We demonstrate a compact, high power tunable laser based on free-space hybrid integration of indium phosphide gain chips with thermally tuned low loss silicon etalons. By optimization of filter fabrication and laser cavity design we achieve 17.6 dBm output power. Integrated thermal control elements enable accurate and wide tuning without the typical external optical feedback or wavelength locking components.

Surface-normal electroabsorption modulators (SNEAMs) are devices with unique characteristics, such as small size, wide bandwidth and polarization insensitive behavior; however, due to the surface-normal configuration and since they operate in reflection, it is challenging to package fiber arrays to SNEAM arrays with many channels. Here, we present a novel approach to package fiber arrays to SNEAM arrays based on passive alignment. We realize an expanded-beam, multi-channel, optical coupling scheme by using a prism lens array and a lens array in between a SNEAM array chip and a standard single mode fiber array. We use this approach to assemble a SNEAM array engine with 8 channels without any active optical alignment. We show that our SNEAM array engine has coupling loss from the fiber inputs to the SNEAMs ranging from 1.2 dB for the best channel to 1.7 dB for the worst channel. Also, we validate our passive alignment packaging scheme by modulating the channels at 25 Gbit/s NRZ-OOK and show that the fiber array is pluggable into the SNEAM array engine. Finally, our approach is independent of the specific SNEAM design, and potentially can be extended to other surface-normal devices, such as lasers or photodiodes.

Future optical communication systems will exploit increasingly wide optical wavelength bands to continue scaling capacity per installed fiber. Currently, optical components such as tunable lasers and modulators are designed to operate in a single wavelength band only and multiple designs are therefore needed for a single system. Improved tunable lasers operating seamlessly over these wider bands would both simplify system deployment and management. Increasing the laser tuning range requires improved wavelength selection mechanisms to simplify calibration and improve performance. We report a tunable laser with an 11THz tuning range and 14 mW output power. This laser is based on what we believe to be a novel silicon optical bench platform augmented with thermal membranes to enable both low tuning power consumption and low crosstalk laser tuning. Reduction of crosstalk simplifies both calibration and control of the laser frequency. The total power consumption of the tunable laser is only 700 mW. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

In this paper, we introduce the design and fabrication of a high-power thermal test vehicle (TTV) equipped with a two-phase cooling system, targeting improved thermal management in Multi-Chip Modules (MCMs) for AI datacenters, 5G RAN, and EDGE compute nodes. With the rise in device integration and component power densities, conventional cooling methods fall short, prompting the need for innovative approaches to achieve efficient heat dissipation. The TTV utilizes advanced heterogeneous integration techniques on a low-temperature co-fired ceramic (LTCC) substrate, designed to reliably dissipate over 1000 W of heat. This provides a robust platform for testing advanced two-phase cooling strategies to effectively remove heat from densely packed silicon dies, thus addressing the thermal challenges inherent in modern electronics.We elaborate on the fabrication of two variations of the TTV: the first comprising six X1 MCM modules, each measuring 25 mm × 38 mm, and the second a single X6 module measuring 76 mm × 76 mm, showcasing the robustness of the process. These TTVs are engineered to manage power dissipation of up to 1008 W, with logic chips experiencing background power densities of approximately 34 W/cm^2 and hotspots peaking at 400W/cm^2, while HBM stack chips exhibit a heat flux of 16 W/cm^2. The logic chips, measuring 20 mm x 20 mm, and the HBM stacks, measuring 10 mm x 10 mm, closely replicate the specifications of cutting-edge AI hardware.The importance of this work lies in its capacity to offer a scalable and dependable testing platform for advanced thermal management strategies in high-performance computing. By leveraging two-phase cooling, it paves the way toward more reliable and efficient computing infrastructures, effectively addressing the challenges posed by high power and heat flux in contemporary electronic devices.

Thin-film lithium niobate (TFLN) based frequency doublers have widely been recognized as an essential component for both classical and quantum optical communications. Nonetheless, the efficiency (unit: %/W) of these devices is hindered by imperfections present in the quasi-phase matching (QPM) spectrum. In this report, we present a thorough experimental study of spectral imperfections in TFLN frequency doublers with varying lengths, ranging from 5 to 15 mm. A non-destructive diagnostic method based on scattered light imaging is proposed and employed to identify the waveguide sections and primary waveguide parameters contributing to the imperfections in the QPM spectrum. By applying this method, we obtain the evolution of the QPM spectrum along the waveguide’s length. Correlating this information with the measurements of the relevant geometric parameters along the waveguides suggests that the TFLN film thickness variation is the primary source for the measured spectral distortions. Furthermore, we numerically reproduce the QPM spectra with the mapped TFLN film thickness across the entire waveguiding regions. These findings align with and complement the simulation results from previous numerical studies, providing further evidence of the effectiveness of the developed diagnostic method. This comprehensive investigation offers valuable insights into the identification and mitigation of spectral imperfections in TFLN-based frequency doublers, paving the way for the realization of nonlinear optical devices with enhanced efficiency and improved spectral fidelity.

We unveil the primary origin of imperfections in quasi-phase-matching (QPM) spectrum from thin-film lithium niobate (TFLN) frequency doublers using scattered light imaging. We conclude the measured spectral distortion arises from non-uniformities in the film thickness.

We demonstrate, for the first time, fully-passive, optical packaging of an 8-channel array of surface-normal electroabsorption modulators to arrays of standard single-mode fibers. We validate our packaging approach through 25 Gbit/s NRZ-OOK modulation.

Short-reach communication systems use electro-optic transmission engines based on low-voltage, wide bandwidth modulators to achieve high capacity and low power operation. Here, we demonstrate, for the first time, integration of a 4-channel array of surface-normal electroabsorption modulators (SNEAMs) with a 4-channel array of electronic drivers with low output voltage (~1.25-1.45 Vpp). We use this 4-channel SNEAM-driver array electro-optic engine to demonstrate $4 \times 53$ Gbit/s non-return-to-zero on-off-keying transmission across up to 2 km of standard single mode fiber over a broad wavelength range (about 26 nm), the widest band of operation achieved with SNEAMs. Integration of a SNEAM array with a low output voltage driver array, a result that we achieved thanks to the use of SNEAMs that operate with low voltage swings, represents a fundamental milestone toward the realization of optical modules based on SNEAMs.

We propose a neural nonlinearity using a surface-normal photodetector with a response time of 5.7 µ s and an energy efficiency of < 10 nW/pixel. This device offers a significant improvement in free-space diffractive optical neural networks.

We experimentally demonstrate simultaneous generation and propagation of photon pairs in defect-free surface modes in an array of coupled sinusoidal waveguides. The measured biphoton correlations remain robust to tuning the curvature.

We demonstrate a WDM passive optical network that uses high-speed, polarization-independent surface normal modulators as upstream 25-Gb/s transmitters. A band of CW wavelengths, sourced at the optical line terminal, establishes the upstream channels. System performance in our single-fiber architecture is limited by Rayleigh backscattering, but is below the FEC threshold.

Surface-normal electroabsorption modulators (SNEAMs) are appealing for short-reach communication systems because of their outstanding properties, such as ultrawide bandwidth and polarization-insensitive response; however, due to their small active volumes, large voltage swings are typically required to obtain the best performance. Here we propose and demonstrate a novel, to the best of our knowledge, design that dramatically reduces the voltage needed by SNEAMs and significantly increases their extinction ratio. By shrinking the multiple quantum well stack of SNEAMs to the minimum and by optimizing their reflectivity with dielectric coatings of suitable refractive index and thickness, we obtain modulators that require drive voltages of only 1-2Vpp. We show that these novel devices largely outperform conventional SNEAMs.

Short reach communication systems, such as datacenters and access networks, exhibit steep capacity growth and require opto-electronic technologies with small size, low complexity, and low power consumption. Here, we demonstrate large-scale arrays of reflective surface normal electroabsorption modulators (SNEAMs). With very small active volumes, SNEAMs enable ultra-wide electro-optic bandwidth (>>65 GHz). We show modulation at 25 Gbit/s with 1 V-pp drive voltage on packaged SNEAMs and ultra-high bit-rate modulation at 107 Gbit/s with bare chips. These modulators are polarization-independent and have very low total input/output coupling loss of 0.7 dB to single-mode-fibers. We package SNEAM arrays with arrayed waveguide gratings into wavelength division multiplexing transmitters. Due to their broad wavelength range of modulation, SNEAMs do not need power hungry wavelength tuning or locking systems. Future co-integration of SNEAM arrays with low-power electronic driver arrays will enable high-capacity, low-power electro-optic engines.

We measure performance of 44-Gb/s (22-GBd) PAM-4 short-reach direct detection links with a polarization-independent surface-normal electro-absorption modulator. Performance below the KP-4 FEC threshold is demonstrated in standard single-mode fiber links with no dispersion compensation for distances up to 18 km.

Surface-normal electroabsorption modulators (SNEAMs) have unique electro-optic modulation properties; however, their behavior and performance at high light intensity is affected by thermal nonlinearities that take place in the modulator active volume. Here we show a novel, to the best of our knowledge, approach to make SNEAMs insensitive to optical power without the use of power-hungry heaters or feedback control systems. By passively compensating for the thermo-optic dependence of the SNEAM resonant cavity, we obtain an eight-fold reduction in the wavelength shift of the SNEAM response at 4 dBm of input power. Furthermore, we show no appreciable degradation in the SNEAM eye diagram at 25 Gbit/s, when the input power is increased up to 2 dBm, which is about four times higher than in conventional SNEAMs.

We report multi-level modulation in polarization-independent surface-normal electro-absorption modulators (SNEAMs). Four-level pulse amplitude modulation (PAM-4) at a line rate of 44 Gb/s is demonstrated on a fully packaged SNEAM with a 30 µm active area diameter and a 14 GHz electro-optic bandwidth. High-capacity PAM-4 transmission at 112 and 160 Gb/s is demonstrated on an unpackaged SNEAM chip, with a 15 µm active area diameter and ultrawide electro-optic bandwidth ( ≫ 65 G H z ). Fiber transmission is investigated for direct detection link lengths up to 23 km at 44 Gb/s and 2 km at 112 and 160 Gb/s, the highest multi-level modulation rates achieved on a SNEAM.

We demonstrate arrays of surface-normal electroabsorption modulators with ultrawide bandwidth (>>65 GHz), polarization insensitive response and ultralow total coupling loss to single-mode-fibers (0.7 dB). We show modulation up to 107 Gbit/s and packaging with arrayed-waveguide-gratings.

We demonstrate grating coupler based, efficient optical I/Os for silicon photonic(SiPh) chip-to-fiber and chip-to-chip applications. Standard single-mode fiber(SSMF)-to-chip interface experimentally shows coupling efficiency of -1.3dB. The reported I/Os are fabricated in standard SiPh process.

This paper reports for the first time, the dielectric characterization of a new, electronically tuneable electrochromic (EC) thin-film material over the frequency range 1-67 GHz, at temperatures of 7 degrees C, 23 degrees C, and 50 degrees C. Test cells composed of a microstrip line terminated with coplanar waveguide (CPW) transitions were fabricated to facilitate onwafer RF measurements and the application of different bias voltages using a standard CPW probe station. A precise curve-fitting technique based on full-wave simulations was used to extract the permittivity and loss tangent values of the material. The validity of the dielectric extraction technique was first demonstrated by employing a known material, silicon dioxide (SiO2). It is shown that the dielectric tunability of the EC material varies between 11.3% (1 GHz) and 7.5% (67 GHz) at 23 degrees C, and the measured loss tangent varies between 0.012 (OFF, 0 V, state) and 0.025 (ON, 6 V, state). Above room temperature, the devices exhibit higher values of dynamic tunability and a small increase in insertion loss. The results obtained for this first generation of tuneable EC material are encouraging, and many of the dielectric properties are shown to compare favourably with other, more mature bulk tuneable media, such as liquid crystals.

Controlling the magnetization reversal process of magnetic elements is important for a wide range of applications that make use of magnetoresistive effects, but is difficult to achieve for devices that require adjacent thin film structures capable of contacting an individual molecule or quantum dot. We report on the fabrication and measurement of ferromagnetic break junction devices with planar, elliptical leads to address the particular challenge of controlling the relative magnetization alignment between neighboring electrodes. Low temperature transport measurements, supported by finite-element micromagnetic simulations, are used to characterize the magnetoresistance response across a range of conductance levels. We demonstrate that an in-plane external field applied parallel to the hard axis of the ellipses may be used to controllably switch the magnetization of the source and drain electrodes between monodomain-like parallel and antiparallel configurations for devices in the tunneling regime.