We have demonstrated a new smart grid model by our novel green photonics technology based on self-organized optical networks realizing an autonomous peer-to-peer electric power transmissions without centralized control for the power grid. In this optical network, we introduced an adaptive algorithm for concurrent peer-to-peer communications, with a simple optical-electrical hybrid bistable circuit composed of such as light emitting diode (LED) and photo diode (PD) by utilizing optical nonlinearity depending only on the signal strength passing through the network. In the experiment, the method uses a simple, local adaptation of transmission weights at each network node, which we call a power gate unit (PGU) that enables self-organizing functions of the network. Based on this method, we have demonstrated experimentally a new smart grid model applicable for ad-hoc electric power distribution systems mediated power consumptions. In this model, electric power flow is controlled autonomously through the self-organized network nodes associated with individual power facilities having photovoltaics and electric storage devices, etc., and the nodes convert the amounts of electric power supply and/or consumption to the light intensity values using above mentioned transmission weights at each node. As a consequence, we have experimentally demonstrated a simple short haul system model for ad-hoc electric power distribution with a self-organized optical network as a novel green photonics technology application for smart grid consumptions. In this model, electric power flow is controlled autonomously through the selforganized network nodes associated with individual power facilities having photovoltaics and electric storage devices, etc., and the nodes convert the amounts of electric power supply and/or consumption to the light intensity values using above mentioned transmission weights at each node. As a consequence, we have experimentally demonstrated a simple short haul system model for ad-hoc electric power distribution with a self-organized optical network as a novel green photonics technology application for smart grid.
In this work, we have proposed electro-optical nonlinear delayed feedback systems (NDFS) using VCSEL. NDFS is composed by non-linear function unit, a transfer function unit, a gain adjusting unit and delay elements unit. In this system, with the increase of the feedback gain, cyclic oscillations from the non-oscillating state arise, and they repeatedly come to be harmonic or bifurcation transitions, leading to chaotic oscillation. With our experiments, we carried out the simulations, to prove the waveform generated from our NDFS to be really chaotic. In addition, we examined the influence of the external input signals to this process. As a result, we proved that random waveforms seen in the experiments to be really chaotic oscillations by comparison to theoretical chaotic feature. Also, we have observed period entrainment by varying external input frequency or delaytime of NDFS when we add sinusoidal wave with appropriate amplitude to LD driving current in the experiment. Moreover we have observed weak entrainment, strong entrainment, and unchanged period or frequency as varying these parameters step by step. Intervals of frequency or delaytime at the very time of occurring entrainment was determined by above mentioned parameters. Thus, we have clarified that intervals of frequency when occurring entrainment corresponds to the reciprocal of the delaytime when we varied frequency so as to stabilize the delaytime. On the other hand, we have also clarified that intervals of delaytime at the occurring entrainment corresponds to the reciprocal of input frequency when we varied delaytime so as to stabilize the frequency. Also, we have measured spectrum with the peak of input frequency as well as integral multiplication of the frequency when entrainments occur. With these results, it is revealed that NDFS in our experiments shows significant characteristics as to vary the waveforms dynamically by external input signal.
In this work, we propose electro-optical nonlinear delayed feedback systems (NDFS) for optical secure communications using VCSEL for the first time. Its optical output can perform more sensitive chaotic dynamics by varying only a few mA of injection current range resulting in very significant charges of VCSEL’s operation conditions from threshold to maximum rating. This enables us to vary chaotic output dynamically by a slight difference of initial values in NDFS. We have proposed a chaos synchronization system using two identical NDFS’s of VCSEL, and realized chaos synchronization by optical injection. As a result of experiment the correlation coefficient up to about 0.88 was obtained. Moreover, by varying the delay time and feedback gain in the parameters of NDFSs, we have confirmed that the variations of these parameters may affect variations of correlation.
In this work we have proposed chaotic synchronization system using two identical electro-optical nonlinear delayed feedback systems (NDFS) utilizing VCSEL. This first time proposal has high potential to perform more sensitive chaotic dynamics for improvement of encrypted communications quality. In this system we have demonstrated the reduction of robustness to prevent tapping by someone else attaining higher correlation but only if the feedback gain is the same value. We have also demonstrated the variations of correlation if feedback gain has the slight difference. Moreover, we have demonstrated applications to encrypted communications using VCSEL.
We have experimentally demonstrated a new smart grid model which can control DC electric power flow autonomously among individual homes, by using an optical self-organized node with optical non-linear characteristics, and these homes are assumed to be installed by distributed power supplies, and electric power storage devices, and also supposed to be supplied partly by the commercial electric power grid utilities. An electric power network is composed of nodes and devises called Power Gate Unit (PGU). The nodes have optical nonlinearity for self-organizing informations about surplus or shortage of electric power as to individual homes. The PGU is a distributing unit of actual electric power based on above informations of power surplus or shortage at each home. The PGU at each home is electrically connected to both the onsite power supplies and household load such as a solar panel, a DC motor, and a storage battery as well as the commercial electric power grid utilities. In this work, we composed our experimental self-organized DC power grid with above components and supposed the supplied maximum power from the commercial electric power grid utilities to be limited to 5V-0.5A. In this network, information about surplus or shortage of electric power will propagate through the nodes. In the experiments, surplus electric current 0.4A at a particular node was distributed toward a PGU of another node suffering from shortage of electric current. We also confirmed in the experiments and simulations that even when signal propagation path was disconnected accidentally the network could recover an optimized path. The present smart grid system we have attained may be applied by optical fiber link in the near future because our essential components controlling PGU, i.e. the nodes are electro-optical hybrid which are easily applicable to fiber optical link so as to control electric power transmission line.
In this work, we have achieved for the first time an effective speckle noise reduction simply by means of just high
frequency LD driving current superposition for an ultla compact micro-electro-mechanical-systems (MEMS) based high
resolution scanning beam RGB-laser projectors including the direct green emission LD. In the experiments, we have
carried out quantitative evaluations of the speckle noise by overlaying the projected images using a CCD camera with
histogram based estimation of speckle noise intensities. Moreover, we have examined the reduction of granular images
seen by humane eyes in higher ratios in color stereo image pairs using double-stimulus continuous-quality scale
(DSCQS) method. As a consequence, the noise reduction rate of 53.5% for the red laser diode, 80.1% for the green laser
diode, and 50.3% for the blue laser diode was attained with histogram based estimation, and the image quality was also
enhanced by speckle noise reduction with all RGB LD's using DSCQS method. Moreover, we have also investigated the
noise reduction mechanisms in these RGB LD's in relation with the relaxation oscillation frequencies from viewpoint of
chaotic multi-mode oscillations with existence of optical feedback.
We have demonstrated a hyper coherent spectral linewidth evaluation for a frequency stabilized 405nm GaN violet laser
diode (LD) based on the delayed self-heterodyne beat. The laser light source was stabilized to a reference confocal
Fabry-Perot (CFP) cavity by negative electrical feedback to the injection current of the LD under the Pound-Drever-Hall
technique. In addition, by introducing optical feedback from another tilted CFP cavity, the spectral linewidth has been
efficiently narrowed. In this scheme, we have achieved 1.65×10-11 estimated with Allan variance for the feedback error
signal from CFP cavity. We also measured the linewidth directly by a separate FP interferometer, which resulted in close
coincidence with above Allan variance estimations. In this work, we have tried to measure our narrowed linewidth by the
delayed self heterodyne technique which consists of optical fiber of about 1km~3km length to have delay time the light
of our stabilized violet laser. In conclusion, we have achieved a practical and inexpensive linewidth control for a high
power violet LD to attain hyper coherent conditions of the semiconductor lasers.
In laser projection displays, countermeasure technique against glares on the screen called speckle noise is one of the
focuses. In the experiments, a quarter-waveplate with slow axis rotated by 45 degrees against the polarization axis of the
incident green laser source was inserted into the optical path of our laser projection display system. Only in such a setup,
an enough coherence alleviation was attained. We have also carried out quantitative evaluations of the speckle noise by
overlaying the projected images using a CCD camera on the histogram-based estimations of speckle noise intensities.
Noise reduction of about 20% was accomplished.
In this work, we have demonstrated a new smart grid model by our novel green photonics technology based on selforganized
optical networks realizing an autonomous peer-to-peer electric power transmissions without centralized
control for the power grid. In this optical network, we introduced an adaptive algorithm for concurrent peer-to-peer
communications, by utilizing optical nonlinearity depending only on the signal strength passing through the network.
This method is applicable for autonomous organization of functions for ad-hoc electric power distribution systems for
the power grid. For this purpose, a simple optical- electrical hybrid bistable circuit composed of such as light emitting
diode (LED) and photo diode (PD), has been incorporated into the network node. In the experiment, the method uses a
simple, local adaptation of transmission weights at each network node, which enables self-organizing functions of the
network, such as self-routing, self-optimization, self-recovery and self-protection. Based on this method, we have
demonstrated experimentally a new smart grid model applicable for ad-hoc electric power distribution systems mediated
by power comsumptions. In this model, electric power flow is controlled autonomously through the self-organized
network nodes associated with individual power facilities having photovoltaics and electric storage devices, etc., and the
nodes convert the amounts of electric power supply and/or comsumption to the light intensity values using above
mentioned transmission weights at each node. As a consequence, we have experimentally demonstrated a simple shorthaul
system model for ad-hoc electric power distribution with a self-organized optical network as a novel green
photonics technology application for smart grid.
We have achieved a simple and precise frequency stabilization technique for commercially available 1mW, 850nm
vertical cavity surface emitting laser (VCSEL) based on optical heterodyne beat frequency control by introducing two
sets of frequency stabilized VCSEL's with Fabry-Perot resonator (FPR) as frequency discriminator. The stabilized
VCSEL's were quite similarly fabricated with each other, in which the electrical negative feedback was supplied for
stabilization. We have also detected optical heterodyne beat between these two VCSEL's by adjusting the locking
frequency of each VCSEL. Thus, we have further reduced the frequency fluctuations from these stabilized VCSEL's by
controlling their feedback current so that the variation in the optical beat frequency should be minimized. As a result, we
have successfully suppressed the amount of optical beat frequency fluctuations within 2MHz at measuring time of 1 sec.
That is, the attained Allan variance is within the order of 10-9. In this work, we have achieved simple and inexpensive
and precise frequency stabilization for 850nm VCSEL by optical heterodyne beat frequency control, which is quite
applicable to nanomanufacturing.
We have demonstrated a compact and inexpensive frequency stabilization technique for commercially available 1mW,
850nm Vertical Cavity Surface Emitting Laser (VCSEL) using a Fabry-Perrot Resonator (FPR) as frequency standard.
We have performed frequency discrimination using a transmitted light from FPR, and frequency stabilization has been
carried out by electrical negative feedback to injection current. Optical frequency fluctuation of VCSEL is estimated by
error signal, and its stability is evaluated by Allan variance. We have achieved to detect optical beat frequency signal of
850nm type VCSEL for the first time, by fabricating two sets of frequency stabilized VCSEL, which are quite similar
with each other by controlling each locking frequency. We have estimated VCSEL's frequency accurately fluctuations
from the beat signal. As a result, we have successfully suppressed the amount of frequency fluctuations for the
free-running VCSEL of as much as 600MHz to be within 80MHz. In this paper, we propose compact, inexpensive and
precise frequency stabilization for 850nm VCSEL, and describe an accurate method for estimating its fluctuations.
We have demonstrated a compact and efficient frequency stabilization system based on Pound-Drever-Hall method,
along with optical feedback. The frequency of a 30mW 405nm GaN violet laser diode (LD) was stabilized to a reference
confocal Fabry-Perot cavity (CFP cavity) by negative electrical feedback to the injection current of the LD based on
Pound-Drever-Hall technique. Moreover, by employing optical feedback from another tilted CFP cavity, the residual
frequency noise has been efficiently suppressed. The minimum square root of the Allan variance was 1.65×10-11 at the
integration time of 0.5s under the optical-electrical double feedback condition. We have achieved the stabilization of
visible violet LD by optical feedback method for the first time.
KEYWORDS: Semiconductor lasers, Laser stabilization, Signal detection, Light sources, Frequency modulation, Fermium, Digital holography, Computing systems, Control systems, Geometrical optics
In the present work, we have developed an efficient and well stablized hyper coherent diode laser light source as
compact as even portable using commercially available visible 400 nm band laser diodes. The attained coherence of the
present system can always be controlled at the best condition indifferent to changes in its settled environmental
conditions by applying Pound-Drever-Hall technique in which the frequency of a 160mW type 405nm GaN violet laser
diode is locked to a reference Fabry-Perot cavity by negative electrical feedback for the injection current of the laser
diode based on FM sideband technique. In addition to this frequency stabilization system, we have also realized a
stability evaluation system that can measure the Allan variance of the frequency fluctuations of our frequency stabilized
laser source in real-time basis by using simple devices of a portable computer and a digital signal processing unit. As a
result, we have accomplished a compact and efficient hyper coherent laser system which can always perform its
optimum conditions even if the environmental conditions around the laser are to be dynamically changed when used in a
field basis. The attained values of power spectral density (PSD) of FM noise calculated from the error signals of our
system under controlled condition were better by about 1~2 orders than typical values of free-running conditions in the
fourier frequency domain from 100Hz to 300kHz. The best achieved value of PSD was about 2.56×107 [Hz2/Hz] in the
fourier frequency domain from 100Hz to 1kHz, while as for the Allan variance as another measure of frequency
stability, the achieved value of the minimum square root of Allan variance was 3.46×10-11 in a 400nm type violet laser
diode at integration time of 10 ms, which has been well comparable to the hyper coherent condition for the laser diode
light sources.
We have demonstrated a compact and inexpensive frequency stabilization technique for commercially available 1mW,
850nm vertical cavity surface emitting laser (VCSEL) using a Fabry-Perrot cavity as frequency standard. Recently
VCSEL has been widely prevailed for uses of low cost and small sized sensors, since it may afford low power
operations and manufacturing costs in comparison with edge emitting type Fabry-Perrot laser diodes. Therefore, a
highly versatile and inexpensive frequency stabilized coherent light source which can be mass producible will be
available if the frequency stabilization for this type of VCSEL's is carried out. Generally, it has been commonly
accepted that a satisfactory degree of coherence may be easily obtained from VCSEL's without any additional frequency
stabilization technique since highly reflective coatings are to be put on their laser cavity edges. Nevertheless, some
VCSEL devices, especially inexpensive type commercial products show multi-mode behaviors along with polarization
instabilities. In the present work, as a simple and inexpensive approach to commercially available VCSEL devices, we
have demonstrated a frequency stabilization scheme using a Fabry-Perrot cavity. The error signal was derived by phase
sensitive detection for the transmitted light from the Fabry-Perrot resonator. Thus, the lasing frequency of the VCSEL
was locked to the zero-crossing of the error signal by negative feedback for injection current via a PID controller. As a
result, we have successfully suppressed the amount of frequency fluctuations in the free-running VCSEL of as much as
2GHz to be within 500MHz at measuring time of 30sec, that is, the attained Allan variance is 4.1×10E-8.
Peer-to-peer (P2P) optical communication network is presently attracting much attention in the application of smallscale
network. We proposed a network element called as a node fabricated by optoelectronics hardware based on the
optical bistable devices. These nodes can compose a self-organizing optical network being interconnected with each
other. We also proposed an adaptive node with gate function which detects the differences of signal types as to the
amplitude modulation (AM) signal in the network and switches their routings. Thus, the adaptive node allows optical
P2P concurrent communications between multiple pairs of communicators in the network simultaneously.
Moreover, we have proposed in the present work an optical nonblocking operation using the pseudorandom numbers
fabricated into the above mentioned adaptive nodes. We have newly considered a switching scheme which identifies
such pseudorandom numbers and forms automatically a signal propagation path so that the nodes with the same input
pseudorandom numbers are to be linked. Since such a pseudorandom-number based switching may also prevent any
irregular interception of established links among nodes, our scheme is proved to be a nonblocking operation. Therefore,
this scheme allows multiple signals from input nodes to travel in the network simultaneously via only a single
propagation path being established by the self-organized adaptive nodes. We have also demonstrated this switching
operation experimentally by fabricating it into our optoelectronics hardware based on the optical bistable devices. As a
consequence, nonblocking photonic switching scheme for P2P self-organized optical concurrent communications
network has been achieved by our pseudorandom-number based adaptive nodes proposed by the present work.
We have demonstrated for the first time the analysis of noise properties in a 65mW, 405nm violet laser diode and also stabilized its frequency fluctuations as low as hyper coherent level. We measured the longitudinal mode behavior in some operation conditions, including the ambient temperature and optical feedback amount and so on. With some optical feedback amounts usually seen in typical optical pick-up systems, we have confirmed that the average relative intensity noise (RIN) value measures up to about -125dB/Hz, while the external cavity length dependences of the RIN show maximal and minimal spikes repeatedly at certain points where the external cavity length coincides with integral multiples of the effective internal cavity length of our sample LD. Under such circumstances, we have achieved the suppression of the optical feedback noise to about - 132dB/Hz by selecting the polarization of the feedback light. Moreover, we have proved the measured 65mW, 405nm violet laser diode sample tends to oscillate in multiple modes, so that we should carry out the single longitudinal mode operation by controlling the ambient temperature about 15°C. Thus, we have finally attained the frequency stabilization of the violet laser diode using a reference Fabry-Perot cavity based on the Pound-Drever- Hall method. As a result, we have achieved for the first time the frequency stability of 1.71×10-10 of the minimum square root of Allan variance in a 400nm type violet laser diode.
We have demonstrated our newly considered self-organizing network nodes which realize optical concurrent communications. Using optical devices such as light emitting diode (LED) and photo diode (PD), we have experimentally composed the non-linear characteristics required for the practical adaptive nodes. We also have accomplished to incorporate some functions which realize the optical concurrent communications into our opto-electronic hybrid circuits. Therefore, without any problem of cross talking or miss formation of the propagation routes, a number of potential communicator pairs may have concurrent access to this self-organizing network formed by interconnecting our nodes. We confirmed the performance of our present nodes experimentally as well as numerically. As a consequence, our present optical nodes have been proved to be practical for the optical peer-to-peer self-organizing network in which concurrent communications are allowed.
We have investigated for the first time optical feedback noise characteristics of violet laser diode (LD) and also demonstrated its noise reduction by selecting the polarization of the feedback light in a typical optical disk pick-up system using 160mW type 405 nm GaN violet LD. The polarization axes of feedback light have been selected by means of rotatable quarter-wave plate (QWP). In this method, we have attained certain noise reduction without superposition of a high frequency (HF) component on driving current, which makes the pick-up system simple and inexpensive. As a result of our experiments, by selecting the angle of QWP relative to the original polarization axis of LD, we could suppress the optical output fluctuations caused by optical feedback from external cavity to less than 20% of peak-to-peak value in our violet laser diodes. In addition, we also measured noise reduction effect by the method of HF superposition. We achieved the noise suppression by selection of feedback light polarization as good as that of HF superposition. As a consequence, our present method could be a new approach for practical and simplified industrial fabrications of inexpensive, substantially low noise optical disk pick-up systems for high power violet laser diode.
We demonstrated our newly designed architecture of optical self-organizing network which enables concurrent peer-to-peer communications of more than two pairs in our previous model. We have realized this architecture by expanding the previous two dimensional lattice connection into three dimensional lattice connection. Two main features achieved by our present work are as follows. First, we have designed the tubular shaped architecture of equivalent peer-to-peer type network which enables two pairs to perform transmission from any open ports located at each end of the tubular connected nodes. Secondly, we have considered to layer the tubular shaped network structure described above in order to increase the limit of pairs by which concurrent communications are possible. In numerical simulation, we have confirmed the efficiency of our above mentioned two architectures of networks. The merit of these two networks is that they can be composed by our previously reported three-port node we have simply realized in optoelectronic hardware or by just adding the fourth port to it. As a consequence, we have proved that our present scheme of simple architectures of optical self-organizing network has potential utility value in actual use for peer-to-peer optical communications.
We have realized optical self-organizing nodes in which nonlinear weighting is enabled by an opt-electronic hybrid circuit based on optical bistability attained simply by coupling a light emitting diode (LED) and a photo diode (PD), which have their own nonlinearity. By connecting each nodes, we have demonstrated a self-organizing link which can build up a signal propagation path autonomously by itself, applying our newly considered adaptive algorithm. This algorithm is based on the fact that the nonlinearity attained by our coupled LED and PD devices can be regarded to be available for a well established nonlinear function which appears in typical adaptive control theory. We have also demonstrated our first fabrication of self-organizing optical network system with seven adaptive nodes. In this scheme, we have intentionally generated a disconnection or a breaking of wire link between certain nodes in the network, and then we have also confirmed that the optimum alternative route can be made autonomously and the transmission recovered. As a consequence, the present optical self-organizing network system can be a step toward a new method for peer-to-peer communications in optical transmission network.
For the purpose of heterodyne optical phase-locked-loop (OPLL), a compact and efficient frequency stabilization system has been developed using a single reference cavity for simultaneous application of optical feedback along with electrical feedback. Using the identical reference cavity for each feedback technique makes the system compact. The phase margin of optical feedback loop can be maximized by stabilizing the center frequency of a laser diode (LD) to the reference cavity mode, which is identical to the optical injection locking mode based on negative electrical feedback. To improve the long-term frequency stability relative to the reference frequency, the optical feedback path length has also been controlled by using frequency error signal obtained by Pound-Drever-Hall technique. With present system, the linewidth of a 35mW visible LD has been reduced to less than 40kHz. Using this frequency stabilized LD as a master light source, heterodyne optical phase-locking has also been carried out with Littorow configuration extended-cavity slave LD in order to evaluate applicability of our system to the OPLL. The achieved minimum square root of the Allan variance of the beat frequency fluctuation was 3.8×10-13 at integration time of 10 sec. Throughout this phase-locking experiment, we could confirm that our master system maintained good time base stability, not showing any system instabilities such as mode hopping or disturbances.
KEYWORDS: Laser stabilization, Semiconductor lasers, Fermium, Frequency modulation, Spectrum analysis, Servomechanisms, Digital signal processing, Signal processing, Optical amplifiers, Laser optics
We have stabilized frequency of 35mW 680nm visible laser diode (LD) by using simple frequency stabilization system based on optical-electrical double feedback method. For the long-term frequency stabilization, frequency of the LD was stabilized to a reference confocal Fabry-Perot cavity (CFP cavity) by negative electrical feedback to the injection current of the LD based on Pound-Drever technique. By employing optical feedback from another tilted CFP cavity along with electrical feedback, the residual frequency noise has been efficiently suppressed. The achieved PSD of frequency fluctuation under optical-electrical double feedback condition was less thani x 1 05[Hz2 1Hz] within the Fourier frequency <10 MHz. The reduced linewidth under the double feedback condition is estimated to be narrower than at least 400 kFIz, which seems to be the resolution limit of our measurement. The minimum square root of the Allan variance is 3 .9 x 10' at the integration time of 0.1 msec under the double feedback condition.
We have demonstrated a simple method for controlling the nonlinear oscillations using only semiconductor lasers and photodetectors. An electro-optical NDFS (nonlinear delayed feedback system) has been composed by making use of this method. With this system, multi-stable oscillations and chaotic transitions with various patterns have been observed. In addition, some characteristic routing sequences form period-doubling bifurcation to chaos have been reproducibly observed when some external modulations with acoustic frequencies are applied to the NDFS. In this case, we have proved that the harmonic numbers of the multi- stable oscillation modes to appear as system output are to be controlled in terms of timing (phase) as well as frequencies of external input signals at the moment they are applied. And we have also confirmed such remarkable transition behaviors of the multi-stable oscillation modes by numerical analysis based on nonlinear delayed differential equations describing our NDFS. Consequently, we have demonstrated that the oscillation harmonic numbers can be directly chosen from the 1st order up to the 9th by setting the frequencies of the external input signals to be their characteristic values specifying the desired harmonic numbers to appear for output and also by setting the timing of input signals with respect to the phase of original waveform of the oscillating modes. Thus, our system is expected to be a potential for something novel, intelligent communication technique based on chaos.
We have demonstrated a novel WDM and self-routing scheme as well as electro-optical logic-gate operations based on the mode-hopping phenomenon previously considered as a cause of bad noise in the Fabry-Perot type semiconductor lasers. In our routing scheme, data signals can be sent through adequate routes because they have information on their own destinations assigned by hopped wavelengths in their carrier light wave form a laser diode. The hopped wavelength can be controlled by only switching temporarily the d.c. bias levels of the driving current of the laser diode. The performed speed of the 1XN channel wavelength-switching was estimated at about 167 nanoseconds, limited by insufficiencies in our electronics, not by the phenomenon itself. The number of destination channels 'N' has been limited to the number of allowed hopping modes in the sample laser diode. Since the mode-hopping phenomenon itself has been reported to be faster than nanoseconds, more efficient and ultra-fast self-routing or WDMA systems based on this phenomenon will be performed. In addition, we have performed electro-optical logic-gate operations by modulating the injection current of the laser diode through mode-hopping regions. The achieved data rate of our gate operations for AND, Ex-OR and NOR gates was typically 3 X 12 Mbit/s with two simultaneously modulated input signals.
We have demonstrated a color recognition system composed by a novel, self-organized optical neural network system that includes genetic algorithms along with back propagation schemes, which make it possible that the system avoids the local minimum problems and make the learning processes faster and better. Our system is composed of a color liquid crystal display panel (LCD), bistable semiconductor lasers, photo-diodes, and liquid crystal light projector (LCP). The LCD weighs the intensities of light that passes through it and works as synapses in the neural network. The optical bistable semiconductor lasers originate the optical sigmoid functions and serve as threshold processing units. Using these devices can simplify the configuration of the optical neural network system. The color of light emitted from the LCP will be recognized by the neural network system. A monochromatic light beam generated by the LCP is illuminated on all over the LCD surface displaying the colored boxes in the three primary components. Thus, the light beam is weighed when it passes through the boxes on the LCD. As a consequence, we have achieved a novel, simplified color recognition system using the genetic algorithms for self- organization of the optical neural network. The unique feature of this system is to make use of the genetic algorithms and the back propagation at the same time to derive selectively the merits from these two methods. By this system, more naturalized color recognition like human will be performed, being able to distinguish the colors under different conditions of environment, e.g. lightening conditions, surface conditions of colored material, etc.
We have demonstrated a color recognition system composed of a novel, self-organized optical neural network system that includes genetic algorithms along with back propagation schemes, which make it possible that the system avoids the local minimum problems and make the learning processes faster and better. Our system is composed of a color liquid crystal display panel, bistable semiconductor lasers, photo- diodes, and liquid crystal light projector.
We demonstrate a simple method for controlling the nonlinear oscillations by only using a semiconductor laser and photo detectors. The nonlinearity necessary for exhibiting period- doubling bifurcations and chaotic phenomenon was realized by appropriately superposing the threshold characteristics of semiconductor lasers on the saturation characteristics of photodiodes in their electric current vs. light intensity properties. An electro-optical NDFS (nonlinear delayed feedback system) has been composed by making use of this nonlinearity. A low-pass filter was inserted into this NDFS as an electric feedback element, which gave variety to the behavior of the nonlinear oscillations. With this system, multi-stable oscillations and chaotic transitions with various patterns have been observed. In this scheme, an optical dynamical memory function has been demonstrated to perform binary data writing. In addition, we have applied an external light input to the NDFS, for example, some sinusoidal wave modulations with acoustic frequencies. If the external input light effects to the oscillation waveform are to be reproducibly derived, new application to a waveform recognition system and cryptography will be expected.
In this work, we have demonstrated experimentally the electro-optical
switch, logic and memory operations at the speed of as fast as nanosecond
region, utilizing the mode-hopping phenomenon of a laser diode. We have also
confirmed the hysteresis (wavelength bistability) region being still effective
under even such a high speed. The sample laser diode used in the experiments
was a O.8m GaAlAs-type and 1.3m InGaAsP-type one.
The measured speed of switching was within nanosecond region, which was
limited by the driving capabilities and the light detection response, not by the
phenomenon itself. In order to confirm the reproducibility of the hopped
wavelength in the experiments, the fluctuations in the ambient temperature of
the laser diode are precisely controlled to be within 1.0 mK through a
thermoelectric cooler attached to the heat sink of the laser diode by which both
cooling and heating are possible. As an example of the fast logic operation, we
have achieved the actual N X N channel optical wavelength-division-multiplexing
system using a O.8m GaAlAstypevvisible injection laser diode and also a 1.3m
InGaAsP-type long-wavelength laser diode of which the wavelength is rather
suitable for fiber optic routing systems.
Moreover we carried out the simulation to explain the behavior of the
wavelength bistability seen in these laser diode samples and also estimated how
fast these switches or memories can operate, based on some well-known analyses
for the mode-hopping phenomenon. In addition, the gain-suppression mechanism
in semiconductor lasers was included in this analysis. As a consequence, the
result of estimation suggests that the speed of wavelength-switching may become
about an order of magnitude longer than the carrier lifetime of the device.
Therefore, we can conclude that the dominating physics of the wavelength
bistability based on the mode-hopping phenomenon is a very fast thermal
processes caused by modulating the injection current.
A new scheme of digital optical switching, optical analog-to-digital conversion, and wavelength bistability is presented which can be applied to digital optical, memory operations, utilizing the mode-hopping phenomenon of Fabry-Perot cavity-type injection laser diode. The measured speed of switching was within the nsec region, which was limited by the driving capabilities and the light detection response, not by the phenomenon itself.
KEYWORDS: Cadmium, High power lasers, Chemical species, Gas lasers, Modes of laser operation, Electronics, Hydrogen, Metals, Numerical simulations, Doppler effect
It has been recognized that since the He-CdII lasers are usually operated under considerably high buffer-gas pressure, the oscillation modes in these lasers can automatically reduced by their homogeneous broadening mechanism due to the high buffer-gas pressure. Therefore, it has been expected that the oscillation scheme in these lasers can easily be single-moded when they are operated in high power. We have examined this fact with a most high-power (100mW) He-CdII white light laser which has just come to be commercially available in Japan. As a result, this is true only in the cases of the 537.8 nm and 636.Onm lines, but in the case of the 441.6nm lines an anomalous broadening of the spectral width, which amounts to as much as more than 2GHz has been measured. This degrades the coherence length of this blue line less than 15cm. Such a large broadening can be attributed to the isotopes involved in the natural cadmium metal used for the laser material.
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