Optical: systems and elements – Polarization without modulation – Polarization using a time invariant electric – magnetic – or...
Reexamination Certificate
2000-12-01
2002-04-02
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Polarization without modulation
Polarization using a time invariant electric, magnetic, or...
C359S490020, C359S490020
Reexamination Certificate
active
06366402
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical technology, and more particularly to a method and system for providing an in-line optical circulator.
BACKGROUND OF THE INVENTION
Conventional optical circulators are used for many purposes. For example, conventional optical circulators may be employed in systems transmitting optical signals in order to transmit optical signals in a particular direction. In a three port optical circulator, an optical signal input at the first port will be transmitted to the second port. An optical signal input at the second port will be transmitted to the third port. However, optical signals will not be transmitted in the reverse direction. For example, an optical signal input at the second port will not be transmitted to the first port. Optical circulators can also come in a variety of configurations. One desirable configuration is an in-line optical circulator in which the first and third ports are adjacent, while the second port is at the opposing side of the system.
One prior art optical circulator is described in U.S. Pat. No. 5,909,310 by Li, et al and shown in FIG.
1
A. This conventional optical in-line circulator
10
includes a first port
12
, a second port
14
and a third port
16
. The conventional optical in-line circulator
10
also includes a first collimator
18
, a first birefringent crystal
20
, a first pair of half wave plates
22
A and
22
B, a first Faraday rotator
24
, a conventional Wollaston prism
26
, a second birefringent crystal
28
, a second pair of half wave plates
30
A and
30
B, a second Faraday rotator
30
, a third birefringent crystal
34
, a second collimator
36
and the fiber for the second port
14
.
This conventional optical in-line circulator suffers from two disadvantages. First, the half wave plates
22
A and
22
D in the first pair of wave plates need to be aligned to each other. Similarly, the wave plates
30
A and
30
B in the second pair of wave plates also need to be aligned to each other. They are difficult to aligned respectively to each other in the manufacture process. Therefore, the alignment angular tolerance on the wave plates
22
A,
22
B and
30
A,
30
B are relatively high, which yields a lower isolation. Second, the Wollaston prism
26
is expensive and relatively more complicated to manufacture since it is composed of two wedges
26
A and
26
B with their optical axis parallel and perpendicular to their side direction, as shown in FIG.
1
B. These two wedges
26
A and
26
B has to be separately manufactured and polished, then brought together to form the Wollaston prism
26
. As a result, it make the manufacture process more complex and higher the cost.
U.S. Pat. No. 6,049,426 by Xie et al. (“Xie”) describes another conventional in-line optical circulator.
FIG. 2
depicts a conventional in-line optical circulator
50
in accordance with the teachings of Xie. It does not utilize any half wave plates, also eliminates one birefringent crystal, but uses an additional Wollaston prism
52
having wedges
52
A and
52
B. One of ordinary skill in the art will readily realize that the conventional in-line optical circulator
50
is relatively difficult to manufacture with higher cost. The optical circulator
50
suffers from two drawbacks. First, the optical circulator
50
uses two Wollaston prisms
26
′ and
52
. The cost is thus increased by the additional number of Wollaston prism. Second, since the beam deflection angular tolerance introduced by Wollaston prisms is accumulated with the number of Wollaston prisms used, the beam deflection angular tolerance introduced by Wollaston prisms
26
′ and
52
in circulator
50
is doubled compared with the circulator with only one Wollaston prism, making optical alignment and, therefore, manufacture more difficult and complex.
Accordingly, what is needed is a system and method for providing an optical circulator that is simpler to manufacture with a lower cost. The present invention addresses such a need.
SUMMARY OF THE INVENTION
The present invention provides a method and system for providing an optical circulator. The optical circulator comprises a first port, a second port, a third port and means for establishing a first optical path and a second optical path, the second port is opposite to the first port, while the third port is adjacent to the first port. The first optical path is from the first port to the second port, while the second optical path from the second port to the third port. The optical path establishing means include a first and a second half wave plate, a first and a second rotator pair, and a polarization beam deflector. The first rotator pair is between the first port and the first half wave plate. The second rotator pair is between the second port and the second half wave plate. The polarization beam deflector is for altering a direction of the first optical path and the second optical path. The polarization beam deflector is located between the first rotator pair and the first half wave plate. Thus, when an optical signal is input at the first port, the optical signal travels along the first optical path to the second port. When the optical signal is input to the second port, the optical signal travels along the second optical path to the third port.
According to the system and method disclosed herein, the present invention provides an in-line optical circulator which can be more easily and manufactured with lower cost than conventional in-line optical circulators.
REFERENCES:
patent: 5878176 (1999-03-01), Cheng
patent: 6026202 (2000-02-01), Chang
patent: 6111695 (2000-08-01), Lee et al.
Bay Photonics, Inc.
Sawyer Law Group LLP
Schuberg Darren
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