Integrable fiberoptic coupler and resulting devices and systems

Details Integrable fiberoptic coupler and resulting devices and systems Integrable fiberoptic coupler and resulting devices and systems

1999-12-21

2001-03-06

Sanghavi, Hemang (Department: 2874)

Optical waveguides

With optical coupler

Plural

C385S034000, C385S074000

Reexamination Certificate

active

06198858

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention is related to the field of optical fiber technology and, more particularly, to fiberoptic couplers, especially wavelength division multiplexed (WDM) couplers, and fiberoptic isolator devices.
In strict fiberoptic terminology, fiberoptic “couplers” are devices which transfer the light signals from a plurality of input fibers to a plurality of output fibers. “Combiners” are devices by which the light signals from more than one input fiber are combined into a single output fiber. However, as explained below, the present invention is readily adaptable to both types of devices. Hence the term, “coupler,” as used with respect to the devices of the present invention is meant to be interpreted broadly and to cover both terms.
A WDM coupler transfers input signals from a plurality of input information channels to a plurality of output information channels in response to the wavelength of the input signals. A goal for any WDM coupler is that the crosstalk between channels is zero, i.e., that an untargeted output channel is effectively isolated from the signals on a targeted output channel so that none of the signals leak onto the untargeted channel.
FIG. 1A
is a representational diagram of a 2×2 WDM coupler found in the prior art. The cladding and core of a pair of optical fibers are fused together to form a WDM coupler
10
enclosed by dotted lines. The coupler
10
has two input fibers
11
,
12
and two output fibers
13
,
14
. The first input fiber
11
carries signals of wavelength &lgr;
1
and the second input fiber
12
carries signals of wavelength &lgr;
2
. Ideally, only one of the output fibers, say output fiber
13
, should carry the signals of wavelength &lgr;
1
, while the other output fiber
14
should carry the signals of wavelength &lgr;
2
, as shown in FIG.
1
A. Crosstalk occurs if the &lgr;
1
signals appear on the output fiber
14
or the &lgr;
2
signals appear on the output fiber
13
.
An application of the fused coupler of
FIG. 1A
is a partially integrated WDM coupler and isolator device, which is described in U.S. Pat. No. 5,082,343, issued Jan. 21, 1992 to D. G. Coult et al. The fused WDM coupler is illustrated in FIG.
1
B. The coupler
20
(again enclosed by dotted lines) has two input fibers
15
,
16
and an output fiber
17
. The two input fibers
15
and
16
are fused together and signals from the fused fibers are directed toward a collimator
18
. A second collimator
19
refocuses the collimated light signals from the collimator
78
into the output fiber
17
. The collimators
18
and
19
are shown as standard lens for purposes of illustration. One input fiber
15
carries signals of wavelength &lgr;
1
; the second input fiber
16
carries a signals of wavelength &lgr;
2
. A wavelength selective element
21
between the collimators
18
and
19
reflects the light of one of the wavelengths, say &lgr;
1
, and passes the &lgr;
2
wavelength light. Thus the output fiber
17
carries the &lgr;
2
signals.
The problem with this WDM coupler and isolator arrangement is the crosstalk between the fibers
15
and
16
carrying the reflected &lgr;
1
signals. As explained below, the &lgr;
1
signal should ideally be reflected into the input fiber
16
only. In reality, some of the &lgr;
1
signal is reflected back into the input fiber
15
; there is crosstalk. Besides crosstalk, another problem is that the insertion losses and polarization dependent losses of such couplers are high. Additionally, the device is rather large, which has an adverse effect upon the reliability and robustness of the device. Sealing the device, for example, is more of a problem with a large device. The large size also makes the device difficult to insert into various points of a fiberoptic network system, as may be desired. Still another disadvantage of the described device is that other desirable components, such as a tap coupler for monitoring signals through the device, must still be linked by fiber splicing. This lowers the performance of the overall system and creates further reliability problems.
In contrast, the present invention avoids, or substantially mitigates, the problems of the fused coupler. A fiberoptic coupler according to the present invention has a much higher optical performance and is easily integrated with other optical elements to create integrated couplers and optical isolators with advanced features and performance. Among these coupler and isolator devices is included an integrated WDM coupler and isolator device with high isolation between channels. The device is a great improvement over the WDM coupler and isolator described in the patent noted above.
Furthermore, these advanced couplers and isolators provide for advanced fiberoptic systems of higher performance, lower cost, and superior reliability.
SUMMARY OF THE INVENTION
The present invention provides for a fiberoptic coupler which has a first sleeve, a second sleeve, a first collimating GRIN or conventional lens, and a second collimating GRIN or conventional lens. The first sleeve has an end face, a longitudinal axis and an aperture parallel to the longitudinal axis through the end face. The aperture holds end sections of two or more input optical fibers. The second sleeve has an end face, a longitudinal axis and an aperture parallel to the longitudinal axis through the end face with the aperture holding an end of at least one output optical fiber. The end face of the second sleeve faces the first sleeve end face. The first collimating GRIN or conventional lens in front of the first sleeve end face collimates light signals from the input optical fibers and the second collimating GRIN or conventional lens in front of the second sleeve end face focusses light signals from at least one of the input optical fibers into the single output fiber, or at least one of the output optical fibers.
With an equivalent number of output optical fibers to input optical fibers, the first sleeve holding the ends of the input optical fibers and the second sleeve holding the ends of the output optical fibers, the first and second collimating lenses of the coupler are arranged so that light signals from one input optical fiber passes into one output optical fiber. Light signals from another input optical fiber passes into another output optical fiber, and so forth.
If the coupler is required for certain functions, other fiberoptic elements, such as an optical isolator core or a long-pass filter, can be integrated into the coupler between the optical path formed between the first and second collimating lenses. The long-pass filter has a cut-off wavelength above which light signals are passed and below which light signals are reflected. The filter is arranged with respect to the first collimating lens and the ends of the input optical fibers are arranged with respect to each other so that light from a first input fiber and reflected by the long-pass filter passes into the second input fiber and light from the first input fiber and passed by the long-pass filter leaves the long-pass filter as collimated light.
By inserting both an optical isolator and a long-pass filter, the present invention also provides for an integrated WDM coupler and isolator highly suited for combination with fiberoptic amplifiers and pumping lasers for the fiberoptic amplifiers. If an optical tap is desired, a planar grating may be added in the optical path between the two collimating lenses. The grating deflects a small portion of the light away from the optical path to a photodetector circuit which is used to monitor the intensity of light in the optical path.
With the present invention, a laser diode may also integrated into the coupler. The laser directs its output against the long-pass filter, which reflects the laser output onto the optical path. This arrangement not only integrates the pumping laser into an integrated package, but also increases the performance over the prior art.
The present invention also provides for an advanced system for transmitting light signals from a plurality of

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