Fiber laser with wide-range and fast center frequency tuning

Abstract

A fiber laser with a wide-range, fast-tuning center frequency is disclosed. The device comprises a pump laser with a pump laser controller, a wavelength division multiplexer, a gain fiber, a fiber circulator, a first fiber coupler, a second fiber coupler, a third fiber coupler, an electro-optic phase modulator, a broadband filter, and an electro-optic phase modulator controller. This invention combines fiber interferometer mode selection technology with rapid phase modulation technology of the electro-optic phase modulator. Rapid phase modulation of the electro-optic phase modulator enables rapid changes in the equivalent cavity length within the fiber interferometer, ultimately achieving rapid changes in the fiber interferometer modes. Furthermore, a fiber optic F-P tunable filter filters out redundant fiber interferometer modes, ultimately realizing a fiber laser with a wide-range, fast-tuning center frequency, exhibiting both a wide tuning range and a large tuning bandwidth.

Description

Technical Field

[0001] This invention relates to fiber lasers, and more particularly to a fiber laser with a wide range of rapidly tuned center frequencies. This method can be applied to fields such as coherent laser communication, fiber optic sensing, and high-resolution laser spectroscopy. Background Technology

[0002] With the rapid development of low-noise fiber laser technology in recent years, it has found important applications in coherent laser communication, fiber optic sensing, high-precision spectroscopy, and synthetic aperture lidar. These applications not only require lasers with low noise and high coherence (ultra-narrow linewidth), but also the ability to rapidly tune the laser's center frequency. However, current tunable fiber lasers still face a series of bottlenecks in terms of tuning range and tuning bandwidth. Therefore, developing fiber laser technology that can simultaneously achieve narrow linewidth, wide tuning range, and large tuning bandwidth has significant academic and practical value.

[0003] EDIVAnoijen proposed a technique for tuning the center frequency of a laser using an acousto-optic modulator (see prior art [1]: "Laser frequency stabilization using Doppler-free bichromatic spectrocopy", Applied Physics B, Vol. 79, 57-59 2004). The basic principle is to modulate the laser frequency using an acousto-optic modulator (AOM), and the center frequency of the output laser can be moved by adjusting the modulation frequency of the AOM. However, due to the limitations of the crystal used in the acousto-optic modulator, the tuning range of its center frequency is limited, only down to the pm level.

[0004] On the other hand, Zhang proposed a laser tuning technique based on a fiber filter tuning structure (see prior art [2]: "Ultra-narrow linewidth full C-band tunable single-frequency linear-polarization fiber laser", Optics Express. Vol 24, No. 23, 26209, 2016). This scheme achieves a tuning range of 40nm by using a chirped fiber grating FP interferometer and a fiber FP tunable filter. The advantage is that it can achieve a wide center frequency tuning range, but it has the following main disadvantages:

[0005] 1. The tuning in the scheme is achieved by applying mechanical stretching and temperature changes to the chirped fiber grating FP interferometer. The tuning accuracy is not high, generally around 1 pm.

[0006] 2. The tuning speed in the scheme is limited by the speed of mechanical stretching, so the tuning bandwidth is generally below kHz. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and propose a fiber laser with a wide range of rapidly tuned center frequencies. By combining fiber interferometer mode selection technology with electro-optic phase modulator phase fast modulation technology, the rapid phase modulation of the electro-optic phase modulator enables rapid changes in the equivalent cavity length inside the fiber interferometer, ultimately achieving rapid changes in the fiber interferometer modes. Furthermore, redundant interferometer modes are filtered out by a fiber FP tunable filter, ultimately achieving laser output with a wide range of rapidly tuned center frequencies, while also possessing the characteristics of a wide tuning range and a large tuning bandwidth.

[0008] The technical solution of the present invention is as follows:

[0009] A fiber laser with a wide range of fast center frequency tuning is characterized by comprising a pump laser with a pump laser controller, a wavelength division multiplexer, a gain fiber, a fiber circulator, a first fiber coupler, a second fiber coupler, a third fiber coupler, an electro-optic phase modulator, a broadband filter, and an electro-optic phase modulator controller.

[0010] The first and second fiber couplers form an equivalent fiber interferometer. The electro-optic phase modulator is located between the first and second fiber couplers. The electro-optic phase modulator controller is used to control the phase change of the electro-optic phase modulator. The broadband filter is located between the first fiber coupler and the electro-optic phase modulator and is used to filter out redundant modes of the fiber interferometer to achieve single-mode laser output.

[0011] The pump light emitted by the pump laser enters the gain fiber through a wavelength division multiplexer. The generated laser is input through port 1 of the fiber circulator and output from port 2 of the fiber circulator. It then enters the fiber interferometer. After mode selection by the fiber interferometer, the laser is input through port 2 of the fiber circulator, output through port 3 of the fiber circulator, and output as a tunable laser through the third fiber coupler.

[0012] The phase modulation bandwidth of the electro-optic phase modulator determines the tuning bandwidth of the fiber laser. The bandwidth of the broadband filter determines the tuning range of the fiber laser.

[0013] Compared with prior art, the present invention has the following advantages and positive effects:

[0014] 1. Compared with the prior art [2], the frequency tuning of the fiber laser with a wide range of fast center frequency tuning in this invention is achieved by phase modulation of an electro-optic phase modulator, and the tuning bandwidth can generally reach the level of 100kHz to MHz.

[0015] 2. Compared with the prior art [2], the frequency tuning of the fiber laser with a wide range of fast center frequency tuning in this invention is achieved by phase modulation of an electro-optic phase modulator. The tuning accuracy is determined by the phase control accuracy of the electro-optic phase modulator, and can generally achieve a tuning accuracy better than 0.01pm.

[0016] 3. Compared with the prior art [1], the frequency tuning range of the fiber laser with a wide range of fast tuning of the center frequency of the present invention is determined by the filtering bandwidth of the broadband filter, which can generally reach more than 10nm, much larger than the tuning range of about 1pm in the prior art [1]. Attached Figure Description

[0017] Figure 1 This is the optical path diagram of the fiber laser with a wide range of rapidly tuned center frequencies according to the present invention. Detailed Implementation

[0018] The present invention will be further described below with reference to examples and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0019] See Figure 1 , Figure 1 This is a structural block diagram of the fiber laser with a wide range of rapidly tuned center frequencies according to the present invention. As shown in the figure, the fiber laser with a wide range of rapidly tuned center frequencies according to the present invention includes a pump laser with a pump laser controller, a wavelength division multiplexer, a gain fiber, a fiber circulator, a first fiber coupler, a second fiber coupler, a third fiber coupler, an electro-optic phase modulator, a broadband filter, and an electro-optic phase modulator controller.

[0020] The pump light emitted by pump laser 1 enters the gain fiber 3 through wavelength division multiplexer 2. The generated laser light is input through port 1 of fiber optic circulator 4 and output from port 2 of fiber optic circulator 4. It then enters the fiber interferometer composed of first fiber coupler 5 and second fiber coupler 6. After mode selection by the fiber interferometer, the laser light is input through port 2 of fiber optic circulator 4 and reaches port 3 of fiber optic circulator 4. The final tunable laser light is output through third fiber coupler 10.

[0021] The first fiber coupler 5 and the second fiber coupler 6 form an equivalent fiber interferometer. The laser output from port 2 of the fiber circulator 4 enters this equivalent fiber interferometer to form a mode selection.

[0022] The electro-optic phase modulator 7 is located between the first fiber coupler 5 and the second fiber coupler 6, and the electro-optic phase modulator controller 8 is used to control the phase change of the electro-optic phase modulator. By rapidly modulating the phase change of the electro-optic phase modulator 7, the fiber interferometer mode is rapidly shifted, ultimately achieving rapid tuning of the laser frequency. The phase modulation bandwidth of the electro-optic phase modulator determines the tuning bandwidth of the fiber laser with a wide range of rapidly tuned center frequencies according to this invention.

[0023] The broadband filter 9 is located between the first fiber coupler 5 and the electro-optic phase modulator 7, and is used to filter out redundant modes of the fiber interferometer to achieve single-mode laser output. The filtering bandwidth of the broadband filter determines the tuning range of the fiber laser with a wide range of fast tuning of the center frequency in this invention.

[0024] When the fiber laser, which combines fiber interferometer mode selection technology and electro-optic phase modulator phase fast modulation technology to achieve wide-range and rapid tuning of its center frequency, operates, the specific operating steps are as follows:

[0025] 1. Turn on the pump laser controller to light up the pump laser.

[0026] 2. Gradually increase the pump intensity of the pump laser and observe the fiber laser output power and frequency at the third fiber coupler.

[0027] 3. By changing the phase of the electro-optic phase modulator using the electro-optic phase modulator controller, observe the change in the fiber laser output frequency. Rapid tuning of the fiber laser frequency can be achieved by quickly modulating the phase change of the electro-optic phase modulator.

[0028] This invention combines fiber optic interferometer mode selection technology with electro-optic phase modulator phase rapid modulation technology. Through rapid phase modulation of the electro-optic phase modulator, it achieves rapid changes in the equivalent cavity length within the fiber optic interferometer, ultimately enabling rapid changes in the fiber optic interferometer modes. Furthermore, it uses a fiber optic FP tunable filter to filter out redundant resonant cavity modes, ultimately realizing a fiber laser with a wide-range, rapidly tunable center frequency, characterized by a wide tuning range and large tuning bandwidth. This invention can be widely applied in coherent laser communication, fiber optic sensing, high-precision spectroscopy, synthetic aperture lidar, and other fields.

Claims

1. A fiber laser with wide-range fast tuning of center frequency, characterized in that, The pump laser includes a pump laser controller, a wavelength division multiplexer, a gain fiber, a fiber circulator, a first fiber coupler, a second fiber coupler, a third fiber coupler, an electro-optical phase modulator, a broadband filter, and an electro-optical phase modulator controller. The first fiber coupler (5) and the second fiber coupler (6) form a mode selection cavity of an equivalent fiber Mach-Zehnder interferometer structure. The electro-optical phase modulator (7) is located between the first fiber coupler (5) and the second fiber coupler (6), and the electro-optical phase modulator controller (8) is used to apply a high-speed modulation voltage signal to the electro-optical phase modulator (7) to quickly change the equivalent optical cavity length of the mode selection cavity. The broadband filter (9) is located between the first fiber coupler (5) and the electro-optical phase modulator (7), and is used to filter out other longitudinal modes of the mode selection cavity except the main mode to realize single-mode laser output. The pump light (1) emitted by the pump laser (1) enters the gain fiber (3) through the wavelength division multiplexer (2), and the generated laser is input through port one of the fiber circulator (4) and output from port two of the fiber circulator (4) to enter the fiber interferometer. The phase modulation bandwidth of the electro-optical phase modulator determines the tuning bandwidth of the fiber laser.

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