Thomas R. Clark

Coherent Optical Phase-Modulation Link

We demonstrate and characterize a new class of radio-frequency (RF)-photonic link for the linear transport of analog RF signals. Simultaneous and separate detection and digitization of optical in-phase and quadrature-phase signals is employed for linear phase demodulation in the digital domain. This is shown to allow significantly larger tolerance to imperfect physical implementation of the phase demodulating receiver. Digitizer-limited spur-free dynamic range improvement >12 dBldrHz2/3 is observed in our baseband demonstration. Modulation depths significantly exceeding unity are allowed and demonstrated.

A Phase-Modulation I/Q-Demodulation Microwave-to-Digital Photonic Link

We present theory and experiments for a microwave-to-digital photonic link capitalizing on the linearity of optical phase modulation and coherent optical I/Q demodulation to achieve unprecedented gain and dynamic range performance. We demonstrate, with an optical amplifier noise limited system, direct demodulation spur-free dynamic range (SFDR), gain, and noise figure of 126.8 dB-Hz2/3 (86.8 dB in 1 MHz noise bandwidth), 8 dB, and 18.6 dB, respectively for inputs up to 1 GHz. Additionally we demonstrate complimentary all-photonic downconversion allowing the extension of input operating bandwidth to a modulator limited 40 GHz. Demonstrated microwave to intermediate frequency conversion loss ranges from <; 4 dB @ 4 GHz to <; 13 dB @ 40 GHz. Linear all-photonic downconversion and demodulation is demonstrated at 3 and 10 GHz with optical amplifier noise limited SFDR better than 107 dB-Hz2/3 (67 dB in 1 MHz noise bandwidth). System design issues are discussed including critical parametric sensitivities and optical-electrical-digital sub-system dynamic range matching and technology capability for downconverting microwave-to-digital SFDR performance in excess of 125 dB-Hz2/3 (85 dB in 1 MHz) with current technology.

Tunable millimeter-wave frequency synthesis up to 100 GHz by dual-wavelength Brillouin fiber laser

We demonstrate the generation of microwave and millimeter-wave frequencies from 26 to 100 GHz by heterodyning the output modes of a dual-wavelength fiber laser based on stimulated Brillouin scattering. The output frequency is tunable in steps of 10.3 MHz, equal to the free spectral range of the resonator. The noise properties of the beat frequency indicate a microwave linewidth of <2 Hz. We discuss potential for operation into the terahertz regime.

Photonics for RF Front Ends

In this article, some of the latest technology advancements in microwave photonics, in particular those related to the RF front end were reviewed. The generic salient features and issues associated with microwave photonic links were provided. It is shown that optical amplification and high power photodiodes can lower the noise figure of these links. Photonic downconversion and microwave-to-digital systems and potential photonic simultaneous transmit and receive configurations were also reviewed. Opto-electronic oscillator technologies to create low phase noise RF signals and also the efficient integration of photonic components directly with antennas were examined. While progress is expected to continue in the near future to improve on the efficiency and performance of microwave photonic components and subsystems, significant future challenges will be dominated by activities involving the integration of the technologies discussed into microwave systems to fully realize the benefits discussed. This will require the active involvement and education of RF and microwave system designers to the benefits and interface challenges of microwave photonic systems, as well as the different packaging, powering and controls required. All the technologies reviewed are potential enabling technologies for photonic implementations of RF front ends and point to an expectation for many future improvements and new capabilities enabled.

Experimental Demonstration of Photonic Millimeter-Wave System for High Capacity Point-to-Point Wireless Communications

We present experimental results of 10 Gb/s wireless communications over a distance of 520 meters in the W-band. The transmitter makes use of photonic upconversion with a high bandwidth photodiode to allow for minimum hardware at the antenna. We present results with two receiver configurations. The first uses all electronic methods with a balanced Schottky diode mixer for downconversion, and the second uses photonics to limit the hardware at the receive antenna by photonically generating the local oscillator drive signal and transporting the intermediate frequency signal over a microwave photonic link.

Radio-Over-Fiber Technologies for Emerging Wireless Systems

Radio-over-fiber transmission has extensively been studied as a means to realizing a fiber optic wireless distribution network that enables seamless integration of the optical and wireless network infrastructures. Emerging wireless communication networks that support new broadband services provide increased opportunities for photonics technologies to play a prominent role in the realization of the next generation integrated optical/wireless networks. In this paper, we present a review of recent developments in radio-over-fiber technologies that can support the distribution of broadband wireless signals in a converged optical/wireless network. We also describe some of the challenges for the successful application of radio-over-fiber technologies in future wireless systems, such as 5G and 60-GHz networks.

Experimental Demonstration of a Photonic Analog-to-Digital Converter Architecture With Pseudorandom Sampling

A photonic analog-to-digital converter architecture is demonstrated that uses nonuniform, sub-Nyquist sampling combined with digital signal processing algorithms to unambiguously identify microwave signals of interest. X-band (8-12 GHz) operation is demonstrated with two-tone signals of separation extending to >2 GHz that were directly sampled and digitized at a mean rate of 995.3 MHz resulting in alias-free power spectra.

Millimeter-Wave Wireless Communication Using Dual-Wavelength Photonic Signal Generation and Photonic Upconversion

This paper presents the design and experimental analysis of a system architecture for 60-GHz broadband wireless communications. The architecture uses a dual-wavelength photonic signal source based on stimulated Brillouin scattering to generate the millimeter-wave carrier signal through photomixing. Data is encoded onto the optical signals and is upconverted directly to the millimeter-wave carrier through a photonic upconversion process, which does not require electronic upconversion. The data is encoded onto one optical wavelength in a single-sideband fashion, which affords significant dispersion tolerance over long remoting distances compared with standard double-sideband modulation. The prototype architecture was tested at ranges of 2-30 m indoors and 78 m outdoors, demonstrating a building-to-building link. Binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK) modulation formats were tested, with BPSK data rates up to 3 Gb/s and QPSK data rates up to 2.64 Gb/s. Good bit-error ratios are demonstrated as a function of received power and range for a fixed transmit power.

Wideband Adaptive Feedforward Photonic Link

We present the first demonstration of an adaptive wideband radio-frequency (RF) photonic link architecture suitable for high-dynamic-range microwave signal fiber optic transport. The architecture incorporates feedforward (FF) linearization to correct the electrical-to-optical (E/O) conversion nonlinearity as well as optimized control loops that enable the system performance to be maintained in real time during changing operating conditions. Third-order distortion suppression of greater than 25 dB has been demonstrated over the input frequency range of 2 GHz to >17 GHz. Under manual control of the wideband FF linearized photonic link, a spur-free dynamic range (SFDR) in excess of 120 dB-Hz 2/3 is demonstrated, while an SFDR of >116 dB-Hz2/3 is achieved with adaptive control. We present experimental results of a fully automated wideband FF photonic link and also discuss the potential for the technique.

Photonic Beamsteering of a Millimeter-Wave Array With 10-Gb/s Data Transmission

We present experimental results of 10-Gb/s W-band wireless transmission using a four element linear array. The 10-Gb/s transmission is shown when photonically steered to 0° and ± 35° from antenna boresight. In this letter, photonic techniques are used for signal generation, distribution, and time delay. Photonic true-time delay is shown to allow for steering of broadband millimeter-wave signals with no noticeable beam squint across frequency. High power, high frequency photodiodes are used for optical-to-electrical conversion to directly radiate from the array without power amplifiers.