Theoretical and experimental investigations are presented for a technique to synthesize signals with high phase stability from 1 GHz to 94 GHz by injection-locking two DFB diode lasers to individual modes of an actively mode-locked laser. An application is demonstrated in a photonic frequency-converting system at frequencies up to 94 GHz.

All-optical heterodyne RF signal generation using a mode-locked-laser frequency comb: theory and experiments

Introduction Microwave frequency conversion techniques using analog photonic link technology are reviewed in this chapter. Opto-electronic or photonic radio-frequency (RF) signal mixing refers to converting intensity modulation of an optical carrier at one modulation frequency to intensity modulation or an electrical output at a different frequency. Frequency conversion optical links integrate the functions of electrical frequency mixing, traditionally provided by electronics, together with the transport of the RF carrier by the optical link. Photonic RF signal mixing using fiber optic link technology has recently become a topic of interest for reducing front-end hardware complexity of antenna systems and efficiently extending link frequency coverage into the millimeter-wave (MMW, 30–300 GHz) range. As commercial and military systems push to higher operating frequencies, microwave optical transmission and signal conversion techniques offer attractive benefits to designers of RF systems for communications, radar and electronic warfare applications The frequency converting link diagram displayed in Fig. 10.1 can be used to introduce the concept of photonic link signal mixing as well as to introduce some nomenclature that will be used throughout the chapter. Here, an example antenna remoting configuration is shown that incorporates both optical RF up-conversion for transmit operation and optical RF down-conversion for receive operation. Referring to the transmit-mode up-conversion path of Fig. 10.1, the photonic frequency conversion occurs by multiplying the MMW optical local oscillator (LO) signal at f LO1 , with the lower frequency RF input or information bearing signal at f IF1 in the integrated optical modulator (IOM).

RF Photonic Technology in Optical Fiber Links: Photonic link techniques for microwave frequency conversion

This paper presents an innovative photonics-based ultra wideband RF receiver for spectrum sensing applications. The scheme scans the RF spectrum at discrete steps, down-converting at baseband single portions of the detected spectrum, where they can be precisely acquired. The down-conversion is performed modulating a tunable optical carrier with the RF signal, and beating it with an optical local oscillator. The selection of the desired spectrum portion is achieved tuning the wavelength of the optical carrier, avoiding tunable optical filters and allowing a fast scanning of the detected spectrum. The phase locking between the carrier and the local oscillator by means of a coherent optical comb generator ensures very low phase noise. An experimental validation shows an RF input range of 0.5÷9.5 GHz, with high sensitivity and dynamic range. Increasing the number of comb lines by enhancing the comb generation, the architecture has the potential to detect RF signals up to 100GHz. Moreover, implementing the scheme through integrated photonics technologies will ensure high environmental stability and reduced size weight and power consumption, meeting the increasingly stringent requirements of RF spectrum sensing applications.

A photonics-based ultra wideband scanning RF receiver with high sensitivity and dynamic range

A demonstrator of DC offset-free direct conversion receiver is presented. The innovative architecture exploits optical domain up-conversion and photonic I/Q demodulation to perform a wideband scanning of the RF input spectrum avoiding bulky multiple crystal oscillators and bandpass filters. Moreover, the scheme provides a total immunity to local oscillator self-mixing and to RF-to-baseband feedthrough. The demonstrator achieves a measured DC offset lower than 50 μν and a second-order input-intercept point of 57 dBm. It also shows an operating and instantaneous bandwidth of 0.5÷10.5 GHz and 1 GHz, respectively, with linear dynamic range of 160 dB/Hz and spurious-free dynamic range of 109 dB/Hz2/3, outperforming current pure electronic direct conversion receivers. Further improvements are proposed to enhance the operating bandwidth and to reduce the size and power consumption, making the proposed direct conversion receiver suitable for practical electronic warfare applications.

A DC offset-free ultra-wideband direct conversion receiver based on photonics

RF-photonic approaches have been evaluated for distributing electrically generated local oscillator (LO) signals as well as for performing frequency conversion with optically generated LO signals. For high-fidelity distribution of electrically generated signals, a switched RF photonic link was measured to have a residual phase noise of -145 dBc/Hz at an offset of 10 kHz from the X-band carrier. The switch isolation was better than 80 dB. For efficient frequency conversion with the RF-photonic approach, a relative conversion loss of 6.2 dB was measured for an LO modulation index of 0.97.

RF-photonic links for local-oscillator distribution and frequency conversion

A photonic radio-frequency synthesizer is proposed in which two or more distributed-feedback laser diodes are injection- locked to different optical modes of an actively-mode-locked external-cavity laser diode. The injection-locked laser outputs are combined to produce a high-stability, low-phase- noise heterodyne optical signal with frequency separation in the 1 GHz through millimeter-wave frequency range that is a multiple of the active mode-locking reference oscillator frequency. Since the phase fluctuations of the individual longitudinal modes of the mode-locked laser are highly correlated, the phase fluctuations of the heterodyne output signal are minimized. This approach yields optical heterodyne signals with widely tunable millimeter-wave frequency separations and low phase noise, without the need for a wideband millimeter-wave electronic reference oscillator and frequency-locking control loop as required in previous heterodyne signal generation schemes.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Ronald T. Logan

Papers

Photonic radio frequency synthesizer