A novel photonic analog-to-digital converter (ADC) based on asynchronous delta-sigma modulation (ADSM) has been investigated. The architecture utilizes an optical leaky integrator, optoelectronic bistable quantizer, and positive corrective feedback for a non-interferometric optical implementation of ADSM. The principles of the proposed 1st –order ADSM are mathematically modeled and simulated.
A novel photonic analog-to-binary converter based on the first-order asynchronous delta-sigma modulation (ADSM) has been theoretically investigated and experimentally demonstrated. A fiber-optic prototype ADSM system is constructed and characterized. Delta-sigma modulation is a straightforward approach to A/D conversion because in this case an external clocking is not required and demodulation can be simply performed via a low-pass filtering process. To improve signal-to-noise ratio and thus system ENOB, a non-interferometric optical implementation has been constructed. The ADSM is comprised of three photonic devices: an inverted output photonic leaky integrator, bistable quantizer, and positive corrective feedback. The photonic integrator which is a recirculating loop performs the oversampling of an analog input using the cross-gain modulation in an SOA. We will show that the photonic ADSM produces an inverted non-return-to-zero (NRZ) pulse-density modulated output describing an input analog signal. This fiber-optic ADSM converts up to 7.6 MHz analog input at about 30 MS/s and effective ENOB of 6.
This paper presents a hybrid opto-electronic asynchronous delta-sigma modulator,
implemented in the form of a fiber-optic Analog-to-Digital converter (ADC). This architecture
was chosen for its independence of an external clock and ease of demodulation through a single
low-pass filter stage. The fiber-optic prototype consists of an input laser (wavelength λ1) which
is modulated with an input RF signal, a high-speed comparator circuit working as bi-stable
quantizer, and a fiber-optic loop that includes a SOA and a band-pass filter that act as a leaky
integrator. The fiber-optic loop acts as a fiber-ring resonator (FRR), and defines the resonance
wavelength λ2 of the system. The gain within this loop is modified through cross-gain
modulation (XGM) by the input wavelength λ1, and thus achieves the desired modulation effect.
The proposed architecture has been constructed and characterized at a sampling rate of 15.4
MS/s processing input analog signals in the range of dc-3 MHz with a signal-to-noise ratio of 36
dB and an effective number of bits of 5.7.
The delta sigma modulator (DSM) is a device which transforms the amplitude information of an analog input signal
to the duty cycle and frequency of a binary output. This device, typically employed in oversampled analog-to-digital
converters, is based on a feedback loop which includes at least one integrator and one quantizer in the forward path. In
this paper, a novel photonic second-order DSM is proposed and experimentally demonstrated. The system is composed
of two inverted leaky integrator and one electro-optic quantizer. The maximum input frequency is around 2 MHz,
limited by the fiber length of the accumulator and feedback loops, and the quantizer rise/fall times. The system is
characterized at different input frequencies and waveforms (sinusoidal and saw tooth) to analyze the modulator
performance and linearity. The binary output is acquired, processed and demodulated using a personal computer, in
order to reconstruct the input analog signal. The reported fiber-optic DSM is very promising for future integration
increasing the operation frequency up to GHz range.