Designing an Integrated All-Optical Analog to Digital Converter

Abstract

We present the procedure for designing a high speed and low power alloptical analog to digital converter (AO-ADC), by integrating InGaAsP semiconductor optical amplifier (SOA) with InP based photonic crystal (PhC) drop filters. The self-phase modulation in the SOA can shift the frequency of the Gaussian input pulse. The two output PhC based drop filters are designed to appropriately code the frequency-shifted analog signals by the SOA, converting them to four desired digital output levels. Our numerical results show that in an appropriately designed AO-ADC, the center wavelength (1572 nm) of an amplitude modulated Gaussian pulse of 1.8 ps width and 1.56 pJ energy can be shifted by 6.7 nm, by the SOA, and then be quantized and coded to four digital levels (00, 01, 10, and 11). The two point-defect PhC drop filters, compensating the effect of the frequency shift by SOA, minimize the AO-ADC integral and differential nonlinearity errors.

An integrated 2-bit all optical analog to digital converter based on photonic crystal semiconductor optical amplifier

“…However, this is not the major aim of this proposal. As expected, the PhC-SOA SPM incurs a redshift on the output pulse signal that increases linearly with an increase in the input pulse bandwidth (∆λ1/2) for different values of ng, similar to conventional SOA (Moshfe et al 2020). As shown in Fig.…”

“…The signal gain and the frequency chirp in the pulse signal of a PhC-SOA, while compared with those in a conventional SOA, have been discussed in (Nosratpour et al 2018). It has already been shown that in PhC-SOA, for an input temporal pulse of width p, the larger the signal gain of the amplifying cavity, the larger the shift in the wavelength of the chirped signal (∆λout) (Nosratpour et al 2018), similar to what examined in conventional SOAs (Moshfe et al 2020). However, in PhC-SOA the wavelength shift depends on the group index too.…”

“…The operating principle of the proposed integrated AO-ADC is similar to those of the design presented by (Moshfe et al 2020), such that an active region provides the medium for the SPM nonlinear effect occurrence. A modulated ultra-fast Gaussian pulse chain as an input optical signal, as schematically illustrated in Fig.…”

“…In comparison to (Moshfe et al 2020), we substitute the conventional SOA and square-lattice pillar-based PhC-CDF with shorter length PhC-SOA and high-quality point defects PhC-CDF, all are devised on air-hole hexagonal-lattice based platform. These changes result in achieving an ultra-compact structure with the minimum optical loss between the blocks, operating with a small injection current.…”

“…revealed a 3-bit AO-ADC based on QDSOA, operating at 10 Gs/s with an 8-level optical quantization (Hoshino et al 2018). (Moshfe et al 2020) proposed a 2-bit AO-ADC using the SPM effect on a modulated Gaussian pulse passing through an SOA. Designing appropriate PhC-CDF to compensate for the nonlinear relation of amplitude to wavelength conversion by SOA, a high linear AO-ADC was achieved.…”