This paper reviews the recent progress of quantum-dot semiconductor optical amplifiers developed as ultrawide-band high-power amplifiers, high-speed signal regenerators, and wideband wavelength converters.
The Linear Optical Amplifier (LOA) is a chip-based amplifier that addresses many of the requirements of emerging optical networks: operation under diverse bit rates, channel counts, and switching protocols, as well as reduced cost and size. In this work, we discuss, in detail, the design and operation of the LOA. Specifically, we consider the performance characteristics of the VCSEL and the amplifier, as well as the relationship between the two. Resulting trade-offs are also discussed.
A numerical model for the investigation of the ultrafast gain properties in asymmetrical multiple quantum-well semi-conductor optical amplifiers (AMQW SOAs) has been developed considering propagation of ultrashort optical pulses with different wavelengths. The dynamics of the number of carriers and carrier temperature are investigated for each quantum well. The results agree with the experimental results of pump probe measurements with different wavelengths. It is shown that gain recovery is slower for higher energy wells for pump signals of all wavelengths.
In this paper, we report a theoretical study on the various electromagnetic resonance effects (Horizontal surface plasmons, Cavity modes, 'hybrid' modes) in Metal-Semiconductor-Metal (MSM) Photodetector (PD). Field profiles are calculated using the surface impedance boundary condition technique, which is extended in this paper to model complex transmission gratings. A detailed study on the dependence of these different resonance modes on the structural geometry and material composition is described. Design rules to tailor the properties of the various resonance modes by appropriately varying the structural geometry and material composition for possible use in various applications are discussed. Potential structures of Si and HgCdTe MSM-PD are discussed for use in high-speed operation.
Laser interferometers are important instruments for the measurement of length in today's mechanical engineering and manufacturing technology. The principle on which interferometers have operated to date is that of interference between beams with the same direction of propagation. However, optical beams can interfere with each other not only in the same direction of propagation but also in opposing directions. The name given to this type of interference is the standing wave. A beam of light strikes a plane mirror at 90° to it, is reflected and interferes with the beam currently being reflected at the mirror. The outcome of the interference is a standing wave in front of the plane mirror. The only way of detecting the maxima and minima of the intensity of a standing wave photoelectrically is to use a photoelectric detector which is partially transparent. The photoelectric detector is placed in path of the standing wave, which propagates through it. Phase-shifted signals can be received if two photoelectric detectors with a phase shift between them are positioned in the standing wave. These enable sin and cos signals to be registered so that bi-directional fringe counting can take place. The authors have named this assembly an optical Standing-Wave Interferometer. The form taken by the partially transparent photoelectric detectors is that of photodiodes based on amorphous silicon, in a TCO-pin-TCO structure. Phase-shifted signals are received by two components with a TCO1-(pin)1-TCO2-(pin)2-TCO3 composition, integrated at the engineering stage, which are called by the authors transparent phase selective photodiodes (TPS). The TPS have been used to carry out measurement of length in a technological setting in such a way that the standing-wave interferometer could be compared with a plane mirror interferometer.
Widely tunable lasers that have been developed for the telecommunications industry have many applications in the sensing industry and bring the advantages of technology robustness, volume low cost potential, ultra fast tuning capabilities and high performance. These traits are now being further exploited in sensing applications such as gas sensing, sensor interrogation systems, optical frequency domain reflectometry based systems and interformeteric sensing. The current paper gives an overview of a number of these areas and how tunable laser technologies, particularly those based on monolithic tunable lasers, are being successfully deployed in real world sensing scenarios.
Biosensors rely on optical techniques to obtain high sensitivity and speed, but almost all biochips still require external light sources, optics, and detectors, which limits the widespread use of these devices. The optoelectronics technology base now allows monolithic integration of versatile optical sources, novel sensing geometries, filters, spectrometers, and detectors, enabling highly integrated chip-scale sensors. We discuss biophotonic integrated circuits built on both GaAs and InP substrates, incorporating widely tunable lasers, novel evanescent field sensing waveguides, heterodyne spectrometers, and waveguide photodetectors, suitable for high sensitivity transduction of affinity assays.
Widely tunable lasers are generally considered as key components of future optical communication networks. However, practically all widely tunable lasers that have been fabricated so far suffer from drawbacks, like elaborate calibration procedures that are required for each specific device, low output powers, and limited direct modulation capabilities.
To overcome the aforementioned issues, the sampled or superstructure grating tunable twin-guide or (S)SG-TTG laser diode has been suggested recently. In this paper we will focus on the operation principle, the fabrication, and performance of the first widely tunable twin-guide laser diodes.
The devices operate at ~ 1.55 µm wavelength. By means of Vernier effect tuning, the continuous tuning range of ~ 2 nm is extended to an overall tuning range of 28 nm. Within this tuning range, five supermodes are useable and can be continuously tuned without any mode hops. The side-mode suppression ratio remains between 25 and 37 dB over the whole tuning range. Without any tuning currents applied, a maximum output power of 12 mW has been achieved.
We investigate the nonlinear response of an InP-based optoelectronic wavelength converter by three-dimensional device simulation including an advanced many-body model for gain and absorption in the InGaAsP quantum wells. The wavelength converter combines a pre-amplified receiver with a post-amplified sampled-grating distributed Bragg reflector tunable laser diode. Good agreement between simulation and measurements is obtained. The nonlinear signal transmission is mainly attributed to quantum well saturation effects in amplifier and photo-detector. Saturation related microscopic physical processes are analyzed in detail.
Self-consistent computations of the potential profile in complex semiconductor heterostructures can be successfully applied for comprehensive simulation of the gain and the absorption spectra, for the analysis of the capture, escape, tunneling, recombination, and relaxation phenomena and as a consequence it can be used for studying dynamical behavior of semiconductor lasers and amplifiers. However, many authors use non-entirely correct ways for the application of the method. In this paper the versatile model is proposed for the investigation, optimization, and the control of parameters of the semiconductor lasers and optical amplifiers which may be employed for the creation of new generations of the high-density photonic systems for the information processing and data transfer, follower and security arrangements. The model is based on the coupled Schrödinger, Poisson's and drift-diffusion equations which allow to determine energy quantization levels and wave functions of charge carriers, take into account built-in fields, and to investigate doped MQW structures and those under external electric fields influence. In the paper the methodology of computer realization based on our model is described. Boundary conditions for each equation and consideration of the convergence for the method are included. Frequently encountered in practice approaches and errors of self-consistent computations are described. Domains of applicability of the main approaches are estimated. Application examples of the method are given. Some of regularities of the results which were discovered by using self-consistent method are discussed. Design recommendations for structure optimization in respect to managing some parameters of AMQW structures are given.
The development of high-power GaAs-based ridge wave guide distributed feedback lasers is described. The lasers emit between 760 nm and 980 nm either in TM or TE polarization. Over a large current range, the lasers exhibit stable operation in a single transversal and longitudinal mode. A maximum continuous-wave output power of about 400 mW, a spectral linewidth below 1 MHz and a side mode suppression ratio greater than 50 dB have been demonstrated at room temperature. The distributed feedback is provided by first or second order gratings, formed in an InGaP/GaAsP/InGaP multilayer structure embedded into the p-AlGaAs cladding layer. Applications of such wavelength stabilized devices in non-linear frequency conversion, spectroscopy and for excitation of atomic transitions are discussed.
Large area surface emitting lasers with extended cavity control have produced power levels of several hundred mW cw in a high quality TEM00 beam1. These lasers are highly manufacturable at low cost and differ from edge-emitting semiconductor diode lasers in that they are not waveguide devices but can operate in a circular Gaussian beam similar to solid-sate lasers. The high quality beams generated by these lasers can efficiently convert their output into other wavelengths using nonlinear optical materials. In addition, these lasers can operate with high peak power levels without the catastrophic degradation associated with edge-emitting diode lasers. Arrays of such devices can scale power to high levels with operation in the infrared or visible and UV wavelength regions. These lasers can all be tested at the wafer level to provide "know good die" for very low-cost manufacturing. The price points for manufacture of these lasers can reach levels suitable for many large-scale consumer and commercial applications.
This contribution drafts the problems of the AlGaInP material system and its consequences for the laser applications in vertical-cavity surface-emitting lasers (VCSEL). The epitaxial and technological solutions to overcome at least parts of the inherent problems were discussed. Calculated data by a cylindrical heat dissipation model were compared with measured power-current curves of 660nm oxide-confined VCSEL to improve the heat removal out of the device. At high temperatures pulsed operation of a 670nm VCSEL is demonstrated, where we could exceeded 0.5mW at +120°C and at +160°C still 25µW optical output power were achieved.
A long-wavelength VCSEL has been used for the first time for multi-species gas detection and for trace gas sensing. The VCSEL with a buried tunnel junction (VERTILAS, Germany) was capable of covering a spectral range of 7 nm or 28 cm-1 (central wavelength at 1576.3 nm) with the laser temperature and injection current varied between 0-50 °C and 0.5-5 mA respectively. The pressure of CO:CO2=3:2 gas mixtures buffered with N2 (N2 content 0 - 90 %) was varied from 1 mBar up to 1 Bar. To avoid a non-linear dynamic tuning, the combination of a direct injection current with a saw-tooth waveform was used to sweep the laser frequency across absorption lines. A LabVIEW-based computer code was developed for multi-species gas analysis in time domain. Absorption spectra were averaged over 102-103 laser scans. It has been shown that a cross interference from all collisional partners should be taken into account for accurate multi-component gas detection. A concentration of 600 ppm of CO2 in atmospheric air (fractional absorption ~ 10-4) was detected with laser output power of 120 uW. Long-wavelength VCSELs can be used both for multi-species gas detection in a wide range of pressures and for trace gas monitoring.
Fabricated by four times H+ inclined implantation using tungsten wire as mask, batch vertical cavity surface emitting lasers with better characters than those of common ion implanted devices were obtained. They have the batch threshold current of less than 1.5mA, the lowest threshold current of 1.2mA which is lower than that of common oxide confinement device product, the largest light output power of about 1mW with simple TO package, and the largest 3dB modulation bandwidth of 4GHz. According to the polarization measurement result, the devices showed good 0° linear polarization character and up to 14dB polarization suppress ratio in the whole linear gain region, which is better than that of common oxide confinement devices. Spectrum measurement result showed that their wavelength was around 835nm, and they operated with single transverse mode in linear gain region. Furthermore, the fabrication technology was simple enough for the industry without photolithography and lift-off steps.
With a focus on visible spectrum light emitting diodes (LEDs), three questions frame this update. First, what are the market and financial outlooks for light-producing compound semiconductor materials and devices? Second, which applications offer the greatest growth potential for the next five to ten years and with which technologies will they likely compete for market share? Third, how can photonics experts contribute to accelerated successes for LEDs and other solid-state lighting technologies such as quantum dots? Using the rainbow as a metaphor for the market, the author examines developments in single color, multiple color and "white light" products.
Compact ultraviolet light sources are currently of high interest for a range of applications, including solid-state lighting, short-range communication, and bio-chemical detection. We report on the design and analysis of AlGaN-based light-emitting diodes with an emission wavelength near 280 nm. Internal device physics is investigated by three-dimensional numerical simulation. The simulation incorporates a drift-diffusion model for the carrier transport, built-in polarization, the wurtzite energy band-structure of strained quantum wells, as well as radiative and nonradiative carrier recombination. Critical material parameters are identified and their impact on the simulation results is investigated. Limitations of the internal quantum efficiency by electron leakage and nonradiative recombination are analyzed. Increasing the stopper layer bandgap is predicted to improve the quantum efficiency and the light output of our LED substantially.
The use of micro-structured interfaces has been shown to increase the extracted light portion far beyond the total reflection cone that limits extraction from flat surfaces. However, earlier theoretical treatments based on ray tracing, break down for nano-structured features smaller than the material wavelength. We apply a new analytic method converting the boundary conditions at the interface into surface currents following from the surface discontinuity in the perpendicular electric and parallel displacement vectors. These currents serve as source terms driving the transmitted radiation, computed by applying the full wave propagator. Analytic formulae yield the transmitted fraction for quasi-periodic surface features involving random variation of the feature size and period. A single incidence of an incoming plane wavefront suffices for transmission, while, in the ray tracing approach, many bounces with an opposing surface are required until the randomly changing angle of incidence falls within the extraction cone.
High brightness AlGaInP thin-film resonant cavity LEDs with an emission wavelength around 650 nm are presented. The combination of a thin-film waveguide structure and a resonant cavity with an omnidirectional reflector (ODR) leads to significantly higher efficiencies compared to standard resonant cavity LED (RCLED) structures. Preliminary devices based on this configuration show external quantum efficiencies of 23% and 18% with and without encapsulation, respectively, despite a non-ideal detuning. These devices exhibit a narrow far-field pattern and are therefore adapted for applications requiring high brightness emitters such as for example plastic optical fiber communications. By opting for a negative detuning, i.e. a cavity resonance that is red-shifted compared to the intrinsic emission spectrum, even higher efficiencies should be achievable.
Record high power InP-based diode laser pumps operating at 1450 nm and 1850 nm have been fabricated and tested. Single-element 100 mm stripe lasers and 1 cm long arrays (both with cavity length of 2-2.5 mm) are appropriate for fiber and bulk solid-state laser pumping, respectively. The differential quantum efficiency for 1450 nm lasers was 55% and 47% for1850 nm emitters. The maximum CW output powers for 1 cm diode arrays are 42 W for 1450 nm and 14 W for 1850 nm wavelength ranges. The output photon flow (per facet) at maximum current for 1450 nm sources is 40% higher than that for commercial GaAs-based emitters, while for 1850 nm sources it is 50 % lower. A simple estimation shows that the parameters achieved for 1450 nm diode lasers could provide overall efficiency for an 1640 nm Er3+:YAG laser with InP-based pumping comparable with that of a GaAs laser pumped Er3+:YAG laser. More importantly, the expected active media overheating in the case of InP-based pumping is lower by an order of magnitude compared to a GaAs laser pumped Er3+:YAG laser. Data on the lifetime for InP-based diode arrays confirm that high reliability is an additional advantage of long wavelength pumps compared to traditional GaAs-based pumps.