Er-doped Waveguide Amplifiers Research Articles

On-Chip Waveguide Amplifiers for Multi-Band Optical Communications: A Review and Challenge

Erbium (Er)-doped fiber amplifier (EDFA) has achieved great success in modern optical communications for decades due to its outstanding gain performance in C-band. Nowadays, people are making efforts to make it monolithic integration due to the imperious demands from the advancement of high-performance and multi-function optoelectronic devices and chips. Except for the Er-doped waveguide amplifier, the other ion-doped on-chip waveguide amplifiers have also attracted much attention for multi-band optical communications, since they have own advantages in gain, bandwidth, selectivity of host materials, and integrability. Herein, we review the transmission characteristics of ion-doped on-chip waveguide amplifiers including gain and bandwidth, combining with the emission mechanisms and fabrication processes in applications of long-haul and short-reach optical communications. To facilitate the practical progress of the integrated waveguide amplifiers, from the perspective of gain medium, we also discuss the challenges and potential solutions for future technology roadmap. We expect that the bismuth (Bi)-doped waveguide amplifier would present impressive advantages in multi-band optical communications.

Effect of Substrate Temperature on Morphological, Structural, and Optical Properties of Doped Layer on SiO2-on-Silicon and Si3N4-on-Silicon Substrate.

A high concentration of Er3+ without clustering issues is essential in an Er-doped waveguide amplifier as it is needed to produce a high gain and low noise signal. Ultrafast laser plasma doping is a technique that facilitates the blending of femtosecond laser-produced plasma from an Er-doped TeO2 glass with a substrate to form a high Er3+ concentration layer. The influence of substrate temperature on the morphological, structural, and optical properties was studied and reported in this paper. Analysis of the doped substrates using scanning electron microscopy (SEM) confirmed that temperatures up to approximately 400 °C are insufficient for the incoming plasma plume to modify the strong covalent bonds of silica (SiO2), and the doping process could not take place. The higher temperature used caused the materials from Er-doped tellurite glass to diffuse deeper (except Te with smaller concentration) into silica, which created a thicker film. SEM images showed that Er-doped tellurite glass was successfully diffused in the Si3N4. However, the doping was not as homogeneous as in silica.

Efficient 1.54μm laser property in near- stoichiometric Er:LiNbO3 crystal

Abstract Near-stoichiometric LiNbO3 crystal heavily doped with Er3+ ions (Er:NSLN) was grown by Czochralski technique. An enhancement of 1.54 μm emission and a lengthening lifetime of 4I13/2→4I15/2 transition observed in Er:NSLN crystal would meet the requirement of the greatly shortening optical diffusion route for Er-doped waveguide amplifiers (EDWAs). Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the concentration of Er3+ ion in the crystal. Based on Judd–Ofelt theory, the spectroscopic properties of Er:NSLN crystal were discussed, and the obtained intensity parameters Ωt implied that the increased [Li]/[Nb] ratio had a large influence on the value of Ω2. The emission cross-sections of 1.54 μm emission were calculated by Fuchtbauer–Ladenburg and reciprocity methods. Studies on the gain cross-section, estimated as a function of the population inversion ratio, suggested that Er:NSLN crystal could be considered as a potential material in the application of the tunable lasers around 1.54 μm wavelength.

Overlap factor between intensity profiles of signal and pump light and gain characteristics of Er-doped waveguide amplifier

The model used for analyzing the gain characteristics of Erdoped waveguide amplifier （EDWA） is based on the ratepropagation equations with intensity profiles of pump and signal light. The intensity profiles of pump and signal light for different channel opening width （DCOW） of Erdoped waveguide is discussed. And the numerical method （NM） considering the difference of intensity profiles between signal and pump light in channel waveguide with DCOW is used to solve the gain characteristics of signal light in EDWA. An overlap factor Γsp between light intensity profiles of signal and pump is introduced to modify the conventional simplified method （CSM） in EDWA, which is a revised version of the conventional simplified method （RCSM）. Results show that difference of 297 dB in gain for -10 dBm signal light at 1534 nm due to DCOW of waveguides is obtained for a 4 cm long waveguide amplifier pumped by 80 mw at 980 nm. Comparing with CSM, the gain characteristics of EDWA from RCSM is simpler and better approaches the result from NM. Therefore, the RCSM is valuable in the research of EDWA.

Theoretical and experimental research on Er-doped and Yb-Er co-doped Al2O3 waveguide amplifiers

The rate equations of Er-doped and Yb-Er co-doped systems pumped at 0.98 mm are presented, with consideration for the upconversion mechanisms such as cooperative upconversion, cross relaxation, and excited state absorption. A multi-theoretical model is founded to analyze the gain characteristics of Er-doped and Yb-Er co-doped Al2O3 waveguide amplifiers by using rate equations, a two-dimension waveguide finite element model and propagation equations with forward and backward amplified spontaneous emission. The dependence of the gain on amplifier length, pump power and doping concentration is obtained. The optimum design curve is given for designing waveguide amplifiers. The new theory is used to analyze the gain performance of a practical Yb-Er co-doped Al2O3 waveguide amplifier, and the analyzed results are in accordance with the experimental data.

THE ANALYSIS OF INTENSITY PROFILES OF PUMP AND SIGNAL LIGHT IN Er-DOPED WAVEGUIDE AMPLIFIER

The model used for analyzing the gain characteristics of Er -doped waveguide amplifier (EDWA) is based on the rate-propagation equations with intensity profiles of pump and signal light (IPPSL). This simulation indicates that the IPPSL have significant effect on the gain of signal light. The results show that a gain change 2.3 dB of signal light at 1534 nm is obtained for a 4 cm long channel waveguide amplifier with different intensity profiles pumped by 80 mW at 980 nm. Experiment also shows that a gain change about 2.31 dB at 1534 nm for the channel waveguide of 4 cm length is obtained for different IPPSL. Thus, the effect of IPPSL should be considered to enhance the pump efficiency in the design of EDWA.

Fabrication of ultra-compact Er-doped waveguide amplifier based on bismuthate glass

Due to the possibility of high Er3+ doping and their broadband emission, the bithmuth-oxide-based glasses can be a promising candidate of host materials for a compact waveguide amplifier with high performance. By a novel fabrication process, we have developed a Bi2O3-based waveguide device with propagation loss as low as 0.13 dB/cm, which is comparable to the silica-based waveguides. We have achieved an ultra-compact Er-doped waveguide amplifier with 1 cm2 size by designing a spiral light-wave circuit with low bending loss. This EDWA showed gain values over 15 dB, noise figures lower than 8 dB and gain flatness less than 2 dB over the whole C-band region. The output power of this EDWA reached higher than 12 dBm.

Er$^{3+}$–Yb$^{3+}$ Codoped Silica Waveguide Amplifiers Longitudinally Pumped by Broad-Area Lasers

We present a longitudinal multimode pumping scheme which allows Yb-sensitized Er-doped silica waveguide amplifiers to be effectively pumped by high-power and low-cost broad-area lasers. The proposed configuration is based on evanescent pump light coupling from a multimode low-loss waveguide to a Er-Yb codoped active core. Theoretical predictions, based on propagation and population-rate equations for the coupled Er-Yb system, show that longitudinal multimode pumping by high-power broad-area lasers at around 980 nm can provide up to 4-dB gain per centimeter, suggesting possible integration of low-cost amplifiers with important applications in wavelength-division-multiplexing metro and access optical networks.

Correct determination of net gain in Er-doped optical waveguide amplifier from pump-on/off measurement

Starting with evolution equation of signal optical power in an Er-doped channel waveguide, rigorous theoretical expressions used for correct determination of net gain from signal enhancement measured by using pump-on/off method are derived. These expressions allow to clarify the argument on relationships between net gain, internal gain and signal enhancement in some earlier literatures. Physical implications of net gain, internal gain and signal enhancement expressions are analyzed. Standardized definitions for the three physical quantities are proposed. The definition for net gain is proposed on the basis of practical application of an EDWA in optical fiber communication and the definitions for the latter two are suggested based on the physical implication analysis of their expressions.

Performance analysis of nanocluster-Si sensitized Er-doped waveguide amplifier using top-pumped 470nm LED

We analyze the performance of nanocrystal-Si (nc-Si) sensitized Er-doped waveguide amplifier using coupled nc-Si-Erbium rate equation, and suggest novel structures / operation methods which can be used to enhance its performance figures. With 2-dimensional modified propagation equation applied for the pump / signal waves along with modest assumptions on design parameters, we show that 10dB of gain with 0dBm input signal can be achieved with currently available pump LED power.

A High Index Contrast Silicon Oxynitride Materials Platform for Er-doped Microphotonic Amplifiers

AbstractEr-based optical amplification continues to be the ideal low noise, WDM crosstalk free, broadband candidate for waveguide amplifiers. Design analysis of the applicability of Er-Doped Waveguide Amplifiers (EDWAs) for micron-scale integrated photonics in a planar lightwave circuit concludes: (i) an >80× increase in gain efficiency, and (ii) a >40×increase in device shrink can be realized, for a high index contrast EDWA (with a core-cladding index difference of δn=0.1↔0.7), compared to a conventional Er-doped fiber amplifier. The materials challenge now is to establish a robust materials system which meets this high index difference design requirement while simultaneously leveraging the capability of silicon (Si) processing: a host platform for EDWAs must be found which can integrate with Si Microphotonics. Silicon nitride (Si3N4), silicon oxide (SiO2) and a miscible silicon oxynitride alloy (SiON) of the two meet this materials challenge. We present the results of reactive and conventional magnetron sputtering based materials characterization for this high index host system. Room temperature and 4 K photo-luminescence studies for annealed samples show the reduction of non-radiative de-excitation centers while maintaining an amorphous host structure. Atomic force microscopy shows less than 1 nm peak-to-peak roughness in deposited films. Prism coupler measurements show a reliable reproducibility of host index of refraction with waveguide scattering loss <2 dB/cm. We conclude that the SiON host system forms an optimal waveguide core for an SiO2-clad EDWA. Initial gain measurements show a gain coefficient of approximately 3.9 dB/cm.

Index contrast scaling for optical amplifiers

A scaling methodology for optically pumped waveguide amplifiers is presented as a function of their core-cladding index contrast. Increasing index contrast results in two crucial advantages: 1) an increase in gain efficiency and 2) a decrease in the areal footprint of a planar structure. Increasing index contrast is observed to have no effect on the output noise figure. A figure of merit summarizing these advantages demonstrates the powerful role of index contrast as an enabler for improving planar amplifier performance. Design rules are presented in the form of performance maps, allowing waveguide designers to optimize amplifier length and footprint. Using the Er-doped waveguide amplifier as a case study, we design an optical amplifier with >3-dB/cm gain within a 300/spl times/300-/spl mu/m/sup 2/ area, powered by a single 1-mW pump source. This work represents a design rule approach for making a scalable microphotonic optical amplifier.

A numerical analysis of gain characteristics of Er-doped Al2O3 waveguide amplifiers

The gain characteristics of erbium-doped Al2O3 waveguide amplifiers are investigated by solving numerically rate equations with upconversion effects and propagation equations. We obtained the dependence of gain of erbium-doped Al2O3 waveguide amplifiers on the waveguide length, erbium concentration and pump power at different pumping wavelengths (980 and 1480 nm). The performance of amplifiers pumping at 1480 and 980 nm are compared. It is shown that 980 nm pumping has higher gain and higher pumping efficiency. The parameters of waveguide amplifiers have been optimized. A optical gain of 43 dB can be achieved for a optimum waveguide length of 8.25 cm and 5.8 × 1020 cm−3 Er concentration pumped with 100 mW at 980 nm, that is a gain of 5.2 dB/cm.

Exciton–erbium energy transfer in Si nanocrystal-doped SiO 2

Silicon nanocrystals were formed in SiO 2 using Si ion implantation followed by thermal annealing. The nanocrystal-doped SiO 2 layer was implanted with Er to peak concentrations ranging from 0.015 to 1.8 at.%. Upon 458 nm excitation, a broad nanocrystal-related luminescence spectrum centered around 750 nm and two sharp Er luminescence lines at 982 and 1536 nm are observed. By measuring the temperature-dependent intensities and luminescence dynamics at a fixed Er concentration, and by measuring the Er concentration dependence of the nanocrystal and Er photoluminescence intensity, the nanocrystal excitation rate, the Er excitation and decay rate, and the Er saturation with pump power we conclude that: (1) the Er is excited by excitons recombining within Si nanocrystals through a strong coupling mechanism; (2) the exciton–Er energy transfer rate is >10 6 s −1; (3) the exciton–Er energy transfer efficiency is >60 %; (4) each nanocrystal can have at most ∼1–2 excited Er ions in its vicinity, which is attributed to either an Auger de-excitation or a pair-induced quenching mechanism; (5) at a typical nanocrystal concentration of 10 19 cm −3, the maximum optical gain at 1.54 μm of an Er-doped waveguide amplifier based on Si nanocrystal-doped SiO 2 is ∼0.6 dB cm −1; (6) the effective Er excitation cross-section using this nanocrystal sensitization scheme is σ eff≈10 −15 cm 2 at 458 nm, which is a factor 10 5–10 6 larger than the cross-section for direct optical pumping of Er. This enables the fabrication of an Er-doped nanocrystal waveguide amplifier that can be pumped using a white light source.

Exciton–erbium interactions in Si nanocrystal-doped SiO2

The presence of silicon nanocrystals in Er doped SiO2 can enhance the effective Er optical absorption cross section by several orders of magnitude due to a strong coupling between quantum confined excitons and Er. This article studies the fundamental processes that determine the potential of Si nanocrystals as sensitizers for use in Er doped waveguide amplifiers or lasers. Silicon nanocrystals were formed in SiO2 using Si ion implantation and thermal annealing. The nanocrystal-doped SiO2 layer was implanted with different doses of Er, resulting in Er peak concentrations in the range 0.015–1.8 at. %. All samples show a broad nanocrystal-related luminescence spectrum centered around 800 nm and a sharp Er luminescence line at 1536 nm. By varying the Er concentration and measuring the nanocrystal and Er photoluminescence intensity, the nanocrystal excitation rate, the Er excitation and decay rate, and the Er saturation with pump power, we conclude that: (a) the maximum amount of Er that can be excited via exciton recombination in Si nanocrystals is 1–2 Er ions per nanocrystal, (b) the Er concentration limit can be explained by two different mechanisms occurring at high pump power, namely Auger de-excitation and pair-induced quenching, (c) the excitable Er ions are most likely located in an SiO2-like environment, and have a luminescence efficiency <18%, and (d) at a typical nanocrystal concentration of 1019 cm−3, the maximum optical gain at 1.54 μm of an Er-doped waveguide amplifier based on Si nanocrystal-doped SiO2 is ∼0.6 dB/cm.

Exciting Erbium-Doped Planar Optical Amplifier Materials

AbstractErbium-doped planar optical amplifiers can find numerous applications in photonic integrated circuits operating at 1.5 μm. The challenge is to fabricate these devices with high gain, operating at low pump power, and having small overall size. In this paper a review is given of our recent work in the area of Er-doped waveguide materials and amplifiers based on three materials classes: oxide films (A12O3, Y2O3, SiO2), polymers, and silicon.

Analysis of output statistics of single and double pass Er-doped LiNbO3 waveguide amplifiers

Based on the photon statistics master equation of the linear amplifier, this paper presents a theoretical evaluation of the following important amplifier parameters: the output mean photon number, the standard deviation, the Fano factor, the statistical fluctuation and the spontaneous emission factor for single and double pass configurations and for forward and backward pumping schemes in the case of an Er3+-doped LiNbO3 waveguide amplifier. The simulations were performed using the small gain approximation and the above-mentioned device characteristics versus pump powers, waveguide length and signal wavelength are evaluated.

Ion implantation into amorphous solids

We describe the effects of implantation of silicon into pure amorphous silicon and hydrogenated amorphous silicon and of erbium into soda-lime silicate glass and hydrogenated amorphous silicon. The former implantations and subsequent annealing treatments are used as a means of controlled defect creation. The experiments lead to new insights into the relation between defect density and bond-angle variation in both types of amorphous silicon. Erbium implantation is used to produce planar optical waveguide materials. It is demonstrated that erbium implantation into glass and amorphous silicon leads to efficient photoluminescence. It appears that these materials are attractive candidates for Er-doped waveguide amplifiers.

Optimization of an Er-doped silica glass optical waveguide amplifier

The optical gain performance of a highly Er-doped waveguide amplifier is affected by concentration quenching and cooperative upconversion effects. Based on materials parameters, which were previously determined for Er-doped sodalime-silicate glass, we calculate how the gain performance can be improved by reducing these limiting processes. For amplifiers with an Er concentration exceeding 0.1 at.%, the Er dc-excitation rate is dominated by cooperative upconversion rather than radiative decay or nonradiative decay due to coupling to defects. The effect of lowering the waveguide loss and reducing the optical mode diameter is also demonstrated.

Erbium-doped phosphosilicate glass waveguide amplifier fabricated by PECVD

An Er-doped waveguide amplifier fabricated by plasma enhanced chemical vapour deposition is described. A maximum net gain of 5 dB and a gain coefficient of 0.67 dB/cm are obtained in a 0.48 wt% Er-doped waveguide pumped at 420 mW at a wavelength of 0.98 μm. The 0 dB gain threshold is 23 mW.