JP5244869B2 - Optical modulator module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical modulator module having less temperature drift to a temperature change or having high mechanical reliability to external force. <P>SOLUTION: An optical modulator module comprises: an optical modulator chip including a substrate, an optical waveguide formed on the substrate, and a progressive wave electrode for applying a high frequency electric signal to modulate a phase of light, which constitutes an interaction section for modulating the phase of light by applying the high frequency electric signal with the progressive wave electrode; and a housing in which the optical modulator chip is fixed on a pedestal formed therein with an adhesive. A conductive layer is formed on a part of a rear face of the substrate. The adhesive is composed of a conductive adhesive and a flexible adhesive having a flexible characteristic after hardening which is more excellent than that of the conductive adhesive. The conductive layer and the pedestal are adhered with the conductive adhesive in a first surface region to be a prescribed area portion of the pedestal so that the rear face of the substrate and the pedestal are electrically connected. In a second surface region to be a portion except the first surface region of the pedestal, the conductive layer and the pedestal are adhered with the flexible adhesive. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention belongs to the field of an optical modulator module having a small temperature drift with respect to a temperature change or a high mechanical reliability with respect to an external force.

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) is applied to a high capacity optical transmission system of 2.5 Gbps and 10 Gbps because of its excellent transmission characteristics. Recently, application to an ultra-high capacity optical transmission system of 40 Gbps has been studied, and it is expected as a key device.

(First prior art)
This LN optical modulator includes a type using a z-cut LN substrate and a type using an x-cut LN substrate (or a y-cut LN substrate). Here, as a first prior art, an LN using a coplanar waveguide (CPW) traveling wave electrode having a z-cut LN substrate and two ground conductors, which is disclosed in Patent Document 1, which is advantageous for propagation in a fundamental mode. An optical modulator (or LN optical modulator chip) 40 is shown in FIG.

In the figure, 1 is a z-cut LN substrate, 2 is a transparent SiO ₂ buffer layer having a thickness of about 200 nm to 1 μm in a wavelength region used in optical communication such as 1.3 μm or 1.55 μm, and 3 is a z-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). Here, in order to simplify the description, the Si conductive layer that is normally used to suppress the temperature drift due to the pyroelectric effect is omitted.

  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. In the case of a phase modulator, a straight optical waveguide may be used. The CPW traveling wave electrode 4 includes a central conductor 4a and ground conductors 4b and 4c.

  When an LN optical modulator is used in an optical transmission system, a metal casing (plastic may be used as a material for a package casing, but generally a metal such as stainless steel or Kovar is used. For this reason, the optical modulator module must have a LN optical modulator chip, an optical fiber, and a microwave connector for electrical signals fixed to a metal casing.

FIG. 7 shows an optical modulator module 50 in which a chip of an LN optical modulator is fixed inside a metal housing 5 based on the first prior art disclosed in Patent Document 1. For the sake of simplicity, FIG. 7 omits all of the SiO ₂ buffer layer 2, the optical waveguide 3, the CPW traveling wave electrode 4, etc. shown in FIG. 6 and shows only the z-cut LN substrate 1. It was. Here, the metal housing 5 is provided with a pedestal 6 that is partially protruded, and the entire surface of the LN substrate 1 opposite to the pedestal 6 is fixed to the pedestal 6 by the conductive adhesive 7. Has been. FIG. 8 shows a cross-sectional view taken along line AA ′ of FIG.

  The thermal expansion coefficients of the z-cut LN substrate 1, the metal casing 5 (precisely the pedestal 6), and the conductive adhesive 7 are different from each other. Therefore, when the optical modulator module environmental temperature changes, these cause different amounts of thermal expansion (or thermal contraction). However, the conductive adhesive 7 that fixes the entire surface of the pedestal 5 and the pedestal 6 of the z-cut LN substrate 1 opposite to each other is very hard after curing. Mechanical stress is generated due to the difference in thermal expansion coefficient of the adhesive 7.

  Since the z-cut LN substrate 1 has a piezoelectric effect, the refractive index of the interaction optical waveguides 3a and 3b shown in FIG. 6 changes when subjected to mechanical stress. The optimum DC bias voltage to be applied changes. This is called temperature drift.

  FIG. 9 shows changes in the DC bias voltage (or bias voltage shift) when the environmental temperature of the optical modulator module changes. As shown in this figure, in the first prior art, a large bias voltage shift occurs as the environmental temperature of the optical modulator module changes.

  Furthermore, the z-cut LN substrate 1 may break when the difference in the thermal expansion coefficient described above is large.

(Second prior art)
FIG. 10 shows a second conventional optical modulator module 51 disclosed in Patent Document 2. In FIG. Here, only one protrusion 10 is formed on the base 9 provided in the housing 8, and the z-cut LN substrate 1 is fixed only at the protrusion 10 by the conductive adhesive 7.

  As can be readily seen, the problem with this structure is that it is extremely weak for mechanical strength tests such as vibration and impact tests. Actually, an optical modulator module was prototyped with this structure. However, in the vibration test, the z-cut LN substrate 1 was easily detached from the protrusion 10, and as a result, the optical modulator module was not connected to the LN optical modulator chip. While the illustrated fiber was cut, the LN optical modulator chip was detached from the high-frequency connector (not shown), so that it did not function as an optical modulator module.

Japanese Patent Laid-Open No. 7-64030 JP-A-4-1604

  As described above, it is possible to suppress temperature drift caused by the difference in thermal expansion coefficient of the materials constituting the optical modulator module when the environmental temperature of the optical modulator module changes, and to provide light having sufficient mechanical reliability. The reality is that we are still struggling to develop the modulator module, and there is an urgent need to resolve this.

  In order to solve the above problems, an optical modulator module 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 the substrate. A traveling wave electrode formed of a central conductor and a ground conductor for applying a high frequency electrical signal that modulates the phase of the light, and the traveling wave electrode transmits the high frequency electrical signal. An optical modulator chip that forms an interaction unit for modulating the phase of the light by applying, a housing having a pedestal inside, and the optical modulator chip fixed to the pedestal with an adhesive; and A conductive layer is formed on at least a part of the back surface of the substrate, and the adhesive has a conductive adhesive and a flexible property after curing as compared with the conductive adhesive. Excellent flexible adhesive and The conductive layer and the pedestal are bonded with the conductive adhesive in a first surface region that is a predetermined area portion of the pedestal so that the back surface of the substrate and the pedestal are electrically connected. In addition, the conductive layer and the pedestal are bonded with the flexible adhesive in a second surface region that is a portion other than the first surface region of the pedestal.

  In order to solve the above-mentioned problem, an optical modulator module according to a second aspect of the present invention is the optical modulator module according to the first aspect, wherein the area of the first surface region is the second surface. It is characterized by being narrower than the area of the region.

  In order to solve the above problems, an optical modulator module according to a third aspect of the present invention is the optical modulator module according to the first aspect, wherein the area of the first surface region and the second surface are the same. The area is substantially equal to the area.

  In order to solve the above problem, an optical modulator module according to a fourth aspect of the present invention is the optical modulator module according to the first aspect, wherein the area of the first surface region is the second surface. It is characterized by being wider than the area of the region.

  In order to solve the above problem, an optical modulator module according to claim 5 of the present invention is the optical modulator module according to any one of claims 1 to 4, wherein the first surface region is It is characterized by being formed at a position higher than the second surface region.

  In order to solve the above problem, an optical modulator module according to claim 6 of the present invention is the optical modulator module according to any one of claims 1 to 4, wherein the first surface region is It is characterized by being formed at a height position substantially equal to the second surface region.

  In order to solve the above-mentioned problem, an optical modulator module according to claim 7 of the present invention is the optical modulator module according to any one of claims 1 to 4, wherein the first surface region is It is characterized by being formed at a position lower than the second surface region.

  In order to solve the above problem, an optical modulator module according to an eighth aspect of the present invention is the optical modulator module according to any one of the first to seventh aspects, wherein the first surface region and the optical modulator module are A concave portion is formed at the boundary with the second surface region.

  In order to solve the above problem, an optical modulator module according to claim 9 of the present invention is the optical modulator module according to any one of claims 1 to 8, wherein the first surface region is It is characterized by being formed in the approximate center of the pedestal in the light guiding direction or in the vicinity of the end of the pedestal.

  In the present invention, the conductive layer is formed on the back surface of the LN substrate, and the conductive layer and the pedestal formed on the back surface of the LN substrate are formed with a conductive adhesive in the first surface region that is a part of the pedestal of the metal housing. The conductive layer formed on the back surface of the LN substrate and the pedestal in the second region that is connected and fixed and is a portion other than the first surface region of the pedestal is more flexible than the conductive adhesive after curing. Fix with an adhesive (in other words, softer than the conductive adhesive). Thereby, since the whole back surface of a LN board | substrate becomes the same electric potential as a metal housing | casing, a pyroelectric effect can be suppressed.

  In addition, it is possible to absorb the stress on the LN substrate caused by the difference in the thermal expansion coefficient between the LN substrate and the housing, which is caused by a change in environmental temperature, with a soft adhesive. Further, since the area where the soft adhesive is bonded is wide, high adhesive strength to the pedestal of the LN substrate can be realized.

  As described above, by using the present invention, it is possible to suppress the temperature drift accompanying the change in the environmental temperature and to obtain high mechanical reliability.

Sectional drawing of the optical modulator module which concerns on the 1st Embodiment of this invention The figure explaining the characteristic of the 1st Embodiment of this invention Sectional drawing of the optical modulator module which concerns on the 2nd Embodiment of this invention. Sectional drawing of the optical modulator module which concerns on the 3rd Embodiment of this invention. Sectional drawing of the optical modulator module which concerns on the 4th Embodiment of this invention. 1 is a perspective view of an optical modulator chip built in an optical modulator module according to a first conventional technique. 1 is a perspective view of an optical modulator module according to a first conventional technique. Sectional drawing in AA 'of FIG. The figure explaining the characteristic of embodiment of the 1st prior art Sectional drawing of the optical modulator module which concerns on 2nd prior art

  Hereinafter, embodiments of the present invention will be described. However, since the same reference numerals as those of the conventional embodiments shown in FIGS. 6 to 10 correspond to the same function units, the description of the function units having the same numbers is omitted here. To do. Further, the optical waveguide, the traveling wave electrode, and the interaction unit will be described as being formed in the same manner as in the conventional embodiment, but are not limited thereto.

(First embodiment)
FIG. 1 is a cross-sectional view of an optical modulator module 52 corresponding to FIG. Here, 12 is a conductive layer made of Si or Ti, 13 is a metal casing, 14 is a pedestal provided on the metal casing 13, 15 is a first surface region formed on the pedestal 13, and 16 and 17 are first A second surface region formed through the surface region 15 and the recess, 18 is a conductive adhesive, and 19 is an adhesive different from 18. This adhesive 19 is provided to absorb the difference in thermal expansion coefficient between the z-cut LN substrate 1 and the pedestal 14, and is preferably made of a material having a high adhesive force and relatively soft, such as ultraviolet rays or A material that is cured by heating is used. Specifically, it is an adhesive that has superior flexibility properties after curing (in other words, softer than the conductive adhesive) (hereinafter, 19 is referred to as a flexible adhesive).

  Reference numerals 20 and 21 denote concave portions provided for the escape of the conductive adhesive 18 and the flexible adhesive 19 (to prevent the mixture of both) and are referred to as escape portions.

  Since the conductive layer 12 is formed on the entire back surface (or a predetermined area) of the z-cut LN substrate 1, the entire lower surface of the z-cut LN substrate 1 is pedestal 14, that is, a metal via a conductive adhesive 18. It is electrically connected to the housing 13. Thereby, since the whole lower surface of the LN board | substrate 1 becomes the same electric potential as the metal housing | casing 13, the pyroelectric effect can be suppressed.

  Further, the flexible adhesive 19 can absorb more shear stress to the LN substrate caused by the difference in thermal expansion coefficient.

  Needless to say, the conductive adhesive is not required to enter the recesses 20 and 21 completely or at all.

  In the case where the total length of the pedestal 14 in the longitudinal direction of the optical waveguide is 60 mm, it has been confirmed that the first surface region 15 has a length of about 1 mm to 20 mm in the longitudinal direction of the optical waveguide. Needless to say, the length may be increased to about 30 mm. However, it goes without saying that it may be longer than this in some cases.

  Specifically, the area ratio between the second surface regions 16 and 17 and the first surface region 15 in the longitudinal direction of the optical waveguide is particularly preferable in the range of 9: 1 to 8: 2, and up to about 1: 1. Applicable. Furthermore, the area ratio of the second surface regions 16 and 17 may be smaller.

  In FIG. 2, the solid line indicates the temperature drift characteristics of the optical modulator module according to the present invention. For reference, the case of the first prior art is indicated by a dotted line. The temperature drift referred to here is caused by a mechanical stress accompanying a change in the environmental temperature of the optical modulator module. As can be seen from this figure, the temperature drift characteristics can be greatly improved by applying the present invention.

  In the present embodiment, the first surface region 15 and the second surface regions 16 and 17 have been described as having the same height. However, the first surface region 15 may be configured to be lower, and preferably The first surface region 15 may be configured higher (as will be described in the fourth embodiment).

(Second Embodiment)
FIG. 3 shows a cross-sectional view of the optical modulator module 53 according to the second embodiment of the present invention. Here, 22 is a metal housing, 23 is a base formed on the metal housing 22, 24 is a first surface region formed on the base 22, 25 is a second surface region formed on the base 22, and 7 is conductive. An adhesive 19 is a flexible adhesive. Reference numeral 28 denotes an escape portion of the conductive adhesive 7 and the flexible adhesive 19.

  In the second embodiment, the same effect as that of the first embodiment can be expected, and the conductive adhesive is applied only to the first surface region 24 provided in the vicinity of one end of the base 23. Therefore, it can be said that the structure is more manufacturable as compared with the first embodiment.

  In the present embodiment, the first surface region 24 and the second surface region 25 have been described as having the same height. However, the first surface region 24 may be configured to be lower, and preferably (first The first surface region 24 may be configured higher (as will be described in the fourth embodiment).

(Third embodiment)
FIG. 4 shows a cross-sectional view of the optical modulator module 54 of the third embodiment of the present invention. Here, 29 is a metal casing, 30 is a pedestal, 7 is a conductive adhesive that bonds the conductive layer 12 and the pedestal 30 in a predetermined surface area (first surface area) of the pedestal, and 19 is another pedestal. This is a flexible adhesive that adheres the conductive layer 12 and the pedestal 30 in a predetermined surface region (second surface region).

  In this embodiment, since the escape portion (concave portion) is not provided in the pedestal, it can be said that the structure has a lower cost.

  It should be noted that the portion (first surface region) where the conductive adhesive 7 of the pedestal 30 is in contact with the portion (second surface region) where the flexible adhesive 19 is in contact is different in height (for example, the conductive adhesive 7 is The portion that contacts the conductive adhesive 7 may preferably be configured higher (as described in the fourth embodiment).

(Fourth embodiment)
FIG. 5 shows a cross-sectional view of the optical modulator module 55 in the fourth embodiment of the present invention. Here, 33 is a metal casing, 34 is a pedestal, 35 is a first surface region formed on the pedestal 34, and 37 and 38 are second surface regions formed on the pedestal 34. 7 is a conductive adhesive, and 19 is a flexible adhesive.

  In the present embodiment, the height of the first surface region 35 is higher than that of the second surface regions 37 and 38. As a result, the flexible adhesive 19 is thicker than the conductive adhesive 7 and has a structure that can absorb more shear stress to the LN substrate caused by the difference in thermal expansion coefficient.

  Needless to say, the first surface region 35 does not have to be near the center of the pedestal 34 in the longitudinal direction of the optical waveguide, or may be provided at an end portion.

(About various embodiments)
The present invention is not limited to the form of electrodes. Therefore, although the CPW electrode has been described as an example, 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 type electrode may be used. In addition to the Mach-Zehnder type optical waveguide, other optical waveguides such as directional couplers and straight lines may be used as the optical waveguide.

  The heights of the first surface region and the second surface region provided on the pedestal described in this specification may be the same height or different from each other.

  In the above embodiment, the substrate has an x-cut, y-cut or z-cut plane orientation, that is, a crystal x-axis, y-axis or z-axis in a direction perpendicular to the substrate surface (cut plane). The plane orientation in each of the embodiments described above may be the main plane orientation, and other plane orientations may be mixed as the sub-plane orientation. In addition to the LN substrate, Needless to say, other substrates such as lithium tantalate may be used.

  As described above, the optical modulator according to the present invention is useful as an optical modulator module having a small change in bias voltage with respect to the environmental temperature and high mechanical reliability.

1: z-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 4a: Center conductor 4b, 4c: Ground conductor 5, 8, 13, 22, 29, 33: Metal housing 6, 9, 14, 23, 30, 34: Base 7: Conductive adhesive 12 : Conductive layer 10: protrusions 15, 24, 35: first surface region 16, 17, 25, 37, 38: second surface region 19: flexible adhesive 20, 21, 28: relief (recessed portion)
40: LN optical modulator (LN optical modulator chip)
50, 51, 52, 53, 54, 55: Optical modulator module

Claims (9)

A substrate having an electro-optic effect, an optical waveguide for guiding light formed on the substrate, and a high-frequency electric signal formed on one surface side of the substrate and modulating the phase of the light A traveling wave electrode comprising a central conductor and a grounded conductor, wherein the traveling wave electrode constitutes an interaction unit for modulating the phase of the light by applying the high frequency electrical signal When,
In a light modulator module comprising a pedestal inside, and a housing in which the light modulator chip is fixed to the pedestal with an adhesive,
A conductive layer is formed on at least a part of the back surface of the substrate;
The adhesive is composed of a conductive adhesive and a flexible adhesive whose softness after curing is superior to the conductive adhesive,
The conductive layer and the pedestal are bonded with the conductive adhesive in a first surface region that is a predetermined area portion of the pedestal so that the back surface of the substrate and the pedestal are electrically connected. ,
The optical modulator module, wherein the conductive layer and the pedestal are bonded with the flexible adhesive in a second surface region that is a portion other than the first surface region of the pedestal.   The optical modulator module according to claim 1, wherein an area of the first surface region is smaller than an area of the second surface region.   The optical modulator module according to claim 1, wherein an area of the first surface region and an area of the second surface region are substantially equal.   The optical modulator module according to claim 1, wherein an area of the first surface region is larger than an area of the second surface region.   5. The optical modulator module according to claim 1, wherein the first surface region is formed at a position higher than the second surface region. 6.   5. The optical modulator module according to claim 1, wherein the first surface region is formed at a height position substantially equal to the second surface region. 6.   5. The optical modulator module according to claim 1, wherein the first surface region is formed at a position lower than the second surface region. 6.   8. The optical modulator module according to claim 1, wherein a concave portion is formed at a boundary between the first surface region and the second surface region. 9.   The said 1st surface area | region is formed in the approximate center of the said base in the waveguide direction of the said light, or the edge vicinity of the said base, The one of Claim 1 thru | or 8 characterized by the above-mentioned. Optical modulator module.

Images