An ASE light source structure integrated on a thin-film lithium niobate sheet

Abstract

The invention discloses an ASE light source structure integrated on a thin-film lithium niobate sheet, comprising a pump light source, a wavelength division multiplexer, an erbium-doped lithium niobate waveguide region, a Faraday reflector, an isolator, a beam splitter, a coupling grating group, and a photodetector; the pump light source is connected to the wavelength division multiplexer, and the coupling grating group and the photodetector are connected to the beam splitter; the pump light emitted by the pump light source is transmitted from the waveguide output end in the wavelength division multiplexer to the erbium-doped lithium niobate waveguide region, the erbium-doped lithium niobate waveguide region absorbs the pump light and releases C-band signal light, the C-band signal light is reflected by the Faraday reflector, enters the erbium-doped lithium niobate waveguide region again to absorb and amplify the C-band signal light, the amplified C-band signal light coming out of the erbium-doped lithium niobate waveguide region enters the beam splitter to separate part of the intrinsic signal light, the photodetector monitors the intrinsic signal light, and feeds back the monitoring result to the pump light source in real time. The present invention can be hybrid integrated into a high-precision full-chip optical gyroscope to improve its measurement accuracy and stability.

Description

Technical Field

[0001] The invention belongs to photon integration technology, and in particular relates to an ASE light source structure integrated on a thin-film lithium niobate sheet. Background Art

[0002] With the development of fiber-optic communication components and digital signal processing, the life of interferometric fiber-optic gyroscopes has been greatly improved, and their accuracy is also breaking through the performance limitations of traditional mechanical gyroscopes and laser gyroscopes. Ultra-high precision has become an important advantage of interferometric fiber-optic gyroscopes, and its application directions include space orientation, strategic missile guidance, and submarine inertial navigation. Foreign inertial navigation systems based on fiber-optic gyroscopes have been reported and are being continuously studied, and their zero bias stability reaches 0.0001° / h. High-power Gaussian broadband erbium-doped fiber light sources are key components of ultra-high precision fiber-optic gyroscopes, with advantages such as high power and good wavelength stability. Currently, the commonly used ASE Gaussian light sources are all based on all-fiber structures. During the assembly process, the optical fiber needs to be coiled, which may cause polarization crosstalk. At the same time, there are a large number of fiber fusion points. If the fusion points are not properly handled, the polarization extinction ratio of the light becomes smaller or the polarization state changes. When the all-fiber ASE Gaussian light source is used for a fiber-optic gyroscope, it will affect the measurement accuracy and performance of the fiber-optic gyroscope. Therefore, the structure of the ASE Gaussian light source is optimized and improved, thereby improving the accuracy and stability of the high-precision fiber-optic gyroscope. Summary of the invention

[0003] Purpose of the invention: The purpose of the present invention is to provide an ASE light source structure integrated on a thin-film lithium niobate sheet, which can be hybrid-integrated into a high-precision full-chip optical gyroscope to improve its measurement accuracy and stability.

[0004] Technical solution: The ASE light source structure integrated on the thin-film lithium niobate chip of the present invention comprises a pump light source, a wavelength division multiplexer, an erbium-doped lithium niobate waveguide region, a Faraday reflector, an isolator, a beam splitter, and a coupling grating group arranged on the thin-film lithium niobate chip; the pump light source is connected to the wavelength division multiplexer, the beam splitter is connected to the coupling grating group, and a photodetector is fixed on the upper surface of the coupling grating group; the pump light emitted by the pump light source is transmitted from the waveguide output end in the wavelength division multiplexer to the erbium-doped niobate waveguide region, a Faraday reflector, an isolator, a beam splitter, and a coupling grating group. The erbium-doped lithium niobate waveguide area absorbs the pump light and releases the C-band signal light. The C-band signal light is reflected by the Faraday reflector and enters the erbium-doped lithium niobate waveguide area again to absorb and amplify the C-band signal light. The amplified C-band signal light coming out of the erbium-doped lithium niobate waveguide area enters the beam splitter to separate part of the intrinsic signal light. The intrinsic signal light is received by the photodetector through the coupled grating group. The photodetector monitors the intrinsic signal light and feeds the monitoring result back to the pump light source in real time.

[0005] Furthermore, an isolator is provided on the optical path between the erbium-doped lithium niobate waveguide region and the beam splitter to maintain unidirectional transmission of the C-band signal light and prevent return light from entering the erbium-doped lithium niobate waveguide region, thereby reducing the signal light amplification gain and causing unstable output signal light power.

[0006] Furthermore, when the output power of the intrinsic signal light fluctuates, the photodetector detects the fluctuation ratio and feeds it back to the driving device of the pump light source. The driving device of the pump light source adjusts the driving current according to the fluctuation ratio to ensure stable output of the signal light.

[0007] Furthermore, the pump light source optimizes the molecular bonding process and directly bonds the III-V epitaxy to the thin-film lithium niobate chip, so that the pump laser can be directly diffused into the lithium niobate waveguide without the need for external direct coupling or single lens indirect coupling into the lithium niobate waveguide, which is beneficial to the integrity of the structure and is not affected by vibration.

[0008] Furthermore, the wavelength division multiplexer combines optical signals of different wavelengths into the same medium for transmission.

[0009] Furthermore, the erbium-doped lithium niobate waveguide region is a specific area of ​​the thin-film lithium niobate chip that is doped with Er3+ ions at a high solubility of up to 1×10^20cm^-3.

[0010] Furthermore, the Er3+ ion solubility in the erbium-doped lithium niobate waveguide region is different, and the spectral width of the C band emitted spontaneously is different.

[0011] Furthermore, the Faraday reflector, erbium-doped lithium niobate waveguide region, wavelength division multiplexer, isolator, and beam splitter are integrated on a thin-film lithium niobate chip by photolithography.

[0012] Furthermore, two adjacent devices in the Faraday reflector, erbium-doped lithium niobate waveguide region, wavelength division multiplexer, isolator, and beam splitter are optically interconnected through a thin-film lithium niobate ridge waveguide structure, and the signal light is completely transmitted in the lithium niobate waveguide.

[0013] Furthermore, the thin-film lithium niobate ridge waveguide structure comprises, from bottom to top, a silicon base layer, a silicon dioxide lower cladding layer, a thin-film lithium niobate ridge waveguide layer, and a silicon dioxide lower cladding layer.

[0014] Beneficial effects: Compared with the prior art, the significant technical effects of the present invention are as follows:

[0015] The present invention integrates various passive devices on thin-film lithium niobate materials to construct a dual-pass amplification structure ASE light source. By growing or photolithography micro-devices on thin-film lithium niobate waveguides, the signal light is completely transmitted in the lithium niobate waveguide, and polarization crosstalk caused by pigtail fiber coiling and deterioration of spectral modulation caused by fiber fusion end face reflection will not occur, so that the output power and spectrum are more stable. At the same time, the full-chip design is adopted, and it can be hybrid integrated into a high-precision full-chip optical gyroscope, reducing external connections between devices, realizing the integration of fiber optic gyroscopes, and thus improving the accuracy and stability of high-precision fiber optic gyroscopes. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of the structure of an ASE light source structure integrated on a thin-film lithium niobate sheet disclosed in an embodiment of the present invention;

[0017] Figure 2 A schematic structural diagram of a thin-film lithium niobate ridge waveguide structure disclosed in an embodiment of the present invention;

[0018] Figure 3 A schematic diagram of the structure of a pump light source disclosed in an embodiment of the present invention;

[0019] Figure 4 This is a schematic diagram of the photodetector coupling method disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is described in detail below in conjunction with specific implementation methods and the accompanying drawings of the specification.

[0021] like Figure 1 As shown, the thin-film lithium niobate on-chip integrated ASE light source structure of the present invention comprises a pump light source 1, a wavelength division multiplexer 2, an erbium-doped lithium niobate waveguide region 3, a Faraday reflector 4, an isolator 5, a beam splitter 6, a coupling grating group 7, and a photodetector, which are arranged on a thin-film lithium niobate chip based on a silicon base or a quartz base. Among them, the pump light source 1 is connected to the wavelength division multiplexer 2, the beam splitter 6 is connected to the coupling grating group 7, and a photodetector 8 is fixed on the upper surface of the coupling grating group 7.

[0022] The pump light emitted by the pump light source 1 is transmitted from the waveguide output end in the wavelength division multiplexer 2 to the erbium-doped lithium niobate waveguide area 3. The erbium-doped lithium niobate waveguide area 3 absorbs the pump light and releases C-band signal light. The C-band signal light is reflected by the Faraday reflector 4 and enters the erbium-doped lithium niobate waveguide area 3 again to absorb and amplify the C-band signal light. The amplified C-band signal light coming out of the erbium-doped lithium niobate waveguide area 3 enters the beam splitter 6 to separate part of the intrinsic signal light. The intrinsic signal light is received by the photodetector 8 through the coupling grating group 7. The photodetector 8 monitors the intrinsic signal light and feeds back the monitoring result to the pump light source 1 in real time.

[0023] In order to keep the C-band signal light in unidirectional transmission and prevent the return light from entering the erbium-doped lithium niobate waveguide area 3, reducing the signal light amplification gain and causing the output signal light power to be unstable, an isolator 5 is provided on the optical path between the erbium-doped lithium niobate waveguide area 3 and the beam splitter 6. The amplified C-band signal light enters the beam splitter 6 after passing through the isolator 5, and the amplified C-band signal light is transmitted unidirectionally through the isolator 5. The isolator ensures the unidirectional transmission of the signal light and prevents the return light from entering the erbium-doped lithium niobate waveguide area, absorbing Er3+ ions, competing with the signal light mode, and affecting the output power.

[0024] In this embodiment, the pump light source 1 provides a 980nm pump laser, and the pump light passes through the wavelength division multiplexer 2 and enters the lithium niobate waveguide for transmission; the pump light is transmitted forward through the erbium-doped lithium niobate waveguide area 3, and after the Er3+ ions on the erbium-doped lithium niobate waveguide area 3 absorb the pump light, the atomic transition releases the C-band signal light. The Faraday rotator 4 is used to reflect the signal light, change the propagation direction of the signal light, and make the signal light enter the erbium-doped lithium niobate waveguide area 3 again, and fully absorb the pump light through the back-and-forth secondary absorption amplification, thereby increasing the output signal light power; the spectral reflectivity of the Faraday reflector to the C-band is greater than 99%. The splitting ratio of the beam splitter is 1 / 99, of which the 1% end is connected to the photodetector, and 1% of the local light is used for signal monitoring. The beam splitter 6 is used to provide part of the intrinsic signal light, which is output to the photodetector 8. The photodetector 8 monitors the change state of the reflected part of the intrinsic light. When the output power of the intrinsic signal light fluctuates, the photodetector 8 detects the fluctuation ratio and feeds it back to the driving device of the pump light source 1. The driving device of the pump light source 1 adjusts the driving current according to the fluctuation ratio, thereby changing the current size of the pump light, thereby reducing the power fluctuation of the signal light. The photodetector 8 is used to monitor the fluctuation of the output signal light. When the signal light fluctuates, the photodetector 8 converts the power difference of the fluctuation into the current difference, and feeds it back to the driving current of the pump source, thereby achieving the effect of power stabilization.

[0025] In the present invention, the so-called on-chip refers to various passive devices grown or photolithographically formed on lithium niobate material; in this embodiment, the Faraday reflector 4, the erbium-doped lithium niobate waveguide region 3, the wavelength division multiplexer 2, the isolator 5, the beam splitter 6 and the coupling grating group 7 are integrated on the thin film lithium niobate chip by photolithography.

[0026] The Faraday reflector 4, the erbium-doped lithium niobate waveguide region 3, the wavelength division multiplexer 2, the isolator 5, the beam splitter 6 and the two adjacent devices in the coupling grating group 7 are optically interconnected through the thin film lithium niobate ridge waveguide structure. Figure 2 As shown, the thin-film lithium niobate ridge waveguide structure is composed of a silicon substrate layer Si, a silicon dioxide lower cladding layer SiO2, a thin-film lithium niobate ridge waveguide layer LN Film, and a silicon dioxide lower cladding layer SiO2 from bottom to top.

[0027] like Figure 3 As shown, the pump light source 1 directly bonds the III-V epitaxy to the thin-film lithium niobate chip by optimizing the molecular bonding process, so that the pump laser can be directly diffused into the lithium niobate waveguide without the need for external direct coupling or single lens indirect coupling into the lithium niobate waveguide, which is beneficial to the integrity of the structure and is not affected by vibration. The pump light source 1 emits a pump laser with a wavelength of 980nm, which diffuses into the thin-film lithium niobate ridge waveguide layer LN Film.

[0028] The wavelength division multiplexer 2 utilizes wavelength division multiplexing technology to combine optical signals of different wavelengths into the same medium for transmission.

[0029] Erbium-doped lithium niobate waveguide region 3 is a waveguide of a 2mm thin-film lithium niobate chip with high-solubility Er3+ ions doped with a concentration of up to 1×10^20cm^-3. When Er3+ ions are excited by light with a wavelength of 980nm or 1480nm and absorb the energy of the pump light, the metastable Er3+ ions transition to the ground state by spontaneous radiation and emit C-band light.

[0030] The Er3+ ion solubility of the Er-doped LiNbO3 waveguide region 3 is different, and the spectrum width of the C-band emitted spontaneously is different. By increasing or decreasing the length or solubility of the Er-doped LiNbO3 waveguide region, the ideal output spectrum width and shape can be obtained.

[0031] like Figure 4 As shown, the photodetector 8 is fixed to the upper surface of the coupling grating group 7 using optical glue. The signal light of the waveguide changes the propagation direction of the light through the interference effect and diffraction effect of the coupling grating group 8, and scatters the signal light vertically upward. When the receiving photosensitive surface of the photodetector is large enough, the photodetector can 100% receive the 1% intrinsic light separated from the beam splitter.

[0032] The photodetector is an ordinary InGaAs PIN detection chip with a typical current response η of about 0.95A / W (@1550nm). It is used to monitor the fluctuation of the intrinsic signal light. When the signal light fluctuates, the photodetector converts the power difference of the fluctuation into the current difference, and uses the change in the output current as a feedback signal, which is input into the driving control circuit of the pump light to change the power of the pump light and form a closed-loop feedback state, thereby achieving the purpose of stabilizing the output signal light.

[0033] The present invention integrates various passive devices on thin-film lithium niobate materials, constructs a double-pass amplification structure ASE light source, and increases the output signal light power. By growing or photolithography micro-devices on thin-film lithium niobate waveguides, the signal light is completely transmitted in the lithium niobate waveguide, and polarization crosstalk caused by pigtail fiber coiling and deterioration of spectral modulation caused by fiber fusion end face reflection will not occur, so that the output power and spectrum are more stable. At the same time, the full-chip design is adopted, and it can be hybrid integrated into a high-precision full-chip optical gyroscope, reducing external connections between devices, realizing the integration of fiber optic gyroscopes, and thus improving the accuracy and stability of high-precision fiber optic gyroscopes.

[0034] The present invention integrates various passive devices and heterogeneous growth technology on the thin-film lithium niobate sheet to realize a full-chip ASE light source. This structure has high integration and small size, and can adapt to the needs of various high-precision gyroscope light sources in the future.

Claims

1. An ASE light source structure integrated on a thin-film lithium niobate sheet, characterized in that: The invention comprises a pump light source (1), a wavelength division multiplexer (2), an erbium-doped lithium niobate waveguide region (3), a Faraday reflector (4), an isolator (5), a beam splitter (6), a coupling grating group (7) and a photodetector (8) arranged on a thin-film lithium niobate chip; The pump light source (1) is connected to the wavelength division multiplexer (2), the beam splitter (6) is connected to the coupling grating group (7), and a photodetector (8) is fixed on the upper surface of the coupling grating group (7); The pump light emitted by the pump light source (1) is transmitted from the waveguide output end of the wavelength division multiplexer (2) to the erbium-doped lithium niobate waveguide area (3); the erbium-doped lithium niobate waveguide area (3) absorbs the pump light and releases C-band signal light; the C-band signal light is reflected by the Faraday reflector (4) and enters the erbium-doped lithium niobate waveguide area (3) again to absorb and amplify the C-band signal light; the amplified C-band signal light coming out of the erbium-doped lithium niobate waveguide area (3) enters the beam splitter (6) to separate part of the intrinsic signal light; the intrinsic signal light is received by the photoelectric detector (8) via the coupling grating group (7); the photoelectric detector (8) monitors the intrinsic signal light and feeds back the monitoring result to the pump light source (1) in real time.

2. The ASE light source structure based on a thin film lithium niobate sheet according to claim 1, characterized in that: An isolator (5) is provided on the optical path between the erbium-doped lithium niobate waveguide region (3) and the beam splitter (6) to enable the C-band signal light to maintain unidirectional transmission.

3. The ASE light source structure based on a thin film lithium niobate sheet according to claim 1, characterized in that: When the output power of the intrinsic signal light fluctuates, the photodetector (8) detects the fluctuation ratio and feeds it back to the driving device of the pump light source (1), and the driving device of the pump light source (1) adjusts the driving current according to the fluctuation ratio.

4. The ASE light source structure based on a thin film lithium niobate sheet according to claim 1, characterized in that: The pump light source (1) directly bonds the III-V epitaxy to the thin-film lithium niobate chip by optimizing the molecular bonding process.

5. The ASE light source structure based on a thin film lithium niobate sheet according to claim 1, characterized in that: The wavelength division multiplexer (2) combines optical signals of different wavelengths into the same medium for transmission.

6. The ASE light source structure based on a thin film lithium niobate sheet according to claim 1, characterized in that: The erbium-doped lithium niobate waveguide region (3) is a waveguide of a thin-film lithium niobate chip that is doped with Er3+ ions at a high concentration, with the concentration being as high as 1×10^20cm^-3.

7. The ASE light source structure based on a thin film lithium niobate sheet according to claim 6, characterized in that: The Er3+ ion solubility of the erbium-doped lithium niobate waveguide region (3) is different, and the spectral width of the C band emitted spontaneously is different.

8. The ASE light source structure based on a thin film lithium niobate sheet according to claim 1, characterized in that: The Faraday reflector (4), the erbium-doped lithium niobate waveguide region (3), the wavelength division multiplexer (2), the isolator (5), the beam splitter (6), and the coupling grating group (7) are integrated on a thin-film lithium niobate chip by photolithography.

9. The ASE light source structure based on a thin film lithium niobate sheet according to claim 8, characterized in that: Two adjacent devices in the Faraday reflector (4), the erbium-doped lithium niobate waveguide region (3), the wavelength division multiplexer (2), the isolator (5), the beam splitter (6), and the coupling grating group (7) are optically interconnected via a thin-film lithium niobate ridge waveguide structure.

10. The ASE light source structure based on a thin film lithium niobate sheet according to claim 9, characterized in that: The thin-film lithium niobate ridge waveguide structure comprises, from bottom to top, a silicon base layer, a silicon dioxide lower cladding layer, a thin-film lithium niobate ridge waveguide layer, and a silicon dioxide lower cladding layer.

Images