Highly sensitive, broadband microwave frequency identification using a chip-based Brillouin optoelectronic oscillator.

Detection and frequency estimation of radio frequency (RF) signals are critical in modern RF systems, including wireless communication and radar. Photonic techniques have made huge progress in solving the problem imposed by the fundamental trade-off between detection range and accuracy. However, neither fiber-based nor integrated photonic RF signal detection and frequency estimation systems have achieved wide range and low error with high sensitivity simultaneously in a single system. In this paper, we demonstrate the first Brillouin opto-electronic oscillator (B-OEO) based on on-chip stimulated Brillouin scattering (SBS) to achieve RF signal detection. The broad tunability and narrowband amplification of on-chip SBS allow for the wide-range and high-accuracy detection. Feeding the unknown RF signal into the B-OEO cavity amplifies the signal which is matched with the oscillation mode to detect low-power RF signals. We are able to detect RF signals from 1.5 to 40 GHz with power levels as low as -67 dBm and a frequency accuracy of ± 3.4 MHz. This result paves the way to compact, fully integrated RF detection and channelization.

On-chip multi-stage optical delay based on cascaded Brillouin light storage.

Storing and delaying optical signals plays a crucial role in data centers, phased array antennas, communication, and future computing architectures. Here, we show a delay scheme based on cascaded Brillouin light storage that achieves multi-stage delay at arbitrary positions within a photonic integrated circuit. Importantly these multiple resonant transfers between the optical and acoustic domain are controlled solely via external optical control pulses, allowing cascading of the delay without the need of aligning multiple structural resonances along the optical circuit.

Brillouin spectroscopy of a hybrid silicon-chalcogenide waveguide with geometrical variations.

Recent advances in design and fabrication of photonic-phononic waveguides have enabled stimulated Brillouin scattering in silicon-based platforms such as underetched silicon waveguides and hybrid waveguides. Due to the sophisticated design and, more importantly, high sensitivity of the Brillouin resonances to geometrical variations in micro- and nano-scale structures, it is necessary to have access to the localized opto-acoustic response along those waveguides to monitor their uniformity and maximize their interaction strength. In this Letter, we design and fabricate photonic-phononic waveguides with a deliberate width variation on a hybrid silicon-chalcogenide photonic chip and confirm the effect of the geometrical variation on the localized Brillouin response using a distributed Brillouin measurement.

On-chip Brillouin purification for frequency comb-based coherent optical communications.

In this Letter, for the first time, to the best of our knowledge, we harness on-chip Brillouin scattering for narrowband amplification and spectral purification of frequency comb lines for coherent optical communications. A parametrically generated optical frequency comb with a low carrier-to-noise power ratio was filtered through narrowband Brillouin amplification utilizing the same comb as the optical pump. This was achieved on a photonic chip to enable successful transmission of an advanced modulation format signal: 64-level quadrature amplitude modulation. 96 Gb/s data were modulated on two polarizations on multiple comb lines across 1532.9-1557.5 nm, demonstrating the scalability of this concept for operation in wavelength division multiplexing applications. The small form factor of the photonic chip reduces the polarization drifts when compared to optical fibers and paves the way for photonic integration.

Chip-based Brillouin radio frequency photonic phase shifter and wideband time delay.

We report a chip-based true-time-delay unit based on stimulated Brillouin scattering that uses an on-off Brillouin gain of 52 dB to enable 4 ns delay over a bandwidth of 100 MHz and a phase shift of ∼200°. To verify these operations, we use a two-tap microwave filter configuration and observed changes in the free spectral range of the filter and shift in the spectrum of the filter. The realization of these functionalities on chip-scale devices is critical for phased-array antennas, multibeam satellites, delay lines, arbitrary waveform generation, and reconfigurable microwave photonic filters.

Greater than 50% inversion in Erbium doped Chalcogenide waveguides.

We report Er-doped Ge-Ga-Se films and waveguides deposited using co-thermal evaporation and patterned with plasma etching. Strong photoluminescence at 1.54 µm with intrinsic lifetime of 1 ms was obtained from deposited films with 1490 nm excitation. Erbium population inversion up to 50% was achieved, with a maximum of ~55% possible at saturation for the first time to the author's knowledge, approaching the theoretical maximum of 65%. Whilst gain was not achieved due to the presence of upconversion pumped photoinduced absorption, this nonetheless represents a further important step towards the realization of future chalcogenide Erbium doped waveguide amplifiers at 1550 nm and in the Mid-infrared.

Widely tunable, low phase noise microwave source based on a photonic chip.

Spectrally pure microwave sources are highly desired for several applications, ranging from wireless communication to next generation radar technology and metrology. Additionally, to generate very pure signals at even higher frequencies, these advanced microwave sources have to be compact, low in weight, and low energy consumption to comply with in-field applications. A hybrid optical and electronic cavity, known as an optoelectronic oscillator (OEO), has the potential to leverage the high bandwidth of optics to generate ultrapure high-frequency microwave signals. Here we present a widely tunable, low phase noise microwave source based on a photonic chip. Using on-chip stimulated Brillouin scattering as a narrowband active filter allows single-mode OEO operation and ultrawide frequency tunability with no signal degeneration. Furthermore, we show very low close-to-carrier phase noise. This Letter paves the way to a compact, fully integrated pure microwave source.

Experimental demonstration of linearly polarized 2-10 µm supercontinuum generation in a chalcogenide rib waveguide.

This Letter reports the production of a supercontinuum extending from ≈2 µm to >10 µm generated using a chalcogenide buried rib waveguide pumped with 330 femtosecond pulses at 4.184 µm. This is, to the best of our knowledge, the broadest mid-infrared supercontinuum generated in any planar waveguide platform. Because the waveguide is birefringent, quasi-single-mode, and uses an optimized dispersion design, the supercontinuum is linearly polarized with an extinction ratio >100. Dual beam spectrophotometry is performed easily using this source.

Tailoring of the Brillouin gain for on-chip widely tunable and reconfigurable broadband microwave photonic filters.

An unprecedented Brillouin gain of 44 dB in a photonic chip enables the realization of broadly tunable and reconfigurable integrated microwave photonic filters. More than a decade bandwidth reconfigurability from 30 up to 440 MHz, with a passband ripple <1.9 dB is achieved by tailoring the Brillouin pump. The filter central frequency is continuously tuned up to 30 GHz with no degradation of the passband response, which is a major improvement over electronic filters. Furthermore, we demonstrate pump tailoring to realize multiple bandpass filters with different bandwidths and central frequencies, paving the way for multiple on-chip microwave filters and channelizers.

980nm pumped erbium doped tellurium oxide planar rib waveguide laser and amplifier with gain in S, C and L band.

A thin film based erbium doped tellurium oxide (TeO2) waveguide amplifier producing gain from 1500nm to 1640nm when pumped at 980nm is demonstrated. At measured internal gains exceeding 14dB lasing due to end facet reflection set in producing the first tellurite waveguide laser. High gains were observed despite significant upconversion, whose impact appears to be mitigated to some extent by residual OH contamination. The device displayed no photosensitive effects from either the high pumping intensities used or the intracavity intensity at 1550nm.

High Q factor chalcogenide ring resonators for cavity-enhanced MIR spectroscopic sensing.

We report the characteristics of high Q factor chalcogenide ring resonators designed for sensing in the mid-infrared (MIR). The resonators consisted of an exposed Ge11.5As24Se64.5 core on a Ge11.5As24S64.5 bottom cladding and were fabricated in the racetrack coupled ring structure. Loaded Q factors at 5.2µm up to 58,000were obtained, corresponding to an intrinsic Q of 145,000 and a waveguide propagation loss of 0.84dB/cm.

Internal gain in Er-doped As2S3 chalcogenide planar waveguides.

Low-loss erbium-doped As2S3 planar waveguides are fabricated by cothermal evaporation and plasma etching. Internal gain in the telecommunications band is demonstrated for the first time in any chalcogenide glass and additionally in a thin film planar waveguide amplifier configuration.

Observation of Photon Echoes From Evanescently Coupled Rare-Earth Ions in a Planar Waveguide.

We report the measurement of the inhomogeneous linewidth, homogeneous linewidth, and spin-state lifetime of Pr3+ ions in a novel waveguide architecture. The TeO2 slab waveguide deposited on a bulk Pr3+∶Y2SiO5 crystal allows the 3H4↔1D2 transition of Pr3+ ions to be probed by the optical evanescent field that extends into the substrate. The 2-GHz inhomogeneous linewidth, the optical coherence time of 70±5 µs, and the spin-state lifetime of 9.8±0.3 s indicate that the properties of ions interacting with the waveguide mode are consistent with those of bulk ions. This result establishes the foundation for large, integrated, and high performance rare-earth-ion quantum systems based on a waveguide platform.

Hybrid waveguide from As2S3 and Er-doped TeO2 for lossless nonlinear optics.

The fabrication and characterization of loss-compensated dispersion-engineered nonlinear As(2)S(3) on Er:TeO2 waveguides is reported for the first time, to the best of our knowledge. The hybrid waveguide is a strip loaded structure made from an Er-doped TeO2 slab and an etched As(2)S(3) strip. Almost complete loss compensation is demonstrated with 1480 nm pumping and a fully lossless waveguide with high nonlinear coefficient can be achieved with higher 1480 nm pump power.

Tellurium dioxide Erbium doped planar rib waveguide amplifiers with net gain and 2.8 dB/cm internal gain.

We report for the first time Erbium doped Tellurium dioxide single-mode planar rib waveguide amplifiers with net fiber to fiber gain and wide bandwidth operation. Peak internal gains of up to 14 dB have been achieved in 5 cm long rib waveguides (2.8 dB/cm) fabricated by co-sputtering of Tellurium and Erbium in an oxygen ambient and reactive ion etching.

High power pulsed fiber MOPA system incorporating electro-optic modulator based adaptive pulse shaping.

We demonstrate active pulse shaping using an Electro-Optic Modulator in order to compensate the pulse shaping effects caused by Gain Saturation in a high power Yb doped fiber amplifier chain and to generate various custom-defined output pulse shapes. Square, step and smooth pulse shapes are achieved, with mJ pulse energies. Use of a modulator to shape pulses rather than direct modulation of the diode drive current allows us to eliminate undesired transients due to laser start up dynamics. The required shaping is calculated based on a simple measurement of amplifier performance, and does not require detailed modeling of the amplifier dynamics.

Author Correction: A chip-integrated coherent photonic-phononic memory.

The original version of this Article omitted the Acknowledgements section:"This work was sponsored by the Australian Research Council (ARC) Laureate Fellowship (FL120100029) and the Centre of Excellence program (CUDOS CE110001010). We acknowledge the support of the ANFF ACT."This has now been corrected in both the PDF and HTML versions of the Article.

Photovoltaic Effect of a Ferroelectric-Luminescent Heterostructure under Infrared Light Illumination.

In this report, a ferroelectric-luminescent heterostructure is designed to convert infrared light into electric power. We use BiFeO3 (BFO) as the ferroelectric layer and Y2O3:Yb,Tm (YOT) as the upconversion layer. Different from conventional ferroelectric materials, this heterostructure exhibits switchable and stable photovoltaic effects under 980 nm illumination, whose energy is much lower than the band gap of BFO. The energy transfer mechanism in this heterostructure is therefore studied carefully. It is found that a highly efficient nonradiative energy transfer process from YOT to BFO plays a critical role in achieving the below-band-gap photon-excited photovoltaic effects in this heterostructure. Our results also indicate that by introducing asymmetric electrodes, both the photovoltage and photocurrent are further enhanced when the built-in field and the depolarization field are aligned. The construction of ferroelectric-luminescent heterostructure is consequently proposed as a promising route to enhance the photovoltaic effects of ferroelectric materials by extending the absorption of the solar spectrum.

A chip-integrated coherent photonic-phononic memory.

Controlling and manipulating quanta of coherent acoustic vibrations-phonons-in integrated circuits has recently drawn a lot of attention, since phonons can function as unique links between radiofrequency and optical signals, allow access to quantum regimes and offer advanced signal processing capabilities. Recent approaches based on optomechanical resonators have achieved impressive quality factors allowing for storage of optical signals. However, so far these techniques have been limited in bandwidth and are incompatible with multi-wavelength operation. In this work, we experimentally demonstrate a coherent buffer in an integrated planar optical waveguide by transferring the optical information coherently to an acoustic hypersound wave. Optical information is extracted using the reverse process. These hypersound phonons have similar wavelengths as the optical photons but travel at five orders of magnitude lower velocity. We demonstrate the storage of phase and amplitude of optical information with gigahertz bandwidth and show operation at separate wavelengths with negligible cross-talk.Optical storage implementations based on optomechanical resonator are limited to one wavelength. Here, exploiting stimulated Brillouin scattering, the authors demonstrate a coherent optical memory based on a planar integrated waveguide, which can operate at different wavelengths without cross-talk.

High-resolution, on-chip RF photonic signal processor using Brillouin gain shaping and RF interference.

Integrated microwave photonics has strongly emerged as a next-generation technology to address limitations of conventional RF electronics for wireless communications. High-resolution RF signal processing still remains a challenge due to limitations in technology that offer sub-GHz spectral resolution, in particular at high carrier frequencies. In this paper, we present an on-chip high-resolution RF signal processor, capable of providing high-suppression spectral filtering, large phase shifts and ns-scale time delays. This was achieved through tailoring of the Brillouin gain profiles using Stokes and anti-Stokes resonances combined with RF interferometry on a low-loss photonic chip with strong opto-acoustic interactions. Using an optical power of <40 mW, reconfigurable filters with a bandwidth of ~20 MHz and an extinction ratio in excess of 30 dB are synthesized. Through the concept of vector addition of RF signals we demonstrate, almost an order of magnitude amplification in the phase and delay compared to devices purely based upon the slow-light effect of Brillouin scattering. This concept allows for versatile and power-efficient manipulation of the amplitude and phase of RF signals on a photonic chip for applications in wireless communications including software defined radios and beam forming.