1. The Field of the Invention
The present invention relates to optical transceivers. More specifically, the present invention relates to a variable attenuator for use in optical transceivers and more particularly to a dual pin photodiode that variably attenuates an incident optical signal.
2. Background and Relevant Art
One of the ways that information is transmitted and received over networks is through the use of optical signals. One of the processes that enables data to be transferred using optical signals is signal demodulation. Demodulation is the process of retrieving the data from a modulated optical signal. Demodulation is not a simple process as the modulated optical signals can undergo, for example, attenuation and optical dispersion. Demodulation is further complicated by noise that is often added to the modulated optical signals by optical amplifiers or by a variety of other sources.
An optical transceiver begins demodulating the data in a modulated optical signal by converting the optical signal to an electrical signal or current. Next, the optical transceiver typically filters the electrical signal, performs clock recovery, equalizes the electrical signal, and the like in order to recover the data.
An optical transceiver has a dynamic range that refers to optical signals that can be successfully received and demodulated. The optical sensitivity of the optical transceiver is associated with low optical power. Optical signals having an incident optical power below the optical sensitivity may have an unacceptably high bit error rate. The other end of the dynamic range may be referred to as the saturation power and incident optical signals having too much optical power are not successfully modulated because the transceiver saturates. In other words, the optical sensitivity and saturation power identify a range of signals that can be successfully processed by the optical transceiver.
In a transceiver, a detector converts the incident optical signal to an electrical current and therefore has an impact on the dynamic range of the transceiver. A detector, for instance, generates an electrical current that is related to the optical power of the incident optical signal. When the optical power of the incident optical signal is too great, the transceiver saturates.
One solution to the problem of exceeding the saturation power of the transceiver is to add external attenuators to the optical transceiver. In this situation, it is likely that some architecture or system design work will be required to determine where an attenuator is needed in the system and how much attenuation is required. Once this information is decided, the installation of the external attenuators will need to be performed. In addition to raising cost, the use of external attenuators adds extra components to an optical network.