GB2131247A

GB2131247A - Test equipment for testing an optical fibre transmission system

Info

Publication number: GB2131247A
Application number: GB8330332A
Authority: GB
Inventors: Dr Jens Weber
Original assignee: Krone GmbH
Current assignee: ADC GmbH
Priority date: 1982-11-13
Filing date: 1983-11-14
Publication date: 1984-06-13
Also published as: SE8306221D0; DE3335674A1; DE3335674C2; FR2536228A1; FR2536228B1; IN159452B; GB8330332D0; GB2131247B; SE8306221L; CA1208815A

Abstract

A test equipment for testing an optical fibre transmission system in which at the transmitting location a laser transmitter 1 is caused to transmit a synchronizing signal by operation of a key switch 2 but only when no data is being transmitted. At the remote location of the transmission line the synchronizing signal is detected and as a result a logic signal is outputted which may be displayed by light emitting diode. The logic signal can be transmitted by means of a stand-by circuit on a further wavelength in a reserve channel of a multi-channel signal to the location at which the test has been initiated. <IMAGE>

Description

SPECIFICATION Test equipment for testing an optical fibre transmission system This invention relates to test equipment for testing the operation of an optical fibre information transmission system which includes a high frequencytransmitter, an electroloptical converter which receives the signals from the transmitter and converts the signals into light signals for transmission along an optical fibre cable, an opto/electrical converter which receives the light signals and a high frequency receiver responsive to the electrical signals provided by said optoJelectrical converter.

The employment of wavelength multiplex operated optical fibre communication lines in subscriber stations requires increasing complicated measuring and checking techniques to detect precisely the function of each communication line.

Maintenance staff should have the ability to perform a quick check of the function of the optical transmission path and the transmitted wavelength.

Therefore it is an object of the invention to provide test equipment which allows an assessment of the function of each communication line corresponding to each ofthe transmitted wavelengths on an optical subscriber line which is operated in wavelength multiplex.

According to the invention test equipmentforthe purpose specified comprises a key switch operable to initiate operation of the electroloptical converter only when no information is being transmitted, and means in the high frequency transmitter for generating a continuous synchronising signal which is converted in the electroloptical converter, and means in the high frequency receiverfor detecting said synchronising signal.

The function test of each ofthe transmission lines being allocated to an optical wavelength is carried out by pushing a corresponding key switch (at the transmitter station) and is terminated by the release of the key switch.

An embodiment ofthe invention will be described with reference to the accompanying diagrams in which Figure 1 shows the components at the sending end ofthe transmission line, Figure 2 shows the component at the receiving end ofthetransmission line, and Figure 3 the components at one end of a transmission line.

In Figure 1 there is shown the equipment at the sending end of a transmission line. The equipment includes an electroloptical converter conveniently a lasertransmitter 1 which converts electrical signals into light signals for transmission along an optical fibre transmission line. Signals are supplied to the transmitterthrough a pair oftransmission lines 4,5 from a high frequency transmitter 7, the signals carried by the line 4 being data signals (D) and those carried by the line 5 being bittiming signals (BT).

Associated with the laser transmitter is a key switch 2 which when certain conditions are fulfilled can transmit to the high frequencytransmitter7 along a cabe 6, a logic signal "TEST".

The "TEST" signal is only transmitted when it has been established that no data is being transmitted along the optical fibre and this is conveniently determined by sensing the threshold current of the laser forming part of the transmitter 1. In this respect it is pointed outthat the system is ofthe type which has a standbyfacilitywherebynon essential components of the system are turned off when no data is being transmitted. The "TEST" signal is therefore only generated when the key switch is operated and no data is being transmitted. An RS flip flop can be utilized in the generation of the "TEST" signal and convenientlyan "OR" output is included in the circuit for generating the "TEST" signal so thatthe function ofthe key switch can be effected in other ways.An indication ofthe initiation oftesting can be effected by a suitable indicatorfor example an LED not shown.

The logic signal "TEST" performs two functions the first of which is to switch the high frequencytransmit- ter7 to the ready state which is achieved through the input c/a. The second function which is achieved through the input DS isto cause the high frequency transmitterto generate a continuous synchronizing signal. The output of data signals bythetransmitter7 is prevented as long as the continuous synchronizing signal is being generated. Transmission ofthe synchronizing signal means that in the whole time multiplexframewhich is generated in the transmitter 7 each time position is covered with a synchronizing word.

Atthe receiving end oftheopticalfibretransmission line and as shown in Figure 2there is provided an opto/electrical converter 10which suppliesthedata and bit timing signals to a high frequencyreceiveror series/parallel converter 11. The converter is also able to identify the aforesaid continuous synchronizing signal and when so identified a logic signal "DSE" is generated. The output of the portion of the circuit of the receiver which generates the "DSE" signal is provided with an "OR" element and is connected to a junction point 8 along with the outputs of similar apparatus from transmission lines operating on differentfrequencies.

The logic signal "DSE" is supplied to a stand-by circuit 9 which is allocated to the line with the wavelength A4. Upon application ofthe "DSE"-signal the highfrequencytransmitter7 is switched on by the output e/a of the stand-by circuit 9. In this state the high frequency transmitter7 generates a time-multi plex4rame beginning with a synchronizing block. A PCM multi-channel system (in this embodiment a PCM system with 30 channels (PCM 30) is inserted by the standby circuit 9 through the multiplex device 13 to the time-multiplex-frame. For the time duration of the test the stand-by circuit 9 files the "DSE"-signal in a 8 kbit's-channel ofthe PCM-30 which is reserved for the "DSE"-transmission.The serially supplied data stream D ofthe high frequency transmitter7 which includes also the "DSE"-signal is supplied together with the bit timing signal BTtothe electro-optical converter or lasertransmitter 1.

The test ("forward test") can also be initiated directly at the laser transmitter 1 in the above described manner by operating a key switch 2 which is allocated to the laser transmitter 1. If the test is initiated by the key switch 2 the time frame which is transmitted on the transmission line with the wavelengthA4isfilled uninterruptedwith synchronizing words.

As it is shown in Figure 3 the transmitted information is received by the electro-optical converter 10a and further processed in the following serial/parallelconverter 11. If the transmitted information includes the "DSE"-signal in an 8 kbit/s-channel of a PCM-30system the "DSE"-signal is detected by the multiplex devices 13 and 14 and displayed by a LED 3a. If otherwise the received information consists of synchronizing words the "DSE"-signal is directly detected in the serial/parallel-converter 11 and also can be displayed by a LED.

Figure 3 shows furtherthatthe "DSE"-signal also can be fed in an 8 kbit/s-channel of a PCM-30-system which is transmitted thereupon by the lasertransmitter 1 with the wavelength A1. To this the components: stand-by circuit 9, multiplexer 13 and the high frequencytransmitter7 serve in a manner which has been explained with reference to Figure 2.

The invention offers the possibility of a simple test ofthe operation of the essential parts of a transmission line.

Thereby the transmission of an information consist ing ofsynchronwords is effected at the transmitting station by a key switch using an interlocking device which allows the initiation of the laser transmitter only during the time which is free of services. At the remote location of a transmission line this information is detected and outputted as the logic signal "DSE" and this event is displayed by a LED.

By means of a stand-by circuit 9 the "DSE"-signal can be transmitted back to the location at which the test is initiated by a further wavelength in a reserved channel ofthe multi-channel system.

Claims

1. Test equipmentfortesting the operation of an optical fibre information transmission system which includes a high frequency transmitter, an electro/ optical converterwhich receives the signals from the transmitter and converts the signals into light signals for transmission along an optical fibre cable, an opto/electrical converter which receives the light signals and a highfrequency receiver responsiveto the electrical signals provided by said opto/electrical convertercharacterised by a key switch operable to initiate operation ofthe electro/optical converter only when no information is being transmitted, and means in the high frequencytransmitterfor generating a continuous synchronizing signal which is converted in the electro/optical converter and means in the high frequency receiverfordetecting said synchronizing signal.

2. Equipment according to Claim 1 in which the detection of said synchronizing signal results in the generation of a logic signal which is transmitted in the reverse direction within a channel ofthetransmission system.

3. Test equipment according to Claim 1 or Claim 2 characterised in thatthe electro/optical converter is a Iasertransmitterthethreshold currentthereof serving as a criterium for the operational state thereof.

4. Test equipment according to Claim 2 or Claim 3, characterised in that the output of a signal ("TEST") which is released bythe key switch and the presence ofthe logic signal ("DSE") is displayed by light emitting diodes.

5. Test equipment according to any one ofthe preceding claims, characterised in thatthe high frequency receiver comprises a permanent-synchronizing-word-detection ("DSE").

6. Testequipmentforthe purpose specified comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying circuit diagrams.