Patent Application
20050276546
The invention relates to a bidirectional emitting and receiving module, which emits light having a first wavelength and detects light having a second wavelength. WDM (wavelength division multiplex) applications constitute an exemplary area of use.
Bidirectional emitting and receiving modules are known per se. The known solutions have the disadvantage that the emitting components and receiving components of the modules are in each case realized on separate carriers and/or with separate housings.
EP 0 664 585 A1 discloses an emitting and receiving module for bidirectional optical message and signal transmission. In this case, a laser chip is arranged on a carrier in such a way that it emits radiation onto a slanted interface of an additional body arranged on the carrier. The emitted radiation is deflected at the interface, passed through a lens coupling optical element fitted above the laser chip and the interface, and is coupled into an optical fiber. Beneath the carrier, a photodetector is arranged in a TO housing baseplate and detects radiation that emerges from the optical fiber. The received radiation is directed onto the interface via the lens coupling optical element and passes through the interface and the carrier.
U.S. Pat. No. 5,577,142 discloses an emitting and receiving communication means for optical fibers. The communication means has a total of three carriers arranged in parallel one above the other. On the topmost carrier a photodiode is arranged as a receiver. A laser diode operating as an emitter and a monitor diode for measuring a reference signal are integrated between the three carriers.
The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention, nor to delineate the scope thereof. Rather, the primary purpose of the summary is to present one or more concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention is directed to a bidirectional emitting and receiving module that is distinguished by a compact construction and a high degree of integration.
Accordingly, the emitting and receiving module according to the invention has a carrier, on the top side of which an emitting component is arranged and at the underside of which a receiving component is arranged. In this case, the carrier is transparent to the light to be detected by the receiving component. A slanted interface coated with a wavelength-selective mirror is provided, at which, on the one hand, light emitted by the emitting component is reflected and deflected. On the other hand, at the slanted interface, light to be received by the receiving component is refracted into the adjoining medium. The light to be received that is refracted at the interface traverses the carrier, emerges from the carrier at the underside thereof and is then detected by the receiving component. The receiving component is arranged in a cutout in the underside of the carrier. The cutout is deep enough, in one example, to completely accommodate the receiving element. In particular, the cutout is designed such that a receiving component with a chip thickness of 80 μm to 200 μm can be mounted in the cutout.
The cutout is formed by a trench or a truncated pyramid, for example, which is preferably formed by etching in the carrier. In principle, a trench may in particular also be provided by means of mechanical methods such as milling.
The solution according to one embodiment of the invention is constructed extremely compactly since the emitting component and the receiving component are arranged on only one carrier. In this case, a beam path is provided which enables the received light to emerge on the rear side of the carrier, so that the receiving component can be arranged there. The emergence of the received light from the rear side of the carrier, that is to say the avoidance of any total reflection, is achieved by means of the received light impinging as far as possible perpendicularly on the underside of the carrier. For this purpose, on the one hand, by means of the refractive index of the materials used, it is possible to influence the direction of the light refraction at the slanted interface and thus the direction of light propagation in the carrier. On the other hand, it is possible to provide, if appropriate, slanted cutouts on the rear side of the carrier.
It is pointed out that the arrangement of the receiving component “at the underside” of the carrier should be understood such that the receiving component may be fixed directly to the underside of the carrier but may also be spaced apart from the underside and merely arranged beneath the carrier. There does not have to be any physical contact between carrier and the receiving component.
In one embodiment of the invention, the module has an additional body, which may be a glass body, in particular a glass prism. The additional body is arranged on the carrier and forms the slanted interface with the wave-selective mirror, the light to be received that is refracted at the interface thus traversing the additional body first and then the carrier. In this case, the additional body constitutes a unit that can be coated separately with the wavelength-selective mirror.
In another embodiment, the receiving component is assigned a wavelength-selective filter which is situated at the underside of the carrier and blocks the transmission of light having the first wavelength. The wavelength-selective filter is preferably a high-pass filter or a low-pass filter that transmits or blocks wavelengths in the window of 1,480 to 1,600 nm.
In a further embodiment, the cutout at the underside of the carrier is provided with metallizations. In this case, the receiving component is mounted by flip-chip mounting in the cutout, for which purpose both contacts are arranged on one side. Flip-chip mounting avoids the use of a bonding wire that would disadvantageously project from the cutout in which the receiving component is arranged.
In a further embodiment of the invention, the slanted interface is not formed at an additional body but rather at the carrier itself. This refinement thus manages without a further part that would have to be connected to the carrier. Rather, the slanted interface at which the light of the emitting component is reflected and the light to be detected is refracted into the adjoining medium is integrated into the carrier.
In this case, the slanted interface is formed at the bevel of a cutout at the top side of the carrier. The emitting component is then arranged in the cutout. Another, opposite bevel of the cutout may serve as a beam deflecting unit for a monitor diode that is assigned to the emitting component and detects the rear-side radiation of the laser diode for monitoring purposes. In this case, the monitor diode is arranged on the topmost plane of the top side of the carrier.
In a variation of this embodiment, the underside of the carrier is oriented with regard to the direction of propagation of the light to be received in the carrier in such a way that the light to be received, after traversing the carrier, does not experience any total reflection at the underside of the carrier and can be detected by the receiving component. For this purpose, it may be provided that the carrier has on its underside a cutout with a bevel, from which the light to be received emerges.
In this case, the bevel may serve as a carrier of a wavelength-selective filter which blocks the transmission of light having the first wavelength. The wavelength-selective filter may be formed either at the bevel itself or at a separate carrier, which may be fixed to the bevel by means of an index-matched, transparent adhesive. It is also conceivable for the receiving component to be arranged directly at the bevel. The considered bevel of the cutout at the rear side of the carrier runs parallel to the slanted interface with the wavelength-selective mirror at the top side of the carrier, both running at an angle of 45° with respect to the mounted area of the emitting component. Consequently, two parallel planes are produced in the carrier in this example.
In order to produce the module, it may be provided that the top side of the carrier is formed from a first patterned wafer and the underside of the carrier is formed from a second patterned wafer, which are connected to one another after the patterning by means of wafer fusing. In this case, a unit that can be tested by panel mounting is formed, in the case of which the modules are tested prior to singulation of the wafer.
The carrier, in one example, is composed of silicon. The slanted interface may run at an angle of 45° with respect to the plane of the top side of the carrier, the slanted interface being formed either at an additional element, in particular a glass prism, or in the silicon substrate itself. The respective bevels in one example are produced micromechanically by etching.
To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
The invention is explained in more detail below on the basis of a number of exemplary embodiments with reference to the figures of the drawings, in which:
FIGS. 1 to 6 show a first exemplary embodiment of a bidirectional emitting and receiving module. As can be gathered from
A laser diode 2, a monitor diode 3 and a glass prism 4 are arranged on the top side 101 of the submount 1. Metallizations 5a, 5b and bonding wires 6 are provided for the purpose of contact-connecting the laser diode 2 and the monitor diode 3. The laser diode 2 is formed as a laterally emitting laser. In this case, a small percentage of the laser light is coupled out on the rear side and detected by the monitor diode 3 for monitoring purposes.
The glass prism 4 has an interface 41 running at an angle of 45°, said interface being coated with a wavelength-selective mirror 42 (cf.
The underside of the silicon submount 1 has a cutout 9, which is introduced into the silicon carrier 1 micromechanically by etching. A photodiode 10 with a photosensitive area 110 is situated in the cutout 9. A p-type contact 120 and an n-type contact 130 are arranged on the same side of the photodiode 10, so that it is possible to effect a flip-chip mounting of the photodiode 10 on metallizations 11, 12 at the walls of the cutout 9.
On the underside 102 of the submount 1, solder bumps 13 are arranged on the metallizations 11, 12, and serve for an SMD mounting of the entire module on a ceramic board, for example, as will also be explained with reference to
The underside of the submount 1 firstly has a wavelength-selective filter (blocking filter 14) centrally in the cutout 9, which filter is not transmissive to light of the emitting diode 2 and accordingly blocks this light from the photodiode 10. The blocking filter 14 is preferably either a high-pass filter or a low-pass filter. If the bidirectional module is in this case designed such that the laser 2 emits in the window between 1,260 and 1,360 nm and the photodiode 10 arranged in the cutout 9 detects light having a wavelength in the window of 1,480 to 1,600 nm, then the blocking filter 14 would in this case be embodied as a high-pass filter that blocks the lower wavelengths of 1,260 nm to 1,360 nm and transmits wavelengths starting from 1,480 nm. In the case of a contrasting bidirectional module, which then emits at 1,480 to 1,600 nm, and receives at 1,260 to 1,300 nm, a low-pass filter is provided in a corresponding manner.
Furthermore, an oxide layer 111, 121, a nitride layer 112, 122 and a metallization 113, 123 are once again formed on the underside of the submount 1, and extend along the wall of the cutout 9. It can be gathered from the bottom view of
The function of the emitting and receiving module described is as follows. Light having a first wavelength that is emitted by the laser diode 2 is reflected at the wavelength-selective mirror 42 of the interface 41—running at an angle of 45°—of the glass prism 4 and radiated perpendicular to the surface 101 of the submount. In this case, the reflected laser light passes through the lens 81 arranged above the bevel 41 and is subsequently coupled into an optical fiber. Light having a second wavelength that is coupled out from the corresponding optical fiber and runs in the opposite direction and is to be detected by the photodiode 10 falls through the lens 81 onto the bevel 41 of the glass prism. Since the wavelength-selective mirror 42 is transmissive to the reception wavelength, the light to be received is refracted into the glass prism 4.
In this case, the light is refracted toward the perpendicular on account of the fact that the glass prism 4 has a higher refractive index than air. The light to be received then traverses the glass prism 4 and subsequently enters into the silicon submount 1, which is transparent to the wavelengths considered (above 1 000 nm). In this case, the glass prism 4 is connected to the silicon submount 1 by anodic bonding, by way of example, the refractive index of the glass increasing in the boundary layer of the glass prism 4 with respect to the silicon carrier 1 as a result of indiffused ions and, at the interface, being equal to the refractive index of the adjoining silicon carrier 1, so that the light is not refracted upon the transition between the glass prism 4 and the silicon carrier 1. The light to be received then traverses the silicon carrier 1 and emerges from the silicon carrier 1 at the underside in the region of the cutout 9. The photodiode 10 is arranged in the cutout 9 in such a way that the photosensitive area 110 is irradiated with the light to be received. The light to be detected passes through the blocking filter 14 prior to detection, so that any possible scattered light from the photodiode 2 is coupled out.
It is pointed out that the light to be received, on account of the refractive index of the glass prism 4, is coupled into the glass prism and subsequently into the silicon submount in such a way that it does not experience any total reflection at the underside of the silicon submount 1 and can accordingly be detected by the photodiode 10. The refractive index of the glass prism 4 thus results in a beam path that enables the light to emerge from the plane underside 101 of the silicon submount 1.
Overall, a highly compact arrangement is provided in the case of which the emitting diode 2 and the receiving diode 10 are arranged on a common carrier and this carrier is situated in only one housing, into which light is coupled in and out via an optical coupling.
FIGS. 7 to 10 show a second exemplary embodiment of a bidirectional emitting and receiving module. In this case, identical reference signals identify corresponding structural parts. The embodiment of FIGS. 7 to 10 is explained only insofar as there are differences relative to the exemplary embodiment of FIGS. 1 to 6.
One difference of this embodiment is the fact that the exemplary embodiment of FIGS. 7 to 9 manages without a glass prism. Instead, the slanted interface with the wavelength-selective mirror 42 is formed at the carrier 1 itself. For this purpose, the silicon carrier 1 has at its top side 101 a cutout 23 which has the form of a trench or a pit and which is produced by etching the silicon substrate 1. The cutout 23 forms two opposite bevels 24, 25. The right-hand bevel 24 assigned to the laser diode 2 is etched at an angle of 45° and corresponds in terms of its function to the interface 41 of the glass prism 4 of FIGS. 1 to 6. The wavelength-selective mirror 42 is arranged on the bevel 24.
The opposite bevel 25 in one example has an oblique angle of 63°, which results from the crystal orientation of the silicon. In a development of the exemplary embodiment illustrated, the 63° bevel 25 may serve as a beam deflecting unit for the rear-side radiation of the laser, a monitor diode then being mounted above the bevel 25 on the surface 101 of the carrier. In this configuration, then, unlike in the configuration illustrated, the monitor diode would not be arranged in the cutout 23. This may be expedient particularly when the cutout is relatively small.
The silicon element 8 with the lens 1 is arranged directly on the carrier 1.
A cutout 26 is once again also formed on the underside 102 of the silicon carrier 1. Said cutout likewise has two bevels 27, 32. The left-hand bevel 27 is likewise introduced into the silicon substrate by etching at an angle of 45°. The two 45° faces 24, 27 accordingly lie on the top side and underside of the substrate 1 in parallel planes. In principle, however, this need not be the case and the orientations of these two planes 24, 27 can also deviate from one another. It should be taken into account in this case that, in particular, the cutout 27 can also be produced by sawing or abrasive cutting instead of by etching, so that there is a greater freedom of choice with regard to the angle of the bevel 27.
In the light exit region, a glass or silicon lamina 28 is mounted at the bevel 27 said lamina being provided with a blocking filter which, in accordance with the explanations above, is formed as a high-pass filter or low-pass filter. If the cutout 26 is produced by sawing or abrasive cutting, the lamina 24 may be adhesively bonded on by means of a transparent adhesive. In this case, the adhesive is preferably index-matched, so that it performs the function of an immersion liquid or a matching gel, thereby minimizing the influence of the sawing roughness on the radiation. In the exemplary embodiment of
The beam path of the laser diode 2 corresponds to the beam path of the exemplary embodiment of FIGS. 1 to 6. By contrast, a different beam path 30 results for the receiving radiation on account of the higher refractive index of silicon compared with glass. On account of the higher refractive index, the radiation to be received is refracted toward the perpendicular to the interface 24 to a greater extent, so that the radiation to be received takes a more inclined course in the silicon substrate 1. This would have the effect that the radiation, if no cutout 26 were provided, would fall onto the plane underside 102 of the carrier 1 at an angle greater than the angle of total reflection. The radiation could not then emerge from the silicon carrier at all.
Therefore, the cutout 26 with the bevel 27 is introduced into the silicon substrate 1. The light to be received emerges from the silicon substrate through the bevel 27, in which case, on account of the angular arrangement of the bevel 27, the light can emerge and does not experience any total reflection.
The greater refraction of the light to be received in the silicon substrate is thus compensated for by providing a bevel at the underside of the carrier, from which the light to be received emerges. The light exit plane 27 provided by the cutout 26 is designed such that the critical angle of total reflection in the silicon does not occur at the wavelengths considered of between 1,260 and 1,600 nm if the radiation enters into the silicon carrier 1 via the 45° beam splitter 24. The carrier described is produced for example by etching of a corresponding silicon wafer on the top side and underside and subsequent provision of the metallizations, filters and mirrors and also of the components described. In this case, a preliminary test is preferably effected prior to singulation. However, it is likewise possible to pattern two silicon wafers independently of one another respectively with the structure of the top side 101 and the structure of the underside 102 and to subsequently connect the two wafers to one another by means of wafer fusing. The further production is then effected as described above.
Finally,
In an alternative configuration, however, it may also be provided that the monitor diode is arranged directly at the light exit area or bevel 27 of the carrier substrate 1. Such a configuration is expedient particularly in the case of small-area photodiodes and/or relatively large cutouts 26 at the underside of the silicon carrier 1.
While the invention has been illustrated and described with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. In particular regard to the various functions performed by the above described components or structures (assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component or structure which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the invention.
In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”.
This application is a continuation of International Application No. PCT/DE02/04492 filed Dec. 4, 2002, which was not published in English, and which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/DE02/04492 | Dec 2002 | US |
| Child | 11144892 | Jun 2005 | US |
