JP2605684B2 - Optical amplifier - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical amplifier used in optical communication and the like.

[Conventional technology]

Optical amplifiers have various uses such as optical preamplification, optical direct amplification repeaters, and optical boosters. Conventionally, as an optical amplifier, a semiconductor laser amplifier using dielectric emission and a fiber Raman amplifier using Raman effect have been considered. Further, as the structure of the amplifier, a traveling-wave type optical amplifier that does not include an optical frequency filter therein and a resonator-type optical amplifier that includes an optical frequency filter have been used.

[Problems to be solved by the invention]

Among the above-mentioned conventional optical amplifiers, the former traveling-wave amplifier has a disadvantage that it has a large saturation output but requires an optical filter of about the transmission band. On the other hand, the latter resonator type has a built-in optical filter, but has a disadvantage that the saturation power is reduced because power is stored inside. There are two types of resonators: a transmission type using transmitted light as an output (IEICE Technical Report, OQE82-10, 1982) and a reflection type using reflected light as an output. However, among them, the transmission type has a drawback that the input power is not used effectively because it has the optical power returning to the input side. On the other hand, the reflection type returns all the amplified output to the input side, so that the input power can be used effectively. However, the reflection type requires a circulator to separate the input light and the output light, which is expensive, and has the drawback that the insertion loss increases.

An object of the present invention is to solve the above-mentioned drawbacks of a resonator-type and reflection-type amplifier, in particular, to solve the problem of saturation output and the use of a circulator, to increase the saturation output, and to reduce the cost without using a circulator. An object of the present invention is to provide an optical amplifier having a small insertion loss.

[Means for solving the problem]

An optical amplifier according to the present invention comprises: a plurality of reflection type optical amplifiers; and a directional coupling in which input light is split into two or more and sent to the plurality of reflection type optical amplifiers, and amplified light from the reflection type optical amplifier is returned. And a phase adjuster for phase-matching the amplified light to generate a combined output of the amplified light at one output terminal of the directional coupler.

[Action]

Hereinafter, the principle of the present invention will be described in detail with reference to an example in which two reflection optical amplifiers are used and a half mirror is used as a directional coupler.

In FIG. 2, first, an input light 30 is inputted from an input terminal 1 and is divided into two by a half mirror 2 which is an optical demultiplexer.
Are input to the reflection optical amplifiers 5 and 6 having the same characteristics. The light that has been input to and amplified by the reflection type optical amplifiers 5 and 6 reverses the optical path, is multiplexed by the half mirror 2, and is output to the output terminal 9. At this time, each of the reflection type optical amplifiers 5, 6
The phase of the light output from the half mirror 2 is adjusted by using the phase matching device 4 so that the phase is the same on the output side 9 and input to the half mirror 2. , The output sum of the reflection type optical amplifiers 5 and 6 is obtained, and the amplified output does not return to the input terminal 1. As a result,
When an optical amplifier having this configuration is used, the saturation output can be doubled because two amplifiers are used, and the input light and the output light can be separated without using a circulator.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram of a first embodiment of the present invention. The optical amplifier of this embodiment comprises first and second reflective semiconductor laser amplifiers 5 and 6 and first and second temperature controllers 7 and 8.
It comprises a phase matching unit 4 and a half mirror 2 as a directional coupler.

Next, the operation and operating conditions of this embodiment will be described with reference to FIGS. 1, 3, and 4. FIG. An input light 30 having a wavelength of 1.5 μm modulated by a pulse signal of 400 Mb / s is input from an input terminal 1 and is divided into two by a half mirror 2.
The signal is input to a first reflection type optical amplifier 5 composed of a semiconductor laser amplifier, and the other is input to a second reflection type optical amplifier 6 composed of a semiconductor laser amplifier after passing through a phase matching device 4. Here, the resonance frequency of the semiconductor laser amplifier is the third
Since it depends on the temperature of the amplifier as shown in the figure, first, the first and second resonance frequencies at which the amplification factors of the respective reflection type optical amplifiers 5 and 6 become the same as the frequency of the input light.
Temperature controllers 7 and 8 are adjusted. Next, since the amplification factor of the semiconductor laser amplifier depends on the injection current as shown in FIG. 4, by adjusting the injection current to each of the amplifiers 5 and 6, the amplification factor of each amplifier is adjusted and each amplifier 5 is adjusted. , 6
, The first and second amplified outputs 32 and 34 obtained on the output side have the same level. After performing these adjustments, the phase of the output light 34 of the second amplifier 6 is adjusted using the phase matching device 4 so that the power obtained at the output terminal 9 side is maximized. At this time, the optical path difference of the light input to each of the reflection type optical amplifiers 5 and 6 is made as small as possible. By performing such adjustment, the power obtained at the output side 9 can be increased by the interference effect, and the return light to the input side 1 can be suppressed.

In the present embodiment, the first and second reflection type optical amplifiers 5 and 6 use an AlGaAsP-based semiconductor laser whose end face is coated. Is set to almost 100% and is used below the laser oscillation threshold value. In addition, LiNb
A waveguide-type matching device using O3 is used, and a DC voltage is applied to the crystal to change the refractive index and perform phase matching. In this embodiment, the saturation output was increased by approximately 3 dB. Also, the return light to the input side 1 was almost only spontaneous emission light emitted from the amplifier, and almost no amplified output of the input light was obtained.

FIG. 5 is a configuration diagram of a second embodiment of the present invention. This embodiment is significantly different from the first embodiment in that two sets of amplifiers as shown in the first embodiment are combined to operate as a high saturation output reflective amplifier. Less than,
The operation and operation conditions of this embodiment will be described in detail.
The input light 50 with a wavelength of 1.5 μm modulated by a 400 Mb / s pulse is
From the input end 10, two fibers are brought into close proximity, heated and stretched, and divided into two by a first directional coupler 11, which is input to second and third directional couplers 12, 13 of the same manufacturing method. . here,
First, the second directional coupler 12, the first and second reflection type laser amplifiers 15 and 16, the first phase matching unit 23 and the third directional coupler 13, the third and fourth reflection type lasers First and second two sets of optical amplifiers comprising amplifiers 17, 18, and a second phase matching unit 24
Adjust 40 and 41 respectively. As in the first embodiment, the resonance frequencies and the amplification factors of the reflection type laser amplifiers 15 to 18 are determined by the temperature and the injection current. The adjustment of the phase matching units 23 and 24 is different from that of the first embodiment, and the first output terminal 19 to which the directional coupler 12 is connected and the first output terminal 19 to which the directional coupler 13 is connected so that all amplified outputs return to the input side. The output is adjusted to be minimum at the output terminal 20 of the second. With this adjustment, the first optical amplifier 40 and the second optical amplifier 41 can be regarded as reflection amplifiers each having one saturation output doubled. further,
The outputs of these two sets of optical amplifiers 40 and 41 are adjusted using a third phase matching unit 25 so that they have the same phase at the output terminal 21 to which the directional coupler 11 is connected. At this time, the output terminal 21 can obtain an output four times the saturated output of one reflection amplifier. Further, light returning to the input side can also be suppressed.

In the present invention, there are various modified examples other than the above-described embodiment. For example, a fiber Raman amplifier can be used instead of a semiconductor laser amplifier. As the phase matching device, a type in which the refractive index is changed by compressing the medium with a piezoelectric element can be used, and a waveguide type device can be used as the directional coupler.

[Effects of the Invention] As described above, according to the present invention, the input and output of the reflection type optical amplifier can be separated without using a circulator, and the saturation output can be increased.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention, and FIG.
FIG. 3 is a diagram showing the relationship between the resonance frequency of the semiconductor laser amplifier and the temperature of the laser; FIG. 4 is a diagram showing the relationship between the amplification factor of the semiconductor laser amplifier and the injection current value; FIG. 5 is a block diagram of a second embodiment of the present invention. 2, half mirrors, 4, 23, 24, 25 phase matchers
5, 6, 15, 16, 17, 18 ... Reflection type optical amplifier, 11, 12,
13 …… Directional coupler

Claims (1)

(57) [Claims] A plurality of reflection type optical amplifiers; a directional coupler for splitting input light into two or more light beams and sending the divided light beams to the plurality of reflection type optical amplifiers and returning amplified light from the reflection type optical amplifiers; A phase adjuster for phase-matching the amplified light to generate a combined output of the amplified light at one output terminal of the directional coupler.