Optical waveguides – Planar optical waveguide
Reexamination Certificate
2001-09-28
2002-12-31
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
Planar optical waveguide
C385S046000, C385S024000, C385S014000
Reexamination Certificate
active
06501896
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical waveguide circuit such as an arrayed waveguide grating used for optical transmissions, etc.
BACKGROUND OF THE INVENTION
Recently, optical wavelength multiplexing transmissions have been researched and studied as a method for remarkably increasing transmission capacity, some of which have been used in practical applications. Such an optical wavelength multiplexing transmission is used to transmit, for example, a plurality of light having different wavelengths through multiplexing. In such an optical wavelength multiplexing transmission system, in order to pick up light wavelength by wavelength at the light receiving side from a plurality of transmitted light, it is indispensable that an optical transmission element, etc., which can transmit only light having predetermined wavelengths is provided in the system.
As one example of optical transmission elements, there is an arrayed waveguide grating (AWG: Arrayed Waveguide Grating) as shown in, for example, FIG.
6
. The arrayed waveguide grating is such that it has a waveguide construction, as shown in the same drawing, on a substrate
11
. The waveguide construction of the arrayed waveguide grating is as shown below. That is, an input side slab waveguide
13
is connected to the emission side of incidence waveguides
12
as one or more optical input waveguides juxtaposed to each other. And, a plurality of juxtaposed waveguides
14
are connected to the emission side of the input side slab waveguide
13
. An output side slab waveguide
15
acting as the second slab waveguides is connected to the emission side of the plurality of arrayed waveguides
14
. Emission waveguides
16
acting as a plurality of juxtaposed optical output waveguides are connected to the emission side of the output slab waveguide
15
.
The arrayed waveguides
14
propagate light introduced from the input side slab waveguide
13
, and are formed so as to have lengths different from each other. Also, the emission waveguides
16
are provided so as to correspond to the number of signal light, divided by, for example, an arrayed waveguide grating, having wavelengths different from each other. In addition, a number (for example, 100 lines) of arrayed waveguides
14
are usually provided. However, in the same drawing, in order to simplify the drawing, the number of the respective waveguides
12
,
14
, and
16
is simplified for illustration.
For example, transmission side optical fibers are connected to the incidence waveguides
12
, into which wavelength multiplexed lights are introduced. Subsequently, light which is introduced into the input side slab waveguide
13
, passing through the incidence waveguides
12
, is diffracted by the diffraction effect thereof, and made incident into a plurality of respective arrayed waveguides
14
, wherein the light propagates through the respective arrayed waveguides
14
.
Light which propagated through the respective arrayed waveguides
14
reaches the output side slab waveguide
15
, and is further condensed at the emission waveguides
16
for output. Also, since the lengths of the respective arrayed type waveguides
14
differ from each other, a shift occurs in the phases of individual lights after they propagated through the respective arrayed waveguides
14
. And, the phase front of a light from the arrayed waveguide is inclined in compliance with the quantity of the tilt, wherein the position of condensing the light is determined by the angle of the inclination, and the light condensing positions of light having different wavelengths differ. By forming the emission waveguides
16
at the condensing positions of light having different wavelengths, it is possible to output light having different wavelengths from the emission waveguides
16
wavelength by wavelength.
For example, as shown in the same drawing, as wavelength multiplexed light having wavelengths &lgr;
1
, &lgr;
2
, &lgr;
3
, . . . &lgr;n (n: an integral number) is inputted from one incidence waveguide
12
, the light is diffracted by the input side slab waveguide
13
. And, it reaches the arrayed waveguides
14
, and as described above, is condensed at different positions on the basis of wavelength, passing through the output side slab waveguide
15
. Light having different wavelengths is made incident into different emission waveguides
16
, and are outputted from the emission ends of the emission waveguides
16
, passing through the respective emission waveguides
16
. And, since optical fibers for light output are connected to the emission ends of the respective emission waveguides
16
, it is possible to pick up light of respective wavelengths via the optical fibers.
In the arrayed waveguide grating, the wavelength resolution of the diffraction grating is proportional to a difference (&Dgr;L) in length of the respective arrayed waveguides
14
. Therefore, by designing the &Dgr;L so as to become larger, it will become possible to multiplex and demultiplex wavelength multiplexed light having narrow wavelength intervals, which could not be achieved in prior arts. That is, the arrayed waveguide grating can achieve light multiplex and demultiplex functions (functions to multiplex and demultiplex a plurality of light signals having a wavelength interval of 1 mn or less), which are required in achievement of a high bite rate optical wavelength multiplexed transmission.
The abovementioned arrayed waveguide grating is an optical waveguide circuit that is formed so that an optical waveguide portion
10
having a lower cladding, a core and an upper cladding, which are formed of silica-based glass, is formed on a substrate
11
made of silicon, etc. The arrayed waveguide grating is such that the lower cladding is formed on the substrate
11
made of silicon, etc., the core which constitutes the abovementioned waveguide is formed thereon, and the upper cladding is further formed on the core so as to cover the core. In addition, the upper cladding was made of silica-based glass to which, B
2
O
3
and P
2
O
5
are, respectively, doped on pure silica glass at a ratio of 5 mole %.
FIG. 7
shows a manufacturing process of the arrayed waveguide grating. Hereinafter, a description is given of the manufacturing method of an optical waveguide circuit with reference to the same drawing. First, as shown in the same drawing (a), a film of the lower cladding
1
b
and a film of the core
2
are formed on the silicon substrate
11
in order. Next, as shown in the same drawing (b) , photolithography and reactive ion etching method are applied thereto, using a mask
8
. By the application, as shown in the same drawing (c), an optical waveguide pattern of the arrayed waveguide grating is formed by processing the film of the core
2
, whereby the core
2
of the optical waveguide construction is formed.
Next, as shown in the same drawing (d) , a film of the upper cladding
1
a
is formed on the upper side of the core
2
in a form embedding the core
2
. In addition, the film of the upper cladding
1
a
is formed by depositing the upper cladding glass particles
5
by the flame hydrolysis deposition method and consolidating the upper cladding glass particles
5
at, for example, 1200° C. through 1250° C.
However, originally, in an arrayed waveguide grating that is applied as optical transmission elements for optical wavelength multiplexed transmissions as described above, it is preferable that the polarization dependency loss (PDL) in the TE mode and TM mode is as close to zero as possible. However, in the prior art arrayed wavelength grating, the abovementioned polarization dependency loss (PDL) was 3 dB where the center wavelength &lgr;c is in a range of ±0.1 nm.
Therefore, in order to compensate the polarization dependency loss, the prior art arrayed waveguide grating was constructed as shown in FIG.
8
. That is, a half-wave plate
3
formed of polyimide, etc., is inserted into the middle way of the arrayed waveguide
14
in the form of crossing all the arrayed waveguides
14
. If so, a polarized w
Kashihara Kazuhisa
Nakajima Takeshi
Nara Kazutaka
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