JP5612539B2 - Optical modulator and manufacturing method thereof - Google Patents

Description

  The present invention relates to an optical modulator and a method for manufacturing the same, and more particularly to an optical modulator capable of suppressing electrical crosstalk and a method for manufacturing the same.

FIG. 9 is a structural diagram of a conventional Mach-Zehnder modulator, and FIG. 10 is a sectional view taken along line XX of FIG.
As shown in FIG. 9, the conventional Mach-Zehnder modulator is disposed between two optical waveguides 3, two optical couplers 10 and 11, and two optical couplers 10 and 11, and outputs a high-frequency signal to the optical waveguide 3. The signal line electrode 4 to be applied is provided. A region where a high-frequency signal is applied to the optical waveguide 3 by the signal line electrode 4 is configured as two modulation units 12.

  As shown in FIG. 10, in the modulation unit 12, the optical waveguide 3 is formed on the substrate 1 via the ground layer 2, and the dielectric insulating film 5 is formed on both sides of the propagation direction of the optical waveguide 3. A signal line electrode 4 is patterned on the optical waveguide 3, and ground electrodes 6 are formed on both sides of the dielectric insulating film 5 in the light propagation direction. In the figure, L1 indicates the channel spacing, and L2 indicates the element width.

Ken Tsuzuki, Yasuo Shibata, Nobuhiro Kikuchi, Mitsuteru Ishikawa, Takako Yasui, Hiroyuki Ishii, and Hiroshi Yasaka, “Full C-Band Tunable DFB Laser Array Copackaged With InP Mach-Zehnder Modulator for DWDM Optical Communication Systems”, IEEE Journal of selected topic in quantum electronics, 2009, Vol.15, No.3

  Here, in order to suppress the influence of crosstalk between light and electricity between adjacent modulation sections 12, it is necessary to separate the channel L1. The light crosstalk can be sufficiently suppressed if the distance L1 is 20 μm or more, but the electric signal crosstalk needs to be at least 100 μm apart from the distance L1. For this reason, the influence of crosstalk of electric signals has become a bottleneck for miniaturization of elements.

  The demand for further downsizing of communication optical modulators is increasing along with the trend toward multi-channel and multi-value. Here, the optical modulator device can greatly reduce the size of the element by narrowing the interval between the optical waveguides having the high-frequency signal lines. However, the current structure is further reduced in size due to the influence of the electrical crosstalk. was difficult.

  For this reason, the present invention can be easily manufactured using devices and materials used in the conventional element manufacturing process, and can be applied to a structure that suppresses electrical crosstalk. It is an object of the present invention to provide a small-sized optical modulator capable of narrowing the width and a manufacturing method thereof.

An optical modulator according to a first aspect of the present invention for solving the above problems modulates a plurality of optical waveguides formed in parallel on a substrate via a ground layer and light passing through the optical waveguide. Therefore, in the optical modulator in which an optical modulation unit is configured by a plurality of signal line electrodes respectively provided on the optical waveguide, the optical modulation unit covers a periphery of the optical waveguide and the signal line electrode An insulating film and a ground electrode connected to the ground layer and covering the outer periphery of the dielectric insulating film together with the ground layer are provided.

  An optical modulator according to a second invention for solving the above-described problem is the optical modulator according to the first invention, wherein the optical modulation unit constitutes an optical modulation unit of a Mach-Zehnder optical modulator. Features.

The optical modulator according to a third invention for solving the aforementioned problem, in the optical modulator according to the first invention, the Mach-Zehnder modulator, wherein the light modulating unit has at least two Ma Hhatsuenda optical modulator It constitutes the light modulation part of the device array.

A method for manufacturing an optical modulator according to a fourth aspect of the present invention for solving the above-described problem is to modulate a plurality of optical waveguides formed in parallel on a substrate and light passing through the optical waveguide. An optical modulator manufacturing method in which an optical modulator is configured by a plurality of signal line electrodes respectively provided on the optical waveguide, wherein a surface structure of the optical modulator element is provided on a substrate via a ground layer. the optical waveguide path Te, the dielectric insulating film, the signal line electrode and the first and forming a ground electrode, wherein the optical waveguide and the signal line electrode by patterning on the surface of the ground layer connected to the ground layer having a step of forming the dielectric insulating film only around, and forming a second ground electrode connected to the first ground electrode by vapor deposition on the periphery of the dielectric insulating film And features.

  According to the present invention, it is possible to provide an optical modulator that can suppress crosstalk between signal lines of the optical modulator and can be downsized accordingly. In addition, it is possible to provide a method for manufacturing an optical modulator capable of achieving an electrostatic shielding structure using a device and a material used in a conventional element manufacturing process.

It is sectional drawing which shows the structure of the modulation | alteration part of the optical modulator which concerns on one Embodiment of this invention. It is a block diagram of the electrostatic shielding waveguide EADFB laser array which concerns on Example 1 of this invention. It is explanatory drawing which shows the formation procedure of the electrostatic shielding waveguide EADFB laser array which concerns on Example 1 of this invention. It is explanatory drawing which shows the BER characteristic measurement system of the EADFB laser array which concerns on Example 1 of this invention. It is a block diagram of the electrostatic shielding type Mach-Zehnder modulator which concerns on Example 2 of this invention. It is explanatory drawing which shows the eye pattern measurement system using the Mach-Zehnder modulator which concerns on Example 2 of this invention. It is a block diagram of the electrostatic shielding type Mach-Zehnder modulator array which concerns on Example 3 of this invention. It is explanatory drawing which shows the eye pattern measurement system using the Mach-Zehnder modulator array which concerns on Example 3 of this invention. It is a block diagram of the conventional Mach-Zehnder modulator. It is XX sectional drawing of FIG.

Hereinafter, the details of the optical modulator and the manufacturing method thereof according to the present invention will be described with reference to the drawings.
FIG. 1 shows a cross-sectional structure of an optical modulator of the optical modulator according to the present embodiment. As shown in FIG. 1, the modulation section of the optical modulator according to the present embodiment is configured by patterning signal line electrodes 4 directly on an optical waveguide 3 formed on a substrate 1 via a ground layer 2. Has been. A dielectric insulating film 5 is formed around the optical waveguide 3 and the signal line electrode 4, and a ground electrode 6 is deposited around the dielectric insulating film 5. The optical waveguide 3 includes an optical waveguide core layer 3a and an optical waveguide cladding layer 3b formed above and below the optical waveguide core layer 3a.

Next, a method for manufacturing the optical modulator according to this embodiment will be described. In the present embodiment, the surface structure is formed on the substrate 1 in the same manner as in the conventional manufacturing procedure described above (that is, the optical waveguide layer 3, the dielectric insulating film 5, the signal line electrode 4, and the ground electrode 6 are formed as shown in FIG. Then, the dielectric insulating film 5 is formed only around the signal line electrode 4 by using a patterning technique, and then the ground electrode 6 is formed around the dielectric insulating film 5 by a vapor deposition apparatus. A light modulator is produced by vapor deposition.
In the present embodiment, it is preferable that the optical waveguide 3 is made of a III-V group compound semiconductor composed of at least two kinds of elements of Si, Al, Ga, In, As, P, or Sb, for example.

  In the optical modulator according to this embodiment, the signal line electrode 4 is covered with the dielectric insulating film 5 and the ground electrode 6. Thereby, the electromagnetic waves from the signal line electrode 4 can be electrostatically shielded, and the electromagnetic waves from the signal line electrode 4 can be prevented from spreading outside the ground electrode 6. That is, according to the optical modulator according to this embodiment, crosstalk between adjacent signal lines can be suppressed. For this reason, it is possible to narrow the channel interval of the modulation unit as compared with the conventional case, and thus it is possible to reduce the size of the optical modulator. In addition, according to the method for manufacturing an optical modulator according to this embodiment, an optical modulator capable of suppressing electrical crosstalk can be manufactured using only the devices and materials used for manufacturing the conventional optical modulator. .

(Laser array with waveguide type EA modulator)
A first embodiment of the optical modulator and the manufacturing method thereof according to the present invention will be described with reference to FIGS. This example is an example showing the effect of the present invention, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.

  As shown in FIG. 2, the optical modulator according to the present embodiment constitutes a part of a distributed feedback laser array with a two-channel waveguide type EA modulator (hereinafter referred to as a two-channel waveguide type EADFB laser array). Yes. Specifically, the two-channel waveguide type EADFB laser array shown in FIG. 2 includes two distributed feedback semiconductor lasers (hereinafter referred to as DFB lasers) 7 and an optical waveguide 3 that propagates light output from the DFB laser 7. An optical multiplexer 8 that combines light propagating through the two optical waveguides 3, and a signal line electrode 4 that is disposed between the DFB laser 7 and the optical multiplexer 8 and applies a high-frequency signal to the optical waveguide 3. It is configured with. A region where a high frequency signal is applied to the optical waveguide 3 by the signal line electrode 4 is configured as two waveguide type EA modulators 9.

Note that the II cross-sectional structure of the waveguide type EA modulator 9 of the electrostatic shielding type two-channel waveguide type EADFB laser array shown in FIG. 2 is substantially the same as the structure of the modulation unit shown in FIG. Detailed description is omitted here.
In this embodiment, the channel spacing of the DFB laser 7 is 50 μm, and a multimode interference type multiplexer (hereinafter referred to as an MMI coupler) is used as the optical multiplexer 8.
The bias current of the DFB laser 7 was 100 mA and the signal amplitude voltage was 2 Vpp. The optical fiber was 10 km. The wavelengths of light emitted from the DFB laser 7 were 1305 nm and 1310 nm.

1. Operation Principle and Manufacturing Process The reason why crosstalk between signal lines can be reduced by the optical modulator according to this embodiment will be described below. In the present embodiment, the signal line electrode 4 is covered with the dielectric insulating film 5 and the ground electrode 6 as compared with the conventional configuration, similarly to the configuration shown in FIG. As a result, the electromagnetic wave from the signal line electrode 4 is electrostatically shielded and therefore does not spread outside the ground electrode 6. Therefore, crosstalk between signal lines on adjacent waveguides 3 can be suppressed.

  Next, the reason why the optical modulator according to this embodiment can be easily created will be described with reference to FIG. An optical waveguide layer 3, a signal line electrode 4, a dielectric insulating film 5, and a ground electrode 6 are formed on the substrate 1 as surface structures up to the state of the conventional light modulation unit shown in FIG. (Step (a) in FIG. 3). Next, a dielectric insulating film 5 is formed so as to cover the signal line electrode 4, and a portion where the dielectric insulating film 5 is unnecessary (for example, a portion covering the ground electrode 6 in this embodiment) is removed by patterning. (FIG. 3B). Finally, a ground electrode 6 is formed so as to cover the dielectric insulating film 5 by gold vapor deposition and lift-off (FIG. 3C). At this time, the ground electrode 6 to be finally formed is assumed to be connected to the previously formed ground electrode 6 shown in FIG. Thus, the electrostatically shielded signal line is completed. Here, the dielectric insulating film 5 used in this embodiment and the gold used as the ground electrode 6 are the same as those used in the production of a conventional EADFB laser array. It is only a device used in the process. Therefore, it can be said that a device having this structure can be manufactured using apparatuses and materials used in a conventional element manufacturing process.

2. FIG. 4 shows a measurement system for measuring the modulation characteristics of a two-channel waveguide type EADFB laser array. The 2-channel pulse pattern generator (hereinafter referred to as 2Ch-PPG) 101 shown in FIG. 4 outputs a 40 Gbps signal, and the multi-channel optical transmission module 102 having the 2-channel waveguide type EADFB laser array is provided. Each is connected to the waveguide type EA modulator 9. The two-channel laser drive power source 103 is connected to the channel of each DFB laser 7 in the multi-channel optical transmission module 102. Light output from the EADFB laser array of the multi-channel optical transmission module 102 enters the optical demultiplexer 105 via the single mode fiber 104. Then, one of the demultiplexed lights is attenuated by the optical variable attenuator 106, and then input to the photodetector 107 and converted into an electrical signal. This electrical signal enters the error detector 108. The observed channel was a channel having a wavelength of 1305 nm.

  As a result of measuring the code error rate characteristics (hereinafter referred to as BER characteristics) in the measurement system described above, the minimum reception sensitivity when measured by operating two channels simultaneously is -7 dBm, and the minimum reception sensitivity when operated alone is -7.1 dBm. From this result, it was found that even when the distance is very narrow as 50 μm, the effect of electrostatic shielding can suppress the crosstalk to the extent that the reception sensitivity hardly deteriorates.

As a comparison, BER characteristics were measured for a two-channel waveguide type EADFB laser array having a conventional structure. At this time, the conventional waveguide interval was also set to 50 μm. As a result, the minimum reception sensitivity when measured by operating two channels simultaneously was -6.2 dBm, and the minimum reception sensitivity when operated alone was -7.1 dBm. This deterioration in reception sensitivity is considered to have occurred because the signal waveform deteriorated mainly due to crosstalk.
From the above, it is clear that the waveguide type EADFB laser array including the modulator according to the present embodiment having the electrostatic shielding structure is effective in reducing crosstalk, that is, effective in reducing the size of the laser array.

(MZ modulator)
A second embodiment of the optical modulator and the manufacturing method thereof according to the present invention will be described with reference to FIGS. This embodiment is an example showing the effect of the present invention, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

  As shown in FIG. 5, the optical modulator according to the present embodiment constitutes a Mach-Zehnder modulator. Specifically, two optical waveguides 3, an optical coupler 10 that branches two input optical signals, and an optical coupler 11 that inputs an optical signal branched by the optical coupler 10 and branches it into two. The signal line electrode 4 is disposed between the two optical couplers 10 and 11 and applies a high-frequency signal to the optical waveguide 3. A region where a high-frequency signal is applied to the optical waveguide 3 by the signal line electrode 4 is configured as two modulation units 12.

In this embodiment, the interval between the waveguides 3 of the modulator 12 is 50 μm, and MMI couplers are used as the optical couplers 10 and 11.
The output from the laser light source was +5 dBm, the wavelength was 1550 nm, and the signal amplitude voltage was 3 Vpp. The optical fiber was 40 km.
Note that the II cross-sectional structure of the modulation section 12 of the electrostatic shielding type Mach-Zehnder modulator shown in FIG. 5 is substantially the same as that shown in FIG.

1. Operation Principle and Manufacturing Process The reason why the crosstalk can be reduced between the signal lines on the waveguide 3 of the modulation unit 12 will be described. In the present embodiment, the signal line electrode 4 is covered with the dielectric insulating film 5 and the ground electrode 6 as compared with the conventional configuration, similarly to the configuration shown in FIG. As a result, the electromagnetic wave from the signal line electrode 4 is electrostatically shielded and therefore does not spread outside the ground electrode 6. Therefore, crosstalk between signal lines on adjacent waveguides can be suppressed.

  Next, the reason why the optical modulator according to this embodiment can be easily created will be described with reference to FIG. The optical waveguide layer 3, dielectric insulating film 5, signal line electrode 4, and ground electrode 6 are formed on the substrate 1 as the surface structure up to the state of the conventional optical modulation unit shown in FIG. The process is the same as that of the container (FIG. 3A). Next, a dielectric insulating film 5 is formed so as to cover the signal line electrode 4, and a portion where the dielectric insulating film 5 is unnecessary (for example, a portion covering the ground electrode 6 in this embodiment) is removed by patterning. (FIG. 3B). Finally, a ground electrode 6 is formed so as to cover the dielectric insulating film 5 by gold vapor deposition and lift-off (FIG. 3C). At this time, the ground electrode 6 to be finally formed is assumed to be connected to the previously formed ground electrode 6 shown in FIG. Thus, the electrostatically shielded signal line is completed. Here, the dielectric insulating film 5 and the gold of the ground electrode 6 used in the present embodiment are the same as those used when a conventional Mach-Zehnder modulator is formed. However, it is only a device to use. Therefore, it can be said that a device having this structure can be manufactured using apparatuses and materials used in a conventional element manufacturing process.

2. FIG. 6 shows a measurement system for measuring the modulation characteristics of the Mach-Zehnder modulator. A pulse pattern generator (hereinafter referred to as PPG) 111 outputs a 40 Gbps signal and an inverted signal, which are connected to a Mach-Zehnder modulator in the optical modulator module 112, respectively. The light output from the laser light source 113 is modulated by the optical modulator module 112 and then input to the sampling oscilloscope 115 via the single mode fiber 114, so that the eye pattern can be observed.

As a result of measuring the eye pattern, the extinction ratio was 9 dB.
For comparison, the same measurement was performed with an optical modulator module including a Mach-Zehnder modulator having a conventional structure with a waveguide interval of 50 μm. As a result, the extinction ratio was 8.1 dB. This is considered that the extinction ratio was reduced due to signal degradation due to crosstalk.

  From the above, it is clear that the Mach-Zehnder modulator, which is an optical modulator having an electrostatic shielding structure according to the present embodiment, is effective for reducing crosstalk, that is, effective for downsizing the modulator device.

(Mach-Zehnder modulator array)
A third embodiment of the optical modulator and the manufacturing method thereof according to the present invention will be described with reference to FIGS. This embodiment is an example showing the effect of the present invention, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

  As shown in FIG. 7, the optical modulator according to this embodiment forms part of a Mach-Zehnder modulator array. Specifically, two Mach-Zehnder modulators described in the second embodiment are arranged in parallel, and one of the lights branched by the optical coupler 11 of each of these two Mach-Zehnder modulators is input and branched. An optical coupler 13 is provided. The other configuration is substantially the same as the configuration of the Mach-Zehnder modulator shown in FIG. 5 and described above, and members having the same functions are denoted by the same reference numerals and redundant description is omitted.

In this embodiment, the interval between the waveguides 3 of the modulation unit is 50 μm, and MMI couplers are used as the optical couplers 10, 11, and 13.
The output from the laser light source was +5 dBm, the wavelengths were 1550 nm and 1560 nm, and the signal amplitude voltage was 3 Vpp. The optical fiber was 40 km.
Note that the II cross-sectional structure in the modulation section of the electrostatic shielding type Mach-Zehnder modulator shown in FIG. 7 is almost the same as that shown in FIG.

1. Operation Principle and Manufacturing Process The reason why crosstalk can be reduced between signal lines provided on the waveguide 3 of the modulation unit 12 in this embodiment will be described. In the present embodiment, the signal line electrode 4 is covered with the dielectric insulating film 5 and the ground electrode 6 as compared with the conventional configuration, similarly to the configuration shown in FIG. As a result, the electromagnetic wave from the signal line electrode 4 is electrostatically shielded and therefore does not spread outside the ground electrode 6. Therefore, crosstalk between signal lines on adjacent waveguides 3 can be suppressed.

  Next, the reason why the optical modulator according to this embodiment can be easily created will be described with reference to FIG. The optical waveguide layer 3, dielectric insulating film 5, signal line electrode 4, and ground electrode 6 are formed on the substrate 1 as the surface structure up to the state of the conventional optical modulation unit shown in FIG. The process is the same as that of the container (FIG. 3A). Next, a dielectric insulating film 5 is formed so as to cover the signal line electrode 4, and a portion where the dielectric insulating film 5 is unnecessary (for example, a portion covering the ground electrode 6 in this embodiment) is removed by patterning. (FIG. 3B). Finally, a ground electrode 6 is formed so as to cover the dielectric insulating film 5 by gold vapor deposition and lift-off (FIG. 3C). At this time, the ground electrode 6 to be finally formed is assumed to be connected to the previously formed ground electrode 6 shown in FIG. Thus, the electrostatically shielded signal line is completed. Here, the dielectric insulating film 5 and the gold of the ground electrode 6 used in the present embodiment are the same as those used when a conventional Mach-Zehnder modulator is formed. Only equipment used in the process. Therefore, it can be said that a device having this structure can be manufactured using apparatuses and materials used in a conventional element manufacturing process.

2. FIG. 8 shows a measurement system for measuring the modulation characteristics of the Mach-Zehnder modulator array. A two-channel pulse pattern generator (hereinafter referred to as 2Ch-PPG) 121 outputs two 40 Gbps signals, each of which has a signal and an inverted signal output, and is supplied to the Mach-Zehnder modulator array in the optical modulator module 122. Each is connected. Further, the light output from the two-channel laser light source 123 is modulated by the optical modulator module 122, then cut out by the demultiplexer 125 through the single mode fiber 124, and then output to the sampling oscilloscope 126. The eye pattern can be observed. The observed channel was a channel having a wavelength of 1550 nm.

As a result of measuring the eye pattern, the extinction ratio when only one channel was moved was 9.2 dB, and the extinction ratio when both channels were moved simultaneously was 9.1 dB.
For comparison, the same measurement was performed with an optical modulator module in which the waveguide interval was set to the same 50 μm and a Mach-Zehnder modulator array having a conventional structure was inserted. As a result, the extinction ratio when only one channel was moved was 8.3 dB The extinction ratio when both channels were moved simultaneously was 7.6 dB. This is considered that the extinction ratio was reduced due to signal degradation due to crosstalk.

  From the above, it is clear that the Mach-Zehnder modulator array having the electrostatic shielding structure of this embodiment is effective for reducing electric crosstalk, that is, effective for downsizing the modulator array.

  The present invention is suitable for application to an optical modulator and a method for manufacturing the same.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Ground layer 3 Optical waveguide 3a Optical waveguide core 3b Optical waveguide cladding 4 Signal line electrode 5 Dielectric insulating film 6 Ground electrode 7 Distributed feedback semiconductor laser (DFB laser)
8 Optical multiplexer 9 Waveguide type EA modulator 10, 11, 13 Optical coupler 12 Optical modulator 101 2-channel pulse pattern generator (2Ch-PPG)
102 Multi-channel optical transmission module 103 2-channel laser drive power supply 104 Optical fiber 105 Optical demultiplexer 106 Optical variable attenuator 107 Photo detector 108 Pulse pattern generator 111 Pulse pattern generator (PPG)
112 optical modulator module 113 laser light source 114 optical fiber 115 sampling oscilloscope 121 2 channel pulse pattern generator (2Ch-PPG)
122 Optical modulator module 123 Laser light source 124 Optical fiber 125 Optical demultiplexer 126 Sampling oscilloscope

Claims (4)

Light is generated by a plurality of optical waveguides formed in parallel on the substrate via a ground layer, and a plurality of signal line electrodes respectively provided on the optical waveguide for modulating light passing through the optical waveguide. In the optical modulator in which the modulator is configured,
The light modulator is
A dielectric insulating film covering the periphery of the optical waveguide and the signal line electrode;
An optical modulator comprising: a ground electrode connected to the ground layer and covering the outer periphery of the dielectric insulating film together with the ground layer . The optical modulator according to claim 1, wherein the optical modulator constitutes an optical modulator of a Mach-Zehnder optical modulator. The optical modulator of claim 1, wherein said light modulating unit constituting the light modulation unit of the Mach-Zehnder modulator array having at least two Ma Hhatsuenda optical modulator. A light modulation unit is configured by a plurality of optical waveguides formed in parallel on the substrate and a plurality of signal line electrodes respectively provided on the optical waveguide to modulate light passing through the optical waveguide. A method of manufacturing an optical modulator comprising:
Forming the optical waveguide path as a surface structure of the element of the light modulator on the substrate through the ground layer, a dielectric insulating film, a first ground electrode connected to the signal line electrode and the ground layer,
Forming the dielectric insulating film only around the optical waveguide and the signal line electrode by patterning on the surface of the ground layer ;
Forming a second ground electrode connected to the first ground electrode by vapor deposition around the dielectric insulating film.

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