U.S. patent application number 15/924378 was filed with the patent office on 2018-10-04 for connection structure between optical device and circuit substrate, and optical transmission apparatus using the same.
The applicant listed for this patent is Sumitomo Osaka Cement Co., Ltd. Invention is credited to Toshio KATAOKA, Kei KATOU.
Application Number | 20180288874 15/924378 |
Document ID | / |
Family ID | 63638805 |
Filed Date | 2018-10-04 |
United States Patent
Application |
20180288874 |
Kind Code |
A1 |
KATAOKA; Toshio ; et
al. |
October 4, 2018 |
CONNECTION STRUCTURE BETWEEN OPTICAL DEVICE AND CIRCUIT SUBSTRATE,
AND OPTICAL TRANSMISSION APPARATUS USING THE SAME
Abstract
An optical device includes a connection pad, which is connected
to a conductor pattern on the circuit substrate, at one edge. The
connection pad includes one ground pad, and two or more signal pads
between which the ground pad is interposed from its both sides. The
ground pad includes a concave portion including an opening at the
edge. The circuit substrate is provided with a metal columnar
member in the conductor pattern to which the ground pad is
connected. The conductor pattern and the connection pad are fixed
to each other with solder in a state in which the columnar member
is fitted into the concave portion. Solder, which gradually rises
from the ground pattern to a lateral surface of the columnar
member, is formed between the columnar member and the ground
pattern that is formed in the flexible printed circuit.
Inventors: |
KATAOKA; Toshio; (TOKYO,
JP) ; KATOU; Kei; (TOKYO, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sumitomo Osaka Cement Co., Ltd |
Tokyo |
|
JP |
|
|
Family ID: |
63638805 |
Appl. No.: |
15/924378 |
Filed: |
March 19, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01R 12/65 20130101;
H05K 1/118 20130101; H05K 3/363 20130101; H05K 2201/09736 20130101;
H05K 1/0219 20130101; H05K 2201/09727 20130101; H05K 2201/0969
20130101; G02F 2001/212 20130101; H05K 1/113 20130101; H05K
2201/09336 20130101; H05K 2201/09481 20130101; H05K 2203/167
20130101; H05K 2201/10303 20130101; G02F 1/2255 20130101; H05K
2201/10121 20130101; H01R 12/69 20130101; H01R 12/58 20130101; H05K
2201/09181 20130101; H05K 1/147 20130101; H01R 12/62 20130101; H05K
2201/09354 20130101; H05K 1/0225 20130101; H01R 12/592
20130101 |
International
Class: |
H05K 1/14 20060101
H05K001/14; H05K 1/11 20060101 H05K001/11; H05K 1/02 20060101
H05K001/02; H01R 12/62 20060101 H01R012/62; H01R 12/69 20060101
H01R012/69 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2017 |
JP |
2017-067208 |
Claims
1. A connection structure between an optical device and a circuit
substrate, wherein the optical device includes a flexible printed
circuit including a conductive pattern to which an electrode
configured to input a radio-frequency signal to the optical device
is connected, in the flexible printed circuit, connection pads,
which are connected to a conductor pattern on the circuit
substrate, are arranged at one edge, the connection pads include at
least one ground pad, and at least two signal pads between which
the ground pad is interposed from its both sides, and at least one
concave portion including an opening formed in the one edge is
provided at a portion, at which the ground pad is formed, in the
one edge of the flexible printed circuit, and in the circuit
substrate, the conductive pattern, to which the ground pad is
connected, on a surface of the circuit substrate, is provided with
a columnar member that extends from the conductor pattern to an
upper side of a substrate surface of the circuit substrate and is
formed from a metal, the conductor pattern and the connection pads
are fixed to each other with solder in a state in which the
columnar member is fitted into the concave portion, and solder,
which gradually rises from the ground pattern to a lateral surface
of the columnar member, is formed between the columnar member and
the ground pattern that is formed in the flexible printed
circuit.
2. The connection structure according to claim 1, wherein at least
two concave portions are provided.
3. The connection structure according to claim 1, wherein the
columnar member extends to an upper side of a plate surface of the
flexible printed circuit through the concave portion, and a
protrusion length of the columnar member from the plate surface is
1 mm or greater.
4. The connection structure according to claim 1, wherein the
columnar member includes a portion that is bent at an upper side of
a substrate surface of the circuit substrate and extends along the
substrate surface, a portion including the one edge of the flexible
printed circuit is disposed to be interposed between the portion
that extends along the substrate surface and the substrate surface,
and solder, which gradually rises from the ground pattern to the
lateral surface of the columnar member, is formed between the
portion that extends along the substrate surface and the substrate
surface.
5. The connection structure according to claim 1, wherein the
concave portion has a semi-circular shape in a plan view, and the
columnar member is a pin that has a circular cross-section and is
inserted into via or a through-hole that is provided in the circuit
substrate.
6. An optical transmission apparatus, comprising: an optical
modulator that is an optical device including a flexible printed
circuit; and a circuit substrate on which a circuit that drives the
optical modulator is constructed, wherein the flexible printed
circuit and the circuit substrate are connected to each other with
the connection structure according to claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of Japanese Patent
Application No. 2017-067208 filed Mar. 30, 2017, the disclosure of
which is herein incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present invention relates to a connection structure
between an optical device such as an optical modulator and a
circuit substrate on which an electronic circuit configured to
drive the optical device is mounted, and an optical transmission
apparatus using the connection structure, and more particularly, to
a connection structure between the optical device and the circuit
substrate through a flexible printed circuit of the optical device,
and an optical transmission apparatus using the connection
structure.
Description of Related Art
[0003] In high-frequency/large-capacity optical fiber communication
systems, optical modulators embedded with waveguide-type optical
modulation element are frequently used. Among these, optical
modulation elements in which LiNbO.sub.3 (hereinafter, also
referred to as "LN") having an electro-optic effect is used for
substrates cause only a small optical loss and are capable of
realizing broad band optical modulation characteristics and thus
are widely used for high-frequency/large-capacity optical fiber
communication systems.
[0004] The optical modulation element using an LN substrate is
provided with a Mach-Zehnder optical waveguide, and an electrode
(RF electrode) configured to apply a radio-frequency signal that is
a modulation signal to the optical waveguide. The electrode is
connected to a circuit substrate (hereinafter, abbreviated as a
circuit substrate), on which an electronic circuit that allows the
optical modulator to operate a modulation operation is mounted, via
lead pins or a connector that is provided in a housing of the
optical modulator in which the optical modulation element is
housed.
[0005] With regard to a modulation form in the optical fiber
communication systems, a transmission format such as quadrature
phase shift keying (QPSK) and dual polarization-quadrature phase
shift keying (DP-QPSK), which use multi-level modulation or in
which polarization multiplexing is introduced to the multi-level
modulation, becomes a main stream in pursuit of a recent increase
in transmission capacity. The transmission format is used in a
basic optical transmission network, and is also introduced to a
metro network.
[0006] An optical modulator (QPSK optical modulator) that performs
QPSK modulation or an optical modulator (DP-QPSK optical modulator)
that performs DP-QPSK modulation includes a plurality of
Mach-Zehnder optical waveguides having a box structure, and a
plurality of RF electrodes (for example, refer to Patent Literature
1). Accordingly, the size of the housing of the optical modulator
tends to increase. According to this, particularly, there is a
strong demand for miniaturization.
[0007] As one countermeasure for coping with the demand for
miniaturization, in the related art, there is suggested an optical
modulator in which a push-on type coaxial connector provided in a
housing of the optical modulator as an interface of the RF
electrodes is substituted with lead pins similar to an interface of
bias electrodes, and a flexible printed circuit (FPC) configured to
electrically connect the lead pins and an external circuit
substrate to each other is provided.
[0008] For example, in the DP-QPSK optical modulator, an optical
modulation element including four Mach-Zehnder optical waveguides
each including an RF electrode is used. In this case, in a case
where four push-on type coaxial connectors are provided in the
housing of the optical modulator, it is difficult to avoid an
increase in size of the housing, but when using the lead pins and
the FPC instead of the coaxial connectors, it is possible to
realize miniaturization.
[0009] In addition, the lead pins of the housing of the optical
modulator, and a circuit substrate on which an electronic circuit
configured to allow the optical modulator to perform a modulation
operation is mounted are connected to each other through the FPC.
Accordingly, it is not necessary to perform coaxial cable
excess-length processing that is used in the related art, and thus
it is possible to reduce a mounting space of the optical modulator
in the optical transmission apparatus.
[0010] For example, the FPC that is used in the optical modulator
is prepared by using a flexible polyimide-based material as a
substrate (hereinafter, referred to as "FPC substrate"), and each
of a plurality of through-holes provided in the vicinity of one end
is electrically connected to each of pads provided on the other end
through a wiring pattern. In addition, a plurality of lead pins,
which protrude from a bottom surface or a lateral surface of the
housing of the optical modulator, are respectively inserted into
the plurality of through-holes, and are fixed and electrically
connected to the plurality of through-holes, for example, by using
solder. The plurality of pads are fixed and connected to the
circuit substrate, for example, by using solder. According to this,
a radio-frequency signal, which is applied from the pads on the
circuit substrate, is applied to a corresponding RF electrode of
the optical modulation element through corresponding through-hole
and lead pin, and thus high-frequency optical modulation is
performed.
[0011] In the optical modulator using the FPC, as described above,
it is possible to miniaturize the housing, and it is also possible
to reduce a mounting space of the optical modulator on the circuit
substrate, and thus it is possible to greatly contribute to
miniaturization of the optical transmission apparatus.
[0012] FIG. 7A, FIG. 7B, and FIG. 7C are views illustrating a
configuration of a DP-QPSK optical modulator with the FPC in the
related art. FIG. 7A is a top view of the DP-QPSK optical
modulator, FIG. 7B is a front view thereof, and FIG. 7C is a bottom
view thereof. A DP-QPSK optical modulator 700 includes an optical
modulation element 702, a housing 704 that houses the optical
modulation element 702, a flexible printed circuit (FPC) 706, an
optical fiber 710 through which a light beam is input to the
optical modulation element 702, an optical fiber 708 that guides
the light beam output from the optical modulation element 702 to
the outside of the housing 704.
[0013] The housing 704 is provided with four lead pins 720, 722,
724, and 726 which are respectively connected to four RF electrodes
(not illustrated) of the optical modulation element 702, and the
lead pins 720, 722, 724, and 726 are inserted into the following
through-holes 820, 822, 824, and 826 which are provided in the FPC
706, and are fixed and electrically connected, for example, with
solder.
[0014] FIG. 8 is a view illustrating a configuration of the FPC
706. FIG. 8A and FIG. 8B illustrate two opposite surfaces of the
FPC 706. Here, it is assumed that a surface illustrated in FIG. 8A
is a front surface, and a surface illustrated in FIG. 8B is a rear
surface. The surface illustrated in FIG. 8A corresponds to a
surface of the FPC 706 illustrated in FIG. 7C.
[0015] In the vicinity of one side 802 on a lower side on the front
surface of the FPC 706 illustrated in FIG. 8A, four pads for signal
(signal pads) 810, 812, 814, and 816 are provided in parallel along
a direction of the one side 802. In addition, on another side 804
side that is opposite to the side 802, for example, four
through-holes 820, 822, 824, and 826 are provided in parallel, for
example, along a direction of the side 804. In addition, the four
signal pads 810, 812, 814, and 816 are electrically connected to
the through-holes 820, 822, 824, and 826 by wiring patterns 830,
832, 834, and 836, respectively.
[0016] In addition, on the front surface of the FPC 706, pads for
ground (ground pads) 840a and 840b, 842a and 842b, 844a and 844b,
and 846a and 846b are provided in parallel at positions at which
each of the signal pads 810, 812, 814, and 816 is interposed
between each pair of the ground pads from both sides along a
direction of the side 802. The ground pads 840a, 840b, 842a, 842b,
844a, 844b, 846a, and 846b are respectively connected to ground
patterns 870a, 870b, 872a, 872b, 874a, 874b, 876a, and 876b (to be
described later) on the rear surface through via-holes.
[0017] On the other hand, a ground plane 850 is formed on the rear
surface of the FPC 706 illustrated in FIG. 8B, and the wiring
patterns 830, 832, 834, and 836 on the front surface constitute a
grounded coplanar waveguide (GCPW) in combination with the ground
plane 850 on the rear surface. In addition, the ground plane 850
includes the ground patterns 870a, 870b, 872a, 872b, 874a, 874b,
876a, and 876b which extend to positions corresponding to the
ground pads 840a, 840b, 842a, 842b, 844a, 844b, 846a, and 846b on
the front surface.
[0018] In addition, on the rear surface of the FPC 706, signal pads
860, 862, 864, and 866 are provided at positions corresponding to
the signal pads 810, 812, 814, and 816 on the front surface in the
same size as that of the signal pads 810, 812, 814, and 816. The
signal pads 860, 862, 864, and 866 and the signal pads signal pads
810, 812, 814, and 816 are electrically connected to each other
through via-holes.
[0019] In addition, when mounting the optical modulator 700 in the
optical transmission apparatus, the signal pads 810, 812, 814, and
816 and the ground pads 840a, 840b, 842a, 842b, 844a, 844b, 846a,
and 846b are fixed and electrically connected to corresponding pads
provided in a circuit substrate at the inside of the optical
transmission apparatus, for example, with solder. According to
this, the RF electrode of the optical modulation element 702 housed
in the optical modulator 700, and signal lines of an electronic
circuit provided on the circuit substrate are electrically
connected to each other.
[0020] FIG. 9 is a view illustrating a configuration of a circuit
substrate 900 that is an example of the circuit substrate that is
used in the optical transmission apparatus as described above.
Circuit signal pads 910, 912, 914, and 916, and circuit ground pads
940a, 940b, 942a, 942b, 944a, 944b, 946a, and 946b, to which the
signal pads 810, 812, 814, and 816, and the ground pads 840a, 840b,
842a, 842b, 844a, 844b, 846a, and 846b on the front surface of the
FPC 706 are respectively connected, are provided in parallel on one
side 902 of the circuit substrate 900.
[0021] The circuit signal pads 910, 912, 914, and 916, and the
circuit ground pads 940a, 940b, 942a, 942b, 944a, 944b, 946a, and
946b are provided at positions corresponding to the signal pads
810, 812, 814, and 816, and the ground pads 840a, 840b, 842a, 842b,
844a, 844b, 846a, and 846b, which are disposed on the pads, of the
FPC 706. In addition, it is not necessary for the circuit signal
pad 910 and the like, and the circuit ground pad 940a and the like
to have the same size as that of the signal pad 810 and the like
and the ground pad 840a and the like of the FPC 706. For example,
the width of the circuit signal pad 910 and the like and the
circuit ground pad 940a and the like may be configured to be
narrower or wider than the width of the signal pad 810 and the like
and the ground pad 840a and the like from the viewpoint of
impedance matching between signal lines when the circuit substrate
900 and the FPC 706 are connected to each other.
[0022] Furthermore, FIG. 9 illustrates only a portion in which the
circuit signal pads 910, 912, 914, and 916 and the circuit ground
pads 940a, 940b, 942a, 942b, 944a, 944b, 946a, and 946b are formed
and a peripheral portion thereof in the circuit substrate 900 for
easy understanding while avoiding redundant description. In
addition, various patterns, which constitute an electronic circuit,
maybe provided on the circuit substrate 900. However, for the same
reason, FIG. 9 illustrates only the circuit signal pads 910, 912,
914, and 916, and the circuit ground pads 940a, 940b, 942a, 942b,
944a, 944b, 946a, and 946b to which the signal pads 810, 812, 814,
and 816, and the ground pads 840a, 840b, 842a, 842b, 844a, 844b,
846a, and 846b of the FPC 706 are respectively connected, and
description of the other patterns, which are led to the circuit
signal pads and the circuit ground pads, on the circuit substrate
900 is omitted.
[0023] FIGS. 10A and 10B are views illustrating an example of a
connection structure between the optical modulator 700 and the
circuit substrate 900 in the related art. FIG. 10A is a view when
seen from an upper surface direction of the optical modulator 700,
and FIG. 10B is a view when seen from an X-X cross-sectional arrow
direction in FIG. 10A. In addition, FIG. 11 is a view when seen
from a XI-XI cross-sectional arrow direction in FIG. 10A.
[0024] As illustrated in FIG. 10A, the FPC 706 of the optical
modulator 700 extends to a left side in the drawing, and as
illustrated in FIG. 10B, a left end is bent in an oblique
lower-left direction in the drawing to come into contact with the
circuit substrate 900. According to this, as illustrated in FIG.
11, the signal pads 810, 812, 814, and 816, and the ground pads
840a, 840b, 842a, 842b, 844a, 844b, 846a, and 846b of the FPC 706
are respectively pressed to the circuit signal pads 910, 912, 914,
and 916, and the circuit ground pads 940a, 940b, 942a, 942b, 944a,
944b, 946a, and 946b, and are fixed and electrically connected, for
example, with solder.
[0025] In addition, typically, connection between corresponding
pads in the optical modulator 700 and the circuit substrate 900 is
performed through manual work by using a soldering iron and the
like in a state in which the FPC 706 is simply pressed to a
substrate surface of the circuit substrate 900 to be maintained.
According to this, in the connection structure illustrated in FIGS.
10A, 10B, and 11 in the related art, a relative position of the FPC
706 with respect to the circuit substrate 900 is likely to deviate
in connection work.
[0026] As described above, a modulation operation required for the
optical modulator is performed at a higher frequency and a broader
bandwidth in accordance with an increase in optical transmission
capacity required for the optical fiber communication system, and
in a case of performing a complicate modulation operation as in the
DP-QPSK as means for realizing the modulation operation and the
like, the number of signal lines which are input to the optical
modulator, that is, the number of pads provided in the FPC
increases. In contrast, a demand for miniaturization in size of the
optical modulator is not changed, and thus the size of the pads to
be formed on the FPC is reduced in accordance with the increase in
the number of necessary electrodes as described above. As one
example, in a typical DP-QPSK optical modulator, for example, the
number of signal electrodes is four. In addition, with regard to
the size of the pads formed on the FPC, the width thereof is
several hundreds of micrometers, and the length thereof is
approximately 1.5 mm.
[0027] More specifically, for example, in The optical
internetworking forum (OIF) that is a business organization in an
optical communication field, as an FPC that is provided in an
optical modulator that performs orthogonal phase modulation of
polarization multiplexing, it is recommended that an interval
between adjacent signal pads is set to approximately 4 mm, the
width of the signal pads (length in a direction of the side 802 in
FIG. 8A) is set to approximately 350.+-.50 .mu.m, and the width of
the circuit signal pads of the circuit substrate is set to
approximately 400 .mu.m (OIF-PMQ-TX-01.2 as materials published by
OIF). In addition, in the signal pads and the circuit signal pads
which have the above-described width, the amount of deviation of
the central lines when connecting the signal pads and the circuit
signal pads to each other is recommended to be 100 .mu.m or
less.
[0028] However, in the connection structure of the related art,
relative positioning of the FPC 706 with respect to the circuit
substrate 900 is performed by simply pressing the FPC 706 to the
circuit substrate 900 as described above. Therefore, it may be
difficult to realize the amount of positional deviation between the
signal pads and the circuit signal pads in a predetermined
permissible range of the order of 0.1 mm with satisfactory accuracy
and satisfactory reproducibility.
[0029] In addition, in a case where the interval between the
adjacent signal pads is set to an interval of the order of mm as in
the above-described OIF recommendation, an influence by cross-talk
between the adjacent signal pads on a modulation operation is not
negligible. In addition, in a case where the number of
radio-frequency signals to be input to the optical modulator
increases in correspondence with an increase in the transmission
capacity in the future, the interval between the adjacent signal
pads gradually decreases, and thus the influence by the cross-talk
maybe a significant problem on securement of optical transmission
quality.
SUMMARY OF THE INVENTION
[0030] From the background, in a connection structure between an
optical device such as an optical modulator that operates by using
radio-frequency signals, and a circuit substrate, it is required to
effectively reduce cross-talk between adjacent signal pads while
performing connection between pads in a flexible printed circuit
provided in the optical device and a circuit substrate with high
positional accuracy.
[0031] According to an aspect of the invention, there is provided a
connection structure between an optical device and a circuit
substrate. The optical device includes a flexible printed circuit
including a conductive pattern to which an electrode configured to
input a radio-frequency signal to the optical device is connected.
In the flexible printed circuit, connection pads, which are
connected to a conductor pattern on the circuit substrate, are
arranged at one edge, and the connection pads include at least one
ground pad, and at least two signal pads between which the ground
pad is interposed from its both sides. In addition, at least one
concave portion including an opening formed in the one edge is
provided at a portion, at which the ground pad is formed, in the
one edge of the flexible printed circuit. In the circuit substrate,
the conductive pattern, to which the ground pad is connected, on a
surface of the circuit substrate, is provided with a columnar
member that extends from the conductor pattern to an upper side of
a substrate surface of the circuit substrate and is formed from a
metal. In addition, the conductor pattern and the connection pads
are fixed to each other with solder in a state in which the
columnar member is fitted into the concave portion, and solder,
which gradually rises from the ground pattern to a lateral surface
of the columnar member, is formed between the columnar member and
the ground pattern that is formed in the flexible printed
circuit.
[0032] According to another aspect of the invention, at least two
concave portions may be provided.
[0033] According to still another aspect of the invention, the
columnar member may extend to an upper side of a plate surface of
the flexible printed circuit through the concave portion, and a
protrusion length of the columnar member from the plate surface may
be 1 mm or greater.
[0034] According to still another aspect of the invention, the
columnar member may include a portion that is bent at an upper side
of a substrate surface of the circuit substrate and extends along
the substrate surface, a portion including the one edge of the
flexible printed circuit may be disposed to be interposed between
the portion that extends along the substrate surface and the
substrate surface, and solder, which gradually rises from the
ground pattern to the lateral surface of the columnar member, maybe
formed between the portion that extends along the substrate surface
and the substrate surface.
[0035] According to still another aspect of the invention, the
concave portion may have a semi-circular shape in a plan view, and
the columnar metal maybe a pin that has a circular cross-section
and is inserted into a via or a through-hole that is provided in
the circuit substrate.
[0036] According to still another aspect of the invention, there is
provided an optical transmission apparatus. The optical
transmission apparatus includes: an optical modulator that is an
optical device including a flexible printed circuit; and a circuit
substrate on which a circuit that drives the optical modulator is
constructed. The flexible printed circuit and the circuit substrate
are connected to each other with the connection structure according
to any one of the aspects.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is a view illustrating a configuration of an optical
transmission apparatus that employs a connection structure between
an optical modulator that is an optical device and a circuit
substrate according to an embodiment of the invention;
[0038] FIG. 2A is a view illustrating a configuration of the
optical modulator illustrated in FIG. 1;
[0039] FIG. 2B is a view illustrating the configuration of the
optical modulator illustrated in FIG. 1;
[0040] FIG. 2C is a view illustrating the configuration of the
optical modulator illustrated in FIG. 1;
[0041] FIG. 3A is a view illustrating a configuration of a front
surface of a flexible printed circuit that is provided in the
optical modulator illustrated in FIGS. 2A, 2B, and 2C;
[0042] FIG. 3B is a view illustrating a configuration of a rear
surface of the flexible printed circuit that is provided in the
optical modulator illustrated in FIGS. 2A, 2B, and 2C;
[0043] FIG. 4 is a partial detail view of the circuit substrate
illustrated in FIG. 1;
[0044] FIG. 5A is a view illustrating the connection structure
between the optical modulator and the circuit substrate as
illustrated in FIG. 1;
[0045] FIG. 5B is a II-II cross-sectional view of the connection
structure illustrated in FIG. 5A;
[0046] FIG. 6 is a modification example of the connection structure
illustrated in FIG. 5B;
[0047] FIG. 7A is a view illustrating a configuration of an optical
modulator in the related art;
[0048] FIG. 7B is a view illustrating the configuration of the
optical modulator in the related art;
[0049] FIG. 7C is a view illustrating the configuration of the
optical modulator in the related art;
[0050] FIG. 8A is a view illustrating a configuration of a front
surface of a flexible printed circuit that is provided in the
optical modulator illustrated in FIGS. 7A, 7B, and 7C in the
related art;
[0051] FIG. 8B is a view illustrating a configuration of a rear
surface of the flexible printed circuit that is provided in the
optical modulator illustrated in FIGS. 7A, 7B, and 7C in the
related art;
[0052] FIG. 9 is a partial detail view of a circuit substrate in
the related art to which the flexible printed circuit provided in
the optical modulator illustrated in FIGS. 7A, 7B, and 7C in the
related art is connected;
[0053] FIG. 10A is a view illustrating a connection structure
between the optical modulator and the circuit substrate in the
related art;
[0054] FIG. 10B is a view illustrating the connection structure
between the optical modulator and the circuit substrate in the
related art as illustrated in FIG. 10A when seen from an X-X
cross-sectional arrow direction; and
[0055] FIG. 11 is a view illustrating the connection structure
between the optical modulator and the circuit substrate in the
related art as illustrated in FIG. 10A when seen from a XI-XI
cross-sectional arrow direction.
DETAILED DESCRIPTION OF THE INVENTION
[0056] Hereinafter, an embodiment of the invention will be
described with reference to the accompanying drawings. Furthermore,
in this embodiment, a connection structure between an optical
modulator and a circuit substrate is illustrated as an example, but
the connection structure of the invention is not limited thereto,
and is widely applicable to connection between an arbitrary optical
device (for example, an optical switch) to which a plurality of
radio-frequency signals are input for an operation, and a circuit
substrate.
[0057] FIG. 1 is a view illustrating a configuration of an optical
transmission apparatus that employs the connection structure
between the optical modulator and the circuit substrate according
to an embodiment of the invention. An optical transmission
apparatus 100 includes an optical modulator 102, a circuit
substrate 104 that outputs a radio-frequency signal for driving the
optical modulator 102, and a light source 106 that is mounted on
the circuit substrate 104. The optical modulator 102 includes a
flexible printed circuit (FPC) 108 configured to input a
radio-frequency signal. As to be described later, pads provided on
the FPC 108 and pads provided on the circuit substrate are
soldered, and thus the radio-frequency signal output from the
circuit substrate 104 is input to the optical modulator 102. In
response to the radio-frequency signal, the optical modulator 102
modulates a light beam input from the light source 106, and outputs
the modulated light beam. Then, the light beam that is output is
input to an optical transmission path fiber (not illustrated).
[0058] Furthermore, in the following description, it is assumed
that the connection structure between the optical modulator 102 and
the circuit substrate 104 represents a connection structure between
the FPC 108 and the circuit substrate 104 in a portion A in the
drawing at which the FPC 108 of the optical modulator 102 and the
circuit substrate 104 are connected to each other.
[0059] FIGS. 2A, 2B, and 2C are views illustrating a configuration
of the optical modulator 102.
[0060] The optical modulator 102 includes an optical modulation
element 202, a housing 204 that houses the optical modulation
element 202, the FPC 108, an optical fiber 208 that inputs a light
beam from the light source 106 to the optical modulation element
202, and an optical fiber 210 that guides the light beam output
from the optical modulation element 202 to the outside of the
housing 204.
[0061] For example, the optical modulation element 202 is a DP-QPSK
optical modulator including four Mach-Zehnder optical waveguides
provided on an LN substrate, and four radio-frequency electrodes
(RF electrodes) which are respectively provided on the Mach-Zehnder
optical waveguides and modulate a light wave that propagates
through the inside of the optical waveguides. Two light beams
output from the optical modulation element 202 are combined into
one light beam, for example, by a lens optical system (not
illustrated), and the resultant light beam is guided to the outside
of the housing 204 through the optical fiber 210.
[0062] The housing 204 includes four lead pins 220, 222, 224, and
226 which are respectively connected to four RF electrodes (not
illustrated) which are provided in the optical modulation element
202. The lead pins 220, 222, 224, and 226 provided in the housing
204 are inserted into the following through-holes 320, 322, 324,
and 326 which are provided in the FPC 108, and the through-holes
320, 322, 324, and 326 and the lead pins 220, 222, 224, and 226 are
connected and fixed to each other, for example, with solder.
[0063] FIGS. 3A and 3B are views illustrating a configuration of
the FPC 108. Here, FIG. 3A is a view illustrating a configuration
of one surface (referred to as a front surface) of the FPC 108 that
is in contact with the circuit substrate 104, and FIG. 3B is a view
illustrating a configuration of the other surface (referred to as a
rear surface) of the FPC 108 which is opposite to the one
surface.
[0064] For example, the FPC 108 is prepared by using a substrate
(hereinafter, referred to as an FPC substrate) of which a main
material is polyimide. For example, the FPC 108 is constituted in a
rectangular shape in a plan view. However, the shape of the FPC 108
in a plan view is not limited thereto, and the FPC 108 may have an
arbitrary shape.
[0065] On the front surface of the FPC 108 illustrated in FIG. 3A,
four pads for signal (signal pads) 310, 312, 314, and 316 are
provided in parallel in the vicinity of one side 302 on a lower
side in the drawing along a direction of the one side 302. In
addition, four through-holes 320, 322, 324, and 326 are provided in
parallel on the other side 304 side, which is opposite to the side
302, for example, along a direction of the side 304. In addition,
the four pads 310, 312, 314, and 316 are respectively connected to
the through-holes 320, 322, 324, and 326 by wiring patterns 330,
332, 334, and 336.
[0066] In addition, on the front surface of the FPC 108, pads for
ground (ground pads) 340a and 340b, 342a and 342b, 344a and 344b,
and 346a and 346b are provided in parallel at positions at which
each of the signal pads 310, 312, 314, and 316 is interposed
between each pair of the ground pads from both sides along a
direction of the side 302. The ground pads 340a, 340b, 342a, 342b,
344a, 344b, 346a, and 346b are respectively connected to ground
patterns 370a, 370b, 372a, 372b, 374a, 374b, 376a, and 376b (to be
described later) on the rear surface through via-holes.
[0067] On the other hand, a ground plane 350 is formed on the rear
surface of the FPC 108 illustrated in FIG. 3B, and the wiring
patterns 330, 332, 334, and 336 on the front surface constitute a
grounded coplanar waveguide (GCPW) in combination with the ground
plane 350 on the rear surface. In addition, the ground plane 350
extends to positions corresponding to the ground pads 340a, 340b,
342a, 342b, 344a, 344b, 346a, and 346b on the front surface, and
constitutes the ground patterns 370a, 370b, 372a, 372b, 374a, 374b,
376a, and 376b.
[0068] In addition, signal pads 360, 362, 364, and 366 are provided
on the rear surface of the FPC 108 at positions corresponding to
the signal pads 310, 312, 314, and 316 on the front surface, for
example, in the same size as that of the signal pads 310, 312, 314,
and 316, and the signal pads 360, 362, 364, and 366, and the signal
pads 310, 312, 314, and 316 are electrically connected to each
other through via-holes.
[0069] Particularly, in this embodiment, semi-circular concave
portions 380a, 380b, 382a, 382b, 384a, 384b, 386a, and 386b in a
plan view, which respectively include an opening in the side 302,
are formed in the side 302 of the FPC 108 at portions at which the
ground pads 340a, 340b, 342a, 342b, 344a, 344b, 346a, and 346b are
formed. The concave portions 380a, 380b, 382a, 382b, 384a, 384b,
386a, and 386b are respectively provided a metal film on an inner
surface thereof, and the metal film connect each of the ground pads
340a, 340b, 342a, 342b, 344a, 344b, 346a, and 346b on the front
surface and each of the ground patterns 370a, 370b, 372a, 372b,
374a, 374b, 376a, and 376b on the rear surface. The concave
portions 380a, 380b, 382a, 382b, 384a, 384b, 386a, and 386b can be
prepared, for example, by cutting out a through-hole in which a
metal film is formed on an inner surface and which includes a
circular opening, and by setting the resultant cut-out surface as
the side 302.
[0070] FIG. 4 is a partial detail view of the circuit substrate
104, and in the drawing, a configuration of pads provided at a
portion (that is, the portion A in FIG. 1), which is in contact
with the FPC 108, in the circuit substrate 104. In one side 402, to
which the FPC 108 of the optical modulator 102 is connected, of the
circuit substrate 104, circuit signal pads 410, 412, 414, and 416,
and circuit ground pads 440a, 440b, 442a, 442b, 444a, 444b, 446a,
and 446b, to which the signal pads 310, 312, 314, and 316, and the
ground pads 340a, 340b, 342a, 342b, 344a, 344b, 346a, and 346b on
the front surface of the FPC 108 are respectively connected, are
provided in parallel at positions corresponding to the signal pads
310, 312, 314, and 316, and the ground pads 340a, 340b, 342a, 342b,
344a, 344b, 346a, and 346b.
[0071] Particularly, in this embodiment, the circuit ground pads
440a, 440b, 442a, 442b, 444a, 444b, 446a, and 446b, which are
conductor patterns connected to the ground pads 340a, 340b, 342a,
342b, 344a, 344b, 346a, and 346b of the FPC 108, are respectively
provided with pins 450a, 450b, 452a, 452b, 454a, 454b, 456a, and
456b which are columnar members which extend from the conductor
patterns to an upper side of a substrate surface of the circuit
substrate 104 (in a direction to be spaced apart from the substrate
surface) and have a circular cross-section.
[0072] For example, the pins 450a, 450b, 452a, 452b, 454a, 454b,
456a, and 456b can be provided by inserting metal pins into
through-holes, which are respectively provided in the circuit
ground pads 440a, 440b, 442a, 442b, 444a, 444b, 446a, and 446b, and
by fixing the pins to the through-holes through soldering.
[0073] FIGS. 5A and 5B are views illustrating a structure
(connection structure) of a connection portion (the portion A in
FIG. 1) between the optical modulator 102 (specifically, the FPC
108 provided in the optical modulator 102) and the circuit
substrate 104. FIG. 5A is a view when seen from an upper surface of
the optical modulator 102, and FIG. 5B is a view when seen from a
II-II cross-sectional arrow direction in FIG. 5A, and illustrates a
state in which the pin 456a, the circuit ground pad 446a, the
ground pad 346a, and the ground pattern 376a are soldered.
[0074] In this embodiment, the FPC 108 of the optical modulator 102
is disposed on the circuit substrate 104 so that the pins 450a,
450b, 452a, 452b, 454a, 454b, 456a, and 456b provided in the
circuit substrate 104 are respectively fitted into the concave
portions 380a, 380b, 382a, 382b, 384a, 384b, 386a, and 386b
provided in the side 302 of the FPC 108 (FIG. 5A). According to
this, a relative position of the FPC 108 with respect to the
circuit substrate 104 is determined with high accuracy, and thus
solder-fixing is performed in a state in which relative positions
of the signal pads 310, 312, 314, and 316 of the FPC 108 with
respect to the circuit signal pads 410, 412, 414, and 416 of the
circuit substrate 104 are determined with high accuracy. As a
result, it is possible to effectively reduce reflection and a loss
of a radio-frequency signal at joint portions between the circuit
signal pads 410, 412, 414, and 416 of the circuit substrate 104,
and the signal pads 310, 312, 314, and 316 of the FPC 108, and it
is also possible to reduce a manufacturing variation of the
pads.
[0075] In addition, in this embodiment, as illustrated in FIG. 5B,
in a state in which the pin 456a, the circuit ground pad 446a, the
ground pad 346a, and the ground pattern 376a are soldered, since
the pin 456a exists, a solder portion 506a having, for example, a
meniscus shape, which gradually rises from the ground pattern 376a
to a lateral surface of the pin 456a, is formed. Furthermore, the
configuration illustrated in FIG. 5B represents a configuration of
the pin 456a, the circuit ground pad 446a, the ground pad 346a, and
the ground pattern 376a, which are solder-connected, as an example.
Configurations of respective connection portions between the other
pins 450a, 450b, 452a, 452b, 454a, 454b, and 456b, the other
circuit ground pads 440a, 440b, 442a, 442b, 444a, 444b, and 446b,
the ground pads 340a, 340b, 342a, 342b, 344a, 344b, and 346b, and
the other ground patterns 370a, 370b, 372a, 372b, 374a, 374b, and
376b, which are solder-connected, are the same as the configuration
illustrated in FIG. 5B.
[0076] That is, a solder portion similar to the solder portion 506a
illustrated in FIG. 5B is also formed not only between the pin 456a
and the ground pattern 376a, but also between the pins 450a, 450b,
452a, 452b, 454a, 454b, and 456b, and the ground patterns 370a,
370b, 372a, 372b, 374a, 374b, and 376b. Here, solder portions,
which are the same as the solder portion 506a and are respectively
formed between the pins 450a, 450b, 452a, 452b, 454a, 454b, and
456b, and the ground patterns 370a, 370b, 372a, 372b, 374a, 374b,
and 376b, are referred to as solder portions 500a, 500b, 502a,
502b, 504a, 504b, and 506b.
[0077] The solder portions 506a and the like function as a shield
that electrically shields between respective connection portions of
the circuit signal pad 416 and the like and the signal pad 316 and
the like, the connection portions being adjacent to each other the
ground pattern 376a and the like, on which the solder portion 506a
and the like are formed, interposed therebetween. For example, the
solder portion 506a that is formed between the pin 456a and the
ground pattern 376a as illustrated in FIG. 5B, and the solder
portion 504b that is formed between the pin 454b and the ground
pattern 374b function as a shield between the connection portion of
the circuit signal pad 416 and the signal pad 316, and the
connection portion of the circuit signal pad 414 and the signal pad
314, the connection portions being adjacent to each other with the
ground patterns 374b and 376a interposed therebetween.
[0078] According to this, in the connection structure according to
this embodiment as illustrated in FIG. 5A, cross-talk between
connection portions of the signal pads 310, 312, 314, and 316 of
the FPC 108 and the circuit signal pads 410, 412, 414, and 416 of
the circuit substrate 104 is effectively reduced.
[0079] Here, a height h (FIG. 5B) of the solder portion 506a and
the like is determined by the amount of solder that is applied to
the portion, and a protrusion height H of the pin 456a and the like
from the FPC 108, and it is possible to adjust the reduction amount
of cross-talk between connection portions of the signal pad 310 and
the like and the circuit signal pad 410 and the like by adjusting
the height h through adjustment of the amount of solder and the
height H. For example, the protrusion height H can be set to 1 mm
or greater. As an effect thereof, for example, in a case where a
distance between adjacent signal electrodes is set to approximately
4 mm, and H is set to 1 mm, a reduction effect of approximately of
5 dB is obtained with respect to cross-talk between the adjacent
signal electrodes at a signal frequency of approximately 20
GHz.
[0080] Furthermore, in this embodiment, it is assumed that the pin
456a and the like is a conductor having a linear circular columnar
shape, but the shape of the pin 456a and the like is not limited to
the shape, and may be set to an arbitrary shape as long as a solder
portion that constitutes a shield is formed on an upper side of the
ground pattern 376a and the like. For example, the pin 456a and the
like may be bent after protruding from the circuit ground pad 446a,
and an upper side of the ground pattern 376a and the like may
include a portion that extends along a surface of the FPC 108.
[0081] FIG. 6 is a view illustrating a modification example, which
includes the above-described pin, of the above-described
embodiment. FIG. 6 illustrates a configuration of a portion
corresponding to the portion illustrated in FIG. 5A in this
modification example. In this modification example, a pin 456a'
corresponding to the pin 456a protrudes to an upper side of the
circuit ground pad 446a, and is bent to a right direction in the
drawing to constitute an extension portion 606a that extends in
parallel to the surface of the FPC 108. In addition, a solder
portion 506a' is formed between the extension portion 606a and the
ground pattern 376a.
[0082] In this case, the entirety of the extension portion 606a and
the solder portion 506a' function as a shield, and cross-talk
between adjacent connection portions of the circuit signal pads 416
and 414, and the signal pads 316 and 314 is further effectively
reduced. The other pins 450a, 450b, 452a, 452b, 454a, 454b, and
456b illustrated in FIG. 5A may have the same configuration as that
of the pin 456a', and the same solder portion as that of the solder
portion 506a' may be formed between the pins 450a, 450b, 452a,
452b, 454a, 454b, and 456b, and the ground patterns 370a, 370b,
372a, 372b, 374a, 374b, and 376b.
[0083] Furthermore, a position of a bent portion of the pin 456a'
maybe adjusted in order for the FPC 108 to be interposed between
the extension portion 606a and the circuit substrate 104. According
to this, when solder-connecting the circuit signal pad 410 and the
like, the circuit ground pad 440a and the like, signal pad 310 and
the like, and the ground pad 340a and the like, it is possible to
prevent floating of the FPC 108 with respect to the circuit
substrate 104, and thus the above-described configuration is
preferable from the viewpoint of improving workability. In this
case, the above-described cross-talk reducing effect is obtained
mainly by the extension portion 606a.
[0084] As described above, in the connection structure (that is,
the structure in the portion A in FIG. 1 as illustrated in FIGS. 5A
and 5B) between the optical modulator 102 and the circuit substrate
104 in the optical transmission apparatus 100 according to this
embodiment, the FPC 108, which is provided in the optical modulator
102, includes the signal pad 310 and the like to which a
radio-frequency signal is applied and the like, and the ground pad
340a and the like which are provided at positions, at which the
signal pad 310 and the like are respectively interposed from both
sides, along the one side 302. In addition, the semi-circular
concave portions 380a and the like, which include an opening at the
side 302, are provided at an end of the ground pad 340a and the
like. In addition, the circuit signal pad 410 and the like and the
circuit ground pad 440a and the like, which are respectively
connected to the signal pad 310 and the like and the ground pad
340a and the like, are provided in the one side 402 of the circuit
substrate 104, and the pin 450a and the like, which are
respectively fitted into a plurality of the concave portions 380a
of the FPC 108, are provided in the circuit ground pad 440a and the
like.
[0085] According to this, in the connection structure of the
optical transmission apparatus 100, a relative position of the
signal pad 310 and the like of the FPC 108 with respect to the
circuit signal pad 410 and the like of the circuit substrate 104 is
determined with high accuracy, and thus it is possible to perform
connection in which reflection or a loss of a radio-frequency
signal is small. In addition, for example, the solder portion 500a
having a meniscus shape, which gradually rises along a lateral
surface of the pin 450a, is formed between the pin 450a that is
provided in the circuit ground pad 440a and the like, and the
ground pattern 370a and the like on the rear surface of the FPC
108, it is possible to reduce cross-talk between connection
portions of the circuit signal pad 410 and the like and the signal
pad 310 and the like.
[0086] Furthermore, in this embodiment, it is assumed that the four
signal pads 310, 312, 314, and 316 are provided in the FPC 108, but
the number of the signal pads is not limited thereto and may be set
to an arbitrary number of two or greater.
[0087] In addition, in this embodiment, it is assumed that the pin
450a and the like are provided in the entirety of the circuit
ground pad 440a and the like of the circuit substrate 104, but
there is no limitation thereto. At least two pins may be provided
in arbitrary pads among the circuit ground pad 440a and the like as
long as the at least two pins are provided to determine a relative
position of the FPC 108 with respect to the circuit substrate
104.
[0088] In addition, for example, pins (for example, the pins 450a
and 456b) may not be provided in the circuit ground pads (for
example, the circuit ground pads 440a and 446b) which are not
interposed between adjacent circuit signal pads among the circuit
signal pad 410 and the like which are connected to the signal pad
310 and the like of the FPC 108.
[0089] In addition, in this embodiment, it is assumed that a piece
of the pin 450a and the like are individually provided with respect
to the circuit ground pad 440a and the like, but two or more pins
may be provided with respect to one circuit ground pad. In this
case, a signal pad, which is connected to a circuit ground pad
provided with the two or more pins, may be provided with two or
more concave portions into which the two or more pins are
fitted.
[0090] In addition, in this embodiment, it is assumed that the
concave portion 380a and the like has a semi-circular shape in a
plan view, and the pin 450a and the like are circular columns
having a circular cross-section. However, the shape of the concave
portion 380a and the like in a plan view, and the cross-sectional
shape of the pin 450a and the like are not limited thereto, and may
be arbitrary shapes as long as the pin 450a and the like can be
fitted into the concave portion 380a and the like. For example, the
shape of the concave portion 380a and the like may be set to a
triangular shape in a plan view, and the cross-sectional shape of
the pin 450a and the like may be a rectangular shape of which a
part is inserted in the triangular shape.
* * * * *