Pulse light shaper and pulse light generator

Abstract

To provide a pulse light shaper which is suitable for use with higher power.SOLUTION: Provided is a pulse light shaper for compressing the pulse width of inputted pulse light and outputting it, wherein a fiber pair is connected in two stages or more, the fiber pair composed of a pair of high nonlinear fibers located on the pulse light inputted side and dispersion fibers to which pulse light outputted from the high nonlinear fibers is inputted. The high nonlinear fibers are zero dispersion or normal dispersion in the wavelength of inputted pulse light, and the dispersion fibers are abnormal dispersion in the wavelength of inputted pulse light, where the nonlinearity constant is lower and the absolute value of dispersion is higher than those of the high nonlinear fibers. The absolute value of dispersion in the wavelength of inputted pulse light of dispersion fibers of a second fiber pair, out of two fiber pairs included in the two or more stages of fiber pairs, which is far from the pulse light inputted side, is smaller than 1 / 2 of the absolute value of dispersion in the wavelength of inputted pulse light of dispersion fibers of a first fiber pair close to the pulse light inputted side.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pulsed light shaper and a pulsed light generator. [Background technology]

[0002] Various technological developments have been carried out so far regarding comb-like profiled fibers (CPFs), which are constructed by alternately combining a highly nonlinear fiber (HNLF), which is a nonlinear medium, and an anomalous dispersion fiber, which is a dispersive medium, and which adiabatically compress optical solitons (Patent Document 1).

[0003] The feature of the CPF is that it can perform high-efficiency, high-quality pulse shaping despite its relatively short overall length. High-quality pulse shaping here means pulse shaping that does not cause significant noise amplification due to pedestal enhancement or modulation instability gain, which occur in high-order soliton compression, and the associated timing jitter addition. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5242014 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, with recent developments in optical amplification technology, there are cases where the peak power of pulsed light input to a CPF becomes higher, or where a higher output power is required from a CPF.

[0006] The present invention has been made in view of the above, and an object of the present invention is to provide a pulsed light shaper suitable for use at higher powers, and a pulsed light generator using the same. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, one aspect of the present invention is a pulse light shaper that compresses the pulse width of input pulse light and outputs the compressed pulse light, the pulse light shaper being configured by connecting two or more stages of fiber pairs each composed of a highly nonlinear fiber located on the side where the pulse light is input and a dispersion fiber to which the pulse light output from the highly nonlinear fiber is input, the highly nonlinear fiber has zero dispersion or normal dispersion at the wavelength of the input pulse light, the dispersion fiber has anomalous dispersion having a lower nonlinear constant and a higher absolute value of dispersion than the highly nonlinear fiber at the wavelength of the input pulse light, and the absolute value of dispersion at the wavelength of the input pulse light of the dispersion fiber of a second fiber pair farther from the side where the pulse light is input among two fiber pairs included in the two or more stages of fiber pairs is smaller than 1 / 2 the absolute value of dispersion at the wavelength of the input pulse light of the dispersion fiber of a first fiber pair closer to the side where the pulse light is input.

[0008] The dispersion at the wavelength of the dispersion fiber of the first fiber pair may be not less than 13.3 ps / nm / km and not more than 23 ps / nm / km.

[0009] The dispersion fiber of the first fiber pair may be optical fiber conforming to the ITU-T G.652 or G.654 recommended standards.

[0010] The input pulsed light may have a peak power of 20 W or more.

[0011] The dispersion of the highly nonlinear fiber may be −4 ps / nm / km or more and 0 ps / nm / km or less in a wavelength range including the wavelength of the input pulse light and including 90% of the power of the designed output pulse light.

[0012] In a wavelength range including the wavelength of the input pulsed light and including 90% of the power of the designed output pulsed light, the absolute value of the dispersion of the dispersion fiber of the second fiber pair may be less than or equal to half the absolute value of the dispersion of the first fiber pair.

[0013] The splice loss between the highly nonlinear fiber and the dispersion fiber may be 0.2 dB or less.

[0014] One aspect of the present invention is a pulsed light generator including a pulsed light source that outputs the pulsed light, and the pulsed light shaper. Effect of the Invention

[0015] The present invention has an effect of realizing a pulsed light shaper suitable for use at higher powers and a pulsed light generator using the same. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a pulsed light generator according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing the optical characteristics of each optical fiber in calculation example 1. In FIG. [Diagram 3] FIG. 3 is a diagram showing the length of each optical fiber, the total length, and the characteristics of the pulsed light in calculation example 1. In FIG. [Figure 4] FIG. 4 is a diagram showing pulse waveforms for different input peak powers in calculation example 1. [Diagram 5] FIG. 5 is a diagram showing pulse waveforms for different input peak powers in calculation example 1. In FIG. [Figure 6] FIG. 6 is a diagram showing the relationship between the input peak power and the output peak power in the calculation example 1. In FIG. [Figure 7] FIG. 7 is a diagram showing the relationship between the input peak power and the peak power expansion rate in the calculation example 1. In FIG. [Figure 8] FIG. 8 is a diagram showing the relationship between the input peak power and the output pulse width in calculation example 1. [Figure 9] FIG. 9 is a diagram showing the optical characteristics of each optical fiber in calculation example 2. In FIG. [Figure 10] FIG. 10 is a diagram showing the length of each optical fiber, the total length, and the characteristics of the pulsed light in calculation example 2. [Figure 11] FIG. 11 is a diagram showing the relationship between the input peak power and the output peak power in calculation example 2. In FIG. [Figure 12] FIG. 12 is a diagram showing the relationship between the input peak power and the peak power expansion rate in the calculation example 2. In FIG. [Figure 13] FIG. 13 is a diagram showing the relationship between the input peak power and the output pulse width in calculation example 2. [Figure 14] FIG. 14 is a diagram showing the relationship between the input peak power and the length of the first dispersion fiber in Calculation Example 2. In FIG. [Figure 15] FIG. 15 is a diagram showing the relationship between the dispersion of the second dispersion fiber and the characteristics of the output pulse in Calculation Example 3. In FIG. [Figure 16] FIG. 16 is a diagram showing the relationship between the dispersion of the second dispersion fiber and the output peak power in Calculation Example 3. In FIG. [Figure 17] FIG. 17 is a diagram showing the relationship between the dispersion of the second dispersion fiber and the output pulse width in Calculation Example 3. In FIG. [Figure 18] FIG. 18 is a diagram showing the relationship between the dispersion and the length of the second dispersion fiber in Calculation Example 3. In FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiment described below. In addition, in each drawing, the same or corresponding components are appropriately assigned the same reference numerals. In addition, in this specification, the cutoff wavelength or effective cutoff wavelength refers to the cable cutoff wavelength (λcc) defined in ITU-T G.650.1 of the International Telecommunications Union (ITU). In addition, other terms not specifically defined in this specification shall follow the definitions and measurement methods in G.650.1 and G.650.2.

[0018] (Embodiment) 1 is a schematic diagram of a pulsed light generator according to an embodiment. The pulsed light generator 100 includes a pulsed light source 10 and a pulsed light shaper 20.

[0019] The pulse light source 10 outputs a pulse light L1. The pulse light source 10 may be, for example, a pulse laser light source or a known combination of a continuous wave (CW) laser light source, an intensity modulator, and a modulation signal generator.

[0020] The pulse light shaper 20 compresses the pulse width of the input pulse light L1 and outputs it as pulse light L2. The pulse light shaper 20 is configured by connecting fiber pairs 21, ..., 2n, where n is an integer equal to or greater than 2. The fiber pairs 21, ..., 2n are an example of fiber pairs connected in two or more stages.

[0021] The fiber pair 21 is composed of a highly nonlinear fiber 21-1 located on the side where the pulsed light L1 is input, and a dispersion fiber 21-2 to which the pulsed light output from the highly nonlinear fiber 21-1 is input. The fiber pair 21 is an example of a first fiber pair that is closer to the side where the pulsed light L1 is input, among two fiber pairs included in two or more stages of fiber pairs.

[0022] The fiber pair 2n is composed of a highly nonlinear fiber 2n-1 located on the side where the pulsed light L1 is input, and a dispersion fiber 2n-2 to which the pulsed light output from the highly nonlinear fiber 2n-1 is input. The fiber pair 2n is an example of the second fiber pair farthest from the side where the pulsed light is input, among the two fiber pairs included in the two or more stages of fiber pairs.

[0023] The highly nonlinear fibers 21-1 and 2n-1 have a nonlinear constant γ[W -1 km -1 ] is a relatively high fiber. γ is preferably 8W -1 km -1 The highly nonlinear fibers 21-1 and 2n-1 have zero dispersion or normal dispersion at the wavelength of the input pulse light L1, and the dispersion is, for example, −4 ps / nm / km or more and 0 ps / nm / km or less at the wavelength of the input pulse light L1.

[0024] Moreover, the power spectrum of the output pulsed light L2 with the pulse width of the pulsed light L1 compressed is wider than the power spectrum width including the wavelength of the pulsed light L1. In this case, it is preferable from the viewpoint of ideal pulse compression that the dispersion of the highly nonlinear fibers 21-1, 2n-1 is within a predetermined range in a wavelength range according to the power spectrum of the pulsed light L2. As a specific example, it is preferable that the dispersion of the highly nonlinear fibers 21-1, 2n-1 is -4 ps / nm / km or more and 0 ps / nm / km or less in a wavelength range that includes the wavelength of the input pulsed light L1 at the approximate center and includes 90% of the power of the designed output pulsed light. Moreover, it is preferable that the absolute value of the dispersion slope of the highly nonlinear fibers 21-1, 2n-1 is small. This is because if the absolute value of the dispersion slope is small, the predetermined dispersion range is satisfied in a wider wavelength range.

[0025] Here, "designed output pulse light" means output pulse light designed to have a target pulse width. In pulse light that is a chirp-free Fourier-limited pulse, there is a relational equation that the product of the pulse width (full width at half maximum) Δt and the frequency width (full width at half maximum) Δν of the power spectrum is a constant value. For example, in the case of a Gaussian pulse, Δt × Δν = 0.411, and sech 2 In the case of a Gaussian pulse, Δt×Δν=0.315. Therefore, it is preferable to set the target pulse width to Δt, calculate the frequency width of the power spectrum of the output pulse light as a Fourier limit pulse according to Δt and the spectral distribution shape of the output pulse light, and further calculate the wavelength width. Based on the wavelength width, it is preferable to set the dispersion of the highly nonlinear fibers 21-1, 2n-1 to be -4 ps / nm / km or more and 0 ps / nm / km or less in the wavelength range including 90% of the power of the output pulse light. In the case of a Gaussian pulse, the full width at half maximum is 2.35σ with respect to the deviation value σ, and the range including 90% of the power is 3.3σ. Therefore, the wavelength range including 90% of the power of the output pulse light is a value obtained by multiplying the full width at half maximum of the wavelength by 3.3 / 2.35=approximately 1.4. Also, in the case of a Gaussian pulse, 2 In the case of a pulsed light, the range that includes 90% of the power is about 1.4 times the full width at half maximum. Therefore, the wavelength range that includes 90% of the power of the output pulsed light is about 1.4 times the full width at half maximum of the wavelength, which is at least smaller than 2 times.

[0026] Moreover, the highly nonlinear fibers 21-1 and 2n-1 are preferably single mode fibers at the wavelength of the input pulsed light L1. Therefore, the cutoff wavelengths of the highly nonlinear fibers 21-1 and 2n-1 are preferably equal to or shorter than the wavelength of the input pulsed light L1.

[0027] The dispersion fibers 21-2 and 2n-2 have a lower nonlinear constant γ than the highly nonlinear fibers 21-1 and 2n-1 at the wavelength of the input pulse light L1. -1 km -1 Less than.

[0028] Moreover, the dispersion fibers 21-2 and 2n-2 have anomalous dispersion, in which the absolute value of dispersion is high at the wavelength of the input pulse light L1.

[0029] Here, the absolute value of dispersion at the wavelength of the input pulse light L1 of the dispersion fiber 2n-2 of the fiber pair 2n (an example of the second fiber pair) is smaller than 1 / 2 of the absolute value of dispersion at the wavelength of the input pulse light L1 of the dispersion fiber 21-2 of the fiber pair 21 (an example of the first fiber pair). This allows soliton compression to be suitably generated in the dispersion fiber 21-2 while also in the dispersion fiber 2n-2, thereby achieving suitable pulse compression.

[0030] In addition, when the absolute value of the dispersion of the dispersion fiber 2n-2 at the wavelength of the pulse light L1 is 1 / 2 or more of the absolute value of the dispersion of the dispersion fiber 21-2, in order to generate soliton compression in the dispersion fiber 2n-2 as well, the dispersion fiber 2n-2 must be shortened to balance nonlinearity and dispersion, and it becomes difficult to precisely adjust the length (fiber length) to an appropriate length. In particular, the higher the peak power of the pulse light L1, the shorter the length of the dispersion fiber 2n-2 must be, making the adjustment more difficult.

[0031] Similarly to the highly nonlinear fibers 21-1 and 2n-1, it is preferable that the absolute value of the dispersion of the dispersion fiber 2n-2 is equal to or less than half the absolute value of the dispersion of the dispersion fiber 21-2 in a wavelength range that includes the wavelength of the pulse light L1 at the approximate center and that includes 90% of the power of the designed output pulse light. It is also preferable that the absolute value of the dispersion slope of the dispersion fibers 21-2 and 2n-2 is small.

[0032] The dispersion of the dispersion fiber 21-2 at the wavelength of the input pulse light L1 is, for example, 13.3 ps / nm / km or more and 23 ps / nm / km or less. As such a dispersion fiber 21-2, an optical fiber conforming to the standard recommended by ITU-T G.652 or G.654 can be used. An optical fiber conforming to the standard recommended by ITU-T G.652 or G.654 is sometimes called a standard single mode fiber (SMF).

[0033] The dispersion of the dispersion fiber 2n-2 at the wavelength of the input pulse light L1 is, for example, 11.5 ps / nm / km or less. When the wavelength of the input pulse light L1 is in the 1.55 μm band, for example, an optical fiber called a dispersion shifted fiber can be used as the dispersion fiber 2n-2. A dispersion shifted fiber is a single-mode optical fiber whose zero dispersion wavelength is shifted to the 1.55 μm band.

[0034] Moreover, it is preferable that the dispersion fibers 21-2 and 2n-2 are single mode fibers at the wavelength of the input pulsed light L1. Therefore, it is preferable that the cutoff wavelength of the dispersion fibers 21-2 and 2n-2 is equal to or shorter than the wavelength of the input pulsed light L1.

[0035] Moreover, the splice loss between the highly nonlinear fiber and the dispersion fiber is preferably 0.2 dB or less from the viewpoint of reducing the loss of optical energy. A splice loss of 0.2 dB or less can be achieved, for example, by TEC (Thermally Expanded Core) fusion splicing.

[0036] (calculation example) The effects of this embodiment will be described below using a calculation example based on a simulation calculation. The calculation example is for n=2, that is, for pulse light shaper 20 having a configuration in which fiber pairs are connected in two stages.

[0037] (Calculation example 1) Fig. 2 is a diagram showing the optical characteristics of each optical fiber in calculation example 1. Note that "dispersion," "dispersion slope," "gradient of dispersion slope," "nonlinear constant," "Raman constant," and "propagation loss" are all values ​​at a wavelength of 1550 nm. Also, "HNLF" means highly nonlinear fibers 21-1 and 2n-1, "1st dispersion fiber" means dispersion fiber 21-2, and "2nd dispersion fiber" means dispersion fiber 2n-2.

[0038] In calculation example 1, the dispersion of the dispersion fiber 2n-2 is 4.23 ps / nm / km, which is smaller than half the dispersion of the dispersion fiber 21-2, 16.3945 ps / nm / km.

[0039] FIG. 3 is a diagram showing the length, total length, and characteristics of the pulsed light in the calculation example 1. "Input peak power" means the peak power of the pulsed light L1, that is, the input peak power to the pulsed light shaper 20. The pulsed light L1 is a Gaussian pulse with a wavelength of 1550 nm and a pulse width of 4 ps, and the input peak power was changed from 2 W to 100 W. "1st stage" and "2nd stage" mean the fiber pair 21 in the first stage and the fiber pair 2n in the second stage, respectively. "HNLF length" means the length of the highly nonlinear fiber 21-1 or 2n-1, "1st dispersion fiber length" means the length of the dispersion fiber 21-2, and "2nd dispersion fiber length" means the length of the dispersion fiber 21-2. The lengths of the highly nonlinear fiber 21-1 and the highly nonlinear fiber 2n-1 are optimized so that the ratio of the peak power of the pedestal component to the output peak power is 10% or less. The length of the dispersion fiber 21-2 and the length of the dispersion fiber 2n-2 are optimized so that the frequency chirp generated in the immediately preceding highly nonlinear fiber becomes zero.

[0040] "Output peak power" means the peak power of the pulsed light L2, i.e., the output peak power from the pulsed light shaper 20. "Peak power expansion ratio" means (output peak power) / (input peak power). "Total length" means the sum of the length of the highly nonlinear fiber 21-1, the length of the highly nonlinear fiber 2n-1, the length of the dispersion fiber 21-2, and the length of the dispersion fiber 21-2. "Output pulse width" means the pulse width of the pulsed light L2, i.e., the pulse width of the output pulse from the pulsed light shaper 20.

[0041] 4 and 5 are diagrams showing pulse waveforms for different input peak powers in calculation example 1. Fig. 4(a), (b), (c), and (d) show cases where the input peak powers are 60 W, 50 W, 40 W, and 30 W, respectively, and Fig. 5(a), (b), (c), and (d) show cases where the input peak powers are 20 W, 10 W, 5 W, and 2 W, respectively. In the legend, "input pulse" refers to the pulse waveform of pulsed light L1, "first-stage output" refers to the pulse waveform of pulsed light output from fiber pair 21 and input to fiber pair 2n, and "second-stage output" refers to the pulse waveform of pulsed light L2.

[0042] 3 to 5, in Calculation Example 1, it was confirmed that the output peak power and the peak power expansion ratio increased significantly and the output pulse width was compressed significantly when the input peak power was 10 W or more, and that the output peak power and the peak power expansion ratio increased even more significantly and the output pulse width was compressed even more significantly when the input peak power was 20 W or more. Therefore, in the case of Calculation Example 1, it was confirmed that when the input peak power was 10 W or more, the increase in the output peak power and the effect of pulse compression were noticeable, and when the input peak power was 20 W or more, the increase in the output peak power and the effect of pulse compression were more noticeable.

[0043] FIG. 6 is a diagram showing the relationship between the input peak power and the output peak power in Calculation Example 1, and is a graph of the values ​​shown in FIG. 3. In FIG. 6, the dashed line is a line obtained by extending a straight line that fits the data points in the region where the output peak power increases substantially linearly with respect to the input peak power after a noticeable increase, to the axis line where the output peak power is zero. The input peak power at the intersection of the dashed line and the axis line was about 10 W. It was also confirmed from FIG. 6 that the noticeable effect of increasing the output peak power appears from about 10 W, and the effect becomes more noticeable at 20 W or more.

[0044] FIG. 7 is a diagram showing the relationship between the input peak power and the peak power expansion ratio in Calculation Example 1. FIG. 8 is a diagram showing the relationship between the input peak power and the output pulse width in Calculation Example 1. Both of FIG. 7 and FIG. 8 are graphs of the values ​​shown in FIG. 3. From FIG. 7 and FIG. 8, it was confirmed that the effect of increasing the output peak power and compressing the pulse is more remarkable when the input peak power is 20 W or more. For example, according to FIG. 7, the peak power expansion ratio increases significantly up to the input peak power of about 20 W, but the increase thereafter slows down, and the output pulse width is fully saturated at about 100 W. Similarly, according to FIG. 8, the output pulse width is compressed significantly up to the input peak power of about 20 W, but the compression thereafter slows down, and the output pulse width is fully saturated at about 100 W.

[0045] (Calculation example 2) Next, a description will be given of Calculation Example 2. Calculation Example 2 differs from Calculation Example 1 in the characteristics of the dispersion fiber 21-2.

[0046] 9 is a diagram showing the optical characteristics of each optical fiber in calculation example 2. In calculation example 1, the dispersion value of dispersion fiber 2n-2 is 4.23 ps / nm / km, which is smaller than half the dispersion value of dispersion fiber 21-2, 21.7 ps / nm / km.

[0047] 10 is a diagram showing the length of each optical fiber, the total length, the characteristics of the pulsed light, etc. in calculation example 2. The pulsed light L1 is a Gaussian pulse with a wavelength of 1550 nm and a pulse width of 4 ps, and the input peak power was changed from 5 W to 100 W. The length of the highly nonlinear fiber 21-1, the length of the highly nonlinear fiber 2n-1, the length of the dispersion fiber 21-2, and the length of the dispersion fiber 21-2 are optimized so that the output peak power is maximized at each input peak power.

[0048] As shown in Fig. 10, in calculation example 2, it was confirmed that the output peak power and the peak power expansion ratio increased significantly and the output pulse width was compressed significantly from an input peak power of 20 W. Therefore, in the case of calculation example 2, it was confirmed that when the input peak power is 20 W or more, the effect of increasing the output peak power and compressing the pulse becomes more noticeable.

[0049] FIG. 11 is a diagram showing the relationship between the input peak power and the output peak power in Calculation Example 1, and is a graph of the values ​​shown in FIG. 10. In FIG. 11, the dashed line is a line obtained by extending a straight line that fits the data points in the region where the output peak power increases substantially linearly with respect to the input peak power after a noticeable increase, to the axis line where the output peak power is zero. The input peak power at the intersection of the dashed line and the axis line was about 20 W. It was also confirmed from FIG. 11 that the noticeable effect of increasing the output peak power appears from about 20 W.

[0050] Fig. 12 is a diagram showing the relationship between the input peak power and the peak power expansion ratio in Calculation Example 2. Fig. 13 is a diagram showing the relationship between the input peak power and the output pulse width in Calculation Example 2. Figs. 12 and 13 are both graphs of the values ​​shown in Fig. 10. It was also confirmed from Figs. 12 and 13 that if the input peak power is 20 W or more, the effect of increasing the output peak power and compressing the pulse is significantly exhibited.

[0051] Next, Fig. 14 is a diagram showing the relationship between the input peak power and the length of the first dispersion fiber (dispersion fiber 21-2). As shown in Fig. 14, the length of the dispersion fiber 21-2 increases as the input peak power increases up to an input peak power of 20 W, but decreases as the input peak power increases above 20 W. This is because, up to an input peak power of 20 W, the dispersion compensation effect is mainly effective against pulse compression in the dispersion fiber 21-2, whereas at input peak powers of 20 W or more, the high peak power contributes to the nonlinearity of the dispersion fiber 21-2, causing soliton compression, resulting in a decrease in the length as the peak power increases.

[0052] (Calculation example 3) Next, in Calculation Example 3, the dispersion value of the second dispersion fiber (dispersion fiber 2n-2) in Calculation Example 1 was changed to examine the characteristics of the output pulse. The length of the dispersion fiber 2n-2 was optimized so as to minimize the output pulse width according to each changed dispersion value. The lengths of the other highly nonlinear fibers 21-1, 2n-1, and 21-2 were fixed to the lengths when the input peak power was 50 W shown in Figure 3, that is, 5 m, 37 m, and 0.55 m, respectively.

[0053] 15 is a diagram showing the relationship between the dispersion of the second dispersion fiber (dispersion fiber 2n-2) and the characteristics of the output pulse in calculation example 3. "Dispersion" means the dispersion of the dispersion fiber 2n-2 at a wavelength of 1550 nm, "fiber length" means the length of the dispersion fiber 2n-2, "Peak Power" means the output peak power, and "Pulse Width" means the output pulse width.

[0054] Fig. 16 is a diagram showing the relationship between the dispersion of the second dispersion fiber (dispersion fiber 2n-2) and the output peak power in calculation example 3. Fig. 17 is a diagram showing the relationship between the dispersion of the second dispersion fiber (dispersion fiber 2n-2) and the output pulse width in calculation example 3. Figs. 16 and 17 are both graphs of the values ​​shown in Fig. 15.

[0055] 15 to 17, it was confirmed that the smaller the dispersion of the dispersion fiber 2n-2, the higher the output peak power and the shorter the output pulse width. In particular, when the dispersion of the dispersion fiber 2n-2 is 8 ps / nm / km, which is smaller than 1 / 2 of the dispersion of the dispersion fiber 21-2, 16.3945 ps / nm / km, the output peak power is (1674.8 W / 1159.6 W) = 1.44, i.e., increased by more than 140%, and the output pulse width is (100.2 fs / 64.7 fs) = 1.55, i.e., compressed by more than 150%, compared to when the dispersion of the dispersion fiber 2n-2 is 16 ps / nm / km, which is the same as the dispersion of the dispersion fiber 21-2.

[0056] Moreover, Fig. 18 is a diagram showing the relationship between the dispersion and the length of the second dispersion fiber in Calculation Example 3. Fig. 18 is a graph of the values ​​shown in Fig. 15. As shown in Fig. 18, it was confirmed that the smaller the dispersion of the dispersion fiber 2n-2, the longer the length. In particular, when the dispersion of the dispersion fiber 2n-2 is 8 ps / nm / km, which is smaller than 1 / 2 of the dispersion of the dispersion fiber 21-2, 16.3945 ps / nm / km, the length is about 1 m, which is longer than 0.59 m when the dispersion of the dispersion fiber 2n-2 is 16 ps / nm / km, which is the same as the dispersion of the dispersion fiber 21-2.

[0057] The present invention is not limited to the above-mentioned embodiment. The present invention also includes a configuration in which the above-mentioned components are appropriately combined. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-mentioned embodiment, and various modifications are possible. [Explanation of symbols]

[0058] 10: Pulsed light source 21, 2n: Fiber pair 21-1, 2n-1: Highly nonlinear fiber 21-2, 2n-2: Dispersion fiber 20: Pulse light shaper 100: Pulsed light generator L1: Pulsed light L2: Pulsed light

Claims

1. A pulsed light shaper that compresses the pulse width of an input pulsed light and outputs the compressed pulsed light, a highly nonlinear fiber located on the side where the pulsed light is input and a dispersion fiber to which the pulsed light output from the highly nonlinear fiber is input are connected in two or more stages of fiber pairs, the highly nonlinear fiber has zero dispersion or normal dispersion at the wavelength of the input pulse light, the dispersion fiber has an anomalous dispersion having a lower nonlinear constant and a higher absolute value of dispersion than the highly nonlinear fiber at the wavelength of the input pulse light, and has a length of 0.56 m or more; an absolute value of dispersion per unit length at the wavelength of the input pulsed light of the dispersion fiber of a second fiber pair farther from the side where the pulsed light is input among two fiber pairs included in the two or more stages of fiber pairs is smaller than 1 / 2 of an absolute value of dispersion per unit length at the wavelength of the input pulsed light of the dispersion fiber of a first fiber pair closer to the side where the pulsed light is input, soliton compression occurs due to nonlinearity in the dispersive fiber; When the pulse width of the input pulsed light is 4 ps, the pulse width of the output pulsed light is 80.7 fs or less. Pulsed light shaper.

2. The dispersion per unit length of the dispersion fiber of the first fiber pair at the wavelength is 13.3 ps / nm / km or more and 23 ps / nm / km or less.

2. The pulsed light shaper according to claim 1.

3. The dispersion fiber of the first fiber pair is an optical fiber conforming to the standard recommended by ITU-T G.652 or G.

654.

2. The pulsed light shaper according to claim 1.

4. The peak power of the input pulsed light is 20 W or more.

4. The pulse light shaper according to claim 1.

5. In a wavelength range including the wavelength of the input pulse light and including 90% of the power of the designed output pulse light, the dispersion per unit length of the highly nonlinear fiber is not less than −4 ps / nm / km and not more than 0 ps / nm / km.

5. The pulse light shaper according to claim 1.

6. In a wavelength range including the wavelength of the input pulse light and including 90% of the power of the designed output pulse light, the absolute value of the dispersion per unit length of the dispersion fiber of the second fiber pair is ½ or less of the absolute value of the dispersion of the first fiber pair.

6. The pulse light shaper according to claim 1.

7. The splice loss between the highly nonlinear fiber and the dispersion fiber is 0.2 dB or less.

7. The pulse light shaper according to claim 1.

8. a pulsed light source that outputs the pulsed light; A pulsed light shaper according to any one of claims 1 to 7, A pulsed light generator comprising:

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