Magnus T. L. Hsu

Subpicometer length measurement using heterodyne laser interferometry and all-digital rf phase meters

We present an all-digital phase meter for precision length measurements using heterodyne laser interferometry. Our phase meter has a phase sensitivity of 3 μrad/√Hz at signal frequencies of 1 Hz and above. We test the performance of our phase meter in an optical heterodyne interferometric configuration, using an active Sagnac interferometer test bed that is flexible and low noise. We demonstrate more than 70 dB of laser frequency noise suppression to achieve an optical phase sensitivity of 5 μrad/√Hz and a corresponding displacement sensitivity of 0.5 pm/√Hz at signal frequencies above 10 Hz. In addition, we demonstrate the ability of our phase meter to follow full fringe signals accurately at 100 Hz and to track large signal excursions in excess of 10(5) fringes without cycle slipping. Finally, we demonstrate a cyclic error of ≤1 pm/√Hz, above 10 Hz.

All-Digital Radio-Frequency Signal Distribution Via Optical Fibers

We present a radio-frequency (RF) signal distribution system via optical fibers. We utilize an all-digital platform that encompasses a phase-locked loop, numerically-controlled oscillator, and fiber phase noise cancellation system. Our system achieves a fractional frequency transfer stability of 4 × 10-13 at 1 s and 6 × 10-17 at one day for the distribution of RF signals over 70 km of optical fiber. We demonstrate that this performance can be achieved with standard crystal oscillators. Our system is scalable, configurable, and flexible, allowing distribution of signals at different frequencies while maintaining over two orders of magnitude of the fiber phase noise suppression.

Frequency stabilization for space-based missions using optical fiber interferometry

We present measurement results for a laser frequency reference, implemented with an all-optical fiber Michelson interferometer, down to frequencies as low as 1 mHz. Optical fiber is attractive for space-based operations as it is physically robust, small and lightweight. The small free spectral range of fiber interferometers also provides the possibility to prestabilize two lasers on two distant spacecraft and ensures that the beatnote remains within the detector bandwidth. We demonstrate that these fiber interferometers are viable candidates for future laser-based gravity recovery and climate experiment missions requiring a stability of 30 Hz/√Hz over a 10 mHz-1 Hz bandwidth.

Linearization and minimization of cyclic error with heterodyne laser interferometry

We present a method for the linearization and minimization of interferometer cyclic error. We utilize a polynomial curve fitting and resampling algorithm to correct for nonlinear mirror displacement. In the frequency domain, this algorithm compresses cyclic error into a single-frequency component and enables the precise measurement of cyclic error in a noise-dominated environment. We have applied the technique to determine the cyclic error for a range of interferometer components. In addition, we have used these measurements to optimize interferometer configuration and performance such that we routinely achieve a cyclic error of ∼50 pm for our custom Glan-Laser interferometer and ∼100 pm for a commercial interferometer.

Digitally enhanced optical fiber frequency reference

We use digitally enhanced heterodyne interferometry to measure the stability of optical fiber laser frequency references. Suppression of laser frequency noise by over four orders of magnitude is achieved using post processing time delay interferometry, allowing us to measure the mechanical stability for frequencies as low as 100 μHz. The performance of the digitally enhanced heterodyne interferometer platform used here is not practically limited by the dynamic range or bandwidth issues that can occur in feedback stabilization systems. This allows longer measurement times, better frequency discrimination, a reduction in spatially uncorrelated noise sources and an increase in interferometer sensitivity. An optical fiber frequency reference with the stability reported here, over a signal band of 20 mHz-1 Hz, has potential for use in demanding environments, such as space-based interferometry missions and optical flywheel applications.

An optical fiber-based system for high-stability distribution of reference radio-frequencies

We present a novel optical fiber-based radio-frequency distribution system that incorporates low-cost commercially available components. It has a fractional frequency stability of 7×10⁻¹⁷ (averaged over 10⁴ s) for distribution of an 80-MHz signal.

An all optical fiber frequency reference using digital interferometry

We use digitally enhanced heterodyne interferometry to measure the stability of optical fiber laser frequency references. Suppression of laser frequency noise by over four orders of magnitude is achieved using post processing time delay interferometry. This approach avoids dynamic range and bandwidth issues that can occur in feedback stabilization systems. Thus long fiber lengths may be used resulting in better frequency discrimination, a reduction in spatially uncorrelated noise sources and an increase in interferometer sensitivity. We achieve an optical stability of 30 Hz/√Hz for quasi-static frequencies as low as 20 mHz.

An optical fiber interferometer as a frequency reference for space-based laser rangefinding

We demonstrate a fiber interferometer that is a viable candidate for a laser frequency reference for future space-based missions requiring a stability of 30 Hz/√ over a 10 mHz to 1 Hz bandwidth.

Development of a metrological scanning probe microscope incorporating a quartz tuning fork sensor and heterodyne laser interferometry

We present an overview of the design of the metrological scanning probe microscope (mSPM) currently under development at the National Measurement Institute Australia (NMIA) and report on preliminary results on the characterization of key components. The mSPM is being developed as part of the nanometrology program at NMIA and will provide dimensional measurements made at the nanometer scale that are traceable to the realization of the SI meter at NMIA. The instrument will provide an addressable measurement volume of 100 μm × 100 μm × 25 μm with a target uncertainty of 1 nm for the position measurement. It incorporates a quartz tuning fork (QTF) detector and a high-performance heterodyne laser interferometer system.

A digital phasemeter for precision length measurements

We report on a digital phasemeter for application in precision length measurement using laser interferometry. Our interferometer demonstrates a length sensitivity of 0.5 pm/√Hz above 5 Hz, and a cyclic error of better than 50 pm.