A miniaturized distributed fiber optic sensing system based on integrated optoelectronic chips

Abstract

A miniaturized distributed optical fiber sensing system based on an integrated optoelectronic chip includes a light source, a first erbium-doped fiber amplifier (EDFA), an integrated optoelectronic chip with electro-optical modulation and beat frequency detection functions, a second erbium-doped fiber amplifier (EDFA), a circulator, and a sensing optical fiber. The integrated optoelectronic chip includes: a first end coupler, a directional coupler, a single-stage tunable optical attenuator (VOA), an IQ single-sideband modulator, a cascaded tunable optical attenuator (VOA), a second end coupler, a third end coupler, a 2×2 multimode interferometer (MMI), and an on-chip balanced detector (BPD). The on-chip IQ modulator and the cascaded VOA are combined to realize frequency shift and pulse modulation. The IQ modulator realizes single-sideband modulation, and the cascaded VOA converts continuous light into pulse light and couples it into the optical fiber through the second end coupler for detection. The scattered signal light is coupled to the chip through the third end coupler to beat with the local oscillator reference light, and is detected by the on-chip BPD. The new system is more integrated, miniaturized, highly stable, and has low energy consumption.

Description

Technical Field

[0001] The present invention belongs to the technical field of integrated optoelectronic chips and optical fiber sensing. It relates to a miniaturized distributed optical fiber sensing system based on an integrated optoelectronic chip, and in particular to a novel integrated optical fiber sensing system that integrates traditional discrete devices such as modulation devices, coupling devices, and detection devices on the same chip by using on-chip devices such as end couplers, directional couplers, multi-mode interferometers (MMIs), IQ modulators, multi-level tunable optical attenuators (VOAs), and on-chip balanced detectors (BPDs). Background Art

[0002] Distributed fiber optic sensing technology has the advantages of anti-electromagnetic interference, good concealment, small size and light weight. It also has the advantages of distributed dynamic detection and phase quantitative measurement.

[0003] The traditional structure of the distributed fiber optic sensing system based on heterodyne coherent detection includes discrete narrow linewidth lasers, acousto-optic modulators, erbium-doped fiber amplifiers (EDFA), double-balanced detectors (BPDs), and data acquisition cards. The narrow linewidth continuous laser light source is divided into two parts: local oscillator reference light and detection light through a fiber coupler. The detection light is chopped by an acousto-optic modulator (AOM) to form pulsed light and generate frequency shift. The pulsed light is amplified by an erbium-doped fiber amplifier (EDFA) and injected into the fiber under test (FUT) through a circulator. The scattered light in the fiber and the local oscillator reference light are beat by a 3dB coupler, and the signal after the beat is detected by a double-balanced detector (BPD). The signal output by the BPD is collected by a digital acquisition card, and the amplitude and phase information are demodulated, and further signal processing such as pattern recognition is performed. This traditional structure based on heterodyne coherent detection system is composed of separate optical components, and each component requires a good shock-absorbing environment. The system is easily disturbed by changes in ambient temperature, humidity, etc., which limits its performance.

[0004] Optoelectronic chips can be mass-produced with the help of mature microelectronics processing technology platforms, and have the advantages of low cost, high integration and high reliability. The CMOS process can realize the monolithic integration of optoelectronics and microelectronics, give full play to the advantages of optoelectronic chips in high-speed information transmission and microelectronics in efficient information processing, fully realize the integration of microelectronics and optoelectronics, and complement each other to achieve optoelectronic integrated chips with better performance.

[0005] No implementation method or device similar to the miniaturized distributed optical fiber sensing system based on integrated optoelectronic chips proposed in the present invention has been found in the currently disclosed literature. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the existing traditional distributed optical fiber sensing system based on heterodyne coherent detection, which is based on discrete devices, and propose a miniaturized distributed optical fiber sensing system based on an integrated optoelectronic chip. The new integrated optical fiber sensing system replaces the traditional discrete devices with on-chip devices and integrates them on the same chip, which overcomes the shortcomings of the existing traditional distributed optical fiber sensing system based on heterodyne coherent detection, which is based on discrete devices. It is more integrated and miniaturized, and can improve the stability of the system and reduce the energy consumption of the system.

[0007] The technical solution of the present invention is as follows:

[0008] A miniaturized distributed optical fiber sensing system based on an integrated optoelectronic chip, the system structure includes a light source, a first erbium-doped fiber amplifier (EDFA), an integrated optoelectronic chip with electro-optical modulation and beat frequency detection functions, a second erbium-doped fiber amplifier (EDFA), a circulator, and a sensing optical fiber. The integrated optoelectronic chip includes: an end coupler, a directional coupler, a multi-mode interferometer (MMI), an IQ single-sideband modulator, a monitoring detector, a multi-stage tunable attenuator (VOA), and an on-chip balanced detector (BPD). The connection relationship is as follows:

[0009] The output port of the light source is connected to the input port of the first erbium-doped fiber amplifier (EDFA), and after light amplification, it is coupled to the first end face coupler to couple the narrow line width laser light source into the integrated optoelectronic chip. The on-chip directional coupler divides the light source into two parts: local oscillator reference light and detection light. The local oscillator reference light is connected to a single-stage tunable optical attenuator (VOA) after being output from the second output port of the directional coupler, and then enters a 2×2 multimode interferometer (MMI) from the first port. The detection light is output from the first output port of the directional coupler and enters an IQ single-sideband modulator through a waveguide. The IQ single-sideband modulator is connected to a cascaded tunable optical attenuator (VOA), and the two are combined to achieve frequency shift and pulse modulation. The pulse light output by the cascaded tunable optical attenuator (VOA) is coupled and output through the second end face coupler and connected to the second erbium-doped fiber amplifier (EDFA), and then input from the first port of the circulator, and output from the second port and enter the sensing optical fiber. The signal light scattered back by the sensing optical fiber is inputted by the third port of the circulator and coupled by the third end face coupler into the integrated optoelectronic chip, and then enters the 2×2 multimode interferometer (MMI) through the second port. The signal light and the local oscillator reference light are beat by the 2×2 multimode interferometer (MMI), and the beat signal is received and detected by the on-chip balanced detector (BPD).

[0010] The light source is a continuous stable single-frequency laser light source.

[0011] The first erbium-doped fiber amplifier (EDFA) and the second erbium-doped fiber amplifier (EDFA) are used to compensate for the loss in the loop transmission.

[0012] The on-chip IQ modulator in the integrated optoelectronic chip is split into two I / Q signals by the 1×2MMI at the input end. The I / Q paths are split into two arms of the Mach-Zehnder interferometer by 1×2MMI respectively and modulated by RF signals. The two-arm laser signals of the modulated Mach-Zehnder modulator are combined by 1×2MMI. The Mach-Zehnder modulators of the I / Q paths all work in pull-push mode. The DC bias voltages of the two paths are adjusted to be equal and work at the minimum working point, i.e., V DCI =V DCQ =V π , so that the carrier is suppressed and the side mode suppression ratio SSR ~ 20dB is achieved. In addition to the Mach-Zehnder modulator (MZM), the Q path also has a thermal phase shifter PM. By changing its DC bias voltage, the phase difference between the upper and lower optical signals is adjusted to ±π / 2 to achieve carrier suppressed single sideband modulation. The output signals of the two Mach-Zehnder modulators are combined by a 1×2MMI. The three detectors are used to monitor the working points of the modulators respectively.

[0013] The on-chip IQ modulator and cascaded tunable optical attenuator (VOA) have electro-optical modulation function. The IQ modulator can realize single-sideband modulation. Changing the frequency of the radio frequency signal loaded on the IQ modulator can change the frequency shift amount of the single-sideband. The cascaded VOA can convert continuous light into pulse light. The combination of the two realizes frequency shift and pulse modulation.

[0014] The miniaturized distributed optical fiber sensing system based on an integrated optoelectronic chip adopts heterodyne coherent detection for the scattered signal. The scattered light in the sensing optical fiber and the local oscillator reference light are beat by a 2×2 multimode interferometer (MMI), and the signal after the beat is detected by an on-chip balanced detector (BPD).

[0015] The sensing optical fiber is a common single-mode optical fiber, and can be applied to Φ-OTDR and BOTDR distributed optical fiber sensing systems according to the different frequency shift amounts of the IQ single-sideband modulator.

[0016] The present invention is characterized in that:

[0017] (1) By combining an on-chip IQ modulator and a multi-stage tunable optical attenuator (VOA), frequency shift and pulse modulation are achieved. The IQ modulator implements single-sideband modulation, and the cascaded VOA converts continuous light into pulsed light, which is coupled into the optical fiber through an end coupler for detection.

[0018] (2) The scattered light and the local oscillator reference light are beat by a 2×2 multimode interferometer (MMI), and the beat signal is detected by an on-chip balanced detector (BPD).

[0019] (3) Based on the end coupler, the narrow linewidth laser light source is coupled to the on-chip system and is divided into two parts: local oscillator reference light and detection light through the on-chip directional coupler.

[0020] The advantages of the present invention are:

[0021] A new integrated fiber optic sensing system is developed by integrating traditional discrete devices such as modulation devices, coupling devices and detection devices on the same chip using silicon-based on-chip devices such as end couplers, directional couplers, multi-mode interferometers (MMIs), IQ single-sideband modulators, monitoring detectors, multi-stage tunable attenuators (VOAs) and on-chip balanced detectors (BPDs). This overcomes the shortcomings of the existing traditional distributed fiber optic sensing system structure based on heterodyne coherent detection based on discrete devices, is more integrated and miniaturized, and can improve system stability and reduce system energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the structure of an embodiment of a miniaturized distributed optical fiber sensing system based on an integrated optoelectronic chip of the present invention;

[0023] Figure 2 It is a schematic diagram of the structure of the on-chip IQ single-sideband modulator and the cascaded tunable optical attenuator (VOA) in the present invention.

[0024] In the figure: 1-light source;

[0025] 2- first erbium-doped fiber amplifier (EDFA);

[0026] 3-Integrated optoelectronic chip;

[0027] 4-first end coupler;

[0028] 5-directional coupler, 51-first output port of the directional coupler, 52-second output port of the directional coupler;

[0029] 6- Tunable optical attenuator (VOA);

[0030] 7-on-chip IQ single-sideband modulator; 71-first 1×2 multi-mode interferometer (MMI), 72-second 1×2 multi-mode interferometer (MMI), 73-Mach-Zehnder interferometer arm, 74-thermal phase shifter, 75-third 1×2 multi-mode interferometer (MMI), 76-thermal phase shifter, 77-first detector, 78-second detector; 79-fourth 1×2 multi-mode interferometer (MMI); 710-third detector;

[0031] 8- Cascaded Tunable Optical Attenuator (VOA); 81- Tunable Optical Attenuator (VOA);

[0032] 9- second end coupler;

[0033] 10- second erbium-doped fiber amplifier (EDFA);

[0034] 11-circulator, 111-first port of the circulator, 112-second port of the circulator, 113-third port of the circulator;

[0035] 12-Fiber under test (FUT);

[0036] 14 - a 2×2 multi-mode interferometer (MMI), 141 - a first port of the 2×2 multi-mode interferometer, 142 - a second port of the 2×2 multi-mode interferometer. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with embodiments and drawings, but the protection scope of the present invention shall not be limited thereto.

[0038] See also Figure 1 , Figure 1 This is a schematic diagram of the structure of an embodiment of a miniaturized distributed optical fiber sensing system based on an integrated optoelectronic chip of the present invention. The parameter indicators of the components of the system in this embodiment are as follows:

[0039] The light source 1 is a continuous stable single-frequency laser light source, with an operating wavelength of 1550nm, an output power of 20mW, and a Lorentz linewidth of 3kHz. The first erbium-doped fiber amplifier (EDFA) 2 and the second erbium-doped fiber amplifier (EDFA) 10 are used to compensate for the loss in the loop transmission, with an operating band of 1528nm-1563nm, an input optical power of -20dBm-10dBm, a typical value of 1dBm, and a maximum output optical power of 100W. The integrated optoelectronic chip is a silicon-based integrated optoelectronic chip. The end face couplers 4, 9, and 13 in the integrated optoelectronic chip 3 have an operating band of C band, and a loss of 2.8-3.5dB / facet (without matching oil) and 1.5-2dB / facet (with matching oil). The 1×2 multimode interferometer (MMI) 72, 75, 79 in the on-chip IQ single-sideband modulator 7 operates in the C-band, has an insertion loss of <0.3dB, a splitting ratio of 50 / 50, and a size of 3.6um×11.6um. The Mach-Zehnder electro-optic modulator operates in the C-band, has an insertion loss of ~4dB, a length of 3mm, and a modulation efficiency of V piL=1.7V.cm, 3dB bandwidth is 30GHz. The Pi phase shift power consumption of thermal phase shifters 74 and 76 is 1mW / Pi shift, the resistance is 1698Ω, and the size is 1.5um×190um. Single-stage tunable optical attenuator (VOA) 6, the operating band is C-band, the insertion loss is 0.2dB, the 3dB bandwidth is>100MHz, the maximum adjustable attenuation is 6dB, and the length is 1mm. 2×2 multimode interferometer (MMI) 14, the operating band is C-band, the insertion loss is <0.3dB, the splitting ratio is 50 / 50, and the size is 6um×42.7um. The on-chip balanced detector 15 is a PIN-type Ge photodetector, the operating band is C-band, the responsivity is ≥0.82A / w, the 3dB bandwidth is>35GHz, and the dark current is ≤20nA@1V. The sensing fiber 12 is an ordinary single-mode SMF-28 optical fiber.

[0040] The present invention is a miniaturized distributed optical fiber sensing system based on an integrated optoelectronic chip, and its specific working principle and steps are as follows:

[0041] (1) The continuous stable single-frequency laser emitted by the laser light source 1 is amplified by the first erbium-doped fiber amplifier (EDFA) 2 and then coupled into the integrated optoelectronic chip 3 through the optical fiber array and the first end coupler 4. The continuous light is then divided into detection light and reference light through the directional coupler 5.

[0042] (2) The detection light is split into two I / Q signals at the input of the on-chip IQ single-sideband modulator 7 through 1×2MMI 71. The I / Q paths are split into two arms of the Mach-Zehnder interferometer through 1×2MMI 72 and modulated by the RF signal. The two arms of the modulated Mach-Zehnder modulator are combined through 1×2MMI 75. The Mach-Zehnder modulators of the I / Q paths all operate in pull-push mode. The DC bias voltages loaded by the thermal phase shifters 74 in the two paths are adjusted to be equal and to operate at the minimum operating point, i.e., V DCI =V DCQ =V π , so that the carrier is suppressed and the side mode suppression ratio SSR is 20dB. In addition to the MZM, the Q path also has a thermal phase shifter (PM) 76, which adjusts the phase difference between the upper and lower optical signals to Carrier suppressed single sideband modulation is realized. The output signals of the two Mach-Zehnder modulators are combined by a 1×2 MMI 79. Three detectors 77, 78, and 710 are used to monitor the working point of the modulator. Changing the frequency of the RF signal loaded on the IQ modulator can change the frequency shift of the single sideband to 100 MHz and 11.8 GHz, which are suitable for Φ-OTDR and BOTDR distributed optical fiber sensing systems respectively.

[0043] (3) The continuous laser signal output from the output end of the on-chip IQ single-sideband modulator 7 is attenuated in three stages through a synchronously controlled cascaded tunable optical attenuator (VOA) 8 to form a pulse sequence with a repetition frequency of 20kHz, a rise time of <10ns, and a pulse width of 100ns.

[0044] (4) The pulse sequence is coupled through the end coupler and amplified by the second erbium-doped fiber amplifier (EDFA) 10, and then input from the first port 111 of the circulator, and enters the optical fiber to be tested from the second port 112 of the circulator for detecting the optical fiber link.

[0045] (5) The system adopts heterodyne coherent detection for the scattered signal. The signal light scattered by the optical fiber 12 to be tested is input through the third port 113 of the circulator 11, and then coupled into the integrated optoelectronic chip 3 from the end coupler. The local oscillator reference light is the light attenuated by the tunable attenuator (VOA) 6. The scattered light in the optical fiber and the local oscillator reference light are beat by a 2×2 multimode interferometer (MMI) 14. The signal after the beat is detected by the on-chip balanced detector (BPD) 15, and the amplitude and phase information of the signal are demodulated, thereby realizing event location and quantitative measurement.

Claims

1. A miniaturized distributed optical fiber sensing system based on an integrated optoelectronic chip, characterized in that: The invention comprises a first erbium-doped fiber amplifier (2), a second erbium-doped fiber amplifier (10), a circulator (11) and a sensing fiber (12), and is characterized in that it also comprises a first end face coupler (4) integrated on an optoelectronic chip (3), a directional coupler (5), a single-stage tunable optical attenuator (6), an on-chip IQ single-sideband modulator (7), a cascaded tunable optical attenuator (8), a second end face coupler (9), a third end face coupler (13), a 2×2 multimode interferometer (14) and an on-chip balanced detector (15); After the light source is amplified by the first erbium-doped fiber amplifier (2), it is coupled by the first end face coupler (4) so ​​that the narrow line width laser light source is coupled to the directional coupler (5) and is divided into local oscillator reference light and detection light by the directional coupler (5); The local oscillator reference light passes through the single-stage tunable optical attenuator (VOA) and enters the 2×2 multimode interferometer (14) from the first port (141) of the 2×2 multimode interferometer (14); The detection light sequentially enters the on-chip IQ single-sideband modulator (7) and the cascade tunable optical attenuator (VOA) through the waveguide to achieve frequency shift and pulse modulation; the pulse light output by the cascade tunable optical attenuator (8) sequentially passes through the second end face coupler (9) and the second erbium-doped fiber amplifier (10), is input through the first port (111) of the circulator (11), and is output through the second port (112) to enter the sensing optical fiber (12); the signal light scattered back by the sensing optical fiber (12) is input through the second port (112) of the circulator (11), and is output through the third port (113) to the third end face coupler (13), and after coupling by the third end face coupler (13), is emitted into the 2×2 multimode interferometer (14) through the second port (142) of the 2×2 multimode interferometer (14); The beat signal after the local oscillator reference light and the signal light are beat by the 2×2 multi-mode interferometer (14) is received by the on-chip balanced detector (15).

2. A miniaturized distributed optical fiber sensing system based on an integrated optoelectronic chip according to claim 1, characterized in that The light source (1) is a continuous stable single-frequency laser light source.

3. A miniaturized distributed optical fiber sensing system based on an integrated optoelectronic chip according to claim 1, characterized in that The first erbium-doped optical fiber amplifier (2) and the second erbium-doped optical fiber amplifier (10) are used to compensate for the loss in loop transmission.

4. A miniaturized distributed optical fiber sensing system based on an integrated optoelectronic chip according to claim 1, characterized in that: The on-chip IQ single-sideband modulator (7) and the cascaded tunable optical attenuator (8) have an electro-optical modulation function. The on-chip IQ single-sideband modulator (7) realizes single-sideband modulation. By changing the frequency of the radio frequency signal loaded on the on-chip IQ single-sideband modulator, the frequency shift amount of the single-sideband is changed. The cascaded VOA (8) converts continuous light into pulse light. The combination of the two realizes frequency shift and pulse modulation.

5. A miniaturized distributed optical fiber sensing system based on an integrated optoelectronic chip according to claim 1 or 4, characterized in that: The on-chip IQ single-sideband modulator (7) comprises a first 1×2 MMI (71), two second 1×2 MMIs (72), two first thermal phase shifters (74), two third 1×2 MMIs (75), a second thermal phase shifter (76), a first detector (77), a second detector (78), a fourth 1×2 multimode interferometer (79) and a third detector (710); the on-chip IQ single-sideband modulator (7) and the cascaded tunable optical attenuator (8) are connected by a waveguide, and the cascaded tunable optical attenuator (8) is formed by connecting a plurality of tunable optical attenuators (81) in series; The signal is split into two I / Q signals by the first 1×2MMI (71), and the I / Q signals are split into two arms of a Mach-Zehnder interferometer by the second 1×2MMI (72). In the pull-push mode, the two arms of the Mach-Zehnder modulator are modulated by an RF signal, and the modulated laser signals are combined by the third 1×2MMI (75); Adjust the DC bias voltage of the two paths to be equal and work at the minimum operating point, that is, V DCI =V DCQ =V π , so that the carrier is suppressed and the side mode suppression ratio SSR ~ 20dB is achieved; In addition to the Mach-Zehnder modulator (MZM), the Q path changes its DC bias voltage through the second thermal phase shifter (76) to adjust the phase difference between the upper and lower optical signals to ±π / 2, thereby realizing carrier suppressed single sideband modulation; The output signals of the two Mach-Zehnder modulators are combined via the fourth 1×2 multimode interferometer (79); the first detector (77), the second detector (78) and the third detector (710) are respectively used to monitor the working points of the Mach-Zehnder modulators.

6. A miniaturized distributed optical fiber sensing system based on an integrated optoelectronic chip according to claim 1, characterized in that: The sensing optical fiber (12) is a single-mode optical fiber and can be applied to Φ-OTDR and BOTDR distributed optical fiber sensing systems according to the different frequency shift amounts of the on-chip IQ single-sideband modulator.

Images