This paper proposes a high output power and high burst extinction ratio wavelength (λ)-tunable optical network unit (ONU) transmitter for long-reach and high-splitting ratio wavelength-division multiplexing and time-division multiplexing passive optical network (WDM/TDM-PON) systems. Our λ-tunable ONU burst-mode transmitter (B-Tx) utilizes a simply configured burst-mode controlled booster semiconductor optical amplifier (SOA) that employs the pattern effect mitigation technique of gain peak detuning. A high output power and burst extinction ratio are successfully achieved at all upstream wavelength channels, over +10.0 dBm and 66.0 dB, respectively. This burst extinction ratio performance satisfies the ONU requirement for a 64-split WDM/TDM-PON with crosstalk penalty of better than under 0.1 dB. Moreover, the pattern effect is greatly mitigated and 40 km transmission penalty of under 0.8 dB is achieved. We successfully demonstrate over a 41 dB loss budget and 40 km reach λ-tunable WDM/TDM-PON without an optical-amplifier-based PON repeater.