Optical waveguide circuit, its manufacturing method and...

Details Optical waveguide circuit, its manufacturing method and... Optical waveguide circuit, its manufacturing method and...

1998-10-14

2001-10-16

Font, Frank G. (Department: 2877)

Optical waveguides

Integrated optical circuit

C385S031000, C385S037000, C385S046000

Reexamination Certificate

active

06304687

ABSTRACT:

This application is the national phase of international application PCT/JP98/00626 filed Feb. 16, 1998 which designated the U.S.
1. Technical Field
The present invention relates to a light waveguide circuit used in a field of an optical communication or an optical information processing, a producing method thereof and a light waveguide circuit module having such a lightwaveguide circuit, and more particularly, to a waveguide type optical element whose optical characteristic does not depend on a temperature, and more specifically, a lightwaveguide circuit such as a lightwavelength grating multiplexer constituted by a waveguide formed on a planar substrate and optical characteristic thereof does not depend on a temperature.
2. Background Art
Recently, studies and developments have actively been made for planar lightwave circuits (PLC) comprising quartz glass lightwaveguide formed on a silicone substrate.
In such a planar lightwave circuit, a lightwavelength grating multiplexing function is realized using a light interference of multiple beams or two beams, such as arrayed-waveguide grating multiplexer (AWG) or Mach Zehnder interferometer (MZI).
The arrayed-waveguide grating multiplexer has a feature that bind and separation of waves of wavelength multiple light can collectively be carried out by interference of a plurality of lights which propagate tens to hundreds of juxtaposed arrayed-waveguides having lengths which are different from one other by n×&Dgr;L.
Details are described in “H. Takahashi et al., Arrayed-Waveguide Grating for Wavelength Division Multi/Demultiplexer With Nanometre Resolution, Electron. Lett., vol. 26, no. 2, pp. 87-88, 1990”.
FIG. 1
shows a circuit diagram of the conventional arrayed-waveguide grating multiplexer,
FIG. 2
shows an enlarged sectional view taken along the line a—a in
FIG. 1
, and
FIG. 3
shows one example of a transmittance spectrum from the central input port to the central output port.
In
FIGS. 1 and 2
, an input waveguide
2
, a first slab waveguide
3
, an arrayed-waveguide
4
, a second slab waveguide
5
, an output waveguide
6
, a waveguide core
7
and a clad
8
are mounted to an Si substrate
1
.
It is apparent from
FIG. 3
that only a particular wavelength is transmitted and other lights are prevented from being transmitted.
The transmission band also has a characteristic of a narrow-band of about 1 nm. A wavelength &lgr; c in which the transmission loss becomes minimum is given by the following equation (1):
 &lgr;c=n×&Dgr;L/m  (1)
wherein, the character m denotes a diffraction degree, the character n denotes an effective refractive index of waveguide. &Dgr;L is a difference of length between adjacent arrayed-waveguides and more specifically, is a value of about 10-100 &mgr;m.
As shown in the equation (1), &lgr;c is determined by a difference of light path length of waveguides (the product of effective refractive index multiplied by length), i.e., n×&Dgr;L, but the difference of light path length depends on a temperature, &lgr;c depends on a temperature accordingly.
FIG. 4
shows transmittance spectrums at temperatures of 25° C., 50° C. and 75° C. In addition,
FIG. 5
shows temperature dependence of &lgr; c.
As can be seen from these drawings, a variation width of &lgr;c with respect to temperature change of 50° C. is about 0.5 mm.
Incidentally, it is known that the optical path length temperature coefficient (1/&Dgr;L)×d (n·&Dgr;L)/dT of quartz-based waveguide is about 1×10
−5
(1/° C.), and a calculated value of the temperature coefficient d&lgr;c/dT of &lgr;c is about 0.01 (nm/°C.) which corresponds to a result of FIG.
5
. Therefore, the arrayed-waveguide grating multiplexer is used in a environment in which the temperature change is about 10°C. to 60°C., a precise temperature control is necessary.
FIG. 6
shows a Mach Zehnder interferometer type lightwaveguide photo-multiplexer. An input waveguide
102
, a directional coupler
103
and
106
, two arm waveguides
104
and
105
are formed on a substrate
101
.
A wave-relativity characteristic of the circuit shown in
FIG. 6
is given by the following equation (2):
J(&lgr;)=½×{1+cos[2&pgr;n&Dgr;L/&lgr;]}  (2)
wherein the symbol &lgr; denotes a wavelength, the character n denotes an effective refractive index, and &Dgr;L is a difference of length of two arm waveguides.
From the equation (2), a wavelength &lgr; c in which the transmission ratio becomes maximum is given by the following equation (3):
&lgr;c=n×&Dgr;L/k  (3)
wherein the character k is an integer.
As apparent from the fact that the equation (3) has the same style as the equation (1), &lgr;c of MZI has the same temperature dependence as that of AWG.
Therefore, when the arrayed-waveguide grating multiplexer or the Mach Zehnder interferometer type lightwaveguide photo-multiplexer is used, it is necessary to keep the temperature of lightwaveguide circuit constant using Peltier element or heater.
Further, a power source, control apparatus or the like is required for operating the Peltier element or heater, which increase a volume and price of the entire lightwaveguide grating multiplexer.
For this reason, it had been required to remove the temperature dependency of the lightwaveguide circuit itself, and to unnecessitate the temperature control.
Conventionally, as a method to lower the temperature dependency of the lightwaveguide circuit, there is a structure that the waveguide is formed at its one portion with a core made of material having a different temperature coefficient of a refractive index, thereby keeping n·&Dgr;L constant even if the temperature is changed, as disclosed in Jpn. Pat. Appln. KOKAI Publication No.8-5834.
However, in this method, two kinds of cores having different materials are intermingled on the same substrate, which complicates the structure and thus, it is not manufactured easily.
As another method, it has been reported a method in which a polymeric material is used as a clad layer (for example, Y. Kokubun et al, “Temperature independent Narrow-Band Filter by Athermal Waveguide”, ECOC'96, WeD. 1.5).
However, in this method, in order to keep the light path length constant, temperature change having a great refractive index of clad material is utilized. Therefore, if the temperature is changed, a difference of refractive index of the core and the clad is changed, and if worst comes worst, the waveguide may not introduce light and therefore, this method can not keep up with wide change of environment temperature.
It is an object of the present invention to realize a simple structure which can reduce the temperature dependency of the wavelength characteristic and which can easily be manufactured, and to provide a lightwaveguide circuit, a producing method thereof, and a lightwaveguide circuit module having the lightwaveguide circuit.
DISCLOSURE OF INVENTION
To achieve the above object, according to a conception 1 of the present invention there is provided, in a lightwaveguide circuit including a plurality of waveguides of different optical path lengths, wherein, a core and an upper clad, a material having a temperature coefficient including a refractive index including a symbol different from that of a temperature coefficient of an effective refractive index of the waveguide is (“temperature compensating material” hereinafter) charged into at least one of a groove formed by removing an upper clad and a core from the waveguide, and a groove formed by removing the upper clad, the core and the lower clad from the waveguide, and a difference in length of the removed portions between adjacent waveguides is proportional to a difference in length of the waveguides which was not removed and remained.
According to a conception 2 of the present invention, in a waveguide comprising quartz glass, a temperature coefficient of an effective refractive index of an waveguide has a positive value (about 1×10
−5
) and therefore, a negative temperature coef

Affiliated with

Also associated with

Rating

Optical waveguide circuit, its manufacturing method and... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optical waveguide circuit, its manufacturing method and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical waveguide circuit, its manufacturing method and... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2561288