JP2008276145A - Optical modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical modulator capable of eliminating deterioration in the optical modulation characteristics which are caused by differences in the thermal expansion coefficients of materials accompany the cost reduction of a package. <P>SOLUTION: The optical modulator is provided with a substrate 1 having an electro-optical effect; an optical waveguide 3 formed on the substrate 1 to guide light; an electrode 4, formed on one surface side of the substrate 1 and composed of a center conductors 4a and ground conductors 4b, 4c to apply a high-frequency electrical signal for modulating light; an electrical terminal 8 electrically connected to the electrode 4; and a casing 50, including the substrate 1 and provided with a sidewall 33 and a bottom plate 33. The optical modulator is further provided with a substrate mount 13, arranged in between the substrate 1 and the casing 50 and having a thermal expansion coefficient which is not closer to that of the casing 50 but closer to that of the substrate 1, separate from the casing 50, the substrate 1 is fixed on the substrate mount 13, the substrate mount 13 is partially fixed on the casing 50, and the electrical terminal 8 is fixed on the substrate mount 13. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention belongs to the field of optical modulators that are high-speed, low in driving voltage, low in DC bias voltage, and good in production yield.

An optical waveguide and a traveling wave electrode are provided on a substrate having a so-called electro-optic effect (hereinafter, the lithium niobate substrate is abbreviated as an LN substrate) such as lithium niobate (LiNbO ₃ ) whose refractive index is changed by applying an electric field. The formed traveling wave electrode type lithium niobate optical modulator (hereinafter abbreviated as LN optical modulator) packaged LN optical modulator is 2.5 Gbit / s, 10 Gbit / s because of its excellent chirping characteristics. It is applied to large-capacity optical transmission systems. Recently, application to an ultra large capacity optical transmission system of 40 Gbit / s is also being studied, and it is expected as a key device.

[Conventional technology]
This LN optical modulator includes a type using a z-cut substrate and a type using an x-cut substrate (or y-cut substrate). Here, an x-cut substrate LN optical modulator using an x-cut LN substrate and a coplanar waveguide (CPW) traveling wave electrode is taken up as a prior art, and a top view thereof is shown in FIG. FIG. 8 is a cross-sectional view taken along line AA ′ of FIG. FIG. 9 shows a perspective view of the prior art. The following discussion holds true for z-cut substrates and y-cut substrates as well.

In the figure, 1 is an x-cut LN substrate, 2 is a transparent SiO ₂ buffer layer having a thickness of about 200 nm to 1 μm in the wavelength region used in optical communication such as 1.3 μm or 1.55 μm, and 3 is an x-cut LN. This is an optical waveguide formed by thermally diffusing Ti at 1050 ° C. for about 10 hours after depositing Ti on the substrate 1, and constitutes a Mach-Zehnder interference system (or Mach-Zehnder optical waveguide). Reference numerals 3a and 3b denote optical waveguides (or interactive optical waveguides) in a portion where an electrical signal and light interact (referred to as an interaction portion), that is, two arms of a Mach-Zehnder optical waveguide. The CPW traveling wave electrode 4 in the interaction portion is composed of a central conductor 4a and ground conductors 4b and 4c.

In this prior art, a bias voltage (usually a DC bias voltage) and a high-frequency electric signal (also referred to as an RF electric signal) are superimposed and applied between the center conductor 4a and the ground conductors 4b and 4c. Further, SiO ₂ buffer layer 2 is effective microwave refractive index n _m of the optical waveguide 3a of the electrical signals, 3b by approximating the light of the effective refractive index n _o of propagating, an important role of expanding a light modulation band is doing.

  5 is a case (generally a metal case because it is metal), 6 is a connector for inputting a high-frequency electric signal, 7a is a core wire of the connector 6, and is an area where a high-frequency electric signal is input in the central conductor 4a. It is connected to the center conductor 4a ′ of a certain input feedthrough section 20. 7b and 7c are gold wires for electrically connecting the metal housing 5 and the ground conductors 4b and 4c of the traveling wave electrode 4 (which may be gold ribbons, but here they are collectively referred to as gold wires), 8 , 10a, 10b, and 10c are gold wires that electrically connect the electric terminator 8 and the traveling wave electrode 4 with resistors 9a and 9b formed on an insulating substrate. The electrical signal is connected to the central conductor 4 a ″ of the output feedthrough portion 21, which is a region where the electrical signal propagates to the electrical terminal 8. Since the high frequency driving voltage of the LN optical modulator is several volts, the resistors 9a and 9b that consume the voltage are also increased, and the actual size of the electrical termination 8 patterned with these is large (electrical termination 8). (See Patent Document 1 for the operation principle).

  Reference numeral 11 denotes a pedestal (hereinafter abbreviated as a casing pedestal) provided in a casing for fixing the x-cut LN substrate 1, 30 is a side wall of the metal casing 5, and 31 is a bottom plate of the metal casing 5. . Reference numeral 40 denotes a connector holding portion including the connector core wire 7a. The metal housing 5, the housing pedestal 11, the side wall 30, the bottom plate 31, and the connector holding portion 40 are manufactured integrally. As described above, an LN optical modulator element placed in a casing (or metal casing) 5 which is a package is called an LN optical modulator module, but since it has a long name, it is simply described here. This is called an LN optical modulator. In order to simplify the description, input / output of light to / from the LN optical modulator and capacitors for preventing the aforementioned DC bias voltage from being applied to the resistors 9a and 9b are omitted. Note that these capacitors have large dimensions and are actually mounted on the electrical termination 8, so the width of the electrical termination 8 is much wider than the width of the x-cut LN substrate 1.

  Next, the problem of this prior art will be considered. Up to now, the metal housing 5 has been made by cutting all of the connector holding portion 40, the side wall 30, or the bottom plate 31 and the housing base 11 from a stainless material such as SUS304 using a cutting technique. I have been.

  Cutting technology is expensive in terms of labor costs. And since stainless steel is hard and cutting workability is not good, it takes time to process, and the price of the metal housing 5 is high at present. For this reason, the metal housing 5 occupies most of the cost of the LN optical modulator, which is a main factor that hinders the price reduction of the LN optical modulator.

  On the other hand, in a semiconductor laser module that is also one of optical components, a FeNiCo alloy (so-called Kovar) is widely used in large quantities as a metal casing as a package.

However, regarding the LN optical modulator, if the metal casing 5 that is a package is made of Kovar, the following serious problem occurs. That is, the thermal expansion coefficient in the longitudinal direction of the x-cut LN substrate 1 is close to 17.2 × 10 ⁻⁶ [1 / K] and the thermal expansion coefficient of stainless steel 16.5 × 10 ⁻⁶ [1 / K], but the heat of Kovar The expansion coefficient is significantly different from 4.4 × 10 ⁻⁶ [1 / K], and the difference between the two is 12.8 × 10 ⁻⁶ [1 / K].

Generally, since the length of the x-cut LN substrate 1 (L _{total in} FIGS. 7 and 9) is about 70 mm, for example, a temperature change of about 120 ° C. (for example, a frequently used heat cycle from −40 ° C. to 80 ° C. Due to the temperature change in the test), a length difference of about 108 μm occurs on both sides.

  Since the normal x-cut LN substrate 1 is firmly fixed to the case base 11 which is a part of the metal case 5 by solder or adhesive, the difference in length of about 108 μm is the x-cut LN. Stress is applied to the substrate 1, and the characteristic of the LN optical modulator is changed and the x-cut LN substrate 1 is destroyed.

  Next, in order to avoid these problems in the case where Kovar is used as the material of the metal housing 5, in FIG. 7, the metal which is only Kovar in the vicinity of the input feedthrough portion 20 of the x-cut LN substrate 1. A method of fixing to the housing 5 is conceivable. However, since the reinforcement of the casing base 11 is lost except at the fixed location, the mechanical strength of the x-cut LN substrate 1 is only the strength of the x-cut LN substrate 1 alone, and when vibration or impact is applied. The x-cut LN substrate 1 may be destroyed.

In addition, due to the difference in thermal expansion coefficient between the x-cut LN substrate 1 and the metal housing 5, the gold wires 10a, 10b, and 10c in the longitudinal direction of the x-cut LN substrate 1 are subjected to the heat cycle test. Stretching / shrinking force is repeatedly applied, resulting in a problem such that the metal wire is finally cut due to fatigue, or the gold wires 10a, 10b, 10c are peeled off from the traveling wave electrodes (4a '', 4b, 4c). . In general, since the length of the gold wires 10a, 10b, and 10c is as short as 2 mm or less, it is known that metal fatigue is likely to occur even with a slight expansion and contraction. Even if a connector for extracting a high-frequency electrical signal to the outside of the LN optical modulator is used instead of the electrical termination 8, for example, the phenomenon that the core wire of the connector and the central conductor 4a '' of the traveling wave electrode peel off. Produce.
JP-A-11-183858 (FIG. 1)

  As described above, in the conventional technology, since the metal casing as a package is stainless steel, the labor cost mainly for the cutting process is a main factor in increasing the cost of the LN optical modulator. In addition, when the metal casing is made of Kovar, the characteristics change with the temperature change due to the difference in thermal expansion coefficient between the metal casing and the x-cut LN substrate, and the LN substrate such as x-cut is destroyed. Was causing problems.

  Furthermore, the biggest problem in the prior art is the cutting and peeling of the gold wire due to metal fatigue. That is, when only a part of the LN substrate is fixed to the housing pedestal, such as only in the vicinity of the connector for inputting the high-frequency electric signal of the LN substrate, or only in the vicinity of the input feedthrough portion for inputting the high-frequency electric signal. However, the mechanical strength of the LN substrate in particular in the vertical direction is deteriorated, or the gold wire connecting the central conductor of the output feedthrough portion and the electrical terminal is cut or peeled off. Further, when a connector for outputting a high-frequency electrical signal is used instead of the electrical termination, peeling between the connector core wire and the center conductor of the output feedthrough portion has occurred.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an optical modulator that solves the deterioration of the optical modulation characteristics caused by the difference in the thermal expansion coefficient of the material accompanying the cost reduction of the package. Yes.

  In order to solve the above problems, an optical modulator according to claim 1 of the present invention includes a substrate having an electro-optic effect, an optical waveguide for guiding light formed on the substrate, and one of the substrates. An electrode made of a center conductor and a ground conductor for applying a high-frequency electric signal for modulating the light, formed on the surface side, an electrical terminal electrically connected to the electrode, and the substrate, And a housing having a bottom plate, and a substrate pedestal having a thermal expansion coefficient closer to the substrate than the housing, between the substrate and the housing, separately from the housing. The substrate is fixed to the substrate pedestal, and the substrate pedestal is partially fixed to the housing, and the electrical terminal is fixed to the substrate pedestal.

  The optical modulator according to claim 2 of the present invention is characterized in that the casing is an alloy containing Fe, Ni, and Co.

  The optical modulator according to claim 3 of the present invention is characterized in that the substrate base is made of stainless steel.

  The optical modulator according to claim 4 of the present invention is characterized in that the substrate is made of lithium niobate containing at least one of x-cut and y-cut in the longitudinal direction.

  The optical modulator according to claim 5 of the present invention is characterized in that in the casing, the side wall and the bottom plate are separate.

  The optical modulator according to claim 6 of the present invention is characterized in that the housing includes at least one of a separate connector holding portion or a separate metal block having a screw for fixing to an external device. Features.

  The optical modulator according to claim 7 of the present invention is characterized in that the ground conductor is electrically grounded by electrically connecting the ground conductor and the substrate base.

  In the present invention, first, as a package of an LN optical modulator, a side wall and a bottom plate of a metal housing made of a material such as Kovar having a thermal expansion coefficient significantly different from that of an LN substrate are manufactured separately, and then silver brazing is performed. It is assembled by etc. This simplifies the manufacture of the package (metal housing) and cuts the cost of the package drastically compared to stainless steel cutting. Next, a new substrate base is provided, and the LN substrate is placed and fixed on the substrate base. As a result, the substrate base serves as a reinforcing plate for the LN substrate, and the mechanical strength of the LN substrate can be ensured. And this board | substrate base is partially fixed to the housing | casing base manufactured with materials, such as Kovar, which differ in a thermal expansion coefficient greatly. Since the substrate pedestal and the housing pedestal other than the fixed part are free from each other, they can freely expand and contract with each other in accordance with a change in the heat cycle test and the environmental temperature. Therefore, no mechanical stress is applied to the LN substrate during such a temperature change, so that problems such as changes in characteristics or destruction of the LN substrate do not occur. Furthermore, the most important point of the present invention is that the electrical termination is mounted on the substrate base together with the LN substrate. Therefore, the gold wire does not expand and contract, and the problem of cutting the gold wire due to metal fatigue does not occur. Therefore, by applying the present invention, the cost of the package as the LN optical modulator is significantly reduced, while the change in characteristics as the LN optical modulator and the LN caused by securing the strength of the LN substrate and the difference in thermal expansion coefficient are achieved. Problems such as breakage of the substrate and cutting due to metal fatigue of the gold wire connecting the electrical termination and the traveling wave electrode can be completely solved.

  Hereinafter, embodiments of the present invention will be described. However, since the same numbers as those of the conventional embodiments shown in FIGS. 7 to 9 correspond to the same function units, the description of the function units having the same numbers is omitted here. To do.

[First Embodiment]
FIG. 1 is a perspective view of the first embodiment of the present invention, and FIG. 2 is a top view thereof. Moreover, FIG. 3 shows a cross-sectional view taken along line BB ′ of FIG. In the figure, 50 is a metal housing such as Kovar. One of the major differences between this embodiment and the prior art shown in FIG. 7 is the material and configuration of the metal housing 50 and the method of manufacturing the same.

  In this embodiment, the LN substrate and the substrate base are first firmly fixed, and the substrate base serves as a reinforcing plate for the LN substrate to ensure the mechanical strength of the LN substrate. With respect to the package, first, a connector holder that includes the housing pedestal 12, a bottom plate 33 that is integrated with or separated from the housing pedestal 12, a side wall 32 that is usually four surfaces, and a core wire 7 a of the connector 6. 70 is made as a separate body at the beginning, and thereafter, these are joined by soldering or silver brazing to produce the metal casing 50 (see FIGS. 1 and 3).

  For example, in the case of silver brazing, a series of parts necessary for an LN optical modulator, such as a housing pedestal 12 and a bottom plate 33 and a side wall 32 and a connector holding unit 70 that are integrated with or separated from the housing pedestal 12, are provided. Since it can be easily joined by assembling and passing it through a high-temperature furnace, the metal casing 50 can be manufactured at a significantly lower cost than the method of manufacturing by cutting by cutting in the prior art. It becomes possible to produce.

  Another major difference between the present embodiment and the prior art shown in FIG. 7 is that the x-cut LN substrate 1 is made of a stainless material having a thermal expansion coefficient close to that, and a substrate base 13 having a sufficiently large area is newly provided. , Not only the x-cut LN substrate 1 but also the electrical terminal 8 is mounted and fixed on the wide substrate base 13. A simple structure is used in which the substrate pedestal 13 is placed on the substantially flat housing pedestal 12.

  As described above, the housing pedestal 12 and the bottom plate 33 may be separate or integrated. Even if the housing pedestal 12 is a separate body, it is integrated with the bottom plate 33, the side wall 32, or the connector holding portion 70 by soldering or silver brazing in a high-temperature furnace. That is, finally, the housing pedestal 12, the bottom plate 33, the side wall 32, and the connector holding portion 70 integrally form the metal housing 50. Therefore, fixing the board base 13 to the housing base 12 is equivalent to fixing the board base 13 to the metal housing 50 in other words. Therefore, in this specification, the description that the substrate pedestal 13 is fixed to the casing pedestal 12 means that the substrate pedestal 13 is fixed to the metal casing 50.

  As will be described below, it is extremely important to mount the electrical terminal 8 on the substrate base 13. FIG. 4 is a top view of an example of the substrate base 13. Here, 14 is a fixing screw for fixing the substrate base 13 to the housing base 12. The fixing screw 14 is provided in the vicinity of the joint between the center conductor 4a 'of the input feedthrough 20 for inputting a high-frequency electric signal and the core wire 7a of the connector 6. As described above, FIG. 4 is an example of the substrate pedestal 13, and needless to say, the shape of the substrate pedestal 13 is not limited to this. For example, in FIG. 4, the width of the substrate base 13 is increased as the cutout portion 71 for receiving the connector holding portion 70 of FIG. 1 is provided, but there is an option of not so wide.

  A cross-sectional view taken along the line C-C 'of FIG. 4 is shown in FIG. Here, the bending prevention screw 16 fixes the substrate pedestal 13 to the housing pedestal 12 through a certain gap, and when the LN optical modulator is subjected to mechanical vibration or impact, the substrate pedestal 13 is fixed. And the x-cut LN substrate 1 is prevented from becoming large in the vertical direction. Reference numeral 15 denotes a space for sliding when the substrate base 13 is thermally expanded and contracted. Further, the simple structure of the bending prevention screw 16 and the sliding space 15 prevents the board base 13 from being swayed from side to side. Further, instead of the bending prevention screw 16 and the sliding space 15, the substrate base 13 and the housing base 12 may be fixed using an adhesive having a large elasticity. Furthermore, when the mechanical strength of the substrate base 13 is high, the bending prevention screw 16 and the sliding space 15 or a highly elastic adhesive is unnecessary. These can be said for all embodiments of the present invention.

  Here, the board pedestal 13 and the housing pedestal 12 are mechanically and extremely bonded to each other by the fixing screws 14. The distance between the fixing screw 14 and the core wire 7a of the connector 6 is about several mm, or at most about 10 mm even if the distance is long. Therefore, when the heat cycle test or the environmental temperature changes, the board pedestal 13 and the housing The difference in thermal expansion coefficient for the body pedestal 12 is not a problem. Further, the substrate base 13 and the housing base 12 are mechanically free except for the fixed portion. In this way, firmly fixing only a part is called partially fixing.

Next, the thermal expansion will be considered in detail. When the LN optical modulator is subjected to a heat cycle test or the environmental temperature changes, the substrate pedestal 13 (and the x-cut LN substrate 1 having substantially the same thermal expansion coefficient) and the housing pedestal 12 have very different thermal expansion coefficients. Independently of each other, it expands and contracts greatly. As a result, even if the substrate pedestal 13 and the housing pedestal 12 are designed to have the same length, the substrate pedestal 13 and the housing pedestal 12 differ in the amount of expansion / contraction due to temperature, resulting in different lengths. (As described in the description of the prior art, when the length of the x-cut LN substrate 1 (L _{total in} FIGS. 1 and 2) is about 70 mm, for example, from −40 ° C. to 80 ° C. A difference in length of 108 μm occurs between Kovar, stainless steel, and x-cut LN substrate 1 due to a temperature difference of 120 ° C. in the heat cycle test.

  However, in the present embodiment, the board pedestal 13 and the housing pedestal 12 are mechanically joined to each other by a fixing screw 14 (or may be YAG laser welding or soldering) only in a limited portion, Since the other portions are free from each other, even if the heat cycle test or the actual environmental temperature changes, it can be expanded and contracted through the space 15. Therefore, no great mechanical stress is generated between the substrate base 13 and the housing base 12. Further, no great stress is applied to the x-cut LN substrate 1, and the characteristics as the LN optical modulator are not changed, and the x-cut LN substrate 1 is not destroyed.

  Further, in the present embodiment, a very important point is that the electrical terminal 8 is also fixed to the substrate base 13 together with the x-cut LN substrate 1 as can be seen from FIGS. 1 and 2. Then, the ground conductors 4b and 4c are connected to the substrate base 13 so that the ground conductors 4b and 4c are electrically grounded.

  As can be seen from the above description, since the x-cut LN substrate 1 and the substrate base 13 have substantially the same thermal expansion coefficient, they expand and contract to the same extent. Therefore, the x-cut LN substrate 1 mounted on the substrate pedestal 13 and the electrical terminal 8 are integrated with each other and expand and contract independently of the housing pedestal 12 during the heat cycle test or when the environmental temperature changes. Therefore, the gold wires 10a, 10b, and 10c are not mechanically moved during the heat cycle test, and there is no concern that metal fatigue occurs in the gold wires 10a, 10b, and 10c.

  As a result, it is possible to realize a package (metal housing 50) that is dramatically lower in cost than stainless steel that requires cutting by Kovar. Further, when the heat cycle test or environmental temperature that has been a problem in the prior art changes. Problems such as gold wire cutting and peeling and connector core peeling were completely resolved. In FIG. 3, the substrate pedestal 13 is substantially L-shaped, but if this is a substantially flat plate, the effect of reducing the cost of manufacturing the substrate pedestal 13 is significant.

  In the above description, attention is paid to the high-frequency electric signal. However, with respect to the DC bias voltage that determines the bias point of light modulation, the metal wire caused by thermal expansion due to temperature change is less likely to be a problem because the gold wire becomes longer. However, a line substrate for supplying a DC bias may be separately manufactured, fixed on the substrate base 13, and supplied from this. Alternatively, a DC bias supply line substrate is fixed inside the metal casing 50, and a DC bias supply line is formed on the x-cut LN substrate 1, and the DC bias supply line substrate is x-cut. A DC bias voltage may be supplied to a DC bias supply line formed on the LN substrate 1. At this time, the electrical connection from the DC bias supply line substrate to the DC bias supply line formed on the x-cut LN substrate 1 is an x-cut in the vicinity of the substrate base 13 fixed to the housing base 12. When performed on the LN substrate 1, the influence of thermal expansion can be almost eliminated. These can be said in all the embodiments of the present invention.

  In the present embodiment, the board pedestal 13 is fixed to the housing pedestal 12 in the vicinity of the core wire 7a of the connector 6. However, the fixing position of the board pedestal 13 to the housing pedestal 12 is not limited to this. For example, by fixing the vicinity of the center in the longitudinal direction of the substrate pedestal 13 to the housing pedestal 12 over a length of about 10 mm, the substrate pedestal 13 and the case due to thermal expansion during a heat cycle test or when the environmental temperature changes. The difference in length of the pedestal 12 may be dispersed on both sides in the longitudinal direction. This concept can be applied to all embodiments of the present invention.

[Second Embodiment]
In FIG. 5 illustrating the first embodiment of the present invention, when the LN optical modulator is subjected to mechanical vibration or impact, the bending prevention screw 16 is connected to the substrate base 13 or the x-cut LN substrate 1. He said that it plays a role in preventing the size from increasing in the vertical direction. However, the method of using the bending prevention screw 16 is merely an example as a structure for preventing vertical bending, and there are various other methods.

  Another structural example for preventing this bending is shown in FIG. 6 as a second embodiment of the present invention. Here, 60 is a jig for preventing bending, and the bottom surface is fixed to the bottom plate 33, and the substrate pedestal 13 is suppressed through a very small gap, so that the LN optical modulator is subjected to vibration and shock. At this time, the substrate base 13 and the x-cut LN substrate 1 are prevented from being moved up and down. Of course, since the bending prevention jig 60 and the substrate base 13 are not fixed to each other, the substrate base 13 and the x-cut LN substrate 1 can expand and contract in the longitudinal direction.

  In this case, the bending prevention screw 16 and the space 15 shown in FIGS. 4 and 5 shown as the first embodiment are not necessary. In addition, there are various other methods for preventing bending, but it goes without saying that any method may be used. Also in the present embodiment, left and right shaking of the substrate base 13 is prevented with a simple configuration of the bending prevention jig 60. The present embodiment is also characterized in that left and right shaking can be prevented with a small number of components such as one bending prevention jig 60 and the side wall 32.

[About each embodiment]
In the above description, the CPW electrode has been described as an example of the traveling wave electrode. However, it goes without saying that various traveling wave electrodes such as an asymmetric coplanar strip (ACPS) and a symmetric coplanar strip (CPS), or a lumped constant electrode may be used. . In addition to the Mach-Zehnder type optical waveguide, it goes without saying that other optical waveguides such as directional couplers and straight lines may be used as the optical waveguide. Further, it goes without saying that the present invention can be applied to a planar structure, and can also be applied to a ridge structure or an LN optical modulator having a very thin substrate.

  A screw hole for fixing the LN optical modulator to an external device such as a transponder is usually provided on the back of the metal housing. In order to realize this in the present invention, in the first embodiment shown in FIG. 1, the connector holding portion, the bottom plate, or the side wall is manufactured separately, and then these are fixed with solder, silver solder or the like. Similarly, a metal block having a screw hole for fixing to the transponder may be manufactured separately and fixed to the bottom plate or the side wall by soldering or silver brazing.

  In the above embodiment, the crystal orientation of x-cut, y-cut or z-cut, that is, the x-axis, y-axis or z-axis of the crystal is perpendicular to the substrate surface (cut plane). The surface orientation in each of the embodiments described above may be the main surface orientation, and other surface orientations may be mixed as surface orientations subordinate to these, and not only the LN substrate but also the lithium tantalum. It goes without saying that other substrates such as rates may be used.

  In the present invention, the electrical termination has been described as being mounted on the board pedestal. However, the side wall, the bottom plate, the connector holding part, etc. are manufactured separately and then integrated by soldering, silver brazing, or the like. The idea of constructing a housing can be applied to an electric field sensor that does not use an electrical terminal.

  In the above description, the casing has been described as a metal, but it goes without saying that other materials such as plastic and ceramic may be used.

  As described above, the optical modulator according to the present invention is useful as an optical modulator with low cost, high reliability, and good manufacturing yield.

1 is a schematic perspective view of an optical modulator according to a first embodiment of the present invention. 1 is a schematic top view of an optical modulator according to a first embodiment of the present invention. 2 is a cross-sectional view taken along line A-A ′ of FIG. 2, which is a schematic top view of the optical modulator according to the first embodiment of the present invention. Top view of the bending prevention jig used in the first embodiment of the present invention. FIG. 4 is a cross-sectional view taken along the line C-C ′ of FIG. 4, which is a top view of the bending prevention jig used in the first embodiment of the present invention. Schematic perspective view of the optical modulator according to the second embodiment of the present invention. Top view of the prior art Sectional view taken along line A-A 'of the prior art Prior art perspective view

Explanation of symbols

1: x-cut LN substrate (substrate, LN substrate)
2: SiO ₂ buffer layer (buffer layer)
3: Optical waveguide 3a, 3b: Optical waveguide of the interaction part (optical waveguide)
4: Traveling wave electrode (electrode)
4a, 4a ', 4a'': Center conductor 4b, 4c: Ground conductor 5: Metal casing 6: Connector for RF electric signal input (connector)
7a: Connector wire 7b, 7c: Gold wire 8: Electrical termination 9a, 9b: Resistance 10a, 10b, 10c: Gold wire 11, 12: Housing base 13: Board base 14: Fixing screw 15: Space 16 : Bending prevention screw 20: Input feed-through portion 21: Output feed-through portion 30: Side wall (side wall) of metal housing 5
31: Bottom plate of metal housing 5 (bottom plate)
32: Side wall (side wall) of metal casing 50
33: Bottom plate (bottom plate) of metal housing 50
40: Connector holding part 50: Metal housing (housing)
60: Bending prevention jig 70: Connector holding part 71: Notch part

Claims (7)

A substrate having an electro-optic effect, an optical waveguide for guiding light formed on the substrate, and a center for applying a high-frequency electric signal that is formed on one surface side of the substrate and modulates the light In an optical modulator comprising: an electrode comprising a conductor and a ground conductor; an electrical termination electrically connected to the electrode; and a housing containing the substrate and having a side wall and a bottom plate.
A substrate pedestal that is separate from the housing and has a thermal expansion coefficient closer to the substrate than the housing, the substrate pedestal being fixed to the substrate pedestal, and the substrate pedestal; Is partially fixed to the housing, and the electrical termination is fixed to the substrate base.   The optical modulator according to claim 1, wherein the casing is an alloy containing Fe, Ni, and Co.   The optical modulator according to claim 1, wherein the substrate base is made of stainless steel.   4. The optical modulator according to claim 1, wherein the substrate is made of lithium niobate containing at least one of x-cut and y-cut in the longitudinal direction. 5.   The optical modulator according to any one of claims 1 to 4, wherein the casing includes the side wall and the bottom plate as separate bodies.   6. The housing according to claim 1, wherein the housing includes at least one of a separate connector holding portion or a separate metal block having a screw for fixing to an external device. An optical modulator according to any one of the above.   7. The optical modulator according to claim 1, wherein the ground conductor is electrically grounded by electrically connecting the ground conductor and the substrate base. 8. .

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