JPH01170084A - Integrated type optical amplifier element - Google Patents

Abstract

PURPOSE:To reduce a return light rays reflected from an optical filter section so as to improve a S/N ratio by a method wherein a semiconductor optical waveguide type amplifier and a grating type optical filter are integrated and the grating is provided obliquely toward a direction in which an optical signal advances. CONSTITUTION:A planar optical waveguide 6 is provided in succession along a direction in which an optical signal advances from a core layer 4 of an optical amplifier 1, a grating face 5 is provided to the planar optical waveguide 6, and an optical filter section 2 is provided, where the grating face 5 is arranged so as to enable a grading angle to make an angle of one or more degrees with a direction perpendicular to a direction in which the optical signal advances. By these processes, an S/N ratio is made to decrease much in deterioration by restraining a noise component caused by a naturally released light and a gain saturation can be also restrained. And, as a device of this design can be manufactured through a monolithic processing method, a multi-stage integration is facilitated and the device can be made very small as compared with a device formed of unit components, so that the device is favorable for mounting.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical amplifier (hereinafter referred to as an optical amplifier) that amplifies an optical signal.

[Conventional technology]

As an optical amplifier device for amplifying optical signals, an LD optical amplifier has the same double heterostructure p-n junction as a semiconductor laser diode element (hereinafter referred to as LD) and uses stimulated emission effect to amplify light. There is. This LD
Optical amplifiers can be easily manufactured using the same processing methods as monolithic manufacturing methods for laser diodes. LD optical amplifiers are very small and easy to integrate.

However, while this LD optical amplifier amplifies the optical signal through stimulated emission, it also generates noise components due to spontaneous emission.
This noise component has the disadvantage of causing deterioration in the signal-to-noise ratio (hereinafter referred to as S/N) of the optical signal. Figure 2 is LD
In the spectrum characteristic diagram of the optical amplifier, S is the optical signal component, N is the spontaneous emission light, the horizontal axis λ is the wavelength, and the vertical axis is the light intensity. As shown in Figure <a>, there is a noise component N on the left and right sides of the optical signal S, which is caused by spontaneous emission light and has a small amplitude and has a wide wavelength band of 1100 nm or more. Since this noise component N has a small amplitude but a wide band, its integral value becomes effective and cannot be ignored in the total energy (hereinafter energy is referred to as power) of the output of the optical amplifier. The total power of this optical signal component S and noise component N is
When light is received at D or the like, unnecessary noise components enter the nonlinear region of the APD and cause S/N deterioration.

In addition, the multi-stage dependent connection of this LD optical amplifier as it is,
Problems arise in that the noise figure increases due to the optical signal component S and the noise component N, and the gain decreases due to saturation due to nonlinearity when the optical amplifier is overloaded.

Generally, in order to suppress unnecessary frequency components, a filter (hereinafter referred to as a filter) is installed at the input end, output end, or both ends of an amplifier.

In this case as well, an optical filter is installed after the optical amplifier to improve the S/N ratio in order to suppress unnecessary noise components of the optical amplifier. FIG. 3 is an optical filter characteristic diagram, in which the horizontal axis is the wavelength λ and the vertical axis is the transmittance. The optical filter characteristics are a narrowband bandpass optical filter with a half width of about 10 to 100 A that matches the wavelength of the optical signal. FIG. 2(b) is a spectral characteristic diagram of the LD optical amplifier at the output end of the optical filter, showing how the noise component N due to spontaneous emission light is attenuated with respect to the optical signal component S.

A conventional DBR type LD has a structure in which an LD and a grating type filter are arranged subordinately.

However, in conventional DBR type LDs, the grating angle is precisely aligned perpendicular to the traveling direction in order to reflect only a specific wavelength by the grating and efficiently couple the reflected light to the optical core layer of the LD section. The error is generally 0
．． It is well within 1 degree.

[Problem that the invention seeks to solve]

Conventionally, such a method of connecting an optical filter subordinately to an optical amplifier to improve the S/N ratio has been configured using separate LD optical amplifier modules and optical filter modules. However, the individual modules are large and the overall volume becomes large, making it difficult to increase the number of stages and scale.

[Means for solving problems]

L having a p-n junction, an electrode for injecting current into the junction, and a core layer with a guide structure formed at the p-n junction.
In the D optical amplifier, a planar waveguide is provided continuously in the direction of propagation of the optical signal from the core layer, a grating surface is formed on the planar waveguide, and the grading angle is set at 1 degree from perpendicular to the direction of propagation of the optical signal. The optical filter section is arranged at an angle as described above.

[For production]

The present invention integrates a semiconductor waveguide type optical amplifier and a grating type optical filter, and arranges the grating obliquely with respect to the direction of propagation of the optical signal to reduce reflected return light from the optical filter part and improve S/N. An integrated optical amplifier device was proposed.

〔Example〕

l) FIG. 1 is a plan sectional view and a side sectional view of the integrated optical amplifier device according to the first embodiment of the present invention, taken along the lines BB' and AA'. In the figure, 1 is an optical amplifier section, 2 is an optical filter section, 3 is an electrode, 4 is a core layer, 5 is a grating, 6 is a planar waveguide, 7 is a planar waveguide lens, 8 is a light absorption layer, and 9 is a Non-reflective coating, ■ is input point, M is intermediate point,
0 is the output point. The wavelength of the optical signal S is assumed to be 1.3 μm. The optical amplifier section l has a double heterostructure of InGaAsP having the same composition as the 1.3 μm semiconductor laser. The optical filter section 2 is made of a semiconductor waveguide having a composition with a larger energy gap so that absorption in the 1.3 μm band does not occur. In the optical amplifier section 1, a p-n junction core layer 4 with a narrow guide structure is provided in order to confine light and concentrate the optical signal in the lateral direction. A planar waveguide 6 is provided which is subordinate to the core layer 4 and is not laterally confined for allowing reflected light to escape laterally. The light absorption layer 8 provided on the side wall of the planar waveguide 6 absorbs the light reflected by the buried grating 5, which is embedded with a semiconductor having the same composition as the core layer 4 of the optical amplifier section 1 and has an energy gap of 1.3 μm. It is structured so that it can be absorbed by its effects. The planar waveguide lens 6 near the midpoint M has a Lunebrook type lens on the waveguide to prevent the signal light from spreading and scattering in the optical filter section 2. The planar waveguide lens 7 is shaped like a radio circle. shows.

The operation of this will be explained. By applying a voltage to the electrode 3, the core layer 4
Apply forward current to the input point! The optical signal S inputted through the anti-reflection coat 9 is amplified by the stimulated emission effect, and at the same time generates noise of spontaneous emission light N, and outputs the amplified optical signal S and spontaneous emission light N from the intermediate point M. The optical signal S and spontaneous emission light N are input to the optical filter section 2. The amplified optical signal S and spontaneous emission light N are collimated by a planar waveguide lens 7 and introduced into the grating 5. This grating has a width of approximately 10 to 100A centered around the wavelength of the optical signal.
The optical signal S is designed to transmit wavelengths of 1 and reflect wavelengths outside of the wavelengths, and the optical signal S is outputted as is to the output point O. The unidirectional spontaneously emitted light N is reflected in an oblique direction because the grating 5 disposed in contact with the planar waveguide 6 is inclined with respect to the traveling direction of the optical signal S of the central axis of the core layer 4 of the guide structure. is absorbed by the light absorbing layer 8 of. As a result, the spontaneous emission light N is recombined to the optical amplifier section 1, and the LD
This prevents the amplification operation of the optical amplifier from becoming unstable. Note that if there is reflection at the end face of the chip, a resonator is formed there, and as the current increases, oscillation occurs, so both end faces are coated with a non-reflection coating 9. The reason why the protruding end of the core layer 4 is slanted at the midpoint M in FIG. 1 is to suppress reflection at this point.

(2) FIG. 4 is a plan sectional view of an integrated optical amplifier element according to a second embodiment of the present invention. In the figure, 10 is an optical branching waveguide, 11 is a front-stage integrated optical amplifier element, and 12 is a rear-stage integrated optical amplifier element. The same symbols are used for parts common to the previous embodiment. This configuration operates as an optical power divider with one input and two outputs. That is, the output of the front-stage integrated optical amplifier element 11 was branched by the optical branching waveguide 9 and input to the two rear-stage integrated optical amplifier elements 12, respectively.

In this example, the semiconductor optical amplifier elements of the first example are vertically connected in two stages. L of the front-stage integrated optical amplifier element 11
Since the noise component of the spontaneously emitted light output from the D destination light 7711 is suppressed by the effect of the optical filter section 2, saturation of the amplification gain can be suppressed even if it enters the next stage integrated optical amplifier element 12. It is possible to obtain sufficient gain at each stage. The optical amplifier section 1 and the optical filter section 2 of this circuit are the first
The structure is exactly the same as that of the embodiment, and the optical branching waveguide 9 is made of a semiconductor material having the same composition as the optical filter part 2 through which the signal light is transmitted, and can be manufactured by a monolithic processing method in which a figure 7-shaped optical branching circuit is formed using a mask pattern. It is. Moreover, it is also possible to further integrate in multiple stages.

Note that when the current from the electrode 3 of the LD optical amplifier is cut off, the light incident on the core layer 4 is absorbed by the induced absorption effect, so by taking advantage of the advantage that it can also be used as an optical switch,
It also works as a second optical switch.

〔Effect of the invention〕

This integrated optical amplifier element is constructed by integrating an optical amplifier and an optical filter into a single structure, and suppresses noise components due to spontaneous emission light, thereby minimizing S/N deterioration and suppressing gain saturation. Furthermore, since it can be manufactured using a monolithic processing method, it is easy to integrate it in multiple stages, and it is much smaller than a structure made of individual parts, which is advantageous in terms of packaging. Furthermore, the accuracy of the grating angle from perpendicular to the direction of light travel is greatly reduced.

Although the integrated optical amplifier element of the present invention has been described as an optical amplifier, when no current flows into the waveguide optical amplifier of this structure, the light incident on the active layer is strongly (attenuated) due to induced absorption. It can also be used as an optical switch that connects and disconnects light using electric current.

This case also shows a great effect on S/N deterioration and gain saturation in entertainment. In particular, when using an optical switch as an optical exchanger, the present invention is extremely effective because it is necessary to connect the optical switch in multiple stages and form a matrix.

[Brief explanation of the drawing]

1 is a plan sectional view and a side sectional view of an integrated optical amplifier element according to a first embodiment of the present invention, FIG. 2 is a spectral characteristic diagram of the output light of the LD optical amplifier, and FIG. 3 is an optical filter characteristic diagram. FIG. 4 is a plan cross-sectional view of an integrated optical amplifier element according to a second embodiment of the present invention. 1 is an optical amplifier part, 2 is an optical filter part, 3 is an electrode, 4 is a core layer, 5 is a grating, 6 is a planar waveguide, 7 is a planar waveguide type lens, 8 is a light absorption layer, 9 is a non-reflection coating ,1
0 is an optical branching waveguide, 11 is a pre-stage integrated optical amplifier element, 1
2 is a rear-stage integrated optical amplifier element, ■ is an input point, M is an intermediate point, 0 is an output point, S is an optical signal component, N is spontaneous emission light, and λ is a wavelength. The operation of the present invention is the planar section I of the optical amplifier element! Figure l1 and side view IfT side view No. 1 Figure 4
figure

Claims (3)

[Claims] (1) In a laser diode optical amplifier that is equipped with a p-n junction and an electrode for injecting current into the junction, and in which a core layer with a guide structure is formed at the p-n junction, the core is connected to the core layer. What is claimed is: 1. An integrated optical amplifier element, characterized in that a planar waveguide is provided in which gratings are formed in subordinate layers, and the grating angle is inclined by one degree or more from perpendicular to the direction of propagation of an optical signal. (2) The integrated optical amplifier element according to claim 1, characterized in that a light absorption layer is provided on a side surface of the planar waveguide parallel to the direction of propagation of the optical signal. (3) The integrated optical amplifier device according to claim 2, characterized in that a planar waveguide lens is provided above the planar waveguide.