Gas saturation absorption optical path structure based on dual optical path enhancement

Abstract

The invention provides a gas saturation absorption optical path structure based on dual optical path enhancement, which belongs to the field of laser optical path design and comprises an optical fiber circulator, a gas absorption chamber and an optical fiber reflector. A first port of the optical fiber circulator is connected with a laser output optical fiber, a second port of the optical fiber circulator is connected with an input collimator of the gas absorption chamber, and a third port of the optical fiber circulator is connected with a detector and is used for providing frequency reference for gas absorption; and the optical fiber reflector is connected with the output end of the gas absorption chamber. According to the invention, the physical contradiction between the air chamber size and the optical path gain is broken through, and a compact frequency stabilization system with miniaturization and high stability is realized.

Description

Technical Field

[0001] This invention belongs to the field of laser optical path design, and particularly relates to a gas saturated absorption optical path structure based on dual optical path enhancement. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Frequency-stabilized lasers, as core components of high-precision, low-phase-noise optical frequency standards, play an irreplaceable role in fields such as frequency references for optical communication networks, quantum precision measurement, and coherent optical clock systems. They achieve laser frequency locking through ultra-narrow saturated absorption lines of atomic / molecular energy level transitions, resulting in ultra-high frequency stability and providing a "ruler-level" reference source for optical metrology and sensing.

[0004] The importance of miniaturized frequency-stabilized lasers lies in their ability to overcome the physical limitations of traditional spatial optical path systems, providing a technological foundation for the practical deployment of high-precision optical frequency standards in diverse application scenarios. In emerging fields such as micro-nano photonic integration, on-chip quantum sensing systems, and mobile spectral detection platforms, device size and weight directly constrain system integration and scenario adaptability. Furthermore, miniaturized design, by reducing the free propagation distance of the optical path, can significantly reduce phase noise introduced by environmental influences, thereby improving the long-term stability of the system in non-laboratory environments.

[0005] However, in traditional spatial optical path architectures, the air chamber length and optical path coupling result in a large system size, making it difficult to meet the demands of emerging scenarios such as miniaturization, integration, and lightweighting. In addition, the high sensitivity of free-space optical paths to temperature gradients and mechanical deformations can easily introduce additional frequency drift, limiting their reliability in complex environments.

[0006] In laser frequency stabilization systems based on saturable absorption, traditional optical architectures suffer from three core defects: First, the use of discrete spatial optical elements, including polarization beam splitters, mirrors, and other free-space transmission devices, results in a two-way absorption optical path that is subject to mechanical vibration and thermal drift effects, leading to insufficient optical path alignment stability and severely affecting long-term frequency locking accuracy. Second, the single round-trip optical path is limited by the physical length of the gas chamber, requiring an increase in the gas chamber volume to achieve effective saturable absorption, causing a simultaneous increase in system space occupancy and gas consumption, making it difficult to meet the requirements of integrated and portable applications. Finally, in traditional beam splitting schemes, residual return light is coupled back to the laser cavity via the original path, causing source frequency noise and phase disturbances, reducing the signal-to-noise ratio and exacerbating the complexity of frequency stabilization closed-loop control. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, this invention proposes a gas saturated absorption optical path structure based on dual optical path enhancement. This optical path utilizes a combination of fiber optic mirrors and circulators. On the one hand, it can reduce the size of the optical path device while ensuring the gas absorption optical path. On the other hand, the characteristics of the circulator can effectively avoid the interference of backlight on the laser, providing a new technical solution for the realization and performance improvement of miniaturized frequency-stabilized lasers.

[0008] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions: This invention discloses a gas saturated absorption optical path structure based on dual optical path enhancement, including an optical fiber circulator, a gas absorption chamber, and an optical fiber reflector; The first port of the fiber optic circulator is connected to the output fiber of the laser, the second port of the fiber optic circulator is connected to the input collimator of the gas absorption chamber, and the third port of the fiber optic circulator is connected to the detector to provide a frequency reference for gas absorption. The fiber optic mirror is connected to the output end of the gas absorption chamber. The incident laser is input through the first port of the fiber optic circulator, enters the gas absorption chamber through the collimator connected to the second port, passes through the gas absorption chamber for the first time, is reflected back by the built-in plane mirror at the end of the gas absorption chamber, passes through the gas absorption chamber again and is coupled to the fiber optic mirror, forming a secondary reflection and returning to the gas absorption chamber in the forward direction.

[0009] In a further technical solution, the first port of the fiber optic circulator is connected to the laser output fiber via an FC / APC interface and a fiber optic flange.

[0010] In a further technical solution, one end of the gas absorption chamber is coated with a high-reflectivity film, and the other end serves as the input and output port of a collimating lens.

[0011] In a further technical solution, the high-reflectivity film is a multilayered alternating layer of Ta2O5 and SiO2.

[0012] In a further technical solution, the fiber optic reflector is composed of a reflective film deposited on the end face of the fiber.

[0013] A further technical solution involves the laser output light being transmitted from the first port to the second port of the circulator, forming a collimated Gaussian beam through the input collimator in the gas cell, penetrating the gas cell, being reflected by the gas cell's internal reflector and transmitted in the opposite direction, penetrating the gas cell a second time, being connected to the fiber optic reflector by an optical fiber jumper, being reflected again and then penetrating the gas cell a third time in the forward direction, being reflected a second time by the gas cell's internal reflector, penetrating the gas cell a fourth time, and finally being coupled back to the optical fiber link by the input collimator.

[0014] In a further technical solution, the returned light is directionally transmitted to the detector via the second port to the third port of the circulator.

[0015] In a further technical solution, the fiber optic reflector is connected to the output end of the gas chamber via a collimator.

[0016] In a further technical solution, the second port is connected to the gas chamber input collimator via a fiber optic flange.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) High stability and anti-interference capability of fiber optic links; Traditional spatial optical paths rely on free-space transmission using discrete optical components such as mirrors and beam splitters. This requires precise mechanical alignment and is susceptible to vibration and temperature drift, leading to optical path misalignment. This invention employs an optical fiber link, significantly reducing the impact of environmental disturbances on frequency stabilization accuracy.

[0018] (2) Double equivalent optical path and miniaturized gas chamber; Existing technologies increase absorption intensity by increasing the physical size of the gas chamber, resulting in a bulky system. This invention, through a dual-reflection optical path design with four penetrations through the gas chamber, achieves an equivalent optical path in a small gas chamber, enabling integration and embedding into mobile platforms, and significantly reducing the overall size.

[0019] (3) Non-reciprocal isolation of the circulator reduces backlight interference; Traditional solutions rely on spatial optical isolators to suppress backlight, but these suffer from polarization sensitivity and additional losses. This invention uses an optical fiber circulator to construct a unidirectional optical path, ensuring reverse isolation while featuring a polarization-independent design. It can block backlight coupling to the laser without calibration, improving frequency stabilization and locking accuracy.

[0020] (4) System simplification and cost-effectiveness; Traditional solutions require additional temperature control, vibration isolation modules, and multi-stage optical isolators, resulting in high costs and complex maintenance. This invention, through fiber optic link design, eliminates the need for active temperature control and isolators, significantly reducing costs.

[0021] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0023] Figure 1 This is a schematic diagram of the gas saturated absorption optical path structure based on dual optical path enhancement as described in Embodiment 1 of the present invention. Detailed Implementation

[0024] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, 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 invention pertains.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.

[0026] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0027] Existing technical solutions employ a combination of polarization beamsplitters, lenses, mirrors, and large gas cells. The laser input light passes through the polarization beamsplitter and then enters the gas cell through the lens. The outgoing light is reflected by the mirror and re-enters the gas cell for saturation absorption. The outgoing light is then split by the polarization beamsplitter and enters the detector to provide a frequency-stabilized reference. This solution is a spatial optical path design, with many discrete components, low integration, and a large device size.

[0028] Existing frequency-stabilized laser systems based on spatial optical paths to achieve saturated absorption mainly suffer from the following technical defects: (1) Limited optical path stability: Traditional spatial optical paths rely on free space transmission and precise alignment of discrete optical components (such as mirrors and polarization beam splitters). Mechanical vibration and temperature gradients can damage the collimation of the optical path, introduce additional phase noise, and reduce the long-term stability of frequency locking. At the same time, open optical paths are easily disturbed by ambient airflow, requiring additional vibration isolation and temperature control devices, which further increases the complexity and volume of the system.

[0029] (2) The contradiction between cell size and optical path gain: In order to achieve effective saturated absorption, traditional solutions require lengthening the physical size of the cell, resulting in a large cell volume, usually tens of centimeters, which makes it difficult to meet the miniaturization requirements of the system while ensuring absorption sensitivity. In addition, increasing the cell size will significantly increase gas consumption and increase operating costs.

[0030] (3) Backlight interference and signal-to-noise ratio degradation: In the spatial optical path splitting scheme, the residual reflected light is coupled back to the laser output end along the original path, forming parasitic interference with the main laser field, inducing the light source frequency jump and phase jitter. An additional optical isolator or complex filter circuit needs to be designed to suppress the interference, resulting in a decrease in the system signal-to-noise ratio and increasing the control difficulty of the closed-loop frequency stabilization algorithm.

[0031] Therefore, under the premise of maintaining the signal-to-noise ratio and linewidth of the saturated absorption spectrum, overcoming the physical contradiction between the size of the gas cell and the optical path gain, and developing a miniaturized, highly stable, compact frequency stabilization system is not only the key to improving the engineering applicability of existing optical frequency standards, but also the core technical path to promote the evolution of precision optical instruments towards low cost and high robustness.

[0032] Example 1 In one or more embodiments, a gas saturated absorption optical path structure based on dual optical path enhancement is disclosed, such as... Figure 1 As shown, it includes a fiber optic circulator, a gas absorption chamber, and a fiber optic reflector; The first port of the fiber optic circulator is connected to the output fiber of the laser; the second port of the fiber optic circulator is fused to the input collimator of the gas absorption chamber; the third port of the fiber optic circulator is connected to a detector to provide a frequency reference for gas absorption; and the fiber optic mirror is connected to the output end of the gas absorption chamber.

[0033] Specifically, the first port of the fiber optic circulator is used as the input of the laser source, and the laser output from the second port enters the gas absorption chamber through the fiber optic collimator. After being reflected at the other end of the gas absorption chamber, it is output through the fiber optic collimator at the output end and enters the fiber optic reflector for reflection. The reflected light returns to the gas absorption chamber and returns to the circulator through the original path. It is then output to the detector through the third port of the circulator, providing a high-precision frequency reference for the frequency-stabilized laser.

[0034] In this embodiment, the detector is an indium gallium arsenide photodetector, which is used for photoelectric conversion to realize optical signal acquisition.

[0035] Furthermore, the circulator, the gas absorption chamber with collimation input and output, and the fiber optic mirror are connected by fiber optic jumpers and flanges. The first port of the circulator is connected to the laser output fiber via an FC / APC interface and a fiber optic flange; the second port is connected to the gas chamber input collimator via a fiber optic flange; and the third port is connected to the detector. In this embodiment, a fiber optic link is used instead of traditional space optical elements, eliminating mechanical alignment dependence, improving system stability, reducing the signal-to-noise ratio reduction caused by environmental interference, and eliminating the impact on frequency stabilization accuracy. It should be understood that a fiber optic link means that all optical devices used in the optical path are fiber optic devices, and there are no space optical elements.

[0036] In this embodiment, a miniaturized gas absorption chamber is used.

[0037] Furthermore, a high-reflectivity film is deposited at one end of the miniaturized gas absorption chamber. The high-reflectivity film consists of multiple alternating layers of Ta2O5 and SiO2, while the other end serves as the input and output port for the collimating lens.

[0038] Furthermore, the fiber optic reflector is composed of a reflective film coated on the end face of the fiber, and is connected to the output end of the gas cell by a collimator.

[0039] The working process of the gas saturated absorption optical path structure based on dual optical path enhancement proposed in this embodiment is as follows: Forward transmission: The laser output light is transmitted from the first port to the second port of the circulator, passes through the collimator in the gas cell to form a collimated Gaussian beam, penetrates the gas cell, is reflected by the gas cell's internal reflector and transmitted in the reverse direction, penetrates the gas cell a second time, is coupled to the fiber optic reflector, is reflected again, penetrates the gas cell a third time in the forward direction, is reflected a second time by the gas cell's internal reflector, penetrates the gas cell a fourth time, and the returning light is finally coupled back to the fiber optic link by the output collimator. In this embodiment, the optical path passes through the gas cell reflector and the external reflector, undergoing a total of 4 times the physical length of the gas cell. Compared to the traditional single reflection, the optical path is doubled, which is beneficial for the miniaturization of the gas cell and the high integration of the system.

[0040] Reverse suppression: The return light is directionally transmitted to the detector via the second and third ports of the circulator. Isolation is achieved by utilizing the non-reciprocal transmission of the circulator, ensuring that there is no feedback interference at the laser output.

[0041] Signal extraction: The detector receives saturated absorption signals that pass through the physical gas cell four times, and frequency locking is achieved through circuit processing.

[0042] In this embodiment, the non-reciprocity of the circulator eliminates backlight interference. A fiber optic circulator is used to construct a unidirectional optical path, avoiding backlight interference with the laser output and affecting the frequency stabilization effect.

[0043] To further explain the core mechanism of this invention, which is based on dual optical path enhancement of the fiber optic path and unidirectional optical path isolation of the circulator, and achieves gas saturated absorption optical path guarantee and noise suppression through a miniaturized and compact optical path architecture, as follows: (1) Double reflection optical path multiplication mechanism: The incident laser light enters through port 1 of the fiber optic circulator and then enters the gas absorption chamber through the fiber optic collimator connected to port 2. After the light wave first passes through the gas chamber, it is reflected back by a plane mirror built into the end of the gas chamber, passes through the gas chamber again, and is connected to an external fiber optic mirror by a fiber optic jumper, forming a second reflection before returning to the gas chamber in the forward direction. This dual-reflection path design makes the effective transmission distance of the laser within the gas chamber equivalent to the physical length of four passes through the gas chamber, i.e., incident light - first reflection in reverse - second reflection in forward direction - final emission, achieving a four-fold physical optical path gain within the gas chamber, which doubles the optical path compared to the traditional single reflection. By decoupling the optical path from the gas chamber geometry, this invention can achieve the absorption intensity of a traditional tens of centimeters-sized gas chamber in a miniaturized gas chamber, while reducing gas consumption, thus overcoming the technical contradiction of the incompatibility between gas chamber miniaturization and absorption intensity.

[0044] (2) Fiber mode matching and low-loss coupling mechanism: The matching design between the fiber collimator and the air cell optical window ensures efficient conversion of optical field modes. The incident fiber output light is collimated by the collimator to form a parallel Gaussian beam, the beam waist of which coincides with the focal point of the air cell reflector. The reflected light is then collimated twice and coupled back into the fiber in the fundamental mode. Compared to the free propagation of spatial optical paths, the fiber optic link can suppress beam divergence and spatial distortion through its mode field constraint characteristics, while avoiding polarization-dependent losses introduced by polarization beam splitters, significantly improving the signal-to-noise ratio of saturated absorption lines.

[0045] (3) Circulator non-reciprocal transmission and return optical isolation mechanism: A unidirectional optical path isolation barrier is constructed using the non-reciprocal transmission characteristic of an optical fiber circulator. The laser beam travels unidirectionally from port 1 to port 2 of the circulator into the gas cell optical path, while the returning light from the gas cell can only be directionally transmitted to the detector connected to port 3. This reverse isolation completely blocks the physical path of the returning light coupling to the laser along its original path. This mechanism eliminates the need for an additional optical isolator, reducing system complexity, avoiding the high insertion loss of traditional isolators, and improving the detector's signal-to-noise ratio.

[0046] (4) Robust enhancement mechanism of structural integration: The fiber optic link structure transforms the mechanical alignment dependency of discrete optical components in traditional free-space optical paths into a fixed connection between fiber optic patch cords and flanges, significantly improving its robustness. In addition, the compatibility of the fiber optic link with the standard FC / APC interface allows the system to be directly embedded into existing fiber optic communication networks, providing a plug-and-play solution for distributed frequency reference systems.

[0047] In summary, by leveraging the synergistic effect of fiber optic mirrors and circulators to achieve double the equivalent optical path gain, the gas cell size is reduced to less than 50% of that of traditional solutions while maintaining absorption sensitivity. Simultaneously, backlight interference is eliminated, providing a stable optical path environment for constructing a frequency-stabilized system that combines mechanical robustness, high integration, and low phase noise.

[0048] The "dual optical path enhanced fiber optic path" architecture proposed in this embodiment is specifically implemented as follows: (1) Improve the anti-interference and integration of the optical path: replace free space transmission with optical fiber path to eliminate mechanical alignment dependence and environmental sensitivity. Combine the internal reflector and external optical fiber reflector to form a dual reflection optical path, which increases the effective optical path to four times the physical length of the air chamber. Thus, high absorption efficiency is maintained under the premise of reducing the size of the air chamber by 50%. At the same time, the optical path is stabilized by the natural anti-vibration characteristics of the optical fiber link.

[0049] (2) Breakthrough in miniaturization of gas chambers: Based on double equivalent optical path gain, this invention can achieve an absorption depth comparable to that of traditional tens of centimeters-level gas chambers in miniaturized gas chambers, significantly reducing gas consumption and providing a physical basis for integration and embedding in mobile platforms.

[0050] (3) Eliminate backlight noise: Introduce an optical fiber circulator as the core device for optical path isolation. Its non-reciprocal transmission characteristics can completely block the path of reflected light returning to the laser. The optical path can be transmitted in one direction without the need for an additional isolator. This simplifies the system and enables optical fiber link transmission, significantly improving the detector signal-to-noise ratio and frequency stabilization control accuracy.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A gas saturated absorption optical path structure based on dual optical path enhancement, characterized in that, Includes fiber optic circulator, gas absorption chamber, and fiber optic reflector; The first port of the fiber optic circulator is connected to the output fiber of the laser, the second port of the fiber optic circulator is connected to the input collimator of the gas absorption chamber, and the third port of the fiber optic circulator is connected to the detector to provide a frequency reference for gas absorption. The fiber optic mirror is connected to the output end of the gas absorption chamber. The incident laser is input through the first port of the fiber optic circulator, enters the gas absorption chamber through the collimator connected to the second port, passes through the gas absorption chamber for the first time, is reflected back by the built-in plane mirror at the end of the gas absorption chamber, passes through the gas absorption chamber again and is coupled to the fiber optic mirror, forming a secondary reflection and returning to the gas absorption chamber in the forward direction.

2. The gas saturated absorption optical path structure based on dual optical path enhancement as described in claim 1, characterized in that, The first port of the fiber optic circulator is connected to the laser output fiber via an FC / APC interface and a fiber optic flange.

3. The gas saturated absorption optical path structure based on dual optical path enhancement as described in claim 1, characterized in that, One end of the gas absorption chamber is coated with a high-reflectivity film, and the other end serves as the input and output port of the collimating lens.

4. The gas saturated absorption optical path structure based on dual optical path enhancement as described in claim 3, characterized in that, The high-reflectivity film consists of multiple alternating layers of Ta2O5 and SiO2.

5. The gas saturated absorption optical path structure based on dual optical path enhancement as described in claim 1, characterized in that, The fiber optic reflector is composed of a reflective film coated on the end face of the optical fiber.

6. The gas saturated absorption optical path structure based on dual optical path enhancement as described in claim 1, characterized in that, The laser output light is transmitted from the first port to the second port of the circulator, and is collimated into a Gaussian beam by the input collimator in the gas cell. It penetrates the gas cell, is reflected by the gas cell's internal reflector and transmitted in the opposite direction, penetrates the gas cell a second time, is connected to the fiber optic reflector by the fiber optic jumper, is reflected again and penetrates the gas cell a third time in the forward direction, is reflected a second time by the gas cell's internal reflector, penetrates the gas cell a fourth time, and the returning light is finally coupled back to the fiber optic link by the output collimator.

7. The gas saturated absorption optical path structure based on dual optical path enhancement as described in claim 6, characterized in that, The returned light is directionally transmitted to the detector via the second port to the third port of the circulator.

8. The gas saturated absorption optical path structure based on dual optical path enhancement as described in claim 1, characterized in that, The fiber optic reflector is connected to the output end of the gas chamber via a collimator.

9. The gas saturated absorption optical path structure based on dual optical path enhancement as described in claim 1, characterized in that, The second port is connected to the gas chamber input collimator via a fiber optic flange.

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