Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
  • H04B10/29—Repeaters
  • H04B10/291—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
  • H04B10/2912—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form characterised by the medium used for amplification or processing
  • H04B10/2916—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form characterised by the medium used for amplification or processing using Raman or Brillouin amplifiers
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/35—Non-linear optics
  • G02F1/3515—All-optical modulation, gating, switching, e.g. control of a light beam by another light beam
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/30—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range using scattering effects, e.g. stimulated Brillouin or Raman effects
  • H01S3/302—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range using scattering effects, e.g. stimulated Brillouin or Raman effects in an optical fibre
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
  • H04B10/25—Arrangements specific to fibre transmission
  • H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
  • H04B10/25077—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion using soliton propagation
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/35—Non-linear optics
  • G02F1/3511—Self-focusing or self-trapping of light; Light-induced birefringence; Induced optical Kerr-effect

Definitions

• This invention relates generally to a fiber optic system and more particularly, to a fiber optic system which can concurrently amplify and switch an input signal via a pump signal
• one type of optical switch for an input signal uses a biref ⁇ ngent fiber switch which has an optical fiber with a birefringence that preserves polarization
• the input signal propagates in one of two, perpendicular, polarized modes in the optical fiber
• a gating signal of sufficient energy is coupled into the optical fiber to propagate in the same polarized mode as the input signal initially
• the gating signal induces a nonlinear birefringence in the optical fiber which causes the input signal to switch and propagate in the other polarized mode
• the gating signal in the biref ⁇ ngent fiber switch does not amplify the input signal
• One example of a type of optical amplifier for amplifying an input signal uses an optical fiber and a phenomenon known as Raman gain Again, the input signal propagates in the optical fiber To amplify the input signal using Raman gain, a pump signal whose wavelength is less than the wavelength of the input signal is coupled into the optical fiber which is carrying the input signal The pump signal amplifies the input signal, but does not switch the polarization or propagation of the input signal
• a fiber optic system in accordance with the present invention includes an optical fiber, a coupling device, and a system for generating a pump signal
• the optical fiber has a birefringence which preserves polarization and has a first polarization mode which is substantially perpendicular to a second polarization mode
• the coupling device couples an input signal having an input wavelength into the optical fiber so that the input signal propagates in the first polarization mode in the optical fiber
• the system for generating a pump signal generates a pump signal with a pump wavelength which is within a range of 50 nm to 300 nm less than the input wavelength and which and has a first amount of pump power which is enough power to switch the input signal polarization, but not enough power to create higher order solitons
• the coupling device also couples the pump signal into the optical fiber so that the pump signal propagates in the first polarization mode in the optical fiber
• the pump signal alters the birefringence of the optical fiber which causes the input signal to switch polarization modes and propag
• FIG 2 is a cross-sectional view of the optical fiber taken along lines 2-2 of FIG 1
• Fiber optic system 10 includes an optical fiber 12, a coupler 14, and a pump laser 18 With fiber optic system 10, an input signal can be both amplified and switched concurrently, and thus separate stages for amplification and switching are not required
• fiber optic system 10 includes optical fiber 12 which has a birefringence that preserves polarization
• optical fiber 12 Since optical fiber 12 is biref ⁇ ngent, optical fiber 12 has a first polarization mode which is substantially perpendicular to a second polarization mode An input signal coupled into one end 19 of optical fiber 12 will propagate in either the first or second polarization mode Referring to FIG 2, optical fiber 12 has an elliptical, cross sectional shape with a short or fast axis 20, along which one of the polarization modes runs, and a long or slow axis 22, along which the other one of the polarization modes runs Although an optical fiber 12 with an elliptical shape is shown other types of biref ⁇ ngent optical fibers, such as an optical fiber with stress rods could be used Optical fiber 12 has a core 24, which in this particular embodiment is made from silica, and a cladding 26
• Fiber optic system 10 also includes a pump laser 18 which generates a pump signal which has a pump wavelength that is about 50 nm to 300 nm less than the input wavelength for the input signal
• the pump wavelength and gain are chosen to amplify the signal, but not to the point of creating higher order solitons
• the pump signal is also generated by laser pump 18 to have sufficient energy to induce a non-linear birefringence in optical fiber 12 and cause the input signal to switch between the two polarization modes
• the amount of energy or power needed to induce a non- linear birefringence in optical fiber 12 and cause the input signal to switch polarization modes depends upon the birefringence of optical fiber
• Pump laser 18 outputs the pump signal on optical fiber 29
• any type of system for generating the pump signal could be used
• Fiber optic system 10 also includes coupler 14 which couples the input signal and the pump signal into the optical fiber 12 to propagate in the first polarization mode Coupler 14 is located between an optical fiber 28 and one end 19 of optical fiber 12 and couples the
• Fiber optic system 10 may also include a filter 30 which can be coupled to the other end 32 of optical fiber 12 Filter 30 removes unwanted wavelengths after the input signal has been amplified and switched including any of the pump signal which remains Fiber optic system 10 operates by coupling input and pump signals into optical fiber 12 via coupler 14
• a soliton signal is used as the input signal and as the pump signal, although other types of input and pump signals could be used
• the input signal and the pump signal propagate in a first polarization mode with their electric fields aligned
• input signal and pump signal are input to propagate in the short or fast axis 20
• the pump signal When the pump signal is coupled into optical fiber 12 as described above, part of the energy of the pump signal converts to and combines with the input signal to amplify the input signal Effectively, the pump signal converts its energy to the input signal wavelength
• the amplification of the input signal is the result of a phenomenon called Raman gain For Raman gain to occur in optical fiber 12, there needs to be a difference between the wavelength of the input signal and the wavelength of the pump signal from pump laser 18
• the difference between the two wavelengths should be such that the gain occurs without the creation of higher order solitons Accordingly, in this particular embodiment the gain is on the order of ten to avoid creating higher order solitons
• the wavelength of the pump signal is kept within a range of 50 nm to 300 nm less than the wavelength of the input signal when the wavelength of the input signal is near 1550 nm
• the specific amount of amplification or Raman gain experienced by the input signal in optical fiber 12 is determined by the following equation p
• the gain of the input signal will be approximately e 20 If the wavelength of the pump signal is 300 nm from the wavelength of the input signal, then the amplification factor will be e 2 , or a gain cf about seven
• the input signal is being amplified in optical fiber 12 as described above, the input signal is also being switched in optical fiber 12
• the pump signal from pump laser 18 coupled into and propagating in the first polarization mode of optical fiber 12 has sufficient energy to induce a non- linear birefringence in optical fiber 12 and thus cause the input signal to switch from propagating in the first pola ⁇ zation mode to propagating in the second polarization mode
• the amount of energy or power required to switch the input signal in optical fiber 12 depends upon the biref ⁇ ngence of optical fiber 12, as discussed in M N Islam, Ultrafast Fiber Switching Devices and Systems, Cambridge, University Press, 1992, which is herein incorporated by reference
• the birefringence of the optical fiber 12 can be determined by the equation
• ⁇ N 0 33N 2 (I X - I y )
• N 2 is the index of refraction of the core of optical fiber 12
• l x is the intensity of the input signal along the x-axis
• I is the intensity of the input signal along the y-axis

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Nonlinear Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Optics & Photonics (AREA)
• Plasma & Fusion (AREA)
• General Physics & Mathematics (AREA)
• Lasers (AREA)
• Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

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Publications (3)

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• 1997
  • 1997-07-01 CN CN 97190867 patent/CN1217793A/zh active Pending
  • 1997-07-01 CA CA 2230686 patent/CA2230686A1/en not_active Abandoned
  • 1997-07-01 WO PCT/US1997/011699 patent/WO1998001777A2/en not_active Ceased
  • 1997-07-01 EP EP97933289A patent/EP0870208A4/de not_active Withdrawn
  • 1997-07-01 JP JP10505287A patent/JP2000513830A/ja active Pending
  • 1997-07-01 AU AU36510/97A patent/AU3651097A/en not_active Abandoned

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