Non-carrier suppressed homodyne receiver using standard DFB lasers and analog optical phase-locked loop

112Gb/s transmission is now being considered in next-generation fiber networks worldwide. Optical synchronous coherent detection is attracting greater attention within the proactive military community in order to analyze these high speed transmissions. Coherent detection allows linear recovery both of the amplitude and phase of transmitted optical signals in the post-detector RF domain. Therefore, fiber-based transmission impairments such as chromatic dispersion and polarization mode dispersion can be compensated in the electrical domain using this technique. Additionally, synchronous detection offers the potential of improved receiver sensitivity and extended reach versus direct or interferometric detection schemes, especially for spectrally-efficient, higher level modulation formats. For the newly emerging 112Gb/s transmissions, prospective 28Gbaud and 56Gbaud are prime baudrate choices. For these baudrates, the coherent heterodyne approach is not practical because of the lack of broadband O/E converters and backend RF components designed at 2-3 times the selected baudrate. The coherent intradyne approach, while it does not have the component bandwidth requirements of heterodyne, suffers from highly-complex and high power-consumption back-end RF compensation components. The remaining choice for coherent detection is the homodyne approach. This approach is by definition synchronous, and remains one of the practical choices available to fully exploit the advantages of synchronous coherent detection at these baudrates, when properly implemented. One of the main requirements of the homodyne receiver is optical phase locking between the signal and local oscillator laser (LO). This challenging technical condition has historically stunted homodyne receiver development. Electronic approaches for this task rely upon very complex, fast, and high power-consumption chips, which are not yet commercially available. A homodyne receiver using an analog approach for phase locking would allow for increased system simplicity at a lower cost. Use of commercial-off-the-shelf (COTS) DFB lasers embedded within the receiver would also increase system feasibility for the defense and security sector. We demonstrate synchronous demodulation of a 42.8Gbaud signal using an analog optical phase-locked loop. The homodyne system was optimized to use COTS DFB lasers having an aggregate linewidth of ~2 MHz. We also analyze the impact of uncompensated phase noise on receiver performance. The demonstrated approach can operate at any baudrate contained within 70 percent of the embedded photodetector bandwidth. In addition, this method can be implemented for a generalized class of optical transmissions which contain an optical carrier, subcarrier, or transmission clock line.