Optical module for suppressing optical and electrical...

Details Optical module for suppressing optical and electrical... Optical module for suppressing optical and electrical...

2003-03-03

2004-10-19

Nguyen, Chau N. (Department: 2831)

Optical waveguides

Integrated optical circuit

C385S092000, C385S094000

Reexamination Certificate

active

06807326

ABSTRACT:

BACKGROUND OF THE INVENTION
This application claims the priority of Korean Patent Application No. 2002-47197, filed on Aug. 9, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an optical module, and more particularly, to an optical module incorporating active elements, such as light emitting devices like laser diodes or photo detective devices like photo diodes, mounted on a single substrate.
2. Description of the Related Art
Generally, an optical module incorporating active elements, having light emitting functions and photo detective functions, mounted on a single substrate and electrical wires for transmitting signals at high-speed bit rates is affected by optical crosstalk as well as electrical crosstalk, i.e., sensitivities of the photo detective elements are degraded due to the optical crosstalk, and signals for driving the light emitting elements and photoelectric signals converted via the photo detective elements interfere with each other and are distorted due to the electrical crosstalk.
Not only the optical crosstalk but also the electrical crosstalk should be suppressed particularly in a case of an optical module for processing signals very fast at the rate of or higher than a few giga-bits per second (Gbps). In other words, suppressing the optical and electrical crosstalk is a requisite for excellent sensitivity and signal processing. There have been proposed various methods for suppressing particularly the optical crosstalk.
FIGS. 1
to
5
show various structures of optical modules for suppressing optical crosstalk according to conventional methods. In
FIGS. 1
to
5
, identical elements are referred to by the same reference numerals.
FIG. 1
shows a structure of a conventional optical module, in which light absorption coating
3
made of resin for suppressing optical crosstalk is applied substantially across the surface of a silicon substrate
1
. Reference numerals
5
a
and
5
b
refer to optical fibers.
FIG. 2
shows another conventional structure of the optical module shown in
FIG. 1
, in which the light absorption coating
3
made of resin for suppressing optical crosstalk is applied onto the surface of the silicon substrate
1
likewise in
FIG. 1
, but is removed from the areas where a light emitting device
7
a
and a photo detective device
7
b
are placed. Reference numeral
10
refers to transparent resin.
FIG. 3
shows a structure of another type of a conventional optical module, in which an optical wavelength selection filter
11
for suppressing optical crosstalk is placed between a light emitting device
7
a
and a photo detective device
7
b
mounted on a silicon substrate
1
by inserting the filter
11
into a groove formed in an optical waveguide
9
. Particularly, the optical module shown in
FIG. 3
suppresses faint light by inserting the optical wavelength selection filter
11
across the optical waveguide
9
.
FIG. 4
shows another conventional structure of the optical module shown in
FIG. 3
, which adapts the method shown in FIG.
1
. That is, the optical module shown in
FIG. 4
includes the optical wavelength selection filter
11
mounted on the silicon substrate
1
as shown in
FIG. 3
, and the light absorption coating
3
applied substantially across the surface of the silicon substrate
1
as shown in FIG.
1
. Reference numeral
13
refers to an adhesive for fixing the filter
11
. Light emitted to free space from the optical wavelength selection filter
11
and the light emitting device
7
a
in the structure of
FIG. 3
can be absorbed by the light absorption coating
3
, and accordingly, the optical crosstalk can be more effectively suppressed in the optical module shown in FIG.
4
. Although
FIG. 4
shows the structure wherein the light absorption coating
3
is applied substantially across the surface of the silicon substrate
1
including the areas where the light emitting device
7
a
, photo detective device
7
b
, and the optical wavelength selection filter
11
are mounted, it is also possible to adapt the method shown in
FIG. 2
such that the coating
3
is removed from the areas where a light emitting device
7
a
and a photo detective device
7
b
are placed.
FIG. 5
shows another conventional structure of the optical module shown in
FIG. 4
using an alternative means for blocking light other than the light absorption coating
3
, in which the light emitting device
7
a
, the photo detective device
7
b
, and the optical wavelength selection filter
11
are covered with caps
15
for blocking light, respectively. Briefly,
FIG. 5
shows an optical module including light blocking caps
15
for suppressing faint light. The caps
15
are respectively fixed on the silicon substrate
1
through welding, and are made of a material not transmitting light such as sintered aluminum having airtight characteristics, or other adequately processed material such as resin, glass, etc.
As described above with reference to
FIGS. 1
to
5
, the conventional optical modules incorporate, as means for suppressing optical crosstalk, the light absorption coating
3
applied onto the surface of the silicon substrate
1
, or the optical wavelength selection filter
11
inserted between the light emitting device
7
a
and the photo detective device
7
b
. While the conventional optical modules can suppress the optical crosstalk, the electrical crosstalk are unavoidable, particularly in the case of high-speed signal processing optical modules. Further, since a groove should be formed in the silicon substrate
1
to fix the optical wavelength selection filter
11
, a precise control is required during the fabrication process of the optical module, and accordingly, as the fabrication cost is increased, it is unfavorable for implementing the optical module at low cost.
Meanwhile, the conventional optical module shown in
FIG. 5
has a structure in which the active elements are covered with the caps
15
for suppressing the optical crosstalk. However, since the caps
15
for blocking light are made of dielectric material not transmitting the light, electromagnetic waves cannot be blocked while the light can be blocked, and therefore, the electrical crosstalk cannot be suppressed. Further, since the light can be subject to resonance within the optical module due to the light blocking caps
15
, the light emitting device, e.g., a laser diode can be subject to chaos phenomenon. Furthermore, it is extremely hard to fix the caps
15
having very small sizes corresponding to those of the active elements through welding.
As described above, while the conventional optical modules can basically suppress the optical crosstalk, the electrical crosstalk due to electromagnetic waves are unavoidable, particularly in the case of high-speed signal processing optical modules. In the case of the optical modules for processing signals at low-speed rates, fairly good sensitivities can be achieved by suppressing the optical crosstalk below −40 dB, and isolating electric signal lines for light emitting devices and those for photo detective devices from each other. However, in the case of the optical modules for processing signals very fast at rates of or higher than a few Gbps, not only the optical crosstalk but also the electrical crosstalk should be suppressed in order to achieve good sensitivities and signal processing.
SUMMARY OF THE INVENTION
The present invention provides an optical module having a structure that can suppress not only optical crosstalk but also electrical crosstalk causing interferences between and distortions of signals for driving light emitting devices and photoelectric signals converted via photo detective devices.
An optical module according to an embodiment of the present invention includes a substrate; a plurality of mounting trenches spaced from each other for mounting active elements on the substrate; a blocking trench formed between the active elements mounted on the plurality of mounting tr

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