KR101864697B1 - Multi-level optical signal generator - Google Patents

Abstract

The present invention relates to a multilevel optical signal generating apparatus, and more particularly, to a multilevel optical signal generating apparatus which includes first and second Mach-Zehnder modulators formed on respective arms of a basic Mach-Zehnder modulator, first and second Mach-Zehnder modulators formed on the second arms of the first and second Mach- 1, second and third Mach-Zehnder modulators, and third and fourth Mach-Zehnder modulators formed on the output side of the first and second Mach-Zehnder modulators, A bias voltage generator for generating a DC bias voltage to be applied to the first and second Mach-Zehnder modulators and the basic Mach-Zehnder modulator, A drive signal generator for generating an input drive signal, and a controller for controlling each of the amplifiers.

Description

[0001] MULTI-LEVEL OPTICAL SIGNAL GENERATOR [0002]

The present invention relates to a multilevel optical signal generator, and more particularly, to a multilevel optical signal generator capable of modulating a modulation method of an optical signal to flexibly adjust a transmission capacity according to transmission demand.

Since the current railway communication network uses a 10 Gb / s wavelength division multiplexing (WDM) system and the channel spacing and bandwidth of optical signals are fixed, efficient operation of data traffic Management requires a technique that can dynamically allocate bandwidth.

Generally, on-off keying (OOK) modulation method, which transmits a signal by modulating the intensity of light, is mainly used in the existing optical signal. However, as the demand for transmission increases rapidly and the technology of the electric / optical device rapidly develops, level modulation scheme in which two or more bits are transmitted to a symbol. For such optical signal modulation, a Mach-Zehnder modulator (MZM) based on a Mach-Zehnder interferometer (MZI) is mainly used.

For reference, the Mach-Zehnder modulator (MZM) uses lithium niobate (LiNbO ₃ ) whose refractive index changes when an electric field is applied, through which the phase of an optical signal is modulated and passed through an interferometer, To modulate the size and phase of the light. At this time, the voltage for 180 ^o phase modulation is referred to as V _? Voltage, and in the case of lithium niobate (LiNbO ₃ ), the voltage is generally about 5V. Accordingly, an amplifier for amplifying the magnitude of the electric signal applied for driving the modulator is essentially used.

)가 인가되어 푸시풀(push-pull) 형태로 동작될 수 있다. 푸시풀 방식의 동작은 같은 위상 변조를 위해서 기존 방식보다 인가되는 전압을 1/2로 감소시킬 수 있으므로 높은 출력의 증폭기를 사용하지 않아도 되는 장점이 있다.1 is a diagram for explaining a method of applying a drive signal to a general Mach-Zehnder modulator. As shown in Fig. 1 (a), a Mach-Zehnder modulator MZM modulates an electric signal (I. E., Data) is applied, or electrical signals (i.e., electrical signals) inverted to both arms are applied as shown in Fig. 1 (b)

May be applied and operated in a push-pull manner. The push-pull operation can reduce the applied voltage to 1/2 of the conventional method for the same phase modulation, so that it is advantageous not to use a high output amplifier.

The I / Q modulator modulates two components (e.g., in-phase and quadrature components) of the complex plane to generate a multi-level modulation scheme such as quadrature phase shift keying (QPSK) Is used.

Herein, the I / Q modulator is a dual-parallel MZM structure in which two Mach-Zehnder modulators (MZM) are integrated in parallel, as shown in FIG. At this time, two components (e.g., in-phase and quadrature) data of the optical signal are applied to each Mach-Zehnder modulator (MZM) of the dual-parallel MZM, By applying one data to each MZM as shown in FIG. 2B or applying an inverted signal of each data as shown in FIG. 2B to operate each MZM in a push-pull manner, (Quadrature Phase Shift Keying) optical signal.

Meanwhile, optical transmitters (or optical signal generators) that flexibly generate optical signals of various modulation types according to demand (that is, generate multi-level optical signals) can be classified into two types.

The first is an optical transmitter that uses one optical modulator (or Mach-Zehnder modulator) and uses the driving electrical signal of the optical modulator at multi-level (see FIG. 3), the second uses a combination of multiple optical modulators And uses the driving electrical signal of the optical modulator as a binary signal (see Fig. 4).

3 is a diagram illustrating a schematic configuration of a multi-level optical signal generator using a conventional I / Q modulator, and FIG. 4 shows a schematic configuration of a multi-level optical signal generator in which three conventional optical modulators are connected in series Fig.

First, a first method (e.g., a method of using a multilevel electrical signal in one optical modulator) is performed using a dual-parallel Mach-Zehnder modulator integrated with three Mach-Zehnder modulators (MZM) -parallel MZM) (i.e., an I / Q modulator), and applies a multilevel electrical signal to drive each Mach-Zehnder modulator (MZM). The multilevel electrical signal may be generated by directly synthesizing a binary electrical signal or by using a high-speed digital-to-analog converter (DAC). Accordingly, the multilevel electrical signal inputted to each Mach-Zehnder modulator (MZM) of the optical transmitter is modulated to be two components (for example, in-phase and quadrature components) in the complex plane, thereby generating various multilevel modulation optical signals .

However, in the case of the first method, since a multilevel optical signal is generated using a multilevel electrical signal, the noise and distortion of the electrical signal can directly affect the performance of the optical signal, and a high- There is a problem that the cost of the optical transmitter can be increased because it is necessary to use a high-quality linear driver as well as a high-speed DAC.

The following second scheme (e.g., combining multiple optical modulators and using a binary signal as the driving electrical signal) combines several Mach-Zehnder modulators in parallel and in series, as shown in FIG. 4, A binary signal is used as an electrical signal to drive a modulator (i.e., an optical modulator). Among them, the method proposed by X. Zhou (X. Zhou and J. Yu, "200-Gb / s PDM-16QAM generation using a new synthesizing method," in Proceedings of ECOC2009, paper 10.3.5 A Mach-Zehnder modulator is connected in series to generate a 16-level optical signal (16QAM: 16 quadrature amplitude modulation). As the number of connected Mach-Zehnder modulators increases, the noise and distortion of the modulated optical signal accumulate. There is a problem that it can give.

5 is a diagram illustrating a schematic configuration of a conventional multi-level optical signal generator in which two optical modulators are connected in series. As shown in FIG. 5, two Mach-Zehnder modulators And a binary signal is used as a drive signal.

However, as shown in FIGS. 4 to 5, as the plurality of Mach-Zehnder modulators are connected in series, the optical noise and the distortion are accumulated so that it is difficult to generate a high-quality multi-level optical signal. To solve this problem, a separate equalization algorithm .

BACKGROUND OF THE INVENTION [0002] The background art of the present invention is disclosed in Korean Patent Laid-Open Publication No. 10-2014-0061129 (published May 21, 201, 2009, Optical Transmitter for Multilevel Optical Signal Generation and Method Thereof).

According to an aspect of the present invention, there is provided a method of generating a multi-level optical signal capable of varying a modulation method of an optical signal in order to flexibly adjust a transmission capacity according to a transmission demand, The purpose of the device is to provide.

An apparatus for generating a multilevel optical signal according to an aspect of the present invention includes first and second Mach-Zehnder modulators formed on respective arms of a basic Mach-Zehnder modulator; A first and a second upper and lower beams formed respectively on the second arms of the first and second Mach-Zehnder modulators, and a third upper beam formed on the output side of the second Mach-Zehnder modulator of the first and second Mach- ; An amplifier configured to amplify a magnitude of an electric driving signal applied to an electrode formed on each arm of the first and second Mach-Zehnder modulators; A bias voltage generator for generating a direct current (DC) bias voltage to be applied to the first and second Mach-Zehnder modulators and the basic Mach-Zehnder modulator; A drive signal generator for generating a drive signal input to each of the amplifiers; And a controller for controlling each of the amplifiers.

In the present invention, the multi-level optical signal generating apparatus may further include a demultiplexer that demultiplexes the magnitudes of the respective driving signals amplified through the respective amplifiers, 2 modulator independently of the magnitude of the direct-current (DC) bias voltage applied to the modulator.

The driving signal applied to each arm of the first and second Mach-Zehnder modulators is a binary electric signal whose magnitude is independently adjusted. The driving signal applied to each arm of the first and second Mach- independent electric drive signals are applied at the same timing to the respective electrodes arranged in the arm.

In the present invention, the first, second and third phase shifters are respectively adjusted according to the setting of a direct current (DC) bias voltage applied to the first and second Mach-Zehnder modulators and the basic Mach-Zehnder modulator do.

In the present invention, the multi-level optical signal generating device may be configured such that light incident on one optical path in a light source is equally branched into two optical paths and is incident on the first and second Mach-Zehnder modulators, The light incident on the second Mach-Zehnder modulator is further equally branched into two optical paths and is incident on each arm of the first and second Mach-Zehnder modulators. The electrodes E1- E4) of the first and second Mach-Zehnder modulators, the optical signals modulated through the respective arms of the first and second Mach-Zehnder modulators are finally synthesized and output, Synthesizes the light outputted through the first arm of the first Mach-Zehnder modulator and the light whose phase is adjusted and output through the first phase shifter of the second arm, The light output through the first arm of the modulator and the light of the second arm And the third synthesizing unit synthesizes and outputs the light output through the first synthesizing unit and the third phase shifter.

In the present invention, it is preferable that the arm in which the first and second phase shifters are formed is a second arm in which the arm without the phase shifter is formed in the first and second Mach-Zehnder modulators .

In the present invention, the multi-level optical signal generating apparatus may further include: magnitudes of drive signals applied to the respective arms of the first and second Mach-Zehnder modulators; and magnitudes of the drive signals applied to the basic Mach- Zehnder modulator and the first and second modulators (DC) bias voltage to a predetermined value, and thereby, the on-off keying (OOK), the binary phase shift keying (BPSK), the quadrature phase shift keying (QPSK), and the amplitude and phase shift keying And the optical signal is generated by selecting any one of the modulation methods.

In the present invention, the multi-level optical signal generating apparatus may include first to fourth data (data1 to data4), which are driving signals applied to the first and second arms of the first and second Mach-Zehnder modulators, (Data2), which is data obtained by converting the first data (data1) and the first data (data1) without applying the third data (data3) and the fourth data (data4) 1 Mach-Zehnder modulator (MZM1) to drive the first Mach-Zehnder modulator in a push-pull configuration to generate an optical signal in an OOK or BPSK modulation scheme, the magnitude of a drive signal applied to the first Mach- To a predetermined value to select one of the OOK or BPSK modulation schemes.

,

)에 있는 구동신호를 상기 제1,제2 마하젠더 변조기의 각 제1,제2 암에 각기 인가하여 상기 QPSK 변조방식의 광신호를 생성하는 것을 특징으로 한다.In the present invention, among the first to fourth data (data 1 to data 4), which are driving signals applied to the first and second arms of the first and second Mach-Zehnder modulators,

,

) Is applied to each of the first and second arms of the first and second Mach-Zehnder modulators to generate the optical signal of the QPSK modulation method.

In the present invention, the multi-level optical signal generating apparatus may further include first to fourth data (data1 to data4), which are driving signals respectively applied to the first and second arms of the first and second Mach-Zehnder modulators, And the bias voltages of the first and second Mach-Zehnder modulators and the basic Mach-Zehnder modulator are respectively adjusted to predetermined values to drive four independent data (data1 to data4) to the first and second Mach-Zehnder modulators Signal, and drives the first and second Mach-Zehnder modulators in a push-pull structure to generate the optical signal of the 16APSK modulation method.

In the present invention, the multi-level optical signal generating apparatus may further include a control unit configured to control a magnitude of a drive signal applied to each arm of the first and second Mach-Zehnder modulators according to a modulation scheme to be selected for generating the optical signal, A value for adjusting a magnitude of a direct current (DC) bias voltage applied to the gender modulator and the first and second modulators is preset in a table form.

According to an aspect of the present invention, a modulation method of an optical signal can be varied to flexibly adjust a transmission capacity according to a transmission demand.

1 is an exemplary diagram for explaining a method in which a driving signal is applied to a general Mach-Zehnder modulator;
FIG. 2 is a diagram for explaining a driving signal applying method for operating an I / Q modulator using two conventional Mach-Zehnder modulators in a push-pull manner. FIG.
3 is a diagram illustrating a schematic configuration of a multilevel optical signal generator using a conventional I / Q modulator.
4 is a diagram showing a schematic configuration of a multilevel optical signal generator in which three conventional optical modulators are connected in series.
FIG. 5 is an exemplary diagram showing a schematic configuration of a multilevel optical signal generator in which two optical modulators are connected in series. FIG.
FIG. 6 is an exemplary diagram showing a schematic configuration of a multilevel optical signal generating apparatus according to an embodiment of the present invention; FIG.
FIG. 7 is an exemplary view showing a constellation of a multilevel optical signal generated by adjusting a magnitude of a driving signal applied to first and second Mach-Zehnder modulators and a bias voltage in FIG. 6; FIG.

Hereinafter, an embodiment of a multilevel optical signal generating apparatus according to the present invention will be described with reference to the accompanying drawings.

In this process, the thicknesses of the lines and the sizes of the components shown in the drawings may be exaggerated for clarity and convenience of explanation. In addition, the terms described below are defined in consideration of the functions of the present invention, which may vary depending on the intention or custom of the user, the operator. Therefore, definitions of these terms should be made based on the contents throughout this specification.

FIG. 6 is an exemplary diagram showing a schematic configuration of a multilevel optical signal generating apparatus according to an embodiment of the present invention.

6, the multi-level optical signal generating apparatus according to the present embodiment is characterized in that a plurality of Mach-Zehnder modulators MZM1 and MZM2 are formed in each arm of the basic Mach-Zehnder modulator MZM0 (that is, The first and second Mach-Zehnder modulators MZM1 and MZM2 are formed in parallel and the electrodes E1 to E4 are formed on the respective arms of the first and second Mach-Zehnder modulators MZM1 and MZM2, The first and second upper stages 131 and 132 are formed on one arm of the second Mach-Zehnder modulators MZM1 and MZM2 and the first and second Mach-Zehnder modulators MZM1 and MZM2 The third upper stage 133 is formed on the output side of the second Mach-Zehnder modulator MZM2 and the light outputted from the light source 110 is branched at the same rate to form the first and second Mach- Zehnder modulators MZM1 and MZM2 And the optical path is formed such that light emitted from the first and second Mach-Zehnder modulators (MZM1, MZM2) and the third-stage optical waveguide (133) is synthesized and emitted .

Here, the first, second, and third upper electrodes 131, 132, and 133 are not necessarily formed as separate devices, and phase modulation may be performed through connection of the electrodes. In addition, the positions of the first, second and third stages 131, 132 and 133 are not necessarily limited to the output side of the second arm and the second Mach-Zehnder modulator MZM2, the first Mach-Zehnder modulator MZM1 may be formed on the output side of the first Mach-Zehnder modulator MZM1.

For convenience of explanation, an arm in which no phase shifter is formed in the first and second Mach-Zehnder modulators MZM1 and MZM2 is referred to as a first arm and the first upper arm 131 or the second upper arm An arm provided with the arm 132 is referred to as a second arm.

)(또는 구동신호, 전기 구동신호)의 크기(A₁ ~ A₄)(즉, 진폭)를 각기 증폭하는 증폭기(121 ~ 124)가 형성된다.A binary electric signal (E1 to E4) applied to electrodes E1 to E4 formed on each arm for driving the first and second Mach-Zehnder modulators MZM1 and MZM2

Amplifiers 121 to 124 for amplifying the amplitudes A ₁ to A ₄ (that is, amplitudes) of the driving signals (or driving signals and electric driving signals) are formed.

)에 의해 각기 조절된다.Meanwhile, although not shown in the figure, the first, second and third stages 131 to 133 are connected to the first and second Mach-Zehnder modulators MZM1 and MZM2 and the basic Mach-Zehnder modulator MZM0 The applied direct current (DC) bias voltage (

Respectively.

)을 각기 생성하는 바이어스 전압 생성부(미도시)를 더 포함할 수 있으며, 또한 상기 각 증폭기(121 ~ 124)에 각기 입력되는 이진 전기신호(

)(또는 구동신호, 전기 구동신호)를 생성하는 구동신호 생성부(미도시), 및 상기 각 증폭기(121 ~ 124)를 각기 제어하기 위한 제어부(미도시)를 더 포함할 수 있다.Therefore, the DC bias voltage

And a bias voltage generator (not shown) for generating a binary electric signal (not shown) input to each of the amplifiers 121 to 124

And a control unit (not shown) for controlling each of the amplifiers 121 to 124. The driving signal generating unit may include a driving signal generator (not shown) for generating driving signals (or driving signals, electric driving signals)

)(또는 구동신호)에 의해 광의 굴절률이 변화된다.6, the light incident on one optical path in the light source 110 is equally divided into two optical paths and is incident on the first and second Mach-Zehnder modulators MZM1 and MZM2, and the first and second The light incident on the Mach-Zehnder modulators MZM1 and MZM2 is equally divided into two optical paths again and is incident on each arm of the first and second Mach-Zehnder modulators MZM1 and MZM2, A binary electric signal (e.

) (Or a drive signal).

The electrodes E1 to E4 are arranged close to the respective arms of the first and second Mach-Zehnder modulators MZM1 and MZM2. For example, when the electric field is applied, the refractive index of the light is changed. (LiNbO ₃ ) substrate surface.

)(또는 구동신호, 전기 구동신호)를 인가함으로써, 4개의 광로로 분기된 각각의 광을 제1,제2 마하젠더 변조기(MZM1, MZM2)의 각 암(arm)을 통해 변조한 후 최종적으로 합성하여 출력한다.As described above, the multi-level optical signal generating apparatus according to the present embodiment divides one optical path into four optical paths, and then places the optical paths on each arm of the first and second Mach-Zehnder modulators MZM1 and MZM2 A binary electrical signal (e. G.

(Or a drive signal, an electric drive signal) is applied to each of the first and second Mach-Zehnder modulators MZM1 and MZM2 through respective arms of the first and second Mach-Zehnder modulators MZM1 and MZM2, Synthesized and output.

)을 더하여 위상차를 부여함으로써 위상을 조정한다. 예컨대 이때 상기 더해지는 위상(

)은

일 수 있으며, 다만 반드시 이 값으로 한정하는 것은 아니다.The first and second upper and lower arms 131 and 132 formed on one side arm (e.g., second arm) of the first and second Mach-Zehnder modulators MZM1 and MZM2 form a corresponding arm (Or optical signal) that passes through the arm, such that the optical signal component (e.g., I, or Q) passing through the arm has a phase

) Is added to adjust the phase by giving a phase difference. For example, at this time,

)silver

, But it is not necessarily limited to this value.

)을 더하여 위상차를 부여함으로써 위상을 조정하고, 상기 제1 합성부(211) 및 상기 제3 위상기(133)를 통해 출력되는 광을 합성하는 제3 합성부(213)를 포함한다.The multi-level optical signal generating apparatus according to the present embodiment further includes a first Mach-Zehnder modulator (MZM1), a first Mach-Zehnder modulator (MZM1) A first combiner 211 for combining the light output from the first arm of the second Mach-Zehnder modulator MZM2 and the light output from the second arm of the second Mach-Zehnder modulator MZM2, And a second synthesizing unit 212 synthesizing the output light of which phase is adjusted through the step 132 and the third synthesizing unit 133 synthesizes the light synthesized through the second synthesizing unit 212 The optical signal component (e.g., I, or Q)

And a third combining unit 213 that adjusts the phase by adding a phase difference and synthesizes the light output through the first combining unit 211 and the third phase shifting unit 133.

)(또는 구동신호, 전기 구동신호)는 각가의 데이터 정보(data1, data2, data3, data4)를 포함하며, 상기 제1,제2 마하젠더 변조기(MZM1, MZM2)의 각 암(arm)에 배치된 각 전극(E1 ~ E4)에는 전기 구동신호가 동일한 타이밍으로 인가된다. On the other hand, a binary electric signal (?) Applied independently to the electrodes (E1 to E4) arranged on each arm of the first and second Mach-Zehnder modulators (MZM1 and MZM2)

(Or drive signal, electric drive signal) includes respective data information (data1, data2, data3, data4) and is arranged in each arm of the first and second Mach- Zehnder modulators MZM1 and MZM2 The electric driving signals are applied to the electrodes E1 to E4 at the same timing.

For reference, the data denotes digital information to be transmitted, and the binary electrical signal denotes an analog signal.

Therefore, the driving signals having mutual inverse relationship with each other are applied to the electrodes E1 to E4 disposed on the respective arms of the first and second Mach-Zehnder modulators MZM1 and MZM2 at the same timing.

)의 크기를 각기 조절함으로써, 마하젠더 변조기를 더 적게 사용하는 간단한 구조에 의해 저렴한 비용(예 : 마하젠더 변조기의 개수가 증가하면 비용이 크게 증가함)으로 멀티레벨(예 : OOK, BPSK, QPSK, 16APSK) 광신호를 생성할 수 있도록 한다. In this embodiment, as shown in Table 1 below, the magnitudes (A ₁ to A ₄ ) (i.e., amplitude) of the respective driving signals (or the binary electric signals) amplified through the amplifiers 121 to 124, , And a DC bias voltage applied to the primary Mach-Zehnder modulator MZM0 and the first and second modulators MZM1 and MZM2

(Eg, OOK, BPSK, QPSK, etc.) with a low cost (eg, a large increase in cost when the number of Mach-Zehnder modulators is increased) by a simple structure using fewer Mach-Zehnder modulators , 16 APSK) optical signals.

Where V _π voltage is the voltage for 180 ^° phase modulation.

The transfer function of the multilevel optical signal generator (or optical transmitter) according to the present embodiment is as shown in the following Equation 1, so that up to four electric driving signals are independently applied, It is possible to generate.

)(또는 구동신호, 전기 구동신호)는 제1,제2 마하젠더 변조기(MZM1, MZM2)의 구동을 위해 인가되는 전기 구동신호이며, 이진 전기신호(

)(또는 구동신호, 전기 구동신호)의 크기(A₁ ~ A₄)(즉, 진폭)는 각 증폭기(121 ~ 124)에 의해 조절되고, 또한 상기 제1,제2,제3 위상기(131 ~ 133)의 위상(

)은 제1,제2 마하젠더 변조기(MZM1, MZM2)와 기본 마하젠더 변조기(MZM0)에 인가되는 직류(DC) 바이어스(bias) 전압(

)에 의해 조절된다.Here, the binary electrical signal (

(Or drive signal, electric drive signal) is an electric drive signal applied for driving the first and second Mach-Zehnder modulators MZM1 and MZM2, and a binary electric signal

The magnitudes A ₁ to A ₄ (i.e., amplitudes) of the driving signals (or driving signals and electric driving signals) are adjusted by the amplifiers 121 to 124 and the amplitudes of the first, 131-133)

Is a DC bias bias voltage applied to the first and second Mach-Zehnder modulators MZM1 and MZM2 and the basic Mach-Zehnder modulator MZM0

).

)을 상기 표 1에 기초하여 각기 독립적으로 조절하면 멀티레벨(최대 16레벨)의 광신호 생성이 가능하게 된다. 이때 상기 각 구동신호의 크기(A₁ ~ A₄)(즉, 진폭)는 생성하고자 하는 변조방식에 따라 V_π전압 이하(예 : 0, 0.25V_π, 0.5V_π, V_π)로 조정된다. Therefore, the magnitude (A ₁ to A ₄ ) (i.e., amplitude) of the drive signal applied to the first and second Mach-Zehnder modulators MZM ₁ and MZM 2 and the bias voltage

) Can be independently controlled on the basis of the above Table 1, it is possible to generate multi-level (maximum 16 levels) optical signals. At this time, the magnitudes (A ₁ to A ₄ ) (i.e., amplitudes) of the respective driving signals are not more than V _π voltage (eg, 0, 0.25 V _π , 0.5 V _pi , V _pi ).

Accordingly, the multi-level optical signal generating apparatus (or optical transmitter) according to the embodiment of the present invention uses one optical modulator compared to the conventional method of serially combining a plurality of optical modulators, so that noise and distortion are not accumulated in the optical signal, There is an effect that an optical signal can be generated. In addition, since the present embodiment uses a binary electric signal as a driving signal, it can generate a high-speed electric driving signal of high quality as compared with a conventional multi-level electric driving signal. As a result, There is an effect to be able to do.

FIG. 7 is an exemplary diagram illustrating the constellation of a multilevel optical signal generated by adjusting a magnitude of a driving signal applied to first and second Mach-Zehnder modulators and a bias voltage in FIG.

)을 독립적으로 조절함으로써 멀티레벨(최대 16레벨)의 광신호 생성이 가능하게 된다.7, the multilevel optical signal generator (or optical transmitter) calculates the magnitude (A ₁ ) of the drive signal applied to the first and second Mach-Zehnder modulators (MZM 1 and MZM 2) ~ A ₄ ) (ie amplitude) adjustment and bias voltage (

(Up to 16 levels) of the optical signal can be generated.

For example, FIGS. 7A and 7B are constellations of the optical signals generated by the OOK modulation method and the BPSK modulation method, respectively. This is a modulation method for transmitting one bit per symbol The third data data 3 and the fourth data data 4 are not applied and the second data data 2 which is the data obtained by conversion of the first data data 1 and the first data data 1, 1 Mach-Zehnder modulator MZM1, the first Mach-Zehnder modulator MZM1 can be driven in a push-pull structure to generate an optical signal.

At this time, an OOK or BPSK optical signal can be generated by adjusting the magnitude (i.e., amplitude) of the drive signal based on Table 1. [ That is, OOK scheme light signal to adjust the magnitude of the driving signal (i.e., amplitude) to 0.25V and _π, BPSK scheme light signal may be generated by adjusting the size of the drive signals to the 0.5V _π.

)을 조절함으로써, 제1,제2 마하젠더 변조기(MZM1, MZM2)를 푸시풀(push-pull) 구조로 구동시켜 QPSK 광신호를 생성할 수 있다. 7C is a constellation of the optical signal generated by the QPSK modulation method. Since this is a method of transmitting two bits information per symbol, The magnitude (A ₁ -A ₄ ) (i.e., amplitude) of the signal and the bias voltage

The first and second Mach-Zehnder modulators MZM1 and MZM2 can be driven in a push-pull structure to generate a QPSK optical signal.

)을 조절하여 4개의 독립된 데이터(data1 ~ data4)를 제1,제2 마하젠더 변조기(MZM1, MZM2)에 구동신호로 인가하여 구동함으로써 16APSK 광신호를 생성할 수 있다.7D is a constellation of the optical signal generated by the 16 APSK modulation method. This is a method of transmitting 4 bits information per symbol, and is based on Table 1 The magnitude (A ₁ -A ₄ ) (i.e., amplitude) of the signal and the bias voltage

) To generate 16 APSK optical signals by driving four independent data (data1 to data4) as drive signals to the first and second Mach-Zehnder modulators MZM1 and MZM2.

It should be noted that the magnitude of the drive signal and the bias voltage value shown in Table 1 are described by way of example and are not intended to be limited to this value.

As described above, the multilevel optical signal generating apparatus according to the present embodiment can vary the optical signal modulation method in order to flexibly adjust the transmission capacity according to the transmission demand, and the plurality of Mach-Zehnder modulators (MZM1, MZM2) (OOK), BPSK, QPSK, and 16 APS (amplitude and phase shift keying)) optical signals can be generated by using a single integrated Mach-Zehnder modulator (MZM0) There is an advantage.

Unlike an I / Q modulator (see FIG. 4) in which three Mach-Zehnder modulators, which are conventional multi-level QAM signal generators, are integrated, the multilevel optical signal generating apparatus according to the present embodiment includes an I / Q modulator A dual drive I (which can apply a drive signal independent of the magnitude of the voltage) to each electrode E1 to E4 of the first and second Mach-Zehnder modulators MZM1 and MZM2 integrated in the arm, / Q modulator (dual-drive IQ modulator).

)(또는 구동신호)를 인가하는 차이점이 있다.That is, the conventional I / Q modulator applies one driving signal to each of the Mach-Zehnder modulators (that is, only the inverting and the electric driving signal having the same magnitude of the voltage) (see FIGS. 1 and 2) (That is, a multi-level optical signal generating device) according to the first to the third Mach-Zehnder modulators MZM1 and MZM2 according to the present invention has independent electric driving signals (that is, Independent electrical drive signals). The conventional I / Q modulator for generating a multilevel optical signal uses a multilevel electrical signal as a driving signal (see FIG. 3), but a dual driving I / Q modulator according to the present embodiment Device) generates a binary electrical signal (< RTI ID = 0.0 >

(Or a drive signal) is applied to the sustain pulses.

As described above, there has been a multi-level optical signal generating apparatus using a Mach-Zehnder modulator as described in the background art. However, the multi-level optical signal generating apparatus according to the present embodiment is different from the conventional multi- By reducing the number of modulators, it is possible to reduce the cost with a simple structure and to flexibly change the optical signal modulation method according to the demand of the transmission capacity, thereby making it possible to efficiently use limited spectrum resources It is effective.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, I will understand the point. Accordingly, the technical scope of the present invention should be defined by the following claims.

110: Light source
121 ~ 124: Amplifier
131 to 133:
211 to 213: First to third synthesis units
E1 to E4: electrode
MZM0 to MZM2: Mach-Zehnder modulator, or optical modulator

Claims (10)

First and second Mach-Zehnder modulators formed on each arm of the basic Mach-Zehnder modulator;
A first and a second upper and lower beams formed respectively on the second arms of the first and second Mach-Zehnder modulators, and a third upper beam formed on the output side of the second Mach-Zehnder modulator of the first and second Mach- ;
An amplifier configured to amplify a magnitude of an electric driving signal applied to an electrode formed on each arm of the first and second Mach-Zehnder modulators;
A bias voltage generator for generating a direct current (DC) bias voltage to be applied to the first and second Mach-Zehnder modulators and the basic Mach-Zehnder modulator;
A drive signal generator for generating a drive signal input to each of the amplifiers; And
And a control unit for controlling each of the amplifiers,
The first arm and the second arm of the first and second Mach-Zehnder modulators have a first arm and an arm having no phase shifter formed therein, Cancer,
Depending on the modulation scheme of the optical signal to be generated,
A magnitude of each driving signal amplified through each of the amplifiers, and
Wherein the magnitude of the DC bias voltage applied to the basic Mach-Zehnder modulator and the first and second Mach-Zehnder modulators is independently adjusted.
delete The method according to claim 1,
The driving signal applied to each arm of the first and second Mach-Zehnder modulators is transmitted to the first Mach-
As a biased electrical signal that is independently scaled,
And an independent electric driving signal is applied to each electrode arranged on each arm of the first and second Mach-Zehnder modulators at the same timing.
2. The phase shifter of claim 1, wherein the first, second,
And the DC bias voltage applied to the first and second Mach-Zehnder modulators and the basic Mach-Zehnder modulator, respectively.
2. The multi-level optical signal generating apparatus according to claim 1,
The light incident on one optical path from the light source is equally branched into two optical paths and is incident on the first and second Mach-Zehnder modulators, and the light incident on the first and second Mach- And is incident on each arm of the first and second Mach-Zehnder modulators. The refractive index of light is changed by a drive signal applied to the electrodes E1 to E4 formed on the respective arms And finally synthesizing and outputting optical signals modulated through respective arms of the first and second Mach-Zehnder modulators,
The first combining section combines the light output through the first arm of the first Mach-Zehnder modulator and the light whose phase is adjusted and output through the first phase shifter of the second arm, The third combiner combines the light output through the first arm of the second Mach-Zehnder modulator and the light that is phase-adjusted and output through the second phase shifter of the second arm, And the third phase shifter, and outputs the combined light.
2. The multi-level optical signal generating apparatus according to claim 1,
The magnitude of the drive signal applied to each arm of the first and second Mach-Zehnder modulators and the magnitude of the DC bias voltage applied to the basic Mach-Zehnder modulator and the first and second modulators are adjusted to predetermined values So,
It is possible to generate an optical signal by selecting any one of modulation schemes of OOK (On-Off Keying), BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), and 16 APS (Amplitude and Phase Shift Keying) Level optical signal.
7. The multi-level optical signal generating apparatus according to claim 6,
Among the first to fourth data (data1 to data4), which are driving signals respectively applied to the first and second arms of the first and second Mach-Zehnder modulators,
The third data (data3) and the fourth data (data4) are not applied,
The second data (data2), which is data converted from the first data (data1) and the first data (data1), is applied to the first Mach-Zehnder modulator (MZM1) to push the first Mach- The optical signal is generated by the OOK or BPSK modulation method,
Wherein the controller selects one of the OOK and BPSK modulation schemes by adjusting a magnitude of a driving signal applied to the first Mach-Zehnder modulator to a predetermined value.
8. The method of claim 7,
Among the first to fourth data (data1 to data4), which are driving signals respectively applied to the first and second arms of the first and second Mach-Zehnder modulators,
Mutually inverse relation (

,

) Is applied to each of the first and second arms of the first and second Mach-Zehnder modulators to generate the optical signal of the QPSK modulation method.
7. The multi-level optical signal generating apparatus according to claim 6,
The magnitude of the first to fourth data (data1 to data4), which are drive signals applied to the first and second arms of the first and second Mach-Zehnder modulators, respectively, and the magnitudes of the first and second Mach- By adjusting the bias voltage of the Mach-Zehnder modulator to a predetermined value,
The first and second Mach-Zehnder modulators are driven in a push-pull structure by applying four independent data (data1 to data4) to the first and second Mach-Zehnder modulators as driving signals, and the optical signals of the 16APSK modulation method Level optical signal.
7. The multi-level optical signal generating apparatus according to claim 6,
According to a modulation scheme to be selected for generating the optical signal,
The magnitude of the drive signal applied to each arm of the first and second Mach-Zehnder modulators, and
Wherein a value for adjusting a magnitude of a DC bias voltage applied to the basic Mach-Zehnder modulator and the first and second modulators is preset in a table form.

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