A derivative and subtractive equalization (DSE), which simultaneously transmits both four-level pulse amplitude modulation (PAM-4) and discrete multitone (DMT) signals encoded by quadrature amplitude phase shift keying (QPSK) with the same bandwidth, is proposed. The proposed DSE recovers the DMT signal by tracking the change of derivative value between adjacent sampling points and then subtracting the recovered PAM-4 signal after derivative value tracking from the received signals. A 20-km optical link is implemented to experimentally verify the proposed DSE technique. The bit error rate (BER) of the PAM-4 signal (1 Gbaud) and the error vector magnitude (EVM) of QPSK signal (1 Gbaud) are measured in order to examine the difference in transmission performance before and after using the proposed DSE technique. The 20% EVM of QPSK signal and the 5.4 × 10 − 5 BER of PAM-4 signal is observed at the 25% power ratio of DMT signal to PAM-4 signal. It is found that the signal-to-noise ratio of input PAM-4 and DMT signal should be 25 and 40 dB, respectively, with the 7% forward error correction to successfully transmit them at the same time. The 4-dB power penalty is observed before and after using DSE technique. These experimental results tell us that the transmission capacity of 4 times the bandwidth can be achieved using the proposed DSE technique.
We investigate the relationship between an optical pulse shape and a time lens implemented by means of sinusoidal phase modulation. Based on this investigation, two schemes are proposed to obtain an optical frequency comb (OFC) with exceptionally high flatness and a large number of spectral lines by carving an optical pulse shape to result in a quasilinear chirp via a simple sinusoidal phase modulation technique. The first scheme utilizes an intensity modulator with a single-drive port or with dual-drive ports to carve a narrow pulse. The experimental results show very good spectral profiles with 38 OFC lines at 1.2-dB flatness and 53 lines at 1.5-dB flatness when the intensity modulator is combined with two and three phase modulators for sinusoidal phase modulation, respectively. The second scheme is implemented by replacing the intensity modulator by a dual-parallel Mach–Zehnder modulator (DP-MZM). In this case, we obtain 35 OFC lines at nearly perfect flatness of less than 1 dB and 53 lines at 1.5-dB flatness after combining the DP-MZM with two and three phase modulators, respectively.
We present Augmented Lazy Snapping, an interactive image segmentation algorithm. We investigate the presegmentation step in the Lazy Snapping method and find the method can be improved by changing the middle layer of segmentation pipeline. To be more specific, we try different segmentation algorithms instead of watershed algorithm to find the optimal one for the pre-segmentation step. Augmented Lazy Snapping method can provide better segmented results with the fewer over-segmented regions. Moreover, it improves the efficiency of graph cut solution.
KEYWORDS: Digital signal processing, Frequency shift keying, Modulation, Demodulation, Quadrature amplitude modulation, Light emitting diodes, Phase shift keying, Signal to noise ratio, Frequency modulation, Binary data
A nonorthogonal amplitude, phase, and frequency modulation (APFM) technique that can increase the transmission capacity of an optical wireless link based on white light-emitting diode (LED) is proposed. It is implemented by the simultaneous use of nonorthogonal frequency shift keying (FSK) and quadrature amplitude modulation (QAM). A white LED-based wireless link using a 64-APFM scheme is constructed to experimentally verify the proposed technique, where the 64-APFM scheme is implemented by the combination of nonorthogonal 4-FSK and 16-QAM. Two more bits per symbol are transmitted using the proposed scheme with the same bandwidth of QAM. No intercarrier interference effect is observed at the 0.02-% frequency spacing (0.001 MHz) for the used RF carrier (5 MHz) because the correlation between the received 64-APFM signal and only one carrier at a time is accomplished with the help of digital signal processing. 6-Mbit/s (1-Msymbol/s) data are successfully transmitted through an optical wireless channel with a limited bandwidth of 1 MHz. This indicates that six bits per symbol can be transmitted using the proposed APFM technique at the same physical bandwidth as 16-QAM.
We propose a technique that improves the channel capacity of an optical wireless orthogonal frequency division multiplexing (OFDM) transmission, which employs a visible light-emitting diode. An OFDM waveform encoded by quadrature phase shift keying (QPSK) or 16-quadrature amplitude modulation is compressed and then transformed into a sparse waveform using a proposed advanced systematic sampling. At the optical wireless receiver, the original waveform is recovered by L1-minimization based on a Bayesian compressive sensing. Our experimental results show the significant increase in the channel capacity from 31.12 to 51.87 Mbit/s at forward error correction limit (i.e., error vector magnitude of 32%) in case of QPSK symbols.
We demonstrate a simple method to generate a high speed pulse train from a low speed pulse source by spectral filtering using a high finesse fiber Fabry-Pérot interferometer. Reasonably stable 100 GHz pulses at 1550 nm were obtained from a 10 GHz mode-locked fiber laser.
KEYWORDS: Detection and tracking algorithms, Modulation, Frequency modulation, Fermium, Signal processing, Reticles, Digital signal processing, Interference (communication), Demodulation, Analog electronics
A counter-countermeasures (CCM) algorithm in a target tracking system is required for efficient target tracking under countermeasures (CM) such as infrared flares. Most of the CCM algorithms employ some forms of spectral band discrimination to distinguish between a target and CM. We adopt two detection bands based on the spectral distribution characteristics (SDC) of a target and flares and define the energy ratio between the two band signals (MNR) to represent their SDC and to distinguish them. The proposed algorithm computes the MNR of the incident band signals and its histogram, detects the MNR of flare signal from the histogram, and extracts target signal only from the target and flare mixed signal. To estimate the performance of the proposed algorithm, we simulate it under various conditions. The simulation results show that the proposed algorithm can eliminate the effect of CM well.
Air-to-Air Homing Missile has widely adopted infrared seeker, which makes use of thermal energy emitted from the target to detect it exactly. The target is equipped with countermeasure (CM) such as flare to protect itself from homing missile. The purpose of this paper is to develop counter-countermeasure (CCM) to cope with the CM operated by the target. Not only the radiant features of the target but also that of the flare at ultraviolet band have been compared and analyzed to select the band that can effectively remove the effects of the flare. We use a reference level for removal of the noise effects and the background. The simulation results show that our CCM algorithm can detect precisely the target location in spite of the presence of the flare.
KEYWORDS: Missiles, Target detection, Signal detection, Field emission displays, Signal processing, Gyroscopes, Imaging infrared seeker, Computer simulations, 3D acquisition, Detection and tracking algorithms
The IR seeker is a device that detects heats radiated from a target and provides the target position with servo system of the missile. Among various kinds of seekers, the rosette- scanning seeker ins a tracker in which a single IR detector scans the total field of view (TFOV) in a rosette pattern, and then produces 2D image about a target. Since the detected image has various shapes according to the target position in the TFOV, it is necessary that we investigate the tracking algorithm applicable to the different shapes. In this paper, we present a comparative study of the projective and the moment technique among the various target tracking techniques. Using the 3 degree-of-freedom simulator, we evaluate two algorithms and confirm the better performance of the moment technique as a tracking one.
In order to analyze the aqueous ammonia, we developed a simple and an inexpensive spectrometer, which consisted of a diode laser, an optical fiber with a dipping probe and a photodiode detector. Preliminary results are described here on the performances of the system in terms of the stability of output intensity, sensitivity, and reproducibility. Data on the comparisons of the system with the conventional UV- VIS spectrometer were also given. With the standard indophenol method, the detection limit for the system is 39 (mu) g/L which affords enough sensitivity for the determination of ammonia down to (mu) g/L level. The method was applied to the determination of ammonia in environmental samples including rain and snow. The results shown here indicate a potential for developing a new portable spectrometer useful for the on-site monitoring of environmental samples.
Ultra-short optical pulse generation from gain-switched semiconductor lasers is important for applications such as time-division multiplexed optical communication systems, optical sampling, and soliton generation. Considerable research interest has been focused on reducing pulse widths to sub-picosecond levels. However, as the pulse width is made shorter, pulse-to-pulse timing jitter becomes important and can limit system performance, through such parameters as bit error rate and temporal resolution. Recent work shows that self or, external injection-seeding reduces timing jitter in gain-switched Fabry-Perot (FP) lasers.1,2 We report an experimental investigation of the impact of external seeding on timing jitter in gain-switched FP and distributed feedback (DFB) lasers and show that the timing jitter can be greatly reduced by external injection-seeding with continuous (CW) light, regardless of the laser structure, i.e., FP or DFB. We also show that there exists an optimum seeding power to obtain short pulses with low timing jitter.
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