Martine Doisy

An accurate design and modeling tool for the design of RF SAW filters

The main work for the SAW RF designer is to improve the filter performances and especially the insertion loss which has to be very low in the entire bandwidth, meaning that the control of the passband shape has to be very precise, Due to the proximity of SSBW when using LSAW, it is well known that standard P-matrix or COM models do not accurately predict the performance. The other difficulty is the 3D effects that could have a major impact on performances, especially when using ladder type filters. The third effect is the impact of electrical stray elements which can no longer be neglected. Our model can be separated in different parts. The acoustical model is used to analyze resonators or transducers. For this purpose, one possibility is to characterize test devices. We prefer to base our design directly on theoretical results. One way is to use the periodic FEM/BEM model to extract physical parameters describing the propagation of the wave and to use these parameters in a phenomenological model similar to COM or P matrix. This approach is well suited to periodic or almost periodic structures, as for example the resonators inside a ladder filter.

All-optical acoustic array for underwater surveillance

For underwater surveillance applications, an all-optical acoustic array technology allows enhanced capabilities compared to conventional piezoelectric antenna in terms of compactness, robustness and large distance remote interrogation through small diameter optical cable. This paper presents the results obtained on a first full optical antenna panel based on an innovative wideband pressure and temperature compensated fiber laser hydrophone. The presented mock-up includes 12 fiber-laser optical hydrophones interrogated through a 4 km lead optical cable.

A new generalized two track RSPUDT structure for SAW filter size reduction: design and performance

High volume communication receivers continue to add features such as multimode operation, voice recognition, and Internet access with shrinking size. These evolutions reduce the available space for the RF and IF filtering functions. For systems such as CDMA and PCS the SAW IF filter is one of the largest components. This trend has lead to the development of DART filters, followed by the RSPUDT and recently by the two track RSPUDT. For the CDMA IF SAW filter the length of the SAW die has shrunk from 22 mm for a classical filter to 7/spl times/5 mm/sup 2/ for a two track RSPUDT design with simultaneous filter performance improvements. This paper will discuss the more common two track architectures with parallel and series connected transducer connections and basic principles of operation using the concept of symmetric and antisymmetric modes. We will then present a new generalized two track structure using the RSPUDT. This new structure works by designing each track to be in phase in the passband and out of phase in the rejection bands. This approach leads to steeper transitions and smaller die size. Implementation on the mask of the connections of the two different tracks will then be discussed. Experimental results will be included for both a CDMA (21/spl times/ 8 mm/sup 2/=>9/spl times/5 mm/sup 2/ package) and PCS (13/spl times/6.5 mm/sup 2/=>5/spl times/5 mm/sup 2/ package) filter.

Acoustic antenna based on Fiber Laser Hydrophones

A technique to enhance the response of Brillouin distributed sensors is proposed and experimentally validated. The method consists in creating a multi-frequency pump pulse interacting with a multi-frequency continuous-wave probe. The power of each pulse at a distinct frequency is lower than the threshold for nonlinear effects, while the sensor response remains given by the total power of all pulses. Distinct frequency pulses are delayed to avoid temporal overlapping and cross-interaction; this requires to smartly reconstruct the traces before photo-detection. The method is validated in a 50 km-long sensor using 3 frequencies, demonstrating a signal-to-noise ratio enhancement of 4.8 dB.

A new triply rotated quartz cut for the fabrication of low loss SAW filters

Analysis of the Quartz properties shows the existence of unexplored angular domains for which Rayleigh waves can be efficiently excited, exhibiting physical characteristics better than the ones of the (ST,X) cut. This paper presents a family of quartz cuts allowing significant improvements of SAW devices on Quartz. Experiments have been performed, confirming the above mentioned theoretical predictions. A filter built on this cut is presented showing the interest of the proposed crystal orientations.

Acoustic fiber laser array architecture with reduced optical feedback limitations

Many sensing applications would benefit of multiplexing a maximum number of Distributed FeedBack Fiber Lasers (DFB FLs) on the same optical fiber. However, in such configurations, some physical mechanisms may impact DFB FLs stable operation, limiting, for instance, the number of DFB FLs spliced on the same fiber and the distance between them. The aim of this experimental study is to investigate the impact of optical feedback on DFB FLs stability. The results of our study are used to propose possible associated architectures.