Erbium-doped Waveguide Amplifiers Research Articles

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.

Refractive index change of multicomponent glass films for bismuthate erbium-doped waveguide amplifiers prepared by radio-frequency magnetron sputtering under different magnetic fields of cathode

Bismuthate erbium (Er)-doped waveguide amplifiers consist of an Er-doped core surrounded by an Er-free cladding film with lower refractive index. The propagation loss of a waveguide critically depends on both the thickness and the refractive index of its core and cladding films; hence, these two properties of such films must be controlled. We studied the influence of magnetic fields on a batch-to-batch variation of the refractive index of Er-free multicomponent cladding glass films deposited by radio-frequency magnetron sputtering. We successfully controlled the variation in the refractive indices of the films to within 0.001 throughout the lifetime of the target by applying the design techniques of a weak magnetic field and flat magnetic field lines to a magnetic array for sputtering. We also found that the self-bias voltage maintained a high value irrespective of target consumption. This phenomenon is thought to be related to stabilization of the deposition rate and the refractive index of the films under the experimental sputtering conditions.

Design of application specific long period waveguide grating filters using adaptive particle swarm optimization algorithms

We present design optimization of wavelength filters based on long period waveguide gratings (LPWGs) using the adaptive particle swarm optimization (APSO) technique. We demonstrate optimization of the LPWG parameters for single-band, wide-band and dual-band rejection filters for testing the convergence of APSO algorithms. After convergence tests on the algorithms, the optimization technique has been implemented to design more complicated application specific filters such as erbium doped fiber amplifier (EDFA) amplified spontaneous emission (ASE) flattening, erbium doped waveguide amplifier (EDWA) gain flattening and pre-defined broadband rejection filters. The technique is useful for designing and optimizing the parameters of LPWGs to achieve complicated application specific spectra.

Dual-Core Leaky Waveguide-Based Filters for Erbium-Doped Waveguide Amplifier

This article gives the design of a gain-flattening filter for an erbium-doped waveguide amplifier using a dual-core resonant leaky waveguide. The spectral variation of leakage loss of the waveguide has been used for gain equalization of the erbium-doped waveguide amplifier in the conventional (C) band. Leakage loss of the structure has been calculated by using the transfer matrix method. Numerical simulation results show a 17.5-dB gain with a gain excursion of ±1.35 dB in the C-band (1,526 nm–1,566 nm) of a typical erbium-doped waveguide amplifier. The study should be useful in designing integrated optic gain-flattening filters.

Long-period-grating in a trench assisted planar optical waveguide

We present long-period-grating in a planar optical waveguide that contains a low-index trench in the cladding region. The effect of the trench on transmission spectrum of the grating has been studied. The waveguide structure has been analyzed by the transfer matrix method and the output spectrum of the grating has been calculated by the coupled mode theory. Our numerical results show that position, strength, and width of the trench significantly affect the transmission spectrum of the grating. In particular, we show the appearance of triple resonance between a set of coupled modes and obtain an ultrawide band rejection in the output spectrum. We numerically demonstrate applications of the proposed structure in wideband rejection filters, refractive index sensors, and gain equalization of erbium-doped waveguide amplifiers.

Ion-exchanged silica-on-silicon structured channel erbium-doped waveguide amplifiers

Silica-on-silicon structured channel erbium-doped waveguide amplifiers (EDWAs) were fabricated by a combination of the ion-exchange and sol-gel techniques. A small signal fiber-device-fiber net gain of 0.5 dB at 1531 nm was obtained for a 4 cm long EDWA with an optimized waveguide structure. The low noise figure of 4.0 dB was also achieved. Samples of different waveguide structures and rare-earth ion doping levels were fabricated to compare the EDWA gain properties. The results demonstrate that a better gain spectrum can be obtained by maximizing the distribution overlap of pump and signal mode intensity. The gain performance can be further improved by reducing upconversion efficiency of the EDWA. This work demonstrates that the ion-exchanged silica-on-silicon waveguide structure is an alternative approach for EDWA fabrication.

Vertically Integrated Broadband Duplexer for Erbium-Doped Waveguide Amplifiers Made by Ion Exchange on Glass

The hybrid integration of optical amplifier modules requires the development of a new kind of pump/signal duplexers. In this letter, a new structure highly compatible with pump diode waveguides (λ = 0.98 μm), optical fibers (λ = 1.55 μm), and hybrid erbium-doped waveguide amplifiers is proposed. The device, based on a vertically integrated asymmetric Y-junction, has been realized by cascading three ion exchanges on a glass substrate. Bandwidth of more than 200 nm around the two working wavelengths has been demonstrated with isolations between the two outputs reaching (21 ± 0.4) dB at λ = 0.98 μm and (44 ± 0.4) dB at λ = 1.55 μm and low losses.

Carrier lifetime in erbium-doped GaN waveguide emitting in 1540 nm wavelength

We report the characteristics of an erbium-doped GaN semiconductor waveguide amplifier grown by metal-organic chemical vapor deposition. We demonstrated that both 980 and 1480 nm optical pumping were efficient to create population inversion between the I413/2 and I415/2 energy levels. The carrier lifetime in the I413/2 energy band was measured to be approximately 1.5 ms in room temperature, which is slightly shorter than that in erbium-doped silica due to the interaction between the erbium ions and the semiconductor lattice structure. But it is significantly longer than the carrier lifetime in a typical semiconductor optical amplifier which is in the nanosecond regime.

Near-field enhancement of infrared intensities for f-f transitions in Er3+ ions close to the surface of silicon nanoparticles

Erbium doped waveguide amplifiers can be used in optical integrated circuits to compensate for signal losses. Such amplifiers use stimulated emission from the first excited state ((4) I (13/2)) to the ground state ((4) I (15/2)) of Er(3+) at 1.53 µm, the standard wavelength for optical communication. Since the intra-f transitions are parity forbidden for free Er(3+) ions, the absorption and the emission cross sections are quite small for such doped amplifiers. To enhance the absorption, Si nanoclusters can be embedded in silica matrix. Here we investigate the effect of the Si nanocluster on the Er(3+) emission using ab initio theory for the first time. We combine multi-reference configuration interaction with one-electron spin-orbit Hamiltonian and relativistic effective core potentials. Our calculations show that the presence of a polarizable Be atom at 5Ǻ from the Er(3+) ion in a crystalline environment can lead to an enhancement in the emission by a factor of three. The implications of this effect in designing more efficient optical gain materials are discussed.

Role of Bi 3+ ions for Er 3+ ions efficient 1.54 μm light emission in Er/Bi codoped SiO 2 thin film prepared by sol–gel method

Er/Bi codoped SiO 2 thin films were prepared by sol–gel method and spin-on technology with subsequent annealing process. The bismuth silicate crystal phase appeared at low annealing temperature while vanished as annealing temperature exceeded 1000 °C, characterized by X-ray diffraction, and Rutherford backscattering measurements well explained the structure change of the films, which was due to the decrease of bismuth concentration. Fine structures of the Er 3+-related 1.54 μm light emission (line width less than 7 nm) at room temperature was observed by photoluminescence (PL) measurement. The PL intensity at 1.54 μm reached maximum at 800 °C and decreased dramatically at 1000 °C. The PL dependent annealing temperature was studied and suggested a clear link with bismuth silicate phase. Excitation spectrum measurements further reveal the role of Bi 3+ ions for Er 3+ ions near infrared light emission. Through sol–gel method and thermal treatment, Bi 3+ ions can provide a perfect environment for Er 3+ ion light emission by forming Er–Bi–Si–O complex. Furthermore, energy transfer from Bi 3+ ions to Er 3+ ions is evidenced and found to be a more efficient way for Er 3+ ions near infrared emission. This makes the Bi 3+ ions doped material a promising application for future erbium-doped waveguide amplifier and infrared LED.

170 Gbit/s transmission in an erbium-doped waveguide amplifier on silicon

Signal transmission experiments were performed at 170 Gbit/s in an integrated Al(2)O(3):Er(3+) waveguide amplifier to investigate its potential application in high-speed photonic integrated circuits. Net internal gain of up to 11 dB was measured for a continuous-wave 1532 nm signal under 1480 nm pumping, with a threshold pump power of 4 mW. A differential group delay of 2 ps between the TE and TM fundamental modes of the 5.7-cm-long amplifier was measured. When selecting a single polarization open eye diagrams and bit error rates equal to those of the transmission system without the amplifier were observed for a 1550 nm signal encoded with a 170 Gbit/s return-to-zero pseudo-random 2(7)-1 bit sequence.

Study on the characteristics of erbium-doped waveguide ring laser

A theoretical model of the erbium-doped waveguide ring laser is established according to the theory of erbium-doped waveguide amplifier and the transmission matrix of waveguide directional coupler. The influence of bend radius, coupling coefficient and doped erbium ion concentration on the characteristics of waveguide ring laser is investigated. It is shown that due to the co-action of waveguide bend loss and other relevant loss there is an optimal bend radius which can provide simultaneously low threshold pumping power and high laser light output power. As one part of the resonator’s loss, the laser light coupling coefficient of directional coupler has an impact on the laser property. The analysis indicates that the laser achieves the high output power when the coupling coefficient is about 0.2. The threshold pumping power is the minimum when the doped erbium ion concentration is 0.85×1026 m−3. Increasing the concentration of doped erbium ions will enhance the output power of laser light as long as the concentration doesn’t introduce remarkable up-conversion effect. The results give a good theoretical basis for the design and fabrication of erbium-doped waveguide ring laser devices.

Simultaneously gain-flattened and gain-clamped erbium fiber amplifier

In this paper, we propose and demonstrate a simple erbium amplifier module based on an erbium- doped fiber amplifier (EDFA) and an erbium-doped waveguide amplifier (EDWA) in serial, having gain-flatted (GF) and gain-clamped (GC) functions simultaneously. In first proposed GF amplifier scheme, the maximum gain variation of 2.5 dB can be observed in the effective range of 1528 to 1562 nm and the entire gains are above 35 dB with the input signal power of -30 dBm. Hence, we investigate second scheme by optical feedback method in the proposed fiber amplifier achieving gain-flattened (GF) and gain-clamped (GC) efficiencies simul- taneously. Thus, the maximum gain variations of ± 0.8 and ± 1.8 dB can be obtained in the operating range of 1530 to 1564 nm, when the input signal powers are -16 and -40 dBm, respectively. Moreover, the dynamic gain profile can be adjusted and dynamic input power range is also measured based on the proposed GF and GC fiber amplifier.

Investigation of Transients in Single-Fiber Bidirectional Closed-Loop WDM Ring Network Using High-Power Gain Clamped EDWA

We investigate a transparent WDM ring network design immune to accumulated power transients where simultaneous bidirectional operation is achieved on a single fiber. This allows cost effectiveness, flexible traffic re-routing, and network operation. We demonstrate that add/drop of 15 out of 16 channels generate negligible (< 0.15 dB) power excursion on the surviving channel. These results have been obtained by using new high-gain erbium-doped waveguide amplifiers in an innovative gain-clamped configuration that allows bidirectional operation. The glass-on-silicon waveguide optical amplifiers are able to achieve a clamped flat gain of 15 dB on full C-band with up to 0-dBm input power. This is the highest output power ever reported for an erbium-doped waveguide amplifier. The amplifier can with almost identical performance operate with signals entering together from both ends or even from opposite ends. The gain properties of the amplifier are almost perfectly symmetric.

Evanescent Multimode Longitudinal Pumping Scheme for Si-Nanocluster Sensitized Er$^{3+}$-Doped Waveguide Amplifiers

We present a multimode longitudinal pumping scheme for integrated rare-earth-doped waveguide amplifiers which allows an efficient use of low cost multimode pump sources. The scheme is based on evanescent pump light coupling from a multimode low loss waveguide to a single mode active core. Multimode pump light is gradually coupled to the active waveguide, which is single mode at the signal wavelengths, providing population inversion along the whole amplifier length and overcoming the main limitation of conventional single mode pump butt-coupling in case of strongly absorbing active materials. We propose this pumping scheme at 477 nm for Si-nanocluster sensitized Erbium doped waveguide amplifiers, in which conventional butt-coupling is inefficient due to the strong pump absorption by the Si- nanoclusters , and top pumping by LED arrays is limited by the low pump intensity values achievable within the active region. The coupling between the multimode waveguide and the active core has been numerically studied for slab waveguide structures using a 2-D split-step finite element method.

A semi-weakly confined erbium-doped waveguide amplifier with double-layered buffer/cladding

A semi-weakly confined waveguide structure was designed and fabricated. This waveguide structure has a 350 nm thin core layer. Its optical mode field is weakly confined in vertical direction but is strongly confined laterally. The waveguide can support a nearly circular optical field distribution that matches well with a single-mode fiber. An erbium-doped waveguide amplifier (EDWA) with the new waveguide structure was fabricated by sol-gel method. The EDWA has a passive core and double-layered buffer/cladding. A small coupling loss of 0.4 dB/facet and an internal gain of 1.9 dB via evanescent wave amplification near 1550 nm were obtained.

Erbium and ytterbium co-doped SiO2:GeO2 planar waveguide prepared by the sol–gel route using an alternative precursor

The sol–gel method combined with a spin-coating technique has been successfully applied for the preparation of rare-earth doped silica:germania films used for the fabrication of erbium-doped waveguide amplifiers (EDWA), presenting several advantages over other methods for the preparation of thin films. As with other methods, the sol–gel route also shows some drawbacks, such as cracks related to the thickness of silica films and high hydrolysis rate of certain precursors such as germanium alkoxides. This article describes the preparation and optical characterization of erbium and ytterbium co-doped SiO2:GeO2 crack-free thick films prepared by the sol–gel route combined with a spin-coating technique using a chemically stable non-aqueous germanium oxide solution as an alternative precursor. The non-crystalline films obtained are planar waveguides exhibiting a single mode at 1,550 nm with an average thickness of 3.9 µm presenting low percentages of porosity evaluated by the Lorentz–Lorenz Effective Medium Approximation, and low stress, according to the refractive index values measured in both transversal electric and magnetic polarizations. Weakly confining core layers (0.3% < Δn < 0.75%) were obtained according to the refractive index difference between the core and buffer layers, suggesting that low-loss coupling EDWA may be obtained. The life time of the erbium 4I13/2 metastable state was measured as a function of erbium concentration in different systems and based on these values it is possible to infer that the hydroxyl group was reduced and the formation of rare-earth clusters was avoided.

Gain calculation and propagation characteristics in erbium-doped devices with nonlinear host materials

The influence of host material nonlinearity on erbium-doped fiber and planar waveguide amplifiers is evaluated. The evaluation is based on a transmission line approach, which incorporates the presence of dopants and the nonlinear properties of the host material, providing the effective index and gain coefficient values. Numerical results for the effective index change and the corresponding added dispersion, as well as for the small signal gain, are presented considering a host material with Kerr type nonlinear properties.