1D and 2D compact photonic crystal reflectors on suspended InP membranes are theoretically and experimentally studied under normal incidence. They are based on the coupling of free space waves with slow Bloch modes of the crystal. We first present monomodal 1D photonic crystal reflectors. Then, we focus on multimodal 1D reflectors, which involve two slow Bloch modes of the crystal, and thus present broadband high-efficiency characteristics. 2D broadband reflectors were also investigated. They allow for an accurate control on the polarization dependence of the reflection. A compact (50 μm x 50 μm) demonstrator was realized and characterized, behaving either as a broadband reflector or as a broadband transmitter, depending on the polarization of the incident wave (experimental stop-band superior to 200nm, theoretical stop-band of 350nm). These photonic crystal slabs can be used in new photonic devices as reflectors, where they can replace multilayer Bragg mirrors. The authors report a compact and highly selective tunable filter using a Fabry-Perot resonator combining a bottom micromachined 3-pair-InP/air-gap Bragg reflector with a top photonic crystal slab mirror. It is based on the coupling between radiated vertical cavity modes and waveguided modes of the photonic crystal. The full-width at half maximum (FWHM) of the resonance, as measured by microreflectivity experiments, is close to 1.5nm (around 1.55 μm). The presence of the photonic crystal slab mirror results in a very compact resonator, with a limited number of layers. The demonstrator was tuned over a 20nm range for a 4V tuning voltage, the FWHM being kept below 2.5nm.
This work reports single-frequency laser oscillation at λ = 1003.4 nm of an optically pumped external cavity semiconductor laser. By using a gain structure bonded onto a high conductivity substrate, we demonstrate both theoretically and experimentally the strong reduction of the thermal resistance of the active semiconductor medium, resulting in a high power laser emission. The spectro-temporal dynamics of the laser is also explained. Furthermore, an intracavity frequency-doubling crystal was used to obtain a stable single-mode generation of blue (λ = 501.5 nm) with an output power around 60 mW.
Jacques Giérak, Eric Bourhis, A. Madouri, Martin Strassner, Isabelle Sagnes, Sophie Bouchoule, M. N. Merat Combes, D. Mailly, Peter Hawkes, Ralf Jede, L. Bardotti, Brigitte Prevel, A. Hannour, P. Melinon, Annie Perez, Jacques Ferre, J. Jamet, A. Mougin, Claude Chappert, V. Mathet
We aim to explore the nanostructuring potential of a highly focused pencil of ions. We show that focused ion beam technology (FIB) is capable of overcoming some basic limitations of current nanofabrication techniques and allowing innovative patterning schemes for nanoscience. In this work, we first detail the very high resolution FIB instrument developed specifically to meet nanofabrication requirements. Then we introduce and illustrate some new patterning schemes for next-generation FIB processing. These patterning schemes are: 1. nanoengraving of membranes as a template for nanopores and nanomask fabrication; 2. local defect injection for magnetic thin film direct patterning; 3. function of graphite substrates to prepare 2-D organized arrays of clusters; and 5. selective epitaxy of III-V semiconductors on FIB patterned surfaces. Finally, we show that FIB patterning allows "bottom-up" or "organization" processes.
InP-based micro-opto-electro-mechanical systems (MOEMS) for the long wavelength range (1.3 and 1.55 μm) have been extensively investigated during the last years. The fabrication of ultra-thin and hence ultra-flexible structures that can be actuated electrostatically was limited by residual strain within the structural layers. Highly flexible membranes are necessary if the tuning voltage is to be kept below 10 V and a wide tuning range is required. Adapting the metal-organic vapor phase epitaxial growth conditions, the residual strain was significantly reduced, allowing the fabrication of InP membranes as thin as 30 nm. Tunable micro-cavities (Lcavity=0.5 λ, λ=1.55 μm) with a InP membrane thickness of only 123 nm show an optical tunability of up to 30.5 nm/V2 and a maximum tuning range of more than 160 nm. When reducing the thickness to 123 nm (which corresponds to λ/4) a significant deformation of the membranes was observed that has to be taken into account for the fabrication of MOEMS since additional losses are created. A highly selective, widely tunable filter for dense wavelength division multiplexing systems (WDM) was fabricated and exhibits a selectivity of < 0.4 nm throughout the entire tuning range of 48 nm.
We present the design and characteristics of an optically pumped vertical external cavity surface emitting laser emitting near 1550 nm. The InP-based laser was grown by Metalorganic vapor-phase epitaxy including an InGaAsP gain element and an InP/InGaAsP mirror. The gain element comprises 20 strain compensated quantum wells on top of a distributed Bragg reflector. As an external mirror we used a concave spherical mirror, which also provides the outcoupling of light. Gain is achieved by optical pumping with a high power, 1250 nm fiber Raman laser focused on the gain chip. Essential for achieving high output power is to reduce the temperature of the gain material and this is accomplished by bonding an intra-cavity silicon heat spreader to the surface of the gain element. The maximum output power is 260 mW at multi transverse mode operation and 230 mW at single transverse mode operation with a near Gaussian beam profile (M2=1.22) at 240 K. At room temperature the output power was limited to 12 mW. The maximum output power greatly depends on the operating temperature and studies of pump induced thermal effects show that thermal lensing imposes limitations on the attainable power.
Wavelength Division Multiplexing has become the leading technology for optical transmission systems which operate at 1550 nm. One of the key components of such systems are tunable and wavelength selective receivers. In this paper we present a fibre-coupled two-chip receiver front end, which is highly wavelength selective and tunable over a wide wavelength range. The device is a bulk-micromachined Fabry-Perot pin-photodiode, which features a high finesse of more than 220 with a sufficient tuning range (> 40 nm) to cover wide wavelength region. The bandwidth (full-width half maximum) of the device is < 0.2 nm (25 GHz). The photocurrent crosstalk from an adjacent channel (100 GHz spaced apart) is below -30 dB. The wavelength tuning is achieved by a change in the resonator length, formed by the two chips. This is realized by current induced thermal heating on top of the membrane mirror suspensions, which deflects the membrane. The optical-electrical conversion takes place in the pin-photodiode. This integration reduces the need for any additional components. Fiber-coupling is achieved with a fiber-coupled lens that tailors the Gaussian beam to match with the Fabry-Perot cavity. The alignment process of the two-chip structure, forming the wavelength selective cavity, has been simplified to the point where a simple place-and-fix strategy can be applied.
Tunable vertical cavity surface emitting lasers (VCSELs) are very attractive candidates for employment in various areas of interest, like optical communications or gas sensing. During the last decade these types of components have been demonstrated. In this paper we present a micromechanically realization of an optically pumped 1.55 μm tunable VCSEL and its characteristics. The investigated device comprises two chips. The first chip, a half-cavity VCSEL chip, contains the bottom Bragg-mirror and the active layers. The second chip is a micromechanically manufactured Bragg-mirror membrane chip. After aligning, both chips form together the VCSEL cavity. Wavelength tuning is achieved by thermal actuation of the membrane mirror due to current flow and the subsequent deflection of the mirror membrane resulting in a change of the resonance wavelength. Such a micromachined two-chip VCSEL device is investigated and discussed. In particular, properties like the side mode suppression ratio, relative intensity noise and polarization during actuation and their dependence on the properties of the micromachined mirror-membrane are analyzed. Remarkable results are e.g. the side mode suppression ratio dependence on the pump spot size, the dependence of the relative intensity noise of the VCSEL on the pump laser noise, and stable polarization due to the membrane design.
Ultra-widely tunable microcavity devices implemented by surface micromachining are studied. We model, fabricate, and characterize 1.55-μm vertical-resonator-based optical filters and vertical cavity surface emitting lasers (VCSELs) capable of wide, monotonic, and kink-free tuning by a single control parameter. Our devices are comprised of single or multiple horizontal air gaps in the dielectric and InP-based material system. Distributed Bragg mirrors with multiple air gaps are implemented. Due to the high refractive index contrast between air (n = 1) and InP (n = 3.17), only three periods are sufficient to guarantee a reflectivity exceeding 99.8% and offer an enormous stop-band width exceeding 500 nm. Unlike InGaAsP/InP or dielectric mirrors, they ensure short penetration depth of the optical intensity field in the mirrors and low absorption values. Stress control of the suspended membrane layers is of utmost importance for the fabrication of these devices. By controlling the stress, we are able to fabricate InP membranes that are extremely thin (357 nm thick) and at the same time flat (radius of curvature above 5 mm). Micromechanical single parametric actuation is achieved by both thermal and electrostatic actuation. Filter devices with a record tuning more than 142 nm with 3.2 V are presented.
Surface-micromachined 1.55µm vertical-resonator-based devices, capable of wide, continuous, monotonic and kink-free tuning are designed, technologically implemented and characterized. Tuning is achieved by mechanically actuating one or several membranes in a vertical resonator including two ultra-highly reflective DBR mirrors. The tuning is controlled by a single parameter (actuation voltage). The two different layers composing the mirrors reveal a very strong refractive index contrast. Filters including InP/air-gap DBR's (3.5 periods) using GaInAs sacrificial layers reveal a continuous tuning of up to 9% of the absolute wavelength. Varying a reverse voltage (U=0 .. -3.2V) between the membranes, a tuning range up to 142nm was obtained by electrostatic actuation. The correlation of the wavelength and the applied voltage is accurately reproducible without any hysteresis. Theoretical model calculations are performed for symmetric and asymmetric device structures, varying layer thickness and compositions. Models of highly sophisticated color tuning can be found in nature, e.g. in tunable spectral light filtering by trogon and butterfly wings. Bionics transfers the principles of success of nature into natural science, engineering disciplines and applications (here filters and VCSELs for optical communication on the basis of WDM). Light interferes constructively and destructively with nano- and microstructures of appropriate shape, dimensions and materials, both in the artificial DBR structures fabricated in our labs as well as in the natural ones.
Surface-micromachined 1.55μm vertical-resonator-based devices, capable of wide, continuous, monotonic and kink-free tuning are designed, technologically implemented and characterized. Tuning is achieved by mechanically actuating one or several membranes in a vertical resonator including two ultra-highly reflective DBR mirrors. The tuning is controlled by a single parameter (actuation voltage). The two different layers composing the mirrors reveal a very strong refractive index contrast. Filters including InP/air-gap DBR's (3.5 periods) using GaInAs sacrificial layers reveal a continuous tuning of >9% of the absolute wavelength. Varying a reverse voltage (U=0 .. -3.2V) between the membranes, a tuning range up to 142nm was obtained by electrostatic actuation. The correlation of the wavelength and the applied voltage is accurately reproducible without any hysteresis. Appropriate miniaturization is shown to increase the mechanical stability and the effectiveness of spectral tuning by electrostatic actuation since the relative significance of the fundamental physical forces can be varied considerably by appropriate scaling. Model calculations are performed for symmetric and asymmetric optical filter structures, varying layer thickness and compositions. Finally the filter results are used to design micromachined tunable air-gap VCSEL´s. Theoretical model calculations demonstrate very wide spectral tuning by micromachined actuation of air-gap VCSEL resonators.
Continuously tunable Fabry-Perot filters manufactured using multiple air-gap MOEMS technology are studied and presented. The InP/air-gap filters optimized for optical telecommunication systems using the third optical telecommunication window (1550nm) exhibit a wide tuning range of 142nm and an extremely wide stop-band of 550nm (1250nm-1800nm). The tuning is continuously adjustable requiring ultra-low actuation voltages between 0V (1599nm) and 3.2V (1457nm). The filters are based on a relatively simple vertical structure which is fabricated by few surface micro machining steps. No mirror alignment or subsequent micro mounting are necessary facilitating a compact batch process production.
In technology and nature, tailored scaling represents a principle of success which allows the effectiveness of physical effects to be enhanced. For our optical microsystems, we state that appropriate miniaturization increases the mechanical stability and the effectiveness of spectral tuning by electrostatic and thermal actuation since the relative significance of the fundamental physical forces involved considerably changes with scaling. These basic physical principles are rigorously applied in micromachined 1.55μm vertical-resonator-based filters, capable of wide, monotonic and kink-free tuning by a single control parameter. Tuning is achieved by mechanical actuation of one or several air-gaps which are part of a vertical resonator including two ultra-highly reflective DBR mirrors of strong refractive index contrast: (I) Δn=2.17 for InP/air-gap DBR's (3.5 periods) using GaInAs sacrificial layers and (II)Δn=0.5 for Si3N4/SiO2 DBR’s (12 periods) with a polymer sacrificial layer to implement the air-cavity. In semiconductor multiple air-gap filters, a continuous tuning of >9% of the absolute wavelength is obtained. Varying the reverse voltage (U=0 .. 3.2V) between the membranes (electrostatic actuation), a tuning range up to 142nm was obtained. The correlation of the wavelength and the applied voltage is accurately reproducible without any hysteresis. The extremely wide tuning range and the very small voltage required are record values to the best of our knowledge. Principles of III/V semiconductor micromachining and the detailed technological fabrication process of our filters are focused.
Bionics transfers the principles of success of nature into natural science, engineering disciplines and applications. Often generation and detection of different spectral colors play key roles in communication in both, nature and technology. The latter one refers e.g. to dense wavelength division multiplex optical communication systems. This paper shows interesting parallels in tunable spectral light filtering by butterfly wings and by tunable optical filters used in optical communication systems. In both cases light interferes constructively and destructively with nano- and microstructures of appropriate shape, dimensions and materials. In this paper methodology is strongly emphasized. We demonstrate that tailored scaling allows the effectiveness of physical effects to be enhanced in nature and technology. These principles are rigorously applied in micromachined 1.55μm vertical-resonator-based filters, capable of wide, continuous, monotonic and kink-free tuning by a single control parameter. Tuning is achieved by mechanically actuating one or several membranes embedded by air-gaps in a vertical resonator including two ultra-highly reflective DBR mirrors. The layers of mirrors reveal a very strong refractive index contrast. Filters including InP/air-gap DBR's (3.5 periods) using GaInAs sacrificial layers reveal a continuous tuning of >9% of the absolute wavelength. Varying a reverse voltage (U=0 .. -3.2V) between the membranes, a tuning range up to 142nm was obtained due to electrostatic actuation. Appropriate miniaturization is shown to increase the mechanical stability and the effectiveness of spectral tuning by electrostatic actuation since the relative significance of the fundamental physical forces can be shifted considerably by appropriate scaling.
We present ultra-widely tunable micro-cavity devices realized by micro-opto-electro-mechanical system (MOEMS) technology. We modeled, fabricated and characterized 1.55μm micromachined optical filter and VCSEL devices capable of wide, monotonic and kink-free tuning by a single control parameter. Our vertical cavity devices comprise single or multiple horizontal air-gaps in the dielectric and InP-based material system. Distributed Bragg mirrors with multiple air-gaps are implemented. Due to the high refractive index contrast between air (n=1) and InP (n=3.17) only 3 periods are sufficient to guarantee a reflectivity exceeding 99.8% and offer an enormous stop-band width exceeding 500nm. Unlike InGaAsP/InP or dielectric mirrors they ensure short penetration depth of the optical intensity field in the mirrors and low absorption values. Stress control of the suspended membrane layers is of outmost importance for the fabrication of MOEMS devices. By controlling the stress we are able to fabricate InP membranes which are extremely thin (357nm thickness) and at the same time flat (radius of curvature above 5mm). Micromechanical single parametric actuation is achieved by both, thermal and electrostatic actuation. Filter devices with a record tuning over 127nm with 7.3V are presented.
We study 1.55micrometers filter and VCSEL devices capable of wide and continuous tuning based on a single control parameter. Ultra-high reflective DBR mirrors are realized with a low number of DBR periods using high refractive index contrast: (I) (Delta) n=2.17 for InP/airgap DBR's (3.5 periods) and (II) (Delta) n=0.5 for Si3N4/SiO2 DBR's (12 periods) with a polymer sacrificial layer to implement the air-cavity. Corresponding fabrication technologies are presented in detail. In both cases spectral tuning (>100nm, theoretically) is obtained by micomachined actuation of the included air-cavity. Large stopband widths and very large tuning efficiencies are obtained by model calculations. For VCSEL's a trade-off between lasing efficiency and tuning efficiency is obtained. Experimental results show very good optical properties: high mirror reflectance and clear single-line filter transmission. The first tunable dielectric filter based on polymer sacrificial layers is presented: (Delta) (lambda) /(Delta) U= -7nm/V at 1mA. The potential of the airgap concept: the filter transmission or the laser emission wavelength can be continuously tuned over more than 100nm, thus, the whole spectral gain profile can be addressed by a single control parameter.
We have fabricated InGaAs/InP PIN diodes with a coplanar waveguide design. The diodes have been integrated in a two- chip wavelength-selective Fabry-Perot filter for the use as wavelength-selective PIN receivers for dense wavelength division multiplex systems.
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