CN101272214A - A transmission control method for a wavelength division multiplexing system - Google Patents

Abstract

The present invention relates to the transmission control of the wavelength division multiplexing system (WDM) in the optical fiber transmission system. It proposes a transmission control method of the WDM transmission system. Under the condition of not changing the existing WDM system, the arrayed waveguide grating ( AWG) select channels at intervals for multi-channel signal transmission, the interval number is an integer parameter m, m is greater than zero and less than one-half of the number of channels; the channel of the receiving end AWG corresponding to the channel of the transmitting end AWG transmission signal receives the transmission The original signal transmitted by the terminal AWG channel is downloaded and forwarded or continued to be transmitted. In the adjacent channel of the receiving channel, the demodulated signal of the original signal is received, and the information is selected or directly extracted by filtering. The transmission control method of a WDM system provided by the present invention does not need to make any changes to the original system, nor does it need to add any devices, and can simultaneously realize the demodulation and decomplexation of the non-return-to-zero phase modulation format in the wavelength division multiplexing system It is suitable for the transmission of non-return-to-zero (NRZ) signals and non-return-to-zero differential phase-shift keying (NRZ-DPSK) signals at different rates.

Description

A transmission control method for a wavelength division multiplexing system

technical field

The invention relates to a high-speed and large-capacity optical fiber transmission system, in particular to a dense wavelength division multiplexing system of a non-return-to-zero differential phase-shift keying modulation format in the optical fiber transmission system.

Background technique

As a vector modulation format, the optical differential phase shift keying (DPSK) format can effectively suppress the nonlinear effects of various optical fibers, such as cross-phase modulation, self-phase modulation, etc., because it can realize constant envelope or approximately constant envelope transmission. , which is very suitable for high-speed and large-capacity optical fiber transmission systems, has been extensively studied in recent years. Among them, the non-return-to-zero differential phase-shift keying modulation format (NRZ-DPSK) is very suitable for application in the wavelength division system (WDM) due to its relatively narrow spectral width, which greatly improves the transmission of optical fiber communication systems. distance and capacity.

Generally speaking, a common non-return-to-zero modulation format (NRZ format) is mainly transmitted in a WDM system. The difference between the multi-channel system in NRZ-DPSK format (WDM system) and the multi-channel system in common format (NRZ format) mainly lies in the transmitting and receiving ends. Each NRZ-DPSK signal at the transmitter can be implemented by a phase modulator (PM) or a Mach-Zehnder modulator (MZM) working in a push-pull mode, and the modulator is driven by a differentially encoded electrical NRZ format signal. Generally speaking, the receiving end of the DPSK system is relatively complicated. Because of its constant amplitude, the information it carries cannot be directly detected. Generally, an asymmetric Mach-Zehnder interferometer (AMZI) and balanced detection are required to demodulate the original signal and perform Balanced reception. This method is very sensitive to ambient temperature, vibration, polarization state, etc., and has high requirements on the two-arm delay of AMZI, and the appropriate delay amount must be selected according to the signal rate transmitted in the channel. Especially at high rates, it must be accurate to a few picoseconds and requires temperature control. If a multi-channel NRZ-DPSK system is to be realized, the receiving end will be quite complicated and the cost will be high. This method is a conventional NRZ-DPSK WDM system, and its structure is shown in Figure 1. N channels of signal light with different wavelengths pass through different DPSK signal generating modules to generate multiple DPSK signals, multiplex them together through a multiplexer (AWG), and transmit them in optical fiber links after optical amplification. At the receiving end, through corresponding The demultiplexer (AWG) demultiplexes into N channels of signals, and then demodulates the original data stream through different DPSK demodulation modules (AMZI). In this scheme, the demodulation of each signal at the receiving end must be realized by using AMZI and a balanced detector. The control of the AMZI phase shift also needs to be very precise. The determined AMZI can only be applied to a determined working rate. After the demultiplexer After multiple splitting and combining, the power loss is also relatively large. Generally speaking, the system is more complicated at the receiving end, the system cost is higher, and it is difficult to control and adjust.

In the last two years, an improved WDM system for NRZ-DPSK format has aroused widespread interest. On the basis of the conventional NRZ-DPSK WDM system, if an optical circulator and a periodic fiber grating (FBG) are added to the transmission line, and the transmission end and reflection end are used respectively, two phases similar to AMZI can be obtained. Interference elimination and phase expansion interference output ports to obtain two demodulated signals, and then select one of the two demodulated signals for direct detection, see Figure 2(a); or send them to the subsequent two AWGs respectively The corresponding channels are balanced received by the DPSK receiving module, see Figure 2(b). In this solution, because the FBG is periodic, it can demodulate each WDM signal at the same time, which greatly saves the demodulation device used by the receiving end and saves the cost. However, the disadvantage of this solution is also obvious. An optical circulator and a periodic FBG need to be added to the line, which increases the system cost. For the solution in Figure 2(a), the interval between the added periodic FBG channels needs to be selected according to the signal rate transmitted in the line, which limits the flexibility of the system. For the solution in Figure 2(b), in addition to the above-mentioned problems, two AWGs are required at the receiving end, and a multi-channel DPSK receiving device is still required. In addition, for the FBG added to the line, in addition to being selected according to the working rate, the bandwidth of each channel needs to be specially customized, which should generally be 60% of the working rate. For example, for a 10Gb/s signal, the bandwidth of each channel of FBG should be 6GHz (0.048nm), which is very narrow and difficult to manufacture.

The most critical point is that this improvement scheme destroys the structure of the original WDM system. If another device is introduced, it will not only increase the cost and complexity, but also make the improved system only transmit the fixed-rate NRZ-DPSK format. No longer available for transmission in NRZ format.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the shortcomings that the structure of the receiving end signal demodulation system in the NRZ-DPSK WDM system is quite complicated and the cost is very high, and realize the NRZ without any modification to the existing WDM system structure. - Demultiplexing and demodulation of DPSK signals.

In order to solve the above-mentioned technical problems, the present invention proposes a transmission control method of a WDM transmission system, which is characterized in that, without changing the original WDM system, the AWG at the transmitting end selects channels at intervals for multi-channel signal transmission, The number of intervals is an integer parameter m, m is greater than zero and less than half the number of channels; the channel of the receiving end AWG corresponding to the channel of the transmitting end AWG transmission signal receives the original signal transmitted by the transmitting end AWG channel, downloads and forwards it Or continue the transmission, receive the demodulated signal of the original signal in the adjacent channel of the receiving channel, and select or directly extract the information through filtering; the specific methods include:

When m=1, then,

At the transmitter, select the odd-numbered channels of the AWG at the transmitter to transmit signals, and the even-numbered channels are idle;

At the receiving end, the odd-numbered channel of the receiving end AWG receives the original signal transmitted by the odd-numbered channel of the transmitting end AWG, downloads and forwards or chooses to continue transmission; the even-numbered channel of the receiving end AWG receives its adjacent two odd-numbered channels The demodulation signal of the demodulation signal is selected by the filter at the receiving end from the demodulation signals of the two adjacent odd-numbered channels, and the other one is filtered out for subsequent direct detection and information extraction;

or;

At the transmitting end, select the AWG even-numbered channel of the transmitting end to transmit the signal, and the odd-numbered channel is idle;

At the receiving end, the even channel of the AWG at the receiving end receives the original signal transmitted by the odd channel of the AWG at the transmitting end, downloads and forwards or chooses to continue transmission; at the odd channel of the AWG at the receiving end, it receives two adjacent even For the demodulated signal of the channel, the filter at the receiving end selects one demodulated signal from the demodulated signals of the two adjacent even-numbered channels, and filters out the other one for subsequent direct detection and information extraction;

When m>1, then,

At the transmitting end, select a channel with an interval m of the AWG at the transmitting end to transmit signals, and the unselected channels are idle;

At the receiving end, the channel of the receiving end AWG corresponding to the channel of the transmitting end AWG transmission signal receives the original signal transmitted by the transmitting end AWG channel, downloads and forwards or chooses to continue transmission; on the adjacent channel receiving the original signal channel, the receiving end The demodulated signal of the original signal is used for subsequent direct detection and information extraction.

Theoretical basis of the present invention is as follows:

This invention uses detuned filters to realize the demodulation function of NRZ-DPSK signals, but does not need to use additional detuned filters, but by properly selecting the transmission channel of the existing AWG, the existing AWG can be used Simultaneously realize the functions of demultiplexing and demodulation. It is equivalent to using the adjacent channels of the AWG to achieve proper wavelength detuning, and then the multi-channel phase-modulated signal can be demodulated into an amplitude-modulated signal for direct detection.

For each NRZ-DPSK signal, it is generated by MZM working in push-pull mode as an example, which satisfies

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Among them, E _in and E _out are the input and output light fields of the modulator. V ₁ and V ₂ are the NRZ electrical NRZ signals that drive the two arms of the MZM, and V _π is the half-wave voltage or the switching voltage required to produce a π phase difference output light intensity from maximum to minimum when a single arm works. When the peak values of _V1 and _V2 are equal to _Vπ , an NRZ-DPSK signal is generated.

The filter after the NRZ-DPSK signal uses a first-order Gaussian filter, because its transmission function is closest to the spectral envelope of the RZ signal. Its impulse response is:

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="B"\; filenames="A20081004752800171.png,A20081004752800191.png"\; state="\{\{state\}\}">B</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; i\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

where ω _f is the center frequency of the passband of the filter, ${\mathrm{<figure-callout\; id="0"\; label="B"\; filenames="A20081004752800171.png,A20081004752800191.png"\; state="\{\{state\}\}">B</figure-callout>}}_0=\mathrm{\&pi;}\&Center\; Dot;{\mathrm{<figure-callout\; id="3"\; label="B"\; filenames="A20081004752800141.png,A20081004752800191.png"\; state="\{\{state\}\}">B</figure-callout>}}_{3\mathrm{dB}}/\sqrt{\mathrm{<figure-callout\; id="2"\; label="ln"\; filenames="A20081004752800141.png,A20081004752800161.png"\; state="\{\{state\}\}">ln</figure-callout>}2},$ B _3db is the 3dB bandwidth of the filter.

Convolve equations (1) and (2) to obtain the output demodulated signal:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; de</span>}\mathrm{<span\; class="notranslate">\; mod</span>}\mathrm{<span\; class="notranslate">\; calculation</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{<span\; class="notranslate">\; -</span><span\; class="notranslate">\; \&infin;</span>}^{<span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&infin;</span>}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d\&tau;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Based on formulas (1) to (3), we simulate the process as shown in Figure 4. The left side of Figure 4 is the spectrogram, and the right side is the corresponding waveform diagram. The upper part of Figure 4 corresponds to the original NRZ-DPSK signal, and the lower part of Figure 4 shows the demodulated signal obtained by filtering the original NRZ-DPSK signal. It can be seen that after the detuned filter, the original NRZ-DPSK The carrier in the DPSK signal is partially suppressed, and the high frequency components are extracted. This causes the DC component of the original NRZ-DPSK to be suppressed, and the phase jump part is extracted to generate pulses, which achieves the demodulation process from phase modulation to amplitude modulation. It should be noted that this method has a high tolerance to filter offset and can achieve demodulation results in a wide range.

Using the AWG to demodulate the NRZ-DPSK signal of multiple WDM signals, the principle is similar to the demodulation of one signal. Each of the signals can be seen as being demodulated using a detuned filter. Since each channel of the AWG is in the shape of a Gaussian filter, each channel just demodulates the NRZ-DPSK signals transmitted by its two adjacent channels. In this way, by selecting the transmission channel of the AWG at the transmitting end, different results can be obtained at the corresponding places of the AWG at the receiving end. As shown in Figure 5, the upper row indicated by "AWG1" in the figure is the transmission spectrum of AWG1 at the transmitting end, the middle row indicated by "signal" is the spectrum of multiple NRZ-DPSK signals, and the lower row indicated by "AWG2" One row is the transmission spectrum of AWG2 at the receiving end. It can be seen from the figure that at the transmitting end, the NRZ-DPSK signal is aligned with the odd-numbered channels of AWG1 and transmitted through its odd-numbered channels; the original signal of each NRZ-DPSK signal is obtained from the odd-numbered channels of AWG2 at the receiving end, and the original signal of each NRZ-DPSK signal is obtained at the even-numbered channels of AWG2 It is the demodulation signal of the NRZ-DPSK signal of an adjacent channel. In the figure, the solid line arrow corresponds to the channel for obtaining the original signal, and the dotted line arrow corresponds to the channel for obtaining the demodulated signal.

On the basis of the above theoretical analysis, according to the experimental device in Figure 3, the new NRZ-DPSK WDM system can be simulated by using the commercial optical fiber communication software VPI.

The four NRZ-DPSK signals are 193.1THz, 193.3THz, 193.5THz and 193.7THz respectively, and are multiplexed through an 8-channel AWG. After transmission through the optical fiber link, at the receiving end, an 8-channel AWG is also used to demultiplex and demodulate, and the original NRZ-DPSK signals are obtained on its odd channels, and the original NRZ-DPSK signals are obtained on its even channels. demodulate the signal. The AWG parameters in the simulation are all commercial AWG parameters, the wavelength interval is 100GHz, the transmission function of each channel is a Gaussian function, and the 3dB bandwidth is 55GHz.

Taking each signal transmission 20Gb/s as an example, the simulation results are as follows:

a) After passing through the AWG at the transmitting end, the spectrum diagram of the multiplexed four-way DPSK signal, as shown in Figure 6, the channel spacing is 200GHz;

b) The eye diagram and spectrum of the original NRZ-DPSK1 signal received by different channels of the AWG at the receiving end, as shown in Figure 7, since the NRZ-DPSK signal is generated by the MZM working in the push-pull mode, the phase jump There will be a sag at the place. If the PM is used to obtain the NRZ-DPSK signal, the original NRZ-DPSK signal obtained will not have this sag. But at this time, after passing through the AWG, due to the limited bandwidth of each channel of the AWG, sags will also appear. But whether there is a sag or not, there is a phase jump, so it does not affect the demodulation. The left part of Fig. 7(a) is the eye diagram of the original NRZ-DPSK1 signal received from channel 1 at the receiving end, and the right part is its spectrogram. Comparing the spectrum diagram in Figure 6, it can be found that the shape of the spectrum is consistent, which indicates that the channel 1 of the receiving end obtains a signal that is consistent with the original NRZ-DPSK signal sent by the transmitting end, and the receiving end can be used to download and forward or choose to continue transmission . The left part of Figure 7(b) is the eye diagram of the signal received from channel 2 of the receiving end after demodulation by the filter. It can be seen that the original NRZ-DPSK signal sent by the transmitting end has been demodulated to become Amplitude modulated signal; the right part of accompanying drawing 7(b) is the demodulated spectrogram, compared with the spectrogram in accompanying drawing 6, there are obvious differences.

The other channels will also get the corresponding original signal and demodulated signal at the same time. The simulation result here is 20Gb/s, ideal results can also be obtained for 10 and 40Gb/s, and will not be repeated here.

The transmission control method of a WDM system provided by the present invention can realize the demodulation and demultiplexing of the non-return-to-zero phase modulation format in the wavelength division multiplexing system at the same time, without any modification to the original system, and no need to add any devices, greatly saving costs.

Since the present invention does not need to modify the original system and does not need to introduce a DPSK signal demodulation device, the wavelength division multiplexing system adopting the present invention can be applicable to the transmission of NRZ signals and NRZ-DPSK signals at the same time.

The invention utilizes different channels of the AWG at the receiving end to simultaneously obtain the original NRZ-DPSK signal and its demodulated signal. For the obtained original signal, it can continue to be transmitted or downloaded to the local forwarding and other operations; for the obtained demodulated signal, it can be directly detected by ordinary receivers to obtain the information contained in it. Improve the flexibility of WDM system.

The present invention is also applicable to the transmission of NRZ and NRZ-DPSK signals of different rates.

Description of drawings

Below in conjunction with accompanying drawing, the technical scheme of the utility model is described further in detail.

Figure 1 is the NRZ-DPSK WDM system diagram of the existing conventional scheme.

Figure 2(a) is a schematic diagram of the implementation of an existing improved NRZ-DPSK WDM system.

Figure 2(b) is a schematic diagram of another existing improved NRZ-DPSK WDM system implementation.

Fig. 3 is a schematic diagram showing the structure of signal transmission realized by the NRZ-DPSK WDM system according to the embodiment of the present invention.

FIG. 4 shows the principle basis of the present invention: a schematic diagram of a single detuning filter demodulating a single-channel NRZ-DPSK signal.

FIG. 5 is a schematic diagram showing the spectrum corresponding to signal transmission and demodulation of the NRZ-DPSK WDM system according to the embodiment of the present invention.

Fig. 6 shows the multiplexing spectrum diagram after the transmitting end of the NRZ-DPSK WDM system for signal transmission in a specific embodiment of the present invention passes through the AWG.

Fig. 7 (a) shows the eye pattern and the spectrum of the signal received by AWG channel 1 at the receiving end of the NRZ-DPSK WDM system of the embodiment of the present invention for signal transmission.

Figure 7(b) shows the eye diagram and spectrum of the signal received by the receiving end AWG channel 2 of the NRZ-DPSK WDM system of the embodiment of the present invention for signal transmission.

Detailed ways

As shown in Figure 3, it is a schematic diagram of the launch, transmission and reception of the new NRZ-DPSK WDM system. The working principles, implementation conditions and steps of each part are described in detail below.

Since the key of the present invention is to skillfully select the channels of the AWG at the transmitting end and the receiving end, so as to realize multiple functions. Therefore, first, the channel selection principles of the AWG at the transmitter and receiver are explained and explained:

According to different intervals (ie, channel intervals) of wavelengths (or frequencies) of optical signals transmitted by adjacent channels, the International Telecommunication Union (ITU) has made detailed regulations on the wavelength division multiplexing (WDM) system. WDM systems are divided into Dense Wavelength Division Multiplexing (DWDM) and Coarse Wavelength Division Multiplexing (CWDM).

The channel spacing of the DWDM system can be 12.5GHz, 25GHz, 50GHz, 100GHz, 200GHz, 300GHz, 400GHz, etc.; and the channel spacing of the CWDM system is 2500GHz. It should be noted that the ITU only specifies the channel spacing, but does not specify the signal rate transmitted in each channel. People need to decide which DWDM channel interval to choose according to the signal rate to be transmitted. The higher the signal rate transmitted in each channel, the greater the channel interval. Generally speaking, if you want to transmit a 40Gb/s signal in each channel, the channel spacing must be greater than 40*2=80GHz. So for the 40Gb/s signal, you can choose DWDM 100GHz, 200GHz, 300GHz channel spacing, and CWDM channel spacing. And it can be applied to the channel interval of 40Gb/s signal transmission, and can be compatible with the transmission of lower rate signals, that is, it is applicable to the channel interval of 40Gb/s signal, and also applicable to 20Gb/s, 10Gb/s, etc.

In the specific real-time mode of the present invention, the transmission of high-speed signals from 10Gb/s to 40Gb/s is taken as an example, so the channel spacing (including CWDM) of 100 GHz and above in compliance with ITU regulations will be discussed below.

As for how to realize different channel spacing, taking a commercial AWG with 100GHz channel spacing as an example, it can be realized by the following method:

1) When each channel of the AWG transmits signals, the channel interval is 100GHz; 2) When the AWG only has odd or even channels to transmit signals, other channels are idle, and the channel interval is 200GHz; 3) When this When channels 1, 4, 7, and 10 of the AWG transmit signals, other channels are idle, and the channel interval is 300GHz. Other channel intervals can be deduced by analogy.

The present invention utilizes a certain idle channel of the AWG to demodulate the signals in two adjacent channels, including the following situations:

a) If there are signal transmissions in two adjacent channels of a certain channel, the demodulated signals of these two signals will be obtained at the same time in this channel, but the filter in the subsequent receiver can separate the two signals very well. To demodulate the signal, choose one of them. This case corresponds to the following case 1).

b) If only one of the two adjacent channels of a certain channel has signal transmission and the other channel is idle, then the demodulated signal of this signal is obtained in this channel. This case corresponds to the following case 2).

c) If the AWG has no free channels, that is, each channel has signal transmission, other methods can be used to create some free channels, which corresponds to the following case 3).

Assume that the channels of the AWG (called AWG1) with a channel spacing of 100 GHz at the transmitter are I1, I2, I3, I4, etc., when

1) The channel spacing is 200GHz (Note: The signal rate transmitted by each channel can be 10Gb/s, 20Gb/s and 40Gb/s, the same below)

At this time, select odd-numbered channels such as I1, I3, and I5 of AWG1 to transmit signals, and even-numbered channels are idle (conversely, you can also select even-numbered channels such as I2, I4, and I6 for transmission, and odd-numbered channels are idle). In this way, at the AWG (called AWG2) of the same specification at the receiving end, the odd-numbered channels such as I1, I3, and I5 can obtain the original signals transmitted by the I1, I3, and I5 channels of AWG1. In the even-numbered channels such as I2, I4, and I6 of AWG2, although there is no signal transmitted from the corresponding channel at AWG1, the demodulated signal of its adjacent channel can be obtained (the principle will be analyzed later). For example, in the I2 channel of AWG2, the demodulated signals of the I1 channel and the I3 channel can be obtained at the same time; in the I4 channel of the AWG, the demodulated signals of the I3 channel and the I5 channel can be obtained at the same time. It should be noted that the demodulated signals of two adjacent odd-numbered channels can be obtained in each even-numbered channel, but the ordinary filter in the receiver can select one of the demodulated signals and filter out the other one.

2) The channel spacing is 300GHz and above

Taking the 300GHz channel spacing as an example, channels such as I1, I4, and I7 are selected to transmit signals, and other channels are idle. In this way, the I2 channel of AWG2 can get the demodulated signal of the I1 channel; the I3 and I5 channels can get the demodulated signal of the I4 channel. Moreover, the corresponding channel only obtains the demodulated signal of one adjacent channel, instead of obtaining two demodulated signals as in 1). In this case, optical amplifiers and filters in the receiver can be further saved, and this system can also be used in WDM passive optical networks (PON).

400GHz, 500GHz, 600GHz, etc., including CWDM, are similar to 300GHz, so I won’t repeat them here.

3) The channel spacing is 100GHz

At this point the situation is more complicated. Each channel of AWG1 transmits signals, but at the receiving end, an interleaver is used to divide all channels into two groups, one group of odd channels and one group of even channels. Next, for the cases of odd groups and even groups respectively, it is the same as case 1).

Next, in combination with Figure 3, we will give a detailed description of the 200GHz situation analyzed above.

(1) Transmitter

The transmitting end is the same as the traditional WDM system without any modification. Each channel of NRZ-DPSK signals conforming to the wavelength specified by ITU WDM is multiplexed by AWG (or each channel of continuous light with different wavelengths is multiplexed by AWG1, and then modulated by an MZM or PM). However, the difference from the common system is that one channel is used to transmit a signal here, that is, the AWG that complies with the 100GHz interval specified by the ITU transmits signals at a 200GHz interval. As shown in the figure, the odd-numbered channels of AWG1 transmit the wavelengths specified by ITU, and the even-numbered channels are idle and can also be used for other purposes. It is worth noting that the flexibility of the WDM system is preserved here, and the signal rate transmitted on each channel is variable, such as 10Gb/s, 20Gb/s or 40Gb/s and so on. And since no other devices are introduced, the invention is also applicable to WDM systems in NRZ format.

(2) Receiver

No changes are required on the receiving end either. The AWG at the receiving end is the same as the parameters at the transmitting end, but each channel is used. As shown in AWG2 in the figure, the wavelength of each channel is exactly the same as that of AWG1, which conforms to the regulations of ITU. The odd channel of AWG2 can receive the original NRZ-DPSK signal of each channel, which can be used to download the original signal and forward it or choose to continue the transmission. For example, the first channel (I1) of AWG2 can get the first channel (I1) of AWG1 for transmission At the same time, the even-numbered channel of AWG2 can get the demodulation signal of the DPSK signal of its two adjacent odd-numbered channels, such as the second channel (I2) of AWG2 can get the first channel (I1) and the first channel (I1) of AWG1 The demodulated signal of the NRZ-DPSK signal transmitted in the three channels (I3) is used for subsequent direct detection and information extraction.

But it should be noted that each even-numbered channel of AWG2 will get the demodulated signals of the original two signals, and one of them must be extracted for detection, and the crosstalk of the other channel must be eliminated as much as possible. At this time, subsequent receivers of this channel are used to achieve this purpose without additional processing. A general receiver (receiver) is composed of a preamplifier (EDFA), a filter (filter) and a photodetector (PD), as shown in a dashed box in FIG. 3 . Among them, the function of the filter is to filter out the noise introduced by the EDFA, and its center wavelength is the wavelength of the received optical signal. At the same time, this filter can also be used to select one of the two wavelengths to be received for detection. For example, for the second channel (I2) of AWG2, although there are demodulated signals of two wavelengths (λ ₁ and λ ₂ ), the center wavelength of the filter in the receiver here is λ ₁ , which can filter out λ ₂ , so that the PD receives the information obtained by demodulation of _λ1 .

If the incident signal interval at AWG1 is not 200GHz, but larger, such as 300GHz, this crosstalk problem does not exist. At this time, the incident ports of AWG1 are 1, 4, 7, 10 and so on. Take the first channel (I1) signal of AWG1 as an example. At this time, the first channel of AWG2 still gets the original incident NRZ-DPSK signal, and the second channel can get the demodulated signal of this NRZ-DPSK signal, and will not get AWG1 The I4 demodulated signal, there is no crosstalk problem.

In the present invention, AWG2 can play a dual role: 1. demultiplexing. It can demultiplex the various signals multiplexed by AWG1 to the corresponding ITU channel, continue to transmit or forward, and maintain the flexibility of the WDM system; 2. Demodulation. Cooperating with the follow-up ordinary intensity modulation signal receiver (no DPSK receiver or special device is required), each NRZ-DPSK signal multiplexed by AWG1 can be demodulated into corresponding intensity modulation signals and directly detected. What needs to be emphasized is that these two functions of AWG2 exist and are realized at the same time, and are realized by its odd-numbered channels and even-numbered channels respectively. This allows AWG2 to be used not only at the receiving end, but also in line transmission or network nodes, which greatly improves the flexibility of this NRZ-DPSK WDM system.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention without limitation. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be Modifications or equivalent replacements of the technical solutions without departing from the spirit and scope of the technical solutions of the present invention shall be covered by the scope of the claims of the present invention.

Claims (1)

1. A transmission control method of a wavelength division multiplexing system, characterized in that, without changing the original WDM system, on the transmitting end AWG, select channels at intervals to carry out multi-channel signal transmission, and the interval number is an integer parameter m , m is greater than zero and less than half of the number of channels; the channel of the receiving AWG corresponding to the channel of the transmitting AWG transmission signal receives the original signal transmitted by the transmitting AWG channel, downloads and forwards or continues to transmit, in this Receive the adjacent channel of the channel, receive the demodulated signal of the original signal, and select or directly extract the information through filtering; the specific methods include: When m=1, then, At the transmitter, select the odd-numbered channels of the AWG at the transmitter to transmit signals, and the even-numbered channels are idle; At the receiving end, the odd-numbered channel of the receiving end AWG receives the original signal transmitted by the odd-numbered channel of the transmitting end AWG, downloads and forwards or chooses to continue transmission; the even-numbered channel of the receiving end AWG receives its adjacent two odd-numbered channels The demodulation signal of the demodulation signal is selected by the filter at the receiving end from the demodulation signals of the two adjacent odd-numbered channels, and the other one is filtered out for subsequent direct detection and information extraction; or; At the transmitting end, select the AWG even-numbered channel of the transmitting end to transmit the signal, and the odd-numbered channel is idle; At the receiving end, the even channel of the AWG at the receiving end receives the original signal transmitted by the odd channel of the AWG at the transmitting end, downloads and forwards or chooses to continue transmission; at the odd channel of the AWG at the receiving end, it receives two adjacent even For the demodulated signal of the channel, the filter at the receiving end selects one demodulated signal from the demodulated signals of the two adjacent even-numbered channels, and filters out the other one for subsequent direct detection and information extraction; When m>1, then, At the transmitting end, select a channel with an interval m of the AWG at the transmitting end to transmit signals, and the unselected channels are idle; At the receiving end, the channel of the receiving end AWG corresponding to the channel of the transmitting end AWG transmission signal receives the original signal transmitted by the transmitting end AWG channel, downloads and forwards or chooses to continue transmission; on the adjacent channel receiving the original signal channel, the receiving end The demodulated signal of the original signal is used for subsequent direct detection and information extraction.

Images