Abstract:
An opto-electronic assembly for high speed opto-electronic signal transmission which comprises:
       mounting plate with a top side; wherein the top side contains at least one area at a higher level and at least one area at a lower level,   an electro-optical or opto-electronic transducer component with a number of transducers with the optical port of the transducer component on the top side;   a micro-mirror component;   an optical transmission path assigned to each transducer wherein the transmission axis of each transmission path is oriented substantially parallel to the surface of the transducer component and to the top side of the mounting plate; and   a transducer component that is mounted with the bottom side on the mounting plate below a micro-mirror component that is mounted above the transducer component in such a configuration that the optical transmission path to or from each transducer is reflected at the dedicated mirror surface.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of U.S. patent application Ser. No. 12/805,952, filed Aug. 26, 2010, entitled: “Opto-Electronic Assembly for High Speed Transmission”. The aforementioned application is hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to optoelectronic apparatus, for example to signal interconnects between the electronics and the optical transmission medium and vice versa. 
     Advanced systems for long distance and short distance communication need very high speed interconnects for the inter system as well as intra system information transmission. The standard technology for this purpose is optical transmission over fibres. The key components for the aforementioned technology include the electro-optic (e-o) transducer acting as a transmitter, and the opto-electronic (o-e) transducer acting as a receiver. Such transducers are used in every optical communication system. 
     For the very high transmission speeds of 10 Gigabites per second (10 Gbit/sec) and above it is necessary to apply high speed optical and electronic components as well as special solutions for the packaging of such a transducer module in order to reach the required overall high-frequency (HF) performance. 
     A further increase of the transmission capacity is possible with parallel transmission of several channels. In this case there are additional critical issues that must be solved because a close spacing of radio frequency (RF) channels may lead to crosstalk and signal degradation. Therefore the proper design of the electronics and the packaging is even more challenging. 
     A transmitter or receiver module in general consists of the module housing with an electronic interface and an optical interface and the opto-electronic assembly inside the housing. The opto-electronic assembly consists of an arrangement of: 1) optical components such as laser diode and photodiode chips; 2) active electronic components such as patterned circuit boards and mounted integrated circuits; and 3) other mechanical or passive optical components, wherein all components are placed inside the housing. For parallel transmission there are typical several parallel channels and components on each optical or electronic chip. This configuration has the advantage that it is possible to reach higher density and lower cost. 
     To achieve good HF-performance with such an opto-electronic assembly it is necessary to use a circuit board with impedance-matched electrical transmission lines as well as an assembly and interconnection technology that is optimized for high speed signal transmission. Furthermore, the opto-electronic assembly has to comply with the type and performance specifications of the applied optical and electronic components. 
     Such opto-electronic assemblies are used inside packages that include an optical and an electronic interface (or port) which may have several independent parallel channels each. The optical interface of such a package is attached to an optical connector or optical fibre port and forms what is called a subassembly. The subassemblies with an optical connector for departing or entering optical data signals are called transmitter optical subassemblies (TOSAs) and receiver optical subassemblies (ROSAs), respectively. Such subassemblies are used as building blocks in higher complexity integrated modules such as various types of transceivers or transponders that include a TOSA and a ROSA and also various kinds of electronic functions via an electronic port. For these types of applications there is only a limited physical space and it is necessary that the package is designed in a geometry wherein the optical port and the electronic port are located on opposite sides of the package. Further such subassemblies may contain optical transmitting channels as well as optical receiving channels. Sometimes these subassemblies are called “optical engines”. 
     2. Description of Related Art 
     Prior art of parallel optical assemblies for high speed interconnections with top-emitting transmitters like Vertical Cavity Surface Emitting Lasers (VCSELs) apply an optical polymer component for beam forming which is arranged at some distance on top of the transmitter chip. The polymer component includes a micro-lens, a mirror section and a further micro-lens for each optical channel located in front of each laser (see  FIG. 1 ). A new version of such an optical polymer component is presented in the US patent application entitled “Lens Array and Optical Module Including Lens Array” by Morioka, filed Jul. 6, 2011, patent application Ser. No. 13/177,307, whereas this patent application is hereby incorporated by reference. 
     Another approach is published as “Parallel optical link (PAROLI) for multichannel gigabit rate interconnections”, H. Karstensen et. al., ECTC Conference, pp. 747-754, 1998, whereas this publication is incorporated herein by reference. On top of the transducer chip with several VCSELs an optical fiber is aligned, having the endface polished in a 45° angle. This angled surface is used as a mirror to direct the emitted laser light from the VCSEL into the fiber which is arranged parallel to the surface of the transducer. 
     SUMMARY OF THE INVENTION 
     The present invention discloses an assembly and arrangement for such a high speed package which uses optical transducer chips having the emitting or receiving function perpendicular to the chip surface. Well-known optical transducers of this kind include photodiodes (PD) and vertical cavity surface emitting lasers (VCSELs). 
     In accordance with the characteristics of the present invention, the opto-electronic assembly for high speed opto-electronic signal transmission comprises:
         a mounting plate with a top side used for the mounting of components;   an electro-optical or opto-electronic transducer component with a number of transducers with the optical port of the transducer component on the top side and a bottom side used for assembly;   a micro-mirror component;   an optical transmission path assigned to each transducer wherein the transmission axis of each transmission path is oriented substantially parallel to the surface of the transducer component and to the top side of the mounting plate; and   a transducer component that is mounted with the bottom side on the mounting plate near a micro-mirror component that is mounted above the transducer component in such a configuration that the optical transmission path to or from each transducer is reflected at the dedicated mirror surface such that the transducer is optically coupled to the dedicated transmission path.       

     The various embodiments of the present invention include modifications of designs for the mounting plate and the micro-mirror component, and include the use of various standoff components. The compact assembly will show superior HF-characteristics. Moreover, a single design type of assembly may be used for both transmitter and receiver subassemblies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  presents a cross section of a prior art assembly with parallel channels on a flat mounting plate with an optical polymer lens-mirror component. 
         FIG. 2  shows a three dimensional (3D) drawing of an assembly with transducer components having several transducers. 
         FIG. 3  illustrates the 3D view of an assembly with transducer components having several transducers from the front side. 
         FIG. 4  shows an assembly with a transducer component having several transducers where the transducer component has an additional electrical third port at the bottom side of the transducer component. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a cross section of a prior art of an assembly for parallel optical transmission. The opto-electronic transducer component  20  and the integrated electronic circuit chip  30  are mounted on a flat mounting plate  10 . A multifunctional optical polymer component for beam forming  40  is arranged at some distance on top of the transmitter chip. The polymer component  40  includes a micro-lens, a mirror section and a further micro-lens for each optical channel located in front of each laser. In the direction out of the drawing plane there are several channels arranged neighboring to each other. These channels may form an array of individual opto-electronic channels. Such polymer component is quite large (having dimensions typically exceeding 6 mm×2 mm×2 mm) and needs a very sophisticated manufacturing procedure to reach the optical quality and the necessary tight tolerances. Further the coefficient of thermal expansion of optical transparent polymers is much larger than that of the semiconductors. This may create large mechanical stress if such a configuration is applied to long linear arrays. This may cause misalignment of the optical channels of the individual transducers if the temperature of the assembly is changed. 
     Further the integrated electronic circuit chip  30  is connected electrically to the flat mounting plate  10  with thin wirebonds. Since the mounting plate  10  is flat the wirebonds have to connect the top side of the integrated electronic circuit chip  30  with the lower level surface of the mounting plate  10 . Such connections across a height difference need longer length of the wirebonds which result in limited RF-performance of the assembly only. 
       FIG. 2  presents an exemplary embodiment of the present invention. A three-dimensional (3D) perspective view is shown. The mounting plate  10  comprises an area at higher level  10   a  with high frequency optimized electrical lines  80  and a lower area  10   b . On the lower area  10   b  of the mounting plate  10  the following components are assembled: the electronic integrated circuits  30  and  31  as well as the transducer components  20  and  21 . Each transducer component  20 ,  21  consists of several individual transducers  20   a, b, c, d  and  21   a, b, c, d  on the top side. Further on the top side of the transducer components  20  and  21  are located the electrical contact pads for the electrical connection of each individual transducer to the dedicated electronic circuit. The transducers  20   a, b, c, d  and  21   a, b, c, d  are connected with short and flat wire bonds to the integrated circuits  30  and  31  since the top surfaces of the electronic integrated circuits  30  and  31  as well as the transducer components are approximately at the same height level. Since transducer components and electronic integrated circuits in general do not have the same thickness the transducer components  20 ,  21  are mounted on some submount components  40  and  41 . The height of the submount components  40 ,  41  is adjusted that top surfaces of the electronic integrated circuits  30  and  31  as well as those of the transducer components  20 ,  21  are approximately at the same height level. 
     Further the surface of the higher level  10   a  of the mounting plate is approximately at the same height level as the top surface of the electronic integrated circuits  30  and  31 . Therefore the electronic integrated circuits  30  and  31  can be connected with short and flat wire bonds to the high frequency traces on the higher level  10   a  of the mounting plate  10 . 
     A one skilled in the art will appreciate that it is of high importance to construct the assembly of  FIG. 2  such that the higher level  10   a  of the mounting plate and the top surface of the electronic integrated circuits  30  and  31  are approximately at the same height level. It is preferred that a difference in height levels between the above mention components does not exceed 50 μm (micrometers). Further, it is preferred that a difference in height level between the top surface of the electronic integrated circuits  30  and  31 , on the one hand, and between those of the transducer components  20  and  21 , on the other hand, does not exceed 50 μm. 
     The mirror component  50  is arranged above the transducer components. It is mounted on the stand-off elements  61 ,  62  and  63  in such a position that a gap is formed between the top surface of the transducer components  20 ,  21  and the bottom surface of said micro-mirror component  50 . In addition to the electronic integrated circuits  30  and  31  and the transducer components  20 ,  21  there can be mounted further active or passive electronic components  70  on the mounting plate  10 . 
       FIG. 3  shows a 3D-front view to the exemplary embodiment of the patent. The micro-mirror component  50  has a reflecting mirror surface  50   r  which is oriented at an angle close to forty-five degrees towards the transducer components  20 ,  21 . A one skilled in the art will appreciate that, for proper functionality of the assembly, the angle should be preferably in the interval between 42 degrees and 48 degrees. It is even more preferred that the angle is between 44 degrees and 46 degrees. The mirror surface  50   r  may contain separated surface sections a to h which are oriented each towards an individual transducer on the transducer components  20 ,  21 . The surface sections a to h are coated with a material which is capable to achieve a high reflection of the relevant optical radiation which is transmitted or received by the transducers  20   a, b, c, d  and  21   a, b, c, d.    
     In one embodiment of the present invention the surface  50   r  of the reflecting mirror is one flat surface which has the same form and orientation for all separated surface sections a to h. 
     In another embodiment of the present invention the reflecting mirror surface  50   r  has a special surface characteristic in the separated surface sections a to h different from a plane surface. As an example, the surface characteristic in each separated surface section a to h may be formed as a concave elliptic mirror. 
     Further  FIG. 3  illustrate that the micro-mirror component  50  is located above the transducer components  20 ,  21  in such a configuration that a gap  100  is formed between the top surface of the transducer components  20 ,  21  and the bottom surface of said micro-mirror component  50 . The gap  100  is large enough to provide the space for the short and flat wirebond connections connecting the transducers with the electronic integrated circuits. A one skilled in the art will agree that the gap  100  should be preferably larger than 50 μm. 
       FIG. 4  presents a further embodiment of the present invention. The transducer component  20  has electrical connections for the individual transducers on the top side and an additional electrical connection  110  on the bottom side. The connections on the top side are directly connected with the integrated electronic circuit  30  and are located below the micro-mirror component  50 . The electrical connection at the bottom side  110  is not directly connected with the integrated electronic circuit  30 . This transducer component can apply individual transducers which need three electrical connections with one of the three connections as a common connection for all transducers of the transducer component. One example of such an electro-optical transducer is a laser with integrated modulator, e.g., a VCSEL with an integrated modulator section. Possible embodiments of a VCSEL with an integrated modulator section include, but are not limited to those disclosed in the U.S. Pat. No. 7,369,583 “ELECTROOPTICALLY WAVELENGTH-TUNABLE RESONANT CAVITY OPTOELECTRONIC DEVICE FOR HIGH-SPEED DATA TRANSFER”, filed Jun. 2, 2005, issued May 6, 2008, U.S. Pat. No. 7,593,436 “ELECTROOPTICALLY BRAGG-REFLECTOR STOPBAND-TUNABLE OPTOELECTRONIC DEVICE FOR HIGH-SPEED DATA TRANSFER”, filed Jun. 16, 2006, issued Sep. 22, 2009, and U.S. Pat. No. 8,290,016 “OPTOELECTRONIC DEVICE FOR HIGH-SPEED DATA TRANSFER WITH ELECTROOPTICALLY TUNABLE STOPBAND EDGE OF A BRAGG REFLECTOR”, filed Jul. 27, 2009, issued Oct. 16, 2012, all patents by Ledentsov et al., wherein these patents are hereby incorporated herein as reference. The electrical connection  110  at the bottom side of the transducer component  20  is used to drive all lasers in continuous mode and the high frequency modulation of the modulator section is connected on the top of the transducer component  20  directly to the integrated electronic circuit  30  to reach the good HF-performance. 
     It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination. 
     All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. 
     Although the invention has been illustrated and described with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without departing from the spirit and scope of the present invention. Therefore, the present invention should not be understood as limited to the specific embodiments set out above but to include all possible embodiments which can be embodied within a scope encompassed and equivalents thereof with respect to the feature set out in the appended claims.