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
  • H04B10/299—Signal waveform processing, e.g. reshaping or retiming
• • 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
  • G02F1/01—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 for the control of the intensity, phase, polarisation or colour 
  • G02F1/21—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 for the control of the intensity, phase, polarisation or colour  by interference
  • G02F1/225—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 for the control of the intensity, phase, polarisation or colour  by interference in an optical waveguide structure
• • 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
  • H04B10/2914—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 lumped semiconductor optical amplifiers [SOA]
• • 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
  • G02F1/01—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 for the control of the intensity, phase, polarisation or colour 
  • G02F1/21—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 for the control of the intensity, phase, polarisation or colour  by interference
  • G02F1/212—Mach-Zehnder type
• • 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
  • G02F2203/00—Function characteristic
  • G02F2203/26—Pulse shaping; Apparatus or methods therefor

Definitions

• the invention relates to the field of devices intended to create a difference signal between two optical signals.
• the invention is applicable in particular to a device for reconstituting an optical data transmission signal, in particular a rectangular type signal, for example a coded signal without return to zero.
• the invention is also applicable for the generation of a clock signal at a frequency twice the clock frequency of a first signal.
• An upstream part of the device described in this article is a fiber optic differentiator making it possible to generate from the signal with the NRZ code, a signal with pseudo return to zero, (PRZ).
• the signal PRZ thus formed from the signal NRZ is then used in a known manner to lock self-oscillating means.
• it is a laser fiber cavity in locked mode comprising a non-linear optical loop irror (NOLM).
• NOLM non-linear optical loop irror
• the upstream differentiator comprises an asymmetrical Mach Zehnder interferometric structure having two arms, one having a delay ⁇ of 300 ps in the form of an additional fiber length of 6 cm.
• the NRZ signal is introduced into each of the arms of the asymmetric Mach Zehnder interferometric structure by means of a 3 dB coupler receiving the NRZ signal. It should be clarified for the remainder of the presentation that in the experimental device described in this article the NRZ signal was generated on site by means of a tunable laser diode whose continuous output wave was modulated in a modulator receiving a signal of NRZ modulation delivered by a generator of such a signal.
• the delay ⁇ represents, as explained in the article in column 1 on page 479, the width at 3dB of the pulses constituting the differential output signal.
• this delay ⁇ must be equal to an odd number of half periods of the continuous carrier wave.
• the authors have chosen a diode for generating the continuous wave, tunable with a sufficient resolution to obtain a wavelength adjustment making it possible to obtain a phase shift fulfilling the destruction condition.
• the experimental device described in this article made it possible to obtain a PRZ signal from an NRZ signal at the rate of 1.5 gigabits per second. This signal PRZ is then used to lock a clock signal reconstituting the clock signal of the NRZ signal.
• the wavelength of the signal carrier wave is available on site, and therefore it is easy to act on it to adjust it and thus obtain the destructive condition assuming a phase shift of (2k + l) ⁇ between the signals flowing in each of the arms of the interferometer.
• the device described in this article is hardly susceptible of industrial application because, in practice, one wants to reconstruct the clock signal at the level of a regenerator from a carrier wave of a NRZ signal whose wavelength is a priori unknown.
• the stability of the carrier wave is likely to be insufficient to guarantee, in the long term, the condition of destruction. This is why there is a need for a device making it possible to differentiate two signals, one of which is delayed with respect to the other, ie a device in which the delay between the two signals can be controlled to maintain a path difference which is permanently equal to or close to (2k + l) ⁇ .
• the problem of the phase adjustment between a first signal and a second signal delayed with respect to the first, in order to obtain the condition of destructive interference is solved by a device in which there is a means of creation of 'a continuous wave.
• This continuous wave is sent in a first channel comprising a medium whose refractive index n, is variable according to a characteristic of. signal, for example the frequency or the optical power passing through the medium.
• This same medium, the refractive index n of which is variable as a function of a characteristic of the signal, for example the frequency or the optical power passing through it receives the first signal so that the index n of the medium is modulated by the levels up and down the characteristic of the first signal.
• This continuous wave is also sent in a second channel comprising a medium whose refractive index n is variable under the same conditions.
• This same medium of the second channel receives the second signal so that the index n of the medium is modulated by the high and low levels of the second signal.
• the index n of the first and / or the second medium is modified, and therefore the time of crossing of this medium by the continuous optical wave which crosses them. We can thus adjust the delay of one of the channels relative to the other to obtain a destructive beat between the first and the second signal.
• the invention relates to an optical device for differentiating two optical signals, a first and a second, the second signal being the first signal delayed with respect to the first by a delay ⁇ comprising:
• the first channel comprising a delay means delaying by ⁇ the first signal introduced in this channel, the delayed signal constituting the second signal,
• the phase shift between the first and the second signal is independent of the wavelength of the carrier wave of the signal.
• the delay means delaying the first signal by ⁇ can be placed either upstream or downstream of the optical medium with variable index. Given the vocabulary convention adopted, when the delay ⁇ is upstream of the first medium, it is the second signal which is introduced into the first medium, on the other hand if the delay ⁇ is downstream of the first medium, it is the first signal which is introduced into the first medium.
• the means for introducing the first signal on the first and second channels can be any means of multiplexing a signal arriving on a channel and dividing it between two channels, for example a 3 dB coupler or even a multimode interferometric structure, it goes from even for the output interferometric structure, located downstream of the first and second medium.
• the first and second media are of variable index depending on the optical power that passes through them and are semiconductor optical amplifiers.
• An adjustment of the phase delay is obtained by adjusting the bias current of the amplifier, modifying the gain of the amplifier and therefore the power level passing through the optical medium.
• the variation of the power passing through the optical medium causes the variation of the index of this medium. It can thus be seen that the gain adjustment causes a variation in the propagation time.
• the control of the phase delay is preferably carried out in a closed loop so as to minimize the average level of the difference signal.
• FIG. 1 shows: in part A an example of form d a first signal, in part B the signal of the delayed part A, in part C the difference signal between the signals of parts A and B, in part D a clock signal reconstituted from the pseudo clock signal represented in part C;
• - Figure 2 is a schematic view of a device according to the invention
• - Figure 3 is a schematic view of a device according to the invention in which multimode interferometers serve as input and output structure respectively in and out of the first and second channels;
• FIG. 4 is an example of a device for reconstituting a clock signal, for example an NRZ transmission signal.
• FIG. 1 is intended to explain what a difference signal represents between a first signal and the same delayed signal.
• Parts A and B of FIG. 1 respectively represent the envelope of a signal and of the same delayed signal. It may for example be an NRZ transmission signal. These signals are carried by an optical carrier wave, not shown, the wavelength of which is very small compared to the period of the signal carried.
• the difference signal presents as drawn in part C, a pulse whose duration is equal to the delay, each time that the signal of part A presents a rising edge or a falling edge, that is to say, for a digital signal, each time one goes from 0 to 1 or from 1 to 0.
• the pulses of the difference signal represented in part C represent in this case clock ticks of the NRZ signal.
• These tops can be used to lock a self-oscillating device, for example a fiber cavity laser in locked mode, as described in the document cited above, or a self-oscillating diode.
• FIG. 2 represents an example of device 1 according to the invention.
• the device has two channels 5 and 6.
• a continuous optical wave generated by a continuous wave generator 2, for example a laser diode is coupled via a coupling means 4, for example a 3 dB coupler at each of channels 5 and 6 respectively.
• the first signal carried for example by an optical fiber is also coupled via a coupling means 3, for example a 3 dB coupler to each of the channels 5 and 6 respectively.
• the first channel 5 comprises, arranged in series, a delay means 7 and a medium 10 whose propagation index n is variable as a function of the optical power passing through it.
• the second channel 6 comprises a medium 11 whose propagation index n is variable as a function of the optical power passing through it.
• the media 10 and 11 are constituted by semiconductor optical amplifiers.
• the delay 7 and the semiconductor optical amplifier 10 of the first channel 5 were produced on a single component.
• BERLIN-DE Heinrich Hertz Institute
• This device generates a delay of 7 picoseconds which has proved sufficient to obtain a difference signal, for example from a transmission signal at 2.5 gigabits having a bit period of 400 picoseconds or a 10 gigabit transmission signal having a bit period of 100 picoseconds.
• the delay must be less than the period of the signal carried, that is to say in the two cases cited immediately above less than 400 respectively. and 100 picoseconds.
• the period of time bit is the maximum duration of the delay, its minimum duration has not been explored.
• the duration of the delay represents the width of the pulses resulting from the differentiation. These impulses should be perceptible.
• a delay of between approximately 7 picoseconds and the duration of the bit time may be suitable.
• the delay means 7 can also be produced from an additional length of fiber on the first channel. In this case, the fiber carrying the signal on the first channel 5 is longer than the fiber carrying the signal on the second channel 6.
• the delay 7 can also take the form of a specific component 7 and in this case it can be placed on the first channel 5 downstream of the medium 10 or as shown in dotted lines upstream of medium 10, while being downstream of the entry point on this channel, of the continuous wave coming from the continuous wave generator 2. It can also, as also shown in dotted lines, be upstream of this entry point of the continuous wave from the continuous wave generator 2.
• Means 9 for adjusting a bias current make it possible to adjust the amplification level of the optical amplifier 10, and therefore the time for crossing an optical medium present in a known manner in this amplifier.
• the adjustment is made in a constant and automatic manner thanks to closed-loop regulation tending to minimize the average value of an optical signal representing the difference signal directly at the output of the interferometric structure 8 or preferably still downstream of a filter 23 centered on the wavelength of the continuous wave coming from the continuous wave generator 2.
• the loop includes a detector 22 of the optical power at the output of the filter 23. This detector 22 can for example be a photodiode followed by an integrator circuit. Another embodiment will now be described with reference to FIG. 3.
• the embodiment represented in this figure differs from the previous one by the means for inputting the first signal and the continuous wave on channels 5 and 6.
• An interferometer multimode 13, for example from Fabry Pérot has two inputs, a first 14 and a second 15.
• the first input 14 receives the signal.
• the second input 15 receives the continuous wave from the generator continuous wave 2.
• Two outputs a first 16 and a second 17 of one multimode interferometer 13 each receive the continuous wave from the continuous wave generator 2, and the signal. These first 16 and second 17 outputs are respectively coupled to the first 5 and to the second 6. channel.
• the delay 7 is placed upstream or downstream of the medium 10 on the channel 5.
• the output 19 of the channel 5 and the output 20 of the channel 6 are coupled to a first 19 and to a second 20 input of a multimode output interferometer 18.
• the inputs of this interferometer have the same references 19, 20 as the outputs of channels 5 and 6 because the outputs of channels 5 and 6 also constitute the inputs of the multimode interferometer 13.
• the first and the second channel respectively comprise the first medium 10 and the second medium 11. It can also, depending on the variant embodiments, include or not the delay 7.
• channels 5 and 6 do not comprise not delay 7
• the structure is asymmetrical when delay 7 is present on channel 5, downstream of the signal and continuous wave inputs on this channel.
• the medium 10 receives the continuous wave and the first or the second signal so that the index n of the middle 10 is modulated by the high and low levels of the first signal.
• the continuous wave is also sent into the medium 11, the propagation index n of which is variable as a function of the optical power passing through the medium.
• This same medium 11 of the second channel receives the first signal so that the index n of the medium is modulated by the high and low levels of the first signal.
• the device for creating a clock signal 30 comprises a device 1 according to one of the embodiments of the invention.
• the difference signal present at the output of this device 1 is received by self-oscillating means 31. It may for example be a laser fiber cavity in locked mode, or a self-oscillating diode. In the experimental embodiment, a self-oscillating HHI diode was used.
• the signal at the input of device 1 according to the invention is a NRZ transmission signal
• the difference signal present at the output of device 1 is a pseudo signal with return to 0 (PRZ).
• PRZ pseudo signal with return to 0
• the difference signal present at the output of the device 1 according to the invention is a clock signal having a frequency twice that of the signal d input clock, since there is an output pulse for each rising or falling edge of the input signal.
• the width of each clock pulse is an increasing function of the delay ⁇ between the two waves. Note that when the input signal is a clock signal, a double frequency clock signal is obtained directly without the self-oscillating device 31.
• the device 1 according to the invention can be used to obtain a clock signal having a double frequency of an input signal constituted by a first clock signal.

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• Physics & Mathematics (AREA)
• Nonlinear Science (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Optical Communication System (AREA)
• Light Guides In General And Applications Therefor (AREA)
• Manipulation Of Pulses (AREA)
• Eye Examination Apparatus (AREA)

Applications Claiming Priority (3)

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• 1999
  • 1999-08-03 FR FR9910073A patent/FR2797331B1/fr not_active Expired - Fee Related
• 2000
  • 2000-08-02 JP JP2001513828A patent/JP2003506726A/ja not_active Withdrawn
  • 2000-08-02 WO PCT/FR2000/002219 patent/WO2001010045A2/fr not_active Ceased
  • 2000-08-02 CA CA002345371A patent/CA2345371A1/fr not_active Abandoned
  • 2000-08-02 EP EP00956595A patent/EP1145446A3/de not_active Withdrawn
  • 2000-08-02 US US09/787,892 patent/US6628855B1/en not_active Expired - Fee Related
• 2003
  • 2003-09-25 US US10/671,986 patent/US20040062470A1/en not_active Abandoned

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