JP2002084023A - Optical fiber amplifier, stimulation light source module, and optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber amplifier, a stimulation light source module, and an optical system which can make a device small and low-cost, make it easy to lay an optical fiber, and does not increase the number of welded points, and are excellently stored and handled. SOLUTION: This optical fiber amplifier has a stimulation light source 1 which outputs stimulation light and an optical amplification part 3 which supplies the stimulation light outputted from the stimulation light source 1 to a 1st optical fiber 2 and then amplifies and outputs the signal light inputted to the 1st optical fiber 2. Further, the amplifier 3 also has an optical filter 10 such as a long-cycle grating which is provided to a 2nd optical fiber 9 connecting the stimulation light source 1 and optical amplification part 3, and radiates and attenuates the signal light from the side of the optical amplification part 3 into the clad mode in the 2nd optical fiber 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical fiber amplifier, an excitation light source module, and an optical system.

[0002]

2. Description of the Related Art Generally, an optical fiber amplifier can amplify an optical signal without optical-electrical conversion by using an optical fiber doped with a rare earth element such as erbium (Er).

FIG. 10 shows a conventional optical fiber amplifier FA2.
FIG. 3 is a block diagram showing the configuration of FIG. As shown in FIG.
The conventional optical fiber amplifier FA2 is supplied to the first optical fiber 2 by supplying the pumping light source 1 for outputting pumping light and the pumping light output from the pumping light source 1 to the first optical fiber 2. And an optical amplifier 3 for amplifying and outputting the amplified signal light.

The excitation light source 1 is a semiconductor laser module (L
D module) is used, for example, and outputs 980 nm band excitation light.

[0005] The first optical fiber 2 is, for example, 1550n.
When amplifying m-band signal light, erbium (Er)
Erbium-doped optical fiber is used.

[0006] The optical amplifier 3 transmits an input terminal 4 to which the signal light is input, an output terminal 5 from which the amplified signal light is output, and a signal light only in a direction from the input terminal 4 side to the output terminal 5 side. First isolator 6 for preventing transmission in the opposite direction
An optical coupler for combining the signal light transmitted through the first optical fiber 2 and the pump light transmitted from the pump light source 1 through the second optical fiber 9 and the second isolator 7. And an optical multiplexer 8.

The signal light input from the input terminal 4 is
Is transmitted through the first optical fiber 2 via the isolator 6 of FIG. On the other hand, the excitation light output from the excitation light source 1 is input to the optical fiber 2 via the second optical fiber 9 and the optical multiplexer 8.

The optical fiber 2 is brought into an excited state by the inputted pump light, and amplifies the signal light. The amplified signal light is output from the output terminal 5 via the optical multiplexer 8 and the second isolator 7.

In the conventional optical fiber amplifier FA2, the light from the optical amplifier 3 may leak and reach the pump light source 1 via the second optical fiber 9. The light leaking from the optical amplification unit 3 becomes a noise component that disturbs the light emitting action of the excitation light source 1 and is reflected from a reflection point (for example, an end of an optical fiber) in the excitation light source 1 to become a reflected return light. It also becomes a noise component that disturbs the amplification operation of the unit 3.

According to experiments conducted by the present inventors, 9
The reflectance of light having a wavelength of 1545 nm band in the excitation light source 1 using the 80 nm band LD module depends on the model.
It varied from 5 dB to -13 dB. This is a lot of 98
This is because the 0 nm band LD module is designed without considering the reflection in the 1550 nm band. for that reason,
The amount of reflected return light returning to the optical amplifier 3 also varies, making it very difficult to adjust the light amplification action.
If the design of the LD module and the laser chip in the LD module is changed in consideration of the reflection in the 1550 nm band, other characteristics (for example, output power) of the LD module will be limited.

Therefore, an optical isolator is provided between the pump light source 1 and the optical multiplexer 8, and the optical isolator provides
A technique for preventing the return light from the optical amplification unit 3 from passing through the second optical fiber 9 is considered (hereinafter, referred to as Conventional Example 1).

Further, W is located between the pump light source 1 and the optical multiplexer 8.
A technique has been proposed in which a DM coupler is provided, and a terminal for non-reflectively terminating a port for outputting return light from the optical amplifying unit 3 among ports of the WDM coupler (hereinafter, referred to as “DM coupler”).
Conventional example 2).

[0013]

In the conventional example 1, since the optical isolator is expensive and large in size, there is a problem that the manufacturing cost of the optical fiber amplifier FA2 is increased and the optical fiber amplifier is increased in size. Also, the holder for holding the optical components of the optical isolator is made of iron-based alloy,
When the 980 nm band excitation light source 1 is used, there is a problem that an optical isolator cannot be provided because the iron-based alloy absorbs a 980 nm band light component.

In the second conventional example, since the WDM coupler needs to have a 2 × 1 optical fiber configuration, there are problems such as inconvenient routing of the optical fiber in the device and an increase in the number of fusion spots. Was. In addition, the WDM coupler almost requires a sleeve portion for reinforcement, so that the volume increases by that amount,
Since the thickness is changed by the hard sleeve portion, there is a problem that storage and handling in the device are inconvenient.

As described above, in an optical system in which optical devices such as an optical amplifier and a pumping light source are connected to each other via a connecting means such as an optical fiber, there is always a possibility that a similar problem may occur.

According to the present invention, an optical fiber amplifier, an excitation light source module and an optical fiber amplifier which can reduce the size and cost of an apparatus, simplify the routing of optical fibers, do not increase the number of fusion spots, and are excellent in storage and handling. It is intended to provide an optical system.

[0017]

SUMMARY OF THE INVENTION An optical fiber amplifier according to the present invention comprises a pumping light source for outputting pumping light and a pumping light output from the pumping light source supplied to a first optical fiber. An optical amplifier for amplifying the signal light input to the optical fiber and outputting the amplified signal light, the optical amplifier being provided on the second optical fiber connecting the pumping light source and the optical amplifier, And an optical filter for attenuating the signal light from the second optical fiber in the second optical fiber, for example, by radiating the signal light into a cladding mode.

The optical amplifier amplifies the signal light of the first wavelength band, and the pumping light source outputs a second light different from the first wavelength band.
And outputting an excitation light in a wavelength band, wherein the optical filter includes the first filter.
In the second optical fiber, the signal light in the wavelength band is attenuated, for example, radiated in a clad mode, and the second
May be transmitted.

[0019] The optical filter may be a long-period grating.

The optical filter is constituted by arranging a plurality of long-period gratings, in which the center wavelengths at which the light transmission loss peaks are different from one another at intervals, or changing the grating period from one end to the other. May be a chirped grating that is continuously changed up to the end.

The pumping light source module according to the present invention has a pumping light source for outputting pumping light, and supplies the pumping light output from the pumping light source to the first optical fiber of the optical amplifying unit, thereby providing the first light source. In the pumping light source module for amplifying the signal light input to the optical fiber, the pumping light source and the optical amplifying unit are provided on a second optical fiber, and the signal light from the optical amplifying unit side is transmitted to the second optical fiber. It is characterized in that it is attenuated in the optical fiber by, for example, radiating it into a cladding mode.

The optical amplification section amplifies the signal light of the first wavelength band, and the pumping light source outputs a second light different from the first wavelength band.
And outputting an excitation light in a wavelength band, wherein the optical filter includes the first filter.
The signal light in the wavelength band is radiated in the second optical fiber, for example, in a cladding mode to attenuate the signal light, and the pump light in the second wavelength band is transmitted.

[0023] The optical filter may be a long-period grating.

The optical filter is constituted by arranging a plurality of long-period gratings, in which the center wavelengths at which the light transmission loss peaks are spaced apart from each other, in series, or the grating period is changed from one end to the other. May be a chirped grating that is continuously changed up to the end.

In the optical system according to the present invention, a first optical device that emits light in a first wavelength band and a second optical device that emits light in a second wavelength band are connected by connection means, and the first optical device is connected to the first optical device. The light of the first wavelength band emitted by the first optical device is not mixed into the second optical device through the connecting device, and the light of the first wavelength band emitted by the first optical device is transmitted from the connecting device or the second optical device to the second optical device. An optical component that does not return to the first optical device and transmits light in the second wavelength band emitted from the second optical device to the first optical device through the connection means. is there.

According to the present invention, the excitation light source (second optical device)
An optical filter (optical component) for attenuating light from the optical amplifier side in the second optical fiber is provided in a second optical fiber (connecting means) for connecting the optical amplifier and the optical amplifier (first optical device). Therefore, it is possible to prevent the light from the optical amplification unit from leaking and reaching the pump light source via the second optical fiber.
Even at the point of reflection in the excitation light source (eg at the end of an optical fiber)
Even if the light is reflected from the optical amplifier, the reflected return light can be prevented from reaching the optical amplifier.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. Note that the same components as those of the conventional optical fiber amplifier FA2 shown in FIG. 10 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

FIG. 1 is a block diagram showing a configuration of an optical fiber amplifier FA1 according to an embodiment of the present invention. FIG.
As shown in (1), the embodiment of the present invention is characterized in that an optical filter 10 is provided in a second optical fiber 9 that connects the pump light source 1 and the optical amplifier 3. The optical filter 10 can radiate the light from the optical amplification unit 3 side to the cladding mode in the second optical fiber 9 and attenuate it. The excitation light source 1 and the optical filter 10 constitute an excitation light source module 11.

As the optical filter 10, a long-period fiber grating (LPG) having a refractive index fringe in which the refractive index in the optical axis direction of the core portion of the optical fiber periodically changes is used. The LPG has a grating period of about 100 μm to about 1000 μm, which is about 100 times larger than that of a short period grating for ordinary reflection.

In the case of manufacturing an LPG, first, as shown in FIG. 2A, a long-period mask 14 (a plurality of metal plates are formed on a metal plate) is provided on an optical fiber 13 having a core portion 12 made of germanium-doped quartz. A thin window is formed at a predetermined interval, or a dielectric multilayer film is formed on a quartz glass plate), and ultraviolet light 15 (for example, argon laser) is applied from above the long-period mask 14. Is irradiated. The refractive index of the core portion 12 irradiated with the ultraviolet light 15 is increased, and a refractive index stripe 12a is formed on the core portion 12. Through the above steps, LPG is formed.

In the optical filter 10 using the LPG,
As shown in FIG. 2B, the wavelength λ2
The pump light (for example, 980 nm band) transmits through the waveguide mode of the optical fiber, and the signal light of wavelength λ1 (for example, 1550 nm band) leaked from the optical amplifier 3 is radiated to the cladding mode of the optical fiber and attenuated. Further, even if the light having the wavelength λ1 returns from the excitation light source 1 as reflected return light, the light is attenuated again by the optical filter 10, so that
The amount of light returning into the light amplification unit 3 can be significantly reduced.

Here, the grating period will be described below. FIG. 7A is a graph showing the relationship between the grating period of the optical fiber and the coupling wavelength of the optical fiber.

Since the coupling wavelengths indicated by characteristic lines a to j in FIG. 7A are wavelengths at which the light transmission loss has an extreme value (peak), in this specification, the coupling wavelength is changed from the first-order mode. It is referred to as an N (here, N = 10) mode light transmission loss peak wavelength. In the figure, the characteristic line a is the primary mode, the characteristic line b is the secondary mode, the characteristic line c is the tertiary mode,
The characteristic line d indicates light transmission loss peaks in the 1, 2, 3, 4,..., 10th mode in order from the right side of the figure, such as the fourth mode. Note that the value shown in FIG.
Is the value at.

As shown in FIG. 7A, for example, by setting the grating period (fiber grating period) formed in the optical fiber to 150 μm to about 580 μm, the wavelength becomes 0.9 μm (900 nm) to 1.6 μm (16 μm).
Within the range of (00 nm), a light transmission loss peak wavelength of a multiple order mode can be formed. Also, by changing the fiber grating period, the 25
The peak wavelength at ° C. can be freely determined.

For example, if the grating period is about 440n
7B, the light transmission loss peak wavelength of the first to fifth order modes is formed as shown in FIG. 7B, and the light transmission loss peak of the fourth order mode is obtained when the set order mode is the fourth order mode. The wavelength is about 1510 nm, and the light transmission loss peak wavelength of the fifth-order mode, which is the next-order mode of the set order mode, is longer than 1610 nm (in FIG.
40 nm) and the longer wavelength side (154
(0 nm to 1610 nm), the difference between the maximum value and the minimum value of the light transmission loss characteristic is substantially flattened at 0.5 dB or less. In such an LPG, when the grating is manufactured, the optical fiber jacket is peeled off, and the glass part is exposed, but if the recoating technique of re-covering the part with the jacket is used, the appearance is the same as a normal fiber, Storage and handling can be performed in the same manner as ordinary fibers.

FIGS. 3A and 3B show the optical filter 10.
An example of a protection member 17 for protecting the grating forming portion 16 is shown. FIGS. 3C and 3E show examples in which the protection member 17 shown in FIG. 3A is applied, and FIGS. 3D and 3F show examples in which the protection member 17 shown in FIG. ). FIG.
As shown in FIG.
Is preferably accommodated in a protective member 17 made of a quartz material. The protection member 17 can prevent the grating forming portion 16 from being affected by the outside, and can maintain the light transmission loss characteristics.

The protection member 17 is formed in a cylindrical shape as shown in FIGS.
May be formed, as shown in FIG. 3B,
As shown in (F), a pair of half sleeves may be brought into contact with each other to form a cylindrical shape. FIG. 3 (C),
As shown in (D), both ends of each protective member 17 and the grating forming portion 16 are fixed by an adhesive 18.

FIG. 4 is a graph showing transmittance characteristics when an LPG is attached to the tip of a pigtail fiber of a 980 nm LD module. Here, the LPG has a length of 22 mm and a center wavelength (wavelength at which light transmission loss reaches a peak) is 1545 nm.

The transmittance characteristic of the LPG shown in FIG. 4 relates to the transmission of light in one direction. When there is reflected return light from the pumping light source 1, the light passes through the LPG twice, and is converted into dB. The transmittance is twice that of FIG.

For example, since the transmittance is -6 dB or less in a range of 12 nm from 1539 nm to 1551 nm, the LD having the maximum reflectance (-5 dB) in this wavelength range.
Even if a module is used, -5dB + (-6dB)
Since a loss of × 2 = −17 dB will be obtained, the overall improvement will be 12 dB.

Further, the present inventors prototyped two samples of a long-period grating (LPG) having a center wavelength (wavelength at which light transmission loss peaks) of about 1545 nm (hereinafter referred to as sample S1 and sample S2). 1550n
An experiment for measuring the reflectance of light having a wavelength in the m band was performed. FIG. 8 shows the passing loss of sample S1 and sample S2.
(A) and (B) show. 1550 for samples S1 and S2
The transmission loss in the nm band is about -1 as shown in FIG.
It is around 5 dB.

FIG. 9 is an explanatory diagram for explaining an experimental method performed by the inventor. As shown in FIG. 9, an optical coupler 19 having first to fourth ports P1 to P4 is prepared,
The light from the signal light source 20 in the 1550 nm band passes through the optical isolator 21 and is input to the first port P1 of the optical coupler, is branched into two, and has a second port P2 and a fourth port P4.
Output from Light from the 980 nm band LD module 22 is input to the second port P2 of the optical coupler 19, and similarly output from the first port P1 and the third port P3.

The light output from the third port P3 of the optical coupler 19 is input to the optical output measuring device 24 via the optical isolator 23. The light output from the fourth port P4 of the optical coupler 19 is non-reflectively terminated via the optical isolator 25. In FIG. 10, L is an optical fiber.

The 980 nm band L
The D module 22 has a reflectance of 1550 nm band light of 9
The measurement was performed before (see FIG. 10 (A)) and after (see FIG. 10 (B)) the long period grating samples S1 and S2 were mounted between the 80 nm band LD module 22 and the optical coupler 19, respectively. .

[0045]

[Table 1] Table 1 shows the experimental results. As can be seen from Table 1, when the sample S1 was mounted, 27.
It is improved by 1 dB and 2
It is improved by 6.4 dB. Therefore, the 980 nm band LD
It can be seen that by mounting the long-period grating between the module 22 and the optical coupler 19, the reflectance of the 980-nm band LD module 22 for the 1550 nm band light is significantly reduced.

According to the embodiment of the present invention, the excitation light source 1
Since the optical filter 10 that attenuates the light from the optical amplifying unit 3 by radiating it from the side of the optical amplifying unit 3 to the cladding mode in the second optical fiber 9 is provided in the second optical fiber 9 that connects the Light from the optical amplification unit 3 can be prevented from leaking and reaching the excitation light source 1 via the second optical fiber 9,
Even if the light is reflected from a reflection point (for example, an end of an optical fiber) in the excitation light source 1, the reflected return light is reflected by the optical amplifier 3.
Can be prevented. As a result, a noise component that disturbs the light emitting operation of the pump light source 1 and a noise component that disturbs the amplifying operation of the optical amplifier 3 can be reduced, and the reliability of the optical fiber amplifier FA1 and the pump light source module 11 can be improved. .

When an LPG is used as the optical filter 10, the fiber grating is very small and inexpensive, and in many cases, a sleeve is not required. Therefore, the size and cost of the device can be reduced. .

FIG. 5A shows an optical filter 10 used in an optical fiber amplifier FA1 according to another embodiment of the present invention.
FIG. 3B is a block diagram showing the configuration of FIG.
6 is a graph showing a transmittance characteristic of 0.

As shown in FIG. 5A, in another embodiment of the present invention, the center wavelengths are 1535 nm and 1535 nm, respectively.
Three LPGs 10a, 1 at 45 nm and 1555 nm
0b and 10c are connected and arranged in series. In this case, the net transmittance is as shown in FIG.
The wavelength width having a transmittance of -6 dB or more can be expanded to 30 nm or more.

FIG. 6 is a graph showing transmittance characteristics when 11 stages of 2 mm long LPGs are directly connected. Here, the center wavelengths of the 11 LPGs are 1535 to 155.
It was set every 2 nm up to 5 nm. The total length of LPG is 22 nm, which is the same as when the result of FIG. 4 is obtained.
By connecting in multiple stages, even the same LPG length is -6
The wavelength range for obtaining a transmittance of dB is 1536 nm to
It can be extended to 1753 nm up to 1553 nm. Increasing the number of stages of multi-stage connection is almost equivalent to continuously changing the grating period from one side of the LPG to the other end (so-called chirped grating). Chirped gratings are effective for reducing the reflectance over a wide band.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the technical matters described in the claims.

In the above embodiment, LPG is used as the optical filter 10, but it is not limited to this as long as it is a means for forming a cladding mode. For example, similar effects can be obtained by forming a reflection type secondary grating.

Further, without using the grating, for example, the core profile of the optical fiber may be controlled to give a constant bending to the optical fiber. The bending of the optical fiber changes the refractive index of the core.
It is possible to create a state in which light in the nm band is substantially transmitted, but light in the 1550 nm band is coupled to the radiation mode. When the optical fiber is bent, the light is extracted from the light on the short wavelength side. Therefore, this method is applied when attenuating the light on the short wavelength side.

Further, the radiation mode light drifts in the clad and does not couple with the guided mode. However, if the light contained in the clad is a problem, the light from the optical amplifier 3 between the clad and the jacket is problematic. By sandwiching a material that absorbs light, cladding mode light can be absorbed.

[0055]

According to the present invention, light from the optical amplifier side is radiated to the cladding mode in the second optical fiber and attenuated by the second optical fiber connecting the pumping light source and the optical amplifier. The provision of the optical filter for preventing the light from leaking from the optical amplification unit to reach the excitation light source through the second optical fiber can be prevented. Even if the light is reflected from the end of the fiber), the reflected return light can be prevented from reaching the optical amplifier. As a result, it is possible to reduce a noise component that disturbs the light emitting function of the pump light source and a noise component that disturbs the amplifying function of the optical amplification unit, thereby improving the reliability of the optical fiber amplifier and the pump light source module.

When an LPG is used as an optical filter, the fiber grating is very small and inexpensive, and often does not require a sleeve portion. Therefore, the size and cost of the device can be reduced. Also, when making the grating, the optical fiber jacket is peeled off and the glass part is exposed, but if the recoating technology is used to cover that part again with the jacket, the appearance is the same as a normal fiber, so storage and handling are easy. It can be performed in the same manner as a normal fiber.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an optical fiber amplifier according to an embodiment of the present invention.

FIG. 2A is an explanatory diagram for explaining a method of manufacturing an LPG used in an optical fiber amplifier according to an embodiment of the present invention, and FIG. 2B is an explanatory diagram for explaining an operation of the LPG; .

FIGS. 3A and 3B show an example of a protection member for protecting a grating forming portion of the optical filter, wherein FIGS.
(C) and (D) are side sectional views, and (E) and (F) are front sectional views.

FIG. 4 is a graph showing transmittance characteristics when an LPG is attached to a tip of a pigtail fiber of a 980 nm band LD (laser diode) module.

FIG. 5A is a block diagram illustrating a configuration of an optical filter used in an optical fiber amplifier according to another embodiment of the present invention, and FIG. 5B illustrates a relationship between a wavelength and a transmittance of the optical filter; It is a graph.

FIG. 6 is a graph illustrating transmittance characteristics when 11 stages of 2 mm long LPGs are directly connected.

FIG. 7A is a graph showing the relationship between the grating period of an optical fiber and the coupling wavelength of the optical fiber;
(B) shows that the grating period of the optical fiber is about 440n.
7 is a graph showing light transmission loss characteristics formed in an optical fiber where m is an integer.

FIG. 8A is a graph showing the passing loss of sample S1, and FIG. 8B is a graph showing the passing loss of sample S2.

FIG. 9 is an explanatory diagram for explaining an experimental method performed by the inventor.

FIG. 10 is a block diagram showing a configuration of a conventional optical fiber amplifier.

[Explanation of symbols]

 FA1: optical fiber amplifier 1: pump light source (second optical device) 2: first optical fiber 3: optical amplifier (first optical device) 4: input terminal 5: output terminal 6: first isolator 7: first 2 isolator 8: optical multiplexer 9: second optical fiber (connecting means) 10: optical filter (optical component) 11: pumping light source module 12: core 12a: refractive index stripe 13: optical fiber 14: long period mask 15: Ultraviolet light 16: Grating forming part 17: Protective member 18: Adhesive 19: Optical coupler 20: Signal light source 21: Optical isolator 22: 980 nm band LD module 23: Optical isolator 24: Optical output measuring instrument 25: Optical isolator L : Optical fiber S1, S2: Sample of long period grating

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiaki Tsuda 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Electric Co., Ltd. (72) Inventor Yuichiro Irie 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Etsuji Katayama 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Takeo Shimizu 2-6-1 Marunouchi, Chiyoda-ku, Tokyo F-term in Furukawa Electric Co., Ltd. (reference) 2H049 AA34 AA59 AA62 AA66 5F072 AB09 AK06 JJ01 JJ08 KK07 KK30 PP07 RR01 YY17

Claims (9)

[Claims] An excitation light source for outputting an excitation light and an excitation light output from the excitation light source are supplied to a first optical fiber to amplify a signal light input to the first optical fiber. An optical fiber amplifier having an optical amplifying section that outputs the signal light from the optical amplifier. An optical fiber amplifier, comprising: an optical filter that attenuates the optical fiber. 2. The optical amplification section amplifies signal light in a first wavelength band, the pumping light source outputs pumping light in a second wavelength band different from the first wavelength band, and the optical filter includes: The signal light of the first wavelength band is transmitted to the second
2. The optical fiber amplifier according to claim 1, wherein the optical fiber amplifier emits and attenuates the cladding mode in the optical fiber, and transmits the excitation light in the second wavelength band. 3. The optical fiber amplifier according to claim 1, wherein said optical filter is a long period grating. 4. The optical filter according to claim 1, wherein a plurality of long-period gratings whose center wavelengths at which light transmission loss peaks are different from each other at intervals are arranged in series, or the grating period is changed from one end. 3. The optical fiber amplifier according to claim 1, wherein the optical fiber amplifier is a chirped grating continuously changed to the other end. 5. An excitation light source for outputting an excitation light, wherein the excitation light output from the excitation light source is supplied to a first optical fiber of an optical amplifying unit to be input to the first optical fiber. A pump light source module for amplifying the amplified signal light, the pump light source module being provided on a second optical fiber connecting the pump light source and the optical amplification unit, and attenuating the signal light from the optical amplification unit side in the second optical fiber. An excitation light source module having an optical filter. 6. The optical amplifier amplifies signal light in a first wavelength band, the pumping light source outputs pumping light in a second wavelength band different from the first wavelength band, and the optical filter includes: The signal light of the first wavelength band is transmitted to the second
The pumping light source module according to claim 5, wherein the light is radiated to the cladding mode in the optical fiber to be attenuated, and the pumping light in the second wavelength band is transmitted. 7. An excitation light source module according to claim 5, wherein said optical filter is a long-period grating. 8. The optical filter according to claim 1, wherein a plurality of long-period gratings having different center wavelengths at which light transmission loss peaks at intervals are arranged in series, or the grating period is set at one end. The excitation light source module according to claim 5, wherein the excitation light source module is a chirped grating that is continuously changed from to a second end. 9. A first optical device that emits light of a first wavelength band and a second optical device that emits light of a second wavelength band are connected by connection means, and the first optical device emits light of the first optical device. The light in the wavelength band is not mixed into the second optical device through the connecting means, and the light in the first wavelength band emitted by the first optical device is returned from the connecting means or the second optical device to the first optical device. An optical system, comprising: an optical component that does not transmit light of the second wavelength band emitted from the second optical device to the first optical device through the connection means.