Boo-Gyoun Kim

Optical true time-delay feeder for X-band phased array antennas composed of 2/spl times/2 optical MEMS switches and fiber delay lines

We proposed an optical true time-delay (TTD) feeder for X-band linear phased array antennas (PAAs), which possesses high-speed beam scan capability by selecting different lengths of fiber delay lines with fast 2/spl times/2 optical microelectromechanical system switches. For proof of concept, a 3-bit optical TTD has been built for a 10-GHz linear PAA composed of two antenna elements. Experimental results show that the maximum time-delay error is less than 0.2 ps, corresponding to a radiation angle error of less than 0.84/spl deg/, which is within the equipment resolution. We have also designed a 10-GHz linear PAA composed of eight microstrip patch antenna elements driven by the proposed TTD. The radiation patterns of this PAA have been obtained by simulation.

Blue light generation by resonator‐enhanced frequency doubling of an extended‐cavity diode laser

Frequency doubling of diode laser radiation was achieved by operating an AR‐coated diode laser in an extended laser cavity which contained a monolithic potassium niobate frequency doubling resonator as an intracavity element. Extended cavity operation ensured that the diode laser would oscillate only at frequencies that were resonant with the intracavity resonator. A diffraction grating was used to ensure single mode oscillation at the wavelength needed for noncritically phase‐matched second harmonic generation. At 100 mA of injection current to the GaAlAs diode laser, 14 mW of 429 nm light were produced.

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 vertical directional coupler fabricated using wafer fusion is demonstrated with a very short coupling length of 62 μm. The optical propagation loss introduced by the fused layer is investigated. An excess loss of 1.1 dB/cm at 1.55 μm was measured for waveguides which incorporate a fused junction near the core region. Fused vertical couplers make it possible to realize three-dimensional waveguide structures and compact switching arrays and they solve some of the topology problems of large switch arrays.

-Band Phased Array Antennas

The quad-band antenna, which is composed of two compact dual-band antennas, is presented for portable media player (PMP) applications. The antenna for the broadcasting dual band (DVB-H UHF: 470-862 MHz; L: 1452-1492 MHz) is composed of a planar inverted-F antenna (PIFA) with self-complementary structure (SCS) for the broadband performance. The measured operation bandwidth of the antenna (VSWR <; 4) is 500 MHz (370-870 MHz) at UHF band and 220 MHz (1300-1520 MHz) at L band. The two-channel WLAN multiple-input-multiple-output (MIMO) antenna with high isolation performance for the telecommunication dual band (WLAN 11b: 2.4-2.5 GHz; 11a: 5.15-5.825 GHz) is composed of a PIFA operating at 2-GHz band and a loop antenna operating at 5-GHz band. The proposed antennas are fabricated in a PMP case (εr = 3.2 ).

FUSED VERTICAL COUPLERS

Multisection semiconductor lasers for optical microwave generation have been fabricated that consist of a loss-coupled distributed feedback (LC-DFB), a phase control, and an amplifier section. High-frequency self-pulsations are generated according to the concept of a single-mode laser with short optical feedback. The effect of the optical feedback via the phase control and the amplifier section on the self-pulsation is apparently shown as a result of the superior single-mode characteristic of the LC-DFB section. Continuous frequency tuning is achieved in the range of 17-35 GHz.

Quad-Band Antenna With High Isolation MIMO and Broadband SCS for Broadcasting and Telecommunication Services

Wafer fusion technique for realization of compact waveguide switches and three-dimensional (3-D) photonic integrated circuits is investigated theoretically and experimentally. Calculations based on beam propagation method show that very short vertical directional couplers with coupling lengths from 40 to 220 /spl mu/m and high extinction ratios from 20 to 32 dB can be realized. These extinction ratios can be further improved using a slight asymmetry in waveguide structure. The optical loss at the fused interface is investigated. Comparison of the transmission loss in InGaAsP-based ridge-loaded waveguide structures with and without a fused layer near the core region, reveals an excess loss of 1.1 dB/cm at 1.55 /spl mu/m wavelength. Fused straight vertical directional couplers have been fabricated and characterized. Waveguides separated by 0.6 /spl mu/m gap layer exhibit a coupling length of 62 /spl mu/m and a switching voltage of about 2.2 V. Implications for GaAs-based fused couplers for 850 nm applications will also be discussed.

Loss-coupled distributed-feedback lasers with amplified optical feedback for optical microwave generation

Radiation characteristics of an inductive loaded patch phased array antenna (PAA) are compared to those of a conventional patch PAA. The performance of an inductive loaded patch PAA is significantly improved compared to that of a conventional patch PAA because the mutual coupling between the adjacent inductive loaded patch antennas is very small compared to that between the adjacent conventional patch antennas. The radiation characteristics of an inductive loaded patch PAA show superior performance such as low variations of the main beam gain and sidelobe level over the variation of the main beam direction.

Wafer-fused optoelectronics for switching

A dual-band (UHF: 470-862 MHz; L: 1452-1492 MHz) Digital Video Broadcasting-Handheld (DVB-H) antenna is presented. The proposed antenna is composed of a planar inverted-F antenna (PIFA) with an input impedance matching circuit. The matching circuit improves antenna performance in the broad UHF bands (470-862 MHz: 63%). The proposed antenna has omnidirectional patterns and sufficient gain (average peak gain over 470-862 MHz: 0.9 dBi) for the portable media player (PMP) applications. The antenna is contact with a PMP case (εr = 3.2), which is used as a substrate for the size reduction and compact design.

A Linear Phased Array Antenna Composed of Inductive Loaded Patch Antennas

Various means of increasing the extinction ratio in ultra short directional couplers using slight asymmetry in the coupled waveguide structure are investigated. It is shown that couplers with 10–200 µm coupling length and with high extinction ratios larger than 30 dB can be achieved. Shorter asymmetric couplers have an extinction ratio that is more fabrication tolerant.