KR20040062073A - Optical fiber-coupling system using micro lens array - Google Patents

Abstract

The optical fiber combiner using the microlens array of the present invention comprises an optical fiber combiner 14 for coupling the laser beam generated from the high power laser diode 11 to the output end optical fiber 24 having a small aperture ratio. The combiner 14 is formed by providing a multimode optical fiber 22 and a two-dimensional lens 23 on the upper surface of the silicon substrate 21, and is provided on the silicon substrate 21 by a semiconductor integrated process. By allowing the two-dimensional lens 23 to be made of a thick film photosensitive film, a precise coupler can be manufactured simply and easily, and can be easily modified even when a correction is required after production.

Description

Optical fiber coupler using microlens array {OPTICAL FIBER-COUPLING SYSTEM USING MICRO LENS ARRAY}

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a microscopic optical structure that allows a beam emitted from a laser diode to be incident on an optical bundle. More specifically, the optical bundle of an optical fiber bundle having a small aperture ratio is optically coupled to a high power laser diode array. The present invention relates to a fiber-coupler using a microlens array that is simply fabricated using a semiconductor integrated process to produce a microlens array necessary for collimating a beam emitted from a laser diode for coupling.

Recently, a lot of research is being actively conducted on high power semiconductor lasers as demand for high power laser light increases and new application fields are expanded. Applications include laser-based displays such as CD-RW and DVD-RAM, large-screen projectors, laser radio communications, material processing using lasers (welding, cutting, semiconductor-related fine processing, etc.), medical, Applicability is expanding to military and optical amplifiers, pumping light sources, and the like.

In the case of a pumping light source, a material processing, or a medical laser of a solid laser by a laser, a high light output of several W grade or more is required. In particular, the excitation of a solid laser is a method of making a high power laser diode into an array form. In order to increase the effectiveness of the array of laser diodes, a laser diode array beam is coupled to an optical fiber and bundled into a fiber to emit high light from the laser diode. You can get the output. It is used as a fiber-coupling system combining a microlens array that serves to collimate a diode array beam with an optical fiber array with an appropriate aperture ratio and core diameter, depending on the application.

Conventional fiber couplers, including two-dimensional microlenses, are devices designed for the beam form of multimode high power diode lasers. In order to reduce the divergence of the laser light source and couple to the optical fiber, the conventional optical fiber combiner requires a complicated lens structure of three-dimensional shape and a high performance optical system.

The angle emitted by the laser diode is determined by the structure of the laser diode. In the case of a high power laser diode, the angle is generally in the range of about 32-44 ° in length and 8-12 ° in width. The reason is that the size of the cross section of the semiconductor laser oscillation region is very small (a few micrometers), so that the overall transverse mode distribution is elliptical. Because of this asymmetry of the divergence angle, it is desirable to reduce the divergence angle of the laser beam in order to increase the pumping efficiency of the optical fiber amplifier. In this case, it is possible to reduce the divergence angle and combine the optical fiber with an optical system utilizing a predetermined lens.

1 is a schematic view showing a conventional optical fiber coupler, as shown here, the role of the lens as in a) serves as a lens for collimating a vertical beam shape with a large divergence angle from the diode, and as in b) Its role is to project the beam shape in the lateral direction of the diode into the optical fiber waveguide spot, by which the conventional fiber coupler converts the beam shape of the laser.

As a result, the lens in a) has a high numerical aperture and collimates on the axis with a large divergence angle, and the lens in b) projects an extended light source along the small axis of the diode's divergence angle.

The beam shaping function of the fiber-coupler forms an almost circular spot and can be used to excite the laser mode. The efficiency of this structure depends not only on the optics but also on diode lasers and optical fibers.

To achieve maximum performance with a fiber-coupler, the divergence angle of the laser should be as small as possible and the aperture and core size of the optical fiber should be as large as possible, but accurate alignment is required according to the dimensions of the optical system required. Light entering the optical fiber at a small angle is totally reflected at the core cladding contact surface and some of it is absorbed, which can cause a decrease in output. Therefore, the combiner needs to design the optical system to achieve the maximum coupling efficiency, and the light source including the optical fiber should be considered to be optimized. Collimating lenses reduce the divergence angle of the diode beam and increase the energy density for excitation.

In the case of a high power laser diode array, an aperture ratio of 0.16-0.39 is commonly used, and a core size of 100-600 μm is often used. In particular, fiber laser diodes with a small numerical aperture (N, A) value are important for medical and solid-state laser pumping. Such microlenses use injection molding methods for lenses made of glass. It is manufactured. In addition, the lenses manufactured as described above may be used by attaching two lenses to collimate the beam in the vertical direction. Alternatively, a lens having a cylindrical shape may be applied to the combiner.

However, the conventional optical fiber-coupler as described above is attached to a plurality of lenses in order to focus the beam collimated by the microlenses separately aligned with the laser diode, and to collimate the beam collimated by such microlenses into the optical fiber. Or a bundle of optical fibers arranged at regular intervals to obtain high output beams. However, the lenses used in such conventional optical fiber couplers are manufactured by injection molding using a mold, which is expensive. It was difficult to modify, difficult to assemble, and there was a problem that it was difficult to assemble precisely.

SUMMARY OF THE INVENTION An object of the present invention devised in view of the above problems is to provide a fiber-coupler using a microlens array suitable for simple fabrication and easy modification at low cost using a semiconductor integrated process.

1 is a schematic view showing a conventional optical fiber coupler.

Figure 2 is a perspective view showing an optical fiber coupler using a fine lens array in the present invention.

3 is a plan view of FIG.

4 is a longitudinal cross-sectional view of FIG.

5 is a cross-sectional view taken along the line A-A 'of FIG.

Figure 6 is a longitudinal sectional view showing a manufacturing procedure of the present invention.

Explanation of symbols on the main parts of the drawings

11 laser diode 14 fiber optic coupler

21 silicon substrate 22 multimode optical fiber

23: two-dimensional lens 24: optical fiber

31,32: settling groove

In order to achieve the object of the present invention as described above

In a fine optical system in which a beam emitted from a laser diode is coupled to an optical fiber at an output end by an optical fiber coupler,

The optical fiber-coupler is a silicon substrate installed between the laser diode and the optical fiber,

A multimode optical fiber installed at one end of an upper surface of the substrate and collimating the beam in a vertical direction among beams emitted from a laser diode;

A microlens array comprising a two-dimensional lens made of a thick film photosensitive agent formed on the rear side of the multimode optical fiber by a semiconductor integrated process to collimate the horizontal beam among the beams passing through the multimode optical fiber. There is provided an optical fiber coupler.

Hereinafter, with reference to the embodiment of the accompanying drawings, the optical fiber-coupler using the present invention fine lens array is configured as described in more detail as follows.

2 is a perspective view showing an optical fiber coupler using a microlens array according to the present invention, FIG. 3 is a plan view of FIG. 2, and FIG. 4 is a longitudinal sectional view of FIG. 2.

As shown in the drawing, in the present invention, a plurality of laser diodes 11 for emitting a laser beam are arranged so that a laser diode array 12 is arranged, and an optical fiber array 13 at an output end is arranged on the other side. An optical fiber coupler 14 is disposed between the laser diode array 12 and the optical fiber array 13.

The optical fiber-coupler 14 has a cylindrical multimode optical fiber 22 for focusing the vertical beam emitted from the laser diode 11 in the form of a spot at the front end of the upper surface of the silicon substrate 21 in the shape of a plate. And two-dimensional lenses 23 made of a thick film photosensitive material are formed on the rear of the multi-mode optical fiber 22 so as to collimate the beam in the horizontal direction. In the rear, optical fibers 24 are disposed, respectively.

The multi-mode optical fiber 22 is bonded to the upper surface of the substrate 21 serves to focus the vertical beam in the form of spots of the elliptical diverging beams generated by the diverging angle of the horizontal and vertical in the laser diode 11. Such a multi-mode optical fiber 22 is composed of a cladding and a core showing a slight difference in refractive index, but can be ignored because the beam is incident from the side.

In addition, the two-dimensional lens 23 is a thick film photosensitive agent such as SU-8 formed on the upper surface of the substrate 21 by a semiconductor process, and is made of epoxy resin having excellent optical and chemical properties. The laser beam can be adjusted to a desired angle. In addition, high aspect ratio structures of several hundred μm can be fabricated by patterning them close to vertical. In particular, in order to use a thick film photoresist as a lens, it is preferable that the surface roughness is flat to 1/10 or less of the minimum beam wavelength, and SU-8 has a characteristic that the surface roughness of the side surface after the photographing process is very small, such as several nanometers.

Accordingly, the thickness of the optical fiber 24 can be formed in a thickness of about 100 μm, and the two-dimensional lens 23 formed as described above reduces the vertical and horizontal divergence angle of the beam together with the multi-mode optical fiber 22. It is possible to couple to the optical fiber 24 of the output terminal.

As described above, the dimensional accuracy and alignment of the laser diode 11, the multimode optical fiber 22, and the two-dimensional lens 23 are very important, and it is desirable to have an effective aperture within a tolerance by design. Tolerance is a very important factor such as the distance between the laser diode 11 and the multimode optical fiber 22, the alignment between the multimode optical fiber 22 and the two-dimensional lens 23, the multimode optical fiber 22 And the beam collimated by the two-dimensional lens 23 is focused onto the aligned output end optical fiber 24. At this time, when the optical fiber 24 has an aperture ratio, the effective distance is long, so that the use of the high power beam passing through the rear optical fiber bundle 25 can be efficiently performed. Therefore, proper design is needed for the distance between the components and the curvature of the two-dimensional lens 23 for accurate alignment of the output end optical fiber 24 with the size of the collimated beam and the small aperture ratio. Alignment can be easily manufactured by using a photolithography process and anisotropic silicon wet etching process using the silicon substrate 21 widely used in the semiconductor process. The beam passing through the output stage optical fiber 24 manufactured as described above is combined into one by the optical fiber bundle 25 to be used as a high power pumping source of a solid state laser.

FIG. 5 is a cross-sectional view taken along the line AA ′ of FIG. 2, but the optical fiber bundle 25 in the present embodiment has been described with four optical fibers 24 configured in a bundle form, but the optical fiber 24 has a symmetry and has a honeycomb shape. It is possible to increase the number to 7, 19, 37, etc., and as the optical fiber 24 is increased, the number of laser diodes 11 and the two-dimensional lens 23 corresponding to the same is increased. Although the output port is increased in this way, the precise lenses can be easily configured by the semiconductor integrated process in the present invention.

2, 3, and 4, the multi-mode optical fiber 22 disposed at one end of the upper surface of the silicon substrate 21 has a "V" type seating groove 31 formed at a predetermined depth. It is bonded in the state seated on, the optical fiber 24 installed on the upper surface of the substrate 21 is also bonded in a state seated in the "V" type mounting groove 32 formed in a predetermined depth, and thus formed The mounting grooves 31 and 32 are formed in the (100) silicon substrate 21 by a wet etching process.

FIG. 6 is a longitudinal sectional view showing a manufacturing procedure of the present invention. Referring to the manufacturing method of the present invention with reference to this, mask patterning is performed on the upper surface of the (100) -oriented silicon wafer substrate 21 through a photo drawing process. Then, an anisotropic wet etching process is performed using a chemical solution such as KOH to form seating grooves 31 and 32 having a predetermined depth as in a).

Then, the SU-8 photosensitive agent is coated on the upper surface of the substrate 21, and a two-dimensional lens 23 having a curvature designed as shown in b) is formed through a photographic drawing process.

Thereafter, the multimode optical fiber 22 and the optical fiber 24 at the output end are aligned and bonded to the seating grooves 31 and 32 formed as described above using a UV adhesive or a thermosetting adhesive. At this time, it is preferable that the surface of the optical fiber 24 is polished (polishing).

Finally, MgF is applied to the multimode optical fiber 22, the two-dimensional lens 23, and the optical fiber 24, as in d), to increase the transmission efficiency.₂ It is completed by thinly coating the anti-reflection film 33 such as through a sputtering method or the like.

The most important point in each of the above components is accurate alignment and optical design and manufacture, and the precise alignment with the laser diode 11 is also important.

As described in detail above, the optical fiber-coupler using the microlens array of the present invention is a multiplexer installed on the upper surface of the substrate by a semiconductor integrated process when combining the laser beam generated from a high-power laser diode into an output optical fiber bundle having a small aperture ratio By making the coupling by the mode optical fiber and the two-dimensional lens, it is possible to easily and precisely produce a more precise coupler than when manufacturing a fiber-coupler by installing a plurality of lenses as in the prior art.

In addition, the optical fiber coupler manufactured as described above may be applied as an optical coupler of a device that requires a high power laser such as a display using a laser, an optical communication, a material processing device using a laser, a medical device, an optical amplifier, a pumping light source, and the like.

Claims (3)

In a fine optical system in which a beam emitted from a laser diode is coupled to an optical fiber at an output end by an optical fiber coupler, The optical fiber-coupler is a silicon substrate installed between the laser diode and the optical fiber, A multimode optical fiber installed at one end of an upper surface of the substrate and collimating a vertical beam among beams emitted from a laser diode; A microlens array comprising a two-dimensional lens made of a thick film photosensitive agent formed on the rear side of the multimode optical fiber by a semiconductor integrated process to collimate the horizontal beam among the beams passing through the multimode optical fiber. Fiber-coupler using the. The method of claim 1, The multi-mode optical fiber and the optical fiber of the output terminal is a fiber-coupler using a microlens array, characterized in that seated in the mounting groove formed in a predetermined depth on the upper surface of the substrate and bonded. The method of claim 1, The thick film photosensitive agent is a optical photo-coupler using a microlens array, characterized in that the polymer photosensitive agent SU-8.