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An all-optical computer has remained an elusive concept. To construct a practical computing primitive equivalent to an electronic Boolean logic, one should utilize nonlinearity that overcomes weaknesses that plague many optical processing schemes. An advantageous nonlinearity provides a complete set of logic operations and allows cascaded operations without changes in wavelength or in signal encoding format. Here we demonstrate an all-optical majority gate based on a vertical-cavity surface-emitting laser (VCSEL). Using emulated signal coupling, the arrangement provides Bit Error Ratio (BER) of 10−6 at the rate of 1 GHz without changes in the wavelength or in the signal encoding format. Cascaded operation of the injection-locked laser majority gate is simulated on a full adder and a 3-bit ripple-carry adder circuits. Finally, utilizing the spin-flip model semiconductor laser rate equations, we prove that injection-locked lasers may perform normalization operations in the steady-state with an arbitrary linear state of polarization.

The effect of using graphene as 2D nanoelectrode for continuous wave (CW) terahertz (THz) photomixers were investigated. The multilayer graphene (6–8 and 3–5 MLG) sheets were used as six-finger interdigital nanoelectrodes on a low- temperature-grown (LTG) GaAs photoconductor. The MLG nanoelectrode shows unique properties with high short-circuit current capabilities and reliable high photocurrents. The number of graphene layers play a big role on the electrical and the optical properties of graphene nanoelectrode. In one hand, a thinner graphene increases the transparency of the nanoelectrodes to improve the power conversion efficiency, and on the other hand, a thicker graphene is required to carry high current densities and enhance the photomixer performance.

We report on numerical study of room-temperature terahertz quantum cascade lasers (THz QCLs) based on a nonpolar m-plane ZnMgO/ZnO employing a 2-well design scheme with variable barrier heights and a delta-doped injector well. We show that by varying and optimizing constituent layer widths and doping level of the injector well, high power performance of THz QCLs can be achieved at room temperature: optical gain and radiation frequency is varied from 108 cm−1@ 2.18 THz to 300 cm−1 @ 4.96 THz. These results show that among II-VI compounds the ZnMgO/ZnO material system is optimally suited for high-performance room-temperature THz QCLs.

We demonstrate direct modulation of a widely tunable microelectromechanical system (MEMS) vertical-cavity surface-emitting laser (VCSEL). The wavelength tuning is realized with electrothermal actuation of a SiO $_x$ /SiN $_y$ -based MEMS distributed Bragg reflector (DBR). The DBR is deposited in a low-temperature plasma-enhanced chemical vapor deposition chamber on a InP-based half-VCSEL by means of surface micromachining. More than 60 nm of mode-hop free continuous tuning with a center wavelength of 1554 nm is achieved. A maximum 3-dB small-signal modulation response ( $S_{21}$ ) bandwidth of 7.05 GHz is reported. Quasi-error-free operation of a back-to-back link is demonstrated at 10 Gb/s for a record 47-nm tuning range, showing the compatibility of the MEMS tunable VCSEL as a cost-effective optical source in access networks and interconnects.

New types of continuous-wave (CW) terahertz (THz) photomixers were fabricated using 1-D and 2-D nanocontacts on low-temperature-grown (LTG) GaAs as well as nitrogen-ion-implanted $({\rm N}^{+}{\rm i})$ GaAs. The 1-D and 2-D nanocontacts were formed by silver nanowires and graphene sheets, respectively. A silver nanowire (Ag-NW) with a physical diameter of $\varnothing \hbox{60 nm}$ and $\varnothing \hbox{120 nm}$ can handle currents of $>\! \hbox{10}$ and $>\! \hbox{30 mA}$ , respectively, without electromigration, thus enabling reliable high photocurrents. The small diameter of such a nanowire electrode in 1-D photomixers reduces the device capacitance by a factor of more than ten compared with photomixers with conventional interdigital fingers. Thus, these nanowire properties can be used for the fabrication of photomixers with cut-off frequencies $>\hbox{2 THz}$ and with extremely reliable operation. A multilayer graphene (MLG) of 6–8 layers shows unique properties with high short-circuit current capabilities of $>\hbox{9 mA/(10}~\mu \hbox{m width})$ and reliable high photocurrents. Furthermore, the MLG absorbs only 2.3% of white light and is ideal as a transparent nanocontact. The use of these graphene electrodes in 2-D photomixers allows an efficient optical power illumination for high photocurrent generation and shows the potential for reliable CW THz emission. Initial THz measurements confirmed the high possibilities of these new nanocontact photomixers.

New enhanced type photomixers for continuous wave (CW) terahertz (THz) generation were fabricated using 3–5 layers and 6–8 layers of graphene material. These multilayer graphene (MLG) sheets were used as 2-D nanoelectrodes on low-temperature-grown (LTG) GaAs photoconductor. The MLG nanoelectrode shows unique properties with high short-circuit current capabilities and reliable high photocurrents. Furthermore, due to the transparency of the MLG, the use of these graphene 2-D nanoelectrodes in THz photomixers allows an efficient optical power illumination for high photocurrent generation and shows a reliable CW THz emission.

We present an all-optical computing scheme based on normalization operations of injection-locked lasers. We show cascaded operations in cellular automaton by an all-optical Conway’s Game of Life and simulate 100 generations of gaming.

We report on a new design of room-temperature terahertz quantum cascade lasers (THz QCLs) based on ZnMgSe/ZnSe material systems employing two-well design schemes with alternating quantum barrier heights and n-type delta-doping of the injector well. Our calculations show that this new THz QCLs achieves high optical gain at the emission frequency of 1.33 THz at room-temperature.

A new type of continuous-wave (CW) terahertz (THz) photomixer was fabricated using a nitrogen-doped single layer graphene (N+SLG) powder and silver nanowire (Ag-NW of O 300 nm) on low-temperature-grown (LTG) GaAs. The new hybrid (N+SLG/Ag-NW) structure provides simple fabrication steps and better performance in terms of high current handling together with reliable operation. The THz output power itself can be increased due to high photocurrent of ∼ 1.8mA.

A new miniature black-body radiator with fast electrical modulation capability was fabricated using carbon nanotube (CNT) yarns (O 20–100 μm). The small diameter of the yarn allows a fast pulsed-modulation (> 100 Hz) without the need of a mechanical chopper. Furthermore, the single CNT yarn handles reliably high currents > 100 mA for high power operation. It can be even used in an array configuration with integrated filters and collimator lenses. Thus, these CNT yarns can be applied as electrically modulated broadband THz sources for fast monitoring of thin objects e.g. papers, envelopes and packages in production lines as well as in miniaturized secure thermal infrared communication systems [1] with increased bit rates.

We report continuously widely tunable InP-based pin-photodiodes by integrating a surface micromachined MEMS-based Fabry-Perot filter with FWHM/FSR of 0.3 nm/189 nm. Detection of 36 nm is obtained for WDM- or sensing-applications around 1550 nm.

We investigate a new parallel all-optical clock recovery scheme based on heterodyne beats of an optical sideband-filtered signal. The oscillating clock signal is recovered when the filtered sideband is combined with a stable local oscillator. The filtering is performed with an optical resonator, which by nature provides possibility for multiwavelength operation. The local oscillator could be realized by a multiwavelength laser, whose emission wavelengths are injection seeded with carrier wavelengths of the input data. The output signal of such a configuration benefits from a reduced bit-pattern effect and a stable offset level. The sideband filtering is demonstrated for 23 simultaneous channels at 100 GHz DWDM grid, each hosting a data stream of 10 Gbit/s.

A new, simple, and cost efficient method is experimentally demonstrated to generate 6th order Gaussian derivative optically. Proposed technique is based on directly modulated semiconductor laser, optical filtering and chromatic dispersion of fiber transmission line.

We report frequency-tunable terahertz (THz) generation with a photomixer driven by an ultra-broadband tunable micro-electro-mechanical system vertical-cavity surface-emitting laser (MEMS-VCSEL) and a fixed-wavelength VCSEL, as well as a tunable MEMS-VCSEL mixed with a distributed feedback (DFB) diode. A total frequency span of 3.4 THz is covered in direct detection mode and 3.23 THz in the homodyne mode. The tuning range is solely limited by the dynamic range of the photomixers and the Schottky diode/photoconductor used in the experiment.

We report 12 Gbps transmission over 6.3 km SMF with a directly modulated widely tunable bulk micromachined MEMS-VCSEL. The MEMS is electrothermally actuated for a continuous tuning of >64 nm around 1560 nm center wavelength. Error-free BTB transmission is achieved at 10 Gbps for 50 nm tuning.

A photocathode based on n-doped graphene emitters in series to a GaAs photoswitch was fabricated and used for pulsed field electron emission. The n-doped graphene array emits at low turn-on fields (< 3 V/µm). A fast photomodulation of the emission current with high on/off ratio ∼200 was achieved with a semi-insulating (s.i.) GaAs photoswitch in a diode configuration. Different laser sources were used for these investigations.

Optical UWB pulse generation and wireless propagation through antenna is investigated. Experimental BER results are presented. It is shown due to antenna characteristics monocycle pulse is converted into 3rd-order Gaussian derivative after wireless propagation.

Continuous-wave (CW) terahertz (THz) photomixing requires compact, widely tunable, mode-hop-free driving lasers. We present a single-mode microelectromechanical system (MEMS)-tunable vertical-cavity surface-emitting laser (VCSEL) featuring an electrothermal tuning range of 64 nm (7.92 THz) that exceeds the tuning range of commercially available distributed-feedback laser (DFB) diodes (∼4.8 nm) by a factor of about 13. We first review the underlying theory and perform a systematic characterization of the MEMS-VCSEL, with particular focus on the parameters relevant for THz photomixing. These parameters include mode-hop-free CW tuning with a side-mode-suppression-ratio >50 dB, a linewidth as narrow as 46.1 MHz, and wavelength and polarization stability. We conclude with a demonstration of a CW THz photomixing setup by subjecting the MEMS-VCSEL to optical beating with a DFB diode driving commercial photomixers. The achievable THz bandwidth is limited only by the employed photomixers. Once improved photomixers become available, electrothermally actuated MEMS-VCSELs should allow for a tuning range covering almost the whole THz domain with a single system.

We propose a solution for reconfigurable wired-wireless converged networks with high data rates, based on directly modulated tunable vertical cavity surface emitting lasers (VCSEL). Wired-wireless converged networks require simple and low-cost solutions for the generation of the UWB signal in the optical domain. Direct modulation of VCSEL in combination with optical filtering enable a low-cost generation of ultra-wideband (UWB) pulses. VCSEL typically show large direct modulation bandwidths 10 GBit/s due to their short cavity related short photon lifetime. Another advantage of the short cavity is its inherent large free spectral range (FSR) which enables ultra wide continuous wavelength tuning.

The integration of ultra-wideband (UWB)-over- ber into passive optical network (PON) is of great interest as it bene ts the high bandwidth capability from optical network technologies and the high exibility from wireless network technologies. The later can only be done with a reasonable cost when a universal optical transmitter, which is capable of generation both UWB and PON signals, is available. Direct modulation of semiconductor laser was demonstrated to be suitable for high bit-rate PON systems, however the generation of UWB signals by this technique is still challenging. Using the chirp properties of directly modulated semiconductor lasers, UWB signals are generated. Di erent UWB signal waveforms and polarities are obtained. The received electrical spectra conform to the requirements of indoor UWB systems.

We identified conditions for room-temperature operation of terahertz quantum cascade lasers (THz QCLs) where variable barrier heights are used on ZnSe/Zn1–xMgx Se material systems. The THz QCL devices are based on three-level two-well design schemes. The THz QCL lasers with alternating quantum barriers with different heights were compared with THz QCL laser structures with fixed quantum barrier heights. It is found that the THz QCL device with novel design employing variable barrier heights achieved the terahertz emission of about 1.45 THz at room-temperature (300 K), and has improved laser performance due to the suppression of thermally activated carrier leakage via higher-energy parasitic levels. Thus, THz QCL devices employing the design with variable barrier heights may lead to future improvements of the operating temperature and performance of THz QCL lasers. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

In this paper, we demonstrate for the first time the far-field experimental results and the linewidth characteris- tics for widely tunable surface-micromachined micro-electro-mechanical system (MEMS) vertical-cavity surface- emitting lasers (VCSELs) operating at 1550 nm. The fundamental Gaussian mode emission is confirmed by optimizing the radius of curvature of top distributed Bragg reflector (DBR) membrane and by choosing an ap- propriate diameter of circular buried tunnel junctions (BTJs) so that only the fundamental Gaussian mode can sustain. For these VCSELs, a mode-hop free continuous tuning over 100 nm has already been demonstrated, which is achieved by electro-thermal tuning of the MEMS mirror. The fiber-coupled optical power of 2mW over the entire tuning range has been reported. The singlemode laser emission has more than 40 dB of side-mode suppression ratio (SMSR). The smallest linewidth achieved with these of MEMS tunable VCSELs is 98MHz which is one order of magnitude higher than that of fixed-wavelength VCSELs.

Chirp-managed lasers (CML) are demonstrated as simple low-cost transmitter with high tolerance to chromatic dispersion. This manuscript proposes the use of CML as cost-effective downstream (DS) transmitters for next generation access networks. The laser chirp, which is the main drawback limiting the transmission performance of directly modulated lasers, is now used to generate differential phase-shift keying (DPSK) modulation format by direct modulation. The network architecture using CML as downstream DPSK transmitter is proposed. Bit­ error-rate measurement showed that an optical power budget of 36 dB could be obtained with direct phase-shift­ keying modulation ofCML which proves that the proposed solution is a strong candidate for future WDM-PONs. Budget-extended WDM-PON configuration is also demonstrated using Saturated Collision Amplifier, which is an amplification scheme that uses SOA saturation in order to maximize the output power and minimize the ASE noise and the polarization sensitivity. The extension scheme is demonstrated for four-wavelength 10 Gbit/s unidirectional downstream configuration with 60-dB maximum total optical budget for each wavelength.

Blue InGaN/GaN light-emitting diodes with undoped, heavily Si-doped, Si delta-doped, heavily Mg-doped, Mg delta-doped, and Mg–Si pin-doped GaN barrier are investigated numerically. The simulation results demonstrate that the Mg–Si pin-doping in the GaN barrier effectively reduces the polarization-induced electric field between the InGaN well and the GaN barrier in the multiple quantum well, suppresses the quantum-confined Stark effect, and enhances the hole injection and electron confinement in the active region. For this light-emitting diode (LED) device structure, we found that the turn-on voltage is 2.8 V, peak light emission is at 415.3 nm, and internal quantum efficiency is 85.9% at 100 A cm−2. It is established that the LED device with Mg–Si pin-doping in the GaN barrier has significantly improved efficiency and optical output power performance, and lower efficiency droop up to 400 A cm−2 compared with LED device structures with undoped or Si(Mg)-doped GaN barrier.

A novel and cost-efficient technique is presented to generate non-return-to-zero (NRZ) and ultra-wideband (UWB) signals in different time slots of time division multiplexing-passive optical network (TDM-PON) by using a single chirped controlled semiconductor laser associated with an optical bandpass filter. In this technique, the chirp of the laser is controlled by different bias burst amplitudes (BBA) for different time slots. Through the proper selection of the burst amplitudes, 10 Gbps NRZ and 1.25 Gbps UWB signals are generated in different time slots. Principle of operation is discussed, the complete chirp behavior of the laser is experimentally investigated, data transmission of the generated signals is demonstrated and bit-error-rate (BER) level of 10-sup9/supis achieved.

We report an electrically pumped 1550 nm MEMS tunable VCSEL with a continuous tuning of 101 nm at 22 °C. The top MEMS-DBR with built-in stress gradient within the dielectric layers is deposited in a low-temperature PECVD chamber on an InP-based half-VCSEL, structured by surface-micromachining and electrothermally actuated for continuous wavelength tuning. With 2.6 mA threshold current, the laser shows maximum CW output power of 3.2 mW at 1560 nm. The MEMS-VCSEL operates in single-mode with SMSR > 39 dB across the entire tuning range. At 36 °C, the tuning range reaches up to 107 nm. The divergence angle of the MEMS-VCSEL is approximately 5.6° for all tuning wavelengths. The intrinsic linewidth of an unpackaged device is 21 MHz. Quasi-error-free operation at 12.5 Gbps using a directly modulated MEMS-VCSEL is reported for a record 60 nm tuning, showing the potential of the so-called colorless source in WDM applications.

We present a novel WDM-PON optical power budget extender which provides 61 dB power budget improvement. We demonstrate it experimentally for a 4×10 Gbit/s DPSK WDM-PON upstream scenario.

Long-wavelength VCSELs with emission wavelengths beyond 1.3 μm have seen a remarkable progress over the last decade. This success has been accomplished by using highly advanced device concepts which effectively overcome the fundamental technological drawbacks related with long-wavelength VCSELs such as inferior thermal properties and allow for the realization of lasers with striking device performance. In this presentation, we will give an overview on the state of the technology for long-wavelength VCSELs in conjunction with their opportunities in applications for optical sensing. While VCSELs based on InP are limited to maximum emission wavelengths around 2.3 μm, even longer wavelengths up to the mid-infrared range beyond 3 μm can be achieved with VCSELs based on GaSb. For near-infrared InP-based VCSELs, the output characteristics include sub-mA threshold currents, up to several milliwatts of singlemode output power and ultralow power consumption. New concepts for widely tunable VCSELs with tuning ranges up to 100 nm independent from the material system for the active region are also presented. Today, optical sensing by Tunable Diode Laser Spectroscopy is a fast emerging market. Gas sensing systems are used for a wide range of applications such as industrial process control, environmental monitoring and safety applications. With their inherent and compared to other laser types superior properties including enhanced current tuning rates, wavelength tuning ranges, modulation frequencies and power consumption, long-wavelength VCSELs are regarded as key components for TDLS applications.

For the first time a vertical-cavity surface-emitting laser (VCSEL) with a single-mode wavelength-tuning over 102 nm in the range of 1550 nm is demonstrated. The fiber-coupled optical output power has a maximum of 3.5 mW and is > 2 mW over the entire tuning range. The sidemode suppression ratios are > 45 dB. The wavelength tuning is achieved with the micro-electro mechanical actuation of a mirror membrane fabricated with surface micro-machining for on-wafer mass production. The mirror membrane consists of low cost dielectric materials (SiOx/SiNy) deposited with low temperature (< 100°C) Plasma Enhanced Chemical Vapor Deposition (PECVD).

Widely tunable vertical cavity surface emitting lasers (VCSEL) are of high interest for optical communications, gas spectroscopy and fiber-Bragg-grating measurements. In this paper we present tunable VCSEL operating at wavelength around 850 nm and 1550 nm with tuning ranges up to 20 nm and 76 nm respectively. The first versions of VCSEL operating at 1550 nm with 76 nm tuning range and an output power of 1.3mW were not designed for high speed modulation, but for applications where only stable continious tuning is essential (e.g. gas sensing). The next step was the design of non tunable VCSEL showing high speed modulation frequencies of 10 GHz with side mode supression ratios beyond 50 dB. The latest version of these devices show record output powers of 6.7mW at 20 °C and 3mW at 80 °C. The emphasis of our present and future work lies on the combination of both technologies. The tunable VCSEL operating in the 850 nm-region reaches a modulation bandwidth of 5.5GHz with an output power of 0.8mW.

This paper presents for the first time the network architecture and the multiple-wavelength operation of a novel SOA-based PON extender. In 10-Gbit/s four-wavelength 100-km configuration, the total optical budget for each wavelength is 58 dB.

We show how a stable bound soliton pair (or “soliton molecule”) maintains an equilibrium temporal separation during its propagation along a dispersion alternating fiber. Experimental results of a scheme utilizing this soliton molecule action to re‐time a return‐to‐zero on‐off‐keyed (RZ‐OOK) data stream at 10.7 Gbit/s are presented.

We introduce a polarization insensitive scheme for all-optical clock recovery and demonstrate how it works with data signals highly distorted by chromatic dispersion and self-phase modulation. The scheme which is known for its multi-wavelength and multi-data-rate capabilities is based on a birefringent fiber resonator and a polarizer. In this article we show how it can handle data signals which have undergone distortion due to transmission over dispersive and nonlinear fiber-optic propagation paths and which come in with arbitrary polarization orientation. Bit-pattern dependent amplitude fluctuations of the recovered clock signal are equalized by means of a semiconductor optical amplifier operated in saturation. The experimental results which, as a proof-of-concept, are obtained from single-wavelength channel 10 Gbit/s return-to-zero data agree well with numerical simulations.

We report on a numerical study of the characteristics of p-GaN/n-ZnO light-emitting diodes (LEDs) with p-NiO and n-ZnSe interlayers, and on LED design optimization which includes bandgap engineering, thickness and doping of constituent layers. The current-voltage dependences of investigated LEDs show a threshold voltage of 3.1 V, 5.4 V and 5.6 V for LED devices without and with the presence of p-NiO and n-ZnSe interlayers, respectively. It is found that p-NiO, n-ZnSe and n-ZnO interlayers act as an electron blocking layer, active media layer, and electron transport layer, respectively. It is established that the insertion of both p-NiO and n-ZnSe interlayers leads to the enhancement of charge carrier-confinement in the active region and to the significant increase of internal quantum efficiency (IQE) of the LED device up to 82%, which is comparable with IQE values in order to obtain better AlGaN- and InGaN-based LEDs. It is found that the efficiency of LED devices at 100 A cm−2 is equal to 0.024, 0.09 and 16.4% of external quantum efficiency (EQE), 1.3 × 10−4, 1.6 × 10−4, and 6.4 lm W−1 of PE, and 1.3 × 10−4, 2.9 × 10−4, and 12 cd A−1 of CE for p-GaN/n-ZnO, p-GaN/p-NiO/n-ZnO, and p-GaN/p-NiO/n-ZnSe/n-ZnO LED devices, respectively.

With increasing line rates system tolerances due to both, chromatic dispersion and dispersion slope, become more restrictive. By means of numerical simulations we investigate the influence of temperature fluctuations in cascaded multi-section dispersion-compensated standard single-mode fiber SMF based transmission systems. Eye opening penalty (EOP) for different modulation formats - non-return-to-zero NRZ as well as return-to-zero RZ with duty cycles varying from 0.2 to 0.6 and for different signal power levels varying from -9 to 3 dBm at a line rate of 160 Gbit/s are calculated. Performance degradation due to temperature-induced dispersion variations is investigated for three different scenarios: a) the temperature of the installed terrestrial fiber-optic cable changes, b) the temperature of the temperature-controlled indoor dispersion compensating module DCM changes, c) combined effects.

10 Gb/s transmission experiments in a recirculating loop with standard single-mode and dispersion compensating fibres show that NRZ- and RZ-modulated signals can be transmitted over a trunk length of 2000 km with more than 100 km amplifier spacing.

For the first time a vertical-cavity surface-emitting laser (VCSEL) with singlemode wavelength tuning over 74 nm in the range of 1.55 µm and a wavelength tuning speed of ∼200 kHz is demonstrated. The wavelength tuning is achieved with the electro static actuated of a mirror membrane, fabricated with surface micromachining. The mirror membrane consists of the dielectric materials SiOx and SiNy deposited with low temperature ( 1 mW over the entire tuning range. The sidemode suppression ratio is >40 dB.

The authors show, for the first time, the feasibility of upgrading existing transmission systems, by straight-forward means, to 40 Gbit/s through 617 km and 80 Gbit/s through 412 km of standard singlemode fibre, since 10 Gbit/s-based WDM transmission was achieved without gain-flattening the commercial optical amplifiers and without intermediate filtering. Dispersion management was performed by dispersion compensating fibre units.

A high frequency photocathode based on a carbon nanotube (CNT)-yarn in series to a semi-insulating (s.i.) GaAs was fabricated and used for field electron emission in a diode configuration. This hybrid two-chip technology allows the separate optimization of the yarn emitter and the photoswitch. This concept can overcome the capacitance limitations of miniaturized high-frequency vacuum tubes. The used CNT yarn emitter with $20 \mu \mathrm {m}$ diameter had a threshold electric fields of $\sim 1.8\mathrm {V}/ \mu \mathrm {m}($ defined at 1mA/cm $^{\mathbf {2}}$textbf) with a stable field emitter current up to $400 \mu \mathrm {A}$. The high-voltage photomodulation was up to 100 MHz.

We numerically and experimentally studied the shape of the dissipative dispersion-managed solitons (DM-solitons) stably propagating over the lossy DM fiber-optic systems with lumped amplification. We found that, contrary to the lossless case, the chirp-free points of the dissipative DM-solitons are not located in the middle of the fiber spans in the dispersion map. This constitutes a qualitative difference between the dissipative DM-solitons of the lossy systems and the conservative ones of the lossless systems. The applied numerical method was verified both experimentally and by numerically solving nonlinear Schrodinger equation. (C) 2019 Optical Society of America