U.S. patent application number 09/741792 was filed with the patent office on 2001-07-05 for arrayed waveguide grating type optical multiplexer/demultiplexer and a method of manufacturing the same.
This patent application is currently assigned to THE FURUKAWA ELECTRIC CO., LTD.. Invention is credited to Kashihara, Kazuhisa, Nara, Kazutaka, Nekado, Yoshinobu.
Application Number | 20010006570 09/741792 |
Document ID | / |
Family ID | 27341803 |
Filed Date | 2001-07-05 |
United States Patent
Application |
20010006570 |
Kind Code |
A1 |
Kashihara, Kazuhisa ; et
al. |
July 5, 2001 |
Arrayed waveguide grating type optical multiplexer/demultiplexer
and a method of manufacturing the same
Abstract
An arrayed waveguide grating type optical
multiplexer/demultiplexer in which a light transmission central
wavelength is independent of temperature. A substrate is formed on
a waveguide forming region in which optical input waveguides, a
first slab waveguide, an arrayed waveguide including a plurality of
channel waveguides that are arranged side by side, a second slab
waveguide, and a plurality of optical output waveguides arranged
side by side are sequentially connected. Dividing lines are set to
divide the first slab waveguide into two by intersecting dividing
planes that intersect with a route of light traveling along the
first slab waveguide. A position shifting member is fixed so as to
be secured in a waveguide forming region at its one end and in a
waveguide forming region on its other end. The position shifting
member fixes to a base the waveguide forming region on the side of
a divided slab waveguide and slides the waveguide forming region on
the side of another divided slab waveguide. An arrayed waveguide
grating is then divided at the dividing lines, separating the first
and second waveguide forming regions from each other.
Inventors: |
Kashihara, Kazuhisa; (Tokyo,
JP) ; Nara, Kazutaka; (Tokyo, JP) ; Nekado,
Yoshinobu; (Tokyo, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
THE FURUKAWA ELECTRIC CO.,
LTD.
6-1, Marunouchi 2-chome, Chiyoda-ku
Tokyo
JP
100-8322
|
Family ID: |
27341803 |
Appl. No.: |
09/741792 |
Filed: |
December 22, 2000 |
Current U.S.
Class: |
385/24 ;
385/37 |
Current CPC
Class: |
G02B 6/1203 20130101;
G02B 6/12014 20130101 |
Class at
Publication: |
385/24 ;
385/37 |
International
Class: |
G02B 006/28 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 1999 |
JP |
11-370457 |
Jun 13, 2000 |
JP |
2000-176691 |
Sep 19, 2000 |
JP |
2000-283806 |
Claims
What is claimed is:
1. A method of manufacturing an arrayed waveguide grating optical
multiplexer/demultiplexer, comprising the steps of: preparing an
arrayed waveguide grating having a waveguide forming region for
forming a waveguide structure and at least one slab waveguide;
setting dividing lines for determining dividing planes that
intersect a route of light traveling along said at least one slab
waveguide, said dividing planes dividing said at least one slab
waveguide into first and second divided slab waveguide portions,
and also dividing said waveguide forming region into a first
waveguide forming region that includes the first divided slab
waveguide portion and a second waveguide forming region that
includes the second divided slab waveguide; fixing a position
shifting member to have a first end secured on said first waveguide
forming region and to have a second end secured on said second
waveguide forming region; and dividing said waveguide forming
region into said first waveguide forming region and said second
waveguide forming region along said dividing lines.
2. A method of manufacturing an arrayed waveguide grating optical
multiplexer/demultiplexer according to claim 1, further comprising
the step of: placing said arrayed waveguide grating on a base prior
to said step of setting dividing lines.
3. A method of manufacturing an arrayed waveguide grating optical
multiplexer/demultiplexer according to claim 1, wherein said at
least one slab waveguide includes first and second slab waveguides,
and said prepared arrayed waveguide grating further includes: one
or more optical input waveguides arranged side by side; said first
slab waveguide connected to output ends of said optical input
waveguides; an arrayed waveguide connected to an output end of said
first slab waveguide and including a plurality of channel
waveguides arranged side by side, for transmitting light that has
traveled through said first slab waveguide, said channel waveguides
having different predetermined lengths; said second slab waveguide
connected to an output end of said arrayed waveguide; and one or
more optical output waveguides arranged side by side and connected
to an output end of said second slab waveguide.
4. A method of manufacturing an arrayed waveguide grating optical
multiplexer/demultiplexer according to claim 3, further comprising
the step of: placing said arrayed waveguide grating on a base prior
to said step of setting said dividing lines.
5. An arrayed waveguide grating optical multiplexer/demultiplexer,
comprising: a waveguide forming region configured to form a
waveguide structure and including at least one slab waveguide,
wherein said at least one slab waveguide is divided into two by
dividing planes that intersect a route of light traveling along
said at least one slab waveguide to form first and second divided
slab waveguide portions, and wherein said waveguide forming region
is divided by the dividing planes that divide said at least one
slab waveguide, into a first waveguide forming region that includes
the first divided slab waveguide and a second waveguide forming
region that includes the second divided slab waveguide; and a
position shifting member having a first end secured to said first
waveguide forming region and a second end secured to said second
waveguide forming region, said position shifting member configured
to move at least one of said first waveguide forming region and
said second waveguide forming region along said dividing
planes.
6. An arrayed waveguide grating optical multiplexer/demultiplexer
according to claim 5, wherein said position shifting member expands
and contracts.
7. An arrayed waveguide grating optical multiplexer/demultiplexer
according to claim 5, further comprising: a base on which said
arrayed waveguide grating is placed.
8. An arrayed waveguide grating optical multiplexer/demultiplexer
according to claim 5, wherein said at least one slab waveguide
includes first and second slab waveguides, and further comprising:
one or more optical input waveguides arranged side by side; said
first slab waveguide connected to output ends of said optical input
waveguides; an arrayed waveguide connected to an output end of said
first slab waveguide and including a plurality of channel
waveguides arranged side by side, and configured to transmit light
that has traveled through said first slab waveguide, said channel
waveguides having different predetermined lengths; said second slab
waveguide connected to an output end of said arrayed waveguide; and
one or more optical output waveguides arranged side by side and
connected to an output end of said second slab waveguide.
9. An arrayed waveguide grating optical multiplexer/demultiplexer
according to claim 5, further comprising: metal films formed in
said waveguide forming region; solder provided on said metal films;
and wherein said position shifting member is fixed to said
waveguide forming region through said solder and said metal
films.
10. An arrayed waveguide grating type optical
multiplexer/demultiplexer according to claim 7, wherein one of said
first waveguide forming region and said second waveguide forming
region is fixed whereas the other is moved by said position
shifting member, and further comprising: a clamping member
configured to clamp the fixed waveguide forming region to said
base.
11. An arrayed waveguide grating type optical
multiplexer/demultiplexer according to claim 5, wherein one of said
first waveguide forming region and said second waveguide forming
region is fixed whereas the other is moved by said position
shifting member, and further comprising: a position shift
preventing member configured to prevent said first and second
waveguide forming regions from shifting in a direction
perpendicular to a substrate plane, said position shift preventing
member provided in at least a part of a border region between said
first waveguide forming region and said second waveguide forming
region.
12. An arrayed waveguide grating type optical
multiplexer/demultiplexer according to claim 11, wherein said
position shift preventing member is formed from a plate-like
material having a flat surface and is arranged such that the flat
surface abuts with a front side of said waveguide forming region or
a back side of said substrate.
13. An arrayed waveguide grating type optical
multiplexer/demultiplexer according to claim 6, wherein said
position shifting member is a metal member.
14. An arrayed waveguide grating type optical
multiplexer/demultiplexer according to claim 5, further comprising:
through holes piercing said waveguide forming region and reaching a
substrate and formed in said waveguide forming region in areas
outside said waveguide structure; wherein side walls of said
through holes have smooth surfaces; and wherein said dividing
planes that intersect said at least one slab waveguide start from
one end of said waveguide forming region and extend to connect with
said through holes.
15. An arrayed waveguide grating optical multiplexer/demultiplexer,
comprising: waveguide forming means for forming a waveguide
structure and including at least one slab waveguide means, wherein
said at least one slab waveguide means is divided into two by
dividing means for intersecting a route of light traveling along
said at least one slab waveguide means to form first and second
divided slab waveguide means, and wherein said waveguide forming
means is divided by the dividing means that divide said at least
one slab waveguide means into a first waveguide forming region
means that includes the first divided slab waveguide means and a
second waveguide forming region means that includes the second
divided slab waveguide means; and position shifting means for
moving at least one of said first waveguide forming region means
and said second waveguide forming region means along said dividing
means.
16. An arrayed waveguide grating optical multiplexer/demultiplexer
according to claim 15, wherein said position shifting means expands
and contracts.
17. An arrayed waveguide grating optical multiplexer/demultiplexer
according to claim 15, further comprising: base means for placing
said arrayed waveguide grating thereon.
18. An array waveguide optical multiplexer/demultiplexer according
to claim 15, wherein said at least one slab waveguide means
includes first and second slab waveguide means, and further
comprising: optical input waveguide means; said first slab
waveguide connected to an output end of said optical input
waveguide means; arrayed waveguide means connected to an output end
of said first slab waveguide means for transmitting light that has
traveled through said first slab waveguide; said second slab
waveguide means connected to an output end of said arrayed
waveguide means; and optical output waveguide means connected to an
output end of said second slab waveguide means.
19. An arrayed waveguide grating optical multiplexer/demultiplexer
according to claim 15, further comprising: metal film means formed
in said waveguide forming means; solder means provided on said
metal film means; and wherein said position shifting means is fixed
to said waveguide forming means through said solder means and said
metal film means.
20. An arrayed waveguide grating type optical
multiplexer/demultiplexer according to claim 19, further
comprising: clamping means for clamping one of said first and
second waveguide forming region means to said base means.
21. An arrayed waveguide grating type optical
multiplexer/demultiplexer according to claim 19, further
comprising: position shift preventing means for preventing said
first and second waveguide forming region means from shifting in a
direction perpendicular to a substrate plane.
22. An arrayed waveguide grating type optical
multiplexer/demultiplexer according to claim 19, further
comprising: through hole means for piercing said waveguide forming
region and reaching a substrate; and wherein said dividing means
that intersect said at least one slab waveguide means start from
one end of said waveguide forming region means and extend to
connect with said through hole means.
Description
CROSS-REFERENCES TO RELATED DOCUMENTS
[0001] The present document is related to and claims priority on
Japanese Priority Documents 11-370,457, filed on Dec. 27, 1999, and
2000-176,691, filed on Jun. 13, 2000, the contents of both of which
are hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an arrayed waveguide
grating type optical multiplexer/demultiplexer used as an optical
multiplexer/demultiplexer in, for example, wavelength division
multiplexing optical communications, and to a method of
manufacturing the same.
[0004] 2. Discussion of the Background
[0005] Recently, in optical communications research and development
of optical wavelength division multiplexing communications has
actively been pursued as a way to exponentially increase
transmission volume, and the results are being put into practice.
Optical wavelength division multiplexing communications uses, for
example, a technique of division multiplexing a plurality of light
beams each having a different wavelength from one another to
transmit them. For systems using such optical wavelength division
multiplexing communications, a light transmissive device or the
like is provided to enable the receiver of the optical
communication to take out light beams separately on the basis of
their wavelengths from the transmitted light beams that have
undergone the wavelength division multiplexing. The light
transmissive device only transmits light of certain given
wavelengths.
[0006] Examples of the light transmissive device include an arrayed
waveguide grating (AWG) including a planar lightwave circuit (PLC)
such as shown in FIG. 15. The arrayed waveguide grating has a
waveguide forming region 10 formed from quartz-based glass on a
substrate 1 made of silicon or the like. The waveguide forming
region 10 has a waveguide structure as illustrated in FIG. 15 and
formed from a core.
[0007] The waveguide structure of the arrayed waveguide grating
includes one or more optical input waveguides 2 arranged side by
side, a first slab waveguide 3 connected to the output ends of the
optical input waveguides 2, an arrayed waveguide 4 connected to the
output end of the first slab waveguide 3, a second slab waveguide 5
connected to the output end of the arrayed waveguide 3, and a
plurality of optical output waveguides 6 arranged side by side and
connected to the output end of the second slab waveguide 5. The
size of the arrayed waveguide grating can be set, for example, such
that A=B=40 mm.
[0008] The arrayed waveguide 4 propagates light output from the
first slab waveguide 3, and includes a plurality of channel
waveguides 4a arranged side by side. Lengths of adjacent channel
waveguides 4a are different from each other with the differences
(.DELTA.L) preset. The number of optical output waveguides 6 is
determined, for example, in accordance with how many light beams
having different wavelengths from one another are to be created as
a result of demultiplexing or multiplexing of signal light by the
arrayed waveguide grating. The channel waveguides 4a constituting
the arrayed waveguide 4 are usually provided in a large number, for
example 100. However, FIG. 15 is simplified and the number of the
channel waveguides 4a, the optical output waveguides 6, and the
optical input waveguides 2 in FIG. 15 does not reflect the actual
number thereof.
[0009] The optical input waveguides 2 are connected to, for
example, transmission side optical fibers (not shown), so that
light having undergone the wavelength division multiplexing is
introduced to the optical input waveguides 2. The light output from
the optical input waveguides 2 is introduced to the first slab
waveguide 3, is diffracted by the diffraction effect thereof, and
enters the arrayed waveguide 4 to travel along the arrayed
waveguide 4.
[0010] After traveling through the arrayed waveguide 4, the light
reaches the second slab waveguide 5 and then is condensed in the
optical output waveguides 6 to be output therefrom. Because of the
preset differences in lengths between adjacent channel waveguides
4a of the arrayed waveguides 4, light beams after traveling through
the arrayed waveguides 4 have different phases from one another.
The phase front of many light beams from the arrayed waveguide 4 is
tilted in accordance with the differences and the position where
the light is condensed is determined by the angle of this tilt.
[0011] Therefore, light beams having different wavelengths are
condensed at different positions from one another. By forming the
optical output waveguides 6 at these positions, light beams
.lambda..sub.1, .lambda..sub.2, . . . .lambda..sub.n having
different wavelengths can be output from the respective optical
output waveguides 6 provided for the respective wavelengths.
[0012] In other words, the arrayed waveguide grating has an optical
multiplexing/demultiplexing function. With this function, the
arrayed waveguide grating can demultiplex light input from the
optical input waveguides 2, which has previously undergone the
division multiplexing and possesses different wavelengths from one
another, into light beams of one or more wavelengths, and then
output the light beams from their respective optical output
waveguides 6. The central wavelength of light to be demultiplexed
is in proportion to the differences (.DELTA.L) in lengths of
adjacent channel waveguides 4a constituting the arrayed waveguide 4
and to the effective refractive index n.sub.e of the channel
waveguides 4a.
[0013] Having the characteristics as above, the arrayed waveguide
grating can be used as a light transmissive device for optical
multiplexing/demultiplexing applied to a wavelength division
multiplexing transmission system. For instance, as shown in FIG.
15, light beams which have undergone wavelength division
multiplexing and having wavelengths of .lambda.1, .lambda.2,
.lambda.3, . . . .lambda.n (n is an integer equal to or larger than
2), respectively, are input to one of the optical input waveguides
2. The light beams are diffracted in the first slab waveguides 3,
reach the arrayed waveguides 4, and travel through the arrayed
waveguides 4 and the second slab waveguides 5. Then, as described
above, the light beams are respectively condensed at different
positions determined by their wavelengths, enter different optical
output waveguides 6, travel along their respective optical output
waveguides 6, and are output from the output ends of the optical
output waveguides 6.
[0014] The light beams having different wavelengths can then be
further taken out through optical fibers for outputting light (not
shown) that are connected to the output ends of the optical output
waveguides 6. When connecting the optical fibers to the optical
output waveguides 6 and to the optical input waveguides 2, an
optical fiber array is prepared for each. In the optical fiber
array, connection terminal faces of the optical fibers are arranged
and fixed into a one-dimensional array. The optical fiber array is
fixed to the connection terminal faces of the optical output
waveguides 6 or to the optical input waveguides 2 to thereby
connect the optical fibers to the optical output waveguides 6 or to
the optical input waveguides 2.
[0015] The above arrayed waveguide grating has such light
transmission characteristics (wavelength characteristics of
transmission light intensity in the arrayed waveguide grating) of
light beams output from the optical output waveguides 6 such that
with the respective light transmission central wavelengths (e.g.,
.lambda.1, .lambda.2, .lambda.3, . . . .lambda.n) as the center,
the light transmittance of the output light beams becomes smaller
as the wavelength deviates from their respective light transmission
central wavelength.
[0016] Every light transmission central wavelength .lambda..sub.o
is determined by the effective refractive index n.sub.e of the
arrayed waveguide 4, the difference (.DELTA.L) in length of
adjacent channel waveguides 4a of the arrayed waveguide 4, and
diffraction order m, and is expressed by the following numerical
expression (1).
.lambda..sub.o=n.sub.e.multidot..DELTA.L/m . . . (1)
[0017] Therefore, the wavelength indicative of the light
transmission characteristics with regard to one of the optical
output waveguide 6 is not always one, but there may be plural
central wavelengths depending on the diffraction order set thereto.
It is possible to demultiplex light into a plurality of optical
signals having a certain wavelength interval .DELTA..lambda. (nm)
with the light transmission central wavelength .lambda..sub.o as
the center. Accordingly, only the central wavelength .lambda..sub.o
is considered in the discussion below.
[0018] The arrayed waveguide grating utilizes the principle of
reciprocity (reversibility) of an optical circuit and, hence, has
the function of an optical multiplexer as well as the function of
an optical demultiplexer. That is, in a manner reverse to that
already discussed with respect to FIG. 15, a plurality of light
beams having different wavelengths from one another may be input to
respective optical output waveguides 6. The input light beams
travel along propagation routes opposite to the routes discussed
above with respect to FIG. 15, are multiplexed in the arrayed
waveguide 4 and in the first slab waveguide 3, and then are output
from one of the optical input waveguides 2.
[0019] In such an arrayed waveguide grating as mentioned above, the
wavelength resolution of the grating is in proportion to the
difference in lengths (.DELTA.L) between the channel waveguides 4a
of the arrayed waveguides 4, which are one of the components of the
grating. When the arrayed waveguide grating is designed to have a
large .DELTA.L, it is theoretically possible to
multiplex/demultiplex light to accomplish wavelength division
multiplexing with a narrow wavelength interval. It is thus
theoretically possible for the arrayed waveguide grating to have a
function of multiplexing/demultiplexing a plurality of signal light
beams, specifically, a function of demultiplexing or multiplexing a
plurality of optical signals with a wavelength interval of 1 nm or
less, which is a function deemed necessary for optical wavelength
division multiplexing communications of high density.
[0020] To manufacture an arrayed waveguide grating as discussed
above, for example, first flame hydrolysis deposition is used to
form an under cladding layer and a core layer on a silicon
substrate, then a photomask is prepared on which the waveguide
structure of the arrayed waveguide grating is drawn, a transfer is
performed by photolithography through the photomask, the arrayed
waveguide grating pattern is transferred onto the core layer by
reactive ion etching, and then flame hydrolysis deposition is again
used to form an over cladding layer. The arrayed waveguide grating
is thus manufactured.
[0021] The arrayed waveguide grating of FIG. 15 is conventionally
formed with a quartz-based glass material as a main component, and
due to temperature dependency of this quartz-based glass material,
the light transmission central wavelength .lambda..sub.o of the
arrayed waveguide grating shifts depending on the temperature. This
temperature dependency extends to so great a degree that, for
instance, when the change in temperature is 50.degree. C. or more
in an arrayed waveguide grating designed and manufactured using
setting values generally used in the background art, the light
transmission central wavelength shifts by 0.5 nm or more. The value
0.5 nm is fatal to an arrayed waveguide grating desired to
demultiplex or multiplex light with a very narrow wavelength
interval of 1 nm or less.
SUMMARY OF THE INVENTION
[0022] The present inventors therefore believe that there is a
great importance in realizing an arrayed waveguide grating type
optical multiplexer/demultiplexer that can control the temperature
dependency of the light transmission central wavelength. According
to the view of the present inventors, easiness in manufacturing the
arrayed waveguide grating type optical multiplexer/demultiplexer
and smallness of insertion loss are also objects significant in
putting into practice an arrayed waveguide grating type optical
multiplexer/demultiplexer as a device for wavelength division
multiplexing communications.
[0023] The present invention has been made in order to address the
problems noted above, and an object of the present invention is
therefore to provide an arrayed waveguide grating type optical
multiplexer/demultiplexer that is easy to manufacture, can reduce
temperature dependency of a light transmission central wavelength,
and can reduce insertion loss, and to provide a method of
manufacturing the same.
[0024] To achieve the above and other objects, in an arrayed
waveguide grating type optical multiplexer/demultiplexer of the
present invention, a slab waveguide is divided into two by
intersecting planes that intersect the route of the light traveling
along the slab waveguide. The intersecting planes serve as dividing
planes and divide a waveguide forming region into a first waveguide
forming region that includes one portion of the divided slab
waveguide and a second waveguide forming region that includes the
other portion of the divided slab waveguide. One or both of the
first waveguide forming region and the second waveguide forming
region are moved along the dividing planes by a position shifting
member. Therefore it is possible to compensate, with the use of the
movement by the position shifting member, shifts in light
transmission central wavelengths of the arrayed waveguide grating
which is caused by, for examples the temperature change of the
arrayed waveguide grating.
[0025] In the arrayed waveguide grating type optical
multiplexer/demultiplexer according to the present invention, when
the position shifting member is arranged such that its one end is
secured on the first waveguide forming region and its other end is
secured on the second waveguide forming region, the structure of
the device is simplified and precision is improved. Furthermore,
the cost of the device is reduced and the yield thereof is
increased.
[0026] Further to achieve the above and other objects, in the
method of manufacturing an arrayed waveguide grating type optical
multiplexer/demultiplexer of the present invention, at least one
slab waveguide is divided into two by intersecting planes that
intersect the route of light traveling along the slab waveguide.
The waveguide forming region is divided by the dividing planes into
the first waveguide forming region that includes one portion of the
divided slab waveguide and a second waveguide forming region that
includes the other portion of the divided slab waveguide. A
position shifting member with a function of moving one or both of
the first and second waveguide forming regions along the dividing
planes is fixed before the division such that the position shifting
member secures its one end on the first waveguide forming region
and secures its other end on the second waveguide forming region.
Therefore, the relative positions of the first waveguide forming
region and the second waveguide forming region before the division
are almost the same as those after the division.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] A more complete appreciation of the present invention and
many of the attendant advantages thereof will be readily obtained
as the same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0028] FIGS. 1A and 1B are structural diagrams showing the
structure of the main part of a first embodiment of an arrayed
waveguide grating type optical multiplexer/demultiplexer according
to the present invention, in which FIG. 1A is a plan view thereof
and FIG. 1B is a side view thereof;
[0029] FIGS. 2A to 2C are explanatory plan views illustrating a
part of steps of manufacturing the arrayed waveguide grating type
optical multiplexer/demultiplexer of the first embodiment;
[0030] FIGS. 3A and 3B are explanatory plan views illustrating
steps of manufacturing the arrayed waveguide grating type optical
multiplexer/demultiplexer in the first embodiment subsequent to the
steps shown in FIGS. 2A to 2C;
[0031] FIG. 4 is an explanatory plan view showing the appearance of
the arrayed waveguide grating type optical
multiplexer/demultiplexer in the first embodiment;
[0032] FIG. 5 is a perspective view showing a clip utilized in the
first embodiment;
[0033] FIGS. 6A and 6B are structural diagrams schematically
showing a second embodiment of an arrayed waveguide grating type
optical multiplexer/demultiplexer according to the present
invention, in which FIG. 6A is a plan view thereof and FIG. 6B is a
side view thereof;
[0034] FIGS. 7A and 7B are explanatory plan views illustrating a
part of steps of manufacturing the arrayed waveguide grating type
optical multiplexer/demultiplexer of the second embodiment;
[0035] FIGS. 8A to 8D are explanatory diagrams illustrating steps
of manufacturing the arrayed waveguide grating type optical
multiplexer/demultiplexer in the second embodiment subsequent to
the steps shown in FIGS. 7A and 7B, in which FIGS. 8A and 8C are
side views and FIGS. 8B and 8D are plan views;
[0036] FIG. 9 is a graph showing temperature dependency
characteristic of light output from one optical output waveguide of
the arrayed waveguide grating type optical
multiplexer/demultiplexer in the first and second embodiments;
[0037] FIG. 10 is a structural diagram showing in plan view the
structure of the main part of a third embodiment of an arrayed
waveguide grating type optical multiplexer/demultiplexer according
to the present invention;
[0038] FIGS. 11A to 11D are explanatory diagrams illustrating a
part of steps of manufacturing the arrayed waveguide grating type
optical multiplexer/demultiplexer of the third embodiment, in which
FIG. 11A is a plan view and FIGS. 11B to 11D are side views;
[0039] FIGS. 12A to 12D are explanatory diagrams showing the
structure of the main part of a fourth embodiment of an arrayed
waveguide grating type optical multiplexer/demultiplexer according
to the present invention, in which FIGS. 12A and 12C are side views
thereof and FIGS. 12B and 12D are plan views thereof;
[0040] FIGS. 13A to 13C are explanatory diagrams illustrating a
part of steps of manufacturing the arrayed waveguide grating type
optical multiplexer/demultiplexer in the fourth embodiment, in
which FIGS. 13A and 13C are plan views thereof and FIG. 13B is a
side view thereof;
[0041] FIGS. 14A and 14B are diagrams showing an arrayed waveguide
grating type optical multiplexer/demultiplexer having a waveguide
forming region with through holes, in which FIG. 14A is an
explanatory plan view thereof and FIG. 14B is an explanatory
sectional view showing the structure of the through holes; and
[0042] FIG. 15 is an explanatory plan view showing an arrayed
waveguide grating in the background art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] Embodiments of the present invention will be described below
with reference to the drawings. In the description of the
embodiments, the same reference symbols are used to denote
identical or corresponding parts throughout the several views, and
redundant explanations thereof will not be repeated.
[0044] FIGS. 1A and 1B schematically show a first embodiment of an
arrayed waveguide grating type optical multiplexer/demultiplexer
according to the present invention. FIG. 1A is a plan view of the
optical multiplexer/demultiplexer of this embodiment. FIG. 1B shows
a side view of the same viewed from the right in FIG. 1A.
[0045] As shown in FIGS. 1A and 1B, in the first embodiment, the
first slab waveguide 3 of the arrayed waveguide grating having the
structure illustrated in FIG. 15 is divided into two by
intersecting dividing planes 8 that intersect with a route of light
traveling through the first slab waveguide 3. The intersecting
dividing planes 8 are provided in a waveguide forming region 10
starting from one end (upper end in FIG. 1A) of the waveguide
forming region 10 and stretching to the midsection thereof.
Non-intersecting dividing planes 18 that do not intersect with the
first slab waveguide 3 are formed so as to connect with the
intersecting dividing planes 8. The non-intersecting dividing
planes 18 may be at right angles with the intersecting dividing
planes 8, although that is not a requirement.
[0046] In this first embodiment, the intersecting dividing planes 8
and the non-intersecting dividing planes 18 divide the waveguide
forming region 10 into (1) a first waveguide forming region 10a
that includes a divided slab waveguide 3a on one side and (2) a
second waveguide forming region 10b that includes a divided slab
waveguide 3b on the other side.
[0047] A position shifting member 17 with a thermal expansion
coefficient larger than that of the waveguide forming region 10 is
provided so as to be secured in the first waveguide forming region
10a at its one end and to be secured in the second waveguide
forming region 10b at its other end. The position shifting member
17 expands and contracts to slide the first waveguide forming
region 10a along the intersecting dividing planes 8 with respect to
the second waveguide forming region 10b.
[0048] The position shifting member 17 in this embodiment is placed
in a manner that allows the position shifting member 17 to secure
its one end on the front side of the waveguide forming region 10a
and its other end on the front side of the waveguide forming region
10b. This arrangement prohibits the waveguide forming region 10a
from being displaced upward (in the direction of the Z axis
perpendicular to the X-Y plane) with respect to a base 9, when
sliding the waveguide forming region 10a.
[0049] The position shifting member 17 is formed from, for example,
a copper plate having a thermal expansion coefficient of
1.65.times.10.sup.-5 (1/K). Beneath the position shifting member
17, solder 30 is provided in each fixing site 29.sub.1, 29.sub.2
indicated by the oblique broken lines in FIG. 1A. The underside of
each solder 30 is coated with a metal film (not shown in FIGS. 1A
and 1B). One end of the position shifting member 17 is fixed at the
fixing site 29.sub.1 to the waveguide region 10a through the metal
film and the solder 30, and the other end is fixed at the other
fixing site 29.sub.2 to the waveguide forming region 10b in the
same manner.
[0050] The first waveguide forming region 10a and the second
waveguide forming region 10b are divided and arranged spaced apart.
For instance, the distance between the regions 10a and 10b at an
area A in FIG. 1A (the distance between the non-intersecting
dividing planes 18) can be about 100 .mu.m, and the distance
thereof at an area B in FIG. 1A (the distance between the
intersecting dividing planes 8) can be about 25 .mu.m.
[0051] In this first embodiment, the base 9 is provided below the
substrate 1. Holes 15 are formed in attachment portions
9.sub.1-9.sub.3 that extend outward from the edges of the base 9.
Fastening members (such as screws) engaged with the holes 15 are
used to fix a chip having the waveguide forming region 10 and the
substrate 1 to a housing package 16 (a protective package for the
arrayed waveguide grating) shown in FIG. 4. The second waveguide
forming region 10b may be fixed to the base 9 by clips 19a shown in
FIG. 5 as clamping members which clamp the region at two
positions.
[0052] A silicon plate 35 as a position shift preventing member may
also be provided in a part (shown on the upper side of FIG. 1A) of
a border region between the first waveguide forming region 10a and
the second waveguide forming region 10b in this embodiment. The
silicon plate 35 prevents the first waveguide forming region 10a
and the second waveguide forming region 10b from shifting their
positions in a direction perpendicular to the plane of the
substrate 1. A plate-like material having a flat surface can be
used to form the silicon plate 35. The silicon plate 35 can be
arranged such that its flat surface abuts with the back side of the
substrate 1, and it is clamped by a clip 19b. That the silicon
plate 35 is clamped by the clip 19b does not prohibit the first
waveguide forming region 10a from sliding along the intersecting
dividing planes 8. The clip 19b clamps the silicon plate 35 such
that the position shifting member 17 can slide the first waveguide
forming region 10a along the intersecting dividing planes 8 with
respect to the second waveguide forming region 10b.
[0053] As discussed above, the present invention as shown in FIGS.
1A and 1B provides an operation such that the position shifting
member 17 will expand and contract with changes in temperature.
That position shifting is designed in the present invention to
shift the two portions of the divided slab waveguide 3a to
compensate for temperature induced variations in the arrayed
waveguide grating. For the device of the present invention to
operate properly then, it is important that the position shifting
member 17 expand and contract at an appropriate rate based on the
temperature changes. The position shifting of the position shifting
member 17 is based largely on its material and the length J between
the two fixed ends, as it is that unfixed portion of the position
shifting member 17 extending along the length J which will expand
and contract. As discussed below, a specific example of how to
properly calculate that length J is set forth.
[0054] The arrayed waveguide grating type optical
multiplexer/demultiplexe- r according to the first embodiment is an
arrayed waveguide grating type optical multiplexer/demultiplexer
that is capable of multiplexing and demultiplexing light
corresponding to, e.g., sixteen waves with a frequency interval of
100 GHz, and has the following parameters. The parameters include
FSR (free spectral range) set to 25.6 nm, the diffraction order m
set to 59, and the difference .DELTA.L in length between adjacent
channel waveguides 4a set to 63.1 .mu.m at a temperature of
25.degree. C.
[0055] The parameters also include a focal length L.sub.f set to
12327.06 .mu.m for the first and second slab waveguides 3 and 5, a
pitch D of the arrayed waveguide 4 set to 20 .mu.m, the effective
refractive index n.sub.e set to 1.45115 for the arrayed waveguide
4, an arrayed waveguide group refractive index n.sub.g set to
1.47512, an effective refractive index n.sub.s set to 1.453 for the
first and second slab waveguides 3 and 5, and the central
wavelength .lambda..sub.o of the arrayed waveguide grating set to
1.551 .mu.m.
[0056] Now, in this embodiment, dx is given as a moved distance of
output ends 20 of the optical input waveguides 2, which output ends
are moved with the movement on the side of the divided slab
waveguide 3a. Since the arrayed waveguide grating type optical
multiplexer/demultiplexer according to this embodiment has the
above parameters, when a value representing the relation between
the moved distance dx and a central wavelength shift amount
d.lambda. is calculated by the following numerical expression (2),
it is 0.4 nm (central wavelength shift amount d.lambda.)/10.21
.mu.m (moved distance dx).
dx/d.lambda.=(L.sub.f.times..DELTA.L)/(n.sub.s.times.D.times..lambda..sub.-
o).times.n.sub.g. . . (2)
[0057] J is given as the length of a necessary thermal expansion
coefficient utilizing region of the copper plate of the position
shifting member 17 with respect to the temperature dependency 0.011
nm/.degree.C. of the central wavelength of the arrayed waveguide
grating. Then,
1.65.times.10.sup.-5.times.(J.times.10.sup.3).times.(0.4/10.21)=0.011
is obtained. Calculating J using this expression (the thermal
expansion of the substrate 1 is ignored, for it is a small value),
a calculated value J.sub.c of the length J is 17 mm, in this
example.
[0058] Based on the calculated value J.sub.c, various values are
set to the actual length J (J shown in FIG. 1A) in this embodiment
to examine what characteristics the arrayed waveguide grating type
optical multiplexer/demultiplexer shows when the temperature
dependency of the light transmission central wavelength ranges from
5.degree. C. to 75.degree. C. The present inventors have examined
(1) the case in which the arrayed waveguide grating type optical
multiplexer/demultiplexer is manufactured setting the J to the
calculated value J.sub.c (17 mm), (2) the case in which the arrayed
waveguide grating type optical multiplexer/demultiplexer is
manufactured setting the J to the calculated value J.sub.c+5 mm (22
mm), and (3) the case in which the arrayed waveguide grating type
optical multiplexer/demultiplexer is manufactured setting the J to
the calculated value J.sub.c-5 mm (12 mm).
[0059] The present inventors found from the data obtained by the
above examination and representing the relation between the length
J and the temperature dependency of the light transmission central
wavelength that the length J should be set to 20 mm in order to
make the temperature dependency coefficient of light transmission
central wavelength almost 0. Accordingly, the arrayed waveguide
grating is manufactured determining the length of the position
shifting member 17 and positions to form the solder 30 so that the
length J is set to 20. Lengths E and Q shown in FIG. 1A are 60 mm
and 5 mm, respectively.
[0060] The metal film mentioned above is formed as follows (see
FIG. 2A). First, a resist is applied to the front side of the
waveguide forming region 10. The applied resist is exposed using a
preset pattern, and is then developed to form a resist mask.
Through this resist mask, a metal film 31 is formed by evaporation
or sputtering in each fixing site 29.sub.1, 29.sub.2 on the front
side of the waveguide forming region 10. The metal film 31 serves
as a base film of the solder 30, and is provided to improve
adherence of the solder 30 to the front side (glass surface) of the
waveguide forming region 10. This process adopts a general
semiconductor manufacturing process which utilizes photolithography
and, hence, positioning of high accuracy is not hard to
achieve.
[0061] Examples of films usable as the metal film 31 include a
lamination film including Cr (0.1 .mu.m) and Cu (0.5 .mu.m) layered
in this order, a lamination film including Cr (0.1 .mu.m), Ti (0.1
.mu.m), Pt (0.1 .mu.m) and Au (0.6 .mu.m) layered in this order,
and a lamination film including Ti (0.1 .mu.m), Pt (0.1 .mu.m), and
Au (0.6 .mu.m) layered in this order.
[0062] After the metal film 31 is formed, lift-off is conducted to
peel the resist mask off and remove it using a solvent. This
solvent dissolves only the resist, and acetone, for example, is
suitable for the solvent.
[0063] In this embodiment, matching oil matching the waveguide
forming region 10 in refractive index can be provided in the space
between the intersecting dividing planes 8. Furthermore, the
matching oil can fill the housing package for housing the arrayed
waveguide grating in this embodiment. If the housing package is not
filled with the matching oil, matching grease with high viscosity
may be provided instead in the space between the intersecting
dividing planes 8. Such arrangements make it possible to protect
the lightwave circuit module against adverse influence of moisture
even in a hot and humid environment. It also prevents evaporation
of the refractive index matching agent provided in the space
between the intersecting dividing planes 8 of the arrayed waveguide
grating. Therefore, it is possible to avoid cracking of the arrayed
waveguide grating and to avoid an increase in connection loss at
the intersecting dividing planes 8 due to moisture absorption in a
hot and humid environment.
[0064] The first embodiment is structured as described above. Now,
specific examples are given in relation to a method of
manufacturing the arrayed waveguide grating type optical
multiplexer/demultiplexer according to the first embodiment.
[0065] First, as shown in FIG. 2A, an arrayed waveguide grating
(arrayed waveguide grating chip) is prepared which has the same
structure as the background arrayed waveguide grating shown in FIG.
15. Dividing line 80 for forming dividing planes that include the
intersecting dividing planes 8, 18 (the intersecting dividing
planes 8 and the non-intersecting dividing planes 18 in this
embodiment) are set in advance. The dividing planes are for
dividing the waveguide forming region 10 into the first waveguide
forming region 10a and the second waveguide forming region 10b.
[0066] The arrayed waveguide grating chip is cut along the line
separating the non-intersecting dividing planes 18. The metal film
31 is formed in each fixing site 29.sub.1, 29.sub.2 on the front
side of the arrayed waveguide grating chip. A groove is formed on
the back side of the arrayed waveguide grating chip along the
dividing lines 80. After that, the back side of the arrayed
waveguide grating chip is temporarily fixed to a temporal fixing
plate 49 made of a flat glass plate at temporal fixing areas
32.
[0067] An adhesive, e.g., Cemedine Super 5 (trade name), is applied
to each of the temporal fixing areas 32 in a manner of drawing a
circle with dots, so that the arrayed waveguide grating chip can
later be readily peeled off the temporal fixing plate 49. The
non-intersecting dividing planes 18 are formed by cutting the
arrayed waveguide grating chip by a dicing saw or the like. The
width thereof is, for example, about 100 .mu.m. As shown in FIG.
2C, a groove 38 runs along the dividing lines 80 of the
intersecting dividing planes 8 and is formed on the back side of
the arrayed waveguide grating chip. The groove 38 may have a width
of about 300 .mu.m and a depth of about 0.7 mm, for example.
[0068] After the arrayed waveguide grating chip is temporarily
fixed to the temporal fixing plate 49, a groove 37 is formed as
shown in FIGS. 2B and 2C. The groove 37 runs along the dividing
lines of the intersecting dividing planes 8 on the front side of
the arrayed waveguide grating, and may have a width of about 20
.mu.m. As shown in FIG. 2C, the groove 37 forms, together with the
groove 38 formed on the back side of the arrayed waveguide grating,
the intersecting dividing planes 8. The solder 30, e.g. of Sn/Pb
(60%/40%), is then disposed on each area for forming the metal film
31.
[0069] Thereafter, the solder 30 is melted while the position
shifting member 17 made of copper plate is set in place as shown in
FIG. 3A, thereby fixing the position shifting member 17 to the
waveguide forming region 10 with the solder 30. The solder 30 is
provided to adhere the metal film 31 tightly to the position
shifting member 17. The solder 30 is melted by heating the arrayed
waveguide grating up to 230.degree. C. using, for example, a hot
plate.
[0070] After that, the arrayed waveguide grating chip of the above
structure, having been temporarily fixed to the temporal fixing
plate 49, is immersed in acetone to peel it off the temporal fixing
plate 49 as shown in FIG. 3B. The waveguide forming region 10 is at
this time divided into the first waveguide forming region 10a and
the second waveguide forming region 10b by the intersecting
dividing planes 8 and the non-intersecting dividing planes 18.
[0071] Optical fiber arrays 21 and 22 (FIG. 1A) next are connected
to the arrayed waveguide grating. Optical fibers 23 and 24 (FIG. 4)
are provided in the optical fiber arrays 21 and 22, respectively.
The optical fibers 23 and 24 are aligned so that cores thereof are
bonded to cores of the optical input waveguides 2 of the arrayed
waveguide grating and of the optical output waveguides 6 of the
same, respectively. In this first embodiment, the clips 19a fix the
waveguide forming region 10b and the substrate 1 underneath thereof
to the base 9. The silicon plate 35 is arranged so as to abut with
the back side of the border region (back side of the substrate 1)
between the first waveguide forming region 10a and the second
waveguide forming region 10b. The clip 19b fixes the silicon plate
35 such that the first waveguide forming region 10a can be slid.
The silicon plate 35 may be provided on the back side of the
waveguide forming region 10 or on the front side of the waveguide
forming region 10.
[0072] The arrayed waveguide grating type optical
multiplexer/demultiplexe- r is housed in the housing package 16 as
shown in FIG. 4. The arrayed waveguide grating is fixed to the
housing package 16 using the holes 15 of the base 9. Thereafter,
the housing package 16 is filled with the matching oil and is
sealed tightly.
[0073] According to the first embodiment, the position shifting
member 17 slides the first waveguide forming region 10a along the
intersecting dividing planes 8 with changes in the temperature.
This sliding compensates for the temperature dependency of the
light transmission central wavelengths of the arrayed waveguide
grating. Moreover, the position shifting mechanism is composed of
the position shifting member 17 being arranged so as to place its
one end on the first waveguide forming region 10a and the other end
on the second waveguide forming region 10b, simplifying the overall
structure of the device. The cost of the device is accordingly
reduced and the production yield thereof is improved.
[0074] This first embodiment adopts the above manufacturing method.
According to the manufacturing method, the dividing lines 80 for
dividing the waveguide forming region 10 into the first waveguide
forming region 10a and the second waveguide forming region 10b are
set in advance. The position shifting member 17 is fixed so as to
be secured in the first waveguide forming region 10a at its one end
and in the second waveguide forming region 10b at its the other
end. The waveguide forming region 10 is then divided into the first
waveguide forming region 10a and the second waveguide forming
region 10b along the dividing lines 80 by peeling it off the
temporal fixing plate 49. Therefore, the relative positions of the
first waveguide forming region 10a and the second waveguide forming
region 10b in the Y direction are the same before and after the
division. According to this embodiment, the light transmission
characteristics before the division of the arrayed waveguide
grating chip thus can be maintained after the division takes place,
reducing the insertion loss.
[0075] The present inventors have examined the arrayed waveguide
grating type optical multiplexer/demultiplexer of the first
embodiment to evaluate whether any increase in insertion loss
results when the temperature of the arrayed waveguide grating
changes from 5.degree. C. to 75.degree. C. arises. As a result of
that examination, the insertion loss was found to increase by 0.2
dB, which can be deemed as almost no increase.
[0076] According to this first embodiment, the position shifting
member 17 is fixed to the front side of the waveguide forming
region 10 through the metal film 31 and the solder 30. Therefore,
unlike a case in which an adhesive is used to fix the position
shifting member 17 to the waveguide forming region 10, the solder
30 will not run outside of the designed pattern but will be
contained within, and the position shifting member 17 can be fixed
to the waveguide forming region 10 exactly as designed. This makes
it possible to manufacture an arrayed waveguide grating high in
compensation accuracy of the temperature dependency of the light
transmission central wavelengths of the arrayed waveguide
grating.
[0077] Moreover, the clips 19a clamp the second waveguide forming
region 10b and the substrate 1 underneath thereof in this first
embodiment. The second waveguide forming region 10b therefore is
hardly influenced by the thermal expansion of the base 9, making it
possible to more accurately slide the waveguide forming region 10a
with respect to the waveguide forming region 10b. This eliminates
the temperature dependency of the light transmission central
wavelengths of the arrayed waveguide grating.
[0078] In this first embodiment, matching oil may be provided in
the space between the intersecting dividing planes 8, and the
arrayed waveguide grating is housed in the housing package 16
filled with the matching oil. Therefore, as described above, an
excellent optical multiplexer/demultiplexer can be manufactured
which can avoid an increase in insertion loss even in a hot and
humid environment. It is also possible to surely prevent cracking
of the arrayed waveguide grating due to moisture absorption from
taking place even if it is an arrayed waveguide grating inferior in
moisture resistant characteristics.
[0079] FIGS. 6A and 6B show the structure of the main part of a
second embodiment of an arrayed waveguide grating type optical
multiplexer/demultiplexer according to the present invention. FIG.
6A is a plan view of the optical multiplexer/demultiplexer of this
embodiment. FIG. 6B is a side view thereof viewed from the right in
FIG. 6A, without the optical fibers 24 and the optical fiber array
22.
[0080] The second embodiment is structured in almost the same way
as the first embodiment. However, the second embodiment differs
from the first embodiment in that it omits the silicon plate 35 in
the border region between the first waveguide forming region 10a
and the second waveguide forming region 10b of the first
embodiment.
[0081] The position shifting member 17 in the second embodiment has
a groove 50 formed so as to coincide with the non-intersecting
dividing planes 18. An example of a method of manufacturing the
arrayed waveguide grating type optical multiplexer/demultiplexer
according to the second embodiment is shown in FIGS. 7A to 8D.
[0082] Dimensions E to U shown in FIGS. 6A to 8D are, for example,
as follows in the second embodiment: E=60 mm, F=1 mm, G=2.5 mm,
H=K=5 mm, J=20 mm, P=30 mm, Q=5 mm, R=5 mm, S=1 mm, T=25 mm, and
U=10 mm.
[0083] In manufacturing the arrayed waveguide grating type optical
multiplexer/demultiplexer of the second embodiment, an arrayed
waveguide grating chip as shown in FIG. 7A is prepared. The
dividing lines 80 (not shown) are set in this chip in a manner
similar as in the first embodiment, and the metal film 31 (not
shown in FIG. 7A) is formed thereon for each end of the position
shifting member 17. The solder 30 is then formed on each metal film
31 as shown in FIG. 7B.
[0084] Thereafter, as shown in FIGS. 8A and 8B, the position
shifting member 17 is fixed with solder so as to place its one end
on the first waveguide forming region 10a and the other end on the
second waveguide forming region 10b.
[0085] As shown in FIGS. 8C and 8D, a plate is selected such that
the distance between the waveguide forming region 10a and the
waveguide forming region 10b in the intersecting dividing planes 8
(the distance between the intersecting dividing planes 8) is about
25 .mu.m, and the distance between the waveguide forming region 10a
and the waveguide forming region 10b in the non-intersecting
dividing planes 18 (the distance between the non-intersecting
dividing planes 18) is about 100 .mu.m. The chip is cut along the
dividing lines 80 by a dicing saw or the like, thereby forming the
intersecting dividing planes 8 and the non-intersecting dividing
planes 18 and dividing the waveguide forming region 10 into the
first waveguide forming region 10a and the second waveguide forming
region 10b.
[0086] In the case in which an arrayed waveguide grating type
optical multiplexer/demultiplexer is manufactured by such a
manufacturing method, a crack may take place starting from the tip
of the division in forming the intersecting dividing planes 8 and
the non-intersecting dividing planes 18. However, the crack can be
avoided completely if, as in the first embodiment, the arrayed
waveguide grating is temporarily fixed to the temporal fixing plate
49 while forming the intersecting dividing planes 8 and then the
waveguide forming region 10 is divided into the first waveguide
forming region 10a and the second waveguide forming region 10b.
[0087] The groove 50 is formed in the position shifting member 17
in the second embodiment. However, the groove 50 is not always
required to be formed and it may be omitted. The groove 50
facilitates the work of cutting the waveguide forming region 10 and
the substrate 1 using a dicing saw or the like after the position
shifting member 17 is fixed with solder.
[0088] The second embodiment is structured as above, and has almost
the same effect as in the first embodiment.
[0089] Since the second embodiment omits the silicon plate 35 that
is provided in the first embodiment, it is somewhat less effective
in preventing the first and second waveguide forming regions 10a
and 10b from shifting their positions in a direction perpendicular
to the plane of the substrate 1 as compared with the first
embodiment. However, the second embodiment provides the above
preventive effect regarding the position shifting by arranging the
position shifting member 17 such that its one end is secured on the
first waveguide forming region 10a and its other end is secured on
the second waveguide forming region 10b. The second embodiment has
been found by the inventors to be successful in limiting an
increase in insertion loss when the temperature of the arrayed
waveguide grating changes from 5.degree. C. to 75.degree. C. to 0.8
dB.
[0090] By manufacturing three arrayed waveguide grating type
optical multiplexer/demultiplexers of the second embodiment, the
present inventors examined the temperature dependency of the light
transmission central wavelengths of these optical
multiplexers/demultiplexers. FIG. 9 shows the results thereof. It
is confirmed by FIG. 9 that the arrayed waveguide grating type
optical multiplexer/demultiplexers of the second embodiment are
optical multiplexers/demultiplexers independent of temperature in
which almost no temperature dependency of light transmission
wavelengths can be found.
[0091] FIG. 10 shows the structure of the main part of a third
embodiment of an arrayed waveguide grating type optical
multiplexer/demultiplexer according to the present invention. The
third embodiment is structured in almost the same way as the first
embodiment. However, the third embodiment differs from the first
embodiment in that, without forming the non-intersecting dividing
planes 18, only the intersecting dividing planes 8 are used to
divide the waveguide forming region 10 into the first waveguide
forming region 10a and the second waveguide forming region 10b, and
in that the position shifting member 17 is provided on the front
side of the border region between the first and second waveguide
forming regions 10a and 10b.
[0092] Although not shown in FIG. 10, in the third embodiment also,
the base 9 is provided and the second waveguide forming region 10b
is fixed to the base 9 by the clips 19a.
[0093] In manufacturing the arrayed waveguide grating type optical
multiplexer/demultiplexer of the third embodiment, and as shown in
FIG. 11A, the dividing lines 80 are set and the metal film 31 is
formed for each end of the position shifting member 17. Then, as
shown in FIG. 11B, a groove 37 having, e.g., a width of about 20
.mu.m and a depth of about 0.2 mm is formed on the waveguide
forming region 10. The position shifting member 17 is fixed at its
respective ends to each metal film 31 on the front side of the film
through solder (not shown). The position shifting member 17 is
fixed in a manner that allows the position shifting member 17 to
set its one end on the first waveguide forming region 10a and its
other end on the second waveguide forming region. A groove 38
having a width of, e.g., about 300 .mu.m is then formed on the back
side of the arrayed waveguide grating chip to form the intersecting
dividing planes 8.
[0094] The third embodiment also can provide the same effects as in
the first embodiment, and is successful in limiting an increase in
insertion loss when the temperature of the arrayed waveguide
grating changes from 5.degree. C. to 75.degree. C. to 0.2 dB.
[0095] Note that the present invention is not limited to the above
embodiments but is capable of adopting various modifications. For
instance, the position shifting member 17 is disclosed as formed
from a copper plate in the above discussed embodiments. However, a
metal material other than copper may be used to form the position
shifting member 17, and a material that is not metal but which has
a thermal expansion coefficient larger than that of the waveguide
forming region 10 may also be used.
[0096] The manufacturing methods adopted in the above discussed
embodiments may also be modified and the metal film 31 may be
formed as follows. First, the metal film 31 is formed in a region
on the front side of the waveguide forming region 10, the region
including areas for forming the solder 30. Then, the resist is
applied thereto to conduct exposure and development using the set
pattern, namely, photolithography. The metal film 31 is removed by
etching (reactive ion etching or wet etching), leaving only the
areas for forming the solder 30. The resist is then removed by
immersing it in the solvent mentioned above or in oxygen
plasma.
[0097] If the metal film 31 is formed by this method, similar to
the manufacturing methods adopted in the above discussed
embodiments, the metal film 31 can be formed precisely in the areas
for forming the solder 30 of the preset pattern on the front side
of the waveguide forming region 10. After that, a solder chip
having almost the same size as the size of the metal film 31 is
placed on each metal film 31 in the same manner as in the above
discussed embodiments. The position shifting member 17 is thus
fixed to the waveguide forming region 10 with solder. The rest of
the process follows the manufacturing methods of the foregoing
embodiments. The arrayed waveguide grating type optical
multiplexer/demultiplexer manufactured in this way has the same
effect as in the arrayed waveguide grating type optical
multiplexer/demultiplexers of the above embodiments. The solder 30
used for solder fixing may be fixed to the entire face of the metal
film 31. There is no inconvenience if the solder 30 is not
completely contained within the regions of metal film 31.
[0098] The material of the solder 30 used for solder fixing of the
position shifting member 17 in the arrayed waveguide grating type
optical multiplexer/demultiplexer according to the present
invention is not limited to the ones mentioned in the preceding
embodiments, but is suitably chosen.
[0099] The position shifting member 17 is provided on the front
side of the waveguide forming region 10 in the above discussed
embodiments. However, the position shifting member 17 may be
provided on the back side of the substrate 1.
[0100] The arrayed waveguide grating is formed utilizing the
reciprocity of the optical circuit. Therefore, although it is the
first slab waveguide 3 that is divided into two in the above
discussed embodiments, the second slab waveguide 5 may be divided
instead. When the second slab waveguide 5 is divided into two, one
or both of the divided slab waveguides are slid by the position
shifting member 17 along the intersecting dividing planes 8 in a
direction that makes the temperature dependency of the light
transmission central wavelengths less. This arrangement also
provides the same effect as in the above discussed embodiments and
eliminates the temperature dependency change of the light
transmission central wavelengths.
[0101] The intersecting dividing planes 8 of the first slab
waveguide 3 or of the second slab waveguide 5 are not limited to
planes almost parallel to the X axis as in the above discussed
embodiments. The planes may be slanted in the X axis. It is
sufficient if the dividing planes intersect with a route of light
traveling through the slab waveguide to be divided.
[0102] A plurality of optical input waveguides 2 are provided in
the waveguide structure of the arrayed waveguide grating according
to the above discussed embodiments. However, the number of optical
input waveguides 2 to be provided may be one.
[0103] Although the waveguide forming region 10b is clamped by the
clips 19a to be fixed to the base 9 in the above discussed
embodiments, a clamping member other than the clips 19a may be used
to fix the waveguide forming region 10b to the base 9. It is also
possible to reverse the roles of the waveguide forming regions 10a
and 10b by clamping the periphery of the waveguide forming region
10a to fix the region 10a to the base 9, and by then moving the
waveguide forming region 10b along the intersecting dividing planes
8.
[0104] The position shifting member 17 in the above discussed
embodiments is arranged such that the position shifting member 17
is secured in the first waveguide forming region 10a at its one end
and is secured in the second waveguide forming region 10b at its
other end. The position shifting member 17 can also be arranged as
shown in FIGS. 12A and 12B and still control the insertion loss of
the arrayed waveguide grating type optical
multiplexer/demultiplexer. In FIGS. 12A and 12B, the position
shifting member 17 is arranged to set its one end on the base 9 and
its other end on one or both of the first and second waveguide
forming regions 10a and 10b (on the first waveguide forming region
10a in FIGS. 12(a), 12(b). This arrangement is obtained by the
following manufacturing method.
[0105] An arrayed waveguide grating chip is placed on the base 9
formed from a quartz plate or the like and having a shape of the
letter U, as shown in FIG. 13A. The dividing line 80 is set in
advance. Only the second waveguide forming region 10b is fixed to
the base 9 using a thermally curable adhesive or the like. As shown
in FIGS. 13B and 13C, the position shifting member 17 is then fixed
such that the position shifting member 17 secures its one end on
the first waveguide forming region 10a and its other end on the
base 9. The waveguide forming region 10 is thereafter divided into
the first waveguide forming region 10a and the second waveguide
forming region 10b along the dividing line 80.
[0106] This arrangement maintains the distance between the first
waveguide forming region 10a and the second waveguide forming
region 10b in the intersecting dividing planes 8. Therefore, the
light transmission characteristics before the waveguide forming
region 10 is divided can be maintained after the division.
[0107] Though not shown in FIGS. 12A to 12D, the arrayed waveguide
grating type optical multiplexer/demultiplexer therein may include
a position shift preventing member such as the silicon plate 35
shown in FIG. 1A in the border region between the first waveguide
forming region 10a and the second waveguide forming region 10b.
Precision can be improved in terms of relative positions of the
first waveguide forming region 10a and the second waveguide forming
region 10b in the Z direction by providing such a position shift
preventing member. In the arrayed waveguide grating type optical
multiplexer/demultiplexer thus structured, the inventors have found
that the insertion loss is increased by about 0.5 dB when the
temperature of the arrayed waveguide grating changes from 5.degree.
C. to 75.degree. C.
[0108] The structure of the base 9 is not particularly limited in
the arrayed waveguide grating type optical
multiplexer/demultiplexer to which the above manufacturing method
is applied. However, the U-shaped base 9 obtained by forming a U
groove 40 as above facilitates the division of the arrayed
waveguide grating along the dividing lines 80.
[0109] In comparison with the position shifting member 17 shown in
FIG. 12B, the position shifting member 17 shown in FIG. 12A is more
suitable for accurate control of how far the first waveguide
forming region 10a is moved. This is because the structure shown in
FIG. 12B allows an adhesive 13 to uncontrollably run inward from
its designated position in the longitudinal direction of the
position shifting member 17, whereas there is no such
uncontrollability regarding the adhesive 13 in the structure shown
in FIG. 12A. The running adhesive 13 in the structure of FIG. 12B
may make the length J' in the longitudinal direction of the
position shifting member 17, which functions to move the first
waveguide forming region 10a, shorter than the length J necessary
to accurately move the first waveguide forming region 10a. The
structure of FIG. 12A can prevent the free running of the adhesive
13 and hence the position shifting member 17 can be fixed more
accurately.
[0110] Accordingly, it is preferable in the present invention to
use the position shifting member 17 having the structure of FIG.
12A, or to secure the position shifting member 17 through the metal
film 31 and the solder 30 on the front side of the waveguide
forming region 10 or the back side of the substrate 1 as in the
above discussed embodiments.
[0111] Through holes 25 may be formed in the structure where, as
shown in FIG. 14A, the intersecting dividing planes 8 that
intersect with one or both of the first slab waveguide 3 and the
second slab waveguide 5 (the first slab waveguide 3 in FIG. 14A)
start from one end of the waveguide forming region 10 and stretch
to the midsection thereof. As shown in FIGS. 14A and 14B, the
through holes 25 (25a and 25b) pierce the waveguide forming region
10 (here, the region 10b) from the front side thereof and reach the
substrate 1 to connect with the space between the intersecting
dividing planes 8 and the space between the non-intersecting
dividing planes 18, respectively.
[0112] The through holes 25a and 25b are formed outside the area
where the waveguide structure is formed. The side walls of the
through holes have smooth surfaces. In the example illustrated in
FIGS. 14A and 14B, the through hole 25a has a square-like shape in
the X-Y plane. Each side of the square may be about 4 mm and each
corner thereof may have a radius of curvature of 0.5 mm. The
through hole 25b may also be circular in the X-Y plane and the
diameter thereof may be 2.5 mm.
[0113] The arrayed waveguide grating type optical
multiplexer/demultiplexe- r is reinforced by the through holes 25a
and 25b connected with the space between the intersecting dividing
planes 8 and the space between the non-intersecting dividing planes
18, respectively, as shown in FIGS. 14A and 14B. The strength
thereof is enhanced against cracking or breakage of the ends of the
intersecting dividing planes 8 and of the non-intersecting dividing
planes 18 if, e.g., a module packaging the arrayed waveguide
grating type optical multiplexer/demultiplexer is dropped by
mistake during its handling.
[0114] In the arrayed waveguide grating type optical
multiplexer/demultiplexer having the structure shown in FIGS. 14A
and 14B, the through holes 25a and 25b may be respectively formed
on the tips of dividing lines after the dividing lines are set. The
dividing lines are for forming the dividing planes including the
intersecting dividing planes 8 (here, the intersecting dividing
planes 8 and the non-intersecting dividing planes 18). The dividing
planes are for dividing the waveguide forming region 10 into the
first waveguide forming region 10a and the second waveguide forming
region 10b. Alternatively, the through holes 25a and 25b may be
formed after the dividing lines are set and the metal film 31 is
formed.
[0115] It is possible in the arrayed waveguide grating type optical
multiplexer/demultiplexer having the structure shown in FIGS. 14A
and 14B to form a hole in substrate 1 using etching by KOH or the
like after the through holes 25a and 25b are formed.
[0116] The dividing planes such as the intersecting dividing planes
8 and the non-intersecting dividing planes 18 are formed by cutting
in the embodiment modes above. However, the cleavage method
(split-open) or other methods may be used to form these dividing
planes.
[0117] According to a first aspect of the present invention, in the
method of manufacturing a arrayed waveguide grating type optical
multiplexer/demultiplexer, one or both of a first slab waveguide
and a second slab waveguide are divided into two by intersecting
planes that intersect the route of light traveling along one of the
slab waveguides. The waveguide forming region is divided by the
dividing planes into the first waveguide forming region that
includes one divided slab waveguide and a second waveguide forming
region that includes the other divided slab waveguide. A position
shifting member with a function of moving one or both of the first
and second waveguide forming regions along the dividing planes is
fixed before the division such that the position shifting member
secures its one end on the first waveguide forming region and
secures its other end on the second waveguide forming region.
Therefore, the relative positions of the first waveguide forming
region and the second waveguide forming region before the division
are almost the same as those after the division.
[0118] According to a second aspect of the present invention, in a
method of manufacturing the arrayed waveguide grating type optical
multiplexer/demultiplexer, the arrayed waveguide grating is placed
on a base. As in the first aspect of the present invention, the
waveguide forming region is divided into a first waveguide forming
region and a second waveguide forming region. A position shifting
member with a function of moving one or both of the first and
second waveguide forming regions along the dividing planes is fixed
before the division such that the member secures its one end on the
base and secures its other end on one or both of the first and
second waveguide forming regions. Therefore, the relative positions
of the first waveguide forming region and the second waveguide
forming region before the division are almost the same as those
after the division.
[0119] The arrayed waveguide grating type optical
multiplexer/demultiplexe- r manufactured by applying the
manufacturing method of the present invention thus can maintain,
after the waveguide forming region is divided, the light
transmission characteristics before the division.
[0120] According to an arrayed waveguide grating type optical
multiplexer/demultiplexer of the present invention, one or both of
first and second slab waveguides are divided into two by
intersecting planes that intersect the route of the light traveling
along the waveguides. The intersecting planes serve as dividing
planes and divide the waveguide forming region into a first
waveguide forming region that includes one divided slab waveguide
and a second waveguide forming region that includes the other
divided slab waveguide. One or both of the first waveguide forming
region and the second waveguide forming region are moved along the
dividing planes by a position shifting member. Therefore, it is
possible to compensate, with the use of the movement by the
position shifting member, shifts in light transmission central
wavelengths of the arrayed waveguide grating which is caused by,
for example, the temperature change of the arrayed waveguide
grating.
[0121] In the arrayed waveguide grating type optical
multiplexer/demultiplexer according to the present invention, when
the position shifting member is arranged such that its one end is
secured on the first waveguide forming region and its other end is
secured on the second waveguide forming region, the structure of
the device is simplified and precision is improved. Furthermore,
the cost of the device is reduced and the yield thereof is
increased.
[0122] According to the arrayed waveguide grating type optical
multiplexer/demultiplexer of the present invention, metal films are
formed in the waveguide forming region, solder is formed on front
side of areas for forming the metal films, and the position
shifting member is fixed to the waveguide forming region through
the solder and the metal films. Unlike the case in which the
position shifting member is fixed by an adhesive, for example, the
position shifting member thus can be fixed exactly as designed
without fear of adhesive running uncontrollably. This makes an
excellent arrayed waveguide grating that has high temperature
compensation precision of light transmission wavelengths of the
arrayed waveguide grating.
[0123] According to the arrayed waveguide grating type optical
multiplexer/demultiplexer of the present invention, one of the
first waveguide forming region and the second waveguide forming
region is fixed, whereas the other is moved by the position
shifting member. The fixed waveguide forming region is clamped by
the clamping member and held to the base of the arrayed waveguide
grating type optical multiplexer/demultiplexer. Fixing one
waveguide region makes it easy to smoothly move the other waveguide
forming region.
[0124] According to the arrayed waveguide grating type optical
multiplexer/demultiplexer of the present invention, one of the
first waveguide forming region and the second waveguide forming
region is fixed, whereas the other is moved by the position
shifting member. A position shift preventing member for preventing
the first and second waveguide forming regions from shifting toward
the direction perpendicular to the substrate plane is provided in
at least a part of the border region between the first waveguide
forming region and the second waveguide forming region. The first
and second waveguide forming regions are thus prevented from
shifting toward the direction perpendicular to the substrate plane.
Therefore, an increase in insertion loss by this positional shift
can be controlled.
[0125] According to the arrayed waveguide grating type optical
multiplexer/demultiplexer of the present invention, the position
shift preventing member is formed from a plate-like material having
a flat surface, and is arranged such that the flat surface abuts
with the front side of the waveguide forming region or the back
side of the substrate. The shift position preventing member can
readily be formed using the plate-like material, and the positional
shift of the first and second waveguide forming regions toward the
direction perpendicular to the substrate plane can be
prevented.
[0126] According to the arrayed waveguide grating type optical
multiplexer/demultiplexer of the present invention when the
position shifting member is a metal member, a metal member having a
large thermal expansion rate is used to form the position shifting
member. The arrayed waveguide grating type optical
multiplexer/demultiplexer of the present invention is thus readily
manufactured.
[0127] According to the arrayed waveguide grating type optical
multiplexer/demultiplexer of the present invention, through holes
piercing the waveguide forming region and reaching the substrate
are formed from the front side of the waveguide forming region in
areas outside the waveguide structure. The side walls of the
through holes have smooth surfaces. The dividing planes that
intersect with one or both of the first slab waveguide and the
second slab waveguide start from one end of the waveguide forming
region and stretch to the midsection thereof to communicate with
the through holes. This enhances the strength thereof against
cracking or breakage of the ends of the dividing planes when, e.g.,
a module packaging the arrayed waveguide grating type optical
multiplexer/demultiplexer is dropped by mistake during its
handling.
[0128] In the above discussion the position shifting member 17 has
an operation to expand and contract to move one or both of the
first and second waveguide forming regions along the dividing
planes. In this context the position shifting member 17 operates as
an expansion/contraction member. However, it should be apparent to
those of ordinary skill in the art that other mechanisms for moving
one or both of the first and second waveguides relative to each
other could also be implemented instead of relying on a device
which expands and contracts, as in the embodiments noted above. As
one specific example, it is possible that a stepping motor could be
utilized to shift one or both of the first and second waveguides
relative to each other based on a sensed temperature. One of the
important features of the present invention is that one or both of
the first and second waveguides is shifted relative to each other,
and other mechanisms which can induce such a shifting are also
possible within the scope of the present invention.
[0129] Obviously, numerous additional modifications and variations
of the present invention are possible in light of the above
teachings. It is therefore to be understood that within the scope
of the appended claims, the present invention may be practiced
otherwise than as specifically described herein.
* * * * *