Optoelectronic package having a transmission line between electrical components and optical components

Described herein is a hermetic fiber optic package that may have a wide bandwidth radio frequency (e.g., between 9 kHz and 300 GHz) interface and a multilayer substrate provides a platform to integrated various components such as, for example, integrated circuits having electronic components, optoelectronic components, or optics. In one embodiment, the substrate has a wide bandwidth surface mountable interface that may be a single ended or a differential that allows for an electrical signal to pass from the exterior of the package to the interior. The interior of the package contains a “riser” that is used to bring an electrical signal from the plane of the substrate to the plane close to the optical axis. This riser includes a transmission line to achieve the change in height. The transmission line can be single ended or differential. Also within the package is a “submount” upon which electrical/optical/electro-optic components can be integrated.

TECHNICAL FIELD

The invention relates to optoelectronic packaging. More specifically, the invention relates to an optoelectronic component package having a transmission line between a high frequency interface on a first plane and optical components on a second plane in the component package.

BACKGROUND

As optical components have become increasingly integrated with electronic components, packages for optoelectronic devices have been developed. Individually, optical component packages and electronic component packages have been designed to solve different packaging problems. For example, optical components must be carefully aligned and the alignment must be maintained for proper functionality. Electronic components often require heat dissipation elements to maintain the electronic device in a predetermined operating temperature range.

In order to provide an interface between optical components and electronic components to utilize the bandwidth provided by fiber optics, it is necessary to provide devices which can perform optical to electric, as well as electrical to optical conversion and to pass signals between the electronic and optical domains. Current packages typically have a coaxial radio frequency (RF) interface or ceramic leaded interface. An alternative package is the miniature dual in-line (MINI-DIL) package, which is a ceramic can with ceramic walls and vertical leads.

Devices such as the butterfly package as well as the MINI-DIL package are configured according to a can shape that have various sidewalls. As a result, these devices are not capable of providing a planar platform for optical components, including optical transducers, transponders or the like. Moreover, the configuration of such devices does not enable product fabrication utilizing such techniques as machine vision.

FIG. 1illustrates a butterfly/can package known in the art. When configured as a transmitter, the butterfly/can package ofFIG. 1includes components to convert electrical signals into optical signals and to transmit the optical signals. Another package that can be used to encapsulate electrical and optical components is the MINI-DIL package, which is illustrated inFIG. 2.

DETAILED DESCRIPTION

Optical component packages having a transmission line to couple optical components to electrical components are described.

Overview

Described herein is a hermetic optoelectronic package that may have a wide bandwidth (e.g., >15 GHz) radio frequency (RF) interface. In one embodiment, a multilayer cofired ceramic (e.g., Alumina/Aluminum Nitride) substrate provides a platform to integrate various components such as, for example, integrated circuits having electronic components, optoelectronic components (e.g., laser diodes, photodetectors), or optical components (e.g., isolators, fiber optic couplers, fibers, lenses). In one embodiment, the substrate has an interface that allows for an electrical signal to pass from the exterior of the package to the interior. Note that in different embodiments, signals can pass both directions, e.g., in a transmitter, the electrical signal passes from the exterior to the interior, and in a receiver, the electrical signal passes from the interior to the exterior. The substrate can have a seal ring attached that provides for a hermetic seal to a cap/lid through soldering or laser welding.

Atop the substrate is a “riser” that is used to bring an electrical signal from the plane of the substrate to the plane close to the optical axis of the package (i.e., the height at which light is emitted by a laser diode or received by a photodetector). This riser includes a transmission line to transmit signals from the plane of the electrical signal to the optical components. The transmission line can be single ended or differential. Also within the package is a “submount” upon which electrical/optical/electro-optic components can be integrated, for example, laser diodes, monitor photodiodes, photodetectors, driver amplifiers, transimedance amplifiers, capacitors, inductors, thermistors. Patterning on the submount is used to route the various electrical signals including transmission lines to bring the electrical signal from the riser to the various components.

Package Configuration

FIG. 3illustrates one embodiment of an optical package having a backside recessed connection. Lead frame400is coupled to recessed portions of optical package substrate300. Backside surface of the optical package includes recessed portions, which enable coupling of leads410,420and430to reduce the air gap between the lead frame and a printed circuit board (PCB) or other component within the package.

In one embodiment, the optical package connection includes a recessed, intermediate layer for attaching leads410,420and430, which couples the package to a printed circuit board (PCB) for receiving electrical signals. The recessed configuration of the package increases the space available for mounting optoelectronic components to a top surface of substrate300. In addition, the recessed configuration provides a flat surface on a backside of the package, which improves thermal dissipation. Moreover, the recessed package configuration increases available system space by eliminating coaxial connections for receiving or transmitting signals.

FIG. 4illustrates a top side view of one embodiment of the optical package ofFIG. 3. Substrate300includes the recessed portions on an end opposed to the optical fiber (the opposed end). Along a top surface of the optical package, cap210is coupled to this top surface in order to encapsulate optical and/or electrical components.

Internal Configuration

FIG. 5illustrates one embodiment of a multilayer substrate of the package ofFIGS. 3 and 4. In one embodiment, the multilayer substrate includes layer320, layer340and layer360; however, a different number of layers can be used. In one embodiment, three ceramic layers are coupled together utilizing one or more vias308. In one embodiment, the multilayer substrate300is a cofired, multilayer ceramic substrate.

In one embodiment, multilayer substrate300includes riser380, as well as submount390. Riser380can be, for example, a thick film riser and submount390can be a thin film submount. In one embodiment, a riser metal layer385is provided between riser380and submount390. In addition, a submount metal layer395is formed on a top surface of submount390. Once formed, a patterned transmission line397is formed to provide a RF signal path to the components that reside on a top surface of submount390. In one embodiment, a vertical transmission line provides an interconnection between the electronic components on one plane with optical components on a second plane. In one embodiment, the transmission line is out of the plane of the submount (perpendicular in this case where it is vertical with respect to the submount (e.g., 45 degrees)). In this case, the transmission line can be a truly coplanar line (GSG or GSSG), with no separate ground. While specific layers and/or materials have bee used with respect toFIG. 5and other descriptions, other materials and/or a different number of layers can be used.

A vertical transmission line provides several advantages. The vertical transmission line requires less space within the package as vias to accomplish the same result. In one embodiment, the vertical transmission line is printed on a vertical side of thick film riser380using a metal printing technique. Because vias through relatively thick layers can have an inconsistent thickness, the printed vertical transmission line can provide improved bandwidth.

FIG. 6Aillustrates one embodiment of a first layer of the multilayer substrate ofFIG. 5. In one embodiment, the layer ofFIG. 6Aincludes a bottom surface310, which is metalized ceramic in order to enable RF shielding as well as contact to a heat sink. Adjacent to substrate metalized layer310, the recessed portions302,304and306of the substrate enable coupling of leads410,420and430. Although the layer is illustrated with opposed recessed portions302and304and adjacent portion306, different recessed portions of the layer may be made.

FIG. 6Bfurther illustrates one embodiment of a layer substrate ofFIG. 5. Layer330is metalized to provide an RF signal path from leads430to an interior of the substrate. In one embodiment, layer330includes a plurality of pads (332,334and336) which are utilized to couple to leads410and420. In addition, layer320includes a plurality of vias in order to couple the RF signal path layer330to the metalized substrate layer310.

FIG. 6Cillustrates one embodiment of a direct current (DC) signal layer of the multi-level substrate. In one embodiment, the layer ofFIG. 6Cis fabricated to form DC signal path layer350, which provides DC signal routing from bonding pads342and344to various leads410and420. Wire bonds346couple leads410to bond pad342. Likewise, bond pad344is coupled to leads420by wire bonds348. In one embodiment, the layer ofFIG. 6Cis fabricated to form DC signal path layer350, which provides DC signal routing from bonding pads372and374to various leads410and420. Printed traces356and358and vias in layers340and360couple leads410and420to bond pads372and374.

In one embodiment, layer320is fabricated to form the metalized layer310and RF signal path layer330. Likewise, a top surface of layer340is fabricated to form the DC signal path layer350to leads410,420and430. In addition, a top surface of layer360is fabricated to form a top surface metal layer370. In one embodiment, once each of the layers are metalized, the ceramic layers are cofired together to form the multilayer ceramic substrate300.

FIG. 6Dillustrates one embodiment of a substrate top surface metal layer. Substrate top surface metal layer370enables formation of optoelectronic components onto a top surface of the substrate300. The transmission line, patterned onto the riser, as well as a transmission line, patterned onto a metal layer395of submount390, provide a signal path from the RF signal pads376to the optical electrical components mounted on top of the submount layer395.

In one embodiment, the vertical transmission line is a metal pattern applied to the thick film riser. The vertical transmission line can be a single ended or differential transmission line. While only one vertical transmission line is described with respect toFIG. 6D, any number of vertical transmission lines can be provided.

FIG. 7illustrates one embodiment of a transmitter in a package having a vertical transmission line. In one embodiment, the transmitter package includes lid cap210, which is hermetically sealed to the top surface of substrate300. Seal ring570provides a hermetic seal between substrate200and lid cap210. Riser380, as well as submount390, are further coupled to a top surface of the substrate300. Riser380and submount390enable vertical transmission line540to provide signal paths for RF interface530. The transmitter further includes optoelectronic component510, which can be any type of optoelectronic component, for example, a laser diode.

To provide the optical transmission, the transmitter500further includes an optical component550that transmits optical signals using fiber/flexure560. Conversely, the transmitter500is converted into a receiver by utilizing a semiconductor detector as the optoelectronic components and a transimpedance amplifier as electrical IC520.

Example System Applications

FIG. 8illustrates one embodiment of an optical electronic system. System600includes optical transmitter610which is, for example, the transmitter described above having a vertical transmission line. Optical transmitter610is coupled to printed circuit board640via lead frame620. In one embodiment, optical package610is configured as a transmitter, which includes semiconductor laser630. Optical transmitter610communicates via semiconductor laser630, while transmitting optical signals via optical cable650. The optical signals are received by optical receivers660.

Optical package660is configured as an optical receiver, which utilizes a lead frame670in order to form an electrical connection to PCB680. In order to receive optical signals, optical receiver660includes a semiconductor detector662. The semiconductor detector662receives an optical signal from optical cable650and converts the optical signal into its original electrical signal format. Signals can be transmitted within the receiver using a vertical transmission line as described above.

Other applications include the use of these teachings in line cards or a tranceiver/transponder, as well as other applications.

In one embodiment, the optical transmitter and the optical receiver are components within an electronic system.FIG. 9is a block diagram of one embodiment of an electronic system. The electronic system illustrated inFIG. 9is intended to represent a range of electronic systems, for example, computer systems, network access devices, etc. Alternative systems, whether electronic or non-electronic, can include more, fewer and/or different components.

Electronic system900includes bus901or other communication device to communicate information, and processor902coupled to bus901to process information. In one embodiment, one or more lines of bus901are optical fibers that carry optical signals between components of electronic system900. One or more of the components of electronic system900having optical transmission and/or optical reception functionality can provide a vertical transmission line to connect electronic circuitry to optical devices.

While electronic system900is illustrated with a single processor, electronic system900can include multiple processors and/or co-processors. Electronic system900further includes random access memory (RAM) or other dynamic storage device904(referred to as memory), coupled to bus901to store information and instructions to be executed by processor902. Memory904also can be used to store temporary variables or other intermediate information during execution of instructions by processor902.

Electronic system900also includes read only memory (ROM) and/or other static storage device906coupled to bus901to store static information and instructions for processor902. Data storage device907is coupled to bus901to store information and instructions. Data storage device907such as a magnetic disk or optical disc and corresponding drive can be coupled to electronic system900.

Electronic system900can also be coupled via bus901to display device921, such as a cathode ray tube (CRT) or liquid crystal display (LCD), to display information to a computer user. Alphanumeric input device922, including alphanumeric and other keys, is typically coupled to bus901to communicate information and command selections to processor902. Another type of user input device is cursor control923, such as a mouse, a trackball, or cursor direction keys to communicate direction information and command selections to processor902and to control cursor movement on display921. Electronic system900further includes network interface930to provide access to a network, such as a local area network. In one embodiment, network interface930provides an interface to an optical network by including an optical transmitter having a vertical transmission line and/or an optical receiver having a vertical transmission line as described in greater detail above.

Instructions are provided to memory from a storage device, such as magnetic disk, a read-only memory (ROM) integrated circuit, CD-ROM, DVD, via a remote connection (e.g., over a network via network interface930) that is either wired or wireless providing access to one or more electronically-accessible media, etc. In alternative embodiments, hard-wired circuitry can be used in place of or in combination with software instructions. Thus, execution of sequences of instructions is not limited to any specific combination of hardware circuitry and software instructions.