Optical communications module and substrate for the same

A substrate on which cavities having floors and steps is provided. End faces of a light-emitting device, an optical component, and an optical transmission line are abutted on one of the cavity for positioning, and end faces of a light-receiving device, an optical component, and an optical transmission line are also abutted on the other cavity for positioning. Integrated alignment of optical axes facilitates alignment of optical axes, and thus eliminates the need of a CAN package. Accordingly, the size and height of an optical communications module can be reduced.

TECHNICAL FIELD

The present invention relates to small and short optical modules for communications, and substrates used in the modules that allow easy adjustment of optical axes.

BACKGROUND ART

FIG. 17shows an entire image of a package including a conventional transceiver module for optical communications. The entire package is configured with optical transmission line41, CAN Package for transmission (hereafter “package”)24, and CAN Package for reception (hereafter “package”)25. Fixing jig42secures optical transmission line41. Packages24and25are mounted on printed circuit board (hereafter “board”)34, and enclosed in package21. The name CAN Package comes from the use of a metal can for the package. Fixing jig42and adapter21A of package21are fitted, and the optical axis of optical transmission line41and optical axes of packages24and25are aligned by means of this modular structure.

FIG. 19is a sectional view ofFIG. 18taken along Line A–A′ on board34including the center axes of packages24and25. Light-emitting device29is mounted inside package24, and sealing material33hermetically seals this package24. In addition, optical component27such as lens or window is installed in package24. The light emitted from light-emitting device29enclosed in package24passes through optical component27and enters optical transmission line41whose optical axis is aligned by the modular structure. This enables the module to transmit signals.

In the same way, light-receiving device30is mounted inside package25, and sealing material33hermetically seals this package25. In addition, optical component28such as lens or window is installed in package25. The light output from transmission line41of the reception side whose optical axis is aligned by the modular structure passes through optical component28installed in package25, and arrives at light-receiving device30. This enables the module to receive signals. This type of package, including a transceiver module for optical communications, is disclosed in Japanese Unexamined Patent Publication No. H11-345987.

In the above structure, however, the alignment of optical axes of light-emitting device29and light-receiving device30, and respective optical components27and28depends on packages24and25. Moreover, the alignment of the optical axes of light-emitting device29, light-receiving device30, and optical components27and28and the optical axis of optical transmission line41depends on the modular structure of fixing jig42and adapter21A of package21. For each alignment, the optical axes need to be separately aligned. Furthermore, the size of packages24and25limits downsizing and height reduction because packages24and25are mounted on board34.

DISCLOSURE OF INVENTION

An optical communications module of the present invention employs a substrate that has a cavity with a floor and a step. A light-emitting device, an optical component, and an end face of an optical transmission line are positioned by abutting them on and fitting them into the cavity. A light-receiving device, an optical component and an end face of optical transmission line are positioned by abutting them on and fitting them into the cavity.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are described below with reference to drawings. For reasons of simplicity, the same reference numerals are given to the same structures.

First Exemplary Embodiment

FIGS. 1 and 2are perspective views of a transceiver module for optical communications in a first exemplary embodiment of the present invention.FIG. 3is a sectional view taken along Line A–A′ inFIG. 1orFIG. 2.

InFIG. 1, substrate (hereafter “substrate”)6is a multilayer ceramic substrate on which semiconductor devices5are mounted, and substrate6has cavities3with at least one step and a floor. Semiconductor devices5are components of a photoelectric converting circuit, and are ICs that convert electrical signals to light and vice versa. This photoelectric converting circuit exchanges signals with an external circuit via terminal7. Fixing jig2for optical transmission line secures two cores of optical transmission lines1. Optical transmission lines1are abutted on cavities3on substrate6. The transceiver module for optical communications of the exemplary embodiment is configured as described above. The top steps of cavities3have substantially the same shape as optical transmission line1, and optical components4such as a refractive lens, diffractive lens, optical iris, and window which have substantially the same outline as optical transmission line1are also disposed on this top steps. Cavity3can also have two or more steps, and optical transmission line1and optical components4can be disposed on the same step.

At the optical system on the transmission side, the refractive lens or the diffractive lens focuses the light output from light-emitting device8, and apply this light to optical transmission line1of the transmission side at high efficiency. At the optical system on the reception side, the refractive lens or the diffractive lens focuses the light output from optical transmission line1of the reception side, and applies the light to light-receiving device9at high efficiency. Moreover, the diffractive lens shortens the focal distance so as to shorten the distance between light-emitting device8or light-receiving device9and optical transmission line1. In the optical system at the transmission side, the optical iris removes excess light in the light output from light-emitting device8and then applies the light to optical transmission line1of the transmission side. In the optical system on the reception side, the optical iris removes excess light in the light output from optical transmission line1of the reception side, and applies the light to light-receiving device9.

To position optical transmission line1and optical components4by the top step of cavity3, the outlines of optical transmission line1, the top step of cavity3, and optical components4are made substantially the same, as shown inFIG. 1. However, if optical transmission line1is uniquely positioned, cavity3and optical components4can have other shapes, as shown inFIG. 2, such as a square and triangle.

InFIG. 3, electric line12, via hole13, and passive elements11including a coil, a capacitor, and a resistor, which are components of the photoelectric converting circuit, are disposed on inner layers of substrate6which is a multilayer ceramic substrate.

Cavities3created on the surface of substrate6have at least one step, and light-emitting device8and light-receiving device9are mounted on their floors. In addition, optical components4are disposed on the top steps of cavities3, and hermetically sealed by sealing material10made such as of glass, resin, and solder. Optical transmission lines1are abutted immediately on optical components4such that optical transmission lines1contact optical components4. Sealing of optical components4in the multi-step cavities allows reduction of the number of components, thus simplifying the structure. In addition, the performance of hermetically sealed light-emitting device8or light-receiving device9is stabilized, suppressing secular changes in light-emitting device8or light-receiving device9. The use of resin for sealing facilitates sealing. The use of solder for sealing eliminates the need to apply kovar glass to optical components4.

In the example shown inFIG. 3, a light-emitting diode (LED) chip and photo diode (PD) chip are mounted respectively as light-emitting device8and light-receiving device9. Diffractive lens4A and window4B made of glass are disposed as optical components4. Optical transmission lines1, each made of a plastic-clad fiber, are then abutted on cavities3. Each cavity3has two steps for allowing electrical connection of the surface of the LED chip or PD chip to an upper step by wire bonding. Laser diode (LD) can also be used as light-emitting device8. Photoelectric conversion is simplified by use of these optical semiconductor devices as light-emitting device8and light-receiving device9.

In the example shown inFIGS. 16A and 16B, electrode51formed in cavity3on substrate6and light-emitting device8fitted in cavity3are connected by wire52made such as of gold. In this structure, electrode51is formed on a groove where a backoff is created for the bonding tip at a wire bonding for electrical connection. This achieves an equivalent optical system by cavity3with only a single step. In both cases, the outlines of the top steps of cavities3and optical components4disposed on the top steps are made substantially the same. And the outline of these members and that of optical transmission lines1are made substantially the same to uniquely determine the position of optical transmission lines1. This allows positioning of one of optical components4and optical transmission line1using only a single step.

InFIG. 3, the light output from light-emitting device8is focused through lens4A, and enters optical transmission line1of the transmitting side. The light from the optical transmission line of the reception side passes through window4B, and is applied to light-receiving device9. By positioning light-emitting device8, lens4A, and optical transmission line1; and light-receiving device9, window4B, and optical transmission line1by means of each of cavities3, each of the optical axes of the optical systems at the transmission and reception sides can be easily aligned.

In this embodiment, the number of layers in substrate6, which is a multilayer ceramic substrate, is preferably two or more than the number of steps of cavities3. By creating through holes at predetermined positions in each ceramic layer before lamination, cavities3can be easily formed. The thickness of the ceramic layer which becomes the steps one level upper the floors of cavities3created on the surface of substrate6preferably has substantially the same thickness as light-emitting device8and light-receiving device9. This facilitates the positioning of light-emitting device8and light-receiving device9, and also facilitates wire bonding from the surface of light-emitting device8and light-receiving device9. Furthermore, the mechanical strength of entire substrate6can be increased by fabricating the ceramic layer that becomes the floors of cavities3created on the surface of substrate6with firing powder or firing powder and machining.

Second Exemplary Embodiment

FIGS. 4 and 5are perspective views of a transceiver module for optical communications in a second exemplary embodiment of the present invention.FIG. 6is a sectional view taken along Line A–A′ inFIG. 4orFIG. 5.

The transceiver module for optical communications shown inFIG. 4has a different structure for cavities3compared to that in the first exemplary embodiment shown inFIG. 1. However, the other structures are identical. The top steps of cavities3have a shape substantially the same as that of optical transmission lines1. Optical components4such as refractive lens, diffractive lens, optical iris, and window are installed on the steps one level below the top steps. As in the first exemplary embodiment, cavities3and optical components4can have other shapes such as square and triangle, as shown inFIG. 5, as long as the positions of optical transmission lines1are uniquely determined.

InFIG. 6, multi-step cavities3created on the surface of substrate6, which is a multilayer ceramic substrate, have at least two steps, and light-emitting device8and light-receiving device9are mounted on their floors. Optical transmission lines1are abutted on the top steps. Optical components4(lens4A and window4B) are installed on the steps one level below the top steps, and then hermetically sealed by sealing material10.

In the example shown inFIG. 6, the surface of light-emitting device8or that of light-receiving device9to the upper step is electrically connected by wire bonding, and therefore cavities3have three steps. On the other hand, as shown inFIGS. 16A and 16B, an equivalent optical system can be achieved with two-step cavity3by establishing electrical connection using wire bonding onto the floor. In both cases, when cavities3have two or more steps, optical transmission lines1can be positioned without allowing cores1A of optical transmission lines1to contact and damage substrate6or optical components4by the use of two steps, i.e., a top step plus one step below, in cavities3.

Cavities3can also have three or more steps. In this case, optical components4are installed on one of the steps, and optical transmission lines1are installed on any step above the steps holding optical components4.

The depth of the steps where optical components4are installed is preferably greater than the thickness of optical components4. Alternatively, it is preferable to provide a vacant step between the step where one of optical components4is installed and the step where optical transmission line1is installed, as described later with reference toFIG. 10. This prevents contact between optical components4and optical transmission lines1.

The outline of the steps where optical components4are installed is preferably larger than cores1A of optical transmission lines1. This ensures that optical transmission lines1can be positioned so as to prevent cores1A contacting and causing damage to optical components4.

In the above transceiver module for optical communications, the light output from light-emitting device8is focused through diffractive lens4A, and the focused light enters the optical transmission line1of the transmission side. The light from optical transmission line1of the reception side passes through window4B and arrives at light-receiving device9. As described above, the positioning of light-emitting device8, lens4A, and optical transmission line1; and light-receiving device9, window4B, and optical transmission line1with respect to each of cavities3facilitates the alignment of each of the optical axes of the optical systems at the transmission and reception sides in the same way as that in the first exemplary embodiment. In addition, degradation of characteristics by wear is preventable because optical components4and optical transmission lines1do not come into contact.

Third Exemplary Embodiment

FIGS. 7 and 8are perspective views of a transceiver module for optical communications in a third exemplary embodimentFIGS. 9 and 10are sectional views taken along Line A–A′ inFIG. 7orFIG. 8.

The transceiver module for optical communications shown inFIG. 7has a different structure for cavities3compared to that in the first exemplary embodiment shown inFIG. 1. However, the other structures are identical. As in the first exemplary embodiment, cavities3and optical components4can have other shapes such as square and triangle, as shown inFIG. 8, as long as the positions of optical transmission lines1are uniquely determined.

In the following description, the top step of cavity3is called a first cavity, and one level below the top step is called a second cavity, and then a third cavity which is another level below. The first cavity has a shape substantially the same as optical transmission line15, and the second cavity has a shape substantially the same as optical transmission line1which has a smaller diameter than that of optical transmission line15. Optical components4(lens4A and window4B) are installed on the third cavities.

InFIGS. 9 and 10, cavities3created on the surface of substrate6which is a multilayer ceramic substrate has at least three steps, and light-emitting device8and light-receiving device9are mounted on their floors. Moreover, optical transmission lines15are abutted on the first cavities as shown inFIG. 9, and optical transmission lines1are abutted on the second cavities as shown inFIG. 10. Optical components4are installed on the third cavities, and hermetically sealed by sealing material10.

In the example shown inFIG. 9, the surface of light-emitting device8or the surface of light-receiving device9to the upper step is electrically connected by wire bonding, and therefore cavities3have four steps. On the other hand, as shown inFIGS. 16A and 16B, an equivalent optical system can be achieved with three-step cavity3by establishing electrical connection using wire bonding onto the floor.

In the example shown inFIG. 10, optical transmission line15is made of a plastic fiber, unlike that inFIG. 9. It is apparent fromFIGS. 9 and 10that the third exemplary embodiment is applicable to two types of optical transmission lines1and made of plastic-clad fiber and plastic fiber. The core diameters of the plastic fiber and plastic-clad fiber are sufficiently large to permit the light output from light-emitting device8to readily enter optical transmission lines1and15when these types of fibers are used as the optical transmission lines.

InFIG. 9, the light output from light-emitting device8is focused through lens4A, and enters optical transmission line1of the transmission side. The light from optical transmission line1of the reception side passes through window4B, and arrives at light-receiving device9. As described above, the positioning of light-emitting device8, lens4A, and optical transmission line1; and light-receiving device9, window4B, and optical transmission line1with respect to each of cavities3facilitates the alignment of each of the optical axes of the optical systems at the transmission and reception sides. InFIG. 10, the light output from light-emitting device8is focused through lens4A, and enters optical transmission line15of the transmission side. The light from optical transmission line15of the reception side passes through window4B, and arrives at light-receiving device9. In the same way, the positioning of light-emitting device8, lens4A, and optical transmission line15; and light-receiving device9, window4B, and optical transmission line15with respect to each of cavities3facilitates the alignment of each of the optical axes of the optical systems at the transmission and reception sides. In the same way as in the second exemplary embodiment, degradation of characteristics by wear is preventable because optical components4and optical transmission lines1and15do not come into contact. In addition, the third exemplary embodiment is applicable to two types of optical transmission lines1and15, i.e., plastic-clad fiber and plastic fiber.

As described above, cavity3having three or more steps allows the positioning of two or more types of transmission lines1and15which have different outlines via the top step of cavity3and one level below the top step. Cavity3can also be configured with three or more steps, and optical transmission line1can be installed on a step other than the top step. As in the first exemplary embodiment, one of optical components4and optical transmission line1can also be installed on the same step, and optical transmission line15can be installed on one level above that step. This allows cavity3with only two steps to be used for optical transmission lines1and15with different outlines.

Fourth Exemplary Embodiment

FIGS. 11 and 12are perspective views of a transceiver module for optical communications in a fourth exemplary embodiment of the present invention.FIGS. 13 and 14are sectional views taken along Line A–A′ inFIG. 11orFIG. 12.

The module shown inFIG. 11has a different structure for cavities3compared to that in the first exemplary embodiment shown inFIG. 1, but the other structures are identical. Also as in the first exemplary embodiment, cavities3and optical components4can have other shapes such as square and triangle, as shown inFIG. 12, as long as the positions of optical transmission lines1are uniquely determined.

In the following description, the top step of cavity3is called a first cavity, and one level below the top step is called a second cavity, and then a third cavity and fourth step downward. The first cavity has a shape substantially the same as optical transmission line15, and the second cavity is larger than core15A of optical transmission line15. The third cavity has a shape substantially the same as optical transmission line1that has a smaller diameter than that of optical transmission line15. The fourth cavity is larger than core1A of optical transmission line1. Optical components4(lens4A and window4B) are installed on the fourth cavities.

InFIGS. 13 and 14, multi-step cavities3created on the surface of substrate6have at least four steps, and light-emitting device8and light-receiving device9are mounted on their floors. InFIG. 13, optical transmission lines1are abutted on the third cavities. InFIG. 14, optical transmission lines15are abutted on the first cavities. Optical components4are installed on the fourth cavity, and then hermetically sealed by sealing material10.

In the example shown inFIG. 13, the surface of light-emitting device8or that of light-receiving device9to the upper step is electrically connected by wire bonding, and therefor cavities3have five steps. On the other hand, as shown inFIGS. 16A and 16B, an equivalent optical system can be achieved with four-step cavities3by establishing electrical connection using wire bonding onto the floors.

In the example shown inFIG. 14, plastic fibers are used for optical transmission lines15, unlike the example shown inFIG. 13. Accordingly, it is apparent fromFIGS. 13 and 14that this embodiment is applicable to two types of optical transmission lines1and15, i.e., plastic-clad fiber and plastic fiber.

As described above, cavity3having four or more steps enables positioning of optical transmission line1having a smaller diameter than that of optical transmission line15by using two steps which are two levels and three levels below the top step of cavity3. This prevents the cores of optical transmission lines1contacting and being damaging substrate6and optical components4.

Fifth Exemplary Embodiment

FIG. 15is a sectional view of a transceiver module in a fifth exemplary embodiment taken along Line A–A′. A perspective view of the transceiver module for optical communications in this embodiment is the same as that shown inFIG. 7orFIG. 8.

Cavities3created on the surface of substrate6have at least three steps. And the top steps is called the first cavity, and then the second cavity, and third cavity downward. Optical transmission lines1are abutted on the first cavities. Optical components such as optical iris4C and diffractive lens4A are installed on the second and third cavities respectively, and are hermetically sealed using sealing material10. Light-emitting device8and light-receiving device9are mounted on the floors of cavities3. The other structures are the same as those in the third exemplary embodiment.

InFIG. 15, the surface of light-emitting device8or that of light-receiving device9to the upper step is electrically connected by wire bonding, and therefore cavities3have four steps. On the other hand, in the example shown inFIGS. 16A and 16B, an equivalent optical system can be achieved with three-step cavities3by establishing electrical connection using wire bonding onto the floors. In addition, inFIG. 15, optical transmission lines1is positioned in the first cavities, and optical components4(optical iris4C and window4B) are positioned in the second or third cavities to prevent contact between optical transmission lines1and optical components4. However, the number of steps in cavities3can be reduced by one if both optical transmission lines1and optical components4are positioned in the first cavities.

The light output from light-emitting device8is focused through lens4A, and optical iris4C removes excess light. Then, the light enters optical transmission line1of the transmission side. The light from optical transmission line1of the reception side passes through window4B, and arrives at light-receiving device9. As described above, the positioning of light-emitting device8, lens4A, optical iris4C, and optical transmission line1; and light-receiving device9, window4B, and optical transmission line1with respect to each of cavities3facilitates the alignment of each of the optical axes of the optical systems at the transmission and reception sides regardless of the number of optical components4. When optical transmission line1is installed on the top step of cavity3or optical transmission line1and one of optical components4are installed on the top step, the positioning of at least two optical components4with different outlines can be achieved by using remaining steps.

All exemplary embodiments mentioned above refer to a single module for both transmission and reception. It is apparent that the alignment of optical axis described in the present invention is also effective for modules for transmission or reception only.

INDUSTRIAL APPLICABILITY

The present invention allows integrated alignment of optical axis of the optical transmission line, optical components, and light-emitting device or light-receiving device, and thus a smaller and shorter transceiver module for optical communications is achievable.

REFERENCE NUMERALS IN THE DRAWINGS