APPARATUS FOR BROADBAND WAVELENGTH CONVERSION OF DUAL-POLARIZATION PHASE-ENCODED SIGNAL

Abstract

An apparatus and method for wavelength conversion of a signal, for example, a dual-polarization signal, is disclosed. The apparatus implements a single-loop counter-propagating wavelength conversion scheme which provides both up-conversion and down-conversion of the signal within the same loop. Nonlinear wavelength conversion devices in the loop provide both up-conversion and down-conversion of the polarization components of the signal within the loop depending on whether the polarization component travels through the nonlinear conversion device in a clockwise or a counter-clockwise direction. The wavelength-converted signal is available to be extracted from the wavelength-conversion loop. An all-optical wavelength-division multiplexing transponder based on the wavelength-conversion scheme is also disclosed.

Claims

1. A wavelength converter, comprising: an input for receiving a signal having a first wavelength; and a wavelength-conversion loop capable of converting the first wavelength of the signal to a second wavelength, the first wavelength and the second wavelength separated from each other by a broad spectral range; wherein the wavelength-conversion loop is capable of up-converting the first wavelength to the second wavelength without using broadband components.

2. The wavelength converter of claim 1, wherein the wavelength-conversion loop is capable of down-converting the second wavelength to the first wavelength without using broadband components.

3. The wavelength converter of claim 1, wherein the wavelength-conversion loop comprises a first wavelength conversion medium and a second wavelength conversion medium.

4. The wavelength converter of claim 3, wherein the first wavelength-conversion medium is capable of converting the first wavelength to the second wavelength and converting the second wavelength to the first wavelength.

5. The wavelength converter of claim 4, wherein the first wavelength-conversion medium comprises a non-linear medium.

6. The wavelength converter of claim 5, wherein the first wavelength-conversion medium comprises periodically poled lithium niobate.

7. The wavelength converter of claim 3, wherein the second wavelength-conversion medium is capable of converting the first wavelength to the second wavelength and converting the second wavelength to the first wavelength.

8. The wavelength converter of claim 7, wherein the second wavelength-conversion medium comprises a non-linear medium.

9. The wavelength converter of claim 8, wherein the second wavelength-conversion medium comprises periodically poled lithium niobate.

10. The wavelength converter of claim 1, wherein: the signal comprises a first polarization component and a second polarization component, wherein both the first polarization component and the second polarization component have the first wavelength; the first wavelength-conversion medium converts the first wavelength of the first polarization component to the second wavelength; and the second wavelength-conversion medium converts the first wavelength of the second polarization component to the second wavelength.

11. The wavelength converter of claim 3, wherein the first wavelength-conversion medium is capable of converting the first wavelength to the second wavelength and is capable of converting the second wavelength to a third wavelength.

12. The wavelength converter of claim 3, wherein the second wavelength-conversion medium is capable of converting the first wavelength to the second wavelength and is capable of converting the second wavelength to a third wavelength.

13. The wavelength converter of claim 4, wherein: the first wavelength-conversion medium converts the first wavelength to the second wavelength or converts the second wavelength to the first wavelength depending on a direction in which the signal travels through the first wavelength-conversion medium.

14. The wavelength converter of claim 7, wherein: the second wavelength-conversion medium converts the first wavelength to the second wavelength or converts the second wavelength to the first wavelength depending on a direction in which the signal travels through the second wavelength-conversion medium.

15. The wavelength converter of claim 3, wherein the wavelength-conversion loop comprises: a first portion where the signal has the first wavelength; and a second portion where the signal has the second wavelength; wherein the first portion and the second portion are separated by the first wavelength-conversion medium and the second wavelength-conversion medium.

16. The wavelength converter of claim 15, wherein: the first portion of the wavelength-conversion loop is between the first wavelength-conversion medium and the second wavelength-conversion medium and is coupled to an input of the wavelength-conversion loop; and the second portion of the wavelength-conversion loop is between the first wavelength-conversion medium and the second wavelength-conversion medium and is coupled to an output of the wavelength-conversion loop.

17. The wavelength converter of claim 1, wherein: the signal having the first wavelength has a first polarization component and a second polarization component; one of the first and second polarization components travels in a clockwise direction within the wavelength-conversion loop; and the other one of the first and second polarization components travels in a counter-clockwise direction within the wavelength-conversion loop; wherein the first and second polarization components travel within the same optical path.

18. The wavelength converter of claim 1, wherein: the signal having the second wavelength has a first polarization component and a second polarization component; one of the first and second polarization components travels in a clockwise direction within the wavelength-conversion loop; and the other one of the first and second polarization components travels in a counter-clockwise direction within the wavelength-conversion loop; wherein the first and second polarization components travel within the same optical path.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Exemplary embodiments of the present invention will be described with reference to the accompanying figures, wherein:

[0036] FIG. 1 shows a conventional wavelength conversion scheme.

[0037] FIG. 2 shows another conventional wavelength conversion scheme.

[0038] FIG. 3 illustrates an aspect of the operation of the conventional wavelength conversion scheme shown in FIG. 2.

[0039] FIG. 4 shows a wavelength conversion scheme in accordance with the present invention.

[0040] FIG. 5 illustrates an aspect of the wavelength conversion scheme shown in FIG. 4.

[0041] FIG. 6 shows a schematic diagram of an embodiment of a wavelength conversion scheme in accordance with the present invention.

[0042] FIG. 6A illustrates an aspect of the wavelength conversion scheme shown in FIG. 6.

[0043] FIG. 6B shows a modification of the embodiment of the wavelength conversion scheme shown in FIG. 6.

[0044] FIG. 7 illustrates the operation of a conventional wavelength-division multiplexing transponder.

[0045] FIG. 8 shows a schematic diagram of an embodiment of a wavelength-division multiplexing transponder in accordance with the present invention.

[0046] FIG. 8A illustrates an aspect of the operation of the wavelength-division multiplexing transponder shown in FIG. 8.

[0047] FIG. 9 shows output signals provided by the embodiment of the wavelength conversion scheme shown in FIG. 6.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0048] FIG. 4 shows a single-loop counter-propagating wavelength conversion scheme 400 in accordance with embodiments of the present invention. Wavelength conversion is done using a wavelength converting component(s), e.g. a non-linear medium. As is well known to those skilled in the art, mixing a laser input signal and a pump laser signal in a non-linear medium translates the wavelength of the laser input signal to a different wavelength due to sum- and difference-frequency generation. As shown in FIG. 4, wavelength conversion scheme 400 uses two such wavelength converting components 414, 420, which makes it capable of converting dual-polarization signals. In preferred embodiments, one or both of wavelength converting components 414, 420 may be a periodically poled lithium niobate (“PPLN”) waveguide.

[0049] An input signal 402 having a wavelength λ.sub.1 is provided to a wavelength conversion loop 404. A polarization multiplexer/de-multiplexer (e.g. polarizing beam splitter/combiner) 408 separates the input signal 402 into a first polarization component 410 and a second polarization component 412. The first polarization component 410 travels clockwise around wavelength conversion loop 404 and is provided to wavelength conversion component (such as a PPLN) 414. Wavelength conversion component 414 converts the wavelength of the first polarization component 410 from λ.sub.1 to λ.sub.2 and provides a converted first polarization component 416 to a processing unit 418. Similarly, the second polarization component 412 travels counterclockwise around loop 404 and is provided to wavelength conversion component 420. Wavelength conversion component 420 converts the wavelength of the second polarization component 412 from λ.sub.1 to λ.sub.2 and provides a converted second polarization component 422 to processing unit 418.

[0050] The converted first and second polarization components 416, 422 are combined in processing unit 418 into a signal having a wavelength λ.sub.2. This signal is then available to be extracted from processing unit 418 for use outside of wavelength conversion loop 404.

[0051] Wavelength conversion loop 404 can also be used to convert a signal having a wavelength λ.sub.2 from wavelength λ.sub.2 back to wavelength λ.sub.1, the wavelength of input signal 402. The processing unit 418 separates the signal back into converted first and second polarization components 416, 422. The processing unit provides the converted first polarization component 416 to wavelength conversion component 420, which converts the wavelength of converted first polarization component 416 from λ.sub.2 back to λ.sub.1, thereby restoring the original first polarization component 410 traveling in the clockwise direction from wavelength conversion component 420 to polarization multiplexer/de-multiplexer (e.g., polarizing beam splitter/combiner) 408. Similarly, converted second polarization component 422 is then provided to wavelength converting component 414, which converts the wavelength of converted second polarization component 422 from λ.sub.2 back to λ.sub.1, thereby restoring the original second polarization component 412 traveling in the counter-clockwise direction. Both first and second polarization components 410, 412 then complete their respective trips around wavelength conversion loop 404 and are re-combined in polarization multiplexer/de-multiplexer (e.g., polarizing beam splitter/combiner) 408 to restore the original input signal 402, with its wavelength λ.sub.1.

[0052] Unlike the conventional, consecutive counter-propagating scheme shown in FIG. 2, in the single-loop scheme shown in FIG. 4, each one of wavelength conversion components 414, 420 provides both up-conversion and down-conversion of the polarization components that pass through it, depending upon the direction in which the polarization component passes through the wavelength conversion component. As described in connection with FIG. 4, and as shown in FIG. 5, when converted first polarization component 416 passes through wavelength conversion component 420 in a clockwise direction after leaving the processing unit 418, wavelength conversion component 420 wavelength-converts first polarization component 416 from a wavelength λ.sub.2 to a wavelength λ.sub.1. In contrast, when second polarization component 412 passes through wavelength conversion component 420 in a counter-clockwise direction after leaving polarization multiplexer/de-multiplexer (e.g., polarization beam splitter/combiner) 408, wavelength conversion component 420 wavelength-converts second polarization component 412 from a wavelength λ.sub.1 to a wavelength λ.sub.2.

[0053] Similarly, when first polarization component 410 passes through wavelength conversion component 414 in a clockwise direction after leaving polarization multiplexer/de-multiplexer 408, wavelength conversion component 414 wavelength-converts first polarization component 410 from a wavelength λ.sub.1 to a wavelength λ.sub.2. In contrast, when converted second polarization component 422 passes through wavelength conversion component 414 in a counter-clockwise direction after leaving the processing unit 418, wavelength conversion component 414 wavelength-converts second polarization component 422 from a wavelength λ.sub.2 (e.g., 1560 nm) to a wavelength λ.sub.1 (e.g., 633 nm).

[0054] FIG. 6 shows a single-loop counter-propagating wavelength conversion scheme 600 for conversion of an optical input signal in accordance with embodiments of the present invention. An optical input signal 602 having a wavelength λ.sub.1 is provided to a wavelength conversion loop 604 through a circulator 606. A polarization multiplexer/demultiplexer 608 separates the input signal 602 into a first polarization component 610 and a second polarization component 612. The first polarization component 610 travels clockwise around wavelength conversion loop 604 and is provided to wavelength conversion component 614 through an optional polarization controller 616 and a wavelength multiplexer (e.g. WDM, dichroic mirror) 618. Polarization controller 616 can be used to eliminate possible crosstalk between the first and second polarization components 610, 612. The wavelength conversion in wavelength conversion component 614 is based on the sum- and difference-frequency generation in wavelength conversion component (e.g. a nonlinear crystal) 614 using a pump LASER (if needed) 620. The pump LASER 620 is provided to wavelength conversion component 614 through a beam splitter 622 and wavelength-multiplexer 618. Wavelength conversion component 614 converts the wavelength of the first polarization component 610 from λ.sub.1 to λ.sub.2 and provides a converted first polarization component 624 to a polarization multiplexer/de-multiplexer 626 through wavelength multiplexer/de-multiplexer 628.

[0055] Similarly, the second polarization component 612 travels counter-clockwise around loop 604 and is provided to wavelength conversion component 630 through a wavelength-multiplexer/demultiplexer 638. The wavelength conversion in wavelength conversion component 630 is based on the sum- and difference-frequency generation in wavelength conversion component 630 using pump laser 620, which is provided to wavelength conversion component 630 through a beam splitter 622 and wavelength-multiplexer/de-multiplexer 638. Wavelength conversion component 630 converts the wavelength of the second polarization component 612 from λ.sub.1 to λ.sub.2 and provides a converted second polarization component 632 to polarization multiplexer/de-multiplexer 626 through multiplexer/de-multiplexer 634.

[0056] The converted first and second polarization components 624, 632 are combined in polarization multiplexer/de-multiplexer 626 into an output signal 636 having a wavelength λ.sub.2.

[0057] Wavelength converted signal 636 is then available to be extracted from polarization multiplexer/de-multiplexer 626 for use outside of wavelength conversion loop 604. In an exemplary embodiment, the output signal 636 can be propagated in free space before being returned to wavelength conversion loop 604. In another exemplary embodiment, the output signal can be provided to an angle multiplexing system. Systems and methods of angle multiplexing are described in U.S. Pat. No. 10,789,009 which is assigned to the assignee of the present application and is incorporated by reference herein in its entirety.

[0058] Wavelength conversion loop 604 can also be used to convert output signal 636 from wavelength λ.sub.2 back to wavelength λ.sub.1, the wavelength of input signal 602. When the wavelength-converted signal is returned to polarization multiplexer/de-multiplexer 626, polarization multiplexer/demultiplexer 626 separates it back into converted first and second polarization components 624, 632. Converted first polarization component 624 is then provided to wavelength conversion component 630 through wavelength multiplexer/de-multiplexer 634, which converts the wavelength of converted first polarization component 624 from λ.sub.2 back to λ.sub.1, thereby restoring original first polarization component 610. This wavelength conversion in wavelength conversion component 630 could be based on the sum- and difference-frequency generation in a nonlinear crystal such as a PPLN crystal 630 using pump laser 620, which is provided to wavelength conversion component 630 through a beam splitter 622 and wavelength conversion component 634.

[0059] Similarly, converted second polarization component 632 is then provided to wavelength conversion component 614 through wavelength-division multiplexer 628, which converts the wavelength of converted second polarization component 632 from λ.sub.2 back to λ.sub.1, thereby restoring original second polarization component 612. This wavelength conversion in wavelength conversion component 614 could be based on the sum- and difference-frequency generation in nonlinear crystal such as a PPLN crystal 614 using pump laser 620, which is provided to wavelength conversion component 614 through a beam splitter 622 and wavelength-division multiplexer 628.

[0060] Both first and second polarization components 610, 612 then complete their respective trips around wavelength conversion loop 604 and are re-combined in polarization multiplexer/de-multiplexer 608 to restore the original input signal 602, with its wavelength λ.sub.1. The input signal 602 is then returned to circulator 606, from which it is available to be extracted.

[0061] To aid in understanding the operation of wavelength conversion loop 604, FIG. 6A shows the circulation of first polarization component 610 in a clockwise direction around wavelength conversion loop 604 using numbered arrows 1-14. Numbered arrows 1-4 and 11-14 indicate the portions of wavelength conversion loop 604 where first polarization component 610 has a wavelength λ.sub.1. Numbered arrows 5-10 indicate the portions of wavelength conversion loop 604 where first polarization component 610 has a wavelength λ.sub.2. As shown in FIG. 6A, these portions are the “inside” portions of wavelength conversion loop 604 (i.e., between wavelength conversion components 614, 630).

[0062] It should be understood that reversing the directions of numbered arrows 3-12 in FIG. 6A would show the circulation of second polarization component 612 in a counter-clockwise direction around wavelength conversion loop 604. Numbered arrows 1-4 and 11-14 would indicate the portions of wavelength conversion loop 604 where second polarization component 612 has a wavelength λ.sub.1. Numbered arrows 5-10 would indicate the portions of wavelength conversion loop 604 where second polarization component 612 has a wavelength λ.sub.2.

[0063] Wavelength conversion scheme 600 can be implemented in free space or using optical waveguides, and optical fibers, including as appropriate single-mode fibers, multimode fibers, and polarization-maintaining fibers. The wavelength conversion scheme 600 can be implemented based on commercially available optical components.

[0064] In accordance with an embodiment of the present invention, the optical input signal 602 can have a wavelength λ.sub.1 that is in the C band. In accordance with another embodiment of the present invention, the output signal 636 at polarization beam splitter 626 can have a different wavelength λ.sub.2 that is also in the C band. In accordance with yet another embodiment of the present invention, the optical input signal 602 can have a wavelength λ.sub.1 of 1560 nm. In accordance with still another embodiment of the present invention, the output signal 636 at polarization beam splitter 626 can have a wavelength λ.sub.2 of ˜631 nm (satisfying the energy conservations). In accordance with another embodiment of the present invention, the pump laser 620 can have a wavelength of 1060 nm. Given the right selection of pump laser (if needed) and wavelength conversion component it is possible to generate a broad spectral range at the second wavelength λ.sub.2 independent of the first wavelength λ.sub.1. None of the components are required to work at both λ.sub.1 and λ.sub.2. In accordance with yet another embodiment of the present invention, the output signal 636 provided at polarization beam splitter 626 can be at a very broad wavelength range even though wavelength conversion scheme 600 is implemented without using broadband components.

[0065] In accordance with yet another embodiment of the present invention, the wavelength conversion scheme 600 shown in FIG. 6 can be used to provide a single, one-way conversion in either an up or down direction without the need to return to the original wavelength. For example, in a communication system, in order to avoid wavelength collision or contention, a wavelength can be converted to another wavelength and continue propagating in the communication system without the need to reconvert back to the original wavelength. In accordance with still another embodiment of the present invention, the first and second wavelength conversion components 614, 630 of wavelength conversion scheme 600 are capable of converting the first wavelength to the second wavelength and are capable of converting the second wavelength to a third wavelength (which could be the first wavelength).

[0066] A well-known method to perform wavelength conversion is to use a nonlinear process. In this case, usually, a pump laser is needed, and the wavelength conversion medium could be a nonlinear crystal and any form of a nonlinear medium. In some of the non-linear process, the pump laser 620 is undepleted. In view of this fact, in accordance with another embodiment in accordance with the present invention, the wavelength conversion scheme 600 can employ a pump recycling which recirculates residual pump power from one nonlinear conversion medium to be used in another one (or in the same wavelength conversion component). As shown in FIG. 6B, in the wavelength conversion scheme 600, pump recycling can be implemented by connecting wavelength-division multiplexers 628, 634 to one another via connection 640. In alternative embodiments, pump recycling can be implemented using a highly reflective coating inside each wavelength conversion component 628, 634.

[0067] The wavelength conversion schemes described herein have broad applicability, such as, for example, wavelength-converting transmitter/receivers, broadband constellation transparent detectors, ROADM (reconfigurable optical add/drop multiplexers), and optical wavelength-division multiplexing transponders. An optical wavelength-division multiplexing transponder is a wavelength converter that converts a received signal after receiving it and transmits the same signal in another wavelength. Such devices work for both wavelengths. The operation of a conventional optical-electronic-optical (OEO) WDM transponder 700 is shown in FIG. 7. The WDM transponder 700 receives an optical signal 702 having a wavelength λ.sub.1 and electrically converts it to an optical signal 704 having a wavelength λ.sub.2 The WDM transponder 700 then transmits the optical signal 704. Similarly, the WDM transponder 700 can receive the optical signal 704 having a wavelength λ.sub.2 and electrically convert it to the optical signal 702 having a wavelength λ.sub.1 before transmitting the optical signal 702. The main disadvantage of OEO WDM transponder 700 is the optical-to-electrical and electrical-to-optical conversions that are required. An all-optical WDM transponder would achieve the same results without the disadvantageous optical-to-electrical and electrical-to-optical conversions required by OEO WDM transponder 700.

[0068] In another embodiment in accordance with the present invention, an all-optical WDM transponder is provided. FIG. 8 shows an all-optical WDM transponder 800 which can operate at any given wavelength. An input signal 802 having a wavelength λ.sub.1 is provided at the first port of the WDM transponder 800 and will be converted to the new wavelength λ.sub.2 at a second port of the WDM transponder 800.

[0069] An input signal 802 having a wavelength λ.sub.1 is provided to a polarization beam splitter 806, which separates the input signal 802 into a first polarization component 808 and a second polarization component 810. The first polarization component 808 is provided to wavelength converting component 812 through wavelength-division multiplexer 814. Pump laser 816 is also provided to wavelength converting component 812 through wavelength-division multiplexer 814. Wavelength converting component 812 converts the wavelength of the first polarization component 808 from λ.sub.1 to λ.sub.2 and provides a converted first polarization component 818 to a polarization beam splitter 820 through wavelength-division multiplexer 822.

[0070] Similarly, the second polarization component 810 is provided to wavelength converting component 812 through wavelength-division multiplexer 822. Pump laser 824 is also provided to wavelength converting component 812 through wavelength-division multiplexer 822. Wavelength converting component 812 converts the wavelength of the second polarization component 810 from λ.sub.1 to λ.sub.2 and provides a converted second polarization component 826 to polarization beam splitter 820 through wavelength-division multiplexer 814. The converted first and second polarization components 818, 826 are combined in polarization beam splitter 820 into an output signal 804 having a wavelength λ.sub.2. Output signal 804 is then available for transmission.

[0071] The operation of WDM transponder 800 when an input signal having a wavelength λ.sub.2 is provided at the second port of the WDM transponder 800 and is converted to the new wavelength λ.sub.1 at the first port of the WDM transponder 800 will now be described. Referring to FIG. 8A, an input signal 830 having a wavelength λ.sub.2 is provided to the polarization beam splitter 820, which separates the input signal 830 into a first polarization component 834 and a second polarization component 836. The first polarization component 834 is provided to wavelength converting component 812 through wavelength-division multiplexer 822. Pump laser 824 is also provided (if required) to wavelength converting component 812 through wavelength-division multiplexer 822. Wavelength converting component 812 converts the wavelength of the first polarization component 834 from λ.sub.2 to λ.sub.1 and provides a converted first polarization component 838 to polarization beam splitter 806 through wavelength-division multiplexer 814.

[0072] Similarly, the second polarization component 836 is provided to wavelength converting component 812 through wavelength-division multiplexer 814. Pump laser 816 is also provided (if required) to wavelength converting component 812 through wavelength-division multiplexer 814. Wavelength converting component 812 converts the wavelength of the second polarization component 836 from λ.sub.2 to λ.sub.1 and provides a converted second polarization component 840 to polarization beam splitter 806 through wavelength-division multiplexer 822. The converted first and second polarization components 834, 836 are combined in polarization beam splitter 806 into an output signal 844 having a wavelength Output signal 844 is then available for transmission.

[0073] As described above, a signal having a wavelength λ.sub.2 coming from the second port of WDM transponder 800 will be converted to wavelength λ.sub.1 in the first port of WDM transponder 800. Thus, WDM transponder 800 works for both wavelengths as the input wavelength. If the input wavelength is λ.sub.1, then the output wavelength will be λ.sub.2 and vice versa. WDM transponder 800 is format transparent (i.e., it does not matter what signal constellation (phase encoding) the input signals use), can work for both single and double-polarization signals, and can be implemented easily for a broadband application. One main advantage of WDM transponder 800 is its almost instantaneous response time, which makes it suitable for very high bit rate wavelength conversion applications.

[0074] FIG. 9 shows the experimental demonstration of the constellation pattern provided by wavelength conversion scheme 600 of FIG. 6 for the consecutive up- and down-conversion of dual-polarization QPSK data. The 1560 nm dual-polarization QPSK data was up-converted to a wavelength of 633 nm and consecutively down-converted back to the wavelength of 1560 nm. No delay compensation or any amplitude balancing between the two polarizations of the QPSK data was needed.

[0075] The novel and inventive wavelength conversion scheme in accordance with embodiments of the present invention provide several benefits and advantages. The wavelength conversion scheme has a broadband application although it does not require broadband components. It works from continuous-wave to high bit-rate signals since it has an almost instantaneous response time. The wavelength conversion scheme is phase-insensitive, which makes it suitable for phase-encoded signals. In other words, any input signal (regardless of its properties such as polarization, phase, temporal shape, and bitrate) will be converted to another wavelength at the output while preserving the properties of the input signal enabling using more of the spectrum where commercial hardware is not available.

[0076] Since both wavelength conversions are performed in the same loop, the wavelength conversion scheme provides high environmental stability (e.g., reduces the effect of temperature fluctuations) and it reduces the effects of amplitude noise (i.e., distortion) of the converted signal. Since both polarization components travel only in different directions within the same loop, polarization mode dispersion (PMD) is minimized and there is no need to add a delay-line to compensate for PMD. Also, the counter-propagating scheme in the same loop automatically results in a balanced wavelength conversion for both polarizations and reduces the bit error rate penalty due to an imbalance between the two orthogonal polarizations. This resolves the need to balance the two polarizations' amplitudes using a polarization-dependent optical attenuator.

[0077] The wavelength conversion scheme in accordance with the present invention reduces complexity and cost. The single-loop counter-propagating wavelength conversion scheme in accordance with embodiments of the present invention is less complex than a comparable conventional polarization diversity wavelength conversion scheme and is less costly as it only uses two wavelength conversion devices (e.g., PPLNs, nonlinear crystal, nonlinear fibers, etc.) for wavelength conversion. A WDM transponder in accordance with embodiments of the present invention uses only one wavelength conversion device (e.g., a PPLN).

[0078] The single-loop counter-propagating wavelength conversion scheme in accordance with embodiments of the present invention also enables the implementation of all-optical wavelength conversion and an all-optical WDM transponder.

[0079] Finally, due to residual pump recycling in optical embodiments in accordance with the present invention, residual pump laser power from one wavelength conversion device can be used in another wavelength conversion device (or in the same wavelength conversion device), thereby reducing laser pump power consumption considerably and thus increasing total power efficiency.

[0080] While this invention has been described in conjunction with exemplary embodiments outlined above and illustrated in the drawings, it is evident that the principles of the present invention may be implemented using any number of techniques, whether currently known or not, and many alternatives, modifications, and variations in form and detail will be apparent to those skilled in the art. Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the present invention. For example, the components of the systems and apparatuses may be integrated or separated. Also, the system may be implemented in free space, in a waveguide, in optical fiber(s), or a combination of these. Furthermore, the operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components, and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. While the dual-polarization has been used as an example and shown experimentally for this design, however other attributes may be considered such as spatial modes, etc. It should be mentioned that it has been shown experimentally that more than one input signal could be sent to the system for wavelength conversion from λ.sub.1 to λ.sub.2 and back to λ.sub.1.

[0081] In addition, although embodiments in accordance with the present invention have been shown and described with regard to optical signals, it should be understood that the principles of the present invention are not limited to wavelength conversion involving optical signals but encompass as well embodiments that implement wavelength conversion of electromagnetic wave signals generally. Information or any kind of data can be stored as electromagnetic waves (e.g., generated by LASER, optical beam, radio frequency (RF) signals, other types of electromagnetic wave signals, to name a few), which can be transmitted and/or reflected between structures or within structures in various transmission media (e.g., free space, vacuum, crystals, nonlinear media, optical waveguides, optical fibers, to name a few). The terms “electromagnetic wave signal” and “electromagnetic wave beam” are used herein interchangeably. Electromagnetic radiation or electromagnetic beam as used herein may include any kind of electromagnetic signal, including a LASER beam or signal, a MASER beam or signal, an optical beam or signal, or any type of wired or wireless signal, including acoustic waves, radio waves, IR radiation, UV radiation, microwave-band transmission, or any combination of more than one of the foregoing. While referred to herein sometimes simply as a LASER beam or signal, other types of optical signals and other types of electromagnetic radiation transmissions, including radio waves, microwaves, IR, UV, and combinations of bandwidths of wavelengths of electromagnetic radiation, whether guided, shaped, phased, or none of the foregoing, are also intended to be included.

[0082] Accordingly, the exemplary embodiments of the invention, as set forth above, are intended to be illustrative, not limiting, and the spirit and scope of the present invention are to be construed broadly and limited only by the appended claims and not by the foregoing specification.

[0083] In addition, unless otherwise specifically noted, the articles depicted in the drawings are not necessarily drawn to scale.