Optical fiber delay measurement device and method resistant to optical fiber line attenuation changes

Abstract

The present invention provides an optical fiber delay measurement device and method resistant to optical fiber line attenuation changes. The optical fiber delay measurement device comprises: a pulse transmitter, a clock generator, an optical transmitter, an optical direction coupler, an electrically controlled optical attenuator, an optical receiver, a comparison amplifier, a time-to-digital conversion circuit and a control unit. The optical transmitter transmits an optical pulse signal, the optical direction coupler couples the optical pulse signal to the optical fiber under test, and receives the reflected optical signal output by the optical fiber under test, the electrically controlled optical attenuator attenuates the reflected optical signal, the optical receiver converts the attenuated optical signal into an electrical signal and amplifies it, the comparison amplifier regenerates the amplified electrical signal, and the control unit adjusts the attenuation value of the electrically controlled optical attenuator and the comparison threshold of the comparison amplifier according to the amplitude value of the amplified electrical signal, so that the ratio of the amplitude value to the comparison threshold is a preset fixed value, so as to ensure that the rising edge of the pulse signal reflected by the optical fiber under test is stable after being regenerated, thereby improving the accuracy of the optical fiber delay measurement.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber measurement technology, and in particular to an optical fiber delay measurement device and method capable of resisting optical fiber line attenuation changes. Background Art

[0002] The existing fiber delay measurement methods mainly include pulse measurement method, phase measurement method and optical interference measurement method. Among them, the pulse measurement method can utilize the time-to-digital conversion circuit in the mature ToF (time of flight) measurement technology, making the measurement device simple and low-cost. The pulse modulation signal of the optical transmitter is used as the "start" signal of the time-to-digital conversion circuit. The optical pulse signal reflected from the optical reflector at the end of the measured optical fiber is amplified by the optical receiver and simply regenerated by the comparison amplifier, and then used as the "stop" signal of the time-to-digital conversion circuit. The comparison threshold of the comparison amplifier is fixed and does not change with the change of the optical pulse signal level. When the attenuation of the measured optical fiber changes greatly, the pulse rising edge of the "stop" signal is unstable, and a large error occurs when the time measurement is performed. When it is necessary to automatically, quickly, in real time, and onlinely measure the fiber delay of a fiber transmission line as long as 100km, since the attenuation of the optical fiber transmission line is constantly changing with time and environment, the level of the received optical pulse measurement signal also changes accordingly, resulting in inaccurate time position of the rising edge of the regenerated pulse signal, which seriously restricts the accuracy of the fiber delay measurement of the optical fiber transmission line.

[0003] Therefore, it is necessary to improve the current scheme and improve the accuracy of time measurement at a lower cost. Summary of the invention

[0004] The purpose of the present invention is to provide a fiber optic delay measurement device and method that are resistant to fiber optic line attenuation changes, which can improve the measurement accuracy of fiber optic delay.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] An optical fiber delay measurement device resistant to optical fiber line attenuation changes, the optical fiber delay measurement device resistant to optical fiber line attenuation changes comprising:

[0007] A pulse transmitter, used for generating a start pulse signal;

[0008] A clock generator, used for generating a clock signal;

[0009] an optical transmitter, connected to the pulse transmitter, and configured to generate an optical pulse signal according to the start pulse signal;

[0010] An optical directional coupler, arranged in the optical path of the optical pulse signal and connected to one end of the optical fiber under test, for coupling the optical pulse signal to the optical fiber under test and receiving the reflected optical signal output by the optical fiber under test;

[0011] An electrically controlled optical attenuator, arranged on the optical path of the reflected optical signal, for attenuating the reflected optical signal to obtain an attenuated optical signal;

[0012] an optical receiver, arranged on the optical path of the attenuated optical signal, for converting the attenuated optical signal into an electrical signal, and amplifying the electrical signal to obtain an amplified electrical signal;

[0013] A comparison amplifier connected to the optical receiver, used for comparing the level of the amplified electrical signal with that of a comparison threshold, performing signal regeneration, and obtaining a stop pulse signal;

[0014] A time-to-digital conversion circuit is connected to the pulse transmitter, the clock generator and the comparison amplifier respectively, and is used to count time according to the start pulse signal, the clock signal and the stop pulse signal, and convert the time into a time digital signal;

[0015] A control unit is respectively connected to the optical receiver, the electrically controlled optical attenuator, the comparison amplifier and the time digital conversion circuit, and is used to sample the amplified electrical signal to obtain the amplitude value of the amplified electrical signal, adjust the attenuation value of the electrically controlled optical attenuator and the comparison threshold of the comparison amplifier according to the amplitude value, and determine the optical fiber delay value according to the time digital signal.

[0016] Optionally, the optical transmitter includes:

[0017] A laser pulse current driving circuit, connected to the pulse transmitter, for generating a driving current according to the start pulse signal;

[0018] The laser assembly is connected to the laser pulse current driving circuit and is used to generate an optical pulse signal according to the driving current.

[0019] Optionally, the optical transmitter further includes:

[0020] The laser temperature control circuit is connected to the laser component and is used to control the temperature of the laser component.

[0021] Optionally, the optical receiver includes:

[0022] A photoelectric detector, arranged on the optical path of the attenuated optical signal, for converting the attenuated optical signal into an electrical signal;

[0023] a preamplifier, connected to the photodetector, and used to amplify the electrical signal to obtain a first amplified electrical signal;

[0024] The main amplifier is connected to the preamplifier and is used to amplify the first amplified electrical signal to obtain an amplified electrical signal.

[0025] Optionally, the preamplifier is a transimpedance amplifier.

[0026] Optionally, the control unit comprises:

[0027] an analog-to-digital conversion circuit, connected to the optical receiver, for converting the amplified electrical signal into a digital signal;

[0028] an amplitude calculation module, connected to the analog-to-digital conversion circuit, and configured to sample the digital signal to obtain an amplitude value of the amplified electrical signal;

[0029] a controller, connected to the amplitude calculation module and the electrically controlled optical attenuator, respectively, for reducing the attenuation value of the electrically controlled optical attenuator when the amplitude value is less than a minimum amplitude threshold, and increasing the attenuation value of the electrically controlled optical attenuator when the amplitude value is greater than a maximum amplitude threshold, until the amplitude value is greater than or equal to the minimum amplitude threshold and less than or equal to the maximum amplitude threshold, and determining a comparison threshold digital signal according to the amplitude value and a set ratio;

[0030] The digital-to-analog conversion circuit is connected to the controller and the comparison amplifier respectively, and is used to convert the comparison threshold digital signal into an analog signal and send it to the comparison amplifier as a comparison threshold.

[0031] Optionally, the optical directional coupler is an optical circulator or a planar waveguide type equal-dividing 1x2 optical splitter.

[0032] Optionally, the optical fiber delay measurement device resistant to optical fiber line attenuation variation further includes:

[0033] The optical reflector is connected to the other end of the optical fiber under test, and is used to reflect the optical signal output from the other end of the optical fiber under test, and output the reflected optical signal through the optical fiber under test.

[0034] To achieve the above object, the present invention also provides the following solution:

[0035] A method for measuring optical fiber delay that is resistant to optical fiber line attenuation changes, the method comprising:

[0036] A start pulse signal is generated by a pulse transmitter, and a clock generator generates a clock signal;

[0037] Transmitting an optical pulse signal according to the start pulse signal by an optical transmitter;

[0038] The optical pulse signal is coupled to one end of the optical fiber under test through an optical directional coupler, and a reflected light signal output by the optical fiber under test is received;

[0039] Attenuating the reflected light signal by an electrically controlled optical attenuator to obtain an attenuated light signal;

[0040] Converting the attenuated optical signal into an electrical signal through an optical receiver, and amplifying the signal to obtain an amplified electrical signal;

[0041] The control unit samples the amplified electrical signal to obtain an amplitude value of the amplified electrical signal, and adjusts the attenuation value of the electrically controlled optical attenuator and the comparison threshold of the comparison amplifier according to the amplitude value;

[0042] The comparison amplifier compares the level of the amplified electrical signal with that of a comparison threshold, performs signal regeneration, and obtains a stop pulse signal;

[0043] The time digital conversion circuit counts the time according to the start pulse signal, the clock signal and the stop pulse signal, and converts the time into a time digital signal;

[0044] The optical fiber delay value is determined by the control unit according to the time digital signal.

[0045] Optionally, sampling the amplified electrical signal by a control unit to obtain an amplitude value of the amplified electrical signal, and adjusting the attenuation value of the electrically controlled optical attenuator and the comparison threshold of the comparison amplifier according to the amplitude value specifically includes:

[0046] Converting the amplified electrical signal into a digital signal through an analog-to-digital conversion circuit;

[0047] The digital signal is sampled by an amplitude calculation module to obtain an amplitude value of the amplified electrical signal;

[0048] Determine whether the amplitude value is less than a minimum amplitude threshold, and if the amplitude value is less than the minimum amplitude threshold, reduce the attenuation value of the electrically controlled optical attenuator until the amplitude value is greater than or equal to the minimum amplitude threshold;

[0049] Determine whether the amplitude value is greater than a maximum amplitude threshold, and if the amplitude value is greater than the maximum amplitude threshold, increase the attenuation value of the electrically-controlled optical attenuator until the amplitude value is less than or equal to the maximum amplitude threshold;

[0050] The controller determines a comparison threshold digital signal according to the amplitude value and the set ratio, and converts the comparison threshold digital signal into an analog signal through a digital-to-analog conversion circuit and sends it to a comparison amplifier as a comparison threshold.

[0051] According to the specific embodiment provided by the present invention, the present invention discloses the following technical effects: a start pulse signal is generated by a pulse transmitter, and an optical pulse signal is transmitted by an optical transmitter, an optical direction coupler couples the optical pulse signal to the optical fiber under test, and receives a reflected light signal output by the optical fiber under test, an electrically controlled optical attenuator attenuates the reflected light signal, an optical receiver converts the attenuated optical signal into an electrical signal, and amplifies the signal, a comparison amplifier regenerates the amplified electrical signal, and obtains a stop pulse signal, a control unit adjusts the attenuation value of the electrically controlled optical attenuator and the comparison threshold of the comparison amplifier according to the amplitude value of the amplified electrical signal, so that the ratio of the amplitude value to the comparison threshold is a preset fixed value, thereby ensuring that the rising edge of the pulse signal reflected from the optical fiber under test is stable after being regenerated, and does not change with the line attenuation of the optical fiber under test, thereby improving the accuracy of optical fiber delay measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0053] Figure 1 It is a structural schematic diagram of the optical fiber delay measurement device resistant to optical fiber line attenuation changes of the present invention.

[0054] Explanation of symbols:

[0055] Pulse transmitter-1, clock generator-2, optical transmitter-3, laser pulse current drive circuit-31, laser assembly-32, laser temperature control circuit-33, optical direction coupler-4, electrically controlled optical attenuator-5, optical receiver-6, photodetector-61, preamplifier-62, main amplifier-63, comparison amplifier-7, time digital conversion circuit-8, control unit-9, optical reflector-10, optical fiber under test-11. DETAILED DESCRIPTION

[0056] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] The purpose of the present invention is to provide an optical fiber delay measurement device and method that are resistant to optical fiber line attenuation changes. A pulse transmitter generates a start pulse signal, and an optical transmitter transmits an optical pulse signal. An optical direction coupler couples the optical pulse signal to the optical fiber under test, and receives a reflected optical signal output by the optical fiber under test. An electrically controlled optical attenuator attenuates the reflected optical signal. An optical receiver converts the attenuated optical signal into an electrical signal and amplifies it. A comparison amplifier regenerates the amplified electrical signal to obtain a stop pulse signal. A control unit adjusts the attenuation value of the electrically controlled optical attenuator and the comparison threshold of the comparison amplifier according to the amplitude value of the amplified electrical signal, so that the ratio of the amplitude value to the comparison threshold is a preset fixed value, thereby ensuring that the rising edge of the pulse signal reflected from the optical fiber under test is stable after being regenerated, and does not change with the line attenuation of the optical fiber under test, thereby ensuring the accuracy of the optical fiber delay measurement.

[0058] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0059] like Figure 1 As shown, the optical fiber delay measurement device resistant to optical fiber line attenuation changes of the present invention includes: a pulse transmitter 1, a clock generator 2, an optical transmitter 3, an optical directional coupler 4, an electrically controlled optical attenuator 5, an optical receiver 6, a comparison amplifier 7, a time-to-digital conversion circuit 8 and a control unit 9.

[0060] Wherein, the pulse transmitter 1 is used to generate a start pulse signal.

[0061] The clock generator 2 is used to generate a clock signal. In this embodiment, the clock generator 2 is composed of an ECOC-2522-100.000-3-HC chip from ECSInc.International, a 2-frequency division circuit and an 8-frequency division circuit. The ECOC-2522-100.000-3-HC chip provides a 100MHz high-stability clock signal, which is sent to the control unit 9 after passing through the 2-frequency division circuit and to the time digital conversion circuit 8 after passing through the 8-frequency division circuit.

[0062] The optical transmitter 3 is connected to the pulse transmitter 1 , and the optical transmitter 3 is used to generate an optical pulse signal according to the start pulse signal.

[0063] The optical directional coupler 4 is arranged on the optical path of the optical pulse signal and connected to one end of the optical fiber 11 under test. The optical directional coupler 4 is used to couple the optical pulse signal to the optical fiber 11 under test and receive the reflected optical signal output by the optical fiber 11 under test. In this embodiment, the optical directional coupler 4 is an optical circulator or a planar waveguide type 1x2 optical splitter. Specifically, the input end of the optical directional coupler 4 is connected to the optical transmitter 3, the common end of the optical directional coupler 4 is connected to one end of the optical fiber 11 under test, and the output end of the optical directional coupler 4 is connected to the input of the electrically controlled optical attenuator 5.

[0064] Preferably, the length of the optical fiber 11 under test ranges from 20 m to 100 km, and the total attenuation of 100 km of the optical fiber 11 under test at the 1550 nm window is less than 30 dB.

[0065] The electrically controlled optical attenuator 5 is arranged on the optical path of the reflected optical signal, and is used to attenuate the reflected optical signal to obtain an attenuated optical signal. In this embodiment, the variable attenuation value range of the electrically controlled optical attenuator 5 is 0 dB to 60 dB.

[0066] The optical receiver 6 is arranged on the optical path of the attenuated optical signal, and is used to convert the attenuated optical signal into an electrical signal and amplify it to obtain an amplified electrical signal. In this embodiment, the bandwidth of the optical receiver 6 is greater than 50 MHz. It should be noted that the reflected optical signal, the attenuated optical signal, and the amplified electrical signal are all pulse signals.

[0067] The comparison amplifier 7 is connected to the optical receiver 6, and is used to compare the level of the amplified electrical signal and the comparison threshold, perform signal regeneration, and obtain a stop pulse signal. Preferably, the comparison amplifier 7 uses a controllable comparison threshold, and the ratio k of the comparison threshold to the amplitude value of the input pulse signal is a preset value, and the value range of k is 0.1 to 0.9, and the typical value is 0.5. The comparison amplifier 7 uses the TLV3501 chip of TI.

[0068] The time digital conversion circuit 8 is connected to the pulse transmitter 1, the clock generator 2 and the comparison amplifier 7 respectively. The time digital conversion circuit 8 is used to count the time according to the start pulse signal, the clock signal and the stop pulse signal, and convert it into a time digital signal. In this embodiment, the time digital conversion circuit TDC adopts the TDC7201 chip of TI company.

[0069] The control unit 9 is connected to the optical receiver 6, the electrically controlled optical attenuator 5, the comparison amplifier 7 and the time digital conversion circuit 8 respectively. The control unit 9 is used to sample the amplified electrical signal to obtain the amplitude value of the amplified electrical signal, and adjust the attenuation value of the electrically controlled optical attenuator 5 and the comparison threshold of the comparison amplifier 7 according to the amplitude value, and determine the fiber delay value according to the time digital signal. Specifically, the time digital signal is stored in a result register in the time digital conversion circuit, and the clock frequency value is also stored in the result register. The calculation method for calculating the fiber delay value according to the time digital signal can adopt the existing known calculation method. It can be calculated according to the calculation formula provided by different time digital conversion circuit chips and the data stored in the result register in the time digital conversion circuit TDC.

[0070] The control unit 9 adopts ARM or DSP or FPGA circuit, or any combination of the three. This embodiment adopts ARM and FPGA circuit. The control unit 9 is also connected to the clock generator 2.

[0071] Specifically, the optical transmitter 3 includes a laser pulse current driving circuit 31 and a laser component 32 .

[0072] The laser pulse current driving circuit 31 is connected to the pulse transmitter 1 , and the laser pulse current driving circuit 31 is used to generate a driving current according to the start pulse signal.

[0073] The laser component 32 is connected to the laser pulse current driving circuit 31 , and the laser component 32 is used to generate an optical pulse signal according to the driving current.

[0074] Furthermore, the optical transmitter 3 further comprises a laser temperature control circuit 33. The laser temperature control circuit 33 is connected to the laser component 32, and is used to control the temperature of the laser component 32. The laser temperature control circuit 33 uses a MAX1978 chip from MAXIM.

[0075] Furthermore, the laser assembly 32 includes a semiconductor laser, a thermistor and a semiconductor refrigerator. In the present embodiment, the semiconductor laser is a distributed feedback semiconductor laser DFB-LD. The wavelength of the semiconductor laser is in the window of 1310nm and 1550nm. The peak-to-peak power of the optical pulse signal output by the semiconductor laser ranges from 10dBm to 25dBm, and a typical value is 15dBm. The width of the optical pulse signal output by the semiconductor laser ranges from 10ns to 200ns, and a typical value is 50ns. The optical pulse repetition frequency of the semiconductor laser ranges from 1kHz to 500Hz, and a typical value is 500Hz.

[0076] The thermistor is disposed on the semiconductor laser and is used to detect the temperature of the semiconductor laser and send the temperature to the laser temperature control circuit 33 .

[0077] The semiconductor refrigerator is arranged on the laser and connected to the laser temperature control circuit 33. The laser temperature control circuit 33 performs cooling by driving the semiconductor refrigerator.

[0078] The optical receiver 6 includes a photodetector 61 , a preamplifier 62 and a main amplifier 63 .

[0079] The photodetector 61 is disposed on the optical path of the attenuated optical signal, and is used to convert the attenuated optical signal into an electrical signal. Preferably, the photodetector 61 is a PIN photodetector 61 or an APD photodetector 61 .

[0080] The preamplifier 62 is connected to the photodetector 61, and is used to amplify the electrical signal to obtain a first amplified electrical signal. In this embodiment, the preamplifier 62 is a transimpedance amplifier. The transimpedance amplifier uses the OPA858 chip of TI company, and the transimpedance is 20kΩ.

[0081] The main amplifier 63 is connected to the preamplifier 62, and is used to amplify the first amplified electrical signal to obtain an amplified electrical signal. The main amplifier 63 uses a THS4520 chip from TI, and the gain of the main amplifier 63 is 10.

[0082] Furthermore, the control unit 9 includes: an analog-to-digital conversion circuit, an amplitude calculation module, a controller and a digital-to-analog conversion circuit.

[0083] The analog-to-digital conversion circuit is connected to the optical receiver 6 and is used to convert the amplified electrical signal into a digital signal. The analog-to-digital conversion circuit ADC uses the TI ADS4142 chip with a sampling rate of 50MSPS.

[0084] The amplitude calculation module is connected to the analog-to-digital conversion circuit, and is used to sample the digital signal to obtain the amplitude value of the amplified electrical signal. Specifically, the amplitude calculation module can be a circuit that can collect the amplitude value of the pulse signal.

[0085] The controller is connected to the amplitude calculation module and the electrically controlled optical attenuator 5 respectively, and is used to reduce the attenuation value of the electrically controlled optical attenuator 5 when the amplitude value is less than the lowest amplitude threshold, and increase the attenuation value of the electrically controlled optical attenuator 5 when the amplitude value is greater than the highest amplitude threshold, until the amplitude value is greater than or equal to the lowest amplitude threshold and less than or equal to the highest amplitude threshold, and determine the comparison threshold digital signal according to the amplitude value and the set ratio. In this embodiment, the lowest amplitude threshold is 0.1V and the highest amplitude threshold is 0.5V.

[0086] The digital-to-analog conversion circuit is connected to the controller and the comparison amplifier 7 respectively, and is used to convert the comparison threshold digital signal into an analog signal and send it to the comparison amplifier 7 as a comparison threshold. The digital-to-analog conversion circuit DAC uses the DAC124S085 chip of TI.

[0087] Furthermore, the control unit 9 also includes a time position determination module. The time position determination module is connected to the analog-to-digital conversion circuit, and the time position determination module is used to sample the digital signal to obtain the time position of the amplified electrical signal. Specifically, the time position determination module can use a circuit in the prior art that can collect the time position value of the pulse signal.

[0088] The controller is also connected to the time-to-digital conversion circuit 8, and the controller is also used to set the counting window parameters of the time-to-digital conversion circuit 8 according to the time position.

[0089] Preferably, the optical fiber delay measurement device resistant to optical fiber line attenuation variation of the present invention further includes an optical reflector 10. The optical reflector 10 is connected to the other end of the optical fiber 11 under test, and the optical reflector 10 is used to reflect the optical signal output from the other end of the optical fiber 11 under test, and output the reflected optical signal through the optical fiber 11 under test.

[0090] The reflection coefficient of the light reflector 10 ranges from 0 dB to -5 dB, with a typical value of -1 dB.

[0091] The present invention uses a time-to-digital conversion circuit 8, and uses an optical time domain reflectometer OTDR technology, a light source wavelength stabilization circuit, and a high-stability clock oscillator circuit as an aid. The attenuation change of the optical fiber line is automatically balanced through an electrically controlled optical attenuator, and in the process of regenerating the optical pulse signal, the comparison threshold of the comparison amplifier 7 is automatically adjusted so that the ratio of the amplitude of the optical pulse signal to the comparison threshold of the comparison amplifier 7 is a fixed value, so that the rising edge position of the regenerated pulse signal does not change with the change of the input optical pulse signal level, thereby ensuring the measurement accuracy of the optical fiber delay.

[0092] The optical fiber delay measurement device resistant to optical fiber line attenuation variation of the present invention specifically adopts the following steps when measuring the delay of the optical fiber 11 under test:

[0093] 1) Predict the amplitude value and time position of the pulse signal reflected from the end of the measured optical fiber: the pulse transmitter generates a start pulse signal and controls the optical transmitter to transmit an optical pulse signal. The optical receiver receives the reflected signal returned from the measured optical fiber, amplifies it and outputs it to the analog-to-digital conversion circuit in the control unit, samples the reflected signal, and the control unit obtains the amplitude value and time position of the pulse signal reflected from the optical reflector at the end of the measured optical fiber in the reflected signal.

[0094] 2) Adjust the attenuation value of the electrically controlled optical attenuator so that the amplitude value of the pulse signal reflected by the optical reflector at the end of the optical fiber under test is within the range of 0.1V to 0.5V: If the amplitude value of the pulse signal obtained in step 1) is <0.1V, the control unit controls to reduce the attenuation value of the electrically controlled optical attenuator, and then repeats step 1) to finally make the pulse signal amplitude value within the range of 0.1V to 0.5V. If the pulse signal amplitude value is >0.5V, the control unit controls to increase the attenuation value of the electrically controlled optical attenuator, and then repeats step 1) to finally make the pulse signal amplitude value within the range of 0.1V to 0.5V.

[0095] 3) Adjust the comparison threshold of the comparison amplifier required for pulse regeneration: The control unit controls the digital-to-analog conversion circuit to output a voltage to the comparison amplifier as the comparison threshold based on the pulse signal amplitude value obtained in steps 1) and 2), as the pulse signal amplitude prediction value when performing optical fiber delay measurement. The ratio k of the comparison threshold to the pulse amplitude value is a preset value, and the value range of k is 0.1 to 0.9, with a typical value of 0.5.

[0096] 4) Setting the working parameters of the time digital conversion circuit TDC: The control unit sends the counting window parameters to the time digital conversion circuit TDC according to the time position of the pulse signal reflected back by the optical reflector at the end of the measured optical fiber obtained in step 1.

[0097] 5) Perform time-to-digital conversion: The pulse transmitter transmits a start pulse signal to the optical transmitter and the time-to-digital conversion circuit TDC. The start pulse signal serves as the pulse modulation signal of the optical transmitter and the "start" signal of the time-to-digital conversion circuit TDC. The optical receiver receives the reflected light signal reflected from the optical reflector at the end of the optical fiber under test, amplifies it, and outputs it to the input of the comparison amplifier to regenerate the pulse signal, and sends the regenerated pulse signal to the time-to-digital conversion circuit TDC as the "stop" signal of the time-to-digital conversion circuit TDC. The time-to-digital conversion circuit TDC counts the time between the "start" signal and the "stop" signal, and completes the time-to-digital conversion. The counting result is stored in the result register in the time-to-digital conversion circuit TDC;

[0098] 6) The control unit obtains the counting result in the result register of the time digital conversion circuit TDC, and calculates the optical fiber delay value according to the clock frequency value and the counting result according to the formula provided by the manufacturer of the time digital conversion circuit TDC.

[0099] The present invention samples the signal received by the optical receiver through an analog-to-digital conversion circuit ADC. After the control unit obtains the sampled signal, it calculates and predicts the amplitude value of the optical pulse signal reflected by the optical reflector at the end of the measured optical fiber, and then controls the electrically controlled optical attenuator to preliminarily balance the attenuation change of the measured optical fiber line. Then, the output of the digital-to-analog conversion circuit DAC is controlled to finely adjust the comparison threshold of the comparison amplifier so that the ratio of the amplitude value of the optical pulse signal to the comparison threshold is a preset fixed value, thereby ensuring that the rising edge of the pulse signal reflected by the optical reflector at the end of the measured optical fiber is stable after being regenerated and does not change with the attenuation change of the measured optical fiber line, so that the pulse rising edge of the "stop" signal is stable and the error is small when performing time measurement.

[0100] The optical fiber delay measurement method of the present invention that is resistant to optical fiber line attenuation changes comprises:

[0101] The pulse transmitter generates a start pulse signal, and the clock generator generates a clock signal.

[0102] An optical transmitter transmits an optical pulse signal according to the start pulse signal.

[0103] The optical pulse signal is coupled to one end of the optical fiber under test through an optical directional coupler, and a reflected light signal output by the optical fiber under test is received.

[0104] The reflected light signal is attenuated by an electrically controlled optical attenuator to obtain an attenuated light signal.

[0105] The attenuated optical signal is converted into an electrical signal by an optical receiver and amplified to obtain an amplified electrical signal.

[0106] The control unit samples the amplified electrical signal to obtain the amplitude value of the amplified electrical signal, and adjusts the attenuation value of the electrically controlled optical attenuator and the comparison threshold of the comparison amplifier according to the amplitude value.

[0107] The comparison amplifier compares the level of the amplified electrical signal with that of a comparison threshold, performs signal regeneration, and obtains a stop pulse signal.

[0108] The time digital conversion circuit counts the time according to the start pulse signal, the clock signal and the stop pulse signal, and converts the time into a time digital signal.

[0109] The optical fiber delay value is determined by the control unit according to the time digital signal.

[0110] Specifically, the control unit samples the amplified electrical signal to obtain an amplitude value of the amplified electrical signal, and adjusts the attenuation value of the electrically controlled optical attenuator and the comparison threshold of the comparison amplifier according to the amplitude value, specifically including:

[0111] The amplified electrical signal is converted into a digital signal through an analog-to-digital conversion circuit.

[0112] The digital signal is sampled by an amplitude calculation module to obtain an amplitude value of the amplified electrical signal.

[0113] It is determined whether the amplitude value is less than a minimum amplitude threshold value. If the amplitude value is less than the minimum amplitude threshold value, the attenuation value of the electrically controlled optical attenuator is reduced until the amplitude value is greater than or equal to the minimum amplitude threshold value.

[0114] It is determined whether the amplitude value is greater than a maximum amplitude threshold value. If the amplitude value is greater than the maximum amplitude threshold value, the attenuation value of the electrically-controlled optical attenuator is increased until the amplitude value is less than or equal to the maximum amplitude threshold value.

[0115] The controller determines a comparison threshold digital signal according to the amplitude value and the set ratio, and converts the comparison threshold digital signal into an analog signal through a digital-to-analog conversion circuit and sends it to a comparison amplifier as a comparison threshold.

[0116] Compared with the prior art, the optical fiber delay measurement method resistant to optical fiber line attenuation changes of the present invention has the same beneficial effects as the above-mentioned optical fiber delay measurement system resistant to optical fiber line attenuation changes, which will not be repeated here.

[0117] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0118] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. An optical fiber delay measurement device resistant to optical fiber line attenuation changes, characterized in that: The optical fiber delay measurement device resistant to optical fiber line attenuation variation comprises: A pulse transmitter, used for generating a start pulse signal; A clock generator, used for generating a clock signal; an optical transmitter, connected to the pulse transmitter, and configured to generate an optical pulse signal according to the start pulse signal; The optical transmitter comprises: A laser pulse current driving circuit, connected to the pulse transmitter, for generating a driving current according to the start pulse signal; A laser assembly connected to the laser pulse current driving circuit and used to generate an optical pulse signal according to the driving current; A laser temperature control circuit, connected to the laser assembly, for controlling the temperature of the laser assembly; The laser assembly includes a semiconductor laser, a thermistor and a semiconductor refrigerator; the thermistor is arranged on the semiconductor laser, and the thermistor is used to detect the temperature of the semiconductor laser and send it to the laser temperature control circuit; the semiconductor refrigerator is arranged on the semiconductor laser and connected to the laser temperature control circuit, and the laser temperature control circuit performs cooling by driving the semiconductor refrigerator; An optical directional coupler, arranged in the optical path of the optical pulse signal and connected to one end of the optical fiber under test, for coupling the optical pulse signal to the optical fiber under test and receiving the reflected optical signal output by the optical fiber under test; An electrically controlled optical attenuator, arranged on the optical path of the reflected optical signal, for attenuating the reflected optical signal to obtain an attenuated optical signal; an optical receiver, arranged on the optical path of the attenuated optical signal, for converting the attenuated optical signal into an electrical signal, and amplifying the electrical signal to obtain an amplified electrical signal; A comparison amplifier connected to the optical receiver, used to compare the level of the amplified electrical signal with that of a comparison threshold, perform signal regeneration, and obtain a stop pulse signal; A time-to-digital conversion circuit is connected to the pulse transmitter, the clock generator and the comparison amplifier respectively, and is used to count time according to the start pulse signal, the clock signal and the stop pulse signal, and convert the time into a time digital signal; A control unit is respectively connected to the optical receiver, the electrically controlled optical attenuator, the comparison amplifier and the time digital conversion circuit, and is used to sample the amplified electrical signal to obtain the amplitude value of the amplified electrical signal, adjust the attenuation value of the electrically controlled optical attenuator and the comparison threshold of the comparison amplifier according to the amplitude value, and determine the optical fiber delay value according to the time digital signal.

2. The optical fiber delay measurement device resistant to optical fiber line attenuation variation according to claim 1, characterized in that: The optical receiver comprises: A photodetector, arranged on the optical path of the attenuated optical signal, for converting the attenuated optical signal into an electrical signal; A preamplifier, connected to the photodetector, and used to amplify the electrical signal to obtain a first amplified electrical signal; The main amplifier is connected to the preamplifier and is used to amplify the first amplified electrical signal to obtain an amplified electrical signal.

3. The optical fiber delay measurement device resistant to optical fiber line attenuation variation according to claim 2, characterized in that: The preamplifier is a transimpedance amplifier.

4. The optical fiber delay measurement device resistant to optical fiber line attenuation variation according to claim 1, characterized in that: The control unit comprises: an analog-to-digital conversion circuit, connected to the optical receiver, for converting the amplified electrical signal into a digital signal; an amplitude calculation module, connected to the analog-to-digital conversion circuit, and configured to sample the digital signal to obtain an amplitude value of the amplified electrical signal; a controller, connected to the amplitude calculation module and the electrically controlled optical attenuator, respectively, for reducing the attenuation value of the electrically controlled optical attenuator when the amplitude value is less than a minimum amplitude threshold, and increasing the attenuation value of the electrically controlled optical attenuator when the amplitude value is greater than a maximum amplitude threshold, until the amplitude value is greater than or equal to the minimum amplitude threshold and less than or equal to the maximum amplitude threshold, and determining a comparison threshold digital signal according to the amplitude value and a set ratio; The digital-to-analog conversion circuit is connected to the controller and the comparison amplifier respectively, and is used to convert the comparison threshold digital signal into an analog signal and send it to the comparison amplifier as a comparison threshold.

5. The optical fiber delay measurement device resistant to optical fiber line attenuation variation according to claim 1, characterized in that: The optical directional coupler is an optical circulator or a planar waveguide type equal-dividing 1x2 optical splitter.

6. The optical fiber delay measurement device resistant to optical fiber line attenuation variation according to claim 1, characterized in that: The optical fiber delay measurement device resistant to optical fiber line attenuation variation also includes: The optical reflector is connected to the other end of the optical fiber under test, and is used to reflect the optical signal output from the other end of the optical fiber under test, and output the reflected optical signal through the optical fiber under test.

7. A method for measuring optical fiber delay resistant to optical fiber line attenuation changes, applied to the optical fiber delay measuring device resistant to optical fiber line attenuation changes according to any one of claims 1 to 6, characterized in that: The optical fiber delay measurement method resistant to optical fiber line attenuation variation comprises: A start pulse signal is generated by a pulse transmitter, and a clock generator generates a clock signal; Transmitting an optical pulse signal according to the start pulse signal by an optical transmitter; The optical pulse signal is coupled to one end of the optical fiber under test through an optical directional coupler, and a reflected light signal output by the optical fiber under test is received; Attenuating the reflected light signal by an electrically controlled optical attenuator to obtain an attenuated light signal; Converting the attenuated optical signal into an electrical signal through an optical receiver, and amplifying the signal to obtain an amplified electrical signal; The control unit samples the amplified electrical signal to obtain an amplitude value of the amplified electrical signal, and adjusts the attenuation value of the electrically controlled optical attenuator and the comparison threshold of the comparison amplifier according to the amplitude value; The comparison amplifier compares the level of the amplified electrical signal with that of a comparison threshold, performs signal regeneration, and obtains a stop pulse signal; The time digital conversion circuit counts the time according to the start pulse signal, the clock signal and the stop pulse signal, and converts the time into a time digital signal; The optical fiber delay value is determined by the control unit according to the time digital signal.

8. The optical fiber delay measurement method resistant to optical fiber line attenuation variation according to claim 7, characterized in that: The control unit samples the amplified electrical signal to obtain an amplitude value of the amplified electrical signal, and adjusts the attenuation value of the electrically controlled optical attenuator and the comparison threshold of the comparison amplifier according to the amplitude value, specifically including: Converting the amplified electrical signal into a digital signal through an analog-to-digital conversion circuit; The digital signal is sampled by an amplitude calculation module to obtain an amplitude value of the amplified electrical signal; Determine whether the amplitude value is less than a minimum amplitude threshold, and if the amplitude value is less than the minimum amplitude threshold, reduce the attenuation value of the electrically controlled optical attenuator until the amplitude value is greater than or equal to the minimum amplitude threshold; Determine whether the amplitude value is greater than a maximum amplitude threshold, and if the amplitude value is greater than the maximum amplitude threshold, increase the attenuation value of the electrically-controlled optical attenuator until the amplitude value is less than or equal to the maximum amplitude threshold; The controller determines a comparison threshold digital signal according to the amplitude value and the set ratio, and converts the comparison threshold digital signal into an analog signal through a digital-to-analog conversion circuit and sends it to a comparison amplifier as a comparison threshold.

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