KR100627137B1 - Gain-Clamped Semiconductor optical amplifier - Google Patents

Abstract

 BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gain fixed optical amplifier, comprising a 2 × 2 multi-mode interferometer composed of a gain waveguide, and two first waveguides and two second waveguides separated from each other. According to the present invention, the paths through which the resonance between the input and output terminals of the input signal and the diffraction grating are configured are different from each other, so that the light oscillated by the diffraction grating and the amplified optical signal can be separated.

Multimode Interference, Gain Fixed Semiconductor Optical Amplifiers, Diffraction Gratings

Description

Gain-Clamped Semiconductor Optical Amplifier

1 is a view showing a schematic structure of a DFB type gain fixed semiconductor optical amplifier.

Fig. 2 is a diagram showing a schematic structure of a DBR type gain fixed semiconductor optical amplifier.

3 is a schematic diagram of a gain-fixed semiconductor optical amplifier according to a first embodiment of the present invention.

4 is a conceptual diagram illustrating input and output characteristics of the multimode interferer 400.

5 is a conceptual diagram illustrating input and output characteristics of a 2 × 2 multimode interferer.

6 is a schematic structural diagram of a gain fixed semiconductor optical amplifier according to a second embodiment of the present invention.

7 is a schematic structural diagram of a gain fixed semiconductor optical amplifier according to a third embodiment of the present invention.

8 is a schematic structural diagram of a gain fixed semiconductor optical amplifier according to a fourth embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to gain fixed semiconductor optical amplifiers for amplifying optical signals, and more particularly to gain fixed semiconductor optical amplifiers in which the gain of output light is constant over a wide input light intensity range.

When the semiconductor optical amplifier reaches the gain saturation region, mutual interference between channels occurs, and thus the optical amplifier has no role as an amplifier. In order to alleviate this gain saturation phenomenon, a method of inducing oscillation in the diffraction grating formed in the semiconductor optical amplifier and fixing the gain of the amplifier is applied.

The gain-fixed semiconductor optical amplifier according to the prior art is largely used in two ways: a distributed feedback (DFB) method and a distributed bragg reflector (DBR) method. Gain-fixed semiconductor optical amplifiers with a distributed feedback (DFB) method are described by B. Bauer et al, "Gain stabilization of a semiconductor optical amplifier by distributed feedback" (IEEE Photonics Technology Letter, Vol. 6, No. 2, pp 182 ~ 185, 1994.2 For example, a gain-fixed semiconductor optical amplifier of a distributed Bragg reflector (DBR) method is described in M. Bachmann et al, "Polarisation-insensitive clampled-gain SOA with integrated spot-size converter and DBR gratings for WDM applications at 1.55. um wavelength "(IEE Electronics Letter, Vol. 32, No 22, pp 2076-2077, 1996.10).

Hereinafter, a gain-fixed semiconductor optical amplifier according to the related art will be described in detail with reference to the accompanying drawings.

1 is a view showing a schematic structure of a DFB type gain fixed semiconductor optical amplifier. Referring to FIG. 1, the diffraction grating 200 is formed below or above the core layer of the gain waveguide 100. In FIG. 1, λ _sig denotes an input optical signal, λ ′ _sig denotes an amplified optical signal, and λ _Bragg denotes a wavelength signal oscillated by a diffraction grating.

The gain waveguide 100 is composed of a material capable of amplifying an input signal having a wavelength of about 1550 nm, and the gain waveguide uses a mesa width having a spatially single mode. The oscillation wavelength can be controlled by adjusting the period of the diffraction grating. In order to suppress the Fabry-Perot resonance mode in the semiconductor optical amplifier, an antireflection film 700 is formed on the cleaved surfaces of both ends of the device.

Fig. 2 is a diagram showing a schematic structure of a DBR type gain fixed semiconductor optical amplifier. Referring to FIG. 2, the gain waveguide 100 and the passive waveguide 300 are coupled by a butt-joint or evanescent coupling method, and form a diffraction grating 200 below or above the passive waveguide 300. It is a structure. In this case, a gain waveguide and a passive waveguide typically use a mesa width having a single mode in space. In order to suppress the Fabry-Perot resonance mode in the semiconductor optical amplifier, an antireflection film 700 is deposited on the cleaved surfaces of both ends of the device.

As can be seen in Figures 1 and 2, since the light λ _Bragg oscillated by the diffraction grating is emitted together with the amplified optical signal _λ'sig , the oscillation wavelength of the diffraction grating should be outside the wavelength range of the amplified optical signal do.

However, in the case of a single integrated device such as a semiconductor optical amplifier-based wavelength converter or a LD (gate diode) -gate switch, light emitted by a diffraction grating may be injected into another semiconductor optical amplifier. Therefore, it is necessary to separate the light emitted by the amplified optical signal and the diffraction grating.

U. S. Patent No. 5,872, 649 describes a method in an optical fiber gain fixed optical amplifier that separates the amplified signal light and the oscillation wavelength into different paths. When a diffraction grating is formed at both ends of an EDFA (Erbium-Doped Fiber Amplifier) and a pump beam is injected, the gain is fixed by oscillation by the diffraction gratings at both ends of the optical fiber. In this case, when the input signal is injected, it is amplified by the EDFA and output along with the oscillation wavelength. In order to separate the oscillation wavelength coming out of the output stage by mixing with the amplified signal light, a 3 dB optical coupler and a Mach-Gender interferometer are formed behind the output stage and Bragg grating is formed on the arm of the Mach-Gender interferometer.

Using this structure, the oscillation wavelength at the output stage is reflected back by the diffraction grating in the Mach-Gender interferometer and traveled in another path by the 3 dB optical coupler, and the amplified signal light passes through the diffraction grating and passes through the 3 dB optical coupler. Will be combined again. In this case, two phase adjusters are used to correct the path difference between the two arms in the Mach-gender interferometer.

However, since the Mach-gender interferometer and the phase modulator are used to separate the gain-fixed optical amplifier, the amplified signal light and the oscillation wavelength, there is a problem that the structure is very complicated and unstable under external influence.

It is also very difficult to form a diffraction grating having the same diffraction grating in a gain-fixed optical amplifier as a Mach-gender interferometer, and it is very difficult to single-integrate semiconductor optical devices and optical amplifiers of other functions.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a new type of gain fixed semiconductor optical amplifier.

Another object of the present invention is to provide a gain fixed semiconductor optical amplifier in which a wavelength oscillated by a diffraction grating and an amplified optical signal are separated in a conventional gain fixed semiconductor optical amplifier.

As a technical means for solving the above problems, an aspect of the present invention is a 2X2 multi-mode interferer consisting of a gain waveguide; And two first waveguides and two second waveguides each separated from each other, wherein each of the first waveguides and the corresponding second waveguides is determined to form a first path and a second path. A diffraction grating is formed on the first waveguide and the second waveguide in the first path, and through the second path, an optical signal is input and amplified, and an amplified optical signal is output. A gain fixed semiconductor optical amplifier is provided, through which the light oscillated is transmitted.

A second aspect of the invention provides a 2x2 multimode interferer configured with a gain waveguide; And two first waveguides and two second waveguides each separated from each other, wherein each of the first waveguides and the corresponding second waveguides is determined to form a first path and a second path. The first waveguide and the second waveguide in the first path are connected to an optical fiber on which a diffraction grating is formed, and through the second path, an optical signal is input and amplified, and an amplified optical signal is output. A gain fixed semiconductor optical amplifier is provided, through which light oscillated by a diffraction grating is transmitted.

Preferably, the length of the 2 × 2 multimode interferer is an integer multiple of 3L _pi (L _pi is the bit length of the two lowest modes).

The ends of the first and second waveguides are advantageously formed to be inclined with the cleaved surface. Further, a mode size converter is further formed at the ends of the first and second waveguides.

Hereinafter, an embodiment of the present invention will be described in detail. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms, and only the present embodiments are intended to make the disclosure of the present invention complete and to those skilled in the art. It is provided for complete information.

(Example 1)

3 is a schematic diagram of a gain-fixed semiconductor optical amplifier according to a first embodiment of the present invention.

The gain fixed semiconductor optical amplifier includes a 2X2 Multi-Mode Interference (MMI) 400 consisting of two first waveguides 220 and 240 and a gain waveguide 500 and two second waveguides 320 and 340. It is configured by. As shown in FIG. 3, two first waveguides 220 and 240 and two second waveguides 320 and 340 are separated from each other based on the 2 × 2 multi-mode interferometer 400. In this case, the first waveguide 320 includes the first path AD and the second path BC in which the second waveguides 320 and 340 are determined according to the first waveguides 220 and 240, and the first waveguide 220 in the first path AD. ) And the second waveguide 340 are formed with diffraction gratings 230 and 350. Through the second path BC, the optical signal λ _sig is input and amplified, and the amplified optical signal λ ' _sig is output. Through the first path AD, the oscillation is performed by the diffraction gratings 230 and 350. Light is transmitted. The optical signal λ _sig may be input to the first waveguide 240 or may be input to the second waveguide 320.

Meanwhile, in order to suppress the Fabry-Perot resonance mode, an antireflection film 700 may be added to the cleaved surfaces of both ends of the device.

 The 2X2 multi-mode interferer 400 is composed of a gain waveguide 500, and the input / output terminal is composed of first waveguides 220 and 240 and second waveguides 320 and 340 of a passive waveguide having a single mode.

When the length of the 2X2 multimode interferer 400 is 3L _π (L _π is the bit length of the two lowest modes), the second waveguides 320 and 340 are the widths of the multimode interferer 400 with respect to the first waveguides 220 and 240. It is located in a symmetry with respect to the center of the. This will be described later in detail. At this time, a diffraction grating is formed in the passive waveguide of the input / output terminal at the crossing position. That is, the diffraction gratings 230 and 350 are formed in the first waveguide 220 and the second waveguide 340. At this time, when a current is injected into the 2X2 multi-mode interferometer 400 composed of a gain waveguide, spontaneous emission is generated, and the spontaneous emission generated at this time is the diffraction gratings 230 and 350 formed in the first waveguide 220 and the second waveguide 340. By oscillating in the first path AD by oscillation, the oscillation is performed to fix the gain.

At this time, the light λ _Bragg oscillated by the diffraction grating is output to the first waveguide 220 and the second waveguide 340. In addition, when the input signal λ _sig to be amplified is injected into the first waveguide 240, the input signal λ _sig is amplified by the 2 × 2 multimode interferer 400 including the gain waveguide and output to the second waveguide 320.

Therefore, while separating the amplified optical signal λ ' _sig and the light λ _Bragg oscillated by the diffraction grating, the gain is also fixed.

3, the diffraction grating is formed in the first waveguide 240 and the second waveguide 320, and an input signal to be amplified is transferred to the first waveguide 220 or the second waveguide 340. Injecting also has the same effect as shown in FIG. 3.

4 and 5 will be described in detail with reference to the multi-mode interferer 400 of the gain fixed semiconductor optical amplifier of FIG.

4 is a conceptual diagram illustrating input and output characteristics of the multimode interferer 400. The input waveguide in FIG. 4 is a passive waveguide in single mode condition. Light injected into the input terminal at an arbitrary y position is referred to the center of the width of the multimode interferer 400 for every integer multiple of 3L _π (L _π is the bit length of the two lowest modes) in the multimode interferer 400. At the positions symmetric with each other, the single mode is crossed to match the phases.

In a spatially monomode waveguide, light injected into a multimode interferer is split into multiple modes and propagates, but recombines into a single mode at a specific propagation length and location. The basic characteristics of the multimode interferer are L.B. See the paper published by Soldano and ECM Pennings ["Optical Multi-Mode Interference Devices Based on Self-imaging: Principles and Applications" 1995 J. Lightwave Technology, Vol. 13 (4), pp. 615-627]. .

5 is a conceptual diagram illustrating input and output characteristics of a 2 × 2 multimode interferer. As described in FIG. 4, when the length of the multimode interferer 400 is 3L _π (L _π is the bit length of the two lowest modes), the position on the y axis of the output waveguide relative to the input waveguide is determined by the multimode interferer 400. ) Is located at a point symmetrical with respect to the center of the width. Two first waveguides 220 and 240 and two second waveguides 320 and 340 respectively separated based on the 2X2 multi-mode interferer 400 are provided.

In this case, when the input signal is injected into the first waveguide 220, it is output to the second waveguide 340, and the input signal injected into the first waveguide 240 is output to the second waveguide 320. This is called a cross-state. In the case of injecting the input signal in the opposite direction is the same as described above. That is, when an input signal is injected into the waveguide of reference numeral 320, the signal is output to the waveguide of reference numeral 240.

On the other hand, if the length of the multimode interferer of Figure 5 is 6L _π , the position on the y-axis of the output waveguide with respect to the input waveguide is located at the same point with respect to the center of the width of the multimode interferometer 400. In this case, when the input signal is injected into the first waveguide 240, it is output to the second waveguide 340, and when the input signal is injected into the first waveguide 220, it is output to the second waveguide 320. The same applies to the case where the input signal is injected in the opposite direction. That is, when a signal is injected into the waveguide of reference numeral 320, the signal is output to the waveguide of reference numeral 220. This is called bar-state.

In addition, when the length of the multi-mode interferer 400 is in a bar state, a diffraction grating is formed on the first waveguide 220 and the second waveguide 320, and is input to the first waveguide 240 or the second waveguide 340. When configured to inject a signal has the same effect as described above. That is, the length of the multimode interferer 400 can be used as an integer multiple of 3L _pi (L _pi is the bit length of the two lowest modes).

(Example 2)

6 is a schematic structural diagram of a gain fixed semiconductor optical amplifier according to a second embodiment of the present invention. In the description of the second embodiment, for convenience of explanation, the description will be made based on differences from the first embodiment.

As shown in FIG. 6, two first waveguides 220 and 240 and two second waveguides 320 and 340 are separated from each other based on the 2 × 2 multi-mode interferometer 400. In this case, the first waveguide 320 includes the first path AD and the second path BC in which the second waveguides 320 and 340 are determined according to the first waveguides 220 and 240, and the first waveguide 220 in the first path AD. ) And the second waveguide 340 are formed with diffraction gratings 230 and 350.

In Embodiment 2, in order to reduce the reflectance of the waveguides, the ends of the first waveguides and the second waveguides are inclined with respect to the cleaved surface. At this time, the inclination angle θ preferably has a value of 5 to 15 degrees.

(Example 3)

7 is a schematic structural diagram of a gain fixed semiconductor optical amplifier according to a third embodiment of the present invention. In the description of the third embodiment, for convenience of explanation, the description will be made based on the difference from the first embodiment.

Referring to FIG. 7, two first waveguides 220 and 240 and two second waveguides 320 and 340 are separated from each other based on the 2 × 2 multi-mode interferer 400. In this case, the first waveguide 320 includes the first path AD and the second path BC in which the second waveguides 320 and 340 are determined according to the first waveguides 220 and 240, and the first waveguide 220 in the first path AD. ) And the second waveguide 340 are formed with diffraction gratings 230 and 350.

However, in order to increase coupling efficiency between the optical fiber (not shown) connected to the waveguides and the waveguides, a mode size converter is formed at the end of the input / output waveguide. The mode size converter uses a fabricated by tapering the line width of the input / output waveguide to 0.5 μm or less.

In FIG. 7, the end of the waveguides is inclined with respect to the cleavage surface and the mode size converter is formed at the end. However, it is obvious that the end of the waveguides may be applied even when the end of the waveguides is not inclined with respect to the cleavage surface.

(Example 4)

8 is a schematic structural diagram of a gain fixed semiconductor optical amplifier according to a fourth embodiment of the present invention. In the description of the fourth embodiment, for convenience of explanation, the description will be made based on differences from the first embodiment.

Referring to FIG. 8, two first waveguides 220 and 240 and two second waveguides 320 and 340 are separated from each other based on the 2 × 2 multi-mode interferer 400. In this case, the second waveguides 320 and 340 are determined according to the first waveguides 220 and 240, and include the first path AD and the second path BC. The first waveguide 220 and the second waveguide 340 in the first path AD are passive waveguides.

In Embodiment 4, unlike Embodiment 1, the first waveguide 220 is coupled to the optical fiber 900 having the diffraction grating and the second waveguide 340 and the optical fiber 920 having the diffraction grating are combined to secure gain. A semiconductor optical amplifier is constructed. The operating principle is the same as that of the first embodiment, and oscillation is performed by an optical fiber having a diffraction grating.

Although the technical idea of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

As described above, the present invention can fix the gain of an amplifier by inducing oscillation by forming diffraction gratings at input / output waveguides at both ends in a multimode interferometer type semiconductor optical amplifier having a gain waveguide.                     

In addition, the input and output waveguides of the input signal to be amplified and the output waveguides of the light oscillated by the diffraction grating are different from each other, and thus there is an effect of separating the amplified optical signal and the light oscillated by the diffraction grating.

Claims (5)

A 2X2 multimode interferer configured with a gain waveguide; And two first waveguides and two second waveguides each separated from each other, Each first waveguide and a second waveguide corresponding thereto are determined to form a first path and a second path, A diffraction grating is formed on the first waveguide and the second waveguide in the first path, Through the second path, an optical signal is input and amplified optical signal is output, A gain fixed semiconductor optical amplifier through which the light oscillated by the diffraction grating is transmitted through the first path. A 2X2 multimode interferer configured with a gain waveguide; And two first waveguides and two second waveguides each separated from each other, Each first waveguide and a second waveguide corresponding thereto are determined to form a first path and a second path, The first waveguide and the second waveguide in the first path is connected to the optical fiber formed with a diffraction grating, Through the second path, an optical signal is input and amplified optical signal is output, A gain fixed semiconductor optical amplifier through which the light oscillated by the diffraction grating is transmitted through the first path. The method according to claim 1 or 2, And wherein the length of the 2X2 multimode interferer is an integer multiple of 3L _π (L _π is the bit length of the two lowest modes). The method according to claim 1 or 2, A gain fixed semiconductor optical amplifier, wherein the ends of the first and second waveguides are formed to be inclined with the cleaved surface. The method according to claim 1 or 2, A gain fixed semiconductor optical amplifier having a mode size converter further formed at the ends of the first and second waveguides.

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