JPH04249733A - Loop-back method for testing light transceiver - Google Patents

Abstract

PURPOSE:To establish a testing method being suitable for a one-element type light transceiver of a time-division direction-control transmission system, by disposing a light-sensing element in proximity to the end face of a semiconductor laser on the opposite side to a transmitting end thereof. CONSTITUTION:At the time of an ordinary operation, a signal from an information supply source such as a terminal device is supplied to a drive circuit 12, a semiconductor laser 13 is driven by a signal of the circuit and a light signal is delivered to an optical fiber transmission path 20. At the time of a test, a test signal is supplied from a test signal generating circuit 11 to the circuit 12. Based on this test signal, the circuit 12 drives the semiconductor laser 13 and makes it generate a testing light signal. This light signal is emitted also onto the opposite side to a transmitting end of the laser 13. This light is detected by a light-sensing element 14 and outputted to a reception circuit 15. In this way, the test signal generated by the circuit 11 is looped back in the sequence of the circuit 12, the laser 13, the element 14 and the circuit 15, and therefore it can be determined by the signal obtained in the circuit 15 whether these parts are normal or abnormal.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION The present invention is utilized for testing optical transceivers using semiconductor lasers as optical transmitting elements. The present invention is particularly suitable for use in a single-element time-division direction control transmission system (so-called ping-pong transmission system, hereinafter referred to as TCM system) in which a semiconductor laser is used for both transmission and reception in a time-division manner.

0002

2. Description of the Related Art A semiconductor laser is basically a diode with a PN junction, and can be used not only as a light emitting element but also as a light receiving element. That is, if a forward bias equal to or higher than a threshold value is applied, it can be used as a light emitting element, and if a bias lower than that or a reverse bias is applied, it can be used as a light receiving element sensitive to the oscillation wavelength and shorter wavelengths.

FIG. 6 shows a basic configuration example of a one-element type TCM system that utilizes the characteristics of such a semiconductor laser, and FIG. 7 shows a general frame configuration used in this system.

A transmission device (hereinafter referred to as a "transceiver") composed of a transmission/reception switching circuit 1 and a semiconductor laser 2 is composed of a semiconductor laser 4 and a transmission/reception switching circuit 5 via an optical fiber transmission line 3. connected to an optical transceiver. Each optical transceiver is connected to an information supply source and an information supply destination, such as a terminal device, but these are omitted here.

[0005] The transmission/reception switching circuits 1 and 5 respectively switch the operation modes of the semiconductor lasers 2 and 4 to transmit a burst signal to the optical fiber transmission line 3 and to receive a burst signal from the same optical fiber transmission line 3. is done in a time-sharing manner. That is, when the semiconductor laser 2 is in the transmission mode, the semiconductor laser 4 is in the reception mode, and when the semiconductor laser 4 is in the transmission mode, the semiconductor laser 2 is switched to the reception mode.

[0005] This will be explained in detail with reference to FIG.
When the semiconductor laser 2 starts transmitting, the semiconductor laser 4
starts receiving after the transmission delay time TD. The transmission delay time TD is the time required for light to be transmitted through the optical fiber transmission line 3. When the reception is completed, the semiconductor laser 4 is switched to the transmission mode, and starts transmission after the guard time TG for transmission switching has elapsed.

[0006] When the transmission is completed, the semiconductor laser 2 is switched to the reception mode, and the transmission delay time TD until the light transmitted by itself reaches the other party, the guard time TG for switching the transmission of the other party, and the light transmitted by the other party are The reception starts after the transmission delay time TD until the message reaches the user. When reception is completed, transmission starts again after the guard time TG has elapsed.

[0007] In this way, the semiconductor laser 2 and the semiconductor laser 4 repeat transmission and reception in a time-division manner. The cycle of this repetition, that is, one burst time TB, is TB = 2TI + 2TD + 2TG, where TI is the transmission time of the semiconductor lasers 2 and 4, that is, the information transmission time.

[0008]

[Problem to be Solved by the Invention] In such a system, if normal operation is not performed, the optical transceiver constituted by the transmitter/receiver switching circuit 1 and the semiconductor laser 2, the semiconductor laser 4, and the transmitter/receiver an optical transceiver configured with a switching circuit 5 or an optical fiber transmission line 3;
To find out which of these is the cause, a method is needed to test each of them. In this specification, optical transceivers are tested.

[0009] In general transmission systems, a loopback test method is used to test a transmission device, in which a signal supplied from a terminal or other information supply source is transmitted and simultaneously received. However, in the single-element TCM system, since transmission and reception are performed using the same element, it is not possible to perform transmission and reception at the same time, making it impossible to perform loopback tests on optical transceivers.

SUMMARY OF THE INVENTION An object of the present invention is to provide a loopback test method suitable for a single-element type TCM type optical transceiver using a semiconductor laser as a transmitting element and a receiving element.

[0011]

[Means for Solving the Problems] In the loopback test method of the present invention, a light-receiving element is arranged close to the end face of the semiconductor laser opposite to the transmitting end, and the light-receiving element is used to connect the semiconductor laser to the light-receiving element side. It is characterized by detecting emitted light.

The present invention is suitable for loopback testing of optical transceivers used in single-element TCM systems, but can also be used in other systems, such as when a semiconductor laser is used exclusively for transmission.

[0013]

[Operation] Semiconductor lasers are generally used to emit light in one direction, but in reality, light is emitted in the opposite direction as well. Therefore, the semiconductor laser is driven so as to obtain light modulated with a test signal, and the test signal light emitted at that time in the opposite direction to the transmission direction is detected. This method enables loopback testing from the terminal side even for single-element type optical transceivers used in the TCM system.

Detection of light emitted in the opposite direction from a semiconductor laser has been conventionally performed for the purpose of automatic power adjustment. Furthermore, devices in which a semiconductor laser and a photodiode are integrated are also commercially available. The present invention utilizes such an element to test optical transceiver operations such as modulation and transmission rather than power adjustment.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an example of the circuit structure of an optical transceiver for carrying out the present invention.

This optical transceiver includes a test signal generation circuit 11 that generates a loopback test signal, a semiconductor laser 13 for transmission only or for both transmission and reception, whose transmission end is connected to an optical fiber transmission line 20, and a terminal device and other components. a drive circuit 12 that drives the semiconductor laser 13 in accordance with a signal supplied from an information supply source or a test signal generation circuit 11; and a light receiving element 14 disposed close to the end surface of the semiconductor laser 13 opposite to the transmitting end. , and a receiving circuit 15 that receives the signal detected by the light receiving element 14.

During normal operation, a signal from a terminal device or other information supply source is supplied to the drive circuit 12, the semiconductor laser 13 is driven by the signal, and an optical signal is sent to the optical fiber transmission line 20. When the semiconductor laser 13 is used for both transmission and reception, the bias supplied from the drive circuit 12 to the semiconductor laser 13 is set to zero, for example, during reception. As a result, the semiconductor laser 13 enters the reception mode and can receive the optical signal from the optical fiber transmission line 20. The received signal is sent to a terminal device or other information supply destination device via a receiving circuit (not shown).

At the time of testing, a test signal is supplied from the test signal generation circuit 11 to the drive circuit 12. The drive circuit 12 drives the semiconductor laser 13 using this test signal to generate a test optical signal. This optical signal is also emitted to the side opposite to the transmission end of the semiconductor laser 13. This light is detected by the light receiving element 14 and output to the receiving circuit 15. In this way, the test signal generated by the test signal generation circuit 11 is transmitted to the drive circuit 12.
, the semiconductor laser 13, the light receiving element 14, and the receiving circuit 15 are looped back in this order. Thereby, it is possible to determine whether these parts are normal or abnormal based on the signal obtained by the receiving circuit 15.

FIG. 2 is a block diagram showing another example of the circuit configuration of an optical transceiver.

In this example, the optical transceiver includes a control circuit 16 for controlling generation and stop of a test signal, and a switch 17 for connecting and disconnecting the light receiving element 14 and the receiving circuit 15 under the control of the control circuit 16. Equipped with.

In this case as well, the test signal generated by the test signal generation circuit 11 is transmitted to the drive circuit 12,
The semiconductor laser 13, the light receiving element 14, and the receiving circuit 15 are looped back in this order, and whether these parts are normal or abnormal can be determined based on the signal obtained by the receiving circuit 15.

The switch 17 connects the light receiving element 14 and the receiving circuit 15 during a loopback test, but disconnects the light receiving element 14 and the receiving circuit 15 during normal communication. At this time, the output of the light receiving element 14 can also be used for other purposes, such as automatic power adjustment.

FIG. 3 shows the flow of test signals when a loopback signal is generated from a terminal device.

In the above-described example, a test signal was generated within the optical transceiver to perform the test. On the other hand, in the example shown in FIG.
The signal is supplied to the optical transceiver 10 via. At this time, the optical transceiver 10 loops back the test signal and returns the reception result to the terminal device 21. In addition, the terminal device 21
It is also possible to use the station equipment instead of the station equipment and perform a loopback test of the route from the equipment installed at the office to the optical transceiver and back to the office equipment.

FIGS. 4 and 5 show an example of a configuration in which the present invention is implemented in an optical transceiver other than a one-element type.

The example shown in FIG. 4 shows a method for testing an optical transceiver in the case of transmission using two optical fiber transmission lines 20-1 and 20-2. In this case, the semiconductor laser 1
Reference numeral 3 is for transmission only, and a light receiving element 14 is disposed close to the end surface of the semiconductor laser 13 opposite to the transmitting end.
Detects light emitted to the side. Further, for reception, a light receiving element 18 different from the light receiving element 14 is used.

The example shown in FIG. 5 shows a test method when bidirectional transmission is performed using the optical coupler 19. That is, the semiconductor laser 13 for transmission and the light receiving element 18 for reception are connected to the optical fiber transmission line 20 via the optical coupler 19. A light receiving element 14 is arranged on the side opposite to the transmitting end of the semiconductor laser 13 in close proximity to the end face thereof, and the light receiving element 14 detects the light emitted from the semiconductor laser 13 toward the light receiving element 14 side.

[0028]

As explained above, the loopback test method of the present invention can be applied to optical transceivers using semiconductor lasers, especially for single-element type optical transceivers that use semiconductor lasers as both transmitting elements and receiving elements in a time-sharing manner. The operation of optical transceivers used in split direction control transmission systems can be tested. By establishing a test method in this way, economical operation of optical transceivers becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram showing an example of the circuit configuration of an optical transceiver for implementing the present invention.

FIG. 2 is a block configuration diagram showing another example of the circuit configuration of an optical transceiver.

FIG. 3 is a diagram showing the flow of a test signal when a loopback test signal is generated from a terminal device.

FIG. 4 is a block configuration diagram illustrating an example of a configuration in which the present invention is implemented in an optical transceiver other than a single-element type.

FIG. 5 is a block configuration diagram showing another example of a configuration in which the present invention is implemented in an optical transceiver other than a one-element type.

FIG. 6 is a block configuration diagram showing a basic configuration example of a one-element TCM system.

FIG. 7 is a diagram showing a general frame structure used in this method.

[Explanation of symbols]

1, 5 Transmission/reception switching circuit 2, 4, 13 Semiconductor laser 3, 20 Optical fiber transmission line 10 Optical transceiver 11 Test signal generation circuit 12 Drive circuit 14, 18 Photo receiving element 15 Receiving circuit 16 Control circuit 17 Switch 21 Terminal device 22 Connection line

Claims (1)

[Claims] 1. An optical transceiver loop that drives an optical transceiver equipped with a semiconductor laser as a transmitting element with a test signal, detects the optical signal at that time, and determines whether or not the optical transceiver is operating normally. The back test method is characterized in that a light-receiving element is disposed close to an end surface of the semiconductor laser opposite to the transmitting end, and the light-receiving element detects light emitted from the semiconductor laser toward the light-receiving element. Loopback test method for optical transceivers.