JP2016173561A - Transmission device, measurement device using the same, device, and transmission method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce influences due to the dispersion and nonlinear optical effects by an optical fiber.SOLUTION: There is provided a transmission device 100 for transmitting a pulse light 102. The device comprises: a negative dispersing medium 103 having a negative dispersion parameter in a wavelength band included in an incident pulse light; a first optical fiber 104 where the pulse light having passed through the negative dispersing medium are made incident; and a second optical fiber 105 where the pulse light having passed through the first optical fiber are made incident. The first optical fiber has a negative dispersion parameter in the wavelength band included in the incident pulse light, and the second optical fiber has a positive dispersion parameter in the wavelength band included in the incident pulse light. The negative dispersing medium and the second optical fiber have a positive dispersion slope, and the first optical fiber has a negative dispersion slope.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a transmission apparatus using an optical fiber, a measuring apparatus, an apparatus, and a transmission method using the transmission apparatus.

  In the transmission of short pulse light using an optical fiber, there is a problem that the pulse width of the short pulse light is widened due to dispersion of the optical fiber. Also, the short pulse has a peak power that increases as the pulse width becomes shorter, and the pulse waveform may change due to nonlinear optical effects such as self-phase modulation during propagation through the optical fiber.

  As a method for reducing these, there is a method in which an optical element having dispersion opposite to that of the optical fiber is added as dispersion compensation means to the propagation path of the short pulse light. Japanese Patent Application Laid-Open No. H10-228667 describes a method in which short pulse light is incident on an optical fiber via a dispersion compensation means such as a diffraction grating. In Patent Document 1, before being incident on an optical fiber, dispersion of pulse light is given to widen the pulse width to reduce peak power, thereby reducing changes in the pulse waveform due to the nonlinear optical effect. In addition, dispersion can be compensated at the same time by adjusting the amount of dispersion before and after the optical fiber. As the dispersion compensation means, a diffraction grating or a prism is used.

  Moreover, short pulse light has an intensity spectrum with a wide wavelength band. When such short pulse light is used, broadband dispersion compensation is required, and therefore it is required to compensate not only dispersion compensation at a specific wavelength but also a dispersion slope obtained by differentiating the dispersion parameter with respect to wavelength. If the dispersion slope cannot be compensated, the time waveform of the emitted light emitted from the optical fiber is deformed as shown in FIG. 2, and the peak power is reduced as compared with the incident light before entering the optical fiber. As a method for compensating for such a dispersion slope, Patent Document 2 discloses a method in which an appropriate dispersion parameter and dispersion slope are given to a short pulse light in advance using a nonlinear optical effect before transmitting the fiber. .

Japanese Patent Laid-Open No. 10-186424 JP 2012-141422 A

  However, when dispersion compensation means such as a diffraction grating is used, the intensity of the short pulse light may be reduced and transmission efficiency may be reduced. Further, since the diffraction grating of Patent Document 1 has the same positive dispersion slope as that of an optical fiber, even if dispersion compensation at a specific wavelength is possible, compensation considering the dispersion slope is not sufficient, and dispersion may not be compensated in a wide band. is there. Further, the shaping of the pulse waveform of the short pulse light using the nonlinear optical effect as in Patent Document 2 is dependent on the light intensity, and therefore the instability of the output of the short pulse light from the light source is anxiety of the pulse waveform shape. It leads to qualitative.

  The present invention has been made in view of such a problem, and an object of the present invention is to reduce the influence of dispersion caused by an optical fiber and the nonlinear optical effect when transmitting short pulse light using a fiber.

  A transmission device according to one aspect of the present invention is a transmission device that transmits pulsed light, and has passed through the negative dispersion medium having a negative dispersion parameter in a wavelength band included in incident pulsed light, and the negative dispersion medium A first fiber on which pulsed light is incident; and a second fiber on which pulsed light that has passed through the first fiber is incident, the first fiber being a wavelength band included in the incident pulsed light The second fiber has a positive dispersion parameter in the wavelength band included in the incident pulsed light, and the negative dispersion medium and the second fiber have a positive dispersion parameter. It has a slope, and the first fiber has a negative dispersion slope.

  According to the transmission apparatus as one aspect of the present invention, it is possible to reduce the influence due to the dispersion by the optical fiber and the nonlinear optical effect.

The figure explaining the structure of the transmission apparatus of 1st Embodiment. The figure explaining the change of the time waveform when the dispersion slope cannot be compensated. The figure explaining the dispersion characteristic of the transmission apparatus of 1st Embodiment. The figure explaining the change of the intensity spectrum by a nonlinear optical effect. The figure explaining the relationship between the length of a negative dispersion medium, and the intensity spectrum of the light which propagated the negative dispersion fiber. The figure which shows the dispersion characteristic of each structure of the transmission apparatus of 1st Embodiment, and the dispersion characteristic of a transmission apparatus. The figure explaining the time waveform and intensity spectrum of the light inject | emitted from the transmission apparatus of 1st Embodiment. The figure explaining the structure of the transmission apparatus of 2nd Embodiment. The figure explaining the structure of the transmission apparatus of 3rd Embodiment. The figure which shows the dispersion characteristic of the transmission apparatus which concerns on 3rd Embodiment. The figure explaining the structure of the measuring apparatus of 4th Embodiment. The figure explaining the structure of the measuring apparatus of 5th Embodiment.

(First embodiment)
A transmission apparatus 100 according to the present embodiment will be described with reference to FIG. FIG. 1 is a block diagram illustrating the configuration of the transmission apparatus 100. The transmission apparatus 100 includes a negative dispersion medium 103 (hereinafter referred to as “medium 103”), a first fiber 104, and a second fiber 105. The second fiber 105 is connected to the photoconductive element 106, and short pulse light 102 (hereinafter referred to as “laser 102”) from the light source 101 enters the photoconductive element 106 via the transmission device 100. . Here, the short pulse light refers to pulse light having a pulse width on the order of femtoseconds (fs). In this embodiment, in particular, a short pulse light having a pulse width of 100 femtoseconds or less (100 fs or less) is used as the laser 102.

  The light source 101 generates a laser 102. In the present embodiment, a fiber laser that emits a laser 102 having a center wavelength of 1.55 μm (1550 nm), a repetition frequency of 80 MHz, and a peak power of 40 kW is used as the light source 101. The time waveform of the laser 102 is close to the Fourier transform limit and has a Gaussian waveform with a pulse width of 30 fs. An isolator, a quarter-wave plate, a polarizing beam splitter, or the like is provided in the propagation path of the laser 102 and in the vicinity of the light source 101 to prevent the laser 102 from becoming unstable due to the return light reflected by another member. May be. The light source 101 only needs to be able to generate the laser 102 having the same wavelength band and pulse width. For example, a known light source such as a solid-state laser can be used.

  The laser 102 is incident on the medium 103. The medium 103 has a negative dispersion parameter in part or all of the wavelength band included in the laser 102. Further, the medium 103 is a bulk medium having a positive dispersion slope in part or all of the wavelength band included in the laser 102. The medium 103 desirably has a negative dispersion parameter and a positive dispersion slope in all wavelength bands included in the laser 102.

  In the present embodiment, a silicon (Si) plate is used as the medium 103. Note that the medium 103 is not limited to silicon, and zinc selenide, zinc sulfide, KRS-5 (mixed crystal of tantalum bromide and tantalum iodide), potassium bromide, sodium chloride, or the like may be used. The medium 103 preferably has an antireflection film formed on the surface in order for the laser 102 to prevent Fresnel loss at the interface between silicon and air. Alternatively, in order to reduce the Fresnel loss to a minimum, the laser 102 may be S-polarized with respect to the medium 103 and the incident angle may be a Brewster angle.

  The laser 102 that has passed through the medium 103 then enters the first fiber 104. The first fiber 104 is a negative dispersion fiber having a negative dispersion parameter in part or all of the wavelength band included in the laser 102. In the following description, the first fiber 104 is referred to as “negative dispersion fiber 104”. The negative dispersion fiber 104 is an optical fiber having a negative dispersion slope in part or all of the wavelength band included in the laser 102. The negative dispersion fiber 104 desirably has a negative dispersion parameter and a negative dispersion slope in all wavelength bands included in the laser 102.

  A general optical fiber has a positive material dispersion and a small structural dispersion, so it has a positive dispersion parameter and a positive dispersion slope like quartz, but by reducing the diameter of the core (core diameter) A negative dispersion fiber having negative dispersion can be produced by increasing the negative structural dispersion. The negative dispersion fiber can be used as a dispersion compensation means for a general optical fiber (a positive dispersion fiber having a positive dispersion parameter).

  The “dispersion parameter” is an index representing the wavelength dependence of the group velocity, and is caused by the fact that the refractive index of the substance depends on the wavelength. For example, in a medium having a positive dispersion parameter, the group velocity decreases as the wavelength increases. The “dispersion slope” is the wavelength differential amount of the dispersion parameter. In this specification, a fiber having a positive dispersion parameter is referred to as a positive dispersion fiber, and a fiber having a negative dispersion parameter is referred to as a negative dispersion fiber.

The negative dispersion fiber 104 has a smaller core diameter and a smaller MFA (Mode Field Area) than the positive dispersion fiber. Typically, the MFA of the positive dispersion fiber is about 100 μm ² , the negative dispersion fiber is 10 μm ² or less, and the positive dispersion fiber is MFA several tens of times that of the negative dispersion fiber. Therefore, the light density in the negative dispersion fiber 104 is increased. Therefore, the light propagating through the negative dispersion fiber 104 is easily affected by the nonlinear optical effect. That is, reducing the nonlinear optical effect in the negative dispersion fiber 104 is more important for efficient transmission of the laser 102 than reducing the nonlinear optical effect in the positive dispersion fiber as the second fiber 105. Therefore, the laser 102 from the light source 101 is incident on the negative dispersion fiber 104 via the medium 103, thereby widening the pulse width of the laser 102 and reducing the peak power.

In this embodiment, the dispersion parameter at a wavelength of 1.55 μm is −75 ps / nm / km, the dispersion slope is −0.75 ps / nm ² / km, the mode field diameter is 3 μm, and the nonlinear constant is 0.0429 (/ m / W). ) Is used as the negative dispersion fiber 104. As a material, silicon dioxide (SiO ₂ ) is used. The negative dispersion fiber 104 is not limited to this, and a step index type fiber having a negative dispersion and a negative dispersion slope, a photonic crystal fiber, or the like may be used.

  As described above, the light propagating through the negative dispersion fiber 104 is easily affected by the nonlinear optical effect. For this reason, the thickness of the medium 103 in the optical axis direction of the laser 102 propagating through the medium 103 needs to be thick enough to sufficiently reduce the peak power of the laser 102 that has passed through the medium 103. In the present embodiment, the thickness of the medium 103 is 10 mm.

  The second fiber 105 is a positive dispersion fiber having a positive dispersion parameter in part or all of the wavelength band included in the laser 102. The second fiber 105 is a single mode fiber having a positive dispersion slope in part or all of the wavelength band included in the laser 102. In the following description, the second fiber 105 is referred to as “positive dispersion fiber 105”. The positive dispersion fiber 105 desirably has a positive dispersion parameter and a positive dispersion slope in all wavelength bands included in the laser 102. As the positive dispersion fiber 105, specifically, a quartz fiber, a photonic crystal fiber, or the like can be used. The laser 102 propagating through the negative dispersion fiber 104 is incident on the positive dispersion fiber 105. In order to improve robustness, it is desirable to use the negative dispersion fiber 104 and the positive dispersion fiber 105 fused together.

In the present embodiment, SMF-28 from Corning, which is a single mode fiber, is used as the positive dispersion fiber 105. That is, the positive dispersion fiber 105 has a dispersion parameter of 17.41 ps / nm / km at a wavelength of 1.55 μm, a dispersion slope of 0.0584 ps / nm ² / km, a mode field diameter of 10 μm, and a nonlinear constant of 0.00143 (/ m / W) optical fiber. The negative dispersion fiber 104 and the positive dispersion fiber 105 are preferably polarization maintaining fibers.

  Since the negative dispersion fiber 104 has a negative dispersion parameter, the laser 102 incident on the negative dispersion fiber 104 has a larger pulse width and a lower peak power as it propagates through the negative dispersion fiber 104. That is, if the peak power is sufficiently small at the incident position of the negative dispersion fiber 104, the peak power of the laser 102 is sufficiently small at all positions in the negative dispersion fiber 104. Thereafter, the laser 102 is incident on the positive dispersion fiber 105, and the dispersion is compensated at the exit end of the positive dispersion fiber 105, so that the peak power increases.

  The laser 102 emitted from the positive dispersion fiber 105 is preferably compensated for dispersion in the frequency region of the laser 102. Therefore, the lengths of the medium 103, the negative dispersion fiber 104, and the positive dispersion fiber 105 are selected so that the sum of the group velocity dispersion and dispersion slope of the medium 103, the negative dispersion fiber 104, and the positive dispersion fiber 105 approaches zero. To do. In this embodiment, the length of the medium 103 is 10 mm, the length of the negative dispersion fiber 104 is 100 mm, and the length of the positive dispersion fiber 105 is 950 mm. The length of each component will be described later.

  The laser 102 emitted from the positive dispersion fiber 105 is irradiated to the photoconductive element 106. The photoconductive element 106 is an optical element that generates or detects terahertz waves, and is configured using GaAs or InGaAs grown at a low temperature. An antireflection film may be applied to a portion of the photoconductive element 106 to which the laser 102 is irradiated. Note that the material on which the laser 102 from the transmission device 100 is incident is not limited to the photoconductive element 106.

  In order to irradiate the photoconductive element 106 with the positive dispersion fiber 105, a SELFOC (registered trademark) lens, a ball lens, or the like may be integrated at the tip of the positive dispersion fiber 105 on the photoconductive element 106 side. Moreover, the positive dispersion fiber 105 using the pigtail type which processed the front end by the side of the photoconductive element 106 of the positive dispersion fiber 105, or a tip ball fiber etc. may be sufficient. If the mode field diameter of the positive dispersion fiber 105 and the laser beam diameter required by the photoconductive element 106 are approximately the same, the positive dispersion fiber 105 and the photoconductive element 106 are connected by a direct coupling (butt coupling) method. You may let them.

  From here, the lengths of the medium 103, the negative dispersion fiber 104, and the positive dispersion fiber 105 in the optical axis direction of the laser 102 will be described. A simplified diagram of the dispersion characteristics of the medium 103, the negative dispersion fiber 104, and the positive dispersion fiber 105 is shown in FIG. 3A, and the dispersion parameters and the signs of the dispersion slope are shown in Table 1. Here, the wavelength region of the laser 102 is in a longer wavelength region than the zero dispersion wavelength of the positive dispersion fiber 105.

  When the laser 102 propagates through a certain substance, the magnitude of dispersion that the substance gives to the laser 102 can be expressed by a dispersion parameter and a dispersion slope. The dispersion parameter D is given by equation (4), and the dispersion slope S is given by equation (5). Note that the wavelength of the laser 102 is λ, the speed of light is c, and the refractive index of the substance at the wavelength of the laser 102 is n.

  The refractive index n in the equation (4) can be calculated from the Selmeier equation (equation (6)) representing the wavelength dependence of the refractive index (CD Salzberg and JJ Villa, Journal of Optical Society of America, Vol. 47, p.244, (1957)).

The dispersion parameter D and the dispersion slope S can be obtained from the equations (4) to (6). For example, silicon 103 as the medium 103 has a dispersion parameter D of −879.6 ps / nm / km when the wavelength λ is 1550 nm, a dispersion slope S of 1.983 ps / nm ² / km, and negative dispersion in the 1550 nm band. Parameters and a positive dispersion slope.

  As described above, since the negative dispersion fiber 104 has a small MFA, the pulse waveform of the laser 102 propagating through the negative dispersion fiber 104 may change due to the nonlinear optical effect. Therefore, if only the negative dispersion fiber 104 is used to compensate the dispersion in the positive dispersion fiber 105, the pulse waveform of the laser 102 changes due to the nonlinear optical effect. As a result, the time waveform and spectrum shape of the laser 102 change. In order to reduce the influence of the nonlinear optical effect in the negative dispersion fiber 104, the transmission device 100 makes the laser 102 incident on the medium 103 and widens the pulse width of the laser 102 to reduce the peak power.

When a laser 102 that is close to the Fourier limit is propagating through a certain substance, the propagation length L _NL of which the influence on the time waveform and spectrum shape of the laser 102 starts to become noticeable due to the nonlinear optical effect of the propagating substance is (7 ) Expression. Let γ be the nonlinear optical constant of the propagating substance, and P be the peak power of the laser 102 when incident on the substance.

Further, the propagation length L _D of the laser 102 to propagate a substance required for the pulse width increases by the dispersion is expressed by equation (8). Let T _{0 be} the pulse width of the laser 102 immediately before entering the material, and GVD be the group velocity dispersion of the material that the laser 102 is propagating.

  The group velocity dispersion GVD is expressed by the equation (9) using the dispersion parameter D of the substance.

  When both the following formulas (10) and (11) are satisfied for the propagation length L in which the laser 102 propagates through a certain substance, the influence of the nonlinear optical effect on the pulsed light cannot be ignored.

Here, the pulse width of the laser 102 of this embodiment is 30 fs, the peak power is 40 kW, and the center wavelength is 1.55 μm. Dispersion parameter of the negative dispersion fibers 104 ^{-75ps / nm / km (96fs 2} / mm in terms of group velocity dispersion), the nonlinear optical constant is set to 0.0429 (/ m / W), L D is 4.7mm , LNL is 1.1 mm. Therefore, for example, when propagating through the negative dispersion fiber 104 having a length of 10 mm, the expressions (10) and (11) are satisfied at the same time, and the influence of the nonlinear optical effect appears.

  FIG. 4 is a diagram showing a change in the spectrum of the laser 102 when the laser 102 propagates through the negative dispersion fibers 104 having different lengths. FIG. 4A is a diagram illustrating a spectrum of the laser 102 when the laser 102 propagates through the negative dispersion fiber 104 by 1 mm. FIG. 4B is a diagram illustrating a spectrum of the laser 102 when the laser 102 propagates through the negative dispersion fiber 104 by 5 mm. FIG. 4C is a diagram showing the spectrum of the laser 102 when the laser 102 propagates through the negative dispersion fiber 104 by 10 mm. The spectrum indicated by the straight lines in FIGS. 4A to 4C is the spectrum of the laser 102 after propagation through the negative dispersion fiber 104, and the spectrum indicated by the dotted line is the spectrum of the laser 102 output from the light source 101.

As described above, since the negative dispersion fiber 104 has a large nonlinear optical effect, it is considered to reduce the influence of the nonlinear optical effect of the negative dispersion fiber 104 on the laser 102. In order to reduce the influence of the nonlinear optical effect of the negative dispersion fiber 104 on the laser 102, the laser 102 is incident on the negative dispersion fiber 104 through the medium 103 that satisfies the following expressions (1) to (3). Note that the length of the medium 103 in the optical axis direction of the laser 102 is L ₁ , the pulse width of the laser 102 just before entering the medium 103 is T ₀ , and the group velocity dispersion per mm of the medium 103 is b ₂ . Further, the peak power of the laser 102 immediately before passing through the medium 103 is P ₀ , the peak power of the laser 102 immediately after passing through the medium 103 is P ₁ , and the group velocity dispersion per unit length of the medium 103 is b _nd . .

FIG. 5 shows the result of calculating the spectrum of the laser 102 that has passed through the medium 103 and propagated through the negative dispersion fiber 104 having a length of 100 mm. Respective spectra calculated by changing the thickness of the medium 103 to 2 mm, 3 mm, 5 mm, and 10 mm are shown in FIGS. 5 (a) to 5 (d). As the medium 103 becomes thicker, the peak power of the laser 102 incident on the negative dispersion fiber 104 decreases, so that L _NL increases and the value of L _D / L _NL decreases. L _D / L _NL when the thickness of the medium 103 is changed to 2 mm, 3 mm, 5 mm, and 10 mm is 2.3, 1.6, 0.93, and 0.46, respectively.

When L _D <L _NL , that is, when the thickness of the medium 103 is 5 mm or 10 mm, the shape of the spectrum hardly changes as shown in FIGS. 5C and 5D. On the other hand, when L _D > L _NL , that is, when the thickness of the medium 103 is 2 mm or 3 mm, a change is observed in the shape of the spectrum as shown in FIGS. 5 (a) and 5 (b). This is derived from the nonlinear optical effect of the negative dispersion fiber 104, and leads to the collapse of the time waveform and spectrum shape of the laser 102.

  Next, the length of the positive dispersion fiber 105 will be described. The medium 103 and the positive dispersion fiber 105 each have a positive dispersion slope, and the negative dispersion fiber 104 has a negative dispersion slope. Therefore, by appropriately setting the lengths of the medium 103, the negative dispersion fiber 104, and the positive dispersion fiber 105, the dispersion parameter and the dispersion slope can be compensated simultaneously.

The length _{L 1} of the medium 103, the length _{L 2} of the negative dispersion fiber 104, the length _{L 3} of the positive dispersion fibers 105, each of the dispersion _{(D 1, D 2, D} 3) and dispersion slope _(S 1, S ₂ , S ₃ ). That is, it is only necessary to solve the simultaneous linear equations of the expressions (12) and (13), and the ratios of L ₁ , L ₂ , and L ₃ can be uniquely determined.
_{D 1 L 1 + D 2 L} 2 + D 3 L 3 = 0 (12)
S ₁ L ₁ + S ₂ L ₂ + S ₃ L ₃ = 0 (13)

Actually, since higher-order dispersion exists, it is not easy to design such that the sum of dispersion becomes 0 at all wavelengths from the expressions (12) and (13). Therefore, the lengths L ₁ , L ₂ , L ₂ , L ₂ , L ₂ , L ₂ , L ₂ , L ₂ , L ₂ , L ₂ , L ₂ , L ₂ , L ₂ , L ₂ , L ₂ , L ₂ , L ₂ , the L ₃ it is desirable to fine tune.

In this specification, “the total dispersion amount is sufficiently small” means that the total dispersion amount b _2all of the medium 103, the negative dispersion fiber 104, and the positive dispersion fiber 105 is smaller than the pulse width T _{0 in the} spectral region of the laser 102. Define to say. This relationship is expressed by equation (14). Here, the total dispersion amount is the total dispersion of the medium 103, the negative dispersion fiber 104, and the positive dispersion fiber 105, and is represented by the left side of the equation (12).

The dispersion characteristics of the medium 103 and the dispersion characteristics of the positive dispersion fiber 105 are generally determined by the dispersion characteristics of the materials used. On the other hand, the dispersion characteristics of the negative dispersion fiber 104 can be changed according to the cross-sectional structure design. In order to explain the dispersion characteristics that the negative dispersion fiber 104 should have, the total dispersion amount of the medium 103 and the positive dispersion fiber 105 is shown in FIG. The wavelength λ _{0 at} which the total dispersion amount of the medium 103 and the positive dispersion fiber 105 becomes ₀ is longer than the zero dispersion wavelength of the positive dispersion fiber 105. The amount of wavelength shift from the zero dispersion wavelength of the positive dispersion fiber 105 to the wavelength λ ₀ varies depending on the amount of dispersion of the medium 103.

The dispersion characteristics to be possessed by the negative dispersion fiber 104 may be as long as the total dispersion amount of the medium 103 and the positive dispersion fiber 105 is opposite in sign. That is, if the dispersion characteristics of the medium 103 and the dispersion characteristics and length of the positive dispersion fiber 105 are determined, the negative dispersion fiber 104 may be selected so as to have a zero dispersion wavelength λ ₀ and a negative dispersion slope. The zero dispersion wavelength λ ₀ can be adjusted by changing the core diameter or fiber cross-sectional shape of the negative dispersion fiber 104. The amount of dispersion slope can be adjusted by changing the length of the negative dispersion fiber 104. Fine adjustment may be necessary in consideration of higher-order dispersion, but when higher-order dispersion is relatively small, the dispersion characteristics and length of each component can be obtained as described above.

  Note that the laser 102 after being transmitted through the positive dispersion fiber 105 may have a plurality of peaks due to high-order dispersion or the like. When the laser 102 has a plurality of peaks having the same size, it cannot be said that the pulse width is optimized. Therefore, it is desirable that the power of the main peak of the laser 102 occupies 70% or more of the power of the entire laser 102. Further, it is desirable that the power of the main peak of the laser 102 after being transmitted through the transmission device 100 is 70% or more of the peak power of the laser 102 immediately after being output from the light source 101.

In the present embodiment, the thickness of the medium 103 is 10 mm. In this case, the pulse width of the laser 102 emitted from the light source 101 is 30 fs, whereas the pulse width of the laser 102 emitted from the medium 103 is 813 fs. In this case, the propagation length L _D obtained from Equation (2) is 9.42 mm, and the propagation length L _NL obtained from Equation (3) is 15.7 mm, which satisfies Equation (1). Therefore, the transmission apparatus 100 according to the present embodiment can efficiently transmit the laser 102 by reducing the influence of the nonlinear optical effect and dispersion caused by the optical fiber.

When finely adjusting the lengths of the medium 103, the negative dispersion fiber 104, and the positive dispersion fiber 105, it is desirable that the required accuracy of the length is less than the level that does not affect the pulse width of the laser 102. Specifically, if the pulse width of the laser 102 from the light source 101 is T ₀ and the group velocity dispersion amount per unit length of the positive dispersion fiber 605 is b ₂ fiber, the adjustment accuracy required for the length of the positive dispersion fiber 605 is required. It is desirable that ΔL _fiber satisfies the expression (15).

Since the group velocity dispersion amount b _2fiber is −22.1 fs ² / mm and the pulse width T ₀ is 30 fs, ΔL _fiber <40 mm from the equation (15). In the present embodiment, in order to obtain an optimum value more precisely, a combination that minimizes the total dispersion amount is searched for while changing the fiber length by 10 mm. The adjustment accuracy of the length of the medium 103 and the negative dispersion fiber 104 can be obtained in the same manner. When constructing an optical system, it is necessary to optimize the length by a cutback method or the like due to individual differences between the negative dispersion fiber 104 and the positive dispersion fiber 105. The accuracy of the lengths of the negative dispersion fiber 104 and the positive dispersion fiber 105 required at that time is the same as the accuracy obtained by the equation (15). The “cutback method” is a method for obtaining an optimum fiber length by cutting the fiber little by little and examining characteristics and the like while shortening.

The dispersion characteristics of the transmission apparatus 100 when the lengths of the medium 103, the negative dispersion fiber 104, and the positive dispersion fiber 105 are set as described above will be described with reference to FIG. The dispersion characteristics of the medium 103, the negative dispersion fiber 104, and the positive dispersion fiber 105 are shown in FIGS. 6 (a) to 6 (c). Further, the total dispersion amount in the transmission apparatus 100 in which the lengths of the medium 103, the negative dispersion fiber 104, and the positive dispersion fiber 105 are set as described above is shown in FIG. The broken line in FIG. 6D is a line indicating the group velocity dispersion T ₀ ² = −900 fs ² obtained using the equation (6). It can be seen that in the range of approximately 1450 nm to 1650 nm, which is the wavelength band of the laser 102, equation (14) is satisfied and dispersion compensation is performed.

  FIG. 7 shows the results obtained by calculating the time waveform and spectrum of the laser 102 that has passed through the medium 103, the negative dispersion fiber 104, and the positive dispersion fiber 105. FIG. 7A shows a time waveform of the laser 102, and FIG. 7B shows an intensity spectrum having a frequency on the horizontal axis obtained by Fourier transforming the time waveform. In FIG. 7A and FIG. 7B, the dotted line is that of the laser 102 (incident light) before entering the medium 103, and the solid line is that of the laser 102 (emitted light) emitted from the positive dispersion fiber 105. is there.

The time waveform was obtained using a numerical calculation method called a split-step Fourier method (see Govind P. Agrawal, Nonlinear Fiber Optics third Edition, Academic Press). The following equations (16) to (18) were used as differential equations describing the time evolution of the laser 102 (changes in the physical quantity of the laser 102 over time). Note that the wavelength of the laser 102 is λ, the envelope of the electric field of the laser 102 is A (z, t), the second-order group velocity dispersion of the material that the laser 102 propagates is β ₂ , and the third-order of the material that the laser 102 propagates. Let β ₃ be the group velocity dispersion of. Also, let γ be the nonlinear coefficient of the material that the laser 102 propagates and D be the dispersion parameter of the material that the laser 102 propagates.

  In both FIG. 7A and FIG. 7B, since the peak power of the laser 102 was reduced by passing through the medium 103, no major collapse was observed in the time waveform and the shape of the spectrum. Further, by adjusting the lengths of the medium 103, the negative dispersion fiber 104, and the positive dispersion fiber 105 to compensate for the dispersion parameter and the dispersion slope, the shape of the time waveform becomes almost the same as that of the incident light. In the time waveform shown in FIG. 7A, two small side peaks are obtained in addition to the main peak, but the ratio of the main peak power to the total power of the incident light is 82%. Light can be used as irradiation light to the photoconductive element 106.

  The configuration of the transmission apparatus 100 has been described above. According to the transmission apparatus 100 of the present embodiment, by causing the laser 102 to enter the negative dispersion fiber 104 via the medium 103, the influence of the nonlinear optical effect can be reduced to the extent that the pulse waveform of the laser 102 is not affected. Further, by setting the lengths of the medium 103, the negative dispersion fiber 104, and the positive dispersion fiber 105 as described above, the dispersion parameter and the dispersion slope can be compensated. Therefore, the transmission apparatus 100 can transmit short pulse light efficiently by reducing the influence of dispersion by the optical fiber and the nonlinear optical effect.

(Second Embodiment)
A transmission apparatus 800 according to the present embodiment will be described with reference to FIG. FIG. 8 is a diagram for explaining the configuration of the transmission apparatus 800. In this embodiment, a fiber laser 801 is used as the light source 101, and an optical unit including a collimator lens 810 and a condenser lens 811 is disposed on the propagation path of the laser 802 from the fiber laser 801. Since other parts are the same as those of the first embodiment, detailed description thereof is omitted.

  The collimating lens 810, the medium 103, and the condensing lens 811 are fixedly arranged in one housing 850 and integrated. The emission fiber end of the fiber laser 801 is connected to the housing 850, and the laser 802 emitted from the fiber laser 801 is converted into parallel light by the collimator lens 810 and then passes through the silicon plate as the medium 103. The housing 850 is connected to the negative dispersion fiber 104, and the laser 802 that has passed through the medium 103 is collected by the condenser lens 811 and enters the core of the negative dispersion fiber 104.

  By mechanically integrating the collimating lens 810, the medium 103, and the condenser lens 811, the coupling efficiency of the laser 802 incident on the negative dispersion fiber 104 can be improved, and the coupling efficiency can be increased for a long time. Can be stabilized.

  The collimating lens 810 preferably has a configuration for adjusting the relative position with respect to the negative dispersion fiber 104 in a plane direction perpendicular to the optical axis of the laser 802 propagating through the collimating lens 810. Similarly, it is desirable that the condensing lens 811 has a configuration in which the relative position with respect to the negative dispersion fiber 104 can be adjusted. By having a configuration for adjusting the relative position, the coupling efficiency of the laser 802 to the negative dispersion fiber 104 can be optimized.

  If the lengths of the medium 103, the negative dispersion fiber 104, and the positive dispersion fiber 105 are the same as those in the first embodiment, the medium 103 is silicon having a thickness of 10 mm, and the distance from the collimating lens 810 to the condenser lens 811 is 10 mm. That is all you need. The absolute value of the dispersion parameter of silicon as the medium 103 is several tens of times larger than the absolute value of the dispersion parameter of a general positive dispersion fiber. Therefore, compared with the length of the negative dispersion fiber 104 and the length of the positive dispersion fiber 105, a compact free space portion can be designed.

  The laser 802 emitted from the fiber laser 801 may be chirped pulsed light. For example, if the fiber laser 801 can realize the same chirp as the dispersion given by the medium 103, the medium 103 is unnecessary. In this case, a transmission device that transmits pulsed light can be realized by directly fusing the emission fiber of the fiber laser 801 and the negative dispersion fiber 104.

  As described above, according to the transmission apparatus 800 of the present embodiment, it is possible to efficiently transmit short pulse light by reducing the influence of dispersion by the optical fiber and the nonlinear optical effect.

(Third embodiment)
A transmission apparatus 900 according to the present embodiment will be described with reference to FIG. FIG. 9A is a diagram for explaining the configuration of the transmission apparatus 900. In the first embodiment, the laser (short pulse light) 102 from the transmission device 100 is incident on the photoconductive element 106. In this embodiment, the laser 102 from the transmission device 100 is a nonlinear optical for generating terahertz waves. The light enters the element 906 (hereinafter referred to as “element 906”). The transmission apparatus 900 includes a negative dispersion medium 903 (hereinafter referred to as “medium 903”), a first fiber (negative dispersion fiber) 904, and a second fiber (positive dispersion fiber) 905. Detailed description of the same configuration as in the first embodiment will be omitted.

  FIG. 9B is a diagram illustrating the configuration of the element 906. The element 906 includes a waveguide 907 having a nonlinear crystal (nonlinear optical crystal) as a core layer, and a coupling member 908. The coupling member 908 is silicon having a flat surface and a conical curved surface. The coupling member 908 is disposed so that the planar portion of the coupling member 908 is close to the waveguide 907. The rotation axis of the cone is configured to coincide with the central axis of the core layer of the waveguide 907. The height of the cone is about the same as the length of the waveguide 907.

  When the laser 902 propagates through the nonlinear crystal in the waveguide 907, a terahertz wave is generated by the optical rectification effect that is a second-order nonlinear optical effect. The generated terahertz wave is emitted from the waveguide 907, propagates in the coupling member 908 adjacent to the waveguide 907, and exits from the side surface of the cone. This phenomenon is called electro-optic Cherenkov radiation, and since the cross-sectional area of the nonlinear crystal in the waveguide 907 is small, a high light density can be obtained, and a high-intensity terahertz wave generation method using a large nonlinear optical effect Known as. For details, see IEEE Select. Topic. In Quantum Electron, Vol. 19, p. Reference may be made to 8500212, (2013).

Light emitted from the positive dispersion fiber 905 enters the waveguide 907. Typically, the waveguide 907 is designed to have a cross section with a core portion diameter (core diameter) of about 10 μm so that the laser 102 propagates in a single mode. Lithium niobate (LiNbO ₃ ) is used as the nonlinear crystal. LiTaOx, NaTaOx, KTP, ZnTe, GaSe, GaAs, or the like may be used as the nonlinear crystal.

LiNbO ₃ has inherent dispersion characteristics, and the pulse width of the laser 102 incident on the waveguide 907 is widened while propagating through the waveguide 907. Since electro-optic Cherenkov radiation uses the second-order nonlinear optical effect, the reduction in peak power accompanying the broadening of the pulse width results in a reduction in the intensity of the generated terahertz wave. In order to increase the intensity of the generated terahertz wave, the medium 903 and the negative dispersion fiber 904 are set so that the pulse width of the laser 102 is the shortest at the center of the waveguide 907 (position 5 mm from the incident end of the waveguide 907). It is desirable to select the length of the positive dispersion fiber 905.

  Each of the medium 903, the negative dispersion fiber 904, and the positive dispersion fiber 905 is made of the same material as in the first embodiment. Therefore, the lengths of the medium 903, the negative dispersion fiber 904, and the positive dispersion fiber 905 need to be different from those in the first embodiment.

The dispersion characteristics of LiNbO ₃ can be obtained using the Selmeier equation, and the dispersion parameter is 78.30 ps / nm / km and the dispersion slope is 0.305 ps / nm / km at a wavelength of 1550 nm. When the lengths of the medium 903, the negative dispersion fiber 904, and the positive dispersion fiber 905 are 10 mm, 50 mm, and 970 mm, respectively, the total dispersion including the 5 mm long lithium niobate is shown in FIG. As shown in FIG. 10, it is shown that dispersion is compensated over the entire spectral band of the laser 102.

  Therefore, according to the transmission apparatus 900 of the present embodiment, it is possible to efficiently transmit short pulse light by reducing the influence of dispersion by the optical fiber and the nonlinear optical effect.

(Fourth embodiment)
A measurement apparatus (information acquisition apparatus) 1100 according to this embodiment will be described with reference to FIG. FIG. 11 is a diagram for explaining the configuration of the measurement apparatus 1100. The measurement apparatus 1100 is a measurement apparatus that acquires a time waveform of a terahertz wave pulse (hereinafter referred to as “terahertz wave”) reflected by the subject 1112. The measurement apparatus 1100 performs measurement using the principle of terahertz time domain spectroscopy (THz-TDS method: Terahertz Time Domain Spectroscopy).

  The measurement apparatus 1100 includes a light source 1101, a beam splitter 1102, a delay optical unit 1104, a detection unit 1107, a generation unit 1111, an amplification unit 1113, an output unit 1114, a second transmission device 1150, a first transmission device 1151, and an irradiation unit. 1153. The short pulse light from the light source 1101 is branched by the beam splitter 1102 into pump light incident on the generation unit 1111 and probe light incident on the detection unit 1107.

  The first transmission device 1151 is a first transmission unit that transmits pump light to the generation unit 1111, and includes a first negative dispersion medium 1108 (hereinafter referred to as “first medium 1108”) and a first negative transmission medium. A dispersion fiber 1109 and a first positive dispersion fiber 1110 are included. The second transmission device 1150 is a second transmission unit that transmits the probe light to the detection unit 1107. The second transmission device 1150 includes a second negative dispersion medium 1103 (hereinafter referred to as “second medium 1103”) and a second negative dispersion medium. A dispersion fiber 1105 and a second positive dispersion fiber 1106 are included. The first medium 1108, the second medium 1103, the first negative dispersion fiber 1109, the second negative dispersion fiber 1105, the first positive dispersion fiber 1110, and the second positive dispersion fiber 1106 are respectively It has the same characteristics as the corresponding configuration of the embodiment. In addition, the length of each component is set by the method described in the first embodiment.

  When the lengths of the second medium 1103 and the first medium 1108 are the same, the second medium 1103 and the first medium 1108 are removed, and one medium is disposed between the light source 1101 and the beam splitter 1102. The structure to do may be sufficient.

  A voltage signal output from a voltage source (not shown) is applied to the photoconductive element as the generation unit 1111. When pump light is irradiated from the first positive dispersion fiber 1110 to the generator 1111, a terahertz wave is generated. The generation unit 1111 generates a terahertz wave when light enters, and a photoconductive element is used in this embodiment. The generation unit 1111 is not limited to this, and a known unit such as a terahertz wave generation element using a nonlinear crystal such as the element 906 of the third embodiment can be used. The terahertz wave generated by the generation unit 1111 is irradiated to the subject 1112, and the terahertz wave reflected by the subject 1112 reaches the detection unit 1107.

  The detection unit 1107 detects the terahertz wave using the probe light emitted from the second positive dispersion fiber 1106. In this embodiment, a photoconductive element is used as the detection unit 1107. When the probe light is incident on the detection unit 1107 while the terahertz wave is incident on the detection unit 1107, a current is obtained as a signal obtained by detecting the terahertz wave. The obtained current is converted into a voltage signal by the amplifier 1113 and sent to the output unit 1114.

  By making the voltage signal applied to the generation unit 1111 an alternating current, the terahertz wave generated by the generation unit 1111 may be intensity-modulated, and the detection signal of the detection unit 1107 may be lock-in detected. Further, as a means for modulating the intensity of the terahertz wave, the pump light may be modulated using a chopper before entering the first negative dispersion fiber 1109.

  The delay optical unit 1104 is a part that optically adjusts the interval (delay time) at which the terahertz wave enters the detection unit 1107 by changing the optical path length difference between the optical path length of the pump light and the optical path length of the probe light. . By measuring the terahertz wave detected by the detection unit 1107 while changing the delay time, the time waveform is measured using the THz-TDS method. By controlling the delay optical unit 1104 with the output unit 1114, the delay time is changed, and by plotting the terahertz wave signal obtained from the detection unit 1107 for each delay interval, the time waveform of the terahertz wave can be acquired.

  Although the measurement apparatus 1100 of the present embodiment detects the terahertz wave reflected by the subject 1112, the terahertz wave transmitted through the subject 1112 may be detected.

  In addition, a stage for moving the subject 1112 in a direction perpendicular to the parallel propagation region of the terahertz wave is provided, the subject 1112 is moved at an appropriate time interval, and a position (irradiation) where the terahertz wave is irradiated on the subject 1112 The position may be changed. Note that the “parallel propagation region of the terahertz wave” is defined as the focal depth of the terahertz wave collected toward the subject 1112 by the irradiation unit 1153 in terms of wave optics. “Depth of focus” is defined as a range in which the beam diameter of the input pulse 114 is equal to or less than w × √2, where w is the smallest beam diameter when the irradiation unit 1153 narrows the beam diameter of the laser.

  With such a configuration, it is also possible to perform imaging for acquiring an image of the subject 1112 using a result obtained by analyzing a time waveform acquired at each irradiation position. Specifically, using the time waveform data of the terahertz wave acquired for each terahertz wave irradiation position, the shape and peak value of each time waveform, amplitude spectrum and phase spectrum obtained by Fourier transform, complex refractive index, etc. An imaging image can be obtained based on the information.

  The measuring apparatus 1100 of this embodiment transmits pump light and probe light through an optical fiber. If the influence of optical fiber dispersion and nonlinear optical effects is large, problems such as narrowing of the terahertz wave spectrum and lowering of peak power occur due to the broadening of the pulse width of pump light and probe light and the accompanying decrease in peak power. Arise. By having the first transmission device 1151 and the second transmission device 1150, the pump light by the optical fiber and the influence of the dispersion of the probe light and the nonlinear optical effect are reduced, and the pump light and the probe light are efficiently transmitted. it can. For this reason, it is possible to reduce the narrowing of the spectrum of the generated terahertz wave and the reduction in peak power.

  In the present embodiment, the transmission device of the above-described embodiment is used for each of the first transmission unit and the second transmission unit, but a transmission device may be used for either one. Moreover, you may make it the structure which each transmits the pulsed light from a different light source.

(Fifth embodiment)
A measurement apparatus (information acquisition apparatus) 1200 according to the present embodiment will be described with reference to FIG. FIG. 12 is a diagram for explaining the configuration of the measuring apparatus 1200. The measuring apparatus 1200 is an imaging system that acquires an image of the subject 1207. The measurement device 1200 includes a light source 1201, a transmission device 1250, a generation unit 1205, lenses 1206 and 1208, a detection unit 1209, an amplifier 1210, a control unit 1211, and an output unit 1212.

  The generation unit 1205 is a generation element that generates a terahertz wave using a nonlinear crystal. Here, the generation unit 1205 has the same configuration as the element 906 described in the third embodiment, and generates a terahertz wave (terahertz wave pulse) when light from the transmission device 1250 is incident thereon. Terahertz waves are emitted by Cherenkov radiation. As the transmission apparatus 1250, the transmission apparatus 900 of the third embodiment is used. That is, the transmission device 1250 includes a medium 903, a negative dispersion fiber 904, and a positive dispersion fiber 905, and the length of each component is set in consideration of dispersion by the waveguide 907.

  The terahertz wave from the generation unit 1205 is collected by a lens 1206 serving as an irradiation unit and irradiated onto the subject 1207. The terahertz wave that has passed through the subject 1207 enters the detection unit 1209 via the lens 1208. The lenses 1206 and 1208 are optical systems that collect terahertz waves, but may be further added or omitted depending on the spatial spread of the terahertz waves, the size of the detection unit 1209, and the like. Further, a configuration using a parabolic mirror instead of the lenses 1206 and 1208 may be used.

  The detection unit 1209 detects the average output of the terahertz wave that has passed through the subject 1407. As the detection unit 1209, an electronic device such as a Schottky barrier diode type, a plasmon type, an FET type, or a heat-sensitive pyro type or bolometer type can be used. Since the terahertz wave obtained in the present embodiment is a sub-picosecond pulse, the detection unit 1209 cannot measure the time waveform of the terahertz wave. The repetition frequency of the terahertz wave pulse is, for example, 80 MHz, and the detection unit 1209 measures the time average of the intensity of the terahertz wave.

  In order to measure the time average, the measurement band of the detection unit 1209 needs to be sufficiently low, for example, 10 MHz or less, which is about 1/10 of the laser repetition frequency. Therefore, when a detector with a narrow measurement band such as a pyro detector is used as the detection unit 1209, the measurement signal is used as it is, and when a diode or the like is used, band adjustment means such as an integrator or a low-frequency transmission filter is used. Provided for detector output signal.

  A terahertz wave output, a scattering pattern, or the like may be measured using a detector in which a plurality of detection elements are arranged in a two-dimensional array as the detection unit 1209. Further, another detection unit 1213 may be used so that backscattering and reflection of the terahertz wave can be detected. In order to improve the S / N ratio, the control unit 1211 sends a command signal to the light source 1201 to apply intensity modulation to the output light, or uses a chopper in the spatial optical unit to lock the terahertz wave by intensity modulation. It may be configured to detect in.

  The detection result of the detection unit 1209 is amplified by the amplifier 1210 and then sent to the output unit 1212 via the control unit 1211. The control unit 1211 controls each configuration of the measurement device 1200. The output unit 1212 acquires the time waveform of the terahertz wave using the detection result of the detection unit 1209, or acquires the information of the subject 1207 by analyzing the acquired time waveform. Further, an image of the subject 1207 is acquired using the acquired information of the subject 1207.

  In this embodiment, the position of the subject 1207 is fixed, but a moving means such as a stage or a belt conveyor for moving the subject 1207 may be provided. A one-dimensional imaging or a two-dimensional imaging image can be obtained from a combination of a position where the subject 1207 is irradiated with the terahertz wave and an output signal which is a detection result of the detection unit 1209.

  The measuring apparatus 1200 according to the present embodiment transmits light using an optical fiber using a transmission apparatus 1250. If the influence of optical fiber dispersion and nonlinear optical effect is large, narrowing of the terahertz wave spectrum and reduction of peak power may occur due to the broadening of the pulse width of pump light and probe light and the accompanying reduction of peak power. is there. By including the transmission device 1250, it is possible to reduce the influence of dispersion by the optical fiber and the nonlinear optical effect, and to transmit light efficiently. For this reason, it is possible to reduce the narrowing of the spectrum of the generated terahertz wave and the reduction in peak power.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary. For example, the present invention can be applied not only to the above-described embodiment but also to various uses using optical fiber transmission of short pulse laser light by making modifications. Examples of application ranges other than the generation of terahertz waves include a microscope, a medical device, and a pulse processing device. Further, the present invention can also be applied to a device such as a generator or a detector that is modularized by connecting the transmission device described in each of the above-described embodiments and an element that generates or detects an electromagnetic wave such as a terahertz wave. The element that generates or detects electromagnetic waves is a known element that generates electromagnetic waves when pulsed light is incident, such as an element that includes a nonlinear crystal and uses electro-optic Cherenkov radiation, or a photoconductive element. Available.

  In the above-described embodiments, optical fibers such as the first fiber and the second fiber are used. However, these optical fibers do not have to have a core portion and a cladding portion. For example, the optical waveguide member that guides light by confining light by providing a refractive index distribution in a plane perpendicular to the light propagation direction without providing a cladding portion is also used for the first fiber and the second fiber of each embodiment. Included. In this case, the core portion of the optical fiber refers to a portion that exists in the central portion of the optical waveguide member and is higher than the refractive index of the peripheral portion.

100 Transmission Device 103 Negative Dispersion Medium 104 First Fiber (Negative Dispersion Fiber)
105 Second fiber (positive dispersion fiber)

Claims (13)

A transmission device for transmitting pulsed light,
A negative dispersion medium having a negative dispersion parameter in a wavelength band included in incident pulsed light;
A first fiber on which pulsed light that has passed through the negative dispersion medium is incident;
A second fiber on which the pulsed light that has passed through the first fiber is incident,
The first fiber has a negative dispersion parameter in a wavelength band included in incident pulsed light,
The second fiber has a positive dispersion parameter in a wavelength band included in incident pulsed light,
The negative dispersion medium and the second fiber have a positive dispersion slope,
The transmission apparatus, wherein the first fiber has a negative dispersion slope. The negative dispersion medium is configured to satisfy the formula (1),
2. The transmission according to claim 1, wherein the total dispersion amount b _2all is smaller than a pulse width T ₀ of the pulse light incident on the negative dispersion medium in a frequency region included in the pulse light incident on the negative dispersion medium. apparatus.

However,

T ₀ is the pulse width of the pulsed light incident on the negative dispersion medium,
b _2f is a group velocity dispersion per unit length of the first fiber,
P ₀ is the peak power of the pulsed light incident on the negative dispersion medium,
P ₁ is the peak power of the pulsed light immediately after passing through the negative dispersion medium,
γ is the nonlinear coefficient of the first fiber,
c is the speed of light,
L ₁ is the length of the negative dispersion medium in the optical axis direction of the pulsed light incident on the negative dispersion medium The first fiber and the second fiber are single mode fibers,
The transmission apparatus according to claim 1 or 2, wherein a zero dispersion wavelength of the first fiber is longer than a zero dispersion wavelength of the second fiber. 4. The transmission device according to claim 1, wherein a zero dispersion wavelength of the second fiber is smaller than a wavelength included in pulsed light incident on the negative dispersion medium. 5. 5. The transmission device according to claim 1, wherein a pulse width of the pulsed light incident on the negative dispersion medium is 100 femtoseconds or less. An optical unit that focuses the pulsed light incident on the negative dispersion medium onto the negative dispersion medium;
A housing in which the negative dispersion medium and the optical unit are disposed;
The transmission apparatus according to claim 1, wherein the casing and the first fiber are connected. The transmission apparatus according to claim 6, wherein the casing is connected to an emission fiber of a light source that outputs pulsed light incident on the negative dispersion medium. The transmission apparatus according to claim 1, wherein the negative dispersion medium includes silicon. The transmission apparatus according to any one of claims 1 to 8, wherein the first fiber and the second fiber include silicon dioxide. A measuring device that irradiates a subject with terahertz waves to acquire information about the subject,
A generator that generates terahertz waves when pulsed light is incident;
An irradiation unit for irradiating the subject with terahertz waves from the generation unit;
A detection unit for detecting a terahertz wave transmitted from the subject or reflected by the subject;
A transmission unit that transmits pulsed light from a light source to the generation unit or the detection unit,
The measuring apparatus according to claim 1, wherein the transmission unit is the transmission apparatus according to claim 1. An apparatus for generating or detecting terahertz waves,
A transmission apparatus according to any one of claims 1 to 9,
And an element that generates or detects a terahertz wave when pulsed light from the transmission device is incident thereon. The apparatus of claim 11, wherein the element comprises a photoconductive element. The apparatus of claim 11, wherein the element comprises a nonlinear crystal.

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