JPH0459636A - Optical amplifier - Google Patents

Abstract

PURPOSE:To effect light amplification at 1.3mum band and to raise amplification efficiency, having optically functional glass blended with Nd<3+>, by combining a transmission means with a first and a second excitation light sources and an optical means to show a specific action. CONSTITUTION:A signal light at 1.3mum band outputted from a signal light source 13 is passed through a guide 15a of optical fiber into a fiber coupler 15, an optical means. The signal light passed into the fiber coupler 15 is bonded to excitation lights at 5mum and 0.8mum bands and passed into an optical fiber 11. The signal light passed into the optical fiber induces popped Nd<3+> to produce emitted light at 1.3mum wavelength band. In the emission, since emission of light at 1.06mum wavelength band is restricted, induction and release of light at 1.3mum wavelength having lower natural release probability than 1.06mum wavelength band is not obstructed. Consequently, the signal light can be amplified at 1.3mum band. In fiber blended with Nd<3+> and capable of amplifying at 1.3mum band, efficiency of induction release can be raised and amplification gain can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical amplification device used in the 1.3 μm band.

[Conventional technology]

Glass doped with rare earth elements is used to amplify fiber amplifiers, fiber sensors, fiber lasers, etc. for applications in the field of optical communication in the 1 and 3 μm band, which is generally performed in the wavelength range of 1.310 ± 0.025 μm. Efforts are being made to create devices.

For example, neodymium ions (N
A report on the evaluation of the laser oscillation characteristics of an optical fiber formed from a glass doped with d3+) (ELECTRONIC3LETTER3゜19)
90, Vol, 2B, No, 2. pI) 121-12
2) etc. have been done. In this report, regarding the characteristics of the optical fiber, the fluorescence peak wavelength exists at 1.32 μm, the laser oscillation peak wavelength exists at 1.36 μm, and the ES
A (excited 5tate absorption
n) The results show that the peak wavelength exists in the 1.3 μm band.

[Problem to be solved by the invention]

However, in the multi-component glass shown in the above report, the wavelength 1
．． No optical amplification gain was obtained in the 3 μm band. The reason why no gain can be obtained is that the wavelength is 1.32 μm.
The fluorescence peak intensity of Nd3+ present in Nd3+0
It is thought that the fluorescence peak intensity is weak compared to other possible fluorescence peak intensities, and that a relatively large absorption peak due to the ESA transition exists in the 1.3 μm band.

Therefore, in view of the above-mentioned circumstances, the present invention has a wavelength of 1.3 μm.
It is an object of the present invention to provide an optical amplification device that enables optical amplification in the band or has improved amplification efficiency.

[Means to solve the problem]

In order to achieve the above object, an optical amplification device according to the present invention is configured with an optically functional glass in which Nd3+ is added as an active substance to chalcogenide glass, and has a wavelength of 1.3 μm.
a first pump light source that generates a first pump light having a wavelength of 0.8 μm; and a second pump light source that generates a second pump light having a wavelength of 5 μm. , causing the first excitation light from the first excitation light source to enter the transmission means, and causing the second excitation light from the second excitation light source to enter the transmission means.
and an optical means for making the excitation light of 1 to enter the transmission means.

[Effect]

In the optical amplification device according to the present invention, Nd3+, which is an active substance, is excited by the first excitation light in the 0.8 μm band introduced into the transmission means. This wavelength of 0.8 μm corresponds to the ground level ■ Energy 9/2 N d ”0) in the transmitting membrane is excited by the first excitation light and emits light in the 1.06 μm band, 1.3 μm band, etc. The state is such that a transition corresponding to is possible.

Furthermore, in the above optical amplification device, the active substance Nd
Excite 3+. This wavelength of 5 μm is from the ground level I to the energy level 419/2 1
Corresponds to a transition of 1/27'. As a result, the majority of Nd''+ excited by the first excitation light has a wavelength of 1.3 μm.
Luminescence in the 1.06 μm wavelength band, which has a higher probability of spontaneous emission than that in the 1.06 μm band, is suppressed. Therefore, stimulated emission caused by light in the wavelength band of 1.06 μm can be suppressed, and light in the wavelength band of 1.3 μm can be suppressed.
The probability of stimulated emission in the m band can be increased.

〔Example〕

Embodiments of the optical amplification device of the present invention will be described below.

FIG. 1 shows a fiber amplifier, which is an optical amplification device for a wavelength band of 1° to 3 μm. The laser light source 12, which is the first excitation light source, outputs first excitation light having a wavelength of 018 μm. This first excitation light enters a fiber coupler 15, which is an optical means, through an optical fiber guide 12a, and enters an optical fiber 11, which is a transmission means, through an optical connector or the like. The optical fiber 11 is doped with Nd8+ as an active substance, and this Nd3+ is positively pumped by the first excitation light to form a wavelength band of 1.06 μm and a wavelength of 0.88 μm.
It becomes possible to emit light in a wavelength band of 1.33 μm.

At the same time, second excitation light having a wavelength of 5 μm is output from the heater 14, which is a second excitation light source. This 5 μm
The band light also enters the fiber coupler 15 via the guide 14a, and the fiber coupler 15 causes the above 0.8μ
It is combined with an m-band laser beam and enters the fiber 11. The Nd "4" in the end fiber 11 is also excited by the laser beam in the 5 μm band, and the emission of light in the 1.06 μm wavelength band is restricted. The reason why light emission in the wavelength band of 1.06 μm is limited in this way is that the energy level to which electrons should transition due to radiation corresponding to the wavelength band of 1.06 μm is occupied by the excited electrons emitted in the 5 μm band. This is because it has been done.

Signal light with a wavelength of 1.3 μm outputted from the signal light source 13 enters the fiber coupler 15, which is an optical means, via the optical fiber guide 1.3a.

The signal light incident on the fiber coupler 15 has a diameter of 5 μm and 0
．． The light is combined with the 8 μm band excitation light and enters the optical fiber 11 . The signal light incident on the optical fiber induces pumped Nd3+ to generate radiation light in the wavelength band of 1.3 μm. At this time, since light emission in the wavelength band of 1.06 μm is restricted, stimulated emission in the wavelength band of 1.3 μm, which has a lower spontaneous emission probability than in the wavelength band of 1.06 μm, is not hindered. Therefore, it becomes possible to amplify signal light in the 1.3 μm band. Furthermore, for a fiber doped with Nd3+ which is capable of amplification in the 1.3 μm band, it is possible to improve the efficiency of stimulated emission and increase the amplification gain.

A filter 16 provided on the output side of the optical fiber 11 is for cutting the first and second excitation lights, and an optical spectrum analyzer 17 provided beyond that filter measures the amplified signal light. It is a device for

A more detailed description of the embodiments follows.

As the laser light source 12, which is the first excitation light source, a Ti-sapphire laser (argon excitation) with an excitation wavelength of 0.78 μm and an excitation output of 10 mW was used. Also, the intensity of the input signal from the laser light source 12 to the optical fiber 11 is increased by 10 m.
W, and the peak wavelength was set to 1.310 μm.

Heater 14 which is a 5 μm band light source which is a second excitation light source
consists of a combination of a hot wire heater and a suitable filter. The intensity of the input signal from the heater 14 to the optical fiber 11 was 10 mW.

A semiconductor laser was used as the signal light source 13. Its peak wavelength was 1.31 μm.

Below, a brief explanation will be given regarding the production of the optical amplification fiber 11 described above.

First, as the core material of the fiber that is the transmission means, Nd
A chalcokenide glass to which + was added was prepared. The composition of the host glass is 30G e -20A s -5O3
And so. The concentration of neodymium ions as an active substance added to this host glass was 1% by weight. For comparison, a fluoride glass to which the same amount of Nd" The fiber core was set in a drawing device and drawn into a fiber core.The fiber core was covered with an FEP cladding for protection.As a result, an S with a core diameter of 8 μm and an outer diameter of 125 μm was obtained.
M fiber was obtained. This 8M fiber was cut into a sample with a length of 1 m for measurement, and was used as the tip fiber 11 for optical amplification.

The results of optical amplification using the above fiber amplifier are shown in the second
Shown in the table of figures.

Conditions (#-1 and Condition 2 are the results of injecting two kinds of strong and weak 5 μm band excitation light into the optical fiber 11 of chalcogenide glass doped with Nd"+. Condition 3 is the result of fluoride-based excitation light doped with Nd3+. In this case, the fiber 11 made of glass cannot be used because the wavelength band of 5 μm is absorbed by the matrix glass itself.

As is clear from the table, the gain clearly increases when the wavelength of 5 .mu.m band is used for four wavelengths. In other words, in the case of a conventional optical fiber that does not use pumping light in the wavelength band of 5 μm (condition 3), the gain coefficient is 1 dB/mW, or in the case of condition 2, the intensity of the pumping light in the wavelength band of 5 μm is relatively weak. However, the gain coefficient becomes 1 or 2 dB/mW, and in the case of condition 3, where the intensity of the pumping light in the wavelength band of 5 μm is strong, the gain coefficient becomes 10 dB/mW.
mW.

For reference, the wavelength 5 generated by the second excitation light source
Figures 3 and 4 explain the function of the second excitation light in the μm band.
A simple explanation will be given below using diagrams. 〇Figure 4 shows the Nd3+ added to a phosphate-based glass sample.
FIG. 2 is a diagram showing an example of energy levels of .

The absorption/emission transition wavelengths shown in the figure were calculated by measuring a fiber made from this glass using a self-recording spectrophotometer and an optical spectrum analyzer.

0680μ, which is the first excitation light introduced into the optical fiber
The next light in the m band excites Nd3+, and its ground level I
The electron at level 4F9/2 5/
2, and after emitting phonons, the level F.
and level 4r, 4I3/2 9/
When a population inversion is formed between 211/2ゝ4113/2 and I15/2, the wavelength is 0.88 am and the wavelength is 1.06 μm.

It becomes possible to emit light with a peak wavelength of 1.32 am and a wavelength of 1.80 t1m. Among these, wavelength 0.88 μm, wavelength 1.06 μm, and wavelength 1.33 have relatively strong emission intensity.
The results of calculating the peak intensity ratio of the luminescence for μm are as follows:
The ratio was approximately 5:9:1, respectively.

In response to the fact that the probability of light emission in the 1.06 μm wavelength band is extremely high, FIG. 3 shows a method for reducing light emission in the 1.06 μm wavelength band.

The difference between Fig. 3 and Fig. 4 is that Nd is excited by the second excitation light introduced into the optical fiber, which is radiation at the wavelength band of 5 μm, and its ground level 4I9/2'' electrons are excited. and transitions to energy level 111/
2. Therefore, level 4F
A substantial population inversion occurs between and I 3/2
11/2, or the degree of population inversion decreases even if population inversion occurs. Therefore, the probability of light emission in the 1.06 μm wavelength band decreases, resulting in a wavelength of 1.33 μm, that is, 1.06 μm.
The probability of light emission in the 3 μm band increases. In this way, Nd3+ in a state where emission in the 1.06 μm band is suppressed.
When a signal light in the 1.3 μm band is incident on the
The stimulated emission in the band is effectively carried out without being hindered by the emission in the 1.06 μm band. As a result, despite the presence of absorption in the 1.3 μm wavelength band due to ESA transition, optical amplification and light emission in the 1.3 μm wavelength band becomes possible, and the gain of optical amplification can be increased. .

In the optical amplification device of the present invention, chalcogenide glass doped with Nd3+, which is an active substance, is used as the transmission means. Rather than using phosphate glass as the host glass,
The reason why chalcogenide glass is used is that chalcogenide glass has good transmittance for excitation light in the 0.8 μm wavelength band and 5 μm wavelength band and good transmittance for signal light in the 1.3 μm wavelength band.

The transmission means of the present invention is not limited to the above-mentioned fibers. For example, the chalcokenide glass described above may be formed into a planar waveguide or the like. However, it is preferable to form the optical fiber in order to obtain a long optical transmission line. This is because if the small optical loss is utilized, population inversion can be caused in Nd3+ with a low threshold value.

The optical fiber used in the optical amplification device of the present invention can also be applied to devices such as fiber lasers.

Specifically, the fiber laser is configured to include the optical fiber, first and second excitation light sources, optical means, and an optical resonator. Here, the first excitation light source has a wavelength of 0.
．． It generates excitation light in the 8 μm band, and the second excitation light source has a wavelength of 5 μm.
Generates excitation light in the μm band. The optical means also allows excitation light to enter the optical fiber from the first and second excitation light sources. Furthermore, the optical resonator has a wavelength of 1.3μ from within the optical fiber.
The m-band radiation is fed back to the optical fiber.

According to the above-described fiber laser, Nd3+ is excited by excitation light in the wavelength band of 0.8 μm introduced into the fiber by optical means. A part of this excited Nd3+ is emitted from the optical fiber with a wavelength of 1.3 μm and a wavelength of 1.3 μm fed back into the optical fiber.
m-band light, and generates emitted light with a wavelength of 1.3 μm. By repeating this, wavelengths 1 and 3
Laser emission in the μm band becomes possible.

Examples of fiber lasers will be described below.

The specific configuration is similar to a known Er-doped fiber laser (rEr-doped fiber J, Op
lug E, January 1990, pp.

See 112-118, etc. ). However, in the case of this embodiment, the optical fiber of the above embodiment doped with Nd3+ is used as the optical fiber. Further, a laser diode that generates excitation light in a 0.8 μm wavelength band is used as the first excitation light source, and a heater that generates excitation light in a 5 μm wavelength band is used as the second excitation light source.

The excitation light in the wavelength band of 0.8 μm from the laser diode is
It is introduced into the optical fiber shown in the above embodiments by suitable optical means, such as a lens. At the same time, excitation light with a wavelength band of 5 μm from the heater is also introduced into this optical fiber. As a result, Nd3+ within the optical fiber is excited to a predetermined state, allowing efficient light emission in the 1.3 μm wavelength band. Here, since the output end of the fiber is finished with a mirror finish, this output end and the end face of the laser diode constitute a resonator. As a result, when the output of the excitation light exceeds a predetermined value, laser oscillation occurs in the wavelength band of 1.3 μm.

Note that the resonator may be of a type that uses a dielectric mirror or the like.

〔Effect of the invention〕

As explained above, according to the optical amplification device according to the present invention, due to the presence of excitation light in the wavelength band of 5 μm,
Not only is it possible to amplify and emit light in the Nd”
It is possible to increase the efficiency of optical amplification by +.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the optical amplification device according to the present invention,
Figure 2 shows the amplification characteristics of the optical amplifier shown in Figure 1, and Figure 3 shows the amplification characteristics of the optical amplifier shown in Figure 1.
The figure and FIG. 4 are diagrams showing an example of the excited level of N d "-1' on. 11...Fiber which is a transmission means, 12... Wavelength 0
．． 1st excitation light source for 8 bands, 14... 0 second excitation light source for 5 μm wavelength band, 15... Cobra as optical means.

Claims (1)

[Claims] It is composed of a photofunctional glass in which Nd^3^+ is added as an active substance to chalcogenide glass, and has a wavelength of 1.3.
A transmission means for propagating signal light in the μm band and a wavelength of 0.8 μm.
a first excitation light source that generates a first excitation light in a wavelength band; a second excitation light source that generates a second excitation light in a wavelength band of 5 μm; and the first excitation light from the first excitation light source. into the transmission means, and the second excitation light source from the second excitation light source
An optical amplifying device, comprising: an optical means for making the excitation light of the above input into the transmission means.