Optical switching of a proposed stationary optical delay line for OCT
Faculty of Health, Engineering and Science
School of Engineering
In this paper the switching of a proposed Stationary Optical Delay Line (SODL) is demonstrated. This is intended for proof of principle of the switching associated with such a SODL, to be applied to an Optical Coherence Tomography (OCT) system.. The proposed SODL is made up of one dimensional beam expanding cylindrical lenses, a liquid crystal transmissive Spatial Light Modulator (SLM), and a Stepped Mirrored Structure (SMS). The SLM is to be used as an addressable optical switch. The SMS is an array of staggered mirrored steps, where the step height corresponds to half the optical delay length. The required delay length from the SMS can then be selected with the SLM. In this work, beam expanding optics and a nematic Liquid Crystal Display (LCD) are used to demonstrate the ability to select a spatial region consisting of a row of 4 photodiodes substituting for the SMS. The principle of conventional sequential switching, depth hoping, and multicasting of the four windows generated on the SLM are demonstrated. Rise and fall times were 260 and 150 ms, sufficient to prove the principle of switching at 1Hz. A maximum of 2 Hz could be achievable without detriment to the contrast ratio. The contrast ratios between transparent and opaque LCD window states was 2.4 ± 0.2. The contrast ratios between transparent and light-off states was 23 ± 4. Hence, the contrast ratios between opaque and light-off states was 9 ± 1. These values were within the expected ranges for nematic LC SLMs.