Polarization independent semiconductor optical amplifier
By combining a polarization beam splitter and a beam rotator on the SOA chip, L-band coverage with a single SOA chip was achieved, solving the problem of high polarization-dependent gain, reducing cost and power consumption, and simplifying design and manufacturing process.
Patent Information
- Application Number
- CN202511099883.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-05
- Publication Date
- 2025-11-11
AI Technical Summary
In existing technologies, a single polarization-independent SOA chip cannot cover the L-band, and conventional polarization-independent SOA suffers from high polarization-dependent gain, resulting in high cost and high power consumption.
A polarization beam splitter is used to split the incident light into T-beams and R-beams with mutually perpendicular polarization states. A loop is formed through a light guide structure. A Faraday rotator and a polarization rotating waveplate are used to rotate the T-beams and R-beams to parallel polarization on the SOA chip. Combined with precise adjustment, the light obtains the same gain on the SOA chip.
This achieves L-band coverage on a single SOA chip, reduces polarization-dependent gain, lowers cost and power consumption, and simplifies structural design and assembly processes.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention relates to the fields of communication technology and sensing, and in particular to a polarization-independent semiconductor optical amplifier. Background Technology
[0002] Semiconductor optical amplifiers (SOAs) are small in size, low in power consumption, and low in cost, making them suitable for a wide range of applications. With the continuous increase in communication capacity, the bands for trunk communication need to be expanded from C++ to C+L bands. Currently, EDFAs and coherent optical modules urgently require new technologies and products that can cover C+L, creating a pressing need for C+L polarization-independent SOAs.
[0003] Conventional SOAs only amplify TE mode light. Introducing tensile strain into the chip design can achieve TM mode amplification, and the amplification factor of the TM mode depends on the intensity of the tensile strain. Typically, polarization-independent SOAs require very small tensile strain amplitudes, making structural design and process control difficult, resulting in relatively large actual polarization-dependent gains. Furthermore, tensile strain increases the band gap of the quantum well, causing the SOA's operating wavelength to shift to shorter wavelengths. Existing mature material systems, such as InGaAsP and InAlGaAs, cannot fabricate polarization-independent SOAs that cover the L-band.
[0004] To address this issue, some researchers have used a polarization beam splitter to split the input light into two beams with perpendicular polarization states. Two polarization-dependent SOA chips are then used to amplify the two polarized beams, which are then combined using another polarization beam splitter. While this approach can cover the L-band, it requires two chips, resulting in high cost, high power consumption, and a relatively large polarization-dependent gain.
[0005] Therefore, it is necessary to design a new polarization-independent semiconductor amplification device to overcome the above problems. Summary of the Invention
[0006] The purpose of this invention is to solve the problems that a single polarization-independent SOA chip cannot cover the L-band, and that conventional polarization-independent SOA has too large a polarization-dependent gain.
[0007] To achieve the above objectives, one embodiment of this application provides a polarization-independent SOA device, comprising a polarization beam splitter, a light guide structure, a polarization-dependent SOA chip, two Faraday rotators, and a polarization rotating waveplate. The polarization beam splitter splits the incident light into T-beams and R-beams with mutually perpendicular polarization states. The light guide structure connects the T-beams and R-beams to form a loop. A polarization-dependent SOA chip is located on the optical loop. Two Faraday rotators and a polarization rotating waveplate are placed on the optical paths on both sides of the SOA. The combined effect of these three components is to rotate the T-beams and R-beams by mπ and nπ, respectively, ensuring that the polarization planes of the T-beams and R-beams incident on the SOA chip are parallel. The position and orientation of the SOA chip are precisely adjusted so that the T-beams and R-beams can be coupled into the chip, and the TE mode polarization direction of the chip is parallel to the T-beam polarization direction. There are many combinations of Faraday rotators and polarizing waveplates that meet the above requirements. The simplest combination is: two Faraday plates rotate in the same direction, both at 45 degrees, and the waveplate rotates the polarization direction by 90 degrees.
[0008] As an improvement to one embodiment of this application, the function of the 90-degree polarization rotating waveplate is realized by two polarization rotating waveplates. The two polarization rotating waveplates have the same rotation direction and the same rotation angle, both being 45 degrees; moreover, the two polarization rotating waveplates are located on both sides of the SOA. Attached Figure Description
[0009] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:
[0010] Figure 1 This is a schematic diagram of the transmission T-optical path according to the first specific embodiment of the present invention;
[0011] Figure 2 This is a schematic diagram of the reflected R optical path according to the first specific embodiment of the present invention;
[0012] Figure 3 This is a structural schematic diagram of the second specific embodiment of the present invention. Detailed Implementation
[0013] The present application will now be described in detail with reference to the specific embodiments shown in the accompanying drawings.
[0014] The first embodiment of the polarization-independent polarization amplifier of this application includes a polarization beam splitter 1, a light guide structure, a polarization-dependent SOA chip 3, two 45-degree Faraday rotators 41 and 42, and a 90-degree polarization rotating waveplate 5. The polarization beam splitter 1 splits the incident light into transmitted T-beams and reflected R-beams with mutually perpendicular polarization states. The light guide structure consists of three mirrors 21, 22, and 23, which guide the T-beams and R-beams to coincide in their optical paths. Both beams propagate in opposite directions along the same loop, and finally, the T-beams and R-beams intersect again at their bifurcation point on the beam splitter 1. The SOA chip 3, the two Faraday rotators 41 and 42, and the waveplate 5 are all located on the loop optical path. The two Faraday rotators are located on opposite sides of the SOA chip 3, and their polarization rotation directions are consistent.
[0015] Figure 1 and Figure 2 The diagram shows the transmission paths of the transmitted T-light and the reflected R-light in the first embodiment, as well as the changes in their polarization states. In the diagram, "o" represents the polarization state perpendicular to the paper plane, which we define as 0-degree polarization; "|" represents the polarization state parallel to the paper plane, which we define as 90-degree polarization; " / " represents 45-degree polarization, which is the polarization direction after rotating 45 degrees counterclockwise from the 0-degree polarization; and "\" represents 135-degree polarization, which is the polarization direction after rotating 135 degrees counterclockwise from the 0-degree polarization. Note that for simplicity, all polarization symbols are interpreted from the direction of T-light transmission.
[0016] Figure 1 In the process, randomly polarized input light is incident on polarization beam splitter 1 at a non-zero angle, and is split into transmitted T-beams and reflected R-beams with mutually perpendicular polarizations. Polarization beam splitter 1 is a glass block coated with a polarization splitting film. P-beams are transmitted, meaning the polarization direction of T-beams is parallel to the incident plane, i.e., 0-degree polarization. After passing through the first Faraday plate 41, the polarization direction of the T-beam rotates 45 degrees counterclockwise. After passing through waveplate 5, the polarization direction rotates 90 degrees clockwise, becoming -45 degrees, and then enters the polarization-dependent SOA chip 3. The position and orientation of SOA chip 3 are carefully adjusted so that the polarization direction of the SOA TE mode is -45 degrees, and the orientation of the active layer is consistent with the optical path. After being amplified by SOA chip 3, the T-beams pass through the second Faraday plate 42, where the polarization rotation direction rotates 45 degrees counterclockwise, exiting with a 0-degree polarization direction. Then, the T-beam is incident on three mirrors 21, 22, and 23. The positions and angles of the three mirrors are adjusted so that the T-beam is incident on beam splitter 1 along the path reflected by the R-beam. Due to the reversibility of optical paths, the R-beam also propagates in the reverse direction along the T-beam path. Since the polarization direction of the T-beam incident on beam splitter 1 remains unchanged at 0 degrees, the T-beam is transmitted through the polarization beam splitter and continues to propagate.
[0017] Figure 2In the process, the input light is split into transmitted T-beams and reflected R-beams with mutually perpendicular polarization by polarization beam splitter 1. Here, the S-beam is reflected, meaning the R-beam's polarization direction is perpendicular to and parallel to the incident plane, i.e., 90 degrees. After leaving polarization beam splitter 1, the reflected R-beam propagates in the reverse direction along the loop of the T-beam. Waveplates have reversible optical paths; the rotation direction remains clockwise after reverse propagation. However, Faraday plates have irreversible optical paths; after reverse propagation, the rotation becomes clockwise. Therefore, after one loop, the R-beam's polarization direction rotates clockwise by 45 degrees, 90 degrees, and 45 degrees respectively, totaling 180 degrees, while the polarization direction remains unchanged. The R-beam returns to polarization beam splitter 1 as an S-beam and continues propagating after reflection. Before entering the SOA, the R-beam is rotated counterclockwise by 45 degrees by the second Faraday plate 42, changing its polarization direction to 90 degrees + 45 degrees, parallel to the SOA's TE mode polarization direction of -45 degrees, allowing it to be amplified upon entering the SOA chip.
[0018] The T-beam and R-beam converge at a single point after traveling one loop around the circuit. Since they have the same incident angle and overlapping incident surfaces, the amplified T-beam and R-beam combine into a single beam, becoming the output beam. Because the incident light is at a non-zero angle, the output beam is at a certain angle to the incident light and does not overlap, facilitating coupling. In this implementation scheme, regardless of the polarization state of the input light, it can be decomposed into T-beams and R-beams with mutually perpendicular polarization directions. Both beams pass through identical SOA chip 1, achieving the same gain, with very low polarization-dependent gain. It's important to note that polarization-dependent SOA refers to a significant difference in gain between different polarization states under the same input power; it does not require the TM mode to have no gain at all.
[0019] Figure 3 This is a schematic diagram of the second embodiment. Compared to the first embodiment, the 90-degree polarizing waveplate is decomposed into two identical 45-degree polarizing waveplates 51 and 52, which are placed on both sides of the SOA chip 3. The T-light, after passing through the first Faraday rotator 41, rotates 45 degrees counterclockwise, and after passing through the first waveplate 51, rotates 45 degrees clockwise, entering the SOA chip 3 with a 90-degree polarization direction. The TE mode polarization direction of the SOA chip 3 is 90 degrees, and the T-light is amplified after passing through the chip 3. The T-light passes through the second Faraday rotator 42 and the second waveplate 52, maintaining its polarization state, and is transmitted after incident on the beam splitter 1.
[0020] Looking at the direction of R-light transmission, both the Faraday plate and the waveplate rotate clockwise. The combined effect of one Faraday plate and one waveplate is a 90-degree clockwise rotation. Therefore, after the R-light passes through the second waveplate 52 and the second Faraday plate 42, its polarization direction rotates 90 degrees clockwise, becoming -90 degrees, parallel to 90 degrees, and is amplified after entering the SOA chip 3. Then, after passing through the first waveplate 51 and the first Faraday plate 41, its polarization direction continues to rotate 90 degrees clockwise, becoming -180 degrees, parallel to the initial R-light polarization direction, which is the same as the S-light polarization direction. Therefore, it is reflected after returning to the polarization beam splitter 1. In the second embodiment, the SOA chip is placed parallel to the plane of the paper, in the same plane as the entire optical path, and the structural design and assembly process are simpler than the first scheme.
[0021] The above descriptions are merely some preferred embodiments of this application and are not intended to limit the scope of the invention. Equivalent implementations or modifications made by those skilled in the art based on the spirit of this application should be included within the scope of protection of this application, including but not limited to: modifying the number of mirrors, replacing mirrors with waveguides, replacing one optical rotator with multiple optical rotators, satisfying the various optical rotator angle combinations described in claim 1, etc.
Claims
1. A polarization-independent semiconductor optical amplifier device, comprising a polarization beam splitter (1), a light guide structure, a polarization-dependent SOA chip (3), two non-reciprocal polarization rotators (41, 42), and an optically reciprocal polarization rotator (5), characterized in that: The polarization beam splitter (1) splits the incident light into T-light and R-light with mutually perpendicular polarization states. The light guide structure couples the T-light and R-light together. The two light rays are transmitted in opposite directions along the same optical loop and converge again on the polarizer to become the output light. The output light does not coincide with the input light. There is a polarization-dependent SOA chip (3) in the optical loop; Two non-reciprocal polarizers (41, 42) and one reciprocal polarizer (5) are placed on the optical loop. The combined effect of the three is to ensure that the polarization directions of the T-light and R-light do not change after traveling through the loop once. The two non-reciprocal polarizers (41, 42) are located on both sides of the SOA chip (3). The reciprocal polarizer can be located on either side of the SOA chip (3). The three polarizers are rotated at appropriate angles so that the polarization directions of the T-light and R-light entering the SOA chip (3) are parallel. The position and angle of the SOA chip (3) are precisely adjusted so that the polarization direction of the TE mode is parallel to the polarization direction of the T light incident on the chip (3).
2. The polarization-independent semiconductor amplifier device according to claim 1, characterized in that: the light guide structure is composed of three mirrors (21, 22, 23); the two non-reciprocal polarization rotators are Faraday plates and rotate in the same direction, each rotating 45 degrees; the optical reciprocal polarization rotator (5) is made of a waveplate, and the polarization direction of the T-light and R-light rotates 90 degrees after passing through it.
3. The polarization-independent semiconductor amplifier device according to claim 2, characterized in that: the 90-degree optical reciprocal polarization rotating waveplate is replaced by two identical 45-degree polarization rotating waveplates (51, 52), which are located on the left and right sides of the SOA chip (3) respectively.