An integrated optical transmitter and receiver assembly for fiber optic current transformers

Abstract

This invention discloses an integrated optical transmitting and receiving component for fiber optic current transformers, integrating optical elements such as a light source, detector, polarization beam splitter, polarization analyzer, magneto-optical polarization rotation, and waveplate, achieving integrated transmission and reception functions. This invention ensures that all optical power from the light source enters the output polarization-maintaining fiber. For fiber optic sensing systems such as fiber optic gyroscopes and current transformers, the light wave returning to the input after passing through the output polarization-maintaining fiber can all enter the detector, without being injected into the laser to form a feedback effect, thus avoiding mutual interference between the light source and the detector and preventing additional signal-to-noise ratio degradation. This invention enables the returned light wave to undergo one polarization analysis at the polarization beam splitter prism, achieving an extinction ratio of over 20dB. Before entering the detector, it undergoes another polarization analysis by a polarizer, achieving a polarization extinction ratio of over 50dB. With two cascaded optical polarization analyzers, considering alignment errors, the system's polarization analysis effect can meet the requirement of >60dB polarization analysis.

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. 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 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.

[0004] 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.

[0005] 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 system's operational stability.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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, but usually a depolarized light wave with multiple arbitrary polarization directions. This results in an additional optical insertion loss of at least 3dB.

[0010] The incident light wave first enters the polarization-independent power beam splitter and is split into two light waves with similar polarization components, but the other polarization component is not marked in the figure. 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, and some will be reflected multiple times into the detector, forming various uncertain interference sources.

[0011] 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 (though 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.

[0012] 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

[0013] 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.

[0014] An integrated optical transmitter and receiver assembly based on polarization-dependent ring function includes: The system includes one semiconductor light source, one semiconductor photodetector, one cubic polarizing beam splitter (PBS), two polarizers, two collimating lenses, one Garnet magneto-optical rotator, one half-wave plate, one polarization-maintaining fiber, and one right-angle prism. The right-angle prism deflects the light wave by 90 degrees and is used for internal assembly and debugging. The semiconductor light source is equipped with a temperature controller and a temperature-sensing thermistor to control the chip's operating temperature. The semiconductor photodetector is subsequently connected to an analog amplifier circuit to convert the optical signal into an electrical signal for output and to amplify the electrical power. The two polarizers are optical elements that allow only single-polarized light waves to pass through, and they are orthogonal to each other; The cubic polarizing beam splitter PBS is used to separate two beams of light with orthogonal polarization directions, and the polarization extinction ratio of the separated light waves reaches >20dB. A cylindrical collimating lens, either a C-lens or a Grin-Lens, located at the front of the polarization-maintaining fiber, is used to convert the spatial optical mode field to a mode field that matches the fiber. The light wave then propagates in the polarization-maintaining fiber. The returning light wave passes through a half-wave plate and a Garnet magneto-optical rotator, and then rotates 45° to be perpendicular to the polarization direction of the incident light wave. For the cubic polarization beam splitter PBS, this is an s-ray, which is reflected by the PBS film. The output light wave is then analyzed by polarizer 1 and received by a semiconductor photodetector. The semiconductor photodetector is used to receive the returned optical signal and convert the optical signal into an electrical signal.

[0015] Preferably, according to the optical emission and reception integrated component based on polarization-dependent ring function, the semiconductor light source is a broadband superradiative light source, a narrowband FP or DFB light source, with a wavelength of 1310 nm or 1550 nm, and is a single-polarization light source or a dual-polarization light source.

[0016] Preferably, the Garnet magneto-optical rotator itself has a magnetic field, which is used to rotate the polarization direction of the light wave by 22.5°; the half-wave plate is used to rotate the polarization direction of the light wave by 22.5°, and the combined effect of the Garnet magneto-optical rotator and the half-wave plate is to rotate the polarization direction by a total of 45°.

[0017] Preferably, the two polarizers, the Garnet magneto-optical rotator and the half-wave plate, are fixed to the three surfaces of the cubic polarizing beam splitter PBS 8 using chemical adhesive or optical adhesive technology.

[0018] Preferably, the right-angle prism and one side of the cubic polarizing beam splitter PBS are an integral structure or separate structures, on one side of the cubic polarizing beam splitter PBS.

[0019] Preferably, the slow axis of the polarization-maintaining fiber is parallel to the output light wave, i.e., at a 45° angle to the incident surface of the light wave.

[0020] Preferably, the polarization-maintaining fiber is a single-mode fiber, and the diameters of the cladding and coating are 50 μm / 100 μm, 60 μm / 120 μm, 80 μm / 160 μm, 125 μm / 250 μm, or 125 μm / 400 μm, respectively.

[0021] Preferably, the entire optical transmitter and receiver integrated assembly is housed in a 14-pin or 12-pin butterfly-shaped or single-sided metal casing, with a TEC cooler at the bottom, and the operating temperature is controlled by an external circuit to a set temperature.

[0022] Preferably, the semiconductor light source, the semiconductor photodetector, and the associated detector amplification circuit are ultrasonically soldered to internal pins with gold wire for connection to external pins.

[0023] The beneficial effects of this invention include: multiple optical elements can be integrated into a single 14-pin laser housing, resulting in a small overall size; the polarization-dependent ring function enables both light source emission and receiver reception. Because the laser has TEC control, the magneto-optical rotation operates stably over a wide temperature range, from -40℃ to +75℃, offering advantages such as a wide operating temperature range and high optical isolation.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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

[0029] Figure 1 A schematic diagram of a polarization-dependent ring light transmitting and receiving component.

[0030] Figure 2 Polarization-dependent ring light transmitting and receiving component, optical path folding scheme.

[0031] Figure 3Schematic diagram of the working cubic polarizing beam splitter (PBS).

[0032] Figure 4 Top view of the cubic polarizing beam splitter (PBS) in operation.

[0033] Figure 5 A polarization-independent power beam splitter prism, showing the relationship between the reflected polarization splitting ratio and wavelength, and a theoretical calculation diagram.

[0034] Figure 6 A polarization-independent power beam splitter prism, showing the relationship between transmission polarization splitting ratio and wavelength, and a theoretical calculation diagram.

[0035] Figure 7 The relationship between the reflected polarization splitting ratio and wavelength of a cubic polarization beam splitter (PBS) is shown in the theoretical calculation diagram.

[0036] Figure 8 The relationship between the transmission polarization splitting ratio and wavelength of a cubic polarization beam splitter (PBS) is shown in the theoretical calculation diagram.

[0037] Figure 9 Packaging structure of polarization-dependent ring light transmitting and receiving components.

[0038] Figure 10 A polarization-dependent ring-shaped optical transmitter and receiver assembly packaging structure with an optical path folding scheme.

[0039] Figure 11 Optical path diagram of a fiber optic current transformer using discrete components.

[0040] 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 (PBS); 9. Magneto-optic plate; 10. 1 / 2 waveplate; 11. Collimating lens; 12. Polarization-maintaining fiber. Detailed Implementation

[0041] 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.

[0042] Please see Figure 1 Based on the working principle of polarization-dependent optical circulators, one embodiment of the present invention includes...

[0043] The semiconductor light source 2 and the collimating lens 4 can be a spherical lens, an aspherical lens, or other collimating lenses, forming a Gaussian beam that propagates in space.

[0044] After passing through polarizer 2 of polarizer 6, the light enters the cubic polarizing beam splitter PBS 8. The polarization direction of the light relative to the PBS is p-light, which is a TM wave parallel to the incident plane.

[0045] 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°.

[0046] After passing through the half-wave plate 10, the polarization direction of the light wave is further rotated by 22.5°.

[0047] The combined effect of the two Garnet elements and the half-wave plate is to rotate the polarization direction by a total of 45°.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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 cubic polarizing beam splitter (PBS), this is an s-wave, i.e., a TE wave perpendicular to the incident plane, which is reflected by the PBS film.

[0052] The above description explains the basic working principle of a polarization-dependent optical circulator.

[0053] The light wave continues to pass through polarizer 1 and is then analyzed. It then passes through collimating lens 1, which can be a spherical lens, an aspherical lens, or other collimating lens for focusing.

[0054] The light wave carrying the signal eventually enters photodetector 1 and is converted into an electrical signal for reception and detection.

[0055] The returned light wave undergoes a first polarization analysis at the cubic polarizing beam splitter prism PBS 8, achieving a polarization extinction ratio of over 20 dB. Before reaching the detector, it passes through a third polarizer 1 for a second polarization analysis. Since the polarization extinction ratio of the third polarizer 1 can reach over 50 dB, the cascaded optical polarization analysis elements, considering polarization alignment errors, can meet the requirement of >60 dB polarization analysis for current transformers.

[0056] Please see Figure 2In another embodiment, inserting a right-angle prism 7 behind the cubic polarizing beam splitter PBS 8 can deflect the direction of light propagation by 90 degrees, thereby facilitating process assembly.

[0057] 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. An integrated optical transmitting / receiving module for fiber-optic current transformers, characterized by, include: 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, one polarization-maintaining fiber, one cylindrical collimating lens, and one right-angle prism that deflects the light wave by 90 degrees for internal assembly and debugging. The semiconductor light source is equipped with a temperature controller and a temperature-sensing thermistor to control the chip's operating temperature. The semiconductor photodetector is subsequently connected to an analog amplifier circuit to convert the optical signal into an electrical signal for output and to amplify the electrical power. The two polarizers are optical elements that allow only single-polarized light waves to pass through, and they are orthogonal to each other; The cubic polarizing beam splitter is used to separate two beams of light with orthogonal polarization directions, and the polarization extinction ratio of the separated light waves reaches >20dB. A cylindrical collimating lens, either a C-lens or a Grin-Lens, located at the front of the polarization-maintaining fiber, is used to convert the spatial optical mode field to a mode field that matches the fiber. The light wave then propagates in the polarization-maintaining fiber. The returning light wave passes through a half-wave plate and a Garnet magneto-optical rotator, and then rotates 45° to be perpendicular to the polarization direction of the incident light wave. For the cubic polarization beam splitter PBS, this is an s-ray, which is reflected by the PBS film. The output light wave is then analyzed by polarizer 1 and received by a semiconductor photodetector. The semiconductor photodetector is used to receive the returned optical signal and convert the optical signal into an electrical signal.

2. The integrated optical transmitting and receiving unit for fiber-optic current transformers according to claim 1, characterized in that, The semiconductor light source is a broadband superradiative light source, a narrowband FP or DFB light source, with a wavelength of 1310 nm or 1550 nm, and is a single-polarized light source or a dual-polarized light source.

3. The integrated optical transmitting and receiving unit for fiber-optic current transformers according to claim 2, characterized in that, The Garnet magneto-optical rotator itself carries a magnetic field, which is used to rotate the polarization direction of the light wave by 22.5°; the half-wave plate is used to rotate the polarization direction of the light wave by 22.5°, and the combined effect of the Garnet magneto-optical rotator and the half-wave plate is to rotate the polarization direction by a total of 45°.

4. The integrated optical transmitting and receiving unit for fiber-optic current transformers according to claim 1, characterized in that, The two polarizers, the Garnet magneto-optical rotator and the half-wave plate, are fixed to the three faces of the cubic polarizing beam splitter (PBS) using chemical adhesive or optical adhesive techniques.

5. The integrated optical transmitting and receiving unit for fiber-optic current transformers according to claim 1, characterized in that, The right-angle prism and one side of the cubic polarizing beam splitter PBS are either an integral structure or separate structures; the 1 / 2 wave plate is fixed to one side of the cubic polarizing beam splitter PBS using chemical adhesive or optical adhesive technology.

6. The integrated optical transmitting and receiving unit for fiber-optic current transformers according to claim 1, characterized in that, The slow axis of the polarization-maintaining fiber is parallel to the output light wave, that is, at a 45° angle to the incident surface of the light wave.

7. The integrated optical transmitting and receiving unit for fiber-optic current transformers according to claim 1, characterized in that, The polarization-maintaining fiber is a single-mode fiber, with cladding and coating diameters of 50 μm / 100 μm, 60 μm / 120 μm, 80 μm / 160 μm, 125 μm / 250 μm, or 125 μm / 400 μm, respectively.

8. The integrated optical transmitting and receiving unit for fiber-optic current transformers according to claim 1, characterized in that, The entire optical transmitter and receiver integrated assembly is housed in a 14-pin or 12-pin butterfly-shaped or single-sided metal casing, with a TEC cooler at the bottom. The operating temperature is controlled by an external circuit to the set temperature.

9. The integrated optical transmitting and receiving unit for fiber-optic current transformers according to claim 1, characterized in that, The semiconductor light source, the semiconductor photodetector, and the detector amplification circuit are ultrasonically soldered to internal pins with gold wire for connection to external pins.

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