Adil Karim

High Dynamic Range Microwave Photonic Links for RF Signal Transport and RF-IF Conversion

Two different techniques were used to extend the dynamic range of analog optical links operating at microwave frequencies. The link noise figure was reduced by adjusting the bias point of an external Mach-Zehnder intensity modulator. The link distortion was reduced by linearizing the transfer function of the intensity modulator. Frequency conversion was implemented using an additional optical modulator and electrical local oscillator rather than a conventional electronic mixer. A microwave frequency signal transport link was demonstrated with a spur-free dynamic range (SFDR) of 71 dB in a 500-MHz noise bandwidth. A link with down-conversion from a microwave frequency to an intermediate frequency was demonstrated with an SFDR of 64 dB in a 500-MHz noise bandwidth.

Noise Figure Reduction in Externally Modulated Analog Fiber-Optic Links

An octave-bandwidth microwave photonic link with a third-order limited spurious-free dynamic range of 121 dB in a 1-Hz bandwidth has been demonstrated. The link noise figure of 9 dB at a modulation frequency of 2 GHz was achieved by using a bias-shifted Mach-Zehnder modulator with an optical input power of 500 mW. This level of performance was realized without electronic or optical linearization

Low Noise Figure Microwave Photonic Link

The noise figure of an analog fiber-optic link was reduced to 6 dB at 1 GHz by using a bias-shifted Mach-Zehnder modulator with an optical input power of 1 W. The link noise figure was less than 14 dB for modulation frequencies from 1-18 GHz. This level of performance was achieved without electronic pre-amplification. A linearized microwave photonic link using this noise reduction approach has been demonstrated with a spurious-free dynamic range of 130 dB in a 1 Hz bandwidth.

Optimization of an Externally Modulated RF Photonic Link

Abstract The noise figure and sub-octave spurious-free dynamic range of a carrier-suppressed analog RF photonic link are examined. Expressions for noise figure and dynamic range are derived as a function of the modulator bias angle. A closed form expression for the bias angle that optimizes link noise figure and spurious-free dynamic range is also derived. Experimental results are presented and shown to agree with calculations. These experimental results include some of the lowest noise figure and highest dynamic range results published to date for an RF photonic link incorporating a standard Mach-Zehnder modulator: 6 dB and 122 dB·Hz2/3, respectively.

Optimization of Linearity Figure of Merit for Microwave Photonic Links

Optimization of the modulator bias point for a microwave photonic link with an external modulator is proposed based on a linearity figure of merit. This figure of merit and corresponding bias point take into account gain, linearity, noise figure, and power consumption.

Microwave photonic link architectures

Fiber optic links with a low noise figure and high spurious-free dynamic range (SFDR) at microwave frequencies are required for airborne antenna remoting applications. Compared to conventional electronic links operating over coaxial cable, fiber optic links can provide significant advantages in the areas of bandwidth, propagation loss, cable weight and immunity against electromagnetic interference. This paper describes multiple fiber optic link architectures and examines recent advances in performance.

A multi-channel photonic transceiver

This paper presents a novel photonic transceiver architecture for digital array applications. The architecture utilizes optical remoting for minimal hardware impact at the antenna and phase encoding for improved linearity. The individual elements are addressed through wavelength division multiplexing and photonic downconversion is used to increase the linearity of the photonic receiver. The architecture is evaluated through a 10 GHz, two-element experimental prototype system. The phase stability of the system is evaluated by measuring the relative phase drift between the two elements at the outputs of the transmitter and receiver. The transmitter exhibits low phase error, on the order of 10 millidegrees, while the receiver shows a phase error of approximately 1 degree over a time scale of 2 ms at uncontrolled laboratory temperatures.

Modulator bias regimes for analog optical links

In this paper, three distinct operating regimes for an analog fiber optic link with Mach-Zehnder modulators (MZM) are described. A third operating regime for an analog fiber optic link has been described that maximizes a linearity figure of merit. This balanced operating point should be considered for sub-octave applications since it can eliminate the need for electronic amplifiers on both sides of the fiber optic link.

Increased dynamic range for microwave photonic links

Microwave photonic links with increased dynamic range are required for antenna remoting applications. In this work, a linearized microwave photonic link was used for both radio-frequency (RF) signal transport and down-conversion to a lower intermediate frequency (IF).