Optical time domain reflection system and method

Abstract

The invention relates to optical time domain reflectometry systems and methods. In systems and methods of optical time domain reflection, a laser source outputs laser pulses to an optical fiber. The processor samples a backscattered signal generated by the optical fiber in response to the laser pulse. Upon determining from the sample that the backscattered signal has an amplitude that follows the element of the receiver being in a saturated operating state, the processor reduces an amplitude of a subsequent sample of the backscattered signal output by the receiver to within an unsaturated operating state of the element of the receiver. Thereafter, when it is determined from subsequent samples of the backscattered signal that the backscattered signal does not have (or no longer has) an amplitude at which the elements of the receiver will be in a saturated state, the processor increases the amplitude of the samples of the backscattered signal output by the receiver for sampling by the processor.

Description

Technical Field

[0001] The present disclosure relates to systems and methods for Optical Time-Domain Reflectometry. Background Art

[0002] The optical time domain reflectometer is a precision optoelectronic integrated instrument that uses the backscatter signal generated by Rayleigh scattering and Fresnel reflection when light is transmitted in an optical fiber. It is widely used in the detection, maintenance and construction of optical cable lines. Fiber length, fiber transmission attenuation, joint attenuation and fault location can be measured. It has the advantages of short test time, fast test speed and high test accuracy.

[0003] As optical time domain reflectometry develops to a higher dynamic range and a larger detection distance, high-power pulsed lasers are widely used. During the transmission process, the intensity of light generated by Fresnel reflection is about 30dB higher than the intensity of light scattered by Rayleigh, and the reflected echo signal of the high-power pulsed laser will cause pulse saturation of the photodetector. It takes time for the photodetector to return to a normal state from a saturated state and respond to the optical signal again. The saturation duration of the detector increases with the increase of the incident pulse power. During the detector recovery period, the optical time domain reflectometer (OTDR) cannot accurately detect the optical signal, and a blind spot appears in the test results. In addition, when the input signal is large enough, the level of the detector circuit unit and / or the analog / digital converter (ADC) will become oversaturated, resulting in a low signal-to-noise ratio of the circuit and an overshoot of the step signal response, resulting in a large number of nonlinear signals. Therefore, there is significant signal distortion on the OTDR curve. These limit the measurement range of the OTDR.

[0004] In order to improve the measurement accuracy, a conventional method is to subdivide the resistance value of the transconductance resistor. The photocurrent output of the photodetector is converted from the transconductance resistor to a single terminal voltage signal. Different transconductance gains can be selected according to different photocurrent sizes. However, because the light intensity generated by Fresnel reflection during transmission is about 30dB higher than the light intensity of Rayleigh scattering, the input of the input ADC is easily saturated. And too large a gain will also make the measurement time too long.

[0005] To improve the measurement accuracy, another method is to add a dead zone eliminator (also called a launch fiber) between the OTDR and the fiber under test to avoid the OTDR optical outlet dead zone, and then measure the joint loss and connector loss of the fiber under test, so the length of the launch fiber should be greater than the attenuation dead zone. The disadvantage is that the length of the launch fiber will vary with the width of the light pulse and the dissipation time of the photogenerated carriers of the photodetector. If the length of the launch fiber is inappropriate, the test results will be inaccurate and the measurement range will be affected. In addition, the launch fiber can only solve the problem of the dead zone at the OTDR output port, but cannot solve the problem of the dead zone at other locations. Summary of the invention

[0006] An optical time domain reflectometry method is disclosed, comprising: (a) outputting a laser pulse to an optical fiber by a laser source of an optical time domain reflectometer (OTDR); (b) acquiring, by a processor of the OTDR, a sample of a backscattered signal generated by the optical fiber in response to the laser pulse of step (a) from a receiver of the OTDR; (c) determining, by the processor, that at least one element of the receiver is in a saturated operating state based on one or more values ​​of the samples sampled in step (b); (d) in response to step (c), controlling, by the processor, the receiver so that the value of the sample of the backscattered signal sampled by the processor is reduced to within an unsaturated operating state of the at least one element of the receiver; (e) determining, by the processor, based on one or more values ​​of the sample of the backscattered signal sampled after step (d), that if the value of the sample of the backscattered signal sampled by the processor is increased, the at least one element of the receiver will not operate in a saturated operating state; and (f) in response to step (e), controlling, by the processor, the receiver to increase the value of the sample of the backscattered signal sampled by the processor.

[0007] An optical time domain reflectometer (OTDR) is also disclosed, comprising: a laser source, operable to output laser pulses to an optical fiber via a pulse generator under the control of a processor; a receiver, for receiving a backscattered signal generated by the optical fiber in response to the laser pulse output to the optical fiber, wherein the processor is programmed or configured to: (a) determine that at least one element of the receiver is operating in a saturated operating state based on one or more values ​​of a sample of the received backscattered signal; (b) in response to the determination in step (a), control the receiver to reduce one or more values ​​of the sample of the received backscattered signal sampled after step (a), so that the at least one element of the receiver operates in an unsaturated operating state; (c) determine that if the value of the sample of the backscattered signal increases, the at least one element of the receiver will not operate in a saturated operating state based on one or more values ​​of the sample of the received backscattered signal sampled after step (b); and (d) in response to step (c), control the receiver to increase one or more values ​​of the sample of the backscattered signal sampled after step (c).

[0008] Finally, an optical time domain reflectometer (OTDR) is disclosed, comprising: a component for outputting a laser pulse to an optical fiber; a component for receiving an optical backscatter signal generated by the optical fiber in response to the laser pulse output to the optical fiber; a component for determining that at least one element of the receiving component is operating in a saturated state based on the value of a sample of the received optical backscatter signal; and a component for controlling the receiving component to reduce the value of the sample of the optical backscatter signal received by the determining component so that the at least one element of the receiving component operates in an unsaturated state, wherein: the determining component determines that if the value of the sample increases, the at least one element of the receiving component will not operate in a saturated state based on the value of the sample of the optical backscatter signal acquired after reducing the value of the sample; and the determining component controls the receiving component to increase the value of the sample of the optical backscatter signal acquired after the determining component determines that if the value of the sample increases, the at least one element of the receiving component will not operate in a saturated state. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic diagram of an example OTDR according to the principles of the present disclosure, the example OTDR including a transimpedance amplifier (TIA) for performing dynamic transresistance switching on a backscattered signal generated by Rayleigh scattering and Fresnel reflection;

[0010] Figure 2 is a schematic diagram of an example OTDR according to the principles of the present disclosure, the example OTDR including an avalanche photodiode (APD) for performing dynamic gain switching on a backscattered signal generated by Rayleigh scattering and Fresnel reflection;

[0011] Figure 3 is a schematic diagram of an example OTDR according to the principles of the present disclosure, the example OTDR including a variable optical attenuator (VOA) for performing dynamic power adjustment on a backscattered signal generated by Rayleigh scattering and Fresnel reflection; and

[0012] Figure 4 is a method according to the principles of the present disclosure. DETAILED DESCRIPTION

[0013] As used herein, spatial or directional terms, such as "left," "right," "inside," "outside," "upper," "lower," and the like, relate to the present disclosure as it is shown in the accompanying drawings. However, it will be understood that the present disclosure may assume various alternative orientations and, therefore, such terms are not to be considered limiting. Furthermore, as used herein, all numbers expressing dimensions, physical properties, processing parameters, amounts of ingredients, reaction conditions, and the like used in the specification and claims are to be understood as being modified in all instances by the terms "substantially" or "approximately." Therefore, unless otherwise indicated, the numerical values ​​set forth in the following specification and claims may vary depending on the desired properties sought to be obtained by the present disclosure.

[0014] At a minimum, and without attempting to limit the application of the doctrine of equivalents to the scope of the claims, each numerical value should at least be interpreted in terms of the number of reported significant digits and by applying ordinary rounding techniques. Moreover, all ranges disclosed herein will be understood to include the range values ​​at the beginning and end and all subranges contained therein. For example, the specified range of "1 to 10" should be considered to include any and all subranges between (including the minimum value 1 and the maximum value 10) a minimum value of 1 and a maximum value of 10; that is, all subranges starting from a minimum value of 1 or greater and ending with a maximum value of 10 or less, for example, 1 to 3.3, 4.7 to 7.5, 5.5 to 10, and so on. "One" means one or more.

[0015] As used herein, "coupled", "coupling" and similar terms refer to two or more elements that are joined, linked, fastened, connected, communicated or otherwise associated (e.g., mechanically, electrically, fluidically, optically, electromagnetically) with each other. In various examples, the elements may be associated directly or indirectly. As an example, element A may be directly associated with element B. As another example, element A may be indirectly associated with element B, e.g., via another element C. It will be understood that the associations between the various disclosed elements are not all necessarily represented. Therefore, couplings other than those depicted in the figures may also exist.

[0016] As used herein, the phrase "at least one of...", when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one of each item in the list may be required. For example, "at least one of item A, item B, and item C" may include, but is not limited to, item A or item A and item B. This example may also include item A, item B, and item C, or item B and item C. In other examples, "at least one of..." may be, for example, but not limited to, two of item A, one of item B, and ten of item C; four of item B and the rest of item C; and other suitable combinations.

[0017] Various non-limiting examples will now be described with reference to the accompanying drawings, wherein like reference numbers correspond to similar or functionally equivalent elements.

[0018] Figure 1 , Figure 2 and Figure 3 , a functional block diagram of different example OTDRs according to the principles of the present disclosure is shown in FIG, wherein under the control of a processor, a pulse-driven laser generates a laser pulse having a specific wavelength, wherein the width of the laser pulse can be adjusted between 10ns-20000ns. As the laser pulse propagates along the tested optical fiber, due to Rayleigh scattering and Fresnel reflection, the light transmitted in the optical fiber will return to the photodetector of the OTDR through a circulator in response to the laser pulse. In this article, Rayleigh scattering and Fresnel reflection can be collectively referred to as "backscattered signal" or "optical backscattered signal" in the present disclosure. The photodetector converts the backscattered signal into a weak electrical signal, which is then sent to the processor for sampling after amplification and analog-to-digital conversion. By detecting the intensity of the returned light in the backscattered signal and the time taken for the returned light to return to the photodetector, the relative loss information of the tested optical path in the tested optical fiber can be displayed as a coordinate diagram, for example, on a visual display or output on a physical medium (such as paper), so that the loss and fault location of the entire tested optical fiber can be determined.

[0019] In an example, the backscattered signal may be sampled by the processor for a predetermined time corresponding to the length of the fiber under test after the laser pulse is generated, and / or until the processor determines from the sample that the end of the fiber under test has been sampled. However, this is not to be construed in a limiting sense.

[0020] Reference Figure 1 An example OTDR 2 for performing dynamic transresistance switching according to the principles of the present disclosure includes a pulse generator 4, a laser source 6, an optical circulator 8, a photodetector 10 (e.g., a photodiode or photoconductor), a transimpedance amplifier (TIA) 12, a driver 14, an analog-to-digital converter (ADC) 16, and a processor 18 (e.g., a microprocessor or a programmable gate array). The processor 18 may be connected to a display 20 (e.g., for an LCD or OLED display) for displaying a coordinate graph or a printer for printing a coordinate graph on a physical medium (such as paper).

[0021] Under the control of the processor 18, the pulse generator 4 outputs an electrical pulse that drives the laser 6 to generate a laser pulse of a specific wavelength and width. When the laser pulse propagates along the tested optical fiber 22 via the optical circulator 8, the light transmitted in the tested optical fiber 22 will return to the optical detector 10 along the tested optical fiber 22 via the optical circulator 8 due to Rayleigh scattering and Fresnel reflection. The optical detector 10 converts the received backscattered signal into an electrical signal, which can be amplified by the TIA 12 and converted into a digital signal corresponding to the backscattered signal by the ADC 16 before being sent to the processor 18 for processing, storage and output as a coordinate graph on the display 20.

[0022] When the laser pulse is generated, the strong reflection signal generated by the Fresnel reflection may have an amplitude that will saturate the photodetector 10 and / or the ADC 16. After detecting the strong reflection signal via the sample of the digital signal corresponding to the strong reflection signal output by the ADC 16, the processor 18 quickly (e.g., within a few nanoseconds (ns) or milliseconds (ms)) controls the pulse generator 4 via the driver 14 to select the transresistor unit with a lower gain of the TIA 12, whereupon the amplitude of the signal sampled by the ADC 16 from the TIA 12 is reduced to within the sampling range of the ADC 16. After detecting that the strong reflection signal is no longer present in the received backscattered signal via the sample of the digital signal from the ADC 16, the processor 18 quickly controls the pulse generator 4 via the driver 14 to select (or return to) the transresistor unit with a higher gain of the TIA 12. In an example, during the sampling of the backscattered signal corresponding to the entire length of the tested optical fiber, the selection of the transresistor unit with a lower gain and a higher gain may be repeated one or more times as necessary.

[0023] In an example, the transresistor unit with a higher gain may be the same (or a different) transresistor unit used prior to selection of the transresistor unit with a lower gain. However, this is not to be construed in a limiting sense. In an example, the photodetector 10, TIA 12, and ADC 16 may include Figure 1 Components of a receiver of the OTDR 2. Since TIAs are known in the art, details about the TIA 12 will not be described herein for the sake of simplicity.

[0024] Reference Figure 2 Another example OTDR 2 for performing dynamic gain switching according to the principles of the present disclosure is similar to Figure 1 OTDR 2 shown, with the following exceptions. The exceptions are Figure 2 The OTDR 2 shown in FIG. 1 includes an avalanche photodiode 24 to replace the Figure 1 The optical detector 10 and the TIA 12 of the OTDR 2 are shown in FIG.

[0025] Under the control of the processor 18, the pulse generator 4 outputs an electrical pulse that drives the laser 6 to generate a laser pulse of a specific wavelength and width. When the laser pulse propagates along the tested optical fiber 22 via the optical circulator 8, the light transmitted in the tested optical fiber 22 will return to the avalanche photodiode 24 along the tested optical fiber 22 via the optical circulator 8 due to Rayleigh scattering and Fresnel reflection. The avalanche photodiode 24 converts the received backscattered signal into an electrical signal, which can be amplified and converted into a digital signal corresponding to the backscattered signal by the ADC 16 before being sent to the processor 18 for processing and storage.

[0026] When the laser pulse is generated, the strong reflection signal generated by Fresnel reflection may have an amplitude that saturates the avalanche photodiode 24 and the ADC 16. After the strong reflection signal is detected via the sample of the digital signal corresponding to the strong reflection signal output by the ADC 16, the processor 18 quickly controls the pulse generator 4 via the driver 14 to reduce or lower the gain of the avalanche diode 24, whereupon the amplitude of the reflection signal sampled by the ADC 16 is reduced to within the sampling range of the ADC 16. After the strong reflection signal is detected via the sample of the digital signal from the ADC 16 that is no longer present in the received backscattered signal, the processor 18 quickly controls the pulse generator 4 via the driver 14 to increase the gain of the avalanche photodiode 24. In an example, the reduction and increase of the gain of the avalanche photodiode 24 may be repeated one or more times as necessary during the sampling of the backscattered signal corresponding to the entire length of the optical fiber under test.

[0027] In an example, the increased gain of the avalanche photodiode 24 may be the same (or different) than the gain of the avalanche photodiode 24 before being reduced or decreased. However, this is not to be construed in a limiting sense. In an example, the avalanche photodiode 24 and the ADC 16 may include Figure 2 The avalanche photodiode 24 is an element of a receiver of the OTDR 2. Because avalanche photodiodes are known in the art, details about the avalanche photodiode 24 will not be described herein for the sake of simplicity.

[0028] Reference Figure 3 Another example OTDR 2 for performing dynamic power adjustment on a backscattered signal according to the principles of the present disclosure is similar to Figure 2 OTDR 2 shown, with the following exceptions. The exceptions are Figure 3 The OTDR 2 shown in FIG. 1 includes a variable optical attenuator (VOA) 26 connected in series with the optical detector 10 to replace the Figure 2 The avalanche photodiode 24 of the OTDR 2 is shown in FIG.

[0029] Under the control of the processor 18, the pulse generator 4 outputs an electrical pulse that drives the laser 6 to generate a laser pulse of a specific wavelength and width. When the laser pulse propagates along the tested optical fiber 22 via the optical circulator 8, the light transmitted in the tested optical fiber 22 will return to the VOA 26 along the tested optical fiber 22 via the optical circulator 8 due to Rayleigh scattering and Fresnel reflection. The optical detector 10 and the VOA 26 convert the received backscattered signal into an electrical signal, which can be amplified and converted into a digital signal corresponding to the backscattered signal by the ADC 16 before being sent to the processor 18 for processing and storage.

[0030] When the laser pulse is generated, the strong reflection signal generated by Fresnel reflection may have an amplitude that saturates the photodetector 10 and the ADC 16. After detecting the strong reflection signal via a sample of the digital signal corresponding to the strong reflection signal output by the ADC 16, the processor 18 quickly controls the pulse generator 4 via the driver 14 to increase the loss of the VOA 26, whereupon the amplitude of the reflection signal sampled by the ADC 16 is reduced to within the sampling range of the ADC 16. After detecting that the strong reflection signal is no longer present in the received backscattered signal via a sample of the digital signal from the ADC 16, the processor 18 quickly controls the pulse generator 4 via the driver 14 to select (or return to) the reduced loss of the VOA 26. In an example, increasing and decreasing the loss of the VOA 25 may be repeated one or more times as necessary during the sampling of the backscattered signal corresponding to the entire length of the optical fiber under test.

[0031] In an example, the reduced loss of VOA 26 may be the same (or different) than the loss of VOA 26 before being increased. However, this is not to be construed in a limiting sense. In an example, VOA 26, optical detector 10, and ADC 16 may include Figure 3 Components of the receiver of the OTDR 2. Since VOAs are known in the art, details about the VOA 26 will not be described herein for the sake of simplicity.

[0032] Reference Figure 4 , and continuing with reference to all previous figures, a method according to the principles of the present disclosure may include step S1, in which the laser source 6 of the OTDR 2 outputs a laser pulse to the optical fiber 22. In step S2, the processor 18 acquires a sample of a backscattered signal generated by the optical fiber 22 in response to the laser pulse in step S1.

[0033] In step S3, the processor 18 determines that at least one element of the receiver is operating in a saturated operating state based on one or more values ​​of the samples acquired in step S2. In step S4, in response to step S3, the processor 18 controls the receiver to reduce the value of the samples of the backscattered signal acquired by the processor to within the unsaturated operating state of the at least one element of the receiver.

[0034] In step S5, the processor determines, based on one or more values ​​of the samples of the backscattered signal acquired in step S4, that if the value of the samples of the backscattered signal increases, the at least one element of the receiver will not operate in a saturated operating state. Finally, in step S6, in response to step S5, the processor controls the receiver to increase the value of the samples of the backscattered signal acquired by the processor after step S5.

[0035] In an example, the method may be repeated one or more times as necessary during the sampling of the backscattered signal corresponding to the entire length of the optical fiber under test.

[0036] In an example, the values ​​of the samples of the backscattered signal acquired in steps S3 and S6 may be the same, in particular, when the amplitude of the laser pulses is the same when performing steps S3 and S6.

[0037] Other non-limiting examples or aspects of the present disclosure are set forth in the following illustrative exemplary numbered clauses:

[0038] Item 1: An optical time domain reflectometry method, comprising: (a) outputting a laser pulse to an optical fiber by a laser source of an optical time domain reflectometer (OTDR); (b) obtaining, by a processor of the OTDR, a sample of a backscattered signal generated by the optical fiber in response to the laser pulse of step (a) from a receiver of the OTDR; (c) the processor determining, based on one or more values ​​of the samples sampled in step (b), that at least one element of the receiver is in a saturated operating state; (d) in response to step (c), controlling, by the processor, the receiver so that the value of the sample of the backscattered signal sampled by the processor is reduced to within an unsaturated operating state of the at least one element of the receiver; (e) determining, by the processor, based on one or more values ​​of the sample of the backscattered signal sampled after step (d), that if the value of the sample of the backscattered signal sampled by the processor is increased, then the at least one element of the receiver will not operate in a saturated operating state; and (f) in response to step (e), controlling, by the processor, the receiver to increase the value of the sample of the backscattered signal sampled by the processor.

[0039] Item 2: A method as described in Item 1, wherein: the elements of the receiver may include a photodetector and a transimpedance amplifier (TIA); step (d) may include selecting a transresistor unit of the TIA with a lower gain; and step (f) may include selecting a transresistor unit of the TIA with a higher gain.

[0040] Clause 3: The method of clause 2, wherein the higher gain of the TIA in step (f) may be the same as the gain of the TIA in step (c).

[0041] Clause 4: The method of clause 2, wherein the higher gain of the TIA in step (f) can be different from the gain of the TIA in step (c).

[0042] Clause 5: A method as described in Clause 1, wherein: the at least one element of the receiver may include an avalanche photodiode; step (d) may include reducing the gain of the avalanche photodiode; step (f) may include increasing the gain of the avalanche photodiode.

[0043] Item 6: The method of Item 5, wherein the higher gain of the avalanche photodiode in step (f) can be the same as the gain of the avalanche photodiode in step (c).

[0044] Clause 7: The method of clause 5, wherein the higher gain of the avalanche photodiode in step (f) can be different from the gain of the avalanche photodiode in step (c).

[0045] Clause 8: A method as described in Clause 1, wherein: the elements of the receiver may include a variable optical attenuator (VOA) and a photodetector; step (d) may include increasing the loss of the VOA; and step (f) may include reducing the loss of the VOA.

[0046] Clause 9: The method of clause 8, wherein the reduced loss of the VOA in step (f) may be the same as the loss of the VOA in step (c).

[0047] Clause 10: The method of clause 8, wherein the reduced loss of the VOA in step (f) may be different than the loss of the VOA in step (c).

[0048] Clause 11: The method of any of clauses 1-10, wherein the one or more values ​​sampled in step (e) may be the same as the one or more values ​​sampled in step (b).

[0049] Clause 12: The method of any of clauses 1-10, wherein the one or more values ​​sampled in step (e) may be different from the one or more values ​​sampled in step (b).

[0050] Item 13: An optical time domain reflectometer (OTDR) comprising: a laser source operable to output laser pulses to an optical fiber via a pulse generator under the control of a processor; a receiver for receiving a backscattered signal generated by the optical fiber in response to the laser pulses output to the optical fiber, wherein the processor is programmed or configured to: (a) determine that at least one element of the receiver is operating in a saturated operating state based on one or more values ​​of a sample of the received backscattered signal; (b) in response to the determination in step (a), control the receiver to reduce one or more values ​​of the sample of the received backscattered signal sampled after step (a), whereupon the at least one element of the receiver operates in an unsaturated operating state; (c) determine that if the value of the sample of the backscattered signal increases, the at least one element of the receiver will not operate in a saturated operating state based on one or more values ​​of the sample of the received backscattered signal sampled after step (b); and (d) in response to step (c), control the receiver to increase one or more values ​​of the sample of the backscattered signal sampled after step (c).

[0051] Clause 14: An OTDR as described in Clause 13, wherein: the elements of the receiver may include a photodetector and a transimpedance amplifier (TIA); step (b) may include selecting a transresistance unit of the TIA with a lower gain; and step (d) may include selecting a transresistance unit of the TIA with a higher gain.

[0052] Clause 15: An OTDR as described in clause 13, wherein: the at least one element of the receiver may include an avalanche photodiode; step (b) may include reducing the gain of the avalanche photodiode; step (d) may include reducing the gain of the avalanche photodiode.

[0053] Clause 16: An OTDR as described in Clause 13, wherein: the elements of the receiver may include a variable optical attenuator (VOA) and a photodetector; step (b) may include increasing the loss of the VOA; and step (d) may include reducing the loss of the VOA.

[0054] Item 17: An optical time domain reflectometer (OTDR), comprising: a component for outputting a laser pulse to an optical fiber; a component for receiving an optical backscatter signal generated by the optical fiber in response to the laser pulse output to the optical fiber; a component for determining that at least one element of the component for receiving is operating in a saturated state based on the value of a sample of the received optical backscatter signal; and a component for controlling the component for receiving to reduce the value of the sample of the optical backscatter signal received by the component for determining so that the at least one element of the component for receiving operates in an unsaturated state, wherein: the component for determining determines that if the value of the sample of the optical backscatter signal obtained after reducing the value of the sample increases, the at least one element of the component for receiving will not operate in a saturated state; and the component for controlling controls the component for receiving to increase the value of the sample of the optical backscatter signal obtained after the component for determining determines that if the value of the sample increases, the at least one element of the component for receiving will not operate in a saturated state.

[0055] Clause 18: An OTDR as described in Clause 17, comprising at least one of the following: the component for outputting laser pulses to the optical fiber may include a laser source; the component for receiving may include one of a transimpedance amplifier (TIA), a variable optical attenuator (VOA) and an avalanche photodiode; the component for determining may include a processor; and the component for controlling may include the processor.

[0056] Item 19: An OTDR as described in Item 18, wherein the component for receiving may further include one of the following: a photodetector for converting a received optical backscatter signal into a first electrical signal, the TIA converting the first electrical signal into a second electrical signal having an amplitude controlled by a processor, and an analog-to-digital converter (ADC) converting the second electrical signal into samples of the received optical backscatter signal, wherein the samples of the received optical backscatter signal are digitized samples; a photodetector for converting an optical signal output by the VOA in response to the received backscatter signal into an electrical signal, and the analog-to-digital converter (ADC) converting the electrical signal into samples of the received optical backscatter signal, wherein the samples of the received optical backscatter signal are digitized samples; and an analog-to-digital converter (ADC), wherein an avalanche photodiode converts the received optical backscatter signal into an electrical signal, and the ADC converts the electrical signal into samples of the received optical backscatter signal, wherein the samples of the received optical backscatter signal are digitized samples.

[0057] Clause 20: The method of any of clauses 1-12, wherein the samples in steps (b) and (e) may be digital signals output to the processor by an analog-to-digital converter of a receiver of the OTDR.

[0058] Clause 21: An OTDR as described in any of clauses 13-16, wherein the samples in steps (a) and (c) can be digital signals output to the processor by an analog-to-digital converter of a receiver of the OTDR.

[0059] Clause 22: An OTDR as recited in any of clauses 17-19, wherein the at least one element of the means for receiving may be an analog-to-digital converter (ADC).

[0060] Although the present disclosure has been described in detail based on embodiments of what are presently considered to be the most practical preferred embodiments for purposes of illustration, it will be understood that such detail is for that purpose only, and that the present disclosure is not limited to the disclosed embodiments, but rather is intended to cover modifications and equivalent arrangements within the spirit and scope of the appended claims. For example, it will be understood that the present disclosure contemplates that one or more features of any embodiment can be combined to the greatest extent possible with one or more features of any other embodiment.

Claims

1. An optical time domain reflectometry method, comprising: (a) A laser pulse is output from a laser source of an optical time domain reflectometer (OTDR) to an optical fiber; (b) acquiring, by a processor of the OTDR, from a receiver of the OTDR, a sample of a backscattered signal generated by the optical fiber in response to the laser pulse of step (a); (c) determining, by the processor, based on one or more values ​​of the samples taken in step (b), that at least one element of the receiver is in a saturated operating state; (d) in response to step (c), controlling, by the processor, the receiver so that the value of the samples of the backscattered signal sampled by the processor is reduced to within an unsaturated operating state of the at least one element of the receiver; (e) determining, by the processor based on one or more values ​​of samples of the backscatter signal sampled after step (d), that if the values ​​of the samples of the backscatter signal sampled by the processor increase, then the at least one element of the receiver will not operate in a saturated operating state; as well as (f) In response to step (e), the processor controls the receiver to increase the value of the sample of the backscatter signal sampled by the processor.

2. The method according to claim 1, wherein: The receiver's elements include a photodetector and a transimpedance amplifier (TIA); Step (d) includes selecting a transresistor unit of the TIA having a lower gain; and Step (f) includes selecting a transresistor unit of the TIA having a higher gain.

3. The method of claim 2, wherein the higher gain of the TIA in step (f) is the same as the gain of the TIA in step (c).

4. The method of claim 2, wherein the higher gain of the TIA in step (f) is different from the gain of the TIA in step (c).

5. The method according to claim 1, wherein: said at least one element of said receiver comprises an avalanche photodiode; Step (d) includes reducing the gain of the avalanche photodiode; and Step (f) includes increasing the gain of the avalanche photodiode.

6. The method of claim 5, wherein the increased gain of the avalanche photodiode in step (f) is the same as the gain of the avalanche photodiode in step (c).

7. The method of claim 5, wherein the increased gain of the avalanche photodiode in step (f) is different from the gain of the avalanche photodiode in step (c).

8. The method according to claim 1, wherein: The receiver's elements include a variable optical attenuator (VOA) and a photodetector; Step (d) includes increasing the loss of the VOA; and Step (f) includes reducing losses in the VOA.

9. The method of claim 8, wherein the reduced loss of the VOA in step (f) is the same as the loss of the VOA in step (c).

10. The method of claim 8, wherein the reduced loss of the VOA in step (f) is different from the loss of the VOA in step (c).

11. The method of claim 1, wherein the one or more values ​​sampled in step (e) are the same as the one or more values ​​sampled in step (b).

12. The method of claim 1, wherein the one or more values ​​sampled in step (e) are different from the one or more values ​​sampled in step (b).

13. An optical time domain reflectometer (OTDR), comprising: a laser source operable to output laser pulses to the optical fiber via a pulse generator under the control of the processor; a receiver for receiving a backscattered signal generated by the optical fiber in response to a laser pulse output to the optical fiber, wherein the processor is programmed or configured to: (a) determining, based on one or more values ​​of samples of the received backscattered signal, that at least one element of the receiver is operating in a saturated operating state; (b) in response to the determination in step (a), controlling the receiver to reduce one or more values ​​of samples of the received backscattered signal sampled after step (a), whereupon the at least one element of the receiver operates in an unsaturated operating regime; (c) determining, based on one or more values ​​of samples of the received backscatter signal sampled after step (b), that if the values ​​of the samples of the backscatter signal increase, the at least one element of the receiver will not operate in a saturated operating state; as well as (d) in response to step (c), controlling the receiver to increase one or more values ​​of samples of the backscatter signal sampled after step (c).

14. The OTDR according to claim 13, wherein: The receiver components include a photodetector and a transimpedance amplifier (TIA); Step (b) includes selecting a transresistor unit of the TIA having a lower gain; and Step (d) includes selecting a transresistor unit of the TIA having a higher gain.

15. The OTDR according to claim 13, wherein: said at least one element of said receiver comprises an avalanche photodiode; Step (b) includes reducing the gain of the avalanche photodiode; and Step (d) includes increasing the gain of the avalanche photodiode.

16. The OTDR of claim 13, wherein: The receiver's elements include a variable optical attenuator (VOA) and a photodetector; Step (b) includes increasing the loss of the VOA; and Step (d) includes reducing losses in the VOA.

17. An optical time domain reflectometer (OTDR), the OTDR comprising: Components for outputting laser pulses into optical fibers; means for receiving an optical backscattered signal generated by the optical fiber in response to a laser pulse output to the optical fiber; means for determining, from values ​​of samples of the received optical backscatter signal, that at least one element of the means for receiving is operating in a saturated state; as well as means for controlling the means for receiving to reduce the value of the samples of the optical backscatter signal received by the means for determining so that the at least one element of the means for receiving operates in a non-saturated state, wherein: means for determining determining, based on a value of a sample of the optical backscatter signal acquired after reducing the value of the sample, that if the value of the sample increases, the at least one element of the means for receiving will not operate in a saturated state; as well as The means for controlling controls the means for receiving to increase the value of a sample of the optical backscatter signal acquired after the means for determining determines that the at least one element of the means for receiving will not operate in saturation if the value of the sample is increased.

18. The OTDR according to claim 17, comprising at least one of the following: The components for outputting laser pulses to an optical fiber include a laser source; The receiving component includes one of a transimpedance amplifier (TIA), a variable optical attenuator (VOA), and an avalanche photodiode; The means for determining comprises a processor; and The means for controlling comprises the processor.

19. The OTDR of claim 18, wherein the means for receiving further comprises one of: a photodetector for converting a received optical backscatter signal into a first electrical signal, the TIA converting the first electrical signal into a second electrical signal having an amplitude controlled by the processor, an analog-to-digital converter (ADC) converting the second electrical signal into samples of the received optical backscatter signal, wherein the samples of the received optical backscatter signal are digitized samples; a photodetector for converting an optical signal output by the VOA in response to the received backscatter signal into an electrical signal, an analog-to-digital converter (ADC) for converting the electrical signal into samples of the received optical backscatter signal, wherein the samples of the received optical backscatter signal are digitized samples; and An analog-to-digital converter (ADC), wherein the avalanche photodiode converts the received optical backscatter signal into an electrical signal, and the ADC converts the electrical signal into samples of the received optical backscatter signal, wherein the samples of the received optical backscatter signal are digitized samples.

20. The method of claim 1, wherein the samples in steps (b) and (e) are digital signals output to the processor by an analog-to-digital converter of a receiver of the OTDR.

21. The OTDR of claim 13, wherein the samples in steps (a) and (c) are digital signals output to the processor by an analog-to-digital converter of a receiver of the OTDR.

22. The OTDR of claim 17, wherein the at least one element of the means for receiving is an analog-to-digital converter (ADC).

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