Closed-loop Interferometer Research Articles

On the apodized integrated Bragg grating as a binary generator in SI-MZI circuits comprising double closed-loop interferometer

On the apodized integrated Bragg grating as a binary generator in SI-MZI circuits comprising double closed-loop interferometer

High performance fiber optic gyroscope with a radiation-tolerant and temperature-stable scale factor

A simple wavelength-independent scale factor model is established for a closed-loop interferometer fiber optic gyroscope (IFOG) and a method to keep the scale factor radiation tolerant and temperature stable in a high performance IFOG for space application is proposed. The half-wave voltage (Vπ) of the multifunction gyro chip at different wavelengths and temperatures is measured and the radiation-independent inherent parameter of the modulator is picked out and found be proportional to the temperature and slightly wavelength dependent. An experimental IFOG is developed and the scale factor is measured at different temperatures and under Co60 irradiation, respectively. Less than a 10 ppm scale factor instability is achieved within the −40°C to +60°C temperature range and more than 100 krad(Si) total radiation dose.

Oscillating holograms recorded in photorefractive crystals by a frequency detuned feedback loop

We report an optoelectronic feedback loop suitable for generating noise-free interference patterns oscillating at arbitrary waveforms. The technique allows controlling the frequency detuning between the interfering beams through a phase modulator in a closed-loop interferometer. We use the dither signal method and propose a quasisynchronous demodulation scheme to create a phase modulated error signal for driving the loop. The dynamics of the interference fringes is easily controlled by a voltage waveform from a function generator, which is used in association with a time delay circuit for shifting the frequency of the reference signal used for lock-in demodulation. The technique is specially suited for applications involving low-frequency phase oscillations, such as those frequently encountered in the generation of space-charge waves in highly resistive photorefractive materials. The processing scheme allows real time monitoring of the hologram strength, and absolute values for the diffraction efficiency and the holographic phase shift can be obtained. Photorefractive wave oscillations ranging from approximately 100 mHz to 10 Hz were produced in a nominally undoped Bi12TiO20 sample. The technique can be readily applied to other fields of optical interferometry, such as for testing optical surfaces, optimizing adaptive holographic devices, measuring physical quantities, among other applications.

Beating of Aharonov-Bohm oscillations in a closed-loop interferometer

One of the points at issue with closed-loop-type interferometers is beating in the Aharonov-Bohm (AB) oscillations. Recent observations suggest the possibility that the beating results from the Berry-phase pickup by the conducting electrons in materials with the strong spin-orbit interaction (SOI). In this study, we also observed beats in the AB oscillations in a gate-defined closed-loop interferometer fabricated on a $\mathrm{Ga}\mathrm{As}∕{\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}$ two-dimensional electron-gas heterostructure. Since this heterostructure has very small SOI, the picture of the Berry-phase pickup is ruled out. The observation of beats in this study, with the controllability of forming a single transverse subband mode in both arms of our gate-defined interferometer, also rules out the often-claimed multiple transverse subband effect. It is observed that nodes of the beats with an $h∕2e$ period exhibit a parabolic distribution for varying the side gate. These results are shown to be well interpreted, without resorting to the SOI effect, by the existence of two-dimensional multiple longitudinal modes in a single transverse subband. The Fourier spectrum of measured conductance, despite showing multiple $h∕e$ peaks with the magnetic-field dependence that are very similar to that from strong-SOI materials, can also be interpreted as the two-dimensional multiple-longitudinal-modes effect.

Charge detection in a closed-loop Aharonov-Bohm interferometer

We report on a study of complementarity in a two-terminal closed-loop Aharonov-Bohm interferometer. In this interferometer, the simple picture of two-path interference cannot be applied. We introduce a nearby quantum point contact to detect the electron in a quantum dot inserted in the interferometer. We found that charge detection reduces but does not completely suppress the interference even in the limit of perfect detection. We attribute this phenomenon to the unique nature of the closed-loop interferometer. That is, the closed-loop interferometer cannot be simply regarded as a two-path interferometer because of multiple reflections of electrons. As a result, there exist indistinguishable paths of the electron in the interferometer and the interference survives even in the limit of perfect charge detection. This implies that charge detection is not equivalent to path detection in a closed-loop interferometer. We also discuss the phase rigidity of the transmission probability for a two-terminal conductor in the presence of a detector.