All-optical clock recovery using a ridge width varied two-section partly gain-coupled DFB self-pulsation laser

A 1.55 μm InGaAsP-InP partly gain-coupled two-section DFB self-pulsation laser (SPL) with a varied ridge width has been fabricated. The laser produces self-pulsations with a frequency tuning range of more than 135 GHz. All-optical clock recovery from 40 Gb/s degraded data streams has been demonstrated. Successful lockings of the device at frequencies of 30 GHz, 40 GHz, 50 GHz, and 60 GHz to a 10 GHz sidemode injection are also conducted, which demonstrates the capability of the device for all-optical clock recovery at different frequencies. This flexibility of the device is highly desired for practical uses.     

A comparative study of electrode effects on the electrical and luminescent characteristics of Alq3/TPD OLED: Improvements due to conductive polymer (PEDOT) anode

The performance of organic light emitting device (OLED) structures, based on identically fabricated Alq₃/TPD active regions, with various anode and cathode electrode structures are compared, and performance differences related to the different anode structure. The best performance was achieved with a conductive polymer, 3,4-polyethylenedioxythiopene-polystyrenesultonate (PEDOT), used as an anode layer, yielding a brightness of 1720 cd/m² at 25 V, a turn-on voltage of 3 V, and electroluminescence (EL) efficiency and external quantum efficiency of 8.2 cd/A and 2%, respectively, at a brightness of 100 cd/m² and 5 V. Compared to a baseline device (TPD/Alq₃/Al), PEDOT anodes substantially reduce the turn-on voltage and made current injection almost linear after turn-on, whiles devices incorporating a LiF and CuPc layers significantly improved device efficiency while slightly improving turn-on voltage and maintaining superlinear I-V injection. This is attributed to the reduced barrier at the organic-organic interface in PEDOT, the ‘ladder’ effect of stepping the band offset over several interfaces, and the favorable PEDOT film morphology. The benefit of the PEDOT anode is clearly seen in the improvement in device brightness and the high external quantum efficiency obtained.     

Compact SOI arrayed waveguide grating demultiplexer with broad spectral response

A compact eight-channel flat spectral response arrayed waveguide grating (AWG) multiplexer based on silicon-on-insulator (SOI) materials has been fabricated on the planar lightwave circuit (PLC). The 1-dB bandwidth of 48 GHz and 3-dB bandwidth of 69 GHz are obtained for the 100 GHz channel spacing. Not only non-adjacent crosstalk but also adjacent crosstalk are less than −25 dB. The on-chip propagation loss range is from 3.5 to 3.9 dB, and the total device size is 1.5 × 1.0 cm².     

Thermally controlled multiband,mode-switching plasmonic filter operating at terahertz frequencies

A thermally controlled multiband, mode-switching plasmonic filter with periodic subwavelength metal asterisk-shaped air hole arrays has been proposed in the terahertz range. Utilizing the changing properties to terahertz wave propagating on the metal-semiconductor interface and in the semiconductor InSb at varying temperature, thermally controlled multiband, mode-switching plasmonic filter owns an excellent tuning ability to terahertz wave. The simulation results show that the maximum transmittance of the structure is 99.8% at 434 GHz, 80 K, the bandwidths at 80 K are 56 GHz at 0.434 THz, 14 GHz at 944 GHz and maximum intensity modulation depth could reach to 99.8% at 434 GHz between 80 K and 373 K.     

Ultrafast mode switching based on a micro-ring laser

Injection locking and multi-mode switching characteristics of a semiconductor ring laser with the radius of 10 μm are investigated based on a nonlinear time domain multimode rate-equation model. The stable injection locking regions for different target modes are studied as the function of detuning frequency and injection power ratio. The results show that ultra-wide detuning range of ∼100 GHz wide at 5 dB injection power ratio and ultra-low switching power ratio of −27 dB can be realized for this micro-ring laser device. Optimal detuning value and high injection power lead to the minimal switching time. An ultrafast response time of 10 ps indicates that a 10 μm-radius SRL can be utilized for ultrafast all-optical scenarios and high-speed tunable lasers.     

Ultrahigh-channel-count fiber Bragg grating based on the triple sampling method

A triple sampling method to have enabled excellent channel uniformity and high in-band energy efficiency is firstly proposed for the design of an ultrahigh-channel-count fiber Bragg grating (FBG), which is based on the simultaneous utilization of two amplitude-assisted phase sampling (AAPS) functions and a phase-only sampling (POS) function. As an example, one linearly chirped FBG with consecutive 1215 channels enabling to cover all fiber telecom bands (O + E + S + C + L + U) is numerically demonstrated, which has a length of 9 cm, a dispersion of − 1360 ps/nm, and a channel spacing of 50 GHz. The maximum index-change required for 10 dB strength of the FBG is less than 6 × 10^− 3.     

Optical beamforming networks employing phase modulation and direct detection

We propose a novel dispersion-based optical beamforming network scheme employing phase modulation and direct detection. Optical phase modulators have the advantages of simple-structure, low loss and absence of bias. Dispersion-induced phase-to-intensity conversion is utilized to facilitate direct detection. A structure of wideband dispersive device (WDD) cascaded with periodic dispersive device (PDD) is introduced to enhance the system flexibility, so that the delay adjustability and RF response can be properly designed respectively by choosing appropriate dispersions of the WDD and PDD. A concept-proof system with a wideband chirped fiber grating (CFG) as the WDD and two multiband CFGs (MCFG1 and MCFG2) as the PDD separately is built to demonstrate the basic idea. The delay tuning range is 0-1.8 ns with increment of 164.2 ps. The passband center is 30 GHz for MCFG1 and 20 GHz for MCFG2, and the fractional bandwidth is 51.8%. The shot-noise-limited spurious-free dynamic range is also analyzed and measured to be 105.7 dB ⋅ Hz^2/3 when the average photocurrent is 2.7 mA.     

Fabrication and electromagnetic performance of micro-tubular nanocomposites composed of monodisperse iron nanoparticles and carbon

Low density and thin thickness are essential for electromagnetic (EM) wave absorbers. In this study, we fabricated a novel micro-tubular iron nanocomposite (MTIC) that composed of carbon microtubes and monodisperse iron nanoparticles (NPs). The bulk density of MTIC is only 0.35±0.04 g cm⁻³ due to its micro-tubular structure. The presence of iron NPs increased the magnetic loss significantly and therefore enhanced the reflection loss (RL) of MTIC/paraffin composite. The optimum thickness for the composite is 1.5-1.8 mm, with maximum bandwidth of 7.6 GHz for RL<−5 dB and 3.6 GHz for RL<−10 dB. The corresponding frequency at this thickness is 10-18 GHz. Because of low density and broad bandwidth at thin thickness, MTIC is a promising light-weight absorber for EM wave absorption or microwave shielding. This study will also provide new ideas for fabricating microwave absorbers with low density and thin thickness.     

A 1 × 4 polarization and wavelength independent optical power splitter based on a novel wide-angle low-loss Y-junction

A 1 × 4 polarization and wavelength independent optical power splitter is reported. This device is based on a novel wide-angle low-loss Y-junction structure which can give a theoretical TE junction excess loss of 0.26 dB at a branching angle of 16°. To the best of our knowledge, it is so far the lowest reported loss at such a large angle. The detailed design of the device and its fabrication are described. Our experimental results show the measured TE excess loss to be 1.2 dB and TM excess loss 1.8 dB for the whole splitter over the wavelength between 1.47 μm and 1.57 μm.     

Pressure shift and broadening of 110-101 water vapor lines by atmosphere gases

This paper is devoted to the measurement of pressure shift and broadening parameters of water-vapor lines of the pure rotational transition 1₁₀-1₀₁ in the ground vibrational state of H₂¹⁶O at 556.936 GHz, H₂¹⁷O at 552.02 GHz, H₂¹⁸O at 547.676 GHz, and the vibrationally excited state v₂=1 line of H₂¹⁶O at 658.003 GHz. The broadening coefficients of the line at 556.936 GHz (for N₂ and O₂ as perturbing gases) coincide within the errors with the values obtained recently by Seta et al. [Pressure broadening coefficients of the water vapor lines at 556.936 and 752.033 GHz. JQSRT 2008;109:144-50] by means of a very different technique (THz-TDS). Pressure shift and broadening for other lines were measured for the first time. Comparison of our results with previous measurements and theoretical calculations is presented.     

Ring resonator with multimode waveguide turning-mirror couplers in InGaAsP-InP

Compact In_0.67Ga_0.33As_0.6P_0.4/In_0.71Ga_0.29As_0.74P_0.26 on InP single ring resonators incorporating 2 × 2 multimode interference (MMI) turning-mirror couplers with cross coupling factor of 0.15 have been demonstrated. The form of race tracks is a 15-degree arc of 260 μm radius joined with a 60-degree arc of 110 μm radius, and finished with another 15-degree arc of 260 μm radius. The MMI turning-mirror coupler of 128 μm in length is used in the single ring resonators, which correspond to free spectral ranges of 82 GHz. A contrast of 4 dB, a finesse of nearly 3 and full-width at half-maximum (FWHM) of 0.24 nm for the drop port have been achieved in this single ring resonator. From the experimental value T_max/T_min of 21 dB, the experiment coupling factor coincides with the simulation.     

Improved 4H–SiC MESFET with double source field plate structures

An improved 4H–SiC power MESFET with double source field plates (DSFP) for high-power applications is proposed (DSFP-MESFET). The DSFP structure significantly modifies the electric field in the drift layer. The influence of the DSFP structure on saturation current, breakdown voltage (V_b), and small-signal characteristics of the DSFP-MESFET were studied by numerical device simulation. The V_b of 359 V is obtained for the DSFP-MESFET compared to 301 V of the conventional source field plate MESFET (LSFP-MESFET). Hence, the maximum output power density of 24.7 and 21.8 W/mm are achieved for the DSFP-MESFET and LSFP-MESFET, respectively, which means 13% improvement for the proposed device. Also, the cut-off frequency (f_T) of 24.5 and the maximum oscillation frequency (f_max) of 89.1 GHz for the 4H–SiC DSFP-MESFET are obtained compared to 23.1 and 85.3 GHz for that of the LSFP-MESFET structure, respectively. The DSFP-MESFET shows a superior maximum stable gain (MSG) exceeding 23.3 dB at 3.1 GHz, which is presenting the potential of the proposed device for high-power operations.     

Coherence-converted population transfer FTMW-IR double resonance spectroscopy of CH3OD in the OD-stretch region

Rotationally selected infrared spectra of jet-cooled CH₃OD have been recorded and analyzed in the OD-stretch region (2710-2736 cm⁻¹). The observed spectra are obtained by monitoring three E-species microwave transitions (1₋₁ ← 1₀ at 18.957 GHz, 2₋₁ ← 2₀ at 18.991 GHz, and 3₋₁ ← 3₀ at 19.005 GHz) in a narrowband cavity Fourier transform microwave spectrometer, using the background-free coherence-converted population transfer technique. Of the four upper state subbands observed, two (K′ = 0 and −2) are split by perturbations. The E-species deperturbed band origin is at 2718.1 cm⁻¹. The deperturbed reduced term values follow a pattern similar to the ground state. This allows the J′ = 0 torsional tunneling splitting to be estimated as 2.1 cm⁻¹, which can be compared to 2.6 cm⁻¹ in the ground state.     

High-performance 850 nm vertical-cavity surface-emitting laser in Gigabit Ethernet network

High-performance oxide vertical-cavity surface-emitting (VCSEL) laser is fabricated, and its usefulness is demonstrated as a suitable transmitting light source at 850 nm operating wavelength for Gigabit Ethernet application. Utilization of barrier reduction layers reveals low-threshold current requirement for operation at high modulation bandwidth. The electrical and optical characteristics, measured from the fabricated VCSEL, are simulated for Gigabit Ethernet transmission. Data rates of 1.25 Gbps with a bit error rate of 10⁻¹¹ are achieved by the use of a specific multimode network simulator.     

On the carrier generation and HD signal transmission using the millimeter-wave radio over fiber system

The dual sideband optical carrier suppression (DSB-OCS) technique is employed in the optical carrier generation for 40 GHz radio over fiber (ROF) system. A dual electrode Mach-Zehnder modulator (DE-MZM) with the minimum transmission bias (MiTB) technique is employed to build the system. The results show that, a 40 GHz carrier is successfully generated with the amplitude up to −29 dBm and signal to noise ratio (SNR) of 35 dB and a high definition (HD) signal is successfully transmitted using the system. Finally, the bit error rate (BER) measurement is carried out for the system with 1.25 Gbps OOK signal showing an error free 40 GHz ROF system with almost no penalty between the back to back and 20 km fiber for a BER of 10⁻⁹.     

Visible-to-near infrared standard source generation using acetylene (C2H2)-stabilized comb-injection-locked technique

An ultra-stable visible laser source (VLS) was generated by the second harmonic of a selectively injection-locked distributed feedback (DFB) laser from an optical frequency comb with acetylene-stabilized laser seeding. For the second-harmonic generation (SHG) of the injection-locked DFB laser, we used periodically poled lithium niobate (PPLN) crystal and generated the VLS at a region of 771 nm, which was discretely locked to a spacing of 25 GHz within the PPLN bandwidth (180 GHz). The frequency stability of this source was estimated to be 1.1 × 10^− 12 with an average time of 1 s.     

Design of a silicon RCE Schottky photodetector working at 1.55 μm

In this paper, the design of a resonant cavity-enhanced (RCE) Schottky photodetector, based on internal photoemission effect and working at 1.55 μm, is presented. In order to estimate the theoretical quantum efficiency we take the advantage of analytical formulation of the internal photoemission effect (Fowler theory), and its extension for thin films, while for the optical analysis of device a numerical method, based on the transfer matrix method, has been implemented. Finally, we complete our design calculating bandwidth and bandwidth-efficiency product.Our numerical results prove that a quantum efficiency of 0.1% is obtained at resonant wavelength (1.55 μm) with a very thin absorbing metal layer (30 nm). Theoretical values of 100 GHz and 100 MHz were obtained, respectively, for the carrier-transit time limited 3-dB bandwidth and bandwidth-efficiency. The proposed photodetector can work at room temperature and its fabrication is completely compatible with standard silicon technology.     

Simulation of DWDM signals using optimum span scheme with cascaded optimized semiconductor optical amplifiers

We numerically simulated the ten channels at 10 Gb/s dense wavelength division multiplexing (DWDM) transmission faithfully over 17,227 km using 70 km span of single mode fiber (SMF) and dispersion compensating fiber (DCF) using optimum span scheme at channel spacing 20 GHz. For this purpose, inline optimized semiconductor optical amplifiers (SOAs) and DPSK format are used. We optimized the SOA parameters for inline amplifier with minimum crosstalk and amplified spontaneous emission noise with sufficient gain at bias current 400 mA. For this bias current, constant gain 36.5 dB is obtained up to saturation power 21.35 mW. We have also optimized the optical phase modulator bandwidth for 400 mA current which is around 5.5 GHz with crosstalk −14.2 dB between two channels at spacing 20 GHz.We show the 10×10 Gb/s transmission over 70 km distance with inline amplifier has good signal power received as compared to without amplifier, even at equal quality factor. We further investigated the optimum span scheme for 5670 km transmission distance for 10×10 Gb/s with channel spacing 20 at 5.5 GHz optical phase modulator bandwidth. As we increase the transmission distance up to 17,227 km, there is increase in power penalty with reasonable quality.The impact of optical power received and Q factor at 5670 and 17,227 km transmission distance for different span schemes for all channels has been illustrated. For launched optical power less than saturation, all channels are obtained at bit error rate floor of 10⁻¹⁰.     

Tunable negative index metamaterial using yttrium iron garnet

A magnetic field tunable, broadband, low-loss, negative refractive index metamaterial is fabricated using yttrium iron garnet (YIG) and a periodic array of copper wires. The tunability is demonstrated from 18 to 23 GHz under an applied magnetic field with a figure of merit of 4.2 GHz/kOe. The tuning bandwidth is measured to be 5 GHz compared to 0.9 GHz for fixed field. We measure a minimum insertion loss of 4 dB (or 5.7 dB/cm) at 22.3 GHz. The measured negative refractive index bandwidth is 0.9 GHz compared to 0.5 GHz calculated by the transfer function matrix theory and 1 GHz calculated by finite element simulation.     

High sensitivity of palladium on porous silicon MSM photodetector

In this work, the nanocrystalline porous silicon (PS) is prepared through the simple electrochemical etching of n-type Si (1 0 0) under the illumination of a 100 W incandescent white light. SEM, AFM, Raman and PL have been used to characterize the morphological and optical properties of the PS. SEM shows uniformed circular pores with estimated sizes, which range between 100 and 500 nm. AFM shows an increase in its surface roughness (about 6 times compared to c-Si). Raman spectra of the PS show a stronger peak with FWHM=4.3 cm⁻¹ and slight blueshift of 0.5 cm⁻¹ compared to Si. The room temperature photoluminescence (PL) peak corresponding to red emission is observed at 639.5 nm, which is due to the nano-scaled size of silicon through the quantum confinement effect. The size of the Si nanostructures is estimated to be around 7.8 nm from a quantized state effective mass theory. Thermally untreated palladium (Pd) finger contact was deposited on the PS to form MSM photodetector. Pd/PS MSM photodetector shows lower dark (two orders of magnitude) and higher photocurrent compared to a conventional Si device. Interestingly, Pd/PS MSM photodetector exhibits 158 times higher gain compared to the conventional Si device at 2.5 V.