Integrated fiber-optic gyroscope
By introducing polarizers into optical fiber gyroscope chips for polarization and detection, the polarization noise problem of thin-film optical waveguide optical fiber gyroscope chips is solved, and the signal coherence and signal-to-noise ratio are improved.
Patent Information
- Application Number
- CN202422360423.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-26
- Publication Date
- 2025-07-18
- Estimated Expiration
- 2034-09-26
AI Technical Summary
The existing integrated fiber gyroscope chip based on thin-film optical waveguides has large polarization noise, which hinders its promotion and use.
A polarizer is introduced into an optical fiber gyroscope chip to polarize and detect the optical signal, ensuring that the optical signal is coupled to the axis in the lithium niobate film chip, improving the polarization extinction ratio, and filtering out irrelevant polarization noise through the detector pigtail.
The coherence of the optical signal in the Sagnek waveguide ring is significantly improved, optical noise is reduced, and signal-to-noise ratio is improved.
Smart Images
Figure CN223122232U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the field of optical fiber sensing, in particular to an integrated optical fiber gyroscope with low noise. Background Art
[0002] An optical fiber gyroscope is a sensor for measuring the angular rate of a moving carrier, and it has been widely used in inertial measurement applications such as land, sea, air, and space. Figure 1 A typical structure of the optical path of a closed-loop optical fiber gyroscope is shown, which includes components such as a laser, a detector, a coupler, a Y waveguide, an optical fiber loop, a measurement and control circuit, etc.
[0003] In recent years, with the development of integration and miniaturization, using an optical waveguide instead of an optical fiber loop has become a research hotspot. Figure 2 A typical structure of an optical fiber gyroscope chip based on an optical waveguide is shown, which is usually realized by means of a thin-film optical waveguide. Among them, a beam splitter, a combiner, a modulator, and an optical fiber loop (in the form of an optical waveguide) are integrated onto a chip, thereby effectively reducing the volume of the optical fiber gyroscope.
[0004] The Sagnac effect measured by an interferometric optical fiber gyroscope in theory is a non-reciprocal phase information. However, in actual products, there are often various optical path noises, such as polarization noise, birefringence noise, Kerr effect, Faraday effect, backscattering, Rayleigh scattering noise, etc. The influence of these noises mainly exists in the optical fiber loop (or ring-shaped optical waveguide).
[0005] For example, two optical signal beams with the same wavelength, the same polarization state, the same light intensity and within the coherence length will produce stable optical interference with the best coherence degree. However, limited by the actual process, when an optical signal is coupled to an optical fiber or an optical device and propagates therein, the polarization main axis of the input optical signal does not ideally coincide with the polarization main axis of the optical fiber or the optical device, and there is also a certain non-uniformity in the material. In addition, there is the influence of the environment. Therefore, a part of the optical power propagates in the orthogonal polarization state and is coupled and converted back to the main polarization state again, thereby forming polarization noise.
[0006] To reduce polarization noise, a polarizer and an analyzer need to be added to the optical path system to improve the coherence degree of the two optical signal beams, filter out the polarization noise generated during the coupling and transmission processes, and thus reduce the influence of the change in the polarization state of the light wave on the reciprocity of the optical fiber gyroscope.
[0007] In Figure 1 In the closed-loop optical fiber gyroscope scheme based on an optical fiber loop shown, a Y waveguide chip using a proton exchange process can be used to provide the required polarization and analysis functions. However, in Figure 2In the fiber optic gyro chip based on thin film optical waveguide shown, a ridge optical waveguide is used to replace the fiber optic loop. The preparation of the ridge optical waveguide usually uses the ion beam etching process, and its uniformity is limited by the equipment and process level. Therefore, when the input optical signal is coupled into the ridge optical waveguide and propagates therein, polarization noise will also be generated. However, the ridge optical waveguide does not have the functions of polarization and polarization detection, resulting in relatively large polarization noise in this integrated chip of fiber optic gyro based on thin film optical waveguide.
[0008] Therefore, although the existing integrated fiber optic gyro chips implemented based on thin film optical waveguides (on which a beam splitter, a combiner, a modulator, a fiber optic loop, etc. are integrated) can effectively reduce the volume of the fiber optic gyro and have the advantage of miniaturization, they have relatively large polarization noise, which seriously hinders their popularization and use. Utility Model Content
[0009] To solve this problem, the present utility model proposes an integrated fiber optic gyro. Among them, the optical signal emitted by the light source is first polarized by a polarizer and then enters the lithium niobate thin film chip, and it is axis-coupled. Therefore, the polarization extinction ratio of the optical signal transmitted in the optical waveguide of the chip will be significantly improved (greater than 30 dB). This improvement in polarization degree is beneficial to enhancing the coherence of the two optical signals in the Sagnac waveguide loop and is beneficial to improving the signal-to-noise ratio. The optical signal output by the chip also needs to pass through the polarizer and then enter the detector pigtail. At this time, the polarizer acts as a polarization analyzer, filtering out the incoherent polarization noise, further reducing the optical noise, and enhancing the signal-to-noise ratio of the system.
[0010] Specifically, the integrated fiber optic gyro of the present utility model may include a chip, a light source, and a detector;
[0011] The chip includes a thin film substrate and a beam splitter, a 2×2 coupler, a modulator, and a ring waveguide integrated on the thin film substrate;
[0012] It is characterized in that it further includes a polarizer. The polarizer is fixedly connected to the chip through its first surface and is fixedly connected to the pigtail of the light source and the pigtail of the detector through its second surface, wherein the first surface and the second surface face each other;
[0013] The chip further includes a monitoring waveguide integrated on the thin film substrate.
[0014] Furthermore, the chip further includes an input port, an output port, and a monitoring port;
[0015] The beam splitter includes a common end, a first beam splitting end, and a second beam splitting end;
[0016] The 2×2 coupler includes a first end, a second end, a third end, and a fourth end;
[0017] The input port forms an optical connection with the common end of the beam splitter and forms an optical path connection with the pigtail of the light source through the polarizer;
[0018] The first beam splitting end of the beam splitter forms an optical connection with the monitoring port through the monitoring waveguide;
[0019] The second beam splitting end of the beam splitter forms an optical connection with the first end of the 2×2 coupler;
[0020] The second end and the third end of the 2×2 coupler respectively form optical connections with the two ends of the ring waveguide, and the fourth end of the 2×2 coupler forms an optical connection with the output port;
[0021] The modulator is configured to modulate the optical signal in the ring waveguide.
[0022] Preferably, the thin film substrate is a lithium niobate thin film substrate.
[0023] Preferably, the polarizer is a thin film linear polarizer. Wherein, the thickness of the thin film linear polarizer is 0.08 mm - 0.5 mm, and the polarization extinction ratio is greater than 30 dB.
[0024] Furthermore, the monitoring port is configured to monitor the alignment degree between the polarization direction of the polarizer and the main axis of the chip.
[0025] Preferably, the chip, the pigtail of the light source, and the pigtail of the photodetector are bonded to the polarizer through UV glue.
[0026] Preferably, the light source is a broadband high polarization light source, and the pigtail of the light source is a polarization maintaining fiber. Wherein, the optical axis of the pigtail of the light source and the main axis of the chip are both consistent with the polarization direction of the polarizer; or, the light source is a broadband low polarization light source.
[0027] Furthermore, an optical connection is formed between the input port and the beam splitter, between the beam splitter and the coupler, and between the coupler and the output port through waveguides.
[0028] Even further, the waveguide is a ridge waveguide. Description of the Drawings
[0029] The following further elaborates in detail the specific embodiments of the present invention with reference to the drawings.
[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.
[0031] Figure 1 shows a typical structure of a closed-loop fiber optic gyroscope in the prior art;
[0032] Figure 2 shows a typical structure of a fiber optic gyroscope chip based on a thin-film optical waveguide in the prior art;
[0033] Figure 3 shows a preferred example of an integrated fiber optic gyroscope according to the present invention;
[0034] Figure 4 and Figure 5 shows the polarization alignment and fixed connection process between the (light source and detector) pigtails, polarizer, and chip in the integrated fiber optic gyroscope according to the present invention;
[0035] Figure 6 shows an example in which the polarizer 4, lithium niobate thin-film chip 1, and light source pigtail 21 are in a state of aligned polarization directions according to the present invention. Detailed implementation manners
[0036] In the following, the exemplary embodiments of the present invention will be described in detail with reference to the drawings. The following embodiments are provided by way of example to fully convey the spirit of the present invention to those skilled in the art to which the present invention pertains. Therefore, the present invention is not limited to the embodiments disclosed herein.
[0037] Figure 3 shows a preferred example of an integrated fiber optic gyroscope according to the present invention.
[0038] As Figure 3 shown, the integrated fiber optic gyroscope may include a chip 1, a light source 2, and a detector 3, and a polarizer 4 is provided between the chip 1 and the light source 2 and the detector 3.
[0039] In the present invention, the chip 1 uses a crystal thin-film material substrate, and a beam splitter 11, a 2×2 coupler 12, a modulator 13, and a ring waveguide 14 are integrated on the substrate.
[0040] Considering that the lithium niobate material has excellent electro-optic modulation performance and the ridge (optical) waveguide based on the lithium niobate thin film has low transmission loss, the substrate of the chip 1 may preferably adopt a lithium niobate thin-film substrate.
[0041] For the convenience of understanding the present utility model, the concepts of the following technical terms will be introduced first below:
[0042] Polarization direction of the polarizer: It is the light transmission direction of the polarizer. Light polarized along this direction can pass through the polarizer, while polarized light perpendicular to this direction cannot pass through the polarizer. This direction is also the polarization analysis direction of the polarizer.
[0043] Polarization main axis of the pigtail (polarization maintaining fiber): It includes a fast axis and a slow axis. Among them, the cat's eye connection line in the panda fiber is the slow axis direction of the fiber, and the direction perpendicular to the cat's eye connection line is the fast axis direction of the fiber.
[0044] Main axis of the chip (lithium niobate thin film): It is the crystal axis of the lithium niobate thin film wafer (i.e., the crystallographic main axis of lithium niobate). Lithium niobate thin film chips usually use X-cut, Z-cut or Y-cut wafers. Since lithium niobate crystal is a uniaxial crystal, the Z-axis is the optical axis direction (extraordinary light direction), and the X-axis and Y-axis are the corresponding ordinary light polarization directions. When the lithium niobate thin film is applied to an optical fiber gyroscope, an X-cut wafer is used, and the normal direction of the wafer is the X-axis of the lithium niobate crystal. The light propagation direction is in the Y direction, and the electric field direction is in the Z direction. At this time, light is transmitted along the Y-axis. When the polarization direction of the input optical signal is the Z-axis, that is, the extraordinary light direction, the maximum electro-optic modulation coefficient can be used.
[0045] As Figure 3-5 shown, the polarizer 4 has opposite first and second surfaces. Among them, it is fixedly connected to the chip 1 through the first surface, and is fixedly connected to the pigtail 21 of the light source 2 and the pigtail 31 of the detector 3 through the second surface. Therefore, the optical signal output by the light source 2 is transmitted in its pigtail 21 to the polarizer 4, and after passing through the polarizer 4, it is coupled into the chip 1 through the input port of the chip 1; the optical signal output by the (waveguide) Sagnac loop in the chip 1 will be output outward through the output port of the chip 1, and after passing through the polarizer 4, it is coupled and transmitted into the pigtail 31 of the detector 3, and finally input into the detector 3 through the pigtail 31.
[0046] In the present utility model, the polarizer 4 will simultaneously act as a polarizer and a polarization analyzer, that is, it provides a polarization function at the input port of the chip 1 and a polarization analysis function at the output port of the chip 1. Therefore, both the optical signal entering the chip 1 and the optical signal output by the chip 1 will pass through the polarizer, which will allow the polarization degree of the optical signal coupled into the chip 1 and transmitted therein to be effectively improved, and further improve the coherence degree of the optical signal formed by the action of the (waveguide) Sagnac loop of the chip 1; at the same time, before the optical signal output by the chip 1 reaches the detector, the polarization noise that is not coherent can also be filtered out by the action of the polarizer.
[0047] In an optical fiber gyroscope, the light source is usually a broadband light source, which can be divided into a low polarization light source and a high polarization light source according to its polarization attributes.
[0048] The optical signal output by the low polarization light source is close to natural light (i.e., non-polarized light), and 50% of the light will be blocked when it passes through the polarizer 4. Therefore, when coupling the pigtail 21 of the low polarization light source with the polarizer 4, there is no need to adjust the polarization direction of the polarizer 4.
[0049] The optical signal output by the high polarization light source usually has a polarization extinction ratio greater than 15 dB, and its pigtail is usually a polarization-maintaining fiber. Therefore, the optical signal output by the high polarization light source will be transmitted along a polarization main axis (usually the slow axis) in its pigtail. At this time, in order to maximize the optical power passing through the polarizer 4, it is necessary to adjust the main axis direction of the light source pigtail so that the polarization direction of the light output from the light source pigtail is consistent (i.e., aligned) with the light passing direction of the polarizer 4, so as to maximize the light passing power of the polarizer 4.
[0050] Therefore, according to the present invention, a monitoring waveguide 15 can also be integrated on the chip 1 to transmit at least a part of the input optical signal to the monitoring port of the chip 1, so as to allow monitoring the alignment degree between the polarization direction of the polarizer and the main axis of the chip according to the change of the light intensity output from the monitoring port.
[0051] In Figure 3 the example, the beam splitter 11 can include a common end, a first splitting end and a second splitting end. Among them, the optical signal input through the common end is split into two components and output along the first and second splitting ends respectively.
[0052] The first splitting end of the beam splitter 11 can be connected to the monitoring waveguide to allow the first component to be transmitted to the monitoring port of the chip 1, so that the alignment degree between the polarization direction of the polarizer and the main axis of the chip can be determined according to the change of the light intensity of the first component of the input optical signal.
[0053] The second splitting end of the beam splitter 11 can form an optical connection with the first end of the 2*2 coupler 12 to allow the second component of the input optical signal to reach the 2*2 coupler 12 and be split again in the 2*2 coupler 12 and output through the second end and the third end of the 2*2 coupler 12 respectively.
[0054] As an example, the beam splitter 11 can have a splitting ratio of 90:10, that is, the ratio of the first component to the second component is 10:90, thereby allowing monitoring the alignment degree between the polarization direction of the polarizer and the main axis of the chip by means of a small part of the input optical signal.
[0055] The second end and the third end of the 2*2 coupler 12 are respectively optically connected to the two ends of the ring waveguide 14 to form a Sagnac loop. Among them, the modulator 13 is arranged to modulate the optical signal in the ring waveguide.
[0056] The fourth end of the 2×2 coupler 12 forms an optical connection with the output port of the chip 1, allowing the optical signal output from the Sagnac loop to finally output from the output port of the chip 1, then enter the pigtail 31 of the detector through the polarizer 4, and finally reach the detector 3.
[0057] In a preferred example, the polarizer 4 can be a thin-film linear polarizer. The thin-film linear polarizer preferably can have a thickness of 0.08 mm to 0.5 mm and a polarization extinction ratio greater than 30 dB.
[0058] In the chip 1 of the integrated fiber optic gyroscope of the present utility model, the optical connections between the input port and the beam splitter 11, between the beam splitter 11 and the coupler 12, and between the coupler 12 and the output port can be realized by means of thin-film optical waveguides. As a preferred example, the thin-film optical waveguide can be a ridge waveguide.
[0059] Next, in combination with Figure 4 and Figure 5 , the process or implementation method of polarization alignment and fixed connection among the (light source and detector) pigtail, the polarizer, and the chip in the integrated fiber optic gyroscope of the present utility model will be described.
[0060] First, the polarizer 4 is coupled with the light source pigtail 21. When realizing this coupling, a highly polarized light source is used as the (coupling) light source, the light source pigtail 21 is a polarization-maintaining fiber, and the optical signal output by the light source is transmitted along one main axis (usually the slow axis) of the light source pigtail 21. When the optical axis of the light source pigtail 21 for light transmission is aligned with the polarization direction of the polarizer 4, the optical power transmitted through the polarizer is the maximum, and this is used as the criterion for judging whether the optical axis of the polarizer for light transmission is aligned with the optical axis of the light source pigtail for light transmission. When it is determined that they are aligned, the UV glue can be applied and cured between the light source pigtail and the polarizer, thereby realizing the fixed connection between the polarizer and the light source pigtail.
[0061] After completing the coupling connection between the light source pigtail 21 and the polarizer 4, then it is coupled and connected with the chip 1 as a whole. At this time, the alignment between the polarization direction of the polarizer 4 and the main axis of the lithium niobate chip 1 can be judged by monitoring the polarization extinction ratio of the optical signal output from the monitoring port. The lithium niobate chip adopts a ridge waveguide and can simultaneously transmit two orthogonally polarized optical signals. When the polarization direction of the polarizer is aligned with the Z-axis or the X-axis, the polarization extinction ratio of the optical signal at the monitoring port will be the maximum (in order to be able to use the maximum electro-optic modulation coefficient, it is preferred to align the Z-axis with the polarization direction of the polarizer). After judging that the polarization direction of the polarizer 4 is aligned with the main axis of the lithium niobate chip 1, then the UV glue can be applied and cured between the lithium niobate chip 1 and the polarizer 4.
[0062] Figure 6An example of the polarization direction alignment state among the polarizer 4, the lithium niobate thin film chip 1, and the light source pigtail 21 is shown.
[0063] Finally, the pigtail 31 of the detector is coupled to the output port of the chip 1. At this time, a fixed connection between the polarizer 4 and the pigtail 31 of the detector can be achieved by dotting and curing UV glue between the pigtail 31 of the detector and the polarizer 4. Since the detector is a polarization-insensitive device, the polarization main axis direction does not need to be adjusted during the coupling process of the pigtail 31 of the detector and the chip 1.
[0064] In summary, in the integrated optical fiber gyroscope of the present invention, the optical signal emitted by the light source is first polarized by the polarizer and then enters the lithium niobate thin film chip, and it is axis-coupled. Therefore, the polarization extinction ratio of the optical signal transmitted in the lithium niobate thin film waveguide will be significantly improved (greater than 30 dB). This improvement in polarization degree is beneficial to improving the coherence of the two optical signals in the Sagnac waveguide loop and is beneficial to improving the signal-to-noise ratio. The optical signal output by the chip also needs to pass through the polarizer and then enter the pigtail of the detector. At this time, the polarizer acts as an analyzer, filtering out incoherent polarization noise, further reducing the optical noise, and improving the signal-to-noise ratio of the system.
[0065] Although the present invention has been described above with reference to specific embodiments in conjunction with the accompanying drawings, it is easy for those skilled in the art to recognize that the above embodiments are merely exemplary and are used to illustrate the principle of the present invention, and they will not limit the scope of the present invention. Those skilled in the art can make various combinations, modifications, and equivalent replacements of the above embodiments without departing from the spirit and scope of the present invention.
Claims
1. An integrated optical fiber gyroscope, which includes a chip, a light source and a detector; The chip includes a thin film substrate and a beam splitter, a 2×2 coupler, a modulator and a ring waveguide integrated on the thin film substrate; It is characterized in that It further includes a polarizer, the polarizer is fixedly connected to the chip through its first surface, and is fixedly connected to the pigtail of the light source and the pigtail of the detector through its second surface, wherein the first surface and the second surface face each other; the chip further includes a monitoring waveguide integrated on the thin film substrate.
2. The integrated optical fiber gyroscope according to claim 1, wherein The chip further includes an input port, an output port and a monitoring port; The beam splitter includes a common end, a first beam splitting end and a second beam splitting end; The 2×2 coupler includes a first end, a second end, a third end and a fourth end; The input port forms an optical connection with the common end of the beam splitter, and forms an optical path connection with the pigtail of the light source through the polarizer; The first beam splitting end of the beam splitter forms an optical connection with the monitoring port through the monitoring waveguide; The second beam splitting end of the beam splitter forms an optical connection with the first end of the 2×2 coupler; The second end and the third end of the 2×2 coupler respectively form optical connections with both ends of the ring waveguide, and the fourth end of the 2×2 coupler forms an optical connection with the output port; The modulator is configured to modulate the optical signal in the ring waveguide.
3. The integrated optical fiber gyroscope according to claim 1, wherein The thin film substrate is a lithium niobate thin film substrate.
4. The integrated optical fiber gyroscope according to claim 1, wherein The polarizer is a thin film linear polarizer.
5. The integrated optical fiber gyroscope according to claim 4, wherein The thickness of the thin film linear polarizer is 0.08 mm - 0.5 mm, and the polarization extinction ratio is greater than 30 dB.
6. The integrated optical fiber gyroscope according to claim 2, characterized in that, The monitoring port is configured to monitor the alignment degree between the polarization direction of the polarizer and the main axis of the chip.
7. The integrated optical fiber gyroscope according to claim 1, characterized in that The chip, the pigtail of the light source and the pigtail of the detector are bonded to the polarizer by UV glue.
8. The integrated optical fiber gyroscope according to claim 1, wherein: The light source is a broadband high polarization light source, and the pigtail of the light source is a polarization maintaining optical fiber, wherein the optical axis of the pigtail of the light source and the main axis of the chip are both consistent with the polarization direction of the polarizer; or, The light source is a broadband low polarization light source.
9. The integrated optical fiber gyroscope according to claim 2, wherein An optical connection is formed between the input port and the beam splitter, between the beam splitter and the coupler, and between the coupler and the output port through a waveguide.
10. The integrated optical fiber gyroscope according to claim 9, wherein The waveguide is a ridge waveguide.