Chirped Amplitude Modulation Research Articles

Ranging disambiguation of LiDAR using chirped amplitude-modulated phase-shift method.

Ranging ambiguity is the major challenge in most LiDAR techniques with amplitude modulation, which limits the performance of range detection due to the tradeoff between the ranging precision and the unambiguous range. Here we propose a novel disambiguation method using a laser with chirped amplitude modulation (sweeping modulation frequency), which can in theory infinitely expand the unambiguous range and completely solve the ranging ambiguation problem. The usage of the earlier proposed Chirped Amplitude-Modulated Phase-Shift (CAMPS) technique enables us to detect the phase-shift of chirped signals with high precision. Incorporating this technique with the proposed disambiguation method, the absolute distance well beyond the conventional unambiguous range can easily be found with merely <1% frequency sweep range. When certain conditions are met, the Non-Mechanical Spectrally Scanned LiDAR (NMSL) system employing the CAMPS method and the Dispersion-Tuned Swept Laser (DTSL) can also realize disambiguation in non-mechanical line-scanning measurement.

Experimental investigation of chirped amplitude modulation heterodyne ghost imaging.

We have constructed a chirped amplitude modulation heterodyne ghost imaging (CAM-HGI) experimental system that demonstrates a robust ability against background light in experiments. In the experiments, the background light is simulated by irradiating a spatiotemporal random modulated light field onto the target. The effects of background light, modulation depth and modulation duration of the signal light source on CAM-HGI are investigated experimentally. The results show that the quality of CAM-HGI can be improved by increasing the modulation depth and the modulation duration of the signal light source, and more importantly, an image with a good signal-to-noise ratio (SNR) can be achieved even when the irradiation SNR is lower than -30 dB. This technique of CAM-HGI has an important application prospect for laser imaging in strong background light environments.

Detection performance improvement of photon counting chirped amplitude modulation lidar with response probability correction**Project supported by the Fundamental Research Funds for the National Defense Basic Scientific Research, China (Grant No. JCKY2016603C007).

Geiger mode avalanche photodiode detector (Gm-APD) possesses the ultra-high sensitivity. Photon counting chirped amplitude modulation (PCCAM) light detection and ranging (lidar) uses the counting results of the returned signal detected by Gm-APD to mix with the reference signal, which makes PCCAM lidar capable of realizing the ultra-high sensitivity, and this is very important for detecting the remote and weak signal. However, Gm-APD is a nonlinear device, different from traditional linear detectors. Due to the nonlinear response of Gm-APD, the counting results of the returned signal detected by Gm-APD are different from those of both the original modulation signal and the reference signal. This will affect the mixing effect and thus degrade the detection performance of PCCAM lidar. In this paper, we propose a response probability correction method. First, the response probability correction model is established on the basis of Gm-APD Poisson probability response model. Then, the response probability correction model is used to adjust the original modulation signal that is used to drive laser, in order to make the counting results of the returned signal detected by Gm-APD better mix with the local reference signal in the same form. Through this method, the detection performance of PCCAM lidar is enhanced efficiently.

Photon-counting chirped amplitude modulation lidar system using superconducting nanowire single-photon detector at 1550-nm wavelength**Project supported by National Key R&D Program of China (Grant No. 2017YFA0304000), the National Natural Science Foundation of China (NSFC) (Grant Nos. 61501442 and 61671438), and the Joint Research Fund in Astronomy (U1631240) under Cooperative Agreement between the NSFC and Chinese Academy of Sciences (CAS).

We demonstrate a photon-counting chirped amplitude modulation (CAM) light detection and ranging (lidar) system incorporating a superconducting nanowire single-photon detector (SNSPD) and operated at a wavelength of 1550 nm. The distance accuracy of the lidar system was determined by the CAM bandwidth and signal-to-noise ratio (SNR) of an intermediate frequency (IF) signal. Owing to a short dead time (10 ns) and negligible dark count rate (70 Hz) of the SNSPD, the obtained IF signal attained an SNR of 42 dB and the direct distance accuracy was improved to 3 mm when the modulation bandwidth of the CAM signal was 240 MHz and the modulation period was 1 ms.

Design and implement of 9 × 9 fiber array processing of chirp AM lidar

Compared with single-pulse detecting laser radar, the Chirp AM (Amplitude modulation) lidar with advantages of higher range resolution, higher precision, and stronger anti-jamming ability, has a wide application prospect in laser terminal guidance, terrain mapping and other fields. This paper focuses on design and implement of 9×9 fiber array processing of chirp AM lidar, mainly including 9×9 fiber receiving array, 81-channel broad band down conversion and 81-channel signal processing. The detection experiment in which range resolution is 0.249m and angular resolution is 0.6mrad is done, which lays a foundation for development and engineering application of chirp AM lidar.

Premixing photon-counting chirped amplitude modulation lidar for range and velocity measurement in photon starved scenes

A symmetric chirped amplitude modulation of the up-ramp and the down-ramp is implemented on the basis of previous work of premixing photon-counting chirped amplitude modulation lidar. This system is capable of obtaining the range and velocity of target simultaneously in photon starved scenes due to the high sensitivity of single-photon detectors. With the advantages of the premixing method this system breaks the limit of the maximum modulation frequency of the chirped amplitude modulation signal by the sampling rate of the Gm-APD and allows the use of much higher fundamental frequency and modulation bandwidth to improve the range and velocity detection accuracy. This paper demonstrates the working principle of this system, and analyzes the relationship of accuracy and system parameters from theory and experiment.

Photon-Counting Chirped Amplitude Modulation Lidar With 1.5-GHz Gated InGaAs/InP APD

We demonstrated a photon-counting chirped amplitude modulation (CAM) Lidar at 1550 nm. In the previous studies, the CAM bandwidth was limited <;30 MHz due to the large dead time of the single-photon detectors. In our CAM Lidar system, an InGaAs/InP avalanche photodiode was operated in 1.5-GHz sine-wave gated Geiger mode to reduce the dead time to 6.4 ns. As a result, the CAM bandwidth exceeded 200 MHz, while the modulation period was 0.5 ms, leading to a direct distance accuracy of 0.12 m in daylight environment. This system presented a potential for high accuracy and eye-safe CAM Lidar system.

Photon-counting chirped amplitude modulation lidar using a smart premixing method

We proposed a new premixing method for photon-counting chirped amplitude modulation lidar (PCCAML). Earlier studies used the counting results of the returned signal detected by a Geiger mode avalanche photodiode detector (Gm-APD) to mix with the reference signal, called the postmixing method. We use an alternative method known as the premixing method, in which the reference signal is used to directly modulate the sampling gate width of the Gm-APD, and the mixing of the returned signal and the reference signal is completed before the Gm-APD. This premixing method is more flexible and may perform better than the postmixing method in terms of signal-to-noise ratio by cutting down a separated mixer commonly used in the postmixing lidar system. Furthermore, this premixing method lowers the demand for the sampling frequency of the Gm-APD. It allows the use of a much wider modulation bandwidth to improve the range accuracy and resolution. To the best of our knowledge, this is the first report to use the premixing method in the PCCAML system, which will benefit future lidar applications.

Method to improve the signal-to-noise ratio of photon-counting chirped amplitude modulation ladar

Photon-counting chirped amplitude modulation (PCCAM) ladar employs Geiger mode avalanche photodiode as a detector. After the detector corresponding to the echo signal is reflected from an object or target, the modulation depth (MD) of the detection outputs has some certain loss relative to that of the transmitting signal. The signal-to-noise ratio (SNR) of PCCAM ladar is mainly determined by the MD of detection outputs of the echo signal. There is a proper echo signal intensity that can decrease the MD loss and improve the SNR of the ladar receiver. In this paper, an improved PCCAM ladar system is presented, which employs an echo signal intensity optimization strategy with an iris diaphragm under different signal and noise intensities. The improved system is demonstrated with the background noise of a sunny day and the echo signal intensity from 0.1 to 10 counts/ns. The experimental results show that it can effectively improve the SNR of the ladar receiver compared with the typical PCCAM ladar system.

Androgens regulate differences in chirp duration in the weakly electric fish Parapteronotus hasemani

Event Abstract Back to Event Androgens regulate differences in chirp duration in the weakly electric fish Parapteronotus hasemani Jacquelyn Petzold1* and G. Troy Smith1, 2, 3 1 Indiana University - Bloomington, Department of Biology, United States 2 Indiana University - Bloomington, Center for the Integrative Study of Animal Behavior, United States 3 Indiana University - Bloomington, Program in Neuroscience, United States Apteronotid electric fish produce a continuous electric organ discharge (EOD) that functions in electrolocation and communication. The frequency and amplitude of the EOD can be modulated during reproductive and agonistic interactions to produce chirps. In several species, EOD frequency and chirping are sexually dimorphic traits that are regulated by steroid hormones (Zakon & Smith, 2009). However, the signal parameters that differ between the sexes vary greatly among species. We tested how EOD frequency and chirping vary between and within sexes in Parapteronotus hasemani, a species of South American weakly electric fish with extreme sexual dimorphism in body size. We performed playbacks of species-typical EODs to male and female P. hasemani to quantify EOD frequency and chirping. EOD frequency, chirp rate, and chirp amplitude modulation were not sexually dimorphic. However, males produced chirps that were longer in duration than those of females. Thus, chirp duration, but not EOD frequency, is a sexually dimorphic trait that may be used as an honest indicator of sex in P. hasemani. As with sexually dimorphic communication signals in many species, sex differences in EODs and chirping in electric fish are often regulated by androgens (Zakon & Dunlap, 1999). We treated male P. hasemani with the androgen receptor blocker flutamide to test whether androgens maintain male-typical chirp duration. Chirp duration decreased significantly in males treated with flutamide but not in males treated with vehicle. This suggests that sex differences in electrocommunication signals in P. hasemani are likely regulated by activational effects of androgens. Jaw morphology varies substantially among male P. hasemani and may be correlated with age or social status (Cox Fernandes, 2010). To determine whether morphological variation in males was associated with variation in gonadal steroid levels, we measured hormones (11KT, T) and morphology (jaw length, body length, and body mass). Unlike other species of fish that have morphologically distinct classes of males (Bass, 1992), larger males with longer jaws did not have higher concentrations of 11KT. Circulating concentrations of T and 11KT were not correlated with jaw morphology, body size, or EOD frequency in males. Additionally, EOD frequency and chirping were not correlated with jaw length or body size. The lack of a correlation of EOD and chirp parameters with hormone levels or morphological traits in males suggests that these signals may not necessarily serve as reliable indicators of male quality. Acknowledgements Supported by NSF IOS 0950721 and the Indiana University Center for the Integrative Study of Animal Behavior. Keywords: electrocommunication, Hormones, sex differences Conference: Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012. Presentation Type: Poster (but consider for student poster award) Topic: Hormones and Sex Differences Citation: Petzold J and Smith G (2012). Androgens regulate differences in chirp duration in the weakly electric fish Parapteronotus hasemani. Conference Abstract: Tenth International Congress of Neuroethology. doi: 10.3389/conf.fnbeh.2012.27.00336 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 30 Apr 2012; Published Online: 07 Jul 2012. * Correspondence: Ms. Jacquelyn Petzold, Indiana University - Bloomington, Department of Biology, Bloomington, IN, 47405, United States, jpetzold@indiana.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. 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Detection performance improvement of chirped amplitude modulation ladar based on Gieger-mode avalanche photoelectric detector

This paper presents an improved system structure of photon-counting chirped amplitude modulation (AM) ladar based on the Geiger-mode avalanche photoelectric detector (GmAPD). The error-pulse probability is investigated with statistical method. The research shows that most of the error pulses that are triggered by noise are distributed in the intensity troughs of the chirped AM waveform. The error-pulse probability is lowered with the sliding window and the threshold. With the average intensity of noise and signal being 0.3 count/sample and 1 count/sample, respectively, the probability of error pulses is reduced from 12% to 1.0%, and the SNR is improved by 2.2 dB in the improved system.

Development of an all-fiber heterodyne lidar for range and velocity measurements

A 1550-nm all-fiber monostatic lidar system based on linear chirp amplitude modulation and heterodyne detection for the measurements of range and velocity is presented. The signal processing method is given, after which the relationship between the peak frequency values in the final signal spectrum, the target's range, and the line-of-sight velocity is obtained in the presence of the fiber end-face-reflected signal plaguing many monostatic lidar systems. The range of an electric fan as well as the line-of-sight fan speed of different levels is tested. This proposed system has a potential application for the space-borne landing system.

Phylogenetic comparative analysis of electric communication signals in ghost knifefishes (Gymnotiformes: Apteronotidae)

Electrocommunication signals in electric fish are diverse, easily recorded and have well-characterized neural control. Two signal features, the frequency and waveform of the electric organ discharge (EOD), vary widely across species. Modulations of the EOD (i.e. chirps and gradual frequency rises) also function as active communication signals during social interactions, but they have been studied in relatively few species. We compared the electrocommunication signals of 13 species in the largest gymnotiform family, Apteronotidae. Playback stimuli were used to elicit chirps and rises. We analyzed EOD frequency and waveform and the production and structure of chirps and rises. Species diversity in these signals was characterized with discriminant function analyses, and correlations between signal parameters were tested with phylogenetic comparative methods. Signals varied markedly across species and even between congeners and populations of the same species. Chirps and EODs were particularly evolutionarily labile, whereas rises differed little across species. Although all chirp parameters contributed to species differences in these signals, chirp amplitude modulation, frequency modulation (FM) and duration were particularly diverse. Within this diversity, however, interspecific correlations between chirp parameters suggest that mechanistic trade-offs may shape some aspects of signal evolution. In particular, a consistent trade-off between FM and EOD amplitude during chirps is likely to have influenced the evolution of chirp structure. These patterns suggest that functional or mechanistic linkages between signal parameters (e.g. the inability of electromotor neurons increase their firing rates without a loss of synchrony or amplitude of action potentials) constrain the evolution of signal structure.

Soliton control in chirped photonic lattices

We study optical solitons in chirped periodic optical lattices whose amplitude or frequency changes in the transverse direction. We discover that soliton propagation in such lattices can be accompanied by the progressive self-bending of the soliton trajectory, and we show that the soliton bending rate and output position can be controlled by varying the lattice depth, as well as the chirp amplitude and frequency modulation rate. This effect has potential applications for controllable soliton steering and routing.

Modeling of the static and dynamic responses of an integrated laser Mac-Zehnder modulator and comparison with an integrated laser EA modulator

In an integrated laser Mach-Zehnder modulator (ILMZ), as well as in an integrated laser electroabsorption (EA) modulator (ILM), optical feedback can lead to a high level of frequency chirp and relaxation oscillations, compared to the case of a laser coupled into a discrete external modulator through an optical isolator. To investigate these aspects, in the particular case of the ILMZ, an original model has been developed. Analytical expressions of the frequency modulation (FM) and amplitude modulation (AM) responses of two types (2/spl times/1 and 2/spl times/2 output couplers) of ILMZ are given by the model, and the direct and indirect contributions to the FM responses are identified. The model can be used in the design and optimization of the ILMS, aiming at a small optical frequency chirp and small AM perturbation at resonance frequency. Numerical simulation of the small signal response (AM and FM modulations) has been performed for both ILMZ configurations and an ILM. A lower chirp is obtained for the ILMZ compared to the ILM. A high extinction ratio and a low negative effective chirp parameter are predicted at output B of the 2/spl times/2 ILMZ, as well as for the /spl pi/-phase-shifted 2/spl times/1 ILMZ.

Evoked chirping in the weakly electric fish Apteronotus leptorhynchus: a quantitative biophysical analysis

Apteronotus leptorhynchus, a gymnotiform fish, produces highly regular electric organ discharges of 600–1000 Hz. Short-term modulations of the electric organ discharge ("chirps") were elicited by imitating the discharges of neighboring fish. Chirps displayed an increase in frequency of approximately 100 Hz, a duration of about 15 ms, and an absolute amplitude of 0.5–2 mV. Since, similar to natural conditions, chirps summated with the beat caused by interference of the fish's own electric organ discharge and the imitating discharge, the size and shape of the chirp's amplitude envelope varied greatly according to its phase relative to the beat cycle; however, the frequency of the chirp amplitude modulation was always 50–100 Hz. All 21 males examined chirped, but their rate of chirping varied considerably (range 2–59 chirps/30 s; mean 22 chirps/30 s). In contrast, only one out of nine females chirped (mean 0.25 chirps/30 s). The latency between stimulus onset and first chirp was variable and often long (range 1.0–25.0 s; median 3.3 s). We propose that chirps are not a sensory reflex but a communicatory behavior regulated by hypothalamic peptidergic input.