Coherent light generators – Particular beam control device – Modulation
Reexamination Certificate
1997-10-24
2001-02-27
Scott, Jr., Leon (Department: 2874)
Coherent light generators
Particular beam control device
Modulation
C372S025000, C372S006000, C372S040000, C372S030000
Reexamination Certificate
active
06195369
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to optical information and communication systems, and more particularly to a high-repetition-rate soliton source for use in optical information and communication systems to transmit data over optical fibers.
STATEMENT OF RELATED ART
Sources of short optical pulses of high-repetition-rate (10-100 GHz) are important for time-division-multiplexed (TDM) optical communication systems, optical switching, optoelectronics, and optical computing. Among the different high-repetition-rate optical pulse sources, soliton sources are of particular interest. In optical communication, the top data transmission speed is limited by pulse broadening. Because an optical soliton does not change its waveform as it propagates along an optical fiber, short soliton pulses can be transmitted at a high rate over long distances, thereby enabling high-speed communication over optical fiber networks. A general discussion of the propagation of solitons in optical fibers can be found, for example, in
Lasers
pp. 392-396 (1986) by Anthony E. Siegman.
One attractive method of generating a high-repetition-rate soliton pulse train is to compress the beat modulation of two optical carrier waves into solitons. Several soliton sources employing such a method have been proposed. Some of those soliton sources use the output of two distribution feedback (DFB) lasers to obtain the beat modulation. Soliton sources of this type were described, for example, by S. V. Chernikov, J. R. Taylor, P. V. Mamyshev, and E. M. Dianov in “Generation of Soliton Pulse Train in Optical Fiber Using Two CW Single-mode Diode Lasers,” Electron. Lett. 28, 931-932 (1992); S. V. Chemikov, D. J. Richardson, R. I. Laming, E. D. Dianov, and D. N. Payne in “70 Gbits/s Fiber Based Source of Fundamental Solitons at 1550 nm,” Electron. Lett. 28, 1210-1212 (1992); and E. A. Swanson and S. R. Chinn, in “23-GHz and 123-GHz Soliton Pulse Generation Using Two CW Lasers and Standard Single-Mode Fiber,” IEEE Photonic Technol. Lett., vol. 6, no. 7, 796-798 (1994). This approach allows for tunability of the soliton pulse repetition rate by adjusting the frequency difference between the output waves of the two lasers. The period of the resultant pulsetrain is rather unstable, however, due to the large free-running laser line-width of the DFB lasers.
In another approach, the output of a single DFB laser, which can be an external cavity laser with a narrow line width, is modulated externally using a stable frequency source. Soliton sources of this type were described, for example, by E. A. Swanson, S. R. Chinn, K. Hall, K. A. Rauschenbach, R. S. Bondurant, and J. W. Miller in “100-GHz Soliton Pulse Train Generation Using Soliton Compression of Two Phase Side Bands from a Single DFB Laser,” IEEE Photonic Technol. Lett., vol. 6, no. 10, 1194-1196 (1994); and E. A. Swanson and S. R. Chinn in “40-GHz Pulse Train Generation Using Soliton Compression of a Mach-Zehnder Modulation Output,” IEEE Photonic Technol. Lett., vol. 7, no. 1, 114-116 (1995). This technique yields a quite stable repetition period, but at the expense of system complexity. The cost of such a soliton source is high due to the need for a stable external frequency driver.
Another proposed approach uses a dual-frequency coupled-cavity erbium-doped fiber laser which has two coupled but separate laser cavities formed with intracore fiber-grating reflectors. Such a soliton source was described, for example, by S. V. Chernikov, J. R. Taylor and R. Kashyep in “Integrated All Optical Fiber Source of Multigigahertz Soliton Pulse Train,” Electron. Lett. 29, 1788-1789 (1993). Although a soliton source of this type can potentially be of low cost, the stability of the generated soliton pulse train is sacrificed because of the use of two separate cavities and the relatively long coupled-cavity length that is required to obtain two-frequency operation. For example, the 59.1-GHz soliton source described by Chernikov et al. is stated to have frequency instability in the multi-MHZ range.
In view of the foregoing, it is a primary object of the present invention to provide a high-repetition-rate soliton source that is highly stable and relatively inexpensive.
It is a more specific object of the present invention to provide a high-repetition-rate soliton source based on the principle of compressing beat modulation into soliton pulses that has a simple structure, is highly stable, and can be made at a relatively low cost.
SUMMARY OF THE INVENTION
In accordance with these and other objects of the present invention, a general aspect of the present invention includes a high-stability soliton source which uses a laser having a single cavity and that is operated in two longitudinal modes with substantially identical amplitudes to form beat modulation. The laser output is passed through a soliton pulse compression fiber which compresses the beat modulation in the laser output into a soliton pulse train.
It is an advantageous feature of the present invention that the beat modulation is generated between two modes of a single laser cavity. Because the two modes belong to the same laser cavity, the frequency of the beat modulation between the two modes is highly stable (i.e., it has very low timing jitter). The stability is achieved without the use of any active stabilization of the laser frequency or the laser temperature.
A further advantage of the soliton source of the present invention is that only one laser is required to generate the beat modulation, and there is no need for an expensive external frequency driver. The soliton source thus has a very simple structure and can be made at a relatively low cost.
These as well as other novel advantages, details, embodiments, features and objects of the present invention will be apparent to those skilled in the art from following the detailed description of the invention, the attached claims and accompanying drawings, listed hereinbelow, which are useful in explaining the invention.
REFERENCES:
Siegman, Anthony,Laserspp. 392-396 (1986).
Chernikov, S.V., Taylor, J.R., Mamyshev, P.V., and Dianov, E.M., “Generation of Soliton Pulse Train in Optical Fiber Using Two CW Single-mode Diode Lasers”,Electron. Lett. 28, 931-932 (1992).
Chernikov, S.V., Richardson, D.J., Laming, R.I., Dianov, E.D., and Payne, D.N., “70 Gibits/Fiber Based Source of Fundamental Solitons at 1550 nm”Electron. Lett. 28, 1210-1212 (1992).
Swanson, E.A., Chinn, S.R., Hall, K., Rauschenbach, K.A., Bondurant, R.S., and Miller, J.W., “100-GHz Soliton Pulse Train Generation Using Soliton Compression of Two Phase Side Bands from a Single DFB Laser”,IEEE Photonic Technol. Lett., vol. 6, No. 10, 1194-1196 (1994).
Swanson, E.A., and Chinn, S.R., “40-GHz Pulse Train Generation Using Soliton Compression of a Mach-Zehnder Modulation Output”,IEEE Photonic Technol. Lett., vol. 7, No. 1, 114-116 (1995).
Chernikov, S.V., Taylor, J.R., and Kashyep R., “Integrated All Optical Fiber Source of Multigigahertz Soliton Pulse Train”,Electron. Lett.29, 1788-1789 (1993).
Anthon, D.W., Pier, T.J., “Diode-pumped Erbium Glass Lasers”,SPIE, vol. 1627 Solid State Laser III (1992).
E.A. Swanson and S.R. Chinn, “23-GHz and 123-GHz Soliton Pulse Generation using Two CW Lasers and Standard Single-Mode Fiber”,IEEE Photonic Technol. Lett., vol. 6, No. 7, 796-798 (1994).
Anthon Douglas W.
Kath William L.
Kumar Prem
Munks Timothy C.
Serkland Darwin K.
Barnhardt III Hubert J.
Gardner Kelly A.
Jr. Leon Scott
Massaroni Kenneth M.
Scientific-Atlanta, Inc.
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