CN112833873A

CN112833873A - Photonic integrated chip and interference type optical fiber gyroscope

Info

Publication number: CN112833873A
Application number: CN202010956979.5A
Authority: CN
Inventors: 杨旭; 李萍
Original assignee: Tianjin Lingxin Technology Development Co ltd
Current assignee: Tianjin Lingxin Technology Development Co ltd
Priority date: 2020-09-12
Filing date: 2020-09-12
Publication date: 2021-05-25

Abstract

The invention discloses a photonic integrated chip and an interference fiber-optic gyroscope, wherein the photonic integrated chip can realize high-density integration of multiple photoelectric device functions such as a waveguide coupler, a polarizer, a mode filter, a phase modulator and the like on a thin film substrate through a photonic circuit structure, and reduces polarization crosstalk or parasitic phase error caused by a substrate radiation mode light wave formed by an asymmetric mode and polarization filtering through a structure that four ports of the photonic integrated chip are placed on the same side of the chip, so that the error influence on the system performance of the fiber-optic gyroscope caused by the photonic integrated chip is reduced. The interference type fiber optic gyroscope is characterized in that optical fibers are respectively placed at four ports of the photonic integrated chip and are respectively connected with the light source, the photoelectric detector and two ports of the optical fiber ring to form an optical path structure of the interference type fiber optic gyroscope.

Description

Photonic integrated chip and interference type optical fiber gyroscope

Technical Field

The invention can be applied to the technical field of inertial sensing of optical fiber gyroscopes and the like, and particularly relates to a photonic integrated chip and an interference type optical fiber gyroscope.

Background

The inertial technology is the core technology for inertial navigation, guidance control, positioning and orientation, attitude stabilization and the like of various moving objects, wherein a gyroscope is used as a core component of an inertial measurement system and is used for measuring the angular displacement and the angular velocity of the moving objects, and the gyroscope plays a key role in the performance of the inertial system. The closed-loop interference type fiber-optic gyroscope based on the Sagnac effect has the advantages of batch production due to the characteristics of no moving part, large dynamic range, high sensitivity, electromagnetic interference resistance, flexible structure and the like and strong compatibility with optical communication devices, and is rapidly developed and widely applied to engineering in recent years.

Referring to fig. 1A, a basic optical path structure of an interference type fiber optic gyroscope is shown, in which a Sagnac interferometer is a main body, and an optical path structure having anisotropy is formed by a light source, a fiber coupler, a photodetector, a Y waveguide modulator, and a fiber ring. The Y waveguide modulator has multiple functions of polarization filtering, light wave mode filtering, light wave beam splitting, phase modulation, light wave beam combining and the like, has very important influence on polarization anisotropy, single mode anisotropy and beam splitting/combining device anisotropy of the interference type fiber-optic gyroscope, and is also an important feedback control element in closed-loop signal processing. The optical fiber coupler is used for introducing a laser beam generated by the light source into the Y waveguide modulator and introducing an interference light wave generated by the Y waveguide modulator into the photoelectric detector for detection.

The optical fiber coupler is used as a passive optical device, and the functions of the optical fiber coupler mainly lie in the wave guiding, beam splitting and beam combining of light waves. The same functionality can also be achieved by fabricating an optical waveguide with a coupler structure, i.e., a waveguide coupler, on an optical crystal using optical waveguide fabrication techniques. For example, a waveguide coupler having a Y-branch structure can also realize passive optical device functions such as wave guiding, beam splitting, and beam combining of light waves. The Y waveguide modulator is an active optical device consisting of a waveguide coupler with a Y-branch structure and a modulation electrode, and the optical structure of the Y waveguide modulator is also a waveguide coupler with a Y-branch structure.

Referring to fig. 1B and fig. 1C, in order to further improve the integration of the optical path structure of the interference-type fiber-optic gyroscope, a prior art adopts a method of manufacturing two waveguide couplers with Y-branch structures on the same optical crystal, and manufacturing a modulation electrode on one of the waveguide couplers, so as to form a dual-Y waveguide modulator with two input ports and two output ports. Wherein one waveguide coupler and its modulating electrodes form the modulator portion (i.e., the active optical device portion, portion B shown in fig. 1B) of the dual Y-waveguide modulator, and the other waveguide coupler forms the coupler portion (i.e., the passive optical device portion, portion a shown in fig. 1B) of the dual Y-waveguide modulator.

However, the dual Y-waveguide modulator and the interferometric fiber-optic gyroscope based on the dual Y-waveguide modulator manufactured by the above-mentioned prior art have the following problems, which may adversely affect the volume, sensing accuracy, reliability, manufacturing cost, etc. of the fiber-optic gyroscope system:

firstly, although the structure of the double-Y waveguide modulator improves the integration level of the device function, because the light wave forms light splitting at the first Y branch, part of the light wave forms asymmetric mode radiation and enters the substrate wafer, and part of the light wave is reflected by the bottom or the side wall of the substrate wafer and is recoupled into the second Y branch, so that a parasitic phase error is formed and the precision of the fiber optic gyroscope is influenced;

secondly, because the Y waveguide applied to the fiber optic gyroscope adopts the proton exchange waveguide with polarization characteristic, and the interference fiber optic gyroscope usually uses a low-polarization light source, a part of the light wave energy incident into the Y waveguide exists in the substrate wafer in a radiation mode, and the light wave energy reflected by the bottom or the side wall of the substrate wafer can be recoupled into the output port of the Y waveguide modulator and exists in the fiber optic gyroscope system in the form of polarization crosstalk noise, thereby affecting the precision of the fiber optic gyroscope;

thirdly, the larger size of the Y waveguide modulator is one of the main limiting factors for the miniaturization of the fiber optic gyroscope, and the miniaturization of the Y waveguide modulator in the prior art is generally realized by shortening the length of the curved waveguide portion, which results in the increase of the bending loss of the Y waveguide modulator on the one hand, and the increase of the half-wave voltage on the other hand, further results in the increase of the driving power consumption of the fiber optic gyroscope system and the increase of the difficulty of signal processing.

Disclosure of Invention

In view of the above problems, a first objective of the present invention is to provide a photonic integrated chip, which can integrate, with high density, various functional optoelectronic devices such as a waveguide coupler, a polarizer, a mode filter, and a phase modulator on a lithium niobate thin film substrate through a photonic circuit structure, so as to reduce the size of the photonic integrated chip, and further reduce the parasitic phase error or polarization crosstalk caused by the substrate radiation mode optical waves formed by an asymmetric mode and polarization filtering by placing four optical waveguide ports of the photonic integrated chip on the same side of the chip, thereby reducing the error influence caused by the photonic integrated chip on an optical fiber gyro system.

Based on the photonic integrated chip, a second objective of the present invention is to provide an interference fiber-optic gyroscope, in which optical fibers are respectively placed at four ports of the photonic integrated chip and are respectively connected with two ports of the laser light source, the photodetector and the fiber ring, so as to form an optical path structure of the interference fiber-optic gyroscope.

To achieve the first object of the present invention, the present invention provides a photonic integrated chip, comprising: a base chip, a lower cladding layer, a thin film substrate, a photonic circuit, a first modulation electrode branch, a second modulation electrode branch,

the base wafer is used for providing mechanical support for the film substrate;

the film substrate is arranged above the lower cladding and is a crystal material carrier for preparing the photonic circuit;

the lower cladding is arranged between the substrate wafer and the film substrate;

the photonic circuit is formed in the thin film substrate and is a wave guide channel of the light wave;

the photonic circuit comprises the following components: the chip comprises a first port, a second port, a first Y-branch coupler, a first circular arc, a straight strip, a second circular arc, a second Y-branch coupler, a third port, a fourth port and a polarizer, wherein the first port, the second port, the third port and the fourth port are arranged on the same side of the chip;

the first port and the second port are optical fiber connection ports of a first Y-branch coupler, the first port is used for being connected with a laser light source through an optical fiber, the second port is used for being connected with a photoelectric detector through an optical fiber, or the second port is used for being connected with the laser light source through an optical fiber, and the first port is used for being connected with the photoelectric detector through an optical fiber;

the third port and the fourth port are optical fiber connection ports of a second Y-branch coupler and are respectively connected with two ports of the optical fiber ring through optical fibers;

the first Y-branch coupler is connected with one end of the straight strip through a first arc, and the second Y-branch coupler is connected with the other end of the straight strip through a second arc;

the first modulation electrode branch and the second modulation electrode branch are used for carrying out phase modulation on the light waves transmitted in the photonic circuit.

Preferably, the thin film substrate is made of optical-grade lithium niobate or lithium tantalate with the same composition, or doped or near stoichiometric lithium niobate or lithium tantalate, the crystal tangential direction of the thin film substrate is X-cut or Z-cut, and the thickness of the thin film substrate is 0.1-10 μm.

Preferably, a layer of non-metal film material is deposited on the upper surface of the film substrate to serve as an upper cladding.

Preferably, an end face B on the corresponding side of the input and output port setting side of the photonic integrated chip Y-branch coupler is provided with a structure for reducing reflection of the substrate radiation mode light wave on the end face B of the photonic integrated chip.

Preferably, the structure for reducing reflection of the substrate radiation mode light wave at the end face B of the photonic integrated chip adopts one of the following structures:

the first method comprises the following steps: the end face B is a roughened surface so as to increase the refraction or transmission of the substrate radiation mode light wave on the end face B;

and the second method comprises the following steps: a layer of metal film or a medium film with the refractive index higher than that of the film substrate forming material is deposited on the end face B;

and the third is that: and the end face B is coated with a light absorption material as a light absorption layer, so that the aim of absorbing light waves in a substrate radiation mode is fulfilled.

Preferably, the photonic circuit includes a polarizer formed in the photonic circuit for polarization filtering the optical wave transmitted in the photonic circuit to obtain the optical wave in a single polarization state.

Preferably, the polarizer is configured in one of the following ways:

the first method comprises the following steps: proton exchange or annealing proton exchange is carried out in an optical sub-circuit of the polarizer part so as to realize the increase or decrease of the refractive index of the ordinary light and the abnormal light in the region, so that one polarized light wave can leak out of the polarizer region in a radiation mode due to the fact that the polarized light wave can not meet the wave guide condition, and polarization filtering is realized;

and the second method comprises the following steps: depositing a layer of film on the upper surface of the photonic circuit of the polarizer part to realize absorption of one polarization state of the optical waves with orthogonal polarization states transmitted in the photonic circuit and realize polarization filtering of the optical waves in the photonic circuit;

and the third is that: the photonic linear path of the polarizer part can be formed by a plurality of tiny circular arcs, and one polarization mode light wave leaks out of the polarizer region due to larger bending loss by utilizing different bending losses of the light waves in different polarization modes, so that polarization filtering is realized.

Preferably, the formation position of the polarizer structure adopts one of the following positions:

the first method comprises the following steps: the polarizer structure is formed in a Y branch arm connected with the laser light source in the first Y branch coupler;

and the second method comprises the following steps: the polarizer structure is formed in the first Y-branch coupler;

and the third is that: the polarizer structure is formed in the second Y-branch coupler;

and fourthly: the polarizer structure is formed in the straight strip;

and a fifth mode: proton exchange is carried out on the whole structure of the photon circuit, or a layer of film capable of realizing the light absorption function is deposited on the whole structure of the photon circuit, so that the photon circuit has the polarizing function.

Preferably, the first modulation electrode branch and the second modulation electrode branch are symmetrically arranged between two arms of the photonic circuit at the second Y-branch coupler and outside the two arms to form a push-pull electrode structure.

In order to achieve the second object of the present invention, the present invention further provides an interference type fiber optic gyroscope, the optical path structure portion of which comprises: the photonic integrated chip as above, further comprising: a first optical fiber module, a second optical fiber module, a third optical fiber module, a fourth optical fiber module, a first input optical fiber, a second input optical fiber, a first output optical fiber, a second output optical fiber, a laser light source, a photoelectric detector and an optical fiber ring,

the optical fiber module I, the optical fiber module II, the optical fiber module III and the optical fiber module IV are respectively arranged at a first port, a second port, a third port and a fourth port of the photonic integrated chip;

the input optical fiber I is placed in the optical fiber module I and is connected with the laser light source or the photoelectric detector, and the input optical fiber II is placed in the optical fiber module II and is correspondingly connected with the photoelectric detector or the laser light source;

the first output optical fiber and the second output optical fiber are respectively placed in the third optical fiber module and the fourth optical fiber module and are respectively connected with two ports of the optical fiber ring.

Preferably, the connection mode with the port in the photonic integrated chip is a mode of bonding and curing by using glue, or a mode of welding and fixing by using a lensed fiber.

Compared with the prior art, the photonic integrated chip and the interference type fiber-optic gyroscope based on the photonic integrated chip have the following beneficial effects:

1. the photonic circuit with high refractive index difference characteristic is prepared in the film substrate, so that the bending radius of the bent optical waveguide structure is favorably reduced, the low loss is kept, the preparation of a small-size circular arc structure and a large-angle Y-branch structure can be realized, the reduction of the size of a photonic integrated chip is favorably realized, and the reduction of the overall size of a fiber-optic gyroscope system is further favorably realized;

2. the arrangement of the circular arc structure realizes that the input or output ports of the two Y-branch couplers are arranged on the same side of the photonic integrated chip, and the structure that the input port and the output port of the existing Y-waveguide modulator or double-Y-waveguide modulator are respectively arranged on two sides of the chip is not adopted, so that the parasitic phase error or polarization crosstalk caused by the substrate radiation mode light wave formed by an asymmetric mode and polarization filtering can be reduced, and the influence of the structure on the performance of the optical fiber gyroscope system can be reduced;

3. the electro-optical modulator obtained based on the photonic circuit structure has the characteristics of small electrode spacing, high electro-optical modulation efficiency and the like, and can remarkably reduce the driving voltage required to be applied for phase modulation in the fiber-optic gyroscope system, so that the aim of miniaturizing a photonic integrated chip can be fulfilled by shortening the length of a modulation electrode, the half-wave voltage cannot be greatly increased, and the increase of the power consumption of the fiber-optic gyroscope system or the increase of the signal processing difficulty can be avoided;

4. the photonic integrated chip structure provided by the invention can be prepared by depending on the current mature CMOS process technology, and is beneficial to realizing the automatic, low-cost and batch scale production of the photonic integrated chip and the fiber-optic gyroscope based on the photonic integrated chip.

Drawings

FIG. 1A: the light path part of the interference type fiber-optic gyroscope in the prior art forms a structural schematic diagram;

FIG. 1B: a schematic diagram of a first construction mode of a double-Y waveguide modulator in the prior art and a fiber-optic gyroscope optical path structure based on the first construction mode;

FIG. 1C: a schematic diagram of a second construction mode of a double-Y waveguide modulator in the prior art and a fiber-optic gyroscope light path structure based on the second construction mode;

FIG. 2A: schematic diagram of the substrate radiation mode in the first configuration of the dual Y-waveguide modulator;

FIG. 2B: schematic diagram of substrate radiation mode in the second construction of the double-Y waveguide modulator; (ii) a

FIG. 2C: in the prior art, polarization filtering forms a light wave propagation path schematic diagram of a substrate radiation mode;

FIG. 3: the invention provides a schematic view of a top-down structure of a photonic integrated chip;

fig. 4A to 4C: schematic diagram of polarizer placement mode in the photonic integrated chip;

FIG. 5: the cross-sectional structure of the second Y-branch coupler part in the photonic integrated chip is shown schematically;

FIG. 6: the invention provides a schematic diagram of an optical path structure of an interference type fiber-optic gyroscope;

the names corresponding to each mark in the figure are respectively: 1. a base wafer; 2. a lower thin layer; 3. a thin film substrate; 401. a first port; 402. a second port; 403. a first Y-branch coupler; 404. a first arc; 405. straight strips; 406. a second arc; 407. a second Y-branch coupler; 408. a third port; 409. a fourth port; 410. a polarizer; 411. a light absorbing layer; 5. an upper cladding layer; 601. modulating the electrode branch I; 602. a modulation electrode branch II; 7. a distribution of light wave modes transmitted in the photonic circuit; 701. a first optical fiber module; 702. a second optical fiber module; 703. a third optical fiber module; 704. a fourth optical fiber module; 801. an input optical fiber I; 802. inputting a second optical fiber; 811. a first output optical fiber; 812. an output optical fiber II; 901. a laser light source; 902. a photodetector; 903. an optical fiber loop; 904. a straight waveguide; 905. and connecting the optical fibers.

Detailed Description

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.

Referring first to fig. 1B, fig. 1C, fig. 2A and fig. 2B, two structural schemes of a dual Y waveguide modulator monolithically integrated by a waveguide coupler and a Y waveguide modulator in the prior art are shown, in which fig. 1B and fig. 2A show that two Y-branch couplers are connected by a straight waveguide 904, and fig. 1C and fig. 2B show that two Y-branch couplers are relatively independent and two structures are connected by a section of connecting fiber 905.

The dual Y-waveguide modulator structure shown in fig. 1B and 2A connects two Y-branch couplers by a straight waveguide, which is very similar to the minimum reciprocal structure required by a fiber optic gyroscope. As is well known to those skilled in the art, when input light is input from one of the ports of the Y-branch coupler, half of the light waves are radiated into the substrate wafer in an asymmetric light wave pattern. The dotted lines and arrows in fig. 2A indicate the propagation path of the base radiation mode optical wave. For the dual Y-waveguide modulator structure shown in fig. 2A, the effect of the straight waveguide 904 as a spatial mode filter is more limited in terms of mode suppression required for the reciprocity. A part of the optical wave radiated into the substrate is re-coupled into the second Y-branch coupler, so that a parasitic phase error is generated between the two waveguide arms of the Y-branch coupler, which affects the sensing accuracy of the fiber optic gyroscope.

The dual Y-waveguide modulator structure shown in fig. 1C and 2B has two Y-branch couplers arranged in parallel, and the straight waveguides 904 of the two Y-branch couplers are connected by using the connecting optical fiber 905, and the connecting optical fiber 905 is used as a spatial mode filter to filter the light waves radiated into the substrate, so as to eliminate the coupling of the non-reciprocal interference optical signals between the two Y-branch couplers. Although this approach can reduce the system noise to some extent, the combined nonreciprocal interference optical signal of the optical wave of the second Y-branch coupler still has a portion coupled to the first Y-branch coupler, and thus the photodetector still receives the nonreciprocal interference optical signal, as shown by the dashed line and arrow in fig. 2B. Moreover, this approach also adds two fiber optic modules, reducing the reliability of the integrated modulator.

Further, fig. 2C is a schematic diagram showing a substrate radiation pattern formed due to polarization mode filtering in the Y waveguide modulator used in the optical fiber gyro. Because the optical waveguide is prepared by adopting a proton exchange process, and the proton exchange waveguide has polarization characteristics, one polarization mode of the orthogonal polarization mode light waves incident into the proton exchange optical waveguide is filtered and radiated into the substrate wafer in the form of a substrate radiation mode. The dotted lines and arrows in fig. 2C show the propagation path of the base radiation mode optical wave. After the light waves in the substrate radiation mode are reflected by the bottom of the substrate wafer, a part of the light waves can be re-coupled into the output optical fiber and form polarization crosstalk, so that the sensing precision of the optical fiber gyroscope is influenced.

Therefore, if the ports of the two Y-branch couplers can be placed on the same side of the substrate wafer and connected through the optical waveguide instead of the connection optical fiber, the influence of noise factors such as substrate radiation mode light waves and non-reciprocal interference optical signals on the sensing accuracy of the interference type optical fiber gyroscope can be reduced, and the reliability of the optical fiber gyroscope system can be improved. This is the subject of the present invention.

The photonic integrated chip and the interferometric fiber-optic gyroscope based on the same provided by the invention are described below with reference to specific embodiments.

As shown in fig. 3, fig. 4A to fig. 4C, and fig. 5, a photonic integrated chip provided in this embodiment includes: a base wafer 1, a lower cladding 2, a film substrate 3, an optical sub-circuit, an upper cladding 5, a first modulation electrode branch 601, a second modulation electrode branch 602,

the base wafer 1 is used to provide mechanical support for the thin film substrate 3, and its constituent material may be lithium niobate, lithium tantalate, silicon, quartz, or other crystals. For example, silicon may be employed as a constituent material of the base wafer 1 to utilize monolithic hybrid integration of silicon-based CMOS integrated circuits with lithium niobate-based multifunctional integrated optoelectronic devices. Alternatively, quartz may be used as a constituent material of the base wafer 1 to reduce a change in refractive index of the crystal material of the thin film substrate due to thermal expansion or thermal conduction of the base crystal by utilizing the stable thermal properties of quartz. Alternatively, a crystal of lithium niobate or lithium tantalate having the same crystal tangent as that of the thin-film substrate 3 may be selected as the constituent material of the base wafer 1. The thickness of the base wafer 1 is 0.2mm to 2mm, preferably 1 mm.

The lower cladding layer 2 is disposed between the base wafer 1 and the thin film substrate 3, and on one hand, the lower cladding layer can play a role in increasing bonding strength between the base wafer and the thin film substrate, and on the other hand, the lower cladding layer also provides a space constraint effect for light waves transmitted in a photon circuit. The material constituting the under clad layer 2 may be any of non-metal materials such as silicon oxide, magnesium oxide, tantalum oxide, aluminum oxide, and silicon nitride, or may be a benzocyclobutene (BCB) polymer material. The thickness of the lower cladding 2 is not less than the wavelength of the light wave transmitted in the photonic circuit. For example, for transmitting light having a wavelength of 0.85 μm, the thickness of the lower cladding layer 2 should not be less than 0.85 μm; alternatively, for transmitting light having a wavelength of 1.31 μm, the thickness of the lower cladding layer 2 is not less than 1.31 μm. Preferably, the thickness of the under clad layer 2 is not less than 2 μm.

The film substrate 3 is arranged above the lower cladding 2 and is a crystal material carrier for preparing the photonic circuit. The constituent material of the film substrate 3 is a crystal having a Pockels linear electro-optic effect, such as a lithium niobate or lithium tantalate crystal. In order to reduce the transmission loss of the photonic circuit, the lithium niobate or lithium tantalate constituting the thin film substrate 3 is generally selected from crystal materials having the same optical grade composition. In order to further improve the light damage resistance of the photonic circuit, the thin film substrate 3 may also be a doped lithium niobate crystal or lithium tantalate crystal doped with metals such as magnesium and zinc, or a near-stoichiometric lithium niobate crystal or lithium tantalate crystal. Preferably, the present invention employs optical grade homogeneous lithium niobate crystals. The crystal tangential direction of the film substrate 3 is X-cut or Z-cut, and the thickness is 0.1-10 μm. In order to reduce the influence of electrostatic factors such as pyroelectric of lithium niobate or lithium tantalate crystals on the overall performance of the fiber-optic gyroscope, X-cut is preferably adopted in the crystal tangential direction of the film substrate 3.

The photonic circuit is formed in the thin film substrate 3 and is a waveguide structure which is a waveguide channel of an optical wave. The photonic circuit can realize the functions of passive optical devices such as guided wave, beam splitting, beam combining and the like of the optical wave, and can modulate the phase of the optical wave transmitted in the photonic circuit through the metal electrode. Compared with the optical waveguide manufactured based on the lithium niobate or lithium tantalate bulk material crystal in the prior art, the optical waveguide manufactured in the lithium niobate or lithium tantalate thin film substrate has higher refractive index difference, and the optical waveguide with the bending radius not more than 100 mu m can be manufactured, so that the preparation and interconnection of optical waveguide structures in various shapes such as straight strips, Y branches, arcs, circular rings and the like can be realized in the thin film substrate, and the optical sub-circuit is formed.

In the thin film substrate 3, in order to obtain an optical waveguide structure of an optical circuit, micromachining means such as ion etching, chemical etching, dielectric film deposition and the like may be employed on the upper surface of the thin film substrate 3 to form a local increase in the effective refractive index. It is of course also possible to include processes such as titanium diffusion, proton exchange, etc. in the prior art, and ion doping is performed in a local area of the thin film substrate 3 to achieve an increase in the effective refractive index.

Further, a non-metallic thin film material, such as silicon dioxide, titanium oxide, tantalum pentoxide, silicon nitride, etc., may be deposited on the upper surface of the thin film substrate 3 as the upper cladding 5. The upper cladding 5 can reduce the refractive index difference of the optical sub-line, on one hand, can reduce the formation of a high-order optical wave mode in the optical waveguide structure, on the other hand, can increase the spot size of the optical waveguide mode, and reduce the coupling loss between the optical sub-line and the optical fiber.

Referring to fig. 3, a schematic diagram of a top view of an photonic circuit chip is shown. The photonic circuit comprises the following components: a first port 401, a second port 402, a first Y-branch coupler 403, a first circular arc 404, a straight bar 405, a second circular arc 406, a second Y-branch coupler 407, a third port 408, a fourth port 409, a polarizer 410.

The first port 401 and the second port 402 are optical fiber connection ports of the first Y-branch coupler 403, wherein the first port 401 (or the second port 402) is used for connecting with the laser light source through an optical fiber, and the second port 402 (or the first port 401) is used for connecting with the photodetector through an optical fiber.

The third port 408 and the fourth port 409 are optical fiber connection ports of the second Y-branch coupler 407, and are connected to two ports of the optical fiber ring through optical fibers, respectively.

The first Y-branch coupler 403 is connected to one end of the straight bar 405 through a first arc 404, and the second Y-branch coupler 407 is connected to the other end of the straight bar 405 through a second arc 406.

Light waves generated by the laser light source enter the first Y-branch coupler 403 from the first port 401, sequentially pass through the first arc 404, the straight strip 405 and the second arc 406, are split by the second Y-branch coupler 407 to obtain two light waves, and enter the optical fiber ring through the third port 408 and the fourth port 409 respectively.

When the optical fiber gyroscope rotates along with a moving object, the phases of the light waves transmitted in the optical fiber ring in the clockwise direction and the counterclockwise direction are changed correspondingly, the light waves carrying different phase information return to the third port 408 and the fourth port 409 again, enter the second Y-branch coupler 407, modulate the phases of the light waves through the electro-optical modulation effect of the second Y-branch coupler 407, and realize the interference of the light waves through the beam combining effect of the second Y-branch coupler 407. The interference light wave passes through the reverse light path, namely, after passing through the second arc 406, the straight bar 405 and the first arc 404 in sequence, and then passes through the beam splitting of the first Y-branch coupler 403, wherein a part of the light wave reaches the photodetector through the second port 402 and detects the light intensity of the light wave.

Comparing the optical waveguide structure in the conventional dual Y-waveguide modulator chip shown in fig. 2A and 2B with the photonic circuit structure in the photonic integrated chip provided by the present invention shown in fig. 3, it can be seen that a significant feature of the photonic integrated chip is that the input or output ports of the two Y-

branch couplers

403 and 407 are both disposed on the same side of the chip through the connection of the

circular arcs

404 and 406. The photonic line formed in the thin film substrate 3 can maintain low bending loss at a small bending radius by virtue of a large refractive index difference (0.2 to 0.7), and thus can realize the preparation of an ultra-small bending radius arc structure of not more than 100 μm.

In the prior art, because the waveguide structure of the Y-branch coupler is mainly prepared by an annealing proton exchange method, the refractive index difference is about 0.01, and it is difficult to manufacture an arc structure with low bending loss and small radius, it is not possible to realize that the input or output ports of the two Y-branch couplers are arranged on the same side of the chip.

Similarly, the Y-branch portion of the Y-branch coupler is also formed by a curved structure, such as a circular arc, a sine-function curve, a cosine-function curve, etc. The high refractive index difference characteristic of the photonic circuit is also beneficial to realizing the increase of the opening angle of the Y-branch part and simultaneously keeping low bending loss, and is beneficial to reducing the whole size of the photonic integrated chip.

As shown by the dotted lines and arrows in fig. 3, the light wave entering the first Y-branch coupler 403 from the first port 401, wherein the substrate radiation mode light wave formed by the asymmetric mode is transmitted to the other end face (end face B) of the photonic integrated chip opposite to the end face (end face a) where the four ports are located, that is, the transmission direction of the substrate radiation light wave is opposite to the two ports of the second Y-branch coupler 407. In the prior art, the propagation direction of the optical wave radiated by the substrate is toward the two ports of the second Y-branch coupler, so that parasitic phase errors are easily formed by re-coupling into the second Y-branch coupler. The structure proposed by the present invention can effectively reduce the re-coupling of the optical wave in the substrate radiation mode into the second Y-branch coupler 407, and reduce the generation of parasitic phase error.

The following may also be used to reduce the reflection of the substrate radiation mode lightwave at the end face B of the photonic integrated chip to further reduce the coupling of the substrate radiation mode lightwave into the second Y-branch coupler 407:

for example, the end face B of the photonic integrated chip is ground or polished to be rough, the refraction or transmission of the substrate radiation mode light wave at the end face B is increased, and the radiation mode light wave is coupled out of the photonic integrated chip through the refraction or transmission;

or, a layer of metal film or dielectric film with refractive index higher than that of the material forming the film substrate 3 or multi-layer dielectric film with anti-reflection function is deposited on the end face B of the photonic integrated chip, so that reflection of the base radiation mode light wave is reduced;

alternatively, a light absorbing material is coated on the end face B to serve as the light absorbing layer 411, thereby absorbing the fundamental radiation mode light wave.

It should be noted that the above-mentioned modes are only some of the various possible modes for reducing the reflection of the light wave in the radiation mode of the substrate, and do not constitute a limitation to the present invention, and other modes for achieving the purpose of reducing the reflection of the end light wave are within the scope of the present invention.

To meet the requirement of the fiber-optic gyroscope for polarization reciprocity, the polarizer 410 is used for polarization filtering of the light waves transmitted in the photonic line to obtain the light waves in a single polarization state. The polarizer 410 is formed in the photonic circuit, belongs to a part of the photonic circuit, and plays a role of performing polarization filtering on the optical wave transmitted in the photonic circuit, and the configuration mode thereof can adopt several feasible modes as follows.

For example, proton exchange or annealing proton exchange can be performed in the photonic circuit of the polarizer 410 portion to realize the increase or decrease of the refractive index of the ordinary light and the extraordinary light in the region, so as to achieve the effect that one polarized light wave leaks out of the polarizer 410 region in a radiation mode due to the failure of satisfying the wave guiding condition, thereby realizing polarization filtering;

or, a thin film, such as a metal thin film of aluminum, titanium, chromium, gold, or the like, or a non-metal thin film of amorphous silicon, or the like, having a refractive index higher than that of the thin film substrate 3, may be deposited on the upper surface of the photonic circuit of the polarizer 410, so as to achieve absorption of one polarization state of the optical waves having orthogonal polarization states transmitted in the photonic circuit, and achieve polarization filtering of the optical waves transmitted in the photonic circuit;

or, the photonic sub-line of the polarizer 410 may be formed by a plurality of tiny arcs, and one of the polarized mode light waves leaks out of the polarizer 410 region due to a larger bending loss by using different bending losses of the polarized mode light waves, so as to implement polarization filtering.

The invention preferably adopts a method of depositing a layer of thin film on the upper surface of the photonic circuit of the polarizer 410 part to realize polarization filtering, so as to reduce the existence of the filtered polarization mode light wave in the photonic circuit or the thin film substrate, reduce the polarization crosstalk formed at the second Y-branch coupler 407, and reduce the influence on the performance of the fiber optic gyroscope system.

Fig. 4A to 4C are diagrams showing examples of several embodiments of the placement position of the polarizer 410, in which fig. 4A shows an example in which the polarizer 410 is placed in one arm of the Y branch where the first Y-branch coupler 401 is connected to the laser light source, fig. 4B shows an example in which the polarizer 410 is placed at the straight bar 405, and fig. 4C shows an example in which the polarizer 410 is placed at both positions. In all the photonic circuits, the polarization function may be provided to suppress the polarization crosstalk to the maximum. For example, a thin film capable of achieving a light absorption function is deposited over the entire photonic circuit structure or proton exchange is performed for the entire photonic circuit structure.

The present embodiment uses a polarizer 410 placed in one arm of the Y-branch where the first Y-branch coupler 401 is connected to the laser source. This arrangement is merely an example of one of the embodiments, and does not limit the embodiments of the present invention, and the polarizing function of the present invention can be achieved by using the placement position of the polarizer 410.

Referring to fig. 3, modulation electrodes, namely, a first modulation electrode branch 601 and a second modulation electrode branch 602, are disposed at the second Y-branch coupler 407, and are used for phase-modulating the light wave transmitted in the optical circuit by the electro-optical effect of the electro-optical crystal material constituting the thin film substrate. The first modulation electrode branch 601 and the second modulation electrode branch 602 are symmetrically arranged between two arms of the photonic circuit at the second Y-branch coupler 407 and outside the two arms to form a push-pull electrode structure. The modulation electrode is composed of a metal film, and the material of the modulation electrode can be a chromium/gold or titanium/gold double-layer metal film, and can also be a titanium/platinum/gold multi-layer metal film, wherein metal chromium or metal titanium is used as a transition layer to improve the adhesion between the film substrate 3 and the gold film.

For the purpose of describing the cross-sectional structure of the photonic integrated chip provided by the present invention, fig. 5 shows the cross-sectional structure of the second Y-branch coupler 407. The first modulation electrode branch 601 is placed between two arms of the photonic circuit, and the second modulation electrode branch 602 is placed outside the two arms of the photonic circuit symmetrically relative to the photonic circuit, so that an electric field formed between the first modulation electrode branch 601 and the second modulation electrode branch 602 can modulate the phase of the optical wave 7 transmitted in the photonic circuit through an electro-optical effect. The electrode distance G between the first modulation electrode branch 601 and the second modulation electrode branch 602 is not less than 2 μm. The total thickness H of the metal films forming the first modulation electrode branch 601 and the second modulation electrode branch 602 is not less than 100 nm.

Fig. 6 is a schematic diagram of an optical path structure of an interference type fiber-optic gyroscope based on the photonic integrated chip according to the present invention, including: the photonic integrated chip comprises the photonic integrated chip, a first optical fiber module 701, a second optical fiber module 702, a third optical fiber module 703, a fourth optical fiber module 704, a first input optical fiber 801, a second input optical fiber 802, a first output optical fiber 811, a second output optical fiber 812, a laser light source 901, a photoelectric detector 902 and an optical fiber ring 903.

The first optical fiber module 701, the second optical fiber module 702, the third optical fiber module 703 and the fourth optical fiber module 704 are respectively placed at the first port 401, the second port 402, the third port 408 and the fourth port 409;

further, the first optical fiber module 701 is connected with the laser light source 901 (or the photodetector 902) through the first input optical fiber 801, and the second optical fiber module 702 is connected with the photodetector 902 (or the laser light source 901) through the second input optical fiber 802;

further, a third optical fiber module 703 and a fourth optical fiber module 704 are respectively connected to two ports of the optical fiber ring 903 through a first output optical fiber 811 and a second output optical fiber 812;

further, the input optical fiber 801, the input optical fiber 802, the output optical fiber 811 and the output optical fiber 812 are polarization maintaining optical fibers or non-polarization maintaining optical fibers which maintain a single mode transmission state at an operating wavelength of 850nm, 1310nm or 1550 nm.

The connection mode between the

optical fibers

801, 802, 811 and 812 and the

ports

401, 402, 403 and 404 in the photonic integrated chip may be bonding and curing by using UV glue, or welding and curing by using tapered lens optical fibers. By way of example, FIG. 6 illustrates the use of UV cured glue for fiber attachment to ports in a photonic integrated chip.

The optical fiber module is composed of a crystal block which is pre-manufactured with a groove or a round through hole, wherein the groove can be manufactured on the surface of the crystal block and is in a square shape, a V shape or a semicircular shape, and the round through hole can be manufactured in the center of the crystal block. The optical fiber is placed in a groove or a circular through hole in the crystal block, the gap between the optical fiber and the groove or the through hole is filled with glue and fully cured, and then the end face of the optical fiber and the end face of the crystal block are subjected to precision grinding and polishing. And precisely aligning the polished optical fiber with a port in the photonic integrated chip, filling UV glue between the end face of the photonic integrated chip and the end face of the crystal block, and exposing and irradiating by using an ultraviolet lamp for full curing to complete the connection between the optical fiber and the port of the photonic integrated chip.

The technical means not described in detail in the present application are known techniques.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. A photonic integrated chip, comprising: a base chip, a lower cladding layer, a thin film substrate, a photonic circuit, a first modulation electrode branch, a second modulation electrode branch,

the base wafer is used for providing mechanical support for the film substrate;

2. The photonic integrated chip of claim 1, wherein the thin film substrate is made of optical homogeneous lithium niobate or lithium tantalate, or doped or near stoichiometric lithium niobate or lithium tantalate, and has a crystal tangent of X-cut or Z-cut and a thickness of 0.1 μm to 10 μm.

3. The photonic integrated chip of claim 1, wherein a non-metallic thin film material is deposited on the upper surface of the thin film substrate as an upper cladding layer.

4. The photonic integrated chip according to claim 1, wherein the photonic integrated chip Y-branch coupler has a structure for reducing reflection of the substrate radiation mode light wave at the photonic integrated chip end face B corresponding to the input and output port arrangement side.

5. The photonic integrated chip according to claim 4, wherein the structure for reducing the reflection of the substrate radiation mode light wave at the photonic integrated chip end face B is one of the following structures:

6. A photonic integrated chip according to claim 1, wherein the photonic circuit comprises a polarizer formed in the photonic circuit for polarization filtering the light wave transmitted in the photonic circuit to obtain the light wave with a single polarization state.

7. The photonic integrated chip of claim 6, wherein said polarizer is configured in one of the following ways:

the first method comprises the following steps: proton exchange is carried out in an optical sub-line of the polarizer part to realize the increase or decrease of the refractive index of the ordinary light and the abnormal light in the area so as to achieve the effect that one polarized light wave leaks out of the polarizer area in a radiation mode due to the fact that the polarized light wave cannot meet the wave guide condition, and polarization filtering is realized;

8. A photonic integrated chip according to claim 6,

the forming position of the polarizer structure adopts one of the following positions:

and fourthly: the polarizer structure is formed in the straight strip;

9. The photonic integrated chip according to claim 1, wherein the first modulation electrode branch and the second modulation electrode branch are symmetrically disposed between and outside the two arms of the photonic circuit at the second Y-branch coupler, forming a push-pull electrode structure.

10. An interference type optical fiber gyro characterized in that an optical path structure portion thereof comprises: the photonic integrated chip of any one of claims 1 to 9, further comprising: a first optical fiber module, a second optical fiber module, a third optical fiber module, a fourth optical fiber module, a first input optical fiber, a second input optical fiber, a first output optical fiber, a second output optical fiber, a laser light source, a photoelectric detector and an optical fiber ring,

11. The interference type fiber-optic gyroscope of claim 10, wherein the input fiber or the output fiber is connected to each port of the photonic integrated chip by bonding and curing with glue or by welding and fixing with a lensed fiber.