Erbium-doped Waveguide Amplifiers Research Articles

Photonic-electronic integrated circuit-based coherent LiDAR engine

Chip-scale integration is a key enabler for the deployment of photonic technologies. Coherent laser ranging or FMCW LiDAR, a perception technology that benefits from instantaneous velocity and distance detection, eye-safe operation, long-range, and immunity to interference. However, wafer-scale integration of these systems has been challenged by stringent requirements on laser coherence, frequency agility, and the necessity for optical amplifiers. Here, we demonstrate a photonic-electronic LiDAR source composed of a micro-electronic-based high-voltage arbitrary waveform generator, a hybrid photonic circuit-based tunable Vernier laser with piezoelectric actuators, and an erbium-doped waveguide amplifier. Importantly, all systems are realized in a wafer-scale manufacturing-compatible process comprising III-V semiconductors, silicon nitride photonic integrated circuits, and 130-nm SiGe bipolar complementary metal-oxide-semiconductor (CMOS) technology. We conducted ranging experiments at a 10-meter distance with a precision level of 10 cm and a 50 kHz acquisition rate. The laser source is turnkey and linearization-free, and it can be seamlessly integrated with existing focal plane and optical phased array LiDAR approaches.

Improvement of differential modal gain in a ring-core few-mode erbium-doped polymer optical waveguide amplifier.

A few-mode erbium-doped waveguide amplifier (FM-EDWA) with a confined Er3+ doped ring structure is proposed to equalize the differential modal gain (DMG). The FM-EDWA amplifying three spatial modes (LP01, LP11a and LP11b) is optimized by genetic algorithm and fabricated using precise lithography overlay alignment technology. We observe gain values of over 14 dB for all modes with DMG of 0.73 dB at 1529 nm pumped only with LP01 for the power of 200 mW. Furthermore, a flat gain of more than 10 dB is demonstrated across 1525-1565 nm, with a sufficiently low DMG of less than 1.3 dB.

Gain optimization of an erbium-ytterbium co-doped amplifier via a Si3N4 photonic platform.

Erbium-doped waveguide amplifiers enable the integration of various active functions on a silicon platform. Er3+ can provide the basis for efficient optical amplification of photonic integrated circuits, but the gain is limited by cooperative upconversion leading to doping concentration limitations and insufficient optimization of the waveguide structure. In this paper, an erbium-ytterbium co-doped Al2O3 amplifier has been innovatively implemented on a low loss Si3N4 waveguide by careful design and optimization with the finite difference method. A more accurate and comprehensive theoretical model of erbium-ytterbium co-doping is established, with consideration of upconversions, energy transfer, amplified spontaneous radiation and propagation loss to perform optimization of the high-gain erbium-ytterbium co-doped waveguide amplifier. The optimized waveguide amplifier achieves a small-signal gain of more than 36 dB at 1550 nm under Er3+ concentration of 3 × 1020 cm-3 and Yb3+ concentration of 3 × 1021 cm-3. Endowing Si3N4 photonic integrated circuits with gain can enable the miniaturization of various on-chip based active devices.

Modeling and simulation of erbium-ytterbium co-doped optical waveguide amplifiers with dual-wavelength pumping at 980 nm and 1480 nm

With the rapid development of silicon photonic chips and integrated photonic circuits, erbium-doped optical waveguide amplifiers have received more and more attention in order to compensate for the transmission and coupling losses caused by the integration of optical devices on a chip. Pumping wavelength and pumping efficiency directly affect the gain and noise figure of the amplifier. In this paper, we propose an innovative dual-wavelength pumping method based on an erbium-ytterbium co-doped optical waveguide amplifier with simultaneous pumping at 980 nm and 1480 nm. A relaxation method based on the fourth-order Range-Kutta method is used to solve the rate and propagation equations and simulate the gain characteristics of the dual-wavelength pumping method for different ytterbium-erbium ion concentration ratios, erbium ion concentrations and ratio K between the 980 nm and total pump power. From the simulation results, it can be seen that the gain of the dual-wavelength pumping method is higher than that of the single-wavelength pumping methods when the erbium ion concentration exceeds 3 × 1026 m−3. At higher erbium ion concentrations, the dual-wavelength pumping method can provide higher gain for optical waveguide amplifiers, and may be able to become a new choice of pumping method for optical waveguide amplifiers.

A short high-gain waveguide amplifier based on low concentration erbium-doped thin-film lithium niobate on insulator

One hotspot of integrated optics is how to realize a highly integrated and high-gain on-chip amplification system in a thin film of lithium niobate on insulator (TFLNOI). Here, a low erbium-doped TFLNOI waveguide amplifier with shorter length is demonstrated using the photolithography-assisted oblique-reactive ion etching technique. A maximum net internal gain of 5.4 dB in the small-signal-gain regime is measured at the peak emission wavelength of 1531.35 nm for a waveguide length of 1.5 mm and an erbium-doped concentration of 0.1 mol. %, indicating a gain per unit length of 36 dB cm−1. This work paves the way for the monolithic integration of diverse active and passive photonic components on the TFLNOI platform.

(Invited) Rare-Earth-Doped Tellurium Oxide Light Emitting Nanophotonic Devices

Tellurium oxide is a promising material for passive, nonlinear and rare-earth-doped active photonic devices because of its high transparency, high refractive index, high nonlinearity and unique structure allowing for high rare-earth solubility. In this talk I present on our recent progress on tellurite glass on-chip light emitting nanophotonic devices. Low-loss passive devices including high-Q-factor microdisks and microring resonators will be discussed. In addition, rare-earth-doped active devices, including erbium-doped and thulium-doped waveguide amplifiers and microlasers will be presented. Using similar structures, we demonstrate nonlinear light emission via four-wave-mixing, supercontinuum generation and third harmonic generation. These tellurium oxide integrated nanophotonic devices are highly promising for compact and low-cost passive, active and nonlinear photonic integrated circuits for applications in communications, computing, and sensing.

Design of an erbium-doped Al[formula omitted] optical waveguide amplifier with on-chip integrated laser pumping source

Erbium-doped optical waveguide amplifier (EDWA) is an important building block for conventional and integrated optical communication and light signal processing systems. In recent years remarkable advancement has been achieved for EDWA to meet the demand for silicon photonic chips and integrated photonic circuits. However, in the currently demonstrated EDWAs all the laser pumping sources are external or off-chip, which not only limits the application field of EDWA, complicates the amplification scheme, but also does not fulfill the expectation of monolithic integration. In this work we propose a design of EDWA using high-gain Er-doped Al2O3 waveguide, low-loss silicon-on-insulator (SOI) waveguide, and on-chip integrated semiconductor laser pumping source. The 1550 nm signal light and 1480 nm pump light are transmitted and combined in SOI waveguide and coupled into the EDWA waveguide embedded in the adjacent layer. The 1480 nm pump light is coupled into the SOI waveguide from a bonded hybrid III–V semiconductor laser. The pump and signal waveguide building scheme, the coupling method and structure, and the integration process of laser pumping source are shown and simulated. The system performance was evaluated by using the device’s structure parameters and Er3+ rate equation model. More than 1 dB/cm net gain and up to 35 dB maximum net gain can be achieved at about 100 mW pump power. It indicates that such an on-chip integration design is feasible and fully on-chip integrated optical waveguide amplifier could be achieved.

8×40 Gbps WDM Amplification in a Monolithically Integrated Al2O3:Er3+-Si3N4 Waveguide Amplifier

On chip waveguide optical amplifiers have been extensively studied over the last years, with a wide variety of materials tested and proposed for different applications. Among the most prominent solutions for on-chip amplification, erbium doped waveguide amplifiers (EDWAs) are able to offer attractive performance metrics that can exceed SOA-based amplification solutions in traditional single and multi-channel systems. In this letter, we experimentally demonstrate a record high $8\times 40$ Gbps non return to zero (NRZ) wavelength division multiplexing (WDM) data amplification through a 5.9 cm long on-chip amplifier consisting of an erbium-doped aluminum oxide spiral waveguide monolithically integrated on the Si3N4 platform. Experimental results show more than 12.7 dB amplification per channel for low saturation total input power of −2.75 dBm, and clear eye diagrams and bit-error rate values below the KR4-FEC limit of $2\times 10 ^{-5}$ for all eight channels without any digital signal processing (DSP) applied to the signal to the receiver or transmitter side. The high losses from the fiber to chip interfaces, however, prevented achieving device net gain.

Design of an on-chip electrically driven, position-adapted, fully integrated erbium-based waveguide amplifier for silicon photonics

Erbium-doped waveguide amplifiers are important for silicon photonic large-scale integration. They boost the optical signal to compensate for the on-chip loss of the whole system, such as insertion, transmission, and coupling loss. Herein, a GaAs-on-silicon-pumped erbium-based waveguide amplifier is proposed. The optical amplifier is based on waveguides evanescently coupled with an erbium-doped thin-film gain medium. The erbium-doped gain region is locally pumped by a hybrid GaAs-SiN/SiO vertical-cavity-emitting pump laser. It can be selectively fabricated on the silicon photonic chip that has good position flexibility when integrated with other devices. The amplifier provides high-quality electrically driven amplification and realizes the full integration of amplifiers with the silicon photonic system without any external pump light source. The modeling analyses show that the proposed amplifier design has a maximum saturated gain of 42.5 dB/cm with a modulation bandwidth of ∼42 GHz. This high-gain, large-bandwidth device fully utilizes the advantages of erbium-doped materials and silicon-based III-V semiconductors, while overcoming their issues, and opens up a new pathway for on-chip amplification.

On-chip erbium-doped lithium niobate waveguide amplifiers [Invited

Lithium niobate on insulator (LNOI), as an emerging and promising optical integration platform, faces shortages of on-chip active devices including lasers and amplifiers. Here, we report the fabrication on-chip erbium-doped LNOI waveguide amplifiers based on electron beam lithography and inductively coupled plasma reactive ion etching. A net internal gain of ~30 dB/cm in communication band was achieved in the fabricated waveguide amplifiers under the pump of a 974-nm continuous laser. This work develops new active devices on LNOI and will promote the development of LNOI integrated photonics.

Erbium-doped hybrid waveguide amplifiers with net optical gain on a fully industrial 300 mm silicon nitride photonic platform.

Recently, erbium-doped integrated waveguide devices have been extensively studied as a CMOS-compatible and stable solution for optical amplification and lasing on the silicon photonic platform. However, erbium-doped waveguide technology still remains relatively immature when it comes to the production of competitive building blocks for the silicon photonics industry. Therefore, further progress is critical in this field to answer the industry's demand for infrared active materials that are not only CMOS-compatible and efficient, but also inexpensive and scalable in terms of large volume production. In this work, we present a novel and simple fabrication method to form cost-effective erbium-doped waveguide amplifiers on silicon. With a single and straightforward active layer deposition, we convert passive silicon nitride strip waveguide channels on a fully industrial 300 mm photonic platform into active waveguide amplifiers. We show net optical gain over sub-cm long waveguide channels that also include grating couplers and mode transition tapers, ultimately demonstrating tremendous progress in developing cost-effective active building blocks on the silicon photonic platform.

Erbium-doped TeO2-coated Si3N4 waveguide amplifiers with 5 dB net gain

We demonstrate 5 dB net gain in an erbium-doped tellurium-oxide-coated silicon nitride waveguide. The amplifier design leverages the high refractive index and high gain in erbium-doped tellurite glass as well as the ultra-low losses and mature, reliable, and low-cost fabrication methods of silicon nitride waveguide technology. We show that the waveguide platform demonstrates low background propagation losses of 0.25 dB/cm based on a ring resonator device with a Q factor of 1.3 × 10 6 at 1640 nm. We measure 5 dB peak net gain at 1558 nm and > 3 dB of net gain across the C band in a 6.7 cm long waveguide for 35 mW of launched 1470 nm pump power. Gain per unit length of 1.7 and 1.4 dB/cm is measured in a 2.2 cm long waveguide for 970 and 1470 nm pump wavelengths, respectively. Amplifier simulations predict that > 10 dB gain can be achieved across the C band simply by optimizing waveguide length and fiber-chip coupling. These results demonstrate a promising approach for the monolithic integration of compact erbium-doped waveguide amplifiers on silicon nitride chips and within silicon-based photonic integrated circuits.

On-Chip Electro-Optic Modulator With Loss Compensation Based on Polymeric Active-Integrated Waveguides

In this paper, an on-chip electro-optic (EO) modulator with loss compensation based on polymeric active-integrated waveguides was demonstrated. An erbium-doped waveguide amplifier was investigated and integrated with the EO modulator to compensate for signal loss. Polymeric active-integrated waveguides were based on the Mach-Zehnder interferometer structure, which consists of an amplified waveguide formed by two symmetric Y-junction branches and an EO waveguide formed by two decoupled waveguide arms. The dimensions of the polymeric active-integrated waveguides and the modulator were carefully designed and simulated. Moreover, a six-level spectroscopic model pumped at 980 nm was presented. The rate equations and propagation equations were solved, and the gain characteristics were simulated. The internal gain of 4.65 dB was achieved when the signal power was 0.1 mW at 1550 nm, the pump power was 100 mW at 980 nm, the Er 3+ concentration was $9.3\times 10^{25}/\text{m}^{3}$ , and the Yb 3+ concentration was $8.6\times 10^{26}/\text{m}^{3}$ in one Y-junction branch with a length of 1.5 cm. With the integrated waveguide amplifier, the loss of the EO modulator can be compensated at 9.3 dB in the two symmetric Y-junction branches. The light output intensity was also statistically presented. The proposed device with active-integrated waveguides could be used in polymer-based photonics integrated circuits.

High optical gain in erbium-doped potassium double tungstate channel waveguide amplifiers.

We report on the optical-gain properties of channel waveguides patterned into lattice-matched KGdxLuyEr1-x-y(WO4)2 layers grown onto undoped KY(WO4)2 substrates by liquid phase epitaxy. A systematic investigation of gain is performed for five different Er3+ concentrations in the range of 0.75 to 10at.% and different pump powers and signal wavelengths. In pump-probe-beam experiments, relative internal gain, i.e., signal enhancement minus absorption loss of light propagating in the channel waveguide, is experimentally demonstrated, with a maximum value of 12 ± 5 dB/cm for signals at the peak-emission wavelength of 1534.7 nm.

Greater than 50% inversion in Erbium doped Chalcogenide waveguides.

We report Er-doped Ge-Ga-Se films and waveguides deposited using co-thermal evaporation and patterned with plasma etching. Strong photoluminescence at 1.54 µm with intrinsic lifetime of 1 ms was obtained from deposited films with 1490 nm excitation. Erbium population inversion up to 50% was achieved, with a maximum of ~55% possible at saturation for the first time to the author's knowledge, approaching the theoretical maximum of 65%. Whilst gain was not achieved due to the presence of upconversion pumped photoinduced absorption, this nonetheless represents a further important step towards the realization of future chalcogenide Erbium doped waveguide amplifiers at 1550 nm and in the Mid-infrared.

Preparation and Characterization of Thermally Stable Silicon-Containing Fluoropolymer Matrix for Application to Erbium-Doped Waveguide Amplifiers

This study focuses on the fabrication of fluoropolymer films as erbium(Er3+) host material with a goal of achieving sufficient thermal stability, optical clarity in the optical communication region and a chemical resistance to withstand typical fabrication processing and operation conditions. To satisfy the demands mentioned above, acrylo-polyhedral oligomeric silsesquioxane as heat-resistance improver, 2,2,3,3,4,4,5,5-octafluoropentyl acrylate as fluorinated acrylic monomer, tetrahydrofurfuryl acrylate as solubility enhancer, 3-(trimethoxysilyl)propyl methacrylate as both a silane coupling agent and another heat-resistance improver and Darocur 4265 as photoinitiator were used. Various compositions were evaluated to obtain high quantity of Er3+ ions in the polymer matrix, high thermal stability and high transparency.

Design optimization of two concatenated long period waveguide grating devices for an application specific target spectrum.

We propose a global optimization method to optimize the parameters of two concatenated long period waveguide gratings (LPWGs) for generating a desired target spectrum. The design consists of two concatenated LPWGs with different grating periods inscribed in the guiding films of a four-layer planar waveguide with finite over cladding. We have used the transfer matrix method to compute the modes of the structure and the coupled mode theory to compute the spectrum of the device. The adaptive particle swarm optimization method has been used to optimize the parameters of LPWGs to generate symmetric as well as asymmetric target spectra. Two concatenated gratings of different lengths and periods have been used to generate the target spectra. To demonstrate the method of optimization we have designed a variety of wavelength filters including a rectangular shape rejection band filter, asymmetric band rejection filters, band rejection filters for flattening the amplified spontaneous emission (ASE) spectrum of an erbium doped fiber amplifier (EDFA), and a gain equalization filter for an erbium doped waveguide amplifier (EDWA) in the C-band. Seven parameters of the proposed LPWG structure have been optimized to achieve the desired spectra. We have obtained an ASE flattening with ±0.8 dB peak-to-peak ripple in case of the EDFA and gain flattening with ±0.4 dB peak-to-peak ripple in case of an EDWA. The study would be useful in the design of wavelength filters for specific applications.

980nm pumped erbium doped tellurium oxide planar rib waveguide laser and amplifier with gain in S, C and L band.

A thin film based erbium doped tellurium oxide (TeO2) waveguide amplifier producing gain from 1500nm to 1640nm when pumped at 980nm is demonstrated. At measured internal gains exceeding 14dB lasing due to end facet reflection set in producing the first tellurite waveguide laser. High gains were observed despite significant upconversion, whose impact appears to be mitigated to some extent by residual OH contamination. The device displayed no photosensitive effects from either the high pumping intensities used or the intracavity intensity at 1550nm.

Efficient 1.54-μm emission through Eu2+ sensitization of Er3+ in thin films of Eu2+/Er3+ codoped barium strontium silicate under broad ultraviolet light excitation

Thin films of Eu2+/Er3+ codoped barium strontium silicate were deposited on a thermal oxide Si substrate by magnetron sputtering. Optical properties suggest that after a rapid annealing process, these films can lead to efficient Er3+ emission at 1.54μm with a lifetime of about 7.9ms. Intense 1.54-μm light emission was achieved under broad ultraviolet light excitation through efficient energy transfer from Eu2+ to Er3+. These results indicate that the Eu2+/Er3+ thin films have potential applications as low cost and compact erbium doped waveguide amplifiers pumped by LEDs.

Potential for large optical gain improvement of erbium-doped slot waveguide amplifiers in silicon photonics

The potential for on-chip optical amplification at λs=1530 nm in silicon photonics using erbium-doped rich polymers integrated in silicon-slot waveguides is investigated by using a four-level spectroscopic model and a pumping wavelength of 1.48 μm. It is shown that the key parameter driving the whole amplification efficiency is the slot waveguide linear loss level, while optimization of the hollow core waveguide cross section leads to a slot width around 130 nm. Our investigations show that an on-chip optical gain of about 10 dB can be obtained with 7 dB/cm loss slot waveguides. Such a propagation loss is directly sustained by experimental results obtained for photonic structures fabricated using silicon technology. Due to the likelihood of improved technological processes in the near future, the slot waveguide loss level was swept in the 3–10 dB/cm range, showing that on-chip optical gain up to 30 dB can be seriously envisaged for slot waveguides with optimized optical losses around 3 dB/cm.