Ultra-Narrow Bandwidth Optical Resonators for Integrated Low Frequency Noise Lasers

The development of narrowband resonators has far reaching applications in integrated optics. As a precise reference of wavelength, filters can be used in sensors, metrology, nonlinear optics, microwave photonics, and laser stabilization. In this work, we develop record high quality factor (Q) Si3N4 waveguide resonators, and utilize them to stabilize a heterogeneously integrated Si/III V laser. To increase the Q factor of waveguide resonators, particular attention is given to loss mechanisms. Propagation loss of <0.1 dB/m is demonstrated on the ultra low loss waveguide platform, a low index contrast, high aspect ratio Si3N4 waveguide geometry fabricated with high quality materials and high temperature anneals. Ideality in the directional couplers used for coupling to the resonators is studied and losses are reduced such that 81 million intrinsic Q factor is achieved. Additional results include 1×16 resonant splitters, low κ narrowband gratings, and a dual layer waveguide technology for low loss and low bend radius in separate regions of the same device layer. We then combine an ultra high Q resonator and a heterogeneous Si/III V laser in a Pound Drever Hall (PDH) frequency stabilization system to yield narrow linewidth characteristics for a stable on chip laser reference. The high frequency noise filtering is performed with Si resonant mirrors in the laser cavity. A 30 million Q factor Si3N4 resonator is used with electrical feedback to reduce close in noise and frequency walk off. The laser shows high frequency noise levels of 60×10^3 Hz^2/Hz corresponding to 160 kHz linewidth, and the low frequency noise is suppressed 33 dB to 10^3 Hz^2/Hz with the PDH system

Continuous wave-pumped wavelength conversion in low-loss silicon nitride waveguides

In this Letter we introduce a complementary metal-oxide semiconductor (CMOS)-compatible low-loss Si3N4 waveguide platform for nonlinear integrated optics. The waveguide has a moderate nonlinear coefficient of 285 W∕km, but the achieved propagation loss of only 0.06 dB∕cm and the ability to handle high optical power facilitate an optimal waveguide length for wavelength conversion. We observe a constant quadratic dependence of the four-wave mixing (FWM) process on the continuous-wave (CW) pump when operating in the C-band, which indicates that the waveguide has negligible high-power constraints owing to nonlinear losses. We achieve a conversion efficiency of −26.1 dB and idler power generation of −19.6 dBm. With these characteristics, we present for the first time, to the best of our knowledge, CW-pumped data conversion in a non-resonant Si3N4 waveguide

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A Kerr-microresonator optical clockwork

Kerr microresonators generate interesting and useful fundamental states of electromagnetic radiation through nonlinear interactions of continuous-wave (CW) laser light. Using photonic-integration techniques, functional devices with low noise, small size, low-power consumption, scalable fabrication, and heterogeneous combinations of photonics and electronics can be realized. Kerr solitons, which stably circulate in a Kerr microresonator, have emerged as a source of coherent, ultrafast pulse trains and ultra-broadband optical-frequency combs. Using the f-2f technique, Kerr combs support carrier-envelope-offset phase stabilization for optical synthesis and metrology. In this paper, we introduce a Kerr-microresonator optical clockwork based on optical-frequency division (OFD), which is a powerful technique to transfer the fractional-frequency stability of an optical clock to a lower frequency electronic clock signal. The clockwork presented here is based on a silicon-nitride (Si$_3$N$_4$) microresonator that supports an optical-frequency comb composed of soliton pulses at 1 THz repetition rate. By electro-optic phase modulation of the entire Si$_3$N$_4$ comb, we arbitrarily generate additional CW modes between the Si$_3$N$_4$ comb modes; operationally, this reduces the pulse train repetition frequency and can be used to implement OFD to the microwave domain. Our experiments characterize the residual frequency noise of this Kerr-microresonator clockwork to one part in $10^{17}$, which opens the possibility of using Kerr combs with high performance optical clocks. In addition, the photonic integration and 1 THz resolution of the Si$_3$N$_4$ frequency comb makes it appealing for broadband, low-resolution liquid-phase absorption spectroscopy, which we demonstrate with near infrared measurements of water, lipids, and organic solvents

Analysis of three epoetin alpha products by LC and LC-MS indicates differences in glycosylation critical quality attributes, including sialic acid content

Erythropoietin (EPO) is one of the main therapeutics used to treat anaemic patients, greatly improving their quality of life. In this study, biosimilars Binocrit and a development product, called here CIGB-EPO, were compared to the originator product, Eprex. All three are epoetin alpha products, reputed to have similar glycosylation profiles. The quality, safety and efficacy of this biotherapeutic depend on the following glycosylation critical quality attributes (GCQAs): sialylation, N-glycolyl-neuraminic acid (Neu5Gc) content, branching, N-acetyl-lactosamine (LacNAc) extensions and O-acetylation pattern. Reverse-phase ultra high pressure liquid chromatography (RP-UHPLC) analysis of acid-released, 1,2-diamino-4,5-methylenedioxybenzene (DMB) labelled sialic acid derivatives and hydrophilic interaction liquid chromatography (HILIC) in combination with mass spectrometry (HILIC-UHPLC-MS) of procainamide (PROC) labelled N-glycans were the analytical tools used. An automated method for enzymatic release and PROC labelling was applied for the first time to the erythropoiesis stimulating agent (ESA) products, which facilitated novel, in-depth characterisation, and allowed identification of precise structural features including the location of O-acetyl groups on sialic acid (SA) moie-ties. Samples were digested by a sialate-O-acetylesterase (NanS) to confirm the presence of O-acetyl groups. It was found that Eprex contained the greatest relative abundance of O-acetylated derivatives, Binocrit expressed the least Neu5Gc, and CIGB-EPO showed the greatest variety of high-mannose-phosphate structures. The sialylation and LacNAc extension patterns of the three ESAs were similar, with a maximum of four N-acetyl-neuraminic acid (Neu5Ac) moieties detected per glycan. Such differences in SA derivatisation, particularly O-acetylation, could have consequences for the quality and safety of a biotherapeutic, as well as its efficacy

An optical-frequency synthesizer using integrated photonics

Optical-frequency synthesizers, which generate frequency-stable light from a single microwave-frequency reference, are revolutionizing ultrafast science and metrology, but their size, power requirement and cost need to be reduced if they are to be more widely used. Integrated-photonics microchips can be used in high-coherence applications, such as data transmission, highly optimized physical sensors and harnessing quantum states, to lower cost and increase efficiency and portability. Here we describe a method for synthesizing the absolute frequency of a lightwave signal, using integrated photonics to create a phase-coherent microwave-to-optical link. We use a heterogeneously integrated iii–v/silicon tunable laser, which is guided by nonlinear frequency combs fabricated on separate silicon chips and pumped by off-chip lasers. The laser frequency output of our optical-frequency synthesizer can be programmed by a microwave clock across 4 terahertz near 1,550 nanometres (the telecommunications C-band) with 1 hertz resolution. Our measurements verify that the output of the synthesizer is exceptionally stable across this region (synthesis error of 7.7 × 10^(−15) or below). Any application of an optical-frequency source could benefit from the high-precision optical synthesis presented here. Leveraging high-volume semiconductor processing built around advanced materials could allow such low-cost, low-power and compact integrated-photonics devices to be widely used

Heterodyne-based hybrid controller for wide dynamic range optoelectronic frequency synthesis

Chip scale optical frequency combs using microresonators can enable a wide variety of applications from metrology to telecommunications. While tremendous progress has been made in miniaturizing the optical components, sources of variability and drift due to ambient conditions often limit their performance. We describe the design and implementation of a mixed-signal controller for optoelectronic frequency synthesis with notable frequency stability by locking it to an RF reference. A C-band tunable laser is phase-locked using commercial off the shelf components and custom board-level designs. Utilizing several laser inputs, our hybrid control loop enables a 50 nm tuning range with less than 10-12&nbsp;frequency instability for 1 second averaging. A heterodyne receiver overcomes poor SNR of the photonics, and also features a scan-and-lock algorithm to facilitate an extended acquisition range. We report &gt; 500 GHz frequency steps in 4.4 ms. All of the frequency settings and loop stability dynamics are programmable in real-time via a custom Graphical User Interface.</p

An Integrated-Photonics Optical-Frequency Synthesizer

Integrated-photonics microchips now enable a range of advanced functionalities for high-coherence applications such as data transmission, highly optimized physical sensors, and harnessing quantum states, but with cost, efficiency, and portability much beyond tabletop experiments. Through high-volume semiconductor processing built around advanced materials there exists an opportunity for integrated devices to impact applications cutting across disciplines of basic science and technology. Here we show how to synthesize the absolute frequency of a lightwave signal, using integrated photonics to implement lasers, system interconnects, and nonlinear frequency comb generation. The laser frequency output of our synthesizer is programmed by a microwave clock across 4 THz near 1550 nm with 1 Hz resolution and traceability to the SI second. This is accomplished with a heterogeneously integrated III/V-Si tunable laser, which is guided by dual dissipative-Kerr-soliton frequency combs fabricated on silicon chips. Through out-of-loop measurements of the phase-coherent, microwave-to-optical link, we verify that the fractional-frequency instability of the integrated photonics synthesizer matches the $7.0*10^{-13}$ reference-clock instability for a 1 second acquisition, and constrain any synthesis error to $7.7*10^{-15}$ while stepping the synthesizer across the telecommunication C band. Any application of an optical frequency source would be enabled by the precision optical synthesis presented here. Building on the ubiquitous capability in the microwave domain, our results demonstrate a first path to synthesis with integrated photonics, leveraging low-cost, low-power, and compact features that will be critical for its widespread use.Comment: 10 pages, 6 figure