The assignee for this patent, patent number 8818195, is
Reporters obtained the following quote from the background information supplied by the inventors: "Optical transmission systems suffer from phase ripple effects which are introduced by various optical components or subsystems (dispersion compensation devices, optical multiplexers, filters and amplifiers) which are used to transmit and process optical signals. Current optical transmission systems, particularly dense wavelength division multiplexing, DWDM, systems use more expensive components which produce less phase ripple. Further, it has been proposed to employ less costly components for implementing an optical transmission system which leads to an increased level of undesired phase ripple that can only be mitigated by keeping transmission distances of the optical transmission system comparatively low. I.e., when avoiding the use of expensive hardware, transmission distance has to be limited to account for the impact of phase ripple.
"Accordingly, it is an object of the present invention to provide an improved method of operating an optical transmission system and an improved optical transmission system which avoid the disadvantages of the prior art."
In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "According to the present invention, regarding the above mentioned method of operating an optical transmission system, this object is achieved by altering a phase of at least one frequency component of said optical signal by phase influencing means to at least partly compensate for said phase ripple of said at least one component, whereby a phase ripple compensated signal is obtained.
"The inventive method advantageously enables to at least partly mitigate the undesired effects of phase ripple imposed upon optical signals that are transmitted via the optical transmission system. I.e., said step of altering a phase enables to introduce a 'compensating phase ripple' which advantageously has a predetermined frequency, amplitude and phase that counteracts the phase ripple of said at least one component.
"According to a further aspect of the present invention, alternatively to or in addition to said step of altering a phase of at least one frequency component of said optical signal, a transmission frequency of said optical signal may be altered by a predetermined amount. According to observations of the Applicant, slightly detuning said transmission frequency of the optical signal surprisingly enables to also at least partly mitigate phase ripple effects, because by said step of detuning, a specific portion of the phase ripple response spectrum of the optical transmission system may be found which is lower in ripple magnitude.
"According to a preferred embodiment, said phase influencing means alter a respective phase of a plurality of frequency components of said optical signal which leads to an improved mitigation of phase ripple, because compensating phase ripple is provided for a plurality of signal frequencies.
"A further very advantageous embodiment of the present invention proposes to use a reconfigurable optical add drop multiplexor, ROADM, which comprises phase control capabilities for implementing the inventive phase influencing means. In many optical transmission systems, ROADMs are present which may be modified to implement the inventive functionality of phase influencing so as to mitigate phase ripple effects.
"Thus, no extra hardware has to be added to an optical transmission system to implement the inventive principle. I.e., a dedicated device for phase ripple compensation is not necessary.
"According to a further embodiment, a liquid crystal on Silicon, LCOS, array and/or a micro-electro-mechanical mirror array (MEMS) are used for altering a phase of at least one frequency component of said optical signal.
"According to a further preferred embodiment, a phase ripple function is applied to the optical signal by said phase influencing means, and a quality measure of said phase ripple compensated signal, particularly a bit error rate, BER, is determined. Thus, the inventive method advantageously enables to iteratively improve the phase ripple compensation by determining such phase ripple functions that lead to low bit error rates. The term phase ripple function denotes information related to phase altering measures involving several frequency components of the optical signal.
"Preferably, according to a further embodiment, a relative phase of said phase ripple function is varied until said quality measure reaches a predetermined threshold value, i.e. a minimum value.
"According to a further embodiment, at first, a transmission frequency of said optical signal is altered by a predetermined amount to minimize a bit error rate of said optical signal, and, after minimizing the bit error rate, said phase of at least one frequency component of said optical signal is altered thus advantageously combining both aspects of the inventive phase ripple mitigation techniques. Thereby, in the first step, a particularly suitable wavelength range with low phase ripple can be determined for transmission, and after that, the further inventive aspect of phase ripple compensation is applied.
"A further solution to the object of the present invention is given by an optical transmission system according to claim 11. Further advantageous embodiments are given by the dependent claims."
For more information, see this patent: Filer, Mark; Tibuleac,
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