JP2004037949A - Multi-wavelength light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-wavelength light source which can output broad band light with flat intensity distribution of light and the production cost and the running cost of which can be reduced. <P>SOLUTION: The light source is equipped with an input light source 1, a broad band waveguide 2 connected to the input light source 1, a nonreciprocal circuit 3 laid in the broad band waveguide 2, and a light exiting part 4 at the end of the broad band waveguide 2. The broad band waveguide 2 is provided with a structure comprising optical couplers 5a, 5b to input the excitation light and excitation light sources 6a, 6b connected to the optical couplers 5a, 5b, respectively, to supply the excitation light. The broad band waveguide 2 shows normal dispersion and flat dispersion characteristics and has a specified amplification gain by addition of erbium. Light pulses having a parabolic profile are transmitted through the broad band waveguide 2 by the effects of self phase modulation, wavelength dispersion, and optical amplification to output broad band light with flat intensity distribution. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light source used for optical communication and the like, and more particularly, to a multi-wavelength light source capable of obtaining broadband light having flat intensity over a predetermined wavelength range.
[0002]
[Prior art]
2. Description of the Related Art In the field of optical communication, a WDM (Wavelength / Division / Multiplexing) system for transmitting a plurality of signal lights having different wavelengths through the same optical fiber has been proposed in the field of optical communication, and some of the systems have been put to practical use. I have. In order to expand the communication capacity by the WDM method or the like, a signal light source that generates a plurality of signal lights over a predetermined wavelength range is required. Research is being conducted on multi-wavelength light sources that can be used.
[0003]
For example, as an example of a multi-wavelength light source that has been studied in the past, a light source using a dispersion reducing optical fiber is known. This has an anomalous dispersion characteristic at the input end, as shown in the graph of FIG. 18, has an optical fiber whose dispersion value tends to decrease as the fiber length increases, and has a soliton-like pulse waveform as input light. It has a structure using light. Specifically, broadband light is realized by a mechanism described below.
[0004]
Since the optical soliton input to the optical fiber satisfies the specified soliton conditions, adiabatic compression of the soliton occurs in the region where the dispersion is anomalous in the optical fiber, and the pulse width is reduced while maintaining a constant pulse power. Is done. The optical soliton whose pulse width has been compressed has a higher light intensity at the peak, and the spectral width gradually increases in the optical fiber mainly by self-phase modulation (Self-Phase Modulation: $ SPM). The spectral width is further expanded mainly by four-wave mixing in the vicinity of the fiber length where the dispersion value becomes 0, and broadband light is obtained (Optical Communication Technology Handbook (Optronics Co., Ltd.)) First Edition P125 to P128 reference).
[0005]
Adiabatic compression of the soliton generated in the optical fiber increases the light intensity of the input light, causing a remarkable nonlinear optical effect. Therefore, the expansion of the spectrum width due to self-phase modulation and four-wave mixing increases, and broadband light Can be obtained. A technique using such a dispersion-reduced optical fiber is disclosed in Japanese Patent Application Laid-Open No. H11-160744.
[0006]
[Problems to be solved by the invention]
However, the multi-wavelength light source using the dispersion-reduced optical fiber has various problems. Specifically, in order to adopt a method of obtaining broadband light using soliton adiabatic compression, it is necessary to precisely control the waveform of the input light and the dispersion characteristics of the dispersion-reducing optical fiber. The following problems arise.
[0007]
First, there is a problem that it is difficult to manufacture the input light source and the dispersion-reducing optical fiber. That is, in order to realize the soliton adiabatic compression, the input light must satisfy a predetermined soliton condition, and therefore, it is necessary to precisely control the pulse waveform of the input light. Similarly, for the dispersion-reduced optical fiber, the input light source and the dispersion-reduced optical fiber are not easily manufactured because the dispersion characteristics need to be precisely controlled in order to realize soliton adiabatic compression. For this reason, there is a problem that the manufacturing cost increases.
[0008]
There is also a problem that it is difficult to realize broadband light with a flat light intensity. When ideal soliton adiabatic compression can be realized, it is possible to realize broadband light with almost completely flat light intensity, but in practice, it is difficult to realize ideal soliton adiabatic compression. For this reason, in an actual device, it is known that a difference of about 20 dB occurs between the intensity of the center wavelength of the output broadband light and the intensity of other wavelengths. Therefore, with a conventional multi-wavelength light source using a dispersion-reduced optical fiber, the central wavelength component cannot be extracted as signal light.
[0009]
The present invention has been made in view of the above-described drawbacks of the related art, and is intended to output broadband light having a flat light intensity over a predetermined wavelength range, and to reduce manufacturing and operation costs. It is an object of the present invention to realize a multi-wavelength light source.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a multi-wavelength light source according to claim 1 includes a light source that outputs a first light and a non-linear optical effect that receives the first light and amplifies the intensity of the first light. And a broadband waveguide for expanding the spectrum width of the first light and outputting the second light having a flat intensity over a certain wavelength range.
[0011]
According to the first aspect of the present invention, since the spectrum width is expanded by generating the nonlinear optical effect while performing the optical amplification, the intensity of the transmitted light can be increased, and the nonlinear optical effect can be sufficiently generated. As a result, the spectrum width is sufficiently expanded, and broadband light having a flat intensity over a wide wavelength range can be obtained.
[0012]
Further, the multi-wavelength light source according to claim 2 is characterized in that, in the above invention, the broadband waveguide has a negative average dispersion value in the longitudinal direction in a wavelength range of the second light. I do.
[0013]
According to the second aspect of the present invention, since the broadband waveguide having an average dispersion characteristic of normal dispersion is provided, the pulse waveform of light transmitted through the wideband waveguide has a parabolic shape, and ripples are generated. No, it is possible to obtain broadband light with extremely flat intensity over a wide wavelength range.
[0014]
The multi-wavelength light source according to claim 3 is characterized in that, in the above invention, the broadband waveguide has a substantially constant dispersion value in the longitudinal direction.
[0015]
Further, in the multi-wavelength light source according to claim 4, in the above invention, an excitation light source for supplying excitation light for amplifying the first light, and optical coupling between the excitation light source and the broadband waveguide. An optical amplifier including an optical coupler is further provided.
[0016]
The multi-wavelength light source according to claim 5 is characterized in that, in the above invention, erbium ions are added to the broadband waveguide.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a multi-wavelength light source and an optical communication system according to the present invention will be described with reference to the drawings. In the drawings, the same or similar parts are denoted by the same or similar reference numerals. It should be noted that the drawings are schematic and different from actual ones. Further, it goes without saying that the drawings include portions having different dimensional relationships and ratios.
[0018]
(Embodiment 1)
First, the multi-wavelength light source according to the first embodiment will be described. The multi-wavelength light source according to the first embodiment has a structure including an optical fiber having a function of amplifying input light, exhibiting normal dispersion with flat dispersion characteristics. FIG. 1 is a schematic diagram illustrating a structure of the multi-wavelength light source according to the first embodiment. Hereinafter, a specific structure of the multi-wavelength light source will be described.
[0019]
The multi-wavelength light source according to the first embodiment includes an input light source 1, a broadband waveguide 2 connected to the input light source 1, a non-reciprocal circuit unit 3 disposed on the middle of the broadband waveguide 2, A light emitting section 4 provided at the end of the waveguide 2. Further, on the way to the broadband waveguide 2, there is provided a structure including optical couplers 5a and 5b for supplying excitation light, and excitation light sources 6a and 6b respectively connected to the optical couplers 5a and 5b.
[0020]
The input light source 1 is for outputting pulsed light or continuous wave light to the broadband waveguide 2. In the first embodiment, pulse light is output, and the input light source 1 is formed by a semiconductor laser device. The pulse waveform of the laser light output from the input light source 1 is not particularly limited as described later.
[0021]
The broadband waveguide 2 is formed of, for example, an optical fiber, and is for amplifying the laser light input from the input light source 1 and expanding the wavelength range to output broadband light. Specifically, as shown in the graph of FIG. 2, the broadband waveguide 2 has a normal dispersion, that is, a negative dispersion value, and a dispersion characteristic in which the dispersion value is constant with the fiber length. The dispersion characteristic of the broadband waveguide 2 is not limited to the one shown in FIG. 2, but it is possible to output broadband light effectively if the dispersion is normal. However, as will be described later, from the viewpoint of flattening broadband light or manufacturing. From the viewpoint of easiness, the dispersion characteristics shown in FIG. 2 are preferable. The tertiary variance is preferably small in absolute value, and more preferably 0. In the first embodiment, the third-order dispersion value is set to 0.
[0022]
The broadband waveguide 2 is provided with an erbium ion (Er) for amplifying the input laser light.³⁺) Is added. Therefore, the broadband waveguide 2 has a function of exciting the added erbium ions with the excitation light having a predetermined wavelength and giving the energy obtained by the excitation to the input light, thereby amplifying the light intensity of the input light. . The material added to the broadband waveguide 2 has an amplifying function even when a rare earth element other than erbium, such as thulium (Tm), praseodymium (Pr), ytterbium (Yb), or terbium (Tb) is used. It is possible. The material for forming the broadband waveguide 2 is not limited to a glass material, but may be a tellurite-based material, a fluoride-based material, or a silica-based material. Alternatively, a material other than these materials may be used as long as the above conditions are satisfied.
[0023]
The non-reciprocal circuit section 3 is for preventing return light from the light emitting section 4 side from being input to the broadband waveguide 2. Specifically, the non-reciprocal circuit section 3 is formed by an optical isolator, a circulator, or the like. The optical isolator is formed by combining, for example, a birefringent crystal having anisotropic refractive index, a wave plate, a Faraday rotator, and the like. If the generation of return light can be suppressed by preventing light reflection at the light emitting unit 4 or the like, a structure in which the nonreciprocal circuit unit 3 is omitted may be adopted.
[0024]
The excitation light sources 6a and 6b are for supplying excitation light. Specifically, the excitation light sources 6a and 6b are formed by, for example, semiconductor laser elements, and output laser beams having wavelengths of about 980 nm and about 1480 nm. However, the wavelength of the excitation light may be about 1530 nm. Note that, in the first embodiment, the bidirectional pumping method in which pumping is performed from the front and rear with respect to the traveling direction of the input light is adopted, but a structure in which optical amplification is performed only by forward pumping or backward pumping may be adopted. . Further, the number of semiconductor laser elements constituting the excitation light sources 6a and 6b is not limited to one, but may be plural.
[0025]
The optical couplers 5a and 5b are for inputting the pump light output from the pump light sources 6a and 6b to the broadband waveguide 2. Specifically, the optical couplers 5a and 5b are formed by an optical coupler, an optical multiplexer / demultiplexer, a circulator, and the like. With the above configuration, the multi-wavelength light source according to the first embodiment is formed.
[0026]
In the multi-wavelength light source according to the first embodiment, the self-phase modulation, the chromatic dispersion, and the optical amplification interact to output broadband light with good light intensity flatness. Hereinafter, after briefly describing these phenomena, the operation of the multi-wavelength light source according to the first embodiment will be described.
[0027]
Self-phase modulation is a kind of nonlinear optical effect, and refers to a phenomenon in which the phase of transmitted light itself is modulated according to the intensity of the transmitted light. In general, the refractive index of a medium such as an optical fiber slightly changes in proportion to the intensity of light transmitted through the medium, so that the phase of the light itself is modulated according to the change in the refractive index. Since the frequency of light is defined by the time derivative of the phase, when self-phase modulation occurs, the frequency of the light changes due to the modulation of the phase of the light, and the wavelength range of the light also changes.
[0028]
Wavelength dispersion refers to a phenomenon in which the pulse width of light changes due to the wavelength dependence of the refractive index of a transmission medium such as an optical fiber. When the refractive index changes for each wavelength, the group velocity of light has a different value for each wavelength. Therefore, when the light to be transmitted has a wavelength within a predetermined range, the pulse width of the input light fluctuates due to chromatic dispersion. In the first embodiment, since the dispersion characteristic of the broadband waveguide 2 becomes normal dispersion, the group velocity of the high-frequency light component decreases and the group velocity of the low-frequency light component increases. Accordingly, in the first embodiment, the light transmitted through the broadband waveguide 2 has a wider pulse width than that at the time of input due to the effect of chromatic dispersion.
[0029]
Optical amplification is performed for the purpose of effectively performing self-phase modulation. This is because, if the optical amplification is not performed, the intensity of the transmitted light decreases, and a high nonlinear optical effect cannot be obtained. In general, the degree of the nonlinear optical effect is proportional to the intensity of light to be transmitted. Therefore, self-phase modulation can be effectively performed by amplifying the light intensity. In particular, in the first embodiment, it is necessary to amplify the light intensity because the pulse width is increased because the light is transmitted through the optical fiber having the normal dispersion, and the peak value is correspondingly reduced. It is. In addition, by amplifying the light intensity, it becomes possible to output broadband light with good flatness of the light intensity due to the interaction with self-phase modulation and chromatic dispersion, which will be described in detail later. explain.
[0030]
Next, the operation of the multi-wavelength light source according to the first embodiment will be described. First, the input light from the input light source 1 is input to the broadband waveguide 2 and propagates through the wideband waveguide 2. Here, the pulse waveform of the input light is not particularly limited as described later, but hereinafter, a case where the input light has a Gaussian-shaped pulse waveform will be described as an example.
[0031]
Here, it will be described that the wavelength range of light transmitted through the broadband waveguide 2 is expanded by self-phase modulation, and the light intensity is flattened over a predetermined wavelength range by the contribution of chromatic dispersion and optical amplification. . First, self-phase modulation when chromatic dispersion and optical amplification do not occur will be described.
[0032]
FIGS. 3A to 3C are graphs showing self-phase modulation when the pulse waveform of the input light has a Gaussian shape. Here, FIG. 3A shows a pulse waveform of the input light, and FIG. 3B is a graph showing a degree of phase modulation with respect to the pulse waveform of FIG. FIG. 3C is a graph showing the amount of change in frequency derived from the amount of change in phase.
[0033]
As shown in FIG. 3A, the Gaussian-shaped pulse waveform has a time T₁And time T₂Has an inflection point, and the slope of the pulse waveform becomes maximum. In addition, as described above, since the amount of phase change in self-phase modulation is proportional to the light intensity, the waveforms shown in FIGS. 3A and 3B are the same. Further, since the frequency change amount shown in FIG. 3C corresponds to the time derivative of the curve shown in FIG. 3B, the time T at which the slope of the pulse waveform becomes maximum is obtained.₁, T₂Take the extremum with.
[0034]
Therefore, when only self-phase modulation occurs, the same frequency change occurs at different times. For example, the time T shown in FIG.₃And time T₄In both cases, the frequency change amount is Δω₁It becomes. Thus, when the same frequency change occurs at different times, the frequency change amount Δω₁Since interference occurs at a wavelength corresponding to the above, there is a possibility that ripples will occur in the output broadband light and flatness will be impaired.
[0035]
On the other hand, when the pulse waveform of the input light has a parabolic shape, it is possible to output broadband light having a flat intensity. FIG. 4 is a graph showing self-phase modulation when the pulse waveform of the input light has a parabolic shape. Note that the graph of FIG. 4 shows the amount of change in the pulse waveform phase and the amount of change in the frequency in order from the top. The parabolic shape is a concept including not only a quadratic function but also a pulse waveform having no other inflection point.
[0036]
As shown in the pulse waveform graph, when there is a parabolic pulse waveform, there is no inflection point, so there is no inflection point on the phase change graph, and as a result, the frequency change amount is This is a graph of a monotonous change in which no extreme value exists. Therefore, there is no plurality of times when the frequency change amounts coincide, and no ripple occurs in the broadband light due to interference.
[0037]
For this reason, it is preferable that the pulse waveform of the light transmitted in the broadband waveguide 2 has a parabolic shape. In the first embodiment, in addition to self-phase modulation, chromatic dispersion and optical amplification are performed together to change the pulse waveform of light transmitted in the broadband waveguide 2 into a parabolic shape.
[0038]
The change in the pulse waveform due to chromatic dispersion will be described with reference to FIGS. 5 (a) and 5 (b). When light having a predetermined pulse waveform, for example, a Gaussian-shaped pulse waveform shown in FIG. 5A is transmitted through the broadband waveguide 2, frequency modulation as shown in FIG. 5B is generated by self-phase modulation. . Here, in the case of normal dispersion, the group velocity of the high-frequency light component decreases and the group velocity of the low-frequency light component increases. Therefore, as indicated by the arrow in FIG. 5B, the light component whose frequency is increased by the self-phase modulation moves in the positive direction with respect to the time axis, and the light component whose frequency is decreased is negative with respect to the time axis. In the direction of. As a result, the pulse waveform of the light transmitted through the broadband waveguide 2 changes to the waveform indicated by the dotted line in FIG. In particular, since the absolute value of the frequency change is the largest at the inflection point, the distance of movement in the time axis direction is larger than that of the other parts due to chromatic dispersion. For this reason, the inflection points in the pulse waveform move toward the ends and disappear, and the pulse waveform has a parabolic shape as shown by the dotted line in FIG.
[0039]
On the other hand, even after the pulse waveform becomes parabolic, the pulse waveform expands in the time axis direction due to wavelength dispersion. For this reason, when the transmission distance is long, the pulse waveform may become more rectangular than parabolic. In the multi-wavelength light source according to the first embodiment, the broadband waveguide 2 is provided with an optical amplification function to increase the influence of self-phase modulation, thereby maintaining a parabolic pulse waveform. Specifically, it is as follows.
[0040]
Since self-phase modulation is a nonlinear optical effect, it is desirable that the intensity of transmitted light be large in order to effectively perform self-phase modulation. In the multi-wavelength light source according to the first embodiment, the light is amplified and the self-phase modulation is performed efficiently because the broadband waveguide 2 has the amplification function. That is, the light transmitted through the broadband waveguide 2 is strongly affected by the self-phase modulation, and the influence of the chromatic dispersion is relatively small. For this reason, by setting the amplification gain to an appropriate value, the input light having an arbitrary pulse waveform is changed into a parabolic pulse waveform in the broadband waveguide 2 and transmitted while maintaining the waveform. Can be done. Therefore, the light input to the broadband waveguide 2 has its spectral width expanded by self-phase modulation throughout the transmission, so that pump light having a flat intensity over a wide wavelength range can be obtained. .
[0041]
In the first embodiment, by providing the broadband waveguide 2 with the optical amplification function, there is an advantage that the peak intensity that decreases during transmission is maintained or increased. That is, the light transmitted through the broadband waveguide 2 has a wavelength range expanded by self-phase modulation and a pulse width expanded by chromatic dispersion, so that the peak value usually decreases. However, in the first embodiment, since the broadband waveguide 2 has an optical amplification function, optical amplification is performed during transmission, and the peak intensity is maintained or further increased. Therefore, in the transmission optical fiber, the wavelength range is expanded more effectively by the self-phase modulation, and the output broadband light can also obtain a sufficient intensity.
[0042]
The above discussion is supported by analyzing the nonlinear Schrodinger equation for light transmitted through the broadband waveguide 2. In the following, the wave function A (z, T) indicates the envelope of the wave function of the electric field of the transmitted light, and | A |²Is the intensity of the transmitted light. In the nonlinear Schrodinger equation, the longitudinal direction of the optical fiber, that is, the direction in which light is transmitted is the z-axis, time T, amplification gain g per unit length, nonlinear coefficient γ, and second-order dispersion β₂, Using the imaginary number i, for the wave function A (z, T):
i (∂A / ∂z) = (1/2) β₂(∂²A / ∂T²) −γ | A |²A + i (g / 2) A (1)
(ME Fermann et al., "Self-similarpropagation and amplification of parabolic pulses in optical fibresers, Phys. Rev. Lett., Vol.60, 60. . Note that the secondary dispersion value β₂Is between the variance D used in the graph of FIG.
D = − (2πc / λ²) Β₂... (2)
It has the relationship that That is, when the variance value D is negative and has a constant value as shown in the graph of FIG.₂Has a positive and constant value.
[0043]
In the equation (1), the left side shows the change of the wave function accompanying the transmission in the optical fiber, and the first term on the right side shows the contribution of the chromatic dispersion to the change of the wave function. The second term on the right-hand side shows the contribution of self-phase modulation which is a nonlinear optical effect on the change of the wave function, and the third term on the right-hand side shows the contribution of the amplification gain g. When γg> 0 holds for the amplification gain g and the nonlinear coefficient γ, in the limit of z → ∞, the expression (1) is
A (z, T) = A₀(Z) ｛1- [T / T₀]²{Exp {iφ (z, T)} (3)
Has an asymptotic solution. As shown in equation (3), the asymptotic solution has a maximum amplitude of A₀(Z), and the pulse waveform is Δ1- [T / T₀]²Oscillates with a phase of φ (z, T) corresponding to｝. Where A₀(Z), φ (z, T) and T₀Is
A₀(Z) = 0.5 (gE_in)^1/3(Γβ₂/ 2)^-1/6exp (gz / 3) ・ ・ ・ (4)
φ (z, T) = φ₀+ (3γ / 2g) A₀ ²− (G / 6β₂) T²・ ・ ・ (5)
T₀(Z) = 0.5 (E_inγβ₂/ 2g²)^1/3exp (gz / 3) (6)
It is expressed as Where E_inIs the energy per pulse of the input light (hereinafter referred to as “input pulse energy”). As shown in equation (3), since the asymptotic solution includes a quadratic equation of time T, the pulse waveform based on the asymptotic solution has a parabolic shape, and the pulse shape is transmitted through the broadband waveguide 2 while maintaining the parabolic shape. Is shown. Further, as shown in the equation (5), since the phase φ is expressed by a quadratic equation of the time T, the frequency corresponding to the differentiation of the phase φ becomes 1 in the time T similarly to the case shown in FIG. This is the number of hours, and it can be seen that broadband light having a flat intensity over a predetermined wavelength range can be obtained.
[0044]
Further, as is apparent from the expressions (3) to (5), the laser light input to the broadband waveguide 2 has an input pulse energy E_inOnly the wave function A (z, T) is affected, and it is understood that the wave function A (z, T) is not affected by the pulse width or pulse waveform of the input laser light. Therefore, the input light supplied from the input light source 1 does not need to have a parabolic pulse waveform, and input light having an arbitrary pulse waveform can be used.
[0045]
FIGS. 6A and 6B show the results of a simulation by numerical calculation actually performed based on equation (1). FIG. 6A is a graph showing a change in pulse waveform due to transmission in the broadband waveguide 2, and a curve l.₁Indicates a pulse waveform immediately after input, and a curve l₂, Curve l₃Shows the pulse waveform after 500 m and 1000 m transmission in the broadband waveguide 2 after input. FIG. 6B is a graph showing the change of the spectrum waveform accompanying the transmission, and the curve l₄, Curve l₅, Curve l₆Indicates the spectrum waveforms immediately after the input, after 500 m transmission, and after 1000 m transmission, respectively. In the simulation, the pulse width of the input light was 2 ps, and the input pulse power was 0.3 pJ. This corresponds to pulsed light having a frequency of 10 GHz and a light intensity of 3 mW. The pulse waveform of the input light was Gaussian. Further, for the broadband waveguide 2, the second order dispersion β₂2ps²/ Km and the nonlinear coefficient γ is 14.2 W^-1km^-1And the amplification gain g is set to 20 dB / km.
[0046]
As shown in FIG. 6A, as the transmission distance increases, the pulse width increases, and the peak value also increases. Also, regarding the pulse waveform, a curve l₁In the input shown in FIG.₂, Curve l₃Has a substantially parabolic shape.
[0047]
Further, as shown in FIG. 6B, in the light transmitted through the broadband waveguide 2, a wavelength region where the spectral width gradually increases and the intensity becomes flat appears, and as the light is further transmitted, the flat wavelength region is changed. Expanding. For example, the curve l₆As shown in (1), the wavelength region where the intensity becomes flat after transmitting 1000 m is expanded to about 2 THz. Therefore, at least in simulation, it is shown that the multi-wavelength light source according to the first embodiment can realize broadband light with good flatness.
[0048]
Next, a simulation was performed to confirm that the broadband light obtained by the multi-wavelength light source according to the first embodiment did not depend on the pulse waveform of the input light, and the results shown in the graph of FIG. 7 were obtained. More specifically, the pulse width is changed from 0.5 ps to 4 ps, and the other conditions are the same as those in the simulation shown in FIGS. 6A and 6B. The variation was examined. Note that the spectrum width was a difference value between the maximum frequency and the minimum frequency of the intensity at which the difference from the peak value was 10 dB.
[0049]
As shown in the graph of FIG. 7, as the pulse width of the input light is increased, the spectrum width of the obtained broadband light monotonically decreases, but the fluctuation width is very small. In particular, in the range of 1 ps to 3 ps, the fluctuation of the spectrum width is suppressed to about 7% even though the pulse width fluctuates three times. Therefore, in the multi-wavelength light source according to the first embodiment, it is apparent that the output broadband light hardly depends on the pulse width of the input light.
[0050]
Next, the multi-wavelength light source according to the first embodiment was actually manufactured, and the spectrum waveform of the output light was measured, and it was confirmed that broadband light having a flat intensity over a predetermined range was obtained. Specifically, the secondary variance β₂Is 6.6ps²/ Km, nonlinear coefficient γ is 14.2W^-1km^-1An optical fiber having a fiber length of 1 km is used as the broadband waveguide 2, and the amount of erbium ions added to the broadband waveguide 2 and the light intensity of the excitation light sources 6a and 6b are adjusted to increase the amplification gain g by 20 dB. / Km. The input light source 1 used was a semiconductor laser device capable of emitting input light having a pulse waveform of Gaussian shape and input pulse energy of 2.5 pJ, 5 pJ, and 10 pJ.
[0051]
FIG. 8 is a graph of a spectrum waveform of output light measured for the multi-wavelength light source having the above structure. Where the curve l₇Shows the case where the input pulse energy is 2.5 pJ, and the curve l₈, Curve l₉Indicates output light when the input pulse energy is 5 pJ and 10 pJ, respectively. In FIG. 8, the dotted line indicates the spectrum waveform of the input light.
[0052]
As is clear from the graph of FIG. 8, the output light obtained from the actual multi-wavelength light source has a spectrum waveform whose intensity is flat over a wide frequency range. In particular, when the input pulse energy is 10 pJ, the flat wavelength range in which the difference from the maximum intensity is 10 dB or less is expanded to about 34.5 nm. The measurement results show that the multi-wavelength light source according to the first embodiment can actually output broadband light having a flat intensity over a wide wavelength range.
[0053]
As described above, the multi-wavelength light source according to the first embodiment has an advantage that it can output broadband light with excellent intensity flatness. In the first embodiment, since the pulse waveform of the light transmitted through the broadband waveguide 2 has a parabolic shape, the same frequency shift does not occur at different times. Therefore, in the outputted broadband light, ripples due to interference due to the same frequency shift do not occur, and broadband light having a flat intensity over a wide wavelength range can be output.
[0054]
Further, the multi-wavelength light source according to the first embodiment has an advantage that it can be easily manufactured. In the first embodiment, since the pulse waveform has a parabolic shape in the broadband waveguide 2 irrespective of the waveform of the input light, no special condition is required for the pulse waveform of the input light. Therefore, a light source that outputs an arbitrary pulse waveform can be used as the input light source 1 as long as light having a predetermined input pulse power can be output.
[0055]
Further, in the first embodiment, as is clear from the equations (1) to (6), the spectrum waveform of the broadband light is determined by various coefficients such as the amplification gain and the input pulse power in addition to the secondary dispersion value. Is done. For this reason, there is an advantage that not much strictness is required for the individual coefficients. For example, even when the secondary dispersion value of the broadband waveguide 2 fluctuates with respect to the transmission distance, the secondary light is appropriately adjusted by adjusting the intensity of the pump light output from the pump light sources 6a and 6b. Broadband light equivalent to the case where the dispersion value is constant can be output. Therefore, the first embodiment has an advantage that the conditions required for the input light source 1, the broadband waveguide 2, and the like are alleviated as compared with the related art, and that it can be easily manufactured.
[0056]
Further, the multi-wavelength light source according to the first embodiment has an advantage that the input pulse power can be suppressed as compared with the related art. In the first embodiment, it is not necessary to satisfy the soliton condition that the input light is equal to or higher than a predetermined intensity, and the structure is such that the light is amplified in the broadband waveguide 2.
[0057]
In the multi-wavelength light source according to the first embodiment, a structure in which a dispersion imparting unit formed by an optical fiber or the like having a predetermined dispersion characteristic between the input light source 1 and the broadband waveguide 2 may be provided. . For example, when the dispersion characteristic of the dispersion imparting unit decreases the dispersion value with respect to the distance, the pulse waveform of the light input from the input light source 1 is compressed in the time axis direction. Therefore, the peak intensity in the pulse waveform is increased, and self-phase modulation in the broadband waveguide 2 can be significantly generated.
[0058]
Further, a structure in which the dispersion imparting unit is disposed between the optical coupler 5b and the light emitting unit 4 may be adopted. When the amplified light passes through the dispersion imparting section, for example, when the dispersion characteristic decreases in the longitudinal direction, a transform-limited pulse waveform can be realized. Such a pulse waveform is largely spread in terms of spectrum, but the pulse width can be significantly reduced, and the full width at half maximum (FWHM) is theoretically as high as 300 fs.
[0059]
Further, for the broadband waveguide 2, the second order dispersion β₂May not be a constant value as shown in FIG. 2, but may have a characteristic of decreasing in the longitudinal direction while maintaining a positive value. Since the distributed gain and the variance are equivalent, the decreasing second-order variance β₂This is because a multi-wavelength light source can be realized by adjusting the distribution gain. Second order dispersion β of the broadband waveguide 2₂Is reduced in the longitudinal direction, the expansion of the pulse width is suppressed, so that the peak intensity can be kept high. Therefore, a nonlinear optical effect is significantly generated, and the spectrum width can be further increased.
[0060]
(Embodiment 2)
Next, a multi-wavelength light source according to the second embodiment will be described. The multi-wavelength light source according to the second embodiment has a structure in which light transmitted through an optical fiber is amplified using Raman amplification. FIG. 9 is a schematic diagram illustrating a structure of the multi-wavelength light source according to the second embodiment.
[0061]
The multi-wavelength light source according to the second embodiment includes an input light source 1, a broadband waveguide 8 connected to the input light source 1, a non-reciprocal circuit unit 3 arranged on the wideband waveguide 8, A light emitting section 4 disposed at an end of the waveguide 8. Further, optical couplers 9 and 10 are arranged in the middle of the broadband waveguide 8, and have a structure in which excitation light can be input to the wideband waveguide 8. The optical coupler 9 is connected to the excitation light sources 13 and 14 via the optical coupler 11, and the optical coupler 10 is connected to the excitation light sources 15 and 16 via the optical coupler 12. Have. Note that portions denoted by the same reference numerals or names as those in the first embodiment have the same functions as those in the first embodiment and exert the same effects unless otherwise specified.
[0062]
The pump light sources 13 to 16 are for amplifying light transmitted through the broadband waveguide 8 by Raman amplification. Specifically, the excitation light sources 13 to 16 output light having a wavelength shorter by about 100 nm than light transmitted through the broadband waveguide 8. The excitation light source 13 and the excitation light source 14 are multiplexed by the optical coupler 11 so that their polarization directions are orthogonal to each other, and are depolarized with respect to the broadband waveguide 8 via the optical coupler 9. Excitation light is input. Similarly, the pumping light source 15 and the pumping light source 16 are multiplexed by the optical coupler 12 so that the polarization directions are orthogonal to each other, and the polarization-free pumping light is applied to the broadband waveguide 8 through the optical coupler 12. Light is input. The excitation light input through the optical coupler 9 is transmitted through the broadband waveguide 8 in the same direction as the light input from the input light source 1, and is input through the optical coupler 12. Is transmitted in the opposite direction to the light input from the input light source 1. That is, in the multi-wavelength light source according to the second embodiment, Raman amplification is performed on light transmitted through the broadband waveguide 8 by the bidirectional pumping method.
[0063]
In the multi-wavelength light source according to the second embodiment, the light source of the excitation light input via the optical couplers 9 and 10 may be configured as a single light source. However, since Raman amplification has polarization dependence, it is preferable to use pump light that has been depolarized by a plurality of light sources as described above. Further, in the second embodiment, Raman amplification is performed by a so-called bidirectional pumping method, but a structure in which Raman amplification is performed only by forward pumping or backward pumping may be adopted.
[0064]
It is preferable to use a broadband waveguide 8 having a large nonlinear coefficient in order to efficiently perform Raman amplification. Since the method of optical amplification is different from that of the multi-wavelength light source according to the first embodiment, it is not necessary to add a rare earth such as erbium ions.
[0065]
The multi-wavelength light source according to the second embodiment amplifies light propagating in the broadband waveguide 2 by Raman amplification. Therefore, by determining the wavelength of the pump light according to the wavelength of the input light, optical amplification becomes possible, and the wavelength of the input light can be arbitrarily selected. Further, when Raman amplification is performed at a plurality of wavelengths, a desired gain characteristic can be obtained over a wide wavelength range. Therefore, the output light of the multi-wavelength light source can be controlled by controlling the light intensity of each pump light source. Can be adjusted.
[0066]
Next, the multi-wavelength light source according to the second embodiment was simulated by numerical calculation. FIG. 10A is a graph showing how the pulse waveform changes according to the transmission distance, and FIG. 10B is a graph showing how the spectrum waveform changes. Here, for the broadband waveguide 8, the nonlinear coefficient γ is set to 20W.^-1km^-1, Second order variance β₂1.0ps²/ Km, third-order variance β₃0.03ps³/ Km, and the amplification gain g per unit length is 10 dB / km. In addition, for light input from the input light source 1, a simulation was performed with a pulse waveform having a Gaussian shape, an input pulse power of 0.2 pJ, and a pulse width of 2 ps.
[0067]
As shown in FIG. 10A, the pulse width increases as the transmission distance increases, and the pulse width becomes a parabolic shape having no inflection point. Correspondingly, the spectrum waveform shown in FIG. 10B also shows that the wavelength range gradually expands, the intensity becomes flat, and broadband light is obtained. In particular, it is shown that after transmission of about 2500 m, the flat range is expanded to about 3 THz, and flat broadband light can be obtained over a wide range.
[0068]
Next, FIGS. 11A and 11B show examples in which the simulation was performed while changing the characteristics of the broadband waveguide 8 and the conditions of the input light. FIG. 11A is a graph showing a change in the pulse waveform, and FIG. 11B is a graph showing a change in the spectrum waveform. In the simulations of FIGS. 11A and 11B, the nonlinear coefficient γ is set to 4.5 W^-1km^-1And the second-order variance β₂0.2ps²/ Km, third-order variance β₃0.0 ps³/ Km, and the amplification gain g per unit length is 5 dB / km. The pulse waveform of the input light was Gaussian, the pulse width of the input light was 2 ps, and the input pulse energy was 0.2 pJ.
[0069]
As shown in FIG. 11A, the pulse waveform gradually changes to a parabola. In this simulation, since the secondary variance was set to a small value, the transmission distance required for the pulse waveform to change to a parabolic shape was longer than that in the case of FIG. However, the overall tendency is the same as in the case of FIG. 10A. After the transmission changes to a parabolic shape during transmission, the pulse waveform is maintained and transmitted through the broadband waveguide 8. Also, the spectrum waveform shown in FIG. 11B corresponding to the change in the pulse waveform has an expanded wavelength range and a region where the light intensity is flat, and the frequency range where the flat intensity is obtained after transmitting 4000 m is about 4 THz. Expand to
[0070]
Next, the simulation was performed again with the pulse width reduced. Specifically, the characteristics of the transmission optical fiber and the input pulse energy were the same as those in FIG. 11, and the pulse width of the input light was 1 ps.
[0071]
As shown in FIG. 12 (a), the pulse waveform changes to a parabolic shape at a stage where the transmission distance is relatively short, and then the pulse waveform is transmitted while maintaining the parabolic shape. In addition, as shown in FIG. 12B, a flat peak appears at a relatively short transmission distance, and the frequency range in which the intensity is flat increases. The frequency range in which the intensity becomes flat is almost 4 THz as in the case of FIG. 11B, and the dependence on the pulse width of the input light is small from the viewpoint of broadening the output light.
[0072]
(Embodiment 3)
Next, a multi-wavelength light source according to the third embodiment will be described. The multi-wavelength light source according to the third embodiment has a structure including an optical filter unit newly connected to a light emitting unit. FIG. 13 is a schematic diagram showing the structure of the multi-wavelength light source according to the third embodiment. Hereinafter, the structure of the multi-wavelength light source will be described with reference to FIG.
[0073]
The multi-wavelength light source according to the third embodiment includes an input light source 1, a broadband waveguide 2 connected to the input light source 1, and a non-reciprocal circuit unit 3 disposed on the broadband waveguide 2. Further, a light emitting unit 4 is provided at the end of the broadband waveguide 2, and the light emitting unit 4 is connected to the optical filter 18. Further, optical couplers 5a and 5b are respectively disposed on the way of the broadband waveguide 2, and the optical coupler 5a is connected to the excitation light source 6a, and the optical coupler 5b is connected to the excitation light source 6b. Note that portions denoted by the same reference numerals or names as those of the first embodiment have the same functions as those of the first embodiment and exhibit the same effects unless otherwise described below.
[0074]
The optical filter 18 is for transmitting a light component having a desired wavelength in the broadband light output from the light emitting unit 4. Specifically, the optical filter 18 is formed by an optical bandpass filter or an optical etalon filter, and has a function of transmitting a light component having a desired wavelength.
[0075]
The operation of the optical filter 18 will be described with reference to FIG. The multi-wavelength light source according to the third embodiment has a wider wavelength range than that at the time of input as shown by a dotted line in FIG. The light is output from the light emitting unit 4. On the other hand, by arranging the optical filter 18 having a predetermined light transmission characteristic in connection with the light emitting unit 4, as shown by the solid line in FIG. Will be output separately.
[0076]
Therefore, the multi-wavelength light source according to the third embodiment can be used, for example, as a signal light source in WDM optical communication. When used as a signal light source, the required number of light sources can be reduced as compared with a structure in which different center wavelengths are output by a plurality of light sources, and the size and cost of the device can be reduced.
[0077]
In addition, since the light is output through the optical filter 18, the wavelength of the output light is stabilized. Specifically, for example, when the signal light source is configured by a semiconductor laser device, the wavelength of the signal light also changes due to a change in the voltage applied to the semiconductor laser device or the temperature of the semiconductor laser device. On the other hand, when the multi-wavelength light source according to the third embodiment is used, even if the wavelength of the input light fluctuates, the wavelength of the light output by passing through the optical filter 18 is set to a constant value. Can be held.
[0078]
(Modification 1)
Next, a first modification of the multi-wavelength light source according to the third embodiment will be described. In the first modification, a structure using an optical demultiplexer instead of the optical filter 18 is employed. FIG. 15 is a schematic diagram illustrating a structure of a multi-wavelength light source according to a modification. As shown in FIG. 15, the modification has a structure in which an optical demultiplexer 19 is connected to the light emitting unit 4 instead of the optical filter 18.
[0079]
The optical demultiplexer 19 converts the broadband light output from the light emitting unit 4 to a wavelength λ.₁~ Λ_nIt is for demultiplexing every time. Specifically, the optical demultiplexer 19 is formed by, for example, melting and connecting cores of a plurality of optical fibers. In this case, by adjusting the heating temperature and the heating time at the time of melting, the ratio of the wavelength to be demultiplexed can be changed to configure the optical demultiplexer 19. In addition to the fusion connection of the cores of a plurality of optical fibers, the optical demultiplexer 19 can be formed using a prism, an arrayed waveguide, a diffraction grating, or the like.
[0080]
(Modification 2)
Next, a second modification of the multi-wavelength light source according to the third embodiment will be described. In the multi-wavelength light source according to the second modification, the optical filter 18 does not transmit a plurality of lights having different center wavelengths, but transmits a single light having a predetermined center wavelength. In this case, for example, by transmitting light having a center wavelength different from that of the input light, it is possible to output light whose center wavelength is shifted by a predetermined range from the input light. Even when the optical filter 18 is configured as described above, there are advantages such as stabilization of the wavelength of output light. Further, even when the optical demultiplexer 19 is used as in the first modification, a structure may be employed in which a single light having a predetermined center wavelength is output instead of splitting into a plurality of lights having different center wavelengths. good.
[0081]
The multi-wavelength light source according to the second modification was actually manufactured, and a graph shown in FIG. 16 was obtained. In FIG.₁₀Represents the spectrum of the input light, and the curve l₁₁Indicates broadband light output from the light emitting unit 4. And the curve l₁₂Indicates output light cut out from the broadband light by the optical filter 18. As shown in FIG. 16, output light whose wavelength is shifted to a higher wavelength side by about 2 nm with respect to the input light is actually obtained.
[0082]
The multi-wavelength light source according to the third embodiment and the first and second modifications is configured using the multi-wavelength light source according to the first embodiment. However, the present invention is not limited to this. It is also possible to adopt a structure in which a filter unit is added to the multi-wavelength light source according to the second embodiment.
[0083]
(Embodiment 4)
Next, an optical communication system according to a fourth embodiment will be described. The optical communication system according to the fourth embodiment uses the multi-wavelength light source according to the third embodiment as a signal light source. FIG. 17 is a schematic diagram illustrating a configuration of the optical communication system according to the fourth embodiment. Hereinafter, the optical communication system according to the fourth embodiment will be described with reference to FIG.
[0084]
The optical communication system according to the fourth embodiment includes a multi-wavelength light source 21, a transmission optical fiber 22 connected to the multi-wavelength light source 21, and an amplification optical system connected to the transmission optical fiber 22 via an optical coupler 26. An optical fiber 23 is provided. Further, a transmission optical fiber 24 is connected via an amplification optical fiber 23 and an optical coupler 28, and a receiver 25 is connected to the transmission optical fiber 24. Further, an excitation light source 27 is connected to the optical coupler 26, and has a structure in which the excitation light can be input to the amplification optical fiber 23 via the optical coupler 26, and an excitation light source 29 is connected to the optical coupler 28. Then, it has a structure in which pumping light can be input to the amplification optical fiber 23. The transmission optical fibers 22 and 24 are formed of, for example, DSF (Dispersion Shifted Fiber) or SMF (Single Mode Fiber).
[0085]
The multi-wavelength light source 21 includes the multi-wavelength light source according to the third embodiment. Therefore, the multi-wavelength light source 21 has a structure in which a plurality of signal lights having different center wavelengths are output, and a high communication capacity can be realized by transmitting the same light through the same fiber. Note that, other than the third embodiment, the multi-wavelength light source according to the first or second embodiment may be used, or the multi-wavelength light source according to the modification of the third embodiment may be used.
[0086]
The amplification optical fiber 23 has a structure to which erbium ions are added. The pumping light from the pumping light source 27 and the pumping light source 29 is input to the amplifying optical fiber 23, and has a function of amplifying the signal light. The rare earth element to be added may be thulium, praseodymium, ytterbium, terbium or the like other than erbium, and may have a structure in which signal light is amplified by Raman amplification without adding these elements.
[0087]
The amplification optical fiber 23 is for amplifying the intensity of the signal light that has been reduced by long-distance transmission, and generates the nonlinear optical effect as in the optical amplification according to the first to third embodiments. It is not to increase. Rather, in order to maintain the accuracy of signal light reception in the receiver 25, the amplification gain is adjusted so that the nonlinear optical effect in the amplification optical fiber 23 does not occur at all, or even if it occurs, it is within an allowable range. Is preferred.
[0088]
The receiver 25 is for receiving the transmitted signal light and converting it into an electric signal. Specifically, the receiver 25 is formed by a photodiode, a photo resistor, or the like, and receives information by converting the signal into an electric signal according to the intensity of the signal light.
[0089]
Next, the operation of the optical communication system according to the fourth embodiment will be briefly described. The signal light output from the multi-wavelength light source 21 is transmitted through the transmission optical fiber 22 and then subjected to optical amplification in the amplification optical fiber 23 to compensate for the reduced light intensity. Then, the amplified signal light reaches the receiver 25 after being transmitted through the transmission optical fiber 24. The signal light received by the receiver 25 is converted into an electric signal to receive information.
[0090]
Here, since the multi-wavelength light source 21 according to the third embodiment is used as the multi-wavelength light source 21, there is an advantage that a single input light source can output a plurality of signal lights having different center wavelengths. Therefore, it is not necessary to provide a number of signal light sources corresponding to the number of signal lights, and an optical communication system can be realized at low cost. In addition, since broadband light having a flat intensity is obtained by the interaction of self-phase modulation, chromatic dispersion, and optical amplification, the intensity of each signal light is also substantially constant.
[0091]
【The invention's effect】
As described above, according to the first to fifth aspects of the present invention, it is possible to increase the intensity of transmitted light because the spectrum width is expanded by the nonlinear optical effect while amplifying light in the broadband waveguide. By sufficiently generating the non-linear optical effect, the spectrum width can be sufficiently expanded, and broadband light with a wide wavelength range can be obtained.
[0092]
Further, when the average dispersion characteristic of the broadband waveguide is normal dispersion and the configuration has a substantially constant dispersion value in the longitudinal direction, the pulse waveform of light transmitted through the broadband waveguide is parabolic. This is advantageous in that a broadband light having a very flat intensity without any ripple can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a configuration of a multi-wavelength light source according to a first embodiment.
FIG. 2 is a graph showing dispersion characteristics of a broadband waveguide.
3A is a graph showing a Gaussian-shaped pulse waveform, FIG. 3B is a graph showing a phase change amount with respect to light having the pulse waveform of FIG. 3A, and FIG. 5 is a graph showing the amount of change in frequency with respect to light having the pulse waveform of FIG.
FIG. 4 is a graph showing, in order from the top, a parabolic pulse waveform, a graph showing a phase change amount with respect to light having the pulse waveform, and a graph showing a frequency change amount with respect to light having the pulse waveform shown in the upper graph. .
FIGS. 5A and 5B are graphs for explaining that a pulse waveform changes due to the influence of chromatic dispersion in the first embodiment.
FIG. 6A is a graph showing that the pulse waveform changes according to the transmission distance by simulation for the multi-wavelength light source according to the first embodiment, and FIG. 6B is a graph showing the transmission distance by simulation. 6 is a graph showing that the spectrum waveform changes according to the following.
FIG. 7 is a graph showing that, in the first embodiment, the spectrum width of output broadband light does not depend on the pulse width of input light.
FIG. 8 is a graph showing that a spectral waveform changes in accordance with a transmission distance for a multi-wavelength light source actually manufactured.
FIG. 9 is a schematic diagram illustrating a structure of a multi-wavelength light source according to a second embodiment.
FIGS. 10A and 10B are graphs obtained by simulation with respect to a waveform change according to a transmission distance, wherein FIG. 10A is a graph showing a change in a pulse waveform, and FIG. 10B is a graph showing a change in a spectrum waveform.
FIGS. 11A and 11B are graphs obtained by simulation with respect to a waveform change according to a transmission distance, in which FIG. 11A is a graph showing a change in a pulse waveform, and FIG. 11B is a graph showing a change in a spectrum waveform.
FIGS. 12A and 12B are graphs obtained by simulation with respect to a waveform change according to a transmission distance; FIG. 12A is a graph showing a change in a pulse waveform; and FIG. 12B is a graph showing a change in a spectrum waveform.
FIG. 13 is a schematic diagram showing a structure of a multi-wavelength light source according to a third embodiment.
FIG. 14 is a schematic graph for explaining an operation of the optical filter according to the third embodiment.
FIG. 15 is a schematic diagram showing a structure of a multi-wavelength light source according to a first modification of the third embodiment.
FIG. 16 is a graph showing measurement results for explaining the operation of an optical filter for a multi-wavelength light source according to a second modification of the third embodiment.
FIG. 17 is a schematic diagram illustrating a structure of an optical communication system according to a fourth embodiment;
FIG. 18 is a graph showing dispersion characteristics of an optical fiber constituting a multi-wavelength light source according to the related art.
[Explanation of symbols]
1 Input light source
2 Optical fiber for transmission
3 Non-reciprocal circuit section
4 Light emitting part
5a, 5b, 9-12, 26, 28 ° optical coupler
6a, 6b, 13-16, 27, 29 ° excitation light source
8 Optical fiber for transmission
13-16 ° excitation light source
18 optical filter
19 optical splitter
21 ° multi-wavelength light source
22, 24 transmission optical fiber
23 ° optical fiber for amplification
25 receiver

Claims (5)

A light source that outputs a first light;
The first light is input, the spectrum width of the first light is expanded by a nonlinear optical effect while amplifying the intensity of the first light, and the second light having a flat intensity over a certain wavelength range. A broadband waveguide that outputs light of
A multi-wavelength light source comprising: The multi-wavelength light source according to claim 1, wherein the broadband waveguide has a negative average dispersion value in a longitudinal direction in a wavelength range of the second light. The multi-wavelength light source according to claim 1, wherein the broadband waveguide has a substantially constant dispersion value in a longitudinal direction thereof. An excitation light source that supplies excitation light for amplifying the first light;
An optical coupler for optically coupling the excitation light source and the broadband waveguide,
The multi-wavelength light source according to any one of claims 1 to 3, further comprising an optical amplifier including: The multi-wavelength light source according to any one of claims 1 to 4, wherein erbium ions are added to the broadband waveguide.

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