CN208173996U - A kind of Tunable Multi-wavelength Fiber Laser - Google Patents

Abstract

The utility model discloses a tunable multi-wavelength fiber laser. The fiber laser includes a pump laser, a wavelength division multiplexer, a gain fiber, a polarization controller, a fiber filter and an optical coupler. way to form a fiber laser resonator. The pump laser is connected to the gain fiber through a wavelength division multiplexer, and the output end of the gain fiber is connected to a polarization controller, a fiber filter and an optical coupler in turn. By adjusting the polarization controller, the incident light has different polarization states, and after passing through the fiber filter The inhomogeneity of the polarization state in the laser resonator is enhanced, thereby generating polarization hole burning in the gain medium, suppressing the mode competition in the cavity, and obtaining multi-wavelength laser output with polarization control and tunable. A high-birefringence micro-nano fiber with all-fiber, small size, simple structure, low cost, and low loss is used as the mode selection unit to achieve low-loss, stable, and narrow-band laser output.

Description

A tunable multi-wavelength fiber laser

technical field

The utility model relates to a tunable multi-wavelength optical fiber laser, which belongs to the technical field of optical fiber lasers.

Background technique

Recently, fiber lasers have become a research hotspot in the field of solid-state lasers because of their all-fiber, high efficiency, and flexible wavelength characteristics. In particular, wavelength division multiplexing (WDM) technology has become the key to meet the high-capacity communication needs of optical fiber communication, and tunable multi-wavelength fiber lasers, as the light source of optical fiber WDM communication systems, have very important research and application value.

Early multi-wavelength tunable lasers were mainly achieved by adding wavelength tunable components such as F-P cavity, dielectric thin film filter and acousto-optic filter to the laser resonator. However, these free-space tuning devices are generally non-fiber structures with large insertion loss, which reduces the efficiency, integration and compactness of the laser. Recently, all-fiber filters, such as fiber Bragg gratings, high birefringence (HiBi) Sagnac interferometers, and highly nonlinear photonic crystal fibers, have been used as tuning components. Among them, the production cost of tunable fiber grating represented by long-period fiber grating is relatively high, and limited by the strain characteristics of fiber grating itself, the wavelength tuning range is small. When a high birefringence (HiBi) Sagnac interferometer is used as a comb filter to select multiple wavelengths, the interference ring is large and difficult to integrate, and is easily affected by the external environment, such as changes in the shape of the ring caused by strain and other factors. The output state changes. Highly nonlinear photonic crystal fiber can convert the energy at the lasing wavelength to the non-lazing wavelength to achieve multi-wavelength output, but this type of laser resonator cavity length is long, the structure is not compact, and the fusion loss of photonic crystal fiber relatively bigger.

Therefore, it is of great research and application value to study and realize a multi-wavelength fiber laser with all-fiber, high stability, low cost, compact structure, low insertion loss and wide-ranging tunable wavelength.

Utility model content

The utility model proposes a tunable multi-wavelength fiber laser for the shortcomings of the prior art, such as high manufacturing cost, poor stability, low compactness, and small tuning range.

The purpose of the utility model will be achieved through the following technical solutions: a tunable multi-wavelength fiber laser, which includes a pump laser, a wavelength division multiplexer, a gain fiber, a polarization controller, a fiber filter and an optical coupler, Each device forms a fiber laser resonator through fiber coupling. The pump laser is connected to the gain fiber through a wavelength division multiplexer, and the output end of the gain fiber is connected to a polarization controller, a fiber filter and an optical coupler in sequence. The output end of the pump laser described above is connected to the input end of the wavelength division multiplexer, the output end of the wavelength division multiplexer is connected to the input end of the polarization controller through the gain fiber, and the output end of the polarization controller is connected to the optical fiber through a fiber filter. The input terminals of the coupler are connected.

Preferably, the optical fiber filter is a Lyot type optical fiber filter with a wavelength tuning function, the optical fiber filter includes an optical isolator and a high birefringence micro-nano optical fiber, and the output end of the polarization controller is connected to the input end of the optical isolator , the output end of the optical isolator is connected with the input end of the optical coupler through a high birefringence micro-nano fiber.

Preferably, the laser mode selection in the fiber laser resonator is realized through high birefringence micro-nano fiber in the fiber laser resonator.

Preferably, the high birefringence micro-nano fiber is made of high birefringence polarization-maintaining fiber fusion tapered, and the mode interference in the tapered fiber is used for laser intracavity mode selection.

Preferably, the high birefringence micro-nano fiber has a non-circularly symmetrical refractive index distribution, and the high birefringence micro-nano fiber includes a silicon-based material region and a stress region.

Preferably, the light field excites multiple modes during transmission in the high birefringence micro-nano fiber, including the fundamental mode and higher-order modes, and has different effective refractive indices. As the diameter of the fiber becomes smaller, more and more higher-order modes cut off, finally only the HE ₁₁ mode, TE ₀₁ mode and TM ₀₁ mode will pass through the uniform waist region, and an interference spectrum with mode selection effect will be formed between the TE ₀₁ mode and the TM ₀₁ mode.

Preferably, the normalized output light intensity T of the TE ₀₁ mode and the TM ₀₁ mode can be expressed as:

in is the phase difference between TE ₀₁ and TM ₀₁ , λ is the wavelength, ΔL=l(n ₁ -n ₂ ) is the optical path difference between TE ₀₁ and TM ₀₁ , by their effective refractive index (n ₁ and n ₂ ) and the length l of the waist of the PM fiber taper.

Preferably, the pump laser is a semiconductor laser.

The advantages of the technical solution of the utility model are mainly reflected in that the fiber laser adopts a high-birefringence micro-nano optical fiber with full optical fiber, small volume, simple structure, low cost and low loss as the mode selection unit, and realizes low loss, stability, narrow-band Laser output, in which the high birefringence micro-nano fiber is made of high birefringence polarization-maintaining fiber taper, and the mode interference in the taper fiber is used to select the laser cavity mode.

In this technical solution, a high birefringence micro-nano fiber and a polarization-dependent optical isolator are combined to form a Lyot-type fiber filter, and the polarization hole-burning effect is introduced, and the polarization controller is adjusted to obtain a narrow-band wide-range wavelength tunable laser spectrum.

The fiber laser is built with all-fiber devices and realizes narrow-band wide-range multi-wavelength tunability. It has the characteristics of good coherence, tunable wavelength frequency and number, high stability, compact structure, low cost, and easy implementation.

Description of drawings

FIG. 1 is a schematic structural diagram of a tunable multi-wavelength fiber laser of the present invention.

Fig. 2 is a schematic cross-sectional view of the high birefringence micro-nano optical fiber of the present invention.

Fig. 3 is a schematic diagram of the structure of three modes existing in the high birefringence micro-nano optical fiber of the present invention.

Fig. 4 is a single-wavelength tunable laser spectrum obtained by using a high-birefringence micro-nano fiber structure combined with a polarization-dependent optical isolator to form a Lyot-type fiber filter for laser mode selection and control obtained by spectrometer testing in the present invention.

Fig. 5 is a dual-wavelength tunable laser spectrum obtained by using a high-birefringence micro-nano fiber structure combined with a polarization-dependent optical isolator to form a Lyot-type fiber filter for laser mode selection and control obtained by spectrometer testing in the present invention.

Fig. 6 is the three-wavelength and four-wavelength tunable laser spectrum obtained by using the high birefringence micro-nano optical fiber structure combined with the polarization-dependent optical isolator to form the Lyot type optical fiber filter for laser mode selection and control obtained by the spectrometer test in the utility model .

Figure 7 is a schematic diagram of the laser output measured every 15 minutes within one hour when the single wavelength of the laser output obtained in the experimental test of the present invention is located at 1561.66nm, without changing the state of the polarization controller and the pump power.

Detailed ways

The objects, advantages and features of the present invention will be illustrated and explained by the following non-limiting description of preferred embodiments. These embodiments are only typical examples of the application of the technical solutions of the utility model, and any technical solutions formed by equivalent replacement or equivalent transformation all fall within the protection scope of the utility model.

The utility model discloses a tunable multi-wavelength fiber laser, as shown in Figure 1, the fiber laser includes a pump laser 1, a wavelength division multiplexer 2, a gain fiber 3, a polarization controller 4, a fiber filter 5 and optical The coupler 6 forms a fiber laser resonator cavity through fiber coupling between various components. In this technical solution, the pump laser 1 is preferably a semiconductor laser.

As shown in Figure 1, the pump laser 1 is connected to the gain fiber 3 through a wavelength division multiplexer 2, and the output end of the gain fiber is connected to a polarization controller 4, a fiber filter 5 and an optical coupler 6 in sequence, and the pump laser The output end of the wavelength division multiplexer is connected to the input end of the wavelength division multiplexer, the output end of the wavelength division multiplexer is connected to the input end of the polarization controller through the gain fiber, and the output end of the polarization controller is connected to the input end of the optical coupler through the optical fiber filter By adjusting the polarization controller, the incident light has different polarization states, and the inhomogeneity of the polarization state in the laser resonator is enhanced after passing through the fiber filter, thereby generating polarization hole burning in the gain medium and suppressing the competition of intracavity modes , and then get the polarization control tunable multi-wavelength laser output.

Described optical fiber filter is Lyot type optical fiber filter, has wavelength tuning function, and this optical fiber filter comprises optical isolator 51 and high birefringence micro-nano optical fiber 52, and described optical isolator 51 is polarization dependent optical isolator, polarization The output end of the controller is connected with the input end of the optical isolator, and the output end of the optical isolator is connected with the input end of the optical coupler through a high birefringence micro-nano fiber. The laser mode selection in the fiber laser resonator is realized through high birefringence micro-nano fiber in the resonator of the fiber laser.

The light field excites multiple modes during the transmission process in the high-birefringence micro-nano fiber, including fundamental mode and high-order mode, and has different effective refractive indices. As the diameter of the fiber becomes smaller, the fiber is tapered and thinned to a certain When it comes to size, more and more high-order modes are cut off, and there are fewer and fewer modes in it, and finally there are only three modes left, and finally only HE ₁₁ mode, TE ₀₁ mode and TM ₀₁ mode will pass through the uniform waist region , and form an interference spectrum with mode selection effect between TE ₀₁ mode and TM ₀₁ mode.

The fiber laser resonator of the present invention is provided with a high birefringence micro-nano optical fiber structure, as shown in Figure 2, the high birefringence micro-nano optical fiber is made of a high birefringence polarization-maintaining optical fiber fusion taper, and the high birefringence The refractive micro-nano fiber has a non-circular symmetric refractive index distribution, and the mode interference in the tapered fiber is used to select the laser cavity mode. After fusing the tapering, the diameter of the waist area of the polarization-maintaining fiber is about 2.66 μm, and the diameter of the fiber core becomes very small due to the tapering, so only the stress area is drawn in Figure 2 without the core. At this time, the air and the tapering The latter high-birefringence polarization-maintaining fiber constitutes a new multimode waveguide structure with a larger refractive index difference, which can accommodate multiple high-order modes. As the PM fiber diameter is further reduced, more higher-order modes are cut off, leaving fewer lower-order modes to interfere. At this time, the structural model of the high birefringence micro-nano fiber includes two parts, the silicon-based material region 7 in the high birefringence micro-nano fiber, and the stress region 8 in the high birefringence micro-nano fiber.

As shown in Figure 3, there are three modes in the high birefringence micro-nano fiber: HE ₁₁ mode 9, TE ₀₁ mode 10 and TM ₀₁ mode 11, but based on HE ₁₁ mode and TE ₀₁ mode, TM ₀₁ mode has no From the fact of energy exchange, it can be known that the interference is generated between the TE ₀₁ mode and the TM ₀₁ mode, so the following interference theory model can be established:

The normalized output light intensity T of TE ₀₁ mode and TM ₀₁ mode can be expressed as:

in is the phase difference between TE ₀₁ and TM ₀₁ , λ is the wavelength, ΔL=l(n ₁ -n ₂ ) is the optical path difference between TE ₀₁ and TM ₀₁ , by their effective refractive index (n ₁ and n ₂ ) and the length l of the waist of the PM fiber taper.

The high birefringence micro-nano optical fiber structure adopted in the utility model is formed by a high birefringence polarization-maintaining optical fiber. The mode interference in the tapered optical fiber is used to select the mode in the laser cavity, and the high birefringence micro-nano optical fiber is combined with the polarization Correlative optical isolators are combined to form a Lyot-type fiber filter. When the polarization controller is adjusted, the incident light has different polarization states. After passing through the filter, the non-uniformity of the polarization state in the laser resonator is enhanced, so that in the gain medium Polarization hole burning is generated, intracavity mode competition is suppressed, and multi-wavelength laser output with polarization control and tunable is obtained.

Figure 4 is a narrow-band single-wavelength tunable laser spectrum obtained by spectrometer testing using a high-birefringence micro-nano fiber structure combined with a polarization-dependent optical isolator to form a Lyot-type fiber filter for laser mode selection and control. The ordinate in the figure is The pump power, the abscissa is the wavelength. It can be seen from the figure that the pump power is 25mW at this time, the 3dB bandwidth of the output laser is less than 0.05nm, and the side mode suppression ratio can reach up to 53dB.

Fig. 5 is the output spectrum of the dual-wavelength laser obtained in the experimental test of the technical solution. The ordinate in the figure is the pump power, and the abscissa is the wavelength. Figure 6 shows the three-wavelength and four-wavelength laser output spectra obtained in the experimental test of this technical solution. The ordinate in the figure is the pump power, and the abscissa is the wavelength.

Figure 7 shows the laser output obtained by the experimental test of this technical solution when the single wavelength of the laser output is located at 1561.66nm. Without changing the state of the polarization controller and the pump power, the laser output is measured every 15 minutes within an hour. Has high stability.

The wavelength tuning function of the fiber laser is realized by a Lyot-type fiber filter composed of a high-birefringence micro-nano fiber and a polarization-dependent optical isolator. By adjusting the polarization controller, the incident light has different polarization states and is enhanced after passing through the filter. The inhomogeneity of the polarization state in the laser resonator is eliminated, thereby generating polarization hole burning in the gain medium, suppressing the mode competition in the cavity, and obtaining multi-wavelength laser output with polarization control and tunable.

The fiber laser uses a high-birefringence micro-nano fiber with all-fiber, small size, simple structure, low cost, and low loss as the mode selection unit to achieve low loss, stable, and narrow-band laser output, and is combined with a polarization-dependent optical isolator A Lyot-type fiber filter is formed to realize a stable all-fiber laser output with tunable wavelength, frequency and number.

The utility model still has multiple implementation modes, and all technical solutions formed by equivalent transformation or equivalent transformation all fall within the protection scope of the utility model.

Claims (8)

1. a kind of Tunable Multi-wavelength Fiber Laser, it is characterised in that：Including pump laser, wavelength division multiplexer, gain light Fibre, Polarization Controller, optical fiber filter and photo-coupler constitute an optical fiber between each device by way of fiber coupling Laser resonant cavity, the pump laser are connected through wavelength division multiplexer with gain fibre, and gain fibre output end is sequentially connected Polarization Controller, optical fiber filter and photo-coupler, the input terminal phase of the output end and wavelength division multiplexer of the pump laser Even, the output end of wavelength division multiplexer is connected by gain fibre with the input terminal of Polarization Controller, the output end of Polarization Controller It is connected by optical fiber filter with the input terminal of photo-coupler.

2. a kind of Tunable Multi-wavelength Fiber Laser according to claim 1, it is characterised in that：The optical fiber filter For Lyot type optical fiber filter, has the function of wavelength tuning, which includes optoisolator and high birefringence micro-nano light Fibre, the output end of Polarization Controller are connected with the input terminal of optoisolator, and the output end of optoisolator passes through high birefringence micro-nano Optical fiber is connected with the input terminal of photo-coupler.

3. a kind of Tunable Multi-wavelength Fiber Laser according to claim 2, it is characterised in that：The optical fiber laser Laser modeling in resonant cavity of fibre-optical laser is realized by high birefringence micro-nano fiber in resonant cavity.

4. a kind of Tunable Multi-wavelength Fiber Laser according to claim 2, it is characterised in that：The high birefringence is micro- Nano fiber is made of high-birefringence polarisation-maintaining optical fiber fused biconical taper, carries out laser intracavity modal using the mode-interference in tapered fiber Selection.

5. a kind of Tunable Multi-wavelength Fiber Laser according to claim 2, it is characterised in that：The high birefringence is micro- Nano fiber is distributed with non-circular symmetrical refraction rate, and the high birefringence micro-nano fiber includes silica-base material region (7) and stressed zone (8)。

6. a kind of Tunable Multi-wavelength Fiber Laser according to claim 5, it is characterised in that：Light field is in high birefringence Multiple modes, basic mode and higher order mode are excited in micro-nano fiber in transmission process, and there are different effective refractive indexs, with optical fiber Diameter becomes smaller, and more and more higher order modes are ended, finally only HE₁₁Mould, TE₀₁Mould and TM₀₁Mould can pass through uniform lumbar region, and In TE₀₁Mould and TM₀₁The interference spectrum with modeling effect is formed between mould.

7. a kind of Tunable Multi-wavelength Fiber Laser according to claim 6, it is characterised in that：

TE₀₁Mould and TM₀₁The normalized output luminous intensity T of mould can be expressed as：

WhereinIt is TE₀₁And TM₀₁Between phase difference, λ is wavelength, Δ L=l (n₁-n₂) it is TE₀₁And TM₀₁Between Optical path difference, by their effective refractive index n₁And n₂It is determined with the length l of polarization maintaining optical fibre cone waist.

8. a kind of Tunable Multi-wavelength Fiber Laser according to claim 1, it is characterised in that：The pump laser For semiconductor laser.