JP2004062028A - Dispersion decreasing optical fiber and ultrawideband optical light source using optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive dispersion decreasing optical fiber which can be manufactured easily and with high performance and an ultrawideband optical light source using the dispersion decreasing optical fiber. <P>SOLUTION: The dispersion decreasing optical fiber 4 which generates ultrawideband light by dispersing an incident optical signal to a prescribed band is constituted as one in which a plurality of optical fibers F<SB>1</SB>to F<SB>10</SB>having prescribed dispersion characteristics are connected in series. An ultrawideband optical light source 1 is provided with the dispersion decreasing optical fiber 4 as a means for generating the ultrawideband light. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a dispersion-reduced optical fiber used for generating ultra-wideband light, so-called supercontinuum light, and an ultra-wideband light source using the optical fiber.
[0002]
[Prior art]
Supercontinuum light is expected to be used as a simple large-capacity OTDM / WDM light source. Conventionally, the dispersion-reducing optical fiber used to generate the supercontinuum light has been constituted by a series of single optical fibers. This conventional dispersion-reduced optical fiber is configured such that an optical signal of a predetermined single wavelength having a high peak value incident from an input end is continuously and gradually dispersed until reaching an output end. As shown in FIG. 10, this dispersion-reduced optical fiber has the characteristic that the dispersion value decreases as the center wavelength becomes the peak and the distance from the center wavelength increases, that is, it becomes convex in the wavelength direction. As shown in FIG. 12, the variance gradually and continuously decreased in the transmission distance direction. Here, FIG. 10 is a graph showing the dispersion characteristics of a conventional dispersion-reduced optical fiber in which the horizontal axis shows the wavelength near the center wavelength and the vertical axis shows the dispersion value. In FIG. 11A, the horizontal axis represents the longitudinal distance of the dispersion-reduced optical fiber, where the input end is 0 m and the output end is 500 m, and the vertical axis is the dispersion value (unit: ps / nm / km). (It is the same as the unit ps / (nm · km) in the JIS standard), and the dispersion characteristic in the longitudinal direction from the input end to the output end of the conventional dispersion-reduced optical fiber is described. Is shown. FIG. 11B is a graph showing the relationship between the wavelength and the light intensity of the ultra-wide band light generated by the conventional dispersion reducing optical fiber. In other words, the obtained ultra-wide band light (super continuum light) has an umbilical light on the short wavelength side and the long wavelength side centered on the center wavelength (the center wavelength of the incident light, in this case, 1.55 μm). In the vicinity of the center wavelength, it has a relatively large light intensity in a bandwidth exceeding 100 nm (0.1 μm). FIG. 12 schematically shows how the dispersion value in the longitudinal direction of a conventional dispersion decreasing optical fiber that continuously disperses gradually changes. That is, FIG. 12 shows a dispersion-reduced optical fiber having a total length of 500 m, the input end of which is set to 0 m, the output end is set to 500 m, and the dispersion value at that position increases from the input end to the output end. It is shown that the variance value is lower than that of.
[0003]
[Problems to be solved by the invention]
In the case of this conventional dispersion-reduced optical fiber, for example, by gradually changing the ratio between the clad diameter and the core diameter of the optical fiber continuously, the dispersion value is gradually changed continuously in a single optical fiber. To go. In this case, for example, the drawing speed of the optical fiber is continuously changed gradually to manufacture the dispersion-reduced optical fiber. In such a manufacturing method, even if the drawing speed is controlled and adjusted, the speed can be adjusted with high accuracy by various conditions that affect the drawing forming delicately, such as a change in temperature during drawing or mechanical vibration. It is extremely difficult to do. In addition, there is a method of manufacturing by adjusting the content ratio of the additive to the optical fiber continuously and gradually in the longitudinal direction of the optical fiber. It is extremely difficult to adjust the content ratio of additives. Therefore, due to this difficulty, there is a problem in that the rate of producing non-defective products that can be used as dispersion-reduced optical fibers is extremely small, and the manufacturing cost increases.
[0004]
Therefore, since the conventional dispersion-reduced optical fiber is expensive, an ultra-wideband light source using the dispersion-reduced optical fiber is also expensive.
[0005]
An object of the present invention is to solve the problem of providing an inexpensive dispersion-reduced optical fiber that can be manufactured easily and with high performance, and an ultra-wideband light source using the dispersion-reduced optical fiber.
[0006]
[Means for Solving the Problems]
(1) A dispersion-reducing optical fiber according to claim 1 of the present invention is a dispersion-reducing optical fiber that generates an ultra-wide band light by dispersing an incident optical signal into a predetermined band, and has a plurality of dispersion characteristics. Are connected in series.
[0007]
Here, the ultra-wide band light is a so-called super continuum light, which is a light in which the incident excitation light is dispersed and its spectrum is spread. The incident excitation light is usually single-wavelength light. The widened bandwidth is preferably 100 nm or more as a wavelength. In order to generate this ultra-wide band light, the dispersion-reduced optical fiber has a dispersion function of broadening the spectrum of the incident pump light, and the light intensity at the center wavelength of the pump light is increased due to the dispersion. Decrease and increase the intensity of other dispersed light. The fact that a plurality of optical fibers are connected in series means that the optical fibers are connected in a line in the longitudinal direction of the fiber so as to be connected continuously from the incident end where the incident light enters to the exit end. That means.
[0008]
According to the invention according to claim 1 of the present invention, even if a plurality of optical fibers having a predetermined dispersion characteristic whose dispersion characteristic does not change in the longitudinal direction of the optical fiber are connected in series, even if they are connected in series, Ultra wide band light can be generated by dispersing the incident light for each optical fiber up to the emission end. Each optical fiber can be manufactured much more easily than an optical fiber whose dispersion characteristics change by keeping the dispersion characteristics unchanged in the longitudinal direction, so that it can be configured as an inexpensive optical fiber.
[0009]
In the dispersion reducing optical fiber according to the present invention, preferably, the plurality of optical fibers connected in series is a combination of optical fibers having different dispersion characteristics. In this case, since the dispersion-reduced optical fiber is formed by adopting optical fibers having different dispersion characteristics so as to further disperse according to the dispersion state, a dispersion-reduced optical fiber in which an incident optical signal is appropriately dispersed is obtained. be able to.
[0010]
In the dispersion-reducing optical fiber according to the present invention, preferably, the band of the plurality of optical fibers connected in series is dispersed stepwise each time an incident optical signal passes through each optical fiber. In this case, the band of the incident optical signal is dispersed in a stepwise manner, thereby easily generating the desired ultra-wideband light similar to the conventional one that gradually widens the band of the optical signal. Although it is possible to employ an optical fiber that can be easily manufactured as the dispersion-reduced optical fiber, it can be configured at low cost.
[0011]
The dispersion-reduced optical fiber according to the present invention is preferably such that three or more optical fibers are connected in series, and the first optical fiber on the incident side of the optical fibers is longer in length than the other optical fibers. The length in the direction is large, and the difference between the respective dispersion characteristics of the first optical fiber and the next optical fiber is the difference between any optical fibers connected on the output side of the next optical fiber. The difference is set larger than the difference between the dispersion characteristics. In this case, a desired bandwidth is sufficiently secured by rapidly dispersing the incident optical signal at an early stage of dispersion, and the subsequent dispersed optical signal is further dispersed. That is, it is possible to obtain an ultra-wide band light that is more similar to an ultra-wide band light obtained by continuously and gradually widening the band of an optical signal as in the related art.
[0012]
The dispersion-reducing optical fiber according to the present invention is preferably such that the absolute value of the dispersion value is 0.1 ps / (nm · km). Here, that the absolute value of the dispersion value is less than 0.1 ps / (nm · km) means that the dispersion value is a, and −0.1 <a <0.1 (ps / (nm · km)) Means that the variance value a satisfies the following condition, that is, | a | <0.1 (ps / (nm · km)). In this case, it is most preferable that an optical fiber having a dispersion value of 0 ps / (nm · km) is used in the final stage on the emission side. In this case, the dispersed spectrum has a spectrum bandwidth with a certain light intensity.
[0013]
In the dispersion reducing optical fiber according to the present invention, preferably, the three optical fibers having the predetermined dispersion characteristics are connected in series, and the dispersion of the optical signal is reduced in three stages. In this case, since the number of optical fibers to be connected is small, the connecting process can be simplified, but the ultra-wide band of the optical signal can be sufficiently achieved.
[0014]
(2) An ultra-wide band light source according to the present invention is characterized in that the dispersion-reducing optical fiber according to the present invention is provided as a means for generating ultra-wide band light.
[0015]
According to the ultra-wideband light source according to the present invention, the ultra-wideband light is generated by using a dispersion-reducing optical fiber that has a predetermined dispersion characteristic and is manufactured using an optical fiber that can be manufactured at low cost. Therefore, the light source can be configured at a low cost as an ultra-wide band light source. As a result, the super-band light source can be employed with high versatility in various devices using ultra-wide band light.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0017]
FIG. 1 is an explanatory diagram schematically showing an example of an ultra-wide band light source.
[0018]
Referring to FIG. 1, an ultra-wide band light source 1 includes an excitation light pulse light source 2 that generates excitation light as pulse light, and an amplification unit that amplifies an optical signal of the excitation light emitted from the excitation light pulse light source 2. 3 (EDFA) and a so-called SC fiber (supercontinuum) for injecting an optical signal of a predetermined wavelength emitted from the amplifying means 3 and dispersing the incident optical signal to generate supercontinuum light. The optical fiber 4 includes a dispersion-reducing optical fiber 4 which is an optical fiber for generating pulsed light, and an oscillator 5 for oscillating an electric signal incident on the excitation light pulse light source 2 to excite the pulse light. The ultra-wideband light source has at least a dispersion reducing optical fiber, and may not include the oscillator 5, the amplifying means 3, the excitation light pulse light source 2 and the like as a unit together with the dispersion reducing optical fiber.
[0019]
In this case, as shown in FIG. 2, the dispersion reducing optical fiber 4 is composed of ten optical fibers F having a predetermined dispersion characteristic and a fiber length of 50 m. ₁ ~ F ₁₀ Are connected in series. For this connection, conventionally known various connection methods such as fusion or coupler connection can be adopted. In FIG. 2, a cross on the straight line indicating the optical fiber 4 indicates that each optical fiber F ₁ ~ F ₁₀ Represents a connection point. Each optical fiber F ₁ ~ F ₁₀ As shown in FIGS. 2 and 3A, an optical fiber F having a constant dispersion characteristic with the highest dispersion value in the dispersion characteristic ₁ From the optical fiber F having the lowest constant dispersion characteristic ₁₀ The dispersion value in the dispersion characteristic becomes smaller in order up to the above. That is, each optical fiber F ₁ ~ F ₁₀ FIG. 2 shows the dispersion characteristics of the first optical fiber F as viewed from the optical signal incident side. ₁ , Middle optical fiber F ₆ , The last optical fiber F ₁₀ As illustrated, the dispersion value becomes smaller as the center wavelength becomes the peak and the further away from the center wavelength, that is, it has a characteristic of becoming convex in the wavelength direction, and the dispersion value becomes smaller for each light in the transmission distance direction. Fiber F ₁ ~ F ₁₀ Has a characteristic that becomes constant at a predetermined value every time. Further, the difference between the dispersion values of the optical fibers before and after the connection is substantially constant, as shown in FIG. Then, the final stage optical fiber F ₁₀ As for, the dispersion value of the dispersion characteristic is 0 ps / (nm · km) at the center wavelength. FIG. 3A is a graph illustrating the dispersion characteristics in the longitudinal direction of the dispersion-reducing optical fiber 4, that is, in the direction of the light passing path from the input end to the output end of the optical signal. In FIG. 3A, the horizontal axis represents the longitudinal distance of the dispersion-reducing optical fiber 4 when the input end is 0 m and the output end is 500 m, and the vertical axis is the dispersion value (unit: ps / nm / km (which is the same as the unit ps / (nm · km) in the JIS standard). FIG. 3B shows the normalized intensity of the dispersion-reduced optical fiber 4 with respect to the wavelength. In this case, the horizontal axis indicates a wavelength near the center wavelength (unit: μm), and the vertical axis indicates the normalized intensity (unit: dB) corresponding to the light intensity. The solid line in FIG. 3B shows the emission signal. The broken line indicates the incident signal. In this case, the center wavelength is 1.55 μm.
[0020]
In this embodiment, compared to the ultra-broadband light obtained with the conventional dispersion-reduced optical fiber shown in the figure, the required bandwidth is approximately 50 nm in wavelength both on the higher side and lower side than the center wavelength. It can be confirmed that the optical signal is spread in a state where it is not largely attenuated in the band, and ultra-broadband light (super continuum light) of about 100 nm is generated and emitted. That is, in this case, the signal light is dispersed in a bandwidth from the wavelength of 1.50 μm to the wavelength of 1.60 μm around the wavelength of 1.55 μm.
[0021]
Next, another embodiment and a dispersion-reduced optical fiber as a comparative example will be illustrated and described in the following (1) to (6), respectively.
[0022]
(1) FIG. 4A shows, as another embodiment, the dispersion characteristics of a dispersion-reduced optical fiber as an example in which three optical fibers having predetermined dispersion characteristics are connected in series. FIG. 4B shows the normalized intensity with respect to the wavelength of the dispersion reducing optical fiber shown in FIG. As shown in FIG. 4A, in the case of the dispersion-reduced optical fiber, of the three optical fibers connected in series, the first one provided with the incident end has a longitudinal length. Is 300 m, the second one has a longitudinal length of 150 m, and the third one provided with an emission end has a longitudinal length of 50 m. The dispersion value of the dispersion characteristic of the third optical fiber at the final stage is almost 0 ps / (nm · km) at the center wavelength. As can be seen from FIG. 4A, the difference between the dispersion values of the first optical fiber and the second optical fiber is significantly larger than the difference between the dispersion values of the second optical fiber and the third optical fiber. ing. As can be seen from FIG. 4 (b), the required bandwidth is such that the optical signal spreads in both the higher side and the lower side than the center wavelength in a state of not being greatly attenuated in the band of about 50 nm. It can be confirmed that ultra-broad band light (super continuum light) of approximately 100 nm is generated and emitted. That is, in this case, the signal light is dispersed in a bandwidth from the wavelength of 1.50 μm to the wavelength of 1.60 μm around the wavelength of 1.55 μm.
[0023]
(2) FIG. 5A shows the dispersion characteristics of a dispersion-reduced optical fiber as an example in which four optical fibers having predetermined dispersion characteristics are connected in series as another embodiment and a comparative example. . FIG. 5B shows the normalized intensity with respect to the wavelength of the dispersion-reduced optical fiber shown in FIG. As shown in FIG. 5 (a), in the case of this dispersion-reduced optical fiber, of the four optical fibers connected in series, the first one provided with the incident end has a length in the longitudinal direction. Is 300 m, the second one has a length in the longitudinal direction of 100 m, the third one has a length in the longitudinal direction of 50 m, and the fourth one provided with the emission end is: Its longitudinal length is 50 m. The dispersion value of the dispersion characteristic of the fourth optical fiber at the last stage is −0.1 ps / (nm · km) at the center wavelength. As can be seen from FIG. 5A, the difference between the dispersion values of the first optical fiber and the second optical fiber is the difference between the dispersion values of the second optical fiber and the third optical fiber. It is significantly larger than the difference between the dispersion values of the fiber and the fourth optical fiber. As can be seen from FIG. 5 (b), the required bandwidth is such that the optical signal spreads on both the higher side and the lower side than the center wavelength in a band of about 50 nm, with a relatively large attenuation. As a result, it can be confirmed that an ultra-wide band light (super continuum light) of about 100 nm is generated and emitted. However, the intensity of the obtained ultra-wide band light fluctuates more in that band than in the above-described embodiment (1), and the attenuation is relatively large near the center wavelength.
[0024]
(3) FIG. 6A shows the dispersion characteristics of a dispersion-reduced optical fiber as an example in which four optical fibers having predetermined dispersion characteristics are connected in series as another embodiment and a comparative example. . FIG. 6B shows the normalized intensity with respect to the wavelength of the dispersion-reduced optical fiber shown in FIG. As shown in FIG. 6 (a), in the case of this dispersion-reduced optical fiber, of the four optical fibers connected in series, the first one provided with the incident end has a longitudinal length. Is 300 m, the second one has a length in the longitudinal direction of 100 m, the third one has a length in the longitudinal direction of 50 m, and the fourth one provided with the emission end is: Its longitudinal length is 50 m. The dispersion value of the dispersion characteristic of the fourth optical fiber at the last stage is 0.1 ps / (nm · km) at the center wavelength. As can be seen from FIG. 6A, the difference between the dispersion values of the first optical fiber and the second optical fiber is the difference between the dispersion values of the second optical fiber and the third optical fiber. It is significantly larger than the difference between the dispersion values of the fiber and the fourth optical fiber. As can be seen from FIG. 6 (b), the required bandwidth is such that the optical signal spreads in both the higher side and the lower side of the center wavelength in a band of approximately 50 nm with relatively little attenuation in the band. As a result, it can be confirmed that an ultra-wide band light (super continuum light) of about 100 nm is generated and emitted. However, the intensity of the obtained ultra-wide band light fluctuates more in that band than in the above-described embodiment (1), and the attenuation is relatively large near the center wavelength.
[0025]
(4) FIG. 7A shows, as another embodiment, the dispersion characteristics of a dispersion-reduced optical fiber as an example in which four optical fibers having predetermined dispersion characteristics are connected in series. FIG. 7B shows the normalized intensity with respect to the wavelength of the dispersion reducing optical fiber shown in FIG. 7A. As shown in FIG. 7 (a), in the case of this dispersion-reduced optical fiber, of the four optical fibers connected in series, the first one provided with the incident end has a length in the longitudinal direction. Is 300 m, the second one has a length in the longitudinal direction of 100 m, the third one has a length in the longitudinal direction of 50 m, and the fourth one provided with the emission end is: Its longitudinal length is 50 m. The dispersion value of the dispersion characteristic of the fourth optical fiber at the last stage is 0 ps / (nm · km) at the center wavelength. As can be seen from FIG. 7A, the difference between the dispersion values of the first and second optical fibers is the difference between the dispersion values of the second and third optical fibers. It is significantly larger than the difference between the dispersion values of the fiber and the fourth optical fiber. As can be seen from FIG. 7 (b), the required bandwidth is such that the optical signal spreads on both the higher side and the lower side than the center wavelength in a band of about 50 nm with relatively little attenuation. As a result, it can be confirmed that an ultra-wide band light (super continuum light) of about 100 nm is generated and emitted. However, the intensity of the obtained ultra-wide band light has a relatively small variation in the band, as in the embodiment (1). However, the attenuation is relatively large near the center wavelength.
[0026]
(5) FIG. 8A shows another embodiment of the dispersion in a dispersion-reduced optical fiber as an example in which four optical fibers having predetermined dispersion characteristics are connected in series similarly to the one shown in FIG. Properties are shown. FIG. 8B shows the normalized intensity with respect to the wavelength of the dispersion-reduced optical fiber shown in FIG. As shown in FIG. 8 (a), in the case of this dispersion-reduced optical fiber, of the four optical fibers connected in series, the first one provided with the incident end has a length in the longitudinal direction. Is 300 m, the second one has a length in the longitudinal direction of 100 m, the third one has a length in the longitudinal direction of 50 m, and the fourth one provided with the emission end is: Its longitudinal length is 50 m. The dispersion value of the dispersion characteristic of the fourth optical fiber at the last stage is almost 0 ps / (nm · km) at the center wavelength. As can be seen from FIG. 8A, the difference between the dispersion values of the first optical fiber and the second optical fiber is the difference between the dispersion values of the second optical fiber and the third optical fiber. It is significantly larger than the difference between the dispersion values of the fiber and the fourth optical fiber. As can be seen from FIG. 8 (b), the required bandwidth is such that the optical signal spreads on both the higher side and the lower side of the center wavelength in a band of about 50 nm, which is not attenuated relatively largely. As a result, it can be confirmed that an ultra-wide band light (super continuum light) of about 100 nm is generated and emitted. However, the intensity of the obtained ultra-wide band light has a relatively small variation in the band, as in the embodiment (1). However, the attenuation is relatively large near the center wavelength.
[0027]
(6) FIG. 9A shows a dispersion characteristic of a dispersion-reduced optical fiber as an example in which four optical fibers having predetermined dispersion characteristics are connected in series as another embodiment and a comparative example. . FIG. 9B shows the normalized intensity with respect to the wavelength of the dispersion reducing optical fiber shown in FIG. 9A. As shown in FIG. 9 (a), in the case of this dispersion-reduced optical fiber, of the four optical fibers connected in series, the first one provided with the incident end has its longitudinal length. Is 50 m, the second one has a longitudinal length of 50 m, the third one has a longitudinal length of 350 m, and the fourth one provided with an emission end is Its longitudinal length is 50 m. The dispersion value of the dispersion characteristic of the fourth optical fiber at the last stage is almost 0 ps / (nm · km) at the center wavelength. However, as can be seen from FIG. 9A, the difference between the dispersion values of the third and fourth optical fibers is the difference between the dispersion values of the first and second optical fibers. Is significantly larger than the difference between the dispersion values of the first optical fiber and the third optical fiber. As can be seen from FIG. 9B, the bandwidth of the outgoing light is slightly wider than that of the incident light, but attenuates more rapidly as the distance from the center wavelength (1.55 μm in this case) to the shorter and longer wavelength sides increases. However, it is not possible to obtain ultra-wide band light that is maintained at a predetermined intensity in a predetermined broad band.
[0028]
The present invention is not limited to the above-described embodiment, and may be applied, for example, or modified as described below.
[0029]
(B) The optical fiber connected in series constituting the dispersion-reduced optical fiber has a predetermined constant dispersion characteristic, that is, one in which the dispersion characteristic does not change in the longitudinal direction. A configuration including at least one or more components that are changed in the longitudinal direction may be used.
[0030]
(B) Each of the dispersion-reduced optical fibers has a dispersion characteristic in which the bandwidth is broadened to approximately the same extent in both the long and short bands around the center wavelength of the incident light. The present invention also includes a band in which one of the long and short bands is broadened so as to be larger than the other with respect to the center wavelength.
[0031]
【The invention's effect】
As described above, according to the dispersion-decreasing optical fiber according to the present invention, even if a plurality of optical fibers having predetermined dispersion characteristics whose dispersion characteristics do not change in the longitudinal direction of the optical fiber are connected in series, Ultra wide band light can be generated by dispersing incident light for each optical fiber from the incident end to the exit end. Each optical fiber can be manufactured much more easily than an optical fiber whose dispersion characteristics change by keeping the dispersion characteristics unchanged in the longitudinal direction, so that it can be configured as an inexpensive optical fiber.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a configuration of an example of an ultra-wideband light source according to the present invention.
FIG. 2 is an explanatory diagram showing a dispersion-reducing optical fiber according to an embodiment of the present invention and dispersion characteristics of each optical fiber constituting the fiber;
3A is a graph showing the dispersion characteristics of the dispersion-reduced optical fiber shown in FIG. 2 in the longitudinal direction of the fiber, and FIG. 3B is a graph showing the relationship between the wavelength of the incident light and the output light of the dispersion-reduced optical fiber with respect to the wavelength. b)
FIG. 4 is a graph (a) showing the dispersion characteristics of the dispersion-reduced optical fiber in the longitudinal direction of the dispersion-reduced optical fiber according to another embodiment of the present invention, and the intensity of the incident light and the output light of the dispersion-reduced optical fiber with respect to the wavelength. Graph (b) showing the relationship
FIG. 5 is a graph (a) showing the dispersion characteristics of the dispersion-reduced optical fiber in the longitudinal direction of the dispersion-reduced optical fiber according to another embodiment of the present invention, and the intensity of the incident light and the output light of the dispersion-reduced optical fiber with respect to the wavelength. Graph (b) showing the relationship
FIG. 6A is a graph showing the dispersion characteristics of the dispersion-reduced optical fiber in the longitudinal direction of the dispersion-reduced optical fiber according to another embodiment of the present invention, and the intensity of the incident light and the output light of the dispersion-reduced optical fiber with respect to the wavelength; Graph (b) showing the relationship
FIG. 7 is a graph (a) showing the dispersion characteristics of the dispersion-reduced optical fiber in the longitudinal direction of the dispersion-reduced optical fiber according to another embodiment of the present invention, and the intensity of the incident light and the output light of the dispersion-reduced optical fiber with respect to the wavelength. Graph (b) showing the relationship
FIG. 8A is a graph showing the dispersion characteristics of the dispersion-reduced optical fiber in the longitudinal direction of the dispersion-reduced optical fiber according to another embodiment of the present invention, and the intensity of the incident light and the output light of the dispersion-reduced optical fiber with respect to the wavelength; Graph (b) showing the relationship
FIG. 9 is a graph (a) showing the dispersion characteristics of the dispersion-reduced optical fiber in the longitudinal direction of the dispersion-reduced optical fiber according to another embodiment of the present invention, and the intensity of the incident light and the output light of the dispersion-reduced optical fiber with respect to the wavelength. Graph (b) showing the relationship
FIG. 10 is a graph showing the relationship between wavelength and dispersion characteristics of a conventional dispersion-reduced optical fiber.
FIG. 11A is a graph showing the dispersion characteristics of the conventional dispersion-reduced optical fiber in the longitudinal direction of the fiber, and FIG. 11B is a graph showing the relationship between the wavelength of the incident light and the intensity of the emitted light of the dispersion-reduced optical fiber;
FIG. 12 is an explanatory diagram showing a dispersion characteristic of a conventional dispersion-reduced optical fiber.
[Explanation of symbols]
1 Ultra-wideband light source
4 Optical fiber with reduced dispersion
F ₁ ~ F ₁₀ Optical fiber with predetermined dispersion characteristics

Claims (7)

A dispersion-reducing optical fiber that generates an ultra-wide band light by dispersing an incident optical signal into a predetermined band,
A dispersion-reduced optical fiber, wherein a plurality of optical fibers having predetermined dispersion characteristics are connected in series. The dispersion-reducing optical fiber according to claim 1,
The dispersion-reduced optical fiber, wherein the plurality of optical fibers connected in series is a combination of optical fibers having different dispersion characteristics. The dispersion reducing optical fiber according to claim 2,
The dispersion-reduced optical fiber, wherein the plurality of optical fibers connected in series have their bandwidths dispersed stepwise each time an incident optical signal passes through each optical fiber. The dispersion reducing optical fiber according to claim 3,
While three or more optical fibers are connected in series, the first optical fiber on the incident side of those optical fibers has a longer length in the longitudinal direction than other optical fibers, and The difference in the dispersion characteristics between the first optical fiber and the next optical fiber is set to be larger than the difference in the dispersion characteristics between any of the connected optical fibers on the output side of the next optical fiber. Dispersion-reducing optical fiber. The dispersion reducing optical fiber according to claim 3,
The dispersion characteristics of the last-stage optical fiber on the emission side among the optical fibers connected in series, wherein the absolute value of the dispersion value is less than 0.1 ps / (nm · km). fiber. The dispersion-reduced optical fiber according to any one of claims 2 to 5,
A dispersion reducing optical fiber, wherein three optical fibers having the predetermined dispersion characteristics are connected in series, and the dispersion of the optical signal is reduced in three stages. An ultra-wideband light source, characterized in that the dispersion-reducing optical fiber according to any one of claims 1 to 6 is provided as a means for generating ultra-wide band light.

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