Abstract
BackgroundCarrier generation based on optical heterodyning techniques where a beat signal is generated from the mixing of two light sources can be interesting solution due to ease on tunability. The free running heterodyning scheme benefits with a very wide tuning capability and the generated carrier can be freely adjusted. However, the drawbacks come in the form of frequency stability. Heterodyning of two optical frequencies coming from a single laser cavity has shown its potential on improvement of frequency stability.MethodsThe impact of the laser parameters (i.e., optical power and linewidth) on the quality of the generated carrier (i.e., phase/frequency stability and carrier-to-noise ratio) is analyzed for a 25×64 elements PAA system. An optically generated carrier signal using a dual-frequency distributed feedback waveguide laser in ytterbium doped aluminum oxide (Al2O3:Yb3+) is analyzed and experimentally demonstrated in this paper. The carrier signal is used for downconversion of the signal received from a phased array antenna (PAA) of a DVB-S (Digital Video Broadcasting-Satellite) system.ResultsAn optical frequency locked loop (OFLL) to stabilize the generated carrier is implemented which results in a microwave frequency at ∼14 GHz with a phase noise of -75 dBc/Hz at 1 MHz offset from the center frequency and gives a loop settling time of 12 μs. By using the proposed OFLL, the long term and the short term frequency stability of the generated carrier has an Allan deviation of more than 1×10−10 for an averaging time of 1000 s and a standard deviation of 39.4 kHz, respectively. The lasers linewidth should be in the order of tens of Hz, with a maximum relative intensity noise (RIN) of -107 dB/Hz and a minimum optical power of 0.94 mW.ConclusionsThe optical carrier generation by OFLL using a DFL to comply with the requirements of the standard carrier used in commercial LNBs has been investigated. The detailed analysis of the OFLL scheme is presented. Specifications requirement on carrier power, linewidth and relative intensity noise of the optically generated carrier have been addressed. The optical carrier generation is experimentally demonstrated and the requirements on CNR have been determined by measuring the noise floor and the optical carrier power. The measured values are compared with the calculated values and found to be very close.
Highlights
Carrier generation based on optical heterodyning techniques where a beat signal is generated from the mixing of two light sources can be interesting solution due to ease on tunability
In the past years, reports on microwave carrier generation by using a Dual frequency laser (DFL) were mainly focused on very low phase noise [48, 49] or large tunability [15, 50]
Our optical frequency locked loop (OFLL) clearly addresses this crucial requirement by achieving a frequency stability of 1 × 10−10 for averaging time of 1000 s
Summary
Carrier generation based on optical heterodyning techniques where a beat signal is generated from the mixing of two light sources can be interesting solution due to ease on tunability. Heterodyning of two optical frequencies coming from a single laser cavity has shown its potential on improvement of frequency stability. A PAA is a set of multiple antennas, called antenna element (AE). Modern PAA consists of a large number of small antenna elements (AEs) and it can achieve the same gain of a large mechanically steerable antenna [3]. When installed on a vehicle a PAA system can be an advantageous solution for receiving satellite signals due to the flatness of its shape provides low aerodynamic profile [2] and to the fact that it can be electronically beamsteered, not requiring continuous mechanical realignment. Additional to that are the possibilities for beam-shaping, tracking and multi-beam reception [7]
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