Optical waveguide part, its manufacturing method, connection...

Details Optical waveguide part, its manufacturing method, connection... Optical waveguide part, its manufacturing method, connection...

2000-09-15

2002-09-03

Palmer, Phan T. H. (Department: 2874)

Optical waveguides

With optical coupler

With alignment device

C285S129200

Reexamination Certificate

active

06445857

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention principally relates to an optical waveguide component for use in optical communications and its manufacturing method.
2. Related art of the Invention
Optical communication systems using optical communications with a wide band characteristic and additionally having functions such as wavelength multiplexing transmission or bidirectional transmission are spreading among public communications, computer networks, or the like in order to obtain high speed and advanced function.
The optical communication systems are developing from a trunk line type to a subscriber type for general homes and offices. The homes and offices each require an optical network unit (ONU); an optical module is essential, which converts optical signals from a station into electric signals and receive them and which converts an electrical signal sent from the subscriber into an optical signals to transmit it to an optical fiber. Costs of the optical module must be lowered in order to diffuse optical fibers to the subscriber-type optical communication systems.
The wavelength division multiplexing method (WDM) is expected to allow optical fibers to be efficiently used to transmit more information. This method allows optical signals of multiple wavelengths to be transmitted through a single optical fiber to increase the amount of transmitted information in proportion to the number of wavelengths.
In dosing so, an optical module in each home requires a function to divide wavelengths.
FIG. 6
shows the configuration of an optical module for a general WDM. Main components of this module are an optical waveguide formed on Si substrate, an interference filter (a wavelength filter), a transmitting laser diode (LD), and a photodiode (PD) for reception or LD optical power monitoring.
The optical waveguide comprises a core embedded in a clad and having a relatively higher refractive index than peripheries thereof. Light propagates while being confined in the core of a high refractive index. By patterning the core into a circuit, functions such as branching and synthesis of light can be implemented.
In
FIG. 6
, light of wavelength 1.3 &mgr;m and light of wavelength 1.55 &mgr;m both from a station are multiplexed before transmission and then input to the optical module through a common port
67
. The light of wavelength 1.3 &mgr;m is used for bidirectional communications between the station and the subscriber, while the light of wavelength 1.55 &mgr;m is used only for signal from the station to the subscriber. After these lights have passed through the optical waveguide, the light of wavelength 1.55 &mgr;m is reflected by an interference filter
62
to leave the module through a port
2
(
68
), whereas the light of wavelength 1.3 &mgr;m passes through a filter
62
and is then branched, so that a portion thereof is received by the receiving PD
64
and converted into an electric signal.
On the other hand, for transmission, the LD
63
is driven so as to be modulated to transmit an optical signal to the station through the common port
67
.
Although such a conventional module is obtained by combining together a large number of parts such as lenses and prisms and accurately positioning them for assembly, the use of the optical waveguide as in the optical module in
FIG. 6
can reduce the number of required part while diminishing the size of the module through assembly.
The module in
FIG. 6
, however, has the following problems in terms of costs and productivity:
One of the problems is high costs of the optical waveguide.
FIG. 7
shows a procedure for manufacturing a general optical waveguide.
(a) A lower clad film
72
is formed on a silicon substrate
71
(film thickness: 20 &mgr;m or larger). A core film
73
is formed thereon (about 10 &mgr;m).
(b) The core film is formed in a predetermined pattern using photolithography or dry etching.
(c) Finally, an upper clad layer
74
is formed (film thickness: 20 &mgr;m or larger).
In this manner, the thin films are deposited on the substrate
71
in the order of the lower clad, the core, and the upper clad. Processes for forming the thin films may include the flame deposition method, the CVD method, and the vacuum evaporation method. Since, however, the optical waveguide requires a large total thickness of about 50 &mgr;m and must meet severe specifications as for film thickness accuracy, it requires a long tact time whatever process is used, resulting in insufficient productivity.
In addition, the patterning is required after the core film has been formed but uses a semiconductor process such as photolithography or dry etching, which requires expensive facilities and a long tact time. This process is thus unsuitable for mass production and does not allow costs to be reduced easily.
Another problem is the need to integrate the interference filter.
As shown in
FIG. 6
, the interference filter
62
has an important function for mutually separating wavelengths. The interference filter comprises a multilayer dielectric oxide film formed on a polyimide and is generally obtained by forming a groove in a substrate beforehand by means of dicing and inserting a filmed polyimide into the groove for adhesion and fixation.
Although the interference filter inherently has a high wavelength selectivity (isolation ratio), its performance varies due to various factors originating from the insertion and assembly of the polyimide into the groove. For example,
FIG. 8
shows a polyimide substrate
81
inserted into a groove
83
as seen from above. The warpage or inclination of the polyimide substrate
81
inside the groove
83
slightly varies. an incident angle with respect to the filter, the position of reflected light, or the like, thereby varying a wavelength separation performance and transmission losses. The positional accuracy achieved when the groove is formed contributes to varying optical power obtained after light has passed through the filter. Reference numeral
82
denotes an optical waveguide and reference numeral
84
denotes an adhesive.
Accordingly, reducing such variations requires a very accurate assembly process, thereby unavoidably elongating the tact time and increasing facility costs. As a result, the current interference filter is unsuitable for mass production and does not allow costs to be reduced easily.
An optical module is also known which is obtained by cutting the optical waveguide at a predetermined position, interposing a wavelength filter at the cut position, and coupling the cut portions of the waveguide together again.
However, this module also requires a positional accuracy of ±1&mgr; in reconnecting the cut portions of the optical waveguide. The position seems to be adjusted based on an outer diameter because the integral object is cut, but cut edges that may occur upon cutting may prevent the required accurate positioning despite the positioning based on the outer dimensions of the optical waveguide.
SUMMARY OF THE INVENTION
In view of the conventional problems, it is an object thereof to provide an optical waveguide part that enables the size and costs of an optical module to be easily reduced and a method for manufacturing this optical waveguide part.
Means for attaining,this object is shown below.
The 1
st
invention of the present invention is an optical waveguide part, wherein a plurality of optical members each having an optical waveguide groove are installed on a substrate with a fixing groove for fixing an optical fiber in such a manner that said optical waveguide grooves are connected together,
an optical element is located between the plurality of optical members with said optical waveguide groove, and
a recess of each of said optical waveguide grooves is filled with a material having a higher refractive index than said substrate and said optical member.
In this configuration, the substrate with the optical fiber-fixing groove functions as a lower clad. The plurality of optical members with the optical waveguide grooves function as an upper clad. In addition, the mat

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