Vertical-cavity Surface-emitting Laser Diodes Research Articles

Highly Reliable Flexible Active Optical Links

We present a process to embed commercially available optical material layers into a flexible foil. Patterning of the embedded layers results in highly transparent low loss flexible waveguides. Bending of the foil down to a bending radius of 5 mm causes no additional optical propagation losses. Vertical-cavity surface-emitting laser diodes (VCSELs) and photodiodes are thinned down to 20 ¿m and embedded inside the cladding layer of the waveguides. They are optically coupled with the use of embedded micro-mirrors. The result is a thin foil of 150- ¿m thickness with embedded active optical low-loss links. Accelerated aging tests prove the reliability of the embedded optical links exposed to humidity and temperature cycling.

Diagnostic and characterization of the VCSEL diodes based on GaSb

Vertical-Cavity Surface-Emitting Laser (VCSEL) diodes are among the youngest members of the semiconductor laser diode family. The main aim of our work focuses on the measurement of the basic properties (the spectral range of the laser emission, temperature and current tunability) of experimental VCSEL diode lasers based on GaSb operating in the infrared region around 4250 cm−1. A high-resolution FTIR Bruker IFS 120 HR spectrometer with a maximum resolution of 0.0035 cm−1 was used in the emission setup for the laser diagnostic research. The absorption spectra of atmospheric pollutants like methane, carbon monoxide and ammonia have been measured using these VCSELs for the first time.

Sensitivity of a VCSEL threshold performance to inaccuracies in its manufacturing

AbstractThe paper describes an impact of various possible inaccuracies in manufacturing of verticalcavity surface-emitting diode lasers (VCSELs), like thicknesses and compositions of their layers different from assumed ones, on VCSEL room-temperature (RT) continuous-wave (CW) threshold performance. To this end, the fully self-consistent comprehensive optical-electrical-thermal-recombination VCSEL model has been applied. While the analysis has been carried out for the 1.3-μm oxide-confined intra-cavity contacted GaInNAs/GaAs VCSEL, its conclusions are believed to be more general and concern most of modern VCSEL designs. As expected, the VCSEL active region has been found to require the most scrupulous care in its fabrication, any uncontrolled variation in compositions and/or thicknesses of its layers is followed by unaccepted RT CW lasing threshold increase. Also spacer thicknesses should be manufactured with care to ensure a proper overlapping of the optical standing wave and both the gain and lossy areas within the cavity. On the contrary, less than 5% thickness changes in distributed-Bragg-reflectors are followed by nearly insignificant changes in VCSEL RT CW threshold. However, exceeding the above limit causes a rapid increase in lasing thresholds. As expected, in all the above cases, VCSELs equipped with larger active regions have been confirmed to require more careful technology. The above results should enable easier organization of VCSEL manufacturing.

Enhanced single-fundamental LP01 mode operation of 650-nm GaAs-based GaInP/AlGaInP quantum-well VCSELs

Minimal optical attenuation of plastic (polymer) optical fibres (POFs) corresponds to the 650-nm wavelength. Currently the GaInP/AlGaInP quantum-well (QW) oxide-confined (OC) vertical-cavity surface-emitting diode lasers (VCSELs) are undoubtedly the laser devices most suited to be used in 650-nm POF optical communication, for which the stable single-fundamental-mode LP01 emission (SFM) is definitely the one most desired. In the present paper, the comprehensive fully self-consistent VCSEL model is used to examine mode selectivity of the above VCSELs. An increase in the VCSEL active-region diameter leads to a gradual modification of the current injection into this region and subsequent carrier radial diffusion within it before their recombination, which is followed by an essential transformation of active-region optical-gain profiles deciding upon an excitation of successive transverse modes. In standard arsenide OC VCSELs, SFM operation is usually limited to relatively small active regions. But for a room-temperature continuous-wave operation of the GaInP/AlGaInP VCSELs, the fundamental LP01 mode remains surprisingly the lowest-threshold one up to relatively large active regions of 9-µm diameters. Nevertheless, in such VCSELs, thresholds of many LP modes become very similar to one another, which leads to their relatively poor mode selectivity and an unwanted multi-mode operation for higher output powers.

Optimum Biasing of VCSEL Diodes for All-Optical Up-Conversion of OFDM Signals

Nonlinear behavior of vertical-cavity surface-emitting laser (VCSEL) diodes is exploited to perform all-optical up-conversion by second- and third-order mixing. We investigate and explain conditions for optimum frequency mixing with a common WLAN IEEE 802.11a signal. Then, we apply these findings to the transmission of an ultra-wideband (UWB) multiband-OFDM ECMA-368 signal over a fiber-optic link. We demonstrate direct modulation with the UWB signal up to 10.3 GHz and perform up-conversion to frequencies as high as 16 GHz, far beyond the cutoff frequency of the VCSEL diode.

Strong modes discrimination and low threshold in cw regime of 1300 nm AlInGaAs/InP VCSEL induced by photonic crystal

A self-consistent electrical-thermal-optical-gain modeling of threshold characteristics of an InP-based 1300 nm AlInGaAs photonic-crystal vertical-cavity surface-emitting diode laser is presented. It is shown that low threshold characteristics and strong transverse-mode discrimination can be simultaneously achieved for optimized photonic crystal structure and current aperture. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical Interposer Technology using Buried Vertical-Cavity Surface-Emitting Laser Chip and Tapered Through-Silicon Via for High-Speed Chip-to-Chip Optical Interconnection

A novel optical interposer with optical interconnections is proposed for integrating three-dimensional (3D) LSI chips on this interposer. Vertical-cavity surface-emitting laser diode (VCSEL) chips and photo diode (PD) chips are buried in the optical interposer with polymeric optical waveguides. The VCSEL is 0.25 mm in width, 0.35 mm in length, and 0.15 mm in height. We realize precise passive alignment between the optical waveguides and the VCSEL/PD chips using two-step alignment processes consisting of cavity-assisted positioning and the subsequent surface-tension-powered self-assembly with a molten solder. In addition, we demonstrate the basic operation of the buried VCSEL chips in the optical interposer through tapered through-silicon vias (TSVs). The tapered TSVs are successfully formed by copper electroplating and are 64 µm in top width, 34 µm in bottom width, and 168 µm in length.

Room-temperature continuous-wave operation of the In(Ga)As/GaAs quantum-dot VCSELs for the 1.3 µm optical-fibre communication

Efficient room-temperature (RT) continuous-wave (CW) lasing operation of the 1.3 µm MBE (molecular-beam epitaxy) In(Ga)As/GaAs quantum-dot (QD) top-emitting oxide-confined vertical-cavity surface-emitting diode lasers (VCSELs) for the second-generation optical-fibre communication has been achieved. In their design, a concept of a QD inside a quantum well (QW) has been utilized. The proposed In(Ga)As/GaAs QD active region is composed of five groups of three 8 nm In0.15Ga0.85As QWs, each containing one InAs QD sheet layer. In each group located close to successive anti-node positions of the optical standing wave within the 3λ cavity, QWs are separated by 32 nm GaAs barriers. Besides, at both active-region edges, additional single InGaAs QWs are located containing single QD layers. For the 10 µm diameter QD VCSELs, the RT CW threshold current of only 6.2 mA (7.9 kA cm−2), differential efficiency of 0.11 W A−1 and the maximal output power of 0.85 mW have been recorded. The experimental characteristics are in excellent agreement with theoretical ones obtained using the optical-electrical-thermal-recombination self-consistent computer model. According to this, for the 10 µm devices, the fundamental linearly polarized LP01 mode remains the dominating one up to the current of 9.1 mA. The lowest RT CW lasing threshold below 5 mA is expected for 6 µm devices.

Structure optimisation of modern GaAs-based InGaAs/GaAs quantum-dot VCSELs for optical fibre communication

AbstractRoom-temperature (RT) continuous-wave (CW) performance of modern 1300-nm oxide-confined In(Ga)As/GaAs quantum-dot (QD) vertical-cavity surface-emitting diode lasers (VCSELs) taking advantage of many QD sheets is investigated using our comprehensive self-consistent simulation model to suggest their optimal design. Obviously, quantum dots should be as uniform as possible and as dense as possible to ensure high enough optical gain. Besides, our simulation reveals that efficient and uniform current injection into VCSEL active regions necessary to enhance excitation of the desired fundamental LP01 mode is accomplished in the VCSEL configuration with the broad-area bottom contact and the ring upper one as well as with the oxide aperture localized within the first period of the upper p-type DBR. The doping of the DBR mirrors is chosen as a compromise between their high enough electrical conductivity and low enough free-carrier absorption. The oxide aperture is additionally introducing the radial optical waveguiding. Moreover, our analysis has been concluded that VCSEL active regions should be composed of at least 9 QD sheets to acquire efficient RT CW operation. Furthermore, rather longer optical cavities are recommended in this case because localization of QD sheets should be adjusted to the anti-node positions of the optical cavity standing wave.

高速レーザープリンタ用VCSELアレイ

高速レーザープリンタ用VCSELアレイ

Diagnostics of the inductively coupled plasma by diode laser absorption spectroscopy

A vertical-cavity surface-emitting diode laser is used as a tunable emission source to measure the radius-integrated gas temperature in an inductively coupled plasma reactor. Relevant data are obtained by profiling the Doppler-broadened absorption of metastable Ar atoms at 763.51 nm in argon and argon-nitrogen (3, 45, and 90% N2 in Ar) plasmas in the pressure range 0.5–70.0 Pa and at an inductive power of 100 and 300 W. The results are compared with the rotational temperature of molecular nitrogen. The difference between the integrated rotational and Doppler temperatures is attributed to the nonuniform spatial distributions of the temperature and thermometric atomic and molecular species (Ar* and N*2). These distributions are computed in terms of the nonequilibrium hydrodynamic model of plasma. The objective of this work is to develop a contactless (nonintrusive) technique for measuring the temperature and concentration of different particles in the reactor with a microsensor.

New Architecture of Interconnect for High-Speed Optical Computerized Data Networks (Nonlinear Response)

In the present paper, architecture of optical interconnect is built up on the bases of four Vertical-Cavity Surface-Emitting Laser Diodes(VCSELD) and two optical links where thermal effects of both diodes and links are included. Nonlinear relations are correlated to investigate the power-current and the voltage-current dependences. The good performance (high speed) of the interconnect is deeply and parametrically investigated under wide ranges of the affecting parameters. The high speed performance is processed through three different effects, namely the device 3-dB bandwidth, the link dispersion characteristics, and the transmitted bit rate (soliton). Eight combinations are investigated, each possesses its own characteristics. The best architecture is the one composed of a VCSELD that operates at 850 nm and the silica fiber whatever the operating set of causes. This combination possesses the largest device 3-dB bandwidth, the largest link bandwidth and the largest soliton transmitted bit rate. The increase of the ambient temperature reduces the high-speed performance of the interconnect.

Low-Loss Optical Interposer with Recessed Vertical-Cavity Surface-Emitting Laser Diode and Photodiode Chips into Si Substrate

A new interposer with an optical interconnection called optical interposer has been proposed for a high-performance parallel processor system. The optical interposer is composed of polynorbornene (PNB) optical waveguides with 45° micromirrors and a Si substrate having chip-sized through-Si holes of 150 µm depth. The polymeric waveguides are formed on the Si substrate before forming the through-Si holes by deep reactive ion etching (DRIE). Vertical-cavity surface-emitting laser diode (VCSEL) and photodiode (PD) chips are placed onto the photolithographically defined hole patterns that are 15 µm larger than the size of the chips. In addition, the chips can be precisely aligned and recessed into the holes by passive alignment of self-assembly driven by the surface tension of a lead-free solder. We can fabricate the low-loss optical interposer with an insertion loss of below 0.2 dB measured at the waveguide length of 5 cm and a coupling loss of 0.5 dB measured with a 45° micromirror.

Modal gain and confinement factors in top- and bottom-emitting photonic-crystal VCSEL

We investigate the modal characteristics of a phosphide photonic-crystal vertical-cavity surface-emitting diode laser (VCSEL) by using the three-dimensional, full vectorial plane wave admittance method. A single-defect, photonic crystal is defined as a regular, hexagonal net of holes with varying depths. The modal gain and confinement factors are compared for two VCSEL structures: with emission either through the DBR with the photonic crystal or through the DBR free of photonic crystal. Significant improvement in the beam quality is demonstrated for the second design.

Threshold characteristics of bottom-emitting long wavelength VCSELs with photonic-crystal within the top mirror

We present self-consistent modeling of InP-based 1300-nm AlInGaAs photonic-crystal vertical-cavity surface-emitting diode laser. We investigate the influence of photonic-crystal parameters on threshold characteristics. We show that a shallow photonic crystal can significantly deteriorate the VCSEL threshold current. The significant reduction of threshold current can be assured by the photonic-crystal etched through the whole top DBR mirror.

Analysis of anticipated performance of 650-nm GaInP/AlGaInP quantum-well GaAs-based VCSELs at elevated temperatures

AbstractThe possibility of application of the 650-nm oxide-confined GaInP/AlGaInP quantum-well vertical-cavity surface-emitting diode lasers (VCSELs) at elevated temperatures as sources of the carrier 650-nm wave in the fibre optical communication using POFs has been investigated with the aid of the comprehensive self-consistent model. An increase in the VCSEL threshold current at higher temperatures has been found to be mostly associated with both the carrier leakage from the valley of the Ga0.43In0.57P quantum-well material to the X-valley of the (Al0.67Ga0.33)0.52In0.48P barriers and the band-to-band absorption within the Ga0.52In0.48P layer of the band-gap comparable with the energy of emitted radiation. Nevertheless, the AlGaInP VCSELs exhibit encouraging thermal behaviour with the characteristic temperature T0 equal to as much as 134 K for the active-region temperatures up to 357 K. For the 5-μm devices, the maximal achievable output has been determined to decrease from a quite high value of 1.0 mW for 293 K to 0.6 mW for 320 K and to still high 0.33 mW for 340 K. However, an efficient operation of the above VCSEL at elevated temperatures requires still some structure modifications leading to a reduction of both the above effects, the electron leakage from the valley and the band-to-band absorption within GaInP layers.

Comparison of Usability of Oxide Apertures and Photonic Crystals Used to Create Radial Optical Confinements in 650-nm GaInP VCSELs

Threshold characteristics of GaAs-based 650-nm gallium indium phosphide (GaInP) vertical-cavity surface-emitting diode lasers (VCSELs) with two different optical confinement structures are investigated with the aid of a self-consistent, fully- physical VCSEL model. Efficacy of the optical confinement introduced by the oxide aperture is compared with an alternative single-defect photonic-crystal design with holes etched throughout the whole VCSEL. Initially, photonic-crystal VCSEL reveals 10% lower threshold electrical power than that of the analogous oxide-confined VCSEL. Further optimization of the current injection allows for an additional 20% threshold reduction. The photonic-crystal confinement concept appears to be a very prospective solution for VCSEL configurations, for which oxidation is unfeasible, e.g., for possible nitride or phosphide VCSELs.

Principles of VCSEL designing

AbstractComprehensive computer simulations are currently the most efficient and cheap methods in designing and optimisation of semiconductor device structures. Seemingly they should be as exact as possible, but in practice it is well known that the most exact approaches are also the most involved and the most time-consuming ones and need powerful computers. In some cases, cheaper somewhat simplified modelling simulations are sufficiently accurate. Therefore, an appropriate modelling approach should be chosen taking into account a compromise between our needs and our possibilities.Modelling of operation and designing of structures of vertical-cavity surface-emitting diode lasers (VCSELs) requires appropriate mathematical description of physical processes crucial for devices operation, i.e., various optical, electrical, thermal, recombination and sometimes also mechanical phenomena taking place within their volumes. Equally important are mutual interactions between above individual processes, usually strongly non-linear and creating a real network of various inter-relations.Chain is as strong as its weakest link. Analogously, model is as exact as its less exact part. Therefore it is useless to improve exactness of its more accurate parts and not to care about less exact ones. All model parts should exhibit similar accuracy. In any individual case, a reasonable compromise should be reached between high modelling fidelity and its practical convenience depending on a main modelling goal, importance and urgency of expected results, available equipment and also financial possibilities. In the present paper, some simplifications used in VCSEL modelling are discussed and their impact on exactness of VCSEL designing is analysed.

Exactness of simplified scalar optical approaches in modelling a threshold operation of possible nitride vertical‐cavity surface‐emitting diode lasers

AbstractModern small‐size vertical‐cavity surface‐emitting diode lasers (VCSELs) require principally fully vectorial optical modelling because their cavity sizes are of the order of the wavelength of emitted radiation. However, much simpler scalar approaches are often surprisingly exact even beyond the limits of their confirmed validity. Therefore, in the present paper, reasonable limits of an application of simplified scalar optical approaches (instead of more exact but also much more involved and time‐consuming rigorous vectorial ones) are determined to model threshold operation of possible nitride VCSELs equipped with tunnel junctions with the aid of a comparison of results of the scalar effective frequency method with those obtained using the fully vectorial three‐dimensional plane wave admittance method. Both these optical methods have been found to give usually quite close results for the fundamental transverse mode. Larger discrepancies between the results of both approaches have been found for first‐order transverse modes (and even larger are expected for higher‐order ones) and for larger (or very small) active regions. Some structural modifications of nitride VCSELs, which may enable their low‐threshold single‐fundamental‐mode room‐temperature continuous‐wave operation, are proposed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High Modulation Bandwidth Implant-Confined Photonic Crystal Vertical-Cavity Surface-Emitting Lasers

High-speed implant-confined photonic crystal vertical-cavity surface-emitting laser (VCSEL) diodes are fabricated and characterized. The maximum achievable 3-dB bandwidth is a function of both the index confinement provided by the etched pattern (which serves to reduce the diffraction loss and provide for stabilized fundamental mode operation) and the increased parasitic resistance caused by the removal of doped material. In optimized designs, the reduction in net loss provided by the etched pattern can more than offset the increased parasitics, resulting in a higher 3-dB bandwidth than possible in an unetched conventional implant VCSELs for both single- and multi transverse mode operation. A maximum 3-dB small-signal modulation bandwidth of 15 and 18 GHz is reported for an optimized single transverse-mode and multimode VCSEL, respectively.