Variable Delay Line Research Articles

New topology for a variable differential delay line using the FGMOS transistor

In this study, we show that floating gate MOS (metal oxide semiconductor) transistors support a low-voltage and low-power variable analogue differential delay line circuit for signals in the audio frequency range. The delay time is dependent and accomplished by a variable bias voltage. Attention is focussed on the fact that the topology will be implemented taking into account low-voltage and low-power. The CMOS (complementary metal oxide semiconductor) circuit design is based on the G m − C low-pass linear integrator as the main core. This way, a delay line circuit with two taps was implemented in a 1.2-μm CMOS technology. The experimental results show a spurious free dynamic range of 56 dB, a total harmonic distortion of 0.56% and power dissipation of 52 μW with a supply voltage of 1.5 V.

Quadrupling Optical Delay Range Using Polarization Properties

We describe a scheme to quadruple an optical delay using polarization properties of light in a fiber and demonstrate a fast variable delay line with a record-setting delay range of 72 mm at a speed of ~ 2 kHz (corresponding to ~ 136 m/s). The method can find various applications where a large optical delay or a high-speed delay variation is required, including optical coherent tomography, optoelectronic oscillator, programmable optical delay lines, and optical delay buffers.

RF Photonics

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In parallel with the development of fiber optics for transmission of digital information, the 1970s and 1980s saw the development of techniques for the transmission of wide-bandwidth analog radio-frequency (RF) signals over optical fibers. The simultaneous need for high linearity and high signal-to-noise in RF photonic links spurred the development of lasers, modulators and detectors matched to the special needs of such links. RF photonics was also explored for the processing of RF signals by means of optically implemented filters and variable-delay lines. Commercial applications of RF photonics included cable television signal distribution and subcarrier-multiplexed digital signals. </para>

Integrated 10 Gb/s AWG-based correlator for multi-wavelength optical header recognition

In this paper we experimentally demonstrate a novel optical correlator employing dual integrated Arrayed Waveguide Grating (AWG) in conjunction with variable delay lines. The variable delay lines provide wavelength-dependent time delays and generate a wavelength profile that matches arbitrary bit patterns, whereas the AWGs are used to demultiplex and multiplex the wavelength components of the multi-wavelength header bit pattern. The recognition of 4-bit optical patterns at different wavelengths is experimentally demonstrated at 10 Gb/s by showing that the correlator produces an autocorrelation waveform of high peak whenever the input bit pattern matches the wavelengths profile, and a low-amplitude cross-correlation function otherwise.

A diffraction-compensating –25ns free space terahertz delay line for coherent quantum control

Free space delay lines provide pulses of variable time spacing for optical experiments such as pump-probe spectroscopy and coherent quantum control, including spin and photon echo techniques. However, in the terahertz region of the spectrum, beam divergence due to diffraction limits the useful length of traditional free space delay lines. We present a novel double-folded variable delay line for light in the frequency range 0.24–1.2THz, which incorporates a symmetric arrangement of lenses whose spacing can be adjusted to compensate for diffraction at each delay. Scalable for use in other wavelength regimes, the design relays an input Gaussian beam waist to the output with up to 25ns (∼8m) total delay and is enclosed in a desiccated volume of &amp;lt;0.5m3. The delay line can deliver two or three pulses with relative amplitudes controlled via variable spacing silicon étalon beam splitters. Profiles of a 0.24THz beam show good agreement with calculations at long delays, with insertion loss per delay stage of ∼3dB.

Continuously tunable incoherent microwave photonic filter using a tunable Mach‒Zehnder interferometer as the slicing filter

AbstractA continuously tunable incoherent microwave photonic filter employing a tunable Mach‐Zehnder interferometer (MZI) as the slicing filter is studied. By incorporating the optical variable delay line (OVDL), the frequency spacing of the MZI can be tuned continuously, which in turn makes the whole microwave photonic filter continuously tunable in a wide frequency range. The frequency response characteristics are studied and some simulation results are also given to optimize the present microwave photonic filter. Experimental results show the present filter has good frequency response characteristics and tuning linearity. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2382–2386, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22732

A tunable and reconfigurable microwave photonic filter based on a Raman fiber laser

A tunable and reconfigurable microwave photonic filter is demonstrated by employing a tunable Mach–Zehnder interferometer (MZI) and a wavelength-controllable Raman fiber laser. The free-spectral-range and spectral response of the microwave photonic filter are tuned and reconfigured by controlling the optical variable delay line in one arm of the MZI and the powers of the pump LDs. Experimental results are given to show the enhanced flexibility of the present microwave photonic filter.

Wavelength-spacing continuously tunable multi-wavelength SOA-fiber ring laser based on Mach–Zehnder interferometer

A Mach–Zehnder interferometer (MZI) which is used as a wavelength-spacing tunable comb filter in a fiber ring laser is built by employing an optical variable delay line (OVDL). Stable multi-wavelength semiconductor optical amplifier (SOA)-fiber ring laser based on an SOA and the MZI comb filter is achieved. Wavelength spacing can be continuously tuned by adjusting the OVDL and, as an example, multi-wavelength lasing with the wavelength spacing of 0.4, 0.8, or 1.6 nm is demonstrated. The output of the proposed multi-wavelength SOA-fiber ring laser is quite stable at room temperature and the output spectrum can be adjusted by controlling the bias current of the SOA.

500-MS/s 5-bit ADC in 65-nm CMOS With Split Capacitor Array DAC

A 500-MS/s 5-bit ADC for UWB applications has been fabricated in a 65-nm CMOS technology using no analog-specific processing options. The time-interleaved successive approximation register (SAR) architecture has been chosen due to its simplicity versus flash and its amenability to scaled technologies versus pipelined, which relies on operational amplifiers. Six time-interleaved channels are used, sharing a single clock operating at the composite sampling rate. Each channel has a split capacitor array that reduces switching energy, increases speed, and has similar INL and decreased DNL, as compared to a conventional binary-weighted array. A variable delay line adjusts the instant of latch strobing to reduce preamplifier currents. The ADC achieves Nyquist performance, with an SNDR of 27.8 and 26.1 dB for 3.3and 239 MHz inputs, respectively. The total active area is 0.9mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and the ADC consumes 6 mW from a 1.2-V supply

Integrated photonic decoder with complementary code processing and balanced detection for two-dimensional optical code division multiple access

We propose a novel integrated photonic decoder for two-dimensional (time spreading, wavelength hopping) optical code division multiple access. The decoder is composed of multiplexers-demultiplexers, variable delay lines, and a coupler, which processes complementary codes and utilizes balanced detection to reduce unwanted cross-correlation interference. We successfully carried out a 10 Gbit/s transmission that demonstrated its effectiveness.

A reconfigurable architecture for continuously variable optical slow-wave delay lines

A novel reconfigurable architecture based on slow-wave propagation in integrated optical ring resonators is proposed for the realization of variable optical delay lines. A continuously variable delay is achieved by combining a coarse discrete (digital) delay, provided by a coupled resonator slow-wave structure, with a fine continuous (analog) delay given by a cascaded ring- resonator phase-shifter. The reflective configuration of the structure enables a simple, accurate and robust tuning of the delay and provides a footprint reduction by a factor 2 with respect to conventional coupled resonator optical waveguides. Proof-of-concept devices realized in 4.4% silicon oxynitride waveguides and activated by a thermal control are discussed. Experimental results demonstrate, in both spectral and time domain, a continuously variable delay, from zero to 800 ps (2 bit fractional delay), on a 2.5 Gbit/s NRZ signal, with less than 8 dB insertion loss and less than 5 mm2 device footprint.

Channel-spacing-tunable multi-wavelength fiber ring laser with hybrid Raman and Erbium-doped fiber gains

A multi-wavelength fiber ring laser of tunable channel spacing is proposed by employing an optical variable delay line (OVDL) in a Mach-Zehnder interferometer. Stable lasing is achieved at room temperature with the hybrid gains of a single mode fiber (as the Raman gain medium) and an Erbium-doped fiber (EDF) in a ring structure. The channel spacing of the present multi-wavelength fiber ring laser can be continuously tuned by adjusting the computer-controlled OVDL.

Wavelength-spacing continuously tunable multiwavelength erbium-doped fibre laser based on DSF and MZI

A novel multiwavelength erbium-doped fibre laser is proposed by incorporating a section of dispersion-shifted fibre (DSF) and a Mach-Zehnder interferometer (MZI). The wavelength spacing of the fibre laser can be continuously tuned by adjusting an optical variable delay line in the MZI-based comb filter. Stable multiwavelength lasing at room temperature with the standard ITU (International Telecommunication Union) channel spacing of 0.2 nm (25 GHz), 0.4 nm (50 GHz), 0.8 nm (100 GHz) or 1.6 nm (200 GHz) is demonstrated.

Continuously Variable Optical Delay Line Based on a Chirped Fiber Bragg Grating

In this letter, a continuously variable optical delay line (ODL), useful for phased array antennas, is experimentally demonstrated. The ODL operates at a single optical wavelength and it is based on a linearly chirped fiber Bragg grating (LCFBG). Continuous true time delay is achieved by changing the temperature of the LCFBG. In order to limit the actuating temperature range, the grating was bonded to a metallic support and the effect of the thermal apparent strain was considered. The time-delay response of the system is measured with an optical signal modulated with double sideband technique at a frequency of 2 GHz. The experimental results demonstrate a time-delay resolution of 3.1 ps employing a temperature controller with a stability of plusmn0.1 degC and a maximum time delay of 96 ps over a temperature range of 16 degC-40degC. The time-delay-temperature characteristic offers a slope of 3.8 ps/degC with a mean-square deviation from the linearity of 3.5 ps. Such a delay line, by operating at a single optical wavelength and by using a simple actuating system, offers many advantages being low cost, compactness, and reliability. The main limitation to the ODL resolution is due to the amplitude ripple of the LCFBG used and a performance enhancement can be obtained with specifically tailored LCFBG

On-Chip Random Jitter Testing Using Low Tap-Count Coarse Delay Lines

An on-chip RMS jitter testing technique for design-for-test (DfT) applications is presented in this paper. In addition to utilizing a less complicated low tap-count variable delay line to sample the jitter's cumulative density function (CDF), a sophisticated post-processing algorithm is developed to enhance process variation tolerance. Our simulation results show that using an eight-tap delay line, the probability of making correct pass/fail decisions is higher than 99% in the presence of up to 30% delay line value deviations.

X-band continuously variable true-time delay lines using air-guiding photonic bandgap fibers and a broadband light source

We propose a novel implementation of true-time delay (TTD) using air-guiding photonic bandgap fibers (PBGFs) and a broadband light source. The air-guiding PBGFs are experimentally studied and used in the TTD module for the first time, to the best of our knowledge. The proposed approach shows the advantages of simple architecture, compact size, larger dispersion, low-temperature sensitivity, and high immunity to nonlinear effects in our experiments. The PBGFs were spliced with single-mode fibers with a 2 dB loss, and the characteristics of the PBGFs were measured. The PBGF-TTD with a continuously tunable time delays from 0 to 500 ps was demonstrated using the amplified spontaneous emission light of an erbium-doped filter amplifier as a broadband light source.

Optical-signal-processing device based on waveguide-type variable delay lines and optical gates

In this paper, an optical-signal-processing device mainly designed for time-slot switching is demonstrated. The device is composed of variable delay-line arrays fabricated by planar lightwave circuit technology and high-speed optical gates. The variable delay-line arrays consist of transversal-form or lattice-form optical circuits. The operating principle is based on serial-to-parallel conversion, adjustment of the delay time between the parallel signals, and the gating of the optical bits or packets in the optical region. The device does not require any interaction between lightwaves through optical nonlinear effects or filter banks for code matching. As an example of its operation, label-processing functions are demonstrated, specifically the label swapping of optical return-to-zero pulses. The merits of the proposed device are described and problems that must be solved are also discussed.

Modeling of periodic distributed MEMS-application to the design of variable true-time delay lines

This paper presents the modeling and design methods of true-time distributed microelectromechanical systems transmission lines (DMTLs) making use of periodic structure theory. New contributions to the analysis and reduction of the microelectromechanical systems (MEMS) shunt capacitors parasitics are also introduced. A prototype of a digital DMTL has been fabricated and measured, showing very good agreement with the comprehensive circuit model used for the design. It is believed that the periodic structure approach presented could be useful for other microwave periodic MEMS devices

New concept of RF functions by microfluidic coupling

We present a new concept that combines microfluidic circuits designed inside planar waveguides for advanced ultra-wide band functions. Feasibility of such approach is demonstrated on a broadband variable delay line operating in the microwave region. We also show that this approach is very well fitted for the future THz circuits. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1912–1916, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21812

Strained Chirped Fiber Bragg Gratings Based all-fiber Variable Optical Delay Line for Optical Coherence Tomography

We present the novel all-fiber optical delay line that can be realized by exploiting the fundamental distributive reflection characteristics of a chirped fiber Bragg gratings (CFBG). With the assist of a strained CFBG and a designed fiber stretcher, the proposed delay line could perform the function (such as attainment of variable large enough optical delay without dispersion mismatch) of the conventional optical delay line within the optical fiber. While the strained CFBG produced 3.1 mm optical delay, the pair of CFBGs in the opposite direction can manage dispersion imbalance of the delay line. The use of the PZT-based fiber stretcher can enable depth scanning at a high repetition rate for real-time imaging. The performance of the delay element is demonstrated with measured experimental results. OCT system embedded with the all-fiber variable optical delay line showed the axial resolution of 100 μm and the dynamic range of 50 dB. The implemented system was used for the imaging of a biomedical sample, which proves the utility of the proposed delay element as a promising alternative of optical delay line.