JP2008263375A - Optical transmitter, optical receiver, and optical communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmitter which is superior in expandability in increasing the capacity of a system, by reducing the number of optical components and increasing the number of wavelength channels. <P>SOLUTION: This light transmitter 1 is provided with a sweep light source (wavelength sweep-out type light source ) 11 for sweeping out the wavelength of an output optical signal at a prescribed repetition frequency; a light modulator 12 for modulating the output light signal of the sweep light source 11 by a base-band signal; and a distribution medium 13 for applying delay time different, according to the wavelength with respect to the output optical signal of the light modulator 12. Thus, it is possible to output the optical signals of a plurality of channels in batch, with simple configurations by using a single light source and a single light modulator. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention provides an optical transmitter that outputs a modulated optical signal having a plurality of wavelengths modulated by a baseband signal, and receives the modulated optical signal having a plurality of wavelengths that is modulated by a baseband signal and performs coherent detection using local light. The present invention relates to an optical receiver that demodulates a baseband signal, and an optical communication system that includes these optical transmitter and optical receiver.

  In an optical communication system that transmits modulated optical signals of multiple wavelengths, high wavelength selectivity is achieved without using an optical filter by coherent detection using a local optical signal when the optical receiver receives the modulated optical signal. A method has been proposed (see Non-Patent Document 1).

  As an example, FIGS. 20 and 21 show conventional optical communication systems that extract signals of desired wavelength channels from optical signals of a plurality of wavelengths by coherent detection. FIG. 20 shows a configuration example of an optical transmission device of a conventional optical communication system and signals in the configuration examples 9a and 9b. The optical transmission device 41 generates a multi-wavelength optical signal (9a) with a predetermined wavelength interval with the multi-wavelength light source 43, demultiplexes with the wavelength demultiplexer 44, and then supports each wavelength channel with the optical modulator 45. Modulated by the transmission data signal, combined by the wavelength multiplexer 46, and transmitted to the optical receiving device.

  FIG. 21 shows a configuration example of an optical receiver of a conventional optical communication system and signals in the configuration examples 9b, 9c, 9d, and 9e. The extraction of a data signal of a desired wavelength channel from a modulated optical signal having a plurality of wavelengths in the optical receiver 42 will be described with reference to FIG. The optical receiver 42 combines the received optical signal (9b) with the local light which is the optical signal of the single spectrum light source 47 in the optical multiplexer 48, and the combined signal (9c) is received by the light receiving element 49. By receiving light, coherent detection is performed to generate an output electric signal (9d). Here, by setting the wavelength of the local light so as to be close to the desired wavelength channel among the received optical signals, the filter 50 in the subsequent stage of the light receiving element 49 has the data signal included in the desired wavelength channel. Only the electric signal can be extracted, and the data signal (9e) of the desired wavelength channel can be reproduced by demodulating the output electric signal of the filter 50 by the demodulator 51.

  Furthermore, if a wavelength tunable light source is used as a light source for outputting local light, the wavelength channel to be extracted can be selectively changed, so that an optical signal transmitted from the optical transmission device can be transmitted to the user by wavelength division multiplexing (WDM) transmission. Multiplexing / service multiplexing and an optical receiving apparatus can realize a flexible optical communication system that extracts a desired signal from a WDM signal as necessary without using a wavelength filter with fixed pass characteristics and the like. .

  Further, the local light does not necessarily have to be in a non-modulated single spectrum state, and as shown in Non-Patent Document 1, even if the wavelength of the local light changes at high speed, the modulation of the modulated optical signal to be received is performed. The desired data can be received if it does not interfere with the component (for example, the amplitude component). As a result, the light source that outputs the local light can be shared as a light source for uplink data transmission from the optical receiver to the optical transmitter.

In this way, in an optical communication system that transmits optical signals of a plurality of wavelengths from an optical transmitter, an optical filter can be used by using a wavelength tunable light source that can arbitrarily set the wavelength of an output optical signal as local light in an optical receiver. High wavelength selectivity can be realized without using it.
Sei Narukawa, Hiroaki Sanjo, Naoya Sakurai, Kiyomi Kumozaki, Takamasa Imai “Transmission / Local Light Source Sharing Using Direct Modulation in Optical FDM Access” 2005 IEICE Communication Society Conference, B-10-57, (2005)

  In the case of the conventional optical communication system described above, an optical tuner function that extracts only a desired optical signal from optical signals of many wavelengths is realized by performing coherent detection using a single-spectrum optical carrier signal as local light. However, on the optical transmitter side, in order to generate optical signals with multiple wavelengths according to the number of channels, it is necessary to install a large number of light sources and optical modulators. Scalability is poor when the capacity is increased to increase the capacity of the system.

  In addition, there is a problem that the reception rate of the signal that can be received by each optical receiving device is limited to the transmission rate per wavelength channel of the above-described optical signals having a plurality of wavelengths. As a means for solving this problem and making the reception rate variable, first, it is conceivable to simultaneously receive signals of a plurality of wavelength channels using a plurality of wavelengths of local light in each optical receiver. In addition, a local light source and a demodulation circuit corresponding to the number of wavelength channels to be received are required, and the configuration of the optical receiver becomes complicated. Secondly, in the optical transmission apparatus, means for changing the transmission rate of each wavelength channel as necessary is conceivable. In this case, it is necessary to install a transmission circuit having a variable modulation band corresponding to each wavelength. And the configuration becomes complicated.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical transmission apparatus having a simple configuration using a single light source and a single optical modulator, and having a plurality of channels. Optical communication system with excellent expandability by generating optical signals all at once and demodulating optical signals of multiple channels at once with a simple configuration using a single local light source. Is to provide.

  In order to achieve the above object, a first invention is an optical transmitter that outputs a modulated optical signal having a plurality of wavelengths modulated by a baseband signal, and sweeps the wavelength of the output optical signal at a predetermined repetition rate. A wavelength-swept light source, an optical modulator that modulates an output optical signal of the wavelength-swept light source with a baseband signal, and a dispersion medium that gives different delay times to the output optical signal of the optical modulator depending on the wavelength It is characterized by providing.

  According to the first aspect of the invention, the optical transmission device can generate optical signals of a plurality of channels at a time with a single light source (wavelength sweep type light source) and an optical modulator. Excellent scalability when increasing the capacity of an optical communication system by increasing the number of wavelength channels.

  A second invention is an optical transmitter that outputs modulated optical signals of a plurality of wavelengths modulated by a baseband signal, a pulsed light source that outputs a pulsed optical signal at a constant repetition frequency, and a pulsed light of the pulsed light source An optical chirp modulator that modulates a signal to chirp a wavelength at a predetermined repetition frequency, an optical modulator that modulates an output optical signal of the optical chirp modulator with a baseband signal, and an output light of the optical modulator And a dispersion medium that gives different delay times depending on wavelengths to the signal.

  A third invention is an optical transmitter that outputs a modulated optical signal having a plurality of wavelengths modulated by a baseband signal, and controls the power of the output light in accordance with a pulse of the input baseband signal, and at the same time, A high-speed frequency modulation light source capable of sweeping the wavelength of an output optical signal at a repetition frequency, and a dispersion medium that gives different delay times depending on the wavelength with respect to the output optical signal of the high-speed frequency modulation light source And

  A fourth invention is the optical transmission device according to any one of the first to third inventions, wherein the output optical signal of the dispersion medium is modulated to chirp the wavelength at a predetermined repetition frequency. A chirp modulator is provided.

  According to the second to fourth inventions, similarly to the first invention, the number of optical components of the optical transmission device is small, and the scalability when increasing the capacity of the optical communication system by increasing the number of wavelength channels is excellent.

A fifth invention is an optical receiver that receives a modulated optical signal having a plurality of wavelengths modulated by a baseband signal and demodulates the baseband signal, and sweeps the wavelength of the output optical signal at a predetermined repetition rate. A coherent detection by receiving the output optical signal of the optical combiner, the optical combiner combining the modulated optical signal of the plurality of wavelengths and the output optical signal of the wavelength sweep optical source, A light receiving element, a filter that selectively passes only a predetermined frequency band of the output electric signal of the light receiving element, a demodulator that demodulates the output of the filter and reproduces the baseband signal,
It is characterized by providing.

  According to the fifth invention, it is possible to collectively receive optical signals of a plurality of wavelength channels among multi-wavelength optical signals to be received using only a single light source in the optical receiver. Further, by adjusting the wavelength sweep characteristic of the wavelength sweep type light source, the number of wavelength channels to be collectively received can be changed and the reception rate can be made variable.

  A sixth invention is an optical transmission device that outputs a modulated optical signal having a plurality of wavelengths modulated by a baseband signal, the wavelength sweeping type light source that sweeps the wavelength of the output optical signal at a predetermined repetition frequency, and And an optical modulator that modulates an output optical signal of the wavelength-swept light source with a baseband signal.

  According to the sixth aspect of the invention, the optical transmission device can collectively generate optical signals of a plurality of channels with a single light source (wavelength sweep type light source) and an optical modulator, and thus the number of optical components is small, Excellent scalability when increasing the capacity of an optical communication system by increasing the number of wavelength channels.

  A seventh invention is an optical transmission device that outputs modulated optical signals of a plurality of wavelengths modulated by a baseband signal, a pulsed light source that outputs a pulsed optical signal at a constant repetition frequency, and a pulsed light of the pulsed light source An optical chirp modulator that modulates a signal to chirp a wavelength at a predetermined repetition frequency, and an optical modulator that modulates an output optical signal of the optical chirp modulator with a baseband signal.

  An eighth invention is an optical transmitter that outputs a modulated optical signal having a plurality of wavelengths modulated by a baseband signal, and controls the power of the output light in accordance with a pulse of the input baseband signal, and at the same time, A high-speed frequency modulation light source capable of sweeping the wavelength of the output optical signal at a repetition frequency is provided.

  According to the seventh and eighth inventions, similarly, the number of optical components of the optical transmission device is small, and the scalability when the capacity of the optical communication system is increased by increasing the number of wavelength channels is excellent.

  A ninth aspect of the invention is an optical receiver that receives a modulated optical signal having a plurality of wavelengths modulated by a baseband signal and demodulates the baseband signal, and sweeps the wavelength of the output optical signal at a predetermined repetition rate. A wavelength-swept light source, a dispersion medium that gives different delay times to the modulated optical signals of the plurality of wavelengths, an output optical signal of the dispersion medium, and an output optical signal of the wavelength-swept light source An optical multiplexer, a light receiving element that performs coherent detection by receiving an optical signal output from the optical multiplexer, and a filter that selectively passes only a predetermined frequency band of the output electric signal of the light receiving element. And a demodulator that demodulates the output of the filter and regenerates the baseband signal.

  According to the ninth aspect of the present invention, it is possible to collectively receive optical signals of a plurality of wavelength channels among multi-wavelength optical signals to be received by using only a single light source in the optical receiver. Further, by adjusting the wavelength sweep characteristic of the wavelength sweep type light source, the number of wavelength channels to be collectively received can be changed and the reception rate can be made variable.

  In a tenth aspect of the invention, a modulated optical signal having a plurality of wavelengths modulated with a baseband signal is output from an optical transmission device, and transmitted to the optical reception device via an optical transmission line. The optical reception device transmits the modulated optical signal. In the optical communication system that receives and demodulates the baseband signal, the optical transmitter is any one of the first to fourth aspects of the invention, and the optical receiver is the light of the fifth aspect. It is a receiving apparatus, or the optical transmitting apparatus is any one of the sixth to eighth inventions, wherein the optical receiving apparatus is a ninth optical receiving apparatus.

  According to the tenth invention, since the optical transmission device can generate optical signals of a plurality of channels with a single light source (wavelength sweep type light source) and an optical modulator, the number of optical components is small, and in the optical reception device Because a single light source can be used to receive optical signals of multiple wavelength channels out of the received multi-wavelength optical signals, the number of wavelength channels can be increased to increase the capacity of the optical communication system. Excellent scalability when converting to Further, by adjusting the wavelength sweep characteristic of the wavelength sweep type light source of the optical receiver, the number of wavelength channels to be collectively received can be changed and the reception rate can be made variable.

As described above, the optical transmission apparatus of the present invention generates an optical signal whose wavelength is swept based on the output optical signal of a single light source, and modulates it with a baseband signal using a single optical modulator. Thus, optical signals of a plurality of channels having a spread on the time axis and the wavelength axis can be generated at a time.
The optical receiver of the present invention is limited to a single wavelength channel by coherently detecting received optical signals of a plurality of wavelengths using local light that has been swept in an arbitrary range at a predetermined repetition time. Without being able to receive signals of a plurality of wavelength channels at the same time, and by adjusting the wavelength sweep characteristic, the rate of the received signal can be made variable.
Due to the above effects, it is possible to provide an optical communication system that is more expandable than conventional techniques by using these optical transmitters and optical receivers.

Next, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 shows a configuration example of an optical transmission device of an optical communication system according to the first embodiment of the present invention, signals in 1a, 1b, and 1d of the configuration example, and dispersion characteristics of a dispersion medium. The optical transmission device 1 sweeps (sweeps) the wavelength of an output optical signal at a predetermined repetition frequency (period), and modulates the output optical signal of the sweep light source 11 with a baseband signal. And a dispersion medium 13 that gives different delay times to the output optical signal of the optical modulator 12 according to the wavelength.

  In the first embodiment, in the optical transmission device 1, the wavelength sweep optical signal (1a) output from the sweep light source 11 is optically modulated by a data signal obtained by multiplexing transmission data of each wavelength channel on the time axis. Modulator 12 The modulated optical signal (1b) indicates that the spectrum of the signal light is expanded by modulating the wavelength sweep signal light having a spectrum like 1a into a short pulse light by the optical modulator 12. Further, by passing the dispersion medium 13 having the dispersion characteristic shown in 1c, an optical signal (OTDM signal: 1b) in which data is time division multiplexed (TDM: Time Division Multiplexing) as shown in 1d is chirped ( After being converted into a multi-wavelength modulated signal (1d) having a symbol length (T), it is transmitted to the optical receiver.

  For example, as shown in FIG. 3, the wavelength sweep optical signal (1a) having a period T is applied to the direct modulation laser 19 that controls the output wavelength by changing the laser injection current, to the lamp waveform injection current having the period T. As shown in FIG. 4, the output of a laser (single spectrum light source) 20 is connected to a phase modulator 21, and a parabolic waveform having a period T is connected to the phase modulator 21. It can also be generated by inputting a voltage. Further, as shown in FIG. 5, an external resonator 22 is connected to one reflection end of the laser 23, and a control signal is input to the external resonator 22 to change the refractive index of the optical waveguide in the external resonator. Alternatively, the wavelength of the output optical signal can be swept (swept) by changing the angle between the external resonator and the optical path by mechanical rotation.

  FIG. 2 shows a configuration example of the optical receiver of the optical communication system according to the first embodiment of the present invention and signals in 1d, 1e, 1f, and 1g of the configuration example. The optical receiver 2 includes a sweep light source (wavelength sweep type light source) 14 that sweeps (sweeps) the wavelength of the output optical signal at a predetermined repetition frequency, a modulated optical signal having a plurality of wavelengths transmitted from the optical transmitter 1, and Of the optical multiplexer 15 that multiplexes the output optical signal of the sweep light source 14, the light receiving element 16 that receives the output optical signal of the optical multiplexer 15, and only the predetermined frequency band among the output electrical signals of the light receiving element 16 Filter 17 to be passed through, and demodulator 18 that demodulates the output of filter 17 and regenerates the baseband signal.

  The modulated optical signals (1d) having a plurality of wavelengths transmitted from the optical transmitter 1 are received by the optical receiver 2 shown in FIG. The optical receiver 2 includes a sweep light source 14 that sweeps the wavelength of the output optical signal at a constant repetition frequency, and uses the output light of the sweep light source 14 as local light. That is, the received modulated optical signals (1d) of a plurality of wavelengths are combined with the output optical signal of the sweep light source 14 in the optical multiplexer 15, and the combined signal indicated by 1e is received by the light receiving element 16 to be coherent. Perform detection. The output electric signal (1f) of the light receiving element 16 is selectively extracted by a filter 17 in a desired frequency band, and then demodulated by a demodulator 18 as indicated by 1g, and the data transmitted from the optical transmission device 1 is demodulated. Play a part.

  Here, it will be described that the reception rate can be varied by adjusting the sweep characteristic of the above-described sweep light source. First, when outputting the sweep light as in the time slot 1, only the data of the adjacent wavelength channel in the received optical signal is extracted by the filter. Similarly, it becomes equal to the transmission rate of each wavelength channel. On the other hand, if the wavelength of the output optical signal of the sweep light source is swept as shown in time slots 2 and 3, signals of a plurality of wavelength channels can be extracted by a filter in one time slot as shown in the figure. The reception rate of the optical receiver can be a multiple of the transmission rate of each wavelength channel. In this way, in the optical receiving apparatus, wavelength-multiplexed (WDM) signals are collectively used by using wavelength-swept light whose wavelength crosses for a plurality of channels of the optical signal transmitted from the optical transmitting apparatus. Thus, it can be converted into a time multiplexed (TDM) signal, and the reception rate can be varied by adjusting the sweep characteristics of the sweep light source.

  As described above, in the conventional technique, since an optical transmission circuit and an optical reception circuit are required for each wavelength channel, the number of optical transmission circuits and optical reception circuits increases as the number of wavelength channels increases. While the configuration of the optical transmitter and the optical receiver is complicated and expensive, in the present invention, by increasing the number of wavelength channels, the wavelength sweep range of the sweep light source of the optical transmitter and the optical receiver, and the optical transmitter Although it is necessary to increase the bandwidth of the optical modulator, the number of parts does not change. For this reason, it can be said that the complexity of the configuration of the optical transmission apparatus when the total transmission rate is increased by increasing the number of wavelength channels is more gradual and excellent in scalability than the conventional technology.

  As described above, the system in which the optical transmission device 1 and the optical reception device 2 are connected at a ratio of 1: 1 as illustrated in FIG. 6 has been described, but one optical transmission device 1 as illustrated in FIG. A so-called PON (Passive Optical Network) type system connected to a plurality of optical receivers 2 via a splitter 24, or an output optical signal of one optical transmitter 1 as shown in FIG. Thus, application to a so-called WDM (Wavelength Division Multiplexing) -PON system that is transmitted to a plurality of different optical receivers 2 according to each wavelength is also possible.

  Also, in FIG. 1, an optical signal (OTDM signal: 1b) obtained by time-division multiplexing (TDM) of data is converted into a chirped multi-wavelength modulation signal (1d) by a dispersion medium installed in the optical transmission device. However, this dispersion medium may not be installed in the optical transmission device but may be installed before the optical multiplexer of the optical reception device.

  In this case, the optical receiver performs the above-described conversion on the OTDM signal (1b) transmitted from the optical transmitter, and performs coherent detection using the wavelength sweep light, thereby obtaining a desired single OTDM signal. Only data in one or more OTDM time slots can be extracted (so-called DEMUX) and received. This optical communication system will be described with reference to FIG.

  FIG. 9 shows a configuration example of the optical transmission device and the optical reception device when the dispersion medium is installed in the optical reception device instead of the optical transmission device, and signals in the configuration examples 8a, 8b, 8c, 8d, and 8e. . The optical transmission device 1 includes a sweep light source (wavelength sweep type light source) 11 that sweeps (sweeps) the wavelength of an output optical signal at a predetermined repetition frequency, and optical modulation that modulates the output optical signal of the sweep light source 11 with a baseband signal. The optical receiver 2 includes a sweep light source (wavelength sweep type light source) 14 that sweeps (sweeps) the wavelength of the output optical signal at a predetermined repetition frequency, and a plurality of wavelengths transmitted from the optical transmitter 1. A dispersion medium 13 that gives different delay times depending on the wavelength, an optical multiplexer 15 that combines the output optical signal of the dispersion medium 13, and the output optical signal of the sweep light source 14, and an optical multiplexer. A light receiving element 16 that performs coherent detection by receiving 15 output optical signals, and a filter 17 that selectively passes only a predetermined frequency band of the output electrical signals of the light receiving element 16; It demodulates the output of the filter 17, and a demodulator 18 for reproducing a baseband signal.

  The optical transmitter 1 transmits an OTDM signal (8a: equivalent to 1b in FIG. 1) in which data is time-division multiplexed modulated based on a wavelength-swept optical signal having a period T. Here, as indicated by 8a in FIG. 9, the data of each time channel is represented as OTDM time slot n (n = 1, 2, 3,...). In the optical receiver 2, the received optical signal (8 a) is input to the dispersion medium 13 having the same dispersion characteristics as 1 c in FIG. 1, and the multi-wavelength modulation signal 8 b (1 d in FIG. Equivalent). As shown in the figure, in this process, each of the OTDM time slots n (n = 1, 2, 3,...) Is converted into optical signals having different wavelengths.

  The output optical signal 8b of the dispersion medium 13 is combined with the local light that is the output optical signal of the sweep light source 14 in the optical multiplexer 15, and the combined signal shown in 8c is received by the light receiving element 16. Perform coherent detection. The output electric signal (8d) of the light receiving element 16 is selectively extracted by a filter 17 in a desired frequency band, and then demodulated in a demodulator 18 as indicated by 8e to reproduce data.

  Here, when focusing on the first cycle (the left cycle in the figure), only the data of the OTDM time slot 1 in the received optical signal (8a) is extracted by the filter. It can be seen that "DEMUX reception of a single OTDM time slot" can be realized. On the other hand, when the wavelength of the output optical signal of the sweep light source is swept as in the second and third periods, as shown in the figure, among the received optical signals 8a, in the second period, the OTDM time slots 1 and 2 Since the data and the data of the OTDM time slots 1, 2 and 3 can be collectively extracted by the filter in the second period, it can be understood that the above-mentioned “DEMUX reception of a plurality of desired OTDM time slots” can be realized.

  In addition, when the optical transmission path between the optical transmission device and the optical reception device has a dispersion characteristic equivalent to that of the above-described dispersion medium, the above-described optical transmission path is not used in the optical transmission device and the optical reception device. Since the conversion is performed, similarly, the OTDM signal (8a) transmitted from the optical transmission device can be DEMUX-received by the optical reception device.

(Second Embodiment)
FIG. 10 shows a configuration example of an optical transmission apparatus of an optical communication system according to the second embodiment of the present invention, signals in the configuration examples 2a, 2c, 2d, and 2f, chirp characteristics of an optical chirp modulator, and dispersion. The dispersion characteristics of the medium are shown. The optical transmission device 1 includes a pulse light source 26 that outputs a pulsed light signal at a constant repetition frequency, and an optical chirp modulator 27 that performs modulation for chirping a wavelength at a predetermined repetition frequency on the pulsed light signal of the pulse light source 26. An optical modulator 28 that modulates the output optical signal of the optical chirp modulator 27 with a baseband signal, and a dispersion medium 29 that gives different delay times to the output optical signal of the optical modulator 28 according to the wavelength. The configuration of the optical receiver of the optical communication system according to the second embodiment is the same as that of the optical receiver of the optical communication system according to the first embodiment shown in FIG.

  In the second embodiment, in the optical transmission device 1, the pulse optical signal (2a) output from the pulse light source 26 with a constant repetition frequency is repeatedly fixed by the optical chirp modulator 27 having the chirp characteristic shown in 2b. Chirp wavelength with frequency. The optical signal (2c) obtained in this modulation process is modulated by a data signal obtained by multiplexing the transmission data of each wavelength channel on the time axis in the optical modulator 28 to generate a modulated optical signal (2d). By passing through the dispersion medium 29 having the dispersion characteristic shown in 2e, a multi-wavelength modulated optical signal having a chirped wavelength at a constant repetition frequency is generated as shown in 2f and transmitted to the optical receiver.

  Here, the above-described optical chirp modulator 27 can be realized, for example, by applying a parabolic waveform voltage to the phase modulator 30 as shown in FIG.

As can be seen from FIG. 10, the transmission optical signal (2f) obtained by the optical transmission apparatus of the second embodiment is the same as the transmission optical signal (1d) in the first embodiment. In the same manner as in the case of increasing the total transmission rate by increasing the number of wavelength channels, the optical spectrum of the pulsed light of the optical transmission device, the optical chirp modulator, the optical modulator that modulates transmission data, and the optical reception device Although it is necessary to widen the wavelength sweep range of the sweep light source, the number of parts does not change, and therefore, the scalability is superior to the conventional technology.
Note that the dispersion medium 29 may be installed in the preceding stage of the optical multiplexer of the optical receiver 2 instead of being installed in the optical transmitter 1 as in the optical communication system shown in FIG.

(Third embodiment)
FIG. 12 shows a configuration example of an optical transmission apparatus of an optical communication system according to the third embodiment of the present invention, signals in the configuration examples 3a and 3c, and dispersion characteristics of a dispersion medium. The optical transmission device 1 controls the power of the output light according to the pulse of the input baseband signal, and at the same time, the high-speed frequency modulation light source 31 capable of sweeping the wavelength of the output optical signal at a predetermined repetition frequency, And a dispersion medium 32 that gives different delay times to the output optical signal of the frequency modulation light source 31 depending on the wavelength. The configuration of the optical receiver of the optical communication system according to the third embodiment is the same as that of the optical receiver of the optical communication system according to the first embodiment shown in FIG.

  In the third embodiment, in the optical transmission device 1, the power and wavelength of the output optical signal are controlled by the data signal obtained by multiplexing the transmission data of each wavelength channel on the time axis using the high-speed frequency modulation light source 31. Then, a multi-wavelength modulation signal as shown in 3a (an optical signal similar to 1b in the first embodiment and 2d in the second embodiment) is generated, and further, a dispersion medium 32 having the dispersion characteristics shown in 3b is provided. By passing, as shown in 3c, a multi-wavelength modulated optical signal having a chirped wavelength at a constant repetition frequency is generated and transmitted to the optical receiver.

  Such a high-speed frequency modulation light source 31 can be realized, for example, by controlling a wavelength control signal at high speed using a DBR (Distributed Bragg Reflector) type laser.

As shown in FIG. 12, the transmission optical signal 3c obtained by the optical transmission apparatus of the third embodiment includes the transmission optical signal (1d) in the first embodiment and the transmission optical signal (2f) in the second embodiment. Therefore, as in the first and second embodiments, when the capacity of the total transmission rate is increased by increasing the wavelength channel, the optical spectrum of the pulse light of the optical transmission device, the optical chirp modulator, Although it is necessary to widen the wavelength sweep range of the optical modulator that modulates the transmission data and the sweep light source of the optical receiver, the number of parts does not change, and the scalability is superior to that of the conventional technology.
Note that the dispersion medium 32 may be installed in the preceding stage of the optical multiplexer of the optical receiver 2 instead of being installed in the optical transmitter 1 as in the optical communication system shown in FIG.

(Fourth embodiment)
FIG. 13 shows a configuration example of an optical transmission device of an optical communication system according to the fourth embodiment of the present invention, signals in 4a and 4c of the configuration example, and chirp modulator characteristics. In the first to third embodiments, modulated optical signals (1d, 2f, 3c) having a plurality of wavelengths each chirped at a constant repetition frequency are transmitted. As shown in FIG. The optical signal (4a = 1d, 2f, 3c) output from the dispersion medium of the optical transmitter 33 in the third embodiment is repeatedly repeated by the optical chirp modulator 34 having the chirp modulator characteristics shown in 4b. By chirping the wavelength by frequency, it is also possible to generate a modulated optical signal (4c) having a plurality of wavelengths in which the wavelength of the signal of each wavelength channel is not chirped, similar to the transmission optical signal (9b) in the prior art. is there.

(Fifth embodiment)
Also, the optical receiver shown in FIG. 2 can be combined with the conventional optical transmitter shown in FIG. 20 to form a system. At this time, it is necessary to install as many optical transmission circuits as the number of channels in the optical transmission device. However, in the optical reception device, only a single local light source (sweep light source) is used as in the first to fourth embodiments. It is possible to collectively receive a desired plurality of channels among the received optical signals of the plurality of channels, and the reception rate can be varied by adjusting the sweep characteristics of the sweep light source.

  Here, for example, as shown in FIG. 14, the multi-wavelength light source shown in FIG. 20 can be generated by combining outputs of a plurality of single spectrum light sources that output optical carrier signals having different wavelengths. Further, as shown in FIGS. 15 and 16, a supercontinuum light source that inputs an electric carrier signal and outputs a multi-wavelength optical carrier signal having a wavelength interval equal to the frequency of the electric carrier signal, or a mode-locked light source Can also be generated.

  Here, as in the first to third embodiments, a case where a modulated optical signal (1d, 2f, 3c) having a plurality of wavelengths chirped at a constant repetition frequency is transmitted from the optical transmitter, FIG. 17 shows the difference in the number of channels that can be collectively received when transmitting modulated optical signals (4c, 9b) having a plurality of wavelengths in which the wavelength of each wavelength channel signal is not chirped as in the fifth embodiment. It explains using. FIG. 17 shows the simultaneous reception of a plurality of channels by coherent detection using wavelength sweep light in the optical receiver when the wavelength of each wavelength channel signal is not chirped and when the wavelength is chirped at a constant repetition frequency. The situation is shown in comparison. As is apparent from the figure, even when the sweep wavelength range of the wavelength sweep light used as the local light in the optical receiver is equal, in the first to third embodiments, the wavelength chirp characteristics of the received optical signal and the local light When the wavelength sweep characteristic of the wavelength sweep light to be used has a reverse polarity, signals of more wavelength channels can be received. Therefore, the number of channels that can be collectively received is larger than in the fourth and fifth embodiments. I understand that I can do it.

(Sixth embodiment)
In the first to fifth embodiments, it is assumed that the light receiving element, the filter, and the demodulator in the optical receiver have sufficient band characteristics corresponding to the variable reception rate range. Even when these optical components and electronic components do not have a sufficient band, the effect of varying the reception rate will be described with reference to FIG.

  FIG. 18 assumes the optical transmission apparatus in the first to third embodiments, and the optical reception apparatus has the same configuration as that shown in FIG. Here, it is assumed that the light receiving element 16, the filter 17, and the demodulator 18 have only band characteristics corresponding to the repetition frequency of the time slot shown in the figure. In the optical receiver 2, the optical signal (6 a) transmitted from the optical transmitter is combined with the local light that is the wavelength sweep light in the optical multiplexer 15, and the combined signal (6 b) is received by the light receiving element 16. Coherent detection is performed by receiving light. Depending on the state of the signal in each time slot, the electrical signal shown in 6c is output from the light receiving element 16, and a desired frequency band is selectively extracted by the filter 17, and then demodulated by the demodulator 18 to 6d. The signal shown is output.

  As assumed in the first to fifth embodiments, when the optical component and electronic component of the optical receiver have sufficient band characteristics, they are included in the multiple wavelength channels as indicated by the dotted line in 6d. However, if it has only band characteristics corresponding to the repetition frequency of the time slot as described above, it is indicated by a dotted line as shown by a solid line in 6d. A waveform obtained by integrating the indicated waveform is output. In practice, the integrated waveform is a waveform with a dull rise and fall, but here, the dullness of this waveform is simply ignored. As is apparent from the figure, the output waveform in this case becomes a multi-value amplitude signal in accordance with the data signal states of a plurality of channels. That is, by transmitting transmission data between a plurality of wavelength channels from an optical transmission device in a multi-value amplitude modulation format, the optical reception device develops a wavelength-multiplexed (WDM) data signal on the amplitude axis and multi-values. It means that it can be reproduced as a data signal.

  As described above, it is understood that the variable reception rate can be realized by the optical communication system of the present invention even when the band characteristics of the optical component and the electronic component of the optical receiver are not sufficient.

(Seventh embodiment)
In any of the above embodiments, as shown in FIGS. 6 to 8, a system for transmitting from a single optical transmission device to a single or a plurality of optical reception devices has been described. However, the optical reception device shown in FIG. As shown in FIG. 19, the present invention can also be applied to a system in which optical signals from a plurality of optical transmission devices are wavelength-multiplexed (WDM) and transmitted to a single optical reception device. In this case, as shown in 7a, the optical receiving apparatus performs coherent detection on the received WDM signal (λ1,..., ΛN) using the local light having a swept wavelength, so that the fourth and fifth Similarly to the embodiment, it is possible to collectively receive the received optical signals of a plurality of channels.

It is a figure which shows the optical transmitter of the 1st Embodiment of this invention. It is a figure which shows the optical receiver of the 1st Embodiment of this invention. It is a figure which shows the structural example of a sweep light source. It is a figure which shows the structural example of a sweep light source. It is a figure which shows the structural example of a sweep light source. It is a figure which shows the topology of the optical communication system to which this invention is applied. It is a figure which shows the topology of the optical communication system to which this invention is applied. It is a figure which shows the topology of the optical communication system to which this invention is applied. It is a figure which shows the structural example which installs a dispersion medium in an optical receiver. It is a figure which shows the optical transmitter of the 2nd Embodiment of this invention. It is a figure which shows the structural example of an optical chirp modulator. It is a figure which shows the optical transmission apparatus of the 3rd Embodiment of this invention. It is a figure which shows the optical transmission apparatus of the 4th Embodiment of this invention. It is a figure which shows the structural example of the multiwavelength light source in the optical transmission apparatus in 5th Embodiment. It is a figure which shows the structural example of the multiwavelength light source in the optical transmission apparatus in 5th Embodiment. It is a figure which shows the structural example of the multiwavelength light source in the optical transmission apparatus in 5th Embodiment. It is a figure which shows the principle of reception rate variable. It is a figure which shows the optical receiver of the 6th Embodiment of this invention. It is a figure which shows the optical communication system of the 7th Embodiment of this invention. It is a figure which shows the optical transmitter of the conventional optical communication system. It is a figure which shows the optical receiver of the conventional optical communication system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,41 Optical transmitter 2,42 Optical receiver 11,14 Sweep light source 12,28,45 Optical modulator 13,29,32 Dispersion medium 15,48 Optical multiplexer 16,49 Light receiving element 17,50 Filter 18,51 Demodulator 19 Direct modulation laser 20, 23 Laser 21, 30 Phase modulator 22 External resonator 24 Power splitter 25 Wavelength splitter 26 Pulse light source 27, 34 Optical chirp modulator 31 High-speed frequency modulation light source 43 Multi-wavelength light source 44 Wavelength demultiplexer 46 Wavelength multiplexer 47 Single spectrum light source

Claims (10)

An optical transmitter that outputs a modulated optical signal having a plurality of wavelengths modulated by a baseband signal,
A wavelength-swept light source that sweeps the wavelength of the output optical signal at a predetermined repetition rate;
An optical modulator that modulates an output optical signal of the wavelength-swept light source with a baseband signal;
A dispersion medium that gives different delay times depending on the wavelength to the output optical signal of the optical modulator;
An optical transmission device comprising: An optical transmitter that outputs a modulated optical signal having a plurality of wavelengths modulated by a baseband signal,
A pulsed light source that outputs a pulsed light signal at a constant repetition frequency;
An optical chirp modulator that modulates the pulsed light signal of the pulsed light source to chirp the wavelength at a predetermined repetition rate;
An optical modulator that modulates an output optical signal of the optical chirp modulator with a baseband signal;
A dispersion medium that gives different delay times depending on the wavelength to the output optical signal of the optical modulator;
An optical transmission device comprising: An optical transmitter that outputs a modulated optical signal having a plurality of wavelengths modulated by a baseband signal,
A high-speed frequency modulation light source capable of controlling the power of the output light according to the pulse of the input baseband signal and simultaneously sweeping the wavelength of the output optical signal at a predetermined repetition frequency;
A dispersion medium that gives different delay times depending on wavelengths to the output optical signal of the high-speed frequency modulation light source;
An optical transmission device comprising: The optical transmission device according to claim 1,
An optical transmission device comprising: an optical chirp modulator that modulates an output optical signal of the dispersion medium to chirp a wavelength at a predetermined repetition frequency. An optical receiver that receives a modulated optical signal of a plurality of wavelengths modulated by a baseband signal and demodulates the baseband signal,
A wavelength-swept light source that sweeps the wavelength of the output optical signal at a predetermined repetition rate;
An optical multiplexer that combines the modulated optical signals of the plurality of wavelengths and the output optical signal of the wavelength-swept light source;
A light receiving element that performs coherent detection by receiving an output optical signal of the optical multiplexer; and
Of the output electric signal of the light receiving element, a filter that selectively passes only a predetermined frequency band,
A demodulator that demodulates the output of the filter and regenerates the baseband signal;
An optical receiving device comprising: An optical transmitter that outputs a modulated optical signal having a plurality of wavelengths modulated by a baseband signal,
A wavelength-swept light source that sweeps the wavelength of the output optical signal at a predetermined repetition rate;
An optical modulator that modulates an output optical signal of the wavelength-swept light source with a baseband signal;
An optical transmission device comprising: An optical transmitter that outputs a modulated optical signal having a plurality of wavelengths modulated by a baseband signal,
A pulsed light source that outputs a pulsed light signal at a constant repetition frequency;
An optical chirp modulator that modulates the pulsed light signal of the pulsed light source to chirp the wavelength at a predetermined repetition rate;
An optical modulator that modulates an output optical signal of the optical chirp modulator with a baseband signal;
An optical transmission device comprising: An optical transmitter that outputs a modulated optical signal having a plurality of wavelengths modulated by a baseband signal,
An optical transmission device comprising: a high-speed frequency modulation light source capable of controlling the power of output light in accordance with a pulse of an input baseband signal and simultaneously sweeping the wavelength of the output optical signal at a predetermined repetition frequency . An optical receiver that receives a modulated optical signal of a plurality of wavelengths modulated by a baseband signal and demodulates the baseband signal,
A wavelength-swept light source that sweeps the wavelength of the output optical signal at a predetermined repetition rate;
A dispersion medium that gives different delay times according to the wavelengths for the modulated optical signals of the plurality of wavelengths;
An optical multiplexer that combines the output optical signal of the dispersion medium and the output optical signal of the wavelength-swept light source;
A light receiving element that performs coherent detection by receiving an output optical signal of the optical multiplexer; and
Of the output electric signal of the light receiving element, a filter that selectively passes only a predetermined frequency band,
A demodulator that demodulates the output of the filter and regenerates the baseband signal;
An optical receiving device comprising: A modulated optical signal of a plurality of wavelengths modulated with a baseband signal is output from the optical transmitter, transmitted to the optical receiver via an optical transmission line, and the modulated optical signal is received by the optical receiver to receive the baseband In an optical communication system that demodulates a signal,
The optical transmission device is any one of the optical transmission devices according to claims 1 to 4, wherein the optical reception device is the optical reception device according to claim 5, or the optical transmission device is 9. The optical communication apparatus according to claim 6, wherein the optical reception apparatus is the optical reception apparatus according to claim 9.

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