Method for improving OTDR performance

Abstract

The invention relates to the technical field of optical time domain reflectometer equipment, in particular to a method for improving the performance of an OTDR (Optical Time Domain Reflectometer), which comprises the following steps of: 1, supplying power to an APD (Avalanche Photo Diode) at a first voltage; 2, sending a test pulse, and measuring a saturation section; step 3, setting the power supply voltage of the APD in the saturation section as a second voltage; 4, resending the test pulse, supplying power to the APD at the second voltage in a saturation section, and supplying power to the APD at the first voltage in an unsaturated section; and 5, offsetting the test curve of the second voltage power supply section, and combining the offset test curve with the test curve of the first voltage power supply section to form a final OTDR test curve.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical time domain reflectometer equipment, and in particular to a method for improving the performance of an OTDR. BACKGROUND

[0002] The statements in this section merely provide background information related to the present application and do not necessarily constitute the prior art.

[0003] An optical time domain reflectometer (OTDR) is a device that transmits a laser pulse to an optical fiber, measures the backscattered Rayleigh scattering and reflected signals of the laser pulse, and obtains an attenuation and reflection characteristic curve along the optical fiber. Based on the analysis of the OTDR measurement curve, the uniformity, defects, breakage, and joint coupling of the optical fiber link can be understood, and thus the OTDR can be used to measure the optical fiber attenuation, joint loss, optical fiber fault point positioning, and the loss distribution along the length of the optical fiber, and is an essential tool for optical cable construction, maintenance, and monitoring.

[0004] The use of the OTDR in the prior art has the following problems:

[0005] 1. Long test time; a first OTDR curve is obtained by first measuring with a small gain, and a second OTDR curve is obtained by measuring with a large gain (illustrated by using two different gains), and then the two OTDR curves are spliced into one curve, and the near-end part of the first curve with a small gain is used to replace the near-end saturated part of the second curve with a large gain. Since complete measurement is required twice, the test time is long.

[0006] 2. High cost; since high-speed low-noise analog devices are relatively expensive, more analog devices are required for multiple gain channels, resulting in high system cost, and since the photoelectric current is relatively weak, the selection switch of multiple gain channels introduces additional noise, affecting the noise performance of the OTDR.

[0007] Therefore, it is necessary to provide a method for improving the performance of an OTDR to solve the above technical problems. SUMMARY

[0008] Therefore, in view of the above technical problems, the present application provides a method for improving the performance of an OTDR.

[0009] The technical solution adopted by the present application to solve the problems in the prior art is as follows:

[0010] The present application provides a method for improving the performance of an OTDR, comprising the following steps:

[0011] Step 1: power the APD with a first voltage;

[0012] Second step: send a test pulse to measure the saturation section;

[0013] Third step: set the APD power voltage of the saturation section to the second voltage;

[0014] Fourth step: resend the test pulse, and supply the APD with the second voltage in the saturation section and the first voltage in the non-saturation section;

[0015] Fifth step: offset the test curve of the second voltage section, and combine it with the test curve of the first voltage section to form the final OTDR test curve.

[0016] Preferably,

[0017] The second step comprises the following steps:

[0018] S1: the controller controls the laser driver to send a test pulse;

[0019] S2: the controller controls the receiving circuit to receive the test pulse in S1, and measures the return signal of the test pulse;

[0020] S3: determine the time interval by the size of the measured return signal, and calculate the saturation interval.

[0021] Preferably,

[0022] In the fourth step, the APD works with low gain in the saturation section, and works with high gain in the non-saturation section.

[0023] Preferably,

[0024] The first voltage and the second voltage are both lower than the APD reverse breakdown voltage VBR.

[0025] Preferably,

[0026] The first voltage is lower than the second voltage.

[0027] Preferably,

[0028] The gain of the APD at the first voltage is G1, and the gain of the APD at the second voltage is G2; G1>G2.

[0029] Preferably,

[0030] The difference between the APD reverse breakdown voltage VBR and the first voltage is greater than the saturation threshold;

[0031] The interpolation of the first voltage and the second voltage is greater than the detection threshold.

[0032] Preferably,

[0033] The saturation threshold is greater than or equal to 0.5V;

[0034] The detection threshold ∈ [2.5, 4].

[0035] Compared with the prior art, the application has the following beneficial effects:

[0036] 1. The test speed is improved, and the test in the saturation interval with low gain and the test in the non-saturation interval with high gain are simultaneously realized in each test pulse; separate tests and combination are not required.

[0037] 2. The OTDR hardware cost is reduced, and only 2 diodes and 1 switch are required to realize gain control, without the need of high-performance analog devices.

[0038] 3. The APD output is connected to the analog amplification circuit and then to the ADC, without the need of additional circuits, and no additional circuit noise is introduced, which is beneficial to improve the performance of the OTDR. BRIEF DESCRIPTION OF DRAWINGS

[0039] The drawings accompanying the specification of the present application form a part thereof, serve to provide further understanding of the present application, and together with the specification explain the present application. The use of these drawings in explaining the present application does not constitute an inappropriate limitation.

[0040] Figure 1 It is an OTDR hardware principle diagram;

[0041] Figure 2 It is an OTDR reflection event saturation and start-end saturation curve diagram;

[0042] Figure 3 It is an OTDR circuit principle diagram of multiple different gain paths;

[0043] Figure 4 It is an APD bias-voltage and gain relationship diagram of the method for improving the performance of the OTDR according to the present application;

[0044] Figure 5 It is an OTDR circuit principle diagram of supporting dynamic adjustment of the APD bias voltage according to the method for improving the performance of the OTDR according to the present application;

[0045] Figure 6 It is an APD bias-voltage switching circuit diagram according to the method for improving the performance of the OTDR according to the present application;

[0046] Figure 7 It is an APD bias-voltage fast switching timing diagram according to the method for improving the performance of the OTDR according to the present application;

[0047] Figure 8 It is an original OTDR curve of APD bias-voltage fast switching according to the method for improving the performance of the OTDR according to the present application;

[0048] Figure 9An OTDR curve after APD bias fast switching processing of a method for improving OTDR performance of the application;

[0049] Figure 10 A support APD bias fast switching OTDR test flow diagram of a method for improving OTDR performance of the application. DETAILED DESCRIPTION

[0050] The application will be further described below in conjunction with the accompanying drawings and embodiments.

[0051] It should be noted that the terms used herein are only intended to describe specific embodiments and are not intended to limit exemplary embodiments according to the present disclosure. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and it should also be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of the features, steps, operations, devices, components and / or combinations thereof.

[0052] In the present disclosure, the terms such as "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "side", "bottom", etc. indicate the orientation or positional relationship shown in the drawings, which are only the relationship words determined for the convenience of describing the structural relationship of the components or elements of the present disclosure, and are not intended to specify any component or element in the present disclosure, and cannot be understood as a limitation of the present disclosure.

[0053] Reference Figure 10 The method for improving OTDR performance of the application comprises the following steps:

[0054] Step 1: power the APD with a first voltage;

[0055] Step 2: send a test pulse and measure the saturation section;

[0056] Step 3: set the APD power supply voltage of the saturation section to a second voltage;

[0057] Step 4: resend the test pulse, and power the APD with the second voltage in the saturation section and the first voltage in the non-saturation section;

[0058] Step 5: offset the test curve of the second voltage supply section and combine it with the test curve of the first voltage supply to form the final OTDR test curve.

[0059] Step 2 comprises the following steps:

[0060] S1: the controller controls the laser driver to send a test pulse;

[0061] S2: the controller controls the receiving circuit to receive the test pulse in S1, and measures the return signal of a test pulse;

[0062] S3: judging the time interval by the size of the measured return signal, and calculating the saturation interval.

[0063] In the fourth step, the APD works at low gain in the saturation interval; and works at high gain in the non-saturation interval.

[0064] In some embodiments, the first voltage and the second voltage are both lower than the APD reverse breakdown voltage VBR; and the first voltage is lower than the second voltage. The gain of the APD at the first voltage is G1, and the gain of the APD at the second voltage is G2; G1>G2.

[0065] And: the difference between the APD reverse breakdown voltage VBR and the first voltage is greater than the saturation threshold; and the interpolation between the first voltage and the second voltage is greater than the detection threshold.

[0066] In some embodiments, the saturation threshold ≥ 0.5V; and the detection threshold ∈ [2.5, 4].

[0067] The following is a specific description:

[0068] Figure 1 The OTDR hardware principle diagram is shown in the figure. In actual application, the high dynamic range OTDR can measure longer optical fiber and has wider application range. In order to improve the detection capability of the OTDR, the detector generally adopts the APD (avalanche photodetector). When the reverse bias voltage VBR (reverse breakdown voltage) of the APD is near, the APD has M times (M is generally > 10 times) gain to the photoelectric current. When the reverse bias voltage is much lower than Vbr, for example, 3.3V, the gain of the APD to the photoelectric current is only about 1 times. According to the dynamic range calculation formula of the OTDR: 5*log10(S / N), to have 30dB dynamic range, S / N needs to be greater than 10^6, and theoretically, 20bit ADC is needed to provide 30dB OTDR dynamic range. At present, the industry 20bit ADC only has a low sampling rate device, which cannot meet the needs of the OTDR product. In actual system, 12-14bit ADC is generally used. When the OTDR is tested, the problem shown in the figure will occur. When the optical signal is relatively large, the photoelectric current is also relatively large. After passing through the analog amplification circuit, the analog circuit is easy to saturate. After the analog circuit saturates, the recovery time is relatively long. When the photoelectric current decreases, the analog circuit cannot amplify immediately, and needs a long saturation recovery time to enter the amplification state again. In the saturation state and the saturation recovery time, the circuit cannot accurately measure the OTDR curve. Figure 2

[0069] ​In order to solve the saturation problem under large dynamic demand, different amplification factors are used to solve it, such as Figure 3 When measuring OTDR, the curves of the near end and the far end are measured through different gain circuits. The signal returned by the near end is strong, so a small gain circuit is selected. The signal returned by the far end is weak, so a large gain circuit is used to solve the dynamic range and saturation problem. However, a large number of gain circuits are required.

[0070] The technical scheme of the present application is based on the relationship between the gain of APD and the bias voltage. By controlling the bias voltage of APD, the bias voltage is set to low voltage and low gain in the large signal (time period that is easy to cause saturation of the receiving circuit), and the bias voltage is set to high voltage and high gain in the small signal (non-saturation section). The complete OTDR curve can be obtained by one measurement, and a large dynamic range can be achieved without the need for multiple gain circuits.

[0071] Figure 4 The figure is the relationship between the bias voltage of APD and the gain Gain. The reverse breakdown voltage of APD is VBR. As long as the reverse voltage of APD is lower than VBR, the reverse breakdown of APD will not occur when APD works. When the bias voltage is set to V1 (V1 < VBR), the gain is G1. When the bias voltage is set to V2 (V2 < VBR), the gain is G2, which is much smaller than G1.

[0072] The hardware implementation scheme for improving the dynamic range of OTDR by dynamically adjusting the bias voltage of APD is shown in Figure 5 The controller increases the control of the bias voltage supply of APD.

[0073] The schematic diagram of the APD bias voltage switching circuit is shown in Figure 6 The rapid switching of APD voltage is realized by controlling the on-off of the switch through Vctrl. When the switch is off, V2 is provided to APD as the bias voltage. When the switch is on, the high voltage V1 output by DC / DC is provided to APD as the bias voltage. D1 and D2 are diodes, which provide V1 and V2 to APD as unidirectional power supply, respectively.

[0074] Figure 7 The timing diagram for rapid switching of APD bias voltage is shown. In the interval [0, T1], the switch is off, and V2 is provided to APD as the bias voltage. At this time, APD works in a low gain state. At T1, the switch is on, and V1 is provided to APD as the bias voltage. At this time, APD works in a high gain state.

[0075] The OTDR original curve measured by the APD bias voltage switching method is shown in Figure 8As shown, in the [0, T1] original saturation interval, the APD works at low gain, and this interval can be measured at a better signal-to-noise ratio due to the relatively large back signal. At the T1 moment (the back signal can no longer cause the receiving amplifier circuit to be saturated), the APD is switched to high gain mode, and the normal OTDR curve is measured. The curve of the [0, T1] time interval is aligned with the curve of the >T1 moment, and the final OTDR curve is obtained, as shown in Figure 9 .

[0076] The OTDR test flow supporting bias switching is as shown in Figure 10 , and is specifically as follows:

[0077] 1) First, the APD is powered by the first voltage, the controller controls the laser driver to send a test pulse, and the receiving circuit is controlled to receive, and the return signal of the test pulse is measured. The size of the return signal (the value of the ADC output, for example, for a 14-bit ADC, the output value greater than 16370 or less than 20 indicates that the receiving circuit is close to saturation) is used to determine which time interval the APD uses large gain to cause the saturation of the receiving circuit. That is, the saturation interval is calculated.

[0078] 2) The saturation interval APD power supply voltage is set to the second voltage, and the APD works at low gain in the saturation interval; the non-saturation interval works at the first voltage (high gain). The laser driver is controlled to send a test pulse, and the OTDR curve is tested.

[0079] 3) The OTDR test curve of the second power supply voltage interval is offset, and the test curve of the first voltage power supply is combined to form the final OTDR curve.

[0080] The method for improving the performance of the OTDR can improve the test speed, and simultaneously realizes the test of low gain in the saturation interval and high gain in the non-saturation interval in each test pulse; separate testing and combination are not required. The OTDR hardware cost is reduced, and only two diodes and one switch are required to realize gain control, high-performance analog devices are not required, the APD output is to the analog amplifier circuit and then to the ADC, no additional circuit is required, and no additional circuit noise is introduced, which is beneficial to improving the performance of the OTDR.

[0081] The above is only a preferred embodiment of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0082] The above describes the specific embodiments of the present application in combination with the drawings, but is not a limitation on the protection scope of the present application, and those skilled in the art should understand that various modifications or changes made by those skilled in the art on the basis of the technical solutions of the present application without creative labor are still within the protection scope of the present application.

Claims

1. A method for improving OTDR performance, characterized by: The following steps are involved: Step 1: Powering the APD with a first voltage; Step 2: Send a test pulse to measure the saturation segment; Step 3: Set the saturation section APD power supply voltage to the second voltage; Step 4: resend the test pulse and power the APD with the second voltage in the saturation section and power the APD with the first voltage in the non-saturation section; Step 5: offset the test curve of the second voltage supply segment and combine it with the test curve of the first voltage supply segment to form a final OTDR test curve.

2. A method for improving OTDR performance according to claim 1, characterized in that: The second step includes the following steps: S1: The controller controls the laser driver to send out a test pulse; S2: The controller controls the receiving circuit to receive the test pulse in S1 and detects a return signal of the test pulse; S3: Determine the time interval by the size of the measured return signal and calculate the saturation interval.

3. A method for improving OTDR performance according to claim 1, characterized in that: In the fourth step, the APD operates at a low gain in the saturation region and at a high gain in the non-saturation region.

4. A method for improving OTDR performance according to claim 1, characterized in that: Both the first voltage and the second voltage are lower than the APD reverse breakdown voltage VBR.

5. The method for improving OTDR performance according to claim 4, wherein: The first voltage is lower than the second voltage.

6. The method for improving OTDR performance according to claim 5, wherein: At the first voltage, the gain of the APD is G1 , and at the second voltage, the gain of the APD is G2 ; G1 > G2 .

7. The method for improving OTDR performance according to claim 6, wherein: The difference between the APD reverse breakdown voltage VBR and the first voltage is greater than the saturation threshold; An interpolation value of the first voltage and the second voltage is greater than a detection threshold.

8. The method for improving OTDR performance according to claim 7, wherein: Saturation threshold ≥ 0.5V; Detection threshold ∈ [2.5, 4].

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