Tham khảo tài liệu 'advances in optical and photonic devices 2011 part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Resonant Tunnelling Optoelectronic Circuits 189 dB absorption changes induced by 1 mV dc voltage increments an exceptionally high transmission change per unit of voltage Figueiredo 2000 . Figure 15 b shows modulator response as function of the dc bias voltage when driven by 3 GHz voltage signals of amplitude from 1 mV to 100 mV also represented is the RTD-EAM dc I -V characteristic. The rf photo-detected power increased by about 15 dB when the device dc bias point moved from the peak to the valley region at driving amplitudes as low as 50 mV. An indication the modulator can be driven by very low voltage signals due to its intrinsic built-in electrical amplifier. Wavelength nm a b rf 1 mV rf 10mV - rf 50 mV rf 100 mV Ị I mA Fig. 15. a InGaAlAs RTD-EAM transmission spectrum in the wavelength range 1500 nm to 1580 nm with the applied voltage as a parameter. b Modulator response as function of the dc bias voltage when driven by 3 GHz rf signals with injected amplitude as a parameter. RTD-EAM high frequency optical characterisation employed a microwave synthesized signal generator with a maximum output of 20 dBm and an upper frequency limit of 26 GHz Figueiredo 2000 . Figure 16 a shows the modulation depth as function of the light wavelength induced by the transition between the two PDC regions produced by a square signal with peak-to-peak voltage slight higher than AVVP V. The devices were dc biased in the valley region in order to minimize thermal effects and avoid self-oscillations. Modulation depths up to 28 dB were measured on devices with active areas around 800 m2 more than 10 dB superior to the values observed on the AlGaAs GaAs devices. The modulator response up to 26 GHz driving signals for two power values is shown in Fig. 16 b . Fig. 16. a Modulation depth as function of the wavelength. b Spectrum of the 26 GHz photo-detected signal at the modulator driving power of -20 dBm and dBm. 190 Advances in Optical and Photonic Devices The photo-detected .
