JP2006287410A - Optical transmitter, optical receiver, and optical transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmitter capable of further increasing the number of channels without adding a frequency converter. <P>SOLUTION: The optical transmitter 10 includes: a single mode light source 11; an external intensity modulation section 12 for applying intensity modulation to light output from the single mode light source 11 with an electric signal from a first signal source 40; a phase modulation section 13 for applying phase modulation to an optical signal output from the external intensity modulation section 12 with an electric signal from a second signal source 50; a local oscillation light source 14 for outputting a local oscillation light; a photocoupler 15 for multiplexing an optical signal output from the phase modulation section with the local oscillation light output from the local oscillation light source 14; an optical detection section 16 for applying heterodyne detection to the optical signal multiplexed by the photocoupler 15 to provide an output of an electric signal; and an optical transmission section 17 for applying intensity modulation to the light source with the electric signal output from the optical detection section 16 and transmitting the resulting signal to an optical transmission line. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical transmitter, an optical receiver, and an optical transmission system that can be used for optical communication, optical CATV, and the like.

In an optical transmission system for transmitting video signals and the like, in order to improve the noise immunity of a transmission line, a technique for converting multi-channel video signals into FM signals or PM signals and transmitting them is considered to be effective. Yes. A conventional optical transmission system includes an optical frequency modulation unit 1 that outputs an optical signal that is frequency-modulated using an electric signal as a modulation input, and an optical frequency local unit that outputs a local oscillation light having an optical frequency that is separated from the optical signal by an intermediate frequency. An oscillating unit 2; an optical combining unit 3 that combines the output light of the optical frequency modulation unit 1 and the local oscillation light; and an output light and a local oscillation light of the optical frequency modulation unit 1 that are input with the combined optical signal. Optical heterodyne detector 4 for outputting an electrical signal having an intermediate frequency equal to the difference between the optical frequencies of the two, and a collective FM video signal frequency stabilization as means for removing noise caused by fluctuations of the optical signal and local oscillation light from the electrical signal And a collective FM video signal light transmission unit 6 as an optical transmission unit that outputs an optical signal that is intensity-modulated by a light source and transmitted to an optical transmission line by an electric signal from the collective FM video signal frequency stabilization unit 5. Have ( In example, see Patent Document 1).
JP-A-8-274714

  By the way, the signals transmitted by the CATV transmitting station by frequency multiplexing include signals of various modulation schemes such as terrestrial analog broadcasting, terrestrial digital broadcasting, and satellite broadcasting.

  However, when these multiplexed signals are spread over a wide band, an optical frequency modulator (single mode laser for optical frequency modulation) is used in a system in which FM signals and PM signals are collectively converted and transmitted as in the conventional optical transmission system. ) And its peripheral circuits (high-frequency amplifiers) require strict input / output frequency characteristics, and it is difficult to achieve a wider bandwidth than the current situation. As a result, in order to increase the number of channels to be transmitted, frequency conversion must be performed. There was a problem that it was necessary to add a frequency converter to save the bandwidth by going.

  The present invention provides an optical transmission device and an optical transmission system capable of further increasing the number of channels to be transmitted without adding a frequency converter.

  In order to solve the above-described conventional problems, an optical transmission device according to the present invention includes a single mode light source that outputs single mode light, and an electrical signal from the first signal source that is output from the single mode light source. An external intensity modulation unit that modulates the intensity of the optical signal, a phase modulation unit that phase-modulates the optical signal output from the external intensity modulation unit with an electric signal from the second signal source, and an optical frequency different from the output light of the phase modulation unit A local light source that outputs the local oscillation light, an optical coupler that combines the optical signal output from the phase modulation unit and the local oscillation light output from the local light source, and an optical signal that is combined by the optical coupler A heterodyne detector to output an electrical signal having an intermediate frequency between the optical frequency of the output of the phase modulator and the optical frequency of the local light source, and a light source based on the electrical signal output from the optical detector. Intensity modulated and transmitted to optical transmission line And a light transmitting unit that outputs that optical signal.

  With such a configuration, it is possible to further increase the number of channels to be transmitted without adding a frequency converter.

  Furthermore, the optical transmission device of the present invention comprises an optical integrated device in which a semiconductor laser element and an optical intensity modulator are integrated, and an optical intensity modulator that inputs an electric signal from a first signal source and outputs an intensity-modulated optical signal A phase modulation unit that further phase-modulates the optical signal output from the light intensity modulation unit with an electric signal from the second signal source, and a station that outputs local oscillation light having a different optical frequency from the output light of the phase modulation unit Light source, optical coupler that combines the optical signal output from the phase modulator and the local oscillation light output from the local light source, and heterodyne detection of the optical signal combined by the optical coupler for phase modulation The optical detector outputs an electrical signal having an intermediate frequency that is the difference between the optical frequency of the output of the optical unit and the optical frequency of the local light source, and the intensity of the light is modulated by the electrical signal output from the optical detector to the optical transmission line Optical transmission that outputs optical signals to be transmitted And a part.

  With such a configuration, the number of channels to be transmitted can be further increased without adding a frequency converter while simplifying the configuration.

  Furthermore, the optical transmission apparatus of the present invention includes a single mode light source that outputs light of a single mode, and an external intensity modulation unit that modulates the intensity of light output from the single mode light source with an electric signal from the first signal source. A phase modulation unit that further phase-modulates the optical signal output from the external intensity modulation unit with an electric signal from the second signal source, and a station that outputs local oscillation light having a different optical frequency from the output light of the phase modulation unit The light source includes an optical coupler that multiplexes the optical signal output from the phase modulator and the local oscillation light output from the local light source.

  With such a configuration, the number of channels to be transmitted can be further increased without adding a frequency converter while simplifying the configuration.

  Furthermore, the optical transmission apparatus of the present invention includes a single mode light source that outputs light of a single mode, and an external intensity modulation unit that modulates the intensity of light output from the single mode light source with an electric signal from the first signal source. And an integration circuit that outputs an electric signal obtained by integrating the electric signal from the second signal source, and a phase modulation of the optical signal output from the external intensity modulator by the electric signal output from the integration circuit A phase modulation unit, a local light source that outputs local oscillation light having an optical frequency different from that of the output light of the phase modulation unit, an optical signal output from the phase modulation unit, and a local oscillation light output from the local light source. Heterodyne detection is performed on the optical coupler to be multiplexed and the optical signal multiplexed by the optical coupler, and an electric signal having an intermediate frequency as the difference between the optical frequency of the output of the phase modulation unit and the optical frequency of the local light source is output. Output from the optical detector and the optical detector And an optical transmission section for outputting an optical signal to transmit the light intensity modulation in the optical transmission line by an electrical signal.

  With such a configuration, it is possible to further increase the number of channels to be transmitted without simplifying the optical receiver and adding a frequency converter.

  Furthermore, the optical transmission apparatus of the present invention is characterized in that the signal input from the first signal source is an FM signal or a digital modulation signal, and the signal input from the second signal source is an AM signal or a QAM signal. .

  With such a configuration, the required characteristics of the phase modulation unit can be relaxed by modulating the optical intensity of an FM signal or digital modulation signal having low required characteristics.

  The optical transmission system according to the present invention further includes an optical transmission device, an optical signal transmitted from the optical transmission device, and a signal corresponding to the electrical signal from the first signal source and the electrical signal from the second signal source. And an optical receiving device that outputs.

  With such a configuration, the number of channels to be transmitted can be further increased without adding a frequency converter.

  The optical receiver of the present invention further includes an O / E converter that receives an optical signal transmitted from the optical transmitter through the optical transmission path and outputs the optical signal as an electrical signal. The electrical receiver output from the O / E converter The signal is branched, one of the branched signals is output as a first signal output, and the other of the branched signals is phase-demodulated and output as a second signal output.

  With such a configuration, the number of channels to be transmitted can be further increased without adding a frequency converter.

  The optical receiver of the present invention further includes an optical detection unit that receives an optical signal transmitted from the optical transmission device through the optical transmission line, detects the heterodyne, and outputs an electrical signal, and outputs the electrical signal output from the optical detection unit. The signal is branched, one of the branched signals is output as a first signal output, and the other of the branched signals is phase-demodulated and output as a second signal output.

  With such a configuration, the number of channels to be transmitted can be further increased without adding a frequency converter while simplifying the configuration of the optical transmission device.

  The optical receiver of the present invention further includes an O / E converter that receives an optical signal transmitted from the optical transmitter through the optical transmission path and outputs the optical signal as an electrical signal. The electrical receiver output from the O / E converter The signal is branched, one branched is output as a first signal output, and the other branched is FM demodulated and output as a second signal output.

  With such a configuration, the number of channels to be transmitted can be further increased without adding a frequency converter while simplifying the configuration.

  According to the present invention, it is possible to obtain an optical transmission device having an effect that the number of channels to be transmitted can be further increased without adding a frequency converter.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
First, the configuration of the optical transmission system according to Embodiment 1 of the present invention will be described with reference to the block diagram shown in FIG.

  As shown in FIG. 1, the optical transmission system according to the first embodiment includes an optical transmission device 10 and an optical reception device 20. The optical transmitter 10 and the optical receiver 20 are connected by an optical fiber 30 that is an optical transmission path.

  The optical transmission device 10 has a single mode light source 11 that outputs single mode light, and the single mode light output from the single mode light source 11 is intensity-modulated by an electrical signal from the first signal source 40. An external intensity modulation unit 12 that outputs an optical signal, a phase modulation unit 13 that outputs an optical signal obtained by phase-modulating the optical signal output from the external intensity modulation unit 12 by an electrical signal from the second signal source 50, and The local light source 14 that outputs local oscillation light having an optical frequency different from the output light of the phase modulation unit 13, the optical signal output from the phase modulation unit 13, and the local oscillation light output from the local light source 14 are combined. The optical coupler 15 that outputs the optical signal and the optical signal combined by the optical coupler 15 are subjected to heterodyne detection, and the difference between the optical frequency of the output of the phase modulator 13 and the optical frequency of the local light source 14 is determined as an intermediate frequency. Output an electrical signal Having an optical detecting unit 16, the electrical signal output from the optical detecting unit 16 and a light transmission unit 17 for outputting an optical signal for transmitting an optical intensity modulation to the optical transmission path.

  As the single mode light source 11 and the local light source 14, a DFB-LD (Distributed Feedback Laser Diode), which is a kind of semiconductor laser diode that outputs a single mode light having a broadband frequency modulation function, is used. The optical frequencies of the single mode light source 11 and the local light source 14 are, for example, 193000 GHz and 193006.1 GHz, respectively. These optical frequencies correspond to light having a wavelength of 1.5 μm. An electrical signal having a center frequency of 6.1 GHz as a difference between the optical frequencies of the two is converted into light and transmitted through the optical fiber 30.

  For the external intensity modulation unit 12 and the phase modulation unit 13, an external optical modulator such as a Mach-Zehnder type is used. A Mach-Zehnder type external optical modulator is an element in which an optical waveguide and an electrode are provided on a crystal substrate having an electro-optic effect (a phenomenon in which the refractive index changes when an electric field is applied). The phase of the light propagating through the waveguide fluctuates, and the light intensity modulation is one in which the intensity of the combined light is fluctuated from a phase shift of the light branched in two and propagating through the two waveguides. The external intensity modulator 12 may be an electroabsorption external light modulator instead of the Mach-Zehnder external light modulator.

  The optical coupler 15 multiplexes the optical signal output from the phase modulator 13 and the local oscillation light output from the local light source 14.

  A photodiode is used for the optical detection unit 16. The optical detector 16 performs heterodyne detection on the optical signal combined by the optical coupler 14 and outputs an electrical signal.

  For the optical transmitter 17, for example, DFB-LD is used. The optical transmission unit 17 modulates the intensity of light with the electrical signal output from the optical detection unit 16 and outputs an optical signal to be transmitted to the optical fiber 30 that is an optical transmission path.

  The optical receiver 20 includes an O / E converter 21 that receives an optical signal transmitted from the optical transmitter 10 through an optical fiber 30 that is an optical transmission path and outputs the optical signal as an electrical signal. PD (Photo-Diode, photodiode) is used as the O / E converter 21. The electric signal output from the O / E conversion unit 21 is branched by the branching unit 22, one of the branched signals is output as a first signal output, and the other of the branched signals is phase-demodulated by the phase demodulation unit 24 to be second. Output as a signal output.

  Next, signals of the respective parts of the optical transmission system according to Embodiment 1 of the present invention will be described using the spectrum diagram of FIG.

  FIG. 2A shows an electrical frequency spectrum of a signal input from the first signal source 40. The signal input from the first signal source 40 is a digital modulation signal such as an FM signal or a PSK signal that is frequency division multiplexed. For example, it is effective for FM signals and QPSK signals such as BS broadcasting (BS-IF: 1.0 to 1.3 GHz) and 110 ° CS broadcasting (CS-IF: 1.6 to 2.1 GHz).

  FIG. 2B shows an electrical frequency spectrum of a signal input from the second signal source 50. The signal input from the second signal source 50 is a multi-channel AM signal or QAM signal that is frequency division multiplexed. For example, it is effective when it is an AM signal or QAM signal such as UHF / VHF band (70 to 770 MHz) terrestrial analog broadcasting, terrestrial digital broadcasting, or the like.

  FIG. 2C shows an optical frequency spectrum of the output of the single mode light source 11. The optical frequency is 193000 GHz.

  FIG. 2D shows the optical frequency spectrum of the output of the phase modulation unit 13. When phase modulation is performed with a multi-channel signal having a low frequency and a narrow frequency interval, such as an AM signal and a QAM signal input from the second signal source 50, not only the primary sideband wave of each channel but also the high-order sideband wave appears. Therefore, a Gaussian distribution with a wide frequency band is obtained. On the other hand, the sideband wave that appears as a result of intensity modulation by the BS / CS signal input from the first signal source 40 overlaps with a Gaussian distribution having a wide frequency band generated by the signal input from the second signal source 50. However, in general, a digital modulation signal such as an FM signal or a PSK signal input from the first signal source 40 has lower required characteristics with respect to distortion and noise than a multi-channel AM video signal. The signal can be demodulated from the electrical signal of one output. As a result, it is possible to reduce the frequency band transmitted to the optical fiber 30 that is an optical transmission line, compared to the case where all signals are modulated only by phase modulation. FIG. 2E shows an optical frequency spectrum of the output of the local light source 14. The optical frequency is 193006.1 GHz.

  FIG. 2F shows an electrical frequency spectrum of the output of the light detection unit 16. The center frequency is 6.1 GHz, which is equal to the difference between the optical frequency of the DFB-LD output and the optical frequency of the local light source output. The optical transmission unit 17 modulates the intensity of light with the electrical signal output from the optical detection unit 16 and outputs an optical signal to be transmitted to the optical fiber 30 that is an optical transmission path. The optical transmission device 10 can reduce the frequency band to be transmitted as compared to the case where all signals are modulated only by phase modulation.

  In the optical fiber 30 that is an optical transmission line, signal degradation occurs due to attenuation and scattering of an optical signal, whereas a phase modulation signal is relatively resistant to such degradation, whereas an intensity modulation signal suffers from such degradation. Relatively weak. However, since the signal input from the first signal source 40 is a digital modulation signal such as an FM signal or a PSK signal having a low required characteristic, there is no particular problem.

  In addition, the scattering of the optical signal in the optical fiber 30 includes, for example, SBS (Stimulated Brillouin Scattering). SBS is a phenomenon in which reflected light having a wavelength slightly deviated from an input wavelength is generated when a strong optical power of a certain amount or more is input to the optical fiber 30 and refers to scattering due to acoustic vibration (phonon).

  The O / E converter 21 receives the optical signal output from the optical transmitter 17, converts it into an electrical signal, and outputs it. The electrical signal output from the O / E converter 21 is branched by the branching unit 22 into the first signal output and the input of the phase demodulation unit 24. The first signal output can reproduce a signal corresponding to the electrical signal from the first signal source 40 by directly connecting a device having an AM / QAM demodulation function. Specifically, it can be demodulated by inputting it directly into a TV tuner. The phase demodulator 24 demodulates the other of the electrical signals branched by the branch unit 22 and outputs a signal corresponding to the electrical signal from the second signal source 50 as a second signal output. Specifically, it can be input to an existing BS, CS broadcast tuner or the like without frequency conversion. The optical receiver 20 can further increase the frequency band to be received by the amount of the first signal output as compared with the case where all signals are demodulated only by phase demodulation.

  As described above, according to the optical transmission apparatus of the first embodiment, it is possible to further increase the number of channels to be transmitted without adding a frequency converter. Moreover, according to the optical receiver of this Embodiment 1, the number of channels to receive can be further increased without adding a frequency converter. Further, according to the optical transmission system of the first embodiment, the number of channels to be transmitted can be further increased without adding a frequency converter. Furthermore, when the same number of channels are used, the required characteristics of the phase modulation section and the like can be relaxed, so that the cost of the optical transmitter, optical receiver, or optical transmission system can be reduced.

(Embodiment 2)
In the second embodiment, instead of the DFB-LD and the external intensity modulation unit 12 that are the single mode light source 11 in the first embodiment, an EA-DFB (DFB- with a built-in external intensity modulation unit) that is the light intensity modulator 18 is used. LD).

  First, the configuration of the optical transmission system according to the second embodiment of the present invention will be described with a focus on differences from the first embodiment with reference to the block diagram of FIG.

  As illustrated in FIG. 3, the optical transmission system according to the second embodiment includes an optical transmission device 103 and an optical reception device 20. The optical transmitter 103 and the optical receiver 20 are connected by an optical fiber 30 that is an optical transmission path.

  The optical transmission device 103 receives an electrical signal from the first signal source 40 and outputs an optical signal whose intensity is modulated, and further outputs the optical signal output from the optical intensity modulator 18 to the second optical signal. Phase modulation unit 13 that performs phase modulation with an electric signal from signal source 50, local light source 14 that outputs local oscillation light having an optical frequency different from the output light of phase modulation unit 13, and light output from phase modulation unit 13 The optical coupler 15 that combines the signal and the local oscillation light output from the local light source 14, and heterodyne detection of the optical signal combined by the optical coupler 15, the optical frequency of the output from the phase modulator 13 and the local light An optical detector 16 that outputs an electrical signal having an intermediate frequency that is the difference from the optical frequency of the light source 14, and an optical signal that is intensity-modulated by the electrical signal output from the optical detector 16 and is transmitted to the optical transmission line. An optical transmitter 17 for output To.

  The optical transmission apparatus 103 according to the second embodiment is different from the optical transmission apparatus 10 according to the first embodiment in the following points. That is, the optical transmission apparatus 103 uses the EA-DFB that is the light intensity modulator 18 instead of the DFB-LD that is the single mode light source 11 and the external intensity modulator 12 shown in FIG. The EA-DFB is an optical integrated device in which a DFB-LD and an electroabsorption optical modulator (EA modulator) are monolithically integrated. With such a configuration, the configuration of the optical transmission device 103 can be simplified.

  As for the signal of each part of the optical transmission system in the second embodiment, the optical signal output from the EA-DFB which is the optical intensity modulator 18 is the same as the optical signal output from the external intensity modulation unit 12 in the first embodiment. The other points are the same as the signals of the respective parts of the optical transmission system according to the first embodiment.

  As described above, according to the optical transmission device of the second embodiment, it is possible to further increase the number of channels to be transmitted without adding a frequency converter while simplifying the configuration. Further, according to the optical transmission system of the second embodiment, the number of channels to be transmitted can be further increased without adding a frequency converter while simplifying the configuration. Furthermore, when the same number of channels are used, the required characteristics of the phase modulation section and the like can be relaxed, so that the cost of the optical transmitter, optical receiver, or optical transmission system can be reduced.

(Embodiment 3)
The third embodiment is configured by omitting the DFB-LD which is the optical detection unit 16 and the optical transmission unit 17 in the first embodiment.

  First, the configuration of the optical transmission system according to the third embodiment of the present invention will be described focusing on differences from the first and second embodiments with reference to the block diagram shown in FIG.

  As illustrated in FIG. 4, the optical transmission system according to the third embodiment includes an optical transmission device 104 and an optical reception device 204. The optical transmitter 104 and the optical receiver 204 are connected by an optical fiber 30 that is an optical transmission path.

  The optical transmission device 104 includes a single mode light source 11 that outputs single mode light, and the single mode light output from the single mode light source 11 is intensity-modulated by an electrical signal from the first signal source 40. An external intensity modulation unit 12 that outputs an optical signal, and a phase modulation unit 13 that outputs an optical signal obtained by further phase-modulating the optical signal output from the external intensity modulation unit 12 with an electrical signal from the second signal source 50 A local light source 14 that outputs a local oscillation light having an optical frequency different from that of the output light of the phase modulation unit 13, an optical signal output from the phase modulation unit 13, and a local oscillation light output from the local light source 14. And an optical coupler 15 for outputting the combined optical signal.

  Thus, the optical transmission device 104 is the same as that of the first embodiment except that the optical detection unit 16 and the LD that is the optical transmission unit 17 in the optical transmission device 10 of the first embodiment are omitted. . With such a configuration, the configuration of the optical transmission device 104 can be simplified.

  As in the second embodiment, instead of the DFB-LD that is the single-mode light source 11 and the external intensity modulator 12 in the optical transmitter 104, the optical intensity modulator 18 in the optical transmitter 103 in the second embodiment. The configuration can be further simplified using the EA-DFB.

  The optical receiver 204 receives the optical signal transmitted from the optical transmitter 104 through the optical fiber 30 that is an optical transmission path, performs heterodyne detection, and outputs the optical frequency of the output from the phase modulator 13 and the light from the local light source 14. The optical detection unit 26 outputs an electric signal having a difference from the frequency as an intermediate frequency. The electric signal output from the optical detection unit 26 is branched by the branching unit 22, and one of the branched signals is output as a first signal. And the other of the branched signals is phase demodulated by the phase demodulator 24 and output as a second signal output.

  As described above, the optical receiver 204 is different from the optical receiver 20 of Embodiment 1 only in that optical heterodyne detection is performed using the optical detector 26.

  As the optical detection unit 26, a photodiode is used as in the optical detection unit 16 in the optical transmission device 10 of the first embodiment.

  The signal of each part of the optical transmission system according to the third embodiment is such that the optical signal output from the optical coupler 15 is output to the optical fiber 30 that is the optical transmission path, and the output of the optical detection unit 26 is branched by the branching unit 22. Only the points differ from those of the first and second embodiments.

  As described above, according to the optical transmission device 104 of the third embodiment, the number of channels to be transmitted can be further increased without adding a frequency converter while simplifying the configuration. Also, according to the optical receiver of the third embodiment, the number of channels to be received can be further increased without adding a frequency converter while simplifying the configuration of the optical transmitter. Further, according to the optical transmission system of the third embodiment, the number of channels to be transmitted can be further increased without adding a frequency converter while simplifying the configuration. Furthermore, when the same number of channels are used, the required characteristics of the phase modulation section and the like can be relaxed, so that the cost of the optical transmitter, optical receiver, or optical transmission system can be reduced.

(Embodiment 4)
In the fourth embodiment, the optical transmission device outputs an electrical signal obtained by integrating the electrical signal from the second signal source, and the optical signal output from the external intensity modulation unit from the integration circuit. A mode having a phase modulation unit that performs phase modulation by an output electric signal will be described.

  First, the configuration of the optical transmission system according to the fourth embodiment of the present invention will be described focusing on differences from the first to third embodiments.

  As illustrated in FIG. 5, the optical transmission system according to the fourth embodiment includes an optical transmission device 105 and an optical reception device 205. The optical transmitter 105 and the optical receiver 205 are connected by an optical fiber 30 that is an optical transmission path.

  The optical transmission device 105 outputs a single-mode light source 11 that outputs single-mode light, and an optical signal obtained by intensity-modulating the light output from the single-mode light source 11 with an electrical signal from the first signal source 40. The external intensity modulation unit 12 to output, the integration circuit 19 to output the electric signal obtained by integrating the electric signal from the second signal source 50, and the optical signal output from the external intensity modulation unit 12 are further integrated A phase modulation unit 13 that outputs an optical signal phase-modulated by an electrical signal output from the circuit 19; a local light source 14 that outputs a local oscillation light having an optical frequency different from that of the output light of the phase modulation unit 13; An optical coupler 15 for outputting an optical signal obtained by combining the optical signal output from the unit 13 and the local oscillation light output from the local light source 14, and heterodyne detection of the optical signal combined by the optical coupler 15. , Phase modulation part 3, an optical detector 16 that outputs an electrical signal having an intermediate frequency that is the difference between the optical frequency of the output 3 and the optical frequency of the local light source 14, and the intensity of the light is modulated by the electrical signal output from the optical detector 16. And an optical transmitter 17 that outputs an optical signal to be transmitted to the transmission path.

  In this way, the optical transmission device 105 is output from the integration circuit 19 that outputs the electrical signal obtained by integrating the electrical signal from the second signal source 50 by the optical transmission device and the external intensity modulation unit 12. This embodiment is the same as that of the first embodiment except that the optical signal includes the phase modulation unit 13 that performs phase modulation on the electrical signal output from the integration circuit 19.

  The electric signal from the second signal source 50 is integrated by the integration circuit 19 and then phase-modulated by the phase modulation unit 13 by the integrated electric signal, so that the external intensity modulation unit 12 is converted by the electric signal from the second signal source 50. The optical signal output from can be FM modulated.

  As in the second embodiment, instead of the DFB-LD that is the single mode light source 11 and the external intensity modulator 12 in the optical transmitter 105, the optical intensity modulator 18 in the optical transmitter 103 in the second embodiment. The configuration can be further simplified using the EA-DFB.

  Further, similarly to the third embodiment, the optical detection unit 16 and the DFB-LD which is the optical transmission unit 17 in the optical transmission device 105 can be omitted to simplify the configuration.

  The optical receiver 205 includes an O / E converter 21 that receives an optical signal transmitted from the optical transmitter 10 through the optical fiber 30 that is an optical transmission path and outputs the optical signal as an electrical signal. The branching unit 22 branches the electrical signal output from the signal, outputs one of the branched signals as a first signal output, and FM-demodulates the other of the branched signals by the FM demodulating unit 25 to output as a second signal output. .

  As described above, the optical receiving apparatus 205 is different only in that the FM demodulating unit 25 is used instead of the phase demodulating unit 24 in the optical receiving apparatus 20 of the first embodiment.

  Since the FM demodulator 25 can be realized with a cheaper and simpler configuration than the phase demodulator 24, the optical receiver 205 can be simplified.

  Although the optical transmitter 105 is complicated by the addition of the integrating circuit 19, the FM demodulator 25 of the optical receiver 205 can be realized with a simpler configuration than the phase demodulator 24. When the receiving device 205 is connected, the configuration of the entire optical transmission system can be simplified.

  In the fourth embodiment, an FM modulation signal corresponding to the electrical signal from the second signal source 50 is transmitted, whereas in the first and second embodiments, the second signal source 50 Some signals are different in that a phase-modulated signal corresponding to the electrical signal is transmitted, and the other signals are the same as those of the optical transmission system in the first and second embodiments.

  As described above, according to the optical transmission device of the fourth embodiment, it is possible to further increase the number of channels to be transmitted without adding a frequency converter while simplifying the optical reception device. Further, according to the optical receiver of the fourth embodiment, it is possible to further increase the number of channels to be received without adding a frequency converter while simplifying the configuration. Further, according to the optical transmission system of the fourth embodiment, it is possible to further increase the number of channels to be transmitted without adding a frequency converter while simplifying the configuration. Furthermore, when using the same number of channels, the required characteristics of the phase modulation section and the like can be relaxed, so that the cost of the optical transmitter, optical receiver, or optical transmission system can be reduced.

  The optical transmission device, the optical reception device, and the optical transmission system according to the present invention have an effect that the number of channels to be transmitted can be further increased without adding a frequency converter, and are useful as optical communication, optical CATV, and the like. It is.

1 is a block diagram showing a configuration of an optical transmission system according to Embodiment 1 of the present invention. Spectrum diagram for explaining signals of respective parts of the optical transmission system in Embodiment 1 of the present invention The block diagram which shows the structure of the optical transmission system in Embodiment 2 of this invention. Block diagram showing a configuration of an optical transmission system according to Embodiment 3 of the present invention. Block diagram showing a configuration of an optical transmission system according to a fourth embodiment of the present invention. Block diagram showing the configuration of a conventional optical transmission system

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 103, 104, 105 Optical transmitter 11 Single mode light source 12 External intensity modulation part 13 Phase modulation part 14 Local light source 15 Optical coupler 16, 26 Optical detection part 17 Optical transmission part 18 Optical intensity modulator 19 Integration circuit 20 , 204, 205 Optical receiver 21 O / E converter 22 Branching unit 24 Phase demodulator 25 FM demodulator 30 Optical fiber 40 First signal source 50 Second signal source

Claims (9)

A single mode light source that outputs single mode light;
An external intensity modulator that modulates the intensity of light output from the single-mode light source with an electrical signal from a first signal source;
A phase modulation unit that further phase-modulates the optical signal output from the external intensity modulation unit with an electric signal from a second signal source;
A local light source that outputs local oscillation light having an optical frequency different from that of the output light of the phase modulation unit;
An optical coupler that combines the optical signal output from the phase modulation unit and the local oscillation light output from the local light source;
An optical detector for heterodyne detection of the optical signal combined by the optical coupler, and outputting an electric signal having an intermediate frequency between the optical frequency of the output of the phase modulator and the optical frequency of the local light source; ,
An optical transmitter that outputs an optical signal that is intensity-modulated by a light source and transmitted to an optical transmission line by an electrical signal output from the optical detector;
An optical transmitter characterized by comprising: A light intensity modulation unit comprising an optical integrated device in which a semiconductor laser element and a light intensity modulator are integrated, and an electric signal is input from a first signal source and an intensity-modulated optical signal is output;
A phase modulation unit that further phase-modulates the optical signal output from the light intensity modulation unit with an electrical signal from a second signal source;
A local light source that outputs local oscillation light having an optical frequency different from that of the output light of the phase modulation unit;
An optical coupler that combines the optical signal output from the phase modulation unit and the local oscillation light output from the local light source;
An optical detector for heterodyne detection of the optical signal combined by the optical coupler, and outputting an electric signal having an intermediate frequency between the optical frequency of the output of the phase modulator and the optical frequency of the local light source; ,
An optical transmitter that outputs an optical signal that is intensity-modulated by a light source and transmitted to an optical transmission line by an electrical signal output from the optical detector;
An optical transmitter characterized by comprising: A single mode light source that outputs single mode light;
An external intensity modulator that modulates the intensity of light output from the single-mode light source with an electrical signal from a first signal source;
A phase modulation unit that further phase-modulates the optical signal output from the external intensity modulation unit with an electric signal from a second signal source;
A local light source that outputs local oscillation light having an optical frequency different from that of the output light of the phase modulation unit;
An optical coupler that combines the optical signal output from the phase modulation unit and the local oscillation light output from the local light source;
An optical transmitter characterized by comprising: A single mode light source that outputs single mode light;
An external intensity modulator that modulates the intensity of light output from the single-mode light source with an electrical signal from a first signal source;
An integrating circuit for outputting an electric signal obtained by integrating the electric signal from the second signal source;
A phase modulation unit that further phase-modulates the optical signal output from the external intensity modulation unit with the electrical signal output from the integration circuit;
A local light source that outputs local oscillation light having an optical frequency different from that of the output light of the phase modulation unit;
An optical coupler that combines the optical signal output from the phase modulation unit and the local oscillation light output from the local light source;
An optical detector for heterodyne detection of the optical signal combined by the optical coupler, and outputting an electric signal having an intermediate frequency between the optical frequency of the output of the phase modulator and the optical frequency of the local light source; ,
An optical transmitter that outputs an optical signal that is intensity-modulated by a light source and transmitted to an optical transmission line by an electrical signal output from the optical detector;
An optical transmitter characterized by comprising: The signal input from the first signal source is an FM signal or a digital modulation signal,
The signal input from the second signal source is an AM signal or a QAM signal.
The optical transmission device according to claim 1, wherein the optical transmission device is an optical transmission device. An optical transmission device according to any one of claims 1 to 5,
An optical receiver that receives an optical signal transmitted from the optical transmitter and outputs an electrical signal from the first signal source and a signal corresponding to the electrical signal from the second signal source;
An optical transmission system comprising: An O / E converter that receives an optical signal transmitted from the optical transmission device according to claim 1 or 2 through an optical transmission line and outputs the optical signal as an electrical signal,
Branching the electrical signal output from the O / E converter,
Outputting one of the branched branches as a first signal output;
Phase-demodulating the other branched and outputting as a second signal output;
An optical receiver characterized by that. An optical detection unit that receives an optical signal transmitted from an optical transmission device according to claim 3 through an optical transmission line, performs heterodyne detection, and outputs an electrical signal;
Branch the electrical signal output from the optical detector,
Outputting one of the branched branches as a first signal output;
Phase-demodulating the other branched and outputting as a second signal output;
An optical receiver characterized by that. An O / E converter that receives an optical signal transmitted from an optical transmission device according to claim 4 through an optical transmission path and outputs the optical signal as an electrical signal,
Branching the electrical signal output from the O / E converter,
Outputting one of the branched branches as a first signal output;
FM demodulating the other branched and outputting as a second signal output,
An optical receiver characterized by that.

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