Patent EA-004485-B1 (EA)
Title: Method and device for handling optical pulse signals
Inventor: GUTIN MICHAEL
IPC: H04B10/299
Filed: 2001-11-23
Abstract: 1. A method for handling an optical pulse signal by ensuring at least one operation from the following: pulse shaping, treatment of nonlinearity and monitoring, the method comprising steps: providing a signal handling device capable of performing a cascaded second harmonic generation (SHG) with respect to a particular fundamental harmonic (FH), selecting an optical path length in said signal handling device, suitable for performing at least one of said operations with respect to an incoming optical pulse signal carried by a wavelength defined by said particular fundamental harmonic (FH), conveying the incoming optical pulse signal carried by said wavelength along the selected optical path in said signal handling device, obtaining from said signal handling device at least one output optical pulse signal from a list comprising: - an output optical pulse signal at the fundamental harmonic (FH), wherein the treatment of nonlinearity and/or the pulse shaping are performed, - an output optical pulse signal at the second harmonic (SH) for further monitoring it and judging about said input optical pulse signal. 2. The method according to Claim 1, enabling the operation of nonlinearity treatment, wherein at the selecting step such an optical path length is selected for conveying the incoming optical pulse signal with a known amplitude via the signal handling device, that is substantially close to the length upon passing which the output optical pulse signal at the fundamental harmonic (FH) reaches the maximum peak power. 3. The method according to Claim 1, ensuring the operation of pulse shaping, wherein at the selecting step such an optical path length is selected for conveying the incoming optical pulse signal with a known amplitude via the signal handling device, that is substantially close to the shortest optical path length upon passing which the output optical pulse signal at the fundamental harmonic (FH) reaches the maximum peak power. 4. The method according to Claim 1, allowing for the monitoring operation, wherein the selecting step comprises selecting such an optical path length for conveying the incoming optical pulse signal via the signal handling device, that enables obtaining from said device the output optical pulse signal at the second harmonic (SH) with a non-zero peak power. 5. The method according to Claim 1, wherein the conveying is performed by passing the signal along a multi-segment trajectory in said device, thereby arranging an extended optical path. 6. The method according to Claim 5, wherein the conveying is performed via a multi-segment "zig-zag" trajectory by arranging one or more internal reflections in the signal handling device. 7. The method according to Claim 2, for nonlinearity compensation, further comprising a preliminary step of ensuring that the sign of the Kerr effect created by said device to said wavelength is negative. 8. The method according to Claim 1, for gradual handling of the optical signal in a fiber optic link, comprising an additional step of conveying the outgoing optical signal via a chain including at least one additional signal handling device, and wherein the devices in the chain are spanned by sections of the fiber optic link. 9. The method according to Claim 1, for handling optical pulse signals in a multi-channel transmission of optical data where each of the optical channels transmits a specific optical signal at a particular optical wavelength, comprising performing steps of Claim 1 with respect to each particular optical channel. 10. The method according to Claim 9, comprising conveying the optical pulse signals of different said optical channels via respective different said signal handling devices. 11. The method according to Claim 9, comprising conveying the optical pulse signals of different said optical channels via one and the same common signal handling device. 12. The method according to Claim 9, comprising selecting optical channels with better results of the signal handling for transmitting information having higher priority. 13. A device for handling an optical pulse signal from the point of at least one of the following operations: pulse shaping, treatment of nonlinearity and signal monitoring, the device being capable of performing a cascaded second harmonic generation (SHG) with respect to a particular fundamental harmonic (FH), the device being characterized by such an optical path length selected for an incoming optical pulse signal carried by a wavelength defined by said particular fundamental harmonic (FH), that upon conveying said incoming optical pulse signal along the selected optical path, the device enables obtaining at least one output optical pulse signal from a list comprising: - an output optical pulse signal at the fundamental harmonic (FH), wherein the treatment of nonlinearity and/or the pulse shaping are performed, - an output optical pulse signal at the second harmonic (SH) suitable for further monitoring and judging about said input optical pulse signal. 14. The device according to Claim 13, having the optical path length close to the shortest one upon passing which the outgoing FH optical pulse signal reaches the maximum peak power, thereby suitable for pulse shaping. 15. The device according to Claim 13 or 14, having the optical path length close to the shortest one upon passing which an output optical pulse signal at the fundamental harmonic (FH) reaches the maximum peak power for further monitoring. 16. The device according to Claim 13, having the optical path length close to the shortest one permitting to obtain an output optical pulse signal at the secondary harmonic (SH) with a non-zero peak power for further monitoring. 17. The device according to Claim 13, comprising a second-harmonic-generating (SHG) element selected from a non-exhaustive list including: a second harmonic generating (SHG) optical crystal and a second harmonic generating (SHG) polymer fiber. 18. The device according to Claim 17, wherein the second-harmonic-generating (SHG)is an optical crystal selected from a non-exhaustive list comprising KTP, KDP and BBO. 19. A device for handling an optical pulse signal, if applied at a particular wavelength, from the point of at least one of the following operations: pulse shaping, treatment of nonlinearity and signal monitoring; the device comprising an SHG element for performing a cascaded Second Harmonic Generation with respect to a Fundamental Harmonic (FH) defined by said particular wavelength, said element being covered by mirror surfaces at least at its two opposite facets and leaving at least two windows at said opposite facets for an incoming optical beam and an outgoing optical beam respectively, the arrangement being such to create one or more internal reflections of the optical beam if passing between said two windows, thereby providing an extended internal optical path. 20. The device according to Claim 19, wherein said extended internal optical path has the length suitable for obtaining an outgoing optical pulse signal on the fundamental harmonic (FH) with a peak power close to maximum and/or an outgoing optical pulse signal on the second harmonic (SH) with a non-zero peak power. 21. The device according to Claim 20, wherein said extended internal optical path has substantially the shortest length upon passing which the outgoing FH optical pulse signal reaches the maximum peak power. 22. The device according to Claim 19, wherein the element has a cubic form and is covered at its two opposite facets by the mirror surfaces leaving two windows at said opposite facets for an incoming optical beam and an outgoing optical beam respectively, the windows being arranged to obtain an extended optical path of the optical beam through the element. 23. The device according to Claim 19, provided with more than two said windows, thereby enabling selection and activation of any pair of the windows for adjusting length of said internal optical path. 24. The device according to Claim 19, further provided with collimators associated with said windows and serving for adjusting the incident angle of the light beam. 25. The device according to Claim 19, adapted for signal handling in a multi-channel transmission format wherein multiple channels transmit optical signals at respective wavelengths differing from each other, said device being capable of Second Harmonic Generation (SHG) with respect to the wavelengths of more than one channels of said format. 26. The device according to Claim 25, wherein the pulse treatment device, being capable of SHG with respect to the wavelengths of a number of the multiple optical channels, is divided into the number of layers for respectively conveying there-through optical signals of said number of the multiple optical channels. 27. The device according to Claim 26, wherein the layers are separated from one another geometrically. 28. The device according to Claim 27, wherein the layers are separated from one another by wavelength filtering means. 29. The device according to Claim 19, integrated with an optical amplifier and placed immediately after said amplifier. 30. A system for handling optical signals passing via optical fiber links from the point of pulse shaping, nonlinearity treatment and/or monitoring, the system comprising two or more signal handling devices according to Claim 13 or 19, inserted in one or more optical fiber links and operative to perform pulse shaping, nonlinearity treatment and/or monitoring with respect to at least one optical pulse signal. 31. A method for designing a device for handling optical signals from the point of at least one operation from a list comprising nonlinearity treatment, pulse shaping and monitoring of an optical pulse if applied to the device at a particular wavelength, the method comprising: selecting a Second Harmonic Generating (SHG) element for the device, sensitive to a fundamental harmonic (FH) defined by the particular waveleng