Digital coherent receivers employing Alamouti-coding are a promising solution for passive optical networks (PON) with downstream rates of 100Gb/s/λ. To reduce cost by utilizing high-volume photodiodes designed for 25Gb/s data-center applications, we consider 28-Gbaud 16-QAM modulation format detected with a single-polarization coherent receiver based on a 3×3 coupler with single-ended detection. We investigate two alternative configurations: first, a receiver with a symmetric 3×3 coupler and subsequently an IQ coupler (asymmetric 3×3 coupler) with Alamouti-coding based polarization diversity. In this paper, we present a detailed investigation as to the feasibility of both the receivers for a wide range of parameters including quantization noise, relative intensity noise (RIN), I/Q mismatch etc. It is found that such receivers can be realized with commercially available components. We also quantify the penalty associated with non-ideal components to allow for lower cost designs with reduced specifications suitable for access applications. In addition, we present the adaptive DSP algorithms required to recover data for single-carrier Alamouti-coded signal. Considering both linear and nonlinear impairments, a power budget of 36.4dB and 33.1dB is found at BER of 3.8×10−3 for receiver with symmetric 3×3 coupler and IQ coupler, respectively and thereby proving their applicability as receivers for 100Gb/s/λ PON.