JPS6146084A - Optical amplifier - Google Patents

Abstract

PURPOSE:To vary the wavelengths of beams, which can be amplified, and to select them arbitrarily by forming a loop, through which the first output side is fed back to the first input side, and a loop through which the second output side is fed back to the second input side, and independently changing the optical length of the loops. CONSTITUTION:Input beams 17 are projected to a waveguide layer 23 through an antireflection film 22, and function as one of three inputs to a star coupler 24. Beams reaching the waveguide layer 23 are divided into three beams 25, 26, 27 by the action of the star coupler 24. Divided one beams 25 are projected to an active layer 28, and are inputted to the star coupler 24 and constitute a first loop 29, and the other beams 26 are projected to an active layer 30, and are inputted to the star coupler again and constitute a second loop 31. Beams 27 are projected as output beams 19 through an antireflection film 36. The optical length of the two loops 29, 31 is changed independently by altering the set values of currents injected to the two active layers 28, 30, thus selecting beams having a desired wavelength from input beams, wavelengths thereof are multiplied, and amplifying them while interrupting the projection of beams toward a light source for input beams.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field 1] The present invention relates to an optical amplifier that selects and amplifies light of a desired wavelength.

[Prior Art 1] FIG. 1 shows a schematic configuration of a conventionally known optical amplifier. In this optical amplifier, the medium inside a Fabry-Perot resonator is filled with an active medium composed of a semiconductor. That is, as shown in the figure, the optical amplifier 11 is an element in which two semi-transparent mirrors 12 and 13 face each other in parallel with a predetermined distance apart, and the space between them is filled with an active medium 14 that emits light.

A DC current is injected from a bias circuit (DC power supply) 15 into an active medium 14 made of a semiconductor via a stabilizing coil 1B. The current value is controlled to be below the laser oscillation threshold of the optical amplifier 11.

Note that when the current injected into the optical amplifier 11 is sufficiently larger than the oscillation threshold, laser oscillation is obtained within the active medium 14.

When input light 17 enters the active medium 14 from the outside through the semi-transparent mirror 12, a part of the input light is reflected as reflected light 18 without entering the active medium 14. On the other hand,
The light incident on the active medium 14 is amplified, and a portion of the light is emitted as output light 18 through the semi-transparent mirror 13.

However, a part of the light that has entered the active medium 14 and has been amplified ends up being emitted as output light 20 through the semi-transparent mirror 12 .

In this conventionally known optical amplifier,
The reflected light 18 is directed toward the light source 21 that emits the input light 17.
and the output light 20 will travel together.

As a result, the light source 21 is affected by these light rays 18 and 20 and cannot stably emit light.

Furthermore, conventional optical amplifiers have the disadvantage that the wavelength of light that can be amplified cannot be arbitrarily selected.

[Objective 1] In view of the above-mentioned points, the object of the present invention is to make it possible to arbitrarily select the wavelength of light that can be amplified without outputting light that travels toward a light source that emits input light to be amplified. An object of the present invention is to provide an optical amplifier according to the present invention.

[Structure of the Invention] In order to achieve the above object, the present invention uses a 3-input and 3-output optical star coupler to form a first loop in which the first output side is fed back to the first input side. , and a second loop formed by feeding back the second output side to the second input side, and a control means for independently changing the optical path length of each of these loops is installed at a predetermined part of the loop. It is characterized by:

Here, it is preferable to insert an active medium into each of the loops to obtain a desired optical amplification factor.

Furthermore, it is preferable that the control means is connected to the active medium via an electrode and configured to inject a current.

Furthermore, it is also possible to connect the control means to a loop other than the active medium via a Ti pole so that the optical path lengths of the two loops can be changed independently.

The active medium may be made of a semiconductor, and may be configured to independently inject current.

[Example] Hereinafter, the present invention will be described in detail based on Examples.

FIG. 2 is a plan configuration diagram showing one embodiment of the present invention, FIG. 3 is a schematic perspective view showing the three-dimensional configuration of the same embodiment, and FIG. 4 is a cross-sectional configuration diagram including electrodes 41 to 43 of the same embodiment. be. here,
Portions corresponding to those of the conventional example shown in FIG. 1 are given the same numbers.

Hereinafter, with reference to FIGS. 2 to 4, the configuration and structure of this embodiment will be explained.
I will explain the action.

As shown in FIG. 2, input light 17 enters waveguide layer 23 via antireflection film 22. As shown in FIG. This waveguide layer 23 is
This is one of the three inputs included in the 3-input, 3-output star coupler 24.

The light reaching the waveguide layer 23 is split into three lights 25, 28, and 27 by the action of the star coupler 24. Then, one of the divided lights 25 enters the active layer 2B and is again input to the star coupler 24, forming the first loop 29. The other light 26 enters the active layer 30 and is input to the star coupler again. , forming the second loop 31.

The incident side (incident surface) of the active layer 2B described above 32. Output side (
output surface) 33 and the input side (incident surface) 34 of the active layer 30
．． All of the emission sides (output surfaces) 35 are set obliquely (0ζ80°) with respect to the traveling direction of the light, so that the light does not form a loop only within the active layer 2B or only within the active layer 30. This is to prevent oscillation. Note that θ=4
When it is set to 0', it is estimated that 1 reflectance becomes about 1O-4.

The light 27 is then emitted as output light 19 via the antireflection film 36.

Further, as shown in FIGS. 3 and 4, the optical amplifier 11
has a semiconductor multilayer structure. That is, n-type InP
On the substrate 37 are a waveguide layer 23 and a star coupler 24.
Ga,,311 n64A! ;0. ggPo, 32.
In addition, the active layer 28 and the active layer 30 are formed of Gaa, +s"a, 57Aso, qspo, o5.Then, the buried layer 38 is formed of P-type InP. Furthermore, the layer above the buried layer 38 is formed of 39 to n-type In
Formed by P. The upper part of the active layer 28, 30, the upper part of the waveguide layer 23, and the upper part of the star coupler 24 are made of
A layer 40 is formed using P.

Gold is preferably used for the electrodes 41, 42, 43.

Stabilizing coils 48 are provided in the active layer 2 and the active layer 30, respectively.
．． A DC power supply 44, 45 is connected via 47, thereby allowing independent injection of DC current.

Now, when the current injected into the active layer 28 is I1, the mode allowed by the first loop 28 is shown by the solid line in FIG. 5(A), and the current injected into the active layer 30 is I2. In some cases, the modes allowed by the second loop 31 are shown by the solid line in FIG. 5(B). However, these electricians and I
2 is a radio wave value such that the optical amplifier 11 does not oscillate without the input light 17 and does not emit the output light 19 even when both are injected at the same time.

At this time, the modes allowed by the optical amplifier 11 are shown in FIG. 5(A).
This is a mode in which the mode shown in FIG. 5 and the mode shown in FIG. 5(B) match, that is, the mode shown by the solid line in FIG. 5(C).

However, the gain distribution of the active layer 28 and the active layer 3G is
Since it exhibits wavelength dependence as shown in FIG. 5(D), in the end only one mode shown by the solid line in FIG. 5(E) is allowed.

By injecting currents Il and I2 in this way,
Only the wavelength input 0 shown by the solid line in FIG. 5(E) can be amplified.

Next, when the current injected into the active layer 2B is changed to ζ, the refractive index of the active layer 28 also changes, so the mode allowed by the first loop 29 is as shown by the dotted line in FIG. 5(A). The wavelength shifts. Similarly, the current injected into the active layer 30 is
J, the refractive index of the active layer 30 also changes, so the wavelength of the mode allowed by the second loop 31 shifts as shown by the dotted line in FIG. 5(B). However, these currents 11
and I2 are set to current values such that, even if both are injected at the same time, no output light 18 is emitted without input light 17.

At this time, the modes allowed by the optical amplifier 11 are shown in FIG. 5(A).
The mode shown by the dotted line in FIG. 5(B) coincides with the mode shown by the dotted line in FIG. 5(C), that is, the mode shown by the dotted line in FIG. 5(C).

However, the gain distribution of the active layer 28 and the active layer 30 is
Since it exhibits wavelength dependence as shown in FIG. 5(A), in the end only one mode shown by the dotted line in FIG. 5(E) is allowed.

By injecting currents 11 and I2 in this way,
It becomes possible to amplify only the wavelength λ0 shown by the dotted line in FIG. 5(E).

Therefore, when light wavelength-multiplexed by two wavelengths, input ◇ and λ0, is injected into the optical amplifier 11 as input light 17, if the injection current is set to IJ and 12, □output light 19
As a result, only the light with the wavelength of λ0 is amplified and output.On the other hand, if the injected current is set to B and B, only the light with the wavelength of input @ is amplified and output.

Moreover, there is no light traveling toward the light source 21 that emits the input light 17.

In addition, the current injected into the two active layers 28 and 30 is maintained at a constant value below the oscillation threshold.
Also, in the case where an electrode is provided independently at a predetermined upper part of the two loops 29 and 31 instead of the upper part of the loop 30, and the current is independently injected, the optical path lengths of the two loops 2f3 and 31 can be changed independently. Therefore, the same action Φ effect as in the above embodiment can be obtained.

Finally, the actions and effects when changing the optical path length of the loop are summarized as follows: Incoming light 17
goes around two loops 29.31 and is emitted as output light 18, but each of these loops 28.31 is a resonator, and the optical path length of each loop (= loop length x refractive index) is equal to the incident light. When the wavelength becomes an integer multiple of the wavelength, stronger output light is emitted. This strongly emitted peak wavelength is the fifth wavelength.
As shown in Figures (A) and (B). That is,
FIG. 5(A) shows the wavelengths allowed in the first loop 29 in the fifth loop.
Figure (B) shows the wavelengths allowed in the second loop 31.

Since the incident light 17 goes around the two loops 29.31, only the wavelengths that are commonly allowed in the two loops 29.31 are allowed, and in the end, the active layer 2
8. Depending on the wavelength dependence of 30, the wavelength input ◇ or input 0
Light with such wavelengths will be output.

In this way, by changing the optical path lengths of the two loops 29 and 31, the wavelength of light allowed changes. At this time, the current value was changed not only by changing the current injected into the active medium (active 528.30) but also by injecting current into some other regions on the two loops 29.31. In this case, this optical path length can also be varied.

Effect E] As explained above, according to the present invention, light of a desired wavelength is selected and amplified from wavelength-multiplexed input light, and the light is not emitted toward the light source of the input light. can get optical amplifier

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventionally known optical amplifier; Figs. 2 to 4 are block diagrams showing an embodiment of the present invention; and Fig. 5 is a diagram showing the operating principle layers of this embodiment. It is. 11... Optical amplifier, 12.13... Semi-transparent mirror, 14.28.30... Active medium (active layer), 15.4
4.45... DC power supply, 18.48.47... Stabilizing coil, 17... Input light, 18... Reflected light, 19.20... Output light, 21... Light source, 22.36...Anti-reflection film, 23...Waveguide layer, 24...Star coupler, 25.28.27...Light, 2!1,31...Loop, 32.34... -Incidence side (incidence surface) to the active layer, 33.
35... Output side (output surface) from the active layer, 37...
n-type 1nP substrate, 3rd...buried layer, 38...layer above the buried layer, 40...layer above the active layer, waveguide layer and star coupler, 41.42.43... electrode.

Claims (1)

[Claims] 1) A first loop formed by using a 3-input 3-output optical star coupler and feeding back the first output side to the first input side;
A second loop is formed by feeding back a second output side to a second input side, and control means for independently changing the optical path lengths of these loops is attached to a predetermined portion of the loop. Characteristic optical amplifier. 2) The optical amplifier according to claim 1, wherein an active medium is inserted into each of the loops. 3) The optical amplifier according to claim 2, wherein the control means is connected to the active medium via an electrode to inject a current. 4) The light according to claim 2, wherein the control means is connected to a loop other than the active medium through an electrode, and the optical path lengths of the two loops are changed independently. amplifier. 5) The optical amplifier according to claim 2, wherein the active medium is made of a semiconductor, and current is injected into each active medium independently.