Ultrabroadband optical chirp linearization for precision metrology applications

Abstract

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.

Multi-dimensional, non-contact metrology using trilateration and high resolution FMCW ladar

“…This laser is actively frequency stabilized to a fiber interferometer using the techniques described in Ref [1]. For these experiments the chirp repetition rate was 30 Hz and approximately 8 ms per repetition period was utilized providing 1.6 THz bandwidth and a Fourier window limited range resolution 94 µm.…”

“…Experimental 2D Trilateration System using FMCW Ladar A stabilized chirped laser source [1] that is amplified with a 1 W EDFA provides an optical fiber delivered FMCW signal that is first split into a 90% path transmission to the target (Tx) and a 10% path that forms the Local Oscillator path (LO). The latter is used as a reference to mix with the returned signal (Rx) providing coherent optical gain and down conversion of the optical information to the RF regime.…”

“…Frequency Modulated Continuous Wave (FMCW) ladar due to its ability to provide much higher bandwidth (100's GHz to a few THz) and range resolution than other ladar and lidar systems is gaining in interest for imaging and noncontact metrology systems [1], [2]. The sub-millimeter range resolution provided by the large bandwidth and the high sensitivity provided by coherent detection allows these FMCW ladar systems to make micron level precision range measurements at standoffs exceeding 10 m and to multiple simultaneous returns [3].…”

Dispersion compensation method based on focus definition evaluation functions for high-resolution laser frequency scanning interference measurement

“…By adjusting the injection current and piezoelectric ceramics (PZT) through an electrical feedback loop, the optical frequency generated by the laser became linear. In turn, a measurement resolution of 31 µm was reached at a distance of 1.5 m [10].…”

Field-programmable gate array-controlled sweep velocity-locked laser pulse generator

“…A closed loop control system based on an optical phase-locked loop (OPLL) that modifies laser output frequency in real-time offers an alternative approach to precisely controlling optical sweep speed (14,15). Recently, a digital-controlled chirped pulse laser based on a digital phase-locked loop (DPLL) design was reported based on modular electronic design (16).…”