Optical technology is increasingly employed as a technology wherein information can be reliably transmitted via a communications network. Networks employing optical technology are referred to as optical communications networks, and are characterized by having high bandwidth and reliable high-speed data transmission.
Optical modules are electronic components that are configured to convert electrical signals to optical signals and vise versa. Optical modules are classified as LD (Laser Diode) modules and PD (Photodiode) modules. Optical transceivers are packaged PD and LD modules. These products are the core devices for any optical communication system such as an optical transponder and an ONU (Optical Network Unit).
Optical modules are divided into several types. One type is known as receptacle modules. This type is represented by a TOSA (Transmitter Optical Sub-Assembly) and ROSA (Receiver Optical Sub-Assembly) Assemblies. Receiver Optical Sub-Assemblies (referred to hereinafter as “ROSA”) are fundamental building blocks in optical communications systems. A ROSA unit is the front end physical layer of an optical receiver—it converts the optical information (i.e. the modulated light) into electrical information (i.e. voltage or current signals). The receiver optical sub-assembly, or ROSA, houses a photo-detector and communicates with a post-amplifier, as well as other devices mounted on a PCB in the module housing. Typically, the ROSA also connects with an optical fiber to allow incoming optical signals to be properly coupled into the ROSA. The housing of the ROSA (or of a ROSA/TOSA transceiver) module provides various functions, including mechanical stability and strength, maintenance of the proper positioning of the ROSA (and TOSA in case of a transceiver), electromagnetic interference containment, electrical connection to the host device, and physical containment and protection for the ROSA, TOSA, PCB, and the devices on the PCB.
An example of such a prior art sub-assembly 100 is illustrated in FIG. 1. The optical signal reaches the reverse-biased photodiode 110 that converts the photonic flux (i.e. optical signal) into electrical current, which in turn is linearly proportional to the photonic flux power. The current generated by the photodiode is fed directly into a Trans-Impedance Amplifier (“TIA”) 120. Typically, a TIA is an integrated circuit (“IC”) that functions as a current-to-voltage amplifier. However, such existing solutions have several drawbacks, among which are the following ones.
The technologies used to manufacture a photodiode are different from the technologies used to manufacture a TIA. Consequentially,                An assembly process is required, in order to combine the two (or more) devices into a single sub-assembly. This process is cumbersome and costly;        The assembly adds parasitic consumers of the generated electric current, which in turn limit the band width of the ROSA. In addition, these parasitic consumers adversely affect the device by making it more sensitive to Electro-Magnetic Interference (EMI) and Radio Frequency Interference (EFI);        It can be shown that the overall self-generated noise of the ROSA is much higher than thermal noise. Dark current noise generated by the photodiode, combined with input referred current noise generated by the TIA form a noise floor that is −40 dB higher than the thermal noise. In other words, a typical solution would be −40 dB worse than the optimal theoretical solution.        
As discussed above, one of the drawbacks associated with the manufacturing of a ROSA is the need to combine the individual devices comprising the sub-assembly, into a single unit. U.S. Pat. No. 6,792,171 describes one example of processes that are involved in manufacturing such a ROSA. The ROSA according to this publication includes a stacked chip design of a semiconductor micro-bench, upon which the photodiode and trans-impedance amplifier are mounted. A flexible electrical connector is attached to the semiconductor micro-bench for electrically connecting the ROSA to a host transceiver device. The flexible electrical connector is fixed to the surface of the semiconductor micro-bench with portions cut-out to receive the amplifier and other electrical components extending therefrom. To facilitate assembly, wells need to be etched from the semiconductor micro-bench, which would correspond to bumps extending from a mounting flange for the optical coupler.
However, with the rapid growth of the optical communication market, the need for improved ROSA technologies increases. The present invention seeks to provide a solution to such a need.