阅读说明：本技术 一种短距多波长多模通信系统 (Short-distance multi-wavelength multimode communication system ) 是由 成煜 袁同乐 苑立波 陈明 于 2020-12-20 设计创作，主要内容包括：一种短距多波长多模通信系统,包括多支波长在850.0nm到950.0nm之间的激光器,片上集成的多路驱动脉冲调制电路,拉锥偏置注入耦合器,50/125μm多模光纤,光栅型解复用器,多个光电探测器和数据接收处理器组成的系统。多个波长的激光器经过片上集成的多路驱动电路调制后,分别耦合到多根标准50/125μm多模光纤进行传输,通过拉锥偏置注入耦合器连接到一根50/125μm宽带多模光纤中,完成多模光纤波分复用过程,拉锥偏置注入使激光中的模式色散显著减少,信号带宽增大,支持更高码速传输,然后利用光栅型解复用器将不同波长分开,并利用多个光电探测器探测接收光信号并将其转变成电信号,最后由数据接收处理器完成信号的处理过程。本发明可实现在宽带多模光纤中完成至多8个波长,单波20Gbps的传输,传输距离100.0～1000.0m。(A short-distance multi-wavelength multimode communication system comprises a plurality of lasers with the wavelength of 850.0nm to 950.0nm, a multi-path driving pulse modulation circuit integrated on a chip, a tapered bias injection coupler, 50/125 mu m multimode optical fibers, a grating type demultiplexer, a plurality of photoelectric detectors and a data receiving processor. The multi-wavelength laser is modulated by a multi-path driving circuit integrated on a chip, and then is respectively coupled to a plurality of standard 50/125 mu m multimode fibers for transmission, and is connected to a 50/125 mu m broadband multimode fiber through a tapered bias injection coupler to complete the multimode fiber wavelength division multiplexing process. The invention can realize the transmission of at most 8 wavelengths and single wave 20Gbps in the broadband multimode fiber, and the transmission distance is 100.0-1000.0 m.)

1. A short-range multi-wavelength multimode communication system, the system comprising:

lasers, which are multiple VECSEL lasers or other lasers with wavelengths between 850.0nm and 950.0 nm;

the control circuit is a multi-path driving pulse modulation circuit integrated on a chip, and the front edge and the rear edge of a pulse are not more than 20 ps;

an optical fiber transmission device: the multi-branch lasers are coupled to a plurality of standard 50/125 mu m multimode fibers and connected to 50/125 mu m multimode fibers or 50/125 mu m broadband multimode fibers through a tapered bias injection coupler.

And the grating type demultiplexer, the photoelectric detector and the data receiving processor.

2. The laser according to claim 1 having an emission wavelength of 850.0nm to 950.0nm, wherein the wavelength interval between different lasers is 50.0nm, or 25.0nm, or 16.7nm, or more preferably 12.5nm, depending on the number of lasers used.

3. The laser of claim 1, wherein: the output of each laser is light with a plurality of modes, the emission wavelength is non-monochromatic light, the spectral line width is less than or equal to 2.0nm, the minimum value of each pulse width is about 50.0ps, and the pulse width is adjustable.

4. The control circuit of claim 1, wherein: the forward driving voltage is more than or equal to 0.4V, the driving current is less than or equal to 80.0mA, the current ripple is less than or equal to 0.02mA, the bias current is less than or equal to 5.0mA, the matching resistance value is more than or equal to 15.0 omega, the constant power automatic control function is realized, and the total output speed is less than or equal to 160 Gbps.

5. The optical fiber transmission device of claim 1, wherein: the tapered biased injection coupler and the 50/125 μm multimode fiber were connected using a movable connector.

6. The tapered offset injection coupler of claim 1 wherein: the optical fiber comprises 8 multimode optical fibers, a part of cladding is eliminated, coupling tapering is stacked, the taper is 1.5-2.0 degrees, the length of a tapering region is 3.0-4.0 mm, the diameter of an initial inscribed circle of the tapering region is 300.0-405.0 micrometers, the diameter of an inscribed circle at the tail end of the tapering region is 110.0-120.0 micrometers, and the distance between fiber cores is 15.0-28.7 micrometers. Each core diameter after tapering was (15. + -. 0.3) μm.

7. The system of claim 1, supporting transmission of no more than 8 wavelengths in standard 50/125 μm multimode fiber, more preferably 50/125 μm broadband multimode fiber, single wave no more than 20Gbps, transmission distance 100.0-250.0 m; or the single wave is not more than 10Gbps, and the transmission distance is 200.0-500.0 m; or the single wave is not more than 5Gbps, and the transmission distance is 400.0-1000.0 m.

(I) technical field

The invention relates to a short-distance multi-wavelength multi-mode communication system which can be used for short-distance, large-capacity and high-speed communication and belongs to the field of multi-mode optical fiber short-distance communication and the technical field of multi-mode wavelength division multiplexing.

(II) background of the invention

Short-range, high-capacity communications have traditionally been multi-mode communications, such as data centers and LANs. The short-distance multimode communication has the advantages of low price of matched equipment, relatively no loss of coupling, small bending loss and the like,

the gradient graded multimode fiber is matched with an LED or VECSEL laser, the bandwidth is within 100 MHz-10 GHz, and the transmission distance is within 50.0-500.0 m.

Lasers, which are multiple VECSEL lasers or other lasers with wavelengths between 850.0nm and 950.0nm, are the most preferred VECSEL lasers. Currently high-speed multimode communication basically employs VECSEL lasers. A VECSEL laser is an F-P laser with the light exit direction perpendicular to the cavity surface. Compared with an edge-emitting laser, the VECSEL laser has the advantages of small volume, circular output light spots, single longitudinal mode output, small threshold current, low price, easy integration into a large-area array and the like.

Multimode parallel communication and wavelength division multiplexing systems have become popular in recent years. A parallel communication module of, for example, 8 multimode optical fibers in conjunction with 8 VECSEL lasers; or a medium-short distance wavelength division multiplexing communication system which is built by adopting OM5 multimode fiber to match with a VECSEL laser with a plurality of wavelengths. Wavelength division multiplexing systems have advantages over parallel communication prices and thus have a more attractive future prospect.

The optical fiber movable connector is a device capable of performing detachable (movable) connection between optical fibers, so that optical signals can be transmitted according to a required channel to ensure the smoothness of an optical fiber link.

According to research, the number of transverse modes of a VECSEL laser is gradually increased in the process of gradually increasing the driving current, so that an output fiber tail fiber of 50/125 μm is adopted by most VECSEL lasers. The total light intensity is increased along with the increase of the driving current, a pulse modulation mode is adopted, the light intensity is detected by adopting a detector at the tail end of multimode transmission, and clear eye pattern data can be obtained for judgment.

To achieve a stable bandwidth, most studies have shown that an offset injection method is required at the injection end face of the multimode fiber. The method comprises the following steps that a single-mode optical fiber is placed at a certain distance from a multimode fiber core and is parallel to the axis of the fiber core; the second method is to use a single mode fiber to be placed at a certain distance from the multimode fiber core but to form a small angle with the axis of the fiber core. The angular offset method is more advantageous than the parallel offset method.

Patent 201910698816.9 discloses a method for preparing a multi-core fiber coupler based on reverse tapering technology, which comprises stripping the coating layer of the multi-core fiber, reversely tapering the multi-core fiber, cutting at the position with the largest diameter of the coating layer, pretreating multiple single-core fibers, preparing a single-core fiber bundle according to the arrangement mode of the cores of the multi-core fiber bundle, stacking and fixing the single-core fiber bundle in a glass capillary, melting and tapering, cutting at the waist of the tapered single-core fiber bundle, aligning with one end of the largest diameter of the coating layer of the multi-core fiber, and completing fusion splicing.

Patent 201710752028.4 discloses a step-mode fiber optical tweezers based on oblique light annular light field, which comprises a light source, a single mode fiber and a step-mode fiber, wherein a capturing tweezer head is arranged at the end of the step-mode fiber; the light source is optically coupled and injected into the single mode fiber, the single mode fiber injects light to the step multimode fiber in an oblique incidence mode, light in the step multimode fiber is spirally transmitted forwards in an oblique light mode to form an annular light field, and the annular light is totally reflected and converged in a cone frustum structure on the end face of the capturing tweezer head to generate strong light trapping force. The device can capture single cells and flying-up micro-droplets, and the light injection angle, position and distance are changed by the oblique incidence adjusting device, so that the operations of accurate capture, transportation, ejection, screening and the like of the cells are realized.

The utility model discloses a 201721083580.0 discloses a step multimode fiber optical tweezers based on oblique light annular light field injects in multimode fiber to one side through single mode fiber, arouses spiral light, and the rotatory optical line of spiral forms annular light field, and this annular light field assembles at the total reflection of catching tweezers head terminal surface, produces strong light trapping power. The oblique incidence adjusting device I and the oblique incidence adjusting device II are designed, and the incidence angle can be adjusted conveniently.

Patent 201510980919.6 proposes a multimode fiber broadband measuring device, comprising: the device comprises a synthetic sweep source, an optical transmitter, an optical injection system, a tested multimode optical fiber, a ring flux test system, an optical receiver, a spectrum analyzer, a frequency meter and a computer. The invention provides a method for evaluating whether a light injection state meets a full injection condition by using an annular flux test system, ensures the measurement repeatability of the device, analyzes and describes the optimization of the measurement repeatability of multimode fiber bandwidth parameters, improves the uncertainty of multimode fiber bandwidth measurement results, and provides a Gaussian line type fitting formula of the multimode fiber bandwidth parameters.

Patent 201480080021.7 discloses a method for characterizing mode group characteristics of multimode light passing through an optical assembly, the method comprising the steps of: disposing a mode group separating optical fiber in an optical path between a light source and the optical assembly; and injecting a reference pulse of light having a wavelength λ t from the light source into the optical component via the mode group separating fiber at a discrete interval between a core center and a core radius of the mode group separating fiber.

Patent 201210404567.6 discloses a method for evaluating power loss for a given bit error rate of a multimode optical fiber, comprising: measuring a set of fundamental fiber responses corresponding to different offset injections of light into the multimode fiber within a core radius; generating a full local fiber response by applying to the set of fundamental fiber responses a set of weighting coefficients and delays that depend on different offset injections of the fundamental fiber response; and calculating a parameter representing the power loss of the optical fiber from the global fiber response, wherein the set of weighting coefficients comprises several subsets of weighting coefficients having a time delay with respect to each other, at least one relative time delay is not set to 0, and the weighting coefficients of the subsets are dependent on different offset injections of the basic fiber response.

Patent 03141953.4 discloses a two-dimensionally confined multimode interference power divider consisting of more than one input single-mode waveguide array, X, Y, and Wxe, which is rational number of the square ratio of equivalent waveguide widths (Wxe, Wye) in two directions²/Wye²＝p/q，In the formula: p and q are integers. The invention adopts the optical waveguide to form the optical power divider with two-dimensional distribution, provides a basic unit device for realizing two-dimensional space optical power distribution, and has the characteristics of compact structure and high integration level. If in the rectangular waveguide area, various light refraction effects, such as an electro-optic effect, a thermo-optic effect, a carrier injection effect and the like, are utilized to control the intensity and phase distribution of output light waves, so that a three-dimensional integrated optical waveguide device is realized, such as a wavelength division multiplexer, a switch light and a light variable attenuator array and the like which can realize two-dimensional spatial distribution by combining a two-dimensional waveguide grating array device.

Patent 03102424.6 coupling of semiconductor laser and double-clad fiber, in particular to a multimode fiber row and prism coupling double-clad fiber device and a coupling method thereof, belonging to the technical field of laser coupling. The invention provides a device with a novel structure and a coupling method thereof. Firstly, a plurality of multimode fiber waveguides are closely arranged, one end of each multimode fiber waveguide is fixed in a row and then is ground and polished to be a light receiving surface, an angle is formed between each multimode fiber waveguide and an optical axis, each multimode fiber waveguide is in optical contact with a double-clad fiber, and pump light is coupled into the double-clad fiber. And secondly, prism waveguide coupling, wherein pump light is injected into an incident plane of the prism waveguide and is directly coupled into an inner cladding of the double-clad optical fiber. Can pump at multiple points simultaneously and can carry out coupling of high pump power. The side pumping of the double-clad fiber, the simultaneous multi-point pumping of the array high-power semiconductor laser to the double-clad fiber, the high-power double-clad fiber laser with various structures, the high-gain amplifier and the superfluorescence light source can be realized.

Patent 200910163912.X discloses transmitting multiple wavelengths in a multimode fiber, each wavelength being provided with a modal dispersion compensating fiber, so that the total dispersion of each wavelength is close to zero; a plurality of wavelength light sources in the system are connected to a multiplexer. The patent mainly solves the problem of bandwidth of multimode fibers at different wavelengths, i.e. the modal dispersion of multimode fibers at different wavelengths is solved by a dispersion compensation scheme, but it does not describe the modulation and injection method of multiple light sources.

Utility model 201820111419.8 discloses a scheme of a space mode from a multimode fiber a plurality of wavelength of separation, mainly adopts drum lens, wavelength division multiplexer, a plurality of wave filter, a plurality of G-lens and a plurality of lens that assemble to constitute. According to the geometrical optics principle, light with different wavelengths is separated at different positions and is converged on different detection chips again after being collimated. The patent mainly solves the problem of the solution of the demultiplexing end, and adopts a space optical mode, so that a plurality of discrete elements are provided, and the reliability is lower.

The current scheme mostly adopts a space alignment mode to perform bias injection on the multimode optical fiber, and the scheme is flexible and convenient, but has poor reliability and repeatability. And a single-mode fiber core-shifting welding mode is adopted for bias injection, the position is fixed, the reliability is high, but the single-mode fiber core-shifting welding mode only can support a single position injection light source.

In summary, in order to realize that the multimode fiber wavelength division multiplexing transmission system transmits the farthest distance with the maximum bandwidth, the best mode is to use the broadband multimode fiber with optimized bandwidth, and match the VECSEL laser with bias injection, so that the short-distance multi-wavelength multimode communication with large capacity can be realized. However, the current solutions mainly solve the problems of single offset injection light source device, complicated multiple wavelength problems, interference between light sources, consistency and mode of injection conditions, and the like, which are not clarified in the literature. The invention mainly aims to solve the problem of short-distance multi-wavelength multimode communication of multiple light source bias injection realized by using a wavelength division multiplexing principle in multimode optical fibers, and the system comprises a light source drive, a tapered bias injection coupler and the like, and has better consistency and larger and more stable transmission bandwidth.

Disclosure of the invention

The invention mainly solves the technical problem of realizing wavelength division multiplexing in a broadband multimode fiber. Described in the present invention is a short-range multi-wavelength multimode communication system, said system comprising: lasers, which are multiple VECSEL lasers or other lasers with wavelengths between 850.0nm and 950.0 nm; the control circuit is a multi-path driving pulse modulation circuit integrated on a chip, and the front edge and the rear edge of a pulse are not more than 20 ps; optical fiber transmission device: the multi-branch lasers are coupled to a plurality of standard 50/125 mu m multimode fibers and are connected to 50/125 mu m multimode fibers or 50/125 mu m broadband multimode fibers through a tapered bias injection coupler; and a grating type demultiplexer, a photodetector, and a data receiving processor. Broadband multimode fibers employ a proprietary deposition technique that is bandwidth optimized, and therefore, supports high bandwidth transmission from 850.0nm to 950.0nm, typically up to 4GHz km or more. Conventional wavelength division multiplexing systems have 2-wave, 4-wave, 6-wave, 8-wave, etc. Aiming at the principle that the system compatibility is good and most requirements are met, the invention takes 8-wave multiplexing as a solution target and is compatible with 2-wave, 4-wave and 6-wave transmission schemes. The 8 wavelengths range between 850.0nm and 950.0 nm. The lasers selected for this experiment were multiple VECSEL lasers or other lasers with wavelengths between 850.0nm and 950.0 nm.

An optical fiber transmission device: the multi-branch lasers are coupled to a plurality of standard 50/125 mu m multimode fibers and connected to 50/125 mu m multimode fibers or 50/125 mu m broadband multimode fibers through a tapered bias injection coupler. 8 multimode fibres of 50/125 μm were coupled to 8 VECSEL lasers. Since the spot size of a VECSEL laser varies with increasing drive current, mainly the divergence angle becomes larger and the spot size becomes larger. An 50/125 μm multimode fibre is very suitable for coupling the spots of such lasers. The emission wavelength of the VECSEL laser is between 850.0nm and 950.0nm, and the wavelength interval of different lasers can be 50.0nm, 25.0nm, 16.7nm and more preferably 12.5nm according to the different numbers (2/4/6/8) of the selected lasers. For example, a group of VECSEL lasers has a central wavelength of 850.0nm, 900.0nm, 950.0 nm. For example, a group of VECSEL lasers has a center wavelength of 850.0nm, 875.0nm, 900.0nm, 925.0nm, 950.0 nm. For example, another group of VECSEL lasers has a center wavelength of 850.0nm, 866.7nm, 883.3nm, 900.0nm, 916.7nm, 933.3nm, 950.0 nm. For example, another group of VECSEL lasers has a center wavelength of 850.0nm, 862.5nm, 875.0nm, 887.5nm, 900.0nm, 912.5nm, 925.0nm, 937.5nm, 950.0 nm. Each laser outputs light having a plurality of modes, for example, at 850.0nm, the modes including LP01, LP02, LP03, LP04, LP05, LP06, LP07, LP11, LP12, LP13, LP14, LP15, LP16, LP21, LP22, LP23, LP24, LP25, LP26, LP31, LP32, LP33, LP34, LP35, LP36, LP41, LP42, LP43, LP44, LP51, LP52, LP53, LP54, LP55, LP56, LP61, LP62, LP63, LP71, LP72, and the like. The emission wavelength is non-monochromatic light, the spectral line width is less than or equal to 2nm, such as 875.0nm, the spectrum is 875.0 +/-1.0 nm, the minimum value of each pulse width is about 50.0ps, and the pulse width is adjustable.

8 multimode optical fibers of 50/125 mu m, after the outer cladding layer is corroded by hydrofluoric acid, 8 multimode optical fibers with part of the cladding removed are put into a quartz capillary tube to be stacked and coupled together for tapering, the taper is 1.5-2.0 degrees, the length of a tapering region is 3.0-4.0 mm, the diameter of an initial inscribed circle of the tapering region is 300.0-375.0 mu m, and the diameter of an inscribed circle at the tail end of the tapering region is 90.0-112.5 mu m. The core pitch is about 13.8 to 15.3 μm. The diameter of the core of the multimode fiber is reduced from 50.0 +/-1.0 mu m to 10.0 +/-0.2 mu m after tapering, and finally the tapered bias injection coupler is manufactured. The 8 multimode fibers are subjected to an adiabatic tapering process, and the high-order mode and the low-order mode are coupled, so that the beam quality of the VECSEL laser can be improved. Therefore, the bandwidth is unstable due to the distortion of the original laser signal, after tapering, part of high-order modes in the optical fiber are dissipated, the mode dispersion in the optical fiber is obviously reduced, the mode spot can be improved to a certain extent, the signal bandwidth is increased, and higher code rate transmission is supported.

And the control circuit is a multi-path driven pulse modulation circuit integrated on a chip, and the front edge and the back edge of a pulse are not more than 20 ps. The signal modulation of multi-channel laser is realized by adopting a mature driving circuit module on the market at present, wherein the forward driving voltage is more than or equal to 0.4V, the driving current is less than or equal to 80.0mA, the current ripple is less than or equal to 0.02mA, the bias current is less than or equal to 5.0mA, the matching resistance value is more than or equal to 15.0 omega, the constant-power automatic control function is realized, and the total output speed is less than or equal to 8 x 20 Gbps. The front edge and the back edge of the pulse modulation circuit integrated on the chip and driven by 8 paths are not more than 20.0 ps.

The optical fiber before tapering is etched on partial cladding by hydrofluoric acid and then is placed in a quartz capillary tube for tapering. The reason for performing the etching operation is to adjust the offset distance of each core, and the core spacing of the tapered offset injection coupler of the invention is larger than 13.8 μm.

Because the wavelengths of the VECSEL lasers connected by different cores are different, when the wavelengths are coupled into the same core for transmission, the problem of crosstalk does not need to be considered.

The tapered offset injection coupler has the advantages that the offset distance of the fiber core has good consistency. The tapering consistency of the optical fiber can be controlled by controlling the temperature of the tapering, the traveling speed of the optical fiber clamp and the traveling speed of flame. And the control precision can meet the requirement by adopting an industrial-grade cone drawing machine, and the manufacturing cost is reduced. The bias injection scheme disclosed by the invention adopts an end surface injection mode, so that the bandwidth consistency of different wavelengths is ensured.

The numerical aperture of the 50/125 μm multimode fiber is 0.2 ± 0.015, so the maximum angle at which the multimode fiber accepts injected light is: 11.5 degrees. The multimode fiber end face center circle radius was 25.0 μm. In the present invention, the offset distance range is designed to be 18.1 μm to 20.0 μm, and the implantation angle range is 1.5 ° to 2.0 °. The injection bias positions and angles of the 8 light sources are completely symmetrical and are injected from the meridian plane of the optical fiber, so that the transmission bandwidth of the optical fiber in the multimode is relatively stable. Since the 8 wavelengths are different from each other, there is no interference phenomenon in the plurality of wavelengths spatially. In the transverse mode structure, the longer the wavelength, the smaller the number of transverse modes, and therefore, the smaller the group velocity difference of the long wavelength and the larger the bandwidth. The taper bias injection coupler and the 50/125 mu m multimode optical fiber connection mode are movable connectors, which are also the connection mode of the current industry standard, and ensure the smoothness of an optical fiber link. However, the exit end face of the tapered bias injection coupler needs to be ground into an APC (automatic Power control) type with an angle of 8 degrees, and the multimode optical fiber also needs to be ground into the APC type with an angle of 8 degrees, so that the return loss is increased, the light source is protected, and the service life is prolonged. The end faces of the two movable connectors are both in an APC type, the connection loss is smaller, and the tapered bias injection coupler is completely symmetrical, so that the influence on the bias injection condition is smaller.

50/125 μm multimode optical fiber has been used in large scale in data centers and the like. And more preferably 50/125 μm broadband multimode fiber, which optimizes the doping composition so that the bandwidth of the fiber in the range of 850.0nm to 950.0nm exceeds 4GHz km, if the system of the present invention is adopted, the transmission can be supported not to exceed 8 wavelengths, and the transmission distance is 100.0m to 250.0m at the rate that the single wave is not more than 20 Gbps; or the single wave is not more than 10Gbps, and the transmission distance is 200.0-500.0 m; or the single wave is not more than 5Gbps, and the transmission distance is 400.0 m-1000.0 m.

(IV) description of the drawings

Fig. 1 is a schematic view of an incident end face of an 8-core tapered multimode offset injection coupler. 8 50/125 μm GI multimode fibers were stacked as shown, with the shaded portions being the fiber core locations, made of SiO₂And GeO₂Has a diameter of 50.0 μm, and a cladding of optical fiber formed of SiO₂The composition had a diameter of 125.0. mu.m.

Fig. 2 is a schematic diagram of an exit end face of a 2-core tapered multimode offset injection coupler. Wherein the shaded part represents the position of the fiber core after tapering, and the fiber core is made of SiO₂And GeO₂The offset distance d between the center of the fiber core after tapering and the center of the fiber core of the injection multimode fiber is 15.0-20.0 mu m, the diameter of the fiber core after tapering is 10.0-20.0 mu m, and the shrinkage of the outer surface of the fiber cladding due to tapering is generated.

Fig. 3 is a schematic diagram of an exit end face of a 4-core tapered multimode offset injection coupler. Wherein the shaded part represents the position of the fiber core after tapering, and the fiber core is made of SiO₂And GeO₂The offset distance d between the center of the fiber core after tapering and the center of the fiber core of the injection multimode fiber is 15.0-20.0 mu m, the diameter of the fiber core after tapering is 10.0-20.0 mu m, and the shrinkage of the outer surface of the fiber cladding due to tapering is generated.

Fig. 4 is a schematic diagram of the exit end face of a 6-core tapered multimode offset injection coupler. Wherein the shaded part represents the position of the fiber core after tapering, and the fiber core is made of SiO₂And GeO₂The offset distance d between the center of the fiber core after tapering and the center of the fiber core of the injection multimode fiber is 16.7-20.0 mu m, the diameter of the fiber core after tapering is 10.0-16.7 mu m, and the shrinkage of the outer surface of the fiber cladding due to tapering is generated.

Fig. 5 is a schematic diagram of an exit end face of an 8-core tapered multimode offset injection coupler. Wherein the shaded part represents the position of the fiber core after tapering, and the fiber core is made of SiO₂And GeO₂The center of the fiber core after tapering and the injection are moreThe offset distance d of the center of the fiber core of the mode optical fiber is 18.1-20.0 mu m, the diameter of the tapered fiber core is 10.0-13.8 mu m, and the shrinkage of the outer surface of the fiber cladding is generated due to tapering.

Fig. 6 is a schematic cross-sectional view of a tapered multimode offset injection coupler. Wherein the shaded part is the core part, and the core is made of SiO₂And GeO₂Is composed of a graded index of refraction, a cladding portion made of SiO₂And (4) forming.

FIG. 7 is a simulated plot of the spot of injected light after each core has been tapered.

FIG. 8 is a graph of the electric field strength of the injected light after tapering of each core.

Fig. 9 is a schematic diagram of a short-range multi-wavelength multimode communication system. The device consists of a multi-path driving pulse modulation circuit 1, n (2/4/6/8) VECSEL lasers 2, n (2/4/6/8) standard 50/125 mu m multimode fibers 3, a tapered multimode bias injection coupler 4, 50/125 mu m broadband multimode fibers 5, a lens 6, a grating 7, n (2/4/6/8) photodetectors 8 and a data receiving processor 9. Reference numeral 10 in fig. 9 denotes an entrance end face of the 8-core tapered multimode offset injection coupler, and reference numeral 11 denotes an exit end face of the 8-core tapered multimode offset injection coupler.

(V) detailed description of the preferred embodiments

The examples are described in further detail below.

Example 1: the two VECSEL lasers of 850.0nm and 900.0nm are subjected to signal modulation through an on-chip integrated 2-path pulse modulator, the generated modulated light passes through a standard 50/125 mu m multimode fiber and is welded with two signal arms of a tapered bias injection coupler, the welded tapered bias injection coupler is connected with a 50/125 mu m broadband multimode fiber through a movable connector, the connection insertion loss is 0.17dB, and the return loss is 60.0 dB. The modulation rate is 20GHz, and the transmission distance of the broadband multimode fiber with the 50/125 μm is 200.0 m.

Example 2: the four VECSEL lasers of 850.0nm, 875.0nm, 900.0nm and 925.0nm are subjected to signal modulation through an on-chip integrated 4-path pulse modulator, the generated modulated light passes through a standard 50/125 mu m multimode fiber, a fusion-spliced biconical taper is in bias injection to four signal arms of a coupler, the fusion-spliced biconical taper is in bias injection to be connected with a 50/125 mu m broadband multimode fiber through a movable connector, the connection insertion loss is 0.15 dB, and the return loss is 60.0 dB. The modulation rate is 10GHz, and the transmission distance of the broadband multimode fiber with the 50/125 μm is 450.0 m.

Example 3: six VECSEL lasers of 850.0nm, 866.7nm, 883.3nm, 900.0nm, 916.7nm and 933.3nm are subjected to signal modulation through an on-chip integrated 6-path pulse modulator, the generated modulated light passes through a standard 50/125 mu m multimode optical fiber and is welded with six signal arms of a tapering bias injection coupler, the welded tapering bias injection coupler is connected with a 50/125 mu m broadband multimode optical fiber through a movable connector, the connection insertion loss is 0.13dB, and the return loss is 61.0 dB. The modulation rate is 5GHz, and the transmission distance of the broadband multimode fiber with 50/125 μm is 700.0 m.

Example 4: eight VECSEL lasers of 850.0nm, 862.5nm, 875.0nm, 887.5nm, 900.0nm, 912.5nm, 925.0nm and 937.5nm are subjected to signal modulation through an on-chip integrated 8-path pulse modulator, generated modulated light passes through a standard 50/125 mu m multimode optical fiber and is welded with eight signal arms of a tapered bias injection coupler, the welded tapered bias injection coupler is connected with a 50/125 mu m broadband multimode optical fiber through a movable connector, the connection insertion loss is 0.11dB, and the return loss is 62.0 dB. The modulation rate is 5GHz, and the transmission distance of the broadband multimode fiber with 50/125 μm is 960.0 m.

Design parameters in the above embodiments although preferred, the above embodiments also describe the present invention in detail, but those skilled in the art can understand that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the spirit and scope of the invention, which is defined by the claims and their equivalents.