JP2017181633A - Optical modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical modulator in which the electric wires on a substrate can be easily led.SOLUTION: An optical modulator includes: a first substrate 1A provided with an optical modulation region for modulating the phase polarization or the quadrature amplitude to modulate the light with a first wavelength of λ1; and a second substrate 1B provided with an optical modulation region for modulating the phase polarization or the quadrature amplitude to modulate the light with a second wavelength of λ2. In the optical modulator, the first substrate 1A and the second substrate 1B are arranged in parallel and are displaced in the length direction of the substrate.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an optical modulator, and more particularly to a structure of a highly integrated modulator such as a two-wavelength integrated type.

  As the speed and capacity of optical communication systems are increasing, the performance and density of optical modulators used therein are increasing. In addition, with the demand for miniaturization of optical modulators, miniaturization of substrates constituting the optical modulators is also being promoted. However, high performance, high density, and miniaturization of optical modulators are contradictory requirements, and a device for achieving both of these is required.

The following invention is proposed regarding such an optical modulator.
For example, Patent Document 1 includes a plurality of modulation substrate portions separated from each other in an optical modulator in which an optical waveguide and a modulation electrode are formed on a substrate, and each of the modulation substrate portions is part of each other's boundary. An optical modulator is disclosed in which a low dielectric constant portion having a lower dielectric constant than the substrate material of the modulation substrate portion is disposed.

JP 2014-197054 A

  In recent years, highly integrated optical modulators such as a two-wavelength integrated type have been developed. FIG. 1 shows a configuration example of a conventional dual wavelength integrated DP-QPSK (Dual Polarization-Quadrature Phase Shift Keying) modulator. The optical modulator shown in the figure includes an optical waveguide modulation unit M1 to which an optical wave having a wavelength λ1 is input and an optical waveguide modulation unit M2 to which an optical wave having a wavelength λ2 different from the wavelength λ1 is input. The parts M1 and M2 are configured to operate independently of each other.

  Each of the optical waveguide modulation units M1 and M2 is provided on the substrate 1 having an electro-optic effect, the optical waveguide 2, the control electrode 3 for controlling the optical wave propagating through the optical waveguide 2, and the optical wave propagating through the optical waveguide 2. And a light receiving element 4 for detecting. The control electrode 3 includes an RF electrode 3a to which a high frequency signal (modulation signal) is applied, and DC electrodes 3b and 3c to which a DC voltage (bias voltage) is applied.

The optical waveguide 2 of each of the optical waveguide modulation units M1 and M2 has a structure in which Mach-Zehnder type waveguides are arranged in a nested manner, and a large number of control electrodes 3 and light receiving elements 4 are provided accordingly. ing. In the figure, four RF electrodes 3a, six DC electrodes 3b and 3c, and two light receiving elements 4 are provided in each of the optical waveguide modulation portions M1 and M2.
A polarization beam combiner 5 is disposed downstream of the optical waveguide modulator M1, and the light wave propagating through the output side arm portion of the main Mach-Zehnder type waveguide is combined by the polarization beam combiner 5 to produce an optical fiber. 6 is output. The same applies to the optical waveguide modulator M2. The polarization combining unit 5 includes a structure that performs polarization combining using a spatial optical system and a structure that performs polarization combining using an optical waveguide.

As described above, the highly integrated optical modulator uses a substrate (chip) on which a large number of control electrodes and light receiving elements are arranged. For this reason, there has been a problem that the wiring (managing) of electric wires (not shown) connected to these components increases and the substrate size increases.
In addition, the wiring from the electric pad provided on the side of the substrate to the action part (the part where the electric field generated from the control electrode acts on the optical waveguide) is concentrated in a part of the area, making it difficult to arrange There was also. This problem is particularly noticeable in high-frequency lines that transmit high-frequency signals. A high-frequency line uses a line structure such as CPW (coplanar waveguide) with controlled impedance, but such a line structure has a low degree of freedom in pattern design, and crosstalk of high-frequency signals occurs between adjacent lines. It is.

There is also a concern that unnecessary light interference may occur between the optical waveguide modulators that transmit light waves of different wavelengths. Examples of unnecessary light include non-coupled light between the fiber and the chip, radiation mode light (off light) from the combined portion of the optical waveguide, and light leaked from the bent or branched portion of the optical waveguide.
Further, for example, in the two-wavelength integrated type, the electrode pattern length of the optical waveguide and the control electrode on one chip is more than double that of the one-wavelength type, so that the pattern yield is less than the square of the one-wavelength type pattern. turn into.

  The problem to be solved by the present invention is to provide an optical modulator capable of solving the above-described problems and facilitating wiring of electric wires on a substrate.

In order to solve the above problems, the optical modulator of the present invention has the following technical features.
(1) a first substrate on which an optical modulation region for phase polarization modulation or quadrature amplitude modulation for modulating light of a first wavelength is formed; and phase polarization modulation for modulating light of a second wavelength; And a second substrate on which a light modulation region for quadrature amplitude modulation is formed. The first and second substrates are arranged in parallel and are shifted in the length direction of the substrate. This is an optical modulator.

(2) In the optical modulator according to (1), a DC electrode and an RF electrode are formed on the first and second substrates, respectively, and the first and second substrates are substrates. The optical modulator is characterized in that the arrangement order of the DC electrode and the RF electrode in the length direction is different.

(3) The optical modulator according to (1) or (2), wherein the first and second substrates are arranged so as to be shifted in a thickness direction of the substrate. .

(4) The optical modulator according to any one of (1) to (3), wherein the first and second substrates have edges of the substrate removed. It is.

  An optical modulator according to the present invention modulates a first substrate on which an optical modulation region for phase polarization modulation or quadrature amplitude modulation for modulating light of a first wavelength is formed, and light of a second wavelength. And a second substrate on which an optical modulation region for phase polarization modulation or quadrature amplitude modulation is formed. The first and second substrates are arranged in parallel and in the length direction of the substrate. Since they are arranged so as to be shifted, it is possible to provide an optical modulator capable of facilitating wiring of electric lines on the substrate.

It is a top view which shows the structural example of the conventional 2 wavelength integrated DP-QPSK modulator. It is a top view explaining the optical modulator which concerns on 1st Example of this invention. It is a top view explaining the optical modulator which concerns on 2nd Example of this invention. It is a top view explaining the optical modulator which concerns on 3rd Example of this invention. It is a top view explaining the optical modulator which concerns on 4th Example of this invention. It is a top view explaining the optical modulator which concerns on 5th Example of this invention. It is side surface sectional drawing explaining the optical modulator which concerns on 5th Example of this invention. It is side surface sectional drawing explaining the modification of the optical modulator which concerns on 5th Example of this invention. It is a side view explaining the optical modulator which concerns on 6th Example of this invention.

Hereinafter, the optical modulator according to the present invention will be described in detail.
For example, as shown in FIG. 2, the optical modulator according to the present invention includes a first substrate 1A on which an optical modulation region for phase polarization modulation or quadrature amplitude modulation for modulating light having a first wavelength λ1 is formed. And a second substrate 1B on which a light modulation region for phase polarization modulation or quadrature amplitude modulation for modulating light of the second wavelength λ2 is formed. In addition, the first substrate 1A and the second substrate 1B are arranged in parallel and are shifted in the length direction of the substrate.

The substrates 1A and 1B may be any substrate that can form an optical waveguide such as quartz or semiconductor, and in particular, a substrate having an electrooptic effect, such as LiNbO ₃ (lithium niobate), LiTaO ₃ (lithium tantalate) or PLZT. A substrate using any single crystal of (lead lanthanum zirconate titanate) can be suitably used.

The optical waveguide 2 formed on the substrates 1A and 1B is formed, for example, by thermally diffusing a high refractive index material such as titanium (Ti) on a LiNbO ₃ substrate (LN substrate). Further, a rib-type optical waveguide in which grooves are formed on both sides of a portion that becomes an optical waveguide and a ridge-type waveguide in which the optical waveguide portion is convex can be used. Further, the present invention can also be applied to an optical circuit in which optical waveguides are formed on different waveguide substrates such as PLC and these waveguide substrates are bonded and integrated.

The substrates 1A and 1B are provided with a control electrode 3 for controlling light waves propagating through the optical waveguide 2. The control electrode 3 includes an RF electrode 3a constituting a modulation electrode, a ground electrode (not shown) surrounding the modulation electrode, and DC electrodes 3b and 3c for applying a DC voltage. These control electrodes 3 can be formed by forming a Ti / Au electrode pattern on the substrate surface and using a gold plating method or the like. Furthermore, a buffer layer such as a dielectric SiO ₂ can be provided on the substrate surface after the formation of the optical waveguide, if necessary.

  The main feature of the optical modulator according to the present invention is that the substrates 1A and 1B are arranged in parallel with each other and shifted in the length direction of the substrate. Hereinafter, a detailed description will be given with reference to examples. In this specification, the length direction of the substrate is “X direction”, and the width direction of the substrate is “Y direction”. The X direction corresponds to the traveling direction of the light wave (the direction of the arrow X in the figure), and the direction orthogonal to this (the direction of the arrow Y in the figure) is the Y direction.

FIG. 2 is a plan view for explaining the optical modulator according to the first embodiment of the present invention.
In the optical modulator of this example, the substrates 1A and 1B are arranged in parallel to each other, and the substrate 1B is arranged to be shifted to the downstream side in the X direction from the substrate 1A.
A termination substrate 11 that terminates a high-frequency signal for the RF electrode 3a of the substrate 1A is provided on the side of the substrate 1A that faces the substrate 1B. A termination substrate 12 that terminates a high-frequency signal for the RF electrode 3a of the substrate 1B is provided on the side of the substrate 1B that faces the substrate 1A. Further, a relay substrate 13 and a DC wiring substrate 16 are also provided on the side of the substrate 1B facing the substrate 1A.

  The relay board 13 is provided with an electric wire 41 that relays a high-frequency signal input from the RF connector 21. The electric wire 41 is electrically connected to the connection pad 31 provided on the side portion of the substrate 1B by wire bonding or the like. The high-frequency signal for the substrate 1A is relayed to the substrate 1A through the electric wire 42 on the substrate 1B and applied to the RF electrode 3a of the substrate 1A. The high frequency signal for the substrate 1B is applied to the RF electrode 3a of the substrate 1B through the electric wire 43 on the substrate 1B. The connection pads 31 can be arranged at intervals of about 500 μm. On the other hand, the RF connector 21 is larger than the connection pad 31, and a space of 2.5 mm or more is required even if it is small. The relay board 13 has a role of adjusting the electric wire 41 connected to the RF connector 21 so that the distance between the electric wire 41 and the connection pad 31 decreases.

  On the DC wiring board 16, an electric wire 44 that relays the DC voltage input from the DC pin 22 is wired. The electric wire 44 is electrically connected to the connection pad 32 provided on the side portion of the substrate 1B by wire bonding or the like. The DC voltage for the substrate 1A is relayed to the substrate 1A through the electric wire 45 on the substrate 1B, and is applied to the DC electrodes 3b and 3c of the substrate 1A. The DC voltage for the substrate 1B is applied to the DC electrodes 3b and 3c of the substrate 1A through electric lines (not shown) on the substrate 1B. That is, the substrate 1A and the substrate 1B share the extraction portion of the DC electrode 3c. In this example, the electric wire 45 for the substrate 1A is formed so as to straddle the substrate 1B by bonding wiring, but may be directly wired on the substrate 1B. Further, the DC pin 22 and the connection pad 32 can be directly connected so that the DC wiring board 16 is not used.

  As described above, by arranging the substrates 1A and 1B in parallel with each other and arranging the substrate 1B so as to be shifted to the downstream side in the X direction with respect to the substrate 1A, it is possible to facilitate wiring of electric lines on the substrate. . In particular, there is an effect that the electric wire 42 to the RF electrode 3a of the substrate 1A can be shortened. That is, for example, when the substrates 1A and 1B are arranged without shifting in the X direction, it is necessary to route the electric wire 42 so as to bypass the electric wire 43 to the RF electrode 3a of the substrate 1B. By deviating in the X direction, there is no need for such a detour. The electric lines 42 and 43 for transmitting high-frequency signals must be impedance-controlled high-frequency lines such as CPW, the line structure is limited, and shortening the wiring length is extremely effective in reducing the loss of high-frequency signals. It is effective for. In addition, since the number of fine patterns of waveguides and electrodes mounted on one chip is reduced as compared with the case where elements for two wavelengths are integrated on one chip, it is possible to reduce yield deterioration due to pattern defects and the like. Furthermore, since the length of the element can be reduced as compared with the case where two wavelengths are integrated, the number of patterns mounted on one wafer can be increased.

FIG. 3 is a plan view for explaining an optical modulator according to the second embodiment of the present invention.
In the optical modulator of this example, the substrates 1A and 1B are arranged in parallel to each other, and the substrate 1B is arranged to be shifted to the downstream side in the X direction from the substrate 1A.
On the substrate 1A, the RF electrode 3a, the DC electrode 3b, and the DC electrode 3c are arranged in this order from upstream to downstream in the X direction. On the other hand, on the substrate 1B, the DC electrode 3c, the RF electrode 3a, and the DC electrode 3b are arranged in this order from upstream to downstream in the X direction. That is, the arrangement order of the DC electrode and the RF electrode in the X direction is different between the substrate 1A and the substrate 1B.

  Thus, by arranging the DC electrode 3c of the substrate 1B upstream of the RF electrode 3a, the substrate 1B is provided with the electric wire 44 upstream of the DC electrode 3c, and the downstream portion of the DC electrode 3c of the substrate 1B. The electric wire 43 can be wired to the cable. Thereby, even if the shift width of the substrates 1A and 1B is reduced, the shift width between the RF electrode 3a of the substrate 1A and the RF electrode 3b of the substrate 1B can be sufficiently secured. That is, even if the shift width of the substrates 1A and 1B is reduced, it is possible to easily carry out wiring that is effective in reducing the loss of high-frequency signals. Therefore, the length L from the end in the X direction upstream of the substrate 1A to the end in the X direction downstream of the substrate 1B matches the arrangement order of the DC electrode and the RF electrode (for example, the structure of the first embodiment) (FIG. 2)). That is, by making the arrangement order of the DC electrode and the RF electrode in the X direction different between the substrate 1A and the substrate 1B, an effect of further reducing the total length in the length direction of the substrate can be obtained.

FIG. 4 is a plan view for explaining an optical modulator according to the third embodiment of the present invention.
In the optical modulator of this example, the substrates 1A and 1B are arranged in parallel to each other, and the substrate 1B is arranged to be shifted to the downstream side in the X direction from the substrate 1A. Further, the substrate 1A and the substrate 1B are separated from each other, and the relay substrate 14 and the DC wiring substrate 16 are disposed between the substrate 1A and the substrate 1B. A high frequency signal for the substrate 1A is input from the RF connector 21, relayed to the substrate 1A through the relay substrate 13, the substrate 1B, and the relay substrate 14, and applied to the RF electrode 3a of the substrate 1A.

  In this way, by making the structure in which the substrate 1A and the substrate 1B are separated from each other, an effect of facilitating the arrangement of the optical system (for example, the polarization beam combiner 6 using a spatial optical system) can be obtained.

FIG. 5 is a plan view for explaining an optical modulator according to the fourth embodiment of the present invention.
In the optical modulator of this example, the substrates 1A and 1B are arranged in parallel to each other, and the substrate 1B is arranged to be shifted to the downstream side in the X direction from the substrate 1A. Further, the arrangement order of the DC electrode and the RF electrode in the X direction is different between the substrate 1A and the substrate 1B. Further, the substrate 1A and the substrate 1B are separated from each other, and the relay substrate 14 and the DC wiring substrate 16 are disposed between the substrate 1A and the substrate 1B.

  That is, the fourth embodiment has a structure in which the second embodiment and the third embodiment are combined. For this reason, not only the wiring of the electric wire on the substrate can be facilitated, but also an effect of shortening the total length in the length direction of the substrate and an effect of easily arranging the optical system can be obtained.

FIG. 6 is a plan view for explaining an optical modulator according to a fifth embodiment of the present invention, and FIG. 7 is a side sectional view thereof.
In the optical modulator of this example, the substrates 1A and 1B are arranged in parallel to each other, and the substrate 1B is arranged to be shifted to the downstream side in the X direction from the substrate 1A. Further, the substrate 1A and the substrate 1B are separated from each other, and the DC wiring substrate 16 is disposed between the substrate 1A and the substrate 1B. Further, the substrate 1A and the substrate 1B are arranged with their positions in the thickness direction of the substrate being shifted. Specifically, the substrate 1A is disposed above the substrate 1B. Further, the relay board 15 to which the RF connector 21 for inputting a high frequency signal to the board 1A is connected is arranged so as to overlap a part of the board 1B.

  According to such a structure, not only the effect of facilitating the arrangement of the optical system can be obtained, but also the electric wire that relays the high-frequency signal for the substrate 1A can be removed from the substrate 1B, and the wiring of the electric wires on the substrate 1B can be performed. Can be further simplified. In addition, the relay substrate 15 is made of a low-loss substrate material, and the high-frequency line has a low transmission loss line structure, so that an optical modulator having a higher high-frequency characteristic than when wired to the substrate 1B. Can be realized.

FIG. 8 is a side sectional view for explaining a modification of the optical modulator according to the fifth embodiment of the present invention.
The optical modulator of this example uses a lead pin 23 as a terminal for inputting a high-frequency signal. That is, a high-frequency signal is not input from the side of the housing through the RF connector 21 provided in the lateral direction (horizontal direction) on the side surface of the optical modulator, but in the vertical direction (vertical direction) on the side surface of the optical modulator. The high-frequency signal is input from the bottom of the housing through the lead pins 23 provided on the housing. With such a structure, high-frequency signal inputs can be arranged in a line.

FIG. 9 is a side view for explaining an optical modulator according to the sixth embodiment of the present invention.
In the optical modulator of this example, the substrate 1A (1B) has a structure in which the edge 8 at the end of the substrate is removed.
Thereby, it can prevent that other components are damaged by the edge of a board | substrate edge part. Such edge removal is applicable in combination with each of the above embodiments.

  The present invention has been described above based on the embodiments. However, the present invention is not limited to the above-described contents, and it is needless to say that the design can be changed as appropriate without departing from the gist of the present invention.

  As described above, according to the present invention, it is possible to provide an optical modulator capable of facilitating wiring of electric wires on a substrate.

1, 1A, 1A Substrate 2 Optical waveguide 3 Control electrode 3a RF electrode 3b, 3c DC electrode 4 Light receiving element 5 Polarization combiner 6 Optical fiber 8 Edge 11, 12 Termination substrate 13-15 Relay substrate 16 DC wiring substrate 21 RF connector 22 DC pin 23 Lead pin 31, 32 Connection pad 41-45 Electric wire

Claims (4)

A first substrate on which a light modulation region for phase polarization modulation or quadrature amplitude modulation for modulating light of a first wavelength is formed;
A second substrate on which a light modulation region for phase polarization modulation or quadrature amplitude modulation for modulating light of a second wavelength is formed,
The optical modulator, wherein the first and second substrates are arranged in parallel and are shifted in the length direction of the substrate. The optical modulator according to claim 1.
A DC electrode and an RF electrode are formed on the first and second substrates, respectively.
The optical modulator, wherein the arrangement order of the DC electrode and the RF electrode in the length direction of the substrate differs between the first and second substrates. The optical modulator according to claim 1 or 2,
The optical modulator, wherein the first and second substrates are arranged so as to be shifted in the thickness direction of the substrate. The optical modulator according to any one of claims 1 to 3,
The optical modulator according to claim 1, wherein the first and second substrates have the edge of the substrate removed.

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