Full Optical System Research Articles

Research on full duplex FSO access system with hybrid 16PSK/256QAM-OFDM downlink and duobinary uplink signals

a 100Gbit/s novel full duplex free space optical (FSO) access system scheme is proposed and demonstrated. Using the downlink hybrid 16phase shift keying (PSK)/256quadrature amplitude modulation (QAM)-orthogonal frequency division multiplexing (OFDM) and duobinary uplink signals. In downlink branch, in-phase/quadrature-phase (I/Q) modulation based on Mach-Zehnder modulator (MZM) and coherent detection technology are adopted. Meanwhile, 0.1Terahertz (THz) wave signal generated by two independent optical sidebands beating frequency at positive intrinsic-negative photodiodes (PIN PDs) for hybrid downlink 16PSK/256QM-OFDM signals. In uplink branch, intensity modulation and direct detection (IM/DD) can achieve reduced the communication budget cost and simplified the system configuration Simulation results show that the value of bit error ratio (BER) less than hardware decision forward error correction (HD-FEC) threshold after 300 m FSO channel transmission under the different weather conditions (such as sunny, rainy and snow).

Tbit/s line-rate satellite feeder links enabled by coherent modulation and full-adaptive optics

Free-space optical (FSO) communication technologies constitute a solution to cope with the bandwidth demand of future satellite-ground networks. They may overcome the RF bottleneck and attain data rates in the order of Tbit/s with only a handful of ground stations. Here, we demonstrate single-carrier Tbit/s line-rate transmission over a free-space channel of 53.42 km between the Jungfraujoch mountain top (3700 m) in the Swiss Alps and the Zimmerwald Observatory (895 m) near the city of Bern, achieving net-rates of up to 0.94 Tbit/s. With this scenario a satellite-ground feeder link is mimicked under turbulent conditions. Despite adverse conditions high throughput was achieved by employing a full adaptive optics system to correct the distorted wavefront of the channel and by using polarization-multiplexed high-order complex modulation formats. It was found that adaptive optics does not distort the reception of coherent modulation formats. Also, we introduce constellation modulation – a new four-dimensional BPSK (4D-BPSK) modulation format as a technique to transmit high data rates under lowest SNR. This way we show 53 km FSO transmission of 13.3 Gbit/s and 210 Gbit/s with as little as 4.3 and 7.8 photons per bit, respectively, at a bit-error ratio of 1 ∙ 10−3. The experiments show that advanced coherent modulation coding in combination with full adaptive optical filtering are proper means to make next-generation Tbit/s satellite communications practical.

Arrays of individually controllable optical tweezers based on 3D-printed microlens arrays.

We present a novel platform of optical tweezers which combines rapid prototyping of user-definable microlens arrays with spatial light modulation (SLM) for dynamical control of each associated tweezer spot. Applying femtosecond direct laser writing, we manufacture a microlens array of 97 lenslets exhibiting quadratic and hexagonal packing and a transition region between the two. We use a digital micromirror device (DMD) to adapt the light field illuminating the individual lenslets and present a detailed characterization of the full optical system. In an unprecedented fashion, this novel platform combines the stability given by prefabricated solid optical elements, fast reengineering by rapid optical prototyping, DMD-based real-time control of each focal spot, and extensive scalability of the tweezer pattern. The accessible tweezer properties are adaptable within a wide range of parameters in a straightforward way.

Optical Chemical Sensor Using Intensity Ratiometric Fluorescence Signals for Fast and Reliable pH Determination.

Optical pH sensors enable noninvasive monitoring of pH, yet in pure sensing terms, the potentiometric method of measuring pH is still vastly superior. Here, we report a full spectrometer-based optical pH sensor system consisting of sensor chemistry, hardware, and software that for the first time is capable of challenging the performance of an electrode-based pH meter in specific applications such as biopharmaceutical process monitoring and in single-use bioproduction. A highly photostable triangulenium fluorophore emitting at 590 nm was immobilized in an organically modified silicon matrix that allows for fast time-response by rapid diffusion of water in and out of the resulting composite polymer deposited on a polycarbonate substrate. Fluctuations from the fiber optical sensor hardware have been reduced by including a highly photostable terrylene-based reference dye emitting at 660 nm, thus enabling intensity-based ratiometric readouts. The dyes were excited by 505 nm light from a light emitting diode. The sensor was operational within a pH range of 4.6-7.6, and was characterized and demonstrated to have properties that are comparable to those of commercial pH electrodes considering time-response ( t90 < 90 s), precision (0.03 pH-units), and drift.

An Annulus-Sector Segmented Primary Mirror

Ultrahigh resolution optical imaging with large aperture is increasingly desired in space-based remote sensing and imaging system, but it is usually limited by volume and mass constraints of launch vehicle due to size and weight of the imaging system. In this paper, an annulus-sector segment primary mirror is presented, which is in high obscuration with circularity symmetrical annulus-sector around. The different structure types of the annulus-sector segment aperture are discussed, while two important parameters, width–diameter ratio and the subaperture angle are also studied. An annulus-sector optical lens is processed to verify the image performance. Experimental results show that modulation transfer function of annulus-sector segment optical system can be up to 0.23(50 lp/mm), which approaches the optical resolution of full aperture optical system with smaller size and lighter weight.

LiNbO&lt;sub&gt;3&lt;/sub&gt; 광도파로 제작에 관한 연구

In this paper, waveguide analysis was interpreted as an optical waveguide using the feedback perturbation method simple and easy to apply compared to the analysis method, while the other almost identical to the numerical calculation method. In addition, efficient coupling with an optical transmission line of optical fiber and the waveguide form the thin film of different functional elements is required in order to achieve the full optical communication system. However, problems arise, such as the light field (field) and the decrease of the access efficiency due to inconsistency in the distribution characteristics of the connection surface by the difference in size of the cross section thereof when connecting the optical fiber and the waveguide directly to the combination of a thin film. Therefore propose a new type of connector structure to increase the efficiency of the connection when connecting the optical fiber waveguide and the thin film was analyzed by applying a coupled mode theory, the binding efficiency of the modified contactor. And by diffusing Ti on the substrate and a wide range of applications in the manufacture of integrated optical material made of a current low-loss Ti: optical waveguide and making the Y-branch waveguide, and the properties were confirmed.

Development of Slewing Mirror Telescope Optical System for the UFFO-pathfinder

The Slewing Mirror Telescope (SMT) is the UV/optical telescope of UFFO-pathfinder. The SMT optical system is a Ritchey-Chretien (RC) telescope of 100 mm diameter pointed by means of a gimbal-mounted flat mirror in front of the telescope. The RC telescope has a 17 × 17arcmin2 in Field of View and 4.3 arcsec resolution (full width half maximum of the point spread function) The beam-steering mirror enables the SMT to access a 35 × 35degree region and point and settle within 1 sec. All mirrors were fabricated to about 0.02 wavelengths RMS in wave front error (WFE) and 84.7% average reflectivity over 200 nm ~ 650 nm. The RC telescope was aligned to 0.05 wavelengths RMS in WFE (test wavelength 632.8 nm). In this paper, the technical details of the RC telescope and slewing mirror system assembly, integration, and testing are given shortly, and performance tests of the full SMT optical system are reported.

Transmission analysis of digital TV signals over a Radio-on-FSO channel

Recently, radio-on-free-space optical (RoFSO) technology is regarded as a new universal platform for enabling seamless convergence of fiber and FSO communication networks, thus extending broadband connectivity to underserved areas. In this article, an experimental demonstration of the newly developed advanced RoFSO system capable of transmitting the Japanese integrated services digital broadcasting- terrestrial (ISDB-T) signals over a 1 km FSO link is presented. Our innovative system combines a new generation full optical FSO system with radio over fiber technology. Important performance quality metrics like the modulation error ratio and bit error rate are measured and analyzed to characterize the deployment environment influencing the transmission of ISDB-T signals over the FSO link. The obtained results can be used for designing, predicting, and evaluating the RoFSO system capable of transmitting multiple wireless services over turbulent FSO links.

Towards portable, real-time, integrated fluorescence microarray diagnostics tools

We present recent results on biochips slides with high fluorescence efficiency and their associated readout systems. To obtain the full performance made possible by such slides, the chemical surface functionalization has to be improved, as formerly unobservable defects of the functionalization are now made observable through the improved efficiency. The systems are based on the integration of the hybridization and readout functions into a single machine instead the usual two separate systems, quite cumbersome and expensive. Ultimate performance is reached with systems using standard imaging circuits, CCD or CMOS, as the biochip substrate. In this case, one can obtain a remarkable miniaturization of the full optical system and the integrated hybridization chamber/readout head can be reduced to the size of a webcam.

Optical sensors based on III-nitride photodetectors for flame sensing and combustion monitoring

Combustion control requires visible photodetectors to sense the CH* CL emission at 430 nm that combined with a visible-blind UV photodetector allows us to obtain the OH*/CH* ratio. UV-visible P-InGaN/GaN multiple quantum well-N photodiodes with 15-18 mm2 areas were fabricated to conduct OH* (308 nm) and CH* CL detection without external filters. Bandpass detectors at 230-390 nm and 360-450 nm presented linear responses over five decades and rejection ratios >10(3) at 430 and 308 nm, respectively. A full optical sensor system was built and detectors operated at 120 degrees C in a combustion chamber, showing linear responses within the dynamic range, maximum signal-to-noise ratios of 103 and response times of <1 s. An exponential association dependence between the optical OH*/CH* CL signals and the gas/air ratios was found.

High speed full range complex spectral domain optical coherence tomography

We present a high speed full range spectral domain optical coherence tomography system. By inserting a phase modulator into the reference arm and recording of every other spectrum with a 90 degrees phase shift (introduced by the phase modulator) we are able to distinguish between negative and positive optical path differences with respect to the reference mirror. A modified two-frame algorithm eliminates the problem of suppressing symmetric structure terms in the final image. To demonstrate the performance of our method we present images of the anterior chamber of the human eye in vivo recorded with an A-scan rate of 10000 depth profiles per second.

Adaptive optics experiments using sodium laser guide stars

The Multiple Mirror Telescope (MMT) has been used in experiments with sodium laser guide stars to sense and correct atmospheric image distortion. The major goal was to develop and test concepts for a full adaptative optics system, to be used in 2 yr when the present array of six 1.8 m telescopes will be replaced with a single 6.5 m mirror. The guide star, produced by a continuous-wave dye laser beam projected out along the optical axis of the telescope, was as bright in the V band as a natural star of m<SUB>v</SUB> = 10.4. Our tests culminated in the first demonstration of a sodium laser guide star used to improve the image of an astronomical telescope, in this case formed by two of the six 1.8 m apertures. Two adaptive servo loops were closed simultaneously. The laser beacon provided a measure of the differential wave-front tilt between the two apertures, and a natural guide star was used to measure the overall wave-front tilt. A factor of 2 improvement in the K-band Strehl ratio was measured, and the resolution improved from 0.58 arcsec to 0.41 arcsec. The experiment demonstrated all the features needed for correction of the 6.5 m telescope to the diffraction limit using a sodium beacon. The accuracy with which the laser beacon measures the atmospheric aberration of starlight across the full 6.9 m aperture of the MMT was examined. From more extensive measurements of binary star wave fronts, we deduce that focus anisoplanatism for the 6.5 m telescope will correspond to a Strehl ratio of typically 88% at K under normal seeing conditions. In a laser-based adaptive system, a natural guide star is still required to sense overall wave-front slope. Our measurements of binary stars also yielded the image degradation to be expected from differences in the overall slopes between the wave fronts from the object of scientific interest and the natural guide star. A Strehl ratio of 80% at K was deduced for an offset of 40 arcsec, implying that good sky coverage will be possible. In general, our results are consistent with calculations based on measurements of atmospheric turbulence at the best sites. Our direct measurements over such a large aperture show clearly the effects of a finite and variable outer scale of turbulence.

Subaperature optical system testing

Full aperture optical system wave-front accuracy obtainable from single or. multiple subaperture wave-front measurements is analytically determined and illustrated with numerical examples. Insight gained from the analytic derivation and confirmed by the examples shows the effect of subaperture size, placement, and accuracy. The analysis also demonstrates that accurate full aperture aberrations (except tilt) can be estimated even with large uncertainty in relative subaperture tilt.

A Monochromatic Variable-Density Recording System

This work was undertaken to determine the benefits of a true monochromatic optical system for variable-density recording in the ultraviolet region. A full quartz optical system consisting of both spherical and cylindrical lenses was used, having a reduction of 10-1 from the light-valve spacing. The reduction in lens distortion and improvement in general image quality is reported along with intermodulation tests on the system, which uses an automatic air-controlled mercury-vapor lamp system.