JP3147570B2 - Optical communication device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an optical communication device used in an optical communication system using an optical fiber as a transmission line.

[0002]

2. Description of the Related Art FIG. 2 shows an outline of the optical communication system described above. FIG. 1A shows a loop type system in which a plurality of optical communication devices 2 are connected in the middle of a loop-shaped optical fiber transmission line 1. FIG. 1B shows a one-to-one opposing communication system, in which a pair of optical communication devices 4 are connected to both ends of an optical fiber transmission line 3. FIG. 1C shows a point-to-multipoint communication system in which a number of optical communication devices 4 are connected to the ends of a number of optical fiber transmission lines 3 star-connected by an optical star coupler 5. ing.

FIG. 3 shows an example of a conventional optical communication device used in the above-mentioned system. Here, only a portion related to transmission and reception of signal light is shown.

FIG. 3A shows an apparatus corresponding to the system shown in FIG. 2A. In FIG. 3, reference numeral 6 denotes an optical branching element, 7 denotes a light receiving element, and 8 denotes a light receiving element control / reception signal processing circuit. is there. The signal light propagating through the optical fiber transmission line 1 is split by the optical splitting element 6 and converted into an electric signal by the light receiving element 7. There is a method in which this optical branching section is used as a line portion and is not used as a component in the device, but the configuration is the same. The light receiving element 7 is usually under an appropriate bias, and is converted into an electric signal that can be easily processed by the light receiving element control / reception signal processing circuit 8 including a preamplifier, a level adjustment circuit, and the like.

FIG. 3 (b) shows a device corresponding to the system shown in FIG. 2 (b) or FIG. 2 (c), particularly a device which performs two-way communication using a single optical fiber transmission line. Denotes a light receiving element, 8 denotes a light receiving element control / received signal processing circuit, 9 denotes an optical branching / joining element, and 10 denotes a light emitting element. Optical fiber transmission line 3
Is split by the optical splitter / combiner 9,
The light incident on the light receiving element 7 is converted into an electric signal. The light receiving element 7 is usually under an appropriate bias, and is converted into an electric signal that can be easily processed by the light receiving element control / reception signal processing circuit 8 including a preamplifier, a level adjustment circuit, and the like. On the other hand, the signal light emitted from the light emitting element 10 is combined (correctly, simply combined) by the optical branching / combining element 9 and sent out to the optical fiber transmission line 3.

[0006]

However, since the above-mentioned device requires an optical branching element or an optical branching and joining element, the number of parts is increased, and the distance between these elements and the optical fiber and between these elements and the light receiving element are increased. Since optical coupling is required in many parts such as between the element and the light emitting element, assembly and adjustment are troublesome, and as a result, there is a problem that it is difficult to reduce the size and cost of the device.

The present invention has been made in consideration of the above-described conventional problems, and has as its object to provide an optical communication device that requires a small number of components and optical coupling portions, and that can be easily reduced in size and cost.

[0008]

In order to achieve the above object, according to the present invention, there is provided a light receiving element for receiving a signal light, and a part of the signal light is taken out of the optical fiber transmission line. In an optical communication device that performs communication by using a light receiving element having a pin structure using InGaAsP as a light receiving element.
The n ^- electrode has a transmission window and is a light absorbing layer.
n ⁻ -InGaAs layer is formed based on light transmittance and absorptance
An optical communication device is proposed in which a transmission type light receiving element having a determined thickness is used and the transmission type light receiving element is inserted in the middle of an optical fiber transmission line. Further, in claim 2, a light-emitting element that generates a signal light and a light-receiving element that receives the signal light,
An optical communication apparatus for performing bidirectional communication by an optical fiber transmission path cardiac, as the light receiving element, the signal transmission timing
Is controlled to transmit outgoing light, and the signal
The transmittance control type is controlled to absorb incident light.
An optical communication device using a light receiving element and inserting the transmittance control type light receiving element between an optical fiber transmission line and a light emitting element is proposed.

[0009]

According to the first aspect of the present invention, since the light receiving element can be constituted only by being inserted in the middle of the optical fiber transmission line, the optical branching element becomes unnecessary, and the number of parts is reduced correspondingly, and the optical coupling is reduced. There are fewer parts. According to the second aspect of the present invention, since the light receiving element can be constituted only by inserting the light receiving element between the optical fiber transmission line and the light emitting element, the light branching / combining element becomes unnecessary, and the number of parts is reduced accordingly, and Fewer joints.

[0010]

FIG. 1 shows an embodiment of the optical communication apparatus according to the present invention. Here, as in the conventional example, only the part relating to transmission and reception of signal light is shown.

FIG. 1 (a) shows an apparatus corresponding to the system shown in FIG. 2 (a).
Denotes a light receiving element control / received signal processing circuit. The transmission type light receiving element 11 has a certain finite non-zero transmittance, and transmits light and absorbs a part of the light to convert it into an electric signal. The transmission type light receiving element 11 is inserted in the optical fiber transmission line 1.

Accordingly, by making the branching ratio of the optical branching element and the transmittance of the transmission type light receiving element 11 in FIG. 3A the same, a part of the signal light propagating through the optical fiber transmission line 1 is Converted to electrical signals. Transmission type light receiving element 11
Is usually under an appropriate bias, and includes a light receiving element control / reception signal processing circuit 12 including a preamplifier and a level adjustment circuit.
Is converted into an electric signal which can be easily processed.

FIG. 1 (b) shows a device corresponding to the system shown in FIG. 2 (b) or FIG. 2 (c), particularly a device for performing two-way communication using a single optical fiber transmission line. Is a transmissive light receiving element, 12 is a light receiving element control / received signal processing circuit,
Reference numeral 13 denotes a semiconductor laser module (light emitting element). The transmission type light receiving element 11 has a certain finite non-zero transmittance, and transmits light and absorbs a part of the light to convert it into an electric signal. The transmission type light receiving element 11 is inserted between the optical fiber transmission line 3 and the semiconductor laser module 13.

Accordingly, by keeping the branching / merging ratio of the optical branching / merging element in FIG. 3 (b) and the transmittance of the transmission type light receiving element 11 the same, the signal light propagating through the optical fiber transmission line 3 becomes an electric signal. Is converted to The transmission type light receiving element 11 is usually under an appropriate bias, and is converted into an electric signal which can be easily processed by the light receiving element control / reception signal processing circuit 12 including a preamplifier and a level adjustment circuit. The signal light emitted from the semiconductor laser module 13 passes through the transmission type light receiving element 11 and is sent to the optical fiber transmission line 3.

According to the above-described embodiment, an optical branching element or an optical branching and joining element is not required, and the number of parts is reduced, and a portion that requires optical coupling is reduced. This simplifies assembly and adjustment.

FIG. 4 shows an example in which the light emitting and receiving parts in the optical communication device shown in FIG. 1B are modularized. That is,
In FIG. 4A, reference numeral 14 denotes a transmitting / receiving optical module,
Transmission type light receiving element 11 and light emitting element (semiconductor laser) 15
Are integrated with the coupling lens 16 interposed therebetween.
In FIG. 4B, reference numeral 14 'denotes a transmission / reception optical module in which the transmission type light receiving element 11 and the light emitting element (semiconductor laser) 15 are connected to one side of the coupling lens 16 by the coupling lens 1.
6 and are integrated.

FIG. 5 shows a specific configuration of the light receiving element. FIG. 5A shows a conventional light receiving element which is not of the transmission type.
(b) shows the transmission type light receiving element used in the present invention.
The present transmissive light-receiving element has a p-type structure using InGaAsP as a material.
In a conventional non-transmissive light receiving element having an in-structure, a window for transmitted light is provided in an n ^- electrode on the lower surface, and the thickness of an n ^-- InGaAs layer as a light absorbing layer is determined by an absorptance and a required transmittance. What is necessary is just to determine and manufacture from the rate.

In the above structure, the incident light is In _1-x Ga
It passes through the _x As _y P _1-y window ^layer, n - -In _0.53
It is absorbed by the Ga _0.47 As layer and becomes a photocurrent. InGaAs
In the case of the s layer, the absorption coefficient for 1.3 μm light having a wavelength sufficiently shorter than the absorption edge is about 1 × 10 ⁴ cm ⁻¹ . Wavelength 1.3
The thickness of the light receiving layer that transmits 50% of light and receives 50% of light with a thickness of 50 μm temporarily ignores the loss except for the absorption layer (the other layers are almost transparent to light with a wavelength of 1.3 μm). Or almost transparent), and assuming that the absorption coefficient is α, exp (thickness × α) = 0.5. Here, if α = 1 × 10 ⁴ cm ⁻¹ is substituted and solved, the thickness becomes 0.7 × 10 ⁻⁴ cm = 0.7 μm. Therefore, in this case, the thickness may be set to 0.7 μm.

At this time, it is important that the substrate is transparent to the signal light. Here, the signal light is 1.3 μm light, and an absorption layer is formed on an InP substrate transparent to this wavelength. It is a pin that has been grown.

In the above-described embodiment, a transmittance control type light receiving element can be used instead of the transmission type light receiving element.
The transmittance control type light receiving element is an element that changes the transmittance by a voltage or a current for driving the element and obtains an electric signal corresponding to the absorption at the time of absorption.

When used in the apparatus shown in FIG. 1A, a part or all of the signal light is absorbed at the timing of receiving the signal light, and the signal light is transmitted at the timing of not receiving the signal light. This transmittance control type light receiving element can be used in a system in which the timing of receiving the signal light and the timing of transmitting the signal light do not overlap in time, and the loss at the time of transmission can be reduced.

When used in the apparatus shown in FIG. 1B or FIG. 4, a part or all of the signal light is absorbed at the timing of receiving the signal light, and the signal light is transmitted at the timing of transmitting the signal light. , And so on. This transmittance control type light receiving element can be used in a system in which the timing of receiving the signal light and the timing of transmitting the signal light do not overlap in time, and the loss at the time of transmission can be reduced.

FIG. 6 shows an example of the relationship between the signal frame and the control of the light receiving element when the transmittance control type light receiving element is used in the apparatus shown in FIG. 1 (b) or FIG. The signal transmission timing and the signal reception timing do not overlap in time. At the signal transmission timing, the device is controlled so as to transmit all or part of the incident light. At the signal reception timing, the element is controlled so as to absorb all or part of the incident light, and the reception signal is sent to the reception signal processing circuit.

FIG. 7 shows another example of the relationship between the signal frame and the control of the light receiving element when the transmission type light receiving element or the transmittance control type light receiving element is used in the apparatus shown in FIG. 1 (b) or FIG. It is. In the apparatus shown in FIG. 1B or FIG. 4, the signal light can be received by the light receiving element when the signal light is transmitted. When the transmittance control type light receiving element is used, the light receiving element is controlled to be in a partial light receiving state. As a result, the light emission intensity of the light emitting element can be monitored, so that APC (light emission intensity control) can be performed. That is,
APC output from light receiving element at transmission (light emission) timing
APC by inputting to the circuit and performing field back
Becomes possible. In this type of device, usually a monitor / AP
Although the light receiving element for C is separately provided, according to the above configuration, this can also be omitted, and the number of components can be further reduced.

FIG. 8 shows an example of a specific configuration of a transmittance control type light receiving element. In this case, InGaAs / InA
1 shows a multiple quantum well (MQW) type transmittance control type light receiving element using 1As. This element has the same structure as the optical modulator, but can be operated as a light receiving element by changing a bias condition.

FIG. 9 explains the operation when the above-mentioned element is used as an optical modulator. Figure (a) shows a wavelength of 1.55μ.
5 shows the voltage dependence of the transmittance intensity for light of m. Since there is a difference of 20 dB in the transmittance between when the applied voltage is 1.2 V and when the applied voltage is 3.4 V, as shown in FIG.
By switching between and 3.4 V, on / off control of the signal can be performed.

FIG. 10 explains the operation in the case where the device is used as a transmittance control type light receiving device. Same figure
(a) shows the wavelength dependence of the light absorption current at several applied voltages. When used as a light receiving element, a bias of a reverse voltage is applied to that when used as an optical modulator. 1.55μ wavelength
At m, a photocurrent does not flow at a voltage of -4 V or more, but -8
At V, a photocurrent that can be sufficiently detected flows. Therefore, the same figure
As shown in (b), when a signal light is received, it operates as a light receiving element by applying a voltage of -8 V, and when transmitting, it becomes a transparent part by applying a voltage of 0 V.

[0028]

As described above, according to the present invention, since the light receiving element can be constituted only by inserting the light receiving element in the middle of the optical fiber transmission line or between the optical fiber transmission line and the light emitting element, the light branching element and the light The need for a branching junction element is eliminated, the number of parts is reduced, and the number of optical coupling parts is reduced. Therefore, downsizing and cost reduction can be realized, and it is particularly useful in optical subscriber systems where low cost and downsizing are important. Yes, it has the advantage of being economical.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of an optical communication device of the present invention.

FIG. 2 is a diagram showing an outline of an optical communication system.

FIG. 3 is a configuration diagram showing an example of a conventional optical communication device.

FIG. 4 is a configuration diagram of a transmission / reception optical module using a transmission type light receiving element.

FIG. 5 is a diagram showing a specific configuration of a light receiving element.

FIG. 6 is a diagram showing an example of a relationship between a signal frame and control of a light receiving element when a transmittance control type light receiving element is used in the apparatus of FIG. 1 (b) or FIG.

FIG. 7 is a diagram showing another example of the relationship between the signal frame and the control of the light receiving element when a transmission type light receiving element or a transmittance control type light receiving element is used in the apparatus of FIG. 1 (b) or FIG.

FIG. 8 is a diagram showing a specific configuration of a transmittance control type light receiving element.

FIG. 9 is an explanatory diagram of an operation when the element in FIG. 8 is used as an optical modulator.

FIG. 10 is an explanatory diagram of an operation in a case where the element in FIG. 8 is used as a transmittance control type light receiving element.

[Explanation of symbols]

1, 3: optical fiber transmission line, 11: transmission type light receiving element, 1
2 ... Light receiving element control / received signal processing circuit, 13 ... Semiconductor laser module.

Continuation of the front page (56) References JP-A-62-179777 (JP, A) JP-A-62-199707 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 31 / 00-31/119 H04B 10/00-10/30 G02B 6/42-6/43

Claims (2)

(57) [Claims] An optical communication device having a light receiving element for receiving signal light and extracting a part of the signal light from the middle of an optical fiber transmission line to perform communication , has a pin structure using InGaAsP as the light receiving element .
A light-receiving element, which has a window for transmission in an n ^- electrode and absorbs light.
The n ⁻ -InGaAs layer, which is the condensing layer, has light transmittance and absorption.
An optical communication device comprising: a transmission type light receiving element whose thickness is determined based on a rate ; and wherein the transmission type light receiving element is inserted in the middle of an optical fiber transmission line. 2. A has a light receiving element for receiving a light emitting element and signal light to generate a signal light, an optical communication device that performs two-way communication with the optical fiber transmission path cardiac, as the light receiving element, the signal transmission timing Transmit outgoing light
And the incoming light is used for signal reception timing.
An optical communication device comprising: a transmittance control type light receiving element controlled to be in an absorbing state ; and wherein the transmittance control type light receiving element is inserted between an optical fiber transmission line and a light emitting element.