JP2526934B2 - Optical amplifier - Google Patents

Description

The present invention relates to an optical amplifier that amplifies and outputs incident light.

[Conventional technology]

FIG. 6 is a perspective view showing an optical waveguide in a conventional optical amplifier.

In this figure, 1 is an optical waveguide having a constant width W,
2 and 3 are a pair of p and n electrodes, and 4 and 5 are resonator end faces having a low reflectance.

 Next, the operation will be described.

When a current is injected into the optical waveguide 1 from the pair of p and n electrodes 2 and 3, a population inversion (excited state) in which laser light is easily generated in the optical waveguide 1 is formed. Next, one resonator end face 4
When the laser light is further incident on the optical waveguide 1, the laser light is amplified and emitted by the other resonator end face 5.

[Problems to be solved by the invention]

In the conventional optical amplifier as described above, the width W of the optical waveguide 1 is
Is constant, the amplification is saturated when the light intensity is large, and when the width W is small, there is a problem that the optical amplifier is broken at a low optical output due to optical damage on the resonator end face 5 on the emitting side.

The present invention has been made to solve such a problem, and an object thereof is to obtain an optical amplifier capable of obtaining a large optical output.

[Means for solving problems]

The optical amplifier according to the present invention, in the double hetero structure,
In an optical amplifier including an inflection-waveguide-type optical waveguide layer in which carriers are confined by injection of a current to be in an excited state, the width of the exit-side end face of the optical waveguide layer is made wider than that of the entrance-side end face and the optical waveguide The divergence angle of the layer in the lateral direction is smaller than the divergence angle of the laser light incident on the optical waveguide layer in the optical waveguide layer.

[Operation] In the present invention, even if the light intensity increases, the gain in the optical waveguide does not saturate up to the emission end face, and optical emission is less likely to occur at the emission end face of the optical waveguide. Further, the mode of incident light is maintained in the optical waveguide.

〔Example〕

1 (a) and 1 (b) are a perspective view of an embodiment of an optical amplifier of the present invention and a top view showing the structure of an optical amplification path.

In these figures, the same reference numerals as those in FIG. 6 indicate the same elements, 11 is an optical waveguide, 12 and 13 are a pair of p and n electrodes, and 14 and 15 are reflectances of 10% or less (here, 3%).
(Reflectance = 97% transmittance), an incident end face and an outgoing end face, 16 is a substrate made of p-type GaAs, and 17 is n having a thickness of 1 μm.
Current confinement layer made of GaAs, 18 is a channel region for determining the position of the optical waveguide 11, 19 is p-type AlGaAs having a thickness of 1 μm
A layer, 20 is an undoped AlGaAs layer having a thickness of 0.2 μm on which the optical waveguide 11 is provided, 21 is an n-type AlGaAs layer, and 22 is a thickness of 2 μm.
Of n-type GaAs. The band gap of the undoped AlGaAs layer 20 is p-type AlGaAs layer 19, n-type AlGa
It is narrower than the forbidden band width of the As layer 21 by several tens of eV and narrower than the forbidden band width corresponding to the wavelength of the incident laser light by, for example, about 0.01 eV.

In addition, W ₁ and W ₂ are the widths of the optical waveguide 11 at the incident end face 14 and the emitting end face 15, L is the length of the optical waveguide 11, and θ is the optical waveguide.
11 divergence angles, each dimension is W ₁ = 3μm, W ₂ = 28
μm, L = 500 μm, Is. Note that θ is the divergence angle {sin ^-1 (1
/ n sin5 °), n: refractive index of the optical waveguide 11} or less.

 Next, the operation will be described.

Also in the optical waveguide of the present invention, the p and n electrodes 12, 13
By injecting more current, a population inversion that easily generates laser light can be formed in the region of the optical waveguide 11. Therefore, the laser light incident on the optical waveguide 11 from the outside through the incident end face 14 is amplified and emitted from the emitting end face 15, but since the width of the optical waveguide 11 becomes wider toward the emitting end face 15, The light amplification never saturates. Further, since the width W ₂ of the optical waveguide on the emitting end face 15 is large, the optical output is not limited by the optical damage on the emitting end face 15. Further, since the divergence angle θ of the optical waveguide 11 is set to be equal to or less than the divergence angle of the incident laser light in the optical waveguide 11, if the incident laser light is the fundamental mode, the emitted laser light is also the fundamental mode. Becomes

Further, considering the structure of the optical amplifier itself, it is not necessary to cause laser oscillation by itself unlike the laser diode, so that the reflectance of the end face can be reduced or the width of the optical waveguide 11 can be widened. -The diode allows a difficult structural design, and a large light output can be easily obtained.

FIG. 2 is a top view showing a second embodiment of the optical waveguide 11 according to the present invention. In this embodiment, a region having a constant width is provided near the end face.

In this figure, L ₁ and L ₂ are the lengths of the regions where the width of the optical waveguide 11 is constant near the entrance end face 14 and the exit end face 15, respectively, and L ₃ is the length of the region where the width of the optical waveguide 11 increases. And the respective dimensions are, for example, L ₁ = L ₂ = 25 μm and L ₃ = 450 μm. Further, W ₂ satisfies W ₂ > W ₁ +2 (L ₂ + L ₃ ) tan θ.

FIG. 3 is a top view showing a third embodiment of the optical waveguide 11 according to the present invention. In this embodiment, the divergence angle of the optical waveguide 11 is made larger than the middle.

In FIG. 3, 11a and 11b are optical waveguides having different divergence angles, θa and θb are divergence angles of the respective optical waveguides 11a and 11b, and θb> θa.

FIG. 4 is a top view showing a fourth embodiment of the optical waveguide 11 in the present invention. In this embodiment, the optical waveguide 11 is divided by dividing the n electrode 13 and the incident laser light is amplified separately. It is possible to do.

In this figure, 13a and 13b are projections of the divided n electrodes on the layer where the optical waveguide 11 is provided.

FIG. 5 is a diagram showing an application example of the present invention in which a laser diode and an optical waveguide are integrated in the same chip.

In this figure, 23 is an optical waveguide of a laser diode, 24 is a region where the optical waveguide 23 of the laser diode and the optical waveguide 11 of the amplifier are shared, and 25 is a laser diode.
The electrode of the diode is projected on the layer on which the optical waveguide 11 is provided, and 26 is the end facet of the laser diode having a reflectance of 60% or more (here, 95%).
It corresponds to the incident end face 14 in FIG. Reference numeral 27 is another end facet of the laser diode having a reflectance of 90%.

That is, in this application example, part of the laser light generated in the optical waveguide 23 of the laser diode is transmitted from the area 24 where the optical waveguide 23 of the laser diode and the optical waveguide 11 of the optical amplifier are shared. It is guided to the waveguide 11 and amplified.

Although the optical amplifier has the SBA laser structure shown in FIG. 1 (a) as an example in the above embodiment, it goes without saying that the present invention is not limited to this.

〔The invention's effect〕

As described above, according to the present invention, the width of the exit side end face of the optical waveguide layer is made wider than that of the entrance side end face, and the lateral divergence angle of the optical waveguide layer is such that the laser light incident on the optical waveguide layer is guided. Since the spread angle is smaller than the divergence angle in the waveguide layer, the gain in the optical waveguide does not saturate up to the emission end face even when the light intensity increases, and the output does not cause optical damage on the emission side end face. Therefore, the mode of the incident light is maintained even in the optical waveguide layer, and the mode of the incident light can be maintained to obtain a large optical output.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the configuration of an embodiment of the optical amplifier of the present invention, and FIGS. 2 to 4 are top views showing other embodiments of the optical waveguide in the optical amplifier of the present invention. FIG. 6 is a top view showing a semiconductor device to which the present invention is applied, and FIG. 6 is a perspective view showing an optical waveguide in a conventional optical amplifier. In the figure, 11 is an optical waveguide, 12 is a p-electrode, 13 is an n-electrode,
14 is an incident end face, 15 is an emission end face, 16 is a substrate, 17 is a current confinement layer, 19 is a p-type AlGaAs layer, 20 is an undoped AlGaAs layer, 21 is an n-type AlGaAs layer, and 23 is an optical waveguide of a laser diode. . The same reference numerals in each drawing indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. An optical amplifier comprising a refractive index waveguide type optical waveguide layer in which carriers are confined by a current injection in a double hetero structure to be in an excited state. The divergence angle in the lateral direction of the optical waveguide layer is made wider than that of the incident side end face, and the divergence angle of the laser light incident on the optical waveguide layer is made smaller than the divergence angle in the optical waveguide layer. Characteristic optical amplifier.