JPH02250042A - Optical amplifying device and semiconductor optical amplifier - Google Patents

Abstract

PURPOSE:To obtain a constant gain even if ambient temperature varies and to constitute the optical amplifying device by a simple optical system by controlling a current applied to the semiconductor optical amplifier so that the photodetection level of a photodetector reaches a reference value. CONSTITUTION:The semiconductor optical amplifier 100 has a nearly proportional relation between the gain and naturally emitted light intensity and when the amplifier is driven with, for example, a constant current, the naturally emitted light intensity decreases if the gain decreases although the ambient temperature rises. For the purpose, this naturally emitted light intensity is monitored and a controller 300 varies the driving current of the semiconductor optical amplifier 100 so that the monitored value reach the reference value, the gain can be held nearly constant. Naturally emitted light is emitted from an active layer 130 in all directions, so the photodetector can photodetect the light even if arranged shifting from the optical axis. Consequently, even if the ambient temperature varies, the nearly constant gain is obtained and the constitution of the device which controls the gain by monitoring the naturally emitted light of the semiconductor optical amplifier is simplified.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a technology for amplifying optical signals as they are.

[Conventional technology]

Optical amplification devices are important devices in many fields such as optical fiber transmission and optical switching equipment. In conventional optical amplification devices, it has been common practice to convert an incoming optical signal into an electrical signal, amplify it, and then convert it back into an optical signal and send it out. In response, progress is being made in the development of semiconductor optical amplifiers that can amplify optical signals as they are. By using this semiconductor optical amplifier, an extremely compact and high-performance optical amplification device can be constructed. The structure of a semiconductor optical amplifier is basically the same as a Fabry-Perot semiconductor laser, which is equipped with a means for injecting current into the active layer.An anti-reflection coating is applied to both end faces of the laser to suppress laser oscillation. I am using it as an amplifier. Regarding this semiconductor optical amplifier, for example, the report of the Institute of Electronics, Information and Communication Engineers Photon Quantum Electronics Study Group (Saito et al.
0QE86-114> etc.

[Problem that the invention attempts to solve]

Conventional semiconductor optical amplifiers have had the following problems. The problem is that the gain changes significantly when the ambient temperature changes. This is because when a semiconductor optical amplifier is driven with a constant current, the gain decreases as the ambient temperature rises. This corresponds to the fact that the threshold value of a semiconductor laser increases with temperature. In order to keep the gain substantially constant even when the temperature changes, it is necessary to control the drive current of the semiconductor optical amplifier by some kind of feedback so that the gain remains constant. The most direct method for this purpose is to provide an optical amplification device that monitors a portion of the optical signal amplified by the semiconductor optical amplifier and provides feedback so that the optical signal level remains constant. However, in this configuration, in order to monitor part of the output signal light,
There are disadvantages that the optical system becomes complicated and the number of transmitted optical signals decreases.

The purpose of the present invention is to improve this drawback, to provide an optical amplifying device that can obtain a substantially constant gain even when the ambient temperature fluctuates, and that can be configured with a simple optical system, and a semiconductor optical amplifier suitable for this optical amplifying device. It is about providing.

[Means to solve the problem]

The present invention has two parts, one of which is a semiconductor optical amplifier comprising a multilayer structure including an active layer that participates in light emission and a means for injecting current into the active layer, and a semiconductor optical amplifier that emits light from the semiconductor optical amplifier. An optical amplification device comprising at least a light receiver that receives spontaneous emission light, and a controller that controls current injected into the semiconductor optical amplifier so that the light reception level of the light receiver matches a reference value. One is a semiconductor optical amplifier that has a multilayer structure including an active layer that participates in light emission, and is equipped with an electrode that injects current into the active layer, in which a part of the electrode is removed and spontaneous emission is emitted from the active layer. This semiconductor optical amplifier is characterized in that it is capable of extracting a portion of light.

〔Example〕

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing the basic configuration of the optical amplification device of the present invention. This optical amplification device includes the same semiconductor optical amplifier 100 as described in the conventional example, a light receiver 200 for receiving spontaneous emission light emitted from the active layer 130, and a light receiver 200 for receiving spontaneous emission light emitted from the active layer 130.
a controller 300 that controls the current injected into the semiconductor optical amplifier 100 so that the light reception level of 0 (that is, the photocurrent level proportional to the spontaneous emission light intensity) substantially matches a reference value;
It consists of a lens 400 for making signal light incident on a semiconductor optical amplifier 100 and for taking it out. Since the light receiver 200 is located at a position offset from the optical axis of the input light, it does not receive signal light, but only receives spontaneously emitted light emitted in a direction offset from the optical axis.

The principle of keeping the gain of the semiconductor optical amplifier 100 approximately constant in this device regardless of the ambient temperature is as follows. That is, in the semiconductor optical amplifier 100, there is an approximately proportional relationship between the gain and the spontaneous emission intensity. For example, when the semiconductor optical amplifier 100 is driven with a constant current, the ambient temperature rises. When the gain decreases, the spontaneous emission light intensity also decreases accordingly. Therefore, by monitoring this spontaneous emission light intensity and changing the drive current of the semiconductor optical amplifier 100 by the controller 300 so that the value matches the reference value, the gain can be kept at a substantially constant value.

Since spontaneous emission light is emitted from the active layer 130 in all directions, it can be received even if the light receiver 200 is placed at a position offset from the optical axis, for example, in the lateral direction of the semiconductor optical amplifier 100.

Below, each component of this device shown in FIG. 1 and the characteristics of the device will be explained. The wavelength of the optical signal to be amplified was set to 1.5 μm band. First, as described in the conventional example, the semiconductor optical amplifier 100 is basically the same in structure as a Fabry-Bello type semiconductor laser. That is, the active layer (InGaAsP with bandgap wavelength λg = 1.6 μm)
It has a double heterostructure with p-type and n-type InP layers sandwiched between the top and bottom of 130, and DC-PBH is used for transverse mode control.
It uses structure. A SiN non-reflection coating film 160 is applied to the light input and output end faces to suppress laser oscillation.

The length of the element is 200 μm. The light receiver 200 is I n
A GaAs PIN7t diode was used. Controller 3
00 consists of a comparator using an operational amplifier. lens 40
0 is coupled to a single mode fiber using a selfoc lens with a spherical tip. The coupling loss was 4 dB on one end.

The characteristics of this device were as follows. 10dB gain between fibers at room temperature for 1.55μm incident light
The above was obtained. The gain variation was less than ±5 dB with respect to a change in ambient temperature of 10 to 50°C. This value was kept to less than one digit compared to ±5 dB when no feedback was applied. In the above embodiment, the reference voltage in the controller 300 was fixed at a constant value so that a gain of 10 dB could be obtained at room temperature. This is the simplest method that takes advantage of the fact that the gain of the semiconductor optical amplifier 100 and the spontaneous emission light intensity are approximately proportional, as described above. In order to perform more precise gain control, memorize in advance the relationship between gain and spontaneous emission light intensity when the ambient temperature changes.
The reference voltage may be finely adjusted depending on the ambient temperature. Thereby, it is possible to suppress gain fluctuations to ±0.2 dB or less. In this case as well, the basic configuration shown in FIG. 1 is exactly the same except that a memory circuit and a temperature sensor are added.

FIG. 2 is a schematic structural diagram of the semiconductor optical amplifier of the present invention.

Although it has almost the same structure as a conventional semiconductor optical amplifier, the feature is that a portion of the electrode 150 is removed, so that spontaneous emission light can be extracted from there. The stacked structure of semiconductor layers and the transverse mode control structure are the same as the conventional one. If a photoreceiver is placed opposite to the window region of the electrode 150, a large amount of spontaneously emitted light can be received, so a large photocurrent can be obtained, and its linear feedback control becomes easy. The manufacturing process of the device is almost the same as that of a normal semiconductor laser, but it will be briefly explained below. First, an n-InP buffer layer 120, an rnGa
AsP active layer (λg=1.6μm>130, p-InP
The cladding layer 140 is grown sequentially. The growth method is to perform mesa etching to create a zero-order buried structure using a liquid phase growth method to form a striped mesa portion 180 sandwiched between two grooves. After this, p-
An n-p current blocking layer 170 is formed. Next, electrodes are formed on the substrate side and growth layer side of the element. Thereafter, a portion of the electrode 150 on the growth layer side is removed to form a window region. After cutting out the semiconductor optical amplifier into a length of 200 μm by cleavage, a non-reflection coating film 16 made of SiN is applied to the light input and output end faces.
form 0. The obtained semiconductor optical amplifier had gain characteristics that were almost the same as those with uniform electrodes. The internal gain of the semiconductor optical amplifier for incident light of 1.55 μm was 20 dB.

The spontaneous emission light received is approximately 1 times smaller than when it is extracted from the side of the semiconductor optical amplifier as in the case of conventional semiconductor optical amplifiers.
I was able to get an order of magnitude larger.

In the embodiment shown in FIG. 2, the windows of the electrodes are formed in stripes along the light emitting region on the growth layer side, but they may be formed in only a portion of the stripes. Furthermore, when mounting a semiconductor optical amplifier on a heat sink with a junction down, a similar effect can be obtained by removing part of the electrode on the substrate side in the same way.

FIG. 3 shows a semiconductor optical amplifier 1 constituting the optical amplifier of the present invention.
This is a cross-sectional view in a direction perpendicular to the optical axis of an integrated device in which the light receiver 200 and the light receiver 200 are formed on one substrate 110 (the light input/output direction is perpendicular to the plane of the paper).
By monolithically integrating 0, the entire optical amplification device can be miniaturized. Also, a light receiver 2 that receives spontaneously emitted light
Position adjustment of 00 is also unnecessary. The manufacturing procedure is not much different from the manufacturing procedure of the semiconductor optical amplifier shown in FIG.
form. In the DC-PBH structure, the active layer 130 is left in addition to the mesa section 180 that performs optical amplification, so this active layer is used as a light absorption layer of the light receiver 200. Specifically, the current blocking layer 170 in the portion that becomes the light receiver 200
Zinc is diffused to form a diffusion region 190 to allow current to flow. The semiconductor optical amplifier 100 and the optical receiver 2
After forming the electrode 150 on the electrode 150, a width of 10 μm between the two regions is removed by etching to achieve electrical isolation. The length of the semiconductor optical amplifier 100 and the light receiver 200 are both 200 μm, and the width of the light receiver 200 is 100 μm.

A non-reflection coating film is formed on the input and output end faces of the semiconductor optical amplifier 100. The characteristics of the semiconductor optical amplifier 100 are completely the same as those of a single semiconductor optical amplifier 100, and since the distance between the photoreceiver 200 and the semiconductor optical amplifier 100 is close to about 50 μm, a large photocurrent can be obtained. When an optical amplifying device similar to that shown in FIG. 1 was constructed using this integrated element, it was not possible to achieve the same performance as when using a single semiconductor optical amplifier.

Although the embodiments have been described in detail above, some additional information will be made here. First, the structures of the semiconductor optical amplifiers described in the embodiments are all buried structures, but other structures such as ridge guide structures may be used. Further, the growth method may be other methods such as organometallic vapor phase epitaxy, and the same effect can be obtained even when the wavelength band of the signal light is other than the 1.3 μm band. However, it is necessary to match the active layer composition of the semiconductor optical amplifier to the wavelength of the signal light. The material system may also be an AfIGaAs system other than the InGaAs system, and the method of integrating the semiconductor optical amplifier and the photoreceiver shown in FIG. 3 does not necessarily require arranging them side by side in the horizontal direction as in the embodiment. In short, since it is sufficient to receive spontaneously emitted light, it is possible to integrate the semiconductor optical amplifier in the vertical direction, that is, in the stacking direction, for example. As a method of integration in the stacking direction, for example, the same method as in the case of integrating a semiconductor optical laser and a light receiver can be applied. Regarding this integration method, please refer to the IEICE Quantum Electronics Study Group Report (Usa Jitsuchi 0QE87-1
79).

Finally, although the optical amplifying device of the present invention was invented primarily for the purpose of suppressing gain fluctuations due to fluctuations in ambient temperature, it is also effective against gain changes due to deterioration of semiconductor optical amplifiers. This is because a decrease in gain due to deterioration is always accompanied by a decrease in spontaneous emission light intensity, so feedback control similar to that in the case of temperature fluctuations is possible.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to realize an optical amplification device that can obtain a substantially constant gain even when the ambient temperature fluctuates. The ambient temperature is 10-5 for incident light of 1.55 μm.
The gain variation when changing to 0°C was 10±0.5 dB. Since the present invention monitors the spontaneous emission light of a semiconductor optical amplifier and controls the gain, the configuration of the device becomes simple. As shown in the conventional example, it is also possible to monolithically integrate some of the components to make the device even smaller and more stable.

170 is a current blocking layer, 180 is a mesa portion, and 190 is a diffusion region.

Claims (2)

[Claims] (1) a semiconductor optical amplifier having a multilayer structure including an active layer that participates in light emission and having means for injecting current into the active layer; and a light receiver that receives spontaneous emission light emitted from the semiconductor optical amplifier; An optical amplification device comprising at least a controller that controls current injected into the semiconductor optical amplifier so that a light reception level of the light receiver matches a reference value. (2) Spontaneous emission light emitted from the active layer when a part of the electrode is removed in a semiconductor optical amplifier equipped with a multilayer structure including an active layer that participates in light emission and an electrode that injects current into the active layer. A semiconductor optical amplifier characterized in that it is possible to take out a part of the semiconductor optical amplifier.