Showing papers in "IEEE Photonics Technology Letters in 2008"
TL;DR: In this paper, the authors describe a link that uses 16 LEDs which are modulated using a resonant driving technique, creating an overall modulation bandwidth of 25 MHz, which is used to implement a 40-Mb/s nonreturn-to-zero on-off keying link which operates at low error rates, and also provides illumination at levels sufficient for a standard office environment.
Abstract: White light-emitting diodes (LEDs) are becoming widespread in commercial lighting applications, and there are predictions that they will be in common use in domestic applications in the future. There is also growing interest in using these devices for both illumination and communications. One of the major challenges in visible light communications is the low modulation bandwidth (BW) available from devices, which is typically several megahertz. In this letter, we describe a link that uses 16 LEDs which are modulated using a resonant driving technique, creating an overall BW of 25 MHz. This is used to implement a 40-Mb/s nonreturn-to-zero on-off keying link which operates at low error rates, and also provides illumination at levels sufficient for a standard office environment.
354 citations
TL;DR: In this paper, a fiber Mach-Zehnder interferometer was realized by concatenating two singlemode fiber tapers separated by a middle section, which had a minimum insertion loss of 3 dB and maximum interferometric extinction ratio over 20 dB.
Abstract: A novel refractive index (RI) sensor based on a fiber Mach-Zehnder interferometer was realized by concatenating two single-mode fiber tapers separated by a middle section. The proposed device had a minimum insertion loss of 3 dB and maximum interferometric extinction ratio over 20 dB. The resolution (0.171 nm) of the two-taper sensor to its surrounding RI change (0.01) was found to be comparable to that (0.252 nm) of similar structures made from an identical long-period gratings pair, and its ease of fabrication makes it a low-cost alternative to existing sensing applications.
334 citations
TL;DR: This letter explores the Gram-Schmidt orthogonalization procedure (GSOP) for compensation of quadrature imbalance in an optical 90deg hybrid and demonstrates the improvement which can be achieved using the GSOP, including the impact of quantization in the digital coherent receiver.
Abstract: This letter explores the Gram-Schmidt orthogonalization procedure (GSOP) for compensation of quadrature imbalance in an optical 90deg hybrid. We present computer simulations for an optical QPSK communication system using a digital coherent receiver and investigate the impact of quadrature imbalance on the required optical signal-to-noise ratio for the receiver and the frequency estimation algorithm. We then demonstrate the improvement which can be achieved using the GSOP, including the impact of quantization in the digital coherent receiver. Finally, we show that the GSOP can equally be applied to polarization-division multiplexed systems, applying the GSOP in conjunction with the constant modulus algorithm to demultiplex a PDM-QPSK signal.
272 citations
TL;DR: In this paper, a fiber Michelson interferometer refractive index (RI) sensor with a single core-offset attenuator and a layer of ~ 500-nm gold coating was demonstrated.
Abstract: Mach-Zehnder and Michelson interferometers using core-offset attenuators were demonstrated. As the relative offset direction of the two attenuators in the Mach-Zehnder interferometer can significantly affect the extinction ratio of the interference pattern, single core-offset attenuator-based sensors appear more robust and repeatable. A novel fiber Michelson interferometer refractive index (RI) sensor was subsequently realized by a single core-offset attenuator and a layer of ~ 500-nm gold coating. The device had a minimum insertion loss of 0.01 dB and maximum extinction ratio over 9 dB. The sensitivity (0.333 nm) of the new sensor to its surrounding RI change (0.01) was found to be comparable to that (0.252 nm) of an identical long period gratings pair Mach-Zehnder interferometric sensor, and its ease of fabrication makes it a low-cost alternative to existing sensing applications.
213 citations
TL;DR: In this article, a microring resonator-based silicon broadband 12-combiner switch is used for simultaneous all-optical switching of 20 continuous-wave wavelength channels.
Abstract: Simultaneous all-optical switching of 20 continuous-wave wavelength channels is achieved in a microring resonator-based silicon broadband 12 comb switch. Moreover, single-channel power penalty measurements are performed during active operation of the switch at both the through and the drop output ports. A statistical characterization of the drop-port insertion losses and extinction ratios of both ports shows broad spectral uniformity, and bit-error-rate measurements during passive operation indicate a negligible increase in signal degradation as the number of wavelength channels exiting the drop port are scaled from one to 16, with peak powers of 6 dBm per channel. A high-speed broadband switching device, such as the one described here, is a crucial element for the deployment of interconnection networks based on silicon photonic integrated circuits.
176 citations
TL;DR: The results show that the RSOA-based WDM PON is operable at 10 Gb/s and the maximum reach can be extended to >20 km with the help of the forward error correction codes.
Abstract: We report on the 1O-Gb/s operation of the reflective semiconductor optical amplifier (RSOA) for the next-generation wavelength-division-multiplexed passive optical network (WDM PON). The bandwidth of the RSOA used in this experiment is merely 2.2 GHz. Nevertheless, a clear eye opening is obtained at 10 Gb/s by using the electronic equalizer processed offline. We investigate the impacts of the network's operating conditions (such as the injection power to the RSOA and the fiber length) on the performances of these equalizers. The results show that the RSOA-based WDM PON is operable at 10 Gb/s and the maximum reach can be extended to >20 km with the help of the forward error correction codes.
173 citations
TL;DR: In this article, the color distribution of white LEDs was analyzed using the Monte Carlo ray tracing method and five packaging methods were investigated and the location of the phosphor layer was varied.
Abstract: Uniform color distribution is essential for the packaging of light emitting diodes (LEDs). The Monte Carlo ray tracing method is applied to analyze the color distribution of white LEDs. Five packaging methods are investigated and the location of phosphor layer is varied. Results reveal that the packaging method is the primary factor affecting the color distribution and a nonreflector packaging method presents better color uniformity. The location of phosphor has a small impact on the color uniformity but remote location, if too far, can reduce the uniformity significantly. The reduction of color uniformity may exceed 88%.
171 citations
TL;DR: In this article, a novel approach to the measurement of microwave frequency based on optical power monitoring is proposed and demonstrated, where the microwave signal with its frequency to be measured is modulated on two optical carriers with their wavelengths set at one peak and one valley of the spectral response of a sinusoidal filter.
Abstract: A novel approach to the measurement of microwave frequency based on optical power monitoring is proposed and demonstrated. The microwave signal with its frequency to be measured is modulated on two optical carriers with their wavelengths set at one peak and one valley of the spectral response of a sinusoidal filter. The modulation is performed by a Mach-Zehnder modulator that is biased to suppress the optical carriers. A mathematical expression relating the optical powers from the two wavelength channels and the microwave frequency to be measured is developed. By simply monitoring the optical powers at the outputs of the two wavelength channels, the microwave frequency can be evaluated. A proof-of-concept experiment is implemented. Frequency measurement with good accuracy for microwave signals at different power levels is realized.
164 citations
TL;DR: In this paper, the authors analyzed theoretically and experimentally the linewidth of the first harmonic of the photocurrent (radio-frequency (RF) linwidth) in monolithic passively mode-locked semiconductor lasers.
Abstract: We have analyzed theoretically and experimentally the linewidth of the first harmonic of the photocurrent (radio-frequency (RF) linewidth) in monolithic passively mode-locked semiconductor lasers. Due to the absence of restoring force, the timing jitter is directly related to the RF linewidth, avoiding possible underestimations made with conventional methods of phase noise measurement. The RF linewidth is also analytically related to the pulse characteristics using Haus's model. The timing stability performance of a promising two-section quantum-dot laser is presented using RF linewidth measurements. Experimental evolution of the RF linewidth with power and pulsewidth is finally compared to the analytical expression.
158 citations
TL;DR: In this article, a novel architecture for orthogonal frequency-division-multiplexing (OFDM) wavelength-division multiplexing passive optical network with centralized lightwave was proposed and experimentally demonstrated.
Abstract: We have proposed and experimentally demonstrated a novel architecture for orthogonal frequency-division- multiplexing (OFDM) wavelength-division-multiplexing passive optical network with centralized lightwave. In this architecture, 16 quadrature amplitude modulation intensity-modulated OFDM signals at 10 Gb/s are utilized for downstream transmission. A wavelength-reuse scheme is employed to carry the upstream data to reduce the cost at optical network unit. By using one intensity modulator, the downstream signal is remodulated for upstream on-off keying (OOK) data at 2.5 Gb/s based on its return-to-zero shape waveform. We have also studied the fading effect caused by double-sideband (DSB) downstream signals. Measurement results show that 2.5-dB power penalty is caused by the fading effect. The fading effect can be removed when the DSB OFDM downstream signals are converted to single sideband (SSB) after vestigial filtering. The power penalty is negligible for both SSB OFDM downstream and the remodulated OOK upstream signals after over 25-km standard single-mode-fiber transmission. Index
156 citations
TL;DR: In this article, a distributed feedback semiconductor laser with optical feedback is employed as the chaotic laser and the bandwidth of the chaotic signal is enhanced roughly three times by optical injection into chaotic laser compared with the bandwidth when there is no optical injection.
Abstract: Bandwidth enhancement of chaotic signal generated from chaotic laser by using continuous-wave optical injection is experimentally demonstrated. A distributed feedback semiconductor laser with optical feedback is employed as the chaotic laser. The bandwidth of the chaotic signal is enhanced roughly three times by optical injection into the chaotic laser compared with the bandwidth when there is no optical injection.
TL;DR: In this article, the authors investigate the signal integrity in silicon photonic nanowire waveguides for wavelength-division-multiplexed optical signals and demonstrate the feasibility of ultra-high-bandwidth integrated photonic networks by transmitting a 1.28-Tb/s data stream (32 wavelengths times 40-Gb/s) through a 5-cm-long silicon wire.
Abstract: An investigation of signal integrity in silicon photonic nanowire waveguides is performed for wavelength-division-multiplexed optical signals. First, we demonstrate the feasibility of ultrahigh-bandwidth integrated photonic networks by transmitting a 1.28-Tb/s data stream (32 wavelengths times 40-Gb/s) through a 5-cm-long silicon wire. Next, the crosstalk induced in the highly confined waveguide is evaluated, while varying the number of wavelength channels, with bit-error-rate measurements at 10 Gb/s per channel. The power penalty of a 24-channel signal is 3.3 dB, while the power penalty of a single-channel signal is 0.6 dB. Finally, single-channel power penalty measurements are taken over a wide range of input powers and indicate negligible change for launch powers of up to 7 dBm.
TL;DR: In this paper, a chaotic correlation optical time domain reflectometer with millimeter and range independent spatial resolution was proposed, using chaotic waveforms generated from a laser diode with an optical fiber ring feedback.
Abstract: We propose a novel technique for chaotic correlation optical time domain reflectometer with millimeter and range- independent spatial resolution. Utilizing chaotic waveforms generated from a laser diode with an optical fiber ring feedback, a proof-of-concept experiment is demonstrated with 6-cm spatial resolution in the 0 ~ 140 m range, which is limited by the bandwidth of the real-time oscilloscope used.
TL;DR: In this article, a frequency quadrupling system using a single integrated Mach-Zehnder modulator without a narrowband optical filter was proposed to remove undesired optical sidebands.
Abstract: This letter demonstrates a novel method to generate high-purity optical millimeter-wave signals with carrier suppression by using a frequency quadrupling technique. To the authors' knowledge, this is the first time that a frequency quadrupling system requires only a single integrated Mach-Zehnder modulator without a narrowband optical filter to remove undesired optical sidebands. Since no optical filter is needed, fast frequency tuning is straightforward and this approach will be particularly attractive for optical up-conversion in wavelength-division-multiplexing radio-over-fiber systems. This letter provides both theoretical analysis and experimental demonstration. The generated optical millimeter-wave signals have very high quality with an optical carrier and harmonic distortion suppression ratio of more than 38 and 36 dB at 40 and 72 GHz, respectively.
TL;DR: In this paper, a Fourier transform white-light interferometry for absolute measurement of fiber-optic extrinsic Fabry-Perot interferometric sensors is presented.
Abstract: A Fourier transform white-light interferometry for the absolute measurement of fiber-optic extrinsic Fabry-Perot interferometric sensors is presented The continuous test shows the variation is plusmn03 mum when measuring a cavity length of 2300 mum By combining with an average calculation, the variation of the measured results is only plusmn10 nm
TL;DR: In this article, a theory and experimentally verify ultraflat comb generation by dual-sine-wave phase-only modulation is proposed and a single optical element is used to generate two optical spectra with 11 comb lines and 1.9dB flatness.
Abstract: We propose a theory and experimentally verify ultraflat comb generation by dual-sine-wave phase-only modulation. This novel approach requires a single optical element and is very practical and efficient in terms of both power budget and bandwidth. Using this approach, we have generated two optical spectra, one with 11 comb lines and 1.9-dB flatness and the other with 9 comb lines and 0.8-dB flatness.
TL;DR: In this article, the use of an ultra wideband (UWB) radio technique is proposed as a viable solution for the distribution of high-definition audio/video content in fiber-to-the-home (FTTH) networks.
Abstract: The use of an ultra-wideband (UWB) radio technique is proposed as a viable solution for the distribution of high-definition audio/video content in fiber-to-the-home (FTTH) networks. The approach suitability is demonstrated by the transmission of standards-based UWB signals at 1.25 Gb/s along different FTTH fiber links with 25 km up to 60 km of standard single-mode fiber length in a laboratory experiment. Experimental results suggest that orthogonal frequency-division-multiplexed UWB signals exhibit better transmission performance in FFTH networks than impulse radio UWB signals.
TL;DR: In this article, a distributed Bragg reflector silicon evanescent laser operating continuous wave at 1596 nm was presented, and the lasing threshold and maximum output power were 65 mA and 11 mW, respectively.
Abstract: We report a distributed Bragg reflector silicon evanescent laser operating continuous wave at 1596 nm. The lasing threshold and maximum output power are 65 mA and 11 mW, respectively. The device generates open eye-diagrams under direct modulation at data rates up to 4 Gb/s.
TL;DR: A combination of orthogonal frequency-division multiplexing and compatible single-sideband modulation (CompSSB) using a standard direct-detection scheme is suggested to overcome chromatic dispersion without explicit compensation.
Abstract: A combination of orthogonal frequency-division multiplexing (OFDM) and compatible single-sideband modulation (CompSSB) using a standard direct-detection scheme is suggested to overcome chromatic dispersion without explicit compensation. Since the proposed type of SSB modulation does not require a spectral gap between optical carrier and subcarriers, it is highly spectrally efficient and the complexity in the analogue part is reduced compared to known direct-detection schemes for OFDM.
TL;DR: In this paper, a waveguide grating coupler that reduces back reflection and enhances coupling efficiency was proposed. But the coupler was not suitable for the fabrication process fluctuations which may lead to random variations in slot width and the duty cycle of the grating periods.
Abstract: We report the simulation, fabrication, and measurement results of a waveguide grating coupler that could efficiently couple light between submicrometer-sized planar waveguides and vertical optical fibers. The coupler comprises a section of chirped grating which reduces back reflection and enhances coupling efficiency. Coupling efficiency of over 34% was measured and a 3-dB bandwidth of 45 nm was obtained. An experimental study showed that the coupling efficiency was tolerant to fabrication process fluctuations which may lead to random variations in slot width and the duty cycle of the grating periods.
TL;DR: In this article, a highly nonlinear photonic crystal fiber (HNL-PCF) based on an octagonal structure with isosceles triangular-latticed cladding is proposed for the telecommunication window.
Abstract: A highly nonlinear photonic crystal fiber (HNL-PCF) based on an octagonal structure with isosceles triangular-latticed cladding is proposed for the telecommunication window. The finite-difference method with anisotropic perfectly matched boundary layer is used to investigate the guiding properties. It is demonstrated that it is possible to design a simple HNL low-loss dispersion-flattened PCF with a nonlinear coefficient of the order 27 W-1km-1 at a 1.55-mum wavelength. According to simulation, ultraflattened dispersion of 0 plusmn 0.5 ps/nm/km is obtained in a 1.46- to 1.66-mum wavelength with low confinement losses less than 0.06 dB/km in the entire band of interest.
TL;DR: In this article, an ultracompact four-channel planar concave grating demultiplexer fabricated in a complimentary metal-oxide-semiconductor line using deep-ultraviolet lithography is presented.
Abstract: We present measurement results of an ultracompact four-channel silicon-on-insulator planar concave grating demultiplexer fabricated in a complimentary metal-oxide-semiconductor line using deep-ultraviolet lithography. The demultiplexer has four output channels separated by 20 nm and a footprint of only 280 mum times 150 mum. The crosstalk is better than 25 dB and the on-chip loss is drastically reduced down to 1.9 dB by replacing each facet by a second-order Bragg reflector.
TL;DR: In this article, the performance of a compact multi-wavelength laser (MWL) source heterogeneously integrated with and coupled to a silicon-on-insulator (SOI) waveguide circuit is reported.
Abstract: We report on the performance of a compact multi- wavelength laser (MWL) source heterogeneously integrated with and coupled to a silicon-on-insulator (SOI) waveguide circuit. The MWL consists of four InP-based microdisk lasers, coupled to a common SOI wire waveguide. The microdisk lasers operate in continuous-wave regime at room temperature, with a threshold current around 0.9 mA and a waveguide-coupled slope efficiency of up to 8 muW/mA, for a microdisk diameter of 7.5 mum. The output spectrum contains four laser peaks uniformly distributed within the free-spectral range of a single microdisk. While thermal crosstalk is negligible, laser peak output powers vary up to 8 dB for equal microdisk drive currents, as a result of loss due to coupling with higher order modes supported by the 1-mum-thick microdisks. This nonuniformity could be eliminated by reducing the microdisk thickness.
TL;DR: In this paper, an approach for the measurement of microwave frequency in the optical domain with adjustable measurement range and resolution is proposed, where two optical wavelengths with a large wavelength spacing are modulated by an unknown microwave signal in a Mach-Zehnder modulator.
Abstract: We propose an approach for the measurement of microwave frequency in the optical domain with adjustable measurement range and resolution. In the proposed approach, two optical wavelengths with a large wavelength spacing are modulated by an unknown microwave signal in a Mach-Zehnder modulator (MZM). The optical output from the MZM is sent to a dispersive fiber to introduce different chromatic dispersions, leading to different microwave power penalties. The two wavelengths are then separated, with the microwave powers measured by two photodetectors. A fixed relationship between the microwave power ratio and the microwave frequency is established. The microwave frequency is estimated by measuring the two microwave powers. The frequency measurement range and resolution can be adjusted by tuning the wavelength spacing. Different frequency measurement ranges and resolutions are demonstrated experimentally.
TL;DR: In this paper, a single-sideband modulation with low-frequency local oscillator (LO) signals is proposed and experimentally demonstrated to generate optical mm-wave (mm-wave) signals.
Abstract: We have proposed and experimentally demonstrated a novel scheme to generate optical millimeter-wave (mm-wave) signals by using single-sideband modulation with low-frequency local oscillator (LO) signals. In this architecture, by incorporating the proper dc bias of the modulator in central office, the optical mm-wave carriers are generated with two times frequency of the LO signal while largely reducing the bandwidth requirement of the modulator. We quantify the optical carrier-to-sideband ratio (CSR) of downstream transmission in this radio-over-fiber (ROF) link and establish that the performance of the ROF system can be significantly improved when the optical signals are transmitted at CSR equal to 0 dB.
TL;DR: In this paper, a vertical light-emitting diodes (LEDs) were successfully fabricated by a chemical lift-off process using a selectively etchable CrN buffer layer.
Abstract: Vertical light-emitting diodes (LEDs) were successfully fabricated by a chemical lift-off process using a selectively etchable CrN buffer layer. The novel CrN metallic layer worked well as a buffer layer for growth of the GaN LED and was etched out clearly during selective chemical etching. The vertical LED by chemical lift-off showed very good current-voltage performance with low series resistance of 0.65 Omega and low operated voltage of 3.11 V at 350 mA. Also, this device could be operated at a much higher injection forward current (1118 mA at 3.70 V) by thermally conductive metal substrate which enabled the high current operation with excellent heat dissipation.
TL;DR: In this paper, a novel approach to generating linearly chirped microwave pulses in the optical domain based on spectral shaping and linear frequency-to-time mapping is proposed and experimentally demonstrated.
Abstract: A novel approach to generating linearly chirped microwave pulses in the optical domain based on spectral shaping and linear frequency-to-time mapping is proposed and experimentally demonstrated. In the proposed system, the spectrum of a femtosecond pulse generated by a mode-locked fiber laser is spectrum-shaped by an optical filter that consists of two superimposed chirped fiber Bragg gratings (SI-CFBGs) with different chirp rates. The SI-CFBGs form a Fabry-Perot cavity with a cavity length linearly dependent on the resonance wavelength, thus a spectral response with an increased or decreased free spectral range is generated. A chirped microwave pulse with the pulse shape identical to the shaped spectrum is obtained at the output of a high-speed photodetector thanks to the frequency-to-time mapping in a dispersive device. The proposed technique is experimentally demonstrated, a linearly chirped microwave pulse with a central frequency of 15 GHz and a chirp rate of 0.0217 GHz/ps is experimentally generated.
TL;DR: In this paper, a simple and stable single-longitudinal mode (SLM) erbium-doped fiber laser is presented, which consists of an apodized fiber Bragg grating and a high finesse FBG-based Fabry-Perot (FP) etalon in the ring cavity.
Abstract: We present a simple and stable single-longitudinal-mode (SLM) erbium-doped fiber laser. It consists of an apodized fiber Bragg grating (FBG) and a high finesse FBG-based Fabry-Perot (FP) etalon in the ring cavity. The apodized FBG acts as a wavelength discriminative component selecting a few oscillation modes while the FP etalon serves as narrow bandwidth bandpass filter to further discriminate and select SLM efficiently. Stable SLM laser output at 1.55 m with linewidth about 2.5 kHz is acquired. Furthermore, continuous wavelength tuning over 8 nm is achieved by simultaneously applying strain to the FBG and the FP etalon.
TL;DR: In this article, the performance of a continuous-wave Dy:GeAsGaSe chalcogenide glass fiber laser operating on the 6H11/2 rarr 6H13/2 transition at 4.2-4.7 mum is studied using numerical modeling.
Abstract: The performance of a continuous-wave Dy:GeAsGaSe chalcogenide glass fiber laser operating on the 6H11/2 rarr 6H13/2 transition at 4.2-4.7 mum is studied using numerical modeling. A double-clad fiber geometry is assumed, with direct pumping of the 6H11/2 level at 1.7 mum. It is shown that simultaneous lasing on the 6H13/2 rarr 6H15/2 transition serves to effectively depopulate the 6H11/2 level and significantly improve the efficiency and power scalability. A slope efficiency of 0.16 is calculated when the fiber loss is 1 dB/m. For efficient operation, it is necessary to keep the fiber loss below ap5 dB/m.
TL;DR: In this article, a cone-shape-patterned sapphire substrate (CSPSS) was used to grow InGaN-GaN thin films, which showed a shorter lattice constant of 5.1877 Aring along the c-axis for the GaN thin film grown on CSPSS, compared to 5.1913 A for the samples grown on a conventional sappire substrate (CSS).
Abstract: High-quality InGaN-GaN film was grown on a cone-shape-patterned sapphire substrate (CSPSS) by using metal-oganic chemical vapor deposition. The growth mode of GaN on CSPSS was similar to that of the epitaxial lateral overgrowth (ELOG), because the growth, in the initial stage, proceeds only on flat basal sapphire substrate and there is no preferential growth plane on the cone region. An analysis of X-ray diffraction showed a shorter lattice constant of 5.1877 Aring along the c-axis for the GaN thin films grown on CSPSS, compared to 5.1913 A for the samples grown on a conventional sapphire substrate (CSS). This is because the ELOG-like mode of the GaN layer over the cone-shaped region results in less lattice mismatch and incoherency between the GaN layer and the sapphire substrate. The output power of a sideview light-emitting diode (LED) grown on CSPSS was estimated to be 7.3 mW at a forward current of 20 mA, which is improved by 34% compared to that of an LED grown on CSS. The significant enhancement in output power is attributed to both the increase of the extraction efficiency, resulted from the increase in photon escaping probability due to enhanced light scattering at the CSPSS, and the improvement of the crystal quality due to the reduction of dislocation.