WO2018169289A1 - Appareil de génération de laser à fibre optique - Google Patents

Appareil de génération de laser à fibre optique Download PDF

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Publication number
WO2018169289A1
WO2018169289A1 PCT/KR2018/002950 KR2018002950W WO2018169289A1 WO 2018169289 A1 WO2018169289 A1 WO 2018169289A1 KR 2018002950 W KR2018002950 W KR 2018002950W WO 2018169289 A1 WO2018169289 A1 WO 2018169289A1
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high density
density wavelength
wavelength multiplexer
optical fiber
wavelengths
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Korean (ko)
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WO2018169289A9 (fr
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김병윤
이은주
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한국과학기술원
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    • 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
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06791—Fibre ring lasers
    • H—ELECTRICITY
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    • 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
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H—ELECTRICITY
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    • 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
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08086—Multiple-wavelength emission
    • H—ELECTRICITY
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    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • 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
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • 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
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H01S3/1106—Mode locking
    • H01S3/1109—Active mode locking
    • H—ELECTRICITY
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    • 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
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06708—Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering
    • H01S3/06712—Polarising fibre; Polariser
    • H—ELECTRICITY
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    • 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
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
    • H01S3/082—Construction or shape of optical resonators or components thereof comprising three or more reflectors defining a plurality of resonators, e.g. for mode selection or suppression
    • 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
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094003—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light the pumped medium being a fibre
    • H—ELECTRICITY
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    • 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
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
    • H01S3/09415—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
    • 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
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
    • H01S3/107—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using electro-optic devices, e.g. exhibiting Pockels or Kerr effect
    • 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
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/1601—Solid materials characterised by an active (lasing) ion
    • H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
    • H01S3/1608—Solid materials characterised by an active (lasing) ion rare earth erbium

Definitions

  • the present invention relates to an optical fiber laser generator, and more particularly, to an active mode locked optical fiber laser generator in which the wavelength changes discontinuously.
  • the Fourier domain mode locked laser solves the buildup type problem by synchronizing the tunable period with the resonant period.
  • a high tunable rate of several Mhz is achieved by buffering outside the resonator and using an additional fiber amplifier.
  • Another method of increasing the variable speed of the wavelength is to perform active mode locking in a resonator with a very high dispersion.
  • the active mode locking method linearly changes the frequency of the voltage signal applied to the amplitude modulator, thereby modulating the oscillation wavelength. It also changes the wavelength at high speed without a dynamic filter.
  • the instantaneous spectral line width and the variable wavelength range of the laser are inversely proportional to each other, which limits the performance when the laser is used in an optical coherence tomography (OCT).
  • OCT optical coherence tomography
  • a wavelength step-variable laser is implemented using long fiber and harmonic mode locking.
  • This method shows that the depth range of the tomography apparatus can be sufficiently extended without using a bandwidth higher than that of the existing data sensing / acquisition system.
  • the method also ensures linearity of wavelength step changes, eliminating the need for data interpolation before Fourier transforms.
  • the present invention provides an apparatus for generating a laser having a step change of wavelength at a high speed by using a commercial optical communication element in a short resonator.
  • the amplitude modulator the amplitude modulator; A first high density wavelength multiplexer pair connected to the amplitude modulator for receiving a pulse including a plurality of wavelengths and separating and outputting the plurality of wavelengths; An optical fiber amplifier connected to the first high density wavelength multiplexer pair; And a second high density wavelength multiplexer pair connected to the optical fiber amplifier and receiving the separated plurality of wavelengths and combining the plurality of wavelengths into one pulse. It includes.
  • a first output combiner disposed between the first high density wavelength multiplexer pair and the optical fiber amplifier.
  • the optical fiber amplifier includes an erbium-doped optical fiber and a laser diode.
  • a polarization regulator disposed between the second high density wavelength multiplexer pair and the second output coupler.
  • An interval between pulses output by the first high density wavelength multiplexer pair is greater than a width of the pulses.
  • the first high density wavelength multiplexer pair includes an optical fiber having a plurality of different lengths connected between the first high density wavelength multiplexer, the second high density wavelength multiplexer, and the first high density wavelength multiplexer and the second high density wavelength multiplexer.
  • the first high density wavelength multiplexer pair receives a pulse including the plurality of wavelengths and distributes the pulse to the optical fiber.
  • the optical fiber is disposed lengthwise between two high density wavelength multiplexers.
  • the order of the output wavelength is inversely proportional to the length of the optical fiber.
  • the second high density wavelength multiplexer pair includes a first high density wavelength multiplexer, a second high density wavelength multiplexer, and a plurality of different lengths of optical fibers connected between the first high density wavelength multiplexer and the second high density wavelength multiplexer.
  • the second high density wavelength multiplexer pair receives the plurality of separated wavelengths and combines the plurality of wavelengths into one pulse using the optical fiber.
  • the optical fiber is disposed lengthwise between two high density wavelength multiplexers.
  • the length of the optical fiber is inversely proportional to the order of the plurality of separated wavelengths.
  • the laser generating apparatus may generate a laser having a step change of wavelength at high speed by using a commercial optical communication device in a short resonator.
  • FIGS. 1A to 1C are diagrams schematically illustrating an apparatus for generating a step wavelength tunable laser according to an embodiment of the present invention.
  • FIG. 2 is a view showing a step wavelength tunable laser generating apparatus according to an embodiment of the present invention.
  • FIG 3 is a view showing the operation of the amplitude modulator of the laser generating apparatus according to an embodiment of the present invention.
  • 4 is a diagram illustrating characteristics of a mode-locked single wavelength laser for each channel.
  • FIG. 5 shows the optical spectrum, pulse waveform and radio frequency spectrum of each of the mode locked pulses when a modulation frequency of 3.12134 Mhz is used.
  • FIG. 6 is a diagram showing an oscilloscope waveform of a wavelength when three wavelengths are simultaneously locked in mode.
  • FIG. 7 is a diagram showing an optical spectrum and a pulse waveform when three wavelength channels oscillate simultaneously.
  • FIG. 8 is a diagram illustrating a noise spectrum in three channels.
  • spatially relative terms below “, “ beneath “, “ lower”, “ above “, “ upper” It may be used to easily describe the correlation of a device or components with other devices or components. Spatially relative terms are to be understood as including terms in different directions of the device in use or operation in addition to the directions shown in the figures. For example, when flipping a device shown in the figure, a device described as “below” or “beneath” of another device may be placed “above” of another device. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device can also be oriented in other directions, so that spatially relative terms can be interpreted according to orientation.
  • FIGS. 1A to 1C are diagrams schematically illustrating an apparatus for generating a step wavelength tunable laser according to an embodiment of the present invention.
  • the step wavelength tunable laser generator 100 may include an optical fiber amplifier 110, first and second high density wavelength multiplexers (DWDMs) 101 and 103, an amplitude modulator 120, and a first modulator 120. And a first and second output combiner (OC) 105, 106.
  • DWDMs high density wavelength multiplexers
  • OC output combiner
  • the first high density wavelength multiplexer pair 101 is connected to the first output combiner 105, and the first output combiner 105 is connected to the optical fiber amplifier 110.
  • the optical fiber amplifier 110 is connected to the second high density wavelength multiplexer pair 103, and the second high density wavelength multiplexer pair 103 is connected to the second output combiner 106.
  • the second output coupler 106 is also connected to the amplitude modulator 120.
  • the first high density wavelength multiplexer 101 includes N channels and selects a laser wavelength.
  • the first high density wavelength multiplexer 101 distributes different laser wavelengths into N different length optical fibers.
  • the second high density wavelength multiplexer 103 combines the dispersed N wavelengths into one optical fiber.
  • One pulse is input to the first high density wavelength multiplexer 101, and the pulse including the plurality of wavelengths passes through the first high density wavelength multiplexer 101 and becomes N pulses that are completely separated. At this time, the optical time delay between adjacent pulses having different wavelengths in the first high density wavelength multiplexer 101 is longer than the width of the pulse.
  • Pulses having different wavelengths passing through the first high density wavelength multiplexer 101 pass through the optical fiber amplifier 110 at different times and gain is amplified.
  • the gain recovery time of the optical fiber amplifier 110 is shorter than the interval between pulses, gain competition between adjacent pulse components having different wavelengths may be avoided.
  • the second high density wavelength multiplexer 103 receives the pulses output from the optical fiber amplifier 110 to accurately compensate for the optical delay difference generated in the first high density wavelength multiplexer 101 and to make the resonator lengths of all the wavelength components equal. do.
  • the signals output from the first output combiner 105 are pulses having a step change in wavelength, and the signals output from the second output combiner 106 are single pulses mixed with different wavelengths.
  • the frequency of the signal applied to the amplitude modulator 120 coincides with the resonant frequency so that the output pulses are mode locked.
  • Mode lock is a resonant frequency determined by the length of the laser generating device, which means that the phase between these frequencies is kept constant to generate periodic pulse output.
  • the amplitude modulator 120 may be a lithium-niobate amplitude modulator.
  • the step wavelength tunable laser generator 100 is annular and can be active mode locked at a fundamental frequency (6 Mhz). Active mode locking means forcibly mode locking from the outside using an active device.
  • the first and second high density wavelength multiplexers 101 and 103 simultaneously serve as static filters for selecting the oscillation wavelength and as optical delay elements for temporally separating and combining pulses having different center wavelengths. .
  • 1B is a view showing the operation of the first high density wavelength multiplexer 101 of the laser generating apparatus according to the embodiment of the present invention.
  • the first high density wavelength multiplexer 101 receives a single pulse including N wavelengths.
  • the first high density wavelength multiplexer 101 includes N different lengths of optical fibers.
  • a single pulse including a plurality of wavelengths is divided into N pulses having N different lengths of wavelengths, and the separated N pulses are applied to N optical fibers of different lengths, respectively.
  • the pulse applied to the optical fiber has a different time depending on the length of the optical fiber. That is, pulses applied to the shortest optical fiber are separated first and pulses applied to the longest optical fiber are separated last.
  • N pulses applied to N different lengths of optical fibers are again applied to one optical fiber. At this time, N pulses have an optical time delay longer than the width of the pulse.
  • 1C is a view showing the operation of the second high density wavelength multiplexer 103 of the laser generating apparatus according to the embodiment of the present invention.
  • the second high density wavelength multiplexer 103 includes N different lengths of optical fibers.
  • the second high density wavelength multiplexer 103 receives N pulses having wavelengths of different lengths.
  • N pulses have an optical time delay longer than the width of the pulse and are applied to N different lengths of optical fibers, respectively.
  • Pulses applied to the optical fiber are delayed at different times according to the optical fiber length.
  • the pulse applied first is applied to the longest optical fiber and the pulse applied last is applied to the shortest optical fiber.
  • N pulses applied to N different lengths of optical fibers are again applied to one optical fiber and combined into a single pulse.
  • FIG. 2 is a view showing a step wavelength tunable laser generating apparatus according to an embodiment of the present invention.
  • the step-wavelength laser generator includes a fiber amplifier, first and second high density wavelength multiplexer pairs 101 and 103, a polarization controller (PC) 107, and first and second outputs. Couplers 105, 106, isolators 108, and intensity modulator (IM) 120.
  • PC polarization controller
  • IM intensity modulator
  • the first high density wavelength multiplexer pair 101 is connected with a first output combiner 105, the first output combiner 105 is connected with an isolator 108, and the isolator 108 is connected with an optical fiber amplifier.
  • the optical fiber amplifier is connected with the second high density wavelength multiplexer 103 pair, the second high density wavelength multiplexer 103 pair is connected with the polarization regulator 107 and the polarization regulator 107 is connected with the second output combiner 106.
  • a second output coupler 106 is coupled with the amplitude modulator 120.
  • the first high density wavelength multiplexer pair 101 includes four optical fibers each having a different length and connected between the first high density wavelength multiplexer, the second high density wavelength multiplexer, and the first and second high density wavelength multiplexers, respectively. .
  • the four optical fibers also have the same number between the first high density wavelength multiplexer and the second high density wavelength multiplexer.
  • the second high density wavelength multiplexer pair 103 includes four optical fibers each having a different length and connected between the first high density wavelength multiplexer, the second high density wavelength multiplexer, and the first and second high density wavelength multiplexers, respectively. .
  • the four optical fibers also have the same number between the first high density wavelength multiplexer and the second high density wavelength multiplexer.
  • the length of the optical fiber becomes longer.
  • the length of the optical fiber becomes shorter.
  • the optical fibers having the same number of the first high density wavelength multiplexer pair 101 and the second high density wavelength multiplexer pair 103 have a corresponding relationship.
  • the wavelength applied to the first optical fiber shared by the first high density wavelength multiplexer pair 101 and the second high density wavelength multiplexer pair 101 is the first of the second high density wavelength multiplexer pair 103. It is applied to the first optical fiber shared by the high density wavelength multiplexer and the second high density wavelength multiplexer. Therefore, one pulse including a plurality of wavelengths passes through the first high density wavelength multiplexer pair 101 and is separated into a plurality of pulses, and passes through the second high density wavelength multiplexer pair 103 and is combined into one pulse.
  • the isolator 108 allows the signal output from the first high density wavelength multiplexer 101 to proceed in only one direction.
  • the optical fiber amplifier includes an erbium doped fiber (EDF) 112 and a laser diode 111 (LD) 111.
  • EDF erbium doped fiber
  • LD laser diode 111
  • the erbium-doped optical fiber 112 is combined with a laser diode 111 having a length of 3 m and a wavelength of 980 nm, and pumped by the laser diode 111.
  • the optical fiber amplifier 110 may be an optical fiber amplifier having fast gain recovery characteristics such as a semiconductor optical amplifier (SOA).
  • SOA semiconductor optical amplifier
  • erbium-doped fiber lasers has effects such as gain competition and relaxation vibrations.
  • Each of the first and second high density wavelength multiplexers 101, 103 pairs comprises two commercially available high density wavelength multiplexers.
  • the high density wavelength multiplexer has four channels spaced at 100 GHz.
  • the central wavelength of each of the four channels is 1554.13 nm, 1554.94 nm, 1555.75 nm, 1556.56 nm.
  • the 3-dB transmission bandwidth in each channel is about 0.11 nm.
  • the total length of the laser generating apparatus is about 31m including the length of the erbium-doped optical fiber, which corresponds to the resonance frequency of the laser of 6.3Mhz and the laser generator round trip time of 160ns.
  • the time delay difference between channel 1 and channel 2 in the first high density wavelength multiplexer pair 101 is about 18.0 ns, and about 14.8 ns between channel 2 and channel 3.
  • the optical fiber spacing between adjacent channels of the first high density wavelength multiplexer pair 101 may be about 3m to 4m.
  • the second high density wavelength multiplexer pair 103 is adjusted within a range of 50 ps to compensate for the interchannel time delay caused by the first high density wavelength multiplexer pair 101.
  • the inter-channel time delay difference in the first high density wavelength multiplexer 101 may be set longer than 1.9 ns, which is a theoretically predicted pulse width by the Kuizenga-Siegman formula.
  • the amplitude modulator 120 includes a function generator 122 and a power supply 123.
  • the function generator 122 supplies a square wave voltage signal modulated by the amplitude modulator 120.
  • the power supply 123 supplies power for driving the amplitude modulator 120.
  • Pulses of different center wavelengths are separated through the optical fiber amplifier 110 including the erbium-doped optical fiber, and the time delay interval between the pulses may be longer than the gain recovery time of the amplifier.
  • Lithium niobate magenent-type amplitude modulators can be used for active mode locking of the laser. Since the amplitude modulator operates at a single polarization, the polarization regulator 107 is used to maximize the transmission of light through the amplitude modulator. Since the loss of the laser generating apparatus 100 depends on the polarization, all wavelengths should be the same polarization. Polarization control is achieved by changing the birefringence of the optical fiber.
  • FIG. 2 a method of optimizing birefringence for each channel of the laser generating apparatus using only one polarization controller 107 is used, but the polarization controller 107 may be connected to all channels of the high density wavelength multiplexer pair.
  • FIG 3 is a view showing the operation of the amplitude modulator of the laser generating apparatus according to an embodiment of the present invention.
  • the graph 201 at the upper left shows the relationship between voltage and transmittance.
  • Transmittance refers to the ratio of light to input. For example, when the input light is output without loss, the transmittance is 1, and when 50% is output, the transmittance is 0.5.
  • the graph at the bottom left shows the square wave voltage signal applied to the amplitude modulator.
  • the square wave voltage signal has a rise or fall time of about 18 ns and is applied to the modulator with an amplitude of 2.5 V in a 2 T R period. Since T R is equal to the time the laser reciprocates the resonator, the mode lock of the laser occurs.
  • the square wave voltage signal applied to the modulator is a DC biased voltage and is set such that the rising edge and the falling edge round the maximum transmission voltage of the amplitude modulator at the same time interval.
  • the longitudinal mode refers to a resonance frequency determined by the length of the laser generator.
  • the graph in the upper right corner shows that the square wave voltage signal applied to the amplitude modulator is modulated.
  • the square wave voltage signal 203 applied to the amplitude modulator is modulated by the amplitude modulator and has a transmission peak having a period of T R.
  • the background loss of the amplitude modulator is about 4.17 dB and the half width of the transmission waveform 202 may be about 16 ns. This is similar to the rise or fall time of a square wave.
  • the two output couplers 105, 106 may use 5% fiber coupler.
  • 4 is a diagram illustrating characteristics of a mode-locked single wavelength laser for each channel. 2 and 4, the polarization regulator such that the modulation frequency of the square wave input to the modulator is optimized, only one wavelength signal is selected, and the selected signal has the clearest pulse shape in order to realize the best mode lock mode. 107 is adjusted.
  • the laser output signal is observed using an optical spectrum analyzer, a light detector with a bandwidth of 12 GHz, and a digital oscilloscope with a bandwidth of 1 GHz.
  • (a) to (c) show the light spectra when mode locked in channels 1 to 3, respectively.
  • the horizontal axis of the light spectrum graph represents wavelength and the vertical axis represents output.
  • the optimized modulation frequencies for channels 1 to 3 are 3.121790, 3.120890 and 3.120893 MHz, respectively.
  • Graphs 407, 408, and 409 shown inside of (a) to (c) show fitting the spectra near the spectral peaks with Gaussian curves.
  • the center wavelengths of each channel are 1554.25, 1555.00, and 1555.80 nm
  • the 3-dB spectral widths are 0.24 nm, 0.14 nm, and 0.15 nm, respectively.
  • the spectra in (a) to (c) represent the spectra in the time domain calculated by averaging 255 samples.
  • (d) to (f) show the pulse waveforms 404, 405, 406 and the radio frequency spectrum 410, 411, 412 of each channel.
  • the horizontal axis of the frequency spectrum graph represents time and the vertical axis represents intensity in units of V.
  • the black dots represent the data and the red lines represent the approximation of the black dots in a Gaussian form.
  • the average pulse width of each channel is 1.4ns, 1.0ns, and 1.2ns, which is similar to Gaussian form.
  • the average pulse width may be shorter than the pulse width of 1.93 ns, which is calculated assuming sine wave amplitude modulation.
  • amplitude modulation waveform may be more sharp than when sine wave amplitude modulation is assumed.
  • the quality of the mode lock may also be sensitive to polarization control. Each wavelength channel operates properly at each optimized amplitude frequency.
  • the graph at the upper right of (d) to (f) shows the radio frequency spectrum.
  • the radio frequency spectrum represents the radio frequency spectrum of the laser.
  • the peak frequency interval of the radio frequency spectrum corresponds to the frequency of the signal applied to the amplitude modulator. As the frequency increases, the signal strength decreases and the rate of change of the signal to frequency increases. The smaller the value, the shorter the pulse width. This means that the wider the range of the radio frequency spectrum, the better the mode lock.
  • the radio frequency spectrum maintains a flat height up to about 300 MHz, which means that mode lock works well.
  • one modulation frequency should be used that is not optimized for any one channel. Detuning at the optimized modulation frequency results in degraded laser performance.
  • one frequency whose frequency difference is similar in all channels can be selected to analyze the effects of frequency shifting on a single laser wavelength.
  • FIG. 5 shows the optical spectrum 501, 502, 503, pulse waveforms 504, 505, 506 and the radio frequency spectrum 510, 511, 512 of each of the mode locked pulses when a modulation frequency of 3.12134 Mhz is used.
  • the frequency shifts of channels 1 to 3 are 900 Hz, -900 Hz, and -894 Hz, respectively.
  • the frequency output from the amplitude modulator is twice the frequency applied to the amplitude modulator. For example, if the frequency shifted from the optimized modulation frequency is 450 Hz different from the optimized modulation frequency, the output frequency has a difference of 900 Hz from the frequency at which the optimized modulation frequency is applied to the amplitude modulator and output.
  • the spectra of (a) to (c) indicate that only one wavelength is oscillated using the polarization controller 107.
  • the center wavelengths of the spectra of each channel approximated by a Gaussian curve are 1554.20 nm, 1555.05 nm, and 1555.95 nm, respectively, and the 3-dB spectral widths are 0.15 nm, 0.09 nm, and 0.17 nm, respectively.
  • (d) to (f) show the pulse waveforms 504, 505 and 506 and the radio frequency spectrums 510, 511 and 512 of each channel.
  • the horizontal axis of the frequency spectrum graph represents time and the vertical axis represents intensity in units of V.
  • the black dots represent the data and the red lines represent the approximation of the black dots in a Gaussian form.
  • the pulse waveform is a shape slightly deviating from the ideal Gaussian form.
  • the widths of the pulses for the channels 1 to 3 are 1.2, 1.4, and 1.2ns, respectively, which are similar to the widths of the pulses for the channels 1 to 3 of FIGS. 4 (d) to (f).
  • the degradation of mode locked pulses can also be caused by polarization mismatches that occur outside of the optimized modulation frequency or in the process of suppressing other wavelength components with one polarization controller.
  • Graphs 510, 511 and 512 in the upper right of (d) to (f) show the radio frequency spectrum. Comparing the radio frequency spectrum with Figs. 4 (d) to 4 (f) confirms the degraded mode locking performance.
  • FIG. 6 is a diagram showing an oscilloscope waveform of a wavelength when three wavelengths are simultaneously locked in mode.
  • (a) to (b) show oscilloscope waveforms for the outputs of the first output combiner 105 and the second output combiner 106 when the modulation frequency is 3.12134 Mhz.
  • the three pulses that simultaneously passed through the modulator are completely separated while passing through the first high density multiplexer pair 101 and the fiber amplifier 110.
  • the time interval between the three pulses is 18ns between channel 1 and channel 2 and 14.8ns between channel 2 and channel 3.
  • FIG. 7 is a diagram showing an optical spectrum and a pulse waveform when the wavelengths in three channels oscillate simultaneously.
  • (a) shows the light spectrum 701 when the wavelengths in three channels oscillate simultaneously.
  • the horizontal axis in (a) represents the wavelength and the vertical axis represents the output.
  • the center wavelength of each channel of the Gaussian approximated spectrum is 1554.20 nm in channel 1, 1555.05 nm in channel 2, and 1555.95 nm in channel 3, and the corresponding 3 dB spectral widths are 0.04 nm, 0.08 nm, and 0.07 nm, respectively.
  • (b) through (d) show the pulse waveforms 702, 703, 704 and the radio frequency spectrum 705, 706, 707, indicating that each wavelength signal has been filtered after passing through a channel suitable for another external high density wavelength multiplexer. ).
  • the horizontal axis in (b) to (d) represents time and the vertical axis represents intensity in units of V.
  • the red lines in (b) to (d) represent ideal Gaussian waveforms and the black dots represent data.
  • the pulse waveforms 702, 703, 704 and the radio frequency spectrums 705, 706, 707 of (b) to (d) are out of the ideal Gaussian waveform, and when the three wavelengths simultaneously oscillate, Waveform and radio frequency spectrum results may vary.
  • individual polarization controllers 107 can be used for each channel inside the pair of high-density wavelength multiplexers, or a laser-generated device can be manufactured with polarization-maintaining fibers to prevent the pulse and frequency spectra from deviating from the ideal Gaussian waveform. have.
  • FIG. 8 is a diagram illustrating a noise spectrum in three channels.
  • the amplitude and phase noise of each channel are measured using the noise spectrum, and the characteristics of the noise spectrum are analyzed.
  • the spectrum of the first peak of the radio frequency spectrum and the vicinity of the higher harmonic peaks are compared, and for each channel the spectrum is measured when it is separated in the range of 100 Hz to 500 kHz from the peak frequency, and the RMS fluctuations in amplitude and timing Is expected.
  • the first and 40th radio frequency spectral peaks are used, with frequency offsets below 5 kHz measured at 30 Hz resolution and frequency offsets below 500 kHz with 10 kHz resolution.
  • each graph of FIG. 8 represents frequency offset and the vertical axis represents single sideband noise. The smaller the number, the less noise. That is, -40 means less noise than -60.
  • (a)-(c) indicate when a single wavelength oscillates at an optimized modulation frequency
  • (d)-(f) indicate when a single wavelength oscillates at a shifted frequency.
  • (g)-(i) indicates Shown when three wavelengths oscillate in frequency.
  • the noise peak at the relaxation frequency can be greater when there is a shift in the modulation frequency.
  • the relaxation frequency peaks of channels 1 to 3 are around 50 kHz. Table 1 summarizes the results of measuring RMS amplitude and time fluctuations.
  • Amplitude and timing fluctuations may increase due to gain competition between oscillation wavelengths, and amplitude and timing fluctuations may be solved by using an optical fiber amplifier 110 having fast gain recovery characteristics compared to pulse intervals.
  • Amplitude and timing fluctuations are very sensitive to the state of the polarization controller 107 and it may not be easy to find the conditions of polarization that are optimized at all wavelengths.
  • amplitude and timing fluctuations occur.
  • amplitude and timing fluctuations may occur due to nonlinear polarization rotation that occurs when the peak power of the pulse increases.
  • a laser generating device made of a polarization maintaining optical fiber is preferable.
  • the laser generating apparatus may generate mode locked pulses of three different wavelengths with a repetition rate of 6.24 MHz near the 1555 nm center wavelength.
  • the laser generating device may be a length of 31m.
  • Laser generating apparatus can generate a laser using a commercially available high density wavelength multiplexer pair that can easily implement a larger number of step wavelengths, the laser is a short generator length and relatively narrow Because of its spectral linewidth, it can be used in many applications, including tomography equipment.
  • Laser generating apparatus can greatly improve the operating characteristics of the laser.
  • the laser generating apparatus can simply implement a laser having a step change at a high speed in a short resonator using a commercial optical communication device.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Optics & Photonics (AREA)
  • Lasers (AREA)

Abstract

La présente invention concerne un appareil de génération de laser à fibre optique et, en particulier, un appareil de génération de laser à fibre optique à mode verrouillé actif pour générer une lumière laser ayant une longueur d'onde modifiée de manière discontinue.
PCT/KR2018/002950 2017-03-13 2018-03-13 Appareil de génération de laser à fibre optique WO2018169289A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100587519B1 (ko) * 2003-04-15 2006-06-08 한국과학기술연구원 편광유지 레이저 공진기를 이용한 펄스진폭 균일화방법
JP2012038866A (ja) * 2010-08-05 2012-02-23 High Energy Accelerator Research Organization レーザー発振装置
KR20120044391A (ko) * 2010-08-04 2012-05-08 부산대학교 산학협력단 능동형 모드 잠김 레이저를 이용한 광 결맞음 단층 영상기기
KR101312407B1 (ko) * 2013-01-30 2013-09-27 주식회사 지에이치허브 레이저 광원 생성 장치 및 그 방법
KR101382443B1 (ko) * 2012-02-21 2014-04-08 서울시립대학교 산학협력단 Ｑ-스위칭 및 모드 락킹을 이용한 펄스 레이저 생성 장치

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100587519B1 (ko) * 2003-04-15 2006-06-08 한국과학기술연구원 편광유지 레이저 공진기를 이용한 펄스진폭 균일화방법
KR20120044391A (ko) * 2010-08-04 2012-05-08 부산대학교 산학협력단 능동형 모드 잠김 레이저를 이용한 광 결맞음 단층 영상기기
JP2012038866A (ja) * 2010-08-05 2012-02-23 High Energy Accelerator Research Organization レーザー発振装置
KR101382443B1 (ko) * 2012-02-21 2014-04-08 서울시립대학교 산학협력단 Ｑ-스위칭 및 모드 락킹을 이용한 펄스 레이저 생성 장치
KR101312407B1 (ko) * 2013-01-30 2013-09-27 주식회사 지에이치허브 레이저 광원 생성 장치 및 그 방법

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