GB2362475A

GB2362475A - Focussing semiconductor laser with lens onto a tapered optic fibre

Info

Publication number: GB2362475A
Application number: GB0026925A
Authority: GB
Inventors: Masahiro Kanda
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 1999-11-04
Filing date: 2000-11-03
Publication date: 2001-11-21
Anticipated expiration: 2020-11-03
Also published as: CA2324808A1; JP2001133664A; GB2362475B; GB0026925D0; CA2324808C

Abstract

A semiconductor laser diode 1 uses lens 3 or a lens system to focus light onto tapered end portion 21 of optic fibre 2. A predetermined spacing is left between the semiconductor laser diode and the lens and between said lens and the optical fiber such that magnification of the lens or lens system may be just less than one (see Fig 4). The laser diode may be mounted on heat sink 11 and fixed to a carrier 7 by soldering. The carrier may be fixed to a cooling substrate of a Peltier cooler 10 for controlling the temperature of the semiconductor laser diode in order to stabilize a power level and a lasing wavelength of an optical signal. The Peltier cooler may be fixed to an internal bottom surface of a module package 4. A photodiode 8 for monitoring outputted light power of the semiconductor laser diode and the lens for focussing a light emitted therefrom may be mounted on the carrier. The optical fiber may be adjusted so as to be optically coupled with the lens with a high efficiency, and may be fixed to the carrier via an optical fiber-holder 22. A clearance between the module package and the optical fiber may be filled with solder with a low melting point. The laser diode may form part of a sub-package (31, Fig 5) which is hermetically sealed by means of the lens.

Description

2362475 SEMICONDUCTOR LASER MODULE

FIELD OF THE INVENTION

This invention relates to a semiconductor laser module, and especially to a semiconductor laser module of 980 nm band.

BACKGROUND OF THE INVENTION

A radiation pattern of a semiconductor laser diode of 980 nm band is elliptic; a half -width angle thereof in the vertical plane is 20 to 40', and that in the horizontal plane is 50 to 150. When the semiconductor laser diode of the 980 nm band is optically coupled with an optical fiber, a mode field diameter of which is almost circular, a coupling loss therebetween becomes excessively large.

In an attempt to overcome the aforementioned difficulty, an experiment was conducted in which a laser beam emitted from the semiconductor laser diode of the 980 nm band was focused by a cylindrical lens. In this experiment, the laser beam is focused only in the vertical plane with intent to make the shape of the radiation pattern of the laser beam nearly circular. However, since the laser beam is not focused in the horizontal plane, a coupling efficiency between the semiconductor laser diode and the optical fiber cannot be improved. Although the use of a beam-shaping lens or an optical fiber with an elliptic cross-section has been proposed as another method for solving the aforementioned difficulty, there is a problem that a structure becomes complicated or the optical fiber is hard to process.

As a means for solving the aforementioned problems and improving the coupling efficiency between the semiconductor laser diode and the optical fiber, there is a method in which the optical fiber is so processed that an input end portion thereof tapers off to a point. According to this method, the end portion of the optical fiber is easily processed by polishing. Moreover, since the optical fiber closely approaches the semiconductor laser, it is unquestionable that the laser beam is focused in the vertical plane.

As shown in FIG. 1, in the aforementioned semiconductor module, the semiconductor laser diode 1 is mounted on a heat sink 11 and fixed to a carrier 7 by soldering.

The carrier 7 is fixed to the cooling substrate of a Peltier cooler 10 which controls temperature of the semiconductor laser diode 1 in order to stabilize a power level and a lasing wavelength of an optical signal. The Peltier cooler 10 is fixed to an internal bottom surface of a module package 4.

A photodiode (a PD, hereinafter) 8 for monitoring outputted light power of the semiconductor laser diode 1 is mounted on the carrier 7. The optical fiber 2 is fixed to the carrier 7 via an optical fiber-holder 22 so that a tapered end portion 21 of the optical fiber 2 approaches the semiconductor laser diode 1 closely. A clearance between the module package 4 and the optical fiber 2 is filled with solder with a low melting point in order to airtightly seal the semiconductor laser diode 1.

As shown in FIG. 2, an optical configuration of the -3conventional semiconductor module is composed of the semiconductor laser diode I and the tapered end portion 21 of the optical fiber 2 only. In FIG. 2, the light emitted from the semiconductor laser diode 1 is concentrated on the optical fiber 2, and taken out through the optical fiber 2 and transmitted towards the outside. In this case, under optimum optical coupling an interval between the semiconductor laser diode 1 and the optical fiber 2 is L2.

However, in the aforementioned structure, since the interval between the optical fiber 2 and the semiconductor laser diode 1 under the optimum optical coupling is several tens gm, the optical fiber 2 may well collide with the semiconductor laser diode 1 and be damaged.

SUMMARY OF THE INVENTION

Accordingly, it is an object ofthe preferred embodiments of the invention to solve the aforementioned problems, better protect a semiconductor laser diode from damage, and provide a semiconductor laser module with a high coupling efficiency.

According to a feature of the invention, a semiconductor laser module comprises:

an optical fiber with an input end portion which tapers off to a point; a semiconductor laser diode which is optically coupled with the optical fiber; and, a lens which is situated between the semiconductor laser diode and the optical fiber at predetermined spacing between the semiconductor laser diode and the lens and between the lens and the optical fiber.

That is to say, in the semiconductor laser module according to the invention, the semiconductor laser diode and the optical fiber are better protected from damage, and a high coupling efficiency therebetween can be obtained by using the lens and the optical fiber with the input end portion which tapers off to a point. It should be noted that a similar effect can be obtained in a case where the lens is replaced with a lens system composed of plural lenses arranged along a common optical axis.

More particularly, the semiconductor laser module according to the invention is composed of the semiconductor laser diode of 980 nm band, the optical fiber with the input end portion which tapers off to a point and the lens which focuses a light emitted from the semiconductor laser diode and has magnification of approximately one.

The light emitted from the semiconductor laser diode is focused on the optical fiber, and the optical fiber is optically coupled with the semiconductor laser diode. Although the interval between the optical fiber and the semiconductor laser diode is several tens Am when there is no lens, in the semiconductor laser module comprising the lens, the interval between the semiconductor laser diode and the lens and that between the lens and the optical fiber can be increased noticeably.

In the semiconductor laser module of the 980 nm band with the aforementioned structured, the semiconductor laser and the -5optical fiber are prevented from being damaged at the time of adjustment, and the coupling efficiency therebetween can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred features of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:FIG. 1 shows a structure of a conventional semiconductor laser module; FIG. 2 shows an optical configuration of a conventional semiconductor laser module; FIG. 3 shows a structure of a semiconductor laser module according to the first preferred embodiment of the invention; FIG. 4 shows an optical configuration of a semiconductor laser module according to the first preferred embodiment of the invention; and, FIG. 5 shows a structure of a semiconductor laser module according to the second preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, the first preferred embodiment of the invention will be explained referring to the appended drawings. FIG. 3 shows a semiconductor module according to the first preferred embodiment of the invention. In FIG. 3, a semiconductor laser diode I is mounted on a heat sink 11, which is f ixed to a carrier 7 by soldering.

The carrier 7 is f ixed by soldering to a cooling substrate of a Peltier cooler 10 for controlling temperature of the semiconductor laser diode 1 in order to stabilize a power level and a lasing wavelength of an optical signal. The Peltier cooler 10 is fixed to an interval bottom surface of a module package 4 by soldering.

A PD 8, for monitoring outputted power of the semiconductor laser diode I and a lens 3 for focusing the light emitted therefrom, is mounted on the carrier 7. Magnification of the lens 3 or a lens system composed of plural lenses is approximately one. That is to say, the lens 3 is situated between the semiconductor laser diode 1 and the optical fiber 2 so that spacings with predetermined widths are respectively inserted between the semiconductor laser diode 1 and the lens 3 and between the lens 3 and the optical fiber 2 in order to sufficiently separate the semiconductor laser diode I and the optical fiber 2 from each other.

A position and an attitude of the optical fiber 2 with a tapered end portion 21 is so adjusted that the optical fiber 2 is optically coupled with the lens 3 under the optimum condition. The optical fiber 2 is fixed to the carrier 7 via an optical fiber-holder 22. A clearance between the module package 4 and the optical fiber 2 is filled with solder with a low melting point in order to airtightly seal the semiconductor laser diode 1.

FIG. 4 shows an optical configuration of the semiconductor laser module according to the first preferred embodiment of the -7invention. As shown in FIG. 4, the light emitted from the semiconductor laser diode 1 is concentrated by the lens 3 which is situated near the semiconductor laser diode 1 at a certain interval of L1, and focused on a certain point which is situated near the lens 3 at the same interval of L1.

Since magnification of the lens 3 or the lens system is almost one, the aforementioned focal point can be regarded a light-emitting point of the semiconductor laser diode 1. Moreover, since light power is focused on the optical fiber 2, light power can be taken out through the optical fiber 2 and transmitted towards the outside. In case that the optical fiber 2 is optically coupled with the lens 3 under the optimum condition, since an interval between the light emitting point (the focal point) and the optical fiber 2 is L2, a distance between the lens 3 and the optical fiber is given as Ll + L2.

As shown in FIG. 2, the interval between the semiconductor laser diode 1 and the optical fiber 2 is L2 when the optical fiber 2 is optionally coupled with the semiconductor laser diode 1 under the optimum condition in the conventional optical configurations. In the first preferred embodiment of the invention, the interval between the optical fiber 2 and the lens 3 become larger than that between the optical fiber 2 and the semiconductor laser diode 1 in the conventional optical configuration by L1. Accordingly, there is hardly a possibility that the semiconductor laser diode 1 and the optical fiber 2 may be damaged at the time of adjustment, and the semiconductor module with a high coupling efficiency can be provided.

As mentioned 1 and the optical by inserting the 1 and the optical 1 and the optical in the above, the semiconductor laser diode fiber 2 can be prevented from being damaged lens 3 between the semiconductor laser diode f iber 2 so that the semiconductor laser diode fiber 2 are remote from each other.

Although the semiconductor laser diode 1 closely approaches the optical fiber 2 and the interval therebetween is several Am to several tens Am in a case where there is no lens 3, it can be increased by a factor of several tens by inserting the lens 3 between the semiconductor laser diode 1 and the optical fiber 2. Moreover, the optical fiber 2 never collides with the semiconductor laser diode 1, because the lens 3 is situated in front of the semiconductor laser diode 1.

FIG. 5 shows a semiconductor laser module according to the second preferred embodiment of the invention. As shown in FIG. 5, a semiconductor laser diode 1, fixed to a heat sink 11, and a PD 8 are mounted in the inside of a sub-package 31 which is airtightly sealed by a lens 3.

An optical fiber 2 is fixed to the sub-package 31 via an optical fiberholder 32 by YAG-welding (welding by means of a YAG laser). At this time, the lens 3 is inserted between the sub-package 31 and the optical fiberholder 32.

The sub-Package 31 to which the optical fiber 2 is fixed to a cooling substrate of a Peltier cooler 10 by soldering. The Peltier cooler 10 is fixed to an internal bottom surface of a module package 4. A method for fixing the optical fiber 2 is not restricted to the aforementioned one, and the optical fiber 2 may be f ixed to a carrier similarly to the f irst preferred embodiment when the carrier is used.

In the case of the conventional semiconductor laser module in which there is no lens 3, since the interval between the semiconductor laser diode 1 and the optical fiber 2 is narrow, the clearance between the optical fiber 2 and the module package 4 is airtightly sealed. In this case, it is necessary to metallize the optical fiber 2 in order to perform sealing by means of soldering. According to the aforementioned method, there is a possibility that a residual stress may arise in the optical fiber 2 when it is cooled and solidified, which may deteriorate reliability of the product.

on the other hand, in the semiconductor laser module according to the second preferred embodiment of the invention, the intervals between the semiconductor laser diode 1 and the lens 3 and between the lens 3 and the optical f iber 2 are respectively extended by inserting the lens 3 between the semiconductor laser diode I and the optical fiber 2. Accordingly, it becomes possible to airtightly seal the semiconductor laser diode 1 by means of the lens 3.

Although the Peltier cooler 10 is used in the f irst and second preferred embodiments, the Peltier cooler may be omitted if the power level and the lasing wavelength of the optical signal are both stabilized.

Although a single lens 3 is used in the embodiments shown in FIGs. 3 and 5, the lens 3 may be replaced with a lens system which is composed of plural lenses, such as collimator lenses, _10and has magnification of almost one. When the lens system composed of the plural lenses are used, the first lens seals the sub-package and the remaining lenses are situated outside the sub-package. The last lens faces the input end portion of the optical fiber in the module package.

As mentioned in the above, according to the invention, in the semiconductor laser module in which the optical fiber with the tapered end portion is optically coupled with the semiconductor laser diode, the semiconductor laser diode and the optical fiber are prevented from damage by inserting the lens between the semiconductor laser diode and the optical fiber so that adequate spacing is respectively inserted between the semiconductor laser diode and the lens and between the lens and the optical fiber. As a result, the optical fiber is optically coupled with the semiconductor laser diode with a high coupling efficiency.

Although the invention has been described with respect to specific embodiments for complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embo dying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.

Each feature disclosed in this specification (which term includes the claims) and/or shown in the drawings may be incorporated in the invention independently of other disclosed and/or illustrated features.

The text of the abstract filed herewith is repeated here as part of the specification.

A semiconductor laser diode is mounted on a heat sink and f ixed to a carrier by soldering. The carrier is fixed to a cooling substrate of a Peltier cooler for controlling temperature of the semiconductor laser diode in order to stabilize a power level and a lasing wavelength of an optical signal. The Peltier cooler is fixed to an internal bottom surface of a module package. A photodiode for monitoring outputted light power of the semiconductor laser diode and a lens for focusing a light emitted therefrom are mounted on the carrier. An optical fiber with an end portion which tapers off to a point is adjusted so as to be optically coupled with the lens with a high efficiency, and fixed to the carrier via an optical fiber-holder. A clearance between the module package and the optical fiber is filled with solder with a low melting point.

Claims

CLAIMS:

1. A semiconductor laser module comprising: an optical fiber with an input end portion which tapers off to a point; a semiconductor laser diode which is optically coupled with said optical fiber; and, a lens which is situated between said semiconductor laser diode and said optical fiber at predetermined spacing between said semiconductor laser diode and said lens and between said lens and said optical fiber.

2. A semiconductor laser module according to claim 1, wherein magnification of said lens is just less than one.

3. A semiconductor laser module according to claim 2, wherein said lens is situated between said semiconductor laser diode and said optical f iber so that a distance between said semiconductor laser diode and said lens and that between said lens and said optical fiber are the same as, or slightly longer than, a focal distance of said lens.

4. A semiconductor laser module according to claim 1, further comprising a sub-package which accommodates said semiconductor laser diode and hermetically seals said semiconductor laser diode by means of said lens.

A semiconductor laser module according to claim 4, wherein an optical fiber-holder for supporting said optical fiber is fixed to said subpackage.

6. A semiconductor laser diode comprising: an optical fiber with an input end portion which tapers off to a point; a semiconductor laser diode which is optically coupled with said optical fiber; and, a lens system, composed of plural lenses arranged along a common optical axis, which is situated between said semiconductor laser diode and said optical fiber so that predetermined spacing is respectively inserted between said semiconductor laser and a first side end of said lens system and between a second side end of said lens system and said optical fiber.

7. A semiconductor laser diode according to claim 6, wherein magnification of said lens system is just less than one.

8. A semiconductor laser module substantially as herein described with reference to and as shown in Figures 3 to 5 of the accompanying drawings.

9. A semiconductor laser diode substantially as herein described with reference to and as shown in Figures 3 to 5 of the accompanying drawings.