Yongqiang Jiang

80-micron interaction length silicon photonic crystal waveguide modulator

An ultracompact silicon electro-optic modulator was experimentally demonstrated based on silicon photonic crystal (PhC) waveguides for the first time to our knowledge. Modulation operation was demonstrated by carrier injection into an 80μm-long silicon PhC waveguide of a Mach-Zehnder interferometer (MZI) structure. The π phase shift driving current, Iπ, across the active region is as low as 0.15mA, which is equivalent to a Vπ of 7.5mV when a 50Ω impedance-matched structure is applied. The modulation depth is 92% operating at 1567nm.

Dispersion-enhanced photonic crystal fiber array for a true time-delay structured X-band phased array antenna

Tunable optical true time-delay modules based on highly dispersive photonic crystal fibers (PCFs) are demonstrated to provide continuous radio-frequency squint-free beam scanning for an X-band (8-12 GHz) phased array antenna system. The dispersion of the fabricated PCF is as high as -600 ps/nm /spl middot/ km at 1550 nm. The time delay is continuously tunable from -31 to 31 ps between adjacent delay lines by tuning the laser wavelength continuously from 1528 to 1560 nm. The far field radiation patterns of a 1/spl times/4 subarray were measured from -45/spl deg/ to 45/spl deg/ scanning angles. Squint-free operation is experimentally confirmed.

Design of a broadband highly dispersive pure silica photonic crystal fiber

A highly dispersive dual-concentric-core pure silica photonic crystal fiber is designed with a maximum chromatic dispersion value of about -9500 ps/(nm km) around the 1.56 microm wavelength region and a full width at half-maximum (FWHM) of 55 nm. The change in the dispersion-bandwidth product as a function of period is carefully studied by using the plane wave expansion method. The coupled mode theory matches well with the plane wave expansion method that was used to simulate the chromatic dispersion. This kind of a photonic crystal fiber structure is suitable for high-dispersion application in phased array antenna systems based on photonic crystal fiber arrays.

2-bit reconfigurable true time delay lines using 2/spl times/2 polymer waveguide switches

A 2-bit (four delays) polymer waveguide delay device is demonstrated and characterized. The device is composed of polymer waveguide delay lines, optical fiber delay lines, and polymer thermooptical 2/spl times/2 switches. The insertion loss for the fully integrated device ranges between 8.12 and 9.81 dB depending on the delay path chosen. The polarization-dependant loss is 0.04 dB. Measured delays are 0, 37.8, 160.4, and 199.2 ps. The switching speed is less than 4 ms. The designed polymer waveguide delays match well with the measured values.

Nano-photonic crystal waveguides for ultra-compact tunable true time delay lines

Nanophotonics including photonic crystals promises to have a revolutionary impact on the landscape of photonics technology. Photonic crystal line defect waveguides show high group velocity dispersion and slow photon effect near transmission band edge. By using photonic crystal waveguides to build true time delay based phased array antenna or other optical signal processing systems, the length of the tunable true time delay lines can be dramatically reduced inversely proportional to group velocity dispersion in dispersion enhanced system architecture or reduced inversely proportional to group index in slow photon enhanced system architecture. The group index of the fabricated silicon photonic crystal line defect waveguide is experimentally demonstrated as high as 40 at optical wavelength around 1569 nm. The group velocity dispersion of the fabricated silicon photonic crystal line defect waveguide is as high as 50 ps/nm∙mm at wavelength around 1569 nm, which is more than 107 times the dispersion of the standard telecom fiber (D = 3 ps/nm∙km). Due to the integration nature of photonic crystals, system-on-chip integration of the true time delay modules can be easily achieved.

Continuously delay-time tunable-waveguide hologram module for X-band phased-array antenna

Tunable optical true time-delay modules based on a dispersive waveguide hologram are presented to provide continuous radio-frequency beam scanning for an X-band (8-12 GHz) phased-array antenna system. The true time-delay modules operating in the 1550-nm region were fabricated with continuously tunable time delays from 5 to 64 ps. The far-field radiation patterns were measured with different delay combinations and the continuity of the scanning angles from 35/spl deg/ to 55/spl deg/ was experimentally confirmed at X-band frequencies.

True-time-delay modules based on a single tunable laser in conjunction with a waveguide hologram for phased array antenna application

A wavelength-controlled continuous beam-steering four-element X-band (8- to 12-GHz) phased array antenna system is presented. The system is based on the continuously tunable optical true-time-delay technique. Dispersion-enhanced waveguide holograms were proposed and used to fabricate the optical true-time-delay devices. The devices are characterized both theoretically and experimentally. The wavelength of a laser was tuned within the system to get continuously tunable true time delay. The time delay was measured for a wavelength tuning range from 1537 to 1547 nm in 10-nm steps. The far-field radiation patterns of the antenna system were measured at 9 and 10.3 GHz, and they showed no beam squint. The true-time-delay formation idea presented here is suitable for not only X-band, but also for higher microwave frequencies, such as K-band.

Highly dispersive photonic crystal fibers for true-time-delay modules of an x-band phased array antenna

•A two-dimensional optically controlled phased array antenna (PAA) system is proposed. The system employs highly dispersive photonic crystal fibers (HDPCFs) to provide the true-time-delays (TTD). Independent azimuth and elevation control is obtained through a mid-stage optical wavelength conversion process. The dispersion of the fabricated is as high as -600 ps/nmkm around 1550 nm which is 33 times of conventional telecom SMF. By employing the PCFs to increase the dispersion, the TTD module size can be proportionally reduced. A 64-element (8x8) PCF-based PAA system is under construction. Simulation results operating at X-band are shown in this paper.

Effects of temperature fluctuation on highly dispersive photonic crystal fibers

Chromatic dispersion of highly dispersive photonic crystal fibers (PCFs) is theoretically simulated and experimentally measured as a function of temperature. We have theoretically confirmed that PCFs designed at highly dispersive region show stronger temperature dependence than conventional telecommunication fibers and dispersion compensation fibers due to phase matching wavelength shift and large dispersion slope. For a fabricated highly dispersive PCF, the variation of the dispersion is measured to be around +0.28%∕°C from 21to80°C, and around +0.21%∕°C from 21to50°C at an optical wavelength around 1550nm.

High-spatial-frequency liquid crystal phase gratings with double-sided striped electrodes

High diffraction efficiency and large diffraction angle are two major concerns in designing a liquid crystal (LC) phase grating for its applications in beam diffractive devices. High-spatial-frequency grating is capable of providing a large diffraction angle. However, fringing-field effect becomes more severe when the grating pitch size decreases, which imposes a limitation on the phase modulation depth and the diffraction efficiency of the LC grating. In this paper, a novel LC grating with striped electrodes patterned on both the top and bottom sides was proposed and fabricated. By using a specified biasing configuration, vertical electric fields are generated and well confined between the facing electrodes. Meanwhile, horizontal electrical fields are created between adjacent electrodes which help reducing the undesirable deformation of the LC director axis resulting from the fringing filed. Computer simulations show, in our novel structure, a maximum phase modulation depth of 4.15 rad (for 1.55 μm) can be achieved, which is large enough to satisfy the 1.17 π phase-shift requirement for maximum first order diffraction in sinusoidal phase gratings. Both the conventional single-sided and the novel double-sided LC gratings were fabricated and tested. Measurements showed, there was an efficiency enhancement of 77 times achieved by the double-sided structure comparing the conventional structure. A first order diffraction with diffraction angle at 14.5o and diffraction efficiency of ~31% is experimentally achieved, of which the efficiency approaches the theoretical upper limit at 33.8% for a sinusoidal phase grating.