In this paper, we investigate the integration of passive optical networks (PONs) with optical burst switched (OBS) networks. Owing to the decomposition of the operations between the PONs and OBS nodes, serious problems have been observed. One of them is data burst assembly problem. In some situations, burst assembly delay exceeding tens seconds may be required if the general purpose PON access schemes are used. To solve this problem, we propose to have the optical network units (ONUs) take over the burst assembly function from the OBS nodes. Large reduction of the burst assembly delay is obtained. Four ONU data burst scheduling schemes have also been investigated. We observe that a simple scheduling scheme is itself adequate in most situations.