Fabrication of waveguides in sputtered films of GeAsSe glass via photodarkening with above bandgap light

We have fabricated and characterized waveguides in thin films of Ge₅As₃₄Se₆₁ glass sputtered onto silicon wafer substrates. The 5-μm width waveguides were fabricated by exposure to 514.5 nm light from an Ar³⁺ laser, with a lithographic exposure mask used to provide the lateral patterning for the waveguides. The measured losses of the waveguides ranged from 3.5 to 6.4 dB/cm. From SEM imaging, we concluded that scattering from microcracks at the glass–substrate interface was the dominant source of loss.     

Fabrication and characterization of UV-written channel waveguides in Bi2O3-based glass

Light-induced refractive index change was investigated in an erbium-doped Bi₂O₃-based bulk glass using direct UV laser writing at 244 nm. Single mode channel waveguides were obtained with a positive refractive index change of 4 × 10⁻⁴ at 633 nm. An upper limit for propagation losses at 980 nm was estimated at 4 dB/cm. A morphological study of the exposed regions revealed that strong interactions occurred between the UV beam and the glass sample, causing physical damage and stresses in the material. To our knowledge, this is the first paper reporting the use of 244 nm laser beam to produce waveguides in a Bi₂O₃-based glass.     

Fabrication of Yb3+/Er3+ codoped Bi2O3–WO3–TeO2 pedestal type waveguide for optical amplifiers

We report, for the first time to our knowledge, experimental results on pedestal waveguides produced with Yb³⁺/Er³⁺ codoped Bi₂O₃–WO₃–TeO₂ thin films deposited by RF Sputtering for photonic applications. Thin films were deposited using Ar/O₂ plasma at 5 mTorr pressure and RF power of 40 W on substrates of silicon wafers. The definition of the pedestal waveguide structure was made using conventional optical lithography followed by plasma etching. Propagation losses around 2.0 dB/cm and 2.5 dB/cm were obtained at 633 and 1050 nm, respectively, for waveguides in the 20–100 μm width range. Single-mode propagation was measured for waveguides width up to 10 μm and 12 μm, at 633 nm and 1050 nm, respectively; for larger waveguides widths multi-mode propagation was obtained. Internal gain of 5.6 dB at 1530 nm, under 980 nm excitation, was measured for 1.5 cm waveguide length (∼3.7 dB/cm). The present results show the possibility of using Yb³⁺/Er³⁺ codoped Bi₂O₃–WO₃–TeO₂ pedestal waveguide for optical amplifiers.     

Advances on the fabrication process of Er3+/Yb3+:GeO2–PbO pedestal waveguides for integrated photonics

The present work reports the fabrication, passive and active characterization of Yb³⁺/Er³⁺ codoped GeO₂–PbO pedestal waveguides. We show the advances obtained in pedestal fabrication by comparing waveguides obtained under different processes parameters. The thin films were deposited on previously oxidized silicon wafers in Ar plasma at 5 mTorr; pedestal waveguides, with 1–100 μm width range were defined by conventional lithography procedure, followed by reactive ion etching (RIE). A comparison between the results of propagation losses and internal gain is presented in order to show that the improvement of fabrication process contributed to enhance the performance of the pedestal waveguides. Reduction of about 50% was observed for the propagation losses at 632 and 1068 nm, whereas enhancement of approximately 50% was obtained for the internal gain at 1530 nm (4 and 6 dB/cm, for 70 μm waveguide width), under 980 nm excitation. The present results demonstrate the possibility of using Yb³⁺/Er³⁺ codoped GeO₂–PbO as pedestal waveguide amplifiers.     

NIR luminescent Er/Yb co-doped SiO2–ZrO2 nanostructured planar and channel waveguides: Optical and structural properties

Optical and structural properties of planar and channel waveguides based on sol–gel Er³⁺ and Yb³⁺ co-doped SiO₂–ZrO₂ are reported. Microstructured channels with high homogeneous surface profile were written onto the surface of multilayered densified films deposited on SiO₂/Si substrates by a femtosecond laser etching technique. The densification of the planar waveguides was evaluated from changes in the refractive index and thickness, with full densification being achieved at 900 °C after annealing from 23 up to 500 min, depending on the ZrO₂ content. Crystal nucleation and growth took place together with densification, thereby producing transparent glass ceramic planar waveguides containing rare earth-doped ZrO₂ nanocrystals dispersed in a silica-based glassy host. Low roughness and crack-free surface as well as high confinement coefficient were achieved for all the compositions. Enhanced NIR luminescence of the Er³⁺ ions was observed for the Yb³⁺-codoped planar waveguides, denoting an efficient energy transfer from the Yb³⁺ to the Er³⁺ ion.     

Optical rib waveguides based on sol-gel derived silica-titania films

Rib channel waveguides were produced with the application of chemical wet etching of the sol-gel derived silica-titania (SiO₂-TiO₂) waveguide films. The silica-titania films were etched in water solutions of ammonia fluoride. In the etching process, the waveguide films were selectively masked with a photoresist. This paper presents the theoretical analysis of rib channel waveguides as well as the results of experimental research on slab and rib channel waveguides. For slab waveguides the attenuation of 0.15 dB/cm was obtained, and for the produced single mode rib channel waveguides, the attenuation of 1.7 dB/cm was obtained.     

Luminescence at 2.8 μm: Er3+-doped chalcogenide micro-waveguide

This paper reports the fabrication of luminescent optical rib/ridge waveguides made of erbium doped Ga-Ge-Sb-S films deposited by RF magnetron sputtering. Several fluorescence emissions of Er³⁺ ions from the visible to the middle infrared spectral domain were clearly observed within the films. The study of the ⁴I_13/2 level lifetime enabled development of a suitable annealing treatment of the films to reach the value of the bulk counterpart while the variation in surface roughness was limited, thus ensuring reasonable optical losses (0.7–0.9 dB/cm). Amplification experiments were carried out at 1.54 μm leading to complete characterization of the erbium-doped micro-waveguide with ∼3.4 dB/cm on/off gain. A demonstration of mid-IR photoluminescence from Er³⁺-doped chalcogenide micro-waveguide was recorded at ∼2.76 μm. The multi-luminescence from the visible to mid-IR generated using erbium doped chalcogenide waveguiding micro-structures might find easy-to-use applications concerning telecommunication technologies or on-chip optical sensors for which luminescent sources or amplifiers operating at different wavelengths are required.     

Continuous-wave lasing at 1.06 μm in femtosecond laser written Nd:KGW waveguides

We report on the buried channel waveguide laser at 1065 nm in Nd:KGW waveguides fabricated by femtosecond laser writing with dual-line approach. A relatively high scanning speed of 0.5 mm/s enables acceptable propagation loss less than 2 dB/cm. The fluorescence emission spectra of Nd³⁺ ions measured shows that the fluorescence properties were well preserved in the waveguide region. A stable continuous wave laser at 1065 nm has been obtained at room temperature in the buried channel waveguides by optical pumping at 808 nm. A maximum output power of 33 mW and a slope efficiency of 52.3% were achieved in the Nd:KGW waveguide laser system.     

Er:YAl3(BO3)4 glassy thin films from polymeric precursor and sol-gel methods: Waveguides for integrated optics

This paper presents the characterization of single-mode waveguides for 980 and 1550 nm wavelengths. High quality planar waveguide structure was fabricated from Y_1 − xEr_xAl₃(BO₃)₄ multilayer thin films with x = 0.02, 0.05, 0.1, 0.3, and 0.5, prepared through the polymeric precursor and sol-gel methods using spin-coating. The propagation losses of the planar waveguides varying from 0.63 to 0.88 dB/cm were measured at 632.8 and 1550 nm. The photoluminescence spectra and radiative lifetimes of the Er^{3+ 4}I_13/2 energy level were measured in waveguiding geometry. For most samples the photoluminescence decay was single exponential with lifetimes in between 640 μs and 200 μs, depending on the erbium concentration and synthesis method. These results indicate that Er doped YAl₃(BO₃)₄ compounds are promising for low loss waveguides.     

High-purity TeO2–WO3–(La2O3, Bi2O3) glasses for fiber-optics

TeO₂–WO₃, TeO₂–WO₃–La₂O₃ and TeO₂–WO₃–La₂O₃–Bi₂O₃ glasses were produced by high-purity oxides mixtures melting in crucibles of gold or platinum in purified oxygen atmosphere. The total content of Cu, Mn, Fe, Co and Ni impurities was not more than 0.1–2 ppm wt in glasses and below 0.1 ppm wt in the initial oxides. The hydroxyl groups absorption coefficients of the tellurite glasses at the maximum of the absorption band (λ ∼ 3 μm) lay in the region of 0.01–0.001 cm⁻¹. Stability to crystallization characterized by T_x − T_g = 150–190 °C was demonstrated for high purity 75TeO₂–25WO₃ glasses by DSC-measurements. There were no thermal effects of crystallization and crystallized phases fusion in case of La₂O₃-containing glasses.The optical absorption losses, measured by the laser calorimetry method at λ = 1.06, 1.56 and 1.97 μm, did not exceed 40–120 dB/km for glass samples. The multimode optical fibers with optical losses of 50–250 dB/km at 1.2–2.2 μm were produced from high-purity TeO₂–WO₃–(La₂O₃, Bi₂O₃) glasses.     

Study of optical losses of Nd doped silicon rich silicon oxide for laser cavity

Planar and strip-loaded waveguides made of Nd³⁺-doped silicon rich silicon oxide (SRSO) have been fabricated by reactive magnetron sputtering and characterized, with special emphasis on the optical losses. The refractive index of Nd³⁺-doped SRSO layers was measured by both m-line method and reflectance spectroscopy. From these measurements, the Si volume fraction and also the Nd³⁺-doped SRSO index dispersion were deduced by using the Bruggeman model. At 1.06 μm, Nd³⁺-doped SRSO refractive index was equal to 1.543 corresponding to a Si volume fraction of 6.5%. The opto-geometrical parameters of waveguides have been studied in order to obtain single mode waveguides at 1.06 μm. The optical losses are measured as a function of wavelength and are found to be about 0.8 and 0.4 dB/cm at 1.06 and 1.55 μm, respectively. Measurements are confirmed by theoretical models showing that the losses are essentially attributed to surface scattering. From these optical loss values, a percentage value of the Nd active concentration superior of 14.5% was deduced to have a positive modal gain of waveguide.     

Comparison of epoxy- and siloxane-based single-mode optical waveguides defined by direct-write lithography

This paper reports on the fabrication and characterization of single-mode polymer optical waveguides at telecom and SOI compatible wavelengths; by making a comparison between an epoxy and a siloxane polymer waveguide material system (both commercially-available). The proposed waveguides can be used in short-reach optical interconnects targeting chip-to-chip communication on the interposer level or providing a coupling interface between single-mode optical fibers and photonic integrated circuits (PICs). This technology enables the integration of optoelectronic chips for photonic packaging purposes. First, the single-mode dimensions (4 × 4 μm² and 5 × 5 μm²) for both materials at selected wavelengths (1.31 μm and 1.55 μm) were determined based on the refractive index measurements. Then, the waveguides were patterned by a direct-write lithography method. The fabricated waveguides show a high-quality surface with smooth sidewalls. The optical propagation losses were measured using the cut-back method. For the siloxane-based waveguides, the propagation losses were found to be 0.34 dB/cm and 1.36 dB/cm at 1.31 μm and 1.55 μm respectively while for the epoxy-based waveguides the losses were 0.49 dB/cm and 2.23 dB/cm at 1.31 μm and 1.55 μm respectively.     

Production and properties of high purity TeO2–ZnO–Na2O–Bi2O3 and TeO2–WO3–La2O3–MoO3 glasses

High-purity TeO₂–ZnO–Na₂O–Bi₂O₃ and TeO₂–WO₃–La₂O₃–MoO₃ glasses were produced by melting the high-purity oxides mixtures in platinum or gold crucible at 800 °C in hermetic chamber in the purified oxygen atmosphere. The content of limiting impurities in the produced initial oxides and glasses, the optical properties as well as the stability to crystallization were investigated. The optical fibers were produced from high-purity tellurite glasses with losses at the level of several hundreds of dB/km.The total content of 3d-transition metals in the glasses was not more than 1 ppm wt and content of hydroxyl groups corresponded to the absorption level of 0.001–0.002 cm⁻¹ at ∼3 μm. The absorption band, monotonically increasing with the increase in MoO₃ content, was observed in dry TeO₂–WO₃–La₂O₃–MoO₃ glasses with the maximum at about 3.7 μm.     

Organic materials for nonlinear optics

This review discusses nonlinear optical (NLO) polymeric materials. As an example of a second-order NLO material, a novel copolymer with a diazo dye attached is investigated. The second-order NLO coefficient χ⁽²⁾ of the copolymer reaches 1.0 × 10^?6 esu, which is 7 times larger than that of LiNbO₃. A third-order NLO coefficient χ⁽³⁾ larger than 10^?10 esu is obtained for polymers where NLO dyes are introduced into the polymer backbone. The optical transmission loss of these polymers is revealed to be around 2 dB/cm. As these polymers can be formed into channel waveguides using the photo-bleaching technique, they show promise for use in NLO devices because of their processability, transparency and large optical nonlinearity.     

Elaboration,structural characterization and optical properties of the yttrium alkoxide derived Y2O3 planar optical waveguides

Y₂O₃ optical planar waveguides are fabricated by the sol–gel method and the dip-coating technique. High purity yttrium alkoxide (yttrium 2-methoxyethoxide) is used as starting material for the Y₂O₃ sol and acetylacetone is added to improve the stability of the sol. Highly concentrated sol up to 0.8 M is prepared and six stacked layers are enough to support four propagation modes at wavelength from 488 to 632.8 nm. The cubic phase of Y₂O₃ is crystallized after an annealing treatment at 700 °C. X-ray diffraction is conducted on the films for their structural analysis. Optical properties of the waveguides are determined by multi-wavelength m-lines spectroscopy and attenuation coefficient measurement. The attenuation coefficient of the prepared Y₂O₃ waveguiding thin films is in the range between 1 and 2 dB/cm at 632.8 nm.     

The properties of InGaAsP/InP heterolasers with step-divergent waveguides

InGaAsP/InP laser heterostructures with step-divergent waveguides and two stressed quantum wells were obtained by metalorganic VPE. The lasers emitting at 1.55 μm provide for an intrinsic quantum yield of η_i=85%. An optical power of 5.2 W in the continuous operation mode was achieved at a laser diode temperature of 10°C. The internal optical losses in the laser heterostructure studied amount to 3.6 cm⁻¹, which is comparable with the level of losses in similar structures with uniform divergent waveguides.     

Application of swift and heavy ion implantation to the formation of chalcogenide glass optical waveguides

We demonstrate the application of swift and heavy ion implantation to generate optical waveguides in amorphous materials. Gallium lanthanum sulfide (GLS) and gallium lanthanum oxysulfide (GLSO) glass waveguides are fabricated using Ar implantation at 60 MeV and 2 × 10¹² ions/cm². A “well” region with increased refractive index (0.1% for GLS and 0.3% for GLSO) is formed near the surface of the glass based on the electronic energy deposition; a “barrier” layer with decreased refractive index is formed inside the glass due to the nuclear energy deposition. As a result, the waveguides exhibit a refractive index distribution of “well + barrier” type. It is supposed that the change in local structure order of the substrate causes the “well” formation. The propagation loss is 2.0 dB/cm for GLS and 2.2 dB/cm for the GLSO glass waveguide.     

Strong reduction of propagation losses in LiNbO3 ridge waveguides

We propose optimized processes for the reproducible production of LiNbO₃ ridge waveguides with propagation losses lower than 0.2 dB/cm. The performances are achieved for both Z-propagating and Y-propagating waveguides, TE and TM polarizations, in X-cut LiNbO₃ congruent substrates, and could be easily extrapolated to Z-cut substrates. The fabrication procedure is composed of three steps: titanium deposition, optical grade dicing and diffusion at high temperatures, so that lithography or cleanroom facilities are not required. The reproducible smooth waveguides with low propagation losses result from the diffusion step, which is performed after the production of the ridges. We also show how the losses can be evaluated from the Fabry–Perot effect in the waveguides, without any assumption on the input and output reflection coefficients.     

III–Vs on Si for photonic applications—A monolithic approach

Epitaxial lateral overgrowth (ELOG) technology is demonstrated as a viable technology to realize monolithic integration of III-Vs on silicon. As an alternative to wafer-to-wafer bonding and die-to-wafer bonding, ELOG provides an attractive platform for fabricating discrete and integrated components in high volume at low cost. A possible route for monolithic integration of III–Vs on silicon for silicon photonics is exemplified by the case of a monolithic evanescently coupled silicon laser (MECSL) by combining InP on Si/SiO₂ through ELOG. Passive waveguide in MECSL also acts as the defect filtering mask in ELOG. The structural design of a monolithic evanescently coupled silicon laser (MECSL) and its thermal resistivity are established through simulations. Material studies to realize the above laser through ELOG are undertaken by studying appropriate ELOG pattern designs to achieve InP on narrow regions of silicon. We show that defect-free InP can be obtained on SiO₂ as the first step which paves the way for realizing active photonic devices on Si/SiO₂ waveguides, e.g. an MECSL.     

Optical effects caused by high laser powers in ion-implanted Bi4Ge3O12 waveguides

Abstract

The ‘optical writing’ of permanent channel waveguides in the surface of He⁺ ion-implanted bismuth germanate, Bi₄Ge₃O₁₂, has been studied, using end-coupled argon and Ti:sapphire CW laser beams. Comparisons of the self-focusing effect in waveguides and bulk samples have been made for both Nd³⁺ doped and undoped material. The permanent ‘writing’ effect has been compared with the structural change observed earlier in ion-implanted Bi₄Ge₃O₁₂ waveguides annealed at high temperature.