This invention relates to optical fibers (e.g., fiber lasers and fiber amplifiers), and systems containing such optical fibers. More particularly, the invention is directed toward fiber-based discrete optical amplifiers used in telecommunications, cable television and other fiber-optics applications.
In response to rising demand for information processing services, communications service providers have implemented optical communication systems, which have the capability to provide substantially larger information transmission capacities than traditional electrical communication systems. Information can be transported through optical systems in audio, video, data, or other signal format analogous to electrical systems. Likewise, optical systems can be used in telephone, cable television, LAN, WAN, and MAN systems, as well as other communication systems.
The development of the erbium doped fiber optical amplifier (EDFA) provided a cost effective means to optically amplify attenuated optical signal wavelengths in the 1550 nm range. EDFAs have been widely used in communication systems because their bandwidth coincides with the lowest loss window in optical fibers commonly employed in optical communication around 1550 nm. For wavelengths shorter than about 1525 nm, however, erbium atoms in typical glasses will absorb more than amplify. To broaden the gain spectra of EDFAs, various dopants have been added. For example, codoping of the silica core with aluminum or phosphorus can broaden the emission spectrum. Nevertheless, the absorption wavelength for various glasses is still around 1530 nm.
Raman fiber amplifiers offer an alternative to EDFAs.
Certain optical fibers can be used as fiber amplifiers or fiber lasers.
Fiber amplifiers are typically used to amplify an input signal. Often, the input signal and a pump signal are combined and passed through the fiber amplifier to amplify the signal at an input wavelength. The amplified signal at the input wavelength can then be isolated from the signal at undesired wavelengths.
Raman fiber lasers can be used, for example, as energy sources. In general, Raman fiber lasers include a pump source coupled to a fiber, such as an optical fiber, having a gain medium with a Raman active material. Energy emitted from the pump source at a certain wavelength λp, commonly referred to as the pump energy, is coupled into the fiber. As the pump, energy interacts with the Raman active material in the gain medium of the fiber, one or more Raman Stokes transitions can occur within the fiber, resulting in the formation of energy within the fiber at wavelengths corresponding to the Raman Stokes shifts that occur (e.g., λ1, λ2, λ3, λ4, etc.).
Generally, the Raman active material in the gain medium of a Raman fiber laser may have a broad Raman gain spectrum. Usually, conversion efficiency varies for different frequencies within the Raman gain spectrum and many Raman active materials exhibit a peak in their gain spectrum, corresponding to the frequency with highest conversion efficiency. Additionally, the gain spectrum for different Raman active materials may be substantially different, partially overlapping, or of different conversion efficiency.
Typically, a Raman fiber Laser is designed so that the energy formed at one or more Raman Stokes shifts is substantially confined within the fiber. This can enhance the formation of energy within the fiber at one or more higher order Raman Stokes shifts. Often, the fiber is also designed so that at least a portion of the energy at wavelengths corresponding to predetermined, higher order Raman Stokes shifts (e.g., λsx where x is equal to or greater than one) is allowed to exit the fiber.
Raman fiber amplifiers can be adapted to amplify a broad range of wavelengths.
In general, the invention relates to optical fibers (e.g., fiber lasers and fiber amplifiers), and systems containing such optical fibers.
In one aspect, the invention features a fiber amplifier for amplifying an optical signal having a signal wavelength. The fiber amplifier includes an optical fiber for transmitting the optical signal, a pump energy source and a plurality of waveguides. The optical fiber has a plurality of discrete portions. Each discrete portion includes first and second components disposed at first and second respective locations and configured to substantially prevent energy having an intermediate wavelength in the discrete portion from entering other discrete portions of the optical fiber. The pump energy source is capable of emitting energy at a pump wavelength. Each waveguide is coupled to the pump energy source and to one of the plurality of discrete portions of the optical fiber. Each waveguide is configured to direct energy at the pump wavelength from the pump energy source to its corresponding discrete portion, thereby increasing an intensity of light at the discrete portion's intermediate wavelength in the corresponding discrete portion of the optical fiber. In embodiments, the fiber amplifier can be included in a system that also includes a signal source configured to direct the optical signal into the optical fiber, and a signal receiver configured to detect an output optical signal in the optical fiber. The output signal can be, for example, an optical signal that has been amplified by the fiber amplifier.
In another aspect, the invention features a fiber amplifier for amplifying an optical signal having a signal wavelength. The fiber amplifier includes an optical fiber having a plurality of discrete portions. Each discrete portion includes first and second components positioned at first and second respective locations in the discrete portion and configured to substantially prevent light having an intermediate wavelength in the portion from entering other portions of the optical fiber. The fiber amplifier also includes a coupler configured to couple pump energy from a pump energy source into the discrete portion so that the pump energy interacts with the optical fiber to increase the intensity of the intermediate wavelength in each portion.
In a further aspect, the invention features a fiber amplifier that includes an optical fiber having first and second sections coupled to each other. The first section is a double clad fiber laser, and the second section is an optical amplifier having a gain medium including P2O5. In embodiments, the fiber amplifier can be in a system that includes an input waveguide coupled to the second section of the fiber amplifier, and an output waveguide connected to the first coupler.
In certain embodiments, the fibers can be used as amplifiers rather than lasers.
Features, objects and advantages of the invention are in the description, drawings and claims.
Like reference symbols in the various drawings indicate like elements.
The indices + and − represent propagation in the fiber from left to right and from right to left, respectively. Ip and Is represent the intensities of energy propagating the fiber at wavelengths λp and λs, respectively. The Raman gain coefficient is g, and αp and αs are the loss coefficients of energy propagating in the fiber at wavelengths λp and λs, respectively.
These equations can be solved analytically and the following formula obtained:
Here, Ip is the power of the injected pump, and L is the length of the fiber. R1 and R1′ represent the reflectivities of the reflectors (e.g., fiber Bragg gratings) in
We now consider that there is a signal wave introduced in the cavity (see
Here, {tilde over (g)} is the Raman gain coefficient, and the system of coordinates is reversed (y=−z) for simplicity of calculation. The signal wave is considered weak enough not to deplete the Stokes wave. Equation (3) then has the following solution for the output signal:
which gives us amplification in dB as follows:
We can then substitute Equation (2) in Equation (5) and obtain:
If we consider a completely closed cavity (i.e. R1=R1′=1), then
We can then roughly evaluate the pump power level required to achieve, for example, 10 dB gain in a 100 m cavity. The following values will be used:
Finally,
Thus, 133 mW power at 1345 nm pump will provide amplification of 10 dB for a signal wave at about 1526 nm wavelength in a 100 m long cavity.
In a closed cavity with high finesse, the intensity of the Stokes wave builds up to a very high magnitude, which allows one to obtain very efficient amplification of a signal wave.
The in-cavity intensity of the Stokes wave for the same parameters (see, e.g., Equation (2)) is:
In a cavity having the parameters defined in (8) and pumped by Ip=133 mW, the intensity of the Stokes wave is:
(Is++Is−)=4.8 W (11)
This result allows for the use of a single low power laser diode to obtain a high gain amplifier as shown in
The current invention provides a highly efficient Raman amplifier suitable for a variety of applications. This invention further allows for a very simple, truly multiple wavelength, Raman amplifier because in this design one can isolate pieces of fiber for generation of individual Stokes waves λsi, where i=1, 2, 3, . . . , using closed cavities, and generate a large number of these wavelengths using a relatively low pump power (1-2 W) at 13xx nm by sharing it between cavities. In this case, the intensities of individual Stokes waves can be easily and independently controlled by a power splitter. One example of such an amplifier 200 is shown in
As shown in
In the embodiment shown in
Referring again to
In the embodiment shown in
While the foregoing description has been made for a system in which the reflectance of a reflector is fixed. In some embodiments, the reflectance of a reflector can be variable. Various combinations of tunable reflectors are contemplated. Furthermore, these systems can include, for example, appropriate electronics to form a feedback loop so that the systems can monitor the intensity of energy output at one or more wavelengths and vary the reflectance of one or more reflectors (e.g., vary the reflectance of one or more reflectors in real time) to obtain one or more desired output intensities at one or more wavelengths. In certain embodiments, a reflector can be formed of a variable output coupler. Such couplers are described, for example, in commonly owned U.S. Provisional Patent Application Ser. 60/300,298, filed on Jun. 22, 2001, and entitled “Variable Spectrally Selective Output Coupler For Fiber Laser”, which is hereby incorporated by reference.
While certain embodiments have been described, the invention is not limited to these embodiments. For example, the reflectors need not be in the form of fiber Bragg gratings. One or more of the reflectors can be a loop mirror, or one or more reflectors can be in the form of a coated mirror (e.g., a coated mirror at one or both ends of a section of optical fiber), etc. As an additional example, the type of laser used for pumping can be varied. Examples of lasers that can be used include semiconductor diode lasers (e.g., high power semiconductor diode lasers), double clad doped fiber lasers, conventional free space coupled lasers, and the like. As another example, various types of optical fibers can be used, including, for example, double clad optical fibers and polarization maintaining optical fibers. Furthermore, the optical fibers can be formed of, for example, silica based materials (e.g., fused silica based) or fluoride based materials. As yet another example, the relative and/or absolute lengths of one or more of the sections of the optical fiber can be varied based upon the intended use of the Raman fiber amplifier.
The foregoing fiber amplifiers can be used in a variety of situations.
Other embodiments are in the claims.
This application is a continuation-in-part of International Application No. PCT/US02/24409, which has an international filing date of Aug. 1, 2002, and is entitled “Optical Fiber Amplifier”, and which in turn claims priority to U.S. Provisional Patent Application Ser. No. 60/310,195, which was filed Aug. 3, 2001 and is entitled “Multi-Pump Discrete Raman Amplifier”. The foregoing applications are incorporated herein by reference.
Number | Name | Date | Kind |
---|---|---|---|
4063106 | Ashkin et al. | Dec 1977 | A |
4616898 | Hicks, Jr. | Oct 1986 | A |
4699452 | Mollenauer et al. | Oct 1987 | A |
4794598 | Desurvire et al. | Dec 1988 | A |
4829528 | Band et al. | May 1989 | A |
4852117 | Po | Jul 1989 | A |
4881790 | Mollenauer | Nov 1989 | A |
5050183 | Duling, III | Sep 1991 | A |
5225925 | Grubb et al. | Jul 1993 | A |
5323404 | Grubb | Jun 1994 | A |
5406411 | Button et al. | Apr 1995 | A |
5497386 | Fontana | Mar 1996 | A |
5537671 | Toyama et al. | Jul 1996 | A |
5623508 | Grubb et al. | Apr 1997 | A |
5659644 | DiGiovanni et al. | Aug 1997 | A |
5673280 | Grubb et al. | Sep 1997 | A |
5721636 | Erdogan et al. | Feb 1998 | A |
5778014 | Islam | Jul 1998 | A |
5815518 | Reed et al. | Sep 1998 | A |
5838700 | Dianov et al. | Nov 1998 | A |
5898716 | Ahn et al. | Apr 1999 | A |
5959750 | Eskildsen et al. | Sep 1999 | A |
5966480 | LeGrange et al. | Oct 1999 | A |
H1813 | Kersey | Nov 1999 | H |
5982791 | Sorin et al. | Nov 1999 | A |
5991068 | Massicott et al. | Nov 1999 | A |
5999545 | Jeon et al. | Dec 1999 | A |
6052393 | Islam | Apr 2000 | A |
6081366 | Kidorf et al. | Jun 2000 | A |
6088152 | Berger et al. | Jul 2000 | A |
6147794 | Stentz | Nov 2000 | A |
6151160 | Ma et al. | Nov 2000 | A |
6163396 | Webb | Dec 2000 | A |
6163552 | Engelberth et al. | Dec 2000 | A |
6163554 | Chang et al. | Dec 2000 | A |
6163636 | Stentz et al. | Dec 2000 | A |
6181464 | Kidorf et al. | Jan 2001 | B1 |
6191877 | Chraplyvy et al. | Feb 2001 | B1 |
6292288 | Akasaka et al. | Sep 2001 | B1 |
6298074 | Jeon et al. | Oct 2001 | B1 |
6304368 | Hansen et al. | Oct 2001 | B1 |
6310899 | Jacobovitz-Veselka et al. | Oct 2001 | B1 |
6344925 | Grubb et al. | Feb 2002 | B1 |
6374006 | Islam et al. | Apr 2002 | B1 |
6407855 | MacCormack et al. | Jun 2002 | B1 |
6424664 | Oh et al. | Jul 2002 | B1 |
6426965 | Chang et al. | Jul 2002 | B1 |
6433920 | Welch et al. | Aug 2002 | B1 |
6449408 | Evans et al. | Sep 2002 | B1 |
6549329 | Vail et al. | Apr 2003 | B2 |
6594288 | Putnam et al. | Jul 2003 | B1 |
6603593 | Fidric et al. | Aug 2003 | B2 |
6603595 | Welch et al. | Aug 2003 | B2 |
6606337 | King | Aug 2003 | B1 |
6621835 | Fidric | Sep 2003 | B1 |
6646785 | Kuksenkov | Nov 2003 | B2 |
6700696 | Dominic et al. | Mar 2004 | B2 |
6721088 | Brar et al. | Apr 2004 | B2 |
6731423 | Brasseur et al. | May 2004 | B1 |
6959021 | Po et al. | Oct 2005 | B2 |
7277610 | Demidov et al. | Oct 2007 | B2 |
20010030796 | Yao | Oct 2001 | A1 |
20020001125 | Chang et al. | Jan 2002 | A1 |
20020003655 | Park et al. | Jan 2002 | A1 |
20020024722 | Tsuzaki et al. | Feb 2002 | A1 |
20020063947 | Islam | May 2002 | A1 |
20020118709 | Islam | Aug 2002 | A1 |
20020126714 | Po et al. | Sep 2002 | A1 |
20020154661 | Hoose et al. | Oct 2002 | A1 |
20020191277 | Chen et al. | Dec 2002 | A1 |
20030011876 | Fidric | Jan 2003 | A1 |
20030016438 | Islam | Jan 2003 | A1 |
20030021302 | Grudinin et al. | Jan 2003 | A1 |
20030076577 | Dominic et al. | Apr 2003 | A1 |
20040130777 | Islam | Jul 2004 | A1 |
20040179797 | Po et al. | Sep 2004 | A1 |
Number | Date | Country |
---|---|---|
0 954 072 | Nov 1999 | EP |
0 954 072 | Apr 2000 | EP |
1 018 666 | Jul 2000 | EP |
1 124 295 | Aug 2001 | EP |
1 225 666 | Jul 2002 | EP |
1 257 023 | Nov 2002 | EP |
1 309 113 | May 2003 | EP |
58121694 | Jul 1983 | JP |
59165488 | Sep 1984 | JP |
63202085 | Aug 1988 | JP |
1196189 | Aug 1989 | JP |
WO 9637936 | Nov 1996 | WO |
WO 9950941 | Oct 1999 | WO |
WO9966607 | Dec 1999 | WO |
WO 0133285 | May 2001 | WO |
WO 0133285 | May 2001 | WO |
WO0152372 | Jul 2001 | WO |
WO 02063728 | Aug 2002 | WO |
WO 02093704 | Nov 2002 | WO |
WO 03005068 | Jan 2003 | WO |
WO 03005068 | Jan 2003 | WO |
WO 02063728 | Mar 2003 | WO |
WO 02063728 | May 2003 | WO |
WO 03014771 | Aug 2004 | WO |
Number | Date | Country | |
---|---|---|---|
20040240043 A1 | Dec 2004 | US |
Number | Date | Country | |
---|---|---|---|
60310195 | Aug 2001 | US |
Number | Date | Country | |
---|---|---|---|
Parent | PCT/US02/24409 | Aug 2002 | US |
Child | 10771002 | US |