Optical circulator

Details Optical circulator Optical circulator

2001-12-05

2004-11-30

Healy, Brian (Department: 2874)

Optical waveguides

With optical coupler

C385S011000, C385S047000, C359S484010, C359S494010, C359S490020, C359S490020, C359S490020, C359S618000, C398S152000

Reexamination Certificate

active

06826323

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to optical circulators.
2. Description of the Related Art
Optical circulators are devices having multiple optical ports and include optical structures that transfer light from an optical port n to another optical port n+1. For example, a three port optical circulator has three optical ports and an optical structure that transfers light from a first optical port to a second optical port and from the second optical port to a third optical port. Various optical structures have been proposed for optical circulators. The schematic in
FIG. 13
shows one example of a typical three port optical circulator having an optical circulator unit
30
, a first optical port
31
and a third optical port
33
arranged adjacent to each other on one end of the optical circulator unit
30
, and a second optical port
32
disposed on the opposite end of the optical circulator.
Light enters an optical circulator at a light entry port and then propagates through the optical circulator to an associated light exit port. In a typical three port optical circulator, the first optical port
31
and the second optical port
32
are light entry ports while the second optical port
32
and the third optical port
33
are light exit ports. Thus, the second optical port
32
functions both as a light entry port, for light propagating to the third optical port
33
, and a light exit port, for light emanating from the first optical port
31
. Due to its relationship with both the first optical port
31
and third optical port
33
, the proper alignment of the second optical port
32
with the first optical port
31
must be done in conjunction with the alignment of the third optical port
33
. In addition, a positional change of one optical port correspondingly affects the other two optical ports.
The optical circulator unit
30
typically contains a series of optical elements functionally structured to pass light from the first optical port
31
to the second optical port
32
and the second optical port
32
to the third optical port
33
. One example of a conventional optical circulator unit showing the optical element structure is depicted in
FIG. 14
, which is the one proposed in the Japanese Patent No. 2,539,563. The optical circulator unit
30
in
FIG. 14
comprises optical elements arranged in a series along an optical axis Z direction, with the optical surfaces (light incidence surface and light exit surfaces) of adjacent optical elements facing each other. The structure of the typical optical circulator unit
30
in
FIG. 14
specifically consists of a first birefringent crystal plate
1
, a first split half wave plate
2
, a first Faraday rotator
3
, a second birefringent crystal plate
4
, a second Faraday rotator
5
, a second split half wave plate
6
, and a third birefringent crystal plate
7
, arranged in that order.
Another structural example of a conventional optical circulator unit is shown in FIG.
15
. While the resulting optical functionality of the optical circulator unit
30
shown in
FIG. 15
is the same as the one shown in
FIG. 14
, the number of optical elements used in the structure of the optical circulator unit
30
in
FIG. 15
has been reduced. Specifically, a first split Faraday rotator
15
in
FIG. 15
replaces the first split half wave plate
2
and the first Faraday rotator
3
, shown in
FIG. 14
, and a second split Faraday rotator
16
as shown in
FIG. 15
replaces the second split half wave plate
6
and the second Faraday rotator
5
shown in FIG.
14
.
One problem with conventional optical circulators is uncontrolled optical system return loss due to reflecting incident light back along the same path it came from. Additionally, optical waveguide core alignment problems relating to the complexity of aligning three associated optical cores can decrease the optical circulator reliability. Optical communication systems employing optical circulators can be adversely affected by both of these problems.
SUMMARY OF THE INVENTION
The invention comprises optical circulators, methods of making optical elements for an optical circulator, methods of controlling light in an optical circulator, and optical communication systems using an optical circulator. Optical circulators are provided for controlling the back propagation of optical signals that occur within the optical circulator. In one embodiment, the invention comprises an optical circulator comprising at least three optical ports and at least one optical element having optical surfaces slanted with respect to an optical axis so as to form at least a pair of oblique optical surfaces, the relative slant of the optical surfaces such that the direction of the optical path exiting the optical element is at least substantially parallel to the direction of the optical path entering the optical element.
In another embodiment, the invention comprises an optical circulator having at least three optical ports and configured to route light input at port n to port n+1 comprising at least one optical element of a non-rectangular parallelepiped shape.
In yet another embodiment, the invention comprises an optical circulator comprising at least three optical signal ports and a substantially parallelepiped shaped optical element disposed so that its optical surfaces are non-perpendicular to an optical axis, whereby at least some incident light is reflected in a direction non-parallel to its incident direction.
In another embodiment, the invention comprises an optical circulator comprising a first lens and a second lens, a first optical waveguide having a first optical port and a third optical waveguide having a third optical port arranged adjacent to each other and facing the first lens, positioned with either the first optical waveguide and the first optical port or the third optical waveguide and the third optical port aligned along the central axis of said first lens, a second optical waveguide having a second optical port disposed facing second lens and aligned along the central axis of the second lens, and a prism disposed adjacent to the first lens adjusting the direction of light emanating from the first optical port and the direction of light propagating to the third optical port so that the optical path of light emanating from the first optical port is parallel to the optical path of light propagating to the third optical port.
In a further embodiment, the invention comprises an optical circulator comprising at least three optical signal ports, at least one optical element having a pair parallel optical surfaces, the optical surfaces having an oblique relative slant with respect to an optical axis, a first lens and a second lens, a first optical waveguide having a first optical port and a third optical waveguide having a third optical port arranged adjacent to each other so that the first optical port and the third optical port face the first lens and positioned with either the first optical waveguide and the first optical port or the third waveguide and the third optical port at least substantially aligned along the central axis of the first lens, and a second optical waveguide having a second optical port disposed facing the second lens and at least substantially aligned along the central axis of the second lens. The optical circulator further comprises a light path adjusting optical element intersecting the light path passing through the first optical port and the light path passing through the third optical port and adjusting the direction of the light paths so the light passing through the first optical port and the light passing through the third optical port is at least substantially parallel to each other, and an optical offset element configured to produce a parallel shift in the optical path of light propagating through the optical offset element.
The invention also comprises methods of making an optical circulator. In one embodiment the invention comprises a method for cutting optical material to form the oblique optical surfaces. The

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