JPH11174503A - White pulse light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a white pulse light source generating white pulse light having a wide band and flatness by decreasing a dispersion value in the center wavelength of exciting pulse light from a positive value in the propagation direction of the exciting pulse light and possessing plural kinds of zero dispersed wavelength in the range of a propagation distance where a maximal value is positive. SOLUTION: The dispersion value D(λ0 , z) of a waveguide type optical nonlinear medium in the center wavelength λ0 of the exciting pulse light is the positive value at an incident end (z=0), and decreased in the propagation direction of the exciting pulse light. Furthermore, two kinds of zero dispersed wavelength λ1 (z) and λ2 (z) are formed on both sides of the center wavelength λ0 of the exciting pulse light in the range of the propagation distance where the maximal value is provided and it is positive. Thus, a spectral spread process by soliton compression and a process to make spectrum rectangular and flat because a soliton is changed to dispersed wave are caused. Therefore, the white pulse light having high flatness and symmetry is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white pulse light source for generating excitation light in a waveguide type optical nonlinear medium to generate white light having a wide band and excellent flatness.

[0002] In recent years, SuperContinium (Su
Percontinuum) Ultra-wideband white pulse light called light is attracting attention as a light source for communication and measurement.

[0003]

2. Description of the Related Art As shown in FIG. 26, a white pulse light source includes an excitation pulse light source and a waveguide type optical nonlinear medium. The excitation pulse light emitted from the excitation pulse light source is
A third-order nonlinear optical effect is induced when propagating through a waveguide-type optical nonlinear medium to generate a broadband white pulse light. Here, it is assumed that the propagation distance of the excitation pulse light in the waveguide type optical nonlinear medium is z, the incident end is z = 0, and the emission end is z = L.

[0004] Regarding such a white pulse light source, Document 1 (Japanese Patent Application Laid-Open No. 8-234249, "Coherent White Light Source") specifies the dispersion slope and the magnitude of dispersion of a waveguide type optical nonlinear medium, and describes this dispersion slope. It is clear that the smaller the is, the wider the white pulse light is generated. An experiment using a single-mode optical fiber as the waveguide-type optical nonlinear medium shows that white pulse light with excellent flatness over a wide band as shown in FIG. 27 was obtained. FIG. 27 also shows the spectrum of the excitation pulse light.

Document 1 also shows that the band of generated white pulse light increases by using a waveguide type optical nonlinear medium whose dispersion value decreases in the propagation direction of the excitation pulse light.

[0006] This is also shown in Document 2 (Okuno et al., "Study of Optical Fiber for Generating High Efficiency Supercontinuum", IEICE 1997-13 General Conference, SB-13-6). That is, as shown in FIG. 28, the dispersion value at the center wavelength λ ₀ of the excitation pulse light of the waveguide type optical nonlinear medium (optical fiber) is changed from the input end (z = 0) to the output end (z =
By changing from positive to negative toward L) and keeping the dispersion slope small, a broadband white pulse light is generated. FIG. 29 shows the spectrum of the white pulse light obtained by the white pulse light source of Document 2.

[0007] Reference 3 (Tamura et al., "Genaratio")
n of 10 GHz pulse trains at 16 wavelengths by spec
trally slicing a high power femtosecond source ", E
electronics Letters, vol.32, no.18, pp.1691-1693, 1
996) discloses a configuration in which a waveguide type optical nonlinear medium (rare-earth-doped fiber) having a gain characteristic is excited to generate white pulse light. With this configuration, white pulse light can be generated even when the intensity of the excitation pulse light is low or when the waveguide type optical nonlinear medium is short.

[0008]

In utilizing white pulse light for communication and measurement, it is important that the spectrum has a wide band and excellent flatness in the wavelength range.

In the prior arts shown in Documents 1 and 2, only the first-order term (dispersion slope) relating to the wavelength of the dispersion value is defined for the waveguide type optical nonlinear medium. Reference 3 only specifies the decreasing property of the dispersion value except that a rare earth element is added to the waveguide type optical nonlinear medium. For this reason, as shown in FIGS. 27 and 29, white pulse light satisfying both broadband characteristics and flatness has not been obtained.

An object of the present invention is to provide a white pulse light source based on a new design guideline for generating white pulse light having a wide band and high flatness.

[0011]

The white pulse light of the present invention has an excitation pulse light source for generating an excitation pulse light having a center wavelength λ ₀ , and a length L [for generating the white pulse light upon incidence of the excitation pulse light. m] of the waveguide type optical nonlinear medium.

The dispersion value D (λ ₀ , z) of the waveguide type optical nonlinear medium at the center wavelength λ ₀ of the pump pulse light takes a positive value at the incident end (z = 0), and the propagation of the pump pulse light It has the characteristic of decreasing in the direction.

Further, in a range L ₁ ≦ z ≦ L (where 0 ≦ L ₁ <L) of a propagation distance z of the excitation pulse light, a dispersion value D (λ,
z) is a local maximum D (λ _p (z), z) at the peak wavelength λ _p (z).
And two zero-dispersion wavelengths λ where the dispersion value D (λ, z) becomes 0 in the range of the propagation distance z where the maximum value is positive.
₁ (z) and λ ₂ (z).

The principle of generation and growth of white pulse light in the white pulse light source of the present invention will be described. White pulse light is generated and grown through a two-step process. That is, a spectrum spreading process by soliton compression and a process of rectangularizing and flattening the spectrum by changing the soliton into a dispersive wave.

The excitation pulse light incident on the waveguide-type optical nonlinear medium has a propagation distance z at which the dispersion value D (λ ₀ , z) of the waveguide-type optical nonlinear medium at the center wavelength λ ₀ becomes positive (abnormal dispersion).
In the range, the spectrum is broadened by soliton compression.
The dispersion value D (λ ₀ , z) decreases with the propagation distance z, and the two zero-dispersion wavelengths λ ₁ (z) and λ ₂ (z) become the center wavelength λ of the pump pulse light.
_As the wavelength approaches ₀ , the wavelength regions at both ends of the spectrum enter a region where the dispersion value is negative (normal dispersion), but the spectrum of the excitation pulse light continues to spread while maintaining the soliton properties as a whole.

Further, the variance value D varies with the propagation distance z.
(λ₀, z) continue to decrease, the wavelength region at both ends of the spectrum
The region loses solitonity due to normal dispersion and becomes dispersive wave
The spectrum broadening stops at that yield point. Toko
The center wavelength λ of the excitation pulse light ₀In the wavelength range close to
Indicates that the variance value is still positive (anomalous
As the tor continues to expand, the light energy density at the yield point
The degree increases and a square spectrum grows. And 2
Zero-dispersion wavelengths closer to the center wavelength of the pump pulse light
Since the yield point also approaches the center wavelength,
A creole is formed.

[0017]

[First Embodiment] A first embodiment of a white pulse light source according to the present invention comprises an excitation pulse light source as shown in FIG. 26 and a waveguide type optical nonlinear medium.
However, the waveguide type optical nonlinear medium used for the white pulse light source of the present invention is characterized by its wavelength-dispersion value characteristics.

[First Wavelength-Dispersion Value Characteristics of Waveguide-Type Optical Nonlinear Medium] FIG. 1 shows the first wavelength-dispersion value characteristics of the waveguide-type optical nonlinear medium used in the white pulse light source of the present invention. . In the figure, the horizontal axis represents wavelength and the vertical axis represents dispersion value.

The dispersion value D (λ ₀ , z) of the waveguide-type optical nonlinear medium at the center wavelength λ ₀ of the excitation pulse light is represented by the incident end (z
= 0), it takes a positive value and decreases in the direction of propagation of the excitation pulse light.

Further, the dispersion value D of the waveguide type optical nonlinear medium
(λ, z) is one local maximum D (λ) at the wavelength λ _p (z).
_p (z), z), and 2 near the peak wavelength λ _p (z).
It is approximated by the following function. It should be noted that although shown as λ ₀ = λ _p (z) in FIG. 1, they do not necessarily have to match, and a predetermined wavelength difference Λ is allowed. The peak wavelength λ _p (z) is a function of the propagation distance z, and may change in the propagation direction of the waveguide-type optical nonlinear medium. These two items will be described later.

In the range of the propagation distance z where the maximum value is positive, the dispersion value D (λ, z) has two zero dispersion wavelengths λ ₁ (z) and λ ₂ (z) (λ ₁ (z) <Λ ₂ (z)). That is, the dispersion value D (λ, z) is 0 [ps / nm / km] or more when the wavelength of the white pulse light is λ ₁ (z) or more and λ ₂ (z) or less, and is λ ₁ (z) or less. It becomes 0 [ps / nm / km] or less at λ ₂ (z) or more. The zero dispersion wavelengths λ ₁ (z) and λ ₂ (z) approach as the dispersion value D (λ ₀ , z) decreases.

As described above, the wavelength-dispersion value characteristic of the waveguide type optical nonlinear medium used for the white pulse light source of the present invention is as follows.
Dispersion at the center wavelength lambda ₀ of the excitation pulse light value D (λ _0,
z) decreases from a positive value in the direction of propagation of the excitation pulse light, and the dispersion value D (λ, z) has a maximum value D (λ _p (z), z), and this maximum value is positive. It has two zero dispersion wavelengths λ ₁ (z) and λ ₂ (z) within a range of a propagation distance z.

This wavelength-dispersion value characteristic is shown, for example, in FIG.
This can be realized by an optical waveguide having a double clad, triple clad, or quadruple clad refractive index distribution as shown in (b) and (c). Here, the double clad is the core, the first
The average refractive index of each of the cladding and the second cladding is n
_Assuming that ₀ , n ₁ , and n ₂ , the relationship of n ₀ > n ₂ > n ₁ is set. In the triple clad, if the average refractive indices of the core, the first clad, the second clad, and the third clad are n ₀ , n ₁ , n ₂ , and n ₃ , n ₀ > n ₂ > n ₃ > It is set to satisfy the relationship of n _1. In the quadruple clad, the average refractive indices of the core, the first clad, the second clad, the third clad, and the fourth clad are respectively n ₀ , n ₁ , n ₂ ,
Assuming that n ₃ and n ₄ , a relationship of n ₀ > n ₂ > n ₄ > n ₃ > n ₁ or n ₀ > n ₂ > n ₄ > n ₃ = n ₁ is set. This refractive index distribution is known, and is described, for example, in Reference 4 (Kawakami et al., “Optical Fibers and Fiber Devices”, Baifukan, 1996) or Reference 5 (LGCohen, e).
t al., "Low-loss quadruple-clad single-mode lightgu
ides with dispersion below 2 ps / nm / km over the 1.2
8 μm-1.65 μm wavelength range ", Electron. Let
t., vol.18, p.1023, 1982).

In such an optical waveguide, the dispersion value can be changed in the longitudinal direction by changing the diameter of the core or the clad or changing the refractive index of the core or the clad.

Here, an example of the spectrum of a white pulse light obtained by injecting the excitation pulse light having the spectrum shown in FIG. 3 into the waveguide type optical nonlinear medium having the wavelength-dispersion value characteristic of FIG. ) Is shown in FIG. It can be seen that white pulse light having a wide band and high flatness can be obtained. This is because the waveguide type optical nonlinear medium satisfies the above condition.

However, only the condition (1), that is, the dispersion value decreases, but the wavelength-dispersion value characteristic is a waveguide type light having only one zero dispersion wavelength like a normal waveguide type optical nonlinear medium (FIG. 28). When a non-linear medium is used, an angular spectrum is generated only on the zero-dispersion wavelength side of the excitation light wavelength. Therefore, the spectrum does not grow symmetrically as in the case where there are two zero dispersion wavelengths, and the spectrum cannot be sufficiently flattened as shown in FIG.

On the other hand, in the case of using a waveguide type optical nonlinear medium having only two conditions, that is, the wavelength-dispersion value characteristic has two zero-dispersion wavelengths but the dispersion value is not reduced, the angle on both sides of the pumping light wavelength. Although a square spectrum is generated, the formation of the angular spectrum does not proceed in the direction of the excitation light wavelength because the yield point does not approach the excitation light wavelength. Therefore, the spectrum cannot be sufficiently flattened as shown in FIG.

[Conditions of Waveguide-Type Optical Nonlinear Medium and Excitation Pulse Light] The conditions of the waveguide-type optical nonlinear medium used in the white pulse light source of the present invention and the conditions of the incident excitation pulse light will be specifically described below.

(1) Relationship between the dispersion value D (λ ₀ , 0) at the entrance end and the dispersion value D (λ ₀ , L) at the exit end Dispersion of the waveguide type optical nonlinear medium at the center wavelength λ ₀ of the pump pulse light. The value D (λ ₀ , z) takes a positive value at the incident end of the excitation pulse light and decreases in the propagation direction. Here, the spectrum of white pulse light generated in a region where the dispersion value D (λ ₀ , z) of the waveguide type optical nonlinear medium is positive (anomalous dispersion) has a dispersion value D (λ ₀ , z) whose incident end ( variance D of z = 0)
Flattening is started from a propagation distance of 1/40 or less of (λ ₀ , 0). Therefore, the dispersion value D (λ ₀ ,
L) is a _{D (λ 0, L) <} D (λ 0, 0) / 40.

The variance D (λ ₀ , z) is negative (normal variance)
, The spectrum hardly spreads. However, the propagation distance L _{ZD where} D (λ ₀ , z) = 0 [ps / nm / km]
Numerical experiments have confirmed that the flatness of the spectrum is improved by propagating through the normal dispersion region for a while, rather than using the output end as the output end. That is, the dispersion value D of the exit end _{(z = L) (λ 0} , L) is the _{D (λ 0, L) ≦} -D (λ 0, 0) / 40.

As described above, the dispersion value D (λ ₀ , L) at the exit end (z = L) of the waveguide type optical nonlinear medium is, as shown in FIG. 6, the dispersion value at the entrance end (z = 0). It is required to be less than 1/40 of D (λ ₀ , 0), and if it is less than −1/40, the flatness of the spectrum can be further improved. Here, the dispersion value D of the exit end (lambda _0, L) is the dispersion value D of the entrance end (lambda _0, 0) of the -
FIG. 7 shows the spectrum of the white pulse light at the propagation distance of 1/20.

(2) Relationship between medium length L _ZD and spectral width of white pulse light Propagation distance (length of waveguide-type optical nonlinear medium) where D (λ ₀ , z) = 0 [ps / nm / km] _{Is the} medium length L _ZD [m].

FIG. 8 shows the relationship between the medium length L _ZD and the spectral width of the white pulse light. The spectral width shall be the wavelength range where the intensity spectrum takes a value of 0.5% (-23 dB) or more of the peak value. The same applies to the following description. As shown in the figure, the medium length L _{ZD at} which the spectral width increases rapidly
This is defined as a threshold value L _{0 of the} medium length.

[0034] (3) relationship diagram 9 of a peak intensity of medium length threshold L ₀ and the excitation pulse light indicates the threshold L ₀ of medium length relationship of the peak intensity of the excitation pulse light. The threshold value L ₀ of the medium length decreases as the peak intensity of the excitation pulse light increases. That is,
Assuming that the peak intensity of the excitation pulse light is P ₀ [W], there is a relationship of γP ₀ L ₀ = 4.6 γ = (ω ₀ n ₂ ) / (c ₀ A). Where c ₀ is the speed of light in vacuum [m / s]
, N ₂ is the nonlinear refractive index of the waveguide type optical nonlinear medium [m ² /
W] and ω ₀ (= 2πc ₀ / λ ₀ ) are the angular frequency of the pump pulse light, and A is the mode field area [m ² ] of the waveguide type optical nonlinear medium at the center wavelength λ ₀ of the pump pulse light.

Therefore, the peak intensity P of the excitation pulse light
_If the medium length L _ZD , which is the propagation distance at which ₀ and the dispersion value D (λ ₀ , z) becomes 0, is set to a value that satisfies the condition of γP ₀ L _ZD ≧ 4.6, white pulse light with a wide spectral width is generated. Can be done. For example, γP
_{When 0} = 0.00775 [1 / m], the medium length L _ZD is about 600
[m] or more.

(4) Relationship between the dispersion value D (λ ₀ , 0) and the spectral width of the white pulse light FIG. 10 shows the dispersion value D (λ ₀ , 0) and the white pulse at the input end of the waveguide type optical nonlinear medium. An example of the relationship between the spectral widths of light is shown. As shown in the figure, there is a range in the dispersion value D (λ ₀ , 0) at which a predetermined spectral width is obtained, and here, there is a lower limit (2 ps / nm / km) and an upper limit (27 ps / nm / km). You can see that.

(5) Relationship between the pulse width of the excitation pulse light and the spectrum width of the white pulse light FIG. 11 shows an example of the relationship between the pulse width of the excitation pulse light and the spectrum width of the white pulse light. As shown in the figure, there is a range in the pulse width (full width at half maximum) of the excitation pulse light in which a predetermined spectrum width is obtained, and it can be seen that there is a lower limit (2 ps) and an upper limit (8 ps).

FIG. 12 shows an example of the relationship between the pulse width of the excitation pulse light and the spectrum width of the white pulse light when the dispersion value D (λ ₀ , 0) is used as a parameter. As shown in the figure, when the dispersion value D (λ ₀ , 0) is set large, the spectrum width can be widened by increasing the pulse width (full width at half maximum) of the excitation pulse light.

Here, the dispersion value D (λ ₀ , 0) at the incident end of the waveguide type optical nonlinear medium and the full width at half maximum Δ of the excitation pulse light
If t is in a relationship of 0.05Δt ² ≦ D (λ ₀ , 0) ≦ 3.0Δt ² , the peak intensity P ₀ of the excitation pulse light and the medium length L _ZD are values satisfying the condition of γP ₀ L _ZD ≧ 4.6. Should be set to. For example, Δt
= 4 [ps], γP ₀ = 0.00775 [1 / m], 2
[ps / nm / km] ≦ D (λ 0, 0) ≦ 27 [ps / nm / km], L ZD ≧ 60
0 [m].

^{Further, 0.2 Δt 2 ≦ D (λ} 0, 0) if ≦ 1.2Δt ^2, the peak intensity P ₀ and the medium length L _ZD of the excitation pulsed light value satisfying the γP ₀ L _ZD ≧ 3.5 conditions Should be set to.

(6) The medium length L _ZD and the dispersion value D (λ ₀ ,
Relationship of 0) The condition of the waveguide type optical nonlinear medium necessary for the generation of the white pulse light is as follows: the medium length Ln = γP ₀ standardized by the peak intensity P ₀ [W] and the full width at half maximum Δt [sec] of the excitation pulse light. L _ZD and the entrance end of the dispersion value _{Dn = D (λ 0, 0} ) / is represented by a universal equation using (γP ₀ Δt ^2), the Ln ≧ a / Dn + b + cDn + dDn 2. However, a = 0.30 × 10 ²⁰ , b = 2.9, c = −0.
17 × 10 ^-20 and d = 0.40 × 10 ^-40 .

For example, the peak intensity P _{0 of the} excitation pulse light
Is 0.5 [W] and the full width at half maximum [Delta] t is 4 [ps], the medium length L
Spectral width of the output light of _ZD and the dispersion value D of the entrance end (lambda _0, 0) for the waveguide type optical nonlinear medium is represented as contour map of Figure 13. Here, the interval between contour lines corresponds to a spectral width of 25 [nm]. At this time, the medium length L _ZD of the waveguide type optical nonlinear medium necessary for generating white pulse light is as follows: L _ZD ≧ 480 / D (λ ₀ , 0) + 374−1.8D (λ ₀ , 0) + 0.34D
(λ ₀ , 0) ² .

Further, many materials (typically, fused silica) used for a waveguide type optical nonlinear medium are used.
ca)) causes an induced Raman effect. Similarly, the contour map of the spectral width of the output light from the waveguide type optical nonlinear medium is obtained when the peak intensity P ₀ and the full width at half maximum Δt of the excitation pulse light are 0.5 [W] and 4 [ps]. It is represented as 14. At this time, the medium length L _ZD of the waveguide type optical nonlinear medium necessary for generating white pulse light is L _ZD ≧ 426 / D (λ ₀ , 0) + 308−1.7D (λ ₀ , 0) + 0.18D
(λ ₀ , 0) ² .

The contour map of the spectrum width in FIG.
13 shows that the threshold value L _{0 of the} medium length with respect to the spectrum width of the white pulse light has become smaller than that of FIG. Conditions of the waveguide type optical nonlinear medium, the universal formula Ln ≧ a / Dn + b + cDn + dDn 2 ^{above, a = 0.26 × 10 20,} b = 2.3, c = -0.16 × 10
^-20 and d = 0.21 × 10 ^-40 .

As described above, in order to generate white pulse light, the dispersion value D at the incident end of the waveguide type optical nonlinear medium is determined.
(λ ₀ , 0), the peak intensity P ₀ of the incident excitation pulse light, the full width at half maximum Δt, and the medium length L _ZD satisfying the dispersion value D (λ ₀ , z) = 0, and there are ranges to be satisfied. Each is interrelated.

[Second Wavelength-Dispersion Value Characteristics of Waveguide-Type Optical Nonlinear Medium] FIG. 15 shows a second wavelength-dispersion value characteristics of the waveguide-type optical nonlinear medium used in the white pulse light source of the present invention. .

The second characteristic of the wavelength-dispersion value characteristic is that the center wavelength λ ₀ of the pump pulse light does not coincide with the peak wavelength λ _p (z), and λ _p (z) −Λ ≦ λ _The wavelength difference 規定 defined by ₀ ≦ λ _p (z) + Λ is allowed.

Here, Λ = 30 [nm], 40 [nm], 50
 Spectrum of white pulse light generated when [nm]
FIGS. 16 (a), (b), and (c). Center wave of excitation pulse light
Long λ ₀Is the peak wavelength λ_p(z) from 30 [nm] or 40 [n
m] When detuning, the spectral symmetry of the white pulse light
Is slightly worse, but the flatness is almost satisfactory.
Can be On the other hand, when the detuning reaches 50 [nm], a flat spectrum
You won't get a creature. This gives two zero-dispersion wavelengths
Cannot take advantage of the wavelength-dispersion value property of having
It is similar to the white pulse light source of Document 2 shown in FIG.
It is thought to be in order.

[Third Wavelength-Dispersion Value Characteristics of Waveguide-Type Optical Nonlinear Medium] In the above description, it is assumed that the peak wavelength λ _p (z) is constant in the propagation direction of the waveguide-type optical nonlinear medium. It does not have to be constant. For example, as shown in FIG. 17, the peak wavelength λ _p (z) may change in the propagation direction of the waveguide-type optical nonlinear medium. Such a third wavelength-dispersion value characteristic occurs, for example, when only the diameters of the core and the clad are changed in the longitudinal direction of the optical waveguide. This third wavelength-
FIG. 18 shows a spectrum of white pulse light generated by a white pulse light source having a dispersion value characteristic. It can be seen that white pulse light having a wide band and high flatness can be obtained as in the case of having the first and second wavelength-dispersion value characteristics.

[Second Embodiment] As described above, the generation of white pulse light always goes through a spectrum spreading process by soliton compression. In order to cause this soliton compression, it is not always necessary to use a waveguide type optical nonlinear medium having two zero dispersion wavelengths. That is, as shown in FIG. 19, two kinds of waveguide type optical nonlinear media are connected in cascade,
The first stage (0 ≦ z ≦ L ₁ ) realizes spectrum broadening using a waveguide type optical nonlinear medium that causes soliton compression, and the second stage (L ₁ ≦ z ≦ L) achieves waveguide type optical nonlinearity satisfying the above conditions. A rectangular or flat spectrum may be realized using a medium. FIG. 20 shows an example of the spectrum of the white pulse light generated by this configuration.

[Third Embodiment] In some cases, the waveguide type optical nonlinear medium is formed into a portion that contributes to the generation and growth of white pulse light and a portion that does not contribute to it during manufacturing.
That is, as shown in FIG. 21, a portion contributing to the generation and growth of white pulse light may be formed in the range of L ₁ ≦ z ≦ L ₂ . In this case, the excitation pulse light incident, to satisfy the occurrence condition of the white pulse light at the position of z = L _1, generation of the white pulse light is possible.

[Fourth Embodiment] As a waveguide type optical nonlinear medium, a waveguide type optical nonlinear medium having a gain characteristic is used. As a result, even if a pump-type optical nonlinear medium with no gain characteristic is used, the intensity of the excitation pulse light is so small that white pulse light cannot be generated, or even if a waveguide-type optical nonlinear medium with a short length is used. Light can be generated. FIG. 22 shows the relationship between the medium length L _ZD of a waveguide type optical nonlinear medium having gain characteristics and the spectral width of white pulse light. The open circle indicates that the gain of the waveguide type optical nonlinear medium is 0.01.
[dB / m], and a black circle indicates a case of 0.05 [dB / m]. In addition, the peak intensity, pulse width,
And dispersion value D at the input end of a waveguide-type optical nonlinear medium
(λ ₀ , 0) was the same condition as in the case of the waveguide type optical nonlinear medium having no gain characteristic shown in FIG.

As can be seen from FIG. 8, when the waveguide type optical nonlinear medium has gain characteristics, the threshold value L _{0 of the} medium length at which the spectral width sharply increases becomes short. Further, the threshold value L _{0 of the} medium length and the peak intensity of the excitation pulse light have the relationship shown in FIG. An equivalent effect can be obtained. That is, in a waveguide type optical nonlinear medium having a gain characteristic, it is possible to generate white pulse light even when a low intensity excitation pulse light or a waveguide type optical nonlinear medium having a short length is used.

FIG. 23 shows the fourth embodiment of the white pulse light source according to the present invention.
1 shows the configuration of the embodiment. The white pulse light source of the present embodiment includes an excitation pulse light source and a waveguide type optical nonlinear medium having gain characteristics, for example, a semiconductor optical amplifier or the like.

[Fifth Embodiment] FIG. 24 shows the configuration of a fifth embodiment of the white pulse light source of the present invention. The white pulse light source of the present embodiment is an excitation pulse light source, a rare earth-doped waveguide type optical nonlinear medium, and an excitation light source that generates excitation light for generating a population inversion in the rare earth doped waveguide optical nonlinear medium. An optical multiplexer for multiplexing the excitation light and the excitation pulse light and inputting the multiplexed light to the rare earth-doped waveguide type optical nonlinear medium.

[Sixth Embodiment] FIG. 25 shows the structure of a white pulse light source according to a sixth embodiment of the present invention. The white pulse light source of the present embodiment is an excitation pulse light source, a rare earth-doped waveguide type optical nonlinear medium, and an excitation light source that generates excitation light for generating a population inversion in the rare earth doped waveguide optical nonlinear medium. An optical multiplexer for inputting pumping light from the output end side of the rare-earth-doped waveguide type optical nonlinear medium, and an optical isolator for preventing pumping light passing through the rare-earth-doped waveguide type optical nonlinear medium from entering the pumping pulse light source. It consists of.

The fifth embodiment (forward excitation configuration) and the sixth embodiment (backward excitation configuration) may be used in combination. Further, a waveguide-type optical nonlinear medium having Raman gain characteristics is used in place of the rare-earth-doped waveguide-type optical nonlinear medium, and pump light for generating Raman gain is input to the waveguide-type optical nonlinear medium. Is also good.

Further, in the configuration of the fourth to sixth embodiments, before or after the waveguide type optical nonlinear medium,
By providing a means for blocking the reflected light returning to the excitation light pulse light source or the waveguide type optical nonlinear medium, the amplification operation can be stabilized.

[Other Embodiments] In each of the embodiments described above, the polarization of the excitation pulse light is kept stable by imparting the polarization maintaining property to the waveguide type optical nonlinear medium, and the polarization of the excitation light is stabilized. The generated white pulse light can be generated.

In each of the embodiments described above, an optical amplifier for amplifying the excitation pulse light may be provided in front of the incident end of the waveguide type optical nonlinear medium. Thus, even when an excitation pulse light source having a small output light intensity is used, the condition for generating white pulse light can be satisfied.

The peak in the excitation pulse light wavelength of the white pulse light spectrum corresponds to the tail of the excitation pulse light that has not been converted to the white pulse light. Therefore, in each of the embodiments described above, a wavelength filter that blocks the wavelength component of the excitation pulse light may be provided after the emission end of the waveguide-type optical nonlinear medium. This makes it possible to remove or suppress a peak in the excitation pulse light wavelength having a light intensity higher than the light intensity of the white pulse light per unit wavelength.

[0062]

As described above, the white pallets of the present invention
Source is the center wavelength λ of the excitation pulse light. ₀Waveguide in
Value of the nonlinear optical nonlinear medium in the propagation direction of the excitation pulse light
Along the line from the positive value to around 0 [ps / nm / km].
Have a maximum value, and within a range of the propagation distance where the maximum value is positive.
Center wavelength λ of excitation pulse light₀Zero-dispersion wavelength on both sides of
To be done. As a result, the soliton compression
Spectral spreading process and solitons change to dispersive waves
The process of rectangularizing and flattening the spectrum
Can wake up. Therefore, high flatness and
It is possible to generate a white pulse light having a characteristic.

Further, by imparting a gain characteristic to the waveguide-type optical nonlinear medium, high flatness and symmetry can be obtained even when excitation pulse light having a smaller intensity or a shorter waveguide-type optical nonlinear medium is used. White pulse light can be generated.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first wavelength-dispersion value characteristic of a waveguide type optical nonlinear medium used for a white pulse light source of the present invention.

FIG. 2 is a diagram showing a refractive index distribution of a waveguide type optical nonlinear medium.

FIG. 3 is a diagram showing a spectrum of excitation pulse light incident on a white pulse light source of the present invention.

FIG. 4 is a diagram showing an example of a spectrum of white pulse light generated by a white pulse light source having a first wavelength-dispersion value characteristic.

FIG. 5 is a diagram illustrating an example of an output spectrum in a case where a dispersion value does not decrease with a propagation distance in a waveguide-type optical nonlinear medium having two zero-dispersion wavelengths.

FIG. 6 is a view for explaining a dispersion value D (λ ₀ , L) at an emission end of a waveguide type optical nonlinear medium.

FIG. 7 is a diagram showing a spectrum of white pulse light at a propagation distance at which the dispersion value at the emission end is -1/20 of the dispersion value at the incidence end.

FIG. 8 is a diagram showing a relationship between a medium length L _ZD and a spectral width of white pulse light.

FIG. 9 is a diagram showing a relationship between a threshold value L ₀ of a medium length and a peak intensity of excitation pulse light.

FIG. 10 is a diagram showing an example of the relationship between the dispersion value D (λ ₀ , 0) at the incident end of a waveguide-type optical nonlinear medium and the spectral width of white pulse light.

FIG. 11 is a diagram showing an example of the relationship between the pulse width of excitation pulse light and the spectrum width of white pulse light.

FIG. 12 is a diagram showing an example of the relationship between the pulse width of excitation pulse light and the spectral width of white pulse light when a dispersion value D (λ ₀ , 0) is used as a parameter.

FIG. 13 is a diagram showing an example of a relationship between a medium length L _ZD and a dispersion value D (λ ₀ , 0) of a light output of a waveguide type optical nonlinear medium with respect to a dispersion value D (λ _0,0) at an incident end.

FIG. 14 is a diagram showing an example of the relationship between the medium length L _ZD and the dispersion value D (λ ₀ , 0) at the input end of the waveguide type optical nonlinear medium (with Raman gain characteristics) output spectrum width.

FIG. 15 is a view showing a second wavelength-dispersion value characteristic of the waveguide type optical nonlinear medium used in the white pulse light source of the present invention.

FIG. 16 is a diagram illustrating an example of a spectrum of white pulse light generated by a white pulse light source having a second wavelength-dispersion value characteristic.

FIG. 17 is a diagram showing a third wavelength-dispersion value characteristic of the waveguide type optical nonlinear medium used in the white pulse light source of the present invention.

FIG. 18 is a diagram showing an example of a spectrum of white pulse light generated by a white pulse light source having a third wavelength-dispersion value characteristic.

FIG. 19 is a diagram showing a configuration of a second embodiment of the white pulse light source of the present invention.

FIG. 20 is a diagram illustrating an example of a spectrum of white pulse light generated by the white pulse light source according to the second embodiment.

FIG. 21 is a diagram showing a configuration of a third embodiment of the white pulse light source according to the present invention.

FIG. 22 is a diagram showing the relationship between the medium length L _ZD of a waveguide-type optical nonlinear medium having gain characteristics and the spectral width of white pulse light.

FIG. 23 is a diagram showing a configuration of a fourth embodiment of the white pulse light source of the present invention.

FIG. 24 is a diagram showing a configuration of a fifth embodiment of the white pulse light source of the present invention.

FIG. 25 is a diagram showing a configuration of a sixth embodiment of the white pulse light source of the present invention.

FIG. 26 is a diagram showing a configuration of a conventional white pulse light source.

FIG. 27 is a diagram showing an example of the spectrum of white pulse light generated by the white pulse light source of Document 1.

FIG. 28 is a diagram showing a wavelength-dispersion value characteristic of a waveguide-type optical nonlinear medium used in a white pulse light source of Document 2.

FIG. 29 is a diagram showing an example of the spectrum of white pulse light generated by the white pulse light source of Document 2.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Masatoshi Saruwatari 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (23)

[Claims] _1. An excitation pulse light source that generates an excitation pulse light having a center wavelength λ ₀ , and a waveguide-type optical nonlinear medium having a length L [m] that receives the excitation pulse light and generates a white pulse light. The dispersion value D (λ ₀ , z) [ps / nm / km] of the waveguide-type optical nonlinear medium at the center wavelength λ ₀ of the pump pulse light is a positive value at the incident end (z = 0). In a white pulse light source having a characteristic of decreasing in the propagation direction of the excitation pulse light, the waveguide-type optical nonlinear medium may have a range L ₁ ≦ z ≦ L (where 0 ≦ L ₁ <L), the dispersion value D (λ, z) becomes the maximum value D at the peak wavelength λ _p (z).
(λ _p (z), z), and two zeros at which the dispersion value D (λ, z) becomes 0 [ps / nm / km] within the range of the propagation distance z where the maximum value is positive. A white pulse light source having a configuration having dispersion wavelengths λ ₁ (z) and λ ₂ (z). 2. The white pulse light source according to claim 1, wherein the two zero-dispersion wavelengths λ ₁ (z) and λ ₂ are reduced as the dispersion value D (λ, z) of the waveguide-type optical nonlinear medium decreases. A white pulse light source characterized in that (z) approaches. 3. The white pulse light source according to claim 1, wherein the center wavelength λ ₀ and the peak wavelength λ _p (z) of the excitation pulse light are λ _p (z) −Λ ≦ λ ₀ ≦ λ _p (z) A white pulse light source characterized by allowing a wavelength difference 規定 defined by a relationship of + Λ. 4. The white pulse light source according to claim 3, wherein a wavelength difference の between the center wavelength λ ₀ and the peak wavelength λ _p (z) of the excitation pulse light is less than 50 [nm]. White pulse light source. 5. The white pulse light source according to claim 1, wherein the dispersion value D (λ ₀ , 0) at the incident end (z = 0) of the waveguide type optical nonlinear medium at the center wavelength λ ₀ of the excitation pulse light is obtained. And a dispersion value D (λ ₀ , L) at the exit end (z = L) is set to satisfy the following relationship: D (λ ₀ , L) <D (λ ₀ , 0) / 40. . 6. The white pulse light source according to claim 1, wherein a dispersion value D (λ ₀ , 0) at an incident end (z = 0) of the waveguide type optical nonlinear medium at a center wavelength λ ₀ of the excitation pulse light. white pulses, characterized in that the dispersion value D of the exit end _{(z = L) (λ 0} , L) is set to _{D (λ 0, L) ≦} -D (λ 0, 0) / 40 relationship light source. 7. The white pulse light source according to claim 1, wherein a dispersion value D (λ ₀ , 0) [ps / nm / km] of the incident end of the waveguide type optical nonlinear medium at the center wavelength λ ₀ of the excitation pulse light. ] and white pulse light source, wherein a full width at half maximum Δt of the excitation pulse light [ps] is set to _{^{0.05Δt 2 ≦ D (λ 0,}} 0) of ≦ 3.0Δt ² relationship. 8. The white pulse light source according to claim 7,
And the peak intensity of the excitation pulse light is P₀[W], excitation pulse light
Center wavelength λ₀Value D of the waveguide type optical nonlinear medium at
(λ₀, z) is 0 [ps / nm / km] as L _ZD [m]
 , Speed of light in vacuum₀[m / s], waveguide type optical nonlinear medium
The quality nonlinear index is n_Two [m^Two/ W], the angle of the excitation pulse light
Frequency ω₀(= 2πc₀/ Λ₀), Center wave of excitation pulse light
Long λ₀Feel of a Waveguide-Type Optically Nonlinear Medium in GaN
Area is A [m^Two], ΓP₀L_ZD≥ 4.6 γ = (ω₀n_Two) / (C₀A) A white pulse light source characterized by the following relationship: 9. The white pulse light source according to claim 1, wherein a dispersion value D (λ ₀ , 0) [ps / nm / km] of the incident end of the waveguide type optical nonlinear medium at the center wavelength λ ₀ of the excitation pulse light. ] and white pulse light source, wherein a full width at half maximum Δt of the excitation pulse light [ps] is set to _{^{0.1Δt 2 ≦ D (λ 0,}} 0) of ≦ 1.7Δt ² relationship. 10. The white pulse light source according to claim 9,
And the peak intensity of the excitation pulse light is P₀[W], excitation pulse light
Center wavelength λ₀Value D of the waveguide type optical nonlinear medium at
(λ₀, z) is 0 [ps / nm / km] as L _ZD [m]
 , Speed of light in vacuum₀[m / s], waveguide type optical nonlinear medium
The quality nonlinear index is n_Two [m^Two/ W], the angle of the excitation pulse light
Frequency ω₀(= 2πc₀/ Λ₀), Center wave of excitation pulse light
Long λ₀Feel of a Waveguide-Type Optically Nonlinear Medium in GaN
Area is A [m^Two], ΓP₀L_ZD≧ 3.4 γ = (ω₀n_Two) / (C₀A) A white pulse light source characterized by the following relationship: 11. The white pulse light source according to claim 1, wherein the excitation pulse light has a peak intensity P ₀ [W] and a full width at half maximum Δt.
[sec], the dispersion value D (λ ₀ , 0) [sec / m ² ] and the dispersion value D (λ ₀ , z) of the incident end of the waveguide-type optical nonlinear medium at the center wavelength λ ₀ of the pump pulse light are 0. in become propagation distance L _ZD variance value Dn of normalized medium length Ln and the incident end obtained from the [m] is _{Ln = γP 0 L ZD Dn =} D (λ 0, 0) / (γP 0 Δt 2) Γ is the speed of light c ₀ [m / s] in vacuum, the nonlinear refractive index n ₂ [m ² / W] of the waveguide type optical nonlinear medium, the angular frequency ω ₀ (= 2πc ₀ / λ ₀ ) of the excitation pulse light. ), When γ = (ω ₀ n ₂ ) / (c ₀ A) using the mode field area A [m ² ] of the waveguide type optical nonlinear medium at the center wavelength λ ₀ of the pump pulse light, satisfy the relationship ln ≧ a / Dn + b + cDn + dDn 2, a = 0.30 × 10 20, b = 2.9, c = -0.
A white pulse light source characterized by 17 × 10 ^-20 and d = 0.40 × 10 ^-40 . 12. The white pulse light source according to claim 1, wherein a waveguide-type optical nonlinear medium having Raman gain characteristics is used as the waveguide-type optical nonlinear medium, and the peak intensity P ₀ [W] of the excitation pulse light and Full width at half maximum Δt
[sec], the dispersion value D (λ ₀ , 0) [sec / m ² ] and the dispersion value D (λ ₀ , z) of the incident end of the waveguide-type optical nonlinear medium at the center wavelength λ ₀ of the pump pulse light are 0. in become propagation distance L _ZD variance value Dn of normalized medium length Ln and the incident end obtained from the [m] is _{Ln = γP 0 L ZD Dn =} D (λ 0, 0) / (γP 0 Δt 2) Γ is the speed of light c ₀ [m / s] in vacuum, the nonlinear refractive index n ₂ [m ² / W] of the waveguide type optical nonlinear medium, the angular frequency ω ₀ (= 2πc ₀ / λ ₀ ) of the excitation pulse light. ), When γ = (ω ₀ n ₂ ) / (c ₀ A) using the mode field area A [m ² ] of the waveguide type optical nonlinear medium at the center wavelength λ ₀ of the pump pulse light, satisfy the relationship ln ≧ a / Dn + b + cDn + dDn 2, a = 0.26 × 10 20, b = 2.3, c = -0.
A white pulse light source characterized by 16 × 10 ^-20 and d = 0.21 × 10 ^-40 . 13. The white pulse light source according to claim 1, wherein the waveguide type optical nonlinear medium has a double (W) clad structure,
A white pulse light source having a double clad structure or a quadruple clad structure, wherein a dispersion value is changed by changing a diameter or a refractive index of a core or a clad in a longitudinal direction thereof. 14. The white pulse light source according to claim 13, wherein the waveguide type optical nonlinear medium has a double clad structure, and the average refractive index of each of the core, the first clad, and the second clad is n ₀ , When n _1, n _2, white pulse light source, characterized in that set in the relation of _{n 0> n 2> n 1} . 15. The white pulse light source according to claim 13, wherein the waveguide type optical nonlinear medium has a triple clad structure, and an average refractive index of each of the core, the first clad, the second clad, and the third clad. Where n ₀ , n ₁ , n ₂ , and n ₃ , n ₀ > n ₂ > n ₃ > n ₁ . 16. The white pulse light source according to claim 13, wherein the waveguide type optical nonlinear medium has a quadruple clad structure, and includes a core, a first clad, a second clad, a third clad, and a fourth clad.
The average refractive index of each of the claddings is n ₀ , n ₁ ,
When n ₂ , n ₃ , and n ₄ , the relationship is set such that n ₀ > n ₂ > n ₄ > n ₃ > n ₁ or n ₀ > n ₂ > n ₄ > n ₃ = n _1. White pulse light source. 17. The white pulse light source according to claim 1, wherein the waveguide type optical nonlinear medium has a polarization maintaining property. 18. The white pulse light source according to claim 1, wherein a waveguide type optical nonlinear medium having a gain characteristic is used as the waveguide type optical nonlinear medium. 19. The white pulse light source according to claim 1, wherein a waveguide-type optical nonlinear medium to which a rare earth element is added is used as the waveguide-type optical nonlinear medium, and a population inversion is generated in the waveguide-type optical nonlinear medium. A white pulse light source comprising: an excitation light source for generating excitation light for causing the excitation light; and excitation light input means for inputting the excitation light into the waveguide type optical nonlinear medium. 20. The white light source according to claim 1, wherein a waveguide type optical nonlinear medium having Raman gain characteristics is used as the waveguide type optical nonlinear medium, and a Raman gain is generated in the waveguide type optical nonlinear medium. A white pulse light source comprising: an excitation light source for generating excitation light for causing the excitation light; and excitation light input means for inputting the excitation light into the waveguide type optical nonlinear medium. 21. The white pulse light source according to any one of claims 18 to 20, further comprising means for blocking reflected return light input to the waveguide type optical nonlinear medium or the excitation light pulse light source. Characteristic white pulse light source. 22. The white pulse light source according to claim 1, further comprising an optical amplifier for amplifying the excitation pulse light incident on the waveguide type optical nonlinear medium. 23. The white pulse light source according to claim 1, further comprising a wavelength filter that blocks a wavelength component of the excitation pulse light, after the emission end of the waveguide-type optical nonlinear medium.