Optical Noise Reduction Research Articles

Reduction of optical noise in near-infrared range laser hygrometry

Reduction of optical noise in near-infrared range laser hygrometry

Reduction of optical beat interference noise using statistical adaptive derivative equalizer

In this paper, we propose a statistical adaptive derivative equalizer (SADE) in order to reduce an optical beat interference (OBI) noise in an optical access link. The proposed SADE generates an output signal similar to the shape of the input pulse amplitude modulation (PAM)-4 signal waveform, which is implemented as an adaptive total variation that responds to the shape of the multi-step signal waveform with the weighting function considering the Lorentzian characteristics of the OBI noise. We implement a 20-km optical link and measure the bit error rate (BER) and signal to noise ratio (SNR) to see if the OBI noise was reduced using the proposed technique. A 1.5-dB SNR gain was observed over the overall SNR range of received PAM-4 signal than that without the use. A power penalty in the case of using only SADE was improved by 1.5 dB at 7% forward error correction (FEC) limit compared to that without the SADE. Furthermore, when the proposed SADE and matched filter were applied simultaneously, about 2.5-dB power penalty was observed at the 7% FEC limit.

Distance Error Correction in Time-of-Flight Cameras Using Asynchronous Integration Time.

A distance map captured using a time-of-flight (ToF) depth sensor has fundamental problems, such as ambiguous depth information in shiny or dark surfaces, optical noise, and mismatched boundaries. Severe depth errors exist in shiny and dark surfaces owing to excess reflection and excess absorption of light, respectively. Dealing with this problem has been a challenge due to the inherent hardware limitations of ToF, which measures the distance using the number of reflected photons. This study proposes a distance error correction method using three ToF sensors, set to different integration times to address the ambiguity in depth information. First, the three ToF depth sensors are installed horizontally at different integration times to capture distance maps at different integration times. Given the amplitude maps and error regions are estimated based on the amount of light, the estimated error regions are refined by exploiting the accurate depth information from the neighboring depth sensors that use different integration times. Moreover, we propose a new optical noise reduction filter that considers the distribution of the depth information biased toward one side. Experimental results verified that the proposed method overcomes the drawbacks of ToF cameras and provides enhanced distance maps.

Markov Chain Investigation of Discretization Schemes and Computational Cost Reduction in Modeling Photon Multiple Scattering

Establishing fast and reversible photon multiple scattering algorithms remains a modeling challenge for optical diagnostics and noise reduction purposes, especially when the scattering happens within the intermediate scattering regime. Previous work has proposed and verified a Markov chain approach for modeling photon multiple scattering phenomena through turbid slabs. The fidelity of the Markov chain method has been verified through detailed comparison with Monte Carlo models. However, further improvement to the Markov chain method is still required to improve its performance in studying multiple scattering. The present research discussed the efficacy of non-uniform discretization schemes and analyzed errors induced by different schemes. The current work also proposed an iterative approach as an alternative to directly carrying out matrix inversion manipulations, which would significantly reduce the computational costs. The benefits of utilizing non-uniform discretization schemes and the iterative approach were confirmed and verified by comparing the results to a Monte Carlo simulation.

원격감시 기능을 갖는 고감도 부분방전센서

Remote monitoring partial discharge sensor, equipping with hybrid filter combining optical and electrical noise reduction capabilities and with signal integrating function to calculate total arc energy, was investigated. Hybrid filter showed insensitivity to fluorescent and incandescent lamps under simulated distribution panel condition. Signal integrating function showed selective detection capability corresponding to different arc energy levels, while convention arc sensor had difficulty to discriminate arc energy level due to bursty arc waveform and peak level detection characteristics. The sensor showed possibility for application to remote monitoring partial discharge sensor, since it detected arc energy level corresponding to normal open and close discharge in low voltage 100A MCCB at 2m distance.

High topographical accuracy by optical shot noise reduction in digital holographic microscopy

In this work, we present a new method to reduce the shot noise in phase imaging of digital holograms. A spatial averaging process of phase images reconstructed at different reconstruction distances is performed, with the reconstruction distance range being specified by the numerical focus depth of the optical system. An improved phase image is attained with a 50% shot noise reduction. We use the integral of the angular spectrum as a reconstruction method to obtain a single-object complex amplitude that is needed to perform our proposal. We also show the corresponding simulations and experimental results. The topography of a homemade TiO2 stepwise of 100 nm high was measured and compared with the atomic force microscope results.

616 生体情報による活動記録システムの研究開発

We developed real-time living activity measurement system that monitored heart beat information and the bodily movement from a photoplethysmography and a acceleration sensor. The outside optical noise reduction technique was performed by the pulse luminescence of LED and high-pass filter proccess. Discerning the basic motion running, walking, and working, etc. became possible by from 3-axes acceleration sensor output.

微型激光光学引擎中光学噪音的抑制

The reason of the two kinds of optical noise including grid noise and speckle noise is analyzed.A method of reducing the both two kinds of optical noise by a moving random phase plate is introduced.And the theoretic principle is deduced.A micro projector model is designed,in which a random phase plate is driving for vibration by a micro electric controlled motor.The projected imaging was obtained by a CCD camera with different F# and exposure time.The speckle contrast of the projected imaging is calculated.It is shown in the results that when the random phase plate is static,the grid noise can be reduced well.When the random phase plate is vibrated in a frequency higher than the frequency based on the vision hysteresis,the two kinds of optical noise can both be reduced.The final speckle contrast of the projected imaging is less than 5%,which can be satisfied with the projection display application.

Optical pulse compression and amplitude noise reduction using a non-linear optical loop mirror including a distributed Gires–Tournois etalon

We propose and analyse numerically a novel dispersion-imbalanced non-linear optical loop mirror (NOLM) scheme allowing simultaneous compression and amplitude noise reduction of chirped ultrashort-pulsed signals. An all-fibre distributed Gires–Tournois etalon (DGTE) made of two uniform fibre Bragg gratings is inserted asymmetrically in the loop, and is used both to dispersion imbalance the NOLM and to compress the pulses. The results show that the output pulses are accompanied by side lobes, which originate from the no-uniformity of the DGTE dispersion spectrum. We analyse the formation of these side lobes and show that, in the case of highly chirped input pulses, side lobes are strongly reduced by the NOLM architecture. In this case, the device operates well even when the signal optical spectrum extends over an entire free spectral range of the DGTE. We believe that this work will be useful for the design of all-optical regeneration schemes for highly chirped data streams in optical transmission systems.

Simultaneous readout of positive and negative images for dc-removed coaxial holographic data storage

A method of reconstructing positive and negative images simultaneously from the same dc-removed coaxial Fourier hologram with the same reference pattern is presented. The simultaneous reconstruction is possible by making the polarization of the additional dc component of the signal beam perpendicular to the polarization of the reconstructed signal beam, in which separately detected s- and p-polarization components create contrast-reversed images. This method provides an aspect of designing dc-removed coaxial holographic storage systems for realizing optical noise reduction and less consumption of dynamic range of the recording medium.

Optical Distribution and Upconversion of MB-OFDM in Ultrawide-Band-Over-Fiber Systems

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Broadband radio-over-fiber networks are raising great interest for intrabuilding distribution and signal processing of ultrawide-band (UWB) signals. In this paper, a unique optical system based on an external modulator biased either in linear or nonlinear regime has been used to realize both distribution of multiband orthogonal frequency-division multiplexing (MB-OFDM) UWB signal and all-optical frequency upconversion of UWB-OFDM subband. The impact of the nonlinearity of the optical link on the MB-OFDM signal is investigated through a simulation model of the complete UWB-over-fiber system. Results have shown enhanced performance of upconverted MB-OFDM subband compared to direct transmission due to optical noise reduction. First experimental results have confirmed simulation results. </para>

Collective-Interaction Control and Reduction of Optical Frequency Shot Noise in Charged-Particle Beams

We present a theoretical model for longitudinal collective Coulomb interactions in a charged-particle beam. It suggests a possibility to control and reduce optical frequency shot-noise current in accelerated electron beams. For short interaction lengths, the model describes well coherent optical transition radiation effects observed in SLAC LCLS and in other laboratories. For longer interaction lengths (quarter plasma oscillation period) the model predicts the possibility to reduce the beam current noise below the classical shot-noise level, an effect not yet observed experimentally at optical frequencies.

Improved performance in coaxial holographic data recording

We describe a coaxial holographic recording system for achieving high recording density. We implement several techniques, such as an objective lens with high numerical aperture (NA), high capacity page data format, a random binary phase mask, and an optical noise reduction element. Our system successfully realizes a hologram recording/retrieving at a low diffraction efficiency less than 2.0 x 10(-3) and achieves a raw data density of 180 Gbit/in.(2), thus demonstrating the potential of a coaxial holographic system for high-density optical storage systems.

Optical noise reduction for dc-removed coaxial holographic data storage

A method of reconstructing positive and negative images from Fourier holograms recorded without the dc components is demonstrated by use of a coaxial holographic storage system. Reconstructed images are obtained by adding a phase-modulated dc component of the signal beam on reading. Contrast reversal of the reconstructed images can be achieved by reversing the readout reference pattern. This method can realize not only optical noise reduction but also less consumption of the dynamic range of the recording medium, potentially contributing to increasing the number of multiplexed holograms.

Optical noise reduction by reconstructing positive and negative images from Fourier holograms in coaxial holographic storage systems

A technique for reconstructing positive and negative images from an identical intensity-modulated hologram is demonstrated theoretically and experimentally by use of a coaxial holographic storage system. Negative images are obtained by adding a phase-modulated dc component of signal beam on reading. By comparing positive and negative images, the bit error rate (BER) is improved by two orders of magnitude. This technique can reduce optical noise of reconstructed images to attain low BERs.

Optical beat noise reduction in WDM-SCM access networks using modulated optical pulse train

We proposed a new method to suppress the optical beat interference (OBI) in wavelength-division-multiplexing/subcarrier-multiple-access network. The proposed scheme uses the modulated optical pulse train that has broad bandwidth in frequency domain. Since the OBI noise is inversely proportional to the optical bandwidth of beating optical signals, the generated OBI noise by beating of optical pulse train signals from several optical network units (ONUs) spreads over wide frequency range. In addition, the chance of optical beating is low because optical pulse trains from different ONU have different pulse timing. We have demonstrated the proposed idea experimentally. In beating experiment, the carrier-to-noise ratio was obtained over 30 dBc regardless of optical beating. In addition, 6-Ms/s 16 quadrature amplitude modulator data at 0.7 GHz was successfully transmitted up to 20 km with an average error-vector-magnitude of 4.5% in presence of optical beating.

Optimum splitting ratio for amplifier noise reduction by an asymmetric nonlinear optical loop mirror

Using a highly asymmetric nonlinear optical loop mirror amplifier noise reduction in the dependence on the splitthg ratio and the input noise were investigated. Noise reduction of more than -5dB was observed.

Optical beat noise reduction in subcarrier multiplexed optical link using dual current modulation of master and slave lasers

A novel method to reduce optical beat noise (OBN) which is critical in subcarrier multiplexed-based optical access link is suggested. The chirped optical signal was generated by using dual current modulation through master and slave lasers. The sidelobes of the slave laser decreased up to -90 dBm close to the noise floor. The OBN was reduced by 20 dB because of the spectral broadening of the slave laser resulted from the increased chirp.

Optical noise reduction in a femtosecond Ti:sapphire laser pumped by a passively stabilized argon ion laser

Ionic gas lasers are widely used as optical pumps for a broad variety of solid-state and dye lasers. In such applications, the power fluctuations of the ionic gas lasers are contributing to the noise of the pumped lasers. In this paper, we report on the observation that a significant noise reduction can be achieved in a Ti:sapphire laser when it is pumped by a multiline argon ion laser stabilized with a passive external cavity. Under optimal conditions, the average optical noise of the argon ion laser beam was reduced by 20 dB over a spectral band ranging from 100 to 800 kHz. A similar noise reduction was observed in a Ti:sapphire laser when its pumping argon ion laser was stabilized with an external cavity; noise reduction occurred both in the continuous-wave regime and in the femtosecond regime. Our results are consistent with a model considering the response of the laser to pump fluctuations. We also compared the noise level of the Ti:sapphire laser when it was pumped by the stabilized argon ion laser to its noise level when it was pumped by an all-solid-state laser; our results indicate that, for frequencies above 125 kHz, the noise of the Ti:sapphire laser was significantly lower when the stabilized argon ion laser was used.

Reduction of optical intensity noise by means of two-photon absorption

We demonstrate an all-optical intensity noise reduction technique by using two-photon absorption of ZnSe in a Z-scan configuration. We measure the nonlinear transmission and the shot-to-shot energy fluctuations of 860-nm intense femtosecond laser pulses. At a 40% nonlinear transmission level the noise in the pulse train is reduced to 24%. This yields an additional 40% reduction in the relative pulse energy fluctuation. A realistic theoretical treatment is presented and is found to be in good agreement with experimental results.