Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With reflector – opaque mask – or optical element integral...
Reexamination Certificate
2002-10-09
2004-11-09
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With reflector, opaque mask, or optical element integral...
C257S680000, C257S697000, C385S088000
Reexamination Certificate
active
06815729
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to devices for converting between electrical and optical signals. More particularly, this invention relates to electro-optical devices and their methods of manufacture and use.
2. Description of Related Art
Electro-optical modules can be used to convert electrical signals into optical signals and vice versa. Many different types of electro-optical modules are presently being manufactured. These modules have many applications, particularly within data-communications technology where electrical signals are carried by fiber optics, and can range in cost from under a hundred dollars to many thousands of dollars per module, depending on their application and functionality.
Different types of electro-optical modules can be used to perform different functions. Receive modules and transmit modules, for example, can each be used to provide half of an electro-optical conversion. More particularly, receive modules convert optical signals into electrical signals as part of a receive function. Transmit modules convert electrical signals into optical signals as part of a transmit function. Transceiver modules can be used to perform the electro-optical conversion for both receive and transmit paths. Transponder modules provide the same functionality as transceiver modules but also provide serialization and deserialization of the electrical signals.
Modules can be further categorized based on the type of light emitter used. Typical light emitters include surface emitting sources (such as Light Emitting Diodes (LEDs) and Vertical Cavity Surface Emitting Lasers (VCSELs)) and edge emitting sources (such as Fabry-Perot lasers and Distributed Feedback (DFB) lasers). Surface emitting light sources are generally used in the manufacture of low-cost modules.
The primary advantages of surface emitting light sources are in testing and assembly. Surface emitters can, for example, be easily tested on whole wafers. No assembly of the individual modules is therefore required before testing the part. The assembly process is also simpler because the edges of the parts do not need to be polished. In addition, surface emitters can be easily assembled into arrays of multiple emitters (for example, a 1×12 array of VCSELs). Surface emitter arrays greatly simplify the assembly of parallel optical modules.
There are several challenges, however, in manufacturing optical modules. Among these challenges, it is difficult to align an optical fiber to an active optical area of a light emitter or a light detector. In addition, emitters may degrade or malfunction at relatively low temperatures, and removing heat from the emitters can be difficult. It is also difficult to test conventional modules. Another challenge is minimizing the number of parts required in the module assembly. A lack of “batch” manufacturing process steps also prevents lower cost manufacturing of modules. Some conventional solutions to these challenges are described briefly below.
Manufacturers of optical modules generally use some type of lens system (such as a spherical lens) to focus light into and out of the optical fiber.
FIG. 1
is a schematic illustration of a conventional lens focusing system for an optical module. Referring to
FIG. 1
, this conventional focusing system includes a spherical lens
1
, a multi-mode optical fiber
2
with an optical core
2
a
, and an electro-optical component
3
with active area
3
a
. These parts collectively form a system having an optical axis
4
and a ray trace
5
. The surrounding material
6
is typically air.
The use of a lens is advantageous for at least two reasons. First, it acts as a light gathering element to collect the light from the emitting side. Second, it acts as a light focusing element to converge the light on the receiving side. These two actions result in a relaxation of the alignment tolerances between the emitting and receiving sides. In effect, the lens acts as a large target area for the emitter, when compared to the size of the receiver, while creating a focused spot that is small compared to the size of the receiver. Thus, the emitter may move around to some extent and still hit the lens, and the receiver may also move around to some extent and still have the focused spot fall within its active area.
Even with a lens, however, the alignment tolerances in a typical module require an active alignment process, which is conducted during the assembly of the optical system. In this process, the optical emitter is switched on and an output of the optical receivers is measured. The whole assembly is then micro-manipulated, typically by a human operator, to maximize the received signal by bringing all sub-components into fine alignment. A flash cure process is then typically performed to freeze the assembly in place once fine alignment has been achieved.
There are disadvantages with the current methods for optical alignment. Optical elements such as glass lens arrays may be expensive. They are also typically small and may be delicate and difficult to handle and manipulate. Given that the optical assembly must be adjusted for fine alignment, some allowance must be made in the module design to facilitate this adjustment step. Active alignment is a slow, human driven process and is consequently expensive and error prone. Problems with optical alignment or failure to align correctly can create a significant rate of failure during the assembly process, further increasing the production costs of the module.
It would be advantageous to achieve optical alignment without an active alignment step through the inherent construction of the module (called “passive alignment”). It would be further advantageous if the optical components were very low cost and if there was no requirement to handle them as a separate sub-assembly.
Thermal management is also difficult in conventional optical modules. Optical transceiver or transponder modules, for example, typically require four different types of discrete semiconductor chips in close physical association with the optical axis. The light emitter and light detector are arranged on the optical axis. A driver chip for the emitter and an amplifier chip for the detector are also typically required. Emitters usually consume a significant amount of electrical power. The connection between the emitter and the driver chip is a major source of Electro-Magnetic Interference (EMI) and the signal degrades as the length of the connection increases. It is therefore advantageous to locate the emitter driver close to the emitter to limit the length of the connection. It is also advantageous to locate the receiver amplifier close to the detector because the detector output signal is very weak and therefore quickly degrades as the connection length increases.
These four semiconductor chips are therefore typically located in a very small area that is physically close to the emitter. Each chip consumes power that is dissipated as heat. In the case of a VCSEL emitter, for example, this heat may cause the VCSEL to function poorly in terms of its optical power output (slope efficiency), threshold current, and center wavelength accuracy. Or it may cause the VCSEL emitter to stop functioning completely. In addition, it may cause premature aging and early failure of the VCSEL. It is therefore desirable to provide an efficient conduction path for drawing heat away from the VCSEL.
FIGS. 2A and 2B
show typical thermal control solutions in a conventional optical module. More particularly,
FIG. 2A
illustrates four semiconductor devices
7
bonded with die attach material
8
to a circuit board
9
. The circuit board
9
contains thermal vias
9
a
and is abutted to a metal heatsink
10
.
FIG. 2B
illustrates two semiconductor components
11
bonded directly to a metal heatsink
13
with die attach material
12
. In both of these examples, the metal heatsink is able to fairly efficiently transfer heat away from the semiconductor components to the cooler surrounding medium.
Conventional thermal manag
Brophy Brenor
Hall Jeff
Hartranft Marc
Shafaat Syed Tariq
Cypress Semiconductor Corp.
Marger Johnson & McCollom
Nelms David
Tran Mai-Huong
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