JPS58121694A - Fiber raman laser - Google Patents

Abstract

PURPOSE:To provide a fiber Raman laser which can simply vary an output waveform with low exciting input by providing an equalizer for compensating the refractive index dispersion of an optical fiber in a resonator. CONSTITUTION:In a drawing, numeral 6 designates a refractive index dispersion compensating equalizer, 7 designates a light delay line 8, designates a synthesizer, 9 designates a branching filter, and 10 designates an etalon. An exciting pulse light source 1 employs a mode synchronous laser having 1.06mum of several tens W of power, and the equalizer 6 employs gratong pairs 61, 62 and 63, 64 which are opposed to each other. The optical fiber exhibits ordinary dispersion at the short wavelength side from zero dispersion wavelength and exhibits abnormal dispersion at the maximum wavelength side. The equalizer which is formed of the grating pairs exhibits abnormal dispersion, and the dispersing amount can be regulated by the distance between the paired gratings, that is the distance between the pair 61 and 62 and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fiber Raman laser, and more particularly to a pulse pumped fiber Raman laser including an equalizer in a resonator to compensate for refractive index dispersion of an optical fiber.

In a low-loss optical fiber, the interaction length between light and matter can be long, and in particular, in a single mode optical 7-iper, the core diameter is 1Oμ.
Since the photon density is small, on the order of m, the photon density is high, and stimulated scattered light by stimulated Raman scattering, stimulated four-photon mixing, etc. can be obtained relatively easily.

A fiber Raman laser is a device that injects laser light into a 7-eyeper to generate stimulated scattered light.

In addition to stimulated Raman scattering, it also includes stimulated four-photon mixing and is broadly called a seven-eye Raman laser.

In pulse-pumped fiber Raman lasers, the refractive index dispersion of the optical fiber is particularly problematic. The number 5 is.

Due to refractive index dispersion, during transmission in an optical fiber, a difference in transit time occurs between the AM optical pulses of different wavelengths and the guided dispersion (1Lft Hals), which causes traveling wave excitation in a long optical fiber. In this case, the substantial gain decreases and stimulated scattered light cannot be generated with high efficiency.

As is well known, the stimulated Raman gain of a fiber Raman laser has a wide gain band of 10100t to 1000ffi-', so if a low-loss, low-volume fiber is used, the stimulated Raman gain can be easily stimulated! by light scattering and haze-guided four-photon combination.

It is possible to obtain output in a wide wavelength range.

Fiber Raman lasers include those with a -pass temperature and those with a resonator configuration. Figure 1 is a schematic diagram showing an example of the configuration of a conventional 7-eye Brahman laser, where l is an excitation pulse light source, and 2
3 is an optical fiber, 3 is a lens 4 is a reflecting mirror, and 5 is a spectroscopic prism. In addition, λ.

is the wavelength of the excitation light, and λ is the wavelength of the stimulated scattering light.

In the example shown in FIG. 1 (6), a single mode optical fiber has recently been pumped with a 1.32 μm Q-switched YAG laser, and using the fact that the optical fiber has ultra-low loss and low dispersion in the vicinity, 1. Stimulated scattered light pulses have been obtained in a wide wavelength range from 0 μm to 1.6 μm. However, although the method shown in Figure 1 has the simplest configuration &1, due to the refractive index dispersion mentioned above, the excitation input cannot be lowered by lengthening the optical fiber, and the resonator configuration It has five drawbacks, including that it requires a larger excitation input than the conventional one.

In the example shown in Figure 1 ■, a resonator configuration using a resonator reflector is used, and the excitation light pulse and stimulated scattered light pulse are separated by a prism, and the light generated during the optical fiber travel at each wavelength is By providing a difference in optical path length by the time difference, the excitation light pulse and the stimulated scattering light pulse are synchronized, thereby reducing the excitation input.

In this example, a 1.06 μm mode-locked YAGI laser is used as the excitation light source, and a 1.07 μm to 1.32 μm
The stimulated 2-Man scattered light is obtained. However, the method shown in FIG. 2(c) has the disadvantage that, in order to obtain multi-wavelength output, a number of reflecting mirrors are required, making the configuration complicated. In addition, since the excitation light is not folded back, it has the disadvantage that the excitation light is not fully utilized, similar to the one-time pass type.

The object of the present invention is to eliminate the above-mentioned drawbacks and, at low excitation inputs, to
Moreover, it is an object of the present invention to provide a fiber-optic laser whose output wavelength can be easily varied.

The present invention is characterized in that it has a resonator configuration and includes inside the resonator an optical fiber that compensates for the refractive index dispersion of the optical fiber and an equalization amount that waits for the opposite dispersion.

Next, a fiber-on laser according to the present invention will be described in detail with reference to the drawings. FIG. 2 is a layout configuration diagram showing the configuration of an embodiment of the present invention, where 6 is an index dispersion compensation equalization amount, 7 is an optical delay path, 8 is a multiplexer, 9 is a demultiplexer, and 10 is an optical delay path.
is an etalon.

In this embodiment, a ring resonator configuration is used. In a ring resonator, there is only one coupling point for the input of the optical fiber for the round trip between the resonator and the resonator, so the coupling loss is the first
There is an advantage that the number of resonators required is half that of the seven Abry-Perot resonators shown in FIG.

In the embodiment of the present invention, the excitation pulse light source 1 is a 1.06 μm mote-synchronous laser with an output of several tens of W, and the optical fiber 2 has a core diameter of 10 μm and a zero dispersion wavelength of 1.4 μm.
GeO□-8i0□ single-mode optical fibers with lengths of several meters to several hundred meters are currently available. As the equalization amount 6,
A pair of grating bears 61, 62, 63, and 64 are used facing each other. As is well known, an optical fiber exhibits zero dispersion, normal dispersion at shorter wavelengths, and anomalous dispersion at longer wavelengths. The amount of equalization consisting of the above-mentioned brating shows anomalous dispersion, and the amount of dispersion is
The distance between the gratings 61 and 62 can be adjusted to several ps/nm, depending on the number of grooves, the size of the gratings, etc. Therefore, on the wavelength side shorter than the zero dispersion wavelength, sufficient compensation can be achieved by the equalization amount formed by the grating.

Figure 93 is a diagram showing an example of the dispersion characteristics in this example,
λ is the wavelength of the excitation light, λ. is the zero dispersion wavelength of the optical fiber. The comedy line is the dispersion of the original fiber, the dotted line is the dispersion of the grading equalization amount, and the dash-dotted line is the dispersion of the sum of these. In FIG. 3, the phase dispersion is approximately zero. Immediately after exiting the optical fiber, there is a travel time difference between the excitation light pulse and the stimulated scattering light pulse depending on the wave difference, but after passing through the equalization amount 6, this time difference is compensated. Optical delay path 7
uses four total reflection mirrors, and is used to adjust the resonator length to synchronize the interval excitation light pulses. However, if the optical fiber has a large dispersion, the length of the optical fiber may be shortened to a certain extent. This has the advantage of killing two birds with one stone by reducing the amount of dispersion and increasing the optical delay accordingly. The etalon 10 is for selecting the output wavelength, and when it is not inserted, scattered light is obtained in a wavelength range corresponding to the fermentation Raman gain. The multiplexer 8 is a semi-transparent mirror for inputting excitation pulse light, and the demultiplexer 9 is a semi-transparent mirror for output extraction.

Next, as is well known, the conditions for obtaining crocodile-guided four-photon mixed light are: 2kp = ks 10kAI +++ +++-o
) However, kp......5.
・・・・・・Wave number kAs of Stokes light・・・・・・
...This is the wave number of anti-Stokes light.

Therefore, in the present invention, as is clear from Figure 183,
Since equation (1) can be easily satisfied, output can be obtained by stimulated four-photon mixing even on the shorter wavelength side than the excitation light.

Note that the above is an example in which the excitation light has a wavelength shorter than the zero-dispersion wavelength, but if the excitation wavelength is longer than the zero-dispersion wavelength, a normal dispersion medium may be used as the equalization amount 6. . Figure 4 is a diagram showing an example of an equalization amount with normal dispersion, and the refractive index is "1m"! Each uses a different prism. As the material, BK, PK, etc. with large dispersion may be used.

Although one embodiment of the present invention has been described above, it goes without saying that various substitutions and transformations of the constituent elements can be made without departing from the purpose of the present invention. For example, a high-power dye laser or other solid-state laser such as a glass laser may be used as the excitation pulse light source 1, or a GeO2 fiber or a fiber with a liquid core such as benzene may be used as the optical fiber 2. It's okay. Alternatively, a 7-eyeper with dispersion of the opposite sign in degrees Celsius or a birefringent filter splitter may be used as the equalization amount.

As described above, according to the present invention, the resonator configuration is used,
In addition, by including the refractive index dispersion compensation equalization amount of the optical fiber, a fiber 7v laser can be obtained in which the output wavelength can be easily selected with a low pumping input.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an example of a conventional configuration, Fig. 2 is a schematic diagram showing a configuration of an embodiment of the present invention, Fig. #13 is an explanatory diagram of refractive index dispersion compensation in Fig. 2, and Fig. 4 is a diagram showing an example of an equalization amount having normal variance. In Figures 1 to 4, [, l is the excitation pulse light source, 2
is an optical fiber, 3 is a lens, 4 is a reflecting mirror 5 is a spectroscopic prism, 6 is an equalization amount, 7 is an optical delay path, 8 is a multiplexer, 9 is a demultiplexer, 10 is an etalon, and 11 is a refractive index n1 prism, 1
2 is a prism with a refractive index.

Claims (1)

[Claims] A pulse-pumped fiber Raman laser having a resonator configuration, characterized in that the resonator includes an optical delay path for synchronizing the pump pulse light and the stimulated scattered light, and an index dispersion compensating equalizer. laser.