A simple millimeter wave and terahertz (THz) receiver scheme that uses subwavelength focusing of electromagnetic beam on the point-contact detector area with waveguide dimensions is studied. A detection system with such an optical coupling scheme is implemented, where the signal to be detected is coupled to a detector through a mesoscale dielectric particle lens based on terajet effect. We have experimentally demonstrated an enhancement of the point-contact detector sensitivity higher than 6 dB and with 1.5 times decreasing of the noise equivalent power value. The results show that the proposed method could be applied to reduce the size and increase the sensitivity of various THz systems, including imaging, which would enable significant progress in different fields such as physics, medicine, biology, astronomy, etc.
For high-power THz wave generation by photomixing of two lightwaves, we proposed the synchronous power combiner which consists of eight-arrayed photomixers/antennas and the THz phase control system. We experimentally confirmed the effectiveness of the power combination by synchronizing the phases of the THz wave by the mechanical optical delay lines and also demonstrated the same functionality at the lightwave-circuit-based optical phase control system. We found that the directional gain is increasing with increasing the number of photomixers from two to three and it reached up to 4.5 dB.
We report on an improvement of the voxel density of three-dimensional (3D) image display by spatially multiplexing
fluxes in light-ray-flux reproduction method. In the basic light-ray-flux reproduction method, a color
filter is projected by the use of an array of white-color point light sources in order to artificially generate a group
of light rays corresponding to light scattered from an object, to thereby generate a 3D image. In the developed
system, we used liquid crystal display (LCD) and pinhole array instead of color filter and white-color point light
source array. The principle of this modified system is the same as the basic system. The light-ray fluxes are
spatially multiplexed by rapidly changing the position of the pinholes. The 2D filter images displayed by the
LCD are changed in synchronized with the position changes of the pinholes. In the experiment, position changes
of the pinholes are realized by mechanically vibrating a slit mask array, which covers the pinhole array. We
confirmed that the voxel density was improved to twice without the degradation of the viewing angle and the
depth of the reconstructed 3D image.
KEYWORDS: 3D displays, 3D image processing, Mirrors, Image display, Semiconductor lasers, Luminescence, Ultraviolet radiation, Commercial off the shelf technology, Goggles
We have developed a new type of volumetric three-dimensional (3D) image display which has a 360-degree,
3D volume group-viewing capability without the use of any special viewing aids or goggles. In our system, a
clear thin photopolymer sheet dissolving Lanthanide(III) complexes is used. The Lanthanide(III) complexes
used in our system are Eu(TTA)3 Phen, designed for 615nm luminescence (red) against an exciting light of
395nm. Arbitrary luminous point is identified by three dimensional control of the excitation position of the
Lanthanide(III) complexes dissolved photopolymer sheet. The specific point (x,y,z) is excited by laser diode
beam. The direction of the exciting laser beam is controlled by two galvano mirrors so as to excite the specific
two-dimensional point (x,y). The depth direction (z) of the 3D object is specified by controlling two galvano
mirrors in synchronization with a photopolymer sheet rotation. The 3D images are expressed as an aggregate
of these luminous point. In the experiment, we observed static 3D objects of a triangle. We also observed
3D animation of a 3D Lissajous curve. Displayed 3D objects integrated with real background because rotating
photopolymer sheet is transparent (transparent 3D display).
We have experimentally demonstrated ultrashort optical pulse generation from a continuous wave (CW) laser using an external electrooptic deflector (EOD). Highly efficient EOD operating at 16.25 GHz has been realized with periodically domain-inverted LiTaO3 crystal. The shape of domain inversion region has been theoretically designed in consideration of the velocity mismatching between the modulation microwave and the light so as to realize spatially linearly-varying phase shift. The deflected CW Ar laser beam passed the Fourier transform lens, and then optical pulses were picked out at a repetition rate of 32.5 GHz through a narrow slit, which was placed at the focal point of the lens. The pulses were observed by streak camera (Hamamatsu: C5948) and the achieved shortest pulse width was estimated to be 0.9 ± 0.1 ps.
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.
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