In this paper, we propose a spectral-slice scheme and a chip-level detection for the TTFR-based asynchronous SPECTS-OCDMA system combined with time-encoding. The spectral-slice scheme can reduce the interference probability because the MAI with the different frequency has no adverse effects on the channel collision rate. Moreover, the chip-level detection can enhance the tolerance of MAI because the channel collision does not occur as long as either of the detection time positions receives no MAI. As a result, these techniques mitigate channel collisions. We analyze the channel collision rate theoretically, and show that the proposed system can achieve a lower channel collision rate in comparison with the conventional systems.