摘要:
Different techniques for generating spectrally efficient carrier-suppressed modulated optical signals, also known as “phase-shaped binary transmission” (PSBT) signals, employ electrical components that generate only 2-level or binary signals, in contrast to techniques that require 3-level electrical drivers. The PSBT modulators can be used with return-to-zero (RZ) modulators for generating RZ-PSBT signals, which have the characteristic of even greater spectral efficiency than NRZ PSBT signals. The technique is generalized to RZ signals with an arbitrary phase difference between pulses. These signals can be generated by shifting the central (carrier) frequency of an RZ modulated optical signal, which can be done using a certain phase modulation or using spectral filtering with a passband offset from the center (carrier) frequency of the modulated optical signal, and the signals can also be generated by phase modulation at a frequency lower than the signaling rate of the modulated signal.
摘要:
In an optical transmitter, continuous wave light from a laser passes through a data modulator (DM) for non-return-to-zero (NRZ) encoding of a data stream and through a pulse modulator to add return-to-zero encoding to the modulated optical signal. A modulator controller monitors the output optical signal power, optimizes the bias setting for the DM and the PM, and optimizes the phase relationship between the pulse and data components of the modulated optical signal. For each optimization, a low amplitude and low frequency dither signal is injected at appropriate points in the modulator. A single photo detector and electrical receiver are used in a multiplexed fashion to monitor the optical output signal and derive separate feedback signals. Remaining control circuitry forces a null in a respective residual dither component in the optical output signal to maintain the desired bias level or phase alignment.
摘要:
Fiber optic cable waste is avoided by measuring amplitude oscillations of four-wave mixing products in positive-dispersion and negative-dispersion fiber optic cable to determine the lengths of a first, positive-dispersion cable segment and a second, negative-dispersion cable segment that are used to provide a specified length of fiber optic cable having a specified amount of path-average chromatic dispersion. The integrated dispersion of a positive-dispersion fiber optic cable as a function of length is measured to provide a first set of data, and the integrated dispersion of a negative-dispersion fiber optic cable as a function of length is measured to provide a second set of data. A fiber-optic cable is simultaneously fed with two optical signals, a first at wavelength .lambda..sub.1 and a second at wavelength .lambda..sub.2, and the number of sinusoidal oscillations that occur in the four-wave mixing products of the Stokes (or anti-Stokes) sideband as a function of cable length are measured. The second set of data is reflected about a line representing zero length, linearly translated by the specified length along a length axis, and then linearly translated by the specified dispersion along an integrated dispersion axis to provide a transformed second set of data. A point of intersection of the first set of data with the transformed second set of data is calculated. A length coordinate of this point of intersection represents the length of the first cable segment. A length for the second cable segment is calculated by subtracting the length of the first cable segment from the specified length.
摘要:
A system and method in which the chromatic dispersion characteristic, as a function of distance along a section of transmissive fiber, is measured. First and second optical signals are launched into a fiber under test to thereby generate, by a four-wave mixing process in the fiber, a probe signal. Because of a wave-vector phase mismatch, the probe signal power oscillates with a spatial frequency that can be measured as a function of distance in the fiber. The intensity oscillations are measurable as, for example, temporal variations in the Rayleigh backscattered light detected at the input end of the fiber. According to the present invention, the dispersion parameter at one or both of the first and second optical signal wavelengths, as a function of length along the fiber, is derived directly from these intensity oscillation measurements. From this information, it is possible to further derive maps at other wavelengths of interest.
摘要:
A soliton transmission system comprising optical filters whose center frequency intentionally differs from the center frequency of adjacent optical filters is disclosed, wherein the filter strength .eta. of the filters is between about 0.3-0.5, and preferably is 0.4. The center frequency of the series of optical filters is translated along the desired length of the system in a predetermined manner at a rate of less than or equal to (2/27).sup.1/2 .eta. and greater than or equal to 0.034.eta.+0.047.eta..sup.2. The center frequencies of the optical filters preferably increase in the direction of propagation.
摘要:
Fiber optic cable waste is avoided by measuring amplitude oscillations of four-wave mixing products in positive-dispersion and negative-dispersion fiber optic cable to determine the lengths of a first, positive-dispersion cable segment and a second, negative-dispersion cable segment that are used to provide a specified length of fiber optic cable having a specified amount of path-average chromatic dispersion. The integrated dispersion of a positive-dispersion fiber optic cable as a function of length is measured to provide a first set of data, and the integrated dispersion of a negative-dispersion fiber optic cable as a function of length is measured to provide a second set of data. A fiber-optic cable is simultaneously fed with two optical signals, a first at wavelength .lambda..sub.1 and a second at wavelength .lambda..sub.2, and the number of sinusoidal oscillations that occur in the four-wave mixing products of the Stokes (or anti-Stokes) sideband as a function of cable length are measured. The second set of data is reflected about a line representing zero length, linearly translated by the specified length along a length axis, and then linearly translated by the specified dispersion along an integrated dispersion axis to provide a transformed second set of data. A point of intersection of the first set of data with the transformed second set of data is calculated. A length coordinate of this point of intersection represents the length of the first cable segment. A length for the second cable segment is calculated by subtracting the length of the first cable segment from the specified length.
摘要:
Apparatus and method for generating a return-to-zero (RZ) optical data stream. A laser or other continuous wave (CW) optical source generates an optical carrier signal which is applied to a phase modulator. A return-to-zero data generator multiplies a non-return-to-zero (NRZ) electrical data stream and a sinusoidal electrical signal to generate an RZ electrical data stream. The phase modulator modulates the RZ electrical data stream onto the optical carrier signal to generate a phase-modulated optical signal. A Stokes portion or an anti-Stokes portion of the phase-modulated optical signal spectrum is then spectrally separated in an optical filter to provide a corresponding output RZ optical data stream. The spectral separation may be provided using a discrete filter coupled to the output of the phase modulator, or using transmission line filtering in a soliton transmission system. The use of the phase modulator to perform data encoding operations avoids the modulation bias drift problems inherent in amplitude modulators.
摘要:
Method and apparatus of soliton transmission using a non-soliton source are described. The soliton transmission is generally in the form of an optical pulse sequence, Intensity and phase modulation of a continuous wave optical signal generates a pair of optical pulse sequences related to Stokes and anti-Stokes components of the doubly modulated optical signal. By proper alignment of the optical frequency of the cw optical signal with the passband of a filtered transmission line, it is possible to have the filtered transmission line comprising sliding frequency-guiding filters permit only one of the pulse sequences to be selected and thereby form a soliton pulse sequence.
摘要:
A method and apparatus for producing high quality optical pulse trains at a high repetition rate first phase modulates a cw optical signal with an external phase modulator. The central optical frequencies (i.e., the carrier frequency and at least one pair of sidebands) of the phase modulated signal are then removed from the signal. Each of the remaining side-bands that have not been removed independently form an optical pulse train of the desired transform-limited pulses.