JP2013168769A - Device and method for generating various modulation type optical signals - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for generating various modulation type optical signals for reducing costs of a transmission device with a simpler constitution.SOLUTION: The transmission device comprises: a dual drive Mach-Zehnder modulator for operating an amplitude and a phase of optical signals; a phase modulator for multiple phase-modulating the operated optical signals; and drive means for generating drive signals for driving the two modulators according to a modulation type. In particular, the amplitude and the phase of the optical signals are operated at A=A/2=V/2 and v=0.58 V, so as to generate eight quadrature amplitude modulation type (8QAM) optical signals.

Description

  The present invention relates to an apparatus and a method for generating optical signals of various modulation formats used in an optical communication system including an optical communication apparatus and an optical fiber link.

  Conventionally, there are two methods for generating an 8 quadrature amplitude modulation (8 QAM) optical signal having an optimal arrangement.

  One method is to use a combined transmitter comprising a π / 4 bias dual parallel Mach-Zehnder modulator DP-MZM (comprising two sub-MZMs integrated with a main MZ interferometer) and a phase modulator ( Non-patent document 1). The π / 4 bias DP-MZM is used to generate a four amplitude and phase modulated signal, each MZM being driven by a binary electrical signal with a different drive voltage. After [0,2π] phase modulation, an 8QAM signal is generated by using a phase modulator.

  Another method uses a single π / 4 bias DP-MZM together with a high-speed arbitrary waveform generator (AWG) or a digital-to-analog converter (DAC) (Non-patent Document 2). With the use of AWG or DAC, the in-phase and quadrature components of the 8QAM signal are each modulated with two independent MZMs of DP-MZM.

In order to efficiently use spectrum resources in a dynamically reconfigurable wavelength division multiplexing (WDM) network, an optical communication device can provide flexibility (that is, the modulation format of an optical signal can be flexibly changed). desired. For this reason, several techniques are proposed. Among these, a new type of transmission device in which a silica planar lightwave circuit (PLC) and a LiNbO ₃ phase modulator are hybridly integrated has been proposed (Non-patent Document 3).

J. Yu, et al., "High-Speed PDM-RZ-8QAM DWDM Transmission (160x114 Gb / s) Over 640 km of Standard Single-Mode Fiber" IEEE PTL, vol.21, no. 18, pp. 1299- 1301, 2009 N. Kikuchi, et al., "Highly Sensitive Optical Multilevel Transmission of Arbitrary Quadrature-Amplitude Modulation (QAM) Signals With Direct Detection" JLT, vol. 28, no. 1, pp. 123-130, 2010 H. Takara, et al., "Experimental Demonstration of 400 Gb / s Multi-flow, Multirate, Multi-reach Optical Transmitter for Efficient Elastic Spectral Routing" ECOC2011, paper Tu.5.A.4

  However, the transmission apparatus configurations of Non-Patent Documents 1 and 2 have a problem of requiring a very expensive device such as a feedback circuit and / or AWG for controlling the bias point of DP-MZM.

  Further, in order to generate an optical signal using the transmission device of Non-Patent Document 3, many control parameters such as a tuning coupler, a phase shifter, and a bias controller are required. As a result, there has been a problem that these transmission devices become complicated and cost increases.

  Therefore, an object of the present invention is to provide an apparatus and a method for generating optical signals of various modulation formats with a simpler configuration and reducing the cost of a transmission apparatus.

  In order to solve the above problems, a transmitter of the present invention includes a dual drive Mach-Zehnder modulator that manipulates the amplitude and phase of an optical signal, a phase modulator that multi-phase modulates the manipulated optical signal, and a modulation format, Drive means for generating a drive signal for driving the two modulators.

  The dual drive Mach-Zehnder modulator preferably manipulates the amplitude and phase of the optical signal with the first drive signal and an inverted signal of the first drive signal.

The amplitude (A ₁ ) of the first drive signal, the amplitude (A ₂ ) of the inverted signal of the first drive signal, and the bias voltage (v _b ) of the dual drive Mach-Zehnder modulator are determined by the drive means. Thus, it is also preferable to adjust the amplitude and phase of the optical signal.

Further, when the dual drive Mach-Zehnder modulator operates A ₁ = A ₂ = v _b = V _π (switching voltage of the dual drive Mach-Zehnder modulator) and M is an even number by manipulating the amplitude and phase of the optical signal. It is also preferred to generate an optical signal of some (differential) M phase shift keying format ((D) xPSK).

The dual drive Mach-Zehnder modulator generates an optical signal of 6 quadrature amplitude modulation format (6QAM) by manipulating the amplitude and phase of the optical signal at A ₁ = A ₂ = v _b = 2V _π / 3 It is also preferable to do.

Further, the dual-drive Mach-Zehnder _modulator, in _{A 1 = A 2/2 =} V π / 2 and _v b = 0.58 V _[pi, by manipulating the optical signal amplitude and phase, 8 quadrature amplitude modulation format ( It is also preferable to generate an optical signal of 8QAM).

The amplitude (G ₁ and G ₂ ) of the drive signal for the phase modulator is preferably adjusted by the drive means for modulating the phase of the optical signal.

It is also preferable that the phase modulator generates a binary modulation type optical signal by manipulating the phase of the optical signal with G ₁ = G ₂ = 0.

It is also preferable that the phase modulator generates an optical signal in a quaternary modulation format by manipulating the phase of the optical signal with G ₁ = _Vπ and G ₂ = 0.

It is also preferable that the phase modulator generates a six-value modulation type optical signal by manipulating the phase of the optical signal with G ₁ = G ₂ = 2V _π / 3.

Further, the phase modulator, by manipulating the phase of the optical signal in _{G 1 = G 2/2 =} V π, it is also preferable to generate an optical signal of 8-level modulation format.

  In order to solve the above problems, a method for generating an optical signal in various modulation formats according to the present invention includes the steps of manipulating the amplitude and phase of an optical signal, multi-phase modulating the manipulated optical signal, Generating a drive signal to drive the two modulators according to a modulation format.

  As described above, the transmission apparatus of the present invention includes only a dual drive Mach-Zehnder modulator and a phase modulator. For this reason, only one feedback control circuit is required for bias control of the dual drive Mach-Zehnder modulator. As a result, the configuration of the transmitter is simplified and the cost is greatly reduced. In addition, the bottom area of the transmitter is reduced.

The structure of the transmission apparatus of this invention is shown. The transfer curve characteristic of DD-MZM for conventional (D) BPSK signal modulation is shown. The arrangement | positioning figure of the (Dx) PSK optical signal produced | generated by this transmitter is shown. The transfer curve characteristic of DD-MZM for 6QAM signal modulation is shown. An arrangement diagram of an optical signal at an output of DD-MZM and an arrangement diagram of a 6QAM optical signal generated by the transmission apparatus are shown. The transfer curve characteristic of DD-MZM for 8QAM signal modulation is shown. FIG. 2 shows an arrangement diagram of optical signals at the output of DD-MZM and an arrangement diagram of 8QAM optical signals generated by the transmission apparatus.

  The best mode for carrying out the present invention will be described in detail below with reference to the drawings. FIG. 1 shows the configuration of the transmission apparatus of the present invention. This transmission apparatus includes a laser light source 1 and an optical phase modulation unit 2, and the optical phase modulation unit 2 includes a dual drive Mach-Zehnder modulator 21 (DD-MZM), a phase modulator 22 (PM), and an encoder 23.

The optical phase modulation unit 2 performs optical phase modulation on the continuous light from the laser light source 1 based on the data v ₁ (t) and v ₂ (t) of the input electrical signal, and outputs the phase modulated optical signal to the optical transmission line. .

によって駆動される。もし、データとその反転データの振幅が一致（つまり、Ａ_１＝Ａ_２）する場合、この変調器はプッシュプルモードで動作するため、チャープ無しの光信号を得ることができる。しかしながら、駆動信号の振幅が異なった状態（Ａ_１≠Ａ_２）で、バイアス電圧ｖ_ｂを変化させることで、光信号のチャープを調整できる。ＤＤ−ＭＺＭ２１の分岐／合成比を同じにすると、ＤＤ−ＭＺＭの伝達関数は、

で表される。ここで、Ｖ_πはＤＤ−ＭＺＭ２１のスイッチング電圧である。したがって、３つのパラメータ（Ａ_１，Ａ_２、ｖ_ｂ）を調節することによって、光信号の振幅と位相を操作することができる。 The DD-MZM 21 includes two Mach-Zehnder modulators (MZM), and the continuous light is branched into two, and after the amplitude and phase are manipulated by the drive signal in each MZM, they are combined and output. Since the chirp of the optical signal can be controlled by adjusting the magnitude of the drive signal, the amplitude and phase of the optical signal can be manipulated. DD-MZM21 is a set of electrical signals,

Driven by. If the amplitude of the data and its inverted data match (that is, A ₁ = A ₂ ), this modulator operates in the push-pull mode, so that an optical signal without chirp can be obtained. However, with the amplitude of the drive signal is different (A ₁ ≠ A _2), by changing the bias voltage v _b, can be adjusted chirp of the optical signal. When the branch / synthesis ratio of DD-MZM21 is the same, the transfer function of DD-MZM is

It is represented by Here, the V _[pi is the switching voltage of the DD-MZM21. Therefore, the amplitude and phase of the optical signal can be manipulated by adjusting the three parameters (A ₁ , A ₂ , v _b ).

The phase modulator 22 performs binary, ternary, or quaternary phase modulation by sending a multi-level electrical signal v ₂ (t), and an optical signal of QPSK, 6PSK / 6QAM, or 8PSK / 8QAM modulation format. Can be modulated.

The encoder 23 drives the DD-MZM 21 using the data signal v ₁ (t) and its inverted data as drive signals. Further, the phase modulator 22 is driven using the data signal v ₂ (t) as a drive signal. At this time, the encoder 23 outputs two drive signals whose amplitudes are adjusted in order to modulate the phase of the optical signal, and drives the phase modulator 22 with the data signal v ₂ (t) obtained by adding them.

  As described above, the transmission apparatus of the present invention can be used to flexibly modulate an optical signal with various modulation formats (BPSK, QPSK, 6PSK / 6QAM, and 8PSK / 8QAM).

  Hereinafter, some examples of the modulation format of the transmission apparatus of the present invention will be described.

The first embodiment shows a (differential) M phase shift keying format ((D) × PSK). Here, M = 2, 4, 6, and 8. FIG. 2 shows a transfer curve characteristic of DD-MZM for conventional (D) BPSK signal modulation. By setting A ₁ = A ₂ = v _b = V _π , a conventional (D) BPSK signal can be obtained at the output of DD-MZM. Thereafter, when nothing is input to the phase modulator, that is, when v ₂ (t) = 0 (G ₁ = G ₂ = 0), the transmission apparatus of the present invention can generate a (D) BPSK optical signal. By inputting a binary value ([0, π / 2] phase modulation) v ₂ (t) with G ₁ = V _π and G ₂ = 0 to the phase modulator, the transmitting apparatus of the present invention can perform (D) QPSK light. A signal can be generated. Similarly, by inputting ternary ([0, π / 3, 2π / 3]) phase modulation v ₂ (t) with G ₁ = G ₂ = 2V _π / 3 to the phase modulator, (D) 6PSK light signals, four values in _{G 1 = G 2/2 =} V π to the phase modulator ([0, π / 4, π / 2,3π / 4] phase _{modulation) v} 2 can be entered in the (t) ( D) An 8PSK optical signal can be generated. FIG. 3 is a layout diagram of (Dx) PSK optical signals generated by the transmission apparatus.

In the second embodiment, 6 quadrature amplitude modulation format (6QAM) is shown. Since this transmitter generates a 6QAM signal with the optimal arrangement shown in the right diagram of FIG. 5, the DD-MZM operates in the push-pull mode, but the amplitude and bias voltage of the drive signal are the same as those in the first embodiment. Slightly different. FIG. 4 shows the transfer curve characteristics of DD-MZM for 6QAM signal modulation. By setting A ₁ = A ₂ = v _b = 2V _π / 3, the optical signal is modulated with a phase difference between the two symbols of π and an amplitude ratio of 1: 2. The left diagram in FIG. 5 shows an arrangement diagram of optical signals at the output of the DD-MZM. Thereafter, 3 values _{G 1 = G 2 = 2V π} / 3 to the phase modulator _{(amplitude v} 2 (t) is 0,2V π _/ 3,4V π / 3) By inputting the electrical signal The transmission apparatus of the present invention can generate a 6QAM optical signal. The right diagram in FIG. 5 shows a layout diagram of 6QAM optical signals generated by this transmission apparatus.

In the third embodiment, 8 quadrature amplitude modulation format (8QAM) is shown. This transmitting apparatus can also be used to generate an 8QAM signal with an optimal arrangement as shown in the right diagram of FIG. In the case of 8QAM modulation, the amplitude of the drive signal of DD-MZM needs to be different. FIG. 6 shows the transfer curve characteristics of DD-MZM for 8QAM signal modulation. By the _{A 1 = A 2/2 =} V π / 2 and _{v b} ≒ 0.58V _π, the phase difference between two symbols 3 [pi] / 4, amplitude ratio (1 + √3): in √2 The optical signal is modulated. The left diagram in FIG. 7 shows an arrangement diagram of optical signals at the output of the DD-MZM. Thereafter, the phase modulator _{G 1 = G 2/2 =} V 4 values _{[pi (amplitude v} 2 (t) is _{0, V π / 2, V} π, and a 3V _π / 2) the electrical signal By inputting, the transmission apparatus of the present invention can generate an 8QAM optical signal. The right diagram of FIG. 7 shows an arrangement diagram of 8QAM optical signals generated by this transmission apparatus.

  In DD-MZM, the phase difference between two symbols is π / 4, the amplitude ratio is (1 + √3): √2, and it is also possible to generate an 8QAM optical signal by modulating the optical signal. It is.

  Moreover, all the embodiments described above are illustrative of the present invention and are not intended to limit the present invention, and the present invention can be implemented in other various modifications and changes. Therefore, the scope of the present invention is defined only by the claims and their equivalents.

DESCRIPTION OF SYMBOLS 1 Laser light source 2 Optical phase modulation part 21 Dual drive Mach-Zehnder modulator 22 Phase modulator 23 Encoder

Claims (12)

A dual drive Mach-Zehnder modulator that manipulates the amplitude and phase of the optical signal;
A phase modulator for multi-phase modulating the manipulated optical signal;
Drive means for generating a drive signal to drive the two modulators according to a modulation format;
A transmission device comprising:   The transmission device according to claim 1, wherein the dual drive Mach-Zehnder modulator controls an amplitude and a phase of an optical signal by a first drive signal and an inverted signal of the first drive signal. The amplitude (A ₁ ) of the first drive signal, the amplitude (A ₂ ) of the inverted signal of the first drive signal, and the bias voltage (v _b ) of the dual drive Mach-Zehnder modulator are the drive means, The transmitter according to claim 1, wherein the transmitter is adjusted to manipulate the amplitude and phase of the optical signal. When the dual drive Mach-Zehnder modulator operates A ₁ = A ₂ = v _b = V _π (switching voltage of the dual drive Mach-Zehnder modulator), M is an even number by manipulating the amplitude and phase of the optical signal ( 4. The transmission apparatus according to claim 3, wherein the transmission apparatus generates an optical signal of a (differential) M phase shift keying format ((D) xPSK). The dual drive Mach-Zehnder modulator generates an optical signal of 6 quadrature amplitude modulation format (6QAM) by manipulating the amplitude and phase of the optical signal at A ₁ = A ₂ = v _b = 2V _π / 3 The transmission apparatus according to claim 3. The dual-drive Mach-Zehnder _modulator, in _{A 1 = A 2/2 =} V π / 2 and _v b = 0.58 V _[pi, by manipulating the optical signal amplitude and phase, 8 quadrature amplitude modulation format (8 QAM) The transmission apparatus according to claim 3, wherein the optical signal is generated. _2. The transmission device according to claim 1, wherein the amplitude (G ₁ and G ₂ ) of the driving signal of the phase modulator is adjusted by the driving unit to modulate the phase of the optical signal. 8. The transmission apparatus according to claim 7, wherein the phase modulator generates an optical signal in a binary modulation format by manipulating the phase of the optical signal with G ₁ = G ₂ = 0. 8. The transmission apparatus according to claim 7, wherein the phase modulator generates an optical signal in a quaternary modulation format by manipulating the phase of the optical signal with G ₁ = V _π and G ₂ = 0. . The transmission device according to claim 7, wherein the phase modulator generates an optical signal in a six-value modulation format by manipulating the phase of the optical signal with G ₁ = G ₂ = 2V _π / 3. . It said phase modulator, by manipulating the phase of the optical signal in _{G 1 = G 2/2 =} V π, transmission apparatus according to claim 7, characterized in that to generate a light signal of 8-level modulation format . Manipulating the amplitude and phase of the optical signal;
Multi-phase modulating the manipulated optical signal;
Generating a drive signal to drive the two modulators in accordance with a modulation format. The method for generating an optical signal in various modulation formats.

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