# Patent

## Title
Fused fiber optic coupler arrangement and method for use thereof

## Abstract

Exemplary embodiments of an article of manufacture and method according to the present disclosure are provided. For example, a first multi-clad fiber arrangement can be provided that comprises a first core and at least one first cladding which is structured to propagate at least one first electro-magnetic radiation therethrough. A second multi-clad fiber arrangement can also be provided that comprises a second core and at least one second cladding which is structured to propagate at least one second electro-magnetic radiation therethrough. Further, at least one portion can be provided in which the first and second claddings are fused to one another.

## Background
CROSS-REFERENCE TO RELATED APPLICATION(S)
This application relates to and claims the benefit of priority from International Patent Application No. PCT/US2009/047988 filed Jun. 19, 2009, and from U.S. Provisional Patent Application Ser. No. 61/074,339 filed Jun. 20, 2008, the disclosures of which are incorporated herein by reference in their entireties.


FIELD OF THE DISCLOSURE
The present disclosure relates to exemplary embodiments of a fiber optical article of manufacture, and more particularly to fused (e.g., mode-selective) fiber optic coupler arrangements and methods for use thereof.
BACKGROUND INFORMATION
As shown in FIG. 1, a conventional dual cladding fiber (DCF) has an internal structure typically consisting of a core 100, an inner cladding 102, an outer cladding 104, and a protection jacket 106. Both the core 100 and inner cladding 102 are structured to guide an optical wave along a longitudinal axis 108. A wave guiding mechanism is provided either by total internal reflection through an appropriate refractive-index profile (see FIG. 1) or Bragg band gap properties. The core 100 can typically be designed to guide only a single spatial mode, so called HE11 mode. The inner cladding 102 can guide hundreds to millions of multiple spatial modes. The DCF have been developed originally for optical fiber amplifiers and lasers. Signal light propagating in a rare-earth-ion-doped core of the DCF can be amplified while interacting with pump waves guided in the cladding. Recently, it was demonstrated that DCF can be applied in biomedical imaging. In particular, the probe light is delivered through the single-mode core to a biological sample, whereas the signal light transmitted through or reflected from the sample can be collected by the inner cladding as well as the core of DCF. This exemplary arrangement can be advantageous over more conventional method based on a single-mode fiber or multi-mode fiber in terms of spatial resolution, light collection efficiency, etc.
In such applications using the DCF, an arrangement or a technique to launch or extract light in and out of either only the core or the inner cladding of the DCF can be used. Conventional arrangements generally include free-space optics. As shown in FIG. 2, the core mode in a DCF 110 is transmitted to the core 100 of a first receiving fiber 112 through lenses 113, a beam splitter 114, and a pinhole 115. The cladding modes of the DCF 110 are received by a second fiber 117 through a beam blocker 118. However, this conventional arrangement may suffer from significant insertion loss due to beam splitting and mode profile mismatch.
Accordingly, there may be a need to address and/or overcome at least some of the deficiencies described herein above.
SUMMARY OF EXEMPLARY EMBODIMENTS OF THE DISCLOSURE
According to exemplary embodiments of the present disclosure, it is possible to provide an article of manufacture and a method which facilitates a smaller loss and the freedom from cumbersome and costly free-space alignment. One of the objects of the exemplary embodiments of the present disclosure is solve at least some of the deficiencies of the conventional arrangements and methods, and can facilitate a fused DCF coupler which can provide efficient mode-selective beam splitting and/or combining.
In one exemplary embodiment, exemplary embodiments of an article of manufacture and method according to the present disclosure can be provided. For example, a first multi-clad fiber arrangement can be provided that comprises a first core and at least one first cladding which is structured to propagate at least one first electro-magnetic radiation therethrough. A second multi-clad fiber arrangement can also be provided that comprises a second core and at least one second cladding which is structured to propagate at least one second electro-magnetic radiation therethrough. Further, at least one portion can be provided in which the first and second claddings are fused to one another.
According to one exemplary embodiment of the present disclosure, the first and second cores can be separated from one another within the portion(s). The separation between the first and second cores within the portion(s) can be greater than a wavelength of at least one of the first and/or second electro-magnetic radiation. In addition, a core mode coupling ratio between the first and second cores within the portion(s) can be less than about 10%, 1%, 0.1%, etc. Further, a cladding mode coupling ratio between the first and second claddings within the portion(s) can be between about 10% and 90%. between about 40% and 60%, approximately 50%, etc.
According to another exemplary embodiment of the present disclosure, the first and second multi-clad fiber arrangements can be double-clad fiber arrangements. Optical properties of the first and second multi-clad fiber arrangements can be substantially identical. Further, at least one single mode fiber arrangement can also be provided which can be coupled to the first and/or second multi-clad fiber arrangement. The single mode fiber arrangement(s) can include at least one third cladding which can be structured to prevent a propagation of an electro-magnetic radiation therethrough.
According to still another exemplary embodiment of the present invention, system and method can be provided. For example, at least one first electro-magnetic radiation can be provided using a first arrangement. Further, the first electro-magnetic radiation(s) can be received from the first arrangement and outputted to a sample using at least one of at least two multi-clad fiber arrangements of a second arrangement. Each of the multi-clad fiber arrangements can comprise a core and at least one cladding which can be structured to propagate the first electro-magnetic radiation(s) therethrough. The second arrangement further can comprise at least one portion in which at least one of the claddings of at least two of the multi-clad fiber arrangements are fused to one another.
Further, it is possible to, with at least first one of the multi-clad fiber arrangements, receive at least one second electro-magnetic radiation from the sample which can be associated with the first electro-magnetic radiation(s), and propagate the second electro-magnetic radiation(s) via the core and the cladding thereof. In addition, it is possible to modify and/or splitting the second electro-magnetic radiation(s) traveling along the cladding of the first one of the multi-clad fiber arrangements in the at least one portion to propagate at least one third electro-magnetic radiation along the cladding of at least second one of the multi-clad fiber arrangements. Additionally, a third arrangement can be provided which is configured to detect the at least one third electro-magnetic radiation. The second electro-magnetic radiation can be a fluorescence radiation or a scattered light.
These and other objects, features and advantages of the exemplary embodiment of the present disclosure will become apparent upon reading the following detailed description of the exemplary embodiments of the present disclosure, when taken in conjunction with the appended claims.



BRIEF DESCRIPTION OF THE DRAWING(S)
Further objects, features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the present invention, in which:
FIG. 1 is a perspective cross-sectional view of a structure of a conventional double clad fiber which includes a refractive index profile thereof.
FIG. 2 is a diagram of a conventional system which can implement free space coupling configurations;
FIG. 3 is a side view of an exemplary embodiment of a fabrication of a fused-type DCF coupler according to the present disclosure;
FIGS. 4A-4C are side views the exemplary DCF coupler implementing exemplary operating principles according to the present disclosure;
FIGS. 5A and 5B are side views further exemplary embodiments of the fused-type DCF coupler according to the present disclosure, and of an exemplary fabrication and/or implementation thereof;
FIG. 6 is a diagram of one exemplary embodiment of an imaging system utilized an exemplary embodiment of the DCF coupler in accordance with the present disclosure; and
FIG. 7 is a diagram of another exemplary embodiment of the imaging system utilized a further exemplary embodiment of the DCF coupler in accordance with the present disclosure.



Throughout the figures, the same reference numerals and characters, unless otherwise stated, are used to denote like features, elements, components or portions of the illustrated embodiments. Moreover, while the subject disclosure will now be described in detail with reference to the figures, it is done so in connection with the illustrative embodiments. It is intended that changes and modifications can be made to the described exemplary embodiments without departing from the true scope and spirit of the subject disclosure as defined by the appended claims.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
An exemplary embodiment of a method of fabricating a DCF coupler can be similar to a conventional method for fabricating fused single-mode fiber couplers or multimode fiber couplers. In this exemplary method, intermediate jacket-stripped sections of two identical fibers contact one another and are twisted together, which can be tapered longitudinally by applying heat. The details of this exemplary fiber fusion method are known in the art. The exemplary embodiment of the DCF fiber according to the present disclosure, at least a portion of which is shown as a side view in FIG. 3.
For example, as shown in FIG. 3, two DCF fibers 110 and 112, which can have identical and/or similar designs, can be tapered and fused in a middle portion 120 by a heat source 130. The heat source 130 can include, but not limited to, hydrogen-oxygen flame, graphite mini-furnace, and CO2 laser. For example, during a pulling process, a probe beam can be used to measure a coupling ratio in situ to generate control feedback to optimize optical characteristics of a fabricated device.
FIGS. 4A-4C illustrate side views of the exemplary embodiment of the arrangement according to the present disclosure shown in FIG. 4 performing exemplary operating principle according to the present disclosure. For example, a signal light 200 (e.g., or any electro-magnetic radiation) propagated in the core 100 of a first fiber 110 can experience small or minimal, e.g., preferably less than 10%, coupling to the other fiber 112 after propagating through a coupler waist section/portion 120. As a result, the signal light (e.g., which can be any electro-magnetic radiation) can remain as the core mode 202 of the first fiber. On another hand, light or other electro-magnetic radiation guided in the inner cladding, or the cladding modes 210, may experience strong coupling, and the output can be provided into the two or more fibers 110, 112, e.g., with nearly equal intensity. This exemplary property can be achieved by controlling a degree of fusion of the coupler waist section/portion 120.
As the degree of fusion of the coupler waist section/portion 120 is increased, mode coupling between cladding modes of the fibers 110, 112 can start, increase gradually, and can reach to a strong coupling regime, before mode coupling between the core modes is even started. For example, the coupling between the core modes may typically begin when the V-value of the core mode is reduced to less than 1 by tapering. For the claddings modes, the exemplary arrangement can act as a conventional multimode fiber coupler. The splitting ratio of an individual cladding mode can vary from about 0 to 100%, depending on the spatial order, wavelength, and polarization, likely yielding an overall power splitting ratio close to about 50/50 between the two outputs 212, 214. For minimum insertion loss, appropriate fiber types can preferably be selected.
FIGS. 5A and 5B illustrate side views of further exemplary embodiments of the arrangements according to the present disclosure and exemplary performance of exemplary procedures using such arrangements, along with a fabrication and/or an implementation of the exemplary fused-type DCF coupler(s). In one exemplary embodiment, e.g., as shown in FIG. 5A, one port of the above-referenced exemplary DCF coupler can be connected to a single mode fiber 300 at an input side 310 thereof, e.g., by fusion splicing. According to another exemplary embodiment as shown in FIG. 5B, one port of the above-referenced exemplary DCF coupler can be connected to another single mode fiber 305 at an output side thereof, e.g., also by fusion splicing.
The single mode fiber(s) 300, 305 can act as a spatial mode filter can facilitate only the core mode (i.e., light and/or electro-magnetic radiation only being transmitted through the core 100) to be launched to the coupler (shown in FIG. 5A) and to be received from the coupler (shown in FIG. 5B). Thus, such exemplary single-mode fibers 300, 305 can prevent or reduce the transmission of the light and/or any other electro-magnetic radiation through cladding thereof. As illustrated in FIG. 5B, e.g., the cladding modes propagating in the first fiber 110, after the coupler waist section/portion 120 can be wasted by radiation to the air or absorption in the jacket of the single mode fiber. Indeed, the light/radiation propagating along the core 100 will continue to propagate along a core 320 of the single-mode fiber 305 as well. The cladding modes coupled to the second fiber 112 can continue to be guided in the inner cladding.
FIG. 6 shows a diagram of one exemplary embodiment of an optical imaging system based on the above-described exemplary DCF coupler in accordance with the present disclosure. For example, the single-mode fiber 300 can be connected to a light source or another electro-magnetic radiation source 400. The light source 400 can include, but not limited to, a monochromatic laser, a mode-locked laser, a Super-Luminescent Diode (SLD), an LED and/or a tunable source. An output of the light source 400 can be delivered to an optical probe 410 through the core 100 of the fiber 110 of the exemplary DCF. The probe light/radiation can illuminate a sample 420, which can be a biological sample. The light/radiation reemitted from the sample 420 via reflection, scattering, and/or fluorescence can be received by the optical probe 410. The optical probe 410 can comprises at least one or more of lens, such as, e.g., objective lens or GRIN lens. The optical energy coupled to the core 100 of the DCF can then be transmitted back toward the light source 400. Approximately a half of the optical energy initially coupled in the claddings 102, 104 of the first fiber 110 of the exemplary the DCF and returning from the sample 420 can be coupled to the second fiber 112 in the cladding 111, 116 thereof, and can be detected by a photo-receiver 430. The photo-receiver 430 can include, but not limited to, a photodiode, a CCD array and/or a CMOS array.
For example, the exemplary optical system shown in FIG. 6 can be realized for two-photon fluorescence imaging as described in M. T. Myaing et al., “Enhanced two-photon biosensing with double-clad photonic crystal fibers,” Opt. Lett. 28, 1224-1226 (2003). In such exemplary embodiment, the light source 400 can be a pulsed laser emitting infrared light. The optical probe 410 can utilize a high NA objective lens focusing the core mode to the sample 420. The fluorescent light generated within the sample 420 and received by the cladding 116 of the DCF through the objective lens can then be measured at the photo-receiver 430 through a dielectric filter filtering the pump wave and transmitting, e.g., only the fluorescence signal light. The optical probe 410 can include a beam scanning actuator to scan the probe beam transversely across the sample 420.
The exemplary embodiment of the imaging system shown in FIG. 6 can also be configured for spectrally-encoded endoscopy as described in D. Yelin et al., “Double clad fiber for endoscopy,” Opt. Lett. 29, 2408-2410 (2004). In this exemplary case, the light source 400 can include a broadband SLD, and the probe 410 can utilize a diffraction grating and lens to focus different wavelengths to different spatial points in the sample 420. The reflected light captured in the cladding 111, 116 of the DCF can be detected by, e.g., a CCD array.
The exemplary imaging system architecture of another exemplary embodiment of the present disclosure can be extended for an interferometric imaging by adding a single-mode fiber coupler 500, a reference mirror 520, and a photodetector 540, as illustrated in FIG. 7. For an exemplary time-heterodyne detection, the reference mirror 520 can be scanned axially. Alternatively or in addition, the photodetector 540 can include a spectrometer which can have a diffraction grating and a detector array for spectral-domain detection. Further or alternatively, a wavelength-tunable light source can be used as a light source 430 for optical frequency domain imaging. Various exemplary techniques for interferometer-based optical imaging are known in the art.
Other exemplary embodiments of the imaging system with configurations modified from FIG. 6 can include reflectance confocal imaging, fluorescence detection, fluorescence confocal imaging, multi photon fluorescence microscopy, coherent Raman microscopy, and second- or third-harmonic generation microscopy. The exemplary DCF coupler can also be used in cladding-pumped optical amplifiers and lasers for combining or splitting the signal and pump waves.
The foregoing merely illustrates the principles of the invention. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. Indeed, the arrangements, systems and methods according to the exemplary embodiments of the present invention can be used with imaging systems, and for example with those described in International Patent Publication WO 2005/047813 published May 26, 2005, U.S. Patent Publication No. 2006/0093276, published May 4, 2006, and U.S. Patent Publication No. 2005/0018201, published Jan. 27, 2005, the disclosures of which are incorporated by reference herein in their entireties. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements and methods which, although not explicitly shown or described herein, embody the principles of the invention and are thus within the spirit and scope of the present invention. In addition, to the extent that the prior art knowledge has not been explicitly incorporated by reference herein above, it is explicitly being incorporated herein in its entirety. All publications referenced herein above are incorporated herein by reference in their entireties.

## Claims

1. An article of manufacture, comprising:
a first multi-clad fiber arrangement which comprises a first core and at least one first cladding which is structured to propagate at least one first electro-magnetic radiation therethrough that is associated with a further radiation provided from at least one sample;
a second multi-clad fiber arrangement which comprises a second core and at least one second cladding which is structured to propagate at least one second electro-magnetic radiation therethrough that is associated with the further radiation; and
at least one portion in which the first and second claddings are fused to one another.

2. The article of manufacture according to claim 1, wherein the first and second cores are separated from one another within the at least one portion.

3. The article of manufacture according to claim 2, wherein a separation between the first and second cores within the at least one portion is greater than a wavelength of at least one of the at least one first electro-magnetic radiation or the at least one second electro-magnetic radiation.

4. The article of manufacture according to claim 2, wherein a core mode coupling ratio between the first and second cores within the at least one portion is less than about 10%.

5. The article of manufacture according to claim 2, wherein a core mode coupling ratio between the first and second cores within the at least one portion is less than about 1%.

6. The article of manufacture according to claim 2, wherein a core mode coupling ratio between the first and second cores within the at least one portion is less than about 0.1%.

7. The article of manufacture according to claim 1, wherein a cladding mode coupling ratio between the first and second claddings within the at least one portion is between about 10% and 90%.

8. The article of manufacture according to claim 1, wherein a cladding mode coupling ratio between the first and second claddings within the at least one portion is between about 40% and 60%.

9. The article of manufacture according to claim 1, wherein a cladding mode coupling ratio between the first and second claddings within the at least one portion is approximately 50%.

10. The article of manufacture according to claim 1, wherein the first and second multi-clad fiber arrangements are double-clad fiber arrangements.

11. The article of manufacture according to claim 1, wherein optical properties of the first and second multi-clad fiber arrangements are substantially identical.

12. The article of manufacture according to claim 1, further comprising at least one single mode fiber arrangement which is coupled to at least one of the at least one first multi-clad fiber arrangement and the least one second multi-clad fiber arrangement, wherein the at least one single mode fiber arrangement includes at least one third cladding which is structured to prevent a propagation of an electro-magnetic radiation therethrough.

13. An article of manufacture, comprising:
a first multi-clad fiber arrangement which comprises a first core and at least one first cladding which is structured to propagate at least one first electro-magnetic radiation therethrough;
a second multi-clad fiber arrangement which comprises a second core and at least one second cladding which is structured to propagate at least one second electro-magnetic radiation therethrough; and
at least one portion in which the first and second claddings are fused to one another,
wherein, after transmitting the at least one first electro-magnetic radiation, the first multi-clad fiber arrangement receives at least one third electro-magnetic radiation from a sample which is associated with the at least one first electro-magnetic radiation, and propagates the at least one third electro-magnetic radiation via the core and the at least one first cladding thereof, and
wherein the at least one third electro-magnetic radiation traveling along the at least one first cladding of the first multi-clad fiber arrangement is at least one of modified or split in the at least one portion to propagate at least one fourth electro-magnetic radiation along the at least one second cladding of the second multi-clad fiber arrangement.

14. The article of manufacture according to claim 13, further comprising a third arrangement which is configured to detect the at least one fourth electro-magnetic radiation.

15. The article of manufacture according to claim 13, wherein the at least one third electro-magnetic radiation is a fluorescence radiation or a scattered light.

16. A system, comprising:
a first arrangement which is configured to provide at least one first electro-magnetic radiation; and
a second arrangement which includes at least two multi-clad fiber arrangements at least one of which receives the at least one first electro-magnetic radiation from the first arrangement and outputs the least one first electro-magnetic radiation to a sample, each of the multi-clad fiber arrangements comprising a core and at least one cladding which is structured to propagate the at least one first electro-magnetic radiation therethrough, the second arrangement further comprising at least one portion in which at least one of the claddings of at least two ofthe multi-clad fiber arrangements are fused to one another,
wherein at least first one of the multi-clad fiber arrangements receives at least one second electro-magnetic radiation from the sample which is associated with the at least one first electromagnetic radiation, and propagates the at least one second electro-magnetic radiation via the core and the cladding thereof, and
wherein the at least one second electro-magnetic radiation traveling along the cladding of the atleast first one of the multi-clad fiber arrangements is at least one of modified or split in the at least one portion to propagate at least one third electro-magnetic radiation along the cladding of at least second one of the multi-clad fiber arrangements.

17. The system according to claim 16, further comprising a third arrangement which is configured to detect the at least one third electro-magnetic radiation.

18. The system according to claim 16, the at least one second electro-magnetic radiation is a fluorescence radiation or a scattered light.

19. The system according to claim 16, wherein the cores of the multi-clad fiber arrangements are separated from one another within the at least one portion.

20. The system according to claim 19, wherein the cores of the multi-clad fiber arrangements within the at least one portion is greater than a wavelength of at least one of the at least one first electro-magnetic radiation or the at least one second electro-magnetic radiation.

21. The system according to claim 19, wherein a core mode coupling ratio between the cores of the multi-clad fiber arrangements within the at least one portion is less than about 10%.

22. The system according to claim 19, wherein a core mode coupling ratio between the cores of the multi-clad fiber arrangements within the at least one portion is less than about 1%.

23. The system according to claim 19, wherein a core mode coupling ratio between the cores of the multi-clad fiber arrangements within the at least one portion is less than about 0.1%.

24. The system according to claim 19, wherein a cladding mode coupling ratio between the claddings of the multi-clad fiber arrangements within the at least one portion is between about 10% and 90%.

25. The system according to claim 19, wherein a cladding mode coupling ratio between the claddings of the multi-clad fiber arrangements within the at least one portion is between about 40% and 60%.

26. The system according to claim 19, wherein a cladding mode coupling ratio between the claddings of the multi-clad fiber arrangements within the at least one portion is approximately 50%.

27. The system according to claim 16, wherein the multi-clad fiber arrangements are double-clad fiber arrangements.

28. The system according to claim 16, wherein optical properties of the multi-clad fiber arrangements are substantially identical.

29. The system according to claim 16, further comprising at least one single mode fiber arrangement which is coupled to at least one of the multi-clad fiber arrangements, wherein the at least one single mode fiber arrangement includes at least one further cladding which is structured to prevent a propagation of at least one of the at least one first electro-magnetic radiation or the at least one second electro-magnetic radiation therethrough.

30. A method, comprising:
providing at least one first electro-magnetic radiation using a first arrangement:
receiving the at least one first electro-magnetic radiation from the first arrangement and outputting the least one first electro-magnetic radiation to a sample using at least one of at least two multi-clad fiber arrangements of a second arrangement, each ofthe multi-clad fiber arrangements comprising a core and at least one cladding which is structured to propagate the at least one first electro-magnetic radiation therethrough, the second arrangement further comprising at least one portion in which at least one of the claddings of at least two of the multi-clad fiber arrangements are fused to one another;
using at least first one of the multi-clad fiber arrangements, receiving at least one second electro-magnetic radiation from the sample which is associated with the at least one first electromagnetic radiation, and propagating the at least one second electro-magnetic radiation via the core and the cladding thereof; and
at least one of modifying or splitting the at least one second electro-magnetic radiation traveling along the cladding of the at least first one of the multi-clad fiber arrangements in the at least one portion to propagate at least one third electro-magnetic radiation along the cladding of at least second one of the multi-clad fiber arrangements.