Ted K. Woodward

GHz-bandwidth optical filters based on high-order silicon ring resonators

Previously demonstrated high-order silicon ring filters typically have bandwidths larger than 100 GHz. Here we demonstrate 1-2 GHz-bandwidth filters with very high extinction ratios (~50 dB). The silicon waveguides employed to construct these filters have propagation losses of ~0.5 dB/cm. Each ring of a filter is thermally controlled by metal heaters situated on the top of the ring. With a power dissipation of ~72 mW, the ring resonance can be tuned by one free spectral range, resulting in wavelength-tunable optical filters. Both second-order and fifth-order ring resonators are presented, which can find ready application in microwave/radio frequency signal processing.

Optically Filtered Microwave Photonic Links for RF Signal Processing Applications

The performance of filtered analog photonic links, useful in signal processing applications, is analyzed along with techniques for compensation of distortion. We analyze the attributes of various link configurations and compare the performance of filtered coherent-detection links with intensity-modulated-direct-detection links. Experimental results on the dynamic range and the compensation of nonlinearities using predistortion compensation are presented for a filtered coherent link. We demonstrate suppression of third-order nonlinearity by 20 dB. In addition to supporting signal processing operations such as filtering and arbitrary intermediate frequency downconversion, at the same detected power, we find filtered coherent links to have up to 9 dB noise figure advantage over unfiltered direct-detection links, dependent on the limits of the operating optical power in the link.

Predistortion Compensation of Nonlinearities in Channelized RF Photonic Links Using a Dual-Port Optical Modulator

High dynamic range is a key requirement in analog applications. In multichannel optical signal processing applications, a wideband radio-frequency signal suffers from distortion from both in-channel and out-of-channel signals due to nonlinear modulator behavior. We demonstrate experimentally the compensation of nonlinearities occurring due to out-of-channel “cross-modulation” with a novel predistortion technique using a dual-port modulator. Predistortion compensation results in suppression of distortion by more than 25 dB.

Thermally-efficient reconfigurable narrowband RF-photonic filter

We present the design and fabrication of thermally-efficient tuning structures integrated into a narrowband reconfigurable radio-frequency (RF)-photonics filter using silicon-on-insulator waveguide optical delay lines. By introducing thermal isolation trenching, we are able to achieve IIR, FIR or arbitrary mixed response with less than 120 mW average tuning power in a single RF-photonic unit cell filter.

A programmable optical filter unit cell element for high resolution RF signal processing in silicon photonics

We demonstrate the first reconfigurable, cascadable silicon photonics unit cell fabricated in commercial wafer-scale processes using a single 500 ps delay line and allowing independent FIR and IIR response for high-resolution RF filtering and correlation applications.

Compensation of cross-gain modulation in filtered multi-channel optical signal processing applications

We experimentally demonstrate compensation of nonlinearity due to cross-gain modulation in wideband analog systems employing narrow-band optical filtering, which is essential for multi-channel optical signal processing in RF channelizer applications.

Multiscale sampling for wide dynamic range electro-optic receivers

We experimentally demonstrate a novel multiscale sampling technique for extending the dynamic range of a phase-modulated analog optical system employing passband signals by 20 dB. Envelope distortion is compensated using digital post-processing.

Analytical expression for large signal transfer function of an optically filtered analog link

We present an analytical expression for the transfer function of an optically-filtered radio frequency photonic link using phase modulation and coherent detection. This solution is applicable to quadrature passband signals and is significant for evaluating the distortion and consequently improving the linearity of such electrical-optical-electrical links. We show that the nonlinearity appears as an envelope distortion and discuss linearization techniques along with experimental validation.

RF photonic link employing optical phase sensitive amplification

We present operation of an optical phase-sensitive amplifier (OPSA) in a RF-photonic link for improved link performance. Enhancement of 3.5dB in OIP3 and 2.5dB.Hz2/3 in SFDR at net OPSA gain of 5dB is observed.

A narrowband reconfigurable RF-photonic filter with efficient thermal tuning structures

We present the design and fabrication of thermally-efficient tuning structures integrated into a narrowband reconfigurable radio-frequency-photonics filter using silicon-on-insulator waveguide optical delay lines. We are able to achieve IIR, FIR or mixed responses with < 100mW total tuning power.