JPS59211339A - Method for extracting information signal on the way of optical transmission line - Google Patents

Abstract

PURPOSE:To decrease inertion losses and to quicken the response speed by inserting an active waveguide path having P-N junction in an optical transmission line and amplifying propagated light with a forward bias normally to extract the optical signal as an electric signal at a reverse bias. CONSTITUTION:Laser light 1 for signal transmission is coupled with the active waveguide device 3 having the P-N junction via an optical system 2. In applying a forward bias across the P-N junction of the waveguide path 3, the laser light 1 is amplified and irradiated from the waveguide path 3 ad irradiated light 4. On the other hand, in applying a reverse bias across the waveguide path 3, the laser light 1 is absorbed while being travelled through the active waveguide path 3 and extracted externally as a light current. Thus, the light is amplified and irradiated to the next stage or the light is extracted as the electric signal by changing over the bias state of the waveguide path 3 in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for electrically extracting information signals from the middle of an optical transmission path.

In recent years, as the range of applications of optical communication systems has expanded, the need for devices with various new functions has increased. One of them is a device (a coupler) that extracts a signal from the middle of an optical transmission path.

This is particularly in demand when optical transmission signals are to be obtained at many points along an optical transmission line, such as in small-scale local communication systems such as optical data buses and optical loops. In order to realize such a coupler, three future methods are being considered.

1) A method using optical branching 2) A method of guiding the optical signal to the detection system only when necessary using an optical switch 3) A method using a repeater These methods will be briefly explained in order. In 1), an optical branch is inserted in the middle of the transmission path and a part of the optical signal being transmitted is guided to the photodetection system.The device used is very cheap and simple, but the branch is the main reason. This has a major drawback of increasing optical loss in the transmission path. 2) uses an optical switch in place of the optical branching in 1), and has the advantage that light is transmitted with almost no loss when there is no need to extract an optical signal. However, in the case of mechanical switches that are currently available for practical use, the insertion loss is small, but the response speed is slow.
In the case of a non-mechanical type, although the speed is generally high, there are limitations on the mode of light used, polarization, etc., and there are problems such as large insertion loss and large shape, which limits the field of application. 3) is an E10 conversion device for optical transmission of the information signal to the next stage after first converting the light into a P O/E by the detection system and converting it into an electrical signal, similar to a repeater used in a normal optical communication system. It is divided into a drive circuit (laser, light emitting diode, etc.) and a signal detection circuit. Since this system is a regenerative amplification system, there is no need to consider insertion loss, and it has the advantage that waveform distortion during transmission can be corrected, but one repeater is extremely expensive and complicated, and one system There are many uses for the price,
There are problems with reliability, etc.

As mentioned above, the methods conventionally considered as means for realizing a coupler each have their own advantages and disadvantages, and at present it is impossible to obtain the optimal one. An object of the present invention is to provide a method for extracting information signals from the middle of an optical transmission path, which has a relatively simple configuration, is inexpensive, and has excellent insertion loss and response speed, while eliminating the drawbacks of the conventional methods as described above. Then there it is.

A method of extracting information signals from an optical transmission line according to the present invention is to insert an active waveguide having a p-n junction made of a semiconductor material in the middle of the optical transmission path, and to set the active waveguide in a normal forward bias state so that the propagating light When it is necessary to amplify the information signal and extract the information signal, the active waveguide is biased and the optical signal is extracted as an electric signal.

To realize the method according to the invention, p
-n junction and a pair of coupling circuits installed before and after the active waveguide and between the active waveguide and the optical transmission line, and a coupling circuit for applying a forward bias to the active waveguide. means for applying a reverse bias to the active waveguide and detecting the photocurrent; means for applying the forward bias to the active waveguide in response to a control signal; and means for applying the forward bias to the active waveguide and detecting the photocurrent. This is possible by using a device that has means for switching the connection between the detection means and the detection means. The present invention will be explained in detail below with reference to the drawings.

In general, a waveguide formed of semiconductor material has an internal p
It is known that in an active waveguide that can form a population inversion by current injection into the -n junction, when light having a wavelength near the peak of its gain spectrum is guided, the guided light is amplified. Semiconductor injection laser utilizes this phenomenon, and GaAtAs /GaAs + InGaAsP/
Double Peter junctions made of materials such as InP are used. Furthermore, in recent years, attempts have been made to utilize this material not as a laser but as an optical amplifier for amplifying light injected from the outside. On the other hand, in a p-n junction in a semiconductor, when a reverse bias is applied, when light with an energy greater than the band gap energy is absorbed, pairs of holes and electrons are generated due to the application of a reverse bias. It drifts in the depletion layer and generates a transverse photocurrent. It functions as a square shift diode, and taking advantage of this fact, pn junctions made of materials such as Si r Ger InGaA1 are used as photodetectors.

Furthermore, the above fact shows that when forward biased, it works as a semiconductor laser, or an optical amplifier. If a p-n junction is used in reverse biased state, it can act as a photodiode that detects light that can be oscillated or amplified when forward biased. This shows that it can also be used.

In fact, attempts have already been made to make a cut in the center of a semiconductor laser to divide it into two parts, and use one part as a laser and the other part as a monitoring photodiode. As described above, the present invention utilizes the fact that an active waveguide having a p-n junction can be used as an optical amplifier or a photodetector depending on the forward bias or reverse bias state.

FIG. 1 is a diagram showing the principle of the present invention.

The laser beam 1 for signal transmission is transmitted by an appropriate optical system 2F)p-n
It is coupled to an active waveguide 3 with a junction. Here, the material for the active waveguide 3 is selected so that the wavelength of the laser beam 1 is near the peak of the optical absorption spectrum. Specifically, it may be made of the same material as the semiconductor laser that generates the laser beam 1. When a forward bias is applied to both ends of the p-n junction of the active waveguide 3, the laser beam 1 is amplified and emitted from the active waveguide 3 as an emitted light 4. Here, the active waveguide may have a resonator structure similar to a laser, or may have a traveling waveform. On the other hand, when a reverse bias is applied to both ends of the active waveguide 3, the laser beam 1 is absorbed while traveling through the active waveguide 3 and is extracted to the outside as a photocurrent.

Therefore, by electrically switching the bias state of the active waveguide from the outside, the light can be amplified and emitted to the next stage, and the light can be extracted as an electrical signal. According to such a method, since the light is amplified when no signal is extracted, the insertion loss can be reduced to zero or minus, and switching and response speeds can be expected to be sufficiently high. Furthermore, since it does not have a complicated structure like a repeater, a simple and inexpensive method for extracting information signals from the middle of an optical transmission path can be obtained.

FIG. 2 is a diagram showing an embodiment of a device for implementing a method of extracting information signals from the middle of an optical transmission line according to the present invention. A laser beam 11a transmitted through an optical transmission line 10a (assumed to be an optical fiber here) and emitted is coupled to an active waveguide 3 having a pn junction by a coupling circuit 12a. The emitted light 11b from the active waveguide 3 is coupled to the optical transmission line 10b again by the coupling circuit 12b and transmitted. A forward bias application circuit 16 and a reverse bias application circuit 14 are connected to the p-n junction electrode of the active waveguide 3 via a switching circuit 13. Bias state is switched. As already explained, when the switching circuit 13 is connected to the forward bias applying circuit 16 side, the output light 11b of the active waveguide 3 is amplified, coupled into the optical transmission line 10b, and transmitted. In this state, the light is amplified, so even if there is a coupling loss in the coupling circuits 12a and 12b, it can be sufficiently compensated for, and insertion loss can be ignored. Next, when it becomes necessary to detect an optical signal, the switching circuit 13 is switched and the active waveguide 3 is connected to the reverse bias applying circuit 16. In this case, the light is absorbed while propagating through the active waveguide 3 and generates hole-electron pairs, so the transmitted optical signal is outputted to the terminal 15 as a photocurrent, making it possible to detect the optical signal. Here, the reverse bias application circuit 14
．． As the forward bias application circuit 16, an extremely simple circuit similar to that used when using a normal photo diode or semiconductor laser can be used. Further, even if the switching circuit 13 is a switching circuit using a normal electric device, a sufficiently high response speed can be expected. The active waveguide 3 is suitably made of the same structural material as that of commonly used semiconductor lasers. GaAtAs/GaAs as the pick material,
A material having a double heterojunction or a multi-quantum well structure using InGaAsP/InP is suitable.

Further, as already mentioned, the active waveguide 3 can be of a co-imaging type similar to a semiconductor laser, or of a traveling wave type. In the embodiment shown in FIG.
, 12b may be integrated with a structure separate from the active waveguide 3, and in that case, it is advantageous in terms of difficulty in adjustment during manufacturing, stability against long-term positional displacement, etc.

As described above in detail, the present invention provides a method and apparatus for extracting an information signal from the middle of an optical transmission path, which has a relatively simple configuration, high response speed, and excellent insertion loss.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the principle of the method of extracting information signals from the middle of an optical transmission line according to the present invention, and FIG. 2 embodies the method of extracting information signals from the middle of an optical transmission line according to the present invention. It is a figure showing one example of the device for. In the figure, 1, 4.11a, 11b are laser beams, 2°1
2a and 12b are coupling circuits, 3 is an active waveguide, and 10a. 10b is an optical transmission line, 13 is a switching circuit, 14 is a reverse bias application circuit, 15 is a terminal, and 16 is a forward bias application circuit.

Claims (1)

[Claims] (1) An active waveguide having a p-n junction made of a semiconductor material is inserted in the middle of the light transmission path, the active waveguide is normally put in a forward bias state, and the active waveguide is turned off when it is necessary to take out an information signal. A method for extracting an information signal from the middle of a light transmission path, characterized by extracting an optical signal as an electrical signal in a reverse bias state.