Telecommunication technologies

Hong–Ou–Mandel peak and NOON interference.

(a) Schematic shows HOM peak experiment arrangement. Red indicates on-chip spatial mode beamsplitter, and blue indicates fibre beamsplitter. Pairs of photons are simultaneously coupled into the fundamental mode (input port 1) and higher-order mode (input port 2) of the on-chip spatial mode beamsplitter. To determine the fundamental mode HOM peak, the photons from the fundamental mode (output port 1) are sent to a fibre beamsplitter, and coincidences are measured using detectors and coincidence logic. The same is done for the higher-order HOM peak using output port 2. (b) Coincidence rate of the fundamental mode output arm after the fibre beamsplitter. There is a peak in coincidences due to HOM bunching. (c) Coincidence rate of the higher-order mode output arm after the fibre beamsplitter. (d) Schematic shows NOON interference experiment arrangement. Red indicates the on-chip spatial mode beamsplitter. Pairs of photons are simultaneously coupled into the fundamental mode (input port 1) and higher-order mode (input port 2) of the on-chip spatial mode beamsplitter. The two photons are sent to the spatial mode phase shifter based on an integrated microheater that applies a phase shift (φ) between the fundamental and higher-order modes. Finally, coincidences are measured using detectors and coincidence logic. (e) Classical Mach–Zehnder interference is shown as a function of heater power that applies the phase shift. (f) NOON interference is shown as a function of heater power. The period of the quantum interference is half that of the classical interference. The error bars indicate standard error of measurement for all plots.


Derivation:
The derivation of the reflection coefficient and attenuation of a waveguide path involves the use of electromagnetic field theory and waveguide boundary conditions. The reflection coefficient and attenuation can be calculated using Maxwell's equations and the transmission line model.
A passive phased array or passive electronically scanned array (PESA) is a phased array in which the antenna elements are connected to a single transmitter and/or receiver, as shown in the first animation at top. PESAs are the most common type of phased array. Generally speaking, a PESA uses one receiver/exciter for the entire array.
An active phased array or active electronically scanned array (AESA) is a phased array in which each antenna element has an analog transmitter/receiver (T/R) module which creates the phase shifting required to electronically steer the antenna beam. Active arrays are a more advanced, second-generation phased-array technology which are used in military applications; unlike PESAs they can radiate several beams of radio waves at multiple frequencies in different directions simultaneously. However, the number of simultaneous beams is limited by practical reasons of electronic packaging of the beam formers to approximately three simultaneous beams for an AESA. Each beam former has a receiver/exciter connected to it.
A hybrid beam forming phased array can be thought of as a combination of an AESA and a digital beam forming phased array. It uses subarrays that are active phased arrays (for instance, a subarray may be 64, 128 or 256 elements and the number of elements depends upon system requirements). The subarrays are combined to form the full array. Each subarray has its own digital receiver/exciter. This approach allows clusters of simultaneous beams to be created.
A digital beam forming (DBF) phased array has a digital receiver/exciter at each element in the array. The signal at each element is digitized by the receiver/exciter. This means that antenna beams can be formed digitally in a field programmable gate array (FPGA) or the array computer. This approach allows for multiple simultaneous antenna beams to be formed.
A conformal antenna is a phased array in which the individual antennas, instead of being arranged in a flat plane, are mounted on a curved surface. The phase shifters compensate for the different path lengths of the waves due to the antenna elements' varying position on the surface, allowing the array to radiate a plane wave. Conformal antennas are used in aircraft and missiles, to integrate the antenna into the curving surface of the aircraft to reduce aerodynamic drag.