JPH02157829A - Optical fiber type optical amplifier - Google Patents

Abstract

PURPOSE:To obtain the optical fiber type optical amplifier which is free from an insertion loss, has a high amplification degree, is small in size, allows easy handling and has high efficiency by using a semiconductor laser module of a specific wavelength band, an optical fiber coupler and an Er-added optical fiber. CONSTITUTION:The fiber 4 for output of the 1.4mum band semiconductor laser module 1 is connected to the input terminal of the optical fiber coupler or waveguide type coupler 2 and stimulating light is made incident to the Er-added optical fiber 3. On the other hand, the 1.5mum band signal light introduced form the fiber 5 for input is made incident from another input terminal of the optical fiber coupler or the waveguide type coupler 2 to the Er-added optical fiber 3. The amplified signal light is obtd. from the terminal of the Er-added optical fiber 3 in this way. Since the 1.4mum band semiconductor laser module and the optical fiber coupler as well as the Er-added optical fiber are used, the optical fiber type optical amplifier which is free from the insertion loss, has >=10dB amplification degree, is small in size, allows easy handling and has the high efficiency is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical fiber type optical amplifier that is small in size and has a high gain, and directly amplifies a 1.5 μm band spectrum.

[Prior Art] Conventionally, as a pumping light source for an E-doped fiber type optical amplifier, one that matches the absorption wavelength range produced by the energy level unique to Er (erbium), as shown in Fig. 7, has been used. The optical excitation of the excitation light source causes the '
An amplification effect is produced by forming a population inversion between the energy levels of I I 3/2"" I I 6/2. Here, the wavelength that can be excited is the Ar ion laser (514.5 nm) shown by the arrow in Figure 7.
(See Document 1 below) 1 dye laser (650r+m)
(See Document 2 below) One-color centered laser (1,49 μm
-1,5(lum) (see document 3 below), and 0
8 μm band semiconductor laser (see Documents 4 and 5 below)
was known.

Reference 1: E, Desurvire et: al.
,"l old 3h-gain erbium-doped
raveling-wave fiber a
improverOptfcs Letters vo
l, 12. p. 888 (1987).

Reference 2: R.J., Mears et al., “L.
ow-noise erbium-doped fi
ber amplifier operating
at 1.54 μm”, Electronics
Letters vol, 23. p, 1026(1
987).

Reference 3: E, 5nitzer et al, -E
rbiuIMfiber laser amplifier
r at 1.55 μm with pu
mp at 1.49 μmand Yb
5ensitjzed Er oscillati
on”, OFG’88 (New Orleans), Po
5tdeadline Paper PD2 (1988
Year).

Reference 4: T. J. Whitley et al.'
1.54 μm Er” doped fiber
amplifier potentially pum
ped at807r+m”, European
Conference on 0ptical
Communication 88. p, 58 (198
8 years).

Document 5: D, C, 1 (anna at al,,”
Efficient operation of
An Yb-5ensitized Er fi
ber 1asar pum-ped in
O, 8μm region, Electro
nics Lettersvol, 24. p. 106
8 (1988).

For example, when pumping (bumping) with an ion laser,
Transition from the ground state I+5/2 to 'Il+/2,
Furthermore, it emits phonons and transitions to ' I l 3/2. In this process, the energy difference between the 281+/2 and 'II3/2 levels is lost as heat and passes through each level, resulting in a time delay in the formation of population inversion.

In other words, the closer the wavelength of the signal light is, the more efficiently there is no time delay and it becomes possible to excite population inversion.
Excitation at .mu.m to 1.50 .mu.m is suitable, but so far there has only been a report using a color-centered laser in the above-mentioned document 3. From the point of view of miniaturization, except for semiconductor lasers in the 08 μm band,
In either case, the excitation light source is large, making it impractical.
Therefore, in order to realize a small and efficient optical amplifier, there is no other way than to use a 0.8 μm band semiconductor laser.

[Problems to be Solved by the Invention] However, in the above conventional example, from the point of view of propagation mode, the pumping efficiency is proportional to the energy density of the pumping light. In the Eri optical fiber, the cutoff wavelength is changed from 11 μm to 1 μm so that the signal light becomes a single mode at 1.5 μm.
It was set between 4 μm. In this case, the above 0.8
Since semiconductor laser light in the μm band is excited up to high-order modes, the propagating light beam spreads and the energy density of the excitation light becomes low. On the other hand, in an optical fiber that has a single mode at a pump wavelength of 0.8 μm, conversely, 1.5
Since the bending loss in μmi cannot be ignored, the gain becomes unstable with respect to the bending of the fiber. Therefore, since an optimal fiber structure cannot be obtained using a semiconductor laser with a pumping wavelength in the 0.8 μm band, it has not been possible to actually realize a No. 1 type highly efficient optical amplifier.

Furthermore, due to the energy level unique to Er, 0.8 μm
In the excitation of '+3/2, some of the excited electrons are excited to a higher level, causing excitation absorption that reduces the population inversion, so this is not the optimal excitation wavelength, so Yb (ytterbium) is co-doped. It was necessary to take methods such as (see Document 5 above and Document 6 below). Even in this case, since energy transfer between Yb-Er ions is utilized, loss inevitably occurs.

Reference 6: M.E.Fermann et al.
-Efficient opera-tion of
An Yb-5ensitized Er fiber
1aser atl, 58μm'', Electron
ics Letters vol, 24. p, 1135
(1988).

In addition, E and 5 of the above-mentioned document 3 using a color-centered laser as an excitation light source with an excitation wavelength of 1.49 μm to 1.50 μm
According to the experimental results by Nitzer et al., no gain was obtained at wavelengths shorter than 1.49 μm, as shown in Figure S8. For this reason, in Er-doped optical fiber amplifiers, pumping with a semiconductor laser in a wavelength region shorter than 1.49 μm has not been attempted so far, and
This was thought to be physically impossible because it results in excitation between levels.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide an optical fiber type optical amplifier that is small in size, highly efficient, and has an amplification degree of 10 dB or more.

[Means for Solving the Problems] In order to achieve the above object, the present invention outputs a 14 μmi semiconductor laser light having an oscillation wavelength range from 1.40 μm to 1,49 μm as an excitation light source, and whose output is A semiconductor laser module (1) modularized so that it can be extracted with a fiber, its semiconductor laser light, and 1.
An optical fiber coupler or waveguide type coupler (2) that combines the 5 μm band signal spectrum and a core doped with the rare earth element Er (erbium) that has a relative refractive index difference and inputs the output of this coupler (2). It has an Er-doped optical fiber (3) consisting of a cladding section and a cladding section that does not contain Er, and demultiplexes excitation light and signal light from or connected to the terminal end of this Er-doped optical fiber (3). It is characterized in that amplified signal light is obtained from the optical fiber coupler or waveguide type coupler (2A) using the Er-doped optical fiber (3) as an amplification medium.

[Function] In the present invention, a 1.4 μmf semiconductor laser beam output from a semiconductor laser module whose oscillation wavelength range is within 1.40 μm to 1.49 μm is used as an excitation light source, and this semiconductor laser beam and 1.5 μm Signal light is combined with an optical fiber coupler or waveguide type coupler, and the combined excitation light and signal light are combined into a core part doped with the rare earth element Er and a cladding that does not contain Er, which has a relative refractive index difference. Since the input is made into an Er-doped optical fiber consisting of a
Amplified signal light is obtained from the 1@ end of the i-adding optical fiber, or from an optical fiber coupler or waveguide type coupler connected to this end that separates the excitation light and signal light.

In this way, in the present invention, 1.4 μm% is used as the excitation light source.
Since a high-output F semiconductor laser is used, it solves the conventional problem of miniaturization of the pump light source, and also easily constructs an Er-doped optical fiber type optical amplifier that can prevent a decrease in amplification due to pump absorption. can.

In addition, we have combined a modularized semiconductor laser module and an optical fiber coupler so that the output light can be extracted through a fiber, so you can easily create an Er-doped optical fiber type optical amplifier by simply splicing the respective fibers or connecting them with a connector. can be easily configured. Furthermore, 1.
Excitation in the 4 μm band is possible because ' I 13/
This is because the distribution of energy levels between 2-I l 5/2 is more complex than previously thought,
This method is significantly different from the prior art in that it utilizes the splitting of the 'I13/2 level.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Entrance J Exit” 1 凰凰 decoy FIG. 1 shows the configuration of a first embodiment of the present invention.

In Figure 1, 1 is modularized so that the output can be taken out with a fiber, and the oscillation wavelength range for excitation is 1.40.
14 μm semiconductor laser module in the range from μm to 1.19 μm, 2 is an optical fiber coupler or waveguide type coupler that combines the output pumping light of this semiconductor module 1 and the 1.5 μm band signal light, and 3 is a coupler 2 Er for amplification in which Er is added to the core part that inputs the output light of
It is a doped optical fiber. Note that the cladding portion of the optical fiber 3 does not contain Er.

The output fiber 4 of the 1.4 μm semiconductor laser module 1 is connected to the input terminal of the optical fiber coupler or waveguide type coupler 2, and the excitation light is made to enter the E-doped optical fiber 3. On the other hand, the input fiber The signal light is input to the Eri optical fiber 3 from the other input terminal of the 15 μm band signal optical fiber coupler or waveguide type coupler 2 introduced from the optical fiber coupler 5. As a result, the amplified signal light is transmitted to the end of the Er-doped optical fiber 3. obtained from.

FIG. 2 shows the oscillation spectrum of the 1.4 μm band semiconductor laser module 1 and the absorption spectrum of the Erd optical fiber 3 used in this example. When using a semiconductor laser beam whose excitation wavelength is centered at the wavelength of 1.48 μm shown by the solid line,
It can be seen that this overlaps with the unique absorption of Er shown by the broken line. The absorption peaks observed at wavelengths of 1.48 μm, 1.53 μm, and 1.55 μm are divided into three transitions at room temperature, corresponding to 1.48 μm from the ground state and 1, 53 μm, or 1.55 μm. It is thought that three levels are formed between the levels. Therefore, a population inversion is formed in the Er-doped optical fiber 3 by the excitation light in the 1.4 μm band,
Stimulated emission occurs due to the signal light, and amplified signal light is obtained from the end of the optical fiber 3.

FIG. 3 shows the coupling characteristics of the optical fiber coupler 2 of this embodiment used for combining the excitation light and the signal light of the 1.4 μm band semiconductor laser module 1. As shown in Figure 3, 1
．． In the 48μm band, 8096, 1.53μm to 1.55
It has a coupling efficiency of 20 to 3 μm.

Ideally, a coupling efficiency of 1oO96 at the excitation wavelength and 0* at the signal light wavelength is desirable, but this is difficult in practice.

FIG. 4 shows experimental results regarding the fiber length dependence of the amplification degree obtained in this example. In this experiment, fibers with different concentrations of Er doped were prepared; for example, fiber N011 was doped with Er at 1300 ppm, and fiber NO12 was doped with Er at 11000 ppm in its core. Excitation light intensity is No.
, 1. No. 32 at the input end of the Er-doped optical fiber 3 of 2
It was mW. Further, the amplification degree (dB) is the ratio of the signal light intensity at the input end and output end of the Er-doped optical fiber.

As is clear from FIG. 4, an amplification degree of about 12 dB is obtained for both fiber No. 011 and fiber No. 2. Also,
The fiber length dependence of the amplification depends on the concentration of Er, and the saturation of the amplification seen in fiber No. 1 occurs because the excitation light is absorbed by Er and is attenuated on the output side. From the above experimental results, it has been confirmed that in this embodiment, a compact and easy-to-handle optical fiber type optical amplifier having an amplification factor of 10 (18 or more) can be easily realized.

l. Figure 5 of Jjiji 11 shows the configuration of a second embodiment of the present invention. This embodiment has a configuration in which an optical fiber buffler or a waveguide coupler 2A is further connected to the terminal end of the Er-doped optical fiber 3 in the configuration of the first embodiment described above, so that signal light and excitation light can be separated. This is an example.

The amplification operation of this embodiment is similar to that of the first embodiment, and an optical fiber coupler or a waveguide coupler 2 with the same characteristics as the coupler 2 at the front stage is used. From the output fiber halo to the coupler 2, a signal light that is amplified and separated from the pumping light is obtained.

C1 Third Embodiment FIG. 6 shows the configuration of a third embodiment of the present invention. In this embodiment, a semiconductor laser module lA similar to 1 is also connected from the signal light output side to the coupler 2 in the configuration of the second embodiment described above.
By inputting the excitation light through the fiber 7,
This is an example of a configuration in which saturation of the amplification degree due to excitation on only one side shown in FIGS. 1 and 4 does not occur.

[Effects of the Invention] As explained above, according to the present invention, a 1.4 μm band semiconductor laser module, an optical fiber coupler, and an Er
Since it uses doped optical fiber, there is no insertion loss.
The effect of providing a compact, easy-to-handle, and highly efficient optical fiber type optical amplifier with an amplification degree of 0 dB or more can be obtained.

6 is a schematic diagram showing the configuration of the third embodiment of the present invention. FIG. 7 is an explanatory diagram showing the relationship between the excitation energy level of Er ions, excitation light, and signal light. FIG. 8 is a schematic diagram showing the configuration of the third embodiment of the present invention. It is a graph showing the experimental results of et al.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of the first embodiment of the present invention. FIG. 2 is a graph showing the oscillation spectrum of the 1.4 μm band semiconductor laser for excitation and the absorption characteristics of the Eri-coupling family in the first embodiment of the present invention. , FIG. 3 is a graph showing the coupling characteristics of the optical fiber coupler for demultiplexing and multiplexing in the first embodiment of the present invention, and FIG. 4 is a graph showing the fiber length dependence of the amplification degree in the first embodiment of the present invention. The graph shown in FIG.
...1.4μm band semiconductor laser module, 2.2A
...Optical fiber coupler or waveguide type coupler, 3...Er-doped optical fiber, 4-7...Fiber. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1) As an excitation light source, the oscillation wavelength range is from 1.40 μm to 1.
．． A semiconductor laser module that outputs a 1.4 μm band semiconductor laser light within 49 μm and is modularized so that the output can be taken out with a fiber, and combines the semiconductor laser light and 1.5 μm band signal light. An optical fiber coupler or a waveguide type coupler, and an Er-doped optical fiber that inputs the output of the coupler and has a relative refractive index difference and is composed of a core portion doped with the rare earth element Er (erbium) and a cladding portion that does not contain Er. amplifying the Er-doped optical fiber using the Er-doped optical fiber as an amplification medium from the terminal end of the Er-doped optical fiber or from an optical fiber coupler or waveguide coupler connected to the terminal end that separates pump light and signal light. An optical fiber type optical amplifier characterized in that it obtains signal light that is