JP2016118750A - Chip type handle fiber multiplexer and chip type multi-wavelength light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact and thin chip type RGB or RGB+NIR multi-wavelength laser light source mounted in a portable mobile phone enabling mass production at low cost and with high reliability and spectacle type laser projector, and a multiplexer of a plurality of laser light sources used in the above laser source.SOLUTION: With N pieces of fiber elements 31i having extremely thin cladding, emission ends 314 thereof are bundled in closely contact manner, and fixed to a chip type plate 305, thereby constituting a bundle fiber multiplexer. Thus, formed is a spatial chip type multiplexer of light beam having a ratio of input to output of N:1. By mounting N pieces of surface-mount type LD light sources 301, 302, 303, a compact chip type multi-wavelength laser light source is formed.SELECTED DRAWING: Figure 3

Description

The present invention is an image processing apparatus, an endoscope and an ophthalmic apparatus, etc., medical diagnosis and treatment using light, optical communication, and a scanning projector using MEMS or a projection projector using LCOS RGB (R = Red, G = Green, B = Blue wavelength) The present invention relates to a technique for increasing the output of a point light source by combining with a multi-wavelength laser in an application device such as a light source or by spatially combining multiple LDs of the same wavelength.

Conventional optical fiber communication multiplexers and demultiplexers using fiber wavelength multiplexing often use array waveguide gratings (AWG = Array Wave-Guide Grating) in the case of Dense Wavelength Division Multiplexing (DWDM). (Patent Document 1 as an example). Recently, since a projector-type small laser display is put into practical use in a mobile phone and a vehicle, there is a miniaturized waveguide-type RGB three-wavelength multiplexer (see, for example, Patent Document 2). There are also low-cost and high-coupling-efficiency fiber outputs and filter-type RGB multiplexers for in-vehicle head-up and glasses-type laser projectors (see, for example, Patent Document 3).

  JP 2005-234245 A   JP 2013-195603 A   JP2013-228651A

Various conventional multi-wavelength multiplexers and demultiplexers can be made by the conventional technology as described above. However, these conventional optical multiplexers and devices such as medical devices using lasers, image processing and display devices, and projection televisions can be used. There are several conditions and restrictions that apply to wavers as follows.

First, the multiplexer according to the conventional technology has a high manufacturing cost, and it is difficult to reduce the cost at the manufacturing stage, especially for the extremely low cost required for mass products such as mobile phones. In addition, there are several conventional techniques for combining wavelengths. However, as the number of combined wavelengths increases, the cost increases while the loss of combined light increases rapidly. It becomes a challenge.

In the conventional technology, there is a limit on the bandwidth of each beam wavelength due to the wavelength dependence of the multiplexer, and as two extreme special cases, the wavelength that cannot have the bundle width is very close or multiple light sources of the same wavelength In addition, in the case of a plurality of light sources in the case where the bundle width is too wide by several hundreds of nanometers or more between wavelengths, there is a problem that such a limitation is imposed, which is a problem to be solved. Furthermore, another object of the present invention is to be able to easily and efficiently input a light beam from a light source to be combined into a multiplexer.

In the multiplexer using the N-to-1 bundle fiber according to the first aspect of the present invention, one specific light in N light beams placed in a specific one in the N fibers side by side on the input side. Is output from the end face of the corresponding fiber as it is in the N fibers bundled on the output side, so that there is almost no loss of the light beam of each wavelength in each fiber inside the multiplexer. The optical efficiency of the main body has reached almost 100%.

In addition, the fiber diameter used for the multiplexer is a glass fiber used for general optical communication. In the case of a single transverse mode fiber, the core diameter is about several μm (= micrometer), but it is easy to handle. The clad diameter becomes 125 μm, and a distance of 125 μm or more is left between the cores of the bundled fibers.

Instead, the fiber strand composed of the N cores and the clad described in the multiplexer of claim 1 has a core diameter of about several μm in the case of a single or low-order transverse mode. The thickness of the clad to be thinned is about 1 μm or less than 1 μm, so the outer diameter of the strands is 10 μm or less, and the output end faces of the N fibers are in close contact with the output side of the multiplexer. Therefore, the distance between each core of each fiber is very close to about 10 μm.

The N beams emitted from the emission ends of the N fibers are converged to one point light source at a practical level on the output side of the multiplexer bundled by the above-described means with such fiber strands. Then, it is combined into one beam and output.

In order to verify this issue, let us examine by collimating the N outgoing beams from the outgoing ends of the N fibers into parallel light using a lens with a focal length = F on the output side of the multiplexer. For example, N = 3 for RGB three-color combination of red, green and blue, and the fiber strand is made into a single mode with NA = 0.12 and core diameter = 5 μm, and the cladding thickness is reduced to 1.5 μm. Assuming that the outer diameter of the wire is Φ = 8 μm, the core-to-core spacing between any two of the three fibers bundled at the output end in the above method is D (= elementary wire outer diameter Φ) = 8 μm. The angle between any two of the three parallel light beams that are collimated and emitted, with the lens set to F = 10 mm,
θ = 2 × tan ⁻¹ (D ÷ 2 ÷ F) = 0.0458 ° ≦ 0.8 mrad
The unit of the angle in the equation is micron arc degree = mard (= milli-radian). Here, the angle of θ ≦ 0.8 mrad is as small as the divergence angle of the three collimated RGB laser beams.

That is, in the case of RGB three wavelengths when a plurality of N = 3, as long as the specifications of the fiber strand described in claim 1 and the conditions for bundling are met, 3 of the three fibers are connected to the output end of the multiplexer. The three RGB beams outputted from the three point light sources from the single emission end face are regarded as one beam emitted from one point light source at a practical level.

The verification regarding the same optical axis property of the three beams coming out from the bundle fiber exit end face when N = 3 is as follows. Applicable to practical level.

The selection of fiber strands used in the multiplexer of claim 1 when N single transverse mode LDs with different N wavelengths are used as the light source. The mode field diameter MFD (= Mode Field Diameter) of the light propagating in the fiber is different depending on the diameter and the numerical aperture NA. In many cases, a single transverse mode cannot be set to all wavelengths with a kind of fiber strands with respect to the total bandwidth of a plurality of N wavelengths combined.

In the case of claim 1, N fibers are used independently and only bundled at the output end. Therefore, the core diameter and NA are independently selected for each fiber according to each wavelength, and the N wavelengths are different. It is possible to satisfy the conditions of a single transverse mode fiber for all of the light beams.

In addition, unlike the general waveguide type and filter type multiplexing, the wavelength dependency of the multiplexer is almost independent in claim 1 since it is based on spatial multiplexing. It will be general purpose. In other words, a spatially independent light source can be applied to a plurality of light sources having only the same wavelength or a plurality of light sources having different wavelengths and the same wavelength. For example, in the case of three LDs with three RGB wavelengths, the multiplexer of claim 1 can also be applied to RGGB, that is, one each of red and blue wavelengths and two green wavelengths, for a total of four LDs.

According to the first aspect of the present invention, since the optical fibers are multiplexed by the bundled fibers, the optical efficiency of the multiplexer main body is almost 100%. Note that the number of light beams combined with light efficiency is irrelevant, and the effect of light efficiency increases as the number increases.

In addition, in the case of beam multiplexing from a multiple wavelength single transverse mode light source, each fiber is individually selected according to the transverse mode of the wavelength beam of each light source to be multiplexed in the bundle fiber system. Maximum spatial coherence of the output beam from each light source can be maintained.

In addition, since the multiplexer using the bundle fiber is a chip type, it is indispensable for the compact and thin chip type multi-wavelength light source made from the multiple surface mount laser diode (LD) light source of the multiple wavelength described in claim 2. There will be no key parts.

Chip-type multiplexers using such bundle fibers can dramatically reduce costs compared to conventional waveguide-type or filter-type multiplexers having a dual wavelength such as long path or short path, In addition, the light coupling efficiency between the single transverse mode LD and the single transverse mode fiber is easily increased, and it is easy to mount between the two. Therefore, the compact and thin chip type RGB laser light source as in claim 2 is used. High reliability and mass production are possible at low cost.

The chip type multiplexer using the bundle fiber described in claim 1 of the present invention, which is used for multiplexing N = 3 and RGB three-wavelength single transverse mode LD, is shown in the CAD drawing of FIG. The basic structure is shown.

Since the light source is a single transverse mode LD, if the strand used is a single transverse mode, that is, NA = 0.12 to 0.13 and the core diameter Φ = 3.5 to 4.0 μm, the beam of the original LD The spatial coherence of is not destroyed.

However, since the clad diameter of the commercially available single transverse mode fiber is Φ125 μm, the ideal fiber strand for the first embodiment has a core diameter of Φ4 μm and a clad diameter of Φ8 to 10 μm. On the practical level, existing fiber strands with NA = 0.2, core diameter Φ7 μm, and cladding diameter Φ10 μm are bundled and used in a multiplexer. In such a first claim, the RGB multiplexer of N = 3 is a chip type having a width and a length of about 6 mm and a thickness of about 2 mm.

FIG. 2 shows a photomicrograph of the output end face of the fiber bundled on the output side of the RGB three-wavelength single transverse mode multiplexer of Example 1 configured in FIG. As shown in the photograph, the distance between adjacent cores of three closely bundled fibers is about 10 μm.

As a manufacturing method, in order to finish the end faces of the three bundled fibers by polishing, a strand is put in a glass tube ferrule having a diameter of about 1 mm and having an outer diameter of about 25 mm, and fixed with an adhesive.

As described above, there is almost no optical propagation loss in the main body of the first embodiment, but when the coupling efficiency of light from the LD to the fiber is examined on the input side of the multiplexer, a laser beam from a single transverse mode 638 nm wavelength LD is obtained. Active alignment, that is, the beam from the LD as the light source is output while adjusting the optical axis of the coupling lens, and the light is input to the fiber entrance end face, with a throughput of about 85% at the bundled fiber exit end. Output has been obtained. In order to further improve the optical efficiency, an antireflection dielectric thin film can be attached to both the incident and exit end faces of the fiber.

The transverse mode characteristics of the 638-nm light beam emitted from the fiber on the output side of the multiplexer were also examined, but the quality of the beam transverse mode M square M ^ = 2 or less. In other words, the transverse mode of the beam actually output in the first embodiment is considerably better than M ^ 2 = 3.4 calculated from the core diameter of the fiber strand main body of 7 μm and NA of 0.2.

The reason for this is that the length of the fiber strand of the first embodiment multiplexer is about 6 mm, the propagation distance of the beam is extremely short, and the effect of mixing the beam into the higher mode is still apparent. In other words, the input beam reaches the output end without breaking the transverse mode.

Further, the light beam emitted from the bundle fiber of RGB of three wavelengths of 638 nm, 520 nm and 450 nm is collimated on the output side of the first embodiment using an achromatic lens having a focal length of 20 mm, and the beam diameter is advanced one meter ahead. The three RGB three-color laser beam spot diameters measured when adjusted to be minimized are approximately Φ1 mm or less (M ^ 2 ≦ 2), and the three wavelength beams are still separated from each other. Since the distance is about ≦ 0.5 mm and is in one concentric circle of Φ1.5 mm, it can be used as one beam of three wavelengths at a practical level.

FIG. 3 shows a basic configuration of a chip-type RGB three-wavelength same-axis output light source described in claim 2 as a second embodiment using the multiplexer according to the first embodiment of the present invention. Yes.

The single transverse mode LD, which is a light source, is a surface-mounted chip type, and its outer shape is 0.8 mm wide, 2.0 mm long, and 0.3 mm thick. For convenience of mounting, three LDs with three wavelengths of RGB are fixed on a heat sink of a copper plate in a horizontal row at equal intervals of 2 mm on the input side of the first embodiment. In the case of the second embodiment, the laser beam is directly coupled from the LD to the fiber without a lens, and an output of about 50% is output to the bundled fiber exit end.

In the arrangement shown in the configuration diagram of FIG. 3, since light is directly coupled one-to-one between one LD emission point and the incident end face of the other fiber, the light is transmitted to the fiber to improve the coupling efficiency. Beam alignment alignment accuracy is essential within ± 0.5μm. In the case of the second embodiment, all three RGB LDs arranged side by side on the light source side and one side of the RGB incident fiber end face arranged side by side on the partner multiplexer input side are also arranged. This is very difficult because it requires the same accuracy within ± 0.5μm.

Instead, by using a coupling lens to couple the light between the LD emission point and the mating fiber receiving end face, the mounting accuracy of the LD and the fiber receiving end face of the mating coupler input side can be adjusted. Can be relaxed. The coupling efficiency of the light to the fiber can be improved by aligning the position of the multiplexer fiber with the V-groove, or by actively aligning and assembling the LD to increase the accuracy.

The RGB three-wavelength chip type light source of Example 2 has an outer shape of 6 mm in width, 8.5 mm in length, and 1.8 mm in thickness as shown in FIG. 3 when light is directly coupled between the LD and the fiber without a lens. The optical coupling efficiency between the LD and the multiplexer fiber can only be about 50%. When a coupling lens is used between the light source LD and the light receiving end face of the multiplexer fiber, the light coupling efficiency can be increased to 75% or more, but the outer shape becomes 11 mm in the length direction. The chip-type RGB light source of Example 2 having a high light throughput thus created is currently at a maximum power of 80 mW for red 638 nm, 55 mW for green 520 nm, and 50 mW for wavelength 450 m blue, both from the fiber to the three wavelengths. It is output with a beam of almost single transverse mode, and has reached the high brightness and high output required for projection projectors for in-vehicle and mobile phones.

The chip-type multiplexer using the bundle fiber according to claim 1 is a single point in which the optical axes are aligned by spatially multiplexing N independent light beams from a plurality of N spatially independent light sources. Since it can be output as a light source, when multiple N = 3, RGB three primary colors, or when N = 4, sensing infrared wavelengths are added, and light from four independent light sources LD is low-cost and highly practical. In addition to RGB three-wavelength or near-infrared NIR (= Near Infrared) in the level, it can be expected to be applied to a laser projector using a MEMS scan as one point light source combined at four wavelengths.

Note that the multi-wavelength light source such as the chip type RGB or RGB + NIR to be miniaturized as in claim 2 is the first to be miniaturized in the glasses type which is extremely compact and requires thinness and the projection type display incorporated in the mobile phone. In addition, it is also indispensable for these applications because it is realized with high brightness and high output more than necessary for in-vehicle and mobile phone projectors.

  As a first embodiment, a three-beam input and one-beam output three-to-one optical beam spatial multiplexer using a plurality of N = 3 bundle fibers described in claim 1   Photomicrograph of the output end face of the three fibers bundled in the ferrule diameter Φ25 μm hole at the output end of the multiplexer of Example 1   As Example 2, three spatially independent lights of 638 nm, 520 nm and 450 nm RGB three-wavelength single transverse mode surface-mounted LDs mounted on the input side of the multiplexer when N = 3 in Example 1 Compact and thin chip type RGB laser light source that is output as one point light source from the beam to the output side of the multiplexer

References relating to FIG.
100 Chip plate 101 to which the fiber of the multiplexer described in claim 1 is fixed. Input side 102 of the multiplexer. Output side 103 of the multiplexer. Groove for determining the fixing position of the fiber on the 100 or more chip template plates. 110 Multiplex N = Three Fiber Outlet Ends 111 Bundled on the Multiplexer Output Side, First End of Fiber Input 112 on the Input Side of the Multiplexer 112 Incoming End Face of the Second Fiber on the Input Side of the Multiplexer 113 Multiplexer The incident end face of the third fiber on the input side.
200 Polished ferrule end face 211 A fiber strand with a cladding diameter of 10 μm bundled with the ferrule end face No. 212 A fiber strand with a cladding diameter of 10 μm bundled with the ferrule end face No. 213 A clad diameter bundled with the ferrule end face of 10 μm Three or more fiber strands Three or more fiber strands are closely bundled into equilateral triangles. 221 Fiber core 222 that is well reflected in the photograph. Scale, unit length = 10μm
References relating to FIG.
301 Blue Wavelength 450nm Surface Mount Single Transverse Mode LD
302 Red (Red) wavelength 638nm surface mount single transverse mode LD
303 Green Wavelength 520nm Surface Mount Single Transverse Mode LD
304 Heat sink copper plate for RGB three-wavelength LD 305 Chip template 31i i = 1, 2, 3, to which the fiber of the multiplexer described in claim 1 is fixed. (1) A plurality of N = 3 fibers mounted in the direct optical coupling method, and in the case of the first embodiment, the core of the three fiber strands has a diameter of Φ7 μm, NA of 0.2, and a cladding diameter of Φ10 μm. 314 Output end face of plural N = 3 fibers bundled on the output side of the multiplexer satisfying the condition described in claim 1

Claims (2)

Spatial multiplexing of N point light sources or N light beams spatially independent from N parallel light output lasers so that the optical axes are aligned to form a single point light source. N optical fiber strands composed of one chip template made of glass or metal, and a core and a clad polished for light guide at the entrance end face and the exit end face in advance. A space in which light input and output sides are provided on both sides of the chip template, and the input ends of the N fiber strands are to be combined at the input side edge of the chip template. Are fixed with an adhesive in a row at regular intervals according to the incident positions of N light beams from N light sources that are independent from each other, and also on the output side edge of the chip template. The exit ends of the N fiber strands are tightly bundled with each other and fixed with an adhesive. When preparing N fiber strands composed of a core and a clad, the clad diameter is made extremely thin in advance, that is, the cladding encased in the core of the N fiber strands is made thinner to the limit. The N light beams output from the N fiber exit end faces, which are usually regarded as N point light sources, are closely bundled with the exit ends of the N fibers. Since the two cores are very close to each other, they are converged and output as one point light source. That is, N light beams from the N light sources spatially independent are output. Spatial multiplexing of a chip-type N-to-1 beam using a bundle fiber characterized in that it is combined and output as a single point light source at a practical level at the output end. vessel A bundle for satisfying the condition described in claim 1 for the purpose of making a compact and thin chip type multi-wavelength light source, and a plurality of N LD (= Laser Diode) light sources having different N wavelengths in a surface mount thin chip type A chip-type N-to-1 spatial multiplexer using fiber is prepared in advance, and N spatially independent light beams from the N light sources are directly joined to the N fibers on the multiplexer input side, or The N light beams that are coupled using a lens and are emitted from the N bundle fibers to the output side of the multiplexer are converged according to the spatial multiplexing principle described in claim 1 and A compact chip-type multi-wavelength laser light source with a point light source output using a bundle fiber multiplexer characterized by being output as a light source