F. Coppinger

Photonic time stretch and its application to analog-to-digital conversion

We demonstrate a new concept for analog-to-digital (A/D) conversion based on photonic time stretch. The analog electrical signal is intensity modulated on a chirp optical waveform generated by dispersing an ultrashort pulse. The modulated chirped waveform is dispersed in an optical fiber, leading to the stretching of its envelope. We have derived analytical expressions for the stretch factor and the resolution of the system. An analog-to-digital converter (ADC) consisting of the photonic time-stretch preprocessor and a 1-Gsample/s electronic ADC is demonstrated. This technique is promising for A/D conversion of ultrafast signals and, hence, for realization of the digital receiver.

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.

All-optical RF filter using amplitude inversion in a semiconductor optical amplifier

We present an all optical delay-line radio-frequency (RF) notch filter. The filter exploits cross-gain modulation in a homogeneously broadened laser medium to obtain a negative tap in an optically incoherent system. Applications including moving-target indication (MTI) in optically controlled radars are discussed.

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.

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.

30 Gsample/s 4-bit time-stretch analog-to-digital converter

Summary form only given.Photonic time stretch preprocessing (TSP) has been proposed as a means to enhance the performance of electronic ADCs. This concept is based on the premise that if the analog signal can be stretched in time free of distortion, then the effective sampling rate and the input bandwidth of the ADC is increased. The technique is best suited for time-limited analog signals, such as those encountered in pulsed radars. In this paper we demonstrate complete time-stretch ADC with 30 Gsample/s sampling rate, and 4 effective number of bits resolution realized over a 4 GHz bandwidth. The system consists of a photonic TSP and a commercially available electronic digitizer with 8 Gsample/s sampling rate and 1.5 GHz bandwidth.

Compact multimode interference couplers in silicon-on-insulator technology

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

Time domain optical sensing

We have demonstrated a simple yet effective spectrometer. It uses chirped supercontinuum pulses as a broadband source and a sampling oscilloscope or A/D converter for spectral analysis. Distinct advantages for this system include the absence of an optical spectrometer, the broad spectral bandwidth available from the supercontinuum source, and the possibility of real time spectral analysis. A passively mode locked erbium doped fiber laser with a pulse compression stage was used as the supercontinuum source.