CN101826700A - 2 mu m single mode fiber collimator with high coupling efficiency for semiconductor laser - Google Patents
2 mu m single mode fiber collimator with high coupling efficiency for semiconductor laser Download PDFInfo
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Abstract
一种用于2μm半导体激光器高效率耦合的2μm单模光纤准直器系统，根据自聚焦透镜的传光原理，针对于1/4节距的自聚焦透镜，对所设计的2μm单模光纤耦合器进行了优化设计。其系统由2μm测试光源、高耦合效率单模光纤准直器、光纤连接器和2μm高灵敏度激光功率计构成，此器件同时可用于平行光光纤耦合，满足了2μm相干激光多普勒测风雷达接收系统对回波进行光纤耦合的要求，可以实现接收系统的全光纤化和小型化，成功地解决了光轴对准调节困难和占据空间大的缺陷，本发明具有耦合效率高、可操作性强和重复性好的特点，且兼备相对成本低，易于实现的优势，在激光器到光纤耦合领域具有很高的实用价值。
A 2μm single-mode fiber collimator system for high-efficiency coupling of 2μm semiconductor lasers. According to the light transmission principle of the self-focusing lens, the 1/4-pitch self-focusing lens is used to couple the designed 2μm single-mode fiber The device has been optimized. Its system is composed of 2μm test light source, high coupling efficiency single-mode fiber collimator, fiber optic connector and 2μm high-sensitivity laser power meter. The requirements of optical fiber coupling for the echo in the receiving system can realize the all-fiber and miniaturization of the receiving system, and successfully solve the defects of difficult optical axis alignment adjustment and large space occupation. The present invention has high coupling efficiency and operability It has the characteristics of high strength and good repeatability, and has the advantages of relatively low cost and easy implementation, and has high practical value in the field of laser to fiber coupling.
Description
Technical Field
The invention relates to a single-mode fiber collimator with high coupling efficiency for a semiconductor laser, in particular to a single-mode fiber collimator for high-efficiency coupling of a 2-micrometer semiconductor laser.
Background
With the development of laser technology, the operating wavelength of a solid laser adopting thulium and holmium doping is about 2 μm, which is higher than the damage threshold of an Nd: YAG laser with the operating wavelength about 1 μm to human eyes, and a diode-pumped solid laser is a hot spot developed in recent decades and has the main characteristics that: the system does not need refrigeration, and has high pump energy coupling efficiency, strong stability, good beam quality, long service life and compact structure. And the diode-pumped solid laser with the diameter of about 2 mu m is the best matching of the coherent laser radar, and the development of the coherent laser radar with the diameter of 2 mu m is promoted in order to improve the resolution and the analysis precision of the perturbation measurement of the small-scale eddy current. At present, the U.S. the united states, the united kingdom, germany, france, the netherlands, irish, japan, etc. are devoted to studies on 2 μm solid-state lasers, detectors, optical systems and their performance tests and applications for measuring the earth's atmosphere, the earth's wind field, etc.
Therefore, 2 μm all-fiber coherent laser doppler wind-measuring radar has become one of the current research hotspots, and the coherent laser doppler wind-measuring radar, whether satellite-borne, airborne or vehicle-mounted, increasingly focuses on the requirement of miniaturization. Therefore, the accepted approach for achieving miniaturization by radar designers is: the optical path in the free space is replaced by the optical fiber, and the optical device in the free space and the adjusting mechanism thereof are replaced by a miniaturized optical fiber device. Meanwhile, the optical fiber can overcome nonlinear errors caused by environmental interference and some light splitting devices in a free space optical path, the requirements of full-fiber and miniaturization of the 2 mu m coherent laser Doppler wind measuring radar are not exceptional, the optical fiber device mainly used in the system is a single-mode optical fiber collimator, the device is generally applied to optical fiber devices such as optical device packaging single-mode output, light source-single-mode optical fiber coupling, single-mode optical fiber-photodiode coupling and optical isolator, and other fields, and the like, and has the characteristics of wide double-window working wavelength range, low insertion loss, firm gradient refractive index lens packaging, small size and the like, so that the device can realize full-fiber and miniaturization of the 2 mu m coherent laser Doppler wind measuring radar.
The single-mode fiber collimator is made of a low-cost gradient refractive index lens, the product has the characteristics of low insertion loss and low back reflection, the standard G652 single-mode fiber is adopted for packaging, and the diameter of an output beam is about 0.5 mm. The method is widely applied to systems matched with optical devices such as laser diodes, photodiode detectors, acousto-optic modulators and the like. Fiber collimators may be used in pairs to couple light into/out of other optical devices. Therefore, the fiber collimator is an ideal device for fiber coupling packaging of other devices.
The working principle of the optical fiber collimator is shown in fig. 1, and the Collimated Beam Diameter (BD) and the total Divergence Angle (DA) of the optical fiber collimator are related to the focal length (f) of the lens, the core Diameter (a) of the optical fiber, and the Numerical Aperture (NA) of the optical fiber. The formula is as follows:
BD(mm)＝2f(mm)NA
DA(mrad)＝a(μm)/f(mm)
wherein, NA: the numerical aperture of the optical fiber; a: the core diameter of the optical fiber; BD: the diameter of the beam; DA: a divergence angle; f: the focal length of the lens.
However, since the 2 μm band belongs to a special laser band recognized internationally, the coupling lens material with high transmittance is less and the processing is difficult, although the visible light and near infrared band single-mode fiber coupling technology is mature at home and abroad, and especially the optical fiber collimator { especially the product in the communication band } in the band is commercialized at home and abroad, the 2 μm band laser-to-single-mode fiber collimator has not been reported yet.
At present, the lasers in the 2 μm all-fiber coherent laser Doppler wind radar system developed by researchers at home and abroad all adopt a mode of injecting seed sources into an amplification level, while general seed sources are all semiconductor lasers with good beam quality, and the semiconductor lasers are subjected to optical fiber coupling by adopting a common lens, so that the defects that the optical axis alignment adjustment between the lens and a fiber core with the diameter of 9 μm is very difficult, and simultaneously, the lens and the fiber core of the optical fiber are respectively subjected to coupling adjustment by an optical adjustment frame, so that a certain working distance is ensured by the two optical adjustment frames, the occupied space is very large, and the requirement on miniaturization of the 2 μm all-fiber coherent laser Doppler wind radar is very unfavorable.
Disclosure of Invention
Therefore, based on the requirement of full fiber miniaturization and miniaturization of 2 μm coherent laser Doppler anemometry radar, the invention aims to provide a 2 μm single-mode fiber collimator.
On one hand, the invention provides a 2 μm single-mode fiber collimator for high-efficiency coupling of a 2 μm semiconductor laser, which is characterized in that: the 2 mu m single-mode fiber collimator with high-efficiency coupling of the 2 mu m semiconductor laser comprises a 2 mu m semiconductor test light source, a high-coupling-efficiency single-mode fiber collimator, a fiber connector and a high-sensitivity 2 mu m laser power meter. The high-coupling-efficiency single-mode optical fiber collimator comprises a gradient refractive index lens, a glass sleeve, a metal sleeve, an optical fiber contact pin and a single-mode optical fiber pigtail. The single-mode fiber pigtail penetrates into the center of the contact pin and is fixed, after the surface of the contact pin is polished, the gradient index lens and the fiber contact pin are placed into the glass sleeve together to achieve alignment, and meanwhile, the metal sleeve is sleeved outside the glass sleeve to play a role in protection. The gradient refractive index lens and the end face of the optical fiber insertion pin are connected in a bevel and spherical mode, the central portion of the contact end keeps a spherical surface, and other portions of the end face are processed into bevels, so that the included angle between the end face and the axis of the optical fiber is smaller than 90 degrees, the contact area can be increased, and optical coupling is tighter. When the included angle between the end face and the optical fiber axis is 8 degrees, the insertion loss is less than 0.5dB, and the reflection loss can reach 68dB after the inclined plane is polished. Meanwhile, the outer component of the pin is made of metal or non-metal material, the inclined surface of the pin contacting with the gradient index lens must be ground, and the other end of the pin usually adopts a bending limiting component to support the optical fiber or the optical fiber flexible cable to release stress. The 2 μm gradient index lens used had a focal length of 1.3mm, a length of 7.7mm, a radius of 1.8mm and a focusing constant of 0.2mm-1The coupling efficiency was 26.8%. The 2 μm semiconductor test light source emits laser under the action of the temperature controller, and 2 μm single-mode fiber is arranged in the direction of the laser optical axis for collimationThe device couples the emitted laser, and the output end of the 2-micron single-mode optical fiber collimator is connected with the 2-micron laser power meter through the optical fiber connector, so that the reading of the laser power coupled into the 2-micron optical fiber core can be observed through the 2-micron laser power meter. The 2 mu m semiconductor test light source emits laser under the action of the temperature controller, the 2 mu m single-mode fiber collimator is arranged in the optical axis direction of the laser to couple the emitted laser, and the output end of the 2 mu m single-mode fiber collimator is connected with the 2 mu m laser power meter through the fiber connector, so that the laser power coupled into the 2 mu m fiber core can observe and read through the 2 mu m laser power meter.
In the above 2 μm single-mode fiber collimator, the gradient index lens is made of a transparent material, and the transparent material includes a silicon wafer, oxide glass, and the like.
In the above 2 μm single-mode fiber collimator, the shape of the incident end surface of the gradient index lens is generally a spherical surface, a plane, an ellipsoid, a conical surface, or a wedge surface.
Furthermore, two end faces of the gradient refractive index lens are plated with antireflection films for increasing the transmission efficiency of the light beam emitted by the test light source.
In the above 2 μm single-mode fiber collimator, the glass sleeve is made of two half-combined, fastened cylindrical members of special materials, including K9 glass, fused silica, ceramic, transparent plastic.
In the above 2 μm single-mode fiber collimator, the metal sleeve is made of a metal material, and the metal material includes gold, copper, aluminum, steel, and the like.
On the other hand, the designed 2-micron single-mode fiber collimator is optimized by using professional ZAMEX software.
The invention skillfully introduces a 2 mu m single-mode fiber collimator into a system for coupling a semiconductor laser with a single-mode fiber, and provides an idea of carrying out fiber coupling on 2 mu m laser with a large divergence angle and safety to human eyes by a graded index lens.
By adopting the technical scheme, the preparation of the 2-micron single-mode fiber collimator can be realized, the coupling efficiency of actual test can reach 25.4 percent to the maximum extent, the requirement of a 2-micron coherent laser Doppler wind measuring radar receiving system on fiber coupling of echo waves is met, full fiber and miniaturization of the receiving system are realized, and the defects of difficult adjustment of optical axis alignment and large occupied space are successfully overcome.
Drawings
Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein:
FIG. 1 is a schematic diagram of the operating principle of a single-mode fiber collimator;
FIG. 2 is a schematic view of the focusing features of a self-focusing lens;
FIG. 3 is a graph showing the relationship between the coupling efficiency and various parameters between a self-focusing lens and a single-mode optical fiber;
FIG. 4 is a schematic diagram of a general structure of a 2 μm single-mode fiber collimator;
FIG. 5 is a schematic diagram of a gradient index lens configuration;
FIG. 6 is a schematic diagram of an optical fiber stub configuration;
FIG. 7 is a schematic view of a glass sleeve structure;
FIG. 8 is a schematic view of a gold plated ferrule configuration;
FIG. 9 is a schematic diagram of a 2 μm semiconductor laser structure;
FIG. 10 is a schematic structural diagram of a 2 μm semiconductor laser fiber coupling test system.
Detailed Description
The single-mode optical fiber collimator consists of mainly self-focusing lens and single-mode optical fiber, the refractive index of the self-focusing rod lens is distributed in gradient mode, and the central refractive index is n0The refractive index at the off-axis r is:
wherein: n is0Is the axis index, r is the self-focusing lens radius,
is the focus constant of the autofocus lens. The focal length of the self-focusing lens is:
wherein: z is the length of the self-focusing lens.
From equation (2), since A is a function of wavelength, f is also a function of wavelength. As shown in fig. 2, at a given wavelength, if z is too long, the focal point is in the lens end plane; conversely, if z is too short, the focal point is outside the lens end face. Therefore, the length error of the lens inevitably affects the beam coupling effect, which is one of the main causes of collimator loss.
The coupling system of 2 μm semiconductor laser to single mode fiber is composed of single mode fiber and 1/4-pitch self-focusing lens, the purpose of using 1/4-pitch self-focusing lens is to facilitate machining, and the focus of 1/4-pitch self-focusing lens is on the end face to facilitate coupling debugging. The coupling principle between them is similar to that of a common lens, and the length of the used self-focusing lens is as follows:
wherein: p is the pitch of the self-focusing lens. Since P is determined from the propagation of the meridional fiber following a sinusoidal path under paraxial approximation conditions. Therefore, the z value calculated by equation (3) is inaccurate, which causes coupling loss and aberration of the self-focusing lens also causes coupling efficiency to decrease and device loss to increase.
When the length of the self-focusing lens is 1/4 pitches, i.e. <math><mrow><msqrt><mi>A</mi></msqrt><mi>z</mi><mo>=</mo><mi>π</mi><mo>/</mo><mn>2</mn><mo>,</mo></mrow></math> According to the mode-field coupling theory, the optical field distribution is phi1Gauss beam and phi2The coupling efficiency of the gaussian beam of (1) is:
by applying the Gaussian beam transmission theory and further deducing, the coupling efficiency between the self-focusing lens and the single-mode fiber under 3 conditions of off-axis coupling, deflection angle coupling and spacing coupling between the self-focusing lens and the single-mode fiber can be respectively obtained.
(1) The off-axis coupling between the self-focusing lens and the single-mode fiber is as follows:
(2) the deflection angle coupling between the self-focusing lens and the single-mode fiber is as follows:
(3) the distance coupling between the self-focusing lens and the single-mode fiber is as follows:
wherein,
here, ω0λ is the mode field radius and wavelength of the gaussian beam, respectively; d is the distance between the self-focusing lens and the single-mode fiber; x is the number of0Is the interaxial distance between the self-focusing lens and the single-mode fiber; θ is the angle between the self-focusing lens and the single-mode fiber.
FIG. 3 is a graph showing the relationship between the coupling efficiency and each parameter between the self-focusing lens and the single-mode optical fiber. The MATLAB is utilized to simulate the relationship between the coupling efficiency and each parameter between the self-focusing lens and the single-mode fiber, and is shown in FIG. 3, wherein FIG. 3(a) is the relationship between the coupling efficiency and the distance between the axes thereof; FIG. 3(b) is a graph of coupling efficiency versus its angle; fig. 3(c) shows the coupling efficiency as a function of its pitch, from which it can be seen that the coupling efficiency decreases rapidly with increasing parameters, and that the coupling efficiency is insensitive to pitch coupling relative to the other two couplings.
Fig. 4 is a general structural diagram of a 2 μm single-mode fiber collimator. The fiber collimator includes a fiber pigtail 401, a fiber stub 402, a glass sleeve 403, a gradient index lens 404, a metal sleeve 407, and a fiber connector 406. According to the light transmission principle of the self-focusing lens, the designed 2-micron single-mode fiber collimator is optimally designed for the self-focusing lens with 1/4 pitches. When the converged light is input from one end face of the self-focusing lens, the converged light is converted into a parallel optical fiber or a converging optical fiber after passing through the self-focusing lens. The single-mode optical fiber collimator is a basic optical device in an optical fiber communication system and an optical fiber sensing system, and is used for collimating or focusing transmitted Gaussian beams so as to improve the coupling efficiency between a light source and an optical fiber. The single-mode optical fiber collimator is characterized in that 2 mu m semiconductor laser with a large divergence angle can be coupled into a single-mode optical fiber.
For a 2 μm semiconductor laser, if the 2 μm semiconductor laser is directly coupled with a single mode fiber, the coupling efficiency will be reduced because the elliptical laser mode field and the circularly symmetric fiber mode field are mismatched. Of course, the loss due to mode mismatch can be reduced by increasing the distance between the laser end face and the fiber end face. However, due to the high divergence of the laser light, the wavefront of the gaussian laser beam becomes more curved while increasing the working distance, which results in phase mismatch between the curved laser beam wavefront and the planar fiber beam wavefront. Also resulting in a reduction in coupling efficiency. Therefore, to improve the coupling efficiency, not only the coupling loss due to the mismatch of mode field radii but also the coupling loss due to the phase mismatch should be reduced. Thus, integrating a gradient index lens into a flat-ended fiber endface, the graded index of the gradient index lens 404 is primarily used to focus the diffused beam at the fiber core diameter to improve coupling efficiency while increasing working distance. Not only the mismatch of the mode field is overcome, but also the loss caused by the mismatch of the phase position is overcome.
Since 2 μm is a special laser band recognized at home and abroad, lens materials with high transmittance at home and abroad are very rare, and the cost is very high when the high transmittance material is found and processed according to requirements. Therefore, after all factors are considered in a compromise way, the single-mode optical fiber collimator is prepared by using a special oxide glass gradient index lens which is a material processed and produced by the company Limited for communication technology of Simian in China, and the material has the characteristics of high transmittance in a 2 mu m waveband and easiness in processing. The self-focusing lens required for preparing the collimator is designed and processed by theoretical calculation and optimization by using ZEMAX software, and the optimized design parameters are shown in Table 1.
TABLE 1 optimized design parameters of collimators
The 2 μm semiconductor laser was coupled to the fiber through the self-focusing lens to calibrate the effective value of the coupling efficiency of the prepared single-mode fiber collimator, and the coupling test apparatus is shown in fig. 10.
The fibers used in the test were all Corning SMF-28 single mode fibers, with a 2 μm optical power meter model of 3A-FS, with a measurement range of 60 μ W to 3W, and other instrument parameters used in the test are shown in tables 2 and 3.
TABLE 22 μm Single mode semiconductor laser parameters
TABLE 32 μm Single mode fiber parameters and test data
The output power of 2 mu m single-mode semiconductor laser is measured by a power meter and is set as a reference, then the 2 mu m semiconductor laser is fixed on a six-dimensional adjusting frame, a gradient refractive index lens 404 and an optical fiber inserting needle 402 are fixed on a pressing plate of the two-dimensional adjusting frame through a sleeve 403 and are not moved, the six-dimensional adjusting frame is carefully adjusted under the monitoring of a microscope, so that the output optical power meter of an optical fiber connector 406 at the tail part of the optical fiber inserting needle 402 is maximum, the maximum coupling efficiency can be calculated by comparing the maximum output power with the output power of the laser, the maximum coupling efficiency is 25.4 percent through a large number of tests and is close to the optimized theoretical value, and the test result shows that the optimization result is correct.
Fig. 5 is a schematic view of a gradient index lens structure. The gradient index lens includes a laser entrance face 502 and a bevel 503 that contacts the ferrule. The laser incidence surface 502 of the gradient index lens is plated with an antireflection film for increasing the transmission efficiency of laser emitted by a laser, the gradient index lens and the end surface of the optical fiber pin are connected in a bevel and spherical mode, the central part of the contact end keeps a spherical surface, and other parts of the end surface are processed into a bevel 503 to enable the included angle between the end surface and the axis of the optical fiber to be smaller than 90 degrees, so that the contact area can be increased, and the optical coupling is tighter. When the included angle between the end face and the optical fiber axis is 8 degrees, the insertion loss is less than 0.5dB, and the reflection loss can reach 68dB after the inclined surface 503 is polished. The 2 μm gradient index lens used had a focal length of 1.3mm, a length of 7.7mm, a radius of 1.8mm and a focusing constant of 0.2mm-1The coupling efficiency was 26.8%. Meanwhile, the inclined surface 503 is also plated with an antireflection film for increasing the transmission efficiency of the laser emitted by the laser. The gradient index lens is made of a columnar transparent material. The transparent material can be silicon chip, oxide glass and the like. The gradient index lens entrance surface may be a plane, or may be designed as a spherical surface, an ellipsoid, a conical surface, a wedge surface, etc. according to specific needs, which is well understood by those skilled in the art.
FIG. 6 is a schematic diagram of a fiber stub configuration. The optical fiber pin comprises an optical fiber core protective glass rod 601, an optical fiber core 602, an end face 603 in contact with a gradient index lens, an optical fiber pigtail 604 and an optical fiber connector 605. The optical fiber contact pin and the end face of the gradient refractive index lens are connected in a bevel and spherical mode, the central part of the contact end keeps a spherical surface, and other parts of the end face are processed into a bevel, so that the included angle between the end face and the axis of the optical fiber is smaller than 90, the contact area can be increased, and the optical coupling is tighter. When the included angle between the end face and the optical fiber axis is 8 degrees, the insertion loss is less than 0.5dB, and the reflection loss can reach 68dB after the inclined plane is polished. Meanwhile, the outer component of the pin is made of metal or non-metal material, the inclined surface of the pin contacting with the gradient index lens must be ground, and the other end of the pin usually adopts a bending limiting component to support the optical fiber or the optical fiber flexible cable to release stress. The protective glass rod 601 not only has the function of fixing the optical fiber core, but also has the function of facilitating the coupling adjustment of the gradient index lens and the optical fiber core because the outer diameter of the protective glass rod 601 is manufactured to be matched with the outer diameter of the gradient index lens. The optical fiber is typically a single mode fiber of the SMF-28 type. The optical fiber connector 605 is generally of an FC/APC type, and can be made into a connector-free type, an FU-FC/UPC type, an SU-SC/UPC type and an SA-SC/APC type according to requirements, an optical fiber core of the optical fiber connector 605 is generally protected by a ceramic rod, an end face of the optical fiber core is generally provided with an 8-degree inclination angle, backward scattering light is still isolated, and insertion loss is reduced, so that the insertion loss is less than 0.5dB, reflection loss after the inclination surface is polished can reach 68dB, the requirement on processing precision of a pin and a glass sleeve is high in order to align an optical fiber as accurately as possible, and the method is well understood by a person skilled in the art.
Fig. 7 is a schematic structural view of the glass sleeve. The glass sleeve is typically made of a transparent material, such as K9 glass, quartz, ceramic, transparent plastic, etc. Fig. 7(a) shows a longitudinal cross-sectional view of the glass sleeve, and fig. 7(b) shows a transverse cross-sectional view of the glass sleeve, including an outer surface 701 and an inner surface 702. The aperture of the inner surface 702 is matched with the diameter of the gradient index lens, and the glass sleeve is used for fixing the gradient index lens and the optical fiber inserting needle inside the glass sleeve 703, so that the gradient index lens and the optical fiber can be conveniently coupled and adjusted according to a certain working distance. Therefore, the requirements for the surface processing quality of the glass sleeve are relatively high, so that the laser can be efficiently coupled into the optical fiber core through the gradient index lens.
Fig. 8 is a schematic structural view of a gold-plated ferrule. The gold-plated sleeve is generally made of a metallic material, such as gold, copper, aluminum, steel, and the like. Fig. 8(a) shows a longitudinal cross-sectional view of the glass sleeve, and fig. 8(b) shows a transverse cross-sectional view of the glass sleeve, including an outer surface 801 and an inner surface 802. The aperture of the inner surface 802 is matched with the outer diameter of the glass sleeve, and the gold-plated sleeve is used for protecting the glass sleeve and enabling the glass sleeve not to be broken easily under the action of external force. The gold-plated sleeve mainly plays a role in protecting internal elements, so that the requirement on the processing precision of the gold-plated sleeve is low, and metal sleeves with various apertures can be manufactured according to specific requirements.
Fig. 9 is a schematic view of a 2 μm semiconductor laser structure. The 2 μm semiconductor laser includes three pins, pin 902, pin 903, and pin 904, and also includes a light emitting surface 901 of the semiconductor laser. The light emitting surface 901 of the semiconductor laser is used for emitting laser emitted by the semiconductor laser along the optical axis direction, the light emitting surface 901 is packaged according to certain requirements when in use, a layer of transparent material is arranged on the light emitting surface 901 to be made into a dustproof window sheet, and the transparent material is quartz, K9 glass, a silicon chip and the like. The three pins 902, 903 and 904 are typically the anode, cathode and ground of a semiconductor laser, and the order of anode, cathode and ground may be different for different 2 μm semiconductor lasers.
The 2-micron semiconductor laser is generally arranged on a specially-made semiconductor laser mounting rack according to a pin sequence, the 2-micron semiconductor laser can work under the action of a temperature controller, the temperature controller is provided with two output ports, one output port is a current output port, and the current output port provides working current for the 2-micron semiconductor laser; the other output terminal is a temperature control terminal, which precisely controls the operating temperature of the 2 μm semiconductor laser, and the temperature control precision is typically 0.001 °, so as to keep the output wavelength of the laser stable, as will be understood by those skilled in the art.
FIG. 10 is a schematic structural diagram of a 2 μm semiconductor laser fiber coupling test device. The coupling test device comprises a semiconductor laser temperature controller 1001, a semiconductor laser mounting rack 1002, a 2-micrometer semiconductor laser 1003, a gradient refractive index lens 1004, a glass sleeve 1005, an optical fiber inserting needle 1006, a high-sensitivity laser power meter 1007 and an optical fiber pigtail 1008. The semiconductor laser 1003 is arranged on a semiconductor laser mounting rack 1002, and the semiconductor laser mounting rack 1002 is connected with a semiconductor laser temperature controller 1001. The graded index lens 1004 and the optical fiber stub 1006 are fixed together according to the working distance by a glass sleeve 1005, the optical fiber connector at the rear end of the optical fiber stub is connected with a 2 μm high sensitivity optical power meter, and for coupling adjustment and testing of the coupling performance of the prepared 2 μm optical fiber collimator, the glass sleeve is usually fixed on a two-dimensional adjusting frame, and the semiconductor laser mounting frame 1002 is fixed on a six-dimensional adjusting frame and is placed at the working distance of the graded index lens 1004.
After all the devices are installed, the semiconductor laser temperature controller 1001 and the power supply of the 2 μm high-sensitivity laser power meter 1007 are turned on, and at this time, the numerical value and the position of the maximum coupling efficiency can be found by observing the reading of the 2 μm high-sensitivity laser power meter 1007 and finely adjusting the position optical system of the 2 μm semiconductor laser 1003 and the gradient refractive index lens 1004.
It should be noted that, before the test, the relationship between the output power of the 2 μm semiconductor laser 1003 and the operating current is calibrated and recorded, so that when the maximum reading position of the 2 μm high-sensitivity laser power meter 1007 is found, the maximum coupling efficiency of the 2 μm single-mode fiber collimator can be calculated.
Finally, the designed single-mode fiber collimator calibrates the effective value of the coupling efficiency through testing, and the testing result shows that the optimization design result of the self-focusing lens is feasible and reliable, so that the method has important guiding significance for the next 2-micron single-mode fiber collimator packaging and product production, and lays a foundation for the miniaturization development of the 2-micron coherent laser Doppler wind radar.
Certainly, according to the needs in practical application, the 2 μm single-mode fiber collimator of the present invention can also be used for coupling a fiber laser and a solid laser, and since the beam quality of the output laser of the two lasers is very good, the coupling efficiency of the two lasers will be higher than that of a semiconductor laser with a large divergence angle, and it can be known that the coupling efficiency of the two lasers is generally over 80% after being optimized by ZEMAX software. Finally, it should be noted that the embodiments in the above drawings are only used for illustrating the structure and technical solution of the single mode fiber collimator of the present invention, but not for limitation. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (9)
1. A2 μm single mode fiber collimator for high efficiency coupling of 2 μm semiconductor laser is characterized in that: the 2 mu m single-mode fiber collimator with the high-efficiency coupling of the 2 mu m semiconductor laser comprises a 2 mu m semiconductor test light source, a high-coupling-efficiency single-mode fiber collimator, a fiber connector and a high-sensitivity 2 mu m laser power meter, wherein the high-coupling-efficiency single-mode fiber collimator comprises a gradient refractive index lens, a glass sleeve, a metal sleeve, a fiber inserting needle and a single-mode fiber tail fiber. The single-mode fiber pigtail penetrates into the center of the contact pin and is fixed, after the surface of the contact pin is polished, the gradient index lens and the fiber contact pin are placed into the glass sleeve together to achieve alignment, and meanwhile, the metal sleeve is sleeved outside the glass sleeve to play a role in protection. The gradient refractive index lens and the end face of the optical fiber insertion pin are connected in a bevel and spherical mode, the central portion of the contact end keeps a spherical surface, and other portions of the end face are processed into bevels, so that the included angle between the end face and the axis of the optical fiber is smaller than 90 degrees, the contact area can be increased, and optical coupling is tighter. When the included angle between the end face and the axis of the optical fiber is 8 degrees, the insertion loss is less than 0.5dB, the reflection loss can reach 68dB after the inclined plane is polished, and the influence of the backward scattering light on the laser is well isolated. Meanwhile, the outer component of the pin is made of metal or non-metal material, the inclined surface of the pin contacting with the gradient index lens must be ground, and the other end of the pin usually adopts a bending limiting component to support the optical fiber or the optical fiber flexible cable to release stress. The 2 μm gradient index lens used had a focal length of 1.3mm, a length of 7.7mm, a radius of 1.8mm, a focusing constant of 0.2mm-1, and a coupling efficiency of 26.8%. The 2 mu m semiconductor test light source emits laser under the action of the temperature controller, the 2 mu m single-mode fiber collimator is arranged in the optical axis direction of the laser to couple the emitted laser, and the output end of the 2 mu m single-mode fiber collimator is connected with the 2 mu m laser power meter through the fiber connector, so that the laser power coupled into the 2 mu m fiber core can observe and read through the 2 mu m laser power meter.
2. The 2 μm single mode fiber collimator system of claim 1, wherein the gradient index lens is made of a transparent material.
3. The 2 μ ι η single mode fiber collimator system of claim 2, wherein the transparent material comprises silicon, oxide glass.
4. The 2 μm single mode fiber collimator system according to claim 2, wherein the gradient index lens has an incident end surface in a shape of a sphere, a plane, an ellipsoid, a cone, or a wedge.
5. The 2 μm single-mode fiber collimator system according to claim 2, wherein both end faces of the gradient index lens are coated with antireflection films for increasing transmission efficiency of the emission beam of the test light source.
6. The 2 μm single mode fiber collimator system of claim 1, wherein the glass sleeve is a two-piece composite, solid cylindrical member made of a special material.
7. The 2 μm single mode fiber collimator system according to claim 6, wherein the special material comprises K9 glass, fused silica, ceramic, transparent plastic.
8. The 2 μm single mode fiber collimator system of claim 1, wherein the metal sleeve is made of a metal material.
9. The 2 μm single mode fiber collimator system according to claim 8, wherein the metal material comprises gold, copper, aluminum, steel, etc.
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