Tunable laser light source for spectrum sensing

Abstract

The invention discloses a spectrum sensing-oriented tunable laser light source, which comprises a tunable DFB laser array chip, a star coupler chip, an SOA array chip and an optical fiber array which are connected through waveguides, tunable lasers in each row are connected through waveguides, the lasers with adjacent wavelengths are distributed on different waveguides, and the lasers with different wavelengths are distributed on the optical fiber array. The light output end of each waveguide is provided with an SOA. According to the invention, the star-shaped coupler is adopted to uniformly distribute energy of light with different wavelengths of the tunable laser array to each light output waveguide, the energy respectively enters different fiber grating sensors or fiber MEMS sensors and the like to simultaneously realize temperature or strain sensing, meanwhile, multiplexing tree-shaped sensing and demodulation are realized, and the energy loss in the transmission process is reduced; the chips of different material systems are coupled by adopting a photon lead bonding or butt joint growth technology, the photon lead bonding technology does not need high-precision alignment, the processing efficiency is high, low-cost hybrid integration among the chips is realized, and the device is integrally compact.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and in particular to a tunable laser light source for spectral sensing. Background Art

[0002] The application of sensing technology in the future information technology field will become increasingly important. Fiber optic sensing is an important branch of sensing technology. Spectral sensing fiber optic sensing includes fiber optic Bragg grating sensing and MEMS fiber optic sensing. Fiber optic Bragg grating sensors have high measurement reliability and accuracy due to their wavelength (frequency) identification. They can replace traditional point-type temperature, strain and stress (pressure) electrical sensors, and can also achieve quasi-continuous monitoring sensing through weak grating sensing technology. They are compatible with fiber optic networks, forming the unique advantages of fiber optic sensing networks. They are widely used in many disciplines such as aircraft, large ship health structure detection, dams, oil exploration, high-speed rail, new energy, geological research and disaster analysis. Especially with the development of artificial intelligence, its simple, accurate, flexible and low-cost detection can play a huge supporting role in the development of intelligent perception science.

[0003] The fiber Bragg grating sensor based on the spontaneous emission light source ASE broadband light source and CCD solution uses volume grating to split the light to CCD for collection. Since its light source is ASE light source, the power density is low, and the sensing channel must be switched through an optical switch. There is also a FP filter-based scanning fiber laser, which uses piezoelectric ceramics to drive the coating cavity to complete wavelength scanning, drive the wavelength of the fiber laser to change, and thus complete the wavelength scanning of the laser. Because it uses mechanical devices, its stability and shock resistance are poor.

[0004] The current mainstream scanning tunable laser is a semiconductor tunable laser based on the distributed reflector DBR structure and the Veriner effect. The tunability of the DBR laser can only be achieved at a series of isolated points within a certain frequency range on the spectrum, but cannot achieve continuous tuning within a certain frequency range. Mode hopping will occur during fast step scanning, which requires algorithm correction, affecting the stability of the test and the measurement effect.

[0005] The use of series-parallel DFB laser arrays can realize tunable lasers, and the wavelength can be changed by changing the temperature inside the laser chip. Since the DFB array is usually written by electron beam exposure equipment, the writing time is long, and the wavelength has a large random error, which will cause the prepared laser to be significantly different from the designed wavelength. The series-parallel tunable DFB laser array has a major disadvantage, that is, after the series-parallel laser array is combined by an N×1 type combiner (such as a cascaded Y waveguide or MMI structure), the final light output energy loss caused by the combination is large. Here N is the number of input parallel waveguides, and the additional loss caused by imperfect process is not considered. After combining, ideally, only 1 / N of the input light of each channel can be coupled to the light output waveguide, resulting in low efficiency and increased power consumption in practical applications.

[0006] For optical interconnection between chips of different material systems, the traditional end-to-end coupling technology requires matching and precise alignment of the waveguide modes on both sides, which is common in coupling between single-channel chips. However, the extremely high precision requirement will result in high processing costs, and as the number of chip waveguides increases, the coupling difficulty will increase exponentially, which cannot cope with actual large-scale production applications. Summary of the invention

[0007] Purpose of the invention: The present invention aims to provide a low-cost tunable laser light source for a multiplexed fiber Bragg grating sensing system.

[0008] Technical solution: The tunable laser light source for spectral sensing described in the present invention is used in a fiber grating sensor or a MEMS fiber sensor. The tunable laser light source includes a tunable DFB laser array chip, an M×M star coupler chip, a semiconductor optical amplifier SOA array chip and an optical fiber array. Each row of tunable lasers is connected by a waveguide, and lasers of adjacent wavelengths are distributed on different waveguides. The M×M star coupler chip, the SOA array chip and the optical fiber array are connected by a waveguide.

[0009] Furthermore, the optical output waveguide of the SOA array chip is an inclined waveguide with an inclination angle of 5° to 15°. The optical output end face of the inclined waveguide is coated with an AR film. The spacing of the SOA array chip is the same as the spacing of the waveguide at the optical output end of the M×M star coupler.

[0010] Furthermore, the backlight end of the tunable DFB laser array chip is provided with an inclined waveguide with a waveguide length of 100 μm to 500 μm, an inclination angle of 7° to 50°, and an AR coating is applied to the end face.

[0011] Furthermore, the M×M type star coupler chip may be replaced by an M×M type multimode interference coupler MMI.

[0012] Furthermore, the waveguides between the tunable DFB laser array chip, the M×M type star coupler chip and the SOA array chip are manufactured by photon wire bonding or butt-joint growth technology, and the waveguides between the SOA array chip and the optical fiber array are manufactured by photon wire bonding technology.

[0013] Furthermore, the tunable DFB laser array chip is manufactured using a reconstruction equivalent chirp technology, where a seed grating is first formed by holographic exposure, and then sampling lithography is performed to introduce an equivalent phase shift or chirp into the +1 or -1 sub-grating, and the laser emission wavelength is changed by designing a sampling period.

[0014] Furthermore, the wavelength interval of the tunable laser of the tunable DFB laser array chip is 1.5 nm to 3.5 nm, and a TEC temperature control module is provided below the tunable laser array chip.

[0015] Furthermore, the waveguide spacing at the optical output ends of the M×M type star coupler chip and the SOA array chip and the spacing between each optical fiber of the optical fiber array are the same, generally 127 μm or 250 μm.

[0016] Furthermore, the tunable DFB laser array chip, the M×M type star coupler chip, the SOA array chip and the optical fiber array are mounted on the same tungsten copper carrier, and the height difference between the chips is compensated by the shape of the tungsten copper carrier.

[0017] Furthermore, SOA is integrated on the waveguide at each optical output end of the tunable DFB laser array chip.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. The present invention uses a star coupler to evenly distribute the energy of different wavelengths of light from the tunable laser array to each optical output waveguide, and respectively enters different fiber grating sensors or fiber MEMS sensors to simultaneously sense temperature or strain, thereby making full use of energy. This solution is equivalent to the effect of simultaneously equipping M groups of traditional tunable light sources, while the overall power consumption of the device is significantly reduced; 2. The present invention uses photon wire bonding or docking growth technology to connect chips of different material systems. 1. The optical output end of the SOA array chip of the present invention is an inclined waveguide with an inclination angle of 5° to 15°, and an AR film is coated on the end face to prevent multi-longitudinal mode lasing caused by end face reflection; 2. The backlight end of the tunable DFB laser is set as an inclined waveguide with a waveguide length of 100μm to 500μm, an inclination angle of 7° to 50°, and an AR coating is used on the end face to ensure that each laser unit works in single mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the present invention;

[0020] Figure 2 It is a schematic diagram of the structure of a single waveguide series laser and semiconductor amplifier SOA;

[0021] Figure 3 The schematic diagram of mounting the tunable DFB laser array chip, the M×M star coupler chip, the SOA array chip and the optical fiber array on the same tungsten copper carrier;

[0022] Figure 4 Schematic diagram of the application of traditional tunable light source in fiber Bragg grating sensing system;

[0023] Figure 5 A schematic diagram of the application of the tunable light source of the present invention in a fiber Bragg grating sensing system;

[0024] Figure 6 Schematic diagram of the structure of integrating SOA on the waveguide at the output end of each row of tunable DFB laser array chip. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the accompanying drawings.

[0026] The tunable laser light source for spectral sensing described in the present invention includes a monolithically integrated M×N matrix-arranged low-cost multi-wavelength tunable laser array chip 1, an M×M star coupler chip 2, an M-channel SOA array chip 3 and an M-channel optical fiber array 4. The output end of each row of the tunable DFB laser array chip integrates SOA to preliminarily balance the optical output power of each row. Each row of tunable lasers is connected by a waveguide, and lasers of adjacent wavelengths are distributed on different waveguides, which are connected to the M×M star coupler chip, the SOA array chip and the optical fiber array through waveguides. Each component is mounted on a tungsten copper substrate, and the height difference between the chips is compensated by the shape of the tungsten copper carrier, so that the waveguides on both sides are almost at the same height. The mounting process only needs to be carried out with the assistance of a CCD with micron-level precision, without the need for complex and precise alignment equipment and operations. The height difference between the waveguides of each chip is generally controlled within 60μm, the horizontal alignment error is generally controlled within 20μm, and the chip spacing is generally controlled within the range of 250-270μm.

[0027] The tunable laser light source for spectral sensing described in the present invention has a total of M optical output ports. Since the M×M star coupler has no energy loss in theory compared to the traditional M×1 combiner, each path can be further split into K paths and connected to K fiber grating sensors respectively. The fiber MEMS sensor can also be connected here. By scanning the laser unit of the same tunable light source, the sensing and demodulation of M×K paths can be realized simultaneously to obtain temperature or strain information, which significantly improves the limit of a single light source. In the traditional solution, if you want to achieve the sensing and demodulation of the same number of paths, you need to set M light sources at the same time, which greatly increases the cost and energy consumption of the system. Specifically, the present invention is explained by taking M=8 and N=3 as an example.

[0028] The 8×3 type monolithic integrated matrix-arranged multi-wavelength tunable laser chip has a total of 8 parallel waveguides, with a spacing generally set to 127μm or 250μm; 3 lasers are made in series on each waveguide. Each laser unit has a different working wavelength, with a wavelength interval of 1.6nm and a starting wavelength of 1529.16nm. A total of 24 laser units can achieve continuous wavelength tuning of the entire C band, and can cover 96 channels with a 50GHz interval specified by the DWDM system in the range of 1529.16-1567.13nm. The continuous wavelength tuning range of each laser unit is 1.6nm, which is the wavelength interval between channels. The tuning process is mainly achieved by changing the temperature. Therefore, a special TEC is set under the tunable laser array chip to control the temperature of the chip. Each laser unit is made using the reconstruction equivalent chirp technology, which can greatly reduce the production cost and achieve precise control of the wavelength. By designing the sampling method, the +1-level sub-grating can be used to introduce an equivalent π phase shift in the resonant cavity. The lasing wavelength of different laser units can be achieved by simply changing the sampling period. In order to ensure that each laser unit can work normally, laser units with adjacent wavelengths are distributed in different waveguides; the lasers with shorter working wavelengths on the same waveguide are closer to the light output end, and when the laser unit far away from the light output end works alone, the laser units through which it emits need to apply transparent current. The end faces on both sides of the chip are coated with an AR film with a reflectivity of 0.1% to ensure the stable single-mode operation of each laser unit. Figure 2The figure shows a schematic diagram of three laser units and a section of SOA in series on a waveguide. Using the reconstruction of equivalent chirp technology, an equivalent π phase shift is introduced in the center of each laser unit. Each laser unit has a different sampling period, corresponding to a different lasing wavelength, where a shorter sampling period means a shorter working wavelength and a position closer to the output end face. When LD2 works alone, LD1 needs to apply a transparent current, and when LD3 works alone, LD1 and LD2 need to apply a transparent current. There is electrical isolation between the laser units to ensure that each laser can work normally independently. The SOA set at the optical output end can preliminarily balance the output power of each channel.

[0029] The star coupler adopts an 8×8 port design, which is used to evenly distribute the light of each wavelength emitted by the 8 ports of the multi-wavelength tunable laser array chip to 8 optical output ports. Each port contains the wavelength incident from each port. Compared with the 8×1 cascaded Y waveguide or MMI structure combiner, it can fully utilize the energy. At the same time, each channel can be connected to the multi-channel fiber grating sensor or fiber MEMS sensor through beam splitting, so that more channels of signal sensing can be achieved while reducing the number of tunable light sources used, and the overall power consumption of the device can be significantly reduced. The star coupler can be made of materials such as silicon, silicon nitride, and silicon dioxide, and can also be made and connected on the same wafer with the tunable laser array chip through ButtJoint technology. The waveguide spacing of the star coupler input port must be consistent with the output waveguides of the multi-wavelength tunable laser array chip; the spacing of the waveguides of the optical output port must match the subsequent connected SOA array chip and single-mode fiber array, which is generally set to 127μm or 250μm.

[0030] The 8-channel SOA array chip is used to amplify the outgoing light of the 8 optical output ports of the star coupler. It can be made on the same wafer as the multi-wavelength tunable array chip. It has a simple structure and is conducive to reducing the overall production cost of the light source. The end faces on both sides of the chip are coated with an AR film with a reflectivity of 0.1%. At the same time, the waveguide at the optical output end is tilted at 7° to prevent the end face reflection from causing multi-longitudinal mode lasing. The waveguide spacing at the ports on both sides of the chip is generally 127μm or 250μm, which is consistent with the channel spacing at the optical output port of the star coupler and the optical fiber array port.

[0031] The conventional spacing of the 8-channel fiber array is 127μm or 250μm, which needs to be consistent with the waveguide spacing of the optical output port of the SOA array chip. The single-mode fiber of each channel is fixed on a glass substrate with a V-groove engraved on the surface. The photon lead bonding process requires the removal of the glass cover on the upper surface of the fiber. The single-mode fiber can be replaced with a polarization-maintaining fiber.

[0032] After the PWB processing is completed, it is developed with PGMEA and isopropyl alcohol respectively, and blown dry with nitrogen. Use a metallographic microscope to inspect the polymer waveguide. If there is no abnormal deformation or disconnection at the port connection, place it on a heating table at 80-85℃ for 1-2 hours to fully solidify the polymer waveguide and increase its structural stability and mechanical strength. In order to ensure the long-term stability of the polymer waveguide structure, it is generally necessary to make an air cladding to cover it.

[0033] In order to further illustrate the remarkable effect of the present invention in the field of spectral sensing, Figure 4 and Figure 5 The applications of the traditional tunable light source and the tunable light source of the present invention in the fiber Bragg grating sensing scenario are respectively demonstrated. The traditional solution uses an 8×1 MMI structure to merge the output light of each channel of the laser array chip into a waveguide. This process causes at least 9dB of energy loss per channel. It is then divided into several channels (generally limited to 16 channels) by an optical splitter. Each channel can be connected to a sensor made with several fiber Bragg gratings connected in series, and the temperature or strain sensing is realized by demodulation; the solution of the present invention uses a star coupler to evenly distribute the emission light of the tunable laser array chip to 8 ports. In theory, there is no energy loss, and each optical output port can achieve the same effect of the traditional solution, so that up to 128 channels of sensing can be supported at the same time. The traditional solution needs to be equipped with 8 tunable laser array chips to achieve this effect, and needs to be equipped with corresponding MMI combiner chips, TEC, etc., which will significantly increase the overall cost and power consumption of the system. Therefore, the advantages of the present invention in the field of spectral perception sensing are obvious.

Claims

1. A tunable laser light source for spectral sensing, used in a fiber grating sensor or a MEMS fiber sensor, characterized in that: The tunable laser light source comprises a tunable DFB laser array chip (1), an M×M type star coupler chip (2), an SOA array chip (3) and an optical fiber array (4); each row of tunable lasers is connected via a waveguide; lasers of adjacent wavelengths are distributed on different waveguides and connected to the M×M type star coupler chip (2), the SOA array chip (3) and the optical fiber array (4) via a waveguide.

2. The tunable laser light source for spectral sensing according to claim 1, characterized in that: The waveguides between the tunable DFB laser array chip (1), the M×M type star coupler chip (2) and the SOA array chip (3) are manufactured by photon wire bonding or butt-joint growth technology, and the waveguides between the SOA array chip (3) and the optical fiber array (4) are manufactured by photon wire bonding (5) technology.

3. The tunable laser light source for spectral sensing according to claim 1, characterized in that: The tunable DFB laser array chip (1) is manufactured by using a reconstruction equivalent chirp technology, wherein a seed grating is first formed by holographic exposure, and then sampling lithography is performed to introduce an equivalent phase shift or chirp into a +1-level or -1-level sub-grating, and the laser emission wavelength is changed by setting a sampling period.

4. The tunable laser light source for spectral sensing according to claim 2, characterized in that: The tunable DFB laser array chip (1) is manufactured by using a reconstruction equivalent chirp technology, wherein a seed grating is first formed by holographic exposure, and then sampling lithography is performed to introduce an equivalent phase shift or chirp into a +1-level or -1-level sub-grating, and the laser emission wavelength is changed by setting a sampling period.

5. The tunable laser light source for spectral sensing according to claims 1-4, characterized in that: The waveguide on the light output side of the SOA array chip (3) is an inclined waveguide with an inclination angle of 5° to 15°. The light output end face of the inclined waveguide is plated with an AR film. The spacing of the SOA array chips is the same as the spacing of the waveguides at the light output end of the M×M type star coupler.

6. The tunable laser light source for spectral sensing according to claims 1-4, characterized in that: The wavelength interval of the tunable laser of the tunable DFB laser array chip (1) is 1.5 nm to 3.5 nm, and a TEC temperature control module is provided below the tunable laser array chip.

7. The tunable laser light source for spectral sensing according to claims 1-4, characterized in that: The M×M type star coupler chip (2) can be replaced by an M×M type multimode interference coupler MMI.

8. The tunable laser light source for spectral sensing according to claims 1-4, characterized in that: The tunable DFB laser array chip (1), the M×M type star coupler chip (2), the SOA array chip (3) and the optical fiber array (4) are mounted on the same tungsten copper carrier, and the height difference between the chips is compensated by the shape of the tungsten copper carrier.

9. The tunable laser light source for spectral sensing according to claims 1-4, characterized in that: The backlight end on the other side of the tunable DFB laser array chip (1) is provided with an inclined waveguide with a length of 100 μm to 500 μm, an inclination angle of 7° to 50°, and an AR coating is applied to the end face.

10. The tunable laser light source for spectral sensing according to claims 1-4, characterized in that: An SOA array is integrated on the optical output waveguide of the tunable DFB laser array chip (1).

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