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Multispectral imagers that capture spatial and spectral information are of growing importance in various fields, particularly in remote sensing and metrology. To enable integrated snapshot multispectral imagers and eliminate the drawbacks of traditional systems, such as bulkiness and slow scanning mechanisms, miniature, broadband multispectral filter arrays with narrow line widths, high transmission, and CMOS compatibility are essential. However, current miniature filter arrays, primarily based on diffraction nanostructures, suffer from limitations such as small working bandwidth, low transmission, poor color purity, and sensitivity to polarization and incident angles. To address these challenges, we present a high-order Fabry-Perot Multispectral Filter Array (MSFA) with selective peak suppression, leveraging subwavelength structures for filter tuning without changing the physical thickness and employing an ultrathin metal layer to exploit high-order resonances, significantly extending the working range and spectral resolution. High color purity across a broad range (400nm-1000nm) is made possible through optical absorption from polysilicon and selective suppression from a platinum layer. The fabricated color filter arrays cover wavelengths from 622nm to 960nm, with Full Width Half Maximum (FWHM) ranging from 13nm to 31nm and average transmissions exceeding 60%. Furthermore, these filters can be downscaled to sizes compatible with modern CMOS imagers, reaching dimensions as small as 1um. The introduction of a resonance combining design further extends the working range (455nm-960nm), aligning with the capabilities of silicon photodetectors. Its adaptability across wavelength ranges and potential for tunable applications hold promise for transformative imaging and display technologies across a wide spectrum., Comment: 24 pages,5 figures,article

The lack of a bulk second-order nonlinearity (\c{hi}(2)) in silicon nitride (Si3N4) keeps this low-loss, CMOS-compatible platform from key active functions such as Pockels electro-optic (EO) modulation and efficient second harmonic generation (SHG). We demonstrate a successful induction of \c{hi}(2) in Si3N4 through electrical poling with an externally-applied field to align the Si-N bonds. This alignment breaks the centrosymmetry of Si3N4, and enables the bulk \c{hi}(2). The sample is heated to over 500{\deg}C to facilitate the poling. The comparison between the EO responses of poled and non-poled Si3N4, measured using a Si3N4 micro-ring modulator, shows at least a 25X enhancement in the r33 EO component. The maximum \c{hi}(2) we obtain through poling is 0.24pm/V. We observe a remarkable improvement in the speed of the measured EO responses from 3GHz to 15GHz (3dB bandwidth) after the poling, which confirms the \c{hi}(2) nature of the EO response induced by poling. This work paves the way for high-speed active functions on the Si3N4 platform., Comment: 9 pages, 4 figures. This work is accepted at Frontier in Optics + Laser Science (FiOLS) 2022 (FW7E.2)

Atomic-level imperfections play an increasingly critical role in nanophotonic device performance. However, it remains challenging to accurately characterize the sidewall roughness with sub-nanometer resolution and directly correlate this roughness with device performance. We have developed a method that allows us to measure the sidewall roughness of waveguides made of any material (including dielectrics) using the high resolution of atomic force microscopy. We illustrate this method by measuring state-of-the-art photonic devices made of silicon nitride. We compare the roughness of devices fabricated using both DUV photo-lithography and electron-beam lithography for two different etch processes. To correlate roughness with device performance we describe what we call a new Payne-Lacey Bending model, which adds a correction factor to the widely used Payne-Lacey model so that losses in resonators and waveguides with bends can be accurately predicted given the sidewall roughness, waveguide width and bending radii. Having a better way to measure roughness and use it to predict device performance can allow researchers and engineers to optimize fabrication for state-of-the-art photonics using many materials., Comment: 16 pages, 10 figures

We present an integrated design to precisely measure optical frequency using weak value amplification with a multi-mode interferometer. The technique involves introducing a weak perturbation to the system and then post-selecting the data in such a way that the signal is amplified without amplifying the technical noise, as has previously been demonstrated in a free-space setup. We demonstrate the advantages of a Bragg grating with two band gaps for obtaining simultaneous, stable high transmission and high dispersion. We numerically model the interferometer in order to demonstrate the amplification effect. The device is shown to have advantages over both the free-space implementation and other methods of measuring optical frequency on a chip, such as an integrated Mach-Zehnder interferometer., Comment: 13 pages, 10 figures

Silicon photonic devices are poised to enter high volume markets such as data-communications, telecommunications, biological sensing, and optical phased arrays; however, permanently attaching a fiber to the photonic chip with high optical efficiency remains a challenge. We present a robust and low-loss packaging technique of permanent optical edge coupling between a fiber and a chip using fusion splicing which is low-cost and scalable to high volume manufacturing. We fuse a SMF-28 cleaved fiber to the chip via CO$_2$ laser and reinforce it with optical adhesive. We demonstrate minimum loss of 1.0dB per-facet with 0.6dB penalty over 160nm bandwidth from 1480nm-1640nm., Comment: 12 page, 6 figures

Nanophotonics provides the ability to rapidly and precisely reconfigure light beams on a compact platform. Infrared nanophotonic devices are widely used in data communications to overcome traditional bandwidth limitations of electrical interconnects. Nanophotonic devices also hold promise for use in biological applications that require visible light, but this has remained technically elusive due to the challenges of reconfiguring and guiding light at these smaller dimensions. In neuroscience, for example, there is a need for implantable optical devices to optogenetically stimulate neurons across deep brain regions with the speed and precision matching state-of-the-art recording probes. Here we demonstrate the first platform for reconfigurable nanophotonic devices in the visible wavelength range and show its application in vivo in the brain. We demonstrate an implantable probe endowed with the ability to rapidly switch and route multiple optical beams using a nanoscale switching network. Each switch consists of a silicon nitride waveguide structure that can be reconfigured by electrically tuning the phase of light and is designed for robustness to fabrication variation, enabling scalable devices. By implanting our probe in mouse visual cortex, we demonstrate in vivo the ability to stimulate identified sets of neurons across layers to produce multi-neuron spike patterns and record them simultaneously with sub-millisecond temporal precision. This nanophotonic platform can be scaled up and integrated with high-density neural recording technologies, opening the door to implantable probe technologies that are able to simultaneously record and stimulate the activity of large neural populations at distant regions of the brain with sub-millisecond precision. We expect this platform will enable researchers to gain a deeper understanding into the spatio-temporal precision of the neural code., Comment: 14 pages, 11 figures

We demonstrate a novel approach to producing coherent, directional supercontinuum via cascaded dispersive wave generation. By pumping in the normal group-velocity dispersion regime, pulse compression of the first dispersive wave results in the generation of a second dispersive wave, resulting in an octave-spanning supercontinuum generated primarily to one side of the pump spectrum. We theoretically investigate the dynamics and show that the generated spectrum is highly coherent. We experimentally confirm this dynamical behavior and the coherence properties in silicon nitride waveguides by performing direct detection of the carrier-envelope-offset frequency of our femtosecond pump source using an f-2f interferometer. Our technique offers a path towards a stabilized, high-power, integrated supercontinuum source with low noise and high coherence, with applications including direct comb spectroscopy.

Broadband mid-infrared (mid-IR) spectroscopy applications could greatly benefit from today's well-developed, highly scalable silicon photonics technology; however, this platform lacks broadband transparency due to its reliance on absorptive silicon dioxide cladding. Alternative cladding materials have been studied, but the challenge lies in decreasing losses while avoiding complex fabrication techniques. Here, in contrast to traditional assumptions, we show that silicon photonics can achieve low-loss propagation in the mid-IR from 3 - 6 um wavelength, thus providing a highly scalable, well-developed technology in this spectral range. We engineer the waveguide cross section and optical mode interaction with the absorptive cladding oxide to reduce loss at mid-IR wavelengths. We fabricate a microring resonator and measure an intrinsic quality (Q) factor of 10^6 at wavelengths from 3.5 to 3.8 um. This is the highest Q demonstrated on an integrated mid-IR platform to date. With this high-Q silicon microresonator, we also demonstrate a low optical parametric oscillation threshold of 5.2 mW, illustrating the utility of this platform for nonlinear chip-scale applications in the mid-IR.

Dual-comb spectroscopy is a powerful technique for real-time, broadband optical sampling of molecular spectra which requires no moving components. Recent developments with microresonator-based platforms have enabled frequency combs at the chip scale. However, the need to precisely match the resonance wavelengths of distinct high-quality-factor microcavities has hindered the development of an on-chip dual comb source. Here, we report the first simultaneous generation of two microresonator combs on the same chip from a single laser. The combs span a broad bandwidth of 51 THz around a wavelength of 1.56 $\mu$m. We demonstrate low-noise operation of both frequency combs by deterministically tuning into soliton mode-locked states using integrated microheaters, resulting in narrow ($<$ 10 kHz) microwave beatnotes. We further use one mode-locked comb as a reference to probe the formation dynamics of the other comb, thus introducing a technique to investigate comb evolution without auxiliary lasers or microwave oscillators. We demonstrate broadband high-SNR absorption spectroscopy of dichloromethane spanning 170 nm using the dual comb source over a 20 $\mu$s acquisition time. Our device paves the way for compact and robust dual-comb spectrometers at nanosecond timescales.

On-chip optical resonators have the promise of revolutionizing numerous fields including metrology and sensing; however, their optical losses have always lagged behind their larger discrete resonator counterparts based on crystalline materials and flowable glass. Silicon nitride (Si3N4) ring resonators open up capabilities for optical routing, frequency comb generation, optical clocks and high precision sensing on an integrated platform. However, simultaneously achieving high quality factor and high confinement in Si3N4 (critical for nonlinear processes for example) remains a challenge. Here, we show that addressing surface roughness enables us to overcome the loss limitations and achieve high-confinement, on-chip ring resonators with a quality factor (Q) of 37 million for a ring with 2.5 {\mu}m width and 67 million for a ring with 10 {\mu}m width. We show a clear systematic path for achieving these high quality factors. Furthermore, we extract the loss limited by the material absorption in our films to be 0.13 dB/m, which corresponds to an absorption limited Q of at least 170 million by comparing two resonators with different degrees of confinement. Our work provides a chip-scale platform for applications such as ultra-low power frequency comb generation, high precision sensing, laser stabilization and sideband resolved optomechanics.

We demonstrate the first low-noise mid-IR frequency comb source using a silicon microresonator. Our observation of strong Raman scattering lines in the generated comb suggests that Raman and four-wave mixing interactions play a role in assisting the transition to the low-noise state. In addition, we characterize, the intracavity comb generation dynamics using an integrated PIN diode, which takes advantage of the inherent three-photon absorption process in silicon., Comment: 7 pages, 5 figures

We demonstrate continuous tuning of the squeezing level generated in a double-ring optical parametric oscillator by externally controlling the coupling condition using electrically controlled integrated microheaters. We accomplish this by utilizing the avoided crossing exhibited by a pair of coupled silicon nitride microring resonators. We directly detect a change in the squeezing level from 0.5 dB in the undercoupled regime to 2 dB in the overcoupled regime, which corresponds to a change in the generated on-chip squeezing factor from 0.9 dB to 3.9 dB. Such wide tunability in the squeezing level can be harnessed for on-chip quantum enhanced sensing protocols which require an optimal degree of squeezing., Comment: 9 pages, 4 figures

Synchronization of many coupled oscillators is widely found in nature and has the potential to revolutionize timing technologies. Here we demonstrate synchronization in arrays of silicon nitride micromechanical oscillators coupled purely through optical radiation field. We show that the phase noise of the synchronized oscillators can be improved by almost 10 dB below the phase noise limit for each individual oscillator. These results open a practical route towards synchronized oscillator networks.

Leveraging the spatial modes of multimode waveguides using mode-division multiplexing (MDM) on an integrated photonic chip allows unprecedented scaling of bandwidth density for on-chip communication. Switching channels between waveguides is critical for future scalable optical networks, but its implementation in multimode waveguides must address how to simultaneously control modes with vastly different optical properties. Here we present a platform for switching signals between multimode waveguides based on individually processing the spatial mode channels using single-mode elements. Using this wavelength-division multiplexing (WDM) compatible platform, we demonstrate a 1x2 multimode switch for a silicon chip which routes four data channels with low (<-20 dB) crosstalk. We show bit-error rates below 10^-9 and power penalties below 1.4 dB on all channels while routing 10 Gbps data when each channel is input and routed separately. The switch exhibits an additional power penalty of less than 2.4 dB when all four channels are simultaneously routed., Comment: 13 pages; 6 figures

Graphene has generated exceptional interest as an optoelectronic material because its high carrier mobility and broadband absorption promise to make extremely fast and broadband electro-optic devices possible. Electro-optic graphene modulators reported to date, however, have been limited in bandwidth to a few GHz because of the large capacitance required to achieve reasonable voltage swings. Here we demonstrate a graphene electro-optic modulator based on the classical Zeno effect that shows drastically increased speed and efficiency. Our device operates with a 30 GHz bandwidth, over an order of magnitude faster than prior work, and a state-of-the-art modulation efficiency of 1.5 dB/V. We also show the first high-speed large-signal operation in a graphene modulator, paving the way for fast digital communications using this platform. The modulator uniquely uses silicon nitride waveguides, an otherwise completely passive material platform, with promising applications for ultra-low-loss broadband structures and nonlinear optics., Comment: 11 pages, 5 figures

We demonstrate a photonic circuit with integrated long-lived quantum memories. Pre-selected quantum nodes - diamond micro-waveguides containing single, stable, and negatively charged nitrogen vacancy centers - are deterministically integrated into low-loss silicon nitride waveguides. Each quantum memory node efficiently couples into the single-mode waveguide (> 1 Mcps collected into the waveguide) and exhibits long spin coherence times of up to 120 {\mu}s. Our system facilitates the assembly of multiple quantum memories into a photonic integrated circuit with near unity yield, paving the way towards scalable quantum information processing., Comment: 5 pages, 4 figures

Optical frequency combs represent a revolutionary technology for high precision spectroscopy due to their narrow linewidths and precise frequency spacing. Generation of such combs in the mid-infrared (IR) spectral region (2-20 um) is of great interest due to the presence of a large number of gas absorption lines in this wavelength regime. Recently, frequency combs have been demonstrated in the MIR in several platforms, including fiber combs, mode-locked lasers, optical parametric oscillators, and quantum cascade lasers. However, these platforms are either relatively bulky or challenging to integrate on-chip. An alternative approach using parametric mixing in microresonators is highly promising since the platform is extremely compact and can operate with relatively low powers. However, material and dispersion engineering limitations have prevented the realization of a microresonator comb source past 2.55 um. Although silicon could in principle provide a CMOS compatible platform for on-chip comb generation deep into the mid-IR, to date, silicon's linear and nonlinear losses have prevented the realization of a microresonator-based comb source. Here we overcome these limitations and realize a broadband frequency comb spanning from 2.1 um to 3.5 um and demonstrate its viability as a spectroscopic sensing platform. Such a platform is compact and robust and offers the potential to be versatile and durable for use outside the laboratory environment for applications such as real-time monitoring of atmospheric gas conditions., Comment: 16 pages, 4 figures

We demonstrate photonic devices based on standard 3C SiC epitaxially grown on silicon. We achieve high optical confinement by taking advantage of the high stiffness of SiC and undercutting the underlying silicon substrate. We demonstrate a 20 um radius suspended microring resonator with Q of 18000 fabricated on commercially available SiC-on-silicon substrates.

The ability to render objects invisible using a cloak - not detectable by an external observer - for concealing objects has been a tantalizing goal1-6. Here, we demonstrate a cloak operating in the near infrared at a wavelength of 1550 nm. The cloak conceals a deformation on a flat reflecting surface, under which an object can be hidden. The device has an area of 225 um2 and hides a region of 1.6 um2. It is composed of nanometre size silicon structures with spatially varying densities across the cloak. The density variation is defined using transformation optics to define the effective index distribution of the cloak., Comment: 12 pages, 5 figures