JP2788801B2 - Optical amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifying device which exhibits an optical amplifying function by exciting light.

[0002]

2. Description of the Related Art In recent years, researches on an optical amplification device utilizing an optical amplification effect at the time of optical excitation of a fluorescent substance such as a rare earth element mixed in a core of a silica-based optical fiber have been actively conducted. As an optical amplifying device using the rare-earth-element-doped optical waveguide, optical amplification in a 1.55 μm band has been confirmed using a silica-based optical fiber doped with Er. Such an optical amplifying apparatus is basically configured as shown in FIGS. 4 and 5, and includes an excitation light source A for performing optical excitation, a multiplexing element B for multiplexing signal light and excitation light, An optical fiber (optical waveguide) with a fluorescent material such as a rare earth element mixed in the core
C. As the multiplexing element B, a multiplexing device (W
DM etc.) are used. In addition, as an excitation method in this optical amplifying device, forward excitation in which the pump light is applied in the light transmission direction as shown in FIG. 4 and excitation light in the opposite direction to the light transmission direction as shown in FIG. There is reverse excitation.

[0003]

In the forward pumping of FIG. 4, an optical isolator D for preventing oscillation due to reflection can be inserted at both ends of the optical waveguide C, and a high-performance optical amplifier can be realized. However, although high gain can be achieved by the backward pumping of FIG. 5, an optical isolator D for preventing oscillation due to reflection cannot be inserted immediately after the optical waveguide C, and there is a problem that oscillation is easy.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to realize an optical amplifier having a high performance, a simple structure, and a low oscillation.

[0005]

An optical amplifying apparatus according to the present invention comprises:
Optical waveguide 1a (FIG. 1), 1a, which obtains gain by stimulated emission of a fluorescent substance such as a rare earth element mixed in a core portion
And 1b (FIG. 3), an excitation light source 2 for supplying excitation light to the optical waveguides 1a, 1a and 1b, and a multiplexing element for multiplexing the excitation light from the excitation light source 2 to the optical waveguides 1a, 1a and 1b. Wherein the non-reciprocal optical element 4 such as an optical circulator is used as the multiplexing element.

[0006]

According to the present invention, the multiplexing device has four ports, and the light incident on the port 4-1 is transmitted to the port 4-2.
From the port 4-2, the light of the port 4-2 is transmitted from the port 4-3.
-3 light from port 4-4 and port 4-4 light from port 4-4.
Optical non-reciprocal element 4 having characteristics emitted from G4-1
Since an optical circulator is used, the optical signal passes through the optical isolator 5 and becomes an optical waveguide (erbium-doped optical fiber).
1a, and after being amplified by the light of the excitation light source 2 incident from the port 4-1 of the optical circulator 4,
The light enters the port 4-2 of the curator 4 and the amplified signal is output from the port 4-3. In this case,
Since the reflected light returning from the port 4-3 is emitted to the unused port 4-4, the light reflected at the port 4-4 (port 4
−3) is not reflected by the optical waveguide 1a, and oscillation in the optical waveguide 1a due to the reflected light can be prevented. Further, since the output from the port 4-2 is not emitted to the port 4-1, reflection at the excitation light source 2 or the like can be prevented.

[0007]

Embodiment 1 In an embodiment of the optical amplifying device of the present invention shown in FIG. 1, a laser having an oscillation wavelength near the 1.48 μm band is used as an excitation light source 2, and an erbium-doped optical fiber is used as an optical waveguide 1a. Then, a 4-port optical circulator was used as the non-reciprocal optical element 4. In this state, when a signal light having a wavelength of λs = 1553.5 nm is incident on the erbium-doped optical fiber 1a through the optical isolator 5, the signal light is amplified by pumping light from the pumping light source 2 during transmission, and is transmitted to the port of the optical circulator 4. 4-3. At this time, the light returning to the port 4-3 is applied to the port 4-3.
4 and does not return to the erbium-doped optical fiber 1a. FIG. 2 shows the result of transmitting the signal light in this embodiment.
As can be seen from FIG. 3A, when a normal multiplexer (WDM) is used, when the gain becomes close to 20 dB, noise oscillation occurs, and as shown in FIG. 3B, the pump light is increased. No further gain was obtained. On the other hand, in the case of the present embodiment using the optical circulator 4, the gain increases as the pump light increases, and no oscillation is observed (FIG. 2 (c)).

[0008]

Embodiment 2 FIG. 3 shows another embodiment of the optical amplifier of the present invention. This embodiment applies the embodiment shown in FIG. 1 and performs simultaneous bidirectional amplification. The downstream signal light enters the port of the optical circulator 4, is amplified by the erbium-doped optical fiber 1a, and is output from the port of the optical circulator 4. The upstream signal light enters the port of the optical circulator 4, is amplified by the erbium-doped optical fiber 1b, and is output from the port of the optical circulator 4. As described above, in this embodiment, simultaneous bidirectional amplification can be easily realized.

Incidentally, the optical amplifying device of the present invention may be other than that shown in FIG. 1. For example, a 3-port optical circulator can be used as the nonreciprocal optical element 4, and the optical amplifying medium can be used. Alternatively, instead of the erbium-doped optical fibers 1a and 1b, an optical waveguide in which a rare earth element or a transition metal ion is mixed in an oxide such as YAG or YLF or a fluorinated crystal can be used.

[0010]

As described above, according to the optical amplifying device of the present invention, it is possible to realize a high-performance optical amplifying device with a simple configuration, which is resistant to oscillation by reflected light.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of an optical amplifier of the present invention.

FIG. 2 (a) is an explanatory diagram showing the relationship between pump light and gain of an embodiment of the optical amplifier of the present invention and a conventional example, and FIG. 2 (b) shows an output waveform of the optical amplifier of the present invention. FIG. 1C is an explanatory diagram showing an output waveform of a conventional optical amplifier.

FIG. 3 is an explanatory view showing another embodiment of the optical amplifying device of the present invention.

FIG. 4 is an explanatory diagram showing an example of a conventional forward-pumped optical amplifier.

FIG. 5 is an explanatory diagram showing an example of a conventional backward-pumped optical amplifier.

[Explanation of symbols]

 1a, 1b Optical waveguide 0 2 Excitation light source 4 Non-reciprocal optical element 5 Optical isolator

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/10 G02B 6/00 G02F 1/35 501 H01S 3/07 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. An optical waveguide for obtaining a gain by stimulated emission of a fluorescent substance such as a rare earth element mixed in a core part,
In an optical amplifying device including an excitation light source for supplying excitation light to the optical waveguide and a multiplexing element for multiplexing the excitation light from the excitation light source to the optical waveguide, a non-reciprocal optical element is used as the multiplexing element. An optical amplifying device characterized by the above-mentioned.