JP3573334B2 - Light generation method and light source - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light generation method and a light source that can be used for WDM communication.
[0002]
[Prior art]
In recent years, in order to increase the transmission capacity of optical fiber communication, optical wavelength division multiplexing communication in which laser beams having different wavelengths are multiplexed and transmitted on one optical fiber has been studied.
Conventionally, a plurality of distributed feedback (DFB) semiconductor lasers have been used as light sources for optical wavelength division multiplexing communication by controlling the oscillation wavelength by controlling the element temperature. However, if the number of multiplexed channels increases, the number of lasers must be increased by the same amount, which is considered to be a costly system.
[0003]
Therefore, in recent years, a multi-wavelength light source that uses laser light including many oscillation modes as a light source, cuts out the mode with an optical filter, and uses it as a channel has been studied. A pulsed light source using direct modulation or a gain switch method can generate many modes. Among them, a mode-locked laser can relatively easily generate a pulse of the Fourier transform limit, that is, Since it is possible to have a wide spectrum band, it is widely studied.
[0004]
A mode-locked laser is a laser that generates pulsed light by synchronizing the phase of a mode generated in a laser resonator, and its spectrum includes many modes at regular intervals on the frequency axis. By cutting out this mode with an optical filter or the like, it can be used as a single mode continuous light source.
[0005]
For example reference "Multiwavelength Light Source with Precise Frequency Spacing Using a Mode-Locked Semiconductor Laser and an Arrayed Waveguide Grating Filter (Hiroaki Sanjoh et al, IEEE Photonics Technology Letters, Vol.9, No.6, pp.818-820, 1997 In (2)), multi-wavelength light at 50 GHz intervals is generated using a mode-locked semiconductor laser.
[0006]
FIG. 17 shows an example shown in the above-mentioned reference. When a 25 GHz sine wave signal is input to the electro-absorption modulator 01a of the mode-locked semiconductor laser 01 and a DC current is input to the gain region 01b, the harmonic mode locking is performed. As a result, multi-wavelength light is generated at intervals of 50 GHz, and the multi-wavelength light is cut out by an arrayed waveguide diffraction grating filter (optical filter) 02 to obtain continuous light of 11 channels within an optical output difference of 17 dB.
[0007]
[Problems to be solved by the invention]
The number of channels obtained from the multi-wavelength light was limited to the amplification gain band of the original mode-locked semiconductor laser 01, and the optical output level of each channel was greatly different from the center of the amplification gain of the laser except for the center.
Further, since the frequency interval of the channel obtained from the multi-wavelength light depends on the mode interval of the mode-locked semiconductor laser 01, the frequency interval is fixed, which makes a flexible configuration of the optical network system difficult.
[0008]
In view of the above prior art, the present invention uses two pulse light generation circuits having the same repetition frequency of pulse light but different oscillation frequencies, and generates a multi-wavelength light having a wide band and the same frequency interval using a nonlinear optical effect. It is an object to provide a light generation method and a light source.
[0009]
It is another object of the present invention to provide multi-wavelength light having a variable frequency interval by changing the oscillation frequencies of two pulse light generation circuits.
[0010]
[Means for Solving the Problems]
The configuration of the present invention that solves the above-mentioned problem includes an oscillation frequency of a first pulse light generation circuit that outputs a first pulse light, and a second pulse light having the same repetition frequency as the repetition frequency of the first pulse light. The oscillation frequency difference, which is the difference between the oscillation frequencies of the second pulsed light generation circuit that outputs
The combined light of the first pulsed light and the second pulsed light is made incident on a nonlinear optical medium to obtain multi-wavelength light having a uniform optical frequency interval.
[0011]
Further, the configuration of the present invention provides a time delay to at least one of the first pulse light and the second pulse light so that the spires of the first pulse light and the second pulse light coincide on the time axis. Give or
Synchronize the first pulse light generation circuit and the second pulse light generation circuit so that the spires of the first pulse light and the second pulse light coincide on the time axis,
The arbitrary positive number is variable.
[0012]
Further, the configuration of the present invention includes a first pulse light generation circuit that outputs a first pulse light, and a second pulse that outputs a second pulse light having the same repetition frequency as the repetition frequency of the first pulse light. An oscillation frequency difference, which is a difference between the oscillation frequency of the first pulsed light generation circuit and the oscillation frequency of the second pulsed light generation circuit, makes the repetition frequency equal to or more than two. Is set to a value divided by a number,
Further, it is characterized by having a non-linear optical medium to which a combined light of the first pulse light and the second pulse light is inputted.
[0013]
Further, the configuration of the present invention includes a first pulse light generation circuit that outputs a first pulse light, and a second pulse that outputs a second pulse light having the same repetition frequency as the repetition frequency of the first pulse light. An oscillation frequency difference, which is a difference between the oscillation frequency of the first pulsed light generation circuit and the oscillation frequency of the second pulsed light generation circuit, makes the repetition frequency equal to or more than two. Is set to a value divided by a number,
Further, a nonlinear optical medium to which a combined light of the first pulse light and the second pulse light is input,
Before the multiplexing, an optical delay circuit for providing a time delay to at least one of the first pulse light and the second pulse light is provided.
[0014]
Further, the configuration of the present invention includes a first pulse light generation circuit that outputs a first pulse light, and a second pulse that outputs a second pulse light having the same repetition frequency as the repetition frequency of the first pulse light. An oscillation frequency difference, which is a difference between the oscillation frequency of the first pulsed light generation circuit and the oscillation frequency of the second pulsed light generation circuit, makes the repetition frequency equal to or more than two. Is set to a value divided by a number,
Further, a nonlinear optical medium to which a combined light of the first pulse light and the second pulse light is input,
It has a synchronization circuit that controls at least one of the first pulse light generation circuit and the second pulse light generation circuit so that the first pulse light and the second pulse light spire coincide with each other. .
[0015]
Further, the configuration of the present invention includes a first pulse light generation circuit that outputs a first pulse light, and a second pulse that outputs a second pulse light having the same repetition frequency as the repetition frequency of the first pulse light. An oscillation frequency difference, which is a difference between the oscillation frequency of the first pulsed light generation circuit and the oscillation frequency of the second pulsed light generation circuit, makes the repetition frequency equal to or more than two. Is set to a value divided by a number,
Further, a nonlinear optical medium to which a combined light of the first pulse light and the second pulse light is input,
An oscillation frequency control circuit for making the oscillation frequency of the first pulse light generation circuit and the oscillation frequency of the second pulse light generation circuit variable is provided.
[0016]
[Action]
According to the present invention, the mode interval of the original pulse laser is different from that of the original pulse laser by using two pulse light generating circuits (pulse lasers) that generate pulse light at the same repetition frequency and a nonlinear optical medium having a nonlinear optical effect. More spaced multi-wavelength light can be obtained regardless of the amplification gain of the laser.
[0017]
In addition, since one or both of the pulse lights generated from the two pulse lasers are time-delayed, the peaks of the pulse lights coincide with each other on the time axis, and the peak of the pulse light incident on the nonlinear medium is obtained. Since the power is increased, a larger nonlinear optical effect can be expected. As a result, a multi-wavelength light with a small difference in the optical output level of each channel with a broadened spectral envelope of output light can be obtained.
[0018]
In addition, since the two pulse lasers are synchronized, the spires of the pulsed light coincide with each other on the time axis, and the peak power of the pulsed light incident on the nonlinear medium increases, so a larger nonlinear optical effect is expected. As a result, the spectral envelope of the output light is broadened, and multi-wavelength light with a smaller difference in the optical output level of each channel is obtained.
[0019]
In addition, since the oscillation frequencies of the two pulse lasers are controlled, the mode interval generated can be made variable.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, various embodiments of the present invention will be described in detail with reference to the drawings.
[0021]
<First embodiment>
FIG. 1 shows a light source according to a first embodiment of the present invention. The first pulse laser 1 shown in FIG. 1 outputs a first pulse light having a constant repetition frequency, and the second pulse laser 2 also has a second pulse light having the same repetition frequency as the first pulse laser 1. Is output. At this time, the difference between the oscillation frequency of the pulse laser 1 and the oscillation frequency of the pulse laser 2 (oscillation frequency difference) is set to a value obtained by dividing (dividing) the repetition frequency of the pulsed light by any positive number of 2 or more. .
[0022]
The “oscillation frequency of the pulse laser” means an optical frequency at which the laser self-oscillates. This oscillation frequency can be considered as the frequency of a carrier wave for the pulsed light.
[0023]
Setting the oscillation frequency difference between the two lasers to a value obtained by dividing (dividing) the repetition frequency of the pulsed light by an arbitrary positive number of 2 or more is the same in other embodiments described later.
[0024]
The pulse light (laser light) output from the pulse lasers 1 and 2 is multiplexed by the optical multiplexer 3, and the multiplexed pulse light is amplified by the optical amplifier 4. The multiplexed and amplified pulse light is input to the nonlinear optical medium 5.
[0025]
The nonlinear optical medium 5 outputs multi-wavelength light having a uniform optical frequency interval different from the mode interval of the pulse lasers 1 and 2 due to the nonlinear optical effect.
[0026]
More specifically, the pulsed lasers 1 and 2 in FIG. 1 are lasers that can generate pulsed light by directly modulating when exciting a gain, or continuous light is converted by an external converter. A pulsed laser, a mode-locked laser, a gain switch laser, a Q switch laser, or the like is used.
[0027]
The optical spectra of the pulse lasers 1 and 2 are modes with frequency intervals δf = 1 / T [Hertz] (where T [sec] is the repetition period of the pulse light) and harmonic components around the central emission line spectrum. It has a mode of n × δf [Hz] intervals, which is a positive multiple of δf (n is a positive number). Here, the frequency in the center bright line spectrum is the oscillation frequency of the pulse laser.
[0028]
The non-linear optical medium 5 in FIG. 1 is a medium whose refractive index is strongly controlled by the second- or higher-order electric susceptibility, such as an optical fiber, an optical semiconductor amplifier, and an organic dye. In general, when a light wave of high intensity is incident on a nonlinear optical medium, various nonlinear optical effects such as self-phase modulation, cross-phase modulation, and four-wave mixing are generated.
[0029]
The nonlinear optical medium 5 may generate a third-order nonlinear effect.
[0030]
When pulse light output from two pulse lasers having a mode of a frequency interval δf [Hertz] and oscillating frequencies different from δf [Hertz] are superimposed using an optical multiplexer 3 such as an optical coupler, the spectrum becomes The frequency interval is different from that of the original pulse laser. This is shown in FIG. The spectrum of the pulse laser 1 is shown by a solid line, and the spectrum of the pulse laser 2 is shown by a broken line. Here, δν [Hertz] is called an oscillation frequency difference.
[0031]
When the superposed light of the two pulse lasers 1 and 2 as described above is amplified by an optical amplifier 4 such as an erbium-doped optical fiber amplifier and made incident on a nonlinear optical medium 5, nonlinear optical such as self-phase modulation or cross-phase modulation is obtained. The effect broadens the envelope of the spectrum, and generates a large number of lights having different frequencies due to a nonlinear optical effect such as four-wave mixing.
[0032]
In the example of FIG. 2, the optical frequency of the pump light is ν ₁ [Hertz], the optical frequency of the probe light is ν ₂ [Hertz] (However, ν ₂ > Ν ₁ ), Ν by four-wave mixing ₁ − (Ν ₂ −ν ₁ ) [Hertz] and ν ₂ + (Ν ₂ −ν ₁ ) [Hertz] signal light is generated. Further newly generated ν ₁ − (Ν ₂ −ν ₁ ) [Hertz] and ν ₂ + (Ν ₂ −ν ₁ ) [Hertz] light becomes pump light or probe light, and generates more modes.
[0033]
Here, the oscillation frequencies of the two pulse lasers are controlled so that the oscillation frequency difference δν [Hertz] of the two pulse lasers 1 and 2 is equal to a value obtained by dividing the mode interval δf [Hertz] by a positive number of 2 or more. Then, the mode of the original pulse laser and the signal light generated by the four-wave mixing are all at intervals of δν [hertz], and multi-wavelength light including many equally-spaced modes can be generated.
[0034]
For example, in the example of FIG. 2, when the oscillation frequency difference δν between the two pulse lasers 1 and 2 is set to １ ／ of the mode interval δf,
ν ₂ = V ₁ + Δf / 4
It becomes. ν ₁ And ν ₂ If the light of the frequency is pump light and probe light, the frequency of the newly generated signal light is
ν ₁ −δf / 4 and ν ₁ + Δf / 2
It becomes. Also, ν ₁ −δf and ν ₂ If −δf is the pump light and the probe light, the frequency of the newly generated signal light is
ν ₁ −5δf / 4 and ν ₁ -Δf / 2
It becomes.
[0035]
Hereinafter, when the same is considered for all the modes of the two pulse lasers 1 and 2, the pump light, the probe light, and the signal light are all arranged on the frequency axis at intervals of δf / 4, that is, at intervals of δν. Wavelength light is generated.
[0036]
In addition, since the envelope of the spectrum incident on the nonlinear optical medium 5 is expanded and output by the self-phase modulation or the cross-phase modulation, the number of channels of the obtained multi-wavelength light is larger than that of the input, and Also reduces the output difference.
[0037]
<Second embodiment>
FIG. 3 shows a light source according to a second embodiment of the present invention, and FIG. 4 is a diagram for explaining the operation principle.
[0038]
In the second embodiment, as shown in FIG. 3, an optical delay circuit 6 for temporally delaying the second pulse light before multiplexing output from the second pulse laser 2 is provided. . Therefore, the first pulsed light output from the first pulsed laser 1 and the second pulsed light output from the second pulsed laser 2 and temporally delayed by the optical delay circuit 6 are compared with each other. , And are multiplexed by the optical multiplexer 3. The configuration of other parts is the same as that of the first embodiment shown in FIG.
[0039]
The time delay in the optical delay circuit 6 changes the refractive index of the medium through which the pulse light generated from the pulse laser 2 propagates by temperature, electro-optic effect, or the like, or physically changes the length of the medium. It can be obtained by:
[0040]
Generally, pulsed light emitted from two independent pulsed lasers 1 and 2 are not synchronized because they have no temporal correlation. Therefore, by giving a time delay to the pulse light emitted from one of the pulse lasers 2 and adjusting the amount of delay by the optical delay circuit 6, as shown in FIG. Can be matched.
[0041]
As a result, the peak power of the pulse light incident on the nonlinear optical medium 5 is increased, so that a larger nonlinear optical effect can be expected. As a result, the spectral envelope of the output light is broadened, and the difference between the optical output levels of the respective channels is increased. And multi-wavelength light with a small amount of light.
[0042]
In order to change the refractive index of the propagation medium of the optical delay circuit 6, if the medium to be propagated is in the atmosphere, a dielectric such as glass is inserted into the optical path to reduce the refractive index of the entire propagation path. Change.
To physically change the length of the medium, for example, if the propagating medium is an optical fiber, the length is changed by pulling the optical fiber with a piezoelectric element or the like.
Various specific embodiments of the optical delay circuit 6 will be described in detail later in seventh (FIG. 9) to tenth (FIG. 12) embodiments.
[0043]
<Third embodiment>
FIG. 5 shows a light source according to a third embodiment of the present invention. As shown in FIG. 5, in the present embodiment, a synchronization circuit 7 having a function of synchronizing pulse light output from the second pulse laser 2 with pulse light output from the first pulse laser 1 is provided. ing. The configuration of other parts is the same as that of the first embodiment shown in FIG.
[0044]
The synchronizing circuit 7 converts an optical signal into an electric signal using a detector, synchronizes the pulsed light with the electric circuit, and supplies one of the pulse lasers 1 and 2 or both pulsed lasers. It is a means for feeding back, or a means for performing signal processing on an optical signal as it is, and negatively feeding back to one pulse laser or both pulse lasers.
[0045]
In the embodiment shown in FIG. 5, the timing of the pulse light output from the pulse laser 2 is controlled by feeding back to the second pulse laser 2 to synchronize the pulse light output from both pulse lasers 1 and 2. I take it.
[0046]
A part of the pulse light oscillated from the two independent pulse lasers 1 and 2 is both branched, and the timing of the pulse light is synchronized by the synchronizing circuit 7, so that the spires of the pulse light coincide on the time axis. Can be. As a result, the peak power of the pulse light incident on the nonlinear optical medium 5 is increased, so that a larger nonlinear optical effect can be expected. As a result, the spectral envelope of the output light is broadened, and the difference between the optical output levels of the respective channels is increased. And multi-wavelength light with a small amount of light.
[0047]
<Fourth embodiment>
FIG. 6 shows a light source according to a fourth embodiment of the present invention. As shown in FIG. 6, in the present embodiment, the first pulse laser 1 is provided with a detector 8a for detecting the oscillation frequency of the pulsed light output from the pulse laser 1, and a signal detected by the detector 8a. An oscillation frequency control circuit 9a for controlling the oscillation frequency of the first pulse laser 1 is provided on the basis thereof. Further, the second pulse laser 2 has a detector 8b for detecting the oscillation frequency of the pulsed light output from the pulse laser 2, and the oscillation frequency of the second pulse laser 2 based on the signal detected by the detector 8b. Is provided with an oscillation frequency control circuit 9b for controlling the oscillation frequency. The configuration of other parts is the same as that of the first embodiment shown in FIG.
[0048]
By controlling the oscillation frequencies of the first and second pulse lasers 1 and 2 in this way, multi-wavelength light with variable frequency intervals can be output. In other words, under the condition that “the oscillation frequency difference between the pulse lasers 1 and 2 is set to a positive value obtained by dividing (division) by an integer of 2 or more of the pulse repetition frequency”, the value of the “positive number” is changed. Can be done.
[0049]
The method of controlling the oscillation frequency of the pulse lasers 1 and 2 includes a method of changing the refractive index of a gain medium in the laser or a method of controlling the oscillation frequency by changing the resonator length of the laser resonator. .
[0050]
Generally, the refractive index of the gain medium of a pulse laser changes by changing the temperature of the gain medium, or in the case of a semiconductor laser, by changing the amount of injection current for excitation.
The resonator length of a laser resonator changes in a solid-state laser, a gas laser, or the like by mechanically moving a mirror that forms the resonator. Also, by changing the refractive index in the resonator, the effective resonator length can be changed.
[0051]
By changing the oscillation frequency difference δν [Hertz] of the two pulse lasers 1 and 2 by the above method so as to be equal to a value obtained by dividing the mode interval δf [Hertz] by a positive number of 2 or more, Multi-wavelength light that oscillates at equal intervals and includes modes with variable frequency intervals can be generated.
[0052]
<Fifth embodiment>
FIG. 7 shows a light source according to a fifth embodiment of the present invention. As shown in FIG. 7, in the present embodiment, mode-locked lasers 11 and 12 are employed as the first and second pulse lasers. The configuration of other parts is the same as that of the first embodiment shown in FIG.
[0053]
The mode-locked lasers 11 and 12 are lasers capable of generating steep pulsed light by synchronizing the phases of several modes generated in the laser resonator. To lock the phase of the mode, the forced mode-locking method that modulates the laser medium, the passive mode-locking method that incorporates a saturable absorber whose transmittance changes according to the light intensity into the laser resonator, or both effects can be used. There is a hybrid mode synchronization method used.
[0054]
The mode-locked lasers 11 and 12 can generate pulse light having a Fourier transform limit relatively easily, and can be used as a light source having a wider spectrum width, so that multi-channel multi-wavelength light can be generated. .
[0055]
<Sixth Embodiment>
FIG. 8 shows a light source according to a sixth embodiment of the present invention. As shown in FIG. 8, in this embodiment, gain switch lasers 13 and 14 are employed as the first and second pulse lasers. The configuration of other parts is the same as that of the first embodiment shown in FIG.
[0056]
The gain switch lasers 13 and 14 are lasers capable of generating steep pulsed light when the laser medium is steeply excited in a delta function.
[0057]
Since the gain switch lasers 13 and 14 can generate pulse light having a Fourier transform limit relatively easily, they become light sources having a wider spectrum width, and thus can generate multi-channel multi-wavelength light. .
[0058]
<Seventh embodiment>
FIG. 9 shows an optical delay circuit 20 using coupling between optical fibers using a spatial collimated beam. This optical delay circuit 20 can be employed as the optical delay circuit 6 shown in FIG.
[0059]
An optical delay circuit 20 utilizing the coupling between optical fibers by a spatial collimated beam includes two optical fibers 21 and 22 for input and output, and a collimator lens for converting the output light from the input optical fiber 21 into parallel light. 23, a collimating lens 24 for converging the parallel light to the output optical fiber 22, and having a drive system capable of moving one or both of the incident or output collimating system in the traveling direction of the parallel light, This is a delay device that changes the optical path length by moving the drive system. In the example of FIG. 9, the collimator lens 23 is fixed and the collimator lens 24 is movable.
[0060]
The optical delay circuit 20 is employed as the optical delay circuit 6 shown in FIG. 3 to adjust the amount of delay so that the spires of both pulse lights output from the pulse lasers 1 and 2 are made to coincide with each other in time. Can be. As a result, the peak power of the pulse light incident on the nonlinear optical medium 5 is increased, so that a larger nonlinear optical effect can be expected. As a result, the spectral envelope of the output light is broadened, and the difference between the optical output levels of the respective channels is increased. And multi-wavelength light with a small amount of light.
Further, by using the optical delay circuit 20, a large delay amount can be obtained with a simple device, and application to a pulse laser having a long repetition period is also possible.
[0061]
<Eighth Embodiment>
FIG. 10 shows an optical delay circuit 30 by controlling the refractive index of an optical waveguide. This optical delay circuit 30 can be employed as the optical delay circuit 6 shown in FIG.
[0062]
The optical delay circuit 30 based on the control of the refractive index of the optical waveguide is a device including an optical waveguide 34 having an input port 31, an output port 32, and a refractive index control unit 33, and provides a refractive index control signal to the refractive index control unit 33. This changes the refractive index and causes a delay.
[0063]
The optical delay circuit 20 is employed as the optical delay circuit 6 shown in FIG. 3 to adjust the amount of delay so that the spires of both pulse lights output from the pulse lasers 1 and 2 are made to coincide with each other in time. Can be. As a result, the peak power of the pulse light incident on the nonlinear optical medium 5 is increased, so that a larger nonlinear optical effect can be expected. As a result, the spectral envelope of the output light is broadened, and the difference between the optical output levels of the respective channels is increased. And multi-wavelength light with a small amount of light.
In addition, by using the optical delay circuit 30, the delay amount can be precisely controlled.
[0064]
<Ninth embodiment>
FIG. 11 shows an optical delay circuit 40 based on refractive index control using the thermo-optic effect. This optical delay circuit 40 can be employed as the optical delay circuit 6 shown in FIG.
[0065]
The optical delay circuit 40 based on the refractive index control using the thermo-optic effect is a device including an optical waveguide 43 having an input port 41 and an output port 42, and a heater 44 for changing the temperature of the optical waveguide 43. By applying a current, the temperature of the optical waveguide 43 changes, and as a result, the refractive index changes and a delay occurs.
[0066]
The optical delay circuit 40 is adopted as the optical delay circuit 6 shown in FIG. 3, and by adjusting the amount of delay, the spires of both pulsed lights output from the pulse lasers 1 and 2 are made to coincide with each other in time. Can be. As a result, the peak power of the pulse light incident on the nonlinear optical medium 5 is increased, so that a larger nonlinear optical effect can be expected. As a result, the spectral envelope of the output light is broadened, and the difference between the optical output levels of the respective channels is increased. And multi-wavelength light with a small amount of light.
Further, by using the optical delay circuit 40, the delay amount can be precisely controlled.
[0067]
<Tenth embodiment>
FIG. 12 shows an optical delay circuit 50 by refractive index control using the electro-optic effect. This optical delay circuit 50 can be employed as the optical delay circuit 6 shown in FIG.
[0068]
The optical delay circuit 50 based on the refractive index control using the electro-optic effect is a device including an optical waveguide 53 having an input port 51 and an output port 52, and a set of electrodes 54 for flowing a control current through the optical waveguide 53. In addition, when a current flows through the optical waveguide 53, the carrier density changes, and as a result, the refractive index changes, and delay occurs.
[0069]
The optical delay circuit 50 is adopted as the optical delay circuit 6 shown in FIG. 3, and by adjusting the amount of delay, the spires of both pulsed lights output from the pulse lasers 1 and 2 are made to coincide with each other in time. Can be. As a result, the peak power of the pulse light incident on the nonlinear optical medium 5 is increased, so that a larger nonlinear optical effect can be expected. As a result, the spectral envelope of the output light is broadened, and the difference between the optical output levels of the respective channels is increased. And multi-wavelength light with a small amount of light.
Further, by using the optical delay circuit 50, the delay amount can be precisely controlled.
[0070]
<Eleventh embodiment>
FIG. 13 shows a light source according to an eleventh embodiment of the present invention. In the present embodiment, the pulse light output from the second pulse laser 102 is synchronized with the pulse light output from the first pulse laser 101 by forming an optical phase locked loop.
[0071]
The configuration excluding the optical phase locked loop will be described first. The first pulse laser 101 outputs pulse light synchronized with the oscillation signal output from the oscillator 103. The second pulse laser 102 outputs a pulse light synchronized with the oscillation signal output from the oscillator 104. The two pulse lights are synchronized by the operation of an optical phase locked loop described later.
[0072]
The pulse light output from the pulse laser 101 and branched by the optical demultiplexer 105 and the pulse light output from the pulse laser 102 and branched by the optical demultiplexer 106 are combined by the optical multiplexer 107. Is done. The multiplexed pulse light is amplified by the optical amplifier 108, and the amplified pulse light is input to the nonlinear optical medium 109.
[0073]
The nonlinear optical medium 109 outputs multi-wavelength light having a different optical frequency interval and a uniform optical frequency interval due to the nonlinear effect of the nonlinear optical medium 109.
[0074]
Describing the optical phase locked loop, the oscillator 103 fixes the phase of the output oscillation signal, and the oscillator 104 can change the phase of the output oscillation signal. The pulse light output from the pulse laser 101 and transmitted through the optical demultiplexer 105 and demultiplexed is input to the first light receiving element 110. The first light receiving element 110 outputs a pulse signal obtained by removing carriers from the input pulse light. The pulse light output from the pulse laser 102 and transmitted through the optical demultiplexer 106 and demultiplexed is input to the second light receiving element 111. The second light receiving element 111 outputs a pulse signal obtained by removing carriers from the input pulse light.
[0075]
The phase comparator 112 compares the phase of the pulse signal output from the first light receiving element 110 with the phase of the pulse signal output from the second light receiving element 111, and outputs a phase difference signal indicating the phase difference between the two. Is output.
[0076]
This phase difference signal is input to the oscillator 104 after passing through the loop filter 113. The oscillator 104 changes the phase of the oscillation signal sent to the pulse laser 102 according to the phase difference signal, and tries to follow the phase of the oscillator 103. Therefore, the phase of the oscillation signal output from the oscillator 104 is synchronized with the phase of the oscillation signal output from the oscillator 103, and the phase of the pulse light output from the pulse laser 102 is changed to the pulse output from the pulse laser 101. Synchronizes with the phase of light.
[0077]
In this configuration, the pulse light of the pulse laser 102 driven by the oscillator 104 with variable phase can be synchronized with the pulse light of the pulse laser 101 driven by the oscillator 103 with fixed phase. , 102 coincide with each other on the time axis. As a result, the peak power of the pulse light incident on the nonlinear optical medium 109 increases, so that a larger nonlinear optical effect can be expected. As a result, the spectral envelope of the output light broadens, and the difference between the optical output levels of the respective channels increases. And multi-wavelength light with a small amount of light.
[0078]
<Twelfth embodiment>
FIG. 14 shows a light source according to a twelfth embodiment of the present invention. In this embodiment, the pulse light output from the first pulse laser 101 and the pulse light output from the second pulse laser 102 are synchronized by forming an optical phase locked loop. The twelfth embodiment is a modification of the configuration of the optical phase locked loop in the eleventh embodiment shown in FIG. For this reason, the parts performing the same functions as in the eleventh embodiment are denoted by the same reference numerals, and redundant description is omitted, and different parts will be described.
[0079]
The first pulse laser 101 outputs pulse light synchronized with the first phase-variable oscillator 201, and the second pulse laser 102 outputs pulse light synchronized with the second phase-variable oscillator 104.
[0080]
The optical phase locked loop will be described. The pulse light output from the pulse laser 101 and transmitted through the optical splitter 105 and split is input to the first light receiving element 110. The first light receiving element 110 outputs a pulse signal obtained by removing carriers from the input pulse light. The pulse light output from the pulse laser 102 and transmitted through the optical demultiplexer 106 and demultiplexed is input to the second light receiving element 111. The second light receiving element 111 outputs a pulse signal obtained by removing carriers from the input pulse light.
[0081]
The first phase comparator 202 compares the phase of the pulse signal output from the first light receiving element 110 with the phase of the reference signal output from the reference oscillator 203, and indicates a first phase difference indicating the phase difference between the two. Outputs the phase difference signal.
[0082]
The first phase difference signal is input to the oscillator 201 after passing through the first loop filter 204. The oscillator 201 changes the phase of the oscillation signal sent to the pulse laser 101 according to the phase difference signal. Due to this change in the phase, the phase of the pulse light output from the first pulse laser 101 becomes equal to the phase of the reference signal of the oscillator 203 serving as a reference.
[0083]
The second phase comparator 205 compares the phase of the pulse signal output from the second light receiving element 111 with the phase of the reference signal output from the reference oscillator 203, and indicates a second phase difference between the two. Outputs the phase difference signal.
[0084]
The second phase difference signal is input to the oscillator 104 after passing through the second loop filter 206. The oscillator 104 changes the phase of the oscillation signal sent to the pulse laser 102 according to the phase difference signal. Due to this phase change, the phase of the pulse light output from the second pulse laser 102 becomes equal to the phase of the reference signal of the oscillator 203 serving as a reference.
[0085]
Eventually, the phases of the pulse lights output from the pulse lasers 101 and 102 are synchronized with the phase of the reference signal of the oscillator 203, and the phases of both pulse lights match. Therefore, the spires of the pulse lights generated from the two pulse lasers 101 and 102 coincide on the time axis. As a result, the peak power of the pulse light incident on the nonlinear optical medium 109 increases, so that a larger nonlinear optical effect can be expected. As a result, the spectral envelope of the output light broadens, and the difference between the optical output levels of the respective channels increases. And multi-wavelength light with a small amount of light.
[0086]
<Thirteenth embodiment>
FIG. 15 shows a light source according to a thirteenth embodiment of the present invention. In the present embodiment, the first active mode-locked laser 301 and the second active mode-locked laser 302 have the same repetition frequency as the frequency of the oscillation signal generated by the same oscillator 306 or the same repetition frequency as its harmonic frequency. It is configured to generate pulsed light.
[0087]
The oscillator 306 is an electrical device necessary for generating pulse light in direct modulation of the active mode-locked lasers 301 and 302, the gain switch laser, or the semiconductor laser.
[0088]
As described above, since the two active mode-locked lasers 301 and 302 use the same oscillator 306, the spires of the pulse light generated from the two active mode-locked lasers 301 and 302 match on the time axis. As a result, since the peak power of the pulse light incident on the nonlinear optical medium 305 after being multiplexed by the optical multiplexer 303 and amplified by the optical amplifier 304 is increased, a larger nonlinear optical effect can be expected. As a result, a multi-wavelength light is obtained in which the spectrum envelope of the output light is widened and the difference in the optical output level of each channel is small.
[0089]
Note that a DC current is supplied from the DC current source 307 to the first active mode-locked laser 301, and a DC current is supplied from the DC current source 308 to the second active mode-locked laser 302.
The direct current is supplied in this way to supply a bias current to the laser. Although not shown, a DC current is supplied to the laser in order to apply a bias current to the laser.
[0090]
<Fourteenth embodiment>
FIG. 16 shows a light source according to a fourteenth embodiment of the present invention. As shown in FIG. 16, in the fourteenth embodiment, the oscillation frequency of the pulse lasers 401 and 402 is controlled by controlling the element temperature, and the optical frequency of the pulse light output from the pulse lasers 401 and 402 is controlled. . Specifically, the temperature elements 403 and 404 such as Peltier elements are controlled to control the oscillation frequency of the pulse lasers 401 and 402, and the pulse light output is set to a desired frequency.
[0091]
Particularly in the case of a semiconductor laser, when the temperature of the laser element changes, the refractive index of the laser medium changes, and the oscillation frequency changes. For this reason, the optical frequency can be controlled, thereby realizing multi-wavelength light including a mode in which the mode interval or the center frequency is variable.
[0092]
Note that the pulse lights output from the pulse lasers 401 and 402 are multiplexed by the optical multiplexer 405, amplified by the optical amplifier 406, and input to the nonlinear optical medium 407.
Note that a part of the light from the pulse lasers 401 and 402 may be taken out before the multiplexing to detect the oscillation frequency and form a negative feedback system for controlling the temperature.
[0093]
【The invention's effect】
As described above, according to the light generation method and the light source of the present invention, multi-wavelength light at equal intervals can be obtained with a larger number of channels regardless of the gain band of the laser.
[0094]
In addition, by providing a configuration for providing a time delay to one or both of the pulse lights generated from the two pulse light generation circuits (pulse lasers), the difference in the optical output level of each channel is reduced. Wavelength light is obtained.
[0095]
Further, by providing a mechanism for synchronizing the two pulse light generation circuits (pulse lasers), multi-wavelength light having a smaller difference in light output level of each channel can be obtained.
[0096]
In addition, by providing a mechanism for controlling the oscillation frequency of the two pulse light generation circuits (pulse lasers), the channel interval can be made variable.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a light source according to a first embodiment of the present invention.
FIG. 2 is a characteristic diagram showing a spectrum state of a pulse laser.
FIG. 3 is a configuration diagram showing a light source according to a second embodiment of the present invention.
FIG. 4 is an explanatory diagram showing the operation principle of the second embodiment of the present invention.
FIG. 5 is a configuration diagram showing a light source according to a third embodiment of the present invention.
FIG. 6 is a configuration diagram showing a light source according to a fourth embodiment of the present invention.
FIG. 7 is a configuration diagram showing a light source according to a fifth embodiment of the present invention.
FIG. 8 is a configuration diagram showing a light source according to a sixth embodiment of the present invention.
FIG. 9 is a configuration diagram showing an optical delay circuit according to a seventh embodiment of the present invention.
FIG. 10 is a configuration diagram showing an optical delay circuit according to an eighth embodiment of the present invention.
FIG. 11 is a configuration diagram showing an optical delay circuit according to a ninth embodiment of the present invention.
FIG. 12 is a configuration diagram showing an optical delay circuit according to a tenth embodiment of the present invention.
FIG. 13 is a configuration diagram showing a light source according to an eleventh embodiment of the present invention.
FIG. 14 is a configuration diagram showing a light source according to a twelfth embodiment of the present invention.
FIG. 15 is a configuration diagram showing a light source according to a thirteenth embodiment of the present invention.
FIG. 16 is a configuration diagram showing a light source according to a fourteenth embodiment of the present invention.
FIG. 17 is a configuration diagram showing a conventional light source.
[Explanation of symbols]
1,2 pulse laser
3 Optical multiplexer
4 Optical amplifier
5 Nonlinear optical medium
6. Optical delay circuit
7 Synchronous circuit
8a, 8b detector
9a, 9b oscillation frequency control circuit
11,12 mode-locked laser
13,14 Gain-switched laser
20, 30, 40, 50 optical delay circuit
101,102 pulse laser
103,104 oscillator
105,106 Optical demultiplexer
107 Optical multiplexer
108 Optical Amplifier
109 Nonlinear Optical Medium
110,111 light receiving element
112 phase comparator
113 Loop filter
201, 203 oscillator
202,205 Phase comparator
204,206 Loop filter
301, 302 Active mode laser
303 optical multiplexer
304 optical amplifier
305 Nonlinear optical medium
306 oscillator
307,308 DC current source
401, 402 pulse laser
403,404 Temperature element
405 optical multiplexer
406 optical amplifier
407 Nonlinear optical medium

Claims (8)

The oscillation frequency of the first pulsed light generation circuit that outputs the first pulsed light, and the second pulsed light generation circuit that outputs the second pulsed light having the same repetition frequency as the repetition frequency of the first pulsed light An oscillation frequency difference, which is a difference between oscillation frequencies, is set to a value obtained by dividing the repetition frequency by an arbitrary positive number of 2 or more,
A light generation method comprising: combining a first pulsed light and a second pulsed light into a nonlinear optical medium to obtain multi-wavelength light having a uniform optical frequency interval. The light generation method according to claim 1,
Light that provides a temporal delay to at least one of the first pulsed light and the second pulsed light so that the spires of the first pulsed light and the second pulsed light coincide on the time axis. How it occurs. The light generation method according to claim 1,
A light generating method for synchronizing the first pulsed light generating circuit and the second pulsed light generating circuit so that the spires of the first pulsed light and the second pulsed light coincide on the time axis. . 2. The light generation method according to claim 1, wherein said arbitrary positive number is variable. A first pulsed light generation circuit that outputs the first pulsed light, and a second pulsed light generation circuit that outputs a second pulsed light having the same repetition frequency as the repetition frequency of the first pulsed light In addition, the oscillation frequency difference, which is the difference between the oscillation frequency of the first pulse light generation circuit and the oscillation frequency of the second pulse light generation circuit, is set to a value obtained by dividing the repetition frequency by any positive number of 2 or more. Has been
Further, the light source has a nonlinear optical medium to which a combined light of the first pulse light and the second pulse light is input. A first pulsed light generation circuit that outputs the first pulsed light, and a second pulsed light generation circuit that outputs a second pulsed light having the same repetition frequency as the repetition frequency of the first pulsed light In addition, the oscillation frequency difference, which is the difference between the oscillation frequency of the first pulse light generation circuit and the oscillation frequency of the second pulse light generation circuit, is set to a value obtained by dividing the repetition frequency by any positive number of 2 or more. Has been
Further, a nonlinear optical medium to which a combined light of the first pulse light and the second pulse light is input,
A light source comprising: an optical delay circuit that provides a time delay to at least one of the first pulse light and the second pulse light before multiplexing. A first pulsed light generation circuit that outputs the first pulsed light, and a second pulsed light generation circuit that outputs a second pulsed light having the same repetition frequency as the repetition frequency of the first pulsed light In addition, the oscillation frequency difference, which is the difference between the oscillation frequency of the first pulse light generation circuit and the oscillation frequency of the second pulse light generation circuit, is set to a value obtained by dividing the repetition frequency by any positive number of 2 or more. Has been
Further, a nonlinear optical medium to which a combined light of the first pulse light and the second pulse light is input,
It has a synchronization circuit that controls at least one of the first pulse light generation circuit and the second pulse light generation circuit so that the first pulse light and the second pulse light spire coincide with each other. light source. A first pulsed light generation circuit that outputs the first pulsed light, and a second pulsed light generation circuit that outputs a second pulsed light having the same repetition frequency as the repetition frequency of the first pulsed light In addition, the oscillation frequency difference, which is the difference between the oscillation frequency of the first pulse light generation circuit and the oscillation frequency of the second pulse light generation circuit, is set to a value obtained by dividing the repetition frequency by any positive number of 2 or more. Has been
Further, a nonlinear optical medium to which a combined light of the first pulse light and the second pulse light is input,
A light source comprising: an oscillation frequency control circuit that varies an oscillation frequency of a first pulse light generation circuit and an oscillation frequency of a second pulse light generation circuit.

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