arXiv subjects

Nima Nader

Publications and source records attributed to Nima Nader.

17 recordsLinked to original sources

arXiv2026

Stimulated Brillouin Scattering in InGaP-on-Insulator Waveguides

Stimulated Brillouin Scattering (SBS) is a nonlinear interaction between optical and acoustic waves in solids. First regarded as a parasitic process in optical fibers, it has gathered significant interest in microwave photonic applications such as optical signal processing and narrow linewidth lasers. While many Brillouin system demonstrations have been done on photonic chips, they struggle to provide simultaneous high Brillouin gain and narrow linewidth in a scalable platform, capable of integration with established photonic integrated circuits. Here, we present a novel integrated InGaP-on-SiO$_2$ platform, where a single crystalline InGaP waveguide layer offers superior material properties and strong nonlinearities to support SBS near 1550 nm wavelength. We demonstrate backward SBS with a measured high Brillouin gain coefficient of $588\, \mathrm{W}^{-1}\,\mathrm{m}^{-1}$ and a record narrow linewidth of 5.2 MHz at 9.346 GHz frequency shift. This work establishes a wafer-scale complementary metal-oxide semiconductor compatible fabrication process, paving a scalable path for high gain and narrow linewidth Brillouin photonics with applications such as precision signal processing.

physics.optics↗

arXiv2025

Heterogeneous tantala photonic integrated circuits for sub-micron wavelength applications

Atomic and trapped-ion systems are the backbone of a new generation of quantum-based positioning, navigation, and timing (PNT) technologies. The miniaturization of such quantum systems offers tremendous technological advantages, especially the reduction of system size, weight, and power consumption. Yet, this has been limited by the absence of compact, standalone photonic integrated circuits (PICs) at the wavelengths suitable for these instruments. Mobilizing such photonic systems requires development of fully integrated, on-chip, active components at sub-micrometer wavelengths. We demonstrate heterogeneous photonic integrated circuits operating at 980 nm based on wafer-scale bonding of InGaAs quantum well active regions to tantalum pentoxide passive components. This high-yield process provides > 95 % surface area yield and enables integration of > 1300 active components on a 76.2 mm (3 inch) silicon wafer. We present a diverse set of functions, including semiconductor optical amplifiers, Fabry-Perot lasers, and distributed feedback lasers with 43 dB side-mode suppression ratio and > 250 GHz single-mode tuning range. We test the precise wavelength control and system level functionality of the on-chip lasers by pumping optical parametric oscillation processes in microring resonators fabricated on the same platform, generating short-wavelength signals at 778 nm and 752 nm. These results provide a pathway to realize fully functional integrated photonic engines for operation of compact quantum sensors based on atomic and trapped-ion systems.

physics.optics↗

arXiv2019

Efficient second harmonic generation in nanophotonic GaAs-on-insulator waveguides

Nonlinear frequency conversion plays a crucial role in advancing the functionality of next-generation optical systems. Portable metrology references and quantum networks will demand highly efficient second-order nonlinear devices, and the intense nonlinear interactions of nanophotonic waveguides can be leveraged to meet these requirements. Here we demonstrate second harmonic generation (SHG) in GaAs-on-insulator waveguides with unprecedented efficiency of 40 W$^{-1}$ for a single-pass device. This result is achieved by minimizing the propagation loss and optimizing phase-matching. We investigate surface-state absorption and design the waveguide geometry for modal phase-matching with tolerance to fabrication variation. A 2.0 $\mu$m pump is converted to a 1.0 $\mu$m signal in a length of 2.9 mm with a wide signal bandwidth of 148 GHz. Tunable and efficient operation is demonstrated over a temperature range of 45 $^{\circ}$C with a slope of 0.24 nm/$^{\circ}$C. Wafer-bonding between GaAs and SiO$_2$ is optimized to minimize waveguide loss, and the devices are fabricated on 76 mm wafers with high uniformity. We expect this device to enable fully integrated self-referenced frequency combs and high-rate entangled photon pair generation.

physics.optics↗

arXiv2019

On-chip polarization rotator for type I second harmonic generation

We demonstrate a polarization rotator integrated at the output of a GaAs waveguide producing type I second harmonic generation (SHG). Form-birefringent phase matching between the pump fundamental transverse electric (TE) mode near 2.0 $\mu$m wavelength and the signal fundamental transverse magnetic (TM) mode efficiently generates light at 1.0 $\mu$m wavelength. A SiN waveguide layer is integrated with the SHG device to form a multi-functional photonic integrated circuit. The polarization rotator couples light between the two layers and rotates the polarization from TM to TE or from TE to TM. With a TE-polarized 2.0 $\mu$m pump, type I SHG is demonstrated with the signal rotated to TE polarization. Passive transmission near 1.0 $\mu$m wavelength shows ~80 % polarization rotation across a broad bandwidth of ~100 nm. By rotating the signal polarization to match that of the pump, this SHG device demonstrates a critical component of an integrated self-referenced octave-spanning frequency comb. This device is expected to provide crucial functionality as part of a fully integrated optical frequency synthesizer with resolution of less than one part in 10$^{14}$.

physics.optics↗

arXiv2019

Nonlinear silicon waveguides generating broadband, spectrally engineered frequency combs spanning 2.0-8.5 um

Nanophotonic waveguides with sub-wavelength mode confinement and engineered dispersion profiles are an excellent platform for application-tailored nonlinear optical interactions at low pulse energies. Here, we present fully air clad suspended-silicon waveguides for infrared frequency comb generation with optical bandwidth limited only by the silicon transparency. The achieved spectra are lithographically tailored to span 2.1 octaves in the mid-infrared (2.0-8.5 um or 1170--5000 cm-1) when pumped at 3.10 um with 100 pJ pulses. Novel fork-shaped couplers provide efficient input coupling with only 1.5 dB loss. The coherence, brightness, and the stability of the generated light are highlighted in a dual frequency comb setup in which individual comb-lines are resolved with 30 dB extinction ratio and 100 MHz spacing in the wavelength range of 4.8-8.5 um (2100-1170 cm-1). These sources are used for broadband gas- and liquid-phase dual-comb spectroscopy with 100 MHz comb-line resolution. We achieve a peak spectral signal-to-noise ratio of 10 Hz^0.5 across a simultaneous bandwidth containing 112,200 comb-lines. These results provide a pathway to further integration with the developing high repetition rate frequency comb lasers for compact sensors with applications in chip-based chemical analysis and spectroscopy.

physics.optics↗

arXiv2019

Multi-functional integrated photonics in the mid-infrared with suspended AlGaAs on silicon

The microscale integration of mid- and longwave-infrared photonics could enable the development of fieldable, robust chemical sensors, as well as highly efficient infrared frequency converters. However, such technology would be defined by the choice of material platform, which immediately determines the strength and types of optical nonlinearities available, the optical transparency window, modal confinement, and physical robustness. In this work, we demonstrate a new platform, suspended AlGaAs waveguides integrated on silicon, providing excellent performance in all of these metrics. We demonstrate low propagation losses within a span of nearly two octaves (1.26 to 4.6 $\mu$m) with exemplary performance of 0.45 dB/cm at $\lambda = 2.4$ $\mu$m. We exploit the high nonlinearity of this platform to demonstrate 1560 nm-pumped second-harmonic generation and octave-spanning supercontinuum reaching out to 2.3 $\mu$m with 3.4 pJ pump pulse energy. With mid-IR pumping, we generate supercontinuum spanning from 2.3 to 6.5 $\mu$m. Finally, we demonstrate the versatility of the platform with mid-infrared passive devices such as low-loss 10 $\mu$m-radius bends, compact power splitters with 96 $\pm$ 1% efficiency and edge couplers with 3.0 $\pm$ 0.1 dB loss. This platform has strong potential for multi-functional integrated photonic systems in the mid-IR.

physics.app-ph↗

arXiv2018

$\chi^{(2)}$ mid-infrared frequency comb generation and stabilization with few-cycle pulses

Mid-infrared laser frequency combs are compelling sources for precise and sensitive metrology with applications in molecular spectroscopy and spectro-imaging. The infrared atmospheric window between 3-5.5 $\mu$m in particular provides vital information regarding molecular composition. Using a robust, fiber-optic source of few-cycle pulses in the near-infrared, we experimentally demonstrate ultra-broad bandwidth nonlinear phenomena including harmonic and difference frequency generation in a single pass through periodically poled lithium niobate (PPLN). These $\chi^{(2)}$ nonlinear optical processes result in the generation of frequency combs across the mid-infrared atmospheric window which we employ for dual-comb spectroscopy of acetone and carbonyl sulfide with resolution as high as 0.003 cm$^{-1}$. Moreover, cascaded $\chi^{(2)}$ nonlinearities in the same PPLN directly provide the carrier-envelope offset frequency of the near-infrared driving pulse train in a compact geometry.

physics.optics↗

arXiv2018

Tunable mid-infrared generation via wide-band four wave mixing in silicon nitride waveguides

We experimentally demonstrate wide-band (>100 THz) frequency down-conversion of near-infrared (NIR) femtosecond-scale pulses from an Er:fiber laser to the mid-infrared (MIR) using four-wave-mixing (FWM) in photonic-chip silicon-nitride waveguides. The engineered dispersion in the nanophotonic geometry, along with the wide transparency range of silicon nitride, enables large-detuning FWM phase-matching and results in tunable MIR from 2.6-3.6 um on a single chip with 100-pJ-scale pump-pulse energies. Additionally, we observe > 20 dB broadband parametric gain for the NIR pulses when the FWM process is operated in a frequency up-conversion configuration. Our results demonstrate how integrated photonic circuits could realize multiple nonlinear optical phenomena on the same chip and lead to engineered synthesis of broadband, tunable, and coherent light across the NIR and MIR wavelength bands from fiber-based pumps.

physics.app-ph↗

arXiv2018

Heterogeneously integrated GaAs waveguides on insulator for efficient frequency conversion

Tremendous scientific progress has been achieved through the development of nonlinear integrated photonics. Prominent examples are Kerr-frequency-comb generation in micro-resonators, and supercontinuum generation and frequency conversion in nonlinear photonic waveguides. High conversion efficiency is enabling for applications of nonlinear optics, including such broad directions as high-speed optical signal processing, metrology, and quantum communication and computation. In this work, we demonstrate a gallium-arsenide-on-insulator (GaAs) platform for nonlinear photonics. GaAs has among the highest second- and third-order nonlinear optical coefficients, and use of a silica cladding results in waveguides with a large refractive index contrast and low propagation loss for expanded design of nonlinear processes. By harnessing these properties and developing nanofabrication with GaAs, we report a record normalized second-harmonic efficiency of 13,000% W-1cm-2 at a fundamental wavelength of 2 um. This work paves the way for high performance nonlinear photonic integrated circuits (PICs), which not only can transition advanced functionalities outside the lab through fundamentally reduced power consumption and footprint, but also enables future optical sources and detectors.

physics.optics↗

arXiv2018

Deuterated silicon nitride photonic devices for broadband optical frequency comb generation

We report and characterize low-temperature, plasma-deposited deuterated silicon nitride thin films for nonlinear integrated photonics. With a peak processing temperature less than 300$^\circ$C, it is back-end compatible with pre-processed CMOS substrates. We achieve microresonators with a quality factor of up to $1.6\times 10^6 $ at 1552 nm, and $>1.2\times 10^6$ throughout $\lambda$ = 1510 -- 1600 nm, without annealing or stress management. We then demonstrate the immediate utility of this platform in nonlinear photonics by generating a 1 THz free spectral range, 900-nm-bandwidth modulation-instability microresonator Kerr comb and octave-spanning, supercontinuum-broadened spectra.

physics.optics↗

arXiv2018

Mid-infrared frequency comb generation via cascaded quadratic nonlinearities in quasi-phase-matched waveguides

We experimentally demonstrate a simple configuration for mid-infrared (MIR) frequency comb generation in quasi-phase-matched lithium niobate waveguides using the cascaded-$\chi^{(2)}$ nonlinearity. With nanojoule-scale pulses from an Er:fiber laser, we observe octave-spanning supercontinuum in the near-infrared with dispersive-wave generation in the 2.5--3 $\text{\mu}$m region and intra-pulse difference-frequency generation in the 4--5 $\text{\mu}$m region. By engineering the quasi-phase-matched grating profiles, tunable, narrow-band MIR and broadband MIR spectra are both observed in this geometry. Finally, we perform numerical modeling using a nonlinear envelope equation, which shows good quantitative agreement with the experiment---and can be used to inform waveguide designs to tailor the MIR frequency combs. Our results identify a path to a simple single-branch approach to mid-infrared frequency comb generation in a compact platform using commercial Er:fiber technology.

physics.optics↗

arXiv2017

Dual frequency comb spectroscopy in the molecular fingerprint region

Spectroscopy in the molecular fingerprint spectral region (6.5-20 $\mu$m) yields critical information on material structure for physical, chemical and biological sciences. Despite decades of interest and effort, this portion of the electromagnetic spectrum remains challenging to cover with conventional laser technologies. In this report, we present a simple and robust method for generating super-octave, optical frequency combs in the fingerprint region through intra-pulse difference frequency generation in an orientation-patterned gallium phosphide crystal. We demonstrate the utility of this unique coherent light source for high-precision, dual-comb spectroscopy in methanol and ethanol vapor. These results highlight the potential of laser frequency combs for a wide range of molecular sensing applications, from basic molecular spectroscopy to nanoscopic imaging.

physics.optics↗

arXiv2017

High-harmonic generation in periodically poled waveguides

Optical waveguides made from periodically poled materials provide high confinement of light and enable the generation of new wavelengths via quasi-phase-matching, making them a key platform for nonlinear optics and photonics. However, such devices are not typically employed for high-harmonic generation. Here, using 200-fs, 10-nJ-level pulses of 4100 nm light at 1 MHz, we generate high harmonics up to the 13th harmonic (315 nm) in a chirped, periodically poled lithium niobate (PPLN) waveguide. Total conversion efficiencies into the visible--ultraviolet region are as high as 10 percent. We find that the output spectrum depends on the waveguide poling period, indicating that quasi-phase-matching plays a significant role. In the future, such periodically poled waveguides may enable compact sources of ultrashort pulses at high repetition rates and provide new methods of probing the electronic structure of solid-state materials.

physics.optics↗

arXiv2017

Maximizing waveguide integration density with multi-plane photonics

We propose and experimentally demonstrate a photonic routing architecture that can efficiently utilize the space of multi-plane (3D) photonic integration. A wafer with three planes of amorphous silicon waveguides was fabricated and characterized, demonstrating $<3\times10^{-4}$ dB loss per out-of-plane waveguide crossing, $0.05 \pm 0.02 $ dB per interplane coupler, and microring resonators on three planes with a quality factors up to $8.2 \times 10^{4}$. We also explore a phase velocity mapping strategy to mitigate the crosstalk between co-propagating waveguides on different planes. These results expand the utility of 3D photonic integration for applications such as optical interconnects, neuromorphic computing and optical phased arrays.

physics.app-ph↗

arXiv2017

Versatile silicon-waveguide supercontinuum for coherent mid-infrared spectroscopy

Infrared spectroscopy is a powerful tool for basic and applied science. The molecular spectral fingerprints in the 3 um to 20 um region provide a means to uniquely identify molecular structure for fundamental spectroscopy, atmospheric chemistry, trace and hazardous gas detection, and biological microscopy. Driven by such applications, the development of low-noise, coherent laser sources with broad, tunable coverage is a topic of great interest. Laser frequency combs possess a unique combination of precisely defined spectral lines and broad bandwidth that can enable the above-mentioned applications. Here, we leverage robust fabrication and geometrical dispersion engineering of silicon nanophotonic waveguides for coherent frequency comb generation spanning 70 THz in the mid-infrared (2.5 um to 6.2 um). Precise waveguide fabrication provides significant spectral broadening and engineered spectra targeted at specific mid-infrared bands. We use this coherent light source for dual-comb spectroscopy at 5 um.

physics.optics↗

arXiv2017

Self-referenced frequency combs using high-efficiency silicon-nitride waveguides

We utilize silicon-nitride waveguides to self-reference a telecom-wavelength fiber frequency comb through supercontinuum generation, using 11.3 mW of optical power incident on the chip. This is approximately ten times lower than conventional approaches using nonlinear fibers and is enabled by low-loss (<2 dB) input coupling and the high nonlinearity of silicon nitride, which can provide two octaves of spectral broadening with incident energies of only 110 pJ. Following supercontinuum generation, self-referencing is accomplished by mixing 780-nm dispersive-wave light with the frequency-doubled output of the fiber laser. In addition, at higher optical powers, we demonstrate f-to-3f self-referencing directly from the waveguide output by the interference of simultaneous supercontinuum and third harmonic generation, without the use of an external doubling crystal or interferometer. These hybrid comb systems combine the performance of fiber-laser frequency combs with the high nonlinearity and compactness of photonic waveguides, and should lead to low-cost, fully stabilized frequency combs for portable and space-borne applications.

physics.optics↗

arXiv2016

A versatile, inexpensive integrated photonics platform

We present an approach to fabrication and packaging of integrated photonic devices that utilizes waveguide and detector layers deposited at near-ambient temperature. All lithography is performed with a 365 nm i-line stepper, facilitating low cost and high scalability. We have shown low-loss SiN waveguides, high-$Q$ ring resonators, critically coupled ring resonators, 50/50 beam splitters, Mach-Zehnder interferometers (MZIs) and a process-agnostic fiber packaging scheme. We have further explored the utility of this process for applications in nonlinear optics and quantum photonics. We demonstrate spectral tailoring and octave-spanning supercontinuum generation as well as the integration of superconducting nanowire single photon detectors with MZIs and channel-dropping filters. The packaging approach is suitable for operation up to 160 \degree C as well as below 1 K. The process is well suited for augmentation of existing foundry capabilities or as a stand-alone process.

physics.optics↗