Optical modulator and optical transmission device using same

Abstract

The purpose of the present invention is to provide an optical modulator in which short circuiting in wiring or the like of a wiring board is reduced even when an electronic circuit element such as a driver circuit and the wiring board are disposed close to each other.　Provided is an optical modulator in which a light modulation element and an electronic circuit element (4) for inputting a high frequency signal to the light modulation element are housed in a housing (1), said optical modulator being characterized in that: the electronic circuit element (4) is adhesively fixed to the opposite surface of a block (40) from one surface in the housing (1) to which the block (40) is fixed; the optical modulator comprises wiring boards (3, 3') which are each disposed adjacent to the electronic circuit element (4) and fixed to the one surface and which are each provided, on the opposite surface thereof from the one surface, with wiring electrically connected to the electronic circuit element (4); and with reference to the one surface, the height (h1) to the surface of the block (40) to which the electronic circuit element (4) is adhesively fixed and the height (h2) to the surface of each of the wiring boards (3, 3') on which the wiring is provided differ from each other.

Description

Optical modulator and optical transmitter using the same

[0001] The present invention relates to an optical modulator and an optical transmission device using the same, and more particularly to an optical modulator that houses an optical modulation element and an electronic circuit element that inputs a high-frequency signal to the optical modulation element in a housing, and an optical transmission device using the same.

[0002] There is a demand for optical modulators that can be driven at high speed, with low driving voltage, and further miniaturized, such as the recent optical modulator HB-CDM (High Bandwidth Coherent Driver Modulator), in which an optical modulation element and electronic circuit elements such as a driver circuit that drives the optical modulation element are incorporated together in a housing.

[0003] 1 shows an example of an optical modulator incorporating a driver circuit, in which an optical modulation element 5 is disposed within a housing 1. The optical modulation element includes an optical waveguide made of a material having an electro-optic effect, and a modulation electrode that applies an electric field to the optical waveguide and modulates the light wave propagating through the optical waveguide.

[0004] The light wave input to the optical modulation element 5 is introduced into the housing 1 by an input collimator 9 connected to an optical fiber FB, and is incident on the optical modulation element 5 via an optical block 8, a lens 7, etc. The light wave modulated by the optical modulation element 5 is led out of the housing 1 via the lens 7 and the optical block 8 equipped with an optical multiplexing / demultiplexing unit, and is incident on the optical fiber FB by an output collimator 10.

[0005] On the other hand, the modulation signal input to the optical modulation element 5 is generated outside the housing 1, introduced into the housing, and supplied to the driver circuit 4 via the wiring of the input board 2. The modulation signal is amplified by the driver circuit 4, and then supplied to the modulation electrode of the optical modulation element 5, and finally introduced into the terminal board 6.

[0006] The driver circuit is supplied with direct current (DC) power for driving the driver circuit 4. The DC power is supplied from a DC power source outside the housing 1 and is supplied to the driver circuit 4 via the wiring board 3 (or 3') inside the housing.

[0007] FIG. 2 shows a cross-sectional view taken along dashed line A-A' in FIG. 1. The housing 1 in FIG. 2 typically has a cover (not shown) covering the upper side of the drawing, but this is omitted here. The driver circuit 4 is glued onto a block 40 fixed to the inner surface of the housing 1. Heat generated by the driver circuit 4 affects the operation of the optical modulation element, so it must be dissipated outside the housing. For this reason, the block 40 is made of a highly thermally conductive material and functions as a heat sink. Furthermore, the adhesive used to bond the driver circuit 4 and block 40 is a highly thermally conductive and electrically conductive material, such as Ag filler or solder paste. Patent Document 1 also proposes using an optical modulation element as one of the heat dissipation means for electronic components.

[0008] On the other hand, wiring is exposed on the surface of the wiring board 3 (3') (the surface opposite to the surface of the wiring board fixed to the housing 1), and the electrode pad portion of the wiring (the portion to be wire-bonded) and the terminal of the driver circuit 4 are bonded with a wire (not shown) such as Au.

[0009] However, the driver circuit 4 and the wiring board 3 (3') are arranged in close proximity, and the joint surface between the driver circuit 4 and the block 40 is configured to be at approximately the same height as the surface of the wiring board 3. Therefore, when the driver circuit 4 is adhered, there is a risk that the adhesive AD will protrude from the joint surface and come into contact with the wiring board 3, causing a short circuit between the wiring arranged on the surface of the wiring board. One way to solve this problem is to increase the distance between the driver circuit 4 and the wiring board 3, but this creates a new problem in that the optical modulator cannot be sufficiently miniaturized.

[0010] JP 2019-207362 A JP 2017-134241 A JP 2022-144126 A International Publication No. WO2023 / 053406A1

[0011] The object of the present invention is to provide an optical modulator that solves the above-mentioned problems and prevents short circuits in the wiring of a wiring board even when an electronic circuit element such as a driver circuit is arranged close to the wiring board, and also to provide an optical transmission device using this optical modulator.

[0012] In order to solve the above problems, the optical modulator of the present invention and an optical transmission device using the same have the following technical features: (1) An optical modulator that houses an optical modulation element and an electronic circuit element that inputs a high-frequency signal to the optical modulation element in a housing, the electronic circuit element being adhesively fixed to a surface opposite to one surface of a block fixed to the inside of the housing, and having a wiring board that is disposed adjacent to the electronic circuit element and fixed to the one surface, the wiring board having wiring on the surface opposite to the one surface that is electrically connected to the electronic circuit element, and the height (h1) from the one surface to the adhesively fixed surface of the block is different from the height (h2) from the one surface to the surface of the wiring board on which the wiring is provided.

[0013] (2) In the optical modulator described in (1) above, the height (h1) of the block is higher than the height (h2) of the wiring board.

[0014] (3) In the optical modulator described in (1) above, the difference between the height (h1) of the block and the height (h2) of the wiring board is 0.2 mm or more.

[0015] (4) The optical modulator according to (1) above is characterized in that at least a part of the periphery of the surface of the block to which the electronic circuit element is bonded is chamfered.

[0016] (5) The optical modulator according to (1) above is characterized in that the adhesive that bonds the electronic circuit element to the block has electrical conductivity.

[0017] (6) In the optical modulator described in (1) above, the optical modulation element and an input board that supplies a high-frequency signal to the electronic circuit element are arranged so as to sandwich the electronic circuit element, and the input board, the electronic circuit element, and the optical modulation element are arranged and fixed within the housing so that the wiring position connecting the input board and the electronic circuit element and the wiring position connecting the electronic circuit element and the optical modulation element are located on the same plane.

[0018] (7) An optical transmitter comprising the optical modulator according to any one of (1) to (6) above and a data generator that supplies a high-frequency signal to the optical modulator. It goes without saying that the present invention is not limited to the above, and that it is possible to combine the technical features according to (2) to (6) above as necessary.

[0019] According to the present invention, an optical modulator that houses an optical modulation element and an electronic circuit element that inputs a high-frequency signal to the optical modulation element in a housing includes an electronic circuit element adhesively fixed to a surface opposite to one surface of a block fixed to the housing, and a wiring board that is arranged adjacent to the electronic circuit element and fixed to the one surface, and has wiring electrically connected to the electronic circuit element on its surface opposite to the one surface, and the height (h1) from the one surface to the adhesively fixed surface of the block and the height (h2) from the one surface to the surface of the wiring board on which the wiring is provided are different from each other, so that even if an electronic circuit element such as a driver circuit and the wiring board are arranged closely to each other, it is possible to provide an optical modulator that prevents short-circuiting of the wiring of the wiring board even if the adhesive protrudes from the joint between the electronic circuit element and the block. Also, it is possible to provide an optical transmitter that uses an optical modulator that achieves such effects.

[0020] 1 is a plan view showing an example of an optical modulator. FIG. 1 is a cross-sectional view taken along dashed dotted line A-A' in FIG. 1. FIG. 2 is a cross-sectional view similar to FIG. 2 of the optical modulator of the present invention. FIG. 2 is another cross-sectional view similar to FIG. 2 of the optical modulator of the present invention. FIG. 1 is a diagram (part 1) explaining the process of attaching an electronic circuit element to an optical modulator. FIG. 1 is a cross-sectional view taken along dashed dotted line B-B' in FIG. 1. FIG. 1 is a diagram explaining a block 40 used in the optical modulator of the present invention. FIG. 1 is a diagram explaining an optical transmitting device in which a data generating unit is connected to the optical modulator of the present invention. FIG. 1 is another conceptual diagram of the optical transmitting device of the present invention. FIG. 1 is a diagram explaining an application example of the optical transmitting device of the present invention.

[0021] The present invention will be described in detail below using preferred embodiments. As shown in Figures 3 and 4, the present invention relates to an optical modulator that houses an optical modulation element and an electronic circuit element 4 that inputs a high-frequency signal to the optical modulation element within a housing 1. The electronic circuit element 4 is adhesively fixed to a surface opposite to one surface of a block 40 fixed to the inside of the housing 1, and a wiring board 3 (3') is disposed adjacent to the electronic circuit element 4 and fixed to the one surface, and has wiring electrically connected to the electronic circuit element 4 on its surface opposite to the one surface. The height (h1) from the one surface to the adhesively fixed surface of the block 40 and the height (h2) from the surface of the wiring board 3 (3') to which the wiring is provided are different from each other. Note that, like Figure 2, Figures 3 and 4 are cross-sectional views of the optical modulator of Figure 1 taken along the dashed dotted line A-A'.

[0022] In the optical modulation element used in the optical modulator of the present invention, various materials can be used to form the optical waveguide, such as substrates with electro-optical effects such as lithium niobate (LN), lithium tantalate (LT), and PLZT (lead lanthanum zirconate titanate), vapor-deposited films made from these materials, and even semiconductor materials and organic materials.

[0023] In an optical modulation element, a modulation electrode is formed along an optical waveguide on the surface of a substrate on which the optical waveguide is formed, and a modulation signal, which is a high-frequency signal, is applied to the modulation electrode to modulate the light wave propagating through the optical waveguide. The substrate on which the optical waveguide is formed can be made thin, about a few micrometers, and can be bonded to a support substrate to form a composite substrate. In addition to the modulation electrode, a bias electrode for applying a DC bias voltage can also be separately disposed.

[0024] For the housing used in the optical modulator of the present invention, a metal material with high thermal conductivity, such as SUS or Kovar, is selected in consideration of assembly processes such as cutting workability, laser welding, and sealing. The housing surface (the lower surface of the housing 1 in FIGS. 3 and 4 ) on which the block 40 described below and other components are fixed can be made of a metal material, while the housing side can be made of a ceramic material or a composite material with laminated ceramics. When the housing side is made of a ceramic material or a composite material, the wiring board 3 (3′) and input board 2 described below can also be formed integrally with the housing side. Although not shown in FIGS. 3 and 4 , a lid made of a metal material is provided on the top side of the housing 1, and the lid and the upper part of the housing side are hermetically sealed by welding or the like.

[0025] The housing surface to which the block 40 etc. are fixed in Figures 3 and 4 may be the bottom surface of the optical modulator body, or as shown in Patent Document 3, it may be the top surface of the optical modulator body, and the housing 1 in Figure 3 etc. may be fixed upside down to a printed circuit board (not shown).

[0026] The electronic circuit element 4 may be a driver circuit for amplifying a modulated signal, or a multiplexer (parallel / serial converter) as described in Patent Document 4. A block 40 with high thermal conductivity is used to conduct heat generated from the electronic circuit element 4 to the outside of the housing 1, and acts as a heat sink. The block 40 is preferably made of a material with higher thermal conductivity than the SUS or Kovar used in the housing 1, and a composite such as Cu-W, Cu-Mo, or Al-SiC is used.

[0027] An adhesive having electrical conductivity and thermal conductivity, such as Ag filler, is preferably used as the adhesive for bonding and fixing the electronic circuit element 4 to the block 40. Furthermore, if a metal surface is formed on the bonding surface of the electronic circuit element 4 by plating or the like, solder paste can also be used.

[0028] As shown in Figures 3 and 4, the optical modulator of the present invention is characterized in that the height (h1) of the block 40 and the height (h2) of the wiring board 3 (3') disposed adjacent to the block are different. In Figure 3, h1 > h2, and even if the adhesive AD interposed between the electronic circuit element 4 and the block 40 overflows from the side, the adhesive AD does not reach the wiring board 3 (3'). Also, in Figure 4, h1 < h2, and the overflowing adhesive AD reaches the side of the wiring board 3 (3'). However, the wiring formed on the wiring board 3 (3') is formed (exposed) on the upper surface of the substrate body (the upper surface of the wiring board 3 (3') in Figure 3 or 4), and no wiring is formed on the side of the substrate body. Therefore, the wiring on the wiring board 3 (3') does not short-circuit.

[0029] 3 and 4, the difference Δh between the height h1 of the block 40 and the height h2 of the wiring board 3 (3') is preferably 0.2 mm or more, more preferably in the range of 0.2 to 0.3 mm. Also, taking into consideration the miniaturization of the optical modulator and the amount of adhesive AD that overflows, it is preferable to set the distance between the block 40 and the wiring board 3 (3') in the range of 0.1 to 0.2 mm.

[0030] The wiring board 3 (3') is a wiring board that supplies power, particularly DC power, to electronic circuit elements 4 such as driver circuits. DC power supplied from a DC power source outside the housing 1 is introduced into the wiring board 3 (3') via DC pins or a flexible printed circuit board (FPC) arranged on the outer wall surface of the housing 1 and further via wiring extending inside the housing. Furthermore, electrode pad portions (terminals of the wiring formed on the upper surface of the board body) of the wiring on the wiring board 3 (3') and terminals of the electronic circuit elements 4 are bonded with wires (not shown) such as Au.

[0031] As in Patent Document 3, when the wiring board 3 (3') and the side wall of the housing 1 are integrally formed, they can be made of a ceramic material or a composite material in which ceramic is laminated. In this case, it is possible to easily perform power supply wiring by connecting an FPC to a terminal exposed on the outside of the side wall (or part of the bottom surface) of the housing 1 and wire bonding to wiring (electrode pad portion) exposed inside the housing at a part of the side wall of the housing that serves as the wiring board.

[0032] The adhesive AD can be applied using a dispenser. Furthermore, it is preferable to use a die bonder to spread the adhesive between the electronic circuit element 4 and the block 40 thinly and uniformly. Specifically, as shown in FIG. 5 , the adhesive AD is applied to the upper surface of the block 40, and then the electronic circuit element 4, which is held by suction or the like with a chuck jig CH, is pressed against the block 40. At this time, the electronic circuit element 4 is pressed against the upper surface of the block while applying a load, and the chuck jig CH is moved in a direction parallel to the upper surface of the block 40, performing a scrubbing operation, as shown in FIG. 6 , thereby enabling the adhesive to be formed thinly and uniformly.

[0033] In order to perform such a scrubbing operation, the electronic circuit element 4 moves parallel to the upper surface of the block 40, so it is preferable that the wiring board 3 (3') placed near the block 40 be lower than the height of the block 40 (h1 > h2).

[0034] As shown in Patent Documents 2 and 3, in order to suppress the propagation loss of the modulated signal, which is a high-frequency signal, it is preferable to configure the wiring positions connecting the input board 2, electronic circuit elements 4 such as a driver circuit, and optical modulation element 5, which are arranged in a housing 1 of the optical modulator, to be located on the same plane, as shown in Fig. 1. As shown in Patent Document 2, it is also preferable to arrange the optical modulation element 5 and the terminal board 6 so that their upper surfaces are located on the same plane.

[0035] The input board 2 is used to introduce modulated signals generated by a data generating unit such as a digital signal processor (DPS) located outside the optical modulator into the housing 1 and supply them to electronic circuit elements 4 such as a driver circuit. As shown in Patent Document 2, the input board 2 can also be formed integrally with the side wall of the housing 1. The main body of the input board 2 is made of a ceramic material or a composite material, and electrical wiring is provided inside and on the surface of the main body.

[0036] The "wiring board" in the optical modulator of the present invention is a concept that encompasses this "input board." The "wiring board" of the present invention can also include an "optical modulation element." Figure 7 is a cross-sectional view taken along the dashed dotted line B-B' in Figure 1, in which the wiring 20 on the top surface of the input board 2, the top surface of the electronic circuit element 4 (the surface on which the connection terminals are arranged), and the top surface of the optical modulation element (the surface on which the modulation electrode and electrode pad portion (terminals) are arranged) are configured to be flush with each other. Wiring electrically connecting each component is omitted.

[0037] Although it depends on the thickness of the electronic circuit element 4, for example, if the thickness of the electronic circuit element 4 is 0.2 mm or more, the position of the adhesive surface between the electronic circuit element 4 and the block 40 will be separated by 0.2 mm or more from the position of the wiring 20 on the upper surface of the input substrate 2 and the position of the terminal of the modulation electrode on the upper surface of the optical modulation element. As a result, even if the adhesive overflows, the adhesive will not short-circuit the wiring 20 on the upper surface of the input substrate 2 or the terminal of the modulation electrode.

[0038] In addition, when the "wiring board" of the present invention includes an "input board," the "height h2 of the wiring board" is the thickness of the input board, and when it includes an "optical modulation element," it is the sum of the height of the base 50 supporting the optical modulation element 5 and the thickness of the optical modulation element 5 (including an adhesive layer between the two, if any).

[0039] 7, when the upper surfaces of the components are flush with each other, the direction of the scrubbing operation performed when adhesively fixing the electronic circuit element 4 to the block 40 is limited to the direction in which the wiring board 3 (3') is arranged. For this reason, it is preferable to set the height h2 of the wiring board 3 (3') lower than the height h1 of the block 40.

[0040] 8, it is preferable to form a chamfered portion 41 on a part of the periphery of the upper surface of the block 40. This allows the overflowing adhesive AD to be contained in the chamfered portion, and as a result, the amount of adhesive overflowing from the block 40 is reduced.

[0041] Fig. 9 shows an optical transmitting device in which a data generating unit (DSP) is connected to the optical modulator shown in Fig. 1. Also, as shown in Fig. 10, an optical transmitting device 100 can be configured in which a light source LD such as a semiconductor laser that generates a light wave to be input to the optical modulator OM, a data generating unit DSP that generates a modulated signal to be input to the optical modulator OM, and an optical fiber FB for guiding the output light from the optical modulator OM are incorporated into a single package.

[0042] In Figure 11, a light source LD such as a semiconductor laser can be incorporated into the housing 1 of the optical modulator. Furthermore, if the light waves output from the light source LD have multiple wavelengths, it is also possible to separate the light waves generated by the light source into individual wavelengths and perform modulation operations for each light wave. Wavelength separation can be achieved using a filter incorporated together with optical components provided in the light source LD or lenses attached to the end of the optical modulation element. Reference numeral 80 denotes an optical block that performs polarization synthesis for each light wave and outputs output light for each wavelength. A plurality of optical fibers corresponding to each wavelength are connected to the output collimator 12.

[0043] Furthermore, when a light source such as a semiconductor laser is mounted inside the housing 1, it is necessary to securely connect the block (base) supporting the semiconductor laser element to the housing 1, similar to block 40, so that the heat generated from the light source can be sufficiently dissipated to the outside.

[0044] As described above, according to the present invention, it is possible to provide an optical modulator that prevents short circuits between the wiring of the wiring board even when an electronic circuit element such as a driver circuit is disposed close to the wiring board, and also to provide an optical transmission device that uses an optical modulator having such excellent effects.

[0045] REFERENCE SIGNS LIST 1 Housing 2 Input board (wiring board) 3, 3' Wiring board 4 Electronic circuit element (driver circuit etc.) 5 Optical modulation element 6 Terminal board 7 Optical components such as lens 8 Optical multiplexer / demultiplexer section (optical block) DSP Data generation section (digital processing device) LD Light source (semiconductor laser) FB Optical fiber

Claims

1. An optical modulator that houses an optical modulation element and an electronic circuit element that inputs a high frequency signal to the optical modulation element within a housing, wherein the electronic circuit element is adhesively fixed to a surface opposite to one surface of a block fixed to the inside of the housing, and a wiring board is disposed adjacent to the electronic circuit element and fixed to the one surface, the wiring board having wiring on the surface opposite to the one surface that is electrically connected to the electronic circuit element, and wherein, based on the one surface, a height (h1) from the surface of the block to which the adhesive is fixed and a height (h2) from the surface of the wiring board to which the wiring is provided are different from each other.

2. An optical modulator according to claim 1, wherein the height (h1) of the block is greater than the height (h2) of the wiring board.

3. An optical modulator as claimed in claim 1, characterized in that the difference between the height (h1) of the block and the height (h2) of the wiring board is 0.2 mm or more.

4. An optical modulator according to claim 1, wherein at least a part of the periphery of the surface of said block to which said electronic circuit element is bonded is chamfered.

5. An optical modulator according to claim 1, wherein the adhesive for bonding said electronic circuit element to said block is conductive.

6. An optical modulator as claimed in claim 1, characterized in that the optical modulation element and an input board for supplying a high frequency signal to the electronic circuit element are arranged so as to sandwich the electronic circuit element, and the input board, the electronic circuit element and the optical modulation element are arranged and fixed within the housing so that the wiring position connecting the input board and the electronic circuit element and the wiring position connecting the electronic circuit element and the optical modulation element are located on the same plane.

7. An optical transmitter comprising: an optical modulator according to any one of claims 1 to 6; and a data generator for supplying a high-frequency signal to said optical modulator.

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