Switchable interleaved channel separator devices and systems

Details Switchable interleaved channel separator devices and systems Switchable interleaved channel separator devices and systems

2001-01-30

2003-09-02

Dang, Hung Xuan (Department: 2873)

Optical: systems and elements

Optical modulator

Light wave temporal modulation

C359S199200, C359S199200, C359S199200, C359S484010, C359S494010, C359S490020, C385S016000, C385S017000, C385S018000, C385S024000

Reexamination Certificate

active

06614573

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to optical networks, and more particularly, to optical switching, routing, multiplexing and de-multiplexing devices.
BACKGROUND OF THE INVENTION
The use of optical fiber for long-distance transmission of voice and/or data is now common. As the demand for data carrying capacity continues to increase, there is a continuing need to utilize the bandwidth of existing fiber-optic cable more efficiently. An established method for increasing the carrying capacity of existing fiber cable is Wavelength Division Multiplexing (WDM) in which multiple information channels are independently transmitted over the same fiber using multiple wavelengths of light. In this practice, each light-wave-propagated information channel corresponds to light within a specific wavelength range or “band.”
In this document, these individual information-carrying lights are referred to as either “signals” or “channels.” The totality of multiple combined signals in a wavelength-division multiplexed optical fiber, optical line or optical system, wherein each signal is of a different wavelength range, is herein referred to as a “composite optical signal.”
Because of the increased network traffic resulting from the use of the WDM technique, there is an increasing need for sophisticated optical switching and routing devices which can quickly route or re-route numerous channels amongst various optical communications lines.
FIG. 14
illustrates a known apparatus that performs this function. This apparatus
300
has two control states and serves to separate channels of the wavelength spectrum applied to an input port
11
and determines which of two output ports
13
,
14
are coupled to each of the channels. The input WDM signal enters the first birefringent element
30
that spatially separates horizontal and vertically polarized components of the WDM signal. The first birefringent element
30
allows the vertically polarized portion of the optical signal to pass through without changing course. In contrast, horizontally polarized waves are redirected at an angle because of the birefringent walk-off effect. The horizontally polarized component travels along a path
301
as an extraordinary signal in the first birefringent element
30
while the vertically polarized component
302
travels as an ordinary signal and passes through without spatial reorientation.
Both the horizontally and vertically polarized components
301
and
302
are coupled to a switchable polarization rotator
40
under control of a control bit. The polarization rotator
40
consists of two sub-element rotators that form a complementary state, i.e. when one turns on the other turns off, such that, in general, the rotator
40
rotates the signals by either 0° (i.e., no rotation) or 90°.
FIG. 14
illustrates one control state in which the signal
302
is rotated by 90° so that both signals
303
,
304
exiting the rotator
40
have a horizontal polarization.
The stacked waveplates element
61
is a stacked plurality of birefringent waveplates at selected orientations that generate two eigen states. The first eigen state carries a first sub-spectrum with the same polarization as the input, and the second eigen state carries a complementary sub-spectrum at the orthogonal polarization. With horizontal polarizations
303
,
304
input to the stacked waveplates element
61
as shown in
FIG. 14
, orthogonal vertical and horizontal polarizations are generated with the first spectral band residing in horizontal polarization and the second spectral band residing in vertical polarization. With vertical polarizations
303
,
304
input to the stacked waveplates element
61
orthogonal vertical and horizontal polarizations are generated with the first spectral band residing in vertical polarization and the second spectral band residing in horizontal polarization.
The pairs of optical responses
305
,
306
output by the stacked waveplates element
61
are coupled to a second birefringent element
50
. This birefringent element
50
has a similar construction to the first birefringent element
30
and spatially separates the horizontally and vertically polarized components of the input optical signals
305
and
306
. As shown in
FIG. 14
, the optical signals
305
,
306
are broken into vertically polarized components
307
,
308
containing the second spectral band and horizontally polarized components
309
,
310
containing the first spectral band. Due to the birefringent walk-off effect, the two orthogonal polarizations that carry first spectral band
309
,
310
in horizontal polarization and second set spectral band
307
,
308
in vertical polarization are separated by the second birefringent element
50
.
Following the second birefringent element
50
, the optical elements on the input side of the second birefringent element
50
can be repeated in opposite order, as illustrated in FIG.
14
. The second stacked waveplates element
62
has substantially the same composition as the first stacked waveplates element
61
. The horizontally polarized beams
309
,
310
input to the second stacked waveplates element
62
, are further purified and maintain their polarization when they exit the second stacked waveplates element
62
. On the other hand, the vertically polarized beams
307
,
308
experience a 90° polarization rotation and are also purified when they exit the second stacked waveplates element
62
. The 90° polarization rotation is due to the fact that the vertically polarized beams
307
,
308
carry the second spectral band and therefore are in the complementary state of element
62
. At the output of the stacked waveplates element
62
, all four beams
311
,
312
and
313
,
314
have horizontal polarization.
To recombine the spectra of the two sets of beams
311
,
312
and
313
,
314
, a second polarization rotator
41
and a second birefringent element
70
are used. The second rotator
41
has two sub-elements that intercept the four parallel beams
311
-
314
. The two sub-elements of the second rotator
41
are set at a complementary state to the first rotator
40
. In the state illustrated in
FIG. 14
, the polarization of beams
311
and
313
is rotated by 90°, and beams
312
and
314
are passed without change of polarization. This results in an orthogonal polarization pair
315
,
316
and
317
,
318
for each spectral band at the output of the second rotator
41
. Finally, a second birefringent element
70
re-combines the two orthogonal polarizations
315
,
316
and
317
,
318
using the walk-off effect to produce two spectra that exit at ports
14
and
13
, respectively. In the operational state shown in
FIG. 14
, the first and second spectral bands exit at ports
13
and
14
, respectively. In the other operational state of the apparatus
300
, the outputs of the two spectral bands are reversed.
Although the known apparatus
300
(
FIG. 14
) appears to be capable of performing its intended function, the structure of the apparatus
300
entails undesirable complexity since separate sets of elements perform the functions of switching the operational state of the apparatus
300
and of sorting the polarizations of channels according to their respective wavelengths. In the apparatus
300
, the polarization rotators
40
-
41
and the wavelength filters
61
-
62
, respectively, perform the switching and sorting operations. Further, since all the various functions of the apparatus
300
are performed by transmissive optical elements, the input port
11
and output ports
13
-
14
must necessarily be disposed at opposite sides of the apparatus
300
. Such a disposition causes the apparatus
300
to be excessively large and creates difficulty for coupling the apparatus
300
to fiber ferrules or ribbon cables in which all the fibers are disposed within a single bundle or group.
Accordingly, there exists a need for an improved switchable interleaved channel separator. The improved switchable interleaved channel separator should perform the functions of switching and wavelength

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