An integrated non-reciprocal phase shifter and laser

Abstract

The application discloses an integrated non-reciprocal phase shifter and a laser, the non-reciprocal phase shifter comprising an integrated package of a first collimator, a Wollaston prism, a second collimator, a gain optical fiber, a first wave plate and a first polarization beam splitter, an optical rotator, a second wave plate, a second polarization beam splitter, a band-pass filter and a total reflection mirror arranged in sequence, wherein the gain optical fiber is connected with a first end of the first collimator and a first end of the second collimator, a second end of the first collimator is connected with the Wollaston prism, and the second collimator is connected with a first input end of the first polarization beam splitter, and the Wollaston prism is connected with a second input end of the first polarization beam splitter through the first wave plate. The application can improve the repetition frequency of the laser. The application can be widely applied in the technical field of optical devices.

Description

Technical Field

[0001] This application relates to the field of optical device technology, and in particular to an integrated non-reciprocal phase shifter and laser. Background Technology

[0002] In recent years, with the advancement of ultrafast laser technology, high-repetition-rate, narrow-pulse femtosecond fiber lasers have found increasingly widespread applications in many fields. Among them, the 1840nm wavelength, which can be instantaneously absorbed by water molecules, is used for procedures such as vocal cord polyp removal and tonsil ablation, making it a commonly used wavelength in minimally invasive ENT surgery. In addition, 1840nm lasers also have wide applications in cosmetic skin treatments and dental hard tissue manipulation. Frequency doubling of the 1840nm laser to the 920nm band is a hot research area in neuroscience.

[0003] The higher the repetition rate of a laser, the faster it interacts with biological cells (samples), resulting in faster processing speeds. However, the repetition rate of typical fiber lasers is generally only on the order of 100 MHz, severely hindering the improvement of processing speed. Therefore, the repetition rate of lasers needs to be further improved. Summary of the Invention

[0004] The main objective of this application is to propose an integrated non-reciprocal phase shifter and laser, which aims to improve the repetition rate of the laser and obtain laser light around 1840nm.

[0005] To achieve the above objectives, one embodiment of this application proposes an integrated non-reciprocal phase shifter, comprising an integrated packaged first collimator, a Wollaston prism, a second collimator, a gain fiber, a first waveplate, and a first polarization beam splitter, a rotator, a second waveplate, a second polarization beam splitter, a bandpass filter, and a total reflection mirror arranged sequentially. The gain fiber connects the first end of the first collimator and the first end of the second collimator. The second end of the first collimator is connected to the Wollaston prism. The outgoing light from the second collimator reaches the first input end of the first polarization beam splitter. The outgoing light from the Wollaston prism passes through the first waveplate and reaches the second input end of the first polarization beam splitter.

[0006] In some embodiments, the first waveplate and the second waveplate are fixed in a sleeve with a hardness greater than a preset value.

[0007] In some embodiments, the outer surface of the sleeve is threaded.

[0008] In some embodiments, the sleeve is fixed by a double U-shaped structure.

[0009] To achieve the above objectives, another aspect of this application proposes a high repetition rate laser, including a first laser, a second laser, a first isolator, a second isolator, and the aforementioned non-reciprocal phase shifter. The output of the first laser is connected to a first end of the first collimator, the output of the second laser is connected to a first end of the second collimator, the output light of the first polarization beam splitter is output through the first isolator, and the output light of the second polarization beam splitter is output through the second isolator. The laser wavelength range of the first laser is a first preset range, and the laser wavelength of the second laser is a second preset range, both of which include 1570 nm.

[0010] In some embodiments, the gain fiber includes a thulium-doped gain fiber.

[0011] The embodiments of this application include at least the following beneficial effects: This application provides an integrated non-reciprocal phase shifter and laser. The non-reciprocal phase shifter includes an integrated packaged first collimator, a Wollaston prism, a second collimator, a gain fiber, a first waveplate, and a first polarization beam splitter, a rotator, a second waveplate, a second polarization beam splitter, a bandpass filter, and a total reflection mirror arranged in sequence. The gain fiber is connected to the first end of the first collimator and the first end of the second collimator. The second end of the first collimator is connected to the Wollaston prism. The output light from the second collimator reaches the first input end of the first polarization beam splitter. The output light from the Wollaston prism passes through the first waveplate and reaches the second input end of the first polarization beam splitter, thereby increasing the repetition rate of the laser and obtaining laser light near 1840nm. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the structure of an 1840nm mode-locked laser in related technologies; Figure 2 This is a schematic diagram of the integrated non-reciprocal phase shifter provided in the embodiments of this application; Figure 3 This is a schematic diagram of the integrated non-reciprocal phase shifter provided in the embodiments of this application; Figure 4 This is a schematic diagram of the waveplate mounting structure provided in the embodiments of this application; Figure 5 This is a schematic diagram of the external structure of the non-reciprocal phase shifter provided in the embodiments of this application; Figure 6 This is a schematic diagram of the high repetition rate laser provided in the embodiments of this application. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit it. In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with those of this application; they are merely examples of apparatuses and methods consistent with some aspects of the embodiments of this application as detailed in the appended claims.

[0014] It is understood that the terms “first,” “second,” etc., used in this application may be used herein to describe various concepts, but unless otherwise stated, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another. For example, without departing from the scope of the embodiments of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the words “if,” “when,” or “in response to a determination” as used herein may be interpreted as “when…” or “when…” or “in response to a determination.”

[0015] As used in this application, the terms "at least one", "multiple", "each", "any", etc., "at least one" includes one, two or more, "multiple" includes two or more, "each" refers to each of the corresponding multiples, and "any" refers to any one of the multiples.

[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0017] like Figure 1 As shown, a mode-locked laser built using the NALM mode-locking mechanism includes a pump source (1-1), isolator 1 (1-8), and isolator 2 (1-9). The cavity requires a phase shifter (1-3), gain fiber (1-4), wavelength division multiplexer (1-2), 2×2 coupler (1-5), dispersion compensation device (1-6), and a mirror (1-7) (90% reflection, 10% transmission). All these devices are encapsulated in polarization-maintaining (PM) fiber. To fusion splice these devices together, each device's pigtail needs to be at least 150mm (determined by the fusion splicer's performance). Adding the gain fiber (which needs to be >0.5m), the total cavity length is over 2.5m (corresponding to a repetition rate of approximately 80MHz). Even if the pigtail of each device is shortened to 100mm, the cavity length is still around 2m (corresponding to a repetition rate of approximately 100MHz). This explains why mode-locked fiber lasers generally don't have very high repetition rates.

[0018] To increase the repetition rate of a fiber laser, the optical components of the fiber laser need to be as short as possible or even eliminated. Therefore, it is not possible to simply shorten the component's pigtail. Instead, it is necessary to integrate and package all the components of the entire cavity based on the principle of mode-locking of the entire cavity.

[0019] See Figure 2 This application provides an integrated non-reciprocal phase shifter, including an integrated packaged first collimator (2-1), a Wollaston prism (2-2), a second collimator (2-4), a gain fiber (2-5), a first waveplate (2-3), and a first polarization beam splitter (2-6), a rotator (2-7), a second waveplate (2-8), a second polarization beam splitter (2-9), a bandpass filter (2-10), and a total reflection mirror (2-11). The gain fiber (2-5) is connected to the first end of the first collimator (2-1) and the first end of the second collimator (2-4). The second end of the first collimator (2-1) is connected to the Wollaston prism (2-2). The outgoing light from the second collimator (2-4) reaches the first input end of the first polarization beam splitter (2-6). The outgoing light from the Wollaston prism (2-2) passes through the first waveplate (2-3) and reaches the second input end of the first polarization beam splitter (2-6).

[0020] It should be noted that the first and second wave plates are determined based on the actual application, and this embodiment does not impose specific limitations. For example, the second wave plate may include, but is not limited to, a quarter-wave plate, a sixth-wave plate, or an eighth-wave plate.

[0021] The first polarization beam splitter, the second polarization rotator, the first waveplate, the second waveplate, the second polarization beam splitter, the bandpass filter (1840±20nm), and the total reflection mirror are integrated and packaged together. Then, the gain fiber is integrated into the collimator. This ensures the overall cavity gain while significantly shortening the cavity length, making it easy for the fiber laser to achieve a repetition rate of 400MHz. Using gain fibers with higher gain density, it can even reach over 600MHz. The second polarization beam splitter not only ensures mode-locking of the two beams (clockwise and counterclockwise) but also serves as a 2×2 coupler for the output.

[0022] The Wollaston prism can effectively limit the polarization direction of spatial light returning to the gain fiber, ensuring that the polarized light is completely aligned with the slow axis of the gain fiber, thus guaranteeing the smoothness of the mode-locked spectrum and making it more conducive to obtaining narrow pulse widths.

[0023] See Figure 3The laser light reflected by the 0° total internal reflection mirror (red solid arrow) is split into two paths (blue solid line and green solid line) on the second waveplate after passing through the second polarization beam splitter (P-polarized light). These two paths are perpendicular and orthogonal, corresponding to the fast and slow axes of the second waveplate, respectively. These two orthogonal beams are rotated 45° after passing through a Faraday rotator, and then output from the P-polarized end (blue double solid arrow) and S-polarized end (green double solid arrow) of the first polarization beam splitter, respectively. These two beams are coupled into the first and second collimators, respectively, and are aligned with the slow axis of the polarization-maintaining gain fiber. However, the P-polarized light (blue double solid arrow) rotates a certain angle after passing through the first waveplate (blue double solid arrow with a smaller polarization angle). Therefore, a Wollaston prism is needed to correct its polarization axis, allowing it to re-polarize back to the P-polarized state (blue double solid arrow) before being coupled into the gain fiber. The first and second collimators are placed perpendicularly in space (at a 90° angle). Therefore, after passing through the gain fiber, P-polarized light (solid blue double arrow) becomes S-polarized light (dashed blue double arrow), and S-polarized light (solid green double arrow) becomes P-polarized light (dashed blue double arrow) after passing through the gain fiber. These two polarized beams (dashed blue and green double arrows) are combined by the first polarization beam splitter (dashed red arrow) and then rotated 45° by the Faraday rotator (dashed green and blue lines) before coinciding again with the fast / slow axis of the second waveplate. Finally, they interfere and mode-lock at the second polarization beam splitter to output (output 2). Because they pass through the fast / slow axis of the second waveplate twice, and the refractive indices of the fast and slow axes of the second waveplate are different, these two orthogonal beams will accumulate a certain phase shift difference (related to the delay of the waveplate). The first waveplate acts as a power beam splitter, separating a portion (10%-20%) of the P-polarized (blue double-arrow dashed line) light through the first polarization beam splitter, which is then used as output 1.

[0024] In some embodiments, the first wave plate and the second wave plate are fixed in a sleeve with a hardness greater than a preset value.

[0025] It should be noted that the hardness of the sleeve is determined according to the actual application, and this embodiment does not impose specific restrictions. For example, a stainless steel sleeve is first fixed in the stainless steel sleeve with UV glue. Stainless steel has high hardness, so it is not easy to deform when fixed.

[0026] In some embodiments, the outer surface of the sleeve is threaded.

[0027] In some embodiments, the sleeve is fixed by a double U-shaped structure.

[0028] See Figure 4 , Figure 4In the diagram, 3-1 represents a sleeve, 3-2 represents a U-shaped structure, and 3-3 represents a waveplate sleeve. The sleeve has threads for easy fine-tuning. The first waveplate fine-tunes the laser power splitting ratio, making the output power adjustable. The second waveplate can fine-tune the phase offset (phase shift difference), resulting in different spectra when mode-locked.

[0029] The sleeve is fixed with a double U-shaped structure, which ensures that the sleeve is not easily rotated during the fixing process, thus preventing the mold clamping result from shifting and improving the structural stability.

[0030] See Figure 5 Through integrated installation, non-reciprocal phase shifters can be miniaturized to 150*120*50mm (length, width, height), making them suitable for integrated packaging of high-precision equipment.

[0031] See Figure 6 This application provides a high repetition rate laser, including a first laser (2-13), a second laser (2-12), a first isolator (2-14), a second isolator (2-15), and the aforementioned non-reciprocal phase shifter. The output of the first laser (2-13) is connected to the first end of the first collimator (2-1), and the output of the second laser (2-12) is connected to the first end of the second collimator (2-4). The output light of the first polarization beam splitter (2-6) is output through the first isolator (2-14), and the output light of the second polarization beam splitter (2-9) is output through the second isolator (2-15). The laser wavelength range of the first laser (2-13) is a first preset range, and the laser wavelength of the second laser (2-12) is a second preset range. Both the first and second preset ranges include 1570nm.

[0032] It should be noted that the specific ranges of the first preset range and the second preset range are determined according to the actual application. This embodiment does not impose specific restrictions. The first preset range and the second preset range may be equal or unequal, and may also have overlapping parts. For example, the first preset range is 1570±20nm and the second preset range is 1570±10nm.

[0033] In some embodiments, the gain fiber includes a thulium-doped gain fiber.

[0034] The laser's output wavelength is around 1840nm. The transmission wavelength of the thulium-doped gain fiber matches the laser's output wavelength, resulting in lower loss and better transmission performance.

[0035] The embodiments of this application include at least the following beneficial effects: 1. The spectrum of wave output 1 is smooth, making subsequent pulse width compression easier. It also reduces the use of fiber beam splitters, shortens the overall cavity length, and improves the repetition rate.

[0036] 2. The bandpass filter (1840±20nm) plays a filtering role inside, which can suppress long wavelengths / bands (1900-2000nm) to obtain the required mode-locked laser wavelength.

[0037] 3. The Wollaston prism can effectively ensure the polarization direction of the light entering the gain fiber from the spatial light, and strictly align it with the slow axis of the gain fiber, ensuring that the phase shift of the two light paths is constant (the optical path length of the two light paths in the fiber is the same), making it easier to mode lock (lower mode lock threshold), and the mode lock spectrum is smooth.

[0038] 4. Except for the thulium-doped gain fiber, the entire 1840nm mode-locked laser is spatial light, which can greatly reduce the cavity length of the laser and increase the repetition rate of the laser.

[0039] The embodiments described in this application are for the purpose of more clearly illustrating the technical solutions of the embodiments of this application, and do not constitute a limitation on the technical solutions provided by the embodiments of this application. As those skilled in the art will know, with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by the embodiments of this application are also applicable to similar technical problems.

[0040] Those skilled in the art will understand that the technical solutions shown in the figures do not constitute a limitation on the embodiments of this application, and may include more or fewer steps than shown, or combine certain steps, or different steps.

[0041] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0042] Those skilled in the art will understand that all or some of the steps in the methods disclosed above, as well as the functional modules / units in the systems and devices, can be implemented as software, firmware, hardware, or suitable combinations thereof.

[0043] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0044] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0045] The preferred embodiments of the present application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and substance of the embodiments of the present application shall be within the scope of the claims of the present application.

Claims

1. An integrated non-reciprocal phase shifter, characterized in that, The device includes an integrated first collimator, a Wollaston prism, a second collimator, a gain fiber, a first waveplate, and a first polarization beam splitter, a rotator, a second waveplate, a second polarization beam splitter, a bandpass filter, and a total reflection mirror arranged in sequence. The gain fiber connects the first end of the first collimator and the first end of the second collimator. The second end of the first collimator is connected to the Wollaston prism. The output light from the second collimator reaches the first input end of the first polarization beam splitter. The output light from the Wollaston prism passes through the first waveplate and reaches the second input end of the first polarization beam splitter.

2. The non-reciprocal phase shifter according to claim 1, characterized in that, The first waveplate and the second waveplate are fixed in a sleeve with a hardness greater than a preset value.

3. The non-reciprocal phase shifter according to claim 2, characterized in that, The outer surface of the sleeve is engraved with threads.

4. The non-reciprocal phase shifter according to claim 2, characterized in that, The sleeve is fixed by a double U-shaped structure.

5. A high repetition rate laser, characterized in that, The device includes a first laser, a second laser, a first isolator, a second isolator, and a non-reciprocal phase shifter as described in any one of claims 1-4. The output of the first laser is connected to a first end of the first collimator, and the output of the second laser is connected to a first end of the second collimator. The output light of the first polarization beam splitter is output through the first isolator, and the output light of the second polarization beam splitter is output through the second isolator. The laser wavelength range of the first laser is a first preset range, and the laser wavelength of the second laser is a second preset range. Both the first preset range and the second preset range include 1570 nm.

6. The laser according to claim 5, characterized in that, The gain fiber includes thulium-doped gain fiber.

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