JP2652966B2 - Optical amplifier - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-performance optical amplifier that can be used in the field of long-distance, large-capacity communication.

[Conventional technology]

Conventionally, in order to perform long-distance large-capacity communication, it is common to use light as a transmission medium and arrange regenerative repeaters that perform light-to-electricity and electricity-to-light conversion every several tens of kilometers to deal with attenuation. there were. However, the regenerative repeater has a problem in that it requires a special element device for performing light-to-electricity and electricity-to-light conversion, so that it is costly. On the other hand, recent advances in optical device technology including semiconductor optical amplifiers, which have been developed as substitutes for the regenerative repeaters, have enabled repeaterless transmission of 100 km or more. Also in the field of optical switching, it has been studied to use the optical amplifier to compensate for the loss of the optical switch and increase the number of lines.

[Problems to be solved by the invention]

However, conventional optical amplifiers have a structure or configuration that makes the magnitude of the pumping uniform rather than the magnitude of the population inversion, that is, the magnitude of the gain coefficient, in the traveling direction of light,
The magnitude of the gain coefficient becomes spatially non-uniform due to the effects of amplified spontaneous emission light and amplified signal light, and the effects of improving various characteristics such as maximum gain, maximum amplified output, and noise due to increased pumping are suppressed. There was a problem that was.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical amplifier having excellent overall characteristics that can be used in the field of long-distance, large-capacity optical communication.

[Means for solving the problem]

An optical amplifier according to the present invention is an optical amplifier including an optical waveguide that guides and amplifies light, wherein the optical waveguide is divided into a plurality of regions in a light propagation direction, and goes from a central region to regions at both ends. Means for injecting high excitation energy in accordance with the present invention, wherein the magnitude of the population inversion of the injected carriers is kept uniform over the respective regions.

[Action]

Hereinafter, the principle of the present invention will be described using a semiconductor optical amplifier as an example. 2 and 3 are diagrams for explaining the problems of the conventional semiconductor optical amplifier. 2 and 3, (a) schematically shows a main part of a semiconductor optical amplifier that amplifies and guides light, and (b) shows a spatial distribution of light intensity (here, amplified spontaneous emission light). (C) shows the spatial distribution of the excited carrier density, that is, the population inversion, and (d) shows the spatial and wavelength distributions of the gain coefficient. However, FIG. 2 corresponds to the case where the input light intensity is very low, and FIG. 3 corresponds to the case where the input light intensity is high. Fig. 2 (a)
In the case where the current is uniformly injected as in the above, that is, when the uniform excitation is performed, the amplified spontaneous emission light intensity becomes spatially non-uniform as shown in FIG. In general, in the same excited state, the population inversion becomes smaller as the light intensity density becomes larger. However, in this case, the population inversion (excitation carrier density distribution) becomes spatially non-uniform. This means that the gain factor of the amplifier becomes spatially non-uniform. In optical amplifiers, it is known that use in a high gain state is advantageous from the viewpoint of maximum amplification output and S / N,
If there is such spatial non-uniformity, the effect of improving the characteristics of the optical amplifier by increasing the pumping is hindered. Furthermore, in the case of uniform excitation, such spatial non-uniformity tends to increase as the excitation increases. Particularly, in the case of a semiconductor optical amplifier, the wavelength at which the gain becomes maximum differs depending on the magnitude of the population inversion, and the gain coefficient is distributed as shown in FIGS. 2 (d) and 3 (d). A situation may occur in which a signal light having a wavelength has a large gain at a certain portion in the semiconductor optical amplifier, but has a very small gain at another portion. It is clear that in order to eliminate such adverse effects due to the spatial non-uniformity, the excitation may be performed spatially non-uniformly so as to make the population inversion uniform. For example, when the input signal light intensity is weak, the excitation to both ends of the optical amplifier is relatively increased,
When the input signal light intensity is high, the excitation of the output section of the optical amplifier may be relatively increased.

〔Example〕

Next, an embodiment of the present invention will be described with reference to the drawings. First
The figure is a hatched diagram of a semiconductor optical amplifier according to one embodiment of the present invention. First, a non-doped InGaAsP substrate is formed on the upper surface of the n-InP substrate 1.
Active layer 2, Anti-melt back layer (AMB layer) 3, p-InP
The thickness of the cladding layer 4 is 0.2 μm and 0.01 μm, respectively.
m and 1 μm by liquid phase growth. A mesa stripe 5 having a width of 1 μm is formed in the [110] direction of the multilayer semiconductor crystal, and then the p-InP current blocking layer 6 and the n-InP A current blocking layer 7 and a p-I
The nP buried layer 8 and the p ⁺ -InGaAsP contact layer 9 are sequentially formed to have thicknesses of 1 μm, 0.5 μm, 6 μm,
The crystal is grown by MOVPE so as to have a thickness of 0.5 μm. On the contact layer 9, a 3000 mm thick SiO _{2 was} formed by CVD.
A film 10 is formed, and a window is opened in the SiO ₂ film 10 immediately above the active layer,
Further, the SiO ₂ film 10 and to cover the window portion of the SiO ₂ film 10 Cr
An electrode 11 made of / Au is formed. Next, in order to perform non-uniform excitation, the elements were respectively 100 μm, 200 μm, and 10 μm in length.
The electrode 11, the SiO ₂ film 10, and the p ⁺ -InGaAsP contact layer 9 are divided into three regions of 10 μm at boundaries 12 and 13 having a length of 10 μm.
Is removed. Further, an electrode 14 made of AuGeNi is formed under the n-InP substrate 1. Finally, as a non-reflective coating film on both end surfaces, a thickness of 2200 mm
SiON films 15 and 16 are formed.

In the semiconductor optical amplifier thus manufactured, when the input signal light is small, the gain from the input fiber end to the output fiber end when the semiconductor optical amplifier is coupled to the single mode fiber, the gain between the unsaturated fibers is uniform injection. In this case, the current density was 15 dB, but could be increased to 20 dB by controlling the current density ratio injected into the three regions to be 2: 1: 2 without changing the total current value. Although the gain decreases as the input signal light increases, the 3 dB saturation output defined as the amplified output at the point where the 3 dB gain decreases from the unsaturated gain is 7 dBm in the case of uniform injection. By setting the current density ratio injected into the three regions to 2: 3: 4, 1
It could be increased to 2dBm. In addition, the value of the noise figure was 6 dB in the case of the uniform injection, but it became 4 dB by the non-uniform injection, which was close to the quantum limit of 3 dB.

In the embodiment of the present invention, an example is shown in which the semiconductor optical amplifier is divided into three regions in order to perform non-uniform excitation, but the number of regions may be arbitrary. Although the example of the optical amplifier having the PBH structure has been described, the present invention is also effective for a semiconductor optical amplifier having another structure such as a DC-PBH structure or a BH structure. Similar effects can be expected by devising the configuration of other optical amplifiers (for example, fiber optical amplifiers) and making the gain coefficient uniform by non-uniform pumping.

〔The invention's effect〕

The optical amplifier according to the present invention, in which the gain coefficient is spatially uniformed, can improve the overall performance of the optical amplifier as compared with the related art, and is useful in the field of optical communication represented by large-capacity optical communication.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an embodiment of the present invention, FIG. 2 and FIG.
FIG. 1 is a diagram for explaining a problem of a conventional semiconductor optical amplifier. 1 ... n-InP substrate, 2 ... non-doped InGaAsP active layer,
3 ... Anti-melt back layer (AMB layer) 4 ... P-InP
Clad layer, 5 mesa stripe, 6 p-InP current blocking layer, 7 p-InP current blocking layer, 8
p-InP buried layer, 9 ... p ⁺ -InGaAsP contact layer,
10: SiO ₂ film, 11, 14: Electrode, 12, 13: Boundary, 15, 1
6 …… Anti-reflective coating film.

Claims (1)

(57) [Claims] 1. An optical amplifier comprising an optical waveguide for guiding and amplifying light, wherein the optical waveguide is divided into a plurality of regions in a light propagation direction, and from a central region to regions at both ends. An optical amplifier comprising means for injecting high excitation energy, wherein the magnitude of population inversion of injected carriers is kept uniform over each of the regions.