A SESAM-based mode-locked fiber optic oscillator

Abstract

This invention discloses a centrally located SESAM (Self-Sensitive Electron Oscillator) mode-locked fiber optic oscillator, relating to the field of laser technology. A single-mode pump source is connected to a mixing module via optical fiber; the mixing module is connected to a chirped fiber grating via optical fiber; the chirped fiber grating is connected to a gain fiber via optical fiber; the gain fiber is connected to a SESAM double-pigment package via optical fiber; and the SESAM double-pigment package is connected to a high-reflectivity mirror via optical fiber. Through this centrally located SESAM structure, light passes through the device twice within a single cavity cycle, effectively increasing the modulation depth. Dual modulation suppresses noise and parasitic oscillations, achieving improved mode-locking self-starting and pulse output performance.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and more specifically to a SESAM-mediated mode-locked fiber optic oscillator. Background Technology

[0002] SESAM (Semiconductor Saturable Absorber Mirror) is a device used to achieve stable operation of fiber mode-locked oscillators. Its modulation depth, relaxation time, and damage threshold directly determine the output quality of ultrafast laser pulses. Increasing the modulation depth requires increasing the thickness of the absorption layer, but a thick absorption layer is prone to introducing crystal defects, which not only generates additional unsaturated losses but also reduces the device's damage threshold, significantly increasing the manufacturing difficulty of SESAMs with high modulation depth and fast relaxation time.

[0003] Publication No.: CN120073463A, a SESAM-based all-fiber sub-100-femtosecond laser; employing a chirped fiber Bragg grating with a dispersion of 0.115 ps / nm to compensate for intracavity positive dispersion, a mode-locked pulse with a spectral width of 23 nm is achieved. Using a pair of transmission diffraction gratings, the pulse width is compressed to 88 fs, with a near-zero intracavity dispersion of 0.00087 ps. 2 Under these conditions, a maximum spectral width of 27 nm was achieved. This satisfies the condition that the optimal spectral bandwidth of the seed source pulse for a fiber-chilled pulse amplified laser should be greater than 15 nm, reducing the compressed pulse distortion of the amplifier. A linear cavity was used, and the SESAM was bonded to the surface of a single-mode fiber patch cord for initiating mode-locking, realizing an all-fiber structure for the system, suitable for industrial integration applications.

[0004] In traditional structures, the SESAM is only used as an end mirror to allow light to pass through once. It requires a high modulation depth SESAM to overcome parasitic oscillations and strong nonlinear disturbances in the fiber cavity, which leads to difficulties in mode-locking self-starting, poor continuous wave background suppression, and low output pulse stability and time domain contrast. Summary of the Invention

[0005] The purpose of this invention is to solve the problems mentioned in the background art, where the SESAM in the traditional structure only serves as an end mirror to allow light to pass through once. This requires a high modulation depth SESAM to overcome parasitic oscillations and strong nonlinear disturbances in the fiber cavity, resulting in difficulties in mode-locking self-starting, poor continuous wave background suppression, and low output pulse stability and time-domain contrast. Therefore, this invention proposes a SESAM-centered mode-locked fiber oscillator.

[0006] A first aspect of this invention provides a SESAM-centered mode-locked fiber oscillator, comprising: an optical fiber, a single-mode pump source, a hybrid module, a chirped fiber grating, a gain fiber, a SESAM dual-pigment package, and a high-reflection mirror, wherein:

[0007] The single-mode pump source is connected to the hybrid module via the optical fiber, and the hybrid module is connected to the chirped fiber grating via the optical fiber.

[0008] The chirped fiber grating is connected to the gain fiber via an optical fiber, the gain fiber is connected to the SESAM dual-pigment package via an optical fiber, and the SESAM dual-pigment package is connected to the high-reflection mirror via an optical fiber.

[0009] Preferably, the hybrid module includes: a WDM device and an optical isolator;

[0010] The WDM device is connected to the optical isolator via optical fiber; the WDM device is used to couple multiple light sources to obtain a single light source; the optical isolator is used to block reflected light.

[0011] Preferably, the length of the gain fiber is 50 centimeters.

[0012] Preferably, the SESAM dual-pigment package includes: a first collimator pigtail, a second collimator pigtail, and SESAM;

[0013] The first collimator pigtail and the second collimator pigtail are symmetrically arranged on the SESAM.

[0014] Preferably, the gain fiber and the high-reflection mirror are respectively disposed on the side of the first collimator pigtail and the second collimator pigtail away from the SESAM;

[0015] The first collimator pigtail is connected to the gain fiber, and the second collimator pigtail is connected to the high-reflection mirror.

[0016] Preferably, the SESAM dual-tail fiber package further includes: a retaining ring;

[0017] The retaining ring is used to fix the first collimator tail fiber and the second collimator tail fiber;

[0018] The first collimator pigtail and the second collimator pigtail are symmetrically arranged in the middle of the fixing ring.

[0019] Preferably, the SESAM dual-tail fiber package further includes: a heat sink;

[0020] The heat sink is located on the side of the SESAM away from the first collimator pigtail and the second collimator pigtail, and the SESAM is fixedly connected to the heat sink.

[0021] Preferably, the modulation depth of the SESAM is 20%.

[0022] Preferably, the working process of the SESAM-centered mode-locked fiber optic oscillator includes:

[0023] The single-mode pump source injects pump light into the hybrid module, the hybrid module receives the pump light and propagates it in the direction of the chirped fiber grating, the pump light propagates to the gain fiber, and the pump light excites the initial signal light in the gain fiber;

[0024] The initial signal light propagates into the SESAM dual-pig fiber package for modulation to obtain the first signal light. The first signal light propagates towards the high-reflection mirror and is reflected by the high-reflection mirror back to the SESAM dual-pig fiber package for modulation to obtain the second signal light.

[0025] The second signal light propagates towards the mixing module, and after reaching the mixing module, it is output through the mixing module.

[0026] The beneficial effects of this invention are:

[0027] 1) By placing the SESAM in the middle of the resonant cavity and implementing a structure design of two modulations in one cavity cycle, a mode-locking effect with equivalent higher modulation depth and faster relaxation time can be obtained without increasing the modulation depth, relaxation time and damage threshold of the SESAM itself. This reduces the oscillator's dependence on high-performance SESAM and improves the redundancy and practicality of the system for device parameters.

[0028] 2) The two modulation and shaping effects brought by the SESAM center can more effectively suppress interference caused by continuous wave background, fiber nonlinear disturbance and parasitic oscillation, enhance mode-locking self-starting capability, and strengthen the suppression of pulse leading and trailing edges, improve the stability, time domain contrast and pulse quality of output pulse, and make the overall mode-locking state more reliable and the output purer. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a SESAM-based mode-locked fiber optic oscillator provided in an embodiment of the present invention;

[0030] Figure 2 A schematic diagram of a SESAM dual-pigment package structure for a SESAM-centered mode-locked fiber optic oscillator provided in an embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of a hybrid module structure for a SESAM-centered mode-locked fiber optic oscillator provided in an embodiment of the present invention;

[0032] Figure 4 An illustration of a SESAM-based mode-locked fiber optic oscillator provided in an embodiment of the present invention;

[0033] Figure 5This is a first SESAM propagation demonstration diagram of a SESAM-centered mode-locked fiber optic oscillator provided in an embodiment of the present invention;

[0034] Figure 6 This is a second SESAM propagation demonstration diagram of a SESAM-centered mode-locked fiber optic oscillator provided in an embodiment of the present invention;

[0035] Reference numerals: 100, optical fiber; 101, single-mode pump source; 102, hybrid module; 103, chirped fiber grating; 104, gain fiber; 105, SESAM double pigtail package; 106, high-reflection mirror; 1021, WDM device; 1022, optical isolator; 1050, fixing ring; 1051, first collimator pigtail; 1052, second collimator pigtail; 1053, SESAM; 1054, heat sink. Detailed Implementation

[0036] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0037] This invention provides a SESAM-centered mode-locked fiber optic oscillator. See also... Figure 1 , Figure 1 This is a flowchart illustrating a SESAM (Self-Electronic Optimized Fiber Oscillator) with a centrally located mode-locked fiber optic oscillator, provided as an embodiment of the present invention. It includes: an optical fiber 100, a single-mode pump source 101, a hybrid module 102, a chirped fiber grating 103, a gain fiber 104, a SESAM dual-pigment package 105, and a high-reflection mirror 106, wherein:

[0038] The single-mode pump source 101 is connected to the hybrid module 102 via optical fiber 100, and the hybrid module 102 is connected to the chirped fiber grating 103 via optical fiber 100.

[0039] The chirped fiber grating 103 is connected to the SESAM dual pigtail package 105 via gain fiber 104, and the SESAM dual pigtail package 105 is connected to the high-reflection mirror 106 via fiber 100.

[0040] In one implementation, the SESAM1053 is encapsulated as a dual-pigment structure, with a chirped fiber grating 103 and a gain fiber 104 fused to one end, and a high-reflectivity mirror 106 fused to the other end. A single-mode pump source 101 is injected into the resonant cavity from the chirped fiber grating 103 through a hybrid module 102, and a mode-locked pulse is output through the hybrid module 102. The resonant cavity includes: a chirped fiber grating 103, a gain fiber 104, a SESAM dual-pigment encapsulation 105, and a high-reflectivity mirror 106.

[0041] In one implementation, SESAM1053 is suitable for wavelengths from 800nm ​​to 3.0μm and has a relaxation time of 500fs-25ps.

[0042] In one implementation, see [link to implementation details]. Figure 2 , Figure 2 This invention provides a schematic diagram of a SESAM dual-pigment package structure for a SESAM-centered mode-locked fiber optic oscillator, including a cross-sectional view and a structural diagram of the SESAM dual-pigment package 105. The cross-sectional view only shows the first collimator pigtail 1051 and the second collimator pigtail 1052. The first collimator pigtail 1051 and the second collimator pigtail 1052 are obliquely incident on the SESAM 1053, and the two pigtail optical paths are precisely coupled to achieve a low insertion loss reversible optical path. A retaining ring 1050 is used to fix the first collimator pigtail 1051 and the second collimator pigtail 1052. The SESAM 1053 is fixed on a heat sink 1054 to help dissipate heat from the SESAM 1053.

[0043] In one implementation, the WDM (Wavelength Division Multiplexing) device 1021 is a technology that combines two or more optical carrier signals of different wavelengths (carrying various information) at the transmitting end via a multiplexer (also called a multiplexer) and couples them into the same optical fiber for transmission. At the receiving end, the various wavelength optical carriers are separated by a demultiplexer (also called a demultiplexer), and then further processed by an optical receiver to recover the original signal. This technology of simultaneously transmitting two or more different wavelength optical signals in the same optical fiber is called wavelength division multiplexing.

[0044] Optical isolator (ISO 1022): An optical isolator is a passive optical device that allows only unidirectional light to pass through. Its working principle is based on the non-reciprocity of Faraday rotation. Light reflected back from the optical fiber can be effectively isolated by the optical isolator. Optical isolators primarily utilize the Faraday effect of magneto-optical crystals. The characteristics of an optical isolator are: low forward insertion loss, high reverse isolation, and high return loss. An optical isolator is a passive device that allows light to pass in one direction while blocking light from passing in the opposite direction. Its function is to restrict the direction of light, allowing light to propagate in only one direction. Light reflected back from the optical fiber can be effectively isolated by the optical isolator, improving optical wave transmission efficiency.

[0045] See Figure 3 , Figure 3 This is a schematic diagram of a hybrid module structure of a SESAM-centered mode-locked fiber optic oscillator provided in an embodiment of the present invention, wherein the WDM device 1021 and the optical isolator 1022 are connected by optical fiber.

[0046] In one implementation, a single-mode pump source 101 injects pump light into the cavity through a chirped fiber grating 103. The pump light excites signal light in the gain fiber 104. The signal light has certain intensity random fluctuations. After being modulated and shaped for the first time by a saturable absorber mirror SESAM1053, it is reflected again by a high-reflection mirror to the saturable absorber mirror SESAM1053 for a second modulation and shaping. The two modulation and shaping by the saturable absorber mirror SESAM1053 greatly improves the evolution speed of the mode-locked pulse.

[0047] The signal light undergoes a first modulation via the SESAM dual-pigment package 105 in its forward direction. Since the forward direction of the signal light remains unchanged, it is reflected by a high-reflectivity mirror and then undergoes a second modulation via the SESAM dual-pigment package 105. In the first modulation process, the modulation at the pulse's leading edge is stronger than at the trailing edge, resulting in a negative chirp pulse. In the second modulation process, the pulse has a positive chirp, and its leading and trailing edges are opposite to those in the first modulation. Ultimately, this is equivalent to applying two modulations to the pulse's leading and trailing edges. Due to the time characteristics of saturable absorption, more is absorbed at the leading edge and less at the trailing edge. However, due to the SESAM's central structure and chirp reversal, uniform modulation of the pulse's leading and trailing edges is achieved.

[0048] See Figure 4 In the mid-channel SESAM mode-locked oscillator, the pulse signal undergoes two modulation and shaping cycles per cycle, which means that the continuous wave background and the leading and trailing edges of the pulse also undergo two suppressions, which can improve the stability and temporal contrast of the pulse.

[0049] In one implementation, the net dispersion of the femtosecond oscillator is near zero and negative. After the pulse passes through the chirped fiber grating 103, it is chirped inverted to negative chirp. The fiber and gain fiber 104 have positive dispersion at 1 micrometer. Therefore, as the propagation distance increases, the pulse will eventually evolve to positive chirp. So the SESAM position cannot be too far away from the chirped fiber grating 103, or in other words, the fiber between the chirped fiber grating 103 and the SESAM double pigtail package 105 cannot be too long. That is, the SESAM double pigtail package 105 is located in the middle, close to the side of 103.

[0050] In one implementation, the propagation distance is related to the cavity's net dispersion and nonlinearity (especially the self-phase effect, which introduces positive chirp). The following qualitative relationship exists:

[0051]

[0052] That is, this distance is proportional to the net dispersion of the cavity. Inversely proportional to the cavity gain level .

[0053] Specific example: fixed repetition frequency 45MHz, net dispersion -0.03ps 2 The distance between the CFBG (chirped fiber grating 103) and the SESAM double pigtail package 105 is 0.85m. The length of the gain fiber 104 is 0.5m. The length of the passive fibers before and after the gain fiber is 0.175m. The distance between the high-reflection mirror 106 and the SESAM double pigtail package 105 is 1.4m.

[0054] See Figure 5 , Figure 5 This is a demonstration diagram of the first SESAM propagation of a SESAM-centered mode-locked fiber optic oscillator provided in an embodiment of the present invention, showing the first passage through the SESAM; see also... Figure 6 , Figure 6 The diagram shows the second SESAM propagation of a SESAM-centered mode-locked fiber optic oscillator provided in this embodiment of the invention, representing the second passage through the SESAM. The phase of the pulses passing through the SESAM twice exhibits opposite concavity and convexity, and the first derivative of the phase in the time domain has opposite signs, meaning that the pulse chirp characteristics are opposite when passing through the SESAM twice.

[0055] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should still fall within the scope of the claims of the present invention.

Claims

1. A SESAM-based mode-locked fiber optic oscillator, characterized in that, include: The components include: optical fiber (100), single-mode pump source (101), hybrid module (102), chirped fiber grating (103), gain fiber (104), SESAM double pigtail package (105), and high-reflection mirror (106), wherein: The single-mode pump source (101) is connected to the hybrid module (102) via the optical fiber (100), and the hybrid module (102) is connected to the chirped fiber grating (103) via the optical fiber (100). The chirped fiber grating (103) is connected to the gain fiber (104) via an optical fiber (100), the gain fiber (104) is connected to the SESAM double pigtail package (105) via the optical fiber (100), and the SESAM double pigtail package (105) is connected to the high reflection mirror (106) via the optical fiber (100). The SESAM-centered mode-locked fiber oscillator is configured such that, within one oscillation cycle, the optical pulse is negatively chirped when it first passes through the SESAM double pigtail package (105), and positively chirped when it passes through the SESAM double pigtail package (105) a second time after being reflected by the high-reflection mirror (106), so as to complementarily shape the leading and trailing edges of the optical pulse through two modulations with opposite chirping characteristics.

2. A SESAM-based mode-locked fiber optic oscillator according to claim 1, characterized in that, The hybrid module (102) includes: a WDM device (1021) and an optical isolator (1022); The WDM device (1021) and the optical isolator (1022) are connected by optical fiber; the WDM device (1021) is used to couple multiple light sources to obtain a light source beam; the optical isolator (1022) is used to block reflected light.

3. A SESAM-based mode-locked fiber optic oscillator according to claim 1, characterized in that, The length of the gain fiber (104) is 50 cm.

4. A SESAM-based mode-locked fiber optic oscillator according to claim 1, characterized in that, The SESAM dual-pigment package (105) includes: a first collimator pigtail (1051), a second collimator pigtail (1052), and SESAM (1053). The first collimator pigtail (1051) and the second collimator pigtail (1052) are symmetrically arranged on the SESAM (1053).

5. A SESAM-based mode-locked fiber optic oscillator according to claim 4, characterized in that, The gain fiber (104) and the high reflection mirror (106) are respectively provided on the side of the first collimator pigtail (1051) and the second collimator pigtail (1052) away from the SESAM (1053). The first collimator pigtail (1051) is connected to the gain fiber (104), and the second collimator pigtail (1052) is connected to the high reflection mirror (106).

6. A SESAM-based mode-locked fiber optic oscillator according to claim 4, characterized in that, The SESAM dual-tail fiber package (105) also includes: a retaining ring (1050); The retaining ring (1050) is used to fix the first collimator tail fiber (1051) and the second collimator tail fiber (1052). The first collimator tail fiber (1051) and the second collimator tail fiber (1052) are symmetrically arranged in the middle of the fixing ring (1050).

7. A SESAM-based mode-locked fiber optic oscillator according to claim 4, characterized in that, The SESAM dual-tail fiber package (105) also includes: a heat sink (1054); The heat sink (1054) is disposed on the side of the SESAM (1053) away from the first collimator pigtail (1051) and the second collimator pigtail (1052), and the SESAM (1053) is fixedly connected to the heat sink (1054).

8. A SESAM-based mode-locked fiber optic oscillator according to claim 4, characterized in that, The modulation depth of the SESAM (1053) is 20%.

9. A SESAM-based mode-locked fiber optic oscillator according to claim 1, characterized in that, The working process of the SESAM centrally located mode-locked fiber optic oscillator includes: The single-mode pump source (101) injects pump light into the hybrid module (102), the hybrid module (102) receives the pump light and propagates it in the direction of the chirped fiber grating (103), the pump light propagates to the gain fiber (104), and the pump light excites the initial signal light in the gain fiber (104); The initial signal light propagates into the SESAM dual-pig fiber package (105) for modulation to obtain the first signal light. The first signal light propagates towards the high-reflection mirror (106) and is reflected by the high-reflection mirror back to the SESAM dual-pig fiber package (105) for modulation to obtain the second signal light. The second signal light propagates toward the mixing module (102), and after propagating to the mixing module (102), it is output through the mixing module (102).

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