WO2018146796A1

WO2018146796A1 - Light modulation module

Info

Publication number: WO2018146796A1
Application number: PCT/JP2017/004938
Authority: WO
Inventors: 瑞基白尾
Original assignee: 三菱電機株式会社
Priority date: 2017-02-10
Filing date: 2017-02-10
Publication date: 2018-08-16

Abstract

A light modulation module (100) according to the present invention includes: a light modulator (1) that performs light-intensity modulation on continuous light; a light modulator (2) that performs light-intensity modulation on the light that has been subjected to light-intensity modulation by the light modulator (1); a light modulator (3) that performs light-intensity modulation on the light that has been subjected to light-intensity modulation by the light modulator (2); and an electrical-signal generating unit (4) that applies a first electrical signal, which is a binary electrical signal, to the light modulator (1), that applies a second electrical signal, which is a binary electrical signal, to the light modulator (2), and that applies a third electrical signal, which is a binary electrical signal, to the light modulator (3).

Description

Light modulation module

The present invention relates to an optical modulation module that outputs an optical modulation signal corresponding to an electric signal.

In the latest optical Ethernet standards such as 400 Gigabit Ethernet (registered trademark), the PAM4 (4-level Pulse-Amplitude-Modulation) method is used instead of the conventional OOK (On-Off-Keying) method. Patent Document 1 proposes a Mach-Zehnder modulator in which a phase modulation unit is divided into a plurality of means as means for realizing multilevel modulation using a simple electric signal generation circuit. In the system proposed in Patent Document 1, a multi-level modulation signal such as a PAM4 signal can be generated using a plurality of OOK signals that can be generated by a simple circuit.

US Pat. No. 7,483,597

In the Mach-Zehnder modulator described in Patent Document 1, light is quenched by adjusting the phases of both arms and causing interference. For this reason, when a phase difference occurs between the arms, the light is not sufficiently quenched and the quality of the optical modulation signal is lowered. Therefore, in order to prevent the quality of the optical modulation signal from being deteriorated, the phases of both arms need to be precisely controlled, and there is a problem that the apparatus becomes complicated.

The present invention has been made in view of the above, and an object of the present invention is to obtain an optical modulation module capable of generating a multi-level modulation signal without requiring precise phase control.

In order to solve the above-described problems and achieve the object, an optical modulation module according to the present invention includes a first optical modulator that performs optical intensity modulation on continuous light, and an optical intensity by the first optical modulator. A second light modulator that performs light intensity modulation on the modulated light; and a third light modulator that performs light intensity modulation on the light that has been light intensity modulated by the second light modulator. Prepare. The light modulation module applies a first electric signal, which is a binary electric signal, to the first optical modulator, and applies a second electric signal, which is a binary electric signal, to the second optical modulator. And a signal generator that applies a third electrical signal, which is a binary electrical signal, to the third optical modulator.

The light modulation module according to the present invention produces an effect that a multi-level modulation signal can be generated without requiring precise phase control.

1 is a block diagram showing a configuration example of a light modulation module according to a first embodiment. The figure for demonstrating the operation | movement in the light modulation module of Embodiment 1. FIG. The figure which shows the value which the PAM4 signal output from an optical modulation module, ie, an output signal, and the electric signal applied to each optical modulator The figure which shows an example of the voltage dependence of the extinction characteristic of Embodiment 1, and the amplitude of each electric signal External view showing a mounting example of the light modulation module of the first embodiment External view showing a mounting example of the light modulation module of the second embodiment The figure which shows the extinction curve in the optical modulator of Embodiment 2, and the amplitude of the voltage of the electric signal applied to an optical modulator External view showing a mounting example of the light modulation module of the third embodiment The figure which shows the extinction curve in the optical modulator of Embodiment 3, and the amplitude of the voltage of the electric signal applied to an optical modulator The figure which shows the extinction curve in the optical modulator of Embodiment 4, and the amplitude of the voltage of the electric signal applied to an optical modulator FIG. 10 is a diagram illustrating a configuration example of a light modulation module according to a sixth embodiment.

Hereinafter, an optical modulation module according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a block diagram illustrating a configuration example of the light modulation module according to the first embodiment of the present invention. As shown in FIG. 1, an optical modulation module 100 according to the present embodiment includes optical modulators 1 to 3 and an electric signal generation unit 4. The light modulation module 100 generates and outputs a light modulation signal based on a given signal, that is, information. The light modulation module 100 is used in, for example, an optical communication device. When the light modulation module 100 is used in an optical communication device, the information described above is information to be transmitted.

The optical modulator 1 receives continuous light (CW: Continuous Wave) output from a light source (not shown in FIG. 1), modulates the intensity of the continuous light, and outputs a first optical modulation signal that is a signal after intensity modulation. Output. The light source may be provided inside the light modulation module 100 or may be provided outside the light modulation module 100. The optical modulator 2 receives the first optical modulation signal output from the optical modulator 1, intensity-modulates the first optical modulation signal, and outputs a second optical modulation signal that is a signal after intensity modulation. . The optical modulator 3 receives the second optical modulation signal output from the optical modulator 2, intensity-modulates the second optical modulation signal, and outputs a third optical modulation signal that is a signal after intensity modulation. .

That is, the optical modulator 1 is a first optical modulator that performs optical intensity modulation on continuous light. The light modulator 2 is a second light modulator that performs light intensity modulation on the light whose light intensity is modulated by the light modulator 1. The light modulator 3 is a third light modulator that performs light intensity modulation on the light whose light intensity is modulated by the light modulator 2.

The electrical signals output from the electrical signal generator 4 are applied to the optical modulators 1 to 3, respectively. The optical modulators 1 to 3 are formed of semiconductors having the same band structure. The optical modulators 1 to 3 are optical modulators called EAM (Electro-Absorption Modulator) using the semiconductor electroabsorption effect, that is, electroabsorption optical modulators. The electric field absorption effect of a semiconductor is a phenomenon in which, when an electric field is applied to a semiconductor provided with a quantum well structure, the band gap changes due to the Franz Kelish effect or the quantum Stark effect, and the amount of light absorption changes. Due to this phenomenon, the optical modulators 1 to 3 absorb light by reducing the band gap when an electric field is applied compared to when no electric field is applied. Therefore, the optical modulators 1 to 3 change the amount of light absorption in accordance with the applied electric field, that is, the voltage of the electric signal output from the electric signal generator 4, and change the intensity of the output optical signal. Can do.

The electric signal generator 4 generates an electric signal for controlling whether or not an electric field is applied to the optical modulators 1 to 3. The signals applied from the electric signal generator 4 to the optical modulators 1 to 3 are binary signals indicating ON or OFF. That is, the electrical signal generation unit 4 applies a first electrical signal that is a binary electrical signal to the first optical modulator, and a second electrical signal that is a binary electrical signal is subjected to the second optical modulation. And a signal generator that applies a third electrical signal, which is a binary electrical signal, to the third optical modulator. The voltage value of the electrical signal is a first voltage value when off (OFF), and a second voltage value lower than the first voltage value when on (ON). Regarding the on / off of each electric signal, hereinafter, the state corresponding to the case where the level of the PAM4 signal output from the light modulation module 100 is high is referred to as ON, and the state corresponding to the case where the level of the PAM4 signal is low. Call off. Therefore, the voltage applied to each optical modulator in the present embodiment is off because the higher the voltage, the lower the level because the amount of light absorption is larger, and the lower the voltage, the smaller the amount of light absorption. Turns on because the level is higher. This definition of on and off is an example, and the definition may be reversed between on and off.

When the electrical signal is off, an electric field is applied to each optical modulator to which the electrical signal is applied. When the electrical signal is on, an electric field is not applied to each optical modulator to which the electrical signal is applied. Hereinafter, a value obtained by subtracting the second voltage value from the first voltage value is referred to as amplitude. A central voltage between the first voltage value and the second voltage value is referred to as a bias value. The electric signal generation unit 4 generates an electric signal to be applied to the optical modulators 1 to 3 according to the value of one unit signal, that is, two-bit data, with 2 bits of the given signal as one unit. One unit of signal is one of four values of 00, 01, 10, and 11 expressed in binary.

Since the electrical signal generator 4 which is a drive circuit for the optical modulators 1 to 3 outputs binary signals to the optical modulators 1 to 3, respectively, it is realized by a simple circuit that generates a binary signal, that is, an OOK signal. Can do.

As shown in FIG. 1, in the optical modulation module 100 of the present embodiment, each of the optical modulators 1 to 3 performs binary modulation, but the optical modulators 1 to 3 are arranged in series to sequentially perform optical modulation. As a result, the signal finally output from the optical modulator 3 becomes a PAM4 signal which is a four-level optical modulation signal.

The operation of this embodiment will be described. FIG. 2 is a diagram for explaining the operation of the light modulation module according to the present embodiment. In the upper part of FIG. 2, an OOK signal # 1 that is a first electric signal applied from the electric signal generator 4 to the optical modulator 1 and a second signal applied from the electric signal generator 4 to the optical modulator 2 are displayed. 3 schematically shows an OOK signal # 2 that is an electrical signal and an OOK signal # 3 that is a third electrical signal applied to the optical modulator 3 from the electrical signal generator 4.

As shown in FIG. 2, in this embodiment, the light intensity when continuous light is output as it is without being absorbed by any of the optical modulator 1, the optical modulator 2, and the optical modulator 3 is a value of 11. To correspond to. Then, the light intensity when light is absorbed by the optical modulator 1 and output from the optical modulator 3 without being absorbed by the optical modulator 2 and the optical modulator 3 is made to correspond to a value of 10. As described above, the optical modulator 1 performs optical modulation, that is, 11/10 modulation that generates an optical modulation signal corresponding to one of the two values of 11 and 10 depending on whether or not an electric field is applied. Do.

Also, the light intensity when light is absorbed by the light modulator 2 and output from the light modulator 3 without being absorbed by the light modulator 1 and the light modulator 3 is made to correspond to a value of 01. As shown in FIG. 2, the light absorption amount in the optical modulator 2 is larger than the light absorption amount in the optical modulator 1. That is, the amplitude of the OOK signal # 2 is larger than the amplitude of the OOK signal # 1. In this way, the optical modulator 2 performs optical modulation, that is, 11/01 modulation, which generates an optical modulation signal corresponding to one of the two values of 11 and 01 depending on whether or not an electric field is applied. Do.

Also, the light intensity when light is absorbed by the optical modulator 3 and output from the optical modulator 3 without being absorbed by the optical modulator 1 and the optical modulator 2 is made to correspond to a value of 00. As shown in FIG. 2, the light absorption amount in the optical modulator 3 is larger than the light absorption amount in the optical modulator 2. That is, the amplitude of the OOK signal # 3 is larger than the amplitude of the OOK signal # 2. As described above, the optical modulator 3 performs optical modulation, that is, 11/00 modulation that generates an optical modulation signal corresponding to one of the two values of 11 and 00 depending on whether or not an electric field is applied. Do.

As described above, by varying the amplitudes of the OOK signals # 1 to # 3 and determining whether the OOK signals # 1 to # 3 are turned on or off according to the 2-bit information value, The modulation module 100 can output a PAM4 signal. FIG. 3 is a diagram illustrating a PAM4 signal output from the light modulation module 100, that is, a value indicated by the output signal, and an electric signal applied to each light modulator.

As shown in FIG. 3, when an output signal corresponding to 11 is output, the electrical signal applied to the optical modulator 1, the optical modulator 2, and the optical modulator 3 is on. Accordingly, the continuous light input to the optical modulator 1 is output from the optical modulator 3 without being absorbed by any of the optical modulator 1, the optical modulator 2, and the optical modulator 3. As shown in FIG. 3, when an output signal corresponding to 10 is output, the electrical signal applied to the optical modulator 1 is off, and the electrical signal applied to the optical modulator 2 and the optical modulator 3. Is on. Thereby, the continuous light input to the optical modulator 1 is absorbed by the optical modulator 1 and output from the optical modulator 3.

As shown in FIG. 3, when an output signal corresponding to 01 is output, the electrical signal applied to the optical modulator 2 is off, and the electrical signal applied to the optical modulator 1 and the optical modulator 3. Is on. Thereby, the continuous light input to the optical modulator 1 is absorbed by the optical modulator 2 and output from the optical modulator 3. As shown in FIG. 3, when outputting an output signal corresponding to 00, the electrical signal applied to the optical modulator 3 is off, and the electrical signal applied to the optical modulator 1 and the optical modulator 2. Is on. Thereby, the continuous light input to the optical modulator 1 is absorbed by the optical modulator 3 and output from the optical modulator 3.

FIG. 4 is a diagram showing an example of the voltage dependency of the extinction characteristic and the amplitude of each electric signal. In FIG. 4, the horizontal axis indicates the voltage applied to the optical modulator, and the vertical axis indicates the optical output after passing through the optical modulator. A value corresponding to each optical output, that is, the intensity of the optical signal output from the optical modulation module 100 is shown beside the vertical axis in FIG. The extinction curve 200 is a curve indicating the voltage dependence of the extinction characteristics of the modulators used as the optical modulators 1 to 3. In the present embodiment, as the optical modulators 1 to 3, modulators having the same characteristics can be used. FIG. 4 shows an example in which modulators having the same characteristics are used as the optical modulators 1 to 3. In this case, the optical path lengths in the optical modulators 1 to 3 are the same, and the band gap is also the same. The extinction curves 200 of the optical modulators 1 to 3 are the same. The amplitude # 1 indicates the amplitude of the OOK signal # 1, the amplitude # 2 indicates the amplitude of the OOK signal # 2, and the amplitude # 3 indicates the amplitude of the OOK signal # 3. In the PAM4 signal, the light intensity needs to be equally spaced. For this reason, the amplitude is determined based on the extinction curve 200 shown in FIG. 4 so that the intensities of the four-level optical signals output from the optical modulator 3 are equally spaced. That is, the difference between the level corresponding to 11 and the level corresponding to 10 is the same as the difference between the level corresponding to 10 and the level corresponding to 01, and the difference between the level corresponding to 01 and the level corresponding to 00 is the same. Thus, the amplitude of each electrical signal is determined. Thereby, the four levels of light intensity output from the optical modulator 3 can be equally spaced.

In the above-described example shown in FIG. 4, it has been described that the optical modulators 1 to 3 have the same extinction curves, but the optical modulators 1 to 3 may not have the same extinction curves. Even when the extinction curves of the optical modulators 1 to 3 are not the same, considering the extinction curves, the amplitudes of the electric signals applied to the optical modulators 1 to 3 are set so that the four levels of light intensity are equally spaced. You may adjust to.

FIG. 5 is an external view showing a mounting example of the light modulation module of the present embodiment. In the example shown in FIG. 5, the light modulation module 100 is mounted on the semiconductor 5. Further, a CW laser 6 is mounted on the semiconductor 5 as a light source together with the optical modulators 1 to 3. That is, in the example illustrated in FIG. 5, the light modulation module 100 includes a light source that generates continuous light. The CW laser 6 and the optical modulators 1 to 3 are formed side by side in series in the first direction 300 of the semiconductor 5. The electrode 8 is an electrode of the optical modulator 1, the electrode 9 is an electrode of the optical modulator 2, the electrode 10 is an electrode of the optical modulator 3, and the electrode 7 is an electrode of the CW laser 6. . A constant current for driving the CW laser 6 is applied to the CW laser 6 through the electrode 7. As a result, the CW laser 6 outputs continuous light having a constant light intensity. From the electrode 8, the electrode 9, and the electrode 10, an OOK signal # 1, an OOK signal # 2, and an OOK signal # 3 are applied from an electric signal generation unit 4 not shown in FIG. As shown in FIG. 5 described above, the optical modulators 1 to 3 may be formed integrally with the CW laser 6 on the semiconductor 5. That is, the optical modulators 1 to 3 and the CW laser 6 may be integrated and integrated on the same chip. The arrangement order of the optical modulators 1 to 3 is not limited to the example shown in FIG. 5, and the same effect can be obtained even if the arrangement order is changed. The mounting example shown in FIG. 5 is an example, and it is only necessary to realize the operation as the light modulation module 100 of the above-described embodiment, and the shape of each part is not limited to the example of FIG.

As described above, in this embodiment, the optical modulators 1 to 3 are arranged in series and sequentially modulated, and an electric field is applied to each of the optical modulators 1 to 3 by the electric signal applied to each of the optical modulators 1 to 3. Whether or not to apply the voltage is controlled, and the voltage of the electric signal applied to the optical modulators 1 to 3 is determined so that the intensity of each of the four levels of the output optical signals is equally spaced. Thereby, the PAM4 signal can be generated without requiring complicated phase control. Further, since the electric signal generation unit 4 can be configured by a circuit that generates an OOK signal, it can be realized by a simple circuit.

Further, in the Mach-Zehnder modulator in which the phase modulation section described in Patent Document 1 is divided into a plurality of parts, good characteristics cannot be obtained even when a difference in optical branching ratio and loss occurs. Therefore, it is necessary to suppress manufacturing variation. On the other hand, since the optical modulation module of the present embodiment is not affected by the difference between the optical branching ratio and the loss, the demand for manufacturing variation is lower than that of the Mach-Zehnder modulator in which the phase modulation unit is divided into a plurality. Further, a Mach-Zehnder modulator in which the phase modulation unit is divided into a plurality of parts requires a large number of terminals for phase control. On the other hand, the light modulation module of the present embodiment does not require many terminals for phase control. In addition, since the light modulation module of the embodiment can be realized by a semiconductor having the same band structure, it is easy to manufacture.

Embodiment 2. FIG.
Next, the light modulation module 100a according to the second embodiment of the present invention will be described. The description of the same configuration and operation as in the first embodiment will be omitted, and different points from the first embodiment will be described.

FIG. 6 is an external view showing a mounting example of the light modulation module 100a of the present embodiment. The light modulation module 100a includes light modulators 1a to 3a instead of the light modulators 1 to 3 of the first embodiment. The electrode 8a is an electrode of the optical modulator 1a, the electrode 9a is an electrode of the optical modulator 2a, and the electrode 10a is an electrode of the optical modulator 3a. The optical modulators 1a to 3a are, for example, EAMs, and the functions of the optical modulators 1a to 3a are the same as those of the optical modulators 1 to 3. The optical modulators 1a to 3a are formed of semiconductors having the same band structure. The optical modulators 1a to 3a are different from the optical modulators 1 to 3 of the first embodiment in that the optical path length in each of the optical modulators 1a to 3a is greater than the optical path length of the optical modulator 3a> the optical path of the optical modulator 2a. Length> the optical path length of the optical modulator 1a. In the mounting example shown in FIG. 6, the CW laser 6 and the optical modulators 1a to 3a are arranged in series in the first direction of the semiconductor 5, and the optical path length in the optical modulators 1a to 3a is approximately the optical modulator. The length in the first direction is 1a to 3a. Accordingly, the lengths of the optical modulators 1a to 3a in the first direction are shorter in the order of the optical modulator 3a, the optical modulator 2a, and the optical modulator 1a. Hereinafter, the length of the optical modulators 1a to 3a in the first direction is referred to as the length of the optical modulators 1a to 3a. In this way, by using semiconductors having the same band structure for the optical modulators 1a to 3a and making the optical path lengths in the optical modulators 1a to 3a different, the same electric field is generated in the optical modulators 1a to 3a. The amount of light absorption when applied is different.

The electrical signal generator 4 of the present embodiment generates binary signals to be applied to the optical modulators 1a to 3a, respectively. The correspondence between the on / off state of each electrical signal generated by the electrical signal generation unit 4 of the present embodiment and the value indicated by the PAM4 signal output from the light modulation module 100a is the same as in FIG. However, in the present embodiment, unlike the first embodiment, the amplitudes of the voltages of the three electric signals generated by the electric signal generator 4 to be applied to the optical modulators 1a to 3a are the same.

FIG. 7 is a diagram showing an extinction curve in the optical modulators 1a to 3a of the present embodiment and an amplitude of a voltage of an electric signal applied to the optical modulators 1a to 3a. In FIG. 7, the horizontal axis indicates the voltage applied to the optical modulator, and the vertical axis indicates the optical output after passing through the optical modulator, that is, the intensity of the optical signal. A value corresponding to the intensity of each optical output, that is, the optical signal output from the optical modulation module 100a, is shown on the side of the vertical axis in FIG. FIG. 7 shows the extinction curves of the optical modulators 1a to 3a. When the lengths of the optical modulators 1a to 3a are different, the amount of light absorption in each of the optical modulators 1a to 3a with respect to the applied voltage is different. For this reason, in the present embodiment, as shown in FIG. 7, when the optical modulators 1a to 3a are driven with the same amplitude, the optical output after passing through the optical modulators 1a to 3a is Similarly to the PAM4 signal, the lengths of the optical modulators 1a to 3a are determined so that the levels are equally spaced. As a result, the light modulation module 100a of the present embodiment can generate the PAM4 signal as in the first embodiment while driving the light modulators 1a to 3a with electric signals having the same amplitude. The arrangement order of the optical modulators 1a to 3a is not limited to the example shown in FIG. 6, and the same effect can be obtained even if the arrangement order is changed.

According to the light modulation module 100a of the present embodiment, the absorption amount of the light modulators 1a to 3a is adjusted so that a desired PAM4 signal is obtained according to the length of the light modulators 1a to 3a. For this reason, the same effects as those of the first embodiment can be obtained, and the optical modulators 1a to 3a can be driven by electric signals having the same amplitude. Therefore, an integrated circuit (IC) that realizes the electric signal generator 4 is realized. Design of a circuit such as an integrated circuit becomes easy. Further, since electric signals having the same amplitude are input to the optical modulators 1a to 3a, it is not necessary to perform amplitude control for each electric signal, so that the time required for product testing can be reduced. The arrangement order of the optical modulators 1a to 3a is not limited to the example shown in FIG. 6, and the same effect can be obtained even if the arrangement order is changed. It should be noted that the amount of absorption is adjusted according to the length of two of the three optical modulators 1a to 3a using the same amplitude electrical signal as in the present embodiment, and the remaining one of the optical modulators. The optical output may be adjusted according to the amplitude of the electrical signal with an arbitrary length. Also in this case, since the two optical modulators can be driven by electric signals having the same amplitude, an effect of facilitating circuit design can be obtained.

Embodiment 3 FIG.
Next, the light modulation module 100b according to the third embodiment of the present invention will be described. The description of the same configuration and operation as in the first embodiment will be omitted, and different points from the first embodiment will be described.

FIG. 8 is an external view showing a mounting example of the light modulation module 100b of the present embodiment. The light modulation module 100b includes light modulators 1b to 3b instead of the light modulators 1 to 3 of the first embodiment. The electrode 8b is an electrode of the optical modulator 1b, the electrode 9b is an electrode of the optical modulator 2b, and the electrode 10b is an electrode of the optical modulator 3b. The optical modulators 1b to 3b are, for example, EAM. The optical modulators 1b to 3b are different from the optical modulators 1 to 3 of the first embodiment in that the optical modulators 1b to 3b are formed of semiconductors having different band gaps. Specifically, the band gap of the optical modulator 1b> the band gap of the optical modulator 2b> the band gap of the optical modulator 3b. In the present embodiment, since the band gaps of the optical modulators 1b to 3b are different, the light absorption amounts of the optical modulators 1b to 3b are different when the same electric field is applied. The lengths of the optical modulators 1b to 3b are the same.

FIG. 9 is a diagram showing an extinction curve in the optical modulators 1b to 3b of the present embodiment and an amplitude of the voltage of the electric signal applied to the optical modulators 1b to 3b. In FIG. 9, the horizontal axis indicates the voltage applied to the optical modulator, and the vertical axis indicates the optical output after passing through the optical modulator, that is, the intensity of the optical signal. A value corresponding to the intensity of each optical output, that is, the optical signal output from the optical modulation module 100b, is shown beside the vertical axis in FIG. FIG. 9 shows the extinction curves of the optical modulators 1b to 3b. Amplitude # 1, amplitude # 2, and amplitude # 3 indicate the amplitudes of electrical signals applied to the optical modulator 1b, the optical modulator 2b, and the optical modulator 3b, respectively.

In the case of Embodiment 2 in which the lengths of the respective optical modulators are different, as shown in FIG. 7, the extinction curves of the optical modulator 1a and the optical modulator 2a are the same as the extinction curves of the optical modulator 3a. It becomes a shape that is stretched. Therefore, as in the case of the modulation between 11 and 10 in the optical modulator 1a, the optical signal intensity difference is smaller than that of the other

optical modulators

2a and 3a, that is, shallow modulation is performed. The same amplitude as the modulation between 11 and 00 in the optical modulator 3a having a large difference in intensity is required. On the other hand, in the present embodiment, since the optical modulators 1b to 3b have the same length, the extinction curves of the optical modulator 1b and the optical modulator 2b are as shown in FIG. The extinction curve is offset in the voltage direction. Therefore, when generating PAM4 signals at equal intervals, the amplitude of the electrical signal applied to the optical modulator 2b can be made smaller than the amplitude of the electrical signal applied to the optical modulator 3b, and applied to the optical modulator 1b. The amplitude of the electrical signal can be made smaller than the amplitude of the electrical signal applied to the optical modulator 2b.

In the present embodiment, the same effects as in the first embodiment can be obtained, and the lengths of the optical modulators 1b to 3b are made the same, and the band gaps of the optical modulators 1b to 3b are made different. Compared with the second embodiment, the amplitude of the electric signal can be suppressed. For this reason, the power consumption of the electric signal generation unit 4 can be reduced. The arrangement order of the optical modulators 1b to 3b is not limited to the example shown in FIG. 8, and the same effect can be obtained even if the arrangement order is changed.

In the above-described example, the amplitude of the electric signal applied to the optical modulators 1b to 3b is made different. However, the amplitude of the electric signal applied to the optical modulator 1b and the optical modulator 2b is changed to the optical modulator 3b. The electric signal to be applied may be the same. As shown in FIG. 9, the optical output when the electric field is not applied even if the amplitude of the electric signal applied to the optical modulator 1b and the optical modulator 2b is extended to the low voltage side is the same. , PAM4 signals at equal intervals can be generated. In this case, the power consumption is not reduced, but the circuit for realizing the electrical signal generation unit 4 can be simplified and the product test time can be shortened as in the second embodiment. Further, the lengths of the optical modulators 1b to 3b may be different. Also in this case, it is possible to generate PAM4 signals at equal intervals by appropriately setting the amplitude.

Embodiment 4 FIG.
Next, an optical modulation module according to the fourth embodiment of the present invention will be described. The configuration of the light modulation module of the present embodiment is the same as that of the second embodiment. The description of the same configuration and operation as those of the second embodiment will be omitted, and differences from the second embodiment will be described.

In this embodiment, as described in the second embodiment, the optical modulators 1a to 3a having different lengths are used. FIG. 10 is a diagram showing the extinction curves in the optical modulators 1a to 3a of the present embodiment and the amplitude of the voltage of the electric signal applied to the optical modulators 1a to 3a. In FIG. 10, the horizontal axis represents the voltage applied to the optical modulator, and the vertical axis represents the optical output after passing through the optical modulator, that is, the intensity of the optical signal. A value corresponding to the intensity of each optical output, that is, the optical signal output from the optical modulation module 100a, is shown on the side of the vertical axis in FIG. The extinction curves of the optical modulators 1a to 3a in FIG. 10 are the same as the example of FIG. 7 shown in the second embodiment. Amplitude # 1, amplitude # 2, and amplitude # 3 indicate the amplitudes of electrical signals applied to the optical modulator 1a, the optical modulator 2a, and the optical modulator 3a, respectively.

In Embodiment 2, the amplitudes of the electric signals applied to the optical modulators 1a to 3a are the same. On the other hand, in the present embodiment, as shown in FIG. 10, the amplitudes of the electric signals applied to the optical modulators 1a to 3a are different. Specifically, as shown in FIG. 10, amplitude # 3> amplitude # 2> amplitude # 1. However, as shown in FIG. 10, when OFF, that is, when the light is absorbed, the voltage value is the same as that in the example of FIG. 7, and when ON, that is, when the light is not absorbed, the amplitude # 2 and the voltage value are increased. Set amplitude # 1. In this case, in the optical modulator 1a and the optical modulator 2a, even when light is not absorbed, the voltage is higher than in the case of the second embodiment. Therefore, in the present embodiment, the extinction ratios of the optical modulators 1a to 3a are different from each other. The extinction ratio is a ratio between the intensity of light output when an electric field is applied and the intensity of light output when an electric field is applied. If the amplitude # 2 and the amplitude # 1 are set so that the decrease in the light output does not affect the overall performance, there is no practical problem.

As described above, in the present embodiment, the amplitudes of electric signals applied to the optical modulators 1a to 3a are suppressed as compared with the second embodiment using the optical modulators 1a to 3a of the second embodiment. For this reason, the same effects as those of the first embodiment can be obtained, and the power consumption can be suppressed as compared with the second embodiment. The arrangement order of the optical modulators 1a to 3a is not limited to the example shown in FIG. 6, and the same effect can be obtained even if the arrangement order is changed.

Embodiment 5 FIG.
In the first to fourth embodiments, the configuration example in which the CW laser 6 for generating continuous light and the modulator are integrated has been described. The light modulation module of the present embodiment deletes the CW laser 6 from the light modulation module described as the mounting example in the first embodiment. Then, continuous light input from an external light source such as a CW laser is input to the light modulation module. That is, continuous light is input to the light modulation module from the outside. The external light source and the light modulation module are optically connected using an optical lens or by a Butt-Joint connection. The configuration and operation of this embodiment other than those described above are the same as those of the first embodiment.

Similarly, the CW laser 6 may be deleted from the light modulation module described as the mounting example in any one of Embodiments 2 to 4, and optically connected to an external light source. Also in this case, the configuration and operation of the light modulation module are the same as the operations of the corresponding embodiments except that a light source is provided outside and optically connected to the light source.

In this embodiment, since it is not integrated with the light source, the manufacture of the light modulation module is facilitated, and the defect rate at the time of manufacture can be reduced.

Embodiment 6 FIG.
In the first to fourth embodiments, EAM is used as an optical modulator. However, in this embodiment, a switch-type intensity modulator that switches an optical path, that is, an optical path switching element is used as an optical modulator. FIG. 11 is a diagram illustrating a configuration example of the light modulation module 100c according to the present embodiment. FIG. 11 shows an example in which a ring resonator is used as a switch for switching the optical path. An optical modulation module 100c illustrated in FIG. 11 includes a ring resonator 21, a ring resonator 22, and a ring resonator 23, each of which is an optical modulator. The optical modulation module 100 c includes an input port 24,

drop ports

25, 27, 29, through

ports

26, 28, 30 and an output port 31. Electric signals output from the electric signal generator 4 (not shown in FIG. 11) are applied to the ring resonators 21 to 23 of the present embodiment.

The ring resonators 21 to 23 are designed and controlled so that when the applied electrical signal is on, all the light input from the optical waveguide is transferred to the ring resonators 21 to 23 by optical coupling. . Further, when the applied electrical signal is OFF, the light input from the optical waveguide is designed and controlled so that part of it moves to the ring resonators 21 to 23 and the rest moves to the through port. The optical waveguide on the input side of the ring resonator 21 is the input port 24, the optical waveguide on the input side of the ring resonator 22 is the drop port 25, and the optical waveguide on the input side of the ring resonator 23 is the drop port. 27. Further, the light transferred to the ring resonator 21 is transferred to the drop port 25, the light transferred to the ring resonator 22 is transferred to the drop port 27, and the light transferred to the ring resonator 23 is transferred to the drop port 29. Be controlled.

The ring resonator 21 performs 11/10 modulation, the ring resonator 22 performs 11/01 modulation, and the ring resonator 23 performs 11/00 modulation. As in the first embodiment, the electrical signal generator 4 applies an OOK signal to each of the ring resonators 21 to 23 that are optical modulators. Each of the ring resonators 21 to 23 resonates when an electrical signal indicating ON is input, and does not resonate when an electrical signal indicating OFF is input. The correspondence between the PAM4 signal output from the light modulation module 100c of the present embodiment, that is, the value indicated by the output signal, and the electric signal applied to each of the ring resonators 21 to 23 is the same as that shown in FIG. It is the same.

In the light modulation module 100c, when the PAM4 signal having the value 11 is output, the electrical signals applied to all the ring resonators 21 to 23 are on. The continuous light output from the light source is input to the ring resonator 21 through the input port 24, resonates at the ring resonator 21, and moves to the drop port 25. The light transferred to the drop port 25 is input to the ring resonator 22, resonates at the ring resonator 22, and moves to the drop port 27. The light transferred to the drop port 27 is input to the ring resonator 23, resonates at the ring resonator 23, and moves to the drop port 29. The light transferred to the drop port 29 is output from the output port 31 as a PAM4 signal.

Further, in the light modulation module 100c, when a PAM4 signal having a value of 10 is output, the electrical signal applied to the ring resonator 21 is off, and the electrical signal applied to the ring resonator 22 and the ring resonator 23. Is on. For this reason, a part of the continuous light input from the light source via the input port 24 remains in the through port 26 and the rest moves to the drop port 25. At this time, the ring resonator 21 is designed and controlled so that the intensity of light transferred to the drop port 25 becomes an intensity corresponding to a value of 10. Since the ring resonator 22 and the ring resonator 23 are on, the light that has moved to the drop port 25 resonates by the ring resonator 22 and moves to the drop port 27. The light transferred to the drop port 27 is input to the ring resonator 23, resonates at the ring resonator 23, and moves to the drop port 29. The light transferred to the drop port 29 is output from the output port 31 as a PAM4 signal. Similarly, when outputting a PAM4 signal having a value of 01 and outputting a PAM4 signal having a value of 00, the PAM4 signal corresponding to each value is output by applying the electrical signal shown in FIG. Is done. The ring resonator 22 is designed and controlled so that the intensity of light transferred to the drop port 27 becomes a value of 01 when the ring resonator 21 is on and the ring resonator 22 is off. The ring resonator 23 is designed so that the intensity of light transferred to the drop port 29 becomes a value of 00 when the ring resonator 21 and the ring resonator 22 are on and the ring resonator 23 is off. Be controlled.

As described above, in the present embodiment, a PAM4 signal is generated using an OOK signal as in the first embodiment, using a ring resonator as an optical modulator. Therefore, a multilevel modulation signal can be generated without requiring precise phase control. In this embodiment, it is not necessary to use a compound semiconductor used for EAM, and multilevel modulation can be realized using an inexpensive material such as silicon. The same effect can be obtained even if the order of the ring resonators 21 to 23 is changed.

The configuration described in the above embodiment shows an example of the contents of the present invention, and can be combined with another known technique, and can be combined with other configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

100, 100a, 100b, 100c light modulation module, 1, 1a, 1b, 2, 2a, 2b, 3, 3a, 3b light modulator, 4 electrical signal generator, 5 semiconductor, 6 CW laser, 21-23 ring resonance vessel.

Claims

A first light modulator for performing light intensity modulation on the continuous light;
A second light modulator that performs light intensity modulation on the light that has been light intensity modulated by the first light modulator;
A third light modulator that performs light intensity modulation on the light that has been light intensity modulated by the second light modulator;
A first electrical signal, which is a binary electrical signal, is applied to the first optical modulator, and a second electrical signal, which is a binary electrical signal, is applied to the second optical modulator, and binary A signal generator that applies a third electrical signal that is an electrical signal of the second optical modulator to the third optical modulator;
An optical modulation module comprising:
The light modulation module according to claim 1, wherein the first, second, and third light modulators are electroabsorption type light modulators.
The optical modulation module according to claim 2, wherein band gaps of the first, second and third optical modulators are the same.
The optical modulation module according to claim 2, wherein band gaps of the first, second, and third optical modulators are different from each other.
The optical modulation module according to any one of claims 2 to 4, wherein the optical path lengths of the first, second and third optical modulators are the same.
The optical modulation module according to any one of claims 2 to 4, wherein optical path lengths of the first, second, and third optical modulators are different from each other.
The optical modulation module according to claim 6, wherein extinction ratios in the first, second and third optical modulators are different from each other.
A light source for generating the continuous light;
The light modulation module according to claim 1, further comprising:
9. The light modulation module according to claim 8, wherein the first, second, and third light modulators and the light source are integrated on the same chip.
The light modulation module according to any one of claims 1 to 7, wherein the continuous light is input from the outside of the light modulation module.
The light modulation module according to claim 1, wherein the first, second, and third light modulators are light path switching elements.