We describe a method of generating physical random numbers by means of a diode laser that has an extremely wide-band frequency-noise profile. Fluctuations in the laser frequency affect the intensity of the light transmitted through the optical frequency discriminator, detected thereafter as random fluctuations. This allows us to simultaneously generate 8 random bit streams, due to the parallel processing of 8-digit binary numbers sampled by an 8-bit analog-to-digital converter. Finally, we generated physical random numbers at a rate of 3 Gbit/s, by combining one data stream with another stream that is delayed by 2 ms, by exclusive-OR.
A laser diode (LD) has been used in many areas, such as optical communication systems. However, its oscillation
frequency changes, with variations in ambient temperature and injection current, so its frequency stabilization is of vital
importance. In these situations, Rb saturated absorption spectroscopy is the method of choice. We use the beat signal, both
for the purpose of evaluating frequency stability between two independently stabilized LDs, and for generating THz
waves. This work shows a basic experiment using our beat signal observation, by high-speed photodetector. In addition,
we have also used a frequency-stabilized etalon, to improve frequency selectivity.
We have succeeded, thus far, in stabilizing laser diode (LD) frequencies to Rb absorption lines, by means of negative electrical
feedback. While the absorption lines were stable over the long term, the Doppler Effect's influence was evident, in broadened spectrum
linewidth. To avoid the problem in subsequent tests, we used Rb-saturated absorption signals.
In this work, we demonstrated potentials of two applications; one was as a reference signal source for estimation of other LD's
frequency stabilization system, and the other was a light source for generation of THz radiation.¬«W
The semiconductor lasers in use today are on one hand, prized, and highly praised, for their small size, light weight, longevity and
energy-efficiency, -and on the other, criticized for their susceptibility to frequency-fluctuations brought about by changes in
temperature and driving current. Once this "wrinkle" is ironed out, semiconductor lasers will become the default light-sources, for
satellites' onboard interferometers. Our studies have been directed at stabilizing oscillation frequency to the atomic absorption line,
and using negative electrical feedback to the injection current. Frequency stabilization is accomplished, by either; a) applying direct
modulation to the semiconductor laser's driving current, or b) modulating the reference frequency, to obtain the error signal needed
for stabilization. In this instance, Faraday effect-based stabilization was used. This indirect oscillation frequency stabilization has no
discernable effect on spectra width, but, stability was no better than that observed in the system using the direct modulation.
When we compared Faraday effect- and direct modulation-based methods of stabilization, in order to uncover the root-cause of the
discrepancy, sensors picked up system noise, the source of which was heat generated by the heavy current applied to a magnetic coil
used to apply the Faraday effect. We also substituted a permanent magnet for the electromagnet.
The precise interferometric systems employed in today's artificial satellites require semiconductor lasers of the
highest caliber. To this end, efforts to stabilize their oscillation frequencies and narrow spectrum line-widths
continue relentlessly. While a number of different approaches have been tested, none have provided overall,
long-term stability. Most recently, we employed a Doppler-free absorption line of Rb atoms, with a precision
temperature controller and an improved laser mount. In this instance, relative optical frequency stability rated
9.07×10-13≤σ(2,τ)≤7.54×10-10, in averaging time for 0.01s≤τ23s. By introducing an optical feedback, which
narrows the laser's linewidth, we obtained improved frequency stability.
The precise interferometric systems employed in today's artificial satellites require semiconductor lasers of the highest callibur. But,
one particularly large obstacle has stood in the way of their broad application; the stabilization of their oscillation frequencies. While a number of different approaches have been tested, none have provided overall, long-term stability. Most recently, we used a Doppler-free absorption line of Rb atoms with a precision temperature controller and an improved laser mount; in this instance, relative optical frequency stability rated 9.07×10-13 ≤ σ(2,τ) ≤ 7.54×10-10, in averaging time for 0.01s ≤ τ ≤ 23s. Furthermore, we heated the Rb cell to up to 313K, in order to enhance the control signal and improve oscillation frequency stability.
The precise interferometric systems employed in today's artificial satellites require semiconductor lasers of the highest callibur. But,
one particularly large obstacle has stood in the way of their broad application; the stabilization of their oscillation frequencies. While a number of different approaches have been tested, none have provided overall, long-term stability. Most recently, we used a Doppler-free absorption line of Rb atoms with a precision temperature controller and an improved laser mount; in this instance, relative optical frequency stability rated 9.07x10-13≤&sgr;(2,&tgr;)≤7.54x10-10, in averaging time for 0.01s≤&tgr;≤23s. By introducing optical feedback, which narrows the laser's linewidth, we obtained improved frequency stability.
Laser interferometers detect gravitational waves with a degree of accuracy and efficiency unimaginable even a few years
ago. The semiconductor lasers that are the primary light source for these devices are small, lightweight, durable and
energy-efficient. On the downside, the devices currently available are still marked by broad oscillation spectra, and
heightened sensitivity to fluctuations in injection current and /or ambient temperature. By applying a small sine wave to
the injection current, we modulate the oscillation frequency. This frequency-modulated beam is introduced to the
Avalanche photo diode through the Rb cell in the saturated absorption optical setup. The resulting signal and a reference
signal are detected simultaneously and combined, to produce an error signal, which, when fed back to the injection current,
stabilizes the diode's oscillation frequency at 2.12x10-12 ⩽ &sgr;(2,τ) ⩽ 5.88x10-11 in the averaging time between 0.4s to 65s.
An optical feedback method, which introduces the laser beam reflected by a mirror or a grating to the semiconductor laser
itself, is reported to narrow oscillation linewidth and improve frequency stability. We are now combining these two
techniques to further improve frequency stability.
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