Compact add-drop multiplexer with low wavelength temperature...

Details Compact add-drop multiplexer with low wavelength temperature... Compact add-drop multiplexer with low wavelength temperature...

2002-12-02

2003-11-11

Ullah, Akm Enayet (Department: 2874)

Optical waveguides

With optical coupler

Plural

C385S031000, C385S033000, C385S060000, C385S061000

Reexamination Certificate

active

06647177

ABSTRACT:

This nonprovisional application claims priority under 35 U.S.C. § 119(a) on patent application No. 091109166 filed in TAIWAN, R.O.C. on May 2, 2002, which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an add-drop multiplexer for use in optical fiber technology, and particularly to a compact add-drop multiplexer with low wavelength temperature sensitivity.
2. Description of the Related Art
In recent years, the Internet has been widely developed, and requirement of network bandwidth, which relates to network connection speed, has largely increased. Presently, wavelength division multiplexing (WDM) technology is one of the most efficient and low-priced solutions for network bandwidth improvement. In WDM technology, an add-drop multiplexer composed of a WDM filter is widely used.
There are various conventional add-drop multiplexers. An example of the conventional add-drop multiplexer
1
is shown in FIG.
1
. The conventional add-drop multiplexer
1
has a first glass ferrule
2
, a pair of optical fibers
3
a
and
3
b
, a first GRIN lens
4
, a WDM filter
5
, a second GRIN lens
6
, a second glass ferrule
7
and another optical fiber
3
c.
In
FIG. 1
, the first glass ferrule
2
has a first hole
2
a
, with the optical fibers
3
a
and
3
b
disposed therein. Then, an adhesive, such as ultraviolet curing epoxy
8
, is applied to fix an end
2
b
of the first glass ferrule
2
to an end
4
a
of the first GRIN lens
4
by adhering the edges of both the ends
2
b
and
4
a
together. Meanwhile, another adhesive, such as heat curing epoxy
9
, is applied to adhere the WDM filter
5
to the other end
4
b
of the first GRIN lens
4
. Further,
Further the second glass ferrule
7
has a second hole
7
a
, with the optical fiber
3
c
disposed therein. Then, ultraviolet curing epoxy
8
is applied to fix an end
7
b
of the second glass ferrule
7
to an end
6
a
of the second GRIN lens
6
by adhering the edges of both the ends
7
b
and
6
a
together. Meanwhile, heat curing epoxy
9
is applied to adhere the WDM filter
5
to the other end
6
b
of the second GRIN lens
6
.
However, in the above-mentioned add-drop multiplexer
1
, the heat curing epoxy
8
, when heated, is at a thin liquid state before curing and may permeate into the light path between the WDM filter
5
and the GRIN lens
4
and
6
. Thus, the cured heat curing epoxy
8
blocks the light path, which leads to reduced signal intensity.
A further conventional compact add-drop multiplexer is disclosed to solve the above-mentioned problem. An example of the conventional compact add-drop multiplexer
100
is shown in FIG.
2
. The conventional compact add-drop multiplexer
100
has a first glass ferrule
10
, a first GRIN lens
20
, a first spacer ring
31
, a second spacer ring
32
, a WDM filter
40
, a second GRIN lens
25
, a second glass ferrule
15
, a third spacer ring
33
and a fourth spacer ring
34
.
In
FIG. 2
, the first glass ferrule
10
has a first hole
11
, with a pair of optical fibers
51
and
52
disposed therein. The second glass ferrule
15
has a second hole
16
, with an optical fiber
53
disposed therein.
Then, an adhesive, such as heat curing epoxy
9
, is applied to adhere the first spacer ring
31
to an end
21
of the first GRIN lens
20
. Meanwhile, heat curing epoxy
9
is applied to adhere the first glass ferrule
10
to the first spacer ring
31
. Similarly, heat curing epoxy
9
is also applied to adhere the second spacer ring
32
to the other end
22
of the first GRIN lens
20
, and to adhere the WDM filter
40
to the second spacer ring
32
. Thus, a clearance
70
exists between the first glass ferrule
10
and the first GRIN lens
20
.
Similarly, heat curing epoxy
9
is applied to adhere the third spacer ring
33
to an end
26
of the second GRIN lens
25
. Meanwhile, heat curing epoxy
9
is applied to adhere the second glass ferrule
15
to the third spacer ring
33
. Similarly, heat curing epoxy
9
is also applied to adhere the fourth spacer ring
34
to the other end
27
of the second GRIN lens
25
, and to adhere the WDM filter
40
to the fourth spacer ring
34
. Thus, a clearance
71
exists between the second glass ferrule
15
and the second GRIN lens
25
.
The spacer rings
31
,
32
,
33
and
34
applied in the compact add-drop multiplexer
100
are cannular, which prevents heat curing epoxy
9
from permeating the spaces between the WDM filter
40
and the GRIN lens
20
and
25
in the thin liquid state before curing. However, material of the spacer rings
31
,
32
,
33
and
34
is generally different from that of the WDM filter
40
and glass ferrules
10
and
15
. It is multi-layer thin films deposited of the WDM filter
40
that determines the bandwidth of the bandpass central wavelength of the add-drop multiplexer. When the add-drop multiplexer with an ultra-narrow bandpass, such as an add-drop multiplexer with channel spacing of 50 GHz, is applied, the bandpass central wavelength of the add-drop multiplexer is greatly affected by the ambient temperature. Consequently, the ambient temperature affects the compact add-drop multiplexer
100
due to the material difference in the spacer rings and the optical elements.
The ambient temperature effect of the spacer rings
30
and the WDM filter
40
in the compact add-drop multiplexer
100
is hereinafter described with reference to FIG.
3
. The WDM filter
40
has a multi-layer thin films deposited structure
41
on the substrate
42
. There are three types of stress in the thin films structure, an inner stress due to thin films deposited structure itself, thermal stress due to thermal expansion coefficient of the substrate of the WDM filter, and thermal stress due to thermal expansion coefficient of the spacer rings. In
FIG. 3
, the spacer ring
30
is adhered to the WDM filter
40
by an adhesive, such as heat curing epoxy
9
. Since the spacer ring
30
and the WDM filter
40
are of different materials, the thermal expansion coefficients of the spacer ring
30
and the WDM filter
40
are different, so that a compressive thermal stress
60
as shown in
FIG. 3
or a tensive thermal stress may be obtained when the temperature changes. Thus, the thermal stress affects the bandpass central wavelength of the add-drop multiplexer, the so-called “temperature drifting effect.”
SUMMARY OF THE INVENTION
In view of this, the present invention relates to a compact add-drop multiplexer with low wavelength temperature sensitivity, which reduces the temperature drifting effect in the conventional compact add-drop multiplexer by selecting spacer rings with a suitable thermal expansion coefficient to compensate for the thermal stress of the WDM filter.
The present invention discloses a compact add-drop multiplexer with low wavelength temperature sensitivity. The compact add-drop multiplexer has a first glass ferrule, a first GRIN lens, a second glass ferrule, a second GRIN lens, a WDM filter, and four spacer rings.
In the compact add-drop multiplexer of the present invention, the first glass ferrule is provided with a first hole and a pair of optical fibers disposed therein, and the second glass ferrule is provided with a second hole and an optical fiber disposed therein.
Further, the first GRIN lens has a first end corresponding to the first glass ferrule and a second end, and the second GRIN lens has a third end corresponding to the second glass ferrule and a fourth end. A first clearance is formed between the first glass ferrule and the first GRIN lens, and a second clearance is formed between the second glass ferrule and the second GRIN lens.
Further, the WDM filter is disposed between the second end of the first GRIN lens and the fourth end of the second GRIN lens.
Among the four spacer rings, the first spacer ring is provided between the first GRIN lens and the WDM filter by being adhered to the WDM filter and the second end of the first GRIN lens with an adhesive. The second spacer ring is provided between the second GRIN lens a

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