While you could use the Lucene directly under Solr the way Mauricio highlighted, unless you had some special reason, like you can't reindex the data because the data is gone, then I feel like you would be swimming uphill to just put your index into Solr...
And you most likely will need to reindex data anyway at some point, so figuring out how to do it in using the better indexing options that Solr provides would save time in the longer run.
