OOK (on-off keying)-modulates said subcarrier by said digital information.    
     
     
         21 . The optical transmitter-receiver according to  claim 18 , 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 electrical signal to be transmitted which is inputted from outside, to produce said double-modulated optical signal.    
     
     
         22 . The optical transmitter-receiver according to  claim 18 , 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 electrical signal to be transmitted which is inputted from outside, 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 local oscillating portion, to produce said double-modulated optical signal.  
   
     
     
         23 . The optical transmitter-receiver according to  claim 18 , wherein 
 an antenna portion for radiating to a space the subcarrier that is modulated by said electrical signal to be transmitted which is outputted from said high-pass filter portion is set in a back end against the high-pass filter portion.    
     
     
         24 . The optical transmitter-receiver according to  claim 18 , wherein 
 said electrical signal to be transmitted is a carrier modulated by analog information or digital information, the frequency of said carrier is an intermediate frequency lower than that of the subcarrier outputted from said local oscillating portion.    
     
     
         25 . The optical transmitter-receiver according to  claim 18 , wherein 
 said double-modulating portion modulates said main carrier by said subcarrier inputted from said local oscillating portion using a single sideband amplitude modulation technique.    
     
     
         26 . An optical transmitter-receiver in which an optical transmitter and an optical receiver are interconnected such that optical transmission is possible, wherein 
 said optical transmitter comprises 
 a local oscillating portion for outputting a subcarrier having a predetermine frequency, and  
 a double-modulating portion for double-modulating a main carrier which is unmodulated light having a predetermined optical frequency by an electrical signal to be transmitted which is inputted from outside and by said subcarrier inputted from said local oscillating portion, to produce and output a double-modulated optical signal,  
 said optical receiver comprises 
 an optical/electrical converting portion for optical/electrical-converting said double-modulated optical signal transmitted from said optical transmitter, to output an electrical signal,  
 a distributing portion for distributing the electrical signal inputted from said optical/electrical converting portion into at least two electrical signals,  
 a low-pass filter portion for passing a component included in a low frequency band of the electrical signal obtained by the distribution, to output said electrical signal to be transmitted, and  
 a high-pass filter portion for passing a component included in a high frequency band of the electrical signal obtained by the distribution, to output said subcarrier that is modulated by said electrical signal to be transmitted.  
 
   
     
     
         27 . The optical transmitter-receiver according to  claim 26 , wherein 
 said double-modulating portion comprises 
 an electrical modulating portion for amplitude-modulating said subcarrier inputted from said local oscillating portion by said electrical signal to be transmitted which is inputted from outside, 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.  
   
     
     
         28 . The optical transmitter-receiver according to  claim 27 , wherein 
 said electrical signal to be transmitted is digital information, and    said electrical modulating portion OOK (on-off keying)-modulates by said digital information.    
     
     
         29 . The optical transmitter-receiver according to  claim 26 , 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 electrical signal to be transmitted which is inputted from outside, to produce said double-modulated optical signal.  
   
     
     
         30 . The optical transmitter-receiver according to  claim 26 , 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 electrical signal to be transmitted which is inputted from outside, 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 local oscillating portion, to produce said double-modulated optical signal.  
   
     
     
         31 . The optical transmitter-receiver according to  claim 26 , wherein 
 an antenna portion for radiating to a space the subcarrier that is modulated by said electrical signal to be transmitted which is outputted from said high-pass filter portion is set in a back end against the high-pass filter portion.    
     
     
         32 . The optical transmitter-receiver according to  claim 26 , wherein 
 said electrical signal to be transmitted is a carrier modulated by analog information or digital information, the frequency of said carrier is an intermediate frequency lower than that of the subcarrier outputted from said local oscillating portion.    
     
     
         33 . The optical transmitter-receiver according to  claim 26 , wherein 
 said double-modulating portion modulates said main carrier by said subcarrier inputted from said local oscillating portion using a single sideband amplitude modulation technique.    
     
     
         34 . An optical transmitter-receiver in which an optical transmitter and first and second optical receivers are interconnected such that optical transmission is possible, wherein 
 said optical transmitter comprises 
 a local oscillating portion for outputting a subcarrier having a predetermine frequency,  
 a mode locked light source which is mode-locked on the basis of the subcarrier inputted from said local oscillating portion, and oscillating with spacing between optical frequencies related to the subcarrier, to produce and output a mode-locked optical signal,  
 an external optical modulating portion for amplitude-modulating said mode-locked optical signal inputted from said mode locked light source by the electrical signal to be transmitted which is inputted from outside, to produce and output a double-modulated optical signal, and  
 an optical branching portion for branching said double-modulated optical signal inputted from said external optical modulating portion and outputting double-modulated optical signals obtained by the branching,  
 said first optical receiver comprises a low-pass filter portion for passing a component included in a low frequency band of an electrical signal obtained by optical/electrical-converting said double-modulated optical signal transmitted from said optical transmitter, to output said electrical signal to be transmitted, and  
 said second optical receiver comprises a high-pass filter portion for passing a component included in a high frequency band of an electrical signal obtained by optical/electrical-converting said double-modulated optical signal transmitted from said optical transmitter, to output said subcarrier that is modulated by said electrical signal to be transmitted.  
   
     
     
         35 . The optical transmitter-receiver according to  claim 34 , wherein 
 an antenna portion for radiating to a space the subcarrier that is modulated by said electrical signal to be transmitted which is outputted from said high-pass filter portion is set in a back end against said high-pass filter portion.    
     
     
         36 . The optical transmitter-receiver according to  claim 34 , wherein 
 said electrical signal to be transmitted is a carrier modulated by analog information or digital information, the frequency of said carrier is an intermediate frequency lower than that of the subcarrier outputted from said local oscillating portion.    
     
     
         37 . An optical transmitter-receiver in which an optical transmitter and an optical receiver are interconnected such that optical transmission is possible, wherein 
 said optical transmitter comprises 
 a local oscillating portion for outputting a subcarrier having a predetermine frequency,  
 a mode locked light source which is mode-locked on the basis of a subcarrier inputted from said local oscillating portion and oscillating with spacing between optical frequencies related to the subcarrier, to produce and output a mode-locked optical signal, and  
 an external optical modulating portion for amplitude-modulating said mode-locked optical signal inputted from said mode locked light source by an electrical signal to be transmitted which is inputted from outside, to produce and output a double-modulated optical signal, and  
   said optical receiver comprises 
 an optical/electrical converting portion for optical/electrical-converting said double-modulated optical signal transmitted from said optical transmitter, to output an electrical signal,  
 a distributing portion for distributing the electrical signal inputted from said optical/electrical converting portion into at least two electrical signals,  
 a low-pass filter portion for passing a component included in a low frequency band of the electrical signal obtained by the distribution, to output said electrical signal to be transmitted, and  
 a high-pass filter portion for passing a component included in a high frequency band of the electrical signal obtained by the distribution, to output said subcarrier that is modulated by said electrical signal to be transmitted.  
   
     
     
         38 . The optical transmitter-receiver according to  claim 37 , wherein 
 an antenna portion for radiating to a space the subcarrier that is modulated by said electrical signal to be transmitted which is outputted from said high-pass filter portion is set in a back end against said high-pass filter portion.    
     
     
         39 . The optical transmitter-receiver according to  claim 37 , wherein 
 said electrical signal to be transmitted is a carrier modulated by analog information or digital information, the frequency of said carrier is an intermediate frequency lower than that of the subcarrier outputted from said local oscillating portion.    
     
     
         40 . An optical transmitter-receiver in which an optical transmitter and first and second optical receivers are interconnected such that optical transmission is possible, wherein 
 said optical transmitter comprises 
 a first light source for outputting first unmodulated light having a first optical frequency,  
 an external optical modulating portion for amplitude-modulating the first unmodulated light inputted from said first light source by an electrical signal to be transmitted which is inputted from outside, to produce and output a modulated optical signal,  
 a second light source for outputting second unmodulated light having a second optical frequency which differs from said first optical frequency by a predetermined optical frequency,  
 an optical multiplexing portion for multiplexing the modulated optical signal inputted from said external optical modulating portion and the second unmodulated light inputted from said second light source such that polarization of the modulated optical signal and the second unmodulated light coincide with each other, to produce and output an optical signal, and  
 an optical branching portion for branching the optical signal inputted from said optical multiplexing portion and outputting optical signals obtained by the branching,  
   said first optical receiver comprises 
 a low-pass filter portion for passing a component included in a low frequency band of an electrical signal obtained by optical/electrical-converting said optical signal transmitted from said optical transmitter, to output said electrical signal to be transmitted, and  
   said second optical receiver comprises 
 a high-pass filter portion for passing a component included in a high frequency band of an electrical signal obtained by optical/electrical-converting said optical signal transmitted from said optical transmitter, to output said subcarrier that is modulated by said electrical signal to be transmitted.  
   
     
     
         41 . The optical receiver according to  claim 40 , wherein 
 an antenna portion for radiating to a space the subcarrier that is modulated by said electrical signal to be transmitted which is outputted from said high-pass filter portion is set in a back end against said high-pass filter portion.    
     
     
         42 . The optical transmitter-receiver according to  claim 40 , wherein 
 said electrical signal to be transmitted is a carrier modulated by analog information or digital information, the frequency of said carrier is an intermediate frequency lower than that of the subcarrier outputted from said local oscillating portion.    
     
     
         43 . An optical transmitter-receiver in which an optical transmitter and an optical receiver are interconnected such that optical transmission is possible, wherein 
 said optical transmitter comprises 
 a first light source for outputting first unmodulated light having a first optical frequency,  
 an external optical modulating portion for amplitude-modulating the first unmodulated light inputted from said first light source by an electrical signal to be transmitted which is inputted from outside, to produce and output a modulated optical signal,  
 a second light source for outputting second unmodulated light having a second optical frequency which differs from said first optical frequency by a predetermined optical frequency,  
 an optical multiplexing portion for multiplexing the modulated optical signal inputted from said external optical modulating portion and the second unmodulated light inputted from said second light source such that polarization of the modulated optical signal and the second unmodulated light coincide with each other, to produce and output an optical signal, and  
 an optical branching portion for branching the optical signal inputted from said optical multiplexing portion and outputting optical signals obtained by the branching, and  
   said optical receiver comprises 
 an optical/electrical converting portion for optical/electrical-converting said optical signal transmitted from said optical transmitter, to output an electrical signal,  
 a distributing portion for distributing the electrical signal inputted from said optical/electrical converting portion into at least two electrical signals,  
 a low-pass filter portion for passing a component included in a low frequency band of the electrical signal obtained by the distribution, to output an electrical signal to be transmitted, and  
 a high-pass filter portion for passing a component included in a high frequency band of the electrical signal obtained by the distribution, to output said subcarrier that is modulated by said electrical signal to be transmitted.  
   
     
     
         44 . The optical transmitter-receiver according to  claim 43 , wherein 
 an antenna portion for radiating to a space the subcarrier that is modulated by said electrical signal to be transmitted which is outputted from said high-pass filter portion is set in a back end against said high-pass filter portion.    
     
     
         45 . The optical transmitter-receiver according to  claim 43 , wherein 
 said electrical signal to be transmitted is a carrier modulated by analog information or digital information, the frequency of said carrier is an intermediate frequency lower than that of the subcarrier outputted from said local oscillating portion.