Semiconductor Lasers and Photonic Integrated Circuits

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Applications
Overview

10Gb/s SOA-EA Modulator as Colorless ONU for WDM-PON

Description

The use of a reflective SOA (RSOA) has been proposed several times to implement the Optical Network Unit (ONU) in WDM-PONs. However, such elements have limited modulation bandwidth (typically 2.5 - 5 Gb/s). An alternative is to use an integrated structure formed by an SOA section and an electro-absorber section (EA) [1], which can operate at higher bit rates (10 - 40 Gb/s).
In this application example (see Figure 1), the device is MQW-type, formed by one 200um long SOA-section with face reflection 1e-12 and a 100um long EA-section with one (high reflection) HR face of 0.99. The SOA section is biased with a fixed current of 100uA; the data signal is applied at the EA section with bias voltage swinging between -5 v (spaces) and 0 v (marks).

Typical Results

Due to the properties of the EA, the spectral response of the device strongly depends on the applied voltage. As a result, each ONU would transmit with a different power level and signal quality (Figure 2). The spectral properties of the EA can be adjusted in order to homogenize the different WDM channels by adjusting the voltage dependency of the peak absorption and absorption bandwidth (Figure 3).
Figure 4 shows the eye diagrams for the channels at 192.4THz and 193.8THz, representing the outermost channels of a 16 WDM-channel 100GHz-spaced band. The extinction ratio is on the order of 30dB and the difference in the mark levels of the two extreme channels is less than 1.5dB.

Keywords

PICs, semiconductors, multi-section device, electro-absorber, EAM, SOA