Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2002-12-19
2004-09-14
Le, Thien M. (Department: 2876)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
Reexamination Certificate
active
06789956
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical modules for sending and receiving optical signals that have excellent high frequency properties.
BACKGROUND OF THE INVENTION
In recent years, optical fiber communication, which is capable of transmitting large volumes of information with little loss, has been practiced as an alternative to communications employing metallic cable or wireless media.
When video signals are received over an optical fiber, a light-receiving device serves as the light-receiving front end portion. Light-receiving devices are made of a light-receiving element such as a photodiode (PD) that receives optical signals and generates a small current corresponding to those signals, and an element that, once the small current that has been generated is converted into voltage, amplifies the signals up to a reception sensitivity required by a television receiver or the like that is connected at a later stage and demodulates them.
The frequency band of signals processed by such light-receiving devices for receiving video signals has become increasingly high in the case of CATV, for example, as the number of channels increases, and at present is approaching 1 GHz.
A conventional example of a device for optical communications having good high frequency properties in a system that employs optical fiber to distribute video signals for multiple channels is disclosed in JP 2001-345456A, and is a wideband light-receiving device in which a capacitive element with excellent low-distortion properties over a wide frequency band is provided internally in a substrate. In this wideband light-receiving device, semiconductor elements are flip-chip mounted onto a multilayer substrate in which a capacitive element is provided internally in order to reduce parasitic inductance, and as a result the semiconductor elements and the capacitive element can be connected very close to one another, thereby resulting in excellent high frequency properties.
However, the following problems occur if the capacitance of the capacitive element is increased in a conventional module for optical communications.
FIG. 22
is a cross-sectional view showing the configuration of a conventional module for optical communications.
FIGS. 23A-B
is a cross-sectional view showing the processes for manufacturing a separate conventional module for optical communications.
With the module for optical communications shown in
FIG. 22
, an optical element
201
and a semiconductor element
231
are flip-chip mounted to terminal electrodes
202
formed on the surface of a multilayer substrate
203
via bumps
207
. Within the multilayer substrate
203
, an upper electrode
205
and a lower electrode
206
sandwich a dielectric layer
209
and thereby form a capacitive element, and the upper electrode
205
and the lower electrode
206
are connected electrically to the terminal electrodes
202
through via holes
208
. With such a configuration, the capacitive element can be formed inside the multilayer substrate
203
below the semiconductor element
231
. Also, because the dielectric layer
209
is formed spanning the entire area of the multilayer substrate
203
, there is no unevenness in the surface of the multilayer substrate
203
, and the optical element
201
and the semiconductor element
231
can be stably flip-chip-mounted onto the multilayer substrate
203
.
To increase the capacitance of the capacitive element, the dielectric layer
209
can be formed using a material with a high relative permittivity, but because the dielectric layer
209
spans a wide area, there is the problem that stray capacitance may occur at unnecessary areas and that cross-talk may occur in the internal wiring layer.
Accordingly, as disclosed in JP H06-164150A, for example, the dielectric film
209
can be formed in one region only and not formed over a wide area. With the module for optical communications shown in
FIGS. 23A-B
, the dielectric layer
209
is formed in one region using a material that differs from that of the multilayer substrate
203
, and thus the capacitive element is formed only at necessary areas, and the semiconductor element
231
and the capacitive element are connected at a very close distance to one another.
With this configuration, however, unevenness results in the surface of the multilayer substrate
203
at areas where the dielectric layer
209
has not been formed because there are areas within the multilayer substrate
203
where the dielectric layer
209
has been formed. For that reason, if the semiconductor element
231
is flip-chip mounted onto the multilayer substrate
203
from the state shown in
FIG. 23A
, a gap occurs between the bump
207
of the semiconductor element
231
and the terminal electrodes
202
as shown in
FIG. 23B
, and thus the semiconductor element
231
cannot be stably flip-chip mounted.
Moreover, as shown in
FIG. 24
, unevenness in the surface makes it impossible to mount the optical element
201
at a predetermined location of the multilayer substrate
203
and position an optical fiber
230
by passive alignment in a predetermined location using a V-groove
271
. That is, the height difference that occurs between the terminal electrodes
202
a
and
202
b
causes the optical element
201
to be tilted when flip-chip mounted. As a consequence the direction in which the laser is emitted diverges from the predetermined direction and optical coupling with the optical fiber
230
, which is arranged in a predetermined position, cannot be obtained. It should be noted that the V-groove
271
is formed in a bench
261
and the optical module is mounted onto the bench
261
via a connection terminal
251
.
More specifically, a vertical disparity of about 10 &mgr;m occurs between the terminal electrode
202
a
and the terminal electrode
202
b
. For example, if the spacing between the bump
207
a
and the bump
207
b
in the direction of the optical axis is 200 &mgr;m and the vertical disparity between the terminal electrode
202
a
and the terminal electrode
202
b
is 20 &mgr;m, then an emission direction
241
of the optical element
201
is tilted with respect to an optical axis
242
of the optical fiber
230
by 5.7 degrees.
Light that is incident within 5.7 degrees of the optical axis
245
into an ordinary single-mode optical fiber
230
with a numerical aperture of 0.1 can be coupled. However, the light emitted from the optical element
201
, which is a laser element, has a flare angle of a certain degree and its optical strength is in a Gaussian distribution with respect to the emission axis. Thus, a laser element that has a full width at half maximum of 15 degrees or more cannot be optically coupled with the optical fiber
230
.
SUMMARY OF THE INVENTION
The present invention was arrived at in light of the foregoing problems, and it is an object thereof to provide an optical module that has good high frequency properties, in which an optical element and a semiconductor element, for example, are mounted stably onto a multilayer substrate.
An optical module of the present invention is provided with a substrate that includes an insulating layer, a passive element provided inside or on a surface of the insulating layer, and terminal electrodes formed on the surface of the insulating layer, and with at least one active element, which includes at least an optical element and is connected to the terminal electrodes on the substrate surface. The passive element has a dielectric layer, a resistive layer, or a magnetic layer, at least one of the terminal electrodes is connected to the passive element, and at least one of the at least one active element has a protruding electrode and is flip-chip mounted to the terminal electrodes on a principle face of the substrate via the protruding electrode. Taking a plane parallel to the principle face of the substrate as a projection plane, an area of orthographic projection of the dielectric layer, the resistive layer, or the magnetic layer is smaller than an area of orthographic projection of the principle face of the
Iwaki Hideki
Ogura Tetsuyosi
Taguchi Yutaka
Labaze Edwyn
Le Thien M.
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
LandOfFree
Optical module does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical module, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical module will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3214459