KR20100068156A - Optical transmitting apparatus for rz-dpsk and rz-dqpsk - Google Patents

Abstract

PURPOSE: An RZ-DPSK and RZ-DQPSK optizal transmitting device are provided to reduce optical insertion loss and constitute an economic optical transmitter with a simple structure by producing RZ-DPSK or RZDQPSK signal without using an RZ modulator. CONSTITUTION: A mixer(520) receives a data signal and a clock signal of data transmission speed of half frequency of the received the data signal, mixes and outputs a driving data signal. A phase modulator(510) uses the operating data signal to modulate the optical signal outputted in the light source. The phase modulator is a mach-zehnder modulator. The clock signal is electrically synchronized with data signal and is inputted to the mixer.

Description

Optical transmitting apparatus for RZ-DPSK and RZ-DQPSK

The present invention relates to an optical transmission device for transmitting an ultra-high speed optical signal, and more particularly, to an optical transmission device having a phase shift modulation method.

This study is derived from the research conducted as part of the IT source technology development project of the Ministry of Knowledge Economy and the Ministry of Information and Telecommunication Research and Development. [Task Management No .: 2008-F-017-01, Project Name: Development of 100Gbps Ethernet and Optical Transmission Technology] ]

Internet traffic continues to increase. In particular, with the advent of Ethernet-based services such as Internet TV and User Created Contents (UCC), traffic is increasing day by day, and wider network becomes essential. In addition, the wavelength division multiplexing optical transmission system that multiplexes and transmits multiple wavelengths within one optical fiber is recognized as the most efficient means of accommodating the increased traffic, and to this end, it increases the transmission speed per wavelength (channel). However, various modulation schemes have emerged around high-speed channels.

More than 40G signals per wavelength are emerging to meet bandwidth demands at the point where data traffic is concentrated, such as high performance computing, servers, data sensors, enterprise networks, and Internet exchange centers. The transmitter is not only a simple Non-Return-to-Zero (NRZ) or Return-to-Zero (RZ) to turn the size of the optical signal on and off, but also a Differential Phase Shift Key (DPSK) to modulate the phase of the optical signal. Differential quaternary phase shift key (DQPSK) modulation schemes that can send more than two bits per symbol are emerging. Here, the DPSK or DQPSK method has the advantage of overcoming the limitations of the optical / electrical elements in the high speed optical transmission system and suppressing various limitations generated in the optical path.

It is an object of the present invention to provide an optical transmitter capable of generating an RZ-DPSK or RZ-DQPSK signal without using a separate RZ modulator.

RZ-DPSK optical transmission device for achieving the above technical problem has a single phase modulator having the same pattern and phase characteristics of the return-to-zero and differential phase shift key signal Output the signal. According to an aspect, an RZ-DPSK optical transmission apparatus includes a mixer configured to receive a data signal output from a precoder and a clock signal having a half frequency of a data transmission rate and to mix and output a driving data signal; And a phase modulator for modulating the optical signal output from the light source by using the driving data signal output from the mixer.

On the other hand, the RZ-DQPSK optical transmission device for achieving the above-described technical problem is the same pattern and phase characteristics of the signal returned zero (Return-to-zero) and DQPSK (Differential Quaternary Phase Shift Key) through two parallel phase modulator Output the signal. The RZ-DQPSK optical transmission apparatus according to an aspect receives and mixes a first data signal generated by a precoder and a clock signal having a half frequency of a first data signal transmission rate, and then mixes the first data signal to output a first driving data signal. Mixer; A second mixer for receiving and mixing a second data signal generated by the precoder and a clock signal having a frequency half of the second data signal transmission rate, and outputting a second driving data signal; And a first phase modulator for modulating the optical signal of the light source using the first driving data signal output and applied from the first mixer, and an optical signal of the light source using the second driving data signal output and applied from the second mixer. And a phase modulator comprising a second phase modulator to modulate, and a phase shifter for generating an output phase difference between the first phase modulator and the second phase modulator.

Unlike the conventional method, since the RZ-DPSK or RZ-DQPSK signals are generated without using a separate RZ modulator, the optical insertion loss is small, the structure is simple, and the economical efficiency of the optical transmitter can be achieved. A narrow bandwidth RF amplifier can also be used to easily amplify the signal. In addition, since the bias is controlled by measuring only the magnitude of the clock frequency of the data itself, the bias control circuit can be simply configured without an external frequency application circuit.

The foregoing and further aspects of the present invention will become more apparent through the preferred embodiments described with reference to the accompanying drawings. Hereinafter, the present invention will be described in detail to enable those skilled in the art to easily understand and reproduce the present invention.

1 is a configuration diagram of a DPSK optical transmitter, FIG. 2 is a reference diagram illustrating a DPSK generation principle, and FIG. 3 is a reference diagram illustrating a RZ conversion and an RZ-DPSK generation principle.

The light source 100 is a component for outputting an optical signal and may be a laser diode (LD). The DPSK modulator 110 is a component for receiving and modulating an optical signal output from the light source 100 and may be a Mach-Zehnder (MZ) modulator. The optical signal modulated by the DPSK modulator 110 is generated by a precoder to modulate the phase to 0 or π according to the electrical data 111 applied to the DPSK modulator 110. As shown in FIG. 2, the bias is placed at the lowest point on the transfer curve of the DPSK modulator, and when the input electrical data 111 is applied by 2 V pi corresponding to one week of the transfer curve, an eye diagram of the DPSK shown in FIG. diagram).

If a separate RZ modulator 120 is connected to the DPSK modulator 110 in series, an eye diagram of the RZ-DPSK shown in FIG. 1 can be obtained as a final output. By connecting the RZ modulator 120 in series to the DPSK modulator 110, the influence of the pattern of the optical / electrical elements used in the DPSK generation can be reduced, and the same performance can be obtained at an optical signal to noise ratio lower than that of the DPSK. . The method of using a frequency equal to 1/2 of the transmission bit rate with the clock signal 121 applied at the lowest point on the transmission curve and a method using the same frequency as the transmission bit rate as shown in FIG. The duty cycle can be adjusted.

Therefore, the RZ-DPSK output shows a sinusoidal signal pattern with values of 0 and π in the phase plane. Despite the advantages of RZ-DPSK, the optical loss is increased by using two MZ modulators. In addition, an optical / electrical element is additionally required for optical synchronization between the DPSK modulator and the RZ modulator, which causes a complicated structure. In the case of an RF amplifier that amplifies the size of the electrical data applied to the MZ modulator, there is a problem that the bandwidth must have a wide bandwidth from DC to the data transmission frequency.

4 is a configuration diagram of an RZ-DQPSK optical transmitter.

DQPSK modulator 400 comprises two MZ modulators 401, 402 and a phase shifter 403 coupled to the output of either MZ modulator 402. Each MZ modulator 401, 402 corresponds to a DPSK modulator. The phase shifter 403 shifts the output signal of the MZ modulator 402 by π / 2, and then adds the output signals of the two MZ modulators 401 and 402 to output the DQPSK signal. Accordingly, an eye diagram of the DQPSK shown in FIG. 4 can be obtained. The DQPSK scheme has an advantage of doubling the transmission speed compared to the DPSK scheme. For reference, the data signal data1 applied to the MZ modulator 401 and the data signal data2 applied to the MZ modulator 402 are signals for the same role as the data signal 111 of FIG. Signals with different patterns generated.

By connecting a separate RZ modulator 410 in series with the DQPSK modulator 400, an eye diagram of RZ-DQPSK shown in FIG. 4 can be obtained as the final output. When the RZ modulator 410 is connected to the DQOSK modulator 400 in series to generate an RZ-DQPSK signal, the influence of the pattern of the optical / electrical element used in generating the DQPSK may be reduced. In addition, the same performance can be achieved at an optical signal-to-noise ratio lower than DPSK. As a result, the output shows a sinusoidal signal pattern and has values of 0, π / 2, π, and 3π / 2 in the phase plane. However, even in this case, a separate RZ modulator is used, which increases optical loss, requires synchronization of the DQPSK modulator and the RZ modulator, and complicates the structure. In addition, there is a disadvantage that can not constitute an economical optical transmitter.

5 is a block diagram of an RZ-DPSK optical transmission device according to an embodiment of the present invention.

The light source 500 is a component for outputting an optical signal, and a laser diode (LD) may be used. The phase modulator 510 is a DPSK modulator for receiving and modulating an optical signal output from the light source 100. In one embodiment, phase modulator 510 is an MZ modulator. The phase modulator 510 according to an aspect of the present invention does not modulate an optical signal by receiving data output from a precoder, but receives a driving data signal output from the mixer 520 to receive an optical signal. It is characterized by modulation. Here, the mixer 520 receives and mixes the data 521 output from the precoder and the clock 522 signal having a frequency half of the data rate, and then phases the mixed driving data 531 signal. Output to modulator 510.

FIG. 6 is a reference diagram for describing a driving data signal generation method of FIG. 5, and FIG. 7 is a reference diagram for explaining a driving data signal application method.

A data 521 output from the precoder and a clock 522 having a frequency 1/2 of the data transmission rate are applied to the mixer 520 to generate a driving data 531 signal. The data produces a positive and negative signal based on ground level, and the 1/2 frequency clock component is applied to mixer 520 in electrical synchronization with the data signal. Therefore, at the output of the mixer 520, a signal corresponding to the product of the data 521 and the half clock 522 signal is generated. At this time, the data and the driving data have a relationship as shown in Table 1, and when the phase of the 1/2 clock is changed 180 degrees, the phase of the driving data also changes 180 degrees.

Data Driving data 1 -1 1 1 1 1 1 -1 -1 -1 -1 1 -1 1 -1 -1

That is, in the driving data signal, '1 1' becomes '-1 -1' and '1 -1' is changed to '-1 1'. As shown in FIG. 7, when the DC amplified signal is applied to the lowest point or the highest point on the transmission curve of the MZ modulator as shown in FIG. 7, and the amplified signal has a size of 2 Vπ, the frequency is increased by 2 times. Signals such as RZ-DPSK and 0 and π values are generated in the phase plane.

According to a further aspect of the present invention, an RF amplifier 530 may be further included as shown in FIG. 5 to appropriately size the electrical signal. Conventionally, a wideband amplifier is needed because the NRZ data must be amplified to drive the MZ modulator. However, since the output signal of the mixer 520 has the same pattern as the clock, the RF amplifier 530 only needs to amplify the frequency 1/2 of the data rate. Therefore, there is an advantage that can use a narrow band RF amplifier.

8 is a block diagram of an RZ-DQPSK optical transmission device according to an embodiment of the present invention.

The light source 800 is a component for outputting an optical signal, and a laser diode (LD) may be used. The phase modulator 810 is a phase shifter 813 connected in series to an output terminal of the first phase modulator 811, the second phase modulator 812 connected in parallel with the first phase modulator 811, and the second phase modulator 812. DQPSK modulator is configured to include. In one embodiment, the first phase modulator 811 and the second phase modulator 812 are MZ modulators. By placing two MZ modulators in parallel and configuring them in the form of Mach-Zehnder interferometers, a DQPSK modulator is implemented.

The first phase modulator 811 receives the first drive data 823 signal output from the first mixer 820 instead of modulating the optical signal by receiving the first data data1 output from the precoder. Modulate the optical signal. The second phase modulator 812 also receives the second drive data 833 output from the second mixer 830 instead of receiving the second data data2 output from the precoder and modulating the optical signal. Modulate the optical signal. The phase shifter 813 phase shifts the output signal of the second phase modulator 812 by [pi] / 2. This is to create a DQPSK signal, as is well known.

The first mixer 820 receives and mixes the first data 821 output from the precoder and a clock 822 signal having a frequency half of the data rate, and mixes the mixed first drive data 823 signals. Output to the first phase modulator 811. The second mixer 830 also receives and mixes the second data 831 output from the precoder and a clock 832 signal having a frequency half of that data rate, and mixes the mixed second drive data 833 signals. Output to the second phase modulator 812. Here, the first data 821 and the second data 831 have different patterns and have the same transmission speed. The method of generating the first drive data 823 and the second drive data 833 and applying the same to the modulator is the same as the method described with reference to FIGS. 6 and 7. As a result, a signal having 0, π / 2, π, and 3π / 2 values can be generated in the data pattern and phase plane of FIG. 9 using a single MZ type DQPSK modulator.

According to a further aspect of the present invention, the first RF amplifier 840 and the second RF amplifier 850 may be further included as shown in FIG. 8 in order to appropriately size the electrical signal. Conventionally, a wideband amplifier is needed because the NRZ data must be amplified to drive the MZ modulator. However, since the output signals of the first mixer 820 and the second mixer 830 have a clock-like pattern, the first RF amplifier 840 and the second RF amplifier 850 amplify only one half of the data rate. Just do it. Therefore, there is an advantage that can use a narrow band RF amplifier.

According to a further aspect of the present invention, the DQPSK optical transmission apparatus further includes a bias controller 860. In one embodiment, the bias controller 860 includes a photodetector 861, an RF power detector 862, and a bias controller 863. The photo detector 861 is a component for detecting and converting an optical signal branched from the output of the phase modulator 810 into an electrical signal, and may be a photodiode. The RF power detector 862 detects the RF power value of the output optical signal, and the bias controller 863 adjusts the bias according to the detected RF power value.

The pattern of the RZ-DQPSK signal has a sinusoidal shape having the same frequency as the transmission rate as shown in FIG. 9, and the RF power of this signal is maximized at the optimum bias value as shown in FIG. This decrease occurs when the propagation curve characteristics of the modulator change. Therefore, the bias controller 860 may optimize the characteristics of the RZ-DQPSK optical transmission apparatus by feeding back and adjusting the bias of the first phase modulator 811 and the second phase modulator 812 so that the magnitude of the detected clock frequency is maximized. Can be.

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

1 is a configuration diagram of a DPSK optical transmitter.

2 is a reference diagram illustrating a principle of DPSK generation.

3 is a reference diagram showing a principle of RZ conversion and RZ-DPSK generation.

4 is a block diagram of an RZ-DQPSK optical transmitter.

5 is a block diagram of an RZ-DPSK optical transmission device according to an embodiment of the present invention.

6 is a reference diagram for explaining a driving data signal generating method of FIG. 5.

7 is a reference diagram for explaining a driving data signal applying method of FIG. 5.

8 is a block diagram of an RZ-DQPSK optical transmission device according to an embodiment of the present invention.

9 is an RZ-DQPSK optical transmitter output eye diagram and constellation according to FIG. 8;

10 is a graph showing a change in RF power according to a bias value.

Claims (15)

And a single phase modulator for outputting a signal having the same pattern and phase characteristics as those of a return-to-zero and differential phase shift key. The method of claim 1, A mixer configured to receive a data signal output from a precoder and a clock signal having a half frequency of the data transmission rate and to mix and output a driving data signal; And A phase modulator for modulating the optical signal output from the light source by using the driving data signal output from the mixer; Optical transmission device comprising a. The method of claim 2, And the phase modulator is a Mach-Zehnder modulator. The method of claim 2, And the clock signal is input to the mixer in electrical synchronization with the data signal. The method of claim 2, And the driving data signal is a signal multiplied by the data signal and a clock signal having the half frequency. The method of claim 2, An RF amplifier for amplifying the driving data signal output from the mixer and outputting the amplified driving data signal to the phase modulator; The optical transmission device further comprises. The method of claim 6, And the RF amplifier is a narrow band RF amplifier that amplifies only half the frequency of the data signal transmission rate. An optical transmission device characterized by outputting a signal having the same pattern and phase characteristics as those of a return-to-zero and differential quaternary phase shift key (DQPSK) signal through two parallel phase modulators connected in parallel. The method of claim 8, A first mixer configured to receive and mix a first data signal generated by a precoder and a clock signal having a frequency half of the first data signal transmission rate, and output a first driving data signal; A second mixer configured to receive and mix a second data signal generated by a precoder and a clock signal having a frequency half of the second data signal transmission rate, and output a second driving data signal; And A first phase modulator for modulating an optical signal of a light source using a first driving data signal output and applied from the first mixer, and a light of the light source using a second driving data signal output and applied from the second mixer A phase modulator comprising a second phase modulator for modulating a signal, and a phase shifter for generating an output phase difference between the first phase modulator and the second phase modulator; Optical transmission device comprising a. 10. The method of claim 9, And the first phase modulator and the second phase modulator are Mach-Zehnder modulators. 10. The method of claim 9, The clock signal input to the first mixer is electrically synchronized with the first data signal and is input to the first mixer, and the clock signal input to the second mixer is electrically synchronized with the second data signal. And input to the second mixer. 10. The method of claim 9, A first RF amplifier amplifying a first driving data signal output from the first mixer and outputting the first driving data signal to the first phase modulator; And A second RF amplifier amplifying a second driving data signal output from the second mixer and outputting the second driving data signal to the second phase modulator; The optical transmission device further comprises. The method of claim 12, And the first and second RF amplifiers are narrowband RF amplifiers that amplify only half the frequency of the data signal transmission rate. 10. The method of claim 9, A bias controller detecting an output of the phase modulator to adjust biases of the first phase modulator and the second phase modulator; The optical transmission device further comprises. The method of claim 14, wherein the bias controller is: A photo detector for converting an output optical signal of the phase modulator into an electrical signal; An RF power detector detecting an RF power of the converted electric signal; And A bias controller configured to adjust biases of the first phase modulator and the second phase modulator based on the detected RF power; Optical transmission device comprising a.

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