WO2007001092A1

WO2007001092A1 - Light-source module

Info

Publication number: WO2007001092A1
Application number: PCT/JP2006/313362
Authority: WO
Inventors: Kazuhiko Nagano; Shinichiro Sonoda
Original assignee: Fujifilm Corporation
Priority date: 2005-06-28
Filing date: 2006-06-28
Publication date: 2007-01-04
Also published as: TW200710460A; JP2007010693A

Abstract

A light-source module (100, 100', 200) includes: one or more light sources (1, 31-38) which emit one or more light beams (L, L31-L38); an optical fiber (9) which has a light-entrance end face and a light-output end; an optical condensing system (6, 15) which condenses the one or more light beams (L, L31-L38) emitted from the one or more light sources, and makes the one or more light beams (L, L31-L38) converge at the light-entrance end face of the optical fiber (9) so that the one or more light beams are outputted from the light-output end; and a transparent member (8, 81) which is joined to the light-entrance end face so that the one or more light beams (L, L31-L38) enter the optical fiber (9) through the transparent member (8, 81) after the one or more light beams are condensed by the optical condensing system (6, 15).

Description

DESCRIPTION

LIGHT-SOURCE MODULE

Technical Field

The present invention relates to a light-source module having one or more semiconductor light sources, an optical fiber, and an optical condensing system which couples one or more laser beams emitted from the one or more light sources, to an end face of the optical fiber.

Background Art

Conventionally, light-source modules constituted by one or more semiconductor lasers and an optical condensing system which makes laser beams emitted from the semiconductor lasers converge at a light-entrance end face of an optical fiber are known as components for optical communication. In order to stably maintain with micrometer precision the arrangement in which the semiconductor lasers and the light-entrance end face of the optical fiber are optically coupled, the optical fiber, the optical condensing system, and the like are fixed with a bonding means such as solder or an adhesive.

In the above light-source modules, the optical power density at the light-entrance end face of the optical fiber is high since the laser beams, emitted from the semiconductor lasers converge at the light-entrance end face. Therefore, organic materials and the like in the atmosphere are likely to deposit on the light-entrance end face of the optical fiber, so that the laser characteristics and the reliability of the light-source modules deteriorate. In order to solve the above problem, the following techniques (1) to (3) have been proposed for preventing contamination of the light-entrance end face of the optical fiber.

(1) For example, Japanese Unexamined Patent Publication No. 2004-253783 discloses a technique in which a transparent member is fixed to the light-entrance end face of the optical fiber with solder _

so as to protect the light-entrance end face from the atmosphere. (2) Japanese Unexamined Patent Publication No. 7 (1995) -104013 discloses a technique in which an end face of an optical fiber is fixed to a glass plate by use of a fixture. (3) Japanese Unexamined Patent Publication No. 2 (1990) -081008 discloses a technique in which a light-entrance end face of an optical fiber is arranged in close contact with a glass spacer.

However, according to the technique disclosed in Japanese Unexamined Patent Publication No. 2004-253783, the optical fiber is fixed to the transparent member with solder. Therefore, thermal stress remains in and around the solder after the fixing, so that the fixing strength is insufficient. In addition, it is necessary to metalize the portions of the optical fiber and the transparent member at which the optical fiber and the transparent member are fixed. Therefore, additional work and time are necessary for the metallization, and thus the assembly cost of the light-source module increases .

Further, according to the technique disclosed in Japanese Unexamined Patent Publication Nos .7 (1995) -104013 or 2 (1990) -081008, dust can be caught between the light-entrance end face of the optical fiber and the glass plate or spacer during assembly. Therefore, it is impossible to completely protect the light-entrance end face of the optical fiber from contaminants.

Disclosure of Invention

The present invention has been developed in view of the above circumstances .

The object of the present invention is to provide a light-source module which can suppress deposition of contaminants on a light-entrance end face of an optical fiber, and exhibits high reliability.

In order to accomplish the above obj ect, the present invention is provided. According to the present invention, there is provided a light-source module comprising: one or more light sources which _n

emit one or more light beams; an optical fiber which has a light-entrance end face and a light-output end; an optical condensing system which condenses the one or more light beams emitted from the one or more light sources, and makes the one or more light beams converge at the light-entrance end face of the optical fiber so that the one or more light beams are outputted from the light-output end; and a transparent member which is joined to the light-entrance end face so that the one or more light beams enter the optical fiber through the transparent member after the one or more light beams are condensed by the optical condensing system.

Since the transparent member is joined to the light-entrance end face of the optical fiber (for example, by heating) according to the present invention, the air or contaminants do not come into the gap between the transparent member and the light-entrance end face. Therefore, it is possible to prevent contamination of the faces at which the transparent member and the optical fiber are joined, so that the light-source module according to the present invention becomes reliable and can exhibit stable performance.

Preferably, the light-source module according to the present invention may also have one or any possible combination of the following additional features (i) to (iii) .

(i) The transparent member is joined to the light-entrance end face by fusion realized by heat. The heat may be realized by arc discharge, use of nichrome wire, oxyhydrogen flame, or the like. It is preferable to use a means which can realize local heating.

In the case where metallization and soldering or the like are not used for joining the transparent member with the optical fiber, it is possible to save the time and cost of joining the transparent member with the optical fiber. In addition, in the case where the solder or the like is used, thermal stress remains in and around the solder or the like after fixing of the transparent member to the optical fiber, and therefore lowers the strength of the joint. However, in the case where the transparent member is joined to the light-entrance end face by heat generated by the arc discharge or the like, it is possible to increase the strength of the joint. _A

(ii) The one or more light beams are arranged to realize optical power density of 10 W/mm² or less on a light-entrance side of the transparent member. In this case, it is possible to increase the lifetime of the light-source module. (iii) The oscillation wavelengths of the one or more light beams are preferably 350 to 500 run. In this case, it is possible to enhance the effect of preventing contamination of portions of the light-source module in which the one or more light beams are condensed. In particular, when the oscillation wavelengths of the one or more light beams are 350 to 450 nm, the effect of preventing the contamination can be further enhanced.

Brief Description of Drawings

FIG. 1 is a side view, partly in cross section, of a light-source module according to a first embodiment of the present invention.

FIG. 2 is a perspective view of an arrangement for joining an optical fiber to a glass member.

FIGS.3A, 3B, and 3C are diagrams illustrating different types of joints between the optical fiber and the transparent member.

FIG. 4 is a graph indicating a relationship between the optical power density at the light-entrance face of the glass member and the lifetime of the light-source module.

FIG.5 is a side view, partly in cross section, of a variation of the light-source module according to the first embodiment of the present invention, where the glass member is wedge-shaped.

FIG. 6 is a plan view, partly in cross section, of a light-source module according to a second embodiment of the present invention.

Best Mode for Carrying Out the Invention

Preferred embodiments of the present invention are explained in detail below with reference to drawings. In the following explanations, it is assumed that semiconductor lasers are used as light sources, although the light sources are not lmited to semiconductor lasers .

First Embodiment

The first embodiment of the present invention is explained below. FIG. 1 is a side view, partly in cross section, of a light-source module according to the first embodiment of the present invention. In the light-source module 100 illustrated in FIG. 1, a semiconductor laser 1 is mounted on a block 21 in a CAM package 2 with a brazing material such as AuSn, and are hermetically sealed by bonding the edge of a cap 3 to the CAN package 2 by resistance welding in an inert atmosphere. The cap 3 has a light-exit window 12. The CAN package 2 in which the semiconductor laser 1 is hermetically sealed is press-fitted into and fixed to a base plate 11. Alternatively, the CAN package 2 may be fixed to the base plate 11 by welding such as YAG welding, soldering, or use of an adhesive. Wirings 22 for electrically driving the semiconductor laser 1 are led out of the CAN package 2 through an opening arranged in the CAN package 2.

A condensing lens 6 is fixed inside a condensing-lens holder 5 by adhesion or press fit. The condensing-lens holder 5 is held in a chassis 4 so that the condensing-lens holder 5 can slide in the direction of the optical axis of the light-source module 100. The chassis 4 is held on a face, perpendicular to the optical axis of the light-source module 100, of the base plate 11 with a structure which allows adjustment of the position of the chassis 4.

The optical fiber 9 is, for example, amultimode optical fiber having a numerical aperture (NA) of 0.22 and a core diameter of approximately 60 micrometers. The optical fiber 9 is inserted into a ferrule 10. A planar glass plate 8 having parallel surfaces (as the aforementioned transparent member) is fused with the light-entrance end face of the optical fiber 9 by use of a heating means, which utilizes arc discharge, nichrome-wire heating, an oxyhydrogen burner, a CO₂ laser, or the like for heating. In addition, preliminary heating may be performed, for example, by light-condensing heating, which is realized by use of a YAG laser beam, light emitted from a light source such as a lamp, and the like. In all cases, it is desirable that the heating means be able to realize local heating to a melting temperature.

In the case where the optical fiber 9 is a multicomponent optical fiber having low melting temperature, it is possible to use a nichrome-wire heater. On the other hand, in the case where the optical fiber 9 is a quartz-based optical fiber having a melting temperature as high as 2,000°C, it is possible to heat the optical fiber by use of an oxyhydrogen burner, a CO₂ laser, or the like. FIG. 2 shows an arrangement for joining the optical fiber 9 to the glass member 8 by use of arc discharge. As illustrated in FIG. 2, the optical fiber 9 is fixed in a precise V-groove 92. Then, the light-entrance end face of the optical fiber 9 is brought into contact with a contact surface (8a) of the glass member 8, and thereafter electrodes for arc discharge are electrically driven so as to cause arc discharge. Thus, the light-entrance end face of the optical fiber 9 is joined to the contact surface (8a) of the glass member 8 by fusion with the glass member 8.

FIGS.3A, 3B, and 3C are diagrams illustrating different types of joints between the optical fiber 9 and the transparent member 8. The joints between the optical fiber 9 and the transparent member 8 illustrated in FIGS. 3A, 3B, and 3C are formed by bringing the light-entrance end face of the optical fiber 9 into contact with the contact surface 8a of the glass member 8, and heating the portions of the optical fiber 9 and the transparent member 8 at which the optical fiber 9 and the transparent member 8 are in contact. In the joint illustrated in FIG. 3A, the peripheral portion of the light-entrance end face of the optical fiber 9 fuses with an area of the contact surface 8a of the glass member 8, where the area of the contact surface 8a is an area at which the peripheral portion of the light-entrance end face of the optical fiber 9 is in contact with the contact surface 8a of the glass member 8 before the fusion. In the joint illustrated in FIG. 3B, the light-entrance end face of the optical fiber 9 fuses with the contact surface 8a of the glass member 8. In the joint illustrated in FIG. 3C, the light-entrance end face penetrates into the glass member 8 because the heated portion of the glass member 8 is softened during the heating.

As explained above, the light-entrance end face of the optical fiber 9 is joined to the glass member 8 by bringing the light-entrance end face of the optical fiber 9 into contact with the contact surface 8a of the glass member 8, and heating the portions of the optical fiber 9 and the transparent member 8 at which the optical fiber 9 and the transparent member 8 are in contact. In this case, the air or contaminants do not come into the gap between the transparent member 8 and the light-entrance end face of the optical fiber 9. Therefore, it is possible to prevent contamination of the faces at which the transparent member 8 and the optical fiber 9 are joined, so that the light-source module 100 according to the present embodiment becomes reliable and has stable laser characteristics. In addition, since metallization and soldering or the like are not used for joining the transparent member 8 with the optical fiber 9, it is possible to save the time and cost of joining the transparent member 8 with the optical fiber 9. Further, in the case where the solder or the like is used, thermal stress remains in and around the solder or the like after fixing of the transparent member 8 to the optical fiber 9, and therefore lowers the strength of the joint. However, in the case where the transparent member 8 is joined to the light-entrance end face by fusion, it is possible to increase the strength of the joint. Next, the ferrule 10 and the optical fiber 9 are inserted into a holder 7, and the glass member 8 is fixed to the holder 7 with an adhesive or the like. In addition, the ferrule 10 is fixed to the holder 7. Specifically, the surface of the ferrule 10 is metalized, and the ferrule 10 is fixed to the holder 7 with low-melting-point solder, where the holder 7 is plated in advance. Alternatively, the ferrule 10 may be fixed to the holder 7 by TAG welding, use of an adhesive, or the like.

The chassis 4, the condensing-lens holder 5, and the holder 7 are held in such a manner that the position of the chassis 4 can be adjusted in directions perpendicular to the optical axis on a surface of the base plate 11 against which the chassis 4 is pressed, the position of the condensing-lens holder 5 can be adjusted in direction of the optical axis, and the position of the holder 7 can be adjusted in directions perpendicular to the optical axis on a surface of the condensing-lens holder 5 against which the holder 7 is pressed. Therefore, the positions of the chassis 4, the condensing-lens holder 5, and the holder 7 can be adjusted and fixed so that the optical power of the laser light L (the laser beam) incident on the light-entrance end face of the optical fiber 9 is maximized. It is possible to use solder, an adhesive, YAG welding, or the like in fixing the chassis 4, the condensing-lens holder 5, and the holder 7.

Since the light-source module 100 is constructed as above, the laser light L (the laser beam) emitted from the semiconductor laser 1 is outputted from the cap 3 through the light-exit window 12 and condensed by the condensing lens 6, passes through the glass member 8, and enters the optical fiber 9 from the light-entrance end face. Thereafter, the laser light L propagates through the optical fiber 9, and is then outputted from a light-output end (not shown) of the optical fiber 9.

It is preferable that the power density at the light-entrance surface 8b of the glass member 8 on which the laser light L is incident be 10 W/mm² or less when the light-source module 100 is in operation. In this case, it is possible to suppress deposition of contaminants on the light-entrance surface 8b, and reduce the frequency of cleaning of the glass member 8.

FIG. 4 is a graph indicating a relationship between the optical power density at the light-entrance surface 8b of the glass member 8 and the lifetime of the light-source module 100. In FIG. 4, the lifetime of the light-source module is defined as the time elapsing from the start of driving of the light-source module until the output power of the light-sourcemodule falls to 60% of the initial output power. In the relationship indicated in FIG. 4, the lifetime of the light-source module is 18,000 hours when the optical power density is 10 W/mm². However, the relationship indicated in FIG. 4 _n

shows that the lifetime of the light-source module decreases with increase in the optical power density. That is, it is possible to make the lifetime of the light-source module 100 equal to or greater than 18,000 hours by making the optical power density at the light-entrance surface 8b of the glass member 10 W/mm² or less.

Incidentally, Japanese Unexamined Patent Publication No. 2004-253783 indicates that the lifetimes of the light-source modules which are hermetically sealed so that a light-entrance end face of an optical fiber is not exposed to the atmosphere are approximately 20,000 hours. Although the light-entrance end face of the optical fiber 9 in the light-source module 100 according to the present embodiment is not hermetically sealed, the lifetime of the light-source module 100 is shorter than the lifetimes of the hermetically sealed light-source modules by only at most 10%. In order to make the optical power density at the light-entrance surface 8b of the glass member 10 W/mm² or less, the optical fiber 9 is arranged to have a numerical aperture (NA) of 0.22, the incident numerical aperture of the condensed laser light L (i.e., the sine of the maximum convergence angle of the condensed laser light L) is 0.2, and the output of the semiconductor laser 1 is 250 mW. In addition, the glass member 8 is made of glass having the refractive index of 1.5. In this case, the glass member 8 has the numerical aperture of 0.127 with respect to the condensed laser light L. Further, When the thickness of the glass member 8 is 0.77 mm, the optical power density at the light-entrance surface 8b of the glass member 8 becomes 10 W/mm². Therefore, when the thickness of the glass member 8 is 0.77 mm or greater, the optical power density at the light-entrance surface 8b of the glass member 8 becomes 10 W/mm² or less. Thus, in this case, it is possible to suppress contamination of the light-entrance surface 8b of the glass member 8, so that the aging reliability of the light-source module 100 increases .

The construction of the light-source module 100 explained above may be modified or varied as appropriate within the scope of the present invention. For example, the light-entrance surface and the opposite surface of the glass member may not be parallel, e.g., the glass member may be wedge-shaped as illustrated in FIG. 5, which is a side view, partly in cross section, of a variation 100' of the light-source module according to the first embodiment. In the light-source module 100', the glass member 81 is wedge-shaped, and a portion of the laser light Lwhich is reflectedby the light-entrance surface 81b of the glass member 81 propagates in the directions indicated by the dashed lines. Therefore, the semiconductor laser 1 is not irradiated with the portion of the laser light L reflected at the light-entrance surface 81b, so that it is possible to suppress the deterioration of the semiconductor laser 1.

Second Embodiment

The second embodiment of the present invention is explained below. Although the light-source module 100 according to the first embodiment and the light-source module 100' as the variation of the first embodiment each comprise only one semiconductor laser, the light-source module according to the second embodiment comprises a plurality (e.g., eight) of semiconductor lasers.

FIG. 6 is a plan view, partly in cross section, of the light-source module according to the second embodiment of the present invention. As illustrated in FIG. 6, the light-source module 200 has eight GaN-based semiconductor lasers 31 to 38 in a CAN package

46. The collimator-lens array 43 includes collimator lenses for the semiconductor lasers 31 to 38, and has a function of a light-emission window of the CAN package 46.

In FIG. 6, the shapes of the collimator-lens array 43 and a condensing lens 15 are schematically indicated. For simple illustration, only the semiconductor lasers 31 and 38 out of the semiconductor lasers 31 to 38 and the laser beams L31 and L38 out of the laser beams L31 to L38 bear the reference numbers.

Similar to the first embodiment, the semiconductor lasers

31 to 38 are mounted on a block 41 in a CAN package 46 with a brazing material such as AuSn, and are hermetically sealed by bonding the edge of a cap 45 to the CAN package 46 by resistance welding in an inert atmosphere. The CAN package 46 in which the semiconductor lasers 31 to 38 are hermetically sealed is press-fitted into and fixed to a base plate 11. Wirings 42 for electrically driving the semiconductor lasers 31 to 38 are led out of the CAN package 46 through an opening arranged in the CAN package 46. The eight laser beams L31 to L38 emitted from the semiconductor lasers 31 to 38 are divergent laser beams, which are respectively collimated by the corresponding collimator lenses in the collimator-lens array 43. The collimated laser beams L31 to L38 are condensed by the condensing lens 15, and the condensed laser beams L31 to L38 are optically coupled at the light-entrance end face of the optical fiber 9.

The glass plate 8 is fused with the light-entrance end face of the optical fiber 9 by heating in the same manner as the first embodiment. The collimator-lens array 43 and the condensing lens 6 constitute an optical condensing system, and the optical condensing system and the optical fiber 9 constitute an optical combining system . Thus, the laser beams L31 to L38 condensed by the condensing lens 15 enter the optical fiber 9 from the light-entrance end face, propagates through the optical fiber 9, are optically combined into a single laser beam in the optical fiber 9, and are then outputted from a light-exit end (not shown) of the optical fiber 9. Additional Matters

(1) Each semiconductor laser used in each embodiment may be either of a type which outputs a laser beam in a single transverse mode, or a type which outputs a broad laser beam. In the case where a plurality of semiconductor lasers are mounted in a light-source module, the plurality of semiconductor lasers may be a mixture of one or more single-transverse-mode semiconductor lasers and one or more broad-area semiconductor lasers.

(2) The one or more semiconductor lasers used in each embodiment may not be limited to GaN-based semiconductor lasers. However, GaN-based semiconductor lasers emit high-energy laser beams having the wavelengths of 500 nm or shorter. Therefore, in the case where GaN-based semiconductor lasers are used in a light-source module, the optical power density at the laser-emission end faces of the semiconductor lasers or the light-entrance end face of the optical fiber becomes very high, so that contaminants are likely to deposit on the laser-emission end faces and the light-entrance end face. Consequently, in light-source modules each comprising one or more semiconductor lasers which emit high-energy laser light, deposition of contaminants can be effectively suppressed by hermetically sealing the one or more semiconductor lasers in a CAN package, and joining a glass member to the light-entrance end face of the optical fiber. Thus, the light-source modules in which the above provisions is made is highly reliable.

Claims

1. A light-source module comprising: one or more light sources which emit one or more light beams; an optical fiber which has a light-entrance end face and a light-output end; an optical condensing system which condenses said one or more light beams emitted from said one or more light sources, and makes the one or more light beams converge at said light-entrance end face of said optical fiber so that the one or more light beams are outputted from said light-output end; and a transparent member which is joined to said light-entrance end face so that said one or more light beams enter said optical fiber through the transparent member after the one or more light beams are condensed by said optical condensing system.

2. A light-source module according to claim 1, wherein said transparent member is joined to said light-entrance end face by fusion realized by heat.

3. A light-source module according to either one of claims 1 and 2, wherein said one or more light beams are arranged to realize optical power density of 10 W/mm² or less on a light-entrance side of said transparent member.

4. A light-source module according to either one of claims 1 to 3, wherein said one or more light beams have oscillation wavelengths of 350 to 500 nm.