CN103259172B - Radio frequency modulation tunable all-fiber laser based on fiber loop mirror - Google Patents

Abstract

The invention discloses a radio-frequency modulation tunable all-fiber laser based on a fiber optic ring mirror, one arm of the fiber ring mirror, a double-clad non-doped fiber, a double-clad doped fiber, and a signal light of a wavelength division multiplexer The channels and output pigtails are connected head to tail and spliced sequentially, and the pumping source and the pumping optical channel of the wavelength division multiplexer are spliced; the fiber fixing and pulling bracket includes left and right lobes; The groove outside the bracket is pulled and tightened, the triangular column bracket is placed on the piezoelectric ceramic, and a pad is provided at the bottom of the piezoelectric ceramic; the piezoelectric ceramic is connected to a radio frequency power supply. The invention adopts radio frequency tuning to form a long-period fiber grating with adjustable period by ultrasonic vibration to realize the wavelength tuning of the fiber laser. The advantages of compactness, stable and reliable performance, and the laser can achieve a wide range of continuous tuning.

Description

RF-modulated tunable all-fiber laser based on fiber loop mirror

technical field

The invention belongs to the technical field of lasers, and in particular relates to a fiber laser, in particular to a radio-frequency modulation and tunable all-fiber laser based on a fiber loop mirror.

Background technique

Fiber lasers are developing rapidly due to their small size, high efficiency, good stability, and good beam quality. At present, in fiber lasers, the common tunable laser technology is mainly based on rotating grating, compound ring resonance, adjusting the angle of intracavity etalon, using acousto-optic filter, electrically adjustable liquid crystal etalon, fiber grating tuning, fiber ring, sampling grating And polarization control and other technologies, either use a non-full fiber structure, or use a grating that is inconvenient to adjust and has low efficiency, or the adjustment range is relatively narrow, or the output power is too small.

Contents of the invention

Aiming at the problems existing in the existing tuned fiber lasers, the present invention discloses a radio-frequency modulation tunable all-fiber laser based on a fiber loop mirror. The other end uses the 4% Fresnel reflection of the fiber cut end face as the output mirror, and connects an all-fiber structure radio frequency modulation filter in the fiber laser. When the absorption spectrum of the filter and the gain spectrum of the active fiber alternate When stacking, the absorption spectrum of the filter forms a modulation effect on the gain spectrum of the active fiber, and as a result, the central gain wavelength of the modulated gain spectrum is shifted. Under the action of the wide-spectrum mirror, the central wavelength of the excited laser is Will vary with the center wavelength of the gain spectrum to achieve wavelength tuning.

In order to achieve the above object, the present invention adopts the following technical solutions to solve it:

A radio-frequency modulated tunable all-fiber laser based on a fiber loop mirror, including a fiber loop mirror, a fiber fixed pulling bracket, a triangular column bracket, piezoelectric ceramics, a spacer, a radio frequency power supply, a double-clad non-doped fiber, a double-clad Doped fiber, wavelength division multiplexer, pump source and output pigtail, wherein one arm of the fiber loop mirror, double-clad non-doped fiber, double-clad doped fiber, wavelength division multiplexer The signal optical channel and the output pigtail are connected end-to-end and sequentially fused, the other arm of the fiber optic loop mirror is suspended in the air, and the pumping source is fused with the pumping optical channel of the wavelength division multiplexer; the optical fiber fixing and pulling bracket includes left lobe and The right lobe, the left lobe and the right lobe are connected by a rigid support frame; the left lobe and the right lobe are cylinders with outer arcs and inner flats, and a plurality of parallel grooves are engraved on the outer arcs of the left and right lobe; double-wrapped A layer of non-doped optical fiber is wound in the groove outside the fiber fixing and pulling bracket and tensioned. The triangular column bracket is placed on the piezoelectric ceramic, and the bottom of the piezoelectric ceramic is provided with a pad so that the edge of the top of the triangular column bracket contacts the double-clad non-doped optical fiber. ; The piezoelectric ceramic is connected to a radio frequency power supply.

The present invention also includes following other technical characteristics:

The piezoelectric ceramics is connected to a radio frequency power source to cause the vibration of the double-clad non-doped fiber, so that the refractive index of the double-clad non-doped fiber core changes periodically to form a long-period fiber grating, which produces an absorption centered on a certain wavelength. spectrum, when the absorption spectrum overlaps with the gain spectrum of the double-clad doped fiber, the output frequency of the RF power source changes to make the long-period grating absorption spectrum move, thereby making the center wavelength of the gain spectrum move; the output wavelength of the laser is related to the gain The central wavelength of the spectrum coincides, so that the required output wavelength can be achieved by adjusting the output frequency of the radio frequency.

The distance between the left lobe and the right lobe is 8cm-30cm.

The left lobe and the right lobe are both semi-cylindrical, semi-elliptic, or rectangular with semi-cylindrical.

The distance between adjacent grooves on the left lobe and the right lobe is 2 mm to 5 mm, and the groove depth is the radius of the outer cladding of the double-clad non-doped optical fiber.

The tops of the left and right flaps are provided with layering strips.

The apex angle of the triangular prism bracket is 30°-60°.

The double-clad non-doped optical fiber is wound 4 times outside the fiber fixing and pulling bracket, with a distance of 2 mm between each rotation.

The optical fiber loop mirror adopts a coupling ratio of 50:50.

The signal end of the wavelength division multiplexer is used as an output pigtail, and the 4% Fresnel reflection of the cutting surface of the output pigtail is an output mirror.

The invention adopts radio frequency tuning to form a long-period fiber grating with adjustable period by ultrasonic vibration to realize the wavelength tuning of the fiber laser. The advantages of compactness, stable and reliable performance, and the laser can achieve a wide range of continuous tuning.

Description of drawings

Fig. 1 is a structural schematic diagram of the present invention.

Figure 2 is a schematic diagram of the absorption spectrum test.

Fig. 3 is a schematic diagram of the structure of the fiber fixing and pulling bracket.

FIG. 4 is a top view of FIG. 3 .

Fig. 5 is a graph showing the relationship between the RF output frequency of the RF power supply and the output wavelength of the laser of the present invention.

The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments.

Detailed ways

Referring to Fig. 1, the radio frequency modulation tunable all-fiber laser based on the fiber optic loop mirror of the present invention includes a fiber loop mirror 1, an optical fiber fixing and pulling bracket 2, a triangular column bracket 3, a piezoelectric ceramic 4, a spacer 5, a radio frequency power supply 6, Double-clad non-doped fiber 7, double-clad doped fiber 8, wavelength division multiplexer 9, pump source 10 and output pigtail 11, wherein one arm of the fiber loop mirror 1, double-clad non-doped Miscellaneous optical fiber 7, double-clad doped optical fiber 8, signal optical channel of wavelength division multiplexer 9 and output pigtail 11 are connected end-to-end and sequentially fused, the other arm of optical fiber loop mirror 1 is suspended in the air, and pumping source 10 is connected to the wavelength division The pumping optical channel of the multiplexer (9) is welded; the all-fiber laser of the present invention composed of the above components is divided into four parts in principle, which are resonant cavity, gain fiber, pumping part and tunable filter.

The resonant cavity is composed of a fiber loop mirror 1 and an output mirror. The fiber loop mirror 1 is a passive device formed by fusing the two output port fibers of a 2×2 fused tapered broadband fiber coupler together. The coupling ratio is 50:50. Its function is equivalent to a total reflection mirror, and its reflectivity is required to be greater than or equal to 95%; the output mirror uses the signal end of the wavelength division multiplexer 9 to be directly cut, that is, the 4% Fresnel reflection of the cut end face is used as the output mirror . The incident light is split by a 2×2 fused tapered broadband fiber coupler to form two beams of light transmitted clockwise and counterclockwise. The latter has a phase delay of 90° compared to the former. When the beam circles around for a week, it is coupled again The total phase delay of the light wave contributed from the counterclockwise direction in the output end of the beam splitter is 180° compared with the light wave contributed from the clockwise direction [Cao Xue, Li Xinying, et al.(2009). "Fiber Laser Based on Fiber Loop Mirror Optimal Design of . " Optical Communication Technology 07.]. Regardless of the additional loss of the coupler, let the coupling ratio be α: (1-α). When α=0.5, the two kinds of contributed light waves in the output will appear destructive interference. According to the principle of energy conservation, all the input light energy will be given by For the output of the incident end, since the medium in which the light travels in the two directions is exactly the same, its reflection characteristics are wavelength-independent, so it can be used as a wide-spectrum total reflection mirror and an end mirror of a fiber laser. Since both the end mirror and the output mirror are wide-spectrum reflectors, they have no frequency selection effect on the laser output wavelength, and the laser output wavelength is only affected by the net gain spectrum, which is equal to the highest gain wavelength of the net gain spectrum. In this way, the laser output wavelength will be consistent with the central wavelength of the gain spectrum of the gain fiber, that is, the double-clad doped fiber 8 .

The gain fiber is the double-clad doped fiber 8, which can use any existing double-clad single-mode fiber with a wider gain spectrum, as long as it can meet the absorption spectrum of the tunable filter used and the gain of the gain fiber. If the spectrum overlaps, a tunable output can be achieved. The present invention is applicable to all doped fiber lasers, and its main difference for fiber lasers with different doped double-clad fiber media is that: the selected double-clad doped fiber 8 of the fiber laser is different, and the corresponding pump source 10 needs to be To match it, the output frequency band of the corresponding radio frequency power supply 6 also needs to match it. Considering the output mode of the laser, select the corresponding core size and core numerical aperture; according to the absorption of the pump by the double-clad doped fiber 8, determine the size of the inner cladding, cladding absorption rate and fiber length of the fiber to be selected.

The tunable filter is the core component of the present invention, please refer to Fig. 1-Fig. 4, the tunable filter includes the fiber fixed pulling bracket 2, the triangular column bracket 3, the piezoelectric ceramic 4, the spacer 5, the radio frequency power supply 6 and the double package A layer of non-doped optical fiber 7; wherein, the fiber fixing and pulling support 2 includes a left lobe 21 and a right lobe 22, and the left lobe 21 and the right lobe 22 are connected by a rigid support frame 23 and the distance between the two (ie rigid The length of the support frame 23) is 8cm to 30cm; the left lobe 21 and the right lobe 22 are cylinders with outer arcs and inner flats, which can be specifically semi-cylindrical, semi-elliptic, or rectangular with semi-cylindrical, left lobe 21, right lobe 22 The length of the column is based on the principle that the optical fiber can be coiled. The outer arcs of the left lobe 21 and the right lobe 22 are engraved with a plurality of parallel grooves 25. The distance between adjacent grooves 25 is 2 mm to 5 mm. The groove depth is double-clad non-doped The radius of the outer cladding of the miscellaneous optical fiber 7, that is, to ensure that half of the double-clad non-doped optical fiber 7 can be exposed in it, and the top of the left lobe 21 and the right lobe 22 is provided with a bead 24 for pressing and fixing the double-clad non-doped optical fiber 7 .

The filter medium of the tunable filter, that is, the structural size of the double-clad non-doped fiber 7 needs to completely match the gain fiber, which is convenient for fusion splicing and has low loss. Wrap the double-clad non-doped optical fiber 7 in the groove 25 outside the fiber fixing and pulling bracket 2 and tighten it, then place the triangular column bracket 3 on the piezoelectric ceramic 4, and add a cushion block 5 at the bottom of the piezoelectric ceramic 4 Make the edge of the top of the triangular column bracket 3 contact the double-clad non-doped optical fiber 7 to form a structure similar to the strings and brackets of a guqin. The apex angle of the triangular column support 3 is preferably 30° to 60°. The triangular column support 3, piezoelectric ceramics 4, and pads 5 constitute the vibration generation and vibration energy transmission part. The piezoelectric ceramic 4 is connected to the radio frequency power supply 6. When the radio frequency output causes the piezoelectric ceramic 4 to vibrate, the vibration energy is transmitted to the double-clad non-doped optical fiber 7 through the triangular prism bracket 3, and a periodic oscillation is formed in the optical fiber. When the core When the mode and the mode in the inner cladding meet the phase matching conditions, the coupling effect between the core mode and the inner cladding mode will occur, which acts as a long-period fiber grating, and its central absorption spectrum is related to the grating period, and the grating period is It is related to the frequency and vibration amplitude of radio frequency vibration. When the vibration amplitude is constant, the absorption spectrum of the long-period fiber grating can be changed by adjusting the output frequency of the radio frequency power supply 6. When the absorption spectrum of the long-period fiber grating is the same as the gain spectrum of the gain fiber When overlapping occurs, the central wavelength of the net gain spectrum can be changed by adjusting the output frequency of the radio frequency power supply 6 to realize tunable output laser.

In the above structure of the tunable filter, the number of turns of the double-clad non-doped optical fiber 7 wound on the outside of the fiber fixing and pulling support 2 is 1-8 turns, and the more turns, the deeper the depth of the absorption spectrum. Select the appropriate number of turns according to the width and strength of the gain spectrum of the gain medium, in order to achieve effective modulation.

In this structure, the mode coupling effect is related to the intensity of radio frequency vibration and the diameter of the fiber. The more vibration energy, the higher the coupling efficiency, and the finer the fiber, the more obvious the coupling effect is, especially when the double-clad non-doped fiber 7 is removed. After the outer cladding, the coupling effect is significantly enhanced. The reason is that the outer cladding is made of resin material. After removing it, the core and inner cladding materials are all quartz glass, the vibration effect is obviously enhanced, and the absorption depth is also enhanced a lot. This can Reduce the requirement on the output power of the radio frequency power supply 6 . The outer cladding of the optical fiber between the left lobe and the right lobe of the optical fiber fixing and pulling support 2 can be stripped by thermal stripping or chemical corrosion, so as to obtain a stronger mode coupling effect and a larger absorption depth.

In this structure, the absorption center wavelength has a linear relationship with the variation of radio frequency frequency, which satisfies

λ=λ ₀ +kΔf

In the formula, λ is the absorption center wavelength, Δf is the variation of radio frequency frequency, λ ₀ is the measurement reference wavelength, that is, the absorption center wavelength corresponding to Δf=0, and k is the slope of the absorption center wavelength changing with the radio frequency frequency, except for In addition to the structural parameters of the fiber core and the inner cladding, it is also related to the mechanical properties of the fiber. The value of k is -0.1~-1nm/KHz. As the radio frequency increases, the absorption center wavelength will blue-shift.

The pumping part is used to provide the energy required for the laser to work, and is composed of a pumping source 10 and a wavelength division multiplexer 9 . The pump source 10 adopts a semiconductor laser with pigtail output, and its output wavelength needs to meet the pump wavelength required by the gain fiber, and then select the corresponding pump power according to the output power required by the laser of the present invention. The pump light is output by the pump source 10, coupled into the inner cladding of the double-clad doped fiber 8 through the wavelength division multiplexer 9, and then continuously transported from the inner cladding to the core of the double-clad doped fiber 8 In the process, the pump energy is provided for the laser working substance in the fiber core, and the laser working substance excites fluorescence under the action of the pump light. Form the laser output, the output wavelength of the laser output is determined by the result of the joint action of the reflection spectrum and the gain spectrum. In the gain spectrum, preferably in the high-gain region), for wide-spectrum reflectors, in the high-reflectivity wavelength range, the highest gain wavelength is the final laser output wavelength.

In the present invention, by increasing the optical fiber to fix the pulling support 2, the triangular support 3, the piezoelectric ceramic 4, the spacer 5, the radio frequency power source 6 and the double-clad non-doped optical fiber 7, its effect is that the double-clad non-doped The optical fiber 7 forms an absorption spectrum with a certain depth to form a modulation of the original excitation spectrum. When the output frequency of the RF power supply 6 is changed, the central wavelength of the absorption spectrum can be changed, thereby changing the central wavelength of the modulated excitation spectrum.

Example:

As shown in FIG. 1 , following the above-mentioned technical solution of the present invention, the RF-modulated tunable all-fiber laser based on the fiber loop mirror of this embodiment includes four parts: a resonator, a gain fiber, a pump source and a tunable filter.

Resonant cavity: the total reflection mirror is a fiber optic loop mirror with a coupling ratio of 50:50, and the output mirror is a 4% non-Nier reflection of the fiber cut end face of the output pigtail 11. Both are wide-spectrum mirrors and can be adapted to any doped Stray fiber and any wavelength.

Gain fiber: Double-clad doped fiber 8 selects 6/125μm thulium-doped double-clad fiber, the cladding absorption rate is 1.4dB/m790nm, that is, the cladding absorption rate at 790nm is 1.4dB/m, the core value The aperture is 0.23, and the fiber length is 10m. Since the thulium-doped fiber has a wider gain spectrum, it can achieve a larger tuning range; for other doped fiber lasers, the size of the tuning range mainly depends on the gain spectrum of the laser working substance in the doped fiber, the gain spectrum The wider the range that can be tuned, the greater it will be.

Pumping part: the pump source 10 is a semiconductor laser with a 790 nm output pigtail of 100 μm and a maximum output power of 35 W. The wavelength division multiplexer 9 adopts a (1+1*1) wavelength division multiplexer whose output end and signal end are both 6/125 μm, and the pump end is 100 μm.

Tunable filter: the structural size of the double-clad non-doped fiber 7 matches that of the double-clad doped fiber 8, that is, the non-doped double-clad fiber of 6/125 μm is selected, the numerical aperture of the core is 0.23, and the double-clad The non-doped optical fiber 7 is wrapped 4 times on the fiber fixing and pulling support 2, and then pressed down with a bead 24, with a distance of 2 mm between each circle. The left lobe 21 and the right lobe 22 on the fiber fixing and pulling bracket 2 are both 1 cm higher than the top of the triangular column bracket 3 ; The outer cladding of the vibrating part of the fiber is removed. The piezoelectric ceramic 4 is in the shape of a rectangular sheet with a size of 45*8*5mm.

The tuning range of the vibration frequency of the radio frequency power supply 6 needs to be measured in advance, please refer to Fig. 2, from one end of the double-clad non-doped optical fiber 7, inject the wide-spectrum optical signal by the wide-spectrum light source 12 through the lens 13, the light source spectral range should include double For the fluorescence spectrum of doped elements in the cladding-doped optical fiber 8, a spectrometer 14 is placed at the other end of the double-clad non-doped optical fiber 7. After the piezoelectric ceramic 4 is connected to the radio frequency power supply 6, the vibration caused by the radio frequency current is measured and recorded. The generated absorption spectrum is compared with the gain fluorescence spectrum of the double-clad doped fiber 8 , and the frequency corresponding to the overlapping part is the tuning range corresponding to the radio frequency power supply 6 .

Referring to Fig. 3, it is the experimental relationship diagram of the radio frequency output frequency of the radio frequency power supply 6 and the output wavelength of the laser in the present embodiment, therefore, adjust the radio frequency output frequency of the radio frequency power supply 6 according to the output wavelength required by the laser of the present invention, in this example The output adjustment range is 1MHz ~ 1.5MHz. It is better to make the radio frequency output power satisfy the comparison between the absorption spectrum and the gain spectrum, and this parameter can also be obtained through experiments.

After completing the above device selection and testing, the first arm of the fiber optic loop mirror 1, the double-clad non-doped fiber 7, the double-clad doped fiber 8, and the multiplexing ends of the wavelength division multiplexer 9 are welded end-to-end in sequence. The pump source 10 is fused with the pump input end of the wavelength division multiplexer 9, and the signal end of the wavelength division multiplexer 9 is used as an output pigtail 11, and the signal end of the wavelength division multiplexer 9 is directly cut to cut The 4% non-Nier reflection of the end face is used as the output reflector, and the second arm of the fiber loop mirror 1 is suspended in the air, and the fiber core is required to be aligned during fusion splicing.

Claims (10)

1. the rf modulations tunable whole-optical fibre laser based on fiber loop mirror, it is characterized in that, comprise fiber loop mirror (1), tractive support (2) fixed by optical fiber, triangular prism support (3), piezoelectric ceramic (4), cushion block (5), radio-frequency power supply (6), double clad undoped optical fiber (7), double-cladding doped fiber (8), wavelength division multiplexer (9), pumping source (10) and output tail optical fiber (11), wherein, a wherein arm of described fiber loop mirror (1), double clad undoped optical fiber (7), double-cladding doped fiber (8), the flashlight passage of wavelength division multiplexer (9) and export tail optical fiber (11) and to join end to end welding successively, another arm sling sky of fiber loop mirror (1) need not, the pump light passage welding of pumping source (10) and wavelength division multiplexer (9), described optical fiber is fixed tractive support (2) and is comprised left lobe (21) and right lobe (22), is connected between described left lobe (21) and right lobe (22) by rigid cage (23), left lobe (21), right lobe (22) are cylinder flat in outer arc, and left lobe (21), right lobe (22) outer arc carve multiple parallel groove (25), double clad undoped optical fiber (7) to be fixed in the outside groove (25) of tractive support (2) around optical fiber and is strained, triangular prism support (3) is placed on piezoelectric ceramic (4), and piezoelectric ceramic (4) bottom establishes cushion block (5) to make rib contact double clad undoped optical fiber (7) at triangular prism support (3) top, described piezoelectric ceramic (4) connects radio-frequency power supply (6).

2. as claimed in claim 1 based on the rf modulations tunable whole-optical fibre laser of fiber loop mirror, it is characterized in that, described piezoelectric ceramic (4) causes double clad undoped optical fiber (7) to vibrate when passing into radio-frequency power supply (6), double clad undoped optical fiber (7) fiber core refractive index generating period is changed and forms long period fiber grating, produce the absorption spectra centered by a certain wavelength, when the gain spectral of this absorption spectra and double-cladding doped fiber (8) is overlapping, the change of the output frequency of radio-frequency power supply (6) makes long-period gratings absorption spectra move, thus gain spectral centre wavelength is moved, output wavelength and the gain spectral centre wavelength of described laser match, thus by regulating the adjustment of the output frequency of radio-frequency power supply (6) to realize the output wavelength needed.

3., as claimed in claim 1 based on the rf modulations tunable whole-optical fibre laser of fiber loop mirror, it is characterized in that, the distance between described left lobe (21) and right lobe (22) is 8cm ~ 30cm.

4., as claimed in claim 1 based on the rf modulations tunable whole-optical fibre laser of fiber loop mirror, it is characterized in that, described left lobe (21), right lobe (22) are semicolumn, semiellipse post or rectangular band semicolumn.

5. as claimed in claim 1 based on the rf modulations tunable whole-optical fibre laser of fiber loop mirror, it is characterized in that, described left lobe (21), upper adjacent groove (25) spacing of right lobe (22) are 2mm ~ 5mm, and groove depth equals double clad undoped optical fiber (7) surrounding layer radius.

6., as claimed in claim 1 based on the rf modulations tunable whole-optical fibre laser of fiber loop mirror, it is characterized in that, described left lobe (21), right lobe (22) top are equipped with press strip (24).

7., as claimed in claim 1 based on the rf modulations tunable whole-optical fibre laser of fiber loop mirror, it is characterized in that, the drift angle of described triangular prism support (3) is with 30 ° ~ 60 °.

8. as claimed in claim 1 based on the rf modulations tunable whole-optical fibre laser of fiber loop mirror, it is characterized in that, described double clad undoped optical fiber (7) is fixed tractive support (2) outside at optical fiber and is wound around 4 circles, every turn separation 2mm.

9. as claimed in claim 1 based on the rf modulations tunable whole-optical fibre laser of fiber loop mirror, it is characterized in that, described fiber loop mirror (1) adopts coupling ratio to be 50:50.

10. as claimed in claim 1 based on the rf modulations tunable whole-optical fibre laser of fiber loop mirror, it is characterized in that, the signal end of described wavelength division multiplexer (9) is as output tail optical fiber (11), and the Fei Nier exporting 4% of the cut surface of tail optical fiber (11) is reflected into outgoing mirror.