Investigation on the performance of an optically generated RF local oscillator signal in K<inf>u</inf>-band DVB-S systems

Abstract

We investigate a way to externally generate the local oscillator (LO) signal used for downconversion of the K u -band (10.7 − 12.75 GHz) RF signal received from a phased array antenna (PAA). The signal is then translated to an intermediate frequency (950 − 2150 MHz) at the output of the mixer of standard LNBs (Low Noise Block) of a DVB-S (Digital Video Broadcasting-Satellite) reception system. The LO is generated optically by heterodyning of two lasers. We analyze the impact of the laser parameters (optical power and linewidth) on the quality of the generated LO (i.e. phase stability and carrier-to-noise ratio). In addition, a complete system analysis is presented for a 25×64 elements PAA system. We also report the progress on the development of the distributed feedback (DFB) lasers to be used in the heterodyne process. We analyze and experimentally demonstrate that, in order to have an optically-generated LO with equivalent performance to the one of an electronic LO, the laser linewidth should be in the order of tens of Hz, with a maximum relative intensity noise (RIN) of −123 dB/Hz and a minimum optical power of 0.125 mW.

A photonic frequency discriminator based laser linewidth estimation technique

“…In that case, the linewidth of the beat spectrum, measured using an RF spectrum analyzer (RF-SA), often leads to an erroneous estimation of the optically generated LO. some conventional methods used to measure the linewidth of a free running beat spectrum produced from two independent lasers are direct beat spectrum (DBS) measurement (Khan et al, 2011) and recirculating delayed self-heterodyning (DSH) method (Chen et al, 2006) discussed in the following sections.…”

“…Suppose that the average photocurrent during the noise measurement is Iav and the load resistance in the detector is RL, we can write the noise PSD in W/Hz. Assuming that impedance matching has been imposed at the detector, the total noise PSD can be written as (Khan et al, 2011)…”

Highly stable microwave carrier generation using a dual-frequency distributed feedback laser

“…Photonic generation and distribution of high spectral purity microwave or millimeter-wave carriers is interesting for applications like clock distribution, radar and antenna remoting because of stringent phase noise requirement [1][2][3]. Mowever, the optically generated microwave carriers should have excellent long-term frequency stability in order to meet the requirements prescribed by applications such as the receivers of millimeter interferometers like ALMA (Atacama large millimeter/sub-millimeter array) [2] or K u -band (10.7 -12.75 GHz) PAA system [3]. One method to optically generate a microwave carrier is to use optical heterodyning of two laser frequencies either between independent lasers or between two laser modes sharing a common gain and cavity [5].…”