Plasmon Lms, Inc.

Jeffrey M Brooke

Johannes J Verboom

Gary L Kline

Hakan O Hemdal

In order to provide a low noise laser beam, a noise reducing feedback network is provided which creates a noise reducing signal and provides that signal to the laser itself. In order to produce the noise reducing signal, the operation of the laser is monitored and the feedback signal is a direct result of this monitoring. Monitoring is accomplished by a fast-forward sense detector, which receives a portion of the laser beam from the operating laser. The output from this fast-forward sense detector is provided to an amplifier which inverts and amplifies the signal. A noise reduction feedback network then receives the amplified signal, appropriately filters this signal, and provides it to the laser itself so as to reduce noise in the laser-beam for the frequency band of importance for reading the recorded data from the optical medium. The noise reduction feedback signal further has sufficiently high impedance so as to not disturb the traditional CW operation of the laser and to avoid interference with the traditional RF modulation of the laser.

Laser driver with noise reduction feedback for optical storage applications

A switchable active filter circuit is formed which employs a ground based switch to direct a portion of a feedback current away from a virtual ground terminal of an operational amplifier, thereby providing enhanced circuit Q and greater phase control at frequencies approaching an octave from the unity gain crossover frequency of an operational amplifier used to form the filter. The circuit employs a switchable feedback tee which includes a first capacitor, a second capacitor, a third capacitor and a switch. The first capacitor and the second capacitor form a first series circuit which is connected from the output terminal to the input terminal of the operational amplifier. The third capacitor and the first switch are connected as a second series circuit which is coupled from circuit ground potential to a junction of the first capacitor and the second capacitor. When the switch is closed, a feedback current flowing in the feedback tee is divided with a portion of the current flowing through the third capacitor to circuit ground, rather than into the virtual ground terminal of the operational amplifier. This filter topology is particularly well suited for use in a multi-mode read/write channel of a tape storage system.

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Colorado Springs, CO, United States of America

Jeffrey M Brooke