Amplification of Optical Disk Readout Signals by Homodyne Detection

Abstract

We experimentally demonstrated the amplification of optical disk readout signals by homodyne detection. This technique uses optical interference to amplify the signals. We further applied phase-diversity detection to reliably obtain the amplified readout signal. The optical system was carefully designed so that a sufficiently amplified readout signal can be obtained. In particular, we applied a corner cube prism as a reflection mirror to achieve sufficient stability of the interferometric optical system. We experimentally demonstrated a 3.6 times amplification of a Blu-ray Disc readout signal. The estimated signal-to-noise ratio (SNR) improvement for an assumed eight-layer optical disk readout signals by applying homodyne detection on the basis of the observed amplification was +7.9 dB, which significantly enables reliable readout of recorded signals. The present technique will be essential for the real commercialization of next-generation multilayer optical disk because of its outstanding ability of SNR improvement.

Demonstration of readout-signal quality improvement by homodyne detection

“…In the previous reports, we experimentally demonstrated amplification of Blu-ray Disc readout signals by a factor of 3.6 by homodyne detection [10,11]. However, the measured jitter (after using a limit equalizer) of the observed signals increased from 8.1 to 11.5%.…”

“…Homodyne detection is a signal amplification technique which has been developed in the fields of optics such as optical fiber communication [12]. We demonstrated a signal amplification effect, but signal quality improvement has not been observed [10,11]. In this paper, we report modification of the optical system, which results in a significant improvement in readout signal quality.…”

“…We found that this degradation in signal quality was caused by disturbance of the reference light beam pattern as shown in Fig. 1, which mainly occurred in the corner cube prism (CCP) and six-segmented half waveplate [10]. Therefore, we inserted a small aperture in the far field of the reference light as a spatial filter to obtain an ideal flat beam pattern.…”

“…Note that, in the present scheme, using an actuator on which is mounted both an objective lens for the signal light and a reflection component for the reference light is essential in practical [10]. This is because the actuator has the important role of (roughly) canceling the path length difference caused by disc surface fluctuation.…”

“…In addition, a higher readout speed causes a further decrease in the SNR because a wider bandwidth is required [8]. Therefore, we have been developing an optical system where homodyne detection is applied to overcome the low SNR problem [9][10][11]. Homodyne detection is a signal amplification technique which has been developed in the fields of optics such as optical fiber communication [12].…”