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An Inverse Synthetic Aperture LADAR (ISAL) system is capable of providing high resolution surface mapping of near Earth objects which is an ability that has gained significant interest for both exploration and hazard assessment. The use of an ISAL system over these long distances often presents the need to operate the optical system in photon-starved conditions. This leads to a necessity to understand the implications of photon and detector noise in the system. Here a Carrier-to-Noise Ratio is derived which is similar to other optical imaging CNR definitions. The CNR value is compared to the quality of experimentally captured images recovered using the Phase Gradient Autofocus technique both with and without the presence of atmospheric turbulence. A minimum return signal CNR for the PGA to work is observed.

In this paper a wind sensing lidar utilizing a Frequency Stepped Pulse Train (FSPT) is demonstrated. One of the advantages in the FSTP lidar is that it enables direct measurement of wind speed as a function of distance from the lidar. Theoretically the FSPT lidar continuously produces measurements as is the case with a CW lidar, but at the same time with a spatial resolution, and without the range ambiguity originating from e.g. clouds. The FSPT lidar utilizes a frequency sweeping source for generation of the FSPT. The source generates a pulse train where each pulse has an optical carrier frequency shifted a set quantity relative to the carrier frequency of the previous pulse. In the scheme presented here, the measured frequency depends on the distance from which the signal originates. The measured frequency is related to the Doppler frequency shift induced by the wind and an integer number of frequency shifts corresponding to a specific distance. The spatial resolution depends on the repetition rate of the pulses in the pulse train. Directional wind measurements are shown and compared to a CW lidar measurement. The carrier to noise ratio of the FSPT lidar compared to a CW lidar is discussed as well as the fundamental differences between the two systems. In the discussion we describe the most dominant noise sources in our system and what influences these have on the FSPT lidar's ability to measure under different scattering conditions.

In this paper we develop spectral models for windowed speckle-modulated continuous coherent ladar signals with arbitrary coherence time as a function of the window duration and shape. This processing chain (compute the spectrum of the window random signal) is typical for many coherent ladar applications where the target is distributed in range, such as wind lidar. We link the peak of the spectrum to the signal's carrier-to-noise ratio (CNR) and the number of integrated signal photoelectrons. We also develop theoretical models for the SNR of the integrator output and the resultant coherent integration efficiency. In addition, we generalize Goodman's rectangular integrator diversity model to arbitrary window functions and show that the product of diversity and efficiency is close to one for arbitrary integration times and window functions. These general models are then applied to various signal autocorrelation functions and window functions. The analysis demonstrates that the shape of the window function has little impact on the output SNR, efficiency and speckle diversity. We show that if the coherence time is long compared to the integration time then the conventional CNR expression is valid, and the signal has unit diversity and the coherent integration efficiency is 100%. However, when the coherence time is short compared to the integration time, the CNR is reduced by roughly the ratio of these times and the diversity is increased by roughly the same factor. Finally, we also show how signal detectivity is related to SNR and diversity.

This paper deals with several key points including parameter estimation such as frequency of arrival (FOA), time of arrival (TOA) estimation algorithm and signal processing techniques in Medium-altitude Earth Orbit Local User Terminals (MEOLUT) based on Cospas-Sarsat Medium-altitude Earth Orbit Search and Rescue system (MEOSAR). Based on an analytical description of distress beacon, improved TOA and FOA estimation methods have been proposed. An improved FOA estimation method which integrates bi-FOA measurement, FFT method, Rife algorithm and Gaussian window is proposed to improve the accuracy of FOA estimation. In addition, TPD algorithm and signal correlation techniques are used to achieve a high performance of TOA estimation. Parameter estimation problems are solved by proposed FOA/TOA methods under quite poor Carrier-to-Noise (C/N0). A number of simulations are done to show the improvements. FOA and TOA estimation error are lower than 0.1Hz and 11μs respectively which is very high system requirement for MEOSAR system MEOLUT.

The purpose of this study was to investigate which illumination arrangement can provide the highest image quality when using a non-invasive cutaneous imaging system to observe capillaries in nail-fold. We captured the microcirculation images with and without a band-pass filter which wavelength is 556 ± 10 nm in front of a 150 Watt halogen lamp. Furthermore, we varied the illumination angle form 90 degree (co-axial light) to 20 degree to evaluate the image quality under different light source arrangements. The image registration function was used to solve the image movement problem which is due to breathing or slightly movement of volunteers or the imaging device. The contrast-to-noise ratio (CNR) is an evaluation factor to quantify the image quality. The dynamic search method was used to find out the skeleton of a vessel and define the foreground and background parameters for calculating contrast. A Gaussian smooth filter was applied to the original images and noise was resulted from differentiating the coefficient of variance (CV) of the original and processed images. As a result, using a green filter in front of a lamp presents the highest contrast-to-noise ratio when the illumination angle is 20 degree. By normalizing the highest CNR to 1, the CNR of other illumination conditions are 0.49 (without filter, 20 degree), 0.39 (with filter, 90 degree) and 0.28 (without filter, 90 degree), respectively. It is concluded that using a green light source with an illuminating angle of 20 degree will provide better image quality than other arrangements.

Using silicide material as a recording layer, we have achieved good results for a Super-RENS disc. By mainly controlling noble-metal and metal mixture ratio, signal quality was greatly enhanced.

Putting germanium nitride thin-films between Sb-Te and ZnS-SiO2 was effective to improve super-resolution readout durability of a super-RENS disc using PtOx-SiO2 recording layer. 260,000 times readout was possible with CNR over 40 dB.

We proposed a novel linearization technique for DFB LD in Radio-over-Fiber. The proposed scheme is using light injection based on cross-gain modulation (XGM) effect. We experimentally demonstrated and evaluated the enhanced CNR performance using the proposed scheme.

Emerging wide-area synthetic aperture radar (SAR) system concepts call for a single data collection platform to orbit a large (e.g, 20 km) spot at a nominal range of 40 km. The large standoff distance and desire for fine resolution, coupled with a need for persistent real-time sensing, pose a significant challenge in terms of clutter-to-noise ratio (CNR) performance and data processing. Increased CNR and reduced processing load can be achieved by decreasing the range of the SAR system and the size of the area of interest. Employing multiple cooperating SAR systems allows the same overall coverage area to be maintained with a patchwork of SAR footprints. This paper analyzes a high-level system architecture, for multiple SAR systems, that provides uninterrupted coverage over a wide area. System analysis includes eclipsing diagrams, CNR performance and mutual interference issues.

Automatic target recognition (ATR) performance is a function of image quality and its representation in the signature model generation and used in the ATR training process. This paper reports ATR performance as a function of synthetic aperture radar (SAR) image quality parameters including clutter-to-noise ratio (CNR) and multiplicative noise ratio (MNR). Images with specified image quality values were produced by introducing controlled degradations to the MSTAR public release data. Two different families of ATR algorithms, the statistical model-based classifier of DeVore, et al., and optimal tradeoff synthetic discriminant function (OTSDF) are applied to those data. Target classification accuracy was measured as a function of CNR/MNR for both the training and test data, indicating sensitivity of performance to a priori knowledge of these particular image quality parameters. Confusion matrices are expanded to include target aspect bins, providing visibility into performance as a function of aspect angle.

Coherent laser radars observing a resolved (larger than the incident laser mode) target vibrating surface can estimate the target's piston-mode displacement motion from the target's Doppler produced frequency spectrum. We review recent work showing that a newly developed joint time-frequency transform algorithm is superior to older joint time-frequency transforms, the common short-time-Fourier transform (spectrogram) algorithm, and other elementary spectral estimation algorithms for resolving the target's spectra. In this paper we extend these approaches when the ladar is observing an unresolved (smaller than the incident laser mode) piston-mode vibrating object situated on the ground. Because the target is smaller than the laser spot, the surrounding ground produces a narrow-band constant frequency "clutter" signal at the baseband frequency. We show that a recently developed "sech-window" joint time-frequency transform is superior to other algorithms for separating the frequency modulated target piston motion signal from the narrow-band ground return. The analysis in this case includes a "signal-to-clutter ratio" (SCR) parameter variation as well as a "carrier-to-noise ratio" (CNR), or target signal strength to LO-laser noise strength, parameter variation.

We report the random pattern signal characteristics of the super resolution near field structure (Super-RENS) disk in a blue laser optical system. (Laser wavelength 405 nm, numerical aperture 0.85) We introduced new structure for blue laser system, which results in 43 dB carrier to noise ratio (CNR) at the 75 nm mark length signal (which is equivalent to 50 GB capacity with 0.32 micrometer track pitch) and much better readout stability were obtained. The relatively clear eye pattern, phase locked loop (PLL) state and data to clock jitter of around 20% for a 50 GB (2T:75 nm) random pattern signal were realized.

New Ga doped GeSb based phase-change materials are investigated. These materials possess good optical contrast at short wavelengths. Crystallization temperature increasing and grain size refinement are obtained by addition of Ga. More than 50 dB CNR and 25 dB erasability are measured in disks using blue laser.

A hybrid dense-wavelength-division-multiplexing (DWDM) system for CATV, 256-QAM and OC-48 trunking is demonstrated. It used two wavelengths for AM-VSB CATV, two wavelengths for 256-QAM digital passband signals and four wavelengths for OC-48 (2.5 Gb/s) digital baseband signals transport. Good performances of carrier-to-noise ratio (CNR) >50 dB, composite second order (CSO) >64 dB and composite triple beat (CTB) >63 dB were obtained for AM-VSB CATV; and low bit error rate (BER

Fiber optic based CATV distribution systems may need very high powers prior to distribution. High optical powers can be obtained using a cladding pumped fiber amplifier. The performance of an analog transmission system using a high power cladding pumped fiber amplifier has been investigated. Analog signals from a 120-channel CATV signal generator was used to directly modulate 1550 nm distributed feed back laser. The output was amplified to ~1W using a cladding pumped fiber amplifier. The carrier to noise ratio (CNR), composite second order (CSO) and composite triple beat (CTB) of the composite analog signals were measured before and after amplification. No significant change in CNR, CSO and CTB signals were observed which suggests that the amplifier does not introduce any additional non-linearity. Similar experiment was also carried out using a hybrid digital/analog system where the carrier at 223.25 MHz was modulated at 2Mb/s using the BPSK modulation format. Bit error rate (BER) of

A new cyanine dye thin film has been prepared for high-density digital versatile disc-recordable (DVD-R) by means of a spin- coating process. The effects of the optical and thermal properties of the cyanine dye on the recording characteristics were studied. Rapid decomposition of the cyanine dye in a narrow temperature range, which is critical to the clear mark edges, is shown in this paper. A steep absorption edge at the 635 nm is crucial to high reflectivity. The optical recording performance of the cyanine dye thin film shows that high reflectivity contrast (48%) can be obtained at low writing power and narrow writing pulse-width using He-Ne laser (632.8 nm) irradiation. The carrier to noise ratio (CNR) of the single layer disk is greater than 40 dB at the traveling rate of 2.4 m/s.

A coherent array detection system can improve the heterodyne mixing efficiency compared to a conventional coherent detection system which is limited by the finite transverse coherence length of received laser field due to atmospheric turbulence for laser radar and communications. This implies a gain factor in the mean power of the IF signal from the coherent array detection system compared to the conventional coherent detection system even though the two systems receive the same power of laser signal. This gain factor is actually the mean carrier-to-noise ratio (CNR) gain factor of the coherent array detection over the conventional coherent detection if the two systems have the same local oscillator and are shot noise-limited of the local oscillator. But the mean CNR gain factor depends on the conditions of atmospheric turbulence. This paper describes the theoretical analyses of the mean CNR gain factor for the coherent array detection system under different conditions of atmospheric turbulence which include weak, strong, and saturation conditions, corresponding to the lognormal, the K, the I-K, the negative exponential (Rayleigh for amplitude), and the gamma (Nakagami for amplitude) distributions for the laser intensity fluctuations.

In this paper, a cyanine film has been prepared by spin- coating process on the pre-grooved polycarbonate substrate. The transmission, reflection and absorption spectra of the film were measured. The complex refractive index n, k of the film was calculated. Under the recording condition specified by CD-R Orange Book, the carrier to noise ratio (CNR) of the single dye layer disk are greater than 47 dB at traveling rate of 1.4 m/s, 2.8 m/s, and 5.6 m/s. The estimated lifetime of the CD-R using this dye film as the recording medium reaches up to 10 years under normal using condition.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Using a novel organic dye-phthalocyanine compound, organic dye media for write-once optical recording were obtained by vacuum sublimation. The new media exhibited satisfactory optical recording characteristics and provided write-in power 20%, and the ratio of carrier to noise > 45%.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper presents a general method of measuring the carrier-to-noise ratio (C/N) on a sample servo (SS) media. A media spectra model was also developed and it is in good agreement with our experimental results.

Overwrite characteristics have been studied for Ge-Sb-Te phase change media under high linear velocity conditions, ranging from 11.3 m/s to 22.6 m/s, with mark-edge-recording (MER). The Ge 1 Sb 4 Te 7 recording layer composition was chosen for the rapid cooling structure to obtain a sufficient erase ratio under high linear velocity conditions. The optical optimization for the disk structure and the narrow-grooved substrate have been applied to improve erase characteristics with MER. The optical phase-difference-reproduction (PDR) has been studied to realize a high carrier to noise ratio (C/N). The pulse-width-reduction (PWR) recording compensation has been developed for high recording density. A 44.8 dB C/N was obtained for 0.68 micrometers minimum recording mark length. A -26.8 dB erase ratio was obtained at 22.6 m/s linear velocity.

A feasibility of phase change media to an erasable compact disk (CD) was studied. We proposed a quadrilayered optical disk having a recording layer of Ge 12 Sb 39 Te 49 thin film. The ternary material film was crystallized and also amorphized reversibly by laser irradiation of 0.7 microsecond(s) . This transition time was appropriate for the CD which revolves at 1.2-1.4 m/s. A multi-pulse (MP) recording method was also proposed to record EFM signals without teardrop shaped distortions. On the revolving disk, each recording mark of amorphous state was formed by irradiation of 'multi-pulses': a set of one preceding longer pulse and succeeding shorter pulses. Newly developed simple electric circuit for producing the MP waveform was examined to overwrite the single frequency signals of 196 kHz and 720 kHz, alternatively using only one laser beam. As a result, carrier to noise ratio (CNR) of more than 50 dB, secondary harmonic distortion (SHD) of -40 dB, and erasability of 40 dB were obtained. It was observed by a transmission electron microscope that the teardrop shaped distortion of the recording mark was reduced. Eight to fourteen modulation (EFM) signals of the audio CD format were also overwritten successfully and a clear eye-pattern was confirmed. The combination of the GeSbTe phase change media and the MP recording method will be applicable to the erasable compact disk.

Studies on relationships between single beam overwrite characteristics and physical and chemical properties of the phase change recording media and their mechanisms are reviewed. Improvements in overwrite characteristics based on these studies, especially improvements in carrier to noise ratio(C/N) and the life of recorded dots by the addition of one of the transition metal elements or Tt are also reported. The maximum C/N was 61dB and the estimated life of the recorded dots is longer than 100 years at 60°C.

Laser beam is focused on a rotating disk. As the reflected light intensity VDC is modulated by irregularity of an optical disk surface, noise VAC in the VDC is observed. Effect of the irregularity of the optical disk surface is given by S/ND = 20 log(VDC/2√2VAC). If the noise is not increased in recording and the reflected light is modulated 100% by the carrier signal in playback, carrier to noise ratio C/N reaches this S/ND. The carrier signal was recorded on an Al-Cr thin film (observed S/ND was 81 dB) on the glass substrate (S/ND was 87 dB), obtained C/N was 69 dB.

In an optical data storage system, a small-size and light weight optical head is required for high speed track access. A holographic optical element(HOE), which can be combined with focusing error detecting function, tracking error detecting function and beam splitting function, has high potential to realize a small size optical head1). To enable applying the HOE for a magneto-optical(MO) head, it is required that the HOE possesses polarizing characteristics in the HOE's beam splitting function2). For this requirement the authors have developed an MO head using reflection polarizing HOE(R-PHOE). This paper describes the design for the R-PHOE, optical head configuration, fabrication of the R-PHOE and head operation characteristics.

Environmental test results are presented for write-once optical storage media produced by vacuum deposition of a thin film of platinum on a textured polycarbonate substrate that is produced from an interferometrically generated master. This type of storage media can be produced in large quantities using a simple production process. The disk construction is briefly described. Accelerated ageing tests were undertaken on 130mm diameter disks using high temperature and high humidity environments for both continuous and cycled conditions. The resultant changes in defect error rate, bit error rate, carrier to noise ratios and reflectivity are presented. Lifetime in a typical office environment is evaluated. This study indicates that these platinum based optical disks exhibit very long shelf and archival lifetimes and are capable of withstanding harsh environments.

Many optical recording media companies characterize media properties using carrier to noise measurement methods. While this method is easily accomplished with off-the-shelf measurement equipment, it has proven to be a very unreliable method of characterizing the performance of optical recording materials. Optical recording data channel is known to have several unique features relating to nonlinearities and multiplicative noise sources which makes the use of carrier to noise ratio measurements ambigious or inaccurate. Alternative measures of making performance measurements using signal to noise ratio parameters provides substantially greater accuracy, eliminate the ambiguities and provide better insight into the operating properties of the recording material. Signal to noise ratio measurements (SNR) are made using a digitizer and software processing of the data channel output. SNR measurements are useful to both media and drive companies unlike CNR measurements which are useful only as a qualitative measure presented by media companies. The purpose of this paper is to evaluate the differences between CNR and SNR measurement and to show the substantial improvement in characterization accuracy which can be achieved by SNR measurements.

The effect of the groove profile on the characteristic properties of a magneto-optical (MO) disk with a quadrilayer structure (A1N/GdTbFe/A1N/A1) prepared on a glass substrate was investigated, using a micro Kerr-effect measuring apparatus. Taking a diffraction effect into account, we have calculated the dependence of signal quality on the groove profile, being in agreement with experiments. The carrier to noise ratio reaches to 51 dB at high recording density where the bit length is 1.0 μm. In order to obtain a better understanding of the reliability of the MO disk, the MO disks were exposed to various environments with respect to temperatures and humidities. Though the readout signals of recorded bits do not change after the aging tests, the recording sensitivity is reduced slightly after exposing at high temperatures. Therefore, the lifetime of the MO disk depends upon the stability of recording sensitivity and was evaluated as about 18 years using the Arrhenious equation.

A new single beam overwrite method for a phase-change optical disk is proposed to obtain both high carrier to noise ratio (CNR) and high overwrite erasing ratio. Contrary to ordinary method is, both writing and erasing process are controlled over the melting point of a phase-change recording film. To realize new overwriting method, we discuss desired thermal characteristics of a disk and crystallization properties of recording film theoretically. Necessary conditions to realize this method are (1) optical disks must have high thermal conductivity to control cooling rate, (2) recording material may have adequate crystallizing tine within dynamic range of disk's cooling rate. Examination on this method was carried out by using newly developed In-Sb-Te phase-change optical disk. CNR higher than 50dB and erasing ratio higher than 40dB were obtained.

One of the problems to be solved for the development of magneto-optical disc drivers is how to detect signals with a good carrier to noise ratio. The birefringence observed in the disc substrate is one of the factors which give serious effect on the ratio.1 We have studied the optical anisotropy of injection molded polycarbonate substrate and found that the optic axis representing the birefringence is almost perpendicular to the disc surface though it has been widely believed that the axis is parallel to the surface. Based upon the newly found fact, we have calculated the effect of the birefringence upon the carrier to noise ratio.

A single-beam overwrite was achieved by an In-Sb-Te phase-change optical disk. The carrier to noise (C/N) ratio of more than 50 dB and the overwrite modulation of -40 dB were obtained for overwriting frequencies of 2 MHz and 3 MHz using a low power laser diode of 30 The high C/N ratio and the excellent overwrite modulation were due to the large reflectivity difference between the written and erased phases and the use of suitable write/erase power.

Thin film media composed of Te-Te02 (TeOx) containing Pd additive was found to have a feasibility of being applied to high reliability data file optical disks. The carrier to noise ratio (C.N.R.) exceeds 56 dB at 1,200 r.p.m. disk rotation. The response time of saturation amplitude after a pulsed laser power irradiation was less than 300 nsec and is able to apply to high speed read verify systems. From acceleration environmental stress test results, no defect variation was observed. By the Arrhenius plot method, the disk life has been estimated to be more than 10 years at the storage environment 32 degree C, 80 %RH. The recording and degradation mechanism will be also discussed.© (1987) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.