Tunable Time Delay Research Articles

Tunable time delay in active fiber Bragg grating coupler

Slowing down velocity and controlling time delay of optical pulses in fiber have many potential applications in optical communication systems, and a number of theoretical and experimental studies have been done. In this paper, the transmission spectrum and reflective spectrum of active fiber Bragg grating (FBG) couplers are studied, and the analytic expressions of dispersion and time delay are obtained. By changing the detuning and gain coefficient, different dispersions and time delays in active fiber Bragg grating coupler are obtained. The results show that different detunings and gain coefficients can result in various time delays, and thus tunable time delay could be achieved by changing signal frequency or gain coefficient.

An Analog Integrated Circuit Beamformer for High-Frequency Medical Ultrasound Imaging

We designed and fabricated a dynamic receive beamformer integrated circuit (IC) in 0.35-μm CMOS technology. This beamformer IC is suitable for integration with an annular array transducer for high-frequency (30-50 MHz) intravascular ultrasound (IVUS) imaging. The beamformer IC consists of receive preamplifiers, an analog dynamic delay-and-sum beamformer, and buffers for 8 receive channels. To form an analog dynamic delay line we designed an analog delay cell based on the current-mode first-order all-pass filter topology, as the basic building block. To increase the bandwidth of the delay cell, we explored an enhancement technique on the current mirrors. This technique improved the overall bandwidth of the delay line by a factor of 6. Each delay cell consumes 2.1-mW of power and is capable of generating a tunable time delay between 1.75 ns to 2.5 ns. We successfully integrated the fabricated beamformer IC with an 8-element annular array. Experimental test results demonstrated the desired buffering, preamplification and delaying capabilities of the beamformer.

Slow-light element for tunable time delay based on optical microcoil resonator

We propose a simple and compact slow-light element by use of an optical microcoil resonator (OMR) constituted by two microfiber coils. Based on the matrix exponential method, we solve the coupled-wave equations of the OMR with n turns of microfiber coils and obtain a general solution. Simulations indicate that a tunable slow-light propagation can be obtained by controlling the coupling coefficient between the two adjacent microfiber coils by means of regulating the voltage applied to the ferroelectric crystal. A slow-light time delay up to 62 ps with a bandwidth of 0.4 nm is performed at the wavelength around 1.5 μm.

Continuously Tunable Slow and Fast Light by Using an Optically Pumped Tilted Fiber Bragg Grating Written in an Erbium/Ytterbium Co-Doped Fiber

Continuously tunable slow and fast light is achieved by using a tilted fiber Bragg grating (TFBG) written in an erbium/ytterbium co-doped fiber. By pumping the TFBG, the magnitude and group delay responses of the cladding mode resonances are changed, which can be used to achieve a tunable time delay or time advance. The proposed method is demonstrated by an experiment in which a tunable time delay from to 18 ps corresponding to a fast to a slow light is achieved for a 13.5-GHz Gaussian pulse.

Influence of coupling conditions on the time delay characteristics of parallel-cascaded optical waveguide ring resonators

The influence of coupling conditions of parallel-cascaded waveguide ring resonators on the time delay application in the optically phased array antennas is analyzed. Two kinds of coupling conditions, over-coupling and restriction free are considered to achieve a certain target delay time by parallel-cascaded three ring resonators. The results show that the restriction free coupling condition is better than the over-coupling one to obtain a flat time delay response in the target delay bandwidth especially for the small target delay time, which is the advantage of ring-resonator-based tunable true time delay line. The influence of round-trip loss on the time delay response and the transmission amplitude response is also investigated, which indicates that ring resonators with low optical round-trip loss are preferred to achieve a high performance true time delay line.

All-optical switchable Manchester decoder using semiconductor optical amplifier and optical delay line

An all-optical Manchester decoder is proposed and experimentally demonstrated utilising cross-gain modulation in a semiconductor optical amplifier and tunable time delay in an optical delay line. The proposed scheme is switchable between inverted decoding and non-inverted decoding for the input Manchester encoded signal at 10 Gbit/s application.

Free-space optical delay interferometer with tunable delay and phase

A free-space optical delay interferometer (DI) featuring a continuously tunable time delay, polarization insensitive operation with high extinction ratios and accurate phase and time delay monitoring scheme is reported. The polarization dependence is actively mitigated by adjusting a birefringent liquid-crystal device. The DI has been tested for reception of D(m)PSK signals.

Continuously Tunable Time Delay Using an Optically Pumped Linear Chirped Fiber Bragg Grating

A simple method to achieve a large and tunable time delay of an optical signal by using a linearly chirped fiber Bragg grating (LCFBG) written in an erbium-ytterbium (Er/Yb) codoped fiber is proposed and demonstrated. The group delay response of the LCFBG can be tuned by optically pumping the LCFBG with different pumping powers, which leads to the tuning of the time delay. An LCFBG written in an Er/Yb codoped fiber is fabricated. A continuously tunable time delay up to 200 ps for a Gaussian pulse with a full-width at half-maximum of 7.6 GHz is experimentally demonstrated. The influence of the dispersion, the magnitude and group delay ripples of the LCFBG on the time delay performance, and also the stability of operation are investigated.

Electro-optical tunable time delay and advance in a silicon feedback-microring resonator

We report the demonstration of electro-optical tunable time delay and advance using a silicon feedback-microring resonator integrated with p-i-n diodes. By controlling the feedback and round-trip phase shifts through the carrier-injection-based free-carrier dispersion effect, we obtain a large dynamic time tuning range (-88 ps to 110 ps) upon dc bias voltage change in the range of few tens of millivolts at a given resonance wavelength. We also demonstrate tunable time delay and advance at different resonance wavelengths within 0.76 nm wavelength range.

Broadband true time delay for microwave signal processing, using slow light based on stimulated Brillouin scattering in optical fibers

We experimentally demonstrate a novel technique to process broadband microwave signals, using all-optically tunable true time delay in optical fibers. The configuration to achieve true time delay basically consists of two main stages: photonic RF phase shifter and slow light, based on stimulated Brillouin scattering in fibers. Dispersion properties of fibers are controlled, separately at optical carrier frequency and in the vicinity of microwave signal bandwidth. This way time delay induced within the signal bandwidth can be manipulated to correctly act as true time delay with a proper phase compensation introduced to the optical carrier. We completely analyzed the generated true time delay as a promising solution to feed phased array antenna for radar systems and to develop dynamically reconfigurable microwave photonic filters.

Tunable optical time delay of quantum signals using a prism pair

We describe a compact, tunable, optical time-delay module that functions by means of total internal reflection within two glass prisms. The delay is controlled by small mechanical motions of the prisms. The device is inherently extremely broad band, unlike time delay modules based on "slow light" methods. In the prototype device that we fabricated, we obtain time delays as large as 1.45 ns in a device of linear dimensions of the order of 3.6 cm. We have delayed pulses with a full width at half-maximum pulse duration of 25 fs, implying a delay bandwidth product (measured in delay time divided by the FWHM pulse width) of 5.8 x 10(4). We also show that the dispersion properties of this device are sufficiently small that quantum features of a light pulse are preserved upon delay.

Electro-optical tunable time delay and advance in silicon microring resonators

We demonstrate electro-optical tunable time delay and advance in a silicon-microring-resonator-based notch filter integrated with a lateral p-i-n diode. We tune the time delay and advance by controlling the coupling regimes from over- to under-coupling through carrier-injection-based free-carrier dispersion effect. We measure maximum time delay and advance of approximately -95 and approximately 96 ps near critical coupling, with bandwidths of approximately 3.5 and approximately 3 GHz, upon dc power consumption in the range of 1 mW. We model the transmission spectra and time delay/advance using the transfer-matrix method and analyze the time-intensity and time-bandwidth products, which show good agreement with our measurements.

Low distortion, continuously tunable, positive and negative time delays by slow and fast light using stimulated Brillouin scattering

We demonstrate a single optical timing module that can provide both tunable delay and advancement with low distortion using a reconfigurable gain medium based on stimulated Brillouin scattering. Dual-stage intensity modulation method is used to achieve optimized gain profiles for both slow- and fast-light operation. Using 6.5 ns Gaussian pulses, we demonstrate a continuous temporal adjustment from a fractional advancement of 0.31 to a fractional delay of 0.82, giving more than a full pulse width of total tunability.

Gain-assisted time delay of plasmons in coupled metal ring resonator waveguides

Coupled metal ring resonator waveguides filled with optical active materials are proposed to achieve the slow light and tunable time delay. The tunable group index and time delay are realized by the dispersion of the active materials and its interplay with that of the geometric structure of the waveguides. Our results from the transfer matrix analysis and finite-difference time-domain numerical simulation show that the anomalous dispersion of the active materials can help to amplify the group index determined by the waveguide geometry. Based upon this structure, a variable-bit-rate optical time-division-multiplexing system is numerically demonstrated.

Tunable optical delays based on Brillouin dynamic grating in optical fibers

We demonstrate a novel kind of tunable optical delays based on dynamic grating generated by Brillouin scattering in an optical fiber. An axial strain gradient is applied to a 15 m section of a polarizationmaintaining fiber, and the Brillouin reflection grating is generated position-selectively by controlling the optical frequencies of Brillouin pump waves. Tunable time delays of up to 132 ns are achieved with an 82 ns Gaussian pulse.

Adiabatic self-tuning in a silicon microdisk optical resonator

We demonstrate a method for adiabatically self-tuning a silicon microdisk resonator. This mechanism is not only able to sensitively probe the fast nonlinear cavity dynamics, but also provides various optical functionalities like pulse compression, shaping, and tunable time delay.

CRLH Delay Line Pulse Position Modulation Transmitter

A composite right/left-handed delay line pulse position modulation (PPM) transmitter is proposed. This system, compared with conventional transmitters, exhibits the advantages of simple design, continuously tunable time delay and multiple order PPM capability. It is demonstrated by circuit and experimental results for both binary and quaternary PPM.

Ultrawideband monocycle pulse generation using dual-output intensity modulator

An approach to generate ultrawideband (UWB) monocycle pulses is proposed and experimentally demonstrated, based on a dual-output intensity modulator and tunable optical time delay. Positive and negative pulses are obtained from two output ports of the modulator, respectively, and are coupled together through different time delays. The generated monocycle pulse has a 10-dB bandwidth of 6.5 GHz and a central frequency of 3.7 GHz.

An Electronic UWB Continuously Tunable Time-Delay System With Nanosecond Delays

We propose and demonstrate an electronic system achieving continuously tunable time-delays with nanosecond-scale delay excursions for ultra-wideband signals. Our demonstration system yields an adjustable delay of up to 1.6 ns for input signals spanning 3 to 7 GHz. The key component is a dispersive length of microstrip line created by etching a chirped electromagnetic bandgap structure in the conducting strip.

Switchable and tunable microwave photonic filter using a variable polarization beamsplitter in a Sagnac interferometer

A tunable and switchable coherence-free microwave photonic filter configuration is proposed. It is designed using a Sagnac interferometer consisting of a variable polarization beamsplitter-based fiber loop, a phase modulator and a tunable time delay line. The variable polarization beamsplitter generates a phase difference between the clockwise and counterclockwise waves propagating inside the fiber loop interferometer. This structure realizes filters with the capability of switching between bandpass and low pass response. Measured results match closely with the theoretical analysis and demonstrate a robust notch filter response.