Optical waveguides – Temporal optical modulation within an optical waveguide
Reexamination Certificate
2001-02-09
2003-06-03
Duverne, J. F. (Department: 2839)
Optical waveguides
Temporal optical modulation within an optical waveguide
C385S088000
Reexamination Certificate
active
06574379
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical device and its manufacturing method. In particular, the invention relates to an optical modulation device used for optical communication and its manufacturing method.
2. Description of the Related Art
To spread public communication networks using optical fibers, it is important to improve the performance of semiconductor lasers and to increase the yields of semiconductor lasers to manufacture them at low costs.
In particular, to improve the performance of semiconductor lasers, it is indispensable to enable high-speed modulation of laser light to cope with an increase in information quantity. For the purpose of high-speed modulation of laser light, an external modulation scheme is employed to reduce wavelength variation in modulation and thereby enable long-range transmission. In the external modulation scheme, usually, laser light is emitted from a semiconductor laser at constant intensity and then modulated by inputting it to an optical modulator passing or interrupting light (on/off control).
The electro-absorption modulator (hereinafter abbreviated as EAM) is used as an optical modulator in the external modulation scheme. Extinction is attained by using a variation in absorption spectrum due to the Franz-Keldysh effect (in an EAM using a single-layer, thick light absorption layer) or the Stark shift effect (in an EAM using a multiple quantum well structure).
In optical modulators, the degree of absorption of laser light varies depending on the voltage applied. Therefore, if a modulation signal voltage is applied to a high-frequency electric circuit that is connected to an optical modulator, laser light that is emitted from the exit end face of the optical modulator is given intensity modulation corresponding to the signal voltage.
FIG. 11
is a perspective view of a conventional optical device.
In
FIG. 11
, reference numeral
200
denotes an optical device;
202
, an optical modulator;
204
, a coplanar line as a transmission line;
224
, a termination resistor;
228
, bumps;
210
, an optical waveguide layer; and
212
, laser light (indicated by an arrow) that is input to the optical waveguide layer
210
.
FIG. 12
is a perspective view of the conventional optical modulator
202
.
In
FIG. 12
, reference numeral
214
denotes p-side electrode pads;
216
, n-side electrode pads.
FIG. 13
is a perspective view of the conventional transmission line
204
.
In
FIG. 13
, reference symbol
204
a
denotes a signal line of the coplanar line
204
;
204
b
, ground lines of the coplanar line
204
;
224
, a termination resistor; and
226
, a substrate member of the transmission line
204
.
Reference numeral
228
denotes conductive bumps that are placed on the signal line
204
a
and the ground lines
204
b.
Next, an assembling procedure of the conventional optical device
200
will be described.
With the line surface of a coplanar line
204
located above, two bumps
228
are formed on each of the signal line
204
a
and the ground lines
204
b
. The bumps
228
are formed at positions corresponding to the p-side electrode pads
214
and the n-side electrode pads
216
of the optical modulator
202
.
Thereafter, the front surface of the optical modulator
202
is opposed to the coplanar line
204
and then put on the coplanar line
204
in such a manner that the p-side electrode pads
214
and the n-side electrode pads
216
are placed on the respective bumps
228
. The optical modulator
202
and the coplanar line
204
are bonded to each other via the bumps
228
by applying pressure at an increased temperature.
In the conventional optical device
200
that is assembled in the above manner, the bumps
228
have both a role as conductors for electrically connecting the coplanar line
204
and the optical modulator
202
and a role as fixing the optical modulator
202
on the coplanar line
204
and supporting the optical modulator
202
.
Having smaller electrical resistance and inductance than conventional bonding wires, the bumps
228
provide an advantage that the optical device
200
is given superior frequency characteristics.
However, because of a variation in ambient temperature that occurs due to heating of peripheral devices of the optical device
200
or depending on the temperature condition of a use environment, the bumps
228
may be thermally deformed (expansion or contraction) during use of the optical modulator
202
.
In the conventional optical device
200
, since only the bumps
228
have the role of fixing and supporting the optical modulator
202
, thermal deformation of the bumps
228
results in a positional variation of the optical modulator
202
that is supported by the bumps
228
. As a result, the optical modulator
202
deviates from an optical system that is fixed independently of the optical modulator
202
and deterioration occurs in characteristics due to an optical axis deviation or the like.
As described above, in general, bumps, which have smaller electrical resistance and inductance than bonding wires, can provide an optical device having better high-frequency characteristics than an optical device using bonding wires. In particular, bumps enable formation of an optical device having superior frequency characteristics even in a case where a high-frequency modulation signal is handled as in the case of an optical modulator. However, the conventional optical device
200
has a problem that it cannot satisfy both of superior frequency characteristics and high optical axis stability for preventing deteriorations in characteristics due to an optical axis deviation or the like.
One prior art reference is Japanese Unexamined Patent Publication No. Hei. 10-56163. This publication discloses a photodetector that is mounted on a bare-chip IC via bumps and a bare-chip IC that incorporates a photodetector in a monolithic manner in view of the fact that wire bonding cannot provide stable ultrahigh-speed operation. However, in the former case, the photodetector is connected to the bare-chip IC via the bumps and the bare-chip IC is connected to a fixed side via bumps. Similarly, in the latter case, the bare-chip IC is connected to a fixed side via bumps. In either case, the photodetector side is connected, via the bumps, to a system in which an optical system is fixed and hence the above-described problem cannot be solved.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above problem in the art, and an object of the invention is to provide an optical device having superior frequency characteristics and high optical axis stability.
An optical device according to the present invention comprises: an optical device pedestal; an optical modulator having a back surface that is joined to the pedestal and a front surface where a signal electrode pad and a ground electrode pad are arranged; a pair of transmission lines that are provided on the pedestal on both sides of the optical modulator and each of which has a signal line and a ground line on a front surface of a first dielectric substrate; conductive bumps provided on surfaces of the signal line and the ground line of each of the transmission lines and surfaces of the signal electrode pad and the ground electrode pad of the optical modulator, respectively; and a connection transmission line that has a signal connection line and a ground connection line provided on a front surface of a second dielectric substrate, that is oriented in such a manner that the signal connection line and the ground connection line are opposed to the bumps, and that connects, by means of the signal connection line and the ground connection line, the bumps on the electrode pads of the optical modulator with the bumps on the transmission lines.
Accordingly, an optical device according to the present invention is advantageous in that the optical modulator can directly be fixed to the pedestal, a positional deviation from an external optical system can be prevented that would otherwise be caused by a positional variati
Duverne J. F.
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
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