JP4382064B2 - Optical waveguide module - Google Patents

Description

  The present invention generally relates to an optical waveguide module such as an optical modulator module or a polarization scrambler module in which an Au electrode is formed on a waveguide, and more particularly to an optical waveguide module having good high-frequency characteristics.

  In recent optical fiber communication systems, the modulation rate has increased with the increase in transmission rate. In direct intensity modulation of a laser diode, waveform chirping causes waveform distortion. In order to avoid this problem, there is an increasing expectation for an optical modulator module used as an external modulator.

  In addition, high-speed optical transmission systems have been put to practical use, but in high-speed optical transmission systems with long distances and large capacities, deflection-dependent gain and loss due to polarization hole burning and the like cause code error rate degradation. As a means for solving this problem, a polarization scrambler that changes the polarization state of transmitted light at high speed to make it non-polarized is effective.

As a practical external modulator, a Mach-Zehnder type optical modulator (LN modulator) using a dielectric crystal substrate such as lithium niobate (LiNbO ₃ ) has been developed. Carrier light of constant intensity from the light source is supplied to the LN modulator, and an optical signal whose intensity is modulated by a switching operation using optical interference is obtained.

The LN modulator chip forms a pair of optical waveguides that are coupled in the vicinity of both ends of the dielectric substrate made of Z-cut lithium niobate crystal by thermally diffusing titanium to increase the refractive index. A buffer layer made of SiO ₂ is formed thereon, and a signal electrode (traveling wave electrode) and a ground electrode are formed on the buffer layer corresponding to the optical waveguide.

  The signal light incident from one end of the optical waveguide is branched and propagates through the pair of optical waveguides. When a driving voltage is applied to a signal electrode formed on one optical waveguide, a phase difference is generated between both signal lights branched by the electro-optic effect.

  In the LN modulator, these signal lights are combined again and taken out as an optical signal output. An on / off pulse signal can be obtained by applying a drive voltage so that the phase difference between the signal light propagating through the pair of optical waveguides is, for example, 0 or π.

  In order to increase the modulation speed with an LN modulator, it is essential to obtain good high frequency characteristics (microwave attenuation characteristics and electrical reflection microwave characteristics).

  In the conventional LN modulator module, since the ground (ground) of the modulator chip is not completely removed, a dip in the microwave characteristic occurs at high frequencies, and it is difficult to realize sufficient broadband characteristics. There was a problem. This problem similarly occurs in other optical waveguide modules such as a polarization scrambler module or an optical phase modulator module.

  Accordingly, an object of the present invention is to provide an optical waveguide module that can exhibit good high-frequency characteristics.

According to the present invention, a bottom surface, a metal package having a chip insertion groove formed on the bottom surface, a substrate having an electro-optic effect, an optical waveguide formed on the substrate, and driving at an end of the substrate A signal electrode formed at a position where a signal is input and a phase difference is given to a signal propagating through the optical waveguide in a region between the first bent portion and the second bent portion; and a ground electrode formed on the substrate; A waveguide chip that includes the substrate, the optical waveguide, the signal electrode, and the ground electrode, and is inserted and fixed in the chip insertion groove of the metal package, and the ground electrode is the first electrode of the signal electrode. 1 and the second bending portion near and at the end near inputted the driving signals to the signal electrodes only, be characterized in that it is bonding connection by respective gold ribbon to the metal package Optical waveguide module is provided.

  In the present invention, since the ground electrode is bonded and connected to the metal package via the first and second ribbons in the vicinity of the first and second bent portions of the signal electrode, the dip of microwave characteristics at high frequency is effectively reduced. Therefore, the broadband property of the optical waveguide module can be realized.

  Referring to FIG. 1, the appearance of an optical modulator module to which the present invention is applied is shown. This optical modulator module modulates the light received at the input port 2 and outputs the modulated light from the output port 4. In this embodiment, ports 2 and 4 are each optical connectors.

  This optical modulator module has a metal package 6 in which a modulator chip (waveguide chip) described later is built. The metal package 6 is made of stainless steel, for example. At both ends of the package 6, pigtail type fiber assemblies 8 and 10 for connecting the ports 2 and 4 to the package 6 are provided.

  On one side of the package 6, coaxial connectors 12 and 14 for high-speed signals are provided. In order to fix the package 6 to a casing or the like (not shown), a metal fitting 18 is fixed to the bottom of the package 6.

  Referring to FIG. 2, a plan view of an optical modulator module according to an embodiment of the present invention is shown. In this figure, the optical connectors 2 and 4 and the fiber assemblies 8 and 10 shown in FIG. 1 are omitted.

  As best shown in FIGS. 4 and 5, chip insertion grooves 22 are formed in the bottom surface 20 of the metal package 6 in the longitudinal direction of the package. The modulator chip 24 is inserted into the chip insertion groove 22 and fixed by an adhesive 66 (see FIG. 5).

  As shown in FIGS. 2 and 4, a notch 62 is formed on the bottom surface 20 of the metal package 6 for releasing the adhesive when the modulator chip 24 is fixed. Furthermore, as shown in FIG. 5, a narrow groove 64 for releasing the adhesive is formed at one corner of the chip insertion groove 22.

The modulator chip 24 is made of a dielectric material having an electro-optic effect. In the present embodiment, the modulator chip 24 is made of lithium niobate (LiNbO ₃ ). The modulator chip 24 has a Mach-Zehnder type optical waveguide structure 26 indicated by a dotted line in FIG.

  The optical waveguide structure 26 includes an input optical waveguide 28, an output optical waveguide 30, and first and second optical waveguides 32 and 34 extending between the input optical waveguide 28 and the output optical waveguide 30.

The first and second optical waveguides 32 and 34 are connected to the input optical waveguide 28 by the Y branch 36 and are connected to the output optical waveguide 30 by the Y branch 38. The optical waveguide structure 26 is formed by thermally diffusing titanium (Ti) on a LiNbO ₃ substrate.

  The signal light supplied to the input optical waveguide 28 is guided by the first and second optical waveguides 32 and 34 with the optical power substantially divided into two at the Y branch 36. This guided light is coupled to the output optical waveguide 30 at the Y branch 38.

  Light is radiated from the Y branch 38 into the modulator chip 24 according to the phase difference between the light guided through the first and second optical waveguides 32 and 34 and the coupling mode in which the light is guided through the output optical waveguide 30. The radiation mode (leakage mode) is switched.

  In order to change the phase between the branched signal lights, a signal electrode (traveling wave electrode) 40 is provided on the first optical waveguide 32, and a ground electrode 42 is provided on the second optical waveguide 34. It has been. Further, another ground electrode 44 is formed on the substrate opposite to the ground electrode 42 with respect to the first optical waveguide 32.

The signal electrode 40 has two bent portions 40a and 40b that are substantially perpendicular. The signal electrode 40 and the ground electrodes 42 and 44 are formed, for example, by vapor deposition of gold (Au). Although not shown, an SiO ₂ buffer layer is formed under the electrodes 40, 42 and 44.

  The signal electrode 40 is bonded to the terminal pattern 12 a connected to the inner conductor of the coaxial connector 12 by a gold ribbon 46, and is bonded to the terminal pattern 14 a connected to the inner conductor of the coaxial connector 14 by a gold ribbon 48.

  On the other hand, the ground electrode 42 is bonded to the bottom surface 20 of the metal package 6 by two gold ribbons 50 and 52, and the ground electrode 44 is connected to the bottom surface 20 of the metal package 6 by four gold ribbons 54, 56, 58 and 60. Bonded connection.

  In the present invention, the positional relationship of the gold ribbons 58 and 60 with respect to the bent portions 40a and 40b of the signal electrode 40 is particularly important. That is, in order to realize a high-speed optical modulator module, it is important to completely ground the modulator chip 24. In order to realize this, the bending of the signal electrodes 40 of the gold ribbons 58 and 60 is important. It has been found that the positional relationship with respect to the parts 40a and 40b is important.

  As a result of various experiments by the present inventor, in order to reduce the dip of microwave characteristics at high frequencies, the longitudinal direction of the modulator chip 24 with respect to the bent portion 40a of the signal electrode 40 as shown in FIG. It is desirable that the gold ribbon 58 is bonded within a range of 5 mm (range A), and similarly, the gold ribbon 60 is bonded within a range of ± 0.5 mm in the longitudinal direction of the modulator chip 24 around the bent portion 40b.

  FIG. 6 shows the microwave characteristics of the embodiment of the present invention. That is, FIG. 6 shows the microwave characteristics of the optical modulator module when the gold ribbon 58 is bonded within the range of A in FIG. As is apparent from FIG. 6, the dip of microwave characteristics at high frequencies is effectively reduced.

  FIG. 7 shows the microwave characteristics of the optical modulator module when a gold ribbon is bonded at a predetermined distance from the bent portion of the signal electrode. That is, FIG. 7 shows the microwave characteristics when the gold ribbon 58 is bonded within the range of B and C in FIG.

  As is clear from observation of FIG. 7, a dip having a large microwave characteristic occurs at a high frequency. As is apparent from a comparison between FIG. 6 and FIG. 7, in the embodiment of the present invention shown in FIG. 6, the high-frequency micro characteristics are remarkably improved as compared with FIG.

  The gold ribbon used in this embodiment has a width of 0.4 to 0.5 mm. The modulator chip 24 has a cross-sectional shape of about 1 mm × 1 mm, and its length is about 4 to 5 cm.

  In order to realize sufficient grounding of the modulator chip 24, when the modulator chip 24 is inserted into the chip insertion groove 22 as shown in FIG. The distance G between the metal package 6 and the wall surface of the metal package 6 must be 0.5 mm or less. If the distance G is too large, it becomes difficult to sufficiently ground the modulator chip 24 by bonding a plurality of gold ribbons.

  The problem that the microwave characteristic dip occurs at a high frequency is not limited to the optical modulator module, but also occurs in other optical waveguide modules such as a polarization scrambler module or an optical phase modulator module.

  FIG. 9 is a schematic plan view of another embodiment of the present invention. This embodiment is an embodiment when the present invention is applied to a polarization scrambler or an optical phase modulator. The same components as those in the first embodiment shown in FIG.

  The optical phase modulator module has a linear optical waveguide 300 formed on a dielectric substrate and a signal electrode 40 formed on or adjacent to the optical waveguide 300.

  The signal light from the optical fiber 70 enters the optical waveguide 300, and a predetermined drive signal is input to the signal electrode 40, thereby changing the refractive index of the optical waveguide 300 and performing phase modulation of the signal light. The phase-modulated signal light is coupled to the optical fiber 71.

  The polarization scrambler module also includes a linear optical waveguide 300 formed on a dielectric substrate and a signal electrode 40 formed on or adjacent to the optical waveguide 300. Further, in the polarization scrambler module, a polarizer (not shown) is disposed on the input side of the optical waveguide 300 so as to be inclined by 45 ° with respect to the optical waveguide 300.

  The signal light from the optical fiber 70 enters the optical waveguide 300 via a polarizer (not shown), and a predetermined drive signal is input to the signal electrode 40 to rotate the polarization in the optical waveguide 300, Scramble the polarization of light. The scrambled signal light is coupled to the optical fiber 71.

  Also in these optical waveguide modules, ribbons 58 and 60 for connecting the ground electrode 44 and the metal package 6 are provided in the vicinity of the first and second bent portions of the signal electrode 40, so that the same as in the embodiment shown in FIG. Excellent characteristics can be obtained.

It is a top view which shows the external appearance of a modulator module. It is a top view of an embodiment of the present invention. It is a principal part enlarged view of embodiment of this invention. It is a principal part perspective view of this invention embodiment. It is a cross-sectional view of an embodiment of the present invention. It is a figure which shows the microwave characteristic of embodiment of this invention. It is a figure which shows the micro characteristic of the optical modulator module at the time of bonding a ribbon away from the bending part vicinity of a signal electrode. It is a figure which shows the bonding position of the ribbon at the time of the characteristic measurement of FIG.6 and FIG.7. It is a top view of other embodiments of the present invention.

Explanation of symbols

6 Metal package 20 Bottom surface 22 Chip insertion groove 24 Modulator chip 26 Mach-Zehnder waveguide structure 28 Input optical waveguide 30 Output optical waveguide 32 First optical waveguide 34 Second optical waveguide 40 Signal electrodes 42, 44 Ground electrodes 46, 48, 50 , 52,54,56,58,60 gold ribbon

Claims (6)

The bottom,
A metal package having a chip insertion groove formed on the bottom surface;
A substrate having an electro-optic effect;
An optical waveguide formed on the substrate;
A signal electrode formed at a position that gives a phase difference to a signal propagating through the optical waveguide in a region between the first bent portion and the second bent portion when a driving signal is input at an end of the substrate;
A ground electrode formed on the substrate;
Including the substrate, the optical waveguide, the signal electrode, the ground electrode, and a waveguide chip inserted and fixed in the chip insertion groove of the metal package,
The ground electrode is bonded to the metal package with a gold ribbon only in the vicinity of the first and second bent portions of the signal electrode and in the vicinity of the end where the drive signal is input to the signal electrode. An optical waveguide module characterized by that. The bottom,
A metal package having a chip insertion groove formed on the bottom surface;
A substrate having an electro-optic effect;
An optical waveguide structure having an input waveguide formed on the substrate, an output waveguide, and first and second waveguides extending between the input and output waveguides and connected to the input and output waveguides, respectively. When,
A signal electrode formed at a position where a driving signal is input at an end of the substrate and a phase difference is given to a signal propagating on the first waveguide in a region between the first bent portion and the second bent portion; ,
A first ground electrode formed on the second waveguide;
A second ground electrode formed on the substrate opposite to the first ground electrode with respect to the signal electrode;
A modulator chip including the substrate, the optical waveguide structure, the signal electrode, the first ground electrode, the second ground electrode, and being inserted and fixed in the chip insertion groove of the metal package;
The second ground electrode is bonded to the metal package with a gold ribbon only in the vicinity of the first and second bent portions of the signal electrode and in the vicinity of the end where the drive signal is input to the signal electrode. An optical modulator module connected.   Bonding connections in the vicinity of the first and second bent portions of the signal electrode are within a range of ± 0.5 mm in the longitudinal direction of the waveguide chip, centering on the first and second bent portions of the signal electrode, respectively. The optical waveguide module according to claim 1 or the optical modulator module according to claim 2 which is provided.   The optical waveguide module according to claim 1 or the optical modulator module according to claim 2, wherein the bottom surface of the metal package and the top surface of the waveguide chip are substantially at the same height.   3. The optical waveguide module according to claim 1, wherein the substrate is made of LiNbO3, and the optical waveguide is formed by thermally diffusing Ti in the LiNbO3 substrate.   2. The optical waveguide module according to claim 1, wherein a distance between the waveguide chip inserted and fixed in the chip insertion groove and a wall surface of the metal package defining the chip insertion groove is 0.5 mm or less. The optical modulator module according to claim 2.

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