JPWO2010026757A1 - Transmitting apparatus, receiving apparatus, optical transmission system, and optical transmission method - Google Patents

Abstract

Provided are an optical transmission system and an optical transmission method that can be implemented by multiplexing a plurality of signals having different speeds, multiplexing information in a single-peak spectrum shape in a single wavelength slot, and adding a necessary part to an existing system. . The transmission device performs phase modulation with a phase shift amount of π in accordance with the first signal, outputs a phase-modulated optical signal, and based on the second signal that is slower than the first signal The optical signal subjected to phase modulation or frequency modulation of the phase-modulated optical signal is transmitted to the receiving device. The receiving device branches the optical signal obtained from the transmitting device, outputs interference light by performing delayed interference of one of the branched optical signals, converts the interference light into an electrical signal, and full-wave rectifies, The second signal is acquired based on the full-wave rectified electrical signal, and the first signal is acquired based on the other branched optical signal.

Description

  The present invention relates to a method of multiplexing a plurality of signals with light of one wavelength, and more particularly to a transmission device, a reception device, an optical transmission system, and an optical transmission method that transmit a low-speed signal superimposed on a high-speed phase modulation signal.

The optical fiber communication system has become an important technology for realizing long-distance and large-capacity communication. Large-capacity communication is realized using modulation / demodulation devices used for transmission and reception, and the broadband characteristics of optical fibers serving as transmission paths. Taking advantage of this characteristic, in recent years, many technologies capable of realizing an optical transmission system having an interface capacity of 100 Gbps (gigabits per second) have been realized.
Up to now, time division multiplexing systems and wavelength division multiplexing systems have been used as means for aggregating low-speed signals using an optical fiber communication system and realizing large capacity transmission in one system.

  In an optical transmission system using time division multiplexing, a transmitter generates a high-speed electrical signal by electrically multiplexing a group of low-speed signals synchronized in frequency, and modulates and transmits light using the high-speed electrical signal. The method to do is adopted. Further, the receiving apparatus detects the modulated light, discriminates and reproduces it, and separates it in the time division direction, thereby separating the multiplexed signal and reproducing the original low-speed signal group. In this method, high-speed signals can be generated using electrical multiplexing, and optical devices that occupy most of the system cost can be one set of transmission and reception. Has the advantage of being possible.

  On the other hand, in an optical transmission system using a wavelength division multiplexing system, a transmission device uses a plurality of optical transmission units having light sources that oscillate at different signal wavelengths, and outputs light output from these optical transmission units to a plurality of electrical signals. Modulate with. Next, the transmission apparatus multiplexes a plurality of modulated lights using a wavelength multiplexing circuit and transmits the multiplexed light on one fiber. In the receiving apparatus, a plurality of wavelengths are individually separated using an optical separation circuit, and then a signal is detected and identified and reproduced using a plurality of receiving units. In this method, multiplexing is possible even if the low-speed signal has a different method and format. In this system, a very large number of wavelength channels can be multiplexed using a very wide transmission band of an optical fiber, and a large capacity can be easily realized. For this reason, this method has been widely put into practical use in combination with the aforementioned time division multiplexing method.

  By the way, there are two major problems in realizing long-distance transmission of high-speed optical communication. The first is a measure against optical noise accumulation. In the intensity modulation method, when the transmission speed is increased, the signal band to be used increases, and the amount of noise received by the system also increases. As a result, the value of the signal-to-noise ratio in the receiving apparatus becomes small, resulting in a quality deterioration in which code errors increase. Secondly, if the transmission distance is increased, it is necessary to increase the number of optical amplification repeaters for loss compensation. Due to the accumulation of optical noise generated by this optical amplification repeater, the signal-to-noise in the receiving apparatus is increased. Ratio degradation occurs. Therefore, in order to realize high speed and long distance, it is necessary to reduce the accumulation of optical noise or develop a transmission system that is strong against optical noise accumulation.

  In recent years, a phase modulation method, particularly a differential phase shift keying (DPSK) method, has attracted attention for such a problem of optical noise accumulation (for example, Patent Document 1). The differential phase shift keying method is a method in which the phase of light in adjacent bit slots is changed by π in order to transmit digital signals 1 and 0. In particular, a system in which a 1-bit delay detection reception system is combined with a phase modulation system has attracted attention because of its advantages of high performance and simple configuration. In this system, when the transmission data is 1, the transmission apparatus changes the phase of the bit slot by π, and when the transmission data is 0, the optical phase remains unchanged. The receiving apparatus distributes the received signal to two branches having one-bit delay elements arranged on one side, and then causes the two signals to interfere with each other. As a result, when the phase difference between the signal of the current bit slot and the signal of the previous bit slot becomes 2π or 0, the intensity of the interference signal becomes maximum, and when the phase difference becomes π, the signal is extinguished. Using this principle, the receiving apparatus converts the information applied to the phase change into intensity information and receives it.

JP 2003-60580 A

  In the future, there are several requirements for realizing transmission of a larger capacity service. For example, the following requirements are mentioned. First, a plurality of very high-speed electrical signals can be flexibly multiplexed, for example, even asynchronous signals can be multiplexed. Second, to facilitate service management, the multiple signals are accommodated in a single wavelength slot as much as possible. Thirdly, it is necessary to respond flexibly when demand for services occurs, and when it is necessary to increase the speed, it is designed so that necessary parts can be added and mounted.

  In view of these requirements, there are several problems with the conventional techniques in increasing the capacity. Specifically, when the time division multiplexing method is used, it is necessary to multiplex electric signals and modulate light with the electric signals, but it is difficult to process very high-speed electric signals. There's a problem. In addition, since it is necessary to change the multiple electric circuit, it is very difficult to realize a design in which a necessary part is added to an existing optical transmission system.

On the other hand, when wavelength division multiplexing is used, it is generally difficult to accommodate a plurality of signals in a single wavelength slot. In particular, if only the bandwidth of the wavelength slot is used, it is possible to perform wavelength multiplexing within one wavelength slot by multiplexing a plurality of peaks with high density, but monitoring a signal having a plurality of such peaks. Therefore, it is preferable that the spectrum is as unimodal as possible.
Further, when the phase modulation method is used, a plurality of electric signals cannot be multiplexed by the conventional methods.

  The present invention has been made in order to solve the above-described problems. The purpose of the present invention is to multiplex a plurality of signals having different speeds, multiplex information with a single peak spectral shape in a single wavelength slot, and An object of the present invention is to provide a transmission device, a reception device, an optical transmission system, and an optical transmission method that can be implemented by adding necessary parts to the system.

  The present invention has been made in order to solve the above-described problem, and a transmission apparatus according to the present invention is a transmission apparatus that multiplexes two signals having different speeds into one optical signal and transmits the multiplexed signal. A high-speed signal output unit that outputs a signal, a high-speed signal phase modulation unit that performs phase modulation with a phase shift amount π in accordance with the first signal, and a second signal that is slower than the first signal A low-speed signal output unit that outputs a signal, a low-speed signal modulation unit that performs phase modulation or frequency modulation of an optical signal output from the high-speed signal phase modulation unit based on the second signal, and an output from the low-speed signal modulation unit And a transmitter that transmits the optical signal thus received to the receiver.

The receiving apparatus of the present invention is a receiving apparatus that receives one optical signal obtained by multiplexing two signals having different speeds, and performs phase modulation with a phase shift amount π according to the first signal. From an optical branching unit for branching an optical signal that has been phase-modulated or frequency-modulated based on a second signal that is slower than the first signal from a transmitter, and delay interference of the one branched optical signal A delay interference unit that outputs interference light, a light detection unit that converts the interference light into an electrical signal, a rectification unit that full-wave rectifies the electrical signal, and the first signal based on the full-wave rectified electrical signal. A low-speed signal acquisition unit that acquires the second signal and a high-speed signal acquisition unit that acquires the first signal based on the other branched optical signal.
The optical transmission system of the present invention includes the transmitting apparatus of the present invention and the receiving apparatus of the present invention.

  The optical transmission method of the present invention is an optical transmission method in which two signals having different speeds are multiplexed and transmitted in one optical signal, and the first signal is output in accordance with the first signal. , Output a phase-modulated optical signal by performing phase modulation with a phase shift amount of π, output a second signal slower than the first signal, and based on the second signal, Phase modulation or frequency modulation of the phase-modulated optical signal is performed and transmitted to the receiving apparatus.

  The optical transmission method of the present invention is an optical transmission method for receiving one optical signal obtained by multiplexing two signals having different speeds, and performs phase modulation with a phase shift amount π according to the first signal. An optical signal that has been phase-modulated or frequency-modulated based on a second signal that is slower than the first signal and then branched from the transmitter, and performs delayed interference of the one of the branched optical signals, Outputting interference light, converting the interference light into an electrical signal, full-wave rectifying the electrical signal, obtaining the second signal based on the full-wave rectified electrical signal, and branching the other light The first signal is obtained based on the signal.

According to the present invention, the transmitting apparatus superimposes the second signal, which is slower than the first signal, on the optical signal phase-modulated according to the first signal by using phase modulation or frequency modulation. The receiving apparatus performs delayed interference on the optical signal from the transmitting apparatus, converts the interference light into an electrical signal, and acquires the second signal based on the electrical signal that has been full-wave rectified. Further, the receiving device performs phase modulation on the optical signal from the transmitting device based on the optical signal from the transmitting device (for example, by receiving the optical signal from the transmitting device or according to the acquired second signal). Alternatively, the first signal is reproduced (by receiving after frequency modulation). Thereby, the first signal and the second signal can be multiplexed.
According to the invention, the transmitting apparatus superimposes the first signal and the second signal using optical signals having the same wavelength. As a result, the multiplexed signal becomes a unimodal spectrum, and a plurality of signals can be stored in a single wavelength slot.
According to the present invention, the transmission device performs phase modulation according to the first signal by the high-speed signal phase modulation unit, and performs phase modulation or frequency modulation based on the second signal by the low-speed signal modulation unit. Accordingly, it is possible to easily implement by adding a necessary part to an existing optical transmission system, such as adding a low-speed signal modulation unit when necessary.
In addition, according to the present invention, since the transmission apparatus performs superimposition of the second signal by phase modulation or frequency modulation, the intensity of the phase modulation signal corresponding to the first signal is not lost. In addition, since the second signal is removed from the superimposed signal by reproducing the second signal by the receiving device, information on the light intensity is not lost. As a result, the second signal can be multiplexed without greatly losing the long-distance transmission characteristic of the phase-modulated signal corresponding to the first signal.

1 is a schematic block diagram showing a configuration of an optical transmission system according to a first embodiment of the present invention. It is a phase diagram which shows the transition of the phase of the optical signal accompanying the phase modulation of a high-speed signal phase modulation part. It is a phase diagram which shows the transition of the phase of the optical signal accompanying the phase modulation of a low-speed signal phase modulation part. (A) is a figure which shows the transition of the phase of the optical signal which the high-speed signal phase modulation part in 1st Embodiment outputs, (b) is the phase of the optical signal which the low-speed signal phase modulation part in 1st Embodiment outputs. FIG. 4C is a diagram illustrating a voltage transition of an electric signal output from the light detection unit in the first embodiment, and FIG. 4D is a diagram illustrating an electric signal output from the rectification unit in the first embodiment. It is a figure which shows the transition of a voltage. It is a schematic block diagram which shows the structure of the optical transmission system according to the 2nd Embodiment of this invention. (A) is a figure which shows the transition of the bit of the signal which the low-speed signal output part in 2nd Embodiment outputs, (b) is a figure which shows the transition of the bit of the signal which the precoding part in 2nd Embodiment outputs (C) is a figure which shows the transition of the phase of the optical signal which the low-speed signal phase modulation part in 2nd Embodiment outputs, (d) is the voltage of the electric signal which the photon detection part in 2nd Embodiment outputs. The figure which shows a transition, (e) is a figure which shows the transition of the voltage of the electric signal which the rectification | straightening part in 2nd Embodiment outputs. It is a schematic block diagram which shows the structure of the optical transmission system according to the 3rd Embodiment of this invention. (A) is a figure which shows the transition of the phase of the optical signal which the high speed signal phase modulation part in 3rd Embodiment outputs, (b) is the phase of the optical signal which the low speed signal phase modulation part in 3rd Embodiment outputs. FIG. 8C is a diagram showing the transition of the voltage of the electric signal output by the light detection unit in the third embodiment, and FIG. 10D is the electric signal output by the rectification unit in the third embodiment. It is a figure which shows the transition of a voltage. It is a schematic block diagram which shows the structure of the optical transmission system according to the 4th Embodiment of this invention. (A) is a figure which shows the transition of the bit of the signal which the low speed signal output part in 4th Embodiment outputs, (b) shows the transition of the phase of the optical signal which the frequency modulation part in 4th Embodiment outputs. (C) is a figure which shows the transition of the voltage of the electrical signal which the photon detection part in 4th Embodiment outputs, (d) is the transition of the voltage of the electrical signal which the rectification part in 4th Embodiment outputs. FIG. It is a schematic block diagram which shows the structure of the rectification | straightening part according to the 5th Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
First, a first embodiment of the present invention will be described.
FIG. 1 is a schematic block diagram showing a configuration of an optical transmission system according to the first embodiment of the present invention.
The optical transmission system includes a transmission device 100 and a reception device 200.
The transmission apparatus 100 includes a light source unit 101, a high-speed signal output unit 102, a low-speed signal output unit 103, a high-speed signal phase modulation unit 104, a low-speed signal phase modulation unit 105, and a transmission unit 106. The low-speed signal phase modulation unit 105 corresponds to the low-speed signal modulation unit of the present invention.
The light source unit 101 emits CW (Continuous Wave) light. For the light source unit 101, for example, a DFB (Distributed Feedback) laser or the like is used.
The high-speed signal output unit 102 outputs a digital signal having a predetermined frequency (first signal: hereinafter referred to as a high-speed signal). The high-speed signal output unit 102 outputs, for example, a 40 Gbps signal.
The low speed signal output unit 103 outputs a digital signal having a frequency lower than that of the high speed signal (second signal: hereinafter referred to as a low speed signal). The low-speed signal output unit 103 outputs a signal of 10 Gbps, for example.
The high-speed signal phase modulation unit 104 performs phase modulation of CW light according to the high-speed signal.
The low-speed signal phase modulation unit 105 performs phase modulation of the optical signal phase-modulated by the high-speed signal phase modulation unit 104 according to the low-speed signal.
The transmission unit 106 transmits the optical signal subjected to phase modulation by the high-speed signal phase modulation unit 104 and the low-speed signal phase modulation unit 105 to the reception device 200.

The receiving apparatus 200 includes an optical branching unit 201, a delay interference unit 202, a light detecting unit 203, a rectifying unit 204, a low-speed signal decoding unit 205, a phase modulating unit 206, and a high-speed optical receiving unit 207. The low speed signal decoding unit 205 corresponds to the low speed signal acquisition unit of the present invention. The phase modulation unit 206 and the high-speed optical reception unit 207 correspond to a high-speed signal acquisition unit of the present invention.
The optical branching unit 201 acquires an optical signal from the transmission apparatus 100, branches the acquired optical signal, and distributes the optical signal to the delay interference unit 202 and the phase modulation unit 206. The optical branching unit 201 distributes an optical signal using, for example, an optical coupler.
The delay interference unit 202 outputs interference light obtained by superimposing the distributed optical signal and the optical signal obtained by delaying the optical signal. For the delay interference unit 202, for example, a Mach-Zehnder delay interferometer or the like is used.
The light detection unit 203 converts the optical signal output from the delay interference unit 202 into an electrical signal.
The rectification unit 204 performs full-wave rectification on the electrical signal converted by the light detection unit 203.
The low-speed signal decoding unit 205 decodes the full-wave rectified electrical signal to obtain a low-speed signal. The low-speed signal decoding unit 205 performs decoding by changing the pulse level of the output signal at the falling edge of the pulse of the input electric signal. For the low-speed signal decoding unit 205, for example, a toggle flip-flop is used.
The phase modulation unit 206 performs phase modulation on the optical signal distributed from the optical branching unit 201 according to the low-speed signal acquired by the low-speed signal decoding unit 205. At this time, the phase modulation unit 206 performs phase modulation with a logic opposite to that of the low-speed signal phase modulation unit 105 of the transmission apparatus 100. Here, the phase modulation with the logic opposite to that of the low-speed signal phase modulation unit 105 indicates the following. For example, when the same signal is input to the low-speed signal phase modulation unit 105 and the phase modulation unit 206, the phase modulation unit 206 outputs the optical signal output from the low-speed signal phase modulation unit 105 and the light output from the phase modulation unit 206 itself. Phase modulation is performed so that the difference in phase shift from the signal is π.
The high-speed optical receiver 207 receives the optical signal phase-modulated by the phase modulator 206 and acquires a high-speed signal. For the high-speed optical receiver 207, for example, a circuit combining a photodetection circuit and a phase modulation decoding circuit is used.

In the optical transmission system configured as described above, the high-speed signal phase modulation unit 104 of the transmission apparatus 100 outputs an optical signal obtained by phase-modulating the CW light output from the light source unit 101 in accordance with the high-speed signal output from the high-speed signal output unit 102. To do. The low-speed signal phase modulation unit 105 phase-modulates the optical signal output from the high-speed signal phase modulation unit 104 according to the low-speed signal output from the low-speed signal output unit 103. The transmission unit 106 transmits the optical signal output from the low-speed signal phase modulation unit 105 to the reception device 200.
The delay interference unit 202 of the receiving apparatus 200 performs delay interference of one optical signal branched by the optical branching unit 201 and outputs interference light. The low-speed signal decoding unit 205 acquires a low-speed signal from the electric signal converted from the interference light by the light detection unit 203 and full-wave rectified by the rectification unit 204.
The phase modulation unit 206 phase-modulates the other optical signal branched by the optical branching unit 201 according to the low-speed signal acquired by the low-speed signal decoding unit 205. The high-speed optical receiver 207 receives the optical signal phase-modulated by the phase modulator 206 and acquires a high-speed signal.
Thus, the optical transmission system multiplexes a plurality of signals having different velocities with a unimodal spectrum shape in a single wavelength slot.

Next, the operation of the optical transmission system will be described.
First, the high-speed signal phase modulation unit 104 of the transmission apparatus 100 phase-modulates the CW light output from the light source unit 101 with the high-speed signal output from the high-speed signal output unit 102. At this time, the phase shift amount is π.
FIG. 2 is a phase diagram showing the transition of the phase of the optical signal accompanying the phase modulation of the high-speed signal phase modulation unit 104.
The horizontal axis in FIG. 2 indicates the magnitude of the in-phase component of the optical signal, and the vertical axis indicates the magnitude of the quadrature component of the optical signal. The optical signal phase-modulated by the high-speed signal phase modulation unit 104 with the phase shift amount being π becomes a signal whose phase transitions between two points of 0 and π, as shown in FIG. That is, the phase transitions on the in-phase component axis.

Next, the low-speed signal phase modulation unit 105 phase-modulates the optical signal output from the high-speed signal phase modulation unit 104 with the low-speed signal output from the low-speed signal output unit 103. At this time, the phase shift amount is π / 2.
FIG. 3 is a phase diagram showing transition of the phase of the optical signal accompanying the phase modulation of the low-speed signal phase modulation unit 105.
The horizontal axis in FIG. 3 indicates the magnitude of the in-phase component of the optical signal, and the vertical axis indicates the magnitude of the quadrature component of the optical signal. When the low-speed signal phase modulation unit 105 further phase-modulates the optical signal output from the high-speed signal phase modulation unit 104 with a phase shift amount of π / 2, the modulated signal has a phase of 0 as shown in FIG. It becomes a signal that transitions at four points of π / 2, π, and 3π / 2. At this time, the phase transition of the high-speed signal is switched between the phase transition on the in-phase component axis and the phase transition on the orthogonal component axis in response to the switching of the low-speed signal.
When the low-speed signal phase modulation unit 105 outputs an optical signal, the transmission unit 106 transmits the optical signal to the reception device 200.

When the optical branching unit 201 of the receiving device 200 acquires the optical signal from the transmitting device 100, the optical branching unit 201 branches the acquired optical signal into two, and outputs them to the delay interference unit 202 and the phase modulation unit 206. The delay interference unit 202 performs delay interference of one of the branched optical signals. At this time, the delay amount is one symbol time of the high-speed signal. Accordingly, the optical signal output from the delay interference unit 202 has a light intensity when the phase difference is 0, a light intensity when the phase difference is π / 2 or 3π / 2, and a phase difference of π. It becomes an optical signal having three kinds of light intensities. Only when the value of the low-speed signal is switched, the phase difference becomes π / 2 or 3π / 2.
When the delay interference unit 202 outputs an optical signal, the light detection unit 203 converts the optical signal into an electrical signal. The light detection unit 203 sets the voltage of the electric signal to V when the intensity of the optical signal is the intensity when the phase difference is 0, and when the intensity is when the phase difference is π / 2 or 3π / 2. When the voltage of the electrical signal is 0 and the intensity is when the phase difference is π, the voltage of the electrical signal is −V.
The rectification unit 204 performs full-wave rectification on the electrical signal output from the light detection unit 203. That is, an electrical signal that is an absolute value of the electrical signal output by the light detection unit 203 is output. As a result, the voltage becomes 0 when the symbol logic of the low-speed signal is switched, and the voltage becomes V otherwise.
When the rectification unit 204 outputs the full-wave rectified electric signal, the low-speed signal decoding unit 205 performs the full-wave rectification of the electric signal (after removing high-speed waveform fluctuations associated with bit changes of the high-speed signal, as will be described later). Decoding is performed by changing the pulse level of the output signal at the falling edge of the pulse. The output signal thus obtained is the same signal as the low speed signal.

When the low-speed signal decoding unit 205 reproduces the low-speed signal, the phase modulation unit 206 reproduces the other optical signal branched by the optical branching unit 201 by the low-speed signal decoding unit 205 with the reverse logic of the low-speed signal phase modulation unit 105. Phase modulation is performed according to a low-speed signal. At this time, the phase shift amount is set to π / 2 as in the low-speed signal phase modulation unit 105 of the transmission device 100. Thereby, the same signal as the signal which the high-speed signal phase modulation | alteration part 104 performed the phase modulation based on the high-speed signal can be obtained.
When the phase modulation unit 206 performs phase modulation, the high-speed optical reception unit 207 performs high-speed optical demodulation by performing demodulation corresponding to the modulation performed by the high-speed signal phase modulation unit 104 on the phase-modulated signal and converts it to an electrical signal. Get the signal.
Thereby, the receiving apparatus 200 can separate the high-speed signal and the low-speed signal and acquire each signal.
The above is the operation of the optical transmission system.

The optical transmission system will be described below using specific signal examples.
Here, an example in which the high-speed signal output unit 102 outputs a high-speed signal of 40 Gbps and the low-speed signal output unit 103 outputs a low-speed signal of 10 Gbps will be described.
FIG. 4 is a diagram illustrating a waveform of a signal output from each processing unit according to the first embodiment. In FIG. 4, each period divided by a dotted line extending in the vertical direction corresponds to one symbol bit of the low-speed signal. Here, an example is shown in which the bits of the low-speed signal are sequentially changed to 1, 0, 0, 0, 1, 1, 0, 1, 1, 1.
FIG. 4A shows the phase transition of the optical signal output from the high-speed signal phase modulator 104.
In FIG. 4A, the vertical axis indicates the phase, and the horizontal axis indicates time. The phase of the optical signal output from the high-speed signal phase modulation unit 104 transitions between 0 and π.
FIG. 4B shows the phase transition of the optical signal output from the low-speed signal phase modulator 105.
In FIG. 4B, the vertical axis indicates the phase, and the horizontal axis indicates time. The phase of the optical signal output from the low-speed signal phase modulator 105 transitions between 0, π / 2, π, and 3π / 2. Further, the phase transitions between π / 2 and 3π / 2 during the period when the bit of the low-speed signal is 1, and the phase transitions between 0 and π during the period when the bit of the low-speed signal is 0.

FIG. 4C shows the voltage transition of the electric signal output from the light detection unit 203.
In FIG. 4C, the vertical axis represents voltage, and the horizontal axis represents time. The electrical signal output from the light detection unit 203 transitions between V, 0, and −V. The electrical signal output from the light detection unit 203 is obtained by converting the optical signal output from the delay interference unit 202 into an electrical signal. The delay interference unit 202 performs delay interference of the optical signal branched by the optical branching unit 201, that is, the optical signal output from the low-speed signal phase modulation unit 105. At this time, when the phase difference between adjacent symbols is 0, the intensity of the optical signal output from the delay interference unit 202 is twice the intensity of the optical signal branched by the optical branching unit 201. When the phase difference between adjacent symbols is π, the intensity of the optical signal output from the delay interference unit 202 is zero. When the phase difference between adjacent symbols is π / 2 or 3π / 2, the intensity of the optical signal output from the delay interference unit 202 is the same as the intensity of the optical signal branched by the optical branching unit 201. The light detection unit 203 sets the voltage of the output signal to V when the intensity of the input optical signal is twice the intensity of the optical signal branched by the optical branching unit 201. The light detection unit 203 sets the voltage of the output signal to 0 when the intensity of the input optical signal is equal to the intensity of the optical signal branched by the optical branching unit 201. The light detection unit 203 sets the voltage of the output signal to −V when the intensity of the input optical signal is 0. Therefore, the output signal of the light detection unit 203 has a voltage of V or −V according to the phase difference between adjacent symbols of the optical signal output from the low-speed signal phase modulation unit 105, and the symbol bits of the low-speed signal are switched. The voltage is zero only at the points.
FIG. 4D shows the transition of the voltage of the electric signal output from the rectifying unit 204.
In FIG. 4D, the vertical axis represents voltage, and the horizontal axis represents time. The electrical signal output from the rectifying unit 204 transitions between V and 0. The rectification unit 204 outputs an electrical signal that is an absolute value of the electrical signal output by the light detection unit 203. Accordingly, the voltage is 0 only at the switching point of the symbol bit of the low-speed signal, and the voltage is V in the other periods.

  Therefore, the low-speed signal decoding unit 205 changes the pulse level of the output signal at the falling edge of the pulse of the electric signal output from the rectifying unit 204, that is, changes the pulse level of the output signal at a point where the voltage becomes zero. Thus, a low-speed signal can be extracted from the optical signal branched by the optical branching unit 201. It should be noted that the electrical signal output from the rectifying unit 204 is affected by high-speed waveform fluctuations caused by bit changes of the high-speed signal as noise. As a result, there is a possibility that the low-speed signal decoding unit 205 may erroneously recognize noise. Therefore, noise may be removed by limiting the band of the electrical signal output from the rectifying unit 204 to a band of a low-speed signal level using, for example, a low-pass filter.

As described above, according to the present embodiment, the transmission device 100 superimposes the low-speed signal on the optical signal phase-modulated according to the high-speed signal using the phase modulation. The receiving apparatus 200 performs delayed interference, converts the interference light into an electrical signal, and acquires a low-speed signal. The receiving device 200 reproduces a high-speed signal by phase-modulating and decoding the optical signal acquired from the transmitting device 100 according to the low-speed signal acquired from the optical signal. Thereby, a high speed signal and a low speed signal can be multiplexed.
Further, according to the present embodiment, the transmission device 100 superimposes a high-speed signal and a low-speed signal using optical signals having the same wavelength. Thereby, since the multiplexed signal has a unimodal spectrum, a plurality of signals can be accommodated in a single wavelength slot.
Further, according to the present embodiment, the transmission apparatus 100 performs the phase modulation of the high speed signal by the high speed signal phase modulation unit 104 and performs the phase modulation of the low speed signal by the low speed signal phase modulation unit 105. Accordingly, it is possible to easily implement by adding a necessary part to an existing optical transmission system, such as adding a low-speed signal phase modulation unit 105 when necessary.
Further, according to the present embodiment, the transmission device 100 performs superimposition of the low-speed signals by phase modulation, so that the intensity of the optical signal output from the high-speed signal phase modulation unit 104 is not lost. In addition, since the low-speed signal portion is removed from the superimposed signal by reproducing the low-speed signal by the receiving apparatus 200, the information on the light intensity is not lost. As a result, it is possible to multiplex a low-speed signal without greatly losing the long-distance transmission characteristic of the optical signal modulated according to the high-speed signal.

The first embodiment of the present invention has been described in detail above with reference to the drawings. However, the specific configuration is not limited to the above-described one, and various design changes can be made without departing from the scope of the present invention. Etc. are possible.
For example, in the present embodiment, the case where the high-speed signal is 40 Gbps and the low-speed signal is 10 Gbps has been described. However, these two signals do not necessarily have to be synchronized due to frequency multiplication, and it is only necessary to be able to detect switching of a low-speed signal and to reproduce the signal. good.

  In the present embodiment, the case where the delay amount of the delay interference unit 202 corresponds to one symbol time of a high-speed signal has been described, but the present invention is not limited to this. For example, by setting the delay amount to one symbol time of the low-speed signal, the time for which the voltage of the electric signal input to the low-speed signal decoding unit 205 becomes 0 is lengthened, and the identification margin of the low-speed signal decoding unit 205 is widened. The possibility of error may be reduced.

In this embodiment, the case where the high-speed signal phase modulation unit 104 performs phase modulation has been described. However, the present invention is not limited to this, and the high-speed signal phase modulation unit 104 may perform differential phase shift keying. In this case, for example, a LiNbO ₃ Mach-Zehnder modulator or the like is used for the high-speed signal phase modulation unit 104, and a circuit that combines, for example, a Mach-Zehnder type delay interferometer, a photodetection circuit, and a phase modulation decoding circuit, By using a receiving circuit or the like based on the coherent light receiving method, the transmitting device 100 and the receiving device 200 can be mounted.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. The second embodiment is an example of an optical transmission system in which a low-speed signal is pre-coded by the transmission device 100 and the low-speed signal is acquired without the reception device 200 decoding the low-speed signal.
The low-speed signal decoding unit 205 of the receiving apparatus 200 described in the first embodiment changes the level of the output signal in response to the falling edge of the pulse of the input signal. Therefore, if a bit error exists, a signal in which the bits after the erroneous bit are inverted is output. For this reason, when a low-speed signal is decoded in the receiving apparatus 200 in which noise is included in the received optical signal, an error occurs in a burst manner. As a result, not only the error rate of the low-speed signal is increased, but also the output result of the phase modulation unit 206 is erroneous, so that the error rate of the high-speed signal is also increased. Therefore, if the low-speed signal can be acquired without performing decoding processing in the receiving apparatus 200, the error rate can be reduced for both the low-speed signal and the high-speed signal.

FIG. 5 is a schematic block diagram showing the configuration of the optical transmission system according to the second embodiment of the present invention.
The configuration of the optical transmission system according to the second embodiment includes a precoding unit 111 in addition to the transmission device 100 in addition to the first embodiment, and low-speed signal detection instead of the low-speed signal decoding unit 205 of the reception device 200. It is the structure provided with the part 211. The other processing units are the same as those of the optical transmission system according to the first embodiment, and therefore will be described using the same reference numerals. The precoding unit 111 and the low-speed signal phase modulation unit 105 correspond to the low-speed signal modulation unit of the present invention. The low speed signal detection unit 211 corresponds to the low speed signal acquisition unit of the present invention. The phase modulation unit 206 and the high-speed optical reception unit 207 correspond to a high-speed signal acquisition unit of the present invention.
In the present embodiment, the precoding unit 111 of the transmission device 100 performs low-code signal precoding. The precoding unit 111 performs precoding by changing the pulse level of the output signal when the bit of the input electric signal is 1 (when it is at a predetermined level). The low-speed signal phase modulation unit 105 performs phase modulation of the optical signal phase-modulated by the high-speed signal phase modulation unit 104 according to the low-speed signal subjected to precoding. Further, the low-speed signal detection unit 211 of the reception device 200 detects the electric signal that has been full-wave rectified by the rectification unit 204 without performing decoding processing, and acquires a low-speed signal.

The optical transmission system will be described below using specific signal examples.
Here, an example in which the high-speed signal output unit 102 outputs a high-speed signal of 40 Gbps and the low-speed signal output unit 103 outputs a low-speed signal of 10 Gbps will be described.
FIG. 6 is a diagram illustrating a waveform of a signal output from each processing unit according to the second embodiment. Here, an example is shown in which the bits of the low-speed signal are sequentially changed to 0, 1, 0, 0, 1, 0, 1, 1, 0, 0.
FIG. 6A shows bit transition of a signal output from the low-speed signal output unit 103.
In FIG. 6A, the vertical axis indicates a bit value, and the horizontal axis indicates time. The low speed signal transitions between 1 and 0.
FIG. 6B shows bit transition of a signal output from the precoding unit 111.
In FIG. 6B, the vertical axis indicates a bit value, and the horizontal axis indicates time. The output signal of the precoding unit 111 transitions between 1 and 0. The precoding unit 111 inverts the bit value of the output signal when the bit of the low-speed signal becomes 1.
FIG. 6C shows the phase transition of the optical signal output from the low-speed signal phase modulation unit 105.
In FIG. 6C, the vertical axis indicates the phase, and the horizontal axis indicates time. The phase of the optical signal output from the low-speed signal phase modulator 105 transitions between 0, π / 2, π, and 3π / 2. Also, the phase transitions between π / 2 and 3π / 2 during the period when the bit of the output signal of the precoding unit 111 is 1, and the phase is 0 during the period when the bit of the output signal of the precoding unit 111 is 0. Transition to π.

FIG. 6D shows the voltage transition of the electrical signal output from the light detection unit 203.
In FIG. 6D, the vertical axis represents voltage, and the horizontal axis represents time. The electrical signal output from the light detection unit 203 transitions between V, 0, and −V. The electrical signal output from the light detection unit 203 is obtained by converting the optical signal output from the delay interference unit 202 into an electrical signal. The delay interference unit 202 performs delay interference of one optical signal branched by the optical branching unit 201, that is, the optical signal output from the low-speed signal phase modulation unit 105. At this time, when the phase difference between adjacent symbols is 0, the intensity of the optical signal output from the delay interference unit 202 is twice the intensity of the optical signal branched by the optical branching unit 201. When the phase difference between adjacent symbols is π, the intensity of the optical signal output from the delay interference unit 202 is zero. When the phase difference between adjacent symbols is π / 2 or 3π / 2, the intensity of the optical signal output from the delay interference unit 202 is the same as the intensity of the optical signal branched by the optical branching unit 201. The light detection unit 203 sets the voltage of the output signal to V when the intensity of the input optical signal is twice the intensity of the optical signal branched by the optical branching unit 201. The light detection unit 203 sets the voltage of the output signal to 0 when the intensity of the input optical signal is equal to the intensity of the optical signal branched by the optical branching unit 201. The light detection unit 203 sets the voltage of the output signal to −V when the intensity of the input optical signal is 0. Therefore, the output signal of the light detection unit 203 has a voltage of 0 when the bit of the low-speed signal becomes 1, and the voltage is V or −V in other cases.
FIG. 6E shows the transition of the voltage of the electric signal output from the rectifying unit 204.
In FIG. 6E, the vertical axis represents voltage, and the horizontal axis represents time. The electrical signal output from the rectifying unit 204 transitions between V and 0. The rectification unit 204 outputs an electrical signal that is an absolute value of the electrical signal output by the light detection unit 203. Therefore, the voltage of the electrical signal output from the rectifying unit 204 is 0 when the bit of the low-speed signal becomes 1, and the voltage is V when the bit of the low-speed signal is 0.

  Therefore, the low-speed signal detection unit 211 outputs 1 when the voltage of the electrical signal output from the rectification unit 204 becomes 0, and outputs 0 when the voltage is V, thereby acquiring a low-speed signal. it can. It should be noted that the electrical signal output from the rectifying unit 204 is affected by high-speed waveform fluctuations caused by bit changes of the high-speed signal as noise. As a result, there is a possibility that the low-speed signal detection unit 211 may erroneously recognize noise. Therefore, noise may be removed by limiting the band of the electrical signal output from the rectifying unit 204 to a band of a low-speed signal level using, for example, a low-pass filter.

  As described above, according to the present embodiment, the transmission apparatus 100 precodes the low-speed signal, and performs phase modulation of the optical signal phase-modulated according to the high-speed signal in accordance with the precoded low-speed signal. As a result, the receiving apparatus 200 can acquire a low-speed signal without decoding the low-speed signal, and thus can suppress the propagation of errors due to the decoding.

The second embodiment of the present invention has been described in detail above with reference to the drawings. However, the specific configuration is not limited to the above-described one, and various design changes can be made without departing from the scope of the present invention. Etc. are possible.
For example, in the present embodiment, the case where the high-speed signal is 40 Gbps and the low-speed signal is 10 Gbps has been described. However, these two signals do not necessarily have to be synchronized due to frequency multiplication, and it is only necessary to be able to detect switching of a low-speed signal and to reproduce the signal. good.

  In the present embodiment, the case where the delay amount of the delay interference unit 202 corresponds to one symbol time of a high-speed signal has been described, but the present invention is not limited to this. For example, by setting the delay amount to one symbol time of the low-speed signal, the time during which the voltage of the electric signal input to the low-speed signal detection unit 211 is 0 is lengthened, and the identification margin of the low-speed signal detection unit 211 is increased. The possibility of error may be reduced.

(Third embodiment)
Next, a third embodiment of the present invention will be described. The third embodiment performs phase modulation of an optical signal that is phase-modulated in accordance with a high-speed signal in accordance with a signal that is a logical product of a clock signal obtained by dividing the frequency of the high-speed signal by 2 and a low-speed signal. It is an example of an optical transmission system. As a result, the low-speed signal is acquired without decoding the low-speed signal by the receiving apparatus 200.

FIG. 7 is a schematic block diagram showing a configuration of an optical transmission system according to the third embodiment of the present invention.
The configuration of the optical transmission system according to the third embodiment includes a clock output unit 121 and an AND operation unit 122 in addition to the transmission device 100 in addition to the first embodiment, and a low-speed signal decoding unit of the reception device 200. Instead of 205, a low-speed signal detection unit 211 is provided. The other processing units are the same as those of the optical transmission system according to the first embodiment, and therefore will be described using the same reference numerals. The clock output unit 121, the AND operation unit 122, and the low-speed signal phase modulation unit 105 correspond to the low-speed signal modulation unit of the present invention. The low speed signal detection unit 211 corresponds to the low speed signal acquisition unit of the present invention. The phase modulation unit 206 and the high-speed optical reception unit 207 correspond to a high-speed signal acquisition unit of the present invention.
In this embodiment, the clock output unit 121 of the transmission apparatus 100 outputs a clock signal having a frequency obtained by dividing the frequency of the high-speed signal by two (that is, a clock signal whose frequency is half the symbol rate of the high-speed signal). The logical product operation unit 122 outputs a logical product of the low-speed signal output from the low-speed signal output unit 103 and the clock signal output from the clock output unit 121. That is, when the bit of the low-speed signal is 0, the output is 0, and when the bit of the low-speed signal is 1, the optical phase amplitude is switched by π / 2 with one symbol time of the high-speed signal as a cycle. For the AND operation unit 122, for example, an AND circuit is used. The low-speed signal phase modulation unit 105 performs phase modulation of the optical signal phase-modulated by the high-speed signal phase modulation unit 104 in accordance with the signal output from the AND operation unit 122. Further, the low-speed signal detection unit 211 of the reception device 200 detects the electric signal that has been full-wave rectified by the rectification unit 204 without performing decoding processing, and acquires a low-speed signal.

The optical transmission system will be described below using specific signal examples.
Here, an example in which the high-speed signal output unit 102 outputs a high-speed signal of 40 Gbps and the low-speed signal output unit 103 outputs a low-speed signal of 10 Gbps will be described.
FIG. 8 is a diagram illustrating a waveform of a signal output from each processing unit according to the third embodiment. Here, an example is shown in which the bits of the low-speed signal are sequentially changed to 1, 0, 0, 0, 1, 1, 0, 1, 1, 1.
FIG. 8A shows the phase transition of the optical signal output from the high-speed signal phase modulation unit 104.
In FIG. 8A, the vertical axis indicates the phase, and the horizontal axis indicates time. The phase of the optical signal output from the high-speed signal phase modulation unit 104 transitions between 0 and π.
FIG. 8B shows the phase transition of the optical signal output from the low-speed signal phase modulator 105.
In FIG. 8B, the vertical axis indicates the phase, and the horizontal axis indicates time. The phase of the optical signal output from the low-speed signal phase modulator 105 transitions between 0, π / 2, π, and 3π / 2. At this time, the phase is 0 or π during the period when the bit of the low-speed signal is 0. In the period when the bit of the low-speed signal is 1, the signal whose phase is π / 2 or 3π / 2 and the signal whose phase is 0 or π are 25p (= 1 / 40G) s (pico second: pico second: Every second).

FIG. 8C shows the transition of the voltage of the electric signal output from the light detection unit 203.
In FIG. 8C, the vertical axis represents voltage, and the horizontal axis represents time. The electrical signal output from the light detection unit 203 transitions between V, 0, and −V. The electrical signal output from the light detection unit 203 is obtained by converting the optical signal output from the delay interference unit 202 into an electrical signal. The delay interference unit 202 performs delay interference of one optical signal branched by the optical branching unit 201, that is, the optical signal output from the low-speed signal phase modulation unit 105. At this time, when the phase difference between adjacent symbols is 0, the intensity of the optical signal output from the delay interference unit 202 is twice the intensity of the optical signal branched by the optical branching unit 201. When the phase difference between adjacent symbols is π, the intensity of the optical signal output from the delay interference unit 202 is zero. When the phase difference between adjacent symbols is π / 2 or 3π / 2, the intensity of the optical signal output from the delay interference unit 202 is the same as the intensity of the optical signal branched by the optical branching unit 201. The light detection unit 203 sets the voltage of the output signal to V when the intensity of the input optical signal is twice the intensity of the optical signal branched by the optical branching unit 201. The light detection unit 203 sets the voltage of the output signal to 0 when the intensity of the input optical signal is equal to the intensity of the optical signal branched by the optical branching unit 201. The light detection unit 203 sets the voltage of the output signal to −V when the intensity of the input optical signal is 0. Therefore, the output signal of the light detection unit 203 has a voltage of V or −V depending on the phase difference between adjacent symbols of the optical signal output from the low-speed signal phase modulation unit 105. When the bit of the low speed signal is 1, the voltage is 0. The reason is that during the period when the bit of the low-speed signal is 1, the optical signal output from the low-speed signal phase modulation unit 105 is 0 or π in phase with the signal having a phase of π / 2 or 3π / 2. This is because the phase difference between symbols is always π / 2 or 3π / 2 during the period when the bit of the low-speed signal is 1, since the signal is switched every 25 ps.
FIG. 8D shows the transition of the voltage of the electric signal output from the rectifying unit 204.
In FIG. 8D, the vertical axis represents voltage, and the horizontal axis represents time. The electrical signal output from the rectifying unit 204 transitions between V and 0. The rectification unit 204 outputs an electrical signal that is an absolute value of the electrical signal output by the light detection unit 203. Therefore, the voltage is 0 when the bit of the low-speed signal is 1, and the voltage is V when the bit of the low-speed signal is 0.

  Therefore, the low-speed signal detection unit 211 can acquire a low-speed signal by outputting 1 when the voltage of the electrical signal output from the rectification unit 204 is 0 and outputting 0 when the voltage is V. It should be noted that the electrical signal output from the rectifying unit 204 is affected by high-speed waveform fluctuations caused by bit changes of the high-speed signal as noise. As a result, there is a possibility that the low-speed signal detection unit 211 may erroneously recognize noise. Therefore, noise may be removed by limiting the band of the electrical signal output from the rectifying unit 204 to a band of a low-speed signal level using, for example, a low-pass filter.

  As described above, according to the present embodiment, in accordance with the signal that is the logical product of the clock signal obtained by dividing the frequency of the high-speed signal by 2 and the low-speed signal in the transmission apparatus 100, Perform phase modulation. As a result, the receiving apparatus 200 can acquire a low-speed signal without decoding the low-speed signal, and thus can suppress the propagation of errors due to the decoding.

Although the third embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to the above-described one, and various design changes can be made without departing from the scope of the present invention. Etc. are possible.
For example, in the present embodiment, the case where the high-speed signal is 40 Gbps and the low-speed signal is 10 Gbps has been described. However, these two signals do not necessarily have to be synchronized due to frequency multiplication, and it is only necessary to be able to detect switching of a low-speed signal and to reproduce the signal. good.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, the transmitter 100 performs frequency modulation of an optical signal phase-modulated according to a high-speed signal in response to a low-speed signal, and the receiver 200 acquires the low-speed signal without decoding the low-speed signal. It is an example of a transmission system.

FIG. 9 is a schematic block diagram showing a configuration of an optical transmission system according to the fourth embodiment of the present invention.
The configuration of the optical transmission system according to the fourth embodiment includes a frequency modulation unit 131 instead of the low-speed signal phase modulation unit 105 of the transmission device 100 of the first embodiment, and the low-speed signal decoding unit 205 of the reception device 200. The low-speed signal detection unit 211 is provided instead of the frequency modulation unit 231, and the frequency modulation unit 231 is provided instead of the phase modulation unit 206 of the reception device 200. The other processing units are the same as those of the optical transmission system according to the first embodiment, and therefore will be described using the same reference numerals. The frequency modulation unit 131 corresponds to the low-speed signal modulation unit of the present invention. The low speed signal detection unit 211 corresponds to the low speed signal acquisition unit of the present invention. Further, the frequency modulation unit 231 and the high-speed optical reception unit 207 correspond to a high-speed signal acquisition unit of the present invention.

In the present embodiment, the frequency modulation unit 131 of the transmission apparatus 100 performs frequency modulation of the optical signal phase-modulated by the high-speed signal phase modulation unit 104 according to the low-speed signal output from the low-speed signal output unit 103. Further, the frequency modulation unit 131 sets a frequency corresponding to ¼ of the reciprocal of the delay amount of the delay interference unit 202 as the frequency shift amount. For example, when the delay amount of the delay interference unit 202 is 25 ps (pico second), 1 / (25 × 10 ⁻¹² ) × 1/4 = 10 ¹⁰ , so the frequency shift amount is 10 Gbps. .
The low-speed signal detection unit 211 of the reception device 200 detects the electric signal that has been full-wave rectified by the rectification unit 204 without performing a decoding process, and acquires a low-speed signal.
The frequency modulation unit 231 of the reception device 200 performs frequency modulation of the other optical signal branched by the optical branching unit 201 in accordance with the signal output from the low-speed signal detection unit 211. Similarly to the frequency modulation unit 131, the frequency modulation unit 231 uses a frequency corresponding to ¼ of the reciprocal of the delay amount of the delay interference unit 202 as the frequency shift amount.

The optical transmission system will be described below using specific signal examples.
Here, an example in which the high-speed signal output unit 102 outputs a high-speed signal of 40 Gbps and the low-speed signal output unit 103 outputs a low-speed signal of 10 Gbps will be described. Therefore, the delay amount of the delay interference unit 202 is 25 ps, and the frequency shift amount of the frequency modulation units 131 and 231 is 10 Gbps.
FIG. 10 is a diagram illustrating a waveform of a signal output from each processing unit according to the fourth embodiment. Here, an example is shown in which the bits of the low-speed signal are sequentially changed to 1, 0, 0, 0, 1, 1, 0, 1, 1, 1.
FIG. 10A shows bit transition of the signal output from the low-speed signal output unit 103.
In FIG. 10A, the vertical axis represents bits and the horizontal axis represents time. The signal output from the low-speed signal output unit 103 transitions between 0 and 1.
FIG. 10B shows the phase transition of the optical signal output from the frequency modulation unit 131.
In FIG. 10B, the vertical axis indicates the phase, and the horizontal axis indicates time. The phase of the optical signal output from the frequency modulation unit 131 is 0 or π during the period when the bit of the low-speed signal is 0, and the phase continues to shift by π / 2 per 25 ps during the period when the bit of the low-speed signal is 1. . This is because the phase is rotated by π / 2 at 25 ps because frequency modulation is performed with a frequency shift amount of 10 Gbps.

FIG. 10C shows the transition of the voltage of the electric signal output from the light detection unit 203.
In FIG. 10C, the vertical axis represents voltage, and the horizontal axis represents time. The electrical signal output from the light detection unit 203 transitions between V, 0, and −V. At this time, when the bit of the low-speed signal is 1, the voltage is 0, and when the bit of the low-speed signal is 0, the voltage is V or -V. Also, at 25 ps immediately after the bit switching point of the low-speed signal, the voltage smoothly transitions from 0 to V or −V, or from V or −V to 0.
The electrical signal output from the light detection unit 203 is obtained by converting the optical signal output from the delay interference unit 202 into an electrical signal. The delay interference unit 202 performs delay interference of the optical signal branched by the optical branching unit 201, that is, the optical signal output from the frequency modulation unit 131. At this time, when the phase difference between adjacent symbols is 0, the intensity of the optical signal output from the delay interference unit 202 is twice the intensity of the optical signal branched by the optical branching unit 201. When the phase difference between adjacent symbols is π, the intensity of the optical signal output from the delay interference unit 202 is zero. When the phase difference between adjacent symbols is π / 2 or 3π / 2, the intensity of the optical signal output from the delay interference unit 202 is the same as the intensity of the optical signal branched by the optical branching unit 201. The light detection unit 203 sets the voltage of the output signal to V when the intensity of the input optical signal is twice the intensity of the optical signal branched by the optical branching unit 201. The light detection unit 203 sets the voltage of the output signal to 0 when the intensity of the input optical signal is equal to the intensity of the optical signal branched by the optical branching unit 201. The light detection unit 203 sets the voltage of the output signal to −V when the intensity of the input optical signal is 0. Therefore, the voltage output from the delay interference unit 202 is V or −V according to the phase difference between adjacent symbols of the optical signal output from the frequency modulation unit 131, and the bit of the low-speed signal is 1. In this case, the voltage becomes zero. The reason is that in the period when the bit of the low-speed signal is 1, the phase of the optical signal output from the frequency modulator 131 continues to transition by π / 2 per 25 ps. This is because the phase difference between adjacent symbols is always π / 2 or 3π / 2.
FIG. 10D shows the transition of the voltage of the electric signal output from the rectifying unit 204.
In FIG. 10D, the vertical axis represents voltage, and the horizontal axis represents time. The electrical signal output from the rectifying unit 204 transitions between V and 0. The rectification unit 204 outputs an electrical signal that is an absolute value of the electrical signal output by the light detection unit 203. Therefore, the voltage is 0 when the bit of the low-speed signal is 1, and the voltage is V when the bit of the low-speed signal is 0.

  Therefore, the low-speed signal detection unit 211 can acquire a low-speed signal by outputting 1 when the voltage of the electrical signal output from the rectification unit 204 is 0 and outputting 0 when the voltage is V. However, since the electrical signal output from the rectifying unit 204 has a smooth rise and fall of the voltage, the low-speed signal detection unit 211 needs to detect at a timing when the rise or fall of the voltage is stable. It should be noted that the electrical signal output from the rectifying unit 204 is affected by high-speed waveform fluctuations caused by bit changes of the high-speed signal as noise. As a result, there is a possibility that the low-speed signal detection unit 211 may erroneously recognize noise. Therefore, noise may be removed by limiting the band of the electrical signal output from the rectifying unit 204 to a band of a low-speed signal level using, for example, a low-pass filter.

  As described above, according to the present embodiment, the transmitter 100 performs frequency modulation of the optical signal phase-modulated according to the high-speed signal according to the low-speed signal. As a result, the receiving apparatus 200 can acquire a low-speed signal without decoding the low-speed signal, and thus can suppress the propagation of errors due to the decoding.

Although the fourth embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to the above-described one, and various design changes can be made without departing from the scope of the present invention. Etc. are possible.
For example, in the present embodiment, the case where the high-speed signal is 40 Gbps and the low-speed signal is 10 Gbps has been described. However, these two signals do not necessarily have to be synchronized due to frequency multiplication, and it is only necessary to be able to detect switching of a low-speed signal and to reproduce the signal. good.

  In the present embodiment, the case where the delay amount of the delay interference unit 202 corresponds to one symbol time of a high-speed signal has been described, but the present invention is not limited to this. For example, the spectral spread of the optical signal transmitted from the transmission unit 106 may be reduced by setting the delay amount to one symbol time of the low-speed signal and the frequency shift amount of the frequency modulation unit 131 to 2.5 GHz.

  Further, in the present embodiment, the case has been described in which the receiving apparatus 200 includes the frequency modulation unit 231 and removes the low-speed signal component to extract the high-speed signal. For example, when the frequency shift amount given by the frequency modulation unit 131 is small and the high-speed signal can be decoded without removing the low-speed signal component using the frequency modulation unit 231 in the demodulation of the high-speed signal, the frequency modulation unit 231 is provided. Instead, the structure of the receiving apparatus 200 may be simplified by directly decoding the optical signal branched by the optical branching unit 201 by the high-speed optical receiving unit 207.

(Fifth embodiment)
Next, a fifth embodiment of the present invention will be described. In the fifth embodiment, when a high-speed full-wave rectifier circuit is used as the rectifier 204 in the first to fourth embodiments, a signal delay occurs due to a time delay generated in an integrated circuit such as an operational amplifier. This solves the problem of waveform distortion occurring when the frequency is high.

FIG. 11 is a schematic block diagram showing the configuration of the rectifying unit according to the fifth embodiment.
The rectification unit 204 includes a light source unit 241, a Mach-Zehnder modulation unit 242, and a light detection unit 243.
The light source unit 241 outputs CW light.
The Mach-Zehnder modulation unit 242 modulates the intensity of the CW light based on the electric signal output from the light detection unit 203. The Mach-Zehnder modulation unit 242 previously adjusts the bias voltage so that the intensity of the optical signal output when the voltage of the electrical signal output by the light detection unit 203 is 0 is 0. Thereby, when the voltage of the electrical signal output from the light detection unit 203 is 0, the intensity of the optical signal output from the Mach-Zehnder modulation unit 242 becomes 0, and the voltage of the electrical signal output from the light detection unit 203 is V or −. At V, the intensity of the optical signal output from the Mach-Zehnder modulator 242 is maximized.
The light detection unit 243 converts the optical signal output from the Mach-Zehnder modulation unit 242 into an electrical signal. The light detection unit 243 sets the voltage of the electrical signal output when the intensity of the optical signal is 0 to 0, and sets the voltage of the electrical signal output when the intensity of the optical signal is maximum to V.

  Thus, according to the present embodiment, the rectifier 204 can output an electrical signal equivalent to that of the full-wave rectifier circuit. The rectification unit 204 according to the present embodiment does not use an integrated circuit such as an operational amplifier, and the Mach-Zehnder modulation unit 242 can easily operate at high speed, so that a full-wave rectification waveform with little distortion is obtained. Can do.

  The fifth embodiment of the present invention has been described in detail above with reference to the drawings. However, the specific configuration is not limited to the above-described one, and various design changes can be made without departing from the scope of the present invention. Etc. are possible.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

  This application claims the priority on the basis of Japanese application Japanese Patent Application No. 2008-228061 for which it applied on September 5, 2008, and takes in those the indications of all here.

  According to the present invention, a multiplexed signal of a first signal and a second signal that is slower than the first signal can be made a unimodal spectrum, and a plurality of signals can be placed in a single wavelength slot. Can fit in. In addition, according to the present invention, it is possible to easily implement by adding a necessary part to an existing optical transmission system. Furthermore, according to the present invention, it is possible to multiplex the second signal without greatly losing the long-distance transmission characteristics of the phase modulation signal corresponding to the first signal.

  DESCRIPTION OF SYMBOLS 100 ... Transmission apparatus 101 ... Light source part 102 ... High speed signal output part 103 ... Low speed signal output part 104 ... High speed signal phase modulation part 105 ... Low speed signal phase modulation part 106 ... Transmission part 200 ... Reception apparatus 201 ... Optical branching part 202 ... Delay Interference unit 203... Light detection unit 204 .. rectification unit 205... Low-speed signal decoding unit 206... Phase modulation unit 207.

Claims (19)

A transmission device that multiplexes and transmits two signals having different speeds into one optical signal,
A high-speed signal output unit for outputting a first signal;
A high-speed signal phase modulation unit that performs phase modulation with a phase shift amount of π in accordance with the first signal;
A low-speed signal output unit that outputs a second signal that is slower than the first signal;
A low-speed signal modulator that performs phase modulation or frequency modulation of the optical signal output from the high-speed signal phase modulator based on the second signal;
A transmission device comprising: a transmission unit that transmits an optical signal output from the low-speed signal modulation unit to a reception device. A receiving device for receiving one optical signal obtained by multiplexing two signals having different speeds,
An optical signal obtained by performing phase modulation with a phase shift amount π according to the first signal and then performing phase modulation or frequency modulation based on a second signal slower than the first signal is transmitted from the transmission device. An optical branching unit that branches after being acquired; and
A delay interference unit that performs delayed interference of the branched optical signal and outputs interference light;
A light detection unit that converts the interference light into an electrical signal;
A rectifying unit for full-wave rectification of the electrical signal;
A low-speed signal acquisition unit that acquires the second signal based on the full-wave rectified electrical signal;
A high-speed signal acquisition unit that acquires the first signal based on the other branched optical signal.   The transmission apparatus according to claim 1, wherein the low-speed signal modulation unit includes a low-speed signal phase modulation unit that phase-modulates the optical signal output from the high-speed signal phase modulation unit according to the second signal. The optical branching unit obtains, from the transmission device, an optical signal that is phase-modulated according to the second signal after performing phase modulation with a phase shift amount π according to the first signal,
The low-speed signal acquisition unit includes a low-speed signal decoding unit that acquires the second signal by decoding the electric signal subjected to full-wave rectification,
The high-speed signal acquisition unit receives the optical signal that has been phase-modulated by the phase modulation unit and the phase modulation unit that phase-modulates the other optical signal that has been branched in accordance with the acquired second signal. The receiving device according to claim 2, further comprising: a high-speed optical receiving unit that acquires one signal.   The low-speed signal modulation unit receives the second signal, and outputs a precoding unit that changes a pulse level of the output signal when the second signal is at a predetermined level, and the high-speed signal phase modulation unit outputs The transmission apparatus according to claim 1, further comprising: a low-speed signal phase modulation unit that phase-modulates the optical signal according to the output signal of the precoding unit. The optical branching unit is a signal obtained by changing a pulse level of an optical signal that has been subjected to phase modulation with a phase shift amount of π according to the first signal when the second signal is at a predetermined level. To obtain an optical signal phase-modulated according to the transmitter,
The low-speed signal acquisition unit includes a low-speed signal detection unit that detects the full-wave rectified electrical signal and acquires the second signal,
The high-speed signal acquisition unit receives the optical signal that has been phase-modulated by the phase modulation unit and the phase modulation unit that phase-modulates the other optical signal that has been branched in accordance with the acquired second signal. The receiving device according to claim 2, further comprising: a high-speed optical receiving unit that acquires one signal.   The low-speed signal modulation unit includes a clock output unit that outputs a clock signal whose frequency is half the symbol rate of the first signal, and a logical product operation unit that outputs a logical product of the second signal and the clock signal. And a low-speed signal phase modulation unit that phase-modulates the optical signal output from the high-speed signal phase modulation unit according to a signal output from the AND operation unit. The optical branching unit converts an optical signal obtained by performing phase modulation with a phase shift amount π in accordance with the first signal, a clock signal having a frequency that is half the symbol rate of the first signal, and the second signal An optical signal phase-modulated according to the logical product with the signal of
The low-speed signal acquisition unit includes a low-speed signal detection unit that detects the full-wave rectified electrical signal and acquires the second signal,
The high-speed signal acquisition unit receives the optical signal that has been phase-modulated by the phase modulation unit and the phase modulation unit that phase-modulates the other optical signal that has been branched in accordance with the acquired second signal. The receiving device according to claim 2, further comprising: a high-speed optical receiving unit that acquires one signal.   The transmission device according to claim 1, wherein the low-speed signal modulation unit includes a frequency modulation unit that frequency-modulates the optical signal output from the high-speed signal phase modulation unit according to the second signal. The optical branching unit obtains, from the transmission device, an optical signal that has been subjected to phase modulation with a phase shift amount π according to the first signal and then frequency-modulated according to the second signal,
The low-speed signal acquisition unit includes a low-speed signal detection unit that detects the full-wave rectified electrical signal and acquires the second signal,
The receiving apparatus according to claim 2, wherein the high-speed signal acquisition unit includes a high-speed optical reception unit that receives the branched optical signal and acquires the first signal. The high-speed signal acquisition unit further includes a frequency modulation unit that modulates the frequency of the branched optical signal according to the acquired second signal,
The receiving device according to claim 10, wherein the high-speed optical receiver receives the optical signal frequency-modulated by the frequency modulator and acquires the first signal.   The delay interference unit performs delay interference using one symbol time of the first signal or one symbol time of the second signal as a delay amount. A receiving device according to claim 1.   The transmission device according to any one of claims 3, 5, and 7, wherein the low-speed signal phase modulation unit performs phase modulation with a phase shift amount of π / 2.   The receiving device according to claim 4, wherein the phase modulation unit performs phase modulation with a phase shift amount being π / 2.   The frequency modulation unit performs frequency modulation using a frequency corresponding to ¼ of a reciprocal of a delay amount when the optical signal transmitted from the transmission unit is subjected to delay interference by the receiver as a frequency shift amount. The transmitting device according to 1.   The receiving apparatus according to claim 11, wherein the frequency modulation unit performs frequency modulation using a frequency corresponding to ¼ of a reciprocal of the delay amount of the delay interference unit as a frequency shift amount. The transmitting device according to claim 1 and the receiving device according to claim 2, or
The transmission device according to claim 3 and the reception device according to claim 4, or
The transmission device according to claim 5 and the reception device according to claim 6, or
The transmission device according to claim 7 and the reception device according to claim 8, or
An optical transmission system comprising: the transmission device according to claim 9 or claim 15; and the reception device according to claim 10, 11 or 16. An optical transmission method in which two signals having different speeds are multiplexed and transmitted in one optical signal,
Output a first signal;
In accordance with the first signal, a phase modulation with a phase shift amount of π is performed and a phase modulated optical signal is output,
Outputting a second signal that is slower than the first signal;
An optical transmission method for performing phase modulation or frequency modulation on the phase-modulated optical signal based on the second signal and transmitting the result to a receiving apparatus. An optical transmission method for receiving one optical signal obtained by multiplexing two signals having different speeds,
An optical signal obtained by performing phase modulation with a phase shift amount π according to the first signal and then phase-modulating or frequency-modulating based on the second signal that is slower than the first signal is acquired from the transmission device. Branch off
Perform delayed interference of the branched one optical signal, and output interference light,
Converting the interference light into an electrical signal;
Full-wave rectification of the electrical signal,
Obtaining the second signal based on the full-wave rectified electrical signal;
An optical transmission method for obtaining the first signal based on the other branched optical signal.

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