In optical communications applications, optical transmitter modules are used to generate optical data signals, which are then transmitted over an optical waveguide, which is typically an optical fiber. An optical transmitter module includes a driver integrated circuit (IC) that receives an electrical data signal containing bits of data at its input, and produces, at its output, an electrical drive current signal. The electrical drive current signal is applied to a light source, such as, for example, a light emitting diode (LED), which causes it to emit an optical data signal. An optics system (e.g., a lens) receives the optical data signal and couples the optical data signal to the optical fiber, which then transmits the optical data signal over a network to some destination.
An optical receiver modules includes a photo detector such as, for example, a photodiode, which receives an optical data signal transmitted over an optical fiber. An optics system (e.g., a lens) of the receiver module couples the optical data signal from the optical fiber end onto the photodiode. The photodiode converts the optical data signal into an electrical data signal. Electrical circuitry (e.g., amplifiers, filters, clock and data recovery circuitry) of the receiver module conditions the electrical data signal and recovers the data bits.
Optical transmitter and optical receiver modules may be packaged separately, but are often packaged together in an optical transceiver module to provide a single package that has both transmit and receive functionality. A variety of optical transceiver modules are in use today. An optical transceiver module may have multiple transmit channels and multiple receive channels or a single transmit channel and a single receive channel. One common optical transceiver module design of the latter type is commonly referred to as a Fiber Optic Transceiver (FOT) module design.
FIG. 1 illustrates a side perspective view of a typical known FOT module. The module 2 includes a standard four-pin metal lead frame 3, an optical active device 4, an optics system 5, an IC 6, and an encapsulation device 7. The leadframe 3 includes four input/output (I/O) pins 11 that are configured to be electrically connected on their distal ends 11a to electrical contacts (not shown) on a printed circuit board (PCB) (not shown). The proximal ends 11b of the pins 11 are configured to function as surface areas on the leadframe 3 to which electrical devices and/or electro-optical devices can be attached and wire bonded. The leadframe 3 and the devices 4 and 6 attached thereto are encapsulated inside of the encapsulation device 7. The encapsulation device 7 is typically a structure made of a clear polymer material, which secures the leadframe 3 in place. Prior to this molding process being performed, the active device 4 (e.g., an LED) and the IC 6 (e.g., a driver IC) are attached to the leadframe 3 and electrical contacts on the IC 6 are wire bonded to the leadframe 3 by bond wires 12. Electrical contacts on the active device 4 and on the IC 6 are also connected to each other via one or more bond wires 13. During the molding process, the optics system 5, which is typically a spherical lens, is formed in the encapsulation device 7 and is aligned with the active device 4.
The FOT module 2 may be a transmitter module, a receiver module or a transceiver module. In the case in which the FOT module 2 is an optical transceiver module (i.e., has both transmit and receive functionality), a second active device (not shown) may be attached to the leadframe 3 at location 16. If the active device 4 is a laser diode or light emitting diode (LED), for example, the second active device that attaches at location 16 will typically be an optical-to-electrical conversion device, such as a photodiode, for example. In the case in which the FOT module 2 is a transmitter module only, the active device 4 is a laser diode or LED and the IC 6 is a driver IC for driving the laser diode or the LED. In the case in which the FOT module 2 is a receiver module only, the active device 4 is a photodiode and the IC 6 is a receiver IC for processing electrical signals produced by the photodiode.
The design of the FOT module 2 shown in FIG. 1 has certain disadvantages. For example, it can be seen from FIG. 1 that there is very little surface area on the proximal ends 11b of the leadframe 3 to which additional components may be attached. For this reason, any other ICs (e.g., a transceiver micro controller IC) and any passive components (e.g., resistors, capacitors, inductors, etc.) are typically mounted on a motherboard (not shown) that is external to the FOT module 2. As a result, signal quality is often degraded. In addition, the ability to provide additional features and functionality inside of the FOT module 2 is limited.
Another disadvantage of the design of the FOT module 2 shown in FIG. 1 is that the bond wires 12 and 13 are relatively long in length. Creating these long bond wires 12 and 13 during manufacturing can be difficult and can result in the bond wires 12 and 13 having breaks or collapsing. Consequently, manufacturing yield is reduced. In addition, long bond wires can result in other problems, including, for example, performance degradation caused by cross talk between adjacent bond wires, increased inductance, and increased power consumption due to resistive loss.