Range selective phase-shifting frequency-modulated digital holography with temporal-heterodyning.

We demonstrate that a time of flight (TOF) camera can be used to perform range selective temporal-heterodyne frequency-modulated continuous wave digital holography (TH FMCW DH). The modulated arrayed detection of a TOF camera allows efficient integration of holograms at a selected range with range resolutions significantly less than the optical system's depth of field. TH FMCW DH also allows for on-axis geometries to be achieved, where background light not at the internal modulation frequency of the camera is filtered out. Range selective TH FMCW DH imaging was achieved for both image holograms and Fresnel holograms using on-axis DH geometries. A 2.39 GHz FMCW chirp bandwidth resulted in a DH range resolution of 6.3 cm.

Range selective digital holographic imaging using FMCW lidar.

The integration of chirped frequency modulated continuous wave (FMCW) lidar techniques into digital holography enables range selective holographic imaging well beyond the depth of field of the system. The technique uses FMCW transmit and reference beams. By frequency shifting the reference beam to compensate for the typical FMCW beat frequency associated with a particular range, temporally stable holograms are formed for objects at the selected range. The holograms associated with objects at all other ranges oscillate and integrate towards zero. Experimental demonstrations of the technique are presented, showing enhanced imaging of objects at different ranges and cancellation of obscuring objects. The technique is expandable to range-Doppler selective digital holographic imaging.

Digital holographic polarimeter using dual reference beam interferometry.

An off-axis digital holographic imaging polarimeter was developed to estimate the Jones matrices of an object. The Jones vector image of the electric field returned from the object is determined from a single holographic recording using the interference between the dual, nearly orthogonal, reference beams. The technique compensates for phase variations in the optical beam paths between the recorded holograms and relaxes the need to generate orthogonal illumination polarization states. A minimization algorithm was developed to compute an estimation of the Jones matrix image of an object based on a set of measured Jones vector images. A proof-of-concept demonstration was performed to compute an estimated Jones matrix image of a polarimetrically complex object using digital holograms recorded with 6 different illumination polarizations.

Compressive laser ranging.

Compressive sampling has been previously proposed as a technique for sampling radar returns and determining sparse range profiles with a reduced number of measurements compared to conventional techniques. By employing modulation on both transmission and reception, compressive sensing in ranging is extended to the direct measurement of range profiles without intermediate measurement of the return waveform. This compressive ranging approach enables the use of pseudorandom binary transmit waveforms and return modulation, along with low-bandwidth optical detectors to yield high-resolution ranging information. A proof-of-concept experiment is presented. With currently available compact, off-the-shelf electronics and photonics, such as high data rate binary pattern generators and high-bandwidth digital optical modulators, compressive laser ranging can readily achieve subcentimeter resolution in a compact, lightweight package.

Conditions for highly efficient anti-Stokes conversion in gas-filled hollow core waveguides.

Using a four-mode theoretical analysis we show that highly efficient anti-Stokes conversion in waveguides is more challenging to realize in practice than previously thought. By including the dynamics of conversion to 2(nd) Stokes via stimulated Raman scattering and four-wave mixing, models predict only narrow, unstable regions of highly efficient anti-Stokes conversion. Experimental results of single-pass Raman conversion in confined capillary waveguides validate these predictions. This places more stringent conditions on systems that require highly efficient single-pass anti-Stokes conversion.

Accuracy of active chirp linearization for broadband frequency modulated continuous wave ladar.

As the bandwidth and linearity of frequency modulated continuous wave chirp ladar increase, the resulting range resolution, precisions, and accuracy are improved correspondingly. An analysis of a very broadband (several THz) and linear (<1 ppm) chirped ladar system based on active chirp linearization is presented. Residual chirp nonlinearity and material dispersion are analyzed as to their effect on the dynamic range, precision, and accuracy of the system. Measurement precision and accuracy approaching the part per billion level is predicted.

Ultrabroadband optical chirp linearization for precision metrology applications.

We demonstrate precise linearization of ultrabroadband laser frequency chirps via a fiber-based self-heterodyne technique to enable extremely high-resolution, frequency-modulated cw laser-radar (LADAR) and a wide range of other metrology applications. Our frequency chirps cover bandwidths up to nearly 5 THz with frequency errors as low as 170 kHz, relative to linearity. We show that this performance enables 31-mum transform-limited LADAR range resolution (FWHM) and 86 nm range precisions over a 1.5 m range baseline. Much longer range baselines are possible but are limited by atmospheric turbulence and fiber dispersion.

Multigigahertz range-Doppler correlative signal processing in optical memory crystals.

Analog optical signal processing of complex radio-frequency signals for range-Doppler radar information is theoretically described and experimentally demonstrated using crystalline optical memory materials and off-the-shelf photonic components. A model of the range-Doppler processing capability of the memory material for the case of single-target detection is presented. Radarlike signals were emulated and processed by the memory material; they consisted of broadband (> 1 GHz), spread-spectrum, pseudorandom noise sequences of 512 bits in length, which were binary phase-shift keyed on a 1.9 GHz carrier and repeated at 100 kHz over 7.5 ms. Delay (range) resolution of 8 ns and Doppler resolution of 130 Hz over 100 kHz were demonstrated.