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Questions on Stressed RX Test E-O and E-O-E Linearity Lew Aronson – Finisar Abhijit Shanbhag - Scintera August 24, 2004 Page: 1 Lew Aronson Question 1 on TP3 Linearity • With the ISI generator before E-to-O, there will be intramodal dispersion which will lead to cross-products and non-linear ISI after the PIN (due to square-law, similar as with chromatic dispersion), which the EDC may not be intended for. – Not an issue for TP3 test since there is a very short fiber between source and DUT (I.e. no significant optical intramodal dispersion in TP3 test) – [Believe references exist that E-O-E process turns out to be linear. Cross products average out.] Page: 2 Lew Aronson Question 2 on TP3 Linearity • With No Fiber, I(t) is the data-modulated output of the ISI generator and h(t) is the laser filter function (assumed to be perfectly linear), the o/p would be sqrt(I(t))*h(t)). The PD output is then [(sqrt(I(t))*h(t))]^2. The EDC is designed to compensate for channel of the form I(t)*(sqr(p(t))), where p(t) is the cumulative (optical) channel impulse response. – Potential Issue with Low Bandwidth or Non-Linear Source – Can be Controlled by Signal Characterization Test Portion of Stressed RX Test Definition. • Test Signal for TP3 Stressed RX Test Should be Specified and Measured Optically into a Linear Reference Receiver (e.g. with isolated one pattern). • Mismatch between electrical ISI generator and received ISI can be detected and corrected by either by using better E-O source or compensation of electrical ISI in order to achieve the required ISI. Page: 3 Lew Aronson