Dual comb laser

Abstract

The application relates to a dual comb laser. The dual comb laser is connected to two semiconductor saturable absorber mirrors from the part non-common path of a six-port device integrated based on a four-port circulator. The length of two sections of optical fibers between two ports of the six-port device integrated based on the four-port circulator and the two semiconductor saturable absorber mirrors can be adjusted to independently adjust the two-direction mode-locked pulses. The six-port device integrated based on the four-port circulator supports splitting incident light into two beams of different polarization directions, one of which is directly output as a mode-locked pulse, and the other of which participates in the mode-locking process, realizes full utilization of energy, reduces the use of coupling devices, simplifies the cavity structure, makes the cavity structure more compact, and balances the mode-locking and compactness.

Description

Technical Field

[0001] This application belongs to the field of laser design, specifically relating to a dual-comb laser. Background Technology

[0002] Optical frequency combs, or simply optical frequency combs, appear as equally spaced comb lines in the frequency domain and as periodic pulse trains in the time domain. They are an effective light source for precision measurements. Compared to single-comb measurement techniques, dual-comb technology significantly reduces the bandwidth and response speed requirements of signal measurement equipment, expanding the applications of frequency comb technology. Dual-comb technology has shown great application potential in fields such as ranging, gas sensing, and spectroscopy.

[0003] Traditional dual-comb systems consist of two independently operating optical frequency combs with slightly different repetition frequencies. These require a feedback control system to maintain mutual coherence between the two combs, resulting in a complex and costly system. In recent years, single-cavity dual-comb technology has attracted increasing attention from researchers due to its inherent mutual coherence between the two combs, convenience, and lower cost.

[0004] Mode-locking is a major method for generating optical combs. Based on a specific mode-locking mechanism, it maintains a constant phase difference between different longitudinal modes within the cavity, generating stable pulse output. By utilizing multiplexing methods such as wavelength multiplexing, polarization multiplexing, direction multiplexing, and waveform multiplexing within the cavity, dual combs can be generated within a single fiber cavity. Direction multiplexing leverages the characteristic that pulses can oscillate bidirectionally within the fiber cavity to generate mode-locked pulses in both CW (clockwise) and CCW (counter-clockwise) directions.

[0005] Traditional research on generating dual combs based on directional multiplexing employs a fully common-path cavity structure. However, when two backpropagating pulses meet at the saturable absorber, they may generate strong nonlinear interactions, affecting mode locking. Furthermore, since the backpropagating pulses follow the same path, it is impossible to individually adjust one of the pulses, resulting in a lack of flexibility. Summary of the Invention

[0006] Therefore, it is necessary to provide a dual-comb laser that can balance mode-locking and structural compactness.

[0007] This application provides a dual-comb laser, comprising:

[0008] Connect fiber optic cables;

[0009] A laser cavity is formed by connecting a pump source, wavelength division multiplexer, gain medium, a six-port device based on a four-port circulator, and a polarization controller through a closed-loop connection of the connecting optical fiber; wherein, the six-port device based on the four-port circulator supports splitting the incident light into two beams with different polarization directions, one beam being directly output as a mode-locked pulse, and the other participating in the mode-locking process;

[0010] Two semiconductor saturable absorber mirrors are respectively connected to two ports of the six-port device based on the four-port circulator via optical fibers to support mode-locked pulse output in both clockwise and counterclockwise directions.

[0011] In one embodiment, the six-port device based on a four-port circulator integration includes:

[0012] A four-port circulator is connected to the polarization controller and the gain medium respectively via the connecting optical fiber;

[0013] Two polarization beam splitters are symmetrically placed on the connecting optical fiber relative to the four-port circulator. The output ends of the two polarization beam splitters are used to output mode-locked pulses in the clockwise and counterclockwise directions, respectively.

[0014] In one embodiment, the outputs of both polarization beam splitters output the mode-locked pulses through single-mode optical fibers.

[0015] In one embodiment, the four-port circulator and the polarization beam splitter are integrated into a single device.

[0016] In one embodiment, the semiconductor saturable absorber mirror is connected to two of the ports of the six-port device based on a four-port circulator via a polarization-maintaining fiber.

[0017] In one embodiment, the length of the polarization-maintaining fiber between two ports of the six-port device based on a four-port circulator and the semiconductor saturable absorber mirror to which they are respectively connected is adjustable.

[0018] In one embodiment, the polarization beam splitter is connected to the port of the four-port circulator via a polarization-maintaining fiber.

[0019] In one embodiment, the polarization controller employs a squeeze-type structure.

[0020] In one embodiment, the gain medium is erbium-doped fiber.

[0021] In one embodiment, the pump source uses a 980nm light source.

[0022] The dual-comb laser provided in this application embodiment connects a partially non-common path from a six-port device integrated based on a four-port circulator to two semiconductor saturable absorber mirrors. By adjusting the lengths of the two fiber segments between the two ports of the six-port device integrated based on the four-port circulator and the two semiconductor saturable absorber mirrors, the mode-locked pulses in two directions can be independently adjusted. The six-port device integrated based on the four-port circulator supports splitting the incident light into two beams with different polarization directions. One beam is directly output as a mode-locked pulse, while the other participates in the mode-locking process, achieving full energy utilization, reducing the use of coupling devices, simplifying the cavity structure, and making the cavity structure more compact, thus balancing mode-locking and structural compactness. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a structural diagram of a dual-comb laser provided in one embodiment;

[0025] Figure 2 for Figure 1 A schematic diagram of a six-port device based on a four-port circulator integration. Detailed Implementation

[0026] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be more thorough and complete.

[0027] 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 particular embodiments only and is not intended to be limiting of the application.

[0028] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, in this specification, the term “and / or” includes any and all combinations of the associated listed items.

[0029] This application provides a dual-comb laser, comprising:

[0030] Connect fiber optic cables;

[0031] A laser cavity is formed by connecting a pump source, a wavelength division multiplexer (WDM), a gain medium, a six-port device based on a four-port circulator, and a polarization controller (PC) through a closed-loop connection of the connecting optical fiber; wherein, the six-port device based on the four-port circulator supports splitting the incident light into two beams with different polarization directions, one beam is directly output as a mode-locked pulse, and the other participates in the mode-locking process;

[0032] Two semiconductor saturable absorber mirrors (SESAMs) are connected to two ports of the six-port device integrated based on a four-port circulator via optical fibers to support mode-locked pulse output in both clockwise and counterclockwise directions.

[0033] Among them, the connecting optical fiber is used to connect the various parts to form a complete laser cavity.

[0034] A six-port device based on a four-port circulator refers to a device that adds two ports to a four-port circulator, forming a six-port device. This six-port device supports polarization beam splitting of optical signals and the output of mode-locked pulses, thus eliminating the need for an additional coupler. A circulator is a non-reciprocal optical device that allows optical signals to propagate in one direction while blocking signal transmission in the opposite direction. A four-port circulator has four ports, typically labeled 1, 2, 3, and 4. The six-port device based on the four-port circulator is responsible for guiding the optical signal to circulate within the laser cavity.

[0035] A mode-locked pulse is an extremely short laser pulse generated through mode-locking technology. By introducing a fixed phase relationship between different modes in the laser cavity, the interference between these modes causes the laser to generate a series of pulses. Depending on the properties of the laser, these pulses may have extremely short durations, even reaching the femtosecond level. Since ultrashort pulses have a certain bandwidth, dual-comb lasers used for short pulses (especially in the sub-picosecond region) require a gain medium with a large gain bandwidth. That is, the dual-comb laser provided in this application can support the output of ultrashort pulses by introducing a gain medium. A polarization controller participates in the nonlinear polarization rotation mode-locking process.

[0036] Specifically, the dual-comb laser provided in this application embodiment has a partially non-common path from a six-port device integrated based on a four-port circulator to two semiconductor saturable absorber mirrors. By adjusting the lengths of the two fiber segments between the two ports of the six-port device integrated based on the four-port circulator and the two semiconductor saturable absorber mirrors, the mode-locked pulses in two directions can be independently adjusted. The six-port device integrated based on the four-port circulator supports splitting the incident light into two beams with different polarization directions. One beam is directly output as a mode-locked pulse, and the other participates in the mode-locking process, realizing full utilization of energy (avoiding waste of optical power), reducing the use of coupling devices, simplifying the cavity structure, and making the cavity structure more compact, thus balancing mode-locking and structural compactness.

[0037] In one embodiment, the six-port device based on a four-port circulator integration includes a four-port circulator and a polarization beam splitter.

[0038] Among them, such as Figure 2 As shown, the four-port circulator is connected to the polarization controller and the gain medium via the connecting optical fiber. Two polarization beam splitters are symmetrically placed on the connecting optical fiber relative to the four-port circulator, and the outputs of the two polarization beam splitters are used to output mode-locked pulses in the clockwise and counterclockwise directions, respectively.

[0039] A polarization beam splitter (PBS) is an optical device that separates optical signals according to their polarization direction. For example... Figure 2 As shown, the two polarization beam splitters can be labeled PBS1 and PBS2, respectively. They are connected to different ports of the four-port circulator and split the optical signal into two beams with different polarization directions.

[0040] Specifically, when an optical signal propagates within the laser cavity from one direction (e.g., from polarization beamsplitter PBS1 to polarization beamsplitter PBS2), it is first split into two beams with different polarization directions by polarization beamsplitter PBS1. One of these beams serves as the mode-locked output (e.g., as shown in the image). Figure 1The CW output shown in the diagram), and another beam of light enters port 1 of the four-port circulator (as shown in the diagram) through an optical fiber. Figure 2 (As shown).

[0041] Inside the four-port circulator, the beam of light entering from port 1 exits from port 2 and is transmitted through the optical fiber connected to port 2 to a semiconductor saturable absorber mirror (SESAM). The SESAM is a key component for passive mode-locking, which can reflect light signals of a specific intensity to achieve mode-locked laser output.

[0042] The beam reflected from SESAM returns to the four-port circulator via port 2, then exits the circulator via port 3, passes through a fiber, and returns to the laser cavity via polarization beam splitter PBS2.

[0043] The pulse from the other direction enters from the polarization beam splitter PBS2 and is similarly split into two beams with different polarization directions. One of these beams serves as the mode-locked output in that direction (e.g., as shown in the image). Figure 2 (The mode-locked pulse in the CCW direction shown) Another beam enters port 3 of the four-port circulator, exits from port 4 through the interior, and the beam exiting from port 4 is transmitted through the optical fiber to the SESAM connected to it. After being reflected and modulated by the SESAM, it is reflected back to port 4, returns to the four-port circulator, and then exits through port 1 of the four-port circulator. After passing through a section of optical fiber, the beam returns to the laser cavity from the polarization beam splitter PBS1, thus achieving a cycle.

[0044] The dual-comb laser provided in this application employs a mode-locking mechanism combining SESAM (saturable absorber mirror) and NPR (nonlinear polarization rotation) to achieve a bidirectional mode-locked laser, integrating passive and active mode-locking. Furthermore, this mode-locking mechanism enables the dual-comb laser to generate a stable and uniformly distributed frequency comb.

[0045] In one embodiment, the outputs of both polarization beam splitters output the mode-locked pulses via single-mode fiber (SMF). The outputs of the polarization beam splitters are transmitted via single-mode fiber, taking advantage of the relatively stable transmission characteristics of single-mode fiber. Figure 2 For example, the output ports of PBS1 and PBS2 are both connected to SMF. When the laser cavity is formed, the output ports of PBS1 and PBS2 are connected to other optical fibers in the laser cavity without the need for additional polarization control elements, which simplifies the system structure of the dual-comb laser.

[0046] In addition, the relatively low manufacturing cost of single-mode fiber helps reduce the overall cost of the dual-comb laser.

[0047] In one embodiment, the four-port circulator and the polarization beam splitter are integrated into a single device. By integrating the PBS and the four-port circulator into a single device, no additional coupler is needed to achieve the output. Both beams split by the PBS can be utilized, simplifying the structure of the dual-comb laser and improving its compactness.

[0048] In one embodiment, the semiconductor saturable absorber mirror is connected to two ports of the six-port device integrated with a four-port circulator via a polarization-maintaining fiber. Connecting the SESAM and the six-port device based on the four-port circulator via the polarization-maintaining fiber ensures that the polarization state of the polarized beam generated by the six-port device is maintained, reducing losses caused by polarization state changes and contributing to improved efficiency and stability of the dual-comb laser.

[0049] In one embodiment, the lengths of the polarization-maintaining fibers between two ports of the six-port device integrated with a four-port circulator and their respective connected semiconductor saturable absorber mirrors are adjustable. Independent adjustment of the bidirectional dual-comb structure can be achieved by separately adjusting the lengths of the polarization-maintaining fibers at the points where the two ports of the six-port device integrated with the four-port circulator intersect with the SESAM.

[0050] In one embodiment, the polarization beam splitter is connected to the port of the four-port circulator via a polarization-maintaining fiber. This connection ensures that the polarized light split by the beam splitter maintains its polarization state, which helps improve the efficiency and stability of the dual-comb laser.

[0051] In one embodiment, apart from the polarization-maintaining fiber portion constrained in the above embodiment, the remaining portion of the connecting fiber may be single-mode fiber. For example, the fiber between PBS1 and the polarization controller via the polarization controller PC, pump source, WDM, gain medium to PBS2 may be single-mode fiber.

[0052] In one embodiment, the polarization controller employs a compression-type structure. Since the optical fiber within the laser cavity lacks a plastic protective sheath, the compression-type structure allows for more effective adjustment of the polarization state of the light within the fiber, while also providing some protection to the fiber in the operational area.

[0053] In one embodiment, the gain medium is erbium-doped fiber (EDF).

[0054] In one embodiment, the pump source uses a 980nm light source. When the pump source uses a 980nm light source and the gain medium is EDF, the 980nm pump source can excite erbium ions in the EDF, thereby generating effective optical amplification and laser emission near 1550nm.

[0055] In one embodiment, the wavelength division multiplexer is a 980nm / 1550nm wavelength division multiplexer, which is a three-port integrated device. The pump source enters through the 980nm port, and the other two ports are connected to the laser cavity.

[0056] It should be noted that, in addition to supporting mode-locked pulses in the 1550nm band, mode-locked pulse output in other optical bands can also be achieved by adjusting the pump source, optical fiber and wavelength division multiplexer, depending on actual needs. For example, in the 1µm band, dual-comb generation of the corresponding band can also be achieved.

[0057] To better illustrate the implementation process of the dual-comb laser provided in this application, we will take the generation of mode-locked pulses in the 1550nm band as an example.

[0058] The pump source is a 980nm laser, which is connected to the laser cavity through a 980nm / 1550nm WDM. The gain medium is an EDF. A section of EDF is connected to one port of the WDM in the laser cavity. The 980nm pump source excites the erbium ions in the EDF to generate laser emission near 1550nm.

[0059] First, we introduce the propagation of the CCW-direction mode-locked pulse within the laser cavity. The other end of the EDF is connected to a 1550nm SMF, and the other end of the SMF is connected to the SMF external to port 2 of the PBS2 device, which is based on a four-port circulator. After passing through PBS2, the light is split into two beams with different polarization directions. One beam is used as the output of the CCW-direction mode-locked pulse, and the other beam is transmitted through the polarization-maintaining fiber in the laser cavity. It enters the four-port circulator through port 3, rotates to the left along the inside of the four-port circulator, leaves the four-port circulator through port 4, and propagates along the polarization-maintaining fiber. The light is incident on the SESAM, and after the saturable absorption effect of the SESAM, a mode-locked pulse is generated. After passing through the mirror, the light returns to the four-port circulator from port 4 along the polarization-maintaining fiber, rotates to port 1, leaves the four-port circulator, and then propagates through the polarization-maintaining fiber to PBS1, returning to the fiber laser cavity to continue the cycle.

[0060] The propagation of the CW-direction pulse is described below. The other port of the WDM is connected to a 1550nm SMF (Superficial Microfiber), which can be directly connected to the SMF connected to PBS1. The mode-locked pulse in the CW direction moves in the opposite direction to the CCW direction. In the CW direction, the light splits into two beams with different polarization directions after passing through PBS1. One beam serves as the output in the CW direction, while the other beam is transmitted through a polarization-maintaining fiber, enters the four-port circulator through port 1, propagates to the right along the circulator, exits through port 2, propagates along the polarization-maintaining fiber to SESAM, then returns via a mirror, returns to the four-port circulator through port 2, and finally exits through port 3, re-enters PBS2 along the polarization-maintaining fiber, and returns to the cavity for the next cycle. A squeeze-type polarization controller (PC) is installed on the single-mode fiber inside the laser cavity to adjust the polarization state of the pulse propagating within the fiber.

[0061] The dual-comb laser provided in this application adopts a mode-locking mechanism combining NPR and SESAM. By circulating the back-propagating pulses in the cavity, stable mode-locked pulse outputs in the CW and CCW directions can be obtained at the output end.

[0062] In the description of this specification, references to terms such as "some embodiments," "other embodiments," and "ideal embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.

[0063] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features of the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0064] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A dual-comb laser, characterized in that, include: Connect fiber optic cables; A laser cavity is formed by connecting a pump source, a wavelength division multiplexer, a gain medium, a six-port device integrated based on a four-port circulator, and a polarization controller in a closed loop via the connecting optical fiber. The six-port device integrated based on the four-port circulator includes a four-port circulator and two polarization beams symmetrically placed on the connecting optical fiber relative to the four-port circulator. The four-port circulator is connected to the polarization controller and the gain medium via the connecting optical fiber, respectively. The outputs of the two polarization beams are used to output mode-locked pulses in clockwise and counterclockwise directions, respectively. The four-port circulator and the polarization beams are integrated into one device. The six-port device supports splitting the incident light into two beams with different polarization directions; one beam is directly output as a mode-locked pulse, and the other participates in the mode-locking process. Two semiconductor saturable absorber mirrors are respectively connected to two ports of the six-port device based on a four-port circulator via two polarization-maintaining fiber segments. The lengths of the two polarization-maintaining fiber segments are adjustable to support independent adjustment of the mode-locked pulse output in both clockwise and counterclockwise directions.

2. The dual-comb laser according to claim 1, characterized in that, The outputs of both polarization beam splitters output the mode-locked pulses through single-mode optical fibers.

3. The dual-comb laser according to claim 1, characterized in that, The polarization beam splitter is connected to the port of the four-port circulator via a polarization-maintaining fiber.

4. The dual-comb laser according to claim 1, characterized in that, The polarization controller adopts a squeeze-type structure.

5. The dual-comb laser according to claim 1, characterized in that, The gain medium is erbium-doped optical fiber.

6. The dual-comb laser according to claim 1, characterized in that, The pump source uses a 980nm light source.

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