JP5761704B2 - Optical time division multiplexing transmission method and optical time division multiplexing transmission system - Google Patents

Description

  The present invention relates to an optical time division multiplexing transmission method and an optical time division multiplexing transmission system.

Although the transmission rate required for optical communication is increasing year by year due to the rapid development of the Internet, the operation speed of electronic devices is reaching its limit. The number of codes (symbols) that can be transmitted per unit time is called the symbol rate. To transmit a signal at a symbol rate that exceeds the upper limit of the electronic device, optical time division multiplex transmission (OTDM) that multiplexes the signal in the optical domain Is required.
For example, assume that there are N intensity modulation transmitters, and optical signals are output at a rate of f0 [baud / sec], respectively. When these N optical signals are converted into serial signals by optical time division multiplexing transmission, signals can be transmitted at a symbol rate of f ′ = N × f0 [baud / sec] (see FIG. 5). The receiver divides the OTDM signal into N parallel signals (Demux) and performs signal processing for each channel.

  In order to perform this Demux operation, a reference signal (clock) having a frequency equal to the symbol rate (= f0) of the original transmitter is required. Therefore, the receiver is required to have a so-called optical clock extraction function for generating this clock signal from the received optical signal. Normally, in the optical clock extraction, an electrical signal or optical pulse train having a frequency f ′ / N that is phase-synchronized with the OTDM signal is extracted.

In the OTDM system, it is necessary to execute signal processing such as multiplexing / division at a speed exceeding the operation limit of the electronic device. For this, an optical device using a nonlinear optical effect is used. A general optical device has an input / output port for signal light and an input port for control light, and controls the intensity and phase of the signal light by turning on / off the control light.
Typical ultrahigh-speed optical devices include those utilizing four-wave mixing generated by nonlinear fibers and cross-phase modulation indicated by semiconductor intersubband transition (ISBT). So far, OTDM with a symbol rate of 172 Gbaud / s has been realized using an ISBT optical gate (see Non-Patent Document 1, for example).

Several methods for performing optical clock extraction have been proposed. Generally, since the OTDM signal does not contain information on the channel, the phase relationship between the extracted clock signal and the data channel is not necessarily constant. As shown in FIG. 5, there is a possibility that clocks are extracted at N different timings (see, for example, Non-Patent Document 2).
Since the Demux operation cannot be performed accurately if the phase of the clock signal fluctuates, it is desirable that the clock signal is always extracted at a constant timing with respect to the data. As shown in FIG. 7, the simplest method for this is to simultaneously transmit a signal whose intensity is modulated at a clock frequency f0 together with data.

  However, this method requires that the clock be transmitted using a wavelength different from that of the data so that the receiver can separate the clock signal from the data, and the spectrum utilization efficiency is lower than when only the data is transmitted. There is. Also, because the clock and data propagate at different speeds due to the dispersion of the transmission path, the phase relationship between the received signal and the extracted clock cannot be kept constant when the transmission path or transmission distance varies.

On the other hand, a method of adding channel identification information to an OTDM signal as shown in FIG. 8 instead of transmitting a clock pulse has been proposed (see, for example, Non-Patent Document 3).
In this method, intensity modulation is performed at a frequency required for the OTDM signal by applying a periodic phase shift to the pulse laser beam which is a carrier wave of the OTDM signal. For example, in FIG. 8, the phase of channel 1 is shifted by π from the phase of other channels, and the receiving side can directly extract the clock frequency phase-synchronized with channel 1 from the OTDM signal.
In this method, it is necessary to always keep the phase relationship of all optical pulses constant, and high fabrication accuracy is required for the optical signal multiplexing (MUX) unit. In addition, it is necessary to perform feedback control on the optical path length so that the phase between pulses does not change even with respect to a temperature change or the like, and the system becomes more complicated as the multiplicity N increases.

Takasu Kurosu et al., "Transmission of Super Hi-Vision Video Using Optical Time Division Multiplexing", IEICE Technical Report, IEICE Technical Report, IA2009-91, p.53-p.58, (2010) Keiyuki Ome, Kyoichi Onoji, Ikuo Yamashita, Katsuji Higuchi, "Examination of 10GHz clock signal extraction from 160Gbit / s optical RZ signal", IEEJ Trans.EIS, vol.125, No.10, p.1608-p .1613, (2005) Kozo Fujii, “Development of Ultra High-Speed Optical Signal Processing Technology”, Oki Technical Review, No. 204, Vol.72, No.4, p.70-p.75, October 2005

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide an optical time division multiplexing transmission method and an optical time division multiplexing with a simple system configuration without reducing the spectrum utilization efficiency. To get a transmission system.

The above problem is solved by the following means.
(1) An optical time division multiplex transmission method characterized by adding channel identification information to an optical time division multiplexed signal by performing phase modulation on a signal of a specific channel.
(2) a transmission unit that transmits an optical time division multiplexed signal to which channel identification information is given by performing phase modulation on a signal of a specific channel, and receives the optical time division multiplexed signal and receives the optical time division multiplexed signal from the optical time division multiplexed signal. An optical time division multiplex transmission system comprising means for extracting channel identification information, and including a receiving unit for dividing the optical time division multiplexed signal based on the channel identification information obtained by the means.
(3) The optical time division multiplex transmission system according to (2), wherein the means for extracting the channel identification information includes a delay interferometer, a differential photodetector, and a clock extractor.
(4) The transmission unit includes an optical signal multiplexing unit and an optical modulator that gives a phase shift to signal light of a specific channel from the optical signal multiplexing unit (2) or (3) The optical time division multiplex transmission system described in 1.
(5) The transmission unit includes an optical signal multiplexing unit that multiplexes the signal light of a specific channel to which a phase shift is given and the signal light of another channel, according to (2) or (3) The optical time division multiplex transmission system described.

In the present invention, a clock signal can always be extracted from an OTDM signal with a constant phase relationship with each channel. Therefore, even when the transmission path or transmission distance changes, the Demux operation can be performed efficiently and accurately. In addition, since clock information is included in the data itself, the spectrum utilization efficiency does not decrease.
In addition, since it is not necessary to control the phase of all optical pulses in the present invention, the system configuration is simple and suitable for practical use compared to the conventional method of adding channel identification information to the OTDM signal.

The figure explaining the principle of the optical time division multiplexing transmission method of this invention Configuration diagram of rate converter First configuration example of optical time division multiplexing transmission system Second configuration example of optical time division multiplexing transmission system Diagram explaining the principle of optical time division multiplexing transmission Diagram explaining phase relationship between clock and data in normal optical clock extraction Diagram explaining the method of distributing clock pulses with data One method for adding channel identification information to an optical time division multiplex transmission signal

  The present invention makes it possible for the receiving side in OTDM to always extract a clock signal at a constant timing for each channel of data. The principle is shown in FIG. The transmission side transmits an OTDM signal to which channel identification information is added. The reception side guides a part of the reception signal to the rate conversion unit, extracts a specific channel from the OTDM signal using the identification information, and generates an electric signal having a symbol rate of f0. If a clock is extracted from this electrical signal using a normal electronic circuit, the clock signal can be extracted with a constant phase relationship with each channel of the OTDM signal.

  In order to add channel identification information to the OTDM signal, the transmission side performs phase modulation on a specific channel (referred to as a reference channel) before or after multiplexing (muxing) the N-channel signal. The rate converter does not output a signal when an optical signal not subjected to phase modulation is input, and a voltage signal depending on the intensity of the input signal when an optical signal subjected to phase modulation is input. Is output. Therefore, only the signal of the reference channel is converted into a voltage signal and output from the rate conversion unit.

The rate conversion unit includes a delay interferometer and a differential optical receiver (see FIG. 2). The delay interferometer is adjusted so that light of the same intensity is output from the two output ports when non-phase modulated light is input, and the output of the differential optical receiver is zero. However, when phase-modulated light is input, an intensity difference occurs between the two output signals of the delay interferometer, and the differential optical receiver generates a voltage signal.
In order to apply phase modulation to a specific channel of an OTDM signal after time division multiplexing, a very high-speed phase modulator in the picosecond range is required. Such ultra-high speed modulation can be performed by using a nonlinear optical effect device even if it cannot be realized by a conventional electronic device.

FIG. 3 shows a first configuration example of an optical time division multiplexing transmission system according to the present invention.
The transmitting side generates an OTDM signal with a symbol rate of f ′ (= N × f0) by optical time division multiplexing the outputs of N transmitters with a symbol rate of f0. Next, this signal is passed through a phase modulator to perform phase modulation on some channels (referred to as reference channels).
On the receiving side, a part of the signal is guided to the delay interferometer, and the data of one or several bits before and the signal are caused to interfere in each channel. The light output from the two ports is received by a photo receiver, and the intensity difference is output as a voltage. This voltage signal has a symbol rate of f0, and a clock signal is extracted using a normal clock extractor. The extracted clock signal is guided to the Demux device and used to separate the OTDM signal.

In order to perform phase modulation only on a specific channel of the OTDM signal, a non-linear optical device capable of ultra-high speed operation is used. As the nonlinear optical device, a device using a nonlinear fiber, ISBT, or the like having a small intensity modulation effect at the time of phase modulation is desirable.
The nonlinear optical device is driven by an optical pulse train generated by a short pulse light source synchronized with the transmitter. “0”, “π / 2”, “0”, “π / 2”, “0”, “π / 2”, and “0”, “π / 2”, “0”, “π / 2”, ... When phase modulation is applied, a voltage signal with a symbol rate of f0 is generated at the receiver. If the receiving unit can obtain a voltage signal with a symbol rate of f0 / m (m: integer), the OTDM signal may be modulated using another pattern.

FIG. 4 shows a second configuration example of the optical time division multiplexing transmission system according to the present invention.
The transmitting side generates a OTDM signal with a symbol rate of f ′ (= N × f0) by time division multiplexing after performing phase modulation on a signal of a specific channel among N transmitters with a symbol rate of f0.
On the receiving side, a part of the signal is guided to the delay interferometer, and the data of one or several bits before and the signal are caused to interfere in each channel. The light output from the two ports is received by a photo receiver, and the intensity difference is output as a voltage. Since this voltage signal has a symbol rate of f0 or a fraction thereof, a clock signal is extracted using a normal electronic device. The extracted clock signal is guided to the Demux device and used to separate the OTDM signal.

  When phase modulation is alternately applied to the reference channel data as “π / 2”, “-π / 2”, “π / 2”, “-π / 2”, “π / 2”,. In the receiving unit, a voltage signal having a symbol rate of f0 / 2 is generated. If the receiving unit can obtain a voltage signal with a symbol rate of f0 / m (m: integer), the reference channel may be phase-modulated using another pattern.

The optical time division multiplex transmission method and optical time division multiplex transmission system of the present invention have been described in detail above. However, the present invention is not construed as being limited thereto, and so long as it does not depart from the scope of the present invention. Various changes, modifications, and improvements can be made based on the knowledge of those skilled in the art.

Claims (7)

An optical time division multiplex transmission method for transmitting and receiving an optical time division multiplex signal composed of N-channel data with a symbol rate of f0 ,
Phase modulation shifted between adjacent signals of the one data channel to the extent that a voltage signal with a symbol rate of f0 can be detected on the receiving side only for the signal of one data channel of the optical time division multiplexed signal on the transmitting side sending optical time division multiplex signal facilities phase modulation in an amount,
On the receiving side, the differential optical detector receives the transmitted optical time division multiplexed signal and receives the phase modulation amount of the adjacent signal of the one phase-modulated data channel input to the delay interferometer. Extracting a clock signal having a symbol rate f0 from a voltage signal having a detected symbol rate f0, and dividing the received optical time division multiplexed signal into N-channel data having a symbol rate f0;
An optical time division multiplex transmission method. An optical time division multiplexing transmission system for transmitting and receiving an optical time division multiplexing signal composed of N-channel data with a symbol rate of f0,
Phase modulation with a phase modulation amount shifted between adjacent signals of the one data channel to such an extent that a voltage signal with a symbol rate of f0 can be detected in the receiver only for the signal of one data channel of the optical time division multiplexed signal A transmitter for transmitting the optical time division multiplexed signal subjected to
A symbol detected by a differential photodetector by the deviation of the phase modulation amount of the adjacent signal of the one phase-modulated data channel received in the transmitted optical time division multiplexed signal and input to the delay interferometer a reception unit that rate is the symbol rate of the optical time division multiplexed signal by extracting a clock signal and the received symbol rate f0 from a voltage signal f0 is divided into data of N channels f0,
An optical time division multiplex transmission system comprising: The phase modulation to be the data signal of the one data channel is a repetition sequence of “0”, “π / 2”, “0”, “π / 2”, “0”, “π / 2”. The optical time division multiplex transmission system according to claim 2, wherein: In the transmitting portion, the front phase modulation applied to the signal of one data channel of the optical signal multiplexing of data of N channel, or any of claims 2 to 3, characterized in that after one The optical time division multiplex transmission system according to item. Optical time division multiplex transmission system according to claim 4, wherein the phase modulation applied to the signal of one data channel is performed using the ISBT device. 2. The optical time division multiplex transmission method according to claim 1, wherein the phase modulation applied to the signal of the one data channel is performed after optical time division multiplexing using an ISBT device. An optical time division multiplex transmission transmitter for transmitting an optical time division multiplex signal composed of N channel data having a symbol rate of f0,
Between adjacent signals of one data channel to such an extent that a voltage signal having a symbol rate of f0 can be detected in a receiver that receives the optical time division multiplexed signal only for the signal of one data channel of the optical time division multiplexed signal. An optical time division multiplex transmission transmitter that transmits an optical time division multiplex signal subjected to phase modulation with a phase modulation amount shifted by.