JP3717639B2 - Optical modulator module - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention generally relates to an optical modulator module for modulating light from a light source, and more particularly to the structure of an optical modulator module for monitoring optical power.
[0002]
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.
[0003]
[Prior art]
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 having a 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.
[0004]
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.
[0005]
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.
[0006]
In the LN modulator, these signal lights are combined again and taken out as an optical signal output. If a drive voltage is applied so that the phase difference of the signal light propagating through the pair of optical waveguides becomes, for example, 0 or π, an on / off pulse signal can be obtained.
[0007]
A drawback of the LN modulator often pointed out is that an operating point shift due to temperature drift and DC drift occurs. In order to cope with this operating point shift, the power of the light output from the LN modulator is monitored, and control for stabilizing the operating point is performed based on the electric signal obtained as a result.
[0008]
[Problems to be solved by the invention]
In order to monitor the power of the light output from the optical modulator, a part thereof may be branched by an optical coupler and the branched light may be received by a photodetector. However, in this case, there is a problem that the power of the optical signal output from the optical modulator is reduced, the number of parts is increased, and the apparatus is increased in size.
[0009]
In view of such a point, radiated light (leakage light) radiated from the coupling portion of the waveguide is monitored using a photodetector at the end face of the waveguide, and in response to a change in an electrical signal output from the photodetector. For example, Japanese Patent Laid-Open No. 3-145623 proposes a technique for controlling the operating point of an optical modulator by changing a DC bias of an input electric signal applied to a traveling wave electrode (signal electrode).
[0010]
However, in the prior art, a large amount of man-hours are required for the loss of signal light due to a part of the main signal light being blocked by the chip carrier mounting the photodiode provided on the end face of the waveguide, and the alignment of the chip carrier mounting the photodiode. Had occurred.
[0011]
The present invention has been made in view of the above points, and the object of the present invention is not to cause loss in the main signal light and to realize reduction in the number of steps for alignment of the monitor chip carrier. It is to provide an optical modulator module that can.
[0012]
[Means for Solving the Problems]
According to the present invention, package and; and a modulator chip mounted on the package, the Mach-Zehnder type optical waveguide including a Y branch portion formed on the substrate and a Y coupling portion having an electrooptic effect, said Y A Ti highly doped region provided on both sides of the optical waveguide downstream of the coupling portion and guiding the radiated light emitted from the Y coupling portion to the lower side of the modulator chip, and a traveling wave electrode formed on the optical waveguide and a modulator chip having a ground electrode; equipped with the modulator photodetector for receiving the radiation emitted from the end face of the chip, depending on the radiation guided downward by the Ti highly doped region photodetector comprises a carrier that is mounted on the package so that the position below the said optical waveguide Te, the carrier, while being positioned at the bottom and two sides of the package, before the substrate Optical modulator, characterized in that the said optical waveguide end face is within the end surface is configured to cut out so as not to block the light path of the main signal light to be emitted is provided.
[0013]
By positioning the carrier on which the photodetector is mounted on the bottom surface and the two side surfaces of the package, the number of steps for carrier alignment can be reduced. Further, by providing the carrier with a notch, it is possible to prevent loss of the main signal light due to the carrier blocking part of the main signal light.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
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.
[0016]
This optical modulator module has a package 6 in which a modulator chip described later is built. 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. Reference numerals 3 and 5 denote optical fibers.
[0017]
High-speed signal connectors 12 and 14 are provided on one side surface of the package 6, and a low-speed signal connector 16 is provided on the other side surface. A metal fitting 18 is fixed to the bottom of the package 6 in order to fix the package 6 to a case or the like (not shown).
[0018]
Referring to FIG. 2, a plan view of the modulator chip 20 incorporated in the package 6 is shown. The modulator chip 20 has a Mach-Zehnder type optical waveguide 24 provided by a dielectric chip 22.
[0019]
Dielectric chip 22 is made of, for example, lithium niobate (LiNbO3), to form a result optical waveguide 24 to the thermal diffusion of titanium (Ti). The optical waveguide 24 has a Y branch portion 26 and a Y coupling portion 28. The optical waveguide 24 is branched into a pair of optical waveguides between the Y branch portion 26 and the Y coupling portion 28.
[0020]
The signal light supplied to the input end 36 is guided by the respective optical waveguides after the optical power is substantially bisected by the Y branch portion 26. The guided light is coupled by the Y coupling portion 28 and exits from the exit end 38.
[0021]
A coupling mode in which an output beam is obtained at the output end 38 in accordance with a phase difference of light guided through the pair of branch optical waveguides, and a radiation mode (leakage) in which light is emitted from the Y coupling portion 28 into the dielectric chip 22. Mode).
[0022]
In order to change the phase between the branched signal lights, a signal electrode 30 is provided on one optical waveguide, and ground electrodes 32 and 34 are provided on the other optical waveguide and on the dielectric chip 22. Is provided.
[0023]
The signal electrode 30 is a traveling wave type, and its input end is connected to the internal conductor of the connector 12 and its output end is connected to the internal conductor of the connector 14. The shields of the connectors 12 and 14 and the ground electrodes 32 and 34 are grounded via the package 6.
[0024]
The electrodes 30, 32, and 34 are formed, for example, by vapor deposition of gold (Au). Although not shown, a SiO ₂ buffer layer for temperature stabilization is provided between the dielectric chip 22 and the electrodes 30, 32, 34.
[0025]
Ti doped regions 40 and 42 are provided on the downstream side of the Y coupling portion 28. Ti doped regions 40 and 42 are provided to guide the radiated light emitted from the Y coupling portion 28 below the dielectric chip 22 as shown in FIG.
[0026]
Referring to FIG. 3, the signal light from the optical fiber 3 is coupled to the input end 36 of the optical waveguide 24 by the aspheric lens 7. On the other hand, the signal light beam 48 from the output end 38 of the optical waveguide 24 is coupled to the optical fiber 5 by the aspheric lens 9.
[0027]
The radiated light radiated from the Y coupling portion 28 is guided below the dielectric chip 22 by the Ti-doped region 40 and radiated as a radiated light beam 50 from the end face of the chip. The emitted light beam 50 is received by a monitoring photodiode (PD) 44 mounted on the chip carrier 46.
[0028]
The operating point of the modulator chip 20 is controlled by changing the DC bias of the electric signal applied to the signal electrode (traveling wave electrode) 30 by a signal control circuit (not shown) according to the change of the electric signal output from the photodiode 44. To do.
[0029]
Referring to FIG. 4, the positional relationship of the light receiving region 45 of the monitoring photodiode 44 with respect to the radiated light distribution is shown. In FIG. 4, 24 indicates an optical waveguide, and 50 indicates a radiation distribution. Reference numeral 46 denotes a chip carrier, and reference numeral 45 denotes a light receiving area by the monitoring photodiode 44.
[0030]
As is clear from this figure, the monitor area 45 of the emitted light can be disposed relatively below the modulator chip 20, and sufficient light receiving sensitivity can be obtained at this position.
[0031]
Next, a first embodiment of the optical modulator module of the present invention will be described with reference to FIGS. The modulator chip 20 shown in FIG. 2 is mounted on the bottom surface of the package 6. The package 6 is formed with an opening 52 for extracting output light from the modulator chip 20 and a recess 54 for mounting the chip carrier 46.
[0032]
The reason why the concave portion 54 is formed on the bottom surface of the package 6 is that the chip carrier 46 needs to have a certain size from the viewpoint of handleability, but the photodiode chip (PD chip) 44 mounted on the chip carrier 46 has a certain size. This is to make the height coincide with the position where the radiation light output from the modulator chip 20 can be received.
[0033]
The chip carrier 46 is made of ceramic, and a gold pattern 56 is deposited on the surface thereof as seen in FIG. The PD chip 44 and the gold pattern 56 are bonded by a gold wire 58, and the terminal 60 and the gold pattern 56 are bonded by a gold wire 62. Terminal 60 is connected to connector 16.
[0034]
In this embodiment, the notch 46a is formed in the chip carrier 46 so that a part of the chip carrier 46 has a substantially trapezoidal cross section. Since the notches 46a are formed, the main signal light output from the modulator chip 20 is not blocked by the chip carrier 46, and loss of the main signal light due to the chip carrier is prevented. The cutout 46a may be any cutout as long as it does not block the main signal light.
[0035]
Further, since the shape and size of the chip carrier 46 with respect to the shape and size of the package 6 are selected in advance, the chip carrier 46 can be positioned on the bottom surface and the two side surfaces of the package 6, and the alignment man-hours of the chip carrier 46 can be reduced. It can be greatly reduced.
[0036]
Referring to FIG. 7, a plan view of the second embodiment of the present invention is shown. 8 is a cross-sectional view taken along line 8-8 in FIG. In the present embodiment, even when the chip carrier 46A is formed thin and the mounting surface of the modulator chip 20 and the mounting surface of the chip carrier 46A are set to the same height, the chip carrier 46A is output from the modulator chip 20. The signal light is not blocked.
[0037]
For example, if the height of the modulator chip 20 is about 1 mm, the thickness of the chip carrier 46A is desirably about 500 μm or less. When the chip carrier 46A is thinned as described above, the handling property is hindered to some extent, but it is not necessary to form the recess 54 in the package 6 as in the first embodiment, so the structure of the package 6 is simplified.
[0038]
Also in this embodiment, since the chip carrier 46A does not block the main signal light output from the modulator chip 20, the chip carrier 46A is positioned on the bottom surface and the two side surfaces of the package 6, so that the chip carrier 46A alignment man-hours can be greatly reduced.
[0039]
Referring to FIG. 9, a plan view of a third embodiment of the present invention is shown. 10 is a cross-sectional view taken along line 10-10 of FIG. In the present embodiment, the side wall 6a of the package 6 that defines the opening 52 is formed thick, and the width of the chip carrier 46B is about 500 μm or less.
[0040]
As described above, even when the package sidewall 6a is formed thick and the width of the chip carrier 46B is narrowed, the same effects as those of the first and second embodiments described above can be obtained.
[0041]
【The invention's effect】
According to the present invention, loss of signal light due to the shape of the carrier on which the monitoring photodiode is mounted can be prevented, and the number of alignment steps when mounting the carrier on the package can be reduced.
[Brief description of the drawings]
FIG. 1 is a plan view showing an external appearance of an optical modulator module.
FIG. 2 is a plan view of a modulator chip.
FIG. 3 is a diagram showing a schematic configuration of an optical modulator module.
FIG. 4 is a diagram showing a positional relationship of a monitor PD with respect to a radiation distribution.
FIG. 5 is a plan view of the first embodiment of the present invention.
6 is a cross-sectional view taken along line 6-6 of FIG.
FIG. 7 is a plan view of a second embodiment of the present invention.
8 is a cross-sectional view taken along line 8-8 in FIG.
FIG. 9 is a plan view of a third embodiment of the present invention.
10 is a cross-sectional view taken along line 10-10 of FIG.
[Explanation of symbols]
6 Package 20 Modulator chip 24 Optical waveguide 26 Optical branching portion 28 Optical coupling portion 30 Signal electrodes 32 and 34 Ground electrodes 40 and 42 Ti doped region 44 PD chip for monitoring 46 Chip carrier 46a Notch

Claims (3)

With package;
A modulator chip mounted in the package, the Mach-Zehnder type optical waveguide including a Y-branch portion and a Y-coupling portion formed on a substrate having an electro-optic effect, and the optical waveguide downstream of the Y-coupling portion. A modulator having a Ti highly doped region provided on both sides of a waveguide and guiding radiation emitted from the Y-coupled portion below the modulator chip, and a traveling wave electrode and a ground electrode formed on the optical waveguide With chips;
Equipped with a photodetector for receiving the radiation emitted from the end face of the modulator chip, the photodetector in response to the emitted light guided downward by the Ti highly doped region from said optical waveguide Comprising a carrier mounted in the package to be in a lower position ;
Said carrier while being positioned at the bottom and two sides of the package, a configuration in which notched so as not to block the light path of the main signal light emitted from the optical waveguide end face is within the end face of the substrate An optical modulator module.   2. The optical modulator module according to claim 1, wherein a bottom surface of the package has a recess having a predetermined depth, and the carrier is mounted on the recess. The optical modulator module according to any of claims 1-2 wherein the carrier is characterized in that it is formed of ceramic.

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