JP4435003B2 - Laser diode array or optical coupling structure for coupling with laser diode - Google Patents

Description

The present invention relates to a laser diode array or an optical coupling structure for coupling with a laser diode.

  A laser diode array in which a plurality of light emitting surfaces (emitter surfaces) are arranged in parallel on the same substrate is similarly coupled to an optical fiber array in which a plurality of optical fibers are arranged in parallel, thereby providing a high-power laser light source system. It is used. This laser light source system is used in, for example, the optical communication field, the medical laser field, and the processing laser field because of its high output characteristics.

As a method of optically coupling the laser diode array and the optical fiber array, a method of matching the laser diode array and the optical fiber array is common.
However, the light emitting point of the laser diode array has a different numerical aperture (NA) between the vertical direction and the horizontal direction. Generally, the numerical aperture in the horizontal direction is 0.1 to 0.2, whereas the numerical aperture (NA) is vertical. Since the number is as large as 0.3 to 0.4, the output light energy emitted from the emitter surface is rapidly diverged. Therefore, in order to efficiently couple the two, an optical fiber array is configured using optical fibers having a numerical aperture larger than the numerical aperture in the vertical direction of the emitter surface, and the light incident surface of the optical fiber array is set as the laser diode array. It is necessary to place it as close as possible to the emitter surface.

Various proposals have been made so far in order to efficiently couple the output light of the laser diode array to the optical fiber array (see, for example, Patent Documents 1 to 4). When such a high-power laser light source system is used in the optical communication field, the medical laser field, and the processing laser field, a higher optical power density is required. Therefore, it is desirable that the cross-sectional area of the core of the optical fiber that receives the output light from the laser diode array be as small as possible.
JP-A-5-93828 Japanese Utility Model Publication No. 5-1111 US Pat. No. 5,734,766 U.S. Pat. No. 4,818,062

However, when an optical fiber having a general quartz core / quartz cladding is used as an optical fiber for constituting an optical fiber array, a difference in refractive index between the core and the cladding cannot be sufficiently obtained. It is impossible to make the core of the optical fiber have a numerical aperture larger than the numerical aperture of the emitter surface of the array. In this case, by installing a lens array between the emitter surface of the laser diode array and the light receiving surface of the optical fiber, it is possible to optically couple by changing the numerical aperture, but the cross-sectional area of the core of the optical fiber is large. As a result, the optical power density is reduced.
In the case of an optical fiber using a resin clad with a low refractive index instead of an optical fiber having a quartz cladding, the numerical aperture of the core increases, but the output light of the laser diode array may cause burning on the optical fiber receiving surface. Is expensive.

This invention is made | formed in view of the said situation, and makes it a subject to provide the optical coupling structure which can achieve a sufficiently large numerical aperture and incidence of a higher optical power density simultaneously.

In order to solve the above-mentioned problems, the present invention provides a laser diode array in which a plurality of emitter surfaces are arranged in parallel, and an optical fiber array in which a plurality of optical fibers for receiving the output from the laser diode array are arranged in parallel. In the optical coupling structure of the laser diode array and the optical fiber array, the optical fiber includes a core extending along the longitudinal direction, and a plurality of holes provided so as to surround the core and extending along the core And a clad having a photonic crystal structure formed in the radial direction of the fiber, and the numerical aperture of the core of the optical fiber with respect to the wavelength λ of the output light of the laser diode array is greater than or equal to the vertical numerical aperture of the emitter surface and horizontal such that the direction of higher numerical aperture, the diameter and the distance between the centers of the holes are set, the outer peripheral shape of the cladding The circular, the laser diode array and the light, wherein the cross-sectional shape of the core has a shape to match the shape of the emitter surface such that the minimum cross-sectional area required to receive the rectangular and said output An optical coupling structure with a fiber array is provided.

According to another aspect of the present invention, there is provided an optical coupling structure of a laser diode and an optical fiber comprising a laser diode and an optical fiber for receiving an output from the laser diode, wherein the optical fiber extends along a longitudinal direction. A core and a clad provided around the core and having a photonic crystal structure formed in the fiber radial direction by a plurality of holes extending along the core; the numerical aperture of the core of the fiber, so that the above numerical aperture of the vertical emitter surface and the horizontal than the numerical aperture, the the pore diameter and center-to-center distance is set, the outer peripheral shape of the cladding circular, fit into the emitter surface such that the minimum cross-sectional area required for the cross-sectional shape of the core to receive rectangular and said output Providing optical coupling between the laser diode and the optical fiber, characterized in that the a shape.

  According to the optical fiber of the present invention, by optimizing the hole diameter and the hole interval in accordance with the wavelength or numerical aperture of the output light of the laser diode array, the output light of the laser diode array can be optical fiber with high efficiency. Transmission at a high power density is possible.

In the present invention, a photonic crystal fiber (PCF: Photonic Crystal Fiber) having a hole layer is used as an optical fiber for constituting an optical fiber array that receives output light from a laser diode array.
1 and 2 show examples of the optical fibers 10 and 10A of this embodiment. These optical fibers 10 and 10 </ b> A have a core 1 extending along the longitudinal direction of the optical fibers 10 and 10 </ b> A, and clads 2 and 3 provided so as to surround the core 1. The clads 2 and 3 include a hole layer 2 (first clad 2) provided so as to surround the core 1 in the center of the optical fibers 10 and 10A, and a second clad provided so as to surround the hole layer 2. 3 and a photonic crystal structure is formed in the fiber radial direction.

  In the optical fibers 10 and 10A of this embodiment, the core 1 and the clads 2 and 3 can be made of, for example, quartz. The hole layer 2 is formed by a plurality of holes 4, 4... Provided so as to surround the core 1 and extending along the core 1. As a result, the portion surrounded by the hole layer 2 becomes the core 1 of the optical fibers 10 and 10A, the hole layer 2 becomes the first cladding 2 with respect to the core 1, and the portion outside the hole layer 2 becomes the second cladding 3. . The outer peripheral shape of the second cladding 3 is circular, which is convenient when configuring an optical fiber array.

The hole layer 2 is provided so that the cross-sectional area of the core 1 is minimized. By using the photonic crystal structure, most of the hole layer 2 is occupied by a gas (air) having a low refractive index. Therefore, the numerical aperture (NA) of the core 1 surrounded by the hole layer 2 is a quartz core. / It can be made sufficiently larger than the numerical aperture of the core of an optical fiber having a quartz clad structure.
The numerical aperture of the core 1 is determined by the diameter d and interval Λ of the holes 4 in the hole layer 2 (see FIG. 1C) and the wavelength λ of light passing through the core 1. The interval Λ of the holes 4 is the distance between the centers of the adjacent holes 4 and 4. Further, in order to prevent the peripheral edges of the adjacent holes 4 and 4 from overlapping each other, it is necessary to satisfy the relationship of Λ> d.

  In other words, in the present invention, the diameter d and interval Λ of the holes 4 in the hole layer 2 are set so that the numerical aperture necessary for receiving the output light from the laser diode array can be obtained. A number of cores 1 can be realized. By using such optical fibers 10 and 10A, no lens array is required between the light receiving surface of the optical fiber and the emitter surface of the laser diode array, and the light receiving surface and the emitter surface can be directly abutted and optically coupled. Therefore, the cross-sectional area of the core 1 of the optical fiber is not increased more than necessary, and a high optical power density can be realized.

  For example, when an optical fiber is optically coupled to a laser diode array having a wavelength λ = 980 nm, a vertical numerical aperture of the emitter surface of 0.4, and a horizontal numerical aperture of 0.2, the optical fiber core 1 The required numerical aperture is equal to or greater than the vertical numerical aperture and the horizontal numerical aperture of the emitter surface, that is, 0.4 or greater. In this case, the diameter d of the holes 4 and the interval Λ of the holes 4 are determined so as to satisfy the relationship of the following formulas (1) and (2) (see Japanese Patent Application Laid-Open No. 2004-77891). In the following formulas (1) to (4), the unit of length is μm.

−0.0200 (Λ / λ) ² +0.2285 (Λ / λ) + 0.2455 ≦ d / Λ (1)

Λ / λ ≦ 6 (2)

  By substituting λ = 980 nm = 0.98 μm in the following formulas (1) and (2), the relations of the following formulas (3) and (4) can be obtained.

−0.0208Λ ³ + 0.2332Λ ² + 0.2455Λ ≦ d (3)

Λ ≦ 5.88 (4)

The dimensions of the emitter of the laser diode array is generally a 150 [mu] m (horizontal Direction) × 1 [mu] m (vertical direction). Therefore, for example, when the hole interval Λ is 5.5 μm, the hole diameter d needs to be 4.92 μm or more according to the equation (3). Moreover, in order to ensure the wall thickness between the holes 4 and 4 to be 0.1 μm or more, the hole diameter d needs to be 5.4 μm or less.
By setting the hole diameter d and the hole interval Λ in this way, it is possible to design a laser diode array coupling optical fiber having the core 1 having a numerical aperture of 0.4 or more. By optically coupling such an optical fiber and a laser diode array, laser output light can be incident on the optical fiber and propagated with high coupling efficiency.

In order to optically couple the optical fibers 10 and 10A of this embodiment with a laser diode array, an optical fiber array is configured by using a plurality of optical fibers, and the end faces of the respective optical fibers constituting the optical fiber array are used as light receiving surfaces. This can be realized by abutting the light receiving surface with the respective emitter surfaces of the laser diode array. Since the cross-sectional area of the core of the optical fiber is set to a minimum necessary level, a high optical power density can be obtained.
Since the core 1 and the clads 2 and 3 are made of quartz, even if the output light of the high-power laser diode array is received, no burning occurs on the light receiving surface of the optical fiber 10.

  Furthermore, according to the present invention, the cross-sectional shape of the core 1 is not limited to a circle (see FIG. 2) but can be arbitrarily changed to a rectangle (see FIG. 1) by changing the production position of the holes 4 in the hole layer 2. It can be made into a shape. Therefore, by making the cross-sectional shape of the core 1 match the shape of the emitter surface, light can be guided with a higher optical power density. In addition, the numerical aperture of the core can be made anisotropic by changing the hole diameter d and the hole interval Λ within the same plane.

As mentioned above, although this invention has been demonstrated based on suitable embodiment, this invention is not limited to the above-mentioned example, Various modifications are possible in the range which does not deviate from the summary of this invention. The dimensions and the like in the above-described embodiments are merely examples, and the present invention is not particularly limited.
Since the optical fiber of the present invention is suitable for optical coupling with a laser diode array, it can be used as an optical fiber constituting the optical fiber array in an optical device using the laser diode array and the optical fiber array. As the above-mentioned optical device, for example, it can be used for a pumping light source unit in a high-power optical fiber amplifier or a high-power optical fiber laser. Further, the present invention is not limited to the array structure, and is effective for optical coupling with a laser diode having a single emitter surface as a laser diode coupling optical fiber.

  As shown in FIG. 1, the cross-sectional shape of the core 1 is a rectangle having a size of 200 μm (horizontal direction) × 20 μm (vertical direction), and the outer peripheral shape of the second cladding 3 is a circular shape. A laser diode array coupling optical fiber 10 having a diameter d of the holes 4 of 5.0 μm and an interval Λ of the holes 4 of 5.5 μm was designed. Then, an optical fiber according to the present example was manufactured by producing a quartz optical fiber preform and drawing an optical fiber by a general PCF manufacturing method.

When the numerical aperture of the laser diode array coupling optical fiber 10 of this example was measured, as shown in FIG. 3, the numerical aperture was 0.45, and it was confirmed that it was almost as designed. . In the graph of FIG. 3, the vertical axis represents the intensity of light (intensity), and the horizontal axis represents the numerical aperture (NA).
An optical fiber array was produced using a plurality of laser diode array coupling optical fibers 10 of this example and optically coupled to the laser diode array. The coupling efficiency was 95%, and high coupling efficiency could be realized. It was.

  The present invention can be used for an optical device using a laser diode array and an optical fiber array, such as an optical fiber laser light source, a fiber laser system, and an optical fiber amplifier.

(A) is an end view showing an example of the optical fiber of the present invention, (b) is a schematic longitudinal sectional view of the optical fiber shown in (a), and (c) is an explanation of hole diameter d and hole interval Λ. FIG. (A) is an end view which shows the other example of the optical fiber of this invention, (b) is typical longitudinal cross-sectional view of the optical fiber shown to (a). It is a graph showing the measurement result of the numerical aperture of the optical fiber of an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Core, 2 ... 1st clad (hole layer), 3 ... 2nd clad, 4 ... Hole, 10, 10A ... Optical fiber, d ... Hole diameter, Λ ... Hole interval.

Claims (2)

A laser diode array and an optical fiber array comprising a laser diode array having a plurality of emitter surfaces arranged in parallel and an optical fiber array having a plurality of optical fibers arranged in parallel for receiving the output from the laser diode array In the optical coupling structure with
The optical fiber includes a core extending along the longitudinal direction, and a clad provided around the core and having a photonic crystal structure formed in the fiber radial direction by a plurality of holes extending along the core,
Between the hole diameter and the center so that the numerical aperture of the core of the optical fiber with respect to the wavelength λ of the output light of the laser diode array is not less than the numerical aperture in the vertical direction of the emitter surface and not less than the numerical aperture in the horizontal direction. Distance is set, the outer peripheral shape of the cladding is circular, the cross-sectional shape of the core is rectangular, and the shape matched to the shape of the emitter surface so as to have a minimum cross-sectional area necessary for receiving the output An optical coupling structure of a laser diode array and an optical fiber array. In the optical coupling structure of a laser diode and an optical fiber, which consists of a laser diode and an optical fiber for receiving the output from the laser diode,
The optical fiber includes a core extending along the longitudinal direction, and a clad provided around the core and having a photonic crystal structure formed in the fiber radial direction by a plurality of holes extending along the core,
The diameter of the hole and the distance between centers so that the numerical aperture of the core of the optical fiber with respect to the wavelength λ of the output light of the laser diode is not less than the numerical aperture in the vertical direction of the emitter surface and not less than the numerical aperture in the horizontal direction. The outer peripheral shape of the clad is circular, the cross-sectional shape of the core is rectangular, and the shape is matched to the shape of the emitter surface so as to have a minimum cross-sectional area necessary for receiving the output An optical coupling structure of a laser diode and an optical fiber.

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