Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-09-07
2002-11-05
Mai, Huy (Department: 2873)
Optical waveguides
With optical coupler
Switch
C385S119000
Reexamination Certificate
active
06477292
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical fiber switch employed with an optical fiber communication system or the like and, more particularly, to an improvement in a reflection mirror type optical fiber switch adapted to extend or retract a reflection mirror to or from a gap between a pair of opposing collimator lenses equipped with optical fibers so as to perform switching and coupling of optical fiber circuits.
2. Description of the Related Art
A 2×2 optical fiber switch disclosed under a title “Efficient electromechanical optical switches” (U.S. Pat. No. 5,742,712) belongs to the same category of the aforesaid reflection mirror type optical fiber switch. Referring to FIG.
10
and
FIG. 11
, a configuration of the foregoing conventional reflection mirror type 2×2 optical fiber switch will be described. The switch employs collimator lenses
1
and
2
, and a reflection mirror
3
. For the rod lenses
1
and
2
, SELFOC lens (SFL; a trade name), which has been developed and commercialized by Nippon Sheet Glass Co., Ltd. and is commercially available, may be used.
FIG. 10
illustrates the reflection mirror inserted between the collimator lenses of the switch, and
FIG. 11
illustrates a state wherein the reflection mirror has been removed from an optical path. The switch is a reflection mirror type 2×2 optical fiber switch constructed using the collimator lenses
1
and
2
, and the reflection mirror
3
. For the rod lenses
1
and
2
, SELFOC lens (SFL) developed and commercialized by Nippon Sheet Glass Co., Ltd. and has been commercially available may be used. Optical characteristics, technical information, and typical applications of SELFOC lens have been released from Nippon Sheet Glass Co., Ltd. The foregoing type of switch has been extensively used in an optical wavelength demultiplexer/multiplexer (WDM), an optical splitter, various optical fiber switches, etc.
Referring to FIG.
10
and
FIG. 11
, the rod lenses
1
and
2
having a reference length of 0.25 pitch are disposed so that they oppose each other, with optical axes thereof aligned and a small gap provided between end faces thereof. The reflection mirror
3
is disposed so that it may be repeatedly moved into or out of the gap between the rod lenses
1
and
2
at right angles with respect to the optical axes. Reference characters F
1
, F
2
, F
3
, and F
4
denote optical fibers installed to ferrules or sleeves (not shown) and assembled so that they are positioned symmetrically with the same amount of eccentricity from the optical axes of the rod lenses
1
and
2
.
FIG. 10
shows the reflection mirror
3
that has been inserted between the rod lenses
1
and
2
. In this case, light of a very small mode field that is emitted from the optical fiber F
1
turns into a parallel beam having a mode field that has been expanded through the rod lens
1
, and reaches the reflection mirror
3
. The parallel beam is reflected by the reflection mirror
3
and turned into light having a reduced mode field through the rod lens
1
before being incident on the optical fiber F
2
.
Similarly, light of a very small mode field that is emitted from the optical fiber F
3
turns into a parallel beam having a mode field that has been expanded through the rod lens
2
, and reaches the reflection mirror
3
. The parallel beam is reflected by the reflection mirror
3
and turned into light having a reduced mode field through the rod lens
2
before being incident on the optical fiber F
4
.
FIG. 11
illustrates the state wherein the reflection mirror
3
has been removed from the gap between the rod lenses
1
and
2
. In this case, light of a very small mode field that is emitted from an optical fiber of the optical fiber assembly F
1
turns into a parallel beam having a mode field that has been expanded through the rod lens
1
, then enters and passes through the rod lens
2
to become light of a reduced mode field before entering an optical fiber of the optical fiber assembly F
4
. Similarly, light of a very small mode field that is emitted from an optical fiber of the optical fiber assembly F
3
turns into a parallel beam having a mode field that has been expanded through the rod lens
2
, then passes through the rod lens
1
to become light of a reduced mode field before entering an optical fiber of the optical fiber assembly F
2
. Hence, a circuit of the optical fiber F
1
can be alternately coupled to a circuit of the optical fiber F
2
or the optical fiber F
4
by moving the reflection mirror
3
in or out. Similarly, a circuit of the optical fiber F
3
can be alternately coupled to a circuit of the optical fiber F
2
or the optical fiber F
4
by moving the reflection mirror
3
in or out.
The conventional 2×2 optical fiber switch set forth above has a simple construction, but poses the following problems:
(1) Insertion loss values present a repeatability problem and are susceptible to external influences, such as vibrations and shocks.
(2) Prone to malfunction from magnetic induction under the influences of external magnetic fields.
(3) Poses a structural problem in reducing a size of a switch package to a particular size, namely, a height of 8.5 mm or less to be applicable to a ½ inch printed circuit board.
The problem with the insertion loss values is caused by inconsistent stop positions of the reflection mirror
3
. This problem will be described in detail with reference to FIG.
9
.
When an angle error &sgr;&thgr; with respect to a plane at right angles to an optical axis ZZ of the reflection mirror
3
occurs, a reflection angle of a parallel beam that has been transmitted through the rod lens
1
from the optical fiber assembly F
1
and reflected by the reflection mirror
3
will be smaller by −2&sgr;&thgr;. As a result, the parallel beam is emitted to a point decentered inward from an optical axis of the optical fiber assembly F
2
, leading to the occurrence of an insertion loss attributable to a dislocated axial center. Similarly, a reflection angle of a parallel beam that has been transmitted through the rod lens
2
from the optical fiber assembly F
3
and reflected by the reflection mirror
3
will be larger by +2&sgr;&thgr;. The parallel beam is emitted at a point Q decentered outward from an optical axis of the optical fiber F
2
, resulting in an increased insertion loss.
According to calculated values, if a rod lens having an outside diameter of 2 mm and a pitch of 0.25 are used, two single-mode optical fibers are decentered 0.0065 mm from an optical axis of the rod lens, and a wavelength of 1310 nm is used, then an optical insertion loss will be approximately 1 dB (≈−20%) when an optical squareness error is as follows: &sgr;&thgr;=0.024°. Incidentally, the squareness error is extremely small (tan 0.024°≈0.00042); therefore, if variations in a mechanical position of repeated insertion of the reflection mirror
3
exceed 0.024°, then variations in optical insertion loss will be approximately 1 dB (≈−20%). If the reflection mirror moves due to external forces, such as vibrations or shocks, when the reflection mirror is inserted between the rod lenses, then similar optical insertion loss will incur variations of approximately 1 dB (≈−20%).
In the optical switch disclosed in U.S. Pat. No. 5,742,712, to drive a reflection mirror, the reflection mirror is installed on a distal end of a swing arm attached to a movable piece of a seesaw electric relay. By switching a polarity of current supplied to the seesaw electric relay, a reflection mirror surface at the distal end of the swing arm provided with the reflection mirror is moved into or out of the gap between rod lens surfaces so as to perform switching. This structure in which the reflection mirror is installed on the distal end of the swing arm attached to the movable piece retained by a very small magnetic force of the seesaw electric relay has limitation in reducing size and weight. Furthermore, it is presumed that assembly and ad
Mai Huy
Seikoh Giken Co. Ltd.
Venable
Voorhees Catherine M.
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