KR100276434B1 - Optical fiber raman amplifier structure - Google Patents

Abstract

PURPOSE: An optical fiber amplifier structure is provided to maintain good amplification characteristics and relatively simplified and economic structure, and to use wide range of wavelength using small amounts of optical fiber by improving two stage optical Raman amplifier. CONSTITUTION: An optical fiber amplifier structure has two stage fiber nonlinear Raman amplifier scheme which divided into a wavelength division multiplexing optical coupler(2) and an optical isolator(1) in the center portion thereof and using stokes frequency shift that is nonlinear optical effect of an optical fiber. Any one stage of the nonlinear optical fiber is constituted to be used as a successively cascaded strokes shifted Raman laser resonator and a reversely pumping Raman optical amplifier as well, thereby increasing usage effect of nonlinear optical fiber. The pumping is carried out towards the stage of the optical fiber.

Description

Fiber optic raman amplifier

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber Raman amplifier structure used in optical communication technology, optical amplifier technology, and nonlinear optical technology. In the related art, a fiber grating is performed on a ring-type fiber laser scheme. The Raman laser resonator and the two-stage Raman optical amplifier, which have been sequentially stock-frequency shifted by using), have separate structures.Each laser resonator and Raman amplifier require a separate nonlinear optical fiber. And was somewhat ineffective in economics.

Another conventional technique is a two-stage Raman amplifier structure consisting of an optical isolator and an optical isolator that directly employs a first-order stock frequency shift without having a Raman laser resonator with a successive stock-frequency shift, which is a signal wavelength that is externally amplified. There is a disadvantage in that a light source for supplying a pump light having a short wavelength λ _R having λ _s ) as the primary stock frequency transition wavelength is separately required.

In addition, the conventional single-stage Raman amplifier structure, which consists of a Raman laser resonator that is sequentially stock-frequency shifted using a fiber diffraction grating and overlaps with a Raman optical amplifier, has a signal-to-noise ratio deterioration and optical amplification due to Rayleigh backscattering. There is a disadvantage in that the characteristics are not effectively improved.

A single-stage optical fiber Raman optical amplifier structure is constructed by separately constructing a Raman laser resonator that is sequentially stock-frequency shifted using an optical fiber diffraction grating to secure and pump a pump laser light source whose wavelength is the amplification target signal. Since it is composed of only one stage amplifier using only one nonlinear fiber, it does not effectively improve the deterioration of signal-to-noise ratio and deterioration of optical amplification due to Rayleigh backscattering.

In addition, in this structure, the Raman laser resonator and the nonlinear Raman optical amplifier which are sequentially stock frequency shifted are separated, so that separate nonlinear optical fibers are placed in each to reduce optical fiber utilization efficiency, and the pump laser internally resonates to induce optical amplification. Compared with the structure, there is a disadvantage in that the pump light use efficiency is relatively low.

Next, a single-stage Raman structure is constructed of two ring-shaped resonators with wavelength-division multiple-fiber couplers to induce cascaded stocks shifted Raman laser oscillation. The optical amplifier structure has difficulty in securing a wavelength division multiple fiber coupler with precisely controlled wavelength characteristics, and effectively improves the point that the signal-to-noise ratio characteristics deteriorate and the optical amplifier characteristics deteriorate due to Rayleigh backscattering. It is difficult to construct a two-stage nonlinear Raman amplifier.

In the optical communication technology, erbium-doped fiber amplifiers (EDFAs) are widely used in the 1.5-micron wavelength band, while in the 1.3-micron wavelength band, the optical amplifiers with relatively good performance are still good. It is not developed.

In order to solve the above disadvantages, the present invention is not only a 1.3 탆 optical amplifier but also a Raman fiber amplifier using a nonlinear optical effect of an optical fiber which is expected to be usefully used as an optical amplifier for a wavelength region not secured by the existing EDFA in the 1.5 탆 wavelength band. Its purpose is to provide a nonlinear Raman optical amplifier with a relatively simple and economical structure while maintaining good amplification using a small amount of optical fibers by providing a new and improved structure.

1a to 1b is a structure diagram of a two-stage optical fiber nonlinear Raman amplifier to which the present invention is applied;

2 is an independent structural diagram of a conventional Raman laser resonator and a two-stage Raman optical amplifier;

3 is a structural diagram of a two-stage Raman optical amplifier using a conventional first stock frequency shift;

4 is a structure diagram of a single stage Raman optical amplifier having a conventional Raman laser resonator;

5 is a structure diagram of a single stage Raman optical amplifier separately configured with a conventional pump light source,

FIG. 6 is a schematic diagram of a one-stage Raman optical amplifier with a conventional successive stock frequency shifted multi-stage annular Raman laser composition. FIG.

<Description of the symbols for the main parts of the drawings>

1: optical isolate

2: wavelength division multiple fiber coupler for two wavelengths

3: Wavelength Division Multiple Fiber Coupler for Two Wavelengths of Amplified Signal Light and Raman Amplified Pump Light

4: optical fiber diffraction grating having maximum reflectance at input pump light wavelength

5: an optical fiber diffraction grating having a maximum reflectance at a wavelength shifted to the primary stock frequency with respect to the input pump light wavelength

6: an optical fiber diffraction grating having a maximum reflectance at a wavelength shifted by the second stock frequency with respect to the input pump light wavelength

7: Optical Isolation at Raman Amplification Pump Light Wavelength

8a, 8b, 8c, 8d, 8e, 8f, 8f: Nonlinear Raman Effect Induction Fiber

9,9a: ring resonators 10: wavelength band transmission optical filter

11: optical fiber diffraction grating having reflectance at Raman amplification pump light wavelength

11a: optical fiber diffraction grating with low reflectance

12: light blocking optical filter

13: Raman amplification pump optical fiber for moving the light beam of wavelength

14: Wavelength Division Multiple Fiber Coupler for Input Pump Wavelength and Signal Wavelength

15: Wavelength Division Multiple Fiber Coupler with Multiple Wavelength Characteristics

16: Wavelength Division Multiple Fiber Coupler for Two Wavelengths of Signal Light Wavelength and Raman Amplification Pump Light Wavelength

17: A wavelength division multiple fiber coupler for two wavelengths, the wavelength of the signal and the wavelength shorter than the secondary stock transition.

18: annular resonator for laser oscillation for two wavelengths of wavelengths as short as the primary and tertiary stock transitions to the signal light wavelength

19: annular resonator for laser oscillation for wavelength shifted second stock frequency to input pump light

In order to achieve the above object, the present invention provides an optical fiber comprising an optical amplification path of a two-part silica optical fiber connecting an input terminal of an optical signal to be amplified, an output terminal of an amplified optical signal, and an input signal terminal and an output signal terminal. Terminal for inputting pump light with wavelength shorter than stock signal wavelength in path and optical fiber path in reverse direction from signal light output terminal, and wavelength division multiple optical coupler for inputting signal light and pump light into optical fiber path. , Which is installed at both ends of the optical amplification path at the side where the pump light is incident, is a wavelength that is sequentially stock-frequency shifted with respect to the pump light, and is only maximum for wavelengths up to the shorter wavelength whose signal light wavelength is the primary stock frequency transition wavelength. One or more pairs of wavelength selective elements with reflectance, signal light wavelength and perm Multiplexed optical fiber coupler, which has good transmittance for optical wavelengths and can insert an optical signal of shorter wavelength whose signal light wavelength is a primary stock frequency transition wavelength in the same path, a signal light installed between two optical amplification paths Optical isolator and signal light input terminal for a pair of wavelength-division multiple optocouplers with a wavelength shorter as the primary stock frequency transition wavelength and a signal light wavelength placed in the forward direction with respect to the signal light installed in the signal light path between the pair. A wavelength splitting multiple fiber coupler for two wavelengths of a signal wavelength and a short wavelength having a signal stock wavelength as a primary stock frequency transition wavelength in a signal amplification path placed on the side of the optical amplification path; The primary wavelength of the signal light wavelength located on the pump light input side. Wavelength splitting for optical signals with shorter wavelengths as the talk frequency shifting wavelengths Optical fiber paths with shorter wavelengths as the primary stock frequency transitioning wavelengths, which are connected separately between multiple fiber couplers And an optical isolator for a signal light wavelength installed in the forward direction at the end of the optical signal input terminal, and an optical isolator for a signal light wavelength installed in the forward direction at the end of the optical signal output terminal.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1A to 1B are structure diagrams of a two-stage optical fiber nonlinear Raman amplifier to which the present invention is applied, and a two-stage Raman laser optical amplifier structure having cascaded stimulated laser resonators sequentially at the rear and front ends, respectively. The Raman amplifier scheme is shown.

In FIG. 1A, the pump beam I λ _p1 is inputted through the wavelength-division multiplexing fiber coupler 2 to the optical fiber 8a which induces nonlinearity in the opposite direction from the opposite side of the signal light I λ _s. do.

The input pump beam I _{lambda p1} passes through the optical fiber 8a and then reciprocates while being reflected by an optical fiber grating 4 having a maximum reflectivity at the next pump wavelength λ _p . In the process of passing through the optical fiber 8a, the first stock frequency shifted optical beam I _λst1 is induced by a nonlinear Raman effect.

This first stock frequency shifted beam I _λst1 is caused by laser resonance by a fiber grating pair 5 lying across the optical fiber 8a, which in turn produces a second stock frequency second A stock frequency shifted beam I _λst2 is derived.

Similarly, the second stock frequency shifted beam I _λst2 is again caused by laser resonance by a pair of optical fiber diffraction gratings 6 across the optical fiber 8a, which in turn causes a third stock frequency shift. The resulting light beam I _λst3 .

This third stock frequency shifted ray I _λst3 is a unidirectional annular resonator passing through the wavelength division multiplex fiber couplers 3 and passing through the isolator 7, the fiber 8b and the fiber optic path 9. The formation of a ring-type resonator results in laser oscillation.

This laser beam induces a fourth stock frequency shifted ray in the input signal light I _{λ s} wavelength band and contributes to the optical amplification of the input signal light I _{λ s} .

The wavelength splitting multiple fiber couplers 3 lying between the optical isolators 1 and the optical fibers 8a and 8b at the input and output stages are deteriorated in terms of signal-to-noise ratio characteristics and Rayleigh back scattering. It is used to reduce the deterioration of the optical amplification characteristic.

The optical isolator 1 is at the signal wavelength and at the Raman amplification pump wavelength. The optical isolator 7 has a third stock frequency shifted beam I _{lambda st3} , i.e., the shorter side of which the amplified signal light wavelength is the primary stock frequency shifted wavelength. It has a propagation characteristic in a single direction at the wavelength of light I _{λ R.}

The optical isolator 7 is placed in the direction for the reverse Raman amplifier pump of the input signal light.

The length of each of the nonlinear optical fibers 8a and 8b is adjusted to an appropriate length according to the material and structure of the optical fiber to maximize the optical amplification characteristics.

In addition, the optical fiber diffraction gratings 5 and 6 can be used as the structure removed from the drawing, as the wavelength of the pump beam I _λp1 is the wavelength of the stock frequency shift relative to the input signal light I _λs wavelength. In addition, the wavelength division multiplexed optical coupler 2 is also used as the one having a wavelength characteristic suitable for the signal light and the pump light.

Figure 1b is input into the second nonlinear optical fiber (8a), which leads to non-linearity through the wavelength division multiplexing fiber coupler (2) lies on the side as shown in FIG. 1a and similar to the pump beam I _λp1 the input signal I _λs.

The stock frequency shifted light induced by the input pump beam I _λp1 is a laser resonance oscillated by the optical fiber diffraction gratings and the annular optical path 9 across the optical fiber, which ultimately amplifies the input signal light. It will function.

An optical band pass filter 10 placed at the output end may be used to separate noise signals having wavelength characteristics other than the input signal light wavelength.

FIG. 2 is an independent structural diagram of a conventional Raman laser resonator and a two-stage Raman optical amplifier, in which an induction Raman laser resonator and a second stage are sequentially fabricated using an optical fiber grating on a ring-type laser scheme. The structure of the Raman amplifier independently is shown [US-5623508 (1996.2.12)].

In this structure, a Raman laser oscillated sequentially with an optical diffraction grating and a nonlinear optical fiber 8c in the upper half of the ring is oscillated to secure a pump light source for Raman optical amplification, and in the lower half, a two-stage Raman light An amplifier was configured.

The annular laser resonator 9a of this structure functions almost the same as the laser resonator 9 of Figs. 1A and 1B.

However, in FIGS. 1A and 1B, one of cascaded stock shifted Raman laser resonators and a nonlinear optical fiber used in a two-stage Raman optical amplifier are commonly used. Since the non-linear optical fibers used for the successive stock frequency shifted Raman laser resonator and the two-stage Raman optical amplifier are separated from each other, the need for more nonlinear optical fibers is a relative disadvantage, which is a difference from the present invention.

In the structure of FIG. 2, the optical fiber diffraction gratings 5 and 6 are removed from the figure according to the wavelength of the pump beam I _{lambda p1} relative to the wavelength of the input signal light I _{lambda s.} In addition, the wavelength split multiple optical fiber coupler (2) is also used to have a wavelength characteristic suitable for this signal light and pump light.

In this structure, the length of each of the nonlinear optical fibers 8b, 8c, and 8d is adjusted to an appropriate length according to the material and structure of the optical fiber in order to maximize the characteristics of the pump light source for the Raman amplifier and the Raman amplifier.

3 is a structure diagram of a two-stage Raman optical amplifier using a conventional first stock frequency shift. The signal stock wavelength (λ _s ) that is an amplification target without a stock frequency shifted Raman laser resonator is first-order stock frequency shift (first- The structure of a two-stage Raman optical amplifier using an optical beam I _{λ R2} (= I λ _R ) of a short wavelength (λ _R ) as an order stock frequency shift wavelength is shown as a pump light [US-5673280 (1996.2.12) ].

In order to prevent the deterioration of the optical amplification characteristics due to the deterioration of the signal-to-noise ratio characteristic and the Rayleigh backscattering, a wavelength division multiple optical fiber coupler pair 3 and an optical isolator 1 placed between the nonlinear optical fibers 8d and 8b are used. The above is also used in the structure of this invention.

This structure differs from the structure in the present invention in that the pump light I lambda _p2 having a wavelength λ _R secured from the outside is required.

FIG. 4 is a schematic diagram of a single stage Raman optical amplifier with a conventional Raman laser resonator, showing a one stage optical Raman amplifier scheme having a Raman laser resonator which is sequentially stock-frequency shifted [US] -5323404 (1993.11.2).

The concept of oscillating the successive stock frequency shifted Raman laser used in this structure is used in the present invention, but the final amplification target wavelength (λ _s ) is the first stock frequency shift wavelength at a short wavelength (λ _R ). The laser oscillation also uses a resonator composed of optical fiber diffraction grating pairs 11 in the structure of FIG. 4, whereas the present invention uses a ring resonator at this wavelength.

In addition, since the structure of FIG. 4 includes only a single stage amplifier using only one nonlinear optical fiber 8e, the signal-to-noise ratio characteristic is not improved and the optical amplification characteristic is degraded due to Rayleigh backscattering. .

FIG. 5 is a schematic diagram of a single-stage Raman optical amplifier in which a conventional pump light source is separately configured, and a short wavelength in which amplification target wavelength λ _s is used as a primary stock frequency transition wavelength by separately configuring a Raman laser resonator that is sequentially stock frequency shifted. It shows the structure of a single-stage Raman optical amplifier that secures and pumps an optical pump source of (λ _R ) [OFC '95. Technical digest, San Diego, CA (1995) paper WD1, D. Rdykaar, et. Al.].

The successive stock-frequency shifted Raman laser oscillation in this structure is almost the same as the structure in FIG. 4, except that an optical pump beam of wavelength λ _R is pulled out of the laser resonator to pump the Raman optical amplifier. The difference is that the optical fiber diffraction grating 11a whose reflectance is not maximum at that wavelength is used.

The pump light is then introduced into the nonlinear optical fiber 8g through the optical fiber path 13 and the wavelength division multiplex optical coupler 3 to induce a nonlinear Raman amplification of the signal light I _{lambda s} .

In order to prevent the residual light from the signal light I _{λ s} wavelength band generated from the pump light source from entering the Raman amplifier section and block the remaining light from the signal light I _{λ s} wavelength band flowing in the opposite direction, the optical amplifier characteristic is not deteriorated. An optical filter 12, which is blocked by the light ray of Esau, is inserted between the pump laser resonator and the Raman amplifier.

In addition, as shown in FIG. 1B, the wavelength band transmission optical filter 10 disposed at the output terminal of the Raman amplifier is used to separate a noise signal having a wavelength characteristic other than that of the input signal wavelength band optical signal.

In addition, since the structure of FIG. 5 includes only a single stage amplifier using only one nonlinear optical fiber 8g, the signal-to-noise ratio characteristic is deteriorated and the optical amplification characteristic is deteriorated due to Rayleigh backscattering. .

In addition, in this structure, the Raman laser resonator and the nonlinear Raman optical amplifier, which are sequentially shifted in stock frequency, are separated, so that separate nonlinear optical fibers 8f and 8g are placed on each of the optical fibers to reduce the efficiency of using the optical fibers. 2, the use efficiency of the pump light is relatively low compared to the structure shown in FIG.

FIG. 6 is a schematic diagram of a one-stage Raman optical amplifier with a conventional successive stock frequency shifted multi-stage ringed Raman laser structure, with two ring-resonators with wavelength-division multiplexed fiber couplers. a single-stage Raman light structure configured to form shaped resonators to induce cascaded stocks shifted Raman laser oscillation annually and to obtain optical amplification at the fourth-order stock frequency shifted wavelength. The amplifier structure is shown [CLEO'95 Technical Digest, Baltimore, MD (1995) paper CMB7, SV Chernikov, et al.].

In this structure, instead of using the optical fiber diffraction grating of FIG. 4, the main characteristic is that the optical fiber diffraction grating is designed to perform a similar function instead of the multiplexed optical fiber couplers and the annular resonators.

The wavelength division multiplexed optical coupler 15 has a wavelength λ _1st and λ _3rd corresponding to the pump wavelength λ _p , the first and third stock frequency transitions, and the signal light wavelength λ _{s to be} amplified. Optical fiber coupler capable of multiplexing wavelength multiplexing, together with a wavelength splitting multiple optical coupler (16) and an optical fiber path (18) for two wavelengths of the signal light wavelength (λ _s ) and the third-order stock frequency transition wavelength (λ _3rd ). Ring-type resonators are constructed for Raman laser oscillation at the primary and tertiary stock frequency shifted wavelengths (λ _1st and λ _3rd ).

The wavelength division multiplexing optical fiber coupler 14 is capable of wavelength division multiplexing the pump wavelength λ _p and the wavelength λ _2nd corresponding to the second stock frequency shift with respect to the wavelength, and the signal light wavelength λ _{s as the} amplification target. It is an optical fiber coupler and is a secondary stock frequency transition wavelength with a wavelength division multiple optical fiber coupler 17 and an optical fiber path 19 for two wavelengths of the signal light wavelength (λ _s ) and the secondary stock frequency transition wavelength (λ _2nd ) to be amplified. An annular resonator for Raman laser oscillation at (λ _2nd ) is constructed.

In this structure, it is difficult to secure a wavelength division multiple fiber coupler with precisely controlled wavelength characteristics, and to effectively improve the point that the signal-to-noise ratio characteristics deteriorate and the optical amplification characteristics deteriorate due to Rayleigh backscattering. It is difficult to construct a nonlinear Raman amplifier.

As mentioned above, the two-stage optical fiber nonlinear Raman amplifier structure proposed in the present invention is a simple and economical method that requires a relatively small amount of nonlinear optical fiber in a two-stage nonlinear Raman amplifier with improved signal-to-noise ratio characteristics and Rayleigh backscattering effects. I suggest a structure.

In addition, the number of cascaded stocks shifted Raman laser resonators may be varied according to the difference in the pump wavelength λ _p with respect to the signal wavelength λ _s .

This can eventually eliminate each or all of the optical fiber diffraction gratings 5 and 6 in the structure proposed in the present invention.

According to the selection of the pump light, the Raman optical amplifier can be utilized not only in the 1.3 ㎛ wavelength band but also in the 1.5 ㎛ wavelength band and other wavelength band optical amplifiers, thereby contributing to the development of large capacity optical communication technology.

In addition, other applications besides the fields of application presented in the present invention are possible within the scope or spirit of the present invention.

As described above, the nonlinear Raman optical amplifier structure proposed by the present invention has an effect of improving the efficiency and economic efficiency of the optical fiber with a relatively small amount of optical fibers than the conventional Raman optical amplifier structure.

In addition, by maintaining the good signal-to-noise ratio characteristics and improved Rayleigh backscatter structure of the conventional two-stage Raman optical amplifier, it is possible to secure a non-linear Raman optical amplifier with good economy and performance.

In addition, the Raman optical amplifier proposed in the present invention can be used as a useful optical amplifier in the 1.3㎛ wavelength band according to the selection of the pump light, and in addition to securing a large capacity optical communication system in this wavelength band, the 1.5nm wavelength band and other wavelength band optical It is used as an amplifier to induce the development of large capacity optical communication technology.

In addition, it has the effect of contributing to the development of other applications as well as securing a nonlinear Raman laser that can operate in a wide wavelength range.

Claims (12)

Two-stage fiber nonlinear Raman amplifier scheme using Stocks frequency shift, a nonlinear optical effect of optical fibers, and separated into a wavelength split multiple optical coupler and an optical isolator in the middle of a two-stage optical amplifier. )as, Nonlinear Raman, which uses a nonlinear optical fiber of one of two stages as a cascaded Stokes shifted Raman laser resonator, and a Raman optical amplifier, which improves the efficiency of use of nonlinear optical fibers. Optical amplifier structure. In a two-stage optical fiber nonlinear Raman amplifier structure, an optical fiber Raman amplifier structure using an amplifier structure reversely pumped and a nonlinear optical fiber of the pumped one of the two stages as a stock frequency-shifted Raman laser resonator while being used as a Raman amplifier simultaneously. , An input terminal of the optical signal to be amplified; An output terminal of the amplified optical signal; An optical fiber path connecting between an input signal terminal and an output signal terminal and including an optical amplification path of a two-part silica optical fiber; A terminal capable of reversely inputting pump light having a wavelength shorter than a signal frequency wavelength in the optical fiber path by a second or more stock frequency, and a wavelength division multiple optical coupler for inputting signal light and pump light into the optical fiber path; It is installed at both ends of the optical amplification path at the side where the pump light is incident, and it is a wavelength that is sequentially stock-frequency shifted with respect to the pump light, and the maximum reflectance only for wavelengths up to the short wavelength whose signal light wavelength is the primary stock frequency transition wavelength A pair or several pairs of wavelength selective elements having; A wavelength division multiple optical coupler capable of inserting optical signals of shorter wavelengths having good transmittances for the signal light wavelength and the pump light wavelengths and having the signal light wavelength as the primary stock frequency transition wavelength in the same path; A pair of wavelength-division multiple optocouplers for the shorter wavelength and the signal light wavelength whose primary signal frequency transition wavelength is provided between two portions of the optical amplification paths in the forward direction with respect to the signal light installed in the signal optical path between the pair. An optical isolator for the set signal wavelength; A wavelength division multiple optical coupler for two wavelengths of a signal light wavelength provided on the signal light input terminal side of the optical amplification path placed on the signal light input terminal side and a short wavelength whose signal light wavelength is a primary stock frequency transition wavelength; The primary stock is a signal stock wavelength that connects the wavelength split multiple fiber coupler located at the input side of the signal light and the wavelength split multiple fiber coupler for an optical signal having a shorter wavelength as the primary stock frequency transition wavelength. An optical fiber optical path having a short wavelength as a frequency shifting wavelength and the wavelength band optical isolator located on the path; An optical isolator for a signal light wavelength disposed in the forward direction at an end portion of the optical signal input terminal; An optical fiber Raman amplifier, comprising an optical isolator for a signal light wavelength installed in a forward direction at an end portion of an optical signal output terminal. The device of claim 2, wherein the wavelength selective element An optical fiber Raman amplifier characterized by increasing pump efficiency by reciprocating the pump light by having a maximum reflectance only at the pump light wavelength on the opposite side to which the pump light of the optical path in which the wavelength selective element pairs are located is incident. The method of claim 2, A terminal for inputting pump light in a forward direction from an input terminal side, and a wavelength division multiple optical coupler for inputting signal light and pump light into an optical fiber path; A wavelength division multiple optical coupler for two wavelengths of a signal light wavelength provided on the signal light output terminal side of the optical amplification path placed on the signal light output terminal side and a short wavelength whose signal light wavelength is a primary stock frequency transition wavelength; Transition of the signal light wavelength that separates between the wavelength division multiple fiber coupler located at the output terminal side and the wavelength division multiple fiber coupler for the shorter wavelength optical signal having the signal light located at the input side of the pump light as the primary stock frequency transition wavelength. An optical fiber Raman amplifier comprising an optical fiber optical path having a short wavelength as a wavelength and an optical isolator having a wavelength band located on the optical path. 3. The optical isolator of claim 2 wherein the optical isolator The pump light does not have a Raman laser resonator that is sequentially stock frequency shifted by the optical fiber diffraction grating so that the wavelength of the input optical signal to be amplified is the wavelength of the second stock frequency shift. An optical fiber Raman amplifier characterized by forming a ring-shaped resonator which proceeds in only one direction with respect to a stock frequency shifted light beam having a wavelength as a difference stock frequency transition wavelength, and pumping Raman in the reverse direction. The optical amplifier of claim 2, wherein the optical amplifier The pump light wavelength is 1.05 to 1.06 µm, 1.11 µm wavelength and 1.17 µm wavelength band diffraction grating pairs, three 1.24 µm / 1.3 µm wavelength band multiplexing couplers and one 1.24 µm, 1.06 µm and 1.3 µm wavelength band wavelength division With multiple fiber coupler, 1.05 to 1.06 µm / 1.3 µm wavelength band wavelength-division multiple-optic coupler for pump beam coupling is used to form a Raman laser resonator that is sequentially stock-frequency shifted for these 1.11 µm, 1.17 µm and 1.24 µm wavelengths An optical fiber Raman amplifier comprising a 1.3 μm wavelength band nonlinear Raman optical amplifier for Raman pumping. The method of claim 5, 1.3μm wavelength band nonlinear Raman which uses a 1.24μm / 1.3μm wavelength band wavelength split multiple optical fiber coupler to form a Raman laser resonator with a stock frequency shifted to the 1.24μm wavelength by pumping the Raman pump in the reverse direction. An optical fiber Raman amplifier, forming an optical amplifier. The method according to any one of claims 2 to 5, An optical fiber Raman amplifier comprising a nonlinear Raman optical amplifier for amplifying signal light of a wavelength of 1.5 μm. The method according to any one of claims 2 to 7, An optical fiber Raman amplifier, comprising applying a structure of a two-stage optical fiber Raman optical amplifier to an optical communication system having a wavelength of 1.3 μm. The method of claim 8, A two-stage nonlinear optical fiber Raman amplifier is an optical fiber Raman amplifier characterized in that it is applied to an optical communication system in the 1.5㎛ wavelength band. The method according to any one of claims 2 to 7, A pump light source required for a two-stage nonlinear Raman fiber amplifier is a fiber-optic Raman amplifier characterized by using a Nd: YAG laser pumped with a laser diode. The method according to any one of claims 2 to 7, A pump light source of a two-stage optical fiber nonlinear Raman amplifier is a fiber optic Raman amplifier structure, characterized in that using a double-clad ytterbium-added silica fiber laser pumped by a laser diode.