JP2008211713A - Optical transmission system, optical transmission method, and optical transmission apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve optical spectrum utilization efficiency. <P>SOLUTION: First electric IQ multiplexers (34a, 36a, 38a, 40a, 42a) apply electric IQ multiplexing to a first data signal (ch1(A)) and a second data signal (ch2(A)). Second electric IQ multiplexers (34a, 36b, 38b, 40b, 42b) electrically IQ multiplex a third data signal (ch1(B)) and a fourth data signal (ch2(B)). A laser light source (44) generates coherent laser light. An optical IQ multiplexer (46) uses the relevant coherent laser light outputted from the laser light source (44) to optically IQ multiplex outputted electric signals from the first and second electric IQ multiplexers. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical transmission system, an optical transmission method, and an optical transmission apparatus.

  Multilevel modulation schemes have a number of very important advantages over binary modulation schemes. At the same effective data rate, the signal speed of the multi-level modulation method is lower. Therefore, the multi-level modulation method causes inter-signal interference (ISI) such as polarization mode dispersion (PMD) and chromatic dispersion (CD). It has a higher tolerance for functional impairment. Furthermore, since the optical spectrum of the multi-level modulation method is very small, it is possible to narrow the WDM (wavelength division multiplexing) channel interval, and as a result, higher spectral efficiency can be realized.

One technique that is expected to increase spectral efficiency in optical fiber transmission is a subcarrier multiplexing (SCM) technique in the RF domain (Non-Patent Documents 1 and 2). Another interesting method is the use of Orthogonal Frequency Division Multiplexing (OFDM) (Non-Patent Documents 3 and 4).
J. Chen et al., "An integrated CMOS transceiver for a 40Gb / s SCM optical communication system", in proc. IEEE 2005 Custom integrated circuits conference, 7-6, pp. 135-138. S. Randel et al., "1 Gbit / s transmission with 6.3 bit / s / Hz spectral efficiency in a 100 m standard 1 mm step-index plastic optical fiber link using adaptive multiple sub-carrier modulation", in proc. ECOC PD Th4.4.1, pp. 41-42. A. Lowery et al., "Orthogonal frequency division multiplexing for adaptive dispersion compensation in long haul WDM systems", in proc. OFC PDP39. I. Djordjevic et al., "Orthogonal frequency division multiplexing for high-speed optical transmission", Optics Express, vol. 14, no. 9, pp. 3767-3775.

  SCM and OFDM can use the available bandwidth much more effectively than conventional modulation schemes, but do not provide infinite spectral efficiency.

  An object of the present invention is to provide an optical transmission system, an optical transmission method, and an optical transmission device that can realize high, for example, double spectral efficiency with a simple configuration.

  An optical transmission system according to the present invention is an optical transmission system that transmits first, second, third, and fourth data signals from an optical transmission device to an optical reception device via an optical transmission line. Characteristically, the optical transmitter has a first electrical IQ multiplexer that electrically multiplexes the first data signal and the second data signal, and an electrical IQ multiplex of the third data signal and the fourth data signal. The second electrical IQ multiplexer, the laser light source that generates coherent laser light, and the coherent laser light output from the laser light source are used to output electric signals from the first and second electrical IQ multiplexers. And an optical IQ multiplexer for optical IQ multiplexing. An optical receiver separates an optical signal input from the optical transmission line by optical IQ, and outputs a first received electrical signal and a second received electrical signal, and the first received electrical signal. A first electric IQ separation device for separating a first received data signal corresponding to the first data signal and a second received data signal corresponding to the second data signal from the signal; A third received data signal corresponding to the third data signal, and a second electrical IQ separation device for separating the fourth received data signal corresponding to the fourth data signal from the received electrical signal of It has.

  The optical transmission method according to the present invention includes a first electrical IQ multiplexing step of electrically IQ-multiplexing the first data signal and the second data signal to generate a first electrical IQ multiplexed signal, and third data The first and second data IQ signals are multiplexed by using the second electric IQ multiplexing step for generating the second electric IQ multiplexed signal and the coherent laser light output from the laser light source. The optical IQ multiplexing step of optical IQ multiplexing of the two electrical IQ multiplexed signals to generate the optical IQ multiplexed signal, the optical IQ multiplexed signal is optically IQ separated, and the first received electrical signal and the second received electrical signal are An optical IQ separation step for outputting, a first electrical IQ separation step for separating the first data signal and the second data signal from the first received electrical signal, and the second received electrical signal from the first received electrical signal Third data Characterized by including item and a second electric IQ separation step of separating the fourth data signal.

  An optical transmitter according to the present invention electrically IQ multiplexes a first data IQ multiplex device that electrically IQ multiplexes a first data signal and a second data signal, and a third data signal and a fourth data signal. Using the second electrical IQ multiplexer, a laser light source that generates coherent laser light, and the coherent laser light output from the laser light source, the output electrical signals of the first and second electrical IQ multiplexers are optically transmitted. And an optical IQ multiplexer that performs IQ multiplexing.

  According to the present invention, by using both electrical IQ multiplexing and optical IQ multiplexing, not only the amplitude of the optical signal but also the optical phase can be used together, and the utilization efficiency of the optical spectrum is improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic block diagram of an optical transmitter of an optical transmission system according to an embodiment of the present invention, and FIG. 2 shows a schematic block diagram of the optical receiver. The optical transmitter 10 generates an optical signal that carries data DATA-A and DATA-B, and outputs the optical signal to the optical fiber transmission line 12. The optical receiver 14 receives an optical signal from the optical fiber transmission line 12 and restores data DATA-A and DATA-B.

  The configuration and operation of the optical transmission device 10 shown in FIG. 1 will be described. Characteristically, this embodiment uses both electrical IQ multiplexing and optical IQ multiplexing.

  The OFDM modulator 20a performs OFDM modulation on the data DATA-A. Specifically, the digital modulator 22a digitally modulates the data DATA-A by a multi-level modulation method such as 4-QAM, 16-QAM, or 64-QAM. An inverse Fourier transform (IFFT) circuit 24a performs inverse Fourier transform on the outputs of the plurality of channels of the digital modulator 22a. A parallel / serial (P / S) converter 26a converts the outputs of the plurality of channels of the IFFT circuit 24a into one serial signal.

  The switch 28a alternately separates the output of the P / S converter 26a into two channels at a constant cycle, and supplies them to the buffers 30a and 32a. The buffers 30a and 32a output input data at a rate of 1/2. The switch 28a and the buffers 30a and 32a function as a device that separates serial data into two parallel channels ch1 (A) and ch2 (A). Obviously, this function may be incorporated into the P / S converter 26a.

  The D / A converter 34a converts the data signal of channel ch1 (A) from the buffer 30a into an analog signal, and the D / A converter 36a converts the data signal of channel ch2 (A) from the buffer 32a into an analog signal. Convert to The multiplier 38a up-converts the output signal of the D / A converter 34a by multiplying the output signal of the D / A converter 34a by a cosine wave cos (ωt). The multiplier 40a up-converts the output signal of the D / A converter 36a by multiplying the output signal of the D / A converter 36a by a sine wave sin (ωt). The mixer 42a mixes or multiplexes the output signals of the multipliers 38a and 40a. Thus, the data of the channels ch1 (A) and ch2 (A) are electrically multiplexed with the in-phase (I) component and the quadrature (Q) component.

  Similarly, the OFDM modulator 20b performs OFDM modulation on the data DATA-B. Specifically, the digital modulator 22b digitally modulates the data DATA-B using a multi-level modulation method such as 4-QAM, 16-QAM, or 64-QAM. An inverse Fourier transform (IFFT) circuit 24b performs inverse Fourier transform on the outputs of the plurality of channels of the digital modulator 22b. A parallel / serial (P / S) converter 26b converts the outputs of the plurality of channels of the IFFT circuit 24b into one serial signal.

  The switch 28b alternately separates the output of the P / S converter 26b into two channels at a constant period and supplies them to the buffers 30b and 32b. The buffers 30b and 32b output the input data at a rate of 1/2. The switch 28b and the buffers 30b and 32b function as a device that separates serial data into two parallel channels ch1 (B) and ch2 (B). Obviously, this function may be incorporated into the P / S converter 26b.

  The D / A converter 34b converts the data of the channel ch1 (B) from the buffer 30b into an analog signal, and the D / A converter 36b converts the data of the channel ch2 (B) from the buffer 32b into an analog signal. To do. The multiplier 38b upconverts the output signal of the D / A converter 34b by multiplying the output signal of the D / A converter 34b by the cosine wave cos (ωt). The multiplier 40b multiplies the output signal of the D / A converter 36b by a sine wave sin (ωt) to up-convert the output signal of the D / A converter 36b. The mixer 42b mixes or multiplexes the output signals of the multipliers 38b and 40b. Thus, the data of the channels ch1 (B) and ch2 (B) are electrically multiplexed with the in-phase (I) component and the quadrature (Q) component.

  The electrical IQ multiplexed angular frequency ω for the data DATA-A may or may not coincide with the electrical IQ multiplexed angular frequency ω for the data DATA-B.

  The laser diode (LD) 44 generates coherent laser light serving as an optical carrier, and the output light is supplied to an optical IQ multiplexer 46 that uses a Mach-Zehnder (MZ) interferometer structure. That is, the optical demultiplexer 48 of the optical IQ multiplexer 46 divides the output light of the LD 44 into two and applies one to the optical modulator 50 on the first arm and the other to the light on the second arm. Applied to the modulator 52. A phase shifter 54 that shifts the optical phase by π / 2 is disposed on the second arm. The optical modulator 50 modulates the laser light from the optical demultiplexer 48 in accordance with the output electric signal Sa of the mixer 42a. On the other hand, the optical modulator 52 modulates the laser light from the optical demultiplexer 48 in accordance with the output electric signal Sb of the mixer 42b. The phase shifter 54 shifts the optical phase of the output light from the optical modulator 52 by π / 2. Thus, the two signal lights input to the optical multiplexer 56 have an optical phase difference of 90 degrees and are orthogonal to each other. The optical multiplexer 56 combines the output light of the optical modulator 50 and the output light of the phase shifter 54. As a result, an optical IQ multiplexed signal that carries the signal Sa by the optical I component and the signal Sb by the optical Q component is generated, and this optical IQ multiplexed signal is output to the optical fiber transmission line 12.

  The optical modulators 50 and 52 may be optical crystals such as lithium niobium crystal, semiconductors, or MZ interferometer type optical modulators using these optical elements.

  The optical signal propagated through the optical fiber transmission line 12 is input to the optical receiver 14. With reference to FIG. 2, the configuration and operation of the optical receiver 14 will be described. In optical IQ multiplex transmission, information is coded in both phase and amplitude, thus requiring phase detection. Such phase detection can be realized with a coherent detector that recovers phase information by mixing the received light with the output of the local oscillator. Although coherent detection can be used for both heterodyne and homodyne, here, an example of homodyne detection is shown.

  The signal light from the optical fiber transmission line 12 is input from the input terminal 60 to the coherent mixer 62. The coherent mixer 62 also receives coherent output light from the optical local oscillator 64. The optical local oscillator 64 is a laser diode that generates coherent laser light having a wavelength approximate to the laser wavelength of the laser diode 44.

  The optical multiplexer / demultiplexer 66 of the coherent mixer 62 multiplexes / demultiplexes the signal light from the input terminal 60 and the coherent light from the optical local oscillator 64, and causes the 0-degree interference component to the beam splitter 68 and 90-degree interference. The component is supplied to the beam splitter 70. The beam splitter 68 transmits and reflects the 0-degree interference light from the optical multiplexer / demultiplexer 66, and supplies the transmitted light to the photodiode 72 and the reflected light to the photodiode 78. The beam splitter 70 transmits and reflects the 90-degree interference light from the optical multiplexer / demultiplexer 66, and supplies the transmitted light to the photodiode 74 and the reflected light to the photodiode 80.

  The differential amplifier 76 differentially amplifies the outputs of the photodiodes 72 and 74. The photodiodes 72 and 74 and the differential amplifier 76 constitute a balanced optical receiver. Similarly, the differential amplifier 82 differentially amplifies the outputs of the photodiodes 78 and 80. The photodiodes 78 and 80 and the differential amplifier 82 also constitute a balanced optical receiver.

  The coherent mixer 62, the optical local oscillator 64, the photodiodes 72, 74, 78, and 80, and the differential amplifiers 76 and 82 function as an optical IQ separation device that separates two signals Sa and Sb transmitted by optical IQ multiplexing. To do. However, the optical local oscillator 64 operates independently of the signal light, and means for equalizing the optical IQ multiplex transmission characteristics is required. A / D converters 84 and 86 and a digital signal processor 88 are provided as an equalizing circuit for optical IQ multiplexing. The A / D converter 84 converts the analog output of the differential amplifier 76 into a digital signal. The A / D converter 86 converts the analog output of the differential amplifier 82 into a digital signal. A digital signal processing device (DSP) 88 equalizes the output data of the A / D converters 84 and 86 by digital processing, thereby obtaining a signal Sa indicating an I component of optical IQ multiplexing and a signal Sb indicating a Q component. Restore.

  An optical PLL circuit may be provided, and the wavelength and optical phase of the optical local oscillator 64 may be feedback controlled by the output of the differential amplifier 76 or 82.

  The coherent mixer 62, the optical local oscillator 64, the photodiodes 72, 74, 78, and 80, the differential amplifiers 76 and 82, the A / D converters 84 and 86, and the DSP 88 operate as an optical IQ separation device. Such an optical IQ separation operation is known as a coherent receiver (for example, G. Charlet et al., “Transmission of 40 Gb / s QPSK with Coherent Detection over Ultra-Long Distance Improved by Nonlinearity Mitigation”, ECOC 2006 Proceedings , Vol. 6, Paper Th4.3.4, pp. 35-36).

  The electrical IQ separator 90 multiplies the signal Sa from the DSP 88 by the cosine wave cos (ωt) to separate the signal of the channel ch1 (A), and multiplies the signal Sa from the DSP 88 by the sine wave sin (ωt). Thus, the signal of channel ch2 (A) is separated. The OFDM demodulator 94 demodulates the data DATA-A from the signals of the channels ch1 (A) and ch2 (A) by the reverse processing (S / P conversion, FFT and digital demodulation) to the OFDM modulator 20a. Since the configuration and operation of electrical IQ separation and OFDM demodulation are well known, detailed description thereof is omitted.

  Similarly, the electrical IQ separator 92 multiplies the signal Sb from the DSP 88 by the cosine wave cos (ωt) to separate the signal of the channel ch1 (B), and the signal Sb from the DSP 88 to the sine wave sin (ωt). Is used to separate the channel ch2 (B) signal. The OFDM demodulator 96 demodulates the data DATA-B from the signals of the channels ch1 (B) and ch2 (B) by processing (S / P conversion, FFT and digital demodulation) reverse to that of the OFDM modulator 20b.

  Although an embodiment in which OFDM modulation is performed before electrical IQ multiplexing has been described, other RF multiplexing, for example, SCM may be used instead of OFDM modulation, or a combination of SCM and OFDM may be used.

  FIG. 3 shows a schematic block diagram of an embodiment of an optical transmission system for transmitting four-channel data D1, D2, D3, and D4 by electrical IQ multiplexing and optical IQ multiplexing.

  The optical transmission device 110 generates an optical signal obtained by multiplexing the data D1, D2, D3, and D4 by electrical IQ multiplexing and optical IQ multiplexing, and outputs the optical signal to the optical fiber transmission line 112. More specifically, the D / A converter 134a converts the data D1 into an analog signal, and the D / A converter 136a converts the data D2 into an analog signal. The multiplier 138a upconverts the output signal of the D / A converter 134a by multiplying the output signal of the D / A converter 134a by a cosine wave cos (ωt). The multiplier 140a upconverts the output signal of the D / A converter 136a by multiplying the output signal of the D / A converter 136a by a sine wave sin (ωt). The mixer 142a mixes or multiplexes the output signals of the multipliers 138a and 140a. Thus, the data D1 and D2 are electrically multiplexed with the in-phase (I) component and the quadrature (Q) component.

  Similarly, the D / A converter 134b converts the data D3 into an analog signal, and the D / A converter 136b converts the data D4 into an analog signal. The multiplier 138b upconverts the output signal of the D / A converter 134b by multiplying the output signal of the D / A converter 134b by a cosine wave cos (ωt). The multiplier 140b multiplies the output signal of the D / A converter 136b by multiplying the output signal of the D / A converter 136b by a sine wave sin (ωt). The mixer 142b mixes or multiplexes the output signals of the multipliers 138b and 140b. Thus, the data D3 and D4 are electrically multiplexed with the in-phase (I) component and the quadrature (Q) component.

  As in the first embodiment, the electrical IQ multiplexed angular frequency for the data D1 and D2 may not coincide with the electrical IQ multiplexed angular frequency for the data D3 and D4.

  The laser diode (LD) 144 generates coherent laser light serving as an optical carrier, and the output light is supplied to an optical IQ multiplexer 146 that uses a Mach-Zehnder (MZ) interferometer structure. That is, the optical demultiplexer 148 of the optical IQ multiplexer 146 divides the output light of the LD 144 into two and applies one to the optical modulator 150 on the first arm, while the other is the light on the second arm. Applied to the modulator 152. A phase shifter 154 that shifts the optical phase by π / 2 is disposed on the second arm. The optical modulator 150 modulates the laser beam from the optical demultiplexer 148 in accordance with the output electric signal Sa of the mixer 142a. On the other hand, the optical modulator 152 modulates the laser beam from the optical demultiplexer 148 according to the output electric signal Sb of the mixer 142b. The phase shifter 154 shifts the optical phase of the output light from the optical modulator 152 by π / 2. The optical multiplexer 156 combines the output light of the optical modulator 150 and the output light of the phase shifter 154. As a result, an optical IQ multiplexed signal that carries the signal Sa by the optical I component and the signal Sb by the optical Q component is generated, and this optical IQ multiplexed signal is output to the optical fiber transmission line 112.

  Similar to the optical modulators 50 and 52 of the first embodiment, the optical modulators 150 and 152 are optical crystals such as lithium niobium crystal, semiconductors, or MZ interferometer type optical modulators using these optical elements. May be.

  The optical signal propagated through the optical fiber transmission line 112 is input to the optical receiver 114. The optical IQ separator 160 includes the elements 62 to 88 of the first embodiment, and separates and equalizes the signals Sa and Sb. The electrical IQ separation device 162 separates and outputs each component data D1, D2 of electrical IQ multiplexing from the output signal Sa of the optical IQ separation device 160. The electrical IQ separation device 164 separates and outputs each component data D3 and D4 of electrical IQ multiplexing from the output signal Sb of the optical IQ separation device 160.

  The data D1 and D2 may be components generated by separation from the same data, for example, a real component and an imaginary component. Similarly, the data D3 and D4 may be components generated separately from the same data, for example, a real component and an imaginary component.

  The data D1 and D3 may be components generated and separated from the same data, for example, real components and imaginary components, and the data D2 and D4 may be components generated and separated from the same data, for example, real components and imaginary components. It may be.

  In the first embodiment, two data DATA-A and DATA-B are transmitted using both electric IQ multiplexing and optical IQ multiplexing. However, by using frequency division multiplexing in the electrical phase, more data can be transmitted and the spectral efficiency can be further increased.

  FIG. 4 shows a schematic block diagram of an embodiment capable of transmitting data DATA-A-1 to DATA-An and DATA-B-1 to DATA-Bn of a total of 2n channels. The optical transmission device 210 generates optical signals that carry data DATA-A-1 to DATA-An and DATA-B-1 to DATA-Bn of a total of 2n channels, and sends them to the optical fiber transmission line 212. Output. The optical receiver 214 receives an optical signal from the optical fiber transmission line 212 and restores data DATA-A-1 to DATA-An and DATA-B-1 to DATA-Bn.

In the optical transmitter 210, the OFDM modulator 220a-1 performs OFDM modulation on the data DATA-A-1. Electrical IQ multiplexing device 222a-1 is an OFDM modulated signal output from the OFDM modulator 220a-1, and multiplexed and separated into I and Q components at angular frequency omega _a1. The OFDM modulator 220a-1 corresponds to the OFDM modulator 20a of the embodiment shown in FIG. 1, and the electrical IQ multiplexer 222a-1 corresponds to the portion composed of the elements 28a to 42a of the embodiment shown in FIG.

Similarly, the OFDM modulators 220a-n perform OFDM modulation on the data DATA-A-n. The electrical IQ multiplexer 222a-n separates and multiplexes the OFDM-modulated signal output from the OFDM modulator 220a-n into _an I component and a Q component at _an angular frequency ω _an . The electrical IQ multiplexers 222a-1 to 222a-n use different angular frequencies ω _{b1 to} ω _an .

  The multiplexer 224a multiplexes the output electrical signals of the electrical IQ multiplexers 222a-1 to 222a-n in the frequency domain. Since the multiplexer 224a also functions as the mixer 42a, a circuit corresponding to the mixer 42a may be omitted from the electrical IQ multiplexers 222a-1 to 222a-n.

Similarly, the OFDM modulators 220b-1 to 220b-n perform OFDM modulation on the data DATA-B-1 to DATA-Bn, respectively. The electrical IQ multiplexers 222b-1 to 222b-n separate the OFDM-modulated signals output from the OFDM modulators 220b-1 to 220b-n into I and Q components at angular frequencies ω _{b1 to} ω _bn , respectively. And multiplex. The angular frequencies ω _{b1 to} ω _bn are different from each other. The multiplexer 224b multiplexes the output electrical signals of the electrical IQ multiplexers 222b-1 to 222b-n in the frequency domain. Since the multiplexer 224b also functions as the mixer 42b, the circuit corresponding to the mixer 42b may be omitted from the electrical IQ multiplexers 222b-1 to 222b-n.

  The laser diode (LD) 226 generates coherent laser light serving as an optical carrier, and the output light is supplied to an optical IQ multiplexer 228 that uses a Mach-Zehnder (MZ) interferometer structure. The optical IQ multiplexer 228 has the same configuration as the optical IQ multiplexer 46 shown in FIG. The optical IQ multiplexer 228 uses the output light of the LD 226 to carry the output electrical signal Sa of the multiplexer 224a as an optical I component, and the optical IQ multiplexed signal that carries the output electrical signal Sb of the multiplexer 224b as an optical Q component. Is generated. This optical IQ multiplexed signal is output to the optical fiber transmission line 212.

  The optical signal propagated through the optical fiber transmission line 212 is input to the optical receiver 214. Similar to the optical IQ separator 160, the optical IQ separator 240 includes the elements 62 to 88 of the first embodiment, and separates and equalizes the signals Sa and Sb.

  The demultiplexer 242a, electrical IQ demultiplexers 244a-1 to 244a-n, and OFDM demodulators 246a-1 to 246a-n are output from the output signal Sa of the optical IQ demultiplexer 240 to data DATA-A-1 to DATA-A-. Restore n.

Specifically, the separation device 242a separates the signal components carried at the angular frequencies ω _{a1 to} ω _an from the output signal Sa of the optical IQ separation device 240, and each separated signal component is an electrical IQ separation device 244a-. 1 to 244a-n.

Electrical IQ separator 244a-1, using the sine wave and cosine wave of the angular frequency omega _a1, separating the I and Q components. The OFDM demodulator 246a-1 performs OFDM demodulation on the output signal of the electrical IQ separation device 244a-1, and restores data DATA-A-1. Similarly, the electrical IQ separator 244a-n separates the I component and the Q component using a sine wave and a cosine wave of the angular frequency ω _an , and the OFDM demodulator 246a-n outputs the output of the electrical IQ separator 244a-n. The signal is OFDM demodulated to restore data DATA-A-n.

  Similarly, the demultiplexer 242b, the electrical IQ demultiplexers 244b-1 to 244b-n, and the OFDM demodulators 246b-1 to 246b-n receive the data DATA-B-1 to DATA from the output signal Sb of the optical IQ demultiplexer 240. -Restore Bn.

The angular frequency ω _ai may be equal to or different from the angular frequency ω _bi . However, i is 1 to n. Further, the number of multiplexing frequencies of the multiplexing device 224a may be different from the number of multiplexing frequencies of the multiplexing device 224b.

  Instead of the OFDM modulators 220a-1 to 220a-n and 220b-1 to 220b-n, other modulators may be used.

  Further, the data signal to be transmitted may be directly input to the electrical IQ multiplexers 222a-1 to 222a-n and 222b-1 to 222b-n. This corresponds to a configuration in which the adders 142a and 142b of the embodiment shown in FIG. 3 are changed to a frequency multiplexing device and an electrical IQ multiplexed signal of another angular frequency is multiplexed.

  In the optical IQ separation and equalization configuration of the optical receivers 14, 114, 214, the DSP 88 must operate in the RF signal band. By performing electrical IQ separation, that is, down-conversion in the frequency domain in advance, an equalization device that operates at a lower speed can be used. FIG. 5 shows a schematic block diagram of the optical receiver 314 modified in this way. The same components as those of the optical receiver 14 are denoted by the same reference numerals.

  As described in the first embodiment, the differential amplifier 76 outputs an electric signal corresponding to the signal Sa, and the differential amplifier 82 outputs an electric signal corresponding to the signal Sb. The electrical IQ separation device 384 down-converts the output signal of the differential amplifier 76 at the angular frequency ω, and separates data signals corresponding to the data signals ch1 (A) and ch2 (A). Similarly, the electrical IQ separator 386 down-converts the output signal of the differential amplifier 82 at the angular frequency ω, and separates the data signals corresponding to the data signals ch1 (B) and ch2 (B).

  The A / D converters 388a and 388b convert the output signal of the electrical IQ separation device 384 into a digital signal and supply the digital signal to the digital signal processing device 392. The A / D converters 390a and 390b convert the output signal of the electrical IQ separator 386 into a digital signal and supply the digital signal to a digital signal processor (DSP) 392. In this embodiment, the A / D converters 388a, 388b, 390a, 390b and the digital signal processing device 392 function as an equalizing device that equalizes transmission characteristics of optical IQ multiplexing and electrical IQ multiplexing. The digital signal processing device 392 outputs the equalized data signals ch1 (A) and ch2 (A) to the OFDM demodulator 94 and outputs the equalized data signals ch1 (B) and ch2 (B) to the OFDM demodulator. Output to 96. The OFDM demodulator 94 demodulates the data DATA-A from the signals ch1 (A) and ch2 (A). The OFDM demodulator 96 demodulates the data DATA-A from the signals ch1 (B) and ch2 (B).

  The change in which the equalization by the digital signal processing device 392 is arranged in the subsequent stage of the electrical IQ separation device is effective in both the embodiment shown in FIG. 3 and the embodiment shown in FIG.

  The configuration shown in FIG. 5 requires four A / D converters 388a, 388b, 390a, and 390b, but has a great advantage that the DSP 392 that operates at low speed can be used.

  Although the invention has been described with reference to specific illustrative embodiments, various modifications and alterations may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. This is obvious to an engineer in the field to which the present invention belongs, and such changes and modifications are also included in the technical scope of the present invention.

1 is a schematic configuration block diagram of an optical transmission device 10 according to a first embodiment of the present invention. 1 is a block diagram of a schematic configuration of an optical receiver 14 according to a first embodiment. It is a schematic block diagram of Example 2 of this invention. It is a schematic block diagram of Example 3 of the present invention. It is a schematic block diagram of another structural example of an optical receiver.

Explanation of symbols

10: optical transmitter 12: optical fiber transmission line 14: optical receiver 20a, 20b: OFDM modulator 22a, 22b: digital modulator 24a, 24b: inverse Fourier transform (IFFT) circuit 26a, 26b: parallel / serial (P / S) converters 28a, 28b: switches 30a, 30b: buffers 32a, 32b: buffers 34a, 34b: D / A converters 36a, 36b: D / A converters 38a, 38b: multipliers 40a, 40b: multipliers 42a, 42b: Mixer 44: Laser diode (LD)
46: Mach-Zehnder (MZ) interferometer (optical IQ multiplexer)
48: Optical demultiplexer 50: Optical modulator 52: Optical modulator 54: Phase shifter 56: Optical multiplexer 60: Input terminal 62: Coherent mixer 64: Optical local oscillator 66: Optical multiplexer / demultiplexers 68, 70: Beam splitter 72, 74: Photodiode 76: Differential amplifier 78, 80: Photodiode 82: Differential amplifier 84, 86: A / D converter 88: Digital signal processor 90, 92: Electrical IQ separator 94, 96: OFDM Demodulator 110: Optical transmitter 112: Optical fiber transmission line 114: Optical receivers 134a, 134b: D / A converters 136a, 136b: D / A converters 138a, 138b: multipliers 140a, 140b: multipliers 142a, 142b: Mixer 144: Laser diode (LD)
146: Mach-Zehnder (MZ) interferometer (optical IQ multiplexer)
148: Optical demultiplexer 150: Optical modulator 152: Optical modulator 154: Phase shifter 156: Optical multiplexer 160: Optical IQ separator 162, 164: Electric IQ separator 210: Optical transmitter 212: Optical fiber transmission line 214: optical receivers 220a-1 to 220a-n: OFDM modulators 220b-1 to 220b-n: OFDM modulators 222a-1 to 222a-n: electrical IQ multiplexers 222b-1 to 222b-n: electrical IQ multiplexing Devices 224a, 224b: Multiplexer 226: Laser diode 228: Optical IQ multiplexer 240: Optical IQ separator 242a. 242b: Separation devices 244a-1 to 244a-n: Electric IQ separation devices 244b-1 to 244b-n: Electric IQ separation devices 246a-1 to 246a-n: OFDM demodulators 246b-1 to 246b-n: OFDM demodulators 314: Optical receivers 384, 386: Electric IQ separators 388a, 388b, 390a, 390b: A / D converter 392: Digital signal processor

Claims (14)

The first, second, third and fourth data signals (ch1 (A), ch2) from the optical transmitter (10, 110) to the optical receiver (14, 114) via the optical transmission line (12, 112). (A), ch1 (B), ch2 (B); D1, D2, D3, D4), an optical transmission system,
The optical transmitter (10, 110) is
The first electrical IQ multiplexers (38a, 40a, 42a; 138a, 140a, 140a, 140a, etc.) that perform electrical IQ multiplexing of the first data signals (ch1 (A), D1) and the second data signals (ch2 (A), D2) 142a)
Second electrical IQ multiplexers (38b, 40b, 42b; 138b, 140b, etc.) for performing electrical IQ multiplexing on the third data signal (ch1 (B), D3) and the fourth data signal (ch2 (B), D4) 142b)
A laser light source (44, 144) for generating coherent laser light;
An optical IQ multiplexer (46, 146) that optically IQ-multiplexes the output electrical signals of the first and second electrical IQ multiplexers using the coherent laser light output from the laser light source.
And
The optical receiver (14, 114) is
An optical IQ separator (62, 72) that optically separates an optical signal input from the optical transmission line (12, 112) and outputs a first received electric signal (Sa) and a second received electric signal (Sb). ~ 88; 160), and
Corresponding to the first received data signal corresponding to the first data signal (ch1 (A), D1) and the second data signal (ch2 (A), D2) from the first received electrical signal. A first electrical IQ separation device (90, 162) for separating a second received data signal
Corresponding to the third received data signal corresponding to the third data signal (ch1 (B), D3) and the fourth data signal (ch2 (B), D4) from the second received electrical signal. Second electrical IQ separator (92, 164) for separating the fourth received data signal
An optical transmission system comprising: The optical IQ multiplexer is
A first arm;
A second arm;
The coherent laser light output from the laser light source is divided into first component light and second component light, the first component light is supplied to the first arm, and the second component light is supplied to the second arm. A demultiplexer to supply (48, 148);
A first modulator (50, 150) disposed on the first arm and configured to modulate the first component light in accordance with an output electric signal of the first electric IQ multiplexer;
A second modulator (52, 152) disposed on the second arm and configured to modulate the second component light in accordance with an output electric signal of the second electric IQ multiplexer;
A phase shifter (54, 154) disposed on the second arm for shifting the optical phase by π / 2;
Optical multiplexer (56, 156) for multiplexing the light from the first and second arms
The optical transmission system according to claim 1, further comprising: The optical IQ separator is
An optical local oscillator (64);
The input light from the optical transmission line and the output light of the optical local oscillator (64) are coherently mixed to generate first and second interference lights that are orthogonal to each other, and are orthogonal to each other from the first interference light. A coherent mixer (62) for separating and outputting the first and second polarization components and separating and outputting the third and fourth polarization components orthogonal to each other from the second interference light;
A first differential receiver (72, 74, 76) for differentially receiving the first polarization component and the third polarization component;
A second differential receiver (78, 80, 82) for differentially receiving the second polarization component and the fourth polarization component;
The optical transmission system according to claim 1 or 2, further comprising:   The optical transmission system according to any one of claims 1 to 3, further comprising an equalization device (84, 86, 88) for equalizing an output signal of the optical IQ separation device.   4. An equalizer (388a, 388b, 390a, 390b, 392) for equalizing the output signals of the first and second electrical IQ separators is further provided. The optical transmission system according to item 1. Furthermore,
A first D / A converter (34a, 134a) for converting the first data signal into an analog signal;
A second D / A converter (36a, 136a) for converting the second data signal into an analog signal;
A third D / A converter (34b, 134b) for converting the third data signal into an analog signal;
Fourth D / A converter (36b, 136b) for converting the fourth data signal into an analog signal
And
The first electrical IQ multiplexer is
A first multiplier (38a, 138a) for multiplying the output signal of the first D / A converter by a first cosine wave;
A second multiplier (40a, 140a) for multiplying the output signal of the second D / A converter by a first sine wave;
A first multiplexer (42a, 142a) for multiplexing the output signals of the first and second multipliers
And
The second electrical IQ multiplexer is
A third multiplier (38b, 138b) for multiplying the output signal of the third D / A converter by a second cosine wave;
A fourth multiplier (40b, 140b) for multiplying the output signal of the fourth D / A converter by a second sine wave;
Second multiplexer (42b, 142b) for multiplexing the output signals of the third and fourth multipliers
The optical transmission system according to any one of claims 1 to 5, further comprising: The first OFDM in which the optical transmission device (10) generates the first and second data signals (ch1 (A), ch2 (A)) from the first original data (DATA-A) by OFDM modulation. Second OFDM that generates the third and fourth data signals (ch1 (B), ch2 (B)) from the modulator (20a, 28a) and the second original data (DATA-A) by OFDM modulation Modulators (20b, 28b),
The optical receiver (14)
A first OFDM demodulator (94) for restoring the first original data by OFDM demodulation from the first and second received data signals output from the first electrical IQ separator (90);
A second OFDM demodulator (96) for restoring the second original data by OFDM demodulation from the third and fourth received data signals output from the second electrical IQ separation device (92)
The optical transmission system according to any one of claims 1 to 6, further comprising: A first electrical IQ multiplexing step (138a, 140a, 142a) for electrically IQ-multiplexing the first data signal (D1) and the second data signal (D2) to generate a first electrical IQ multiplexed signal;
A second electrical IQ multiplexing step (138b, 140b, 142b) for electrically IQ-multiplexing the third data signal (D3) and the fourth data signal (D4) to generate a second electrical IQ multiplexed signal;
An optical IQ multiplexing step (146) for optically IQ-multiplexing the first and second electrical IQ multiplexed signals using the coherent laser light output from the laser light source (144) to generate an optical IQ multiplexed signal;
An optical IQ separation step (160) for performing optical IQ separation on the optical IQ multiplexed signal and outputting a first received electrical signal (Sa) and a second received electrical signal (Sb);
A first electrical IQ separation step (162) for separating the first data signal (D1) and the second data signal (D2) from the first received electrical signal;
Second electrical IQ separation step (164) for separating the third data signal (D3) and the fourth data signal (D4) from the second received electrical signal
An optical transmission method comprising:   9. The optical transmission according to claim 8, wherein the optical IQ separation step comprises an equalization step of equalizing the first received electrical signal (Sa) and the second received electrical signal (Sb). Method.   9. The optical transmission method according to claim 8, further comprising an equalizing step for equalizing output signals of the first and second electrical IQ separation steps. The first electrical IQ multiplexers (38a, 40a, 42a; 138a, 140a, 140a, 140a, etc.) that perform electrical IQ multiplexing of the first data signals (ch1 (A), D1) and the second data signals (ch2 (A), D2) 142a)
Second electrical IQ multiplexers (38b, 40b, 42b; 138b, 140b, etc.) for performing electrical IQ multiplexing on the third data signal (ch1 (B), D3) and the fourth data signal (ch2 (B), D4) 142b)
A laser light source (44, 144) for generating coherent laser light;
An optical IQ multiplexer (46, 146) that optically IQ-multiplexes the output electrical signals of the first and second electrical IQ multiplexers using the coherent laser light output from the laser light source.
An optical transmitter characterized by comprising: The optical IQ multiplexer is
A first arm;
A second arm;
The coherent laser light output from the laser light source is divided into first component light and second component light, the first component light is supplied to the first arm, and the second component light is supplied to the second arm. A demultiplexer to supply (48, 148);
A first modulator (50, 150) disposed on the first arm and configured to modulate the first component light in accordance with an output electric signal of the first electric IQ multiplexer;
A second modulator (52, 152) disposed on the second arm and configured to modulate the second component light in accordance with an output electric signal of the second electric IQ multiplexer;
A phase shifter (54, 154) disposed on the second arm for shifting the optical phase by π / 2;
Optical multiplexer (56, 156) for multiplexing the light from the first and second arms
The optical transmission device according to claim 11, further comprising: Furthermore,
A first D / A converter (34a, 134a) for converting the first data signal into an analog signal;
A second D / A converter (36a, 136a) for converting the second data signal into an analog signal;
A third D / A converter (34b, 134b) for converting the third data signal into an analog signal;
Fourth D / A converter (36b, 136b) for converting the fourth data signal into an analog signal
And
The first electrical IQ multiplexer is
A first multiplier (38a, 138a) for multiplying the output signal of the first D / A converter by a first cosine wave;
A second multiplier (40a, 140a) for multiplying the output signal of the second D / A converter by a first sine wave;
A first multiplexer (42a, 142a) for multiplexing the output signals of the first and second multipliers
And
The second electrical IQ multiplexer is
A third multiplier (38b, 138b) for multiplying the output signal of the third D / A converter by a second cosine wave;
A fourth multiplier (40b, 140b) for multiplying the output signal of the fourth D / A converter by a second sine wave;
Second multiplexer (42b, 142b) for multiplexing the output signals of the third and fourth multipliers
The optical transmission device according to claim 11 or 12, comprising: Furthermore,
A first OFDM modulator (20a, 28a) for generating the first and second data signals (ch1 (A), ch2 (A)) from the first original data (DATA-A) by OFDM modulation;
Second OFDM modulators (20b, 28b) for generating the third and fourth data signals (ch1 (B), ch2 (B)) from the second original data (DATA-B) by OFDM modulation
The optical transmission device according to claim 11, further comprising:

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