Monolithically integrated erbium-doped tunable laser on a CMOS-compatible silicon photonics platform

Deep photonic network platform enabling arbitrary and broadband optical functionality

Expanding applications in optical communications, computing, and sensing continue to drive the need for high-performance integrated photonic components. Designing these on-chip systems with arbitrary functionality requires beyond what is possible with physical intuition, for which machine learning-based methods have recently become popular. However, computational demands for physically accurate device simulations present critical challenges, significantly limiting scalability and design flexibility of these methods. Here, we present a highly-scalable, physics-informed design platform for on-chip optical systems with arbitrary functionality, based on deep photonic networks of custom-designed Mach-Zehnder interferometers. Leveraging this platform, we demonstrate ultra-broadband power splitters and a spectral duplexer, each designed within two minutes. The devices exhibit state-of-the-art experimental performance with insertion losses below 0.66 dB, and 1-dB bandwidths exceeding 120 nm. This platform provides a tractable path towards systematic, large-scale photonic system design, enabling custom power, phase, and dispersion profiles for high-throughput communications, quantum information processing, and medical/biological sensing applications.

Wavelength-tunable broadband lasers based on nanomaterials

Nanomaterials are widely used in the fields of sensors, optoelectronics, biophotonics and ultrafast photonics due to their excellent mechanical, thermal, optical, electrical and magnetic properties. Particularly, owing to their nonlinear optical properties, fast response time and broadband operation, nanomaterials are ideal saturable absorption materials in ultrafast photonics, which contribute to the improvement of laser performance. Therefore, nanomaterials are of great importance to applications in wavelength-tunable broadband pulsed lasers. Herein, we review the integration and applications of nanomaterials in wavelength-tunable broadband ultrafast photonics. Firstly, the two integration methods, which are direct coupling and evanescent field coupling, and their characteristics are introduced. Secondly, the applications of nanomaterials in wavelength-tunable broadband lasers are summarized. Finally, the development of nanomaterials and broadband tunable lasers is reviewed and discussed.

Widely tunable silicon-fiber laser at 2 µm

Laser sources operating in the 2 µm spectral region play an important role for sensing and spectroscopy, and potentially for optical communication systems. In this work, we demonstrate a widely tunable hybrid silicon-fiber laser operating in the 2 µm band. By introducing a silicon-integrated Vernier filter in a fiber laser, we achieved continuous wavelength tuning over a range of 100 nm, from 1970 to 2070 nm. Fiber-coupled output power up to 28 mW was measured with a full-width-half-maximum linewidth smaller than 260 kHz and a side-mode-suppression ratio greater than 40 dB over the spectral range.

Towards integrated photonic interposers for processing octave-spanning microresonator frequency combs

Microcombs-optical frequency combs generated in microresonators-have advanced tremendously in the past decade, and are advantageous for applications in frequency metrology, navigation, spectroscopy, telecommunications, and microwave photonics. Crucially, microcombs promise fully integrated miniaturized optical systems with unprecedented reductions in cost, size, weight, and power. However, the use of bulk free-space and fiber-optic components to process microcombs has restricted form factors to the table-top. Taking microcomb-based optical frequency synthesis around 1550 nm as our target application, here, we address this challenge by proposing an integrated photonics interposer architecture to replace discrete components by collecting, routing, and interfacing octave-wide microcomb-based optical signals between photonic chiplets and heterogeneously integrated devices. Experimentally, we confirm the requisite performance of the individual passive elements of the proposed interposer-octave-wide dichroics, multimode interferometers, and tunable ring filters, and implement the octave-spanning spectral filtering of a microcomb, central to the interposer, using silicon nitride photonics. Moreover, we show that the thick silicon nitride needed for bright dissipative Kerr soliton generation can be integrated with the comparatively thin silicon nitride interposer layer through octave-bandwidth adiabatic evanescent coupling, indicating a path towards future system-level consolidation. Finally, we numerically confirm the feasibility of operating the proposed interposer synthesizer as a fully assembled system. Our interposer architecture addresses the immediate need for on-chip microcomb processing to successfully miniaturize microcomb systems and can be readily adapted to other metrology-grade applications based on optical atomic clocks and high-precision navigation and spectroscopy.

Electro-optically tunable microring laser monolithically integrated on lithium niobate on insulator

We demonstrate monolithic integration of an electro-optically (EO) tunable microring laser on lithium niobate on insulator (LNOI) platform. The device is fabricated by photolithography assisted chemo-mechanical etching, and the pump laser is evanescently coupled into the erbium (${\rm{E}}{{\rm{r}}^{3 +}}$)-doped lithium niobate (LN) microring laser using an undoped LN waveguide mounted above the microring. The quality factor of the LN microring resonator is measured as high as ${1.54} \times {{1}}{{{0}}^5}$ at the wavelength of 1542 nm. Lasing action can be observed at a pump power threshold below 3.5 mW using a 980 nm continuous-wave pump laser. Finally, tuning of the laser wavelength is achieved by varying the electric voltage on the microelectrodes fabricated in the vicinity of a microring waveguide, showing an EO coefficient of 0.33 pm/V.

Luminescent Erbium-Doped Silicon Thin Films for Advanced Anti-Counterfeit Labels

The never-ending struggle against counterfeit demands the constant development of security labels and their fabrication methods. This study demonstrates a novel type of security label based on downconversion photoluminescence from erbium-doped silicon. For fabrication of these labels, a femtosecond laser is applied to selectively irradiate a double-layered Er/Si thin film, which is accomplished by Er incorporation into a silicon matrix and silicon-layer crystallization. The study of laser-induced heating demonstrates that it creates optically active erbium centers in silicon, providing stable and enhanced photoluminescence at 1530 nm. Such a technique is utilized to create two types of anti-counterfeiting labels. The first type is realized by the single-step direct laser writing of luminescent areas and detected by optical microscopy as holes in the film forming the desired image. The second type, with a higher degree of security, is realized by adding other fabrication steps, including the chemical etching of the Er layer and laser writing of additional non-luminescent holes over an initially recorded image. During laser excitation at 525 nm of luminescent holes of the labels, a photoluminescent picture repeating desired data can be seen. The proposed labels are easily scalable and perspective for labeling of goods, securities, and luxury items.

Erbium emission in Er:Y2O3 decorated fractal arrays of silicon nanowires

Disordered materials with new optical properties are capturing the interest of the scientific community due to the observation of innovative phenomena. We present the realization of novel optical materials obtained by fractal arrays of silicon nanowires (NWs) synthesized at low cost, without mask or lithography processes and decorated with Er:Y2O3, one of the most promising material for the integration of erbium in photonics. The investigated structural properties of the fractal Er:Y2O3/NWs demonstrate that the fractal morphology can be tuned as a function of the sputtering deposition angle (from 5° to 15°) of the Er:Y2O3 layer. We demonstrate that by this novel approach, it is possible to simply change the Er emission intensity by controlling the fractal morphology. Indeed, we achieved the increment of Er emission at 560 nm, opening new perspectives on the control and enhancement of the optical response of novel disordered materials.

Wideband tunable microwave signal generation in a silicon-micro-ring-based optoelectronic oscillator

Si photonics has an immense potential for the development of compact and low-loss opto-electronic oscillators (OEO), with applications in radar and wireless communications. However, current Si OEO have shown a limited performance. Si OEO relying on direct conversion of intensity modulated signals into the microwave domain yield a limited tunability. Wider tunability has been shown by indirect phase-modulation to intensity-modulation conversion. However, the reported tuning range is lower than 4 GHz. Here, we propose a new approach enabling Si OEOs with wide tunability and direct intensity-modulation to microwave conversion. The microwave signal is created by the beating between an optical source and single sideband modulation signal, selected by an add-drop ring resonator working as an optical bandpass filter. The tunability is achieved by changing the wavelength spacing between the optical source and a resonance peak of the resonator. Based on this concept, we experimentally demonstrate microwave signal generation between 6 GHz and 18 GHz, the widest range for a Si-micro-ring-based OEO. Moreover, preliminary results indicate that the proposed Si OEO provides precise refractive index monitoring, with a sensitivity of 94350 GHz/RIU and a potential limit of detection of only 10⁻⁸ RIU, opening a new route for the implementation of high-performance Si photonic sensors.

A Silicon Photonic Data Link with a Monolithic Erbium-Doped Laser

To meet the increasing demand for data communication bandwidth and overcome the limits of electrical interconnects, silicon photonic technology has been extensively studied, with various photonics devices and optical links being demonstrated. All of the optical data links previously demonstrated have used either heterogeneously integrated lasers or external laser sources. This work presents the first silicon photonic data link using a monolithic rare-earth-ion-doped laser, a silicon microdisk modulator, and a germanium photodetector integrated on a single chip. The fabrication is CMOS compatible, demonstrating data transmission as a proof-of-concept at kHz speed level, and potential data rate of more than 1 Gbps. This work provides a solution for the monolithic integration of laser sources on the silicon photonic platform, which is fully compatible with the CMOS fabrication line, and has potential applications such as free-space communication and integrated LIDAR.

Optical frequency synthesizer with an integrated erbium tunable laser

Optical frequency synthesizers have widespread applications in optical spectroscopy, frequency metrology, and many other fields. However, their applicability is currently limited by size, cost, and power consumption. Silicon photonics technology, which is compatible with complementary-metal-oxide-semiconductor fabrication processes, provides a low-cost, compact size, lightweight, and low-power-consumption solution. In this work, we demonstrate an optical frequency synthesizer using a fully integrated silicon-based tunable laser. The synthesizer can be self-calibrated by tuning the repetition rate of the internal mode-locked laser. A 20 nm tuning range from 1544 to 1564 nm is achieved with ~10^-13 frequency instability at 10 s averaging time. Its flexibility and fast reconfigurability are also demonstrated by fine tuning the synthesizer and generating arbitrary specified patterns over time-frequency coordinates. This work promotes the frequency stability of silicon-based integrated tunable lasers and paves the way toward chip-scale low-cost optical frequency synthesizers.

Lanthanide-Based Luminescent Materials for Waveguide and Lasing

Microlasers and waveguides have wide applications in the fields of photonics and optoelectronics. Lanthanide-doped luminescent materials featuring large Stokes/anti-Stokes shift, long excited-state lifetime as well as sharp emission bandwidth are excellent optical components for photonic applications. In the past few years, great progress has been made in the design and fabrication of lanthanide-based waveguides and lasers at the micrometer length scale. Waveguide structures and microcavities can be fabricated from lanthanide-doped amorphous materials through top-down process. Alternatively, lanthanide-doped organic compounds featuring large absorption cross-section can self-assemble into low-dimensional structures of well-defined size and morphology. In recent years, lanthanide-doped crystalline structures displaying highly tunable excitation and emission properties have emerged as promising waveguide and lasing materials, which substantially extends the range of lasing wavelength. In this minireview, we discuss recent advances in lanthanide-based luminescent materials that are designed for waveguide and lasing applications. We also attempt to highlight challenging problems of these materials that obstacle further development of this field.

Low-loss TeO2-coated Si3N4 waveguides for application in photonic integrated circuits

We report on high-quality tellurium oxide waveguides integrated on a low-loss silicon nitride wafer-scale platform. The waveguides consist of silicon nitride strip features, which are fabricated using a standard foundry process and a tellurium oxide coating layer that is deposited in a single post-processing step. We show that by adjusting the Si₃N₄ strip height and width and TeO₂ layer thickness, a small mode area, small bend radius and high optical intensity overlap with the TeO₂ can be obtained. We investigate transmission at 635, 980, 1310, 1550 and 2000 nm wavelengths in paperclip waveguide structures and obtain low propagation losses down to 0.6 dB/cm at 2000 nm. These results illustrate the potential for compact linear, nonlinear and active tellurite glass devices in silicon nitride photonic integrated circuits operating from the visible to mid-infrared.