S. Yegnanarayanan

Silicon-on-insulator (SOI) phased-array wavelength multi/demultiplexer with extremely low-polarization sensitivity

We demonstrate the first phased-array wavelength multiplexer fabricated in the silicon-on-insulator (SOI) waveguide technology. The four-channel wavelength division multiplexer (WDM) has a channel spacing of 1.9 nm centered at 1550-nm wavelength and a 3-dB channel bandwidth of 0.72 nm. The crosstalk to neighboring channels is less than -22 dB and the on-chip insertion loss is below 6 dB for all channels. The TE-TM shift is less than 0.04 nm which is the smallest attained without compensation techniques in any integrated optic technology.

Recirculating photonic filter: a wavelength-selective time delay for phased-array antennas and wavelength code-division multiple access

A novel wavelength-selective photonic time-delay filter is proposed and demonstrated. The device consists of an optical phased-array waveguide grating in a recirculating feedback configuration. It can function as a true-time-delay generator for squint-free beam steering in optically controlled phased-array antennas and as an encoding-decoding filter for wavelength code-division multiple access.

Continuously tunable photonic radio-frequency notch filter

We present a continuously tunable nonrecursive radio-frequency (RF) photonic filter. The filter provides fine tuning through the use of a novel RF phase shifter and coarse tuning using an an optical variable time delay. This architecture permits wide-band continuous tuning of the filter null frequency and is useful in applications such as moving target indication (MTI) in an airborne radar.

Nonrecursive tunable photonic filter using wavelength-selective true time delay

We present a photonic feed-forward radio-frequency filter with all-optical tunability. The filter incorporates a novel wavelength-selective true time delay in a delay-line-canceler architecture. We demonstrate tuning of the filter null frequency by changing the wavelength of the optical carrier. Application of this technique in optically controlled radars is discussed.

Compact silicon-based integrated optic time delays

We demonstrate a 3-b (eight-channel) guided-wave optical delay line network in the silicon-on-insulator (SOI) waveguide technology with an incremental time delay of 12.3 ps measured over 2-20-GHz frequency range. The high-refractive index (compared to silica) combined with tight optical confinement and low propagation loss in the SOI waveguide enables us to realize a compact time-delay network with fine resolution time delays necessary in a high-frequency phased-array antenna.

5 x 9 integrated optical star coupler in silicon-on-insulator technology

We describe fabrication of the first optical star coupler in silicon-on-insulator (SOI) technology. The 5/spl times/9 coupler consists of two silicon rib waveguide arrays with a radiative slab waveguide region. The star geometry was analyzed and designed using the beam propagation method. The coupler exhibits low loss (average excess insertion loss /spl alpha//spl sim/1.3 dB) and good coupling uniformity (standard deviation /spl sigma//spl sim/1.4 dB) at /spl lambda/=1.55 /spl mu/m. It represents a key component for realization of photonic circuits in a silicon integrated circuit technology.

Nondispersive wavelength-division sampling

We propose and demonstrate a new wavelength-division-sampling technique with high temporal resolution. A discrete-time true-time delay generates multiwavelength near-transform-limited pulses from a supercontinuum source. Pulses sample the analog signal in an electro-optic modulator and are subsequently demultiplexed in a wavelength-division-multiplexing filter. A 100-Gsample/s experimental demonstration of this concept is presented.

Compact multimode interference couplers in silicon-on-insulator technology

Silicon-on-insulator (SOI) technology has emerged as the platform for future electronic integrated circuits.

Compact silicon-based integrated optical time-delay network

Conventional phased-array antennas are limited by the bandwidth and attenuation as well as mechanical rigidity of the coaxial cables employed to perform the microwave phase shift. Photonic technology offers advantages in distribution of the microwave signal including lightweight, compact delay lines, immunity from electromagnetic interference, low rf transmission loss and possibility of optical signal processing on the microwave encoded optical beam. Fiber optic delay lines have been demonstrated already but one requires a precision cut of the fiber length (accurate to a mm) to achieve accurate psec time delay. Guided-wave based approach allows precise definition of the waveguide delay line lengths. In addition, reproducible delays can be mass- produced ensuring low cost modules. In this paper, we demonstrate the first integrated optical delay lines in the silicon-on-insulator waveguide technology.

Recirculating photonic filter: a wavelength-selective time delay for optically controlled phased-array antenna

A wavelength-selective photonic time delay filter is proposed and demonstrated. The device consists of an optical phased-array waveguide grating in a recirculating feedback configuration. It can function as a true-time-delay generator for squint-free beam steering in optically- controlled phased-array antennas. As the photonic filter uses the optical carrier wavelength to select the desired time delay, a one-to-one map is established between the optical carrier wavelength and the desired antenna direction, thus eliminating complex switching networks required to select the appropriate delay line. The proposed device can also function as the encoder/decoder in wavelength-CDMA. The concept uses a waveguide prism in a symmetric feedback (recirculating) configuration. The modulated optical carrier is steered by the waveguide prism to the appropriate integrated delay line depending on the carrier wavelength. The signal is delayed and is fed back into the symmetric input port. The prism then focuses the delayed beam into the common output port. Thus three sequential operations are performed: (1) wavelength demultiplexing, (2) time delay, and (3) wavelength multiplexing. It is important to note that the recirculating photonic filter has no 1/N loss; all the power at a given wavelength is diffracted into the output port. Furthermore, high resolution (6 - 8 bits) can be obtained in a compact integrated device. A prototype regular recirculating photonic filter true-time delay device was realized using a 8-channel arrayed-waveguide grating demultiplexer and external (off-chip) fiber delay lines. The grating was fabricated in the silica waveguide technology with 0.8 nm channel spacing (FSR equals 6.4 nm) and operating in the 1.5 micrometers wavelength range. Light from an external cavity tunable laser was rf modulated at 10 - 40 MHz and was coupled into the arrayed waveguide grating chip and time/phase measurements were performed sing a digital oscilloscope. Feedback delay lines consisted of optical fibers of different lengths connected between 4 symmetric pairs of input and output ports. The results clearly demonstrate the Recirculating Photonic Filters ability to perform wavelength-selective true-time delay. Furthermore, as expected, the delay has the desired property of being independent of rf frequency.