INTEGRATED OPTICAL COMPONENTS WITH WAVELENGTH TUNING AND POWER ISOLATION FUNCTIONS
A tunable optical filter integrates the functions of wavelength tuning and power isolation of back reflection. The optical signal enters a Faraday rotator twice, and isolation is provided by two birefringent crystals, having their optical axes oriented at 45 degrees with respect to each other. The two birefringent crystals are on the same side of the Faraday rotator. The integration of an optical tunable filter and an isolator function into a single packaged component helps to reduce the size and complexity of optical amplifier systems, such as EDFAs and PDFAs, operating in the 1550 nm and 1310 nm transmission bands, respectively.
This application claims priority from, U.S. Provisional Application No. 62/320,188, filed on Apr. 8, 2016, which is hereby incorporated in its entirety by this reference.
BACKGROUNDThe following relates generally to the optical components used in optical communication networks, and specifically to optical devices that can filter optical signals, while providing the functions of wavelength tuning, as well as power isolation of the optical signal.
Erbium-Doped Fiber Amplifiers (EDFAs) or Praseodymium-doped fiber Amplifiers (PDFAs) are widely deployed in optical networks, in the 1550 nm or 1310 nm wavelength windows, respectively.
An optical filter 112 is also used to filter out most of the unwanted ASE noise that exits the output signal port 111, so that only the intended optical signal wavelength or bandwidth is allowed to pass through the filter. In today's advanced, re-configurable optical networks, the signal wavelength can be dynamically changed to provide flexibility in the overall network configuration. Therefore, a tunable optical filter 112 is typically used, and must be tuned or adjusted so that its passband matches the wavelength change in input signal 101.
As has been occurring with cell phones, more and more components are being squeezed into individual optical modules, with the same limited volume, in order to save space, and also to upgrade the performance of network control centers. Fiber splicing between separate fiber optic components is cumbersome, and also occupies space. It is therefore desirable to integrate multiple optical components into a single package. In the case of EDFAs, as illustrated in
A tunable optical filter device includes a diffraction element, oriented to differentially diffract light of different wavelengths of a beam of light incident thereupon from an input port, and a reflector configured to reflect a portion of the beam of light incident on the reflector by the diffraction element to be diffracted a second time by the diffraction element in an optical path between the input port and an output port. A first birefringent element having a first optical axis in included in the optical path between the input port and the diffraction element, and a second birefringent element having a second optical axis is also included in the optical path between the diffraction element and the output port. The second optical axis is oriented substantially at a 45 degree angle with respect to the first optical axis along the optical path. The tunable optical filter device also includes one or more Faraday rotators located in the optical path between the first and second birefringent elements such that the optical path passes through the each of the Faraday rotators one or more times, where the Faraday rotators are configured to provide a combined rotation of polarization to a beam of light traversing the optical path between the first and second birefringent elements substantially equal to the difference in orientation between the optical axes of the first and second birefringent elements. An actuator is connected to change a position of the reflector so that a selected range of wavelengths of the portion of the beam of light incident upon the reflector is reflected along the optical path from the input port to the output port.
A method includes receiving a beam of light from an input port and refracting the beam of light a first time by a first birefringent element having a first optical axis. A diffraction element differentially diffracts light of different wavelengths of the beam of light from the input port that is incident upon it through the first birefringent element. A reflector is positioned so that a first selected range of wavelengths of a portion of the beam of light incident upon the reflector from the diffraction element is reflected along an optical path from the input port to an output port. The diffraction element diffracts a second time the portion of the beam of light incident upon the reflector along a portion the optical path between the reflector and the output port. The beam of light is refracted a second time along a portion the optical path between the diffraction element and the output port by a second birefringent element having a second optical axis, where the second optical axis is oriented substantially at a 45 degree angle with respect to the first optical axis along the optical path. The method also includes rotating one or more times a polarization of a beam of light traversing the optical path between the first and second birefringent elements, wherein the combined rotation from the one or more times is substantially equal to the difference in orientation between the optical axes of the first and second birefringent elements.
Various aspects, advantages, features and embodiments are included in the following description of exemplary examples thereof, which description should be taken in conjunction with the accompanying drawings. All patents, patent applications, articles, other publications, documents and things referenced herein are hereby incorporated herein by this reference in their entirety for all purposes. To the extent of any inconsistency or conflict in the definition or use of terms between any of the incorporated publications, documents or things and the present application, those of the present application shall prevail.
In
As stated above, in the discussion of
An input signal carrying multiple wavelengths inside the input fiber 501 in
For light that is reflected from the output back towards the input port, the optical path for the back reflected light will traverse the isolation elements of the birefringent crystal 505, the Faraday rotator 520 (twice), and the birefringent crystal 506. By passing through the Faraday rotator twice on the return trip, the back reflected light is again rotated by a total of 45 degrees. Consequently, as described above with respect to
By taking the angle α for the first crystal 506 to be −22.5 degrees with respect to the X-axis, the angle β for the second crystal is then +22.5 degrees with respect to the X-axis. This allows for the same type of crystal element to be used for both elements 506 and 505, the first crystal being simply flipped over for the second crystal, which simplifies the production of the device. Although an angle combination where the second angle is 45 degrees greater than the first angle, and where the Faraday rotator provides a corresponding 45 degrees of rotation is optimal, a few degrees of tolerance is generally acceptable, although the deviation will reduce the amount of isolation. Consequently, the preferable angle is substantially of 45 degrees for both the difference in alignment between the birefringent elements and the amount of rotation from the Faraday rotator.
In another embodiment as shown in
Furthermore, it is not necessary to utilize two individual lenses 502 and 503 for the collimation and focusing function. If a lens has a large enough diameter, then both input fiber 501 and output fiber 504 can share it for collimation, and still have individual optical paths that are being spatially coupled to the birefringent crystals 506 and 505, respectively.
As was illustrated by the use of an optical path concentrator 415, as shown in
A number of other variations can also be implemented, depending on the embodiment. For example, the embodiments presented so far have all included a single grating, but other embodiments can include multiple gratings in the optical path, similar to the arrangements described in U.S. Pat. No. 7,899,330 or U.S. patent application Ser. No. 15/139,694, filed on Apr. 27, 2016. With respect to Faraday rotator, a number of additional variations are possible. In
The foregoing detailed description has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. The described embodiments were chosen in order to best explain the principles involved and their practical application, to thereby enable others skilled in the art to best utilize the various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.
Claims
1. A tunable optical filter device, comprising:
- a diffraction element oriented to differentially diffract light of different wavelengths of a beam of light incident thereupon from an input port;
- a reflector configured to reflect a portion of the beam of light incident thereupon by the diffraction element to be diffracted a second time by the diffraction element in an optical path between the input port and an output port;
- a first birefringent element having a first optical axis in the optical path between the input port and the diffraction element;
- a second birefringent element having a second optical axis in the optical path between the diffraction element and the output port, wherein the second optical axis is oriented substantially at a 45 degree angle with respect to the first optical axis along the optical path;
- one or more Faraday rotators located in the optical path between the first and second birefringent elements such that the optical path passes through each of the Faraday rotators one or more times, where the one or more Faraday rotators are configured to provide a combined rotation of polarization to a beam of light traversing the optical path between the first and second birefringent elements substantially equal to the difference in orientation between the optical axes of the first and second birefringent elements; and
- an actuator connected to change a position of the reflector so that a selected range of wavelengths of the portion of the beam of light incident upon the reflector is reflected along the optical path from the input port to the output port.
2. The tunable optical filter device of claim 1, wherein the one or more Faraday rotators is a single Faraday rotator located in the optical path between the first and second birefringent elements such that the optical path passes through the Faraday rotator a single time.
3. The tunable optical filter device of claim 1, wherein the one or more Faraday rotators is a single Faraday rotator located in the optical path between the first and second birefringent elements such that the optical path passes through the Faraday rotator a first time and a second time.
4. The tunable optical filter device of claim 3, wherein the Faraday rotator is located in the optical path between the diffraction element and the reflector, such that the optical path passes through the Faraday rotator a first time and a second time after being diffracted the first time and before being diffracted the second time.
5. The tunable optical filter device of claim 3, wherein the Faraday rotator is located in the optical path between the first and second birefringent elements such that the optical path passes through the Faraday rotator the first time before being diffracted the first time and passes through the Faraday rotator the second time after being diffracted the second time.
6. The tunable optical filter device of claim 5, wherein the first and second birefringent elements and the Faraday rotator are formed into a single assembly.
7. The tunable optical filter device of claim 1, further comprising:
- an optical path compensator located in the optical path between the input port and the output port, configured to recombine polarization components of the beam of light that are spatially separated by the first and second birefringent elements, prior to entering the output port.
9. The tunable optical filter device of claim 1, wherein the actuator changes the position of the reflector by rotating the reflector about one or more axes.
10. The tunable optical filter device of claim 1, further comprising:
- a lens located in the optical path between the input port and the first birefringent element, whereby the beam of light incident on the first birefringent element from the input port is collimated.
11. The tunable optical filter device of claim 1, further comprising:
- a lens located in the optical path between the second birefringent element and the output port, whereby the beam of light incident on the output port from the second birefringent element is focused.
12. A method, comprising:
- receiving a beam of light from an input port;
- refracting the beam of light a first time by a first birefringent element having a first optical axis;
- differentially diffracting, by a diffraction element, light of different wavelengths of the beam of light from the input port that is incident thereon through the first birefringent element;
- positioning a reflector so that a first selected range of wavelengths of a portion of the beam of light incident upon the reflector from the diffraction element is reflected along an optical path from the input port to an output port;
- diffracting a second time by the diffraction element of the portion of the beam of light incident upon the reflector along a portion the optical path between the reflector and the output port;
- refracting the beam of light a second time along a portion the optical path between the diffraction element and the output port by a second birefringent element having a second optical axis, wherein the second optical axis is oriented substantially at a 45 degree angle with respect to the first optical axis along the optical path; and
- rotating one or more times a polarization of a beam of light traversing the optical path between the first and second birefringent elements, wherein the combined rotation from the one or more times is substantially equal to the difference in orientation between the optical axes of the first and second birefringent elements.
13. The method of claim 12, wherein the rotating one or more times is a single rotating having a rotation substantially equal to the difference in orientation between the optical axes of the first and second birefringent elements.
14. The method of claim 12, wherein the rotating one or more times is rotating a first rotation and a second rotation, wherein the combined rotation from the first and second rotations is substantially equal to the difference in orientation between the optical axes of the first and second birefringent elements.
15. The method of claim 14, wherein the rotating is performed by a Faraday rotator located in the optical path between the diffraction element and the reflector, such that the optical path passes through the Faraday rotator a first time and a second time after being diffracted the first time and before being diffracted the second time.
16. The method of claim 14, wherein the rotating is performed by a Faraday rotator located in the optical path between the first and second birefringent elements such that optical path passes through the Faraday rotator the first time before being diffracted the first time and passes through the Faraday rotator the second time after being diffracted the second time.
17. The method of claim 16, wherein the first and second birefringent elements and the Faraday rotator are formed into a single assembly.
18. The method of claim 12, further comprising:
- recombining polarization components of the beam of light that are spatially separated by the first and second birefringent elements, prior to entering the output port.
19. The method of claim 12, wherein the first optical axis lies in a plane orthogonal to a plane that embeds the optical path, oriented at an angle of substantially 22.5 degrees relative to the plane that embeds the optical path.
20. The method of claim 12, wherein positioning the reflector includes rotating the reflector about one or more axes.
21. The method of claim 12, further comprising:
- collimating the beam of light from the input port onto the first birefringent element by a lens located in the optical path between the input port and the first birefringent element.
22. The method of claim 12, further comprising:
- focusing the beam of light incident on the output port from the second birefringent element by a lens located in the optical path between the second birefringent element and the output port.
Type: Application
Filed: May 13, 2016
Publication Date: Oct 12, 2017
Inventor: Ho-Shang Lee (El Sobrante, CA)
Application Number: 15/154,643