Integrated light emitting and receiving assembly for optical fiber current transformer

Abstract

The invention discloses an integrated light emitting and receiving assembly for an optical fiber current transformer, which integrates optical elements such as a light source, a detector, a polarization beam splitter, a polarization analyzer, a magneto-optical polarization rotator, a wave plate and the like, and realizes integrated emitting and receiving functions. According to the invention, the optical power of the light source can completely enter the output polarization maintaining optical fiber; for optical fiber sensing systems such as an optical fiber gyroscope and a current transformer, light waves returned and input through the output polarization maintaining optical fiber can completely enter a detector and are not injected into a laser to form a feedback effect, mutual interference between a light source and the detector cannot be caused, and extra signal-to-noise ratio degradation cannot be caused. According to the invention, returned light waves are subjected to polarization detection once at the polarization beam splitter prism, the extinction ratio can reach more than 20dB, the returned light waves are subjected to polarization detection again through the polaroid before entering the detector, the polarization extinction ratio of the polaroid can reach more than 50dB, the two optical polarization detection elements are cascaded, and the polarization detection effect of the system can be gt in consideration of an alignment error; and the polarization analysis requirement of 60dB is met.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing, mainly for fiber optic current transformers, but can also be used in fiber optic gyroscopes and other related fields such as fiber optic sensing, optical measurement, fiber optic communication, and space optical communication. In particular, it relates to an integrated optical transmitting and receiving component. Background Technology

[0002] refer to Figure 11 Traditional fiber optic current transformers, fiber optic gyroscopes, and other fiber optic sensing solutions typically employ discrete optical components such as light sources, power splitters, and optical power detectors. These systems suffer from drawbacks, including complex fiber optic device assembly processes, and the inability to use circulators to conserve optical power due to their wide operating temperature range. Consequently, they exhibit significant insertion loss in the optical structure, and the alignment, splicing, and assembly of polarization-maintaining fibers are complex, greatly reducing assembly efficiency and leading to high costs. Therefore, solutions are needed to reduce costs, simplify assembly processes, and improve assembly yield.

[0003] The following are existing patents for integrated optical transceiver components. No. Patent Name Application number 1 A miniaturized optical transceiver assembly for fiber optic sensing 201710290654.6 2 An integrated optical transceiver assembly for a three-axis fiber optic gyroscope 202310007962.9

[0004] The patent with application number 201710290654.6 uses a polarization-independent power beam splitter (BS), which is a large-angle (45°) incident beam and has serious design flaws.

[0005] 1. When light waves enter the polarization-independent beam splitter from the light source (not shown in the diagram), nearly half of the light power is reflected multiple times inside the gold-plated metal casing. This severely affects and interferes with the detector at the receiving end, causing the detector's light power to saturate and lose its ability to detect the returned light signal. This structure makes it virtually impossible to detect the returned light power.

[0006] 2. In addition to entering the detector, a portion of the light waves returning from the optical fiber also directly enters the light source, causing oscillations in the light source's optical power. This results in severe instability in the light source's optical power and wavelength, seriously affecting the stability of the system's operation.

[0007] 3. There is a 6dB optical power loss during the round trip of the light wave. For both fiber optic gyroscopes and fiber optic current transformers, the external phase modulator only requires a single polarization light source, which will result in another 3dB optical power loss. Therefore, this system will have a 10dB optical power loss.

[0008] 4. Reference Appendix Figure 3 , attached Figure 4The transmission and reflection spectra of a polarization-independent power beam splitter prism. A so-called polarization-independent prism is actually a polarization-dependent power beam splitter prism, where the polarization splitting ratio differs for different polarization directions. For light waves propagating in two polarization directions with average power, the average polarization value is approximately 50 / 50. However, in a single polarization direction, the polarization is not evenly distributed. This introduces additional power loss and polarization instability.

[0009] The patent with application number 202310007962.9 uses a polarization-independent power beam splitter prism, which also belongs to the large-angle (45°) incident, and still has serious design defects.

[0010] 1. The input polarization-independent power beam splitter (BS) is made of single-mode fiber (80mm narrow-diameter small-mode-field fiber). The polarization direction of the input light wave is not a single polarization light. It is usually a depolarized light wave with multiple arbitrary polarization directions, which leads to an additional optical insertion loss of at least 3dB.

[0011] 2. The incident light wave first enters the polarization-independent power beam splitter, splitting into two light waves with similar polarization components. However, the other polarization component is not marked in the diagram. After the light wave in one direction enters the polarization beam splitter, it will be decomposed into two wavelength-correlated, unequal-power, orthogonal polarization components, which will propagate in two directions respectively. The light wave in the unwanted polarization direction will propagate multiple times inside, passing through multiple polarization beam splitters and polarization-independent beam splitters. Some of it will return to the light source, while some will be reflected multiple times and enter the detector, forming various uncertain interference sources.

[0012] 3. The magnetic field strength of magneto-optical materials varies drastically with temperature, resulting in significant differences in the polarization direction of light waves at different temperatures. Therefore, due to the large rotation angle error, the light wave returning from the output detector inevitably causes another component to be incident on other detectors, leading to mutual interference and introducing substantial error signals. This can even result in the light wave returning directly to the light source, creating feedback and causing severe instability in the light source's power and wavelength. A beam splitter separates the light wave into two light waves with similar polarization components, but the diagram does not label the other polarization component. When one direction of the light wave enters the polarization beam splitter, it is decomposed into two orthogonal polarization components, which propagate in opposite directions. The unwanted polarization component propagates multiple times within the beam splitter, passing through multiple polarization beam splitters and polarization-independent beam splitters. Some of this component returns to the light source, while some is reflected multiple times and enters the detector, creating various uncertainties and interferences.

[0013] 3. The magnetic field strength of magneto-optical materials varies drastically with temperature, resulting in significant differences in the polarization direction of light waves at different temperatures. Consequently, due to the large rotation angle error, another component of the light wave returning from the output detector inevitably incident on other detectors, causing substantial error signals for each detector. Alternatively, it may return to the light source, creating feedback and leading to severe instability in the light source's power and wavelength. Summary of the Invention

[0014] This invention is an integrated optical transmission and reception component based on polarization-dependent ring function, which can perfectly solve the problems existing in the above-mentioned background technology.

[0015] The structural components of this invention are as follows.

[0016] Semiconductor light source 2 can be a broadband superradiative light source, a narrowband FP or DFB light source, with a wavelength of 1310 nm or 1550 nm, and can be a single-polarized light source or a dual-polarized light source.

[0017] Polarizer 1 (3) and polarizer 2 (4) are optical elements that allow only single-polarized light waves to pass through, and they are orthogonal to each other.

[0018] 1. A photodetector is used to receive the returned optical signal and convert it into an electrical signal; 8. A polarizing beam splitter is used to separate two beams of light with orthogonal polarization directions. The polarization extinction ratio of the separated light waves can reach >20dB.

[0019] The entire structure is housed in a 14-pin butterfly or single-sided metal casing, with a TEC cooler at the bottom. The operating temperature can be controlled by an external circuit to a set temperature, such as 25±0.1℃.

[0020] 9. Garnet, a magneto-optical plate, has its own magnetic field and is used to rotate the polarization direction of light waves by 22.5°.

[0021] The half-wave plate 10 is used to rotate the polarization direction of light waves by 22.5°.

[0022] The combined effect of the 9th magneto-optical plate Garnet and the 1 / 2 wave plate 10 is to rotate the polarization direction by a total of 45°.

[0023] Two polarizers, 3, 4, and 9, a magneto-optical plate (Garnet), and a half-wave plate (10) can be bonded together using chemical adhesive or optical adhesive techniques and fixed to the three surfaces of the PBS polarizing beam splitter 8, respectively.

[0024] Folded cavity scheme: The 7 right-angle prism and the 8 polarizing beam splitter cube prism PBS can be an integral structure or a separate structure. The 1 / 2 wave plate 10 can be fixed to the 1st surface of the 8 polarizing beam splitter cube prism PBS using chemical adhesive or optical adhesive technology. The 9 magneto-optical plate Garnet and the 1 / 2 wave plate 10 can be fixed to the output surface of the 7 right-angle prism using chemical adhesive or optical adhesive technology.

[0025] The collimating lens 11 at the front of the output polarization-maintaining fiber 12 is used to convert the spatial optical mode field to a mode field that matches the fiber, so that the light wave can enter the fiber for transmission.

[0026] The slow axis of polarization-maintaining fiber 11 is parallel to the output light wave, that is, it forms a 45° angle with the incident surface of the light wave. Depending on the actual needs of the system, it can also be designed so that the fast axis is parallel to the output light wave.

[0027] The returning light wave passes through the half-wave plate 10 and the 9-magnetic gyroscope Garnet, and then rotates by 45° to be perpendicular to the polarization direction of the incident light wave. For the 8-polarization beam splitter prism PBS, it is an s-ray, which is reflected by the PBS film layer. After being analyzed by the 3-polarizer 1, it enters the photodetector 1 for reception.

[0028] The entire unit is housed in a butterfly-shaped 14-pin double-sided or similar single-sided metal package, including the light source, detector, and passive polarization-dependent circulator. The entire bottom is temperature-controlled by TEC.

[0029] Light source 2, detector 3, and related detector amplification circuits are ultrasonically soldered to internal pins with gold wire for connection with external pins; where the TEC current is relatively large, copper wire soldering can also be used for connection.

[0030] The beneficial effects of this invention are as follows.

[0031] Multiple optical components can be integrated into a single 14-pin laser housing, resulting in a compact overall size. The polarization-dependent ring function enables both light source emission and receiver reception. Because the laser has TEC control, its magneto-optical rotation operates stably over a wide temperature range (-40℃ to +75℃), offering advantages such as a wide operating temperature range and high optical isolation.

[0032] See Figure 1By utilizing a polarization-dependent optical circulator design, the optical structure loss is reduced by 6dB compared to traditional coupler-based solutions. If a single-polarization light source is used, depolarization is unnecessary, further reducing polarization loss by 3dB. Furthermore, due to the working principle of semiconductor quantum wells, the single-polarization light output from a single-polarization source typically has 3dB more power than the dual-polarization light. Therefore, compared to traditional discrete components, this structural design increases the optical power returned to the detector by at least 10dB, representing a 10-fold improvement in signal-to-noise ratio. Since the performance of fiber optic current transformers or fiber optic gyroscope systems is proportional to the square root of the incident optical power on the detector, the system's performance can be improved by a factor of three.

[0033] See Figure 2 One approach is to use an additional reflective prism at the output end to fold the output light wave, change its propagation direction, make full use of the space inside the housing, and reduce interference caused by weak scattered light entering the detector.

[0034] The light power of the light source can all enter the output polarization-maintaining fiber and not enter the photodetector; for fiber optic gyroscope systems, the light waves input through the output polarization-maintaining fiber can all enter the detector and not enter the laser to form a feedback effect. Therefore, it will not cause mutual interference between the light source and the detector, and will not cause additional signal-to-noise ratio degradation.

[0035] For fiber optic current transformers, due to the working principle of polarization rotation detection, a small portion of the light waves in the p-polarized direction will carry signals back to the light source. Since the polarization direction is the same, all devices through which the light waves pass are broadband. Therefore, the output spectrum of the light source remains basically unchanged. The feedback can only cause a change in absolute optical power and will not cause other parameter degradation, so it basically does not affect the performance indicators of the system.

[0036] For fiber optic current transformers, due to the working principle of polarization rotation detection, the polarization extinction ratio of the optical polarizer must be higher than 60dB. In this structure, the returned light wave undergoes one polarization analysis at the polarization beam splitter prism, and the extinction ratio can reach more than 20dB. Before being incident on the detector, it undergoes another polarization analysis by the polarizer, and the polarization extinction ratio of the polarizer can reach more than 50dB. The two optical polarization analysis elements are cascaded. Considering the alignment error, the polarization analysis effect of this system can meet the polarization analysis requirement of >60dB. Attached Figure Description

[0037] Figure 1 A schematic diagram of a polarization-dependent ring light transmitting and receiving component.

[0038] Figure 2 Polarization-dependent ring light transmitting and receiving component, optical path folding scheme.

[0039] Figure 3 Schematic diagram of a polarizing beam splitter.

[0040] Figure 4 Top view of a polarizing beam splitter in operation.

[0041] Figure 5 A polarization-independent power beam splitter prism, showing the relationship between the reflection beam splitting ratio and wavelength, and a theoretical calculation diagram.

[0042] Figure 6 A polarization-independent optical power beam splitter, showing the relationship between transmission beam splitting ratio and wavelength, and a theoretical calculation diagram.

[0043] Figure 7 Polarizing beam splitter prism, relationship between reflection beam splitting ratio and wavelength, theoretical calculation diagram.

[0044] Figure 8 Polarizing beam splitter prism, relationship between transmission beam splitting ratio and wavelength, theoretical calculation diagram.

[0045] Figure 9 Packaging structure of polarization-dependent ring light transmitting and receiving components.

[0046] Figure 10 A polarization-dependent ring-shaped optical transmitter and receiver assembly packaging structure with an optical path folding scheme.

[0047] Figure 11 Optical path diagram of a fiber optic current transformer using discrete components.

[0048] The components in the attached diagram are labeled as follows: 1. Photodetector receiver; 2. Light source; 3. Collimating lens 1; 4. Collimating lens 2; 5. Polarizer 1; 6. Polarizer 2; 7. Right-angle prism; 8. Cubic polarizing beam splitter; 9. Magneto-optic plate; 10. Half-wave plate; 11. Collimating lens; 12. Polarization-maintaining fiber. Detailed Implementation

[0049] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0050] Please see Figure 1 Based on the working principle of polarization-dependent optical circulators, one embodiment of the present invention includes...

[0051] Semiconductor light source 2, collimating lens 4, forming a Gaussian beam that propagates in space.

[0052] After passing through polarizer 2 (6 polarizers), the light enters the PBS polarizing beam splitter 8. The polarization direction for the PBS is p-light, which is a TM wave parallel to the incident plane.

[0053] After the p-light is transmitted through the PBS, it passes through the Garnet magneto-optical plate 9, and then its polarization direction is rotated by 22.5°.

[0054] After passing through the half-wave plate 10, the polarization direction of the light wave is further rotated by 22.5°.

[0055] The combined effect of the two Garnet elements and the half-wave plate is to rotate the polarization direction by a total of 45°.

[0056] The light wave passes through the collimating lens 11 at the front of the polarization-maintaining fiber, which can be a C-Lens, a G-Lens, or other lenses, to convert the spatial optical mode field to a mode field that matches the fiber, and the light wave enters the fiber for transmission.

[0057] The slow axis of polarization-maintaining fiber 12 is parallel to the output light wave, that is, it forms a 45° angle with the incident surface of the light wave. Depending on the actual needs of the system, it can also be designed so that the fast axis is parallel to the output light wave.

[0058] The dashed line represents the returning light wave, which, after passing through the half-wave plate 10 and the Garnet magneto-optical plate 9, continues to rotate by 45°, for a total rotation of 90 degrees.

[0059] Compared to the input light wave, the polarization direction of the returned light wave is perpendicular to the polarization direction of the incident light wave. For a PBS polarizing beam splitter, this is an s-wave, i.e., a TE wave perpendicular to the incident surface, which is reflected by the PBS film.

[0060] The above description explains the basic working principle of a polarization-dependent optical circulator.

[0061] The light wave continues to pass through polarizer 1 for polarization analysis, and then through collimating lens 1 for focusing.

[0062] The light wave carrying the signal eventually enters photodetector 1 and is converted into an electrical signal for reception and detection.

[0063] The returned light wave undergoes a first polarization analysis at the polarizing beam splitter prism 8, achieving a polarization extinction ratio of over 20 dB. Before reaching the detector, it passes through polarizer 1 again for a second polarization analysis. Since polarizer 1 can achieve a polarization extinction ratio of over 50 dB, and considering the polarization direction alignment error, the cascaded two-stage polarization analysis of this system can meet the requirement of >60 dB polarization analysis for current transformers.

[0064] Please see Figure 2 In another embodiment, inserting a 7 right-angle prism behind an 8-polarization beam splitter can deflect the direction of light propagation by 90 degrees, thereby facilitating process assembly.

[0065] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. This invention is an integrated optical transmitter and receiver component based on polarization-dependent ring function, characterized in that, include: The system includes one semiconductor light source, one semiconductor photodetector, one cubic polarizing beam splitter, two polarizers, two collimating lenses, one Garnet magneto-optical rotator, one half-wave plate, and one polarization-maintaining fiber. An additional right-angle prism can be added to deflect the light wave by 90 degrees for internal assembly and debugging. The semiconductor light source is equipped with a temperature controller and a thermistor for precise control of the chip's operating temperature. The semiconductor photodetector is followed by an analog amplifier circuit to convert the optical signal into an electrical signal output and to amplify the electrical power, thereby increasing the load-carrying capacity.

2. The optical transmitting and receiving integrated component based on polarization-dependent ring function according to claim 1, characterized in that: The semiconductor light source can be a broadband superradiative light source, a narrowband FP or DFB light source, and its wavelength can be in the 1310nm band, the 1550nm band, or other bands; it can be a single-polarized light source or a dual-polarized light source; the polarizer 1 and polarizer 2 are optical elements that only allow single-polarized light waves to pass through, and the two are orthogonal to each other; the photodetector is used to receive the returned optical signal and convert it into an electrical signal; the polarization beam splitter is used to separate two beams of light with orthogonal polarization directions, and the polarization extinction ratio of the separated light wave can reach >20dB. The Garnet, a magnetorheological plate, has its own magnetic field and is used to rotate the polarization direction of light waves by 22.5°. The half-wave plate is used to rotate the polarization direction of light waves by 22.5°. The combined effect of the Garnet and the half-wave plate is to rotate the polarization direction by a total of 45°. The two polarizers, the Garnet and the half-wave plate, can be fixed to the three surfaces of the PBS polarizing beam splitter 8 using chemical adhesive or optical adhesive technology.

3. The optical transmitting and receiving integrated component based on polarization-dependent ring function according to claim 2, characterized in that: In the folded cavity scheme, the right-angle prism and the polarization beam splitter cube prism (PBS) can be an integral structure or separate structures. The half-wave plate can be fixed to one side of the polarization beam splitter cube prism (PBS) using chemical adhesive or optical adhesive technology. The magneto-optical plate (Garnet) and the half-wave plate can be fixed to the output surface of the right-angle prism using chemical adhesive or optical adhesive technology. The collimating lens at the front of the output polarization-maintaining fiber is used to convert the spatial optical mode field to a mode field that matches the fiber, allowing the light wave to enter the fiber for transmission. The slow axis of the polarization-maintaining fiber is parallel to the output light wave, i.e., at a 45° angle to the incident plane of the light wave. Depending on the actual needs of the system, it can also be designed so that the fast axis is parallel to the output light wave. The polarization-maintaining fiber can be any commercially available single-mode fiber, with a core diameter of 50 / 100, 60 / 120, 80 / 160, or ordinary 125 / 250 or 125 / 400 fiber. The returned light wave, after passing through the half-wave plate Garnet, continues to rotate by 45°, becoming perpendicular to the polarization direction of the incident light wave. For the polarization beam splitter prism (PBS), this is an s-ray, which is reflected by the PBS film layer, achieving the function of polarization correlation loop. Finally, the output light wave, after being analyzed by polarizer 1, enters the photodetector for reception.

4. The optical transmitting and receiving integrated component based on polarization-dependent ring function according to claim 2, characterized in that: Light source 2, detector 3, and related detector amplification circuits are ultrasonically soldered to internal pins with gold wire for connection to external pins; the TEC current is relatively large, so copper wire soldering can also be used for connection. The entire structure is housed in a 14-pin or 12-pin butterfly or single-sided metal casing, with a TEC cooler at the bottom. The operating temperature can be controlled by external circuitry to a set temperature, such as 25±0.1℃.

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