JPH0511609B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <<Industrial Application Field>> The present invention relates to an optical control device having an optical switch function that can be easily integrated with a semiconductor laser, a light receiving element, etc.

<<Prior Art>> Optical fibers have scattering inherent to glass. Light waves propagating through an optical fiber core undergo Rayleigh scattering due to scattering sources such as dopants within the core. In particular, among this scattered light, the scattered light that is guided toward the rear of the fiber core (in the direction of the light source) is called backscattered light.

OTDR is a method that detects the loss distribution and break point in the length direction of the fiber by sending a light pulse from one end of the optical fiber and observing the backscattered light.
(Optical Time Domain Reflectometry) method.

FIG. 6 is a block diagram showing the basic configuration of an optical fiber testing device using the conventional OTDR method. A light pulse output from a light source 1 passes through a directional coupler 2 and enters a fiber 3 to be measured. A part of this light returns in the opposite direction as backward Rayleigh scattering light, passes through the directional coupler 2 again, enters the light receiving element 4 of the light receiving section 5, and is detected. The control circuit 6 controls the operations of the light source 1, the directional coupler 2, and the light receiving section 5.

<<Problems to be Solved by the Invention>> However, in the conventional OTDR device as described above, the light emitting section, the optical directional coupling section, the light receiving section, etc. are each composed of separate individual parts. Therefore, (a) the device becomes larger;

(b) Optical connection loss is large.

(c) Poor reliability.

(d) The price will be high.

(e) Poor mass production.

There were other problems. Also, these problems are
This problem is not limited to OTDRs, but is a general problem when constructing optical circuits using individual components.

The present invention has been made in order to solve the above problems, and aims to realize an optical control device that is compact, highly reliable, mass-producible, requires no coupling adjustment, and has low loss. There is. Conventionally, optical integrated circuits that integrate this type of optical circuit components have required submicron accuracy for alignment of optical waveguides and electrodes, but the aim is to eliminate the need for this alignment.

<Means for Solving the Problems> The present invention provides a PN bonding layer and a PN bonding layer on a substrate.
An optical waveguide layer having a higher refractive index than the surroundings is provided near the bonding layer, and an electrode is provided to sandwich the PN bonding layer from both upper and lower surfaces, one of which is divided into at least two parts, and a reverse bias voltage to the PN junction is applied. an optical switch portion configured to selectively form an optical waveguide by increasing the refractive index near the optical waveguide layer by applying an electric voltage to the electrode; and electrodes provided to sandwich the PN junction layer from above and below, a semiconductor laser section configured to output output light to one of the optical waveguides via a groove provided at the boundary with the optical switch section; and electrodes provided to sandwich the PN junction layer from above and below, and a light receiving section configured to receive the output light from the other optical waveguide.

"Example" The present invention will be explained in detail below using the drawings.

FIG. 1 shows an embodiment of a light control device according to the present invention.
FIG. 2 is a plan view showing an application to an OTDR. In the optical control device 100, 40 is a T-shaped groove that divides the entire element into three parts and electrically insulates them from each other, 10 is a semiconductor laser section (hereinafter referred to as a laser section) that outputs laser light, and 11 is this laser section. Part 10
20 is an optical switch section into which the output light of the laser section 10 enters; 21, 22, and 23 are arranged in a Y-shape on the surface of the optical switch section 20. An ohmic electrode 30 is provided for forming an optical waveguide, a light receiving section 30 detects the light incident from the optical switch section 20, and 31 is an ohmic electrode provided on the surface of the light receiving section 30 for extracting a signal. The electrode 11 has a long shape in the direction of the optical waveguide in order to output the laser light from the laser section 10 to the optical waveguide of the optical switch section 20.

FIG. 2 is a side view corresponding to FIG. 1. 50
is an n _{- IoP} substrate, 51 is an n- _IoGaAsP epitaxial layer with a thickness of about 1 μm formed on this n _{- IoP} substrate 50, and 52 is an n- _{IoG a} A _s P n- _{I o} having a high refractive index (different component ratio from layer 51) formed with a thickness of about 0.5 μm on P epitaxial layer 51
G _a A _s P waveguide layer (active layer), 53 is this n-I _o G _a A _s
Formed on the P waveguide layer 52 with a thickness of approximately 1 μm, n-I _o
A P _- I _o P layer having a lower refractive index than the layer 52 forms a PN junction 60 at the boundary with the G a A _s P waveguide layer 52 , and 54 serves as a contact layer for making an ohmic contact between the electrodes. _o P formed on the P layer 53
-I _{o Ga As} P layer, 55 is an ohmic electrode provided on the entire lower surface of the n-I _o P substrate 50, and 56 is a film of SiO ₂ or Al ₂ O ₃ on the right end surface of the element 100. This is a highly reflective film that is deposited to increase laser light reflectance. The depth of the groove 40 is here such that it reaches the n-I _o P substrate 50;
Any material that reaches at least layer 51 may be used. The end face of the element forms a cleavage plane. As a method for forming the epitaxial layer, MOCVD (metal organic pyrolysis) method, MBE (molecular beam epitaxy) method, etc. are used. In addition to chemical etching, methods such as reactive ion etching are used to form the grooves.

FIG. 3 is a sectional view taken along the line AA in FIG. 1. The laser section 10 is on the right side of the figure, and the light receiving section 30 is on the left side. In the laser section 10, reference numeral 57 is a groove formed by etching prior to epitaxial growth in order to effectively concentrate the implanted carriers. Electrode 1 of laser section 10
A PN junction 60 is connected between 1 and 55 for current injection.
A forward voltage V ₀ is applied to. The light receiving section 30 forms a light receiving element using a PN heterojunction, and here a resistor R is connected to the electrodes 31 and 55.
Voltage measuring means to measure the voltage at both ends corresponding to the detected current
Measured on VM.

FIG. 4 is a sectional view taken along the line BB in FIG. 1. In order to form an optical waveguide in the optical waveguide layer 52 of the optical switch section 20, the electrodes 21 and 23 are connected to each other to form an optical waveguide.
It is connected to the reverse bias voltage _-V1 for the PN junction 60 via SW1 and SW2.

The operation of the light control device having such a configuration will be explained next. When a current is injected into the upper electrode of the laser section 10, carrier recombination occurs in the n-I _{o Ga As P} active layer, and laser oscillation occurs within the resonator formed by the mirror surface on the side surface of the active layer. One of the mirror surfaces on the side surface of the generation layer is the cleavage surface on the right side of FIG. 1, and the other is a surface formed by etching facing the groove 40. The grooves 57 shown in FIG. 3 allow effective concentration of the injection carriers. Laser output light from the laser section 10 passes through the groove 40 and is guided to the n-I _{o Ga As} P waveguide layer 52 of the optical switch section 29 .
When the switch SW1 is tilted upward and a reverse bias voltage _-V1 is applied to the electrode 21, a depletion layer spreads in a portion corresponding to the shape of the electrode near the PN junction 60. In the depletion layer, the refractive index increases as the carrier concentration decreases, so an optical waveguide is selectively formed under the electrode 21 as shown at 61 in FIG. When a reverse bias voltage is similarly applied to the electrode 22, the laser beam passes through the optical waveguide 61 and is then emitted to an external optical fiber to be measured via the waveguide below the electrode 22. Next, when the return light from an external optical fiber to be measured enters the waveguide below the electrode 22, a reverse bias voltage -V ₁ is applied to the electrode 23 via the switch SW2.
(SW1 is off) to form an optical waveguide 62 under the electrode as described above, and to connect the light receiving part 30 through the groove 40.
guided by. A current is induced in the PN junction portion of the light receiving section 30 by the incident light. This current generates a voltage across the resistor R, and by measuring this with the voltage measuring means VM, the incident light can be detected.

According to the optical control device having such a configuration, it is possible to integrate a semiconductor laser, a light receiving element, and an optical switch, thereby realizing an OTDR element that is compact, highly reliable, and mass-producible.

In addition, in the above embodiment, when the optical waveguide is formed under the electrodes 21 and 22, the etched plane and cleavage plane on the side surface of the waveguide also serve as a resonator, so together with the resonator of the laser section 10, a complex resonator is generated. This provides advantages such as narrowing the oscillation spectrum linewidth and reducing mode hops.

Another advantage is that there is no need for alignment between the electrode and the waveguide.

Furthermore, it is also easy to form an amplifier circuit, a processing circuit, etc. on the same substrate.

Note that although the above embodiment has been explained by taking an n- _Iop substrate as an example, a similar configuration is also possible with a p _- Iop substrate.

In addition, the structure of the laser section 10 may include one in which a plurality of active layers are provided to achieve high output, one in which the active layer has a quantum well structure, and one in which a diffraction grating for distributed feedback is provided as a resonator. It's okay.

Further, a similar configuration is possible not only with I _o P-based compound semiconductors but also with Ga _{As -} based compound semiconductors.

Further, in the above embodiments, the optical waveguide is formed using the depletion layer of the PN junction, but any type of optical waveguide may be used as long as it uses a change in refractive index due to a difference in the concentration of free carriers.

Furthermore, since the refractive index of the optical waveguide described above changes due to the electro-optic effect in response to the applied reverse bias voltage, the oscillation wavelength can be selected by the applied voltage.

Further, the portion of the groove 40 between the light receiving section 30 and the optical switch section 20 can be omitted.

In addition, unnecessary return light such as a large amount of Fresnel reflection from the input end of the optical fiber to be measured can be removed by turning off the electrode 22 (and 21 and 23 if necessary) to mask the light receiving section 30 and the laser section 10. can do.

Further, in the above embodiment, the electrodes of the optical switch section 20 are divided into three parts 21, 22, and 23, but the optical switch is not limited to this, and an optical switch can be constructed as long as the electrodes are divided into at least two parts or more.

FIG. 5 shows an application example of the light control device according to the present invention.
FIG. 2 is a configuration block diagram showing an OTDR or the like that generates short pulses. 71 is a pulse drive circuit, 72
73 is an external laser driven by this pulse drive circuit 71; 73 is a condensing lens that condenses the output light of this external laser 72 and enters the laser unit 10 of the light control device 100; and 74 is a condensing lens of the light control device 100. A ball lens condenses the output light and enters the optical fiber 3 to be measured; 75 is a light receiving circuit connected to the electrode of the light receiving section 30 of the optical control device 100; 76 is each electrode of the optical switch section 20 of the optical control device 100. This is a control circuit that connects to the optical waveguide and controls the optical waveguide.

The operation of the device having such a configuration will be explained next.
A bias current is caused to flow through the laser on the side to be injected in the laser section 10 to near the threshold value, and short pulse light is externally injected from the external laser 72 via the lens 73.
At this time, the laser to be injected oscillates with a shorter pulse than the external laser 72.

According to the device having such a configuration, it is possible to realize shorter pulse generation than when using a single laser in the optical control device.

Although the above embodiment shows a case in which the laser section, optical switch section, and light receiving section are integrated as a single unit for OTDR, it can also be applied to other uses such as optical communication inside a computer. Further, the optical switch section alone or in combination with other sections can be used for other purposes such as a local area network.

<<Effects of the Invention>> As described above, according to the present invention, it is possible to realize an optical control device with a simple configuration that achieves miniaturization, high reliability, mass productivity, no coupling adjustment, low loss, etc. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing one embodiment of the light control device according to the present invention, FIG. 2 is a side view of the same, FIGS. 3 and 4 are sectional views of the same, and FIG. 5 is one application of the embodiment device. A configuration block diagram showing an example, Fig. 6 is a conventional
1 is a configuration block diagram showing an OTDR device. FIG. 10... Semiconductor laser section, 20... Optical switch section, 11, 21, 22, 23, 31, 55... Electrode, 30... Light receiving section, 40... Groove, 50... Substrate, 52... Optical waveguide Layer, 60...PN junction layer, 6
1, 62... optical waveguide, 100... optical control device,
V ₁ ... Reverse bias voltage.

Claims (1)

[Claims] 1. On a substrate, a PN junction layer, an optical waveguide layer provided near the PN junction layer and having a higher refractive index than the surrounding area,
An electrode is provided so as to sandwich the PN bonding layer from both the upper and lower surfaces, and one of the electrodes is divided into at least two parts.
an optical switch section configured to selectively form an optical waveguide by applying a reverse bias voltage for the PN junction to the electrode to increase the refractive index near the optical waveguide layer; A semiconductor laser section configured to sandwich electrodes and output light to one of the optical waveguides through a groove provided at the boundary with the optical switch section, and the PN junction layer from both upper and lower surfaces. A light control device comprising: a light receiving section configured to have electrodes sandwiched therebetween and to receive output light from the other optical waveguide.