Optical-spectrum-encoded analog-to-digital converter

Abstract

A novel optical-spectrum-encoded (OSE) analog-to-digital converter (ADC) is proposed in this letter. To simply exemplify the conversion idea, a 5-bit device structure consisted of Fabry-Perot interferometers (FPI) is analyzed and numerically simulated. The dependence of peak-transmission wavelength on modulation voltage in an electro-optical FPI and the dependence of transmitted power on incident light wavelength in an FPI are discussed and utilized to implement OSEADC.A linearly tunable mode-locked laser, as a voltage-wavelength transformer and a sampler, and chirped grating FPIs, as an encoder array, can be used to obtain much greater sampling rate and bit-resolution. CLC numbers: TH867 + .91, Document code: A Article ID: 1673-1905(2007)03-0227-04 DOI Photonic ADCs utilize optical methods to take the place of one or several of the sampling and holding, encoding, and quantizing. In phase-encoded optical sampling technology [1] including Mach-Zehnder interferometer (MZI) based [2] and Fabry-Perot interferometer (FPI) based [3] ADCs, the voltage period of sampled optical pulse sequence from a higher bit is a twice as high as that from an adjacent lower one due to the halved electrode length, thus sampling and encoding are performed at the same place. However, the analog voltage applied on all electrode pairs simultaneously diminishes the modulation bandwidth, and the voltage requirement is very high for multi-bit conversion, which makes the device size too large and the fabrication difficult. In interleaving methods, including WDM [4] , TDM [5] , and time-stretching (TS) of optical pulses sampled [6] , high-rate sampled pulses are divided into several groups, which are converted separately by low-rate electronical ADCs and then interleaved to obtain high-rate digital outputs. Recently, method of photovoltaic [7] , photoconductive [8] S/H, and photoemissive generation of electron pulse train for deflection by analog voltage onto spatially encoded receiver array [9] are reported. Such as Nonlinear optics based ADC setups achieve, e.g., sampling by four wave mixing (FWM) [10] , encoding and quantizing by soliton self-frequency shift (SSFS) and interleaving filters [10,11] .In this letter, a novel method of separating sampling and encoding is proposed; thereby independent optimizations of sampling rate and bit-resolution are possible. To exemplify the conversion idea simply, a 5-bit device structure consisted of FPIs, as illustrated schematically in Fig. 1, is analyzed and numerically simulated. In the left dash-dotted box, the analog voltage is sampled and transformed into wavelength representation, and in the right one, the output of the first box is encoded in wavelength domain. Sampling is accomplished in the former box, and encoding is in the latter. Fig.1 Device structure of a 5-bit OSEADC.Mode-locked laser pulse is injected into an electro-optical FPI via dispersion-flattened fiber (DFF) and band-pass filter (BPF). The filtered light is distributed to encoder array and reference channels, then detected and comp...