Tunable laser light source for spectrum sensing

Abstract

The utility model discloses a tunable laser light source for spectrum sensing, 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 optical fiber array is connected with the star coupler chip. The light output end of each waveguide is provided with an SOA. According to the utility model, 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, and the energy respectively enters different fiber grating sensors or fiber MEMS sensors and the like to realize temperature or strain sensing at the same time and realize multiplexing tree-shaped sensing and demodulation at the same time; 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] This utility model relates to the field of laser technology, and in particular to a tunable laser source for spectral sensing. Background Technology

[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, and spectral sensing fiber optic sensing includes fiber optic grating sensing and MEMS fiber optic sensing. Because fiber optic grating sensors are wavelength (frequency) identifiers, they offer high measurement reliability and accuracy. They can replace traditional point-type temperature, strain, and stress (pressure) electrical sensors. Through weak grating sensing technology, they can also achieve quasi-continuous monitoring and sensing, and their compatibility with fiber optic networks allows them to form unique advantages in fiber optic sensor networks. These advantages have led to their widespread application in numerous disciplines, including aircraft, large ship health structure monitoring, dams, oil exploration, high-speed rail, new energy, geological research, and disaster analysis. In particular, with the development of artificial intelligence, the simplicity, accuracy, flexibility, and low cost of their detection capabilities can provide significant support for the development of intelligent sensing science.

[0003] Fiber Bragg grating sensors based on spontaneous emission (ASE) broadband light sources and CCD schemes employ volume gratings to split the light for CCD acquisition. Because their light source is an ASE source, its power density is low, necessitating the use of optical switches to switch the sensing channels. Another approach is based on FP filter-type scanning fiber lasers, using piezoelectric ceramics to drive a coated cavity to complete wavelength scanning, thereby changing the wavelength of the fiber laser. However, due to the use of mechanical components, their stability and shock resistance are poor.

[0004] Currently, mainstream scanning tunable lasers are semiconductor tunable lasers based on distributed reflector (DBR) structures and the Vernier effect. The tunability of DBR lasers can only be achieved at a series of isolated points within a certain frequency range in the spectrum, and cannot achieve continuous tuning within a certain frequency range. During rapid step scanning, mode hopping can occur, requiring algorithmic correction, which affects the stability and measurement results.

[0005] Tunable lasers can be realized using series-parallel DFB laser arrays, where the wavelength is changed by altering the temperature inside the laser chip. However, DFB arrays are typically fabricated using electron beam lithography, which is time-consuming and introduces significant random errors in the wavelength, leading to substantial discrepancies between the fabricated laser and the designed wavelength. A major drawback of series-parallel tunable DFB laser arrays is the significant energy loss in the final output light after combining the array using an N×1 type multiplexer (such as a cascaded Y-waveguide or MMI structure). Here, N represents the number of input waveguides in parallel. Ignoring additional losses due to imperfections in the fabrication process, ideally, only 1 / N of the input light from each channel can couple to the output waveguide after combining, resulting in low efficiency and increased power consumption in practical applications.

[0006] For optical interconnects between chips made of different materials, traditional end-to-end coupling technology requires matching and precise alignment of waveguide modes on both sides, which is commonly used for coupling between single-channel chips. However, the extremely high precision requirements result in high processing costs, and the coupling difficulty increases exponentially with the number of waveguides on the chip, making it unsuitable for large-scale production applications. Utility Model Content

[0007] Purpose of the utility model: The present utility model aims to provide a low-cost tunable laser source for fiber optic grating sensing systems with multiplexing serial connections.

[0008] Technical Solution: The tunable laser source for spectral sensing described in this utility model is used in fiber optic grating sensors or MEMS fiber optic sensors. The tunable laser source includes a tunable DFB laser array chip, an M×M star coupler chip, a semiconductor optical amplifier (SOA) array chip, and a fiber array. Each row of tunable lasers is connected by waveguides, and lasers of adjacent wavelengths are distributed on different waveguides. The M×M star coupler chip, SOA array chip, and fiber array are connected by waveguides.

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

[0010] Furthermore, the tunable DFB laser array chip has a tilted waveguide with a waveguide length of 100μm to 500μm and a tilt angle of 7° to 50° at the backlight end, and the end face is coated with AR film.

[0011] Furthermore, the M×M star coupler chip can be replaced with an M×M multimode interference coupler (MMI).

[0012] Furthermore, the waveguides between the tunable DFB laser array chip, the M×M star coupler chip, and the SOA array chip are fabricated using photonic wire bonding or docking growth technology, and the waveguides between the SOA array chip and the fiber array are fabricated using photonic wire bonding technology.

[0013] Furthermore, the tunable DFB laser array chip is fabricated using reconstructed equivalent chirp technology. First, a seed grating is formed by holographic exposure, and then sampling photolithography is performed. An equivalent phase shift or chirp is introduced in the +1 or -1 level sub-grating, and the laser emission wavelength is changed by designing the sampling period.

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

[0015] Furthermore, the waveguide spacing at the optical output end of the M×M star coupler chip and the SOA array chip, as well as the spacing of each fiber in the fiber array, are the same, typically 127μm or 250μm.

[0016] Furthermore, the tunable DFB laser array chip, M×M star coupler chip, SOA array chip, and 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 the optical output end of each row of the tunable DFB laser array chip.

[0018] Beneficial Effects: Compared with the prior art, the significant advantages of this invention are: 1. This invention uses a star coupler to evenly distribute the energy of different wavelengths of light from a tunable laser array to each optical output waveguide, which then enters different fiber Bragg grating sensors or fiber MEMS sensors to simultaneously achieve temperature or strain sensing, thus fully utilizing the energy. This scheme is equivalent to simultaneously equipping M groups of traditional tunable light sources, while significantly reducing the overall power consumption of the device; 2. This invention uses photonic wire bonding or docking growth technology to bond chips of different material systems. Coupled between the components, the photonic wire bonding technology does not require high-precision alignment, has high processing efficiency, achieves low-cost hybrid integration between chips, and the overall device is compact; 3. The optical output end of the SOA array chip of this utility model is a tilted waveguide with a tilt angle of 5° to 15°, and the end face is coated with an AR film to prevent multi-mode lasing caused by end face reflection; 4. The backlight end of the tunable DFB laser is set as a tilted waveguide with a waveguide length of 100μm to 500μm and a tilt angle of 7° to 50°, and the end face is coated with an AR film to ensure that each laser unit operates in single mode. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of this utility model;

[0020] Figure 2 This is a schematic diagram of a single-waveguide series laser and semiconductor amplifier SOA structure.

[0021] Figure 3 A schematic diagram showing the mounting of a tunable DFB laser array chip, an M×M star coupler chip, an SOA array chip, and a fiber array onto the same tungsten copper carrier.

[0022] Figure 4 This is a schematic diagram of the application of a traditional tunable light source in a fiber Bragg grating sensing system.

[0023] Figure 5 This is a schematic diagram illustrating the application of the tunable light source of this invention in a fiber optic grating sensing system.

[0024] Figure 6 This is a schematic diagram of the structure of SOA integrated on the waveguide of each row of optical output of a tunable DFB laser array chip. Detailed Implementation

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

[0026] The tunable laser source for spectral sensing described in this invention comprises 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 fiber array 4. Each row of the tunable DFB laser array chip integrates an SOA at its output end to initially equalize the optical output power of each row. The tunable lasers in each row are connected via waveguides, with lasers of adjacent wavelengths distributed on different waveguides, and connected to the M×M star coupler chip, SOA array chip, and fiber array via waveguides. All components are mounted on a tungsten-copper substrate. The shape of the tungsten-copper substrate compensates for the height difference between the chips, ensuring that the waveguides on both sides are almost at the same height. The mounting process only requires the assistance of a micron-level precision CCD, eliminating the need for complex and precise alignment equipment and operations. The height difference between 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 source for spectral sensing described in this invention has M optical output ports. Since the M×M star coupler theoretically has no energy loss compared to the traditional M×1 combiner, each path can be further split into K paths, which are then connected to K fiber Bragg grating sensors. Alternatively, fiber optic MEMS sensors can be connected. By scanning the laser units of the same tunable source, sensing and demodulation of M×K paths can be achieved simultaneously, obtaining temperature or strain information, significantly improving the limits of a single light source. Traditional solutions require M light sources to achieve the same number of sensing and demodulation paths, greatly increasing system cost and energy consumption. Specifically, this invention is illustrated using M=8 and N=3 as an example.

[0028] The 8×3 type monolithic integrated matrix-arranged multi-wavelength tunable laser chip has eight parallel waveguides, typically spaced 127μm or 250μm apart; three lasers are connected in series on each waveguide. Each laser unit has a different operating wavelength, with a wavelength spacing of 1.6nm and a starting wavelength of 1529.16nm. A total of 24 laser units can achieve continuous wavelength tuning across the entire C-band and cover 96 channels within the 50GHz interval specified by DWDM systems in the 1529.16-1567.13nm range. The continuous wavelength tuning range of each laser unit is 1.6nm, which is the wavelength spacing between channels. Tuning is mainly achieved by changing the temperature; therefore, a dedicated TEC (Temperature Control Unit) is placed below the tunable laser array chip to control the chip's temperature. Each laser unit is fabricated using reconfigured equivalent chirp technology, which significantly reduces manufacturing costs and allows for precise wavelength control. By designing the sampling method, an equivalent π phase shift can be introduced into the resonant cavity using a +1-order sub-grating. The lasing wavelengths of different laser units can be varied simply by changing the sampling period. To ensure the proper functioning of each laser unit, adjacent wavelength laser units are distributed across different waveguides; lasers on the same waveguide with shorter operating wavelengths are positioned closer to the optical output end, and when a laser unit far from the optical output end operates independently, a transparent current needs to be applied to all laser units it passes through. The chip's two end faces are coated with an AR film with a reflectivity of 0.1% to ensure stable single-mode operation of each laser unit. Figure 2The diagram shows three laser units and an SOA (Optical Output Amplifier) ​​connected in series on a waveguide. Using reconfiguration equivalent chirp technology, an equivalent π phase shift is introduced at the center of each laser unit. Each laser unit has a different sampling period, corresponding to a different lasing wavelength; a shorter sampling period means a shorter operating wavelength and a position closer to the output facet. When LD2 operates alone, LD1 requires a transparent current, while when LD3 operates alone, both LD1 and LD2 require transparent currents. Electrical isolation is provided between the laser units to ensure that each laser can operate independently. The SOA at the optical output end can initially equalize the output power of each path.

[0029] The star coupler employs an 8×8 port design to evenly distribute the light emitted from the eight ports of a multi-wavelength tunable laser array chip to eight optical output ports. Each port contains the wavelengths incident from each port. Compared to 8×1 cascaded Y-waveguides or MMI multiplexers, this design achieves fuller energy utilization. Furthermore, each output can be split and connected to multiple fiber Bragg grating sensors or fiber MEMS sensors, thus reducing the number of tunable light sources required while sensing more signals and significantly reducing overall device power consumption. The star coupler can be fabricated using materials such as silicon, silicon nitride, and silicon dioxide, and can also be fabricated and connected to the tunable laser array chip on the same wafer using ButtJoint technology. The waveguide spacing at the input ports of the star coupler must be consistent with the output waveguides of the multi-wavelength tunable laser array chip; the waveguide spacing at the output ports must match the subsequent SOA array chip and single-mode fiber array, typically set to 127μm or 250μm.

[0030] The 8-channel SOA array chip amplifies the output light from each of the eight optical output ports of the star coupler. It can be fabricated on the same wafer as a multi-wavelength tunable array chip, resulting in a simple structure and reducing the overall manufacturing cost of the light source. The chip's two end faces are coated with an AR film with a reflectivity of 0.1%, and the waveguide at the optical output end is tilted at 7° to prevent multi-mode lasing caused by end face reflection. The waveguide spacing at the two ports of the chip is typically 127μm or 250μm, consistent with the channel spacing at the optical output ports of the star coupler and the fiber array ports, respectively.

[0031] The standard spacing of an 8-channel fiber optic array is 127μm or 250μm, which needs to be consistent with the waveguide spacing of the optical output ports of the SOA array chip. Each channel's single-mode fiber is fixed to a glass substrate with V-grooves etched on its surface. Photonic wire bonding requires the removal of the glass cover plate on the upper surface of the fiber. The single-mode fiber can be replaced with polarization-maintaining fiber.

[0032] After PWB processing, the polymer waveguide is developed using PGMEA and isopropanol, and then dried with nitrogen. Microscopic examination using a metallographic microscope is performed. If no abnormal deformation or breakage is found at the port connection, the waveguide is immediately placed on a heating stage at 80-85℃ for 1-2 hours to completely solidify it, increasing its structural stability and mechanical strength. To ensure the long-term stability of the polymer waveguide structure, an air cladding is generally fabricated to encapsulate it.

[0033] To further illustrate the significant effects of this invention in the field of spectral sensing... Figure 4 and Figure 5 The applications of traditional tunable light sources and the tunable light source of this invention in fiber Bragg grating sensing scenarios are demonstrated respectively. The traditional approach uses an 8×1 MMI structure to combine the output light from each path of the laser array chip into a single waveguide. This process results in at least 9dB of energy loss per path. The light is then split into several paths (typically up to 16) by an optical splitter. Each path can be connected to a sensor with several cascaded fiber Bragg gratings for demodulation, enabling temperature or strain sensing. The present invention uses a star coupler to evenly distribute the emitted light from the tunable laser array chip to eight ports, theoretically resulting in no energy loss. Each output port achieves the same effect as the traditional approach, allowing for up to 128 simultaneous sensing paths. Achieving this effect with the traditional approach requires eight tunable laser array chips, along with corresponding MMI combiner chips, TECs, etc., significantly increasing the overall system cost and power consumption. Therefore, the present invention has clear advantages in the field of spectral sensing.

Claims

1. A tunable laser source for spectral sensing, used in fiber Bragg grating sensors or MEMS fiber optic sensors, characterized in that, The tunable laser source includes a tunable DFB laser array chip (1), an M×M star coupler chip (2), an SOA array chip (3), and an optical fiber array (4). Each row of tunable lasers is connected by waveguides, and lasers of adjacent wavelengths are distributed on different waveguides and connected to the M×M star coupler chip (2), SOA array chip (3), and optical fiber array (4) through waveguides.

2. The tunable laser source for spectral sensing according to claim 1, characterized in that, The waveguides between the tunable DFB laser array chip (1), the M×M star coupler chip (2) and the SOA array chip (3) are fabricated by photonic wire bonding or docking growth technology, and the waveguides between the SOA array chip (3) and the fiber array (4) are fabricated by photonic wire bonding (5) technology.

3. The tunable laser source for spectral sensing according to claim 1, characterized in that, The tunable DFB laser array chip (1) is fabricated using reconstructed equivalent chirp technology. First, a seed grating is formed by holographic exposure, and then sampling photolithography is performed. An equivalent phase shift or chirp is introduced in the +1 or -1 level sub-grating. The laser emission wavelength is changed by setting the sampling period.

4. The tunable laser source for spectral sensing according to claim 2, characterized in that, The tunable DFB laser array chip (1) is fabricated using reconstructed equivalent chirp technology. First, a seed grating is formed by holographic exposure, and then sampling photolithography is performed. An equivalent phase shift or chirp is introduced in the +1 or -1 level sub-grating. The laser emission wavelength is changed by setting the sampling period.

5. The tunable laser source for spectral sensing according to any one of claims 1-4, characterized in that, The waveguide on the optical output side of the SOA array chip (3) is a tilted waveguide with a tilt angle of 5°~15°. The optical output end face of the tilted 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.

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

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

8. The tunable laser source for spectral sensing according to any one of claims 1-4, characterized in that, The tunable DFB laser array chip (1), M×M star coupler chip (2), SOA array chip (3) and 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 source for spectral sensing according to any one of claims 1-4, characterized in that, The other side of the tunable DFB laser array chip (1) has a tilted waveguide with a length of 100μm~500μm and a tilt angle of 7°~50°. The end face is coated with AR film.

10. The tunable laser source for spectral sensing according to any one of 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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