Switched Delay Lines Research Articles

Continuously tunable silicon waveguide optical switched delay line based on grating-assisted contradirectional coupler

The integrated optical delay line plays a crucial role in microwave photonic chips. Continuous tunability is a growing trend in filtering and beamforming techniques of microwave photonics. Based on the silicon platform, we present and experimentally demonstrate an integrated continuously optical tunable delay line (OTDL) chip, which contains a 4-bit optical switched delay line (OSDL) and a thermally tunable delay line based on grating-assisted Contradirectional coupler (CDC). The OSDL can achieve stepwise optical delays, while the CDC is introduced to improve delay tuning resolution within one step delay of the OSDL. The combination of the two modules can realize tuning delays from 0 to 160 ps. Additionally, it is easy to increase the maximum delay by cascading more optical switches. The experimental results demonstrate that the proposed OTDL shows outstanding performance and good expansibility.

Design of CMOS Integrated Circulator Based On Sequentially Switched Delay Lines With Body-Floating and Clock Boosting Techniques

Design of CMOS Integrated Circulator Based On Sequentially Switched Delay Lines With Body-Floating and Clock Boosting Techniques

A High Performance Silicon Nitride Optical Delay Line With Good Expansibility

In this paper, based on the double strip silicon nitride platform, we designed and fabricated a low loss continuously tunable broadband optical delay line, which contains a 5-bit optical switched delay line and a single tunable optical ring resonator working at “off-resonance”. Optical double sideband modulation link measurement results show it can achieve continuous delay tuning of 395.5 ps and in-band delay fluctuations of about 4 ps and 1 ps were obtained in 8 GHz and 5 GHz working bandwidths, respectively. In addition, the proposed optical delay line has a low on-chip insertion loss of 3 dB and a very low optical loss delay ratio of 0.0022 dB/ps. Moreover, it's delay tuning range can be easily increased by cascading more thermo-optic switches. The delay bandwidth can be expanded by adopting the optical single sideband modulation or increasing the FSR of the optical ring resonator. This integrated tunable optical delay line with good overall performances and expand ability shows great potential for microwave photonic applications.

Ultra-Wide Band On-Chip Circulator With Sequentially Switched Delay Lines (SSDL)

The Sequentially-Switched Delay Lines (SSDL) consists of a set of RF switches and transmission lines of equal length which provides magnetless nonreciprocity with no theoretical bandwidth limit. SSDL circulator architectures are presented in this paper on a GaN MMIC. The SSDL circulators presented here demonstrate nonreciprocity from 10MHz to 1.2GHz with isolation between the transmitter and receiver which is greater than 20dB for most of the measured frequency range. The insertion loss of the GaN MMIC SSDL circulator is reduced to below 3dB from 10MHz to 800MHz, by using matching circuits at the gates of the switching transistors. The spurious-free operation of the SSDL circulator is also verified from 10MHz to 1GHz. It is also demonstrated that with passive bootstrapping, SSDL insertion loss is further reduced to about 2dB and P1dB performance can be significantly enhanced by an additional 10dB. The time-modulation/switching strategy to achieve broadband magnetless nonreciprocity has the potential to be used in future STAR and full duplex communication systems.

Slow light in a 2D semiconductor plasmonic structure

Spectrally narrow optical resonances can be used to generate slow light, i.e., a large reduction in the group velocity. In a previous work, we developed hybrid 2D semiconductor plasmonic structures, which consist of propagating optical frequency surface-plasmon polaritons interacting with excitons in a semiconductor monolayer. Here, we use coupled exciton-surface plasmon polaritons (E-SPPs) in monolayer WSe2 to demonstrate slow light with a 1300 fold decrease of the SPP group velocity. Specifically, we use a high resolution two-color laser technique where the nonlinear E-SPP response gives rise to ultra-narrow coherent population oscillation (CPO) resonances, resulting in a group velocity on order of 105 m/s. Our work paves the way toward on-chip actively switched delay lines and optical buffers that utilize 2D semiconductors as active elements.

Interference and frequency-to-time mapping based high anti-jamming and anti-interception frequency hopping receiving.

We have proposed an interference and frequency-to-time mapping based high anti-jamming and anti-interception frequency hopping receiving scheme. By changing the delay difference between the interference arms through high-speed switchable delay lines and using electrooptical sampling, fast and large-range frequency hopping signals can be received. Benefited from the high shaping resolution for using the interference as the spectral shaping method, more receiving passbands in high frequency bands can be available to enhance the anti-jamming and anti-interception performance. By fast pulse shaping through switchable delay lines, the bandwidth of the electric end, the sampling rate, and the number of frequencies in the frequency hopping pattern are decoupled, and the bandwidth of the electric end can be reduced to improve the receiving selectivity. In experiments, the signal hopping from 15.2 GHz to 35.4 GHz with the switching time up to that of the used optical switch is received. Utilizing a switchable delay line in the interference arm with the tuning step of 2.5 ps, eight available receiving passbands within 25 GHz to 42 GHz are generated. The receiving selectivity is also improved from 18.3 to 43.7 in terms of Q factor by decreasing the electric end's bandwidth in experiments.

A wideband 1[formula omitted]4 optical beam-forming chip based on switchable optical delay lines for Ka-band phased array

Comparing with electronic beam forming, integrated optical beam forming is very promising for optical controlled phase array system, because much broader band beam steering can be achieved without the beam squint effect. The single channel optical true time delay lines based on the cascade microring resonators and switched optical delay waveguides have been extensively investigated. The optical beam forming chip based on multi-channel microring resonators have also been demonstrated, however only limited working bandwidth were obtained due to their inherent tradeoff between the delay and bandwidth. The bandwidth limitation can be overcome by using integrated optical beam forming chip composed of switched optical delay waveguides, which has not been demonstrated and evaluated. Here, a 1×4 optical beamforming chip with four integrated switchable delay lines units designed to control the Ka-band phased antenna arrays is proposed and demonstrated experimentally. The maximum delay of 96 ps with a delay increment about 3.02 ps/stage was obtained, which is in accordance with the design well. Based on the measured delay times, the directional diagrams of the optical beamforming network were simulated and beam angle coverage of 90° can be achieved. Furthermore, a magnitude response experiment was carried out to evaluate the performance of the optical beam forming chip, and a remarkable working bandwidth of 29 GHz was achieved.

Fast and large-range frequency hopping receiving based on simultaneous photonic filtering and digitizing.

We propose a frequency hopping receiving method that can receive signals with a large frequency hopping range and rapid hopping speed simultaneously. It is based on simultaneous photonic filtering and digitizing, and the reception frequency is tuned by changing the temporal shape of the sampling optical pulse. The proposed receiving method is verified by an experimental verification scheme. In the verification scheme, the optical pulse from a mode-locked laser is shaped to obtain several sub-pulses with different temporal shapes by spectral shaping and frequency-to-time mapping. The reception of the frequency hopping signal is performed by introducing certain delay through a switchable delay line to select different sub-pulses as the optical sampling pulse. The frequency hopping speed and range of the verification scheme are limited mainly by the speed of the optical switches and the bandwidth of electro-optic modulators, respectively. In experiments, with available devices, frequency hopping signals with a switching time of 250 ns and signals whose carrier frequency hops from 13.35 GHz to 39.30 GHz are successfully received.

Adaptive delay lines for absolute distance measurements in high-speed long-range frequency scanning interferometry

The application of frequency scanning interferometry to long-range (∼10 m) high-speed (upwards of 105 coordinates s−1) absolute distance measurement is currently impractical at reasonable cost due to the extremely high modulation frequencies (typically 100 GHz or more). A solution is proposed here based on an adaptive delay line architecture, in which the reference beam passes through a series of N switchable delay lines, with exponentially-growing delays. The benefits include a reduction by a factor of 2 N in the required signal sampling rate, in the size of dataset to be processed, and in minimum allowable source coherence length, thus paving the way for the use of fast sweeping sources such as vertical-cavity surface-emitting lasers (VCSELs) and Fourier-domain mode-locked (FDML) lasers for long-range lidars. The validity of the principle has been demonstrated experimentally by means of a three-switch prototype.

Magnetic-Free Nonreciprocal Multifunction Device Based on Switched Delay Lines

A magnetic-free multifunction nonreciprocal device based on switched delay lines (SDLs) has been proposed in this paper. It is constructed with two double balanced gyrators (DBGs) and four baluns, each pair of differential ports of the balun connect the ports at the same orientation of the two DBGs, respectively. Due to the asymmetry of the clock control signals acting on the switches, the time reversal symmetry of the transmission line between the Gilbert quad-switch-sets (GQSS) can be broken to achieve non-reciprocity. It can be used as a circulator, gyrator, or isolator by setting different control signals. The device has infinite working bandwidth in theory based on the SDLs. Common mode interference can be better suppressed by using differential transmission structures. Moreover, power capacity can be improved compared to the previous work. Then, experiments have been done to verify the device as a circulator. Broadband property and the anti-interference property have been verified.

A Radio Frequency Nonreciprocal Network Based on Switched Acoustic Delay Lines

This work demonstrates the first non-reciprocal network based on switched low-loss acoustic delay lines. The 4-port circulator is built upon a recently reported frequency-independent, programmable, non-reciprocal framework based on switched delay lines. The design space for such a system, including the origins of the insertion loss and harmonic responses, is theoretically investigated, illustrating that the key to better performance and low-cost modulation signal synthesis lies in a large delay. To implement a large delay, we resort to in-house fabricated low-loss, wide-band lithium niobate (LiNbO3) SH0 mode acoustic delay lines employing single-phase unidirectional transducers (SPUDT). The 4-port circulator, consisting of two switch modules and one delay line module, has been modularly designed, assembled, and tested. The design process employs time-domain full circuit simulation and the results match well with measurements. A 18.8 dB non-reciprocal contrast between insertion loss (IL = 6.6 dB) and isolation (25.4 dB) has been achieved over a fractional bandwidth of 8.8% at a center frequency 155 MHz, using a record low switching frequency of 877.19 kHz. The circulator also shows 25.9 dB suppression for the intra-modulated tone and 30 dBm for IIP3. Upon further development, such a system can potentially lead to future wide-band, low-loss chip-scale nonreciprocal RF systems with unprecedented programmability.

Pseudo-monopulse tracking method for low profile mobile satellite antenna system

A novel pseudo-monopulse tracking (PMT) method is presented for Ku-band Satcom-on-the-move (SOTM). An antenna architecture consisting of multiple distributed panels capable of moving back and forth mechanically is introduced firstly, which can effectively reduce the overall height. Two independent beams with hybrid beam steering approach are introduced to keep the excellent performance in terms of tracking accuracy and antenna gain over wide scan coverage. Then, a hybrid compensation method using switched delay lines and phase shifters is applied to solve the frequency scan effect. Finally, the tracking beam is sequentially scanned at a prescribed offset angle in different directions, and the pointing error is calculated by comparing the corresponding received beacon signal strengths. Simulation results confirm the veracity of the proposed tracking method.

Four‐bit W‐band switched line phase shifter in 90 nm SiGe

A switched delay line phase shifter implemented in a 90 nm SiGe BiCMOS process utilising PIN diodes is presented. The 4-bit phase shifter utilises four SP4T switches for a simplified architecture. The frequency of operation is from 75 to 100 GHz, and the simulated input referred P1dB is 28.5 dBm. This type of phase shifter is especially suitable for high power transmit linear phased arrays. The chip occupies an area of 2.76 mm2 including the pads.

Miniaturized switched line MEMS phase shifter

AbstractIn this article, we propose a novel miniaturized MEMS phase shifter which relies on the loading of meander line and Complementary split ring resonators meta‐material conception to resolve the issues of miniaturization and insertion loss in the transmission line. The proposed phase shifter purely entrenched upon the switchable delay line and a reference line design, which is inline with a metal contact series switch.The phase shifter and RF switches are built on a 50 Ω coplanar waveguide transmission line. One of the unique features of the switch is shaped with triangular to obtain good RF and mechanical characteristics in terms of return loss, isolation, insertion loss, pull in voltage, and stress profile. The result shows, that the mechanical performance of the triangular series switch has low actuation voltage of 5.67 V with a stress value of 5 MPa and the calculated switching time is 3.9 µs. The RF performance of the triangular switch showed an insertion loss of −0.2 with −20 dB of a return loss in the ON state, whereas, in the OFF state, isolation is around −26 dB at DC −20 GHz. The proposed switch was used to build the miniature phase shifter. The average values of the miniaturized 5‐bit phase shifter (11.25, 22.5°, 45°, 90°, and 180°) return loss and insertion loss is −16.68 and −1.35 dB and phase error is less than 0.57°. Overall, 30% size reduction in the miniaturized phase shifter is obtained using triangular single pole single throw switches.

E-Band 4-Bit Phase Shifter using SP4T Flip Chip Switches

Abstract A 4-bit millimeter-wave switched delay line phase shifter is presented. The phase shifter is designed using commercially available SP4T flip-chip millimeter-wave monolithic integrated circuits (MMICs) attached to an alumina substrate. The module operates in the E-Band from 82 – 84 GHz and has an average insertion loss of 20 dB. The size of the module is 10 mm × 7.5 mm. This paper presents a cost effective 4-bit E-Band phase shifter.

Continuously tunable ultra-thin silicon waveguide optical delay line

As light cannot be stopped or directly stored in any media, optical delay lines are usually used to temporally trap the optical signals. We report a wide-range continuously tunable optical delay line chip consisting of a ring resonator array and a Mach–Zehnder interferometer (MZI) switch array on the 60-nm-thick silicon waveguide platform. The ring delay line provides continuous delay tuning of more than 10 ps with a push–pull differential tuning method. The MZI switchable delay line provides digitally programmable delay tuning with a resolution of 10 ps upon reconfiguration of the MZI switches to establish different optical routing paths. Dual-stage MZI switches are used to ensure low crosstalk with an improved signal-to-noise ratio. The delay line chip can generate a maximum delay of >1 ns with an on-chip insertion loss of 12.4 dB. Optical pulse time-division multiplexing and quasi-arbitrary waveform generation are realized based on the delay line chip. These results represent a significant step towards the realization of highly reconfigurable optical signal processors enabled by optical delay manipulation with broad applications for optical communications and microwave photonics.

A Low-Cost 2 <formula formulatype="inline"> <tex Notation="TeX">$\times$</tex> </formula> 2 Planar Array of Three-Element Microstrip Electrically Steerable Parasitic Array Radiator (ESPAR) Subcells

<?Pub Dtl=""?> A low-cost electrically scanned phased array utilizing microstrip patch electrically steerable parasitic array radiator (ESPAR) subarray cells is presented for the first time. Four single-layer three-element ESPAR subarray cells at one-wavelength spacing are uniformly illuminated by a corporate feed network consisting of microstrip Wilkinson power dividers and ring hybrids. The array is scanned using a combination of ESPAR capacitive mutual coupling control and microstrip switched delay line phase shifters at the subarray level to achieve a scanning range from <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$-{\hbox{20}}^{\circ}$</tex></formula> to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$+{\hbox{20}}^{\circ}$</tex></formula> while maintaining high return loss. The ESPAR coupling technique allows a 50% reduction in the number of phase shifters used by utilizing a full wavelength subcell spacing, resulting in excellent performance with inexpensive fabrication. The fabricated prototype exhibits boresight gain of 12.1 dBi with low scan loss and 7.0-dB worst case sidelobe level. The array is compared quantitatively to thinned arrays with and without parasitic elements to illustrate this advantageous technique. A functional prototype is fabricated and measured and is aptly predicted by the full-wave model.

Design and development of a CPW-based 5-bit switched-line phase shifter using inline metal contact MEMS series switches for 17.25 GHz transmit/receive module application

A radio frequency micro-electro-mechanical system (RF-MEMS) phase shifter based on switchable delay line concept with maximum desirable phase shift and good reliability is presented in this paper. The phase shifter is based on the switchable reference and delay line configurations with inline metal contact series switches that employs MEMS systems based on electrostatic actuation and implemented using coplanar waveguide (CPW) configuration. Electromechanical behaviour of the MEMS switch has been extensively investigated using commercially available simulation tools and validated using system level simulation. A detailed design and performance analysis of the phase shifter has been carried out as a function of various structural parameters with reference to the gold-based surface micromachining process on alumina substrate. The mechanical, electrical, transient, intermodulation distortion (IMD) and loss performance of an MEMS switch have been experimentally investigated. The individual primary phase-bits (11.25°/22.5°/45°/90°/180°) that are fundamental building blocks of a complete 5-bit phase shifter have been designed, fabricated and experimentally characterized. Furthermore, two different 5-bit switched-line phase shifters, that lead to 25% size reduction and result in marked improvement in the reliability of the complete 5-bit phase shifter with 30 V actuation voltage, have been developed. The performance comparison between two different CPW-based switched-line phase shifters have been extensively investigated and validated. The complete 5-bit phase shifter demonstrates an average insertion loss of 5.4 dB with a return loss of better than 14 dB at 17.25 GHz. The maximum phase error of 1.3° has been obtained at 17.25 GHz from these 5-bit phase shifters.

Switched Delay Line Reconfigurable L‐Band Filter with High Out‐of‐Band Suppression

ABSTRACTA switched delay line reconfigurable filter with high out‐of‐band suppression using double‐behavior resonator (DBR) is presented. The novel filter has features of higher stopband rejection and easy processing compared to the conventional one. The DBR resonator can produce transmission zeros, which obviously improves the out‐of‐band suppression. The prototype of the filter operating at 1G/1.3G/1.6G with 50‐dB suppression is designed and fabricated. The simulated and measured results show good agreement. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2438–2440, 2013

Photonic integrated Brillouin optical time domain reflection readout unit

Brillouin scattering can be used for determining strain distributions along fibers. This is a convenient way to monitor the structural integrity of large constructions. However, the high cost of the optical circuitry has prevented wide use of this technique. We report on a design study on an integrated optical circuit for a Brillouin optical time domain reflection readout unit with low-cost potential. The circuit contains narrow linewidth tuneable distributed Bragg reflector (DBR) lasers, photodiodes with an optical mixer for coherent detection, a 10-bit digitally switched delay line for frequency tuning, and a switching fabric that allows three modes of operation. Such a circuit can be realized through one of the upcoming foundries in the field of photonic integration.