CN117761847A - Lateral light coupling enhancement method based on 45-degree inclined light well straight Fresnel lens - Google Patents

Abstract

The invention belongs to the technical field of lateral optical coupling of plastic optical fibers, and solves the problem of low lateral coupling efficiency of an LED-plastic optical fiber system. The lateral optical coupling enhancement method of the straight Fresnel lens of the 45-degree inclined optical well comprises the following steps: s1: processing a side coupling optical well on the side surface of the plastic optical fiber; s2: the design and parameter selection of a primary focusing Fresnel lens are carried out, the primary focusing Fresnel lens converges LED radiation light, the light spot area of the primary focusing Fresnel lens is reduced, and the primary focusing Fresnel lens is focused above a light well; s3: and designing and selecting parameters of a secondary subarea collimating Fresnel lens, wherein the secondary subarea collimating Fresnel lens is calculated and subarea according to the position and angle of incident light, and comprises a central hollowed-out area and subarea collimating areas, so that the LEDs are optically coupled into the light well to form an effective conduction mode to the maximum extent. The light well is combined with the Fresnel lens group, so that the lateral coupling efficiency of the LED-plastic optical fiber coupling system is more than 6%, and is far higher than the current level below 1%.

Description

Lateral light coupling enhancement method based on 45-degree inclined light well straight Fresnel lens

Technical field

The invention belongs to the technical field of plastic optical fiber lateral light coupling, and specifically relates to a lateral light coupling enhancement method based on a 45-degree inclined light well straight Fresnel lens.

Background technique

Multi-source scanning is a new type of quasi-distributed optical fiber sensing positioning technology proposed in recent years. Multi-source scanning can be used to achieve low-cost quasi-distributed water leakage measurement, angle measurement, motion analysis, flexible wearable devices, shape reconstruction, etc. . Multi-source scanning uses low-cost LED light strips and lateral light coupling technology to achieve spatial positioning. The lateral coupling efficiency is an important parameter of fiber optic lateral coupling technology. It represents the total radiation power of the light source after lateral coupling. The total power forming an effective conduction mode is the percentage of the total radiated power of the light source.

In the absence of a lens group or other optical path control system, the light that can be coupled into the optical fiber and form a conduction mode is extremely weak, usually less than 1‰ of the total radiation power of the light source. Since the fiber optic system itself will cause attenuation, higher lateral coupling efficiency means longer measurement distance and lower system power consumption; very low lateral coupling efficiency will limit the sensitivity and sensitivity of the sensor based on the above-mentioned multi-source scanning technology. measurement range, and increases system power consumption.

The high-efficiency lateral coupling technology and related processes of the LED-plastic optical fiber coupling system is a technical problem that still needs to be solved. The light-emitting area of the LED is larger than the size of the side coupling structure of the plastic optical fiber. It is equivalent to a surface light source. The relationship between its divergence angle and the normalized radiant power is shown in Figure 1. It can be seen that the LED radiated light diverges in a hemispherical shape. , the radiation angle covers the range of 0-90°, which is much larger than the laser beam divergence angle. The current optical fiber lateral coupling technologies mainly include: fused taper coupling, macrobending coupling and cladding defect coupling.

Fused cone coupling: Since the two optical fibers need to be heated, melted and tapered, the cone part is extremely fragile and needs to be packaged and protected to be completely isolated from the external environment. The devices produced by this method are limited to applications such as optical splitters, couplers, and beam splitters, and are difficult to be actually used in sensing measurements.

Macro-bend coupling: The macro-bending of flexible plastic optical fibers is used to generate a large number of cladding radiation modes. The radiation mode light is laterally coupled into the cladding and core of the optical fiber through another bent optical fiber adjacent to it, and then partially forms conduction. model. However, it should not be ignored that the macrobending coupling process will cause a large amount of light energy loss. It is more effective when used as a single-point sensor. However, when used for long-distance and distributed sensing, its use will largely depend on the optical power. limited by rapid decay.

Cladding defect coupling: The original complete cladding of the optical fiber is damaged to a certain extent. The defects can be in various shapes, including cylinders, cones, spheres, V-shaped grooves, etc. The main processing methods are grinding, drilling and cutting. Taking V-groove coupling as an example, it specifically refers to cutting a smooth and flat V-shaped structure on the side of the optical fiber, and using a lens system to focus the laser on the V-groove reflective surface, and through appropriate angle control, the external light is directed to the optical fiber. Core coupling, the key elements of this method are the flat and smooth cutting of the V-groove and the control of the cutting angle. At present, it is almost impossible to find equipment that can cut V-grooves at specific angles on optical fibers, and it is difficult to ensure the robustness of the cut optical fibers. Therefore, the process is difficult, the processing parameters are difficult to control, and it is difficult to popularize and use it. In addition, previous lens systems were developed for laser-fiber coupling systems, which cannot adapt to the highly divergent characteristics of LED light sources and cannot be directly transplanted to LED-plastic fiber coupling systems.

Contents of the invention

In order to solve at least one of the above technical problems existing in the prior art, the present invention provides a lateral light coupling enhancement method based on a 45-degree inclined light well straight Fresnel lens.

The present invention adopts the following technical solution to realize: a lateral light coupling enhancement method based on a 45-degree inclined light well straight Fresnel lens, including the following steps:

S1: Process the side coupling light well on the side surface of the plastic optical fiber;

S2: Design and parameter selection of the primary focusing Fresnel lens. The primary focusing Fresnel lens converges the LED radiation light, reduces its spot area, and focuses it above the light well;

S3: Design and parameter selection of the secondary partitioned collimating Fresnel lens. The secondary partitioned collimating Fresnel lens is calculated and partitioned according to the position and angle of the incident light, including the central hollow area and the partitioned collimation area. The maximum Limit the LED to light coupling into the light well to form an effective conduction mode;

S4: Install the primary focusing Fresnel lens and the secondary partitioned collimating Fresnel lens between the LED lamp and the plastic optical fiber with an inclined light well to enhance the lateral light coupling of the plastic optical fiber.

Preferably, the inclination angle of the side coupling light well is 45 degrees. The specific processing steps include:

S101: Cut the plastic optical fiber to the required length and grind its end face;

S102: Use the laser etching software system to draw and determine the minimum processing size and graphics as graphic elements;

S103: Use a tilt angle meter to place the plastic optical fiber so that the plastic optical fiber produces the required tilt angle;

S104: Perform vertical one-way drilling of plastic optical fibers and clean the drilled light well;

S105: Measure the through optical power and side coupling optical power of the processed optical fiber single grating, and calculate its insertion loss and side coupling efficiency to determine whether the processed product is qualified.

Preferably, one side of the primary focusing Fresnel lens is flat and the other side is serrated with equal groove depth; and the angles between each serrated tooth are different from each other, and each serrated ring can focus all the projected light rays. a little;

The relationship between the angles in the primary focusing Fresnel lens and the expression of the traditional Fresnel lens formula are:

In the formula, μ _n and μ _n ' represent the angle between the incident light and refracted light and the optical axis FF'; R _n and R' _n are the distances from point A and point B to the lens optical axis respectively; f and f' are respectively The distance from point F and F' to point O; k' _n represents the distance between the center point B on the small sawtooth inclined surface and the flat surface of the condenser, which can be expressed as: K′ _n =tanα _n ×ΔR/2, a _n represents each small The angle between the inclined plane and the base of a triangle;

When the LED light is incident on the plane side of the lens, according to the size of the LED structure, set the sizes f and f' required for the experiment. Since the lens is designed with equal sawtooth width, that is, the width of each small sawtooth is ΔR , and because the height k _n of the sawtooth is much smaller than the focal length f', the formula tanα _n can be expressed as:

In the formula, N represents the ratio of the refractive index of the lens to the refractive index of air; all sawtooth parameters of the primary focusing Fresnel lens can be calculated according to the parameters of the required lens.

Preferably, the secondary partitioned collimating Fresnel lens design method includes the following steps:

S301: Calculate the light angle distribution based on the minimum focal length f’ of the primary focusing Fresnel lens;

S302: Calculate the light angle range of total internal reflection in the light well;

S303: Calculate the angle range of the guided wave light;

S304: Obtain the light angle range that simultaneously satisfies the above steps S301-S303;

S305: Determine the size and position of the secondary partitioned collimating Fresnel lens;

S306: Perform eccentric hollowing processing on the secondary partitioned collimating Fresnel lens;

S307: For the area of the secondary partitioned collimating Fresnel lens except for the eccentric hollow, perform a collimation design based on the incoming light angle.

Preferably, the angle μ' _n between the refracted light and the optical axis FF' can be defined as the light angle of the secondary collimating Fresnel lens; the calculated value range of the light angle μ' _n is: ±45° in a cone shape distributed.

Preferably, the total internal reflection light angle of the light well refers to the light angle of the light that is distributed in a cone of ±45° within the incoming light range obtained in step S301 and is reflected through the light well, and satisfies the total internal reflection of the light at the light well-air interface. Range; calculation method: θ _c -45°＜μ' _n <45°, where θ _c is the total internal reflection angle of the light well interface, After calculation, the total internal reflection light angle range caused by the 45° inclined light well is: -2.76°<μ' _n <+45°.

Preferably, the angle range of the light from the guided wave means that an optical fiber with a specific numerical aperture receives light within a certain angle range and can form a conduction mode in the waveguide; through 45° light well coupling, the conditions for forming a forward waveguide in the plastic optical fiber are: : 0≤θ _in =μ' _n <180°arcsin(NA), where θ _in is the angle between the light and the optical fiber axis after reflection in the light well, NA is the numerical aperture of the optical fiber; after calculation, it can be seen that the numerical aperture NA of the optical fiber is When it is 0.5, the incoming light angle μ' _n is forward deflection: 0° to +30°; the incoming light angle range obtained in step S304 is: forward deflection 0° to +30°.

Preferably, the secondary zoned collimating Fresnel lens is placed close to the surface of the optical fiber; the size of the secondary zoned collimating Fresnel lens is: a cone with the focus of the primary focusing Fresnel lens as the vertex and a cone angle of 90° The size of the projected surface at the location of the upper surface of the optical fiber.

Preferably, the hollow range is: with the focus of the primary focusing Fresnel lens as the vertex, the projection area of the half cone formed by the forward deflection of 30° on the secondary partitioned collimating Fresnel lens; by collimating Directly make the light well deflect the incoming light angle to 0° in the projection area of the secondary partitioned collimating Fresnel lens excluding the hollow part, and illuminate the light well, meeting the conditions for forming a guided wave.

Compared with the prior art, the beneficial effects of the present invention are:

The invention discloses a process method and process parameters for processing a high-efficiency side-coupling light well on the side of a plastic optical fiber. It uses laser processing technology to etch a side-coupling light well with an inclination angle of 45° and a controllable depth on the side surface of the plastic optical fiber. Compared with grinding, drilling, cutting and other processes, the process method introduced in this patent is easier to ensure processing consistency, reduce the fiber damage area, maximize the robustness of the fiber, reduce insertion loss and crosstalk between coupling structures.

This patent also discloses a lateral coupling enhancement method for an LED-fiber coupling system based on a dual-stage Fresnel lens group. The lens group contains a primary focusing Fresnel lens and a secondary partitioned collimating Fresnel lens. The primary focusing lens concentrates the LED radiation light as much as possible, reduces its spot area, and focuses it above the light well. The secondary partitioned collimating lens is calculated and partitioned according to the position and angle of the incident light, including an eccentric hollow area and a collimation area, which effectively improves the lateral coupling efficiency.

The above-mentioned light well combined with the Fresnel lens group can make the lateral coupling efficiency of the LED-plastic optical fiber coupling system exceed 6%, which is much higher than the current level of less than 1‰.

Description of the drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some of the drawings of the present invention. Embodiments, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without exerting creative efforts.

Figure 1 is the relationship between typical LED normalized radiation power and divergence angle;

Figure 2 is a schematic diagram of using laser to etch a 45° inclined light well on the surface of a plastic optical fiber;

Figure 3 is a schematic diagram of the Fresnel lens focusing light;

Figure 4 is a diagram of the installation position of the Fresnel lens group.

In the picture: 1-LED light strip; 2-LED lamp beads; 3-plastic optical fiber; 4-45 degree inclined light well; 5-primary focusing Fresnel lens; 6-secondary partitioned collimating Fresnel lens; 7- Collimation area; 8-Hollow area; 9-Hollow area range angle: 0°~+30°; 10-Light well inclination angle: 45°.

Detailed ways

The technical solutions in the embodiments of the present invention are clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementations obtained by those of ordinary skill in the art without any creative work fall within the scope of protection of the present invention.

It should be noted that the structures, proportions, sizes, etc. shown in the drawings of this specification are only used to coordinate with the content disclosed in the specification for the understanding and reading of those familiar with this technology, and are not used to limit the conditions for the implementation of the present invention. , so it has no technical substantive significance. Any structural modifications, changes in proportions or adjustments in size shall fall within the scope of what is disclosed in the present invention as long as it does not affect the effects that the present invention can produce and the purposes that can be achieved. To the extent that the technical content can be covered, it should be noted that in this specification, relational terms such as first and second are only used to distinguish one entity from several other entities, and do not necessarily require or imply There is no actual relationship or ordering between these entities.

The present invention provides an embodiment:

As shown in Figures 1 to 4, a lateral light coupling enhancement method based on a 45-degree inclined light well straight Fresnel lens includes the following steps:

S1: Process the side coupling light well on the side surface of the plastic optical fiber;

S2: Design and parameter selection of the primary focusing Fresnel lens. The primary focusing Fresnel lens converges the LED radiation light, reduces its spot area, and focuses it above the light well;

S3: Design and parameter selection of the secondary partitioned collimating Fresnel lens. The secondary partitioned collimating Fresnel lens is calculated and partitioned according to the position and angle of the incident light, including the central hollow area and the partitioned collimation area. The maximum Limit the LED to light coupling into the light well to form an effective conduction mode;

S4: Install the primary focusing Fresnel lens and the secondary partitioned collimating Fresnel lens between the LED lamp and the plastic optical fiber with an inclined light well to enhance the lateral light coupling of the plastic optical fiber.

In this embodiment, the inclination angle of the side coupling light well is 45 degrees. The specific processing steps include:

S101: Cut the plastic optical fiber to the required length and grind its end face to make the end face flat and reduce insertion loss;

S102: Use the laser etching software system to draw and determine the minimum processing size and graphics as graphics elements; taking 2mm diameter ck-80 optical fiber as an example, the optimal graphic element diameter size is 110μm, and the graphic element shape is circular; graphic element diameter If it is less than 110μm, the etched air gap will be too narrow and the lateral coupling effect will decrease; if the picture element diameter is greater than 110μm, the insertion loss will increase too fast, and the fiber surface damage area will be too large and increase the crosstalk between coupling structures; therefore, 110μm can be considered comprehensively Taking into account the two parameters of lateral coupling efficiency and insertion loss.

S103: Use a tilt angle meter to place the plastic optical fiber so that the plastic fiber produces the required tilt angle; then perform the drilling operation as shown in Figure 2. The arrow is the laser direction and the angle α is the tilt angle; after repeated tests and verification, the tilt angle is 45° It is the best tilt angle without a lens system; choosing a 45° tilt angle can be compatible with systems that include or do not include a lens combination, which is the most compatible choice for the product.

S104: Perform vertical one-way drilling of the plastic optical fiber, and clean the drilled light well to remove the residue after laser burning; taking a 40W laser engraving machine and a 2mm diameter ck-80 optical fiber as an example, the optimal output power 16.5%, the mode is vertical one-way. The above-mentioned laser power that is too high causes an increase in insertion loss and affects the robustness. If the power is too low, the etching depth is insufficient, and the side coupling efficiency is too low.

S105: Measure the through optical power and side coupling optical power of the processed optical fiber single grating, and calculate its insertion loss and side coupling efficiency to determine whether the processed product is qualified.

Fresnel lenses are composed of many fine wedge-shaped layers, mostly injection molded from polyolefin materials. They are lighter in weight than ordinary lenses, which can effectively reduce production time and costs. Fresnel lenses can focus a wide and large optical path to a single point, and their light-gathering ability is stronger than that of ordinary lenses. This patent uses a 45-degree inclined light well combined with a Fresnel lens set to enhance the optical coupling efficiency of the LED-plastic optical fiber system.

One side of the primary focusing Fresnel lens is flat and the other side is serrated with equal groove depth; and the angles between each serration are different from each other, and each serrated ring can focus all the projected light at one point.

In the design of the primary focusing Fresnel lens, the light-gathering performance of the lens is analyzed. According to the law of refraction, we can get:

In the formula, N represents the ratio of the refractive index of the lens to the refractive index of air; β _n and β' _n respectively represent the incident angle and refraction angle of light P _n on the working surface of the lens at A; θn and θ'n represent respectively at B The angle of incidence and refraction of the plane at the base of the lens. It can be seen from Figure 3

θ′ _n ＝μ′ _n +a _n ,a _n ＝θ _n +β′ _n ,β _n ＝μ _n (1-2)

In the formula, a _n represents the angle between the slope and the base of each small triangle, and μ _n and μ _n ' represent the angles between the incident light and the refracted light and the optical axis FF'.

sinθ′ _n =sin(μ′ _n +a _n ),sinθ′ _n =Nsinθ＝Nsin(a _n -β′ _n ) (1-3)

Nsin(a _n -β′ _n )=sin(μ′ _n +a _n ) (1-4)

Expand both sides of the above formula so that

sina _n (Ncosβ′ _n -cosμ′ _n )=cosa _n (sinμ′ _n +Nsinβ′ _n ) (1-5)

Right now:

From formula (1-1), we get

Substituting formula (1-7) into (1-6) we get:

The relationship between the angles and the traditional Fresnel lens formula can be obtained from the geometric relationship:

In the formula, f and f' are the distances from points F and F' to point O respectively; R _n and R' _n are the distances from point A and point B to the optical axis of the lens respectively.

k' _n represents the distance between the center point B on the small sawtooth inclined surface and the flat surface of the condenser, which can be expressed as:

K′ _n =tanα _n ×ΔR/2 (1-10)

When the LED light is incident on the plane side of the lens as shown in Figure 3, the size of f and f' required for the experiment is set according to the size of the LED structure. Furthermore, the required lenses are designed with equal sawtooth width, that is, each small The width of the sawtooth is ΔR, and because the height k _n of the sawtooth is much smaller than the focal length f', formula (1-8) can be expressed as:

All sawtooth parameters of the Fresnel lens can be calculated based on the required lens parameters.

Specifically in this patent, according to Figure 1: The relationship between LED typical normalized radiation power and divergence angle, the maximum value of μ _n cannot be 90° (the incident light is parallel to the lens plane at this time), and the light can only be minimized to minimize the divergence angle. The loss is based on the design and μ _nmax is 80°. Considering the nested installation relationship between the primary Fresnel lens and the LED, f must be greater than the height of the LED lamp bead. Since f is proportional to the radius of the Fresnel lens, in order to minimize the size of the primary Fresnel lens, f is chosen to be just greater than LED lamp bead height. Specifically, the LED size in this patent is: 5mm*5mm*1.6mm. The corresponding primary Fresnel lens design shape is a square base, the size is 20.43*20.43mm, the inscribed circle radius R=10.21mm, and the inner height h=3.4 mm, object distance f=1.8mm.

From a performance perspective, the sawtooth width should be as small as possible. When the sawtooth width is wider, the lens surface becomes smoother and the refraction angle of each small area does not change significantly, which will lead to inaccurate focusing and affect the optics of the lens. performance. But if the sawtooth width is too small, it will lead to manufacturing difficulties and increased costs. Therefore, considering cost and performance factors, the sawtooth width is selected to be 0.3mm.

The choice of focal length f’ is related to the angle of light at the focus, and the angle of light determines whether the light reaching the light well can form a guided wave, so the choice of f’ is crucial. From the perspective of optical performance, the larger f’ is, the better. However, on the other hand, f’ affects the overall structural thickness. From the perspective of packaging, the smaller f’ is, the better. Therefore, under the condition of being limited by the structure size, the single-stage Fresnel lens cannot achieve the optimal design of the lateral coupling optical performance of the LED-plastic optical fiber system. To this end, this patent proposes a design scheme in which a primary focusing Fresnel lens is superimposed on a secondary partitioned collimating Fresnel lens.

The secondary partitioned collimating Fresnel lens design method includes the following steps:

S301: Calculate the incoming light angle distribution based on the minimum focal length f’ of the primary focusing Fresnel lens; determine the acceptable minimum focal length f’ of the primary focusing Fresnel lens from the perspective of structural size. This patent takes the value of 10.21mm as an example.

S302: Calculate the light angle range of total internal reflection in the light well; the angle μ' _n between the refracted light and the optical axis FF' can be defined as the light angle of the secondary collimated Fresnel lens; calculate the value of the light angle μ' _n The range is: ±45° distributed in a cone. (As shown in Figure 3, μ' _n is forward biased counterclockwise and reverse biased clockwise)

S303: Calculate the light angle range of the guided wave; the light well total internal reflection light angle refers to the ±45° conical distribution of light within the light range obtained in step S301, which is reflected through the light well, and satisfies the requirement that total internal reflection occurs at the light well-air interface. The angle range of the reflected light; calculation method: θ _c -45°＜μ' _n <45°, where θ _c is the total internal reflection angle of the light well interface, After calculation, the total internal reflection light angle range caused by the 45° inclined light well is: -2.76°<μ' _n <+45°.

S304: Obtain the light angle range that satisfies the above steps S301-S303; the guided wave light angle range refers to the optical fiber with a specific numerical aperture receiving the light within a certain angle range, which can form a conduction mode in the waveguide; through the 45° light well Coupling, the conditions for forming a forward waveguide in a plastic optical fiber are: 0≤θ _in =μ' _n <180°arcsin(NA), where θ _in is the angle between the light and the optical fiber axis after reflection in the light well, and NA is the optical fiber axis. Numerical aperture; after calculation, it can be seen that when the numerical aperture NA of the optical fiber is 0.5, the light angle μ' _n is forward biased: 0° ~ +30°; the range of the light angle obtained in step S304 is: forward biased 0° ~ + 30°. (As shown in Figure 3, μ' _n is forward biased counterclockwise and reverse biased clockwise).

S305: Determine the size and position of the secondary partitioned collimating Fresnel lens; the secondary partitioned collimating Fresnel lens is placed close to the surface of the optical fiber; the size of the secondary partitioned collimating Fresnel lens is: based on the primary focusing Fresnel lens The focal point of the lens is the vertex, and the size of the projection surface of a cone with a cone angle of 90° on the upper surface of the optical fiber. Taking 2mm plastic optical fiber as an example, the focus of the primary focusing Fresnel lens is set at the axis of the optical fiber. After calculation, it can be found that the radius of the secondary Fresnel lens is 1mm (actual working area radius). Considering the installation fault tolerance performance, the secondary partition The actual processing radius size of the collimating Fresnel lens is: 2mm, and the sawtooth width is 0.1mm.

S306: Since S304 determines that the angle range of the incoming light that satisfies steps S301, S302 and S303 is 0° to +30°, this part of the light can naturally form a conduction mode in the optical fiber and cannot be collimated. Otherwise, it will As a result, most of the above-mentioned light cannot reach the light well, resulting in a significant decrease in coupling efficiency. Therefore, the secondary partitioned collimating Fresnel lens is eccentrically hollowed out; the hollowing range is: with the focus of the primary focusing Fresnel lens as the vertex, the half cone formed by the positive deflection of 30° is in the secondary zone. The projected area on the zoned collimating Fresnel lens;

S307: For the area of the secondary partitioned collimating Fresnel lens except for the eccentric hollow, perform a collimation design according to the angle of the incoming light; through collimation, the light well will be in the projection area of the secondary partitioned collimating Fresnel lens without the hollow part. The incoming light angle is deflected to 0° and irradiated onto the light well, meeting the conditions for forming a guided wave.

In this example, the effect of etching a 45° inclined light well on the surface of CK80 plastic optical fiber on the lateral coupling efficiency is discussed.

The experiment tested six combinations of laser etching power percentages of 15.5%, 16%, and 16.5%, and element diameters of 0.11mm and 0.12mm. A Han's 40-watt CO ₂ laser cutting machine was used to etch light wells on the surface of CK80 plastic optical fiber. The lateral coupling test was conducted using Solebo's high-stability 660nm LED light source. When the light source conditions remained unchanged, the lateral coupling efficiency of the 0° vertical etching light well and the 45° inclined etching light well were compared. The results are shown in Table 1. Show. Under the above six combination conditions, the actual measured lateral coupling efficiency of the 45° inclined etching light well increased by more than 300%.

Table 1 Side coupling efficiency of coupling structures with different tilt angles

Effect of Fresnel lens group on lateral coupling efficiency

Based on the above-mentioned 45° inclined etched light well, a dual-stage Fresnel lens is used to focus and partition the LED light source. The design parameters of the two lenses are shown in Table 2:

Table 2 Fresnel lens group design parameters

Taking the above parameters as an example, it can be estimated by using the projection method (ignoring the uneven light distribution) that the theoretical side coupling efficiency of a single-stage Fresnel lens is: 5.305%. After adding a secondary partitioned collimating Fresnel lens, the double-stage The theoretical side coupling efficiency of the Fresnel lens is: 6.785%. Compared with the theoretical side coupling efficiency of the single-stage Fresnel lens, the dual-stage Fresnel lens group has an improvement of nearly 28%.

Using the 45° inclined light well combined with the dual-stage Fresnel lens set described in this application, the theoretical side coupling efficiency can reach more than 6%. Compared with the 0° vertical etching light well lateral coupling efficiency (according to the measured value of 0.04%), the side coupling efficiency The overall theoretical improvement in coupling efficiency reaches more than 150 times.

The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person familiar with the technical field can easily think of changes or modifications within the technical scope disclosed in the present invention. All substitutions should be within the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims (9)

1. The lateral optical coupling enhancement method based on the 45-degree inclined optical well straight Fresnel lens is characterized by comprising the following steps of:

s1: processing a side coupling optical well on the side surface of the plastic optical fiber;

s2: the design and parameter selection of a primary focusing Fresnel lens are carried out, the primary focusing Fresnel lens converges LED radiation light, the light spot area of the primary focusing Fresnel lens is reduced, and the primary focusing Fresnel lens is focused above a light well;

s3: designing and selecting parameters of a secondary subarea collimating Fresnel lens, calculating and subareas according to the position and angle of incident light, wherein the secondary subarea collimating Fresnel lens comprises a central hollowed-out area and subarea collimating areas, so that LEDs are optically coupled into a light well to form an effective conduction mode to the greatest extent;

s4: and the primary focusing Fresnel lens and the secondary zoned collimating Fresnel lens are arranged between the LED lamp and the plastic optical fiber with the inclined optical well, so that the lateral optical coupling enhancement of the plastic optical fiber is realized.

2. The lateral optical coupling enhancement method based on the 45-degree inclined optical well straight fresnel lens according to claim 1, wherein the method comprises the following steps: the inclination angle of the side coupling light well is 45 degrees, and the specific processing steps comprise:

s101: cutting plastic optical fiber with required length and grinding end face;

s102: drawing by using a laser etching software system, and determining the minimum processing size and the graph as primitives;

s103: placing the plastic optical fiber by using an inclination angle instrument to enable the plastic optical fiber to generate a required inclination angle;

s104: vertically and unidirectionally punching the plastic optical fiber, and cleaning the punched optical well;

s105: and measuring the processed optical fiber single-gate straight-through optical power and side coupling optical power, and calculating the insertion loss and the side coupling efficiency of the optical fiber single-gate straight-through optical power and the side coupling optical power to determine whether a processed finished product is qualified or not.

3. The lateral optical coupling enhancement method based on the 45-degree inclined optical well straight fresnel lens according to claim 2, wherein the method comprises the following steps: one surface of the primary focusing Fresnel lens is in a plane shape, and the other surface of the primary focusing Fresnel lens is in a sawtooth shape with equal groove depth; the angles among the saw teeth are different, and each saw tooth ring can collect all projected light rays at one point;

the relationship between the angles in the primary focusing fresnel lens and the expression of the conventional fresnel lens formula are:

wherein mu is _n 、μ _n 'represents the angle between the incident light and the refracted light and the optical axis FF'; r is R _n And R'. _n The distances from the point A and the point B to the optical axis of the lens; f and F 'are the distances from points F and F' to point O, respectively; k' _n The distance between the center point B on the small sawtooth inclined surface and the straight surface of the collecting lens can be expressed as: k'. _n ＝tanα _n ×ΔR/2，a _n Representing the included angle between each small triangle inclined plane and the bottom side;

when the LED light is incident on one side of the plane of the lens, the f and f' sizes required by the experiment are set according to the size of the LED structure, and the lens with equal saw tooth width is adopted, namely the width of each small saw tooth is delta R, and the height k of the saw tooth _n Far less than the focal length f', the formula tan alpha _n Can be expressed as:

wherein N represents the ratio of the refractive index of the lens to the refractive index of air; and all sawtooth parameters of the primary focusing Fresnel lens can be calculated according to the parameters of the required lens.

4. A method for enhancing lateral optical coupling based on 45-degree inclined optical straight fresnel lenses according to claim 3, wherein: the secondary zone collimating fresnel lens design method comprises the steps of:

s301: calculating the light angle distribution according to the minimum focal length f' of the primary focusing Fresnel lens;

s302: calculating the total internal reflection incoming light angle range of the light well;

s303: calculating the angle range of guided wave incoming light;

s304: obtaining the incoming light angle range which simultaneously meets the steps S301-S303;

s305: determining the size and the position of a secondary partition collimating Fresnel lens;

s306: performing eccentric hollowed-out treatment on the secondary partition collimating Fresnel lens;

s307: and carrying out collimation design on the secondary subarea collimation Fresnel lens except the eccentric hollowed-out area according to the incoming light angle.

5. The lateral optical coupling enhancement method based on the 45-degree inclined optical well straight fresnel lens according to claim 4, wherein the method comprises the following steps: the angle between the refracted light and the optical axis FF 'is mu' _n May be defined as the secondary collimating fresnel lens acceptance angle; calculating the angle of the incoming light mu' _n The value range is as follows: the +/-45 degrees is distributed in a cone shape.

6. The lateral optical coupling enhancement method based on the 45-degree inclined optical well straight fresnel lens according to claim 5, wherein the method comprises the following steps: the total internal reflection light incoming angle of the light well means that the light incoming angle range of + -45 degrees is in cone distribution in the light incoming range obtained in the step S301, the light incoming angle range of the light which is reflected by the total internal reflection at the light well-air interface is met; the calculation method comprises the following steps: θ _c -45°＜μ' _n < 45 DEG, wherein theta _c Is the total internal reflection angle of the optical well interface,the total internal reflection light angle range caused by the 45 ° inclined light well is calculated as follows: -2.76 °<μ' _n <+45°。

7. The lateral optical coupling enhancement method based on the 45-degree inclined optical well straight fresnel lens according to claim 6, wherein the method comprises the following steps: the guided wave light incoming angle range means that an optical fiber with a specific numerical aperture receives incoming light within a certain angle range, and a conduction mode can be formed in the waveguide; the conditions for forming forward guided waves in the plastic optical fiber through 45 DEG optical well coupling are as follows: theta is 0 to or less _in ＝μ' _n < 180 DEG arcsin (NA), wherein θ _in The NA is the numerical aperture of the optical fiber, which is the included angle between the light reflected by the optical well and the optical fiber axis; it is found from the calculation that the angle of arrival μ 'is obtained when the numerical aperture NA of the optical fiber is 0.5' _n Forward bias: 0 to +30°; the angle range of the incoming light obtained in step S304 is: forward bias 0 deg. +30 deg..

8. The lateral optical coupling enhancement method based on the 45-degree inclined optical well straight fresnel lens according to claim 7, wherein: the secondary subarea collimating Fresnel lens is placed against the surface of the optical fiber; the secondary zone collimating fresnel lens has a size of: the projection surface of the cone with the cone angle of 90 degrees on the upper surface position of the optical fiber takes the focus of the primary focusing Fresnel lens as the vertex.

9. The lateral optical coupling enhancement method based on the 45-degree inclined optical well straight fresnel lens according to claim 8, wherein the method comprises the following steps: the hollowed-out range is as follows: taking the focus of the primary focusing Fresnel lens as a vertex, forward biasing a half cone formed by 30 degrees to form a projection area of the half cone formed on the secondary subarea collimating Fresnel lens; the collimation is carried out to enable the light incoming angle of the light coming from the projection area of the secondary subarea collimation Fresnel lens, which is used for removing the hollowed-out part, to be deflected to 0 degrees and to irradiate the light well, so that the condition of forming guided waves is met.