A wavelength tunable laser based on lens chromatic aberration

Abstract

The invention discloses a wavelength-tunable laser based on lens chromatic aberration, comprising: a pump source, a pump coupling optical system, a laser total reflection mirror, a laser gain medium, a dispersion focusing lens, and a laser output mirror. Pump light emitted by the pump source is focused by the pump coupling optical system into the laser gain medium; the laser gain medium absorbs the pump light, causing population inversion and generating laser gain, generating laser oscillation in a laser resonant cavity formed by the laser total reflection mirror and the laser output mirror, and outputting the laser through the laser output mirror; the distance between the dispersion focusing lens in the laser resonant cavity and the laser beam waist on one side of the laser gain medium is greater than the focal length of the dispersion focusing lens, thereby compressing the stable region of the distance between the dispersion focusing lens and the laser output mirror; the dispersion focusing lens and the laser output mirror located near the focal point of the dispersion focusing lens form a cat's eye retroreflector. Adjusting the distance between the dispersion focusing lens and the laser output mirror in the cat's eye retroreflector controls the feedback and loss of lasers of different wavelengths, thereby achieving laser wavelength tuning.

Description

Technical Field

[0001] The present invention relates to the field of lasers, and in particular to a wavelength tunable laser based on lens chromatic aberration. Background Art

[0002] In practical applications, it is often required that the output wavelength of a single laser light source can be changed as needed, that is, the laser wavelength can be tuned. A wide gain spectrum of the laser gain medium is a prerequisite for achieving wavelength-tunable laser output. In lasers with spatial optical path structures, devices such as dispersion prisms or gratings are often used to separate the optical paths corresponding to different wavelengths in space, and the feedback of other devices such as reflectors is used to achieve the effect of wavelength tuning. [1,2] ; You can also use devices such as etalon or birefringent filters to introduce wavelength-varying losses to achieve wavelength selective tuning [3,4] In fiber lasers, the method of applying stress or adjusting the temperature to wavelength selective devices such as fiber Bragg gratings and multimode interference filters can also be used to cause their reflection peaks or transmission peaks to drift, thereby achieving the effect of wavelength tuning. [5] .

[0003] The key to wavelength tuning lies in introducing controllable, wavelength-dependent losses. As mentioned earlier, this requires the use of devices such as dispersion prisms, gratings, etalons, or filters, which makes spectral alignment difficult. Due to the dispersion of optical materials—that is, the different refractive indices of the same material at different wavelengths—the effective focal length of a lens varies with wavelength, resulting in differences in the spatial optical paths of lasers of different wavelengths. This property can be exploited to introduce wavelength-dependent losses, achieving wavelength tuning. The optical path structure is very simple and easy to operate.

[0004] References

[0005] [1]

[0006] [2]T.Chung et al., Special laser wavelength generation using a volumeBragg gratingas Nd:GdVO4 laser mirror, Japanese Journal of Applied Physics, 49,062503(2010).

[0007] [3] T. Waritanant et al., Diode-pumped Nd:YVO4 laser with discrete multi-wavelength tunability and high efficiency, Opt. Lett. 42, 1149 (2017).

[0008] [4] YSTzeng et al., High-power tunable single-and multiwavelength diode-pumped Nd:YAP laser in the 4F3 / 2→4I11 / 2transition, Optics Express, 21, 26261 (2013).

[0009] [5] J. Zhang et al., 1.7-μm thulium fiber laser with all-fiber ringcavity, Optics Communications, 457, 124627 (2020). Summary of the Invention

[0010] The present invention provides a wavelength-tunable laser based on lens chromatic aberration. The present invention utilizes the property of the material's dispersion, which causes the actual effective focal length of the lens to vary with wavelength, to construct a cat's-eye retroreflector. By adjusting the distance between the lens and the reflector in the cat's-eye retroreflector, the feedback and loss of lasers of different wavelengths can be controlled, thereby achieving laser wavelength tuning. Details are described below:

[0011] A wavelength tunable laser based on lens chromatic aberration, the laser comprising: a pump source, a pump coupling optical system, a laser total reflection mirror, a laser gain medium, a dispersion focusing lens, and a laser output mirror.

[0012] The pump light emitted by the pump source is focused by the pump coupling optical system into the laser gain medium; the laser gain medium absorbs the pump light, causing population inversion and generating laser gain, generating laser oscillation in the laser resonant cavity composed of the laser total reflection mirror and the laser output mirror, and then outputting the laser light through the laser output mirror;

[0013] The distance between the dispersive focusing lens in the laser resonator and the laser beam waist on one side of the laser gain medium is greater than the focal length of the dispersive focusing lens, compressing the stable range of the distance between the dispersive focusing lens and the laser output mirror. The dispersive focusing lens and the laser output mirror located near its focal point form a cat's eye retroreflector. Adjusting the distance between the dispersive focusing lens and the laser output mirror in the cat's eye retroreflector controls the feedback and loss of lasers of different wavelengths, thereby achieving laser wavelength tuning.

[0014] Wherein, the dispersion focusing lens is made of glass material with large dispersion.

[0015] Furthermore, the laser gain medium is a laser crystal doped with ytterbium, titanium, or iron ions, such as iron-doped zinc selenide or titanium-doped sapphire; or a glassy or ceramic matrix gain medium in a bulk or fiber structure doped with rare earth ions; or other gain media with a wide emission spectrum.

[0016] The dispersion focusing lens adopts an aspheric surface shape for correcting spherical aberration to avoid the spherical aberration causing the optical paths of different transverse modes to be separated.

[0017] Furthermore, the pump coupling optical system is coated with a pump light wavelength anti-reflection film and is composed of one or more lenses.

[0018] The laser gain medium and the dispersion focusing lens are coated with a laser wavelength anti-reflection film, the laser total reflection mirror is coated with a pump light high transmittance and laser wavelength high reflection film, and the laser output mirror is coated with a laser wavelength partial transmission film.

[0019] Furthermore, the laser operates in continuous wave, modulation, Q-switched pulse, and mode-locked pulse modes.

[0020] The technical solution provided by the present invention has the beneficial effect that: the present invention can tune the laser wavelength by fine-tuning the position of the laser output mirror by simply adding a lens in the cavity, and the device is economical in cost, simple in structure, and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic structural diagram of a wavelength tunable laser based on lens chromatic aberration provided by the present invention;

[0022] Figure 2 Schematic diagram of the change of focal length of the dispersive focusing lens with wavelength;

[0023] Figure 3 Schematic diagram of the relationship between the stable region of the distance between the dispersive focusing lens and the output mirror and the distance between the laser total reflection mirror and the dispersive focusing lens;

[0024] Figure 4 Another structural schematic diagram of a wavelength tunable laser based on lens chromatic aberration provided by the present invention.

[0025] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0026] 1: Pump source; 2: Pump coupling optical system;

[0027] 3: Laser total reflection mirror; 4: Laser gain medium (using titanium sapphire crystal as an example);

[0028] 5: First dispersion focusing lens; 6: First laser output mirror;

[0029] 7: Collimating lens; 8: Second dispersion focusing lens;

[0030] 9: Second laser output mirror. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are described in further detail below.

[0032] A wavelength tunable laser based on lens chromatic aberration, the laser includes: a pump source, a pump coupling optical system, a laser total reflection mirror, a laser gain medium, a dispersion focusing lens, and a laser output mirror.

[0033] The pump light emitted by the pump source is focused into the laser gain medium through the pump coupling optical system; the laser gain medium absorbs the pump light, forming a population inversion and generating laser gain, generating laser oscillation in the laser resonant cavity composed of the laser total reflection mirror and the laser output mirror, and outputting the laser light through the laser output mirror.

[0034] The distance between the dispersive focusing lens in the laser resonant cavity and the laser beam waist on one side of the laser gain medium should be significantly larger than the focal length of the dispersive focusing lens, so that there is a larger spot size at the dispersive focusing lens, thereby producing a significant converging effect on the laser and compressing the stable range of the distance between the dispersive focusing lens and the laser output mirror.

[0035] In this case, the dispersive focusing lens and the laser output mirror located near its focus form a cat's eye retroreflector. The cat's eye retroreflector can only form a good retroreflection effect for the focused light beam, while the out-of-focus light beam will suffer obvious loss. Due to the material dispersion of the dispersive focusing lens, the actual focal positions of lasers of different wavelengths after being focused by the dispersive focusing lens are different. Therefore, when the laser output mirror is at a specific position, it can only provide good retroreflection, that is, feedback, for lasers of a single wavelength. At this time, it is only necessary to fine-tune the position of the laser output mirror back and forth, that is, the distance between it and the dispersive focusing lens, to achieve tuning of the laser wavelength.

[0036] Furthermore, the laser gain medium is a laser crystal doped with ions having a wide emission spectrum, such as Yb:KGW (ytterbium-doped potassium gadolinium tungstate), Ti:Al2O3 (titanium sapphire), or Fe:ZnSe (iron-doped zinc selenide); or a glassy or ceramic matrix gain medium in a bulk or fiber structure doped with rare earth ions, such as neodymium glass and erbium fiber, which has a wide emission bandwidth; or a gain medium having a wide emission spectrum, such as a dye or semiconductor.

[0037] Under the premise of ensuring light transmission in the laser band, the dispersion focusing lens should preferably use glass materials with larger dispersion. For example, flint glasses such as SF6, F9, and LLF1 are preferred in the visible and near-infrared bands to enhance the wavelength selection capability determined by dispersion.

[0038] Among them, the dispersive focusing lens should preferably adopt an aspheric surface type that corrects spherical aberration to avoid the problem that spherical aberration causes the separation of different transverse mode light paths, resulting in different transverse mode lasers of different wavelengths having a common actual focus, thereby oscillating at the same time and not producing a single wavelength laser output.

[0039] Furthermore, the pump coupling optical system is coated with a pump light wavelength anti-reflection film and is composed of one or more lenses.

[0040] The laser crystal and dispersion focusing lens are coated with laser wavelength anti-reflection coating, the laser total reflection mirror is coated with pump light high transmittance and laser wavelength high reflection coating, and the laser output mirror is coated with laser wavelength partial transmission coating;

[0041] Preferably, the laser operates in continuous wave, modulated, Q-switched pulse, or mode-locked pulse mode.

[0042] Example 1

[0043] The embodiment of the present invention provides a wavelength tunable laser based on lens chromatic aberration, the laser comprising: a pump source 1, a pump coupling optical system 2, a laser total reflection mirror 3, a laser gain medium titanium sapphire crystal 4, a first dispersion focusing lens 5, and a first laser output mirror 6;

[0044] The pump source 1 is a laser operating in pulse or continuous wave mode, with an emission wavelength within the absorption band of a laser gain medium, a titanium sapphire crystal 4. The pump coupling optical system 2 is coated with an antireflection coating for the pump light wavelength, focusing the pump light emitted by the pump source into the laser gain medium, the titanium sapphire crystal 4. The laser gain medium, the titanium sapphire crystal 4, is coated with an antireflection coating for both pump light and the laser wavelength band (650-1000nm), absorbing the pump light and generating laser gain. The laser total reflector 3 is a plano-concave reflector with a curvature radius of 50mm, coated on both sides with pump light antireflection coatings, and the concave surface facing the cavity is coated with a high-reflection coating for the laser wavelength band (650-1000nm). The first dispersive focusing lens 5 is a plano-convex or biconvex focusing lens coated with an antireflection coating for the laser wavelength band (650-1000nm). The first laser output mirror 6 is a plane reflector coated with a partial reflective coating (transmittance 1%-30%) for the laser wavelength band (650-1000nm).

[0045] For the plano-convex dispersion focusing lens 5 made of SF6 material with a nominal focal length of 25.0mm at 587.6nm, its actual focal length in the reflection band of 650-1000nm of titanium sapphire crystal is calculated to be 25.26-25.95mm, with a variation range of 0.69mm. For the same facing lens made of BK7 (K9) material, the actual focal length is 25.11-25.46mm, with a variation range of 0.35mm. Figure 2 When the laser resonant cavity length is 500mm, the stable range of the distance between the first dispersion focusing lens 5 and the first laser output mirror 6 is only 26.316-26.471mm, and the range is only 0.155mm. Figure 3 As shown. On the one hand, the stable range is significantly smaller than the actual focal length variation range, and the resonant cavity will inevitably not allow broadband laser oscillation. On the other hand, in such a narrow stable range, even a slight change in the spacing will cause the spot size and the corresponding loss to change dramatically. Only the wavelength where the actual focus strictly coincides with the output mirror can obtain good feedback, and then the laser wavelength can be tuned by fine-tuning the position of the first laser output mirror 6. When the distance between the first dispersive focusing lens 5 and the first laser output mirror 6 is large, the stable range is wider. For example, when the distance is 150mm, the stable range is 30-33.33mm, with a width of 3.33mm. At this time, the wider stable range does not easily produce a clear distinction between the losses of different wavelengths, and the wavelength selection effect is affected.

[0046] In summary, the advantages of the embodiments of the present invention are that they provide a wavelength tunable laser based on lens chromatic aberration, with only one lens added into the cavity, resulting in a simple structure.

[0047] Example 2

[0048] The embodiment of the present invention provides a wavelength tunable laser based on lens chromatic aberration, see Figure 4The laser includes: a pump source 1, a pump coupling optical system 2, a laser total reflection mirror 3, a laser gain medium titanium sapphire crystal 4, a collimating lens 7, a second dispersion focusing lens 8, and a second laser output mirror 9;

[0049] Among them, the pump source 1 is a laser operating in pulse or continuous wave mode, with an emission wavelength within the absorption band of the titanium sapphire crystal; the pump coupling optical system 2 is coated with a pump light wavelength anti-reflection film, which focuses the pump light emitted by the pump source into the laser gain medium titanium sapphire 4; the laser gain medium titanium sapphire crystal 4 is coated with an anti-reflection film for the pump light and laser wavelength band (650-1000nm), which absorbs the pump light and generates laser gain; the laser total reflector 3 is a plane reflector or a plano-concave reflector, with pump light anti-reflection film coated on both sides. The film is coated with a high-reflection film in the laser band (650-1000nm) on the flat or concave surface facing the cavity; the collimating lens 7 is a plano-convex or biconvex focusing lens, coated with an anti-reflection film in the laser band (650-1000nm); the second dispersion focusing lens 8 is a plano-convex or biconvex focusing lens, coated with an anti-reflection film in the laser band (650-1000nm); the second laser output mirror 9 is a plane reflecting mirror, coated with a partial reflection film in the laser band (650-1000nm) (transmittance 1%-30%).

[0050] The distance between collimating lens 7 and the laser beam waist on one side of the laser gain medium 4 in the resonant cavity is approximately equal to its focal length. In this case, the laser beam waist in the cavity is compressed, and the beam divergence is accelerated. The light spot reaching collimating lens 7 is collimated to a larger size before entering the second dispersive focusing lens 8. The stable range of the distance between the second dispersive focusing lens 8 and the second laser output mirror 9 is narrowed, thereby enhancing the discrimination between the loss of lasers of different wavelengths without requiring a longer resonant cavity length.

[0051] In summary, the advantage of the embodiments of the present invention is that by introducing a collimating lens, the laser spot reaching the second dispersive focusing lens 8 is increased, the stable range of the distance between the second dispersive focusing lens 8 and the second laser output mirror 9 is narrowed, and the wavelength selection capability is improved.

[0052] Unless otherwise specified, the embodiments of the present invention do not limit the models of the components. Any component that can perform the above functions may be used.

[0053] Those skilled in the art will understand that the accompanying drawings are only a schematic diagram of a preferred embodiment, and the serial numbers of the embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A wavelength tunable laser based on lens chromatic aberration, characterized in that: The laser includes: a pump source, a pump coupling optical system, a laser total reflection mirror, a laser gain medium, a dispersion focusing lens, and a laser output mirror. The pump light emitted by the pump source is focused by the pump coupling optical system into the laser gain medium; the laser gain medium absorbs the pump light, causing population inversion and generating laser gain, generating laser oscillation in the laser resonant cavity composed of the laser total reflection mirror and the laser output mirror, and then outputting the laser light through the laser output mirror; The distance between the dispersion focusing lens in the laser resonant cavity and the laser beam waist on one side of the laser gain medium is greater than the focal length of the dispersion focusing lens, thereby compressing the stable region of the distance between the dispersion focusing lens and the laser output mirror; the dispersion focusing lens and the laser output mirror located near its focus constitute a cat's eye retroreflector; By adjusting the distance between the dispersion focusing lens and the laser output mirror in the cat's eye retroreflector, the feedback and loss of lasers with different wavelengths can be controlled, thereby achieving tuning of the laser wavelength.

2. The wavelength tunable laser based on lens chromatic aberration according to claim 1, characterized in that: The dispersion focusing lens is made of glass material with large dispersion.

3. The wavelength tunable laser based on lens chromatic aberration according to claim 1, characterized in that: The laser gain medium is a laser crystal doped with ytterbium, titanium, or iron ions; or a glassy or ceramic matrix gain medium in a bulk or optical fiber structure doped with rare earth ions; or other gain media with a relatively wide emission spectrum.

4. The wavelength tunable laser based on lens chromatic aberration according to claim 1, characterized in that: The dispersion focusing lens adopts an aspheric surface type for correcting spherical aberration to avoid the spherical aberration causing the separation of different transverse mode light paths.

5. The wavelength tunable laser based on lens chromatic aberration according to claim 1, characterized in that: The pump coupling optical system is coated with a pump light wavelength anti-reflection film and is composed of one or more lenses.

6. The wavelength tunable laser based on lens chromatic aberration according to claim 1, characterized in that: The laser gain medium and the dispersion focusing lens are coated with laser wavelength anti-reflection films, the laser total reflection mirror is coated with pump light high transmittance and laser wavelength high reflection films, and the laser output mirror is coated with a laser wavelength partial transmission film.

7. The wavelength tunable laser based on lens chromatic aberration according to claim 1, characterized in that: The laser operates in continuous wave, modulation, Q-switched pulse, and mode-locked pulse modes.

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