CA2027448C - Improvements in optical time domain reflectometers - Google Patents
Improvements in optical time domain reflectometersInfo
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- CA2027448C CA2027448C CA002027448A CA2027448A CA2027448C CA 2027448 C CA2027448 C CA 2027448C CA 002027448 A CA002027448 A CA 002027448A CA 2027448 A CA2027448 A CA 2027448A CA 2027448 C CA2027448 C CA 2027448C
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Abstract
The present invention provides an interchangeable computer card capable of being inserted into a computer to provide signal generation and signal detection necessary to allow the computer to generate data and provide the desired graphic display for testing the integrity of an optical fibre transmission line.
Description
This invention relates to improved apparatus for the testing of optical glass fibre transmission lines. In particular, it relates to a means whereby a conventional computer may be used to test and display the transmission characteristics of an optical glass fibre.
In recent years, substantial advances have been made in the technology whereby signals and information may be transmitted by coded light source signals carried in optical glass fibres in a manner analogous to the transmission of electrical signals through a metal wire.
The practical and commercial application of this technology to communications and transmission involves a large number and vast lengths of optical glass fibre conductors.
As with other transmission lines, the effectiveness and efficiency of these lines depends on their ability to carry a signal without substantial losses due to imperfections and poor connections, etc. Because of their small size and enormous footage, direct visual and manual inspection is not possible.
Therefore, devices, known as optical time domain reflectometers, have been developed to test optical fibre transmission lines and, in particular, to locate areas where transmission is substantially interrupted or interfered with by impurities, imperfections, poor connections or breaks.
These devices, referred to hereinafter as OTDRs, are based on the technology whereby a light signal or pulse, usually from a laser source, is sent down the fibre to be tested and the reflected signals, known as Rayleigh backscatter or Fresnel reflection, travelling in the reverse direction towards the original source, is detected and evaluated.
. _ _ _1_ The evaluation of the backscatter takes many sophisticated forms but has two basic characteristics. First of all, if the forward signal is a brief pulse then the Rayleigh backscatter signal received at the transmission end of the fibre will correspond as a function of time to the distance along the fibre from which it was reflected. This enables a OTDR to record the distance along the fibre at which a particular backscatter or reflection occurs.
The level of the Rayleigh backscatter signal at a particular point of time or distance along the transmission fibre will give an indication of the power of the forward signal pulse at that distance. Therefore, any substantial diminishing of the return signal will indicate a point at which the strength of the transmission signal is affected.
Modern OTDRs are designed to plot on a screen a graph in which the signal strength is recorded on the vertical scale against time or distance on the horizontal scale.
Typically, a light pulse signal sent down an optical fibre will produce a graph showing a steadily declining signal strength with distance. However, any imperfection or break in the line, or even a connection, will result in a point of high reflection which will show up as a peak on the graph.
Similarly, such a fault will result in a loss of signal power and the graph will show a lower level from the point of the fault onward. Thus, such a device and the display produced by it, will enable a technician to identify the severity of the fault and where it is located in the length of the optical fibre.
In recent years, substantial advances have been made in the technology whereby signals and information may be transmitted by coded light source signals carried in optical glass fibres in a manner analogous to the transmission of electrical signals through a metal wire.
The practical and commercial application of this technology to communications and transmission involves a large number and vast lengths of optical glass fibre conductors.
As with other transmission lines, the effectiveness and efficiency of these lines depends on their ability to carry a signal without substantial losses due to imperfections and poor connections, etc. Because of their small size and enormous footage, direct visual and manual inspection is not possible.
Therefore, devices, known as optical time domain reflectometers, have been developed to test optical fibre transmission lines and, in particular, to locate areas where transmission is substantially interrupted or interfered with by impurities, imperfections, poor connections or breaks.
These devices, referred to hereinafter as OTDRs, are based on the technology whereby a light signal or pulse, usually from a laser source, is sent down the fibre to be tested and the reflected signals, known as Rayleigh backscatter or Fresnel reflection, travelling in the reverse direction towards the original source, is detected and evaluated.
. _ _ _1_ The evaluation of the backscatter takes many sophisticated forms but has two basic characteristics. First of all, if the forward signal is a brief pulse then the Rayleigh backscatter signal received at the transmission end of the fibre will correspond as a function of time to the distance along the fibre from which it was reflected. This enables a OTDR to record the distance along the fibre at which a particular backscatter or reflection occurs.
The level of the Rayleigh backscatter signal at a particular point of time or distance along the transmission fibre will give an indication of the power of the forward signal pulse at that distance. Therefore, any substantial diminishing of the return signal will indicate a point at which the strength of the transmission signal is affected.
Modern OTDRs are designed to plot on a screen a graph in which the signal strength is recorded on the vertical scale against time or distance on the horizontal scale.
Typically, a light pulse signal sent down an optical fibre will produce a graph showing a steadily declining signal strength with distance. However, any imperfection or break in the line, or even a connection, will result in a point of high reflection which will show up as a peak on the graph.
Similarly, such a fault will result in a loss of signal power and the graph will show a lower level from the point of the fault onward. Thus, such a device and the display produced by it, will enable a technician to identify the severity of the fault and where it is located in the length of the optical fibre.
-2-Typical OTDRs which have been in use prior to the present invention are devices dedicated to the sole purpose and application of testing optical fibres. These usually comprise a laser light pulse signal generator, means to connect the light source to the end of an optical fibre, means to detect a reflected signal returning to the transmission end of the fibre, facilities to measure the signal strength and time delay of a returning signal and to convert these into coordinates of signal strength and distance, and means to display this information in graphic form on a screen.
These dedicated devices, however, are expensive to purchase and have no other utility. Furthermore, except in so far as variable features are built into them, they are not capable of being modified to operate in different ways or to produce different results.
It is, therefore, the purpose of the present invention to provide means whereby conventional, modern, available computers, such as PCs or laptops, may be adapted to perform the function of an OTDR.
It is also the purpose of the present invention to make the test results of an OTDR available to anyone with a computer capable of performing the necessary calculations.
Thus, OTDR test equipment may be made available with less expense by utilizing computers which can also be used for other functions. Furthermore, these computers may be user programmed in such a way as to give particular information desired by the operator or to produce results in an individually designed format.
These dedicated devices, however, are expensive to purchase and have no other utility. Furthermore, except in so far as variable features are built into them, they are not capable of being modified to operate in different ways or to produce different results.
It is, therefore, the purpose of the present invention to provide means whereby conventional, modern, available computers, such as PCs or laptops, may be adapted to perform the function of an OTDR.
It is also the purpose of the present invention to make the test results of an OTDR available to anyone with a computer capable of performing the necessary calculations.
Thus, OTDR test equipment may be made available with less expense by utilizing computers which can also be used for other functions. Furthermore, these computers may be user programmed in such a way as to give particular information desired by the operator or to produce results in an individually designed format.
-3-2027448 ' These, and other objects, are achieved by means of the present invention which provides an interchangeable computer card capable of being inserted into a computer to provide the signal generation and the signal detection necessary to allow the computer to generate data and provide the desired graphic display.
Specifically, the card is designed to be interchangeable, in accordance with industry standards, and provides a glass fibre interface, a fibre splitter, a laser for providing a light pulse signal to the fibre splitter, a photo detector and signal sampler for receiving reflected signals from the fibre splitter, a delay generator, a central processing unit, a random access memory connected to said central processing unit, and a control and interface buffer to connect between the interchangeable card and the computer.
The invention may be better understood by reference to the following description of one embodiment thereof with reference to the drawings in which - Figure 1 is a typical graphic display of an OTDR test signal.
- Figure 2 is a schematic block diagram of an OTDR card incorporating the present invention - Figure 3 is a perspective illustration of a typical personal computer having an optical fibre connection and a screen displaying an OTDR test signal.
As previously mentioned, a typical OTDR is designed to provide a graphic display illustrating locations where there is significant interruption of signal transmission and an indication of the location, in terms of distance, along the length of the fibre where this interruption is occurring.
Specifically, the card is designed to be interchangeable, in accordance with industry standards, and provides a glass fibre interface, a fibre splitter, a laser for providing a light pulse signal to the fibre splitter, a photo detector and signal sampler for receiving reflected signals from the fibre splitter, a delay generator, a central processing unit, a random access memory connected to said central processing unit, and a control and interface buffer to connect between the interchangeable card and the computer.
The invention may be better understood by reference to the following description of one embodiment thereof with reference to the drawings in which - Figure 1 is a typical graphic display of an OTDR test signal.
- Figure 2 is a schematic block diagram of an OTDR card incorporating the present invention - Figure 3 is a perspective illustration of a typical personal computer having an optical fibre connection and a screen displaying an OTDR test signal.
As previously mentioned, a typical OTDR is designed to provide a graphic display illustrating locations where there is significant interruption of signal transmission and an indication of the location, in terms of distance, along the length of the fibre where this interruption is occurring.
-4-In the display shown in Figure 1, the vertical axis 2 represents a measure of the strength of the reflected signal received back at the transmission end of the optical fibre. The horizontal axis 4 represents the delay between the transmitted signal pulse and the receipt of the reflected signal. It is also a measure of the distance along the optical fibre at which various return signals are reflected back.
The "curve" represented by line 6 illustrates the strength of the signal which is reflected back from various points along the length of the optical fibre being tested.
The peak 8 represents the reflection from the connection between the OTDR and the fiber under test. The declining line 10 represents the Rayleigh backscatter from a progressively weaker signal as the reflective distance increases. The peak 12 represents a high reflection (Fresnel reflection) at a point of interruption such as a flaw, break or a connection between two fibres. The drop in the curve at 14 represents the diminished.strength of the signal due to the loss of transmission at the flaw or connection 12. As previously mentioned, the strength of the reflected returning signal from any given point is a proportional measure of the strength of the forward transmitted signal at the same point.
Figure 3 represents pictorially a diagram of a personal computer with a housing 16, a keyboard 18, a display screen 20 and a connection for an optical fibre 22.
The computer shown in Figure 3 is typical of many models which are readily available in the market at prices which are substantially below a dedicated OTDR machine and which are constantly being refined at progressively competitive prices. These computers, however, provide only programmable data processing in a convenient package. All such models would have to be modified to allow them to perform OTDR test functions on optical fibres.
2027448 r An embodiment of the hardware, in accordance with the present invention, suitable for adapting a personal computer to the OTDR
capability is illustrated schematically in Figure 2. This hardware will be in the form of a computer expansion card designed in accordance with industry standards to be interchangeably acceptable into a computer.
Having this hardware designed for a standard XT/AT Bus allows maximum flexibility in choosing a host computer and offers the possibility of developing fibre sensor instruments where multiple OTDRs might be needed. With the ability to do signal processing through software on the host computer almost all of the features of OTDRs currently on the market can be realized at a lower price in a more portable package.
In Figure 2, the computer is represented by Block 30. Its capabilities are "expanded" by the expansion card 32 which has an optical fibre interface 34 which is capable of connection to a length of optical fibre (not shown) to be monitored or tested.
The expansion card 32 has a central processing unit (CPU) 36 such as an Intel (TM) 80196. This microprocessor is connected to the computer 30 by a dual port RAM 38 which can be written to and read from by both the host computer 30 and the CPU 36. The CPU software, which runs the OTDR
2 0 expansion card 32, will be downloaded from the host through this interface, which includes control and buffer interface 40 as illustrated. Data acquired by the OTDR card will be transferred through the RAM to the host 30 for processing and displayed on the screen by the system software running on the host.
Ideally, the CPU 36 has the added feature of an on board analog/digital conversion capability with eight multiplexed inputs and a pulse width modulated digital/analog conversion. There may also be three high speed inputs and three high speed outputs which operate independently of the arithmetic logic unit of the CPU.
A separate clock and delay generator 42 are included in the main board of the expansion card to act as a time base for the OTDR hardware.
The delay generator will trigger the sampler at a predetermined time after the laser pulse has been sent to sample the backscatter light level at the equivalent distance down the fibre which is under test. After a set number of samples have been taken at this delay (for analog box-car averaging purposes) the delay generator is advanced to the next incremental desired sample point.
Thus, a series of signals transmitted into the optical fibre will produce backscatter from each point along the length which, by means of the delay generator, will be sampled incrementally in sequence.
The delay generator provides both a coarse and a fine delay.
The coarse delay is achieved through a 18 bit divided-by-n counter which counts clock pulses. The clock runs at 40 MHz, giving a period of 25ns. The coarse delay then has a 25ns increment and a maximum setting of 218 x 25ns =
2 0 6.55ms. The maximum delay gives the maximum distance along the fibre of 655 km which is considered much greater than is needed.
"1;;~~,.~>
a To get delays finer than 25ns, a separate fine delay generator is used. This could be a commercially available 6 bit programmable delay IC
which gives 0.5 ns steps, or, if this is not suitable, a more conventional voltage ramp and comparator circuit can be used. The comparator circuit is given a 25 ns ramp at one input and a voltage from a 6 bit D/A at the other.
The minimum desired incremental delay is 0.5 ns, giving a corresponding distance resolution of 5 cm.
The aforementioned delay generator is used to trigger a sampling gate which is combined with a photo detector as shown at 44 in the schematic block diagram. The desired sampling gate width is 10 ns, complementing the delay generator and the detector and the shortest laser pulse. The sampling gate will feed the input of a boxcar averager which will provide analog averaging.
The photo detector of block 44 contains an avalanche and photodiode amplifiers) such as a Signetics (TM) NE5211 180 MHZ, 28 kilohm transimpedance amplifier and the Signetics (TM) NE592 video amplifier. The combined bandwidth of the detector should be in excess of 100 MHZ with a sensitivity of less than 20 nW.
The signal is generated by a laser 46 which ideally will be 2 0 housed in a standard 14 pin package. Pulsed laser diodes may be used and four different diodes are required: 850 nm multimode, 1310 nm single mode, 1300 nm multimode, and 1550 nm single mode.
The laser pulse width should be selectable through the CPU
depending on the desired accuracy (the lower the accuracy, the larger the 2 5 dynamic range). The laser is triggered by the CPU through one of the high speed outputs allowing the CPU to control all timing.
_g_ A fibre splitter 48 is provided so that the laser signal may be transmitted into the optical fibre and the returning backscatter signal may be received and carried to the sampler/photo detector 44.
As indicated in the schematic block diagram of Figure 2, the expansion card may be provided in two components, a main board which will include the CPU, RAM and host interface, and CPU control bus and circuitry and the delay generator. A sub board may contain the laser, photo detector/
sampler, and fibre splitter.
It is contemplated that software for the CPU will be loaded into the RAM of the OTDR card by the system (host computer) software. The CPU software will be responsible for all data acquisition including timing, pulse width selection, photo detector gain, etc. The system software will provide signal processing (digital averaging, loss measurements, etc), display, storage, hard copy and user interfacing.
Ideally, the system software will ask the OTDR CPU for a specific number of data points over a specific time span, as governed by what the user has asked to look at, what the length of the fibre is and what is the desired accuracy/resolution. The CPU will determine the required incremental delay, the necessary laser pulse width and repetition rate. The 2 0 CPU then presents sequential sets of data to the host computer which the host then uses to update the display and to process as per the user's request.
The following are typical specifications which might be applicable to the exemplary embodiment and suitable for monitoring and testing some optical fibres:
y:
20 27 44 8 , 850 nm Wavelength;
Mode: multi Measurement Range 64 km Resolution O.lOm Pulse Width: 10 /50 /200 /1000 ns Dynamic Range: 19 dB with 1000 ns pulse width 1300 nm Wavelength:
Mode: multi /single Measurement Range: 128 km Resolution 0.20m Pulse Width: 10 /50 /200 /1000 ns Dynamic Range: 13 d8 for multimode with 1000 ns pulsewidth While certain specific specifications have been provided in connection with describing the exemplary embodiment of the present invention, it should be appreciated that these are only explanatory and may be modified, varied, eliminated or added to by those skilled in the art to create the desired test results.
By means of an expansion card, such as that illustrated in Figure 2 and described in greater detail in the forgoing paragraphs, the conventional product of an OTDR dedicated device may be achieved using a commercially available computer, at reasonable cost and with the prospect of using various machines and taking advantage of improvements as they are developed in the general computer market.
It will, of course, be realized that modifications and variations of the improvement described herein may be employed without departing from the inventive concept herein.
The "curve" represented by line 6 illustrates the strength of the signal which is reflected back from various points along the length of the optical fibre being tested.
The peak 8 represents the reflection from the connection between the OTDR and the fiber under test. The declining line 10 represents the Rayleigh backscatter from a progressively weaker signal as the reflective distance increases. The peak 12 represents a high reflection (Fresnel reflection) at a point of interruption such as a flaw, break or a connection between two fibres. The drop in the curve at 14 represents the diminished.strength of the signal due to the loss of transmission at the flaw or connection 12. As previously mentioned, the strength of the reflected returning signal from any given point is a proportional measure of the strength of the forward transmitted signal at the same point.
Figure 3 represents pictorially a diagram of a personal computer with a housing 16, a keyboard 18, a display screen 20 and a connection for an optical fibre 22.
The computer shown in Figure 3 is typical of many models which are readily available in the market at prices which are substantially below a dedicated OTDR machine and which are constantly being refined at progressively competitive prices. These computers, however, provide only programmable data processing in a convenient package. All such models would have to be modified to allow them to perform OTDR test functions on optical fibres.
2027448 r An embodiment of the hardware, in accordance with the present invention, suitable for adapting a personal computer to the OTDR
capability is illustrated schematically in Figure 2. This hardware will be in the form of a computer expansion card designed in accordance with industry standards to be interchangeably acceptable into a computer.
Having this hardware designed for a standard XT/AT Bus allows maximum flexibility in choosing a host computer and offers the possibility of developing fibre sensor instruments where multiple OTDRs might be needed. With the ability to do signal processing through software on the host computer almost all of the features of OTDRs currently on the market can be realized at a lower price in a more portable package.
In Figure 2, the computer is represented by Block 30. Its capabilities are "expanded" by the expansion card 32 which has an optical fibre interface 34 which is capable of connection to a length of optical fibre (not shown) to be monitored or tested.
The expansion card 32 has a central processing unit (CPU) 36 such as an Intel (TM) 80196. This microprocessor is connected to the computer 30 by a dual port RAM 38 which can be written to and read from by both the host computer 30 and the CPU 36. The CPU software, which runs the OTDR
2 0 expansion card 32, will be downloaded from the host through this interface, which includes control and buffer interface 40 as illustrated. Data acquired by the OTDR card will be transferred through the RAM to the host 30 for processing and displayed on the screen by the system software running on the host.
Ideally, the CPU 36 has the added feature of an on board analog/digital conversion capability with eight multiplexed inputs and a pulse width modulated digital/analog conversion. There may also be three high speed inputs and three high speed outputs which operate independently of the arithmetic logic unit of the CPU.
A separate clock and delay generator 42 are included in the main board of the expansion card to act as a time base for the OTDR hardware.
The delay generator will trigger the sampler at a predetermined time after the laser pulse has been sent to sample the backscatter light level at the equivalent distance down the fibre which is under test. After a set number of samples have been taken at this delay (for analog box-car averaging purposes) the delay generator is advanced to the next incremental desired sample point.
Thus, a series of signals transmitted into the optical fibre will produce backscatter from each point along the length which, by means of the delay generator, will be sampled incrementally in sequence.
The delay generator provides both a coarse and a fine delay.
The coarse delay is achieved through a 18 bit divided-by-n counter which counts clock pulses. The clock runs at 40 MHz, giving a period of 25ns. The coarse delay then has a 25ns increment and a maximum setting of 218 x 25ns =
2 0 6.55ms. The maximum delay gives the maximum distance along the fibre of 655 km which is considered much greater than is needed.
"1;;~~,.~>
a To get delays finer than 25ns, a separate fine delay generator is used. This could be a commercially available 6 bit programmable delay IC
which gives 0.5 ns steps, or, if this is not suitable, a more conventional voltage ramp and comparator circuit can be used. The comparator circuit is given a 25 ns ramp at one input and a voltage from a 6 bit D/A at the other.
The minimum desired incremental delay is 0.5 ns, giving a corresponding distance resolution of 5 cm.
The aforementioned delay generator is used to trigger a sampling gate which is combined with a photo detector as shown at 44 in the schematic block diagram. The desired sampling gate width is 10 ns, complementing the delay generator and the detector and the shortest laser pulse. The sampling gate will feed the input of a boxcar averager which will provide analog averaging.
The photo detector of block 44 contains an avalanche and photodiode amplifiers) such as a Signetics (TM) NE5211 180 MHZ, 28 kilohm transimpedance amplifier and the Signetics (TM) NE592 video amplifier. The combined bandwidth of the detector should be in excess of 100 MHZ with a sensitivity of less than 20 nW.
The signal is generated by a laser 46 which ideally will be 2 0 housed in a standard 14 pin package. Pulsed laser diodes may be used and four different diodes are required: 850 nm multimode, 1310 nm single mode, 1300 nm multimode, and 1550 nm single mode.
The laser pulse width should be selectable through the CPU
depending on the desired accuracy (the lower the accuracy, the larger the 2 5 dynamic range). The laser is triggered by the CPU through one of the high speed outputs allowing the CPU to control all timing.
_g_ A fibre splitter 48 is provided so that the laser signal may be transmitted into the optical fibre and the returning backscatter signal may be received and carried to the sampler/photo detector 44.
As indicated in the schematic block diagram of Figure 2, the expansion card may be provided in two components, a main board which will include the CPU, RAM and host interface, and CPU control bus and circuitry and the delay generator. A sub board may contain the laser, photo detector/
sampler, and fibre splitter.
It is contemplated that software for the CPU will be loaded into the RAM of the OTDR card by the system (host computer) software. The CPU software will be responsible for all data acquisition including timing, pulse width selection, photo detector gain, etc. The system software will provide signal processing (digital averaging, loss measurements, etc), display, storage, hard copy and user interfacing.
Ideally, the system software will ask the OTDR CPU for a specific number of data points over a specific time span, as governed by what the user has asked to look at, what the length of the fibre is and what is the desired accuracy/resolution. The CPU will determine the required incremental delay, the necessary laser pulse width and repetition rate. The 2 0 CPU then presents sequential sets of data to the host computer which the host then uses to update the display and to process as per the user's request.
The following are typical specifications which might be applicable to the exemplary embodiment and suitable for monitoring and testing some optical fibres:
y:
20 27 44 8 , 850 nm Wavelength;
Mode: multi Measurement Range 64 km Resolution O.lOm Pulse Width: 10 /50 /200 /1000 ns Dynamic Range: 19 dB with 1000 ns pulse width 1300 nm Wavelength:
Mode: multi /single Measurement Range: 128 km Resolution 0.20m Pulse Width: 10 /50 /200 /1000 ns Dynamic Range: 13 d8 for multimode with 1000 ns pulsewidth While certain specific specifications have been provided in connection with describing the exemplary embodiment of the present invention, it should be appreciated that these are only explanatory and may be modified, varied, eliminated or added to by those skilled in the art to create the desired test results.
By means of an expansion card, such as that illustrated in Figure 2 and described in greater detail in the forgoing paragraphs, the conventional product of an OTDR dedicated device may be achieved using a commercially available computer, at reasonable cost and with the prospect of using various machines and taking advantage of improvements as they are developed in the general computer market.
It will, of course, be realized that modifications and variations of the improvement described herein may be employed without departing from the inventive concept herein.
Claims (20)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A device for adapting a host computer having a host processing means, a host memory means, and a display means to function as an optical time domain reflectometer for evaluating the transmission characteristic of an optical fibre line, the device comprising:
(a) a central processing unit (CPU) for receiving programming information communicated from the host computer, the CPU
being operable in response to the programming information;
(b) computer interface means for enabling communication between the host computer and the CPU;
(c) fibre interface means for enabling optical transmission between the device and the optical fibre line;
(d) a light generator controlled by the CPU for transmitting a light signal to the optical fibre line via the fibre interface means; and (e) a signal detector controlled by the CPU for receiving and detecting a returning light signal from the optical fibre line via the fibre interface means;
(f) wherein the device is incorporated on a computer card, the computer card being designed to be interchangeably acceptable to the host computer in accordance with computer industry standards.
(a) a central processing unit (CPU) for receiving programming information communicated from the host computer, the CPU
being operable in response to the programming information;
(b) computer interface means for enabling communication between the host computer and the CPU;
(c) fibre interface means for enabling optical transmission between the device and the optical fibre line;
(d) a light generator controlled by the CPU for transmitting a light signal to the optical fibre line via the fibre interface means; and (e) a signal detector controlled by the CPU for receiving and detecting a returning light signal from the optical fibre line via the fibre interface means;
(f) wherein the device is incorporated on a computer card, the computer card being designed to be interchangeably acceptable to the host computer in accordance with computer industry standards.
2. A device as claimed in claim 1 in which the light generator transmits the light signal in response to a trigger signal output by the CPU.
3. A device as claimed in claim 2 in which the signal detector detects the returning light signal in response to a delayed trigger signal.
4. A device as claimed in claim 3 in which the light generation means comprises a laser.
5. A device as claimed in claim 3 in which the detection means comprises - a photodetector for receiving the returning light signal and providing an electrical signal in response; and - sampling means operative in response to the delayed trigger signal for sampling the electrical signal to provide detection data.
6. A device as claimed in claim 3 further comprising a delay generator controlled by the CPU for receiving the trigger signal, delaying the trigger signal by a delay period, and providing the delayed triggered signal in response.
7. A device as claimed in claim 3 in which the computer interface means includes connection means for connecting the host computer to the CPU, a control and interface buffer, and card memory means.
8. A device as claimed in claim 3 in which the fibre interface means comprises a fibre splitter permitting the light generator to transmit the light signal to the optical fibre line and the signal detector to receive and detect the returning light signal from the optical fibre line.
9. A device as claimed in claim 5 further comprising means for storing the detection data.
10. A device as claimed in claim 6 in which the detection data is communicated to the host computer via the computer interface means and processed by the host computer to enable evaluation of the transmission characteristic of the optical fibre line.
11. A device as claimed in claim 10 in which the host computer graphically displays the transmission characteristic of the optical fibre line on the display means of the host computer.
12. A device as claimed in claim 6 wherein the light signal comprises a pulse signal having a pulse width which is controlled by the CPU.
13. A device as claimed in claim 12 wherein the delay period is controlled by the CPU to enable evaluation of different portions of the optical fibre line.
14. A device as claimed in claim 13 wherein the host computer enables a user of the host computer to determine the programming information, including the pulse width of the light signal and the delay period, thereby allowing user-specific evaluations of the transmission characteristic of the optical fibre line.
15. A method of adapting a host computer having a host processing means, a host memory means, and a display means to function as an optical time domain reflectometer for evaluating the transmission characteristic of an optical fibre line, said method comprising the steps of:
(a) coupling a computer expansion card having a card CPU, a computer interface means, a light generator, a fibre interface means, and a signal detector to the host computer, the card being designed to meet computer industry standards;
(b) communicating programming information via the computer interface means from the host computer to the card CPU;
(c) controlling the light generator to generate a light signal and transmit the light signal via the fibre interface means to an optical fibre line; and (d) controlling the signal detector to receive and detect a returning light signal from the optical fibre line via the fibre interface means.
(a) coupling a computer expansion card having a card CPU, a computer interface means, a light generator, a fibre interface means, and a signal detector to the host computer, the card being designed to meet computer industry standards;
(b) communicating programming information via the computer interface means from the host computer to the card CPU;
(c) controlling the light generator to generate a light signal and transmit the light signal via the fibre interface means to an optical fibre line; and (d) controlling the signal detector to receive and detect a returning light signal from the optical fibre line via the fibre interface means.
16. A method as claimed in claim 15 further comprising the steps of:
(e) generating detection data from the returning light signal;
(f) communicating the detection data via the computer interface means to the host computer; and (g) processing the detection data in the host computer to evaluate the transmission characteristic of the optical fibre line.
(e) generating detection data from the returning light signal;
(f) communicating the detection data via the computer interface means to the host computer; and (g) processing the detection data in the host computer to evaluate the transmission characteristic of the optical fibre line.
17. A method as claimed in claim 16 further comprising the step of:
(h) graphically displaying the transmission characteristic of the optical fibre line on the display means of the host computer.
(h) graphically displaying the transmission characteristic of the optical fibre line on the display means of the host computer.
18. A method as claimed in claim 15 in which step (c) comprises using a trigger signal output by the card CPU to control the light generator.
19. A method as claimed in claim 18 in which step (d) comprises using a delayed trigger signal to control the signal detector.
20. A method as claimed in claim 15 in which the programming information is determined by a user of the host computer, allowing user-specific evaluations of the transmission characteristic of the optical fibre line.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002027448A CA2027448C (en) | 1990-10-12 | 1990-10-12 | Improvements in optical time domain reflectometers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002027448A CA2027448C (en) | 1990-10-12 | 1990-10-12 | Improvements in optical time domain reflectometers |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2027448A1 CA2027448A1 (en) | 1992-04-13 |
| CA2027448C true CA2027448C (en) | 1999-09-07 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002027448A Expired - Fee Related CA2027448C (en) | 1990-10-12 | 1990-10-12 | Improvements in optical time domain reflectometers |
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| Country | Link |
|---|---|
| CA (1) | CA2027448C (en) |
-
1990
- 1990-10-12 CA CA002027448A patent/CA2027448C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2027448A1 (en) | 1992-04-13 |
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