Byung-Min Jung

Optical True Time-Delay for Two-Dimensional

An optical true time-delay (TTD) scheme for two-dimensional (2-D) X-band phased array antennas (PAAs) has been proposed. It is composed of a multiwavelength optical source and a delay line matrix consisting of 2times2 optical microelectromechanical system (MEMS) switches with fiber-optic delay lines connected between cross ports. A 2-bit times 4-bit optical TTD for 10-GHz 2-D PAAs has been implemented by cascading a wavelength-dependent TTD (WD-TTD) with a unit time delay of 12 ps in the x-direction and a wavelength-independent TTD (WI-TTD) with that of 6 ps in the y-direction. The time delay error for WD-TTD was measured to be less than 2.8 ps, mainly due to jitter incurred from gain-switching. On the other hand, the error for WI-TTD was less than 0.8 ps, which is within the equipment resolution. Insertion loss of both delay line matrices was less than 1 dB due to the column-wise control of the MEMS switches. This prevents the feed current applied to each antenna element from fluctuating at any radiation angles so that antenna gain and sidelobe level do not deteriorate in this scheme

X

A novel vertical directional coupler switch with a switching-operation-induced section and an extinction-ratio-enhanced section is proposed. Switching operation is achieved by changing the refractive indexes of both cores in the switching-operation-induced section, and an improvement of extinction ratios larger than 30 dB for both cross and bar states is achieved by controlling the asymmetry of the refractive indexes of two cores in the extinction-ratio-enhanced section without changing the refractive index of the inner-cladding layer between the two waveguides. The required refractive indexes for the cores in the switching-operation-induced and extinction-ratio-enhanced sections are calculated for various thickness of the inner-cladding layer.

-Band Phased Array Antennas

We show that the extinction ratio is improved using slight asymmetry in two core refractive indices of polarization independent very short vertical directional couplers with the double-sided deep-ridge waveguide structure. The optimum asymmetry with the maximum extinction ratio increases as the thicknesses of the inner cladding layer and the two core layers decrease. Also, the device length and the tolerance of the device length with the extinction ratio more than 30 dB decrease as the thicknesses of the inner cladding layer and the two core layers decrease.

A novel vertical directional coupler switch with switching-operation-induced section and extinction-ratio-enhanced section

In this paper, we proposed an optical true time-delay (TTD) for planar phased array antennas (PAAs), which is composed of a wavelength-dependent optical true time delay (WDOTTD) followed by a wavelength-independent optical true time delay (WIOTTD). The WDOTTD is a fiber Bragg gratings (FBGs) Prism and the WDOTTD is a fiber delay-lines matrix of which each component consists of a certain length of fiber connected to cross-ports of a 22 MEMS switch. A 10-GHz 2-bit4-bit two-dimensional optical TTD has been fabricated by cascading a WDOTTD with a maximum time delay of 810 ps to a WIOTTD of 50 ps. Time delay and insertion loss for each radiation angle have been measured. Time delay error for the WIOTTD has been measured to be less than 1 ps. We have also designed a two-dimensional 10-GHz PAA composed of 88 microstrip patch antenna elements driven by the proposed TTD. The radiation patterns of this PAA have been obtained by simulation and analyzed.

Improvement of extinction ratios of polarization independent very short vertical directional couplers

In this paper, an optical true time-delay (TTD) for two-dimensional (2-D) phased array antennas (PAAs), composed of a multi-wavelength optical source and a fiber optic delay line matrix consisting of optical switches with optical fiber connected between cross ports, has been proposed. A 2-bit optical TTD for 10-GHz 2-D PAAs has been implemented by cascading a wavelength dependent TTD (WD-TTD) and a wavelength independent TTD (WI-TTD). The unit time delay for WD-TTD and WI-TTD have been chosen as

Optical True Time-Delay for Planar Phased Array Antennas Composed of a FBG Prism and a Fiber Delay Lines Matrix

{\Delta}T

An Optical True Time-Delay for Two-Dimensional X-Band Phased Array Antennas

In this paper, experimental results on a 4-bit TTD for 10-GHz linear PAA systems are reported, using the optical MEMS switches and fiber-optic delay-lines, This 4-bit TTD is capable of scanning a radiation beam to one of 16 different directions within 200 /spl mu/s.

A 4-bit optical-true time-delay for 10-GHz phased array antennas using optical MEMS switches and fiber-optic delay lines

We show that both cross and bar states with high extinction ratio larger than 30 dB can be achieved in ultrashort (<100 /spl mu/m) fused vertical directional coupler switches with two sections by modifying the refractive indices of cores and inner cladding layers by an amount less than 1%. Transfer matrix method and the improved coupled mode theory are used to analyze these structures and the results are compared with those of 2D finite difference beam propagation method. Also, design guidelines to achieve high extinction ratios with large tolerances are presented.