L. Menager

Demonstration of a radio-frequency spectrum analyzer based on spectral hole burning.

Spectral hole-burning (SHB) technology is considered for >10‐GHz instantaneous bandwidth signal-processing applications. In this context we report on what is believed to be the first demonstration of a SHB microwave spectrometer. A set of gratings engraved in a SHB crystal is used to filter one sideband of the optically carried microwave signal. The setup is confined to narrow-bandwidth operation, over a 35-MHz-wide interval. The first findings confirm the validity of the architecture in terms of spectral resolution, angular channel separation, and simultaneous detection of multiple spectral lines.

Demonstration of a radio-frequency spectrum analyser based on spectral hole burning

We demonstrate application of spectral hole burning to the spectral analysis of broad-band rf signals. In quite the same way as an acousto-optic spectrometer, the device operates on an optically carried rf signal and achieves angular separation of the signal spectral components. An instantaneous bandwidth of 2.5 GHz has been achieved, with a power dynamic range of 35 dB, limited by the detector. Extension to greater than 10 GHz instantaneous bandwidth with greater than 1000 channels is consistent with the active material capabilities.

Time-to-frequency Fourier transformation with photon echoes

We propose to use photon echoes in rare-earth-doped crystals to implement the Fourier-transform chirp algorithm. The process is considered for application to spectral analysis of fast radio-frequency signals. Compared with surface acoustic wave devices, the proposed scheme gives access to the larger bandwidths of rare-earth-doped crystals and greater flexibility. An experimental demonstration of the proposed process is reported.

Ultralow Noise and High-Power VECSEL for High Dynamic Range and Broadband RF/Optical Links

We describe a compact, ultralow noise, and high-power semiconductor laser implemented in a high performances wideband externally modulated optical link. The laser is based on a vertical external cavity surface emitting laser (VECSEL) designed for high-power and low-noise operation. Thanks to a specific design of the gain chip, the half-VCSEL, based on a metamorphic Bragg mirror and a report on a copper substrate, an optical power of 110 mW is obtained at 1.55 μm in the single frequency regime. For low-noise operation, the laser cavity is designed for free-relaxation-oscillations operation, i.e., in the so-called class-A regime. The Class-A VECSEL exhibits a relative intensity noise below -170 dB/Hz over a wide frequency bandwidth, from 300 MHz to 40 GHz, except at the laser free spectral range (20.4 GHz). In the low-frequency range, the laser noise, mainly due to transfer of pump noise to laser noise, goes from -110 dB/Hz at 1 kHz down to -158 dB/Hz at 10 MHz. Two externally modulated optical links are implemented and compared in terms of the RF gain and the noise figure. The first optical link is based on the ultralow noise class-A VECSEL and the second one is based on a low noise class-B DFB laser. Thanks to the outstanding noise properties of the designed VECSEL, the VECSEL-based optical link outperforms the DFB-based one, in particular for frequencies larger than 20 GHz.

Direct sampling of Ka-Band signals using a photoconductive switch approach

We report in this paper the direct sampling of a band-limited signal in the Ka Band by optical means. The sampling approach that has been used was based on a photoconductive switch made from low-temperature grown GaAs. The Photonic sampler may be used to down sample RF signals to base band before further conversion in digital by an electronic ADC. Thanks to this approach, the usual frequency mixers used for down-conversion are suppressed and replaced by the Photonic sampler. This very simple approach has a lot of benefits such as high level of integration, extremely low cost, no need of external electrical synchronization signals.

Fresnel diffraction on the edge of causality

Taking advantage of the slow optical response of low-temperature rare earth ion–doped crystal, we explore the similarity between causality and Fresnel diffraction by a straight edge. We relate these features to spectral resolution and selectivity. The concept is illustrated with experimental data.

Accumulated engraving of monochromatic gratings for spectral analysis applications

Summary form only given. The work is part of the development of a very large bandwidth radio frequency (RF) spectrometer, based on the spectral hole burning (SHE) process. This device is considered for applications in RADAR and sub-millimetric wave astronomy. A single-unit bandwidth would outdo that of acousto-optic and autocorrelation spectrometers by a factor better than 10, exceeding 10 GHz. We have described the concept in a recently published patent.

Recent progress on optical modules for analog signal remoting and distribution for airborne systems

Following the increasing availability of reliable optical components, issued from the telecom domain, analog-optical links based on commercial modules have achieved performances which are close enough to system requirements to be extensively considered. With accurate understanding and modeling of these components, it has been demonstrated that RF photonics can be implemented to transmit and process RF signals in equipment. We report on recent progress concerning the development of several photonic modules to implement transmissions of radar (and electronic-warfare) signals in airborne environment.

Recent progress on optical modules for RF signal remoting and distribution in airborne environment

Following the increasing availability of reliable optical components, issued from the telecom domain, RF-optical links based on commercial modules have achieved performances which are close enough to system requirements to be extensively considered. With accurate understanding and modeling of these components, it has been demonstrated that RF photonics can be implemented to transmit and process RF signals in equipments. We report on recent progress concerning the development of several photonic modules to implement transmission of radar and EW signals in airborne environment.

Opto-electronic free-space processor for UMTS signal filtering

The availability of optoelectronic components operating in the multi-gigahertz domain (up to 20 GHz) is very attractive for implementing basic optical processing functions of microwave signals such as spectrum analysis, adaptive filtering, and correlation suitable in radar and electronic communication systems. We present an optoelectronic free-space processor for filtering up-link and down-link signals in UMTS base stations. The system uses a liquid-crystal spatial light modulator to set programmable filtering functions. We have demonstrated signal rejections higher than -40 dB at 2.3 GHz (from 2.1 GHz) and low insertion losses of -18 dB. Moreover, tunability of the filters implemented in the free-space demonstrator has also been successfully addressed