Bit-phase synchronized optical pulse stream local generator

Details Bit-phase synchronized optical pulse stream local generator Bit-phase synchronized optical pulse stream local generator

2001-01-18

2003-05-06

Lee, John D. (Department: 2874)

Optical: systems and elements

Optical frequency converter

Harmonic generator

C359S326000, C331S00100A, C331S018000, C331S025000

Reexamination Certificate

active

06560007

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a bit-phase synchronized optical pulse stream local generator for locally generating an optical pulse stream synchronized in bit-phase with an ultrafast incoming optical signal pulse stream sent over a transmission line at a bit rate in excess of 100 Gbits/s.
With the recent fast-growing use of the Internet, data traffic is now on the increase, providing the impetus for further upgrading of large-capacity photonic networks. Time division multiplexing ranks with wavelength division multiplexing as a scheme effective in increasing the per-fiber channel capacity. The expansion of channel capacity through speedups of electronic circuit operations has now reached a level of 40 Gbits/s, where much difficulty is expected to encounter in further speedups. Optical signal processing based on a nonlinear optical effect that provides a sub-picosecond response speed is regarded as a technique capable of overcoming bandwidth limitations on electronic circuits and is now under research and development aiming at wide application to optical communication.
The optical signal processing that applies the nonlinear optical effect is to carry out switching, wavelength conversion and various other optical signal processing by timed interaction of input signal light with another ray of light (locally generated control light) in a nonlinear optical material. This technique is applicable to the generation of control light synchronized with the input signal light in all ultrafast all-optical control circuits that utilize the nonlinear optical effect, such as an all-optical time-division multiplexer, an all-optical time-division demultiplexer, an all-optical wavelength-division multiplexer and an all-optical add/drop circuit.
The optical signal processing necessitates the use of a bit-phase synchronized optical pulse stream local generator that locally generates an optical pulse stream synchronized with an optical pulse stream of a desired period in the incoming optical pulse streams. The timing accuracy necessary for the locally generated optical pulse stream becomes higher with an increase in the bit rate of the incoming optical pulse stream; for example, for bit rates of the 100-Gbit/s class, the required timing accuracy is better than one picosecond. In optical communications, since the signal light propagates usually over a long distance through an optical fiber transmission line, the timing of arrival of the signal light at the receiving end fluctuates with the expansion or shrinkage of the optical fibers used. To identify or distinguish respective bits of the received signal, it is necessary at the receiving end to extract from the received signal a clock corresponding to the timing fluctuation. The optical signal processing further requires the receiving end to prepare an optical pulse stream with the fluctuating timing.
An optical control pulse stream for processing the incoming signal pulse stream in synchronization therewith is usually generated by a mode-locked laser or similar short-pulse laser and subjected to amplification by an optical fiber amplifier and other processing, thereafter being coupled to the incoming optical signal pulse stream; in this case, the propagation delay through fairly long optical fiber components such as an optical fiber amplifier and a nonlinear pulse compression fiber readily varies (for instance, 50 ps/km/° C.) with an ambient temperature change. It is disclosed in K. L. Hall et al., IEEE Photon. Technol. Lett., vol. 7, pp. 935-937, 1995 to use a nonlinear optical loop mirror as an all-optical bit-phase sensor to synchronize the optical control pulse stream with the incoming optical signal stream having delay fluctuations by temperature variations of the optical fiber components. Because of the use of the nonlinear loop mirror in a phase detecting part, however, the proposed loop circuit has the defects of polarization dependence and incapability of compensating for fluctuations in the propagation delay of the optical fiber used as a nonlinear optical material for the nonlinear loop mirror.
FIG. 1
depicts an example of a conventional bit-phase synchronized optical signal pulse stream local generator identified generally by
100
. In Japanese Patent Application Laid-Open Gazette No. 10-209926 there is described only a synchronized clock generation part
110
composed of an optical modulator
21
, a photo detector
22
, frequency multipliers
23
and
32
, a phase comparator
41
and a voltage-controlled oscillator
51
in the bit-phase synchronized optical signal pulse stream local generator
100
of
FIG. 1. A
part of incoming optical signal pulse stream S
IN
of a bit rate Nf
a
(where N is the number of multiplexed channels), which is a time-division multiplexed optical pulse stream, is provided via an optical branching device
11
to the optical modulator
21
, wherein it is modulated by a signal of a frequency kf
VCO
generated by a k-fold frequency multiplication of the output from the voltage-controlled oscillator
51
by the frequency multiplier
23
. As a result, the photo detector
22
yields an electrical signal of a downconverted frequency Nf
a
−nkf
VCO
. This electrical signal is applied to the phase comparator
41
. The bit rate of the incoming optical signal pulse stream is as high as 100 Gbits/s, for instance, and hence it is difficult to process the optical signal pulse stream of such a high bit rate by an electronic circuit. The technique of downconverting the frequency by the optical modulator
21
as mentioned above is disclosed in, for example, Japanese Patent Application Laid-Open Gazette No. 10-65225. On the other hand, a local oscillation signal S
VCO
of a frequency f
VCO
generated by the voltage-controlled oscillator
51
is multiplied h-fold by the frequency multiplier
32
(assumed to be set at a multiplication number of h), and the resulting locally generated, multiplied signal of a frequency hf
VCO
is applied to the phase comparator
41
for phase comparison with the output from the photo detector
22
. The voltage-controlled oscillator
51
is controlled so that the phases of the two input signals to the phase comparator
41
are locked relative to each other. The constants N, n, k and h are integers equal to or greater than 1. These constants are predetermined such that the frequencies of the two input signals to the phase comparator
41
are Nf
a
−nkf
VCO
=hf
VCO
, that is, such that the oscillation frequency of the voltage-controlled oscillator
51
is f
VCO
=Nf
a
/(nk+h) and that the value of N/(nk+h) becomes a natural number (an integer equal to or greater than 1). Accordingly, a phase error or difference signal obtained by the phase comparison is fed back as a control voltage V
C
to the voltage-controlled oscillator
51
to control its local oscillation frequency f
VCO
. In consequence, the voltage-controlled oscillator
51
is controlled so that the phases of the two input signals to the phase comparator
41
are locked relative to each other. That is, the frequency multiplier
32
, the phase comparator
41
and the voltage-controlled oscillator
51
constitute a phase-locked loop PLL. The local oscillation signal S
VCO
output from the voltage-controlled oscillator
51
is phase-synchronized with the incoming optical signal pulse stream S
IN
, and drives a local optical pulse source
52
. Accordingly, the local optical pulse source
52
outputs a locally generated optical pulse stream S
L
of a frequency f
VCO
=Nf
a
/(nk+h) that is synchronized in bit phase with the incoming optical signal pulse stream S
IN
.
In the conventional bit-phase synchronized optical pulse stream local generator
100
depicted in
FIG. 1
, a delay fluctuation occurs in the local optical pulse source
52
, causing a phase fluctuation in the output pulse stream.
The local oscillation signal S
VCO
output from the voltage-controlled oscillator
51
ought to be synchronized in phase with the incoming optical signal pulse stream S
IN
under

Affiliated with

Also associated with

Rating

Bit-phase synchronized optical pulse stream local generator does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Bit-phase synchronized optical pulse stream local generator, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Bit-phase synchronized optical pulse stream local generator will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3027076