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Laser-Feedback Noise Reduction by Optical Path Length Selection

IP.com Disclosure Number: IPCOM000100709D
Original Publication Date: 1990-May-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 68K

Publishing Venue

IBM

Related People

Call, DE: AUTHOR [+2]

Abstract

Laser-feedback noise is a strong function of the phase difference between the modulated irradiance of the laser and the reflected light intensity. High-frequency modulation of the laser is a well-known technique for reducing laser-feedback noise. In this technique, a high frequency modulation current is superimposed on the DC bias current that drives the laser. By driving the laser through threshold, a pulsed output is obtained and the laser is forced to operate multi-mode. Operating with a pulsed output, laser noise was found to be sensitive to the phase of the reflected power with respect to the emitted power.

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Laser-Feedback Noise Reduction by Optical Path Length Selection

       Laser-feedback noise is a strong function of the phase
difference between the modulated irradiance of the laser and the
reflected light intensity.  High-frequency modulation of the laser is
a well-known technique for reducing laser-feedback noise.  In this
technique, a high frequency modulation current is superimposed on the
DC bias current that drives the laser.  By driving the laser through
threshold, a pulsed output is obtained and the laser is forced to
operate multi-mode.  Operating with a pulsed output, laser noise was
found to be sensitive to the phase of the reflected power with
respect to the emitted power.

      The optical phase delay (OPD) of the reflected laser power is
defined as follows:
   OPD = f x (2L/c) x 360o                         (1)
where OPD is the optical phase delay of the reflected power
referenced to the emitted power, (the phase delay we are discussing
is not an interferometic phase delay based on the wavelength of
light, but rather one based on the electrical modulation frequency),
f is the sinusoidal modulation frequency, L is the optical path
length from the laser cavity to the reflecting surface, and c is the
speed of light in air.

      It was discovered that the operating point with minimum
laserfeedback noise occurred for an OPD of 90o and repeated in
increments of 360o .  The data to support this is shown is Figs. 1A
and...