For optical fiber spectrum of LAMOST, the requirement for magnitude difference between neighbor fibers is less than 5 magnitudes to avoid faint sources being contaminated by their bright neighbors. However, sometime, neither bright nor faint sources are dense enough to fill a whole plate (4000 fibers). To make full use of all the fibers, they have better be put into the same plate. To resolve crosstalk, we propose that photons fed into a fiber can be degraded by offsetting the fiber from disc center of the bright star. Thus the bright and faint sources can be observed in the same plate without crosstalk contamination. We test the feasibility of the program with the test observation of LAMOST, and the results show that our program is consistent with the expectation.