Simplified Homodyne Detection for FM Chirped Lidar

The investigation of global warming requires more sensitive altimeters to better map the global ice reserves. A homodyne detection scheme for FM chirped lidar is developed in which dechirping is performed in the optical domain, simplifying both the optical and the RF circuits compared to heterodyne detection. Experiments show that the receiver sensitivity approaches the quantum limit and surpasses the performance of direct and heterodyne detection. In addition, the required electrical bandwidth of the photodiode and receiver RF circuitry are both significantly reduced, facilitating the use of large area photodetector arrays. A field trial using a 5"-aperture diameter telescope and a 370-m target range verified the sensitivity estimation and demonstrates the feasibility of this technique. The problem of homodyne carrier fading is addressed by incorporating a phase diversity receiver using a 90-degree optical coupler. Finally, an outline of the future direction of research is given

Fully digital intensity modulated LIDAR

AbstractIn several applications, such as collision avoidance, it is necessary to have a system able to rapidly detect the simultaneous presence of different obstacles. In general, these applications do not require high resolution performance, but it is necessary to assure high system reliability also within critical scenarios, as in the case of partially transparent atmosphere or environment in presence of multiple objects (implying multiple echoes having different delay times.) This paper describes the algorithm, the architecture and the implementation of a digital Light Detection and Ranging (LIDAR) system based on a chirped optical carrier. This technique provides some advantages compared to the pulsed approach, primarily the reduction of the peak power of the laser. In the proposed architecture all the algorithms for signal processing are implemented using digital hardware. In this way, some specific advantages are obtained: improved detection performance (larger dynamics, range and resolution), capability of detecting multiple obstacles having different echoes amplitude, reduction of the noise effects, reduction of the costs, size and weight of the resulting equipment. The improvement provided by this fully digital solution is potentially useful in different applications such as: collision avoidance systems, 3D mapping of environments and, in general, remote sensing systems which need wide distance and dynamics

Range-Speed Mapping and Target-Classification Measurements of Automotive Targets using Photonic-Radar

The frequency-modulated continuous-wave radar is an ideal choice for autonomous vehicle and surveillance-related industries due to its ability to measure the relative target-velocity, target-range, and target-characterization. Unlike conventional microwave radar systems, the photonic radar has the potential to offer wider bandwidth to attain high range-resolution at low input power requirements. Subsequently, a frequency-modulated continuous-wave photonic-radar is developed to measure the target-range and velocity of the automotive mobile targets concurrently with acceptable rang resolution keeping in mind the needs of the state-of-the-art autonomous vehicle industry. Furthermore, the target-identification is also an important parameter to be measured to enable the futuristic autonomous vehicles for the recognition of the objects along with their dimensions. Therefore, the reported work is extended to characterize the target-objects by measuring the specular-reflectance, diffuse-reflectance, the ratio of horizontal-axis to vertical-axis, refractive index constants of the targets using the bidirectional reflectance distribution function. Furthermore, the reflectance properties of the target-objects are also measured with different operating wavelengths at different incident angles to assess the influence of the operating wavelength and the angle at which the radar-pulses incident on the surface of the targets. Moreover, to validate the performance of the demonstrated work, a comparison is also presented in distinction with the conventional microwave FMCW-RADAR

Frequency-modulated Chirp Signals for Single-photodiode Based Coherent LiDAR System

In this paper, we investigate two categories of linear frequency-modulated chirp signals suitable for single-photodiode based coherent light detection and ranging (LiDAR) systems, namely, the frequency-modulated continuous-wave (FMCW) single-sideband (SSB) signal and the amplitude-modulated double-sideband (DSB) signal, and compare their achievable receiver sensitivity performance. The DSB signal requires a simpler transmitter design, as it is real-valued and can be generated using a single-drive Mach-Zehnder modulator (MZM), while the SSB signal, which is frequency/phase modulated, requires an in-phase and quadrature modulator (IQM)-based transmitter. A theoretical analysis of direct-detection (DD) beating interference (BI) especially the local oscillator (LO) beating with itself, known as LO-LO BI, is presented. Both Monte Carlo simulations and experimental demonstrations are carried out. Good agreement between simulations and experiments is achieved. In comparison with the SSB system, the DSB signal-based system is affected by laser phase noise-induced power fluctuation, and also suffers a significant sensitivity penalty due to nonlinear LO-LO BI. A spectral guard band for mitigating LO-LO BI is necessary for the DSB signal, achieved at the expense of requiring a larger electrical bandwidth. In system tests with a delay line of 385 m, the SSB signal outperforms the DSB signal with a 10 dB better receiver sensitivity in the case with a guard band, and 25 dB better sensitivity without a guard band

NASA SBIR abstracts of 1990 phase 1 projects

The research objectives of the 280 projects placed under contract in the National Aeronautics and Space Administration (NASA) 1990 Small Business Innovation Research (SBIR) Phase 1 program are described. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses in response to NASA's 1990 SBIR Phase 1 Program Solicitation. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 280, in order of its appearance in the body of the report. The document also includes Appendixes to provide additional information about the SBIR program and permit cross-reference in the 1990 Phase 1 projects by company name, location by state, principal investigator, NASA field center responsible for management of each project, and NASA contract number

The NASA SBIR product catalog

The purpose of this catalog is to assist small business firms in making the community aware of products emerging from their efforts in the Small Business Innovation Research (SBIR) program. It contains descriptions of some products that have advanced into Phase 3 and others that are identified as prospective products. Both lists of products in this catalog are based on information supplied by NASA SBIR contractors in responding to an invitation to be represented in this document. Generally, all products suggested by the small firms were included in order to meet the goals of information exchange for SBIR results. Of the 444 SBIR contractors NASA queried, 137 provided information on 219 products. The catalog presents the product information in the technology areas listed in the table of contents. Within each area, the products are listed in alphabetical order by product name and are given identifying numbers. Also included is an alphabetical listing of the companies that have products described. This listing cross-references the product list and provides information on the business activity of each firm. In addition, there are three indexes: one a list of firms by states, one that lists the products according to NASA Centers that managed the SBIR projects, and one that lists the products by the relevant Technical Topics utilized in NASA's annual program solicitation under which each SBIR project was selected

Small business innovation research. Abstracts of 1988 phase 1 awards

Non-proprietary proposal abstracts of Phase 1 Small Business Innovation Research (SBIR) projects supported by NASA are presented. Projects in the fields of aeronautical propulsion, aerodynamics, acoustics, aircraft systems, materials and structures, teleoperators and robots, computer sciences, information systems, data processing, spacecraft propulsion, bioastronautics, satellite communication, and space processing are covered

Ultra Wideband Impulse Radio Superregenerative Reception

Postprint (published version