Photonic Delay Line Research Articles

Highly stable fiber-based photonic delay line with large and tunable delay.

A stable photonic delay line with large and tunable delay is essential for large-distance simulation, beamforming, and diverse photonic signal processing applications. Here, we demonstrate a fiber-based tunable photonic delay line (TPDL) with a maximum delay of 905 µs. Its environmental-related delay jitter is compensated for by a homodyne phase-locked loop (PLL). Precise delay tuning is realized by changing the phase of the reference with a minimum tuning step of 0.5 ps without breaking its locking state. The demonstrated delay line shows exceptional stability, as indicated by an overlapping Allan deviation (ADEV) of 2.06 × 10-17 at the averaging time of 1000 s and the delay jitter below 20 fs. Its high stability, wide delay range, wideband characteristics, and precise tunability make the TPDL an ideal photonic delay line for the above-mentioned applications.

High-density integrated delay line using extreme skin-depth subwavelength grating waveguides.

Optical delay lines control the flow of light in time, introducing phase and group delays for engineering interferences and ultrashort pulses. Photonic integration of such optical delay lines is essential for chip-scale lightwave signal processing and pulse control. However, typical photonic delay lines based on long spiral waveguides require extensively large chip footprints, ranging from mm2 to cm2 scales. Here we present a scalable, high-density integrated delay line using a skin-depth engineered subwavelength grating waveguide, i.e., an extreme skin-depth (eskid) waveguide. The eskid waveguide suppresses the crosstalk between closely spaced waveguides, significantly saving the chip footprint area. Our eskid-based photonic delay line is easily scalable by increasing the number of turns and should improve the photonic chip integration density.

Calibration of an RF/Microwave Phase Noise Meter with a Photonic Delay Line

The main advantage of phase noise meters with photonic (fiber) delay lines is that they do not require high-performance, low-noise reference oscillators. On the other hand, some additional calibrations are required, which are the subject of this paper. First, the quadrature must be maintained on the mixer by precise adjustment of the phase and/or delay. Next, since the response of the mixer is proportional to the square of the input test signal, a precise amplitude calibration is required. Finally, the frequency response of the FFT spectrum analyzer and its corresponding anti-aliasing low-pass filter needs to be known precisely. In this paper, to the best of our knowledge, we present innovative solutions for all three calibrations. All three calibrations were built in and tested in our phase noise meter. The result is a simple and robust phase noise meter suitable for non-laboratory environments.

Ultralow-loss compact silicon photonic waveguide spirals and delay lines

Low-loss and compact optical waveguides are key for realizing various photonic integrated circuits with long on-chip delay lines, such as tunable optical delay lines, optical coherence tomography, and optical gyroscopes. In this paper, a low-loss and compact silicon photonic waveguide spiral is proposed by introducing broadened Archimedean spiral waveguides with a tapered Euler S-bend. A 100-cm-long waveguide spiral is realized with a minimal bending radius as small as 10 μm by using a standard 220-nm-thick silicon-on-insulator foundry process, and the measured propagation loss is as low as 0.28 dB/cm. Furthermore, the present waveguide spirals are used to realize a 10-bit tunable optical delay line, which has a footprint as small as 2.2 mm × 5.9 mm and a dynamic range of 5120 ps with a fine resolution of 10 ps.

Ultra-Low Phase Noise Measurement of Microwave Sources Using Carrier Suppression Enabled by a Photonic Delay Line

We propose and demonstrate a photonic delay line based carrier suppression interferometer system for measuring the phase noise of microwave sources. We show both theoretically and experimentally for the first time that carrier suppression is capable of suppressing the effects of the residual phase noise of the microwave amplifiers and the relative intensity noise of light in the system by up to 70 dB, and therefore effectively eliminates the contributions of these noise sources to the noise floor of the phase noise measurement system. Using a 2-km photonic delay line, we achieved phase noise measurement floors of −126 dBc/Hz at 1 kHz and −152 dBc/Hz at 10 kHz around a 10 GHz carrier, respectively, which are 15 and 20 dB lower than those of a frequency discriminator based phase noise measurement system using the same length of fiber delay and the same optical and microwave components. The noise floor of −152 dBc/Hz at 10 kHz is also 8 dB and 17 dB lower than those of a Keysight E5052B phase noise measurement system with 100-times cross-correlation and without cross-correlation, respectively. Even lower phase noise floors are expected for such a carrier suppression system if microwave phase shifters with lower residual phase noise or a longer photonics delay line are used.

Multi-Stage Mach–Zehnder Based Continuously Tunable Photonic Delay Line

Multi-Stage Mach–Zehnder Based Continuously Tunable Photonic Delay Line

Distortionless Pulse Transmission in Valley Photonic Crystal Slab Waveguide

A valley photonic crystal is one type of photonic topological insulator, the realization of which needs only P-symmetry breaking. The domain wall between two valley-contrasting photonic crystals supports robust edge states, which can wrap around sharp corners without backscattering. Using the robust edge states, one can achieve pulse transmission. Here, using time-domain measurements in the microwave regime, we show distortionless pulse transmission in a sharply bended waveguide. An \ensuremath{\Omega}-shaped waveguide with four 120\ifmmode^\circ\else\textdegree\fi{} bends is constructed with the domain wall between two valley photonic crystal slabs. Experimental results show the progress of Gaussian pulse transmission without distortion, and the full width at half maximum of the output signal changes slightly in the \ensuremath{\Omega}-shaped waveguide. By measuring the steady-state electric field distribution, we also confirm the confined edge states without out-of-plane radiation, which benefits from dispersion below the light line. Our work provides a way for high-fidelity optical pulse signal transmission and the development of high-performance optical elements, such as photonic circuits or optical delay lines.

Broadband continuously tunable microwave photonic delay line based on cascaded silicon microrings.

We present a novel broadband continuously tunable microwave photonic delay line consisting of a modulator, a four-stage microring resonator delay line, a tunable optical bandpass filter, and a photodetector. Unlike the traditional microring delay lines working at the on-resonant wavelength, the microring resonators in our chip work at the anti-resonant wavelengths, leading to a large delay bandwidth and a small delay ripple. The experimental results show that relative group delay can be continuously tuned from 0 to 160 ps for microwave frequencies in the range of 0 to 16 GHz. The delay ripple is less than 6.2 ps. These results represent an important step towards the realization of integrated continuously tunable delay lines demanded in broadband microwave phased array antennas.

Performance analysis of reconfigurable multifunctional photonic filters using triple coupled microring resonators

In this paper, we have introduced a new device architecture based on triple coupled microring resonators structure. The analytical model of the device is developed and performance analysis is carried out. The novelty of this device is that it performs as a multifunctional reconfigurable photonic filter in which multiple filtering functions such as notch, bandpass and bandstop responses are achieved by programming the coupling coefficients associated with it using thermal or electro optic tuning. Moreover, it can be used as a tuneable photonic true time delay line. As a bandpass reconfigurable filter, the maximally flat-top rectangular shape like bandpass response of 42 dB suppression ratio, and maximally flat-top bandwidth tunability of 1 GHz to 45 GHz are achieved. The notch filter response has an ultra-high rejection ratio of 148 dB. The flat bottom bandstop response has high suppression ratio of 81.5 dB within 7 GHz bandwidth. The device exhibits minimum group delay distortion over 18 GHz bandwidth, and a minimum of 8 ps and a maximum of 58 ps time delay tunability.

Optical sensor network interrogation system based on nonuniform microwave photonic filters.

Based on the nonuniformly spaced microwave photonic delay-line filter technology, a new design of a generic optical fiber sensor network interrogation platform is proposed and demonstrated. Sensing information from different types of optical sensors embedded in filter taps is converted into the variations of delay time and amplitude of each filter tap individually. Information to be measured can be decoded from the complex temporal impulse response of the microwave photonic filter. As proof-of-concept, our proposed approach is verified by simulations and experimental demonstrations successfully. Four optical sensors of different types are simultaneously interrogated via inverse Fourier transform of the filter frequency response. The experiment results show good linearity between the variation of temporal impulse response and the variations of the twist, the lateral pressure, the transversal loading and the temperature. The sensitivity of the sensors in the proposed platform is -2.130×10-5 a.u/degree, 6.1039 ps/kPa, -1.9146×10-5 a.u/gram, and 5.1497 ps/°C, respectively. Compared to the conventional optical sensors interrogation system, the presented approach provides a centralized solution that works for different types of optical sensors and can be easily expanded to cover larger optical sensor networks.

Communications: PhotonicsViews 6/2019

PhotonicsViewsVolume 16, Issue 6 p. 12-15 CommunicationsFree Access Communications: PhotonicsViews 6/2019 First published: 14 November 2019 https://doi.org/10.1002/phvs.201970604AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Reference: X. Ji et al.: On-chip Tunable Photonic Delay Line, APL Photonics, online September 17, 2019; DOI: 10.1063/1.5111164 D. A. Walker et al.: Rapid, large-volume, thermally controlled 3D printing using a mobile liquid interface, Science 366, 360 (2019); DOI: 10.1126/science.aax1562 Volume16, Issue6December 2019/January 2020Pages 12-15 ReferencesRelatedInformation

On-chip tunable photonic delay line

An on-chip tunable photonic delay line is a key building block for applications including sensing, imaging, and optical communication. However, achieving long and tunable delay lines within a small footprint remains challenging. Here, we demonstrate an on-chip tunable photonic delay line using ultralow loss high confinement Si3N4 waveguides with integrated microheaters. As an example of potential application, we embed a 0.4 m delay line within an optical coherence tomography (OCT) system. We show that the delay line can extend the OCT imaging range by 0.6 mm while maintaining a high signal to noise ratio. Our tunable photonic delay line is achieved without any moving parts which could provide high stability, critical for interference based applications.

Can a universal quantum cloner be used to design an experimentally feasible near-deterministic CNOT gate?

We propose a non-deterministic CNOT gate based on a quantum cloner, a quantum switch based on all optical routing of single photon by single photon, a quantum dot spin in a double-sided optical microcavity with two photonic qubits, delay lines and other linear optical photonic devices. Our CNOT provides a fidelity of 78% with directly useful outputs for a quantum computing circuit and requires no ancillary qubits or electron spin measurements.

Phase noise measurement of an optoelectronic oscillator based on the photonic-delay line cross-correlation method.

Phase noise measurement of a dual-loop optoelectronic oscillator (OEO) based on a dual- photonic-delay line cross-correlation method is proposed and experimentally demonstrated. The dual-loop OEO and the phase noise measurement system are combined by sharing the transmitter of the optical link, which makes the structure of the system simpler. In part of the dual-loop OEO, the 10km long fiber is shared by the two loops of the OEO utilizing a wavelength division multiplexing technique. Higher quality factors are obtained simultaneously by the two loops. In part of the phase noise measurement system, a lower phase noise floor is realized through a cross-correlation method. In the experiments, a signal with oscillation frequency of 10.664GHz and a side-mode suppression ratio of 82.4dB is generated. Its phase noise is evaluated by the proposed system and PN9000C. The measured results of the two systems are in perfect agreement. The phase noise of the signal is measured as -122 dBc/Hz at a 10kHz frequency offset, and the phase noise floor of the 10μs delay phase noise measurement system is -148 dBc/Hz at a 10kHz offset at 10.6GHz, when the number of averaged results is 100.

Photonics-Based Broadband Microwave Instantaneous Frequency Measurement by Frequency-to-Phase-Slope Mapping

A photonics-based broadband microwave instantaneous frequency measurement (IFM) method is proposed by monotonously mapping the frequency to the slope of the time-varying phase of the microwave signal under test. This frequency-to-phase-slope mapping approach is realized utilizing a variable photonic delay line and a microwave photonic in-phase/quadrature (I/Q) mixer, where the I/Q mixer is composed of two phase modulators connected tail to tail within a fiber loop, an optical 90° hybrid, and a pair of low-speed balanced photodiodes. Thanks to the monotonous frequency-to-phase-slope mapping property, as well as the use of photonic delay line and microwave photonic I/Q mixing, the IFM system can achieve a wide-range frequency measurement without ambiguity. An experiment is performed. The established IFM system is able to operate from 5 to 67 GHz with a measurement error of less than 500 MHz, which achieves the widest frequency measurement range ever recorded by photonics-based IFM systems. In addition, the influences of the I/Q phase mismatch and the amplitude noise on the performance of the IFM system are also discussed. We believe that this photonics-based IFM system is a promising solution for wideband microwave frequency measurements.

Optimization of on-chip photonic delay lines for telecom wavelengths

In this work, we experimentally studied optical delay lines on silicon nitride platform for telecomm wavelength (1550 nm). We modeled the group delay time and fabricated spiral optical delay lines with different waveguide widths and radii as well as measured their transmission. For the half etched rib waveguides we achieved the losses in the range of 3 dB/cm

A Theoretical Model of Dual Tunable Optoelectronic Oscillator

A theoretical model of an electronically tunable multi-loop optoelectronic oscillator (OEO) based on photonic and microwave multiferroic delay lines has been developed. The theory takes into account a dispersion of electromagnetic waves in optical fibers and a dispersion of spin-electromagnetic waves in ferrite-ferroelectric structures. An expression for transfer function of the OEO circuitry was derived. The theory enables one to calculate transmission characteristics and suppression of spurious harmonics of the multi-loop OEOs. The features of both magnetic and electric tunabilities are investigated.

Photonic Delay Lines Based on Silicon Coupled Resonator Optical Waveguide Structures

We propose a Coupled Resonator Optical Waveguide Structure based on silicon microring resonators. The proposed structure is designed on Silicon on Insulator platform so as to scale down the device dimensions as silicon on insulator platform provides the advantage of large index contrast, miniaturization of device dimensions. Tunability is incorporated on the structure in the simulation environment by placing thermal heaters on the top of the rings which change the refractive indices of the rings thereby changing the resonance wavelength. Finite difference time domain method is used to simulate the structure. Variable delays are achieved by tuning the necessary number of ring structures to their resonant wavelengths. This structure can be helpful in realizing optical delay lines for on chip optical interconnects.

Microcomb-Based True-Time-Delay Network for Microwave Beamforming With Arbitrary Beam Pattern Control

Microwave phased array antennas (PAAs) are very attractive to defense applications and high-speed wireless communications for their abilities of fast beam scanning and complex beam pattern control. However, traditional PAAs based on phase shifters suffer from the beam-squint problem and have limited bandwidths. True-time-delay (TTD) beamforming based on low-loss photonic delay lines can solve this problem. But it is still quite challenging to build large-scale photonic TTD beamformers due to their high hardware complexity. In this paper, we demonstrate a photonic TTD beamforming network based on a miniature microresonator frequency comb (microcomb) source and dispersive time delay. A method incorporating optical phase modulation and programmable spectral shaping is proposed for positive and negative apodization weighting to achieve arbitrary microwave beam pattern control. The experimentally demonstrated TTD beamforming network can support a PAA with 21 elements. The microwave frequency range is $\mathbf{8\sim20\ {GHz}}$, and the beam scanning range is $\mathbf{\pm 60.2^\circ}$. Detailed measurements of the microwave amplitudes and phases are performed. The beamforming performances of Gaussian, rectangular beams and beam notch steering are evaluated through simulations by assuming a uniform radiating antenna array. The scheme can potentially support larger PAAs with hundreds of elements by increasing the number of comb lines with broadband microcomb generation.

Photonic-Delay Line Cross Correlation Method Based on DWDM for Phase Noise Measurement

A dual photonic-delay line cross-correlation method for phase noise measurement of microwave signal based on dense wavelength division multiplexing (DWDM) is proposed and experimentally demonstrated. The kilometer-long delay fiber is used together by the two mutually independent channels through the DWDM technology, which makes it easier to get the same delay between two channels. And it reduces the cost of the system by reducing the use of several kilometers of fiber and a Mach-Zendher modulator. Then, it uses variable optical fiber delay lines to replace the electronic phase shifters and a broader operation bandwidth can be obtained. A lower phase noise floor has been obtained by more averaging of the cross-correlation spectrum. In the experiments, the phase noise of a 10-GHz microwave signal has been measured accurately. A large operation bandwidth of 4-11 GHz is achieved and a measurement phase noise floor of -152.6 dBc/Hz at 10 kHz offset at 10 GHz in a 20 μs delay measurement system is realized by averaging 100 times.