Article comprising means for optical pulse reshaping

Details Article comprising means for optical pulse reshaping Article comprising means for optical pulse reshaping

1999-03-15

2001-03-13

Lee, John D. (Department: 2874)

Optical waveguides

Having nonlinear property

C385S024000, C385S037000, C359S199200

Reexamination Certificate

active

06201916

ABSTRACT:

FIELD OF THE INVENTION
This invention pertains to articles (e.g., an optical fiber communication system) that comprise means for optical pulse reshaping.
BACKGROUND OF THE INVENTION
Early optical fiber communication systems typically used opto-electronic pulse regenerators, referred to as “repeaters”. Regeneration involved detection of an incoming optical pulse, amplification, re-shaping and re-timing of the resulting detector output, and generation of the outgoing optical pulse. This approach was relatively expensive but otherwise satisfactory as long as the communication systems had relatively low bit rates. However, the above-referred to optoelectronic re-generation provides a bottleneck that has to be overcome before very high speed (e.g., data rates above about 40 Gb/s per channel) systems could be installed.
The development of optical fiber amplifiers was an important step towards elimination of the opto-electronic bottleneck. However, such amplifiers do not provide pulse shaping and re-timing.
All-optical processing is the key to overcoming the opto-electronic bottlenecks in high-speed communications networks. In particular, as the technology heads towards bit rates of 100 Gbits/s per channel in transparent communication systems, all-optical pulse regeneration is widely recognized as an important replacement for conventional electronic repeater technology.
Beside optical limiting and clock recovery, pulse re-shaping is one of the main concerns of optical pulse regeneration.
During propagation of an optical pulse from transmitter to receiver of an optical fiber communication systems, fiber-intrinsic properties such as dispersion and non-linearities are responsible for pulse distortion both in the temporal and the spectral domain. As a consequence, the bit error rate of the system is significantly increased in both time division multiplexed (TDM) and wavelength division multiplexed (WDM) systems. Thus, it would be desirable to have available all-optical means for pulse reshaping. Desirably, such means would be compact, adjustable, wavelength selective and cost effective, and would be applicable to any dispersive, nonlinear optical fiber communication system. This application discloses such means, and communication systems that comprise such means. M. Nakazawa et al.,
Electronics Letters,
Vol. 29 (9), p.729, April 1993, disclose a soliton transmission system wherein the transmission fiber is soliton transmission fiber with average negative group velocity dispersion of −0.4 ps/km
m. The system is selected to maintain the pulses as soliton pulses throughout, with the soliton peak power of a fundamental (N=1) soliton being as low as 0.65 mW, and the average soliton period being as long as 935 km. J. K. Lucek et al.,
Optical Letters,
Vol. 18 (15), p. 1226, August 1993, disclose an all-optical signal regenerator comprising a nonlinear fiber loop mirror. S. Bigo et al.,
IEEE J. of Selected Topics in Quantum Electronics,
Vol. 3 (5), p. 1208, October 1997 disclose soliton regeneration by means that comprise a nonlinear optical loop mirror. B. J. Eggleton et al.,
Optics Letters,
Vol. 22(12), p. 883, June 1997, disclose all-optical switching and pulse reshaping in long-period fiber gratings that couple light between co-propagating core and cladding modes. B. J. Eggleton et al.,
Physical Review Letters
Vol. 76 (10), p. 1627, March 1996, disclose the observation of nonlinear propagation effects in fiber Bragg gratings, resulting in nonlinear optical pulse compression and soliton propagation. They also disclose soliton formation in periodic structures.
For background on optical solitons see, for instance, “Optical Fiber Telecommunications”, Vol. III A, Chapter 12, pp. 373-460, L. F. Mollenauer et al.; “Optical Solitons-Theory and Experiment”, R. Taylor, editor, Cambridge University Press, 1992, especially pp. 30-37 and 80-81; and “Nonlinear Fiber Optics,” 2
nd
edition, G. P. Agrawal, Academic Press, (1995), especially pp. 42-43 and 144-147.
All references cited herein are incorporated herein by reference.
GLOSSARY AND DEFINITIONS
A “soliton” pulse herein is a substantially transform limited optical pulse that represents a balance between the effects of non-linearity and quadratic dispersion in the transmission medium, e.g., an optical fiber. An ideal soliton corresponds to a solution of a non-linear wave equation, e.g., the nonlinear Schroedinger equation. For practical purposes it is not necessary that a pulse be fully transform-limited to be herein considered a soliton pulse, and substantially transform-limited pulses generally are acceptable in the practice of the invention.
An optical pulse herein is a “transform limited” pulse if the product of its spectral bandwidth and its temporal width are the minimum allowed by the Fourier time-frequency relations. An optical pulse herein is “substantially transform limited” if the product of its spectral and temporal widths is at most 10% larger than the minimum allowed by the Fourier time-frequency relations.
An optical pulse herein is an electromagnetic pulse of a wavelength usable for optical fiber communications, not limited to wavelengths in the visible portion of the spectrum.
A periodic optical structure is “apodized” if at least one end thereof is designed to minimize out-of-band reflection lobes in the spectrum, corresponding to impedance matching the periodic structure to the contiguous transmission medium.
A physical quantity P is a non-linear function of a physical quantity Q if the quantity P(Q) can be expressed in the form P(Q)=&khgr;
0
+&khgr;
1
Q+&khgr;
2
Q
2
+&khgr;
3
Q
3
. . . , wherein at least one of susceptibilities &khgr;
2
, &khgr;
3
, . . . non-zero. Herein, Q typically is electric field and P typically is polarization, with &khgr;
0
, &khgr;
1
, . . . generally refereed to as susceptibilities.
A “nonlinear optical loop mirror” (NOLM) comprises an optical coupler and a nonlinear optical fiber connecting the two output ports of the coupler, and can provide intensity-dependent switching.
“Anomalous group velocity dispersion” herein corresponds to the condition &bgr;
2
<0, with &bgr;
2
as defined below.
“Chalcogenide glass” refers to amorphous material comprising one or more column VI element (e.g., S, Se, Te), and typically also comprising one or more of Ge, As, Sb or Te. An exemplary chalcogenide glass has composition As
2
S
3
.
By “photonic bandgap” we mean herein a frequency band in which electromagnetic wave propagation is forbidden. In particular, only small transmission occurs within the frequency band, exemplarily about 20 dB less than out of the frequency band.
SUMMARY OF THE INVENTION
In optical fiber communication systems, linear pulse compression techniques can correct for linear pulse distortions as introduced by dispersion. However, nonlinear technologies are required to compensate for nonlinear distortions commonly encountered in optical pulse transmission.
The pulse reshaping means according to the invention comprise a nonlinear optical waveguide (optical fiber or planar) with optical properties that vary periodically along the longitudinal axis of the waveguide. In preferred embodiments the effective refractive index of the waveguide core varies periodically, forming a Bragg grating.
For ease of exposition, the nonlinear waveguide with periodically varying optical property (or properties) will henceforth be referred to as a “grating”, regardless of the type of variation that is used.
Optical pulses of the appropriate wavelength and amplitude are launched into the grating and propagate therethrough, experiencing an effective group velocity dispersion which typically is anomalous and large, exemplarily many orders of magnitude larger than in conventional optical fibers.
More specifically, if the peak power of an incoming distorted pulse exceeds a threshold value (to be discussed below), the grating nonlinearity balances the dispersion, and the distorted pulse is transformed into a substantially transform-limited pulse. The incoming pulse typically is dis

Affiliated with

Also associated with

Rating

Article comprising means for optical pulse reshaping does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Article comprising means for optical pulse reshaping, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Article comprising means for optical pulse reshaping will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2481947