Showing papers in "IEEE Photonics Technology Letters in 1991"
TL;DR: In this paper, the authors describe the design of an integrated N*N multiplexer capable of simultaneously multiplexing and demultiplexing a large number (up to about 50) of input and output wavelength channels.
Abstract: The author describes the design of an integrated N*N multiplexer capable of simultaneously multiplexing and demultiplexing a large number (up to about 50) of input and output wavelength channels. The multiplexer is a generalization of the 2*2 Mach-Zehnder multiplexer. It consists of two N*M star couplers connected by M paths of unequal length. Aberrations caused by mutual coupling in the waveguide arrays are minimized by a correction scheme that causes each star coupler to accurately perform a Fourier transformation. The multiplexer should be useful as a wavelength routing device for long haul and local area networks. >
540Â citations
TL;DR: In this paper, the authors report the measured performance of an integrated N*N multiplexer fabricated using SiO/sub 2/Si waveguides, and they show that the insertion loss for N=7 was typically lower than 2.5 dB, and crosstalk was less than -25 dB.
Abstract: The authors report the measured performance of an integrated N*N multiplexer fabricated using SiO/sub 2//Si waveguides. The insertion loss for N=7 was typically lower than 2.5 dB, and crosstalk was less than -25 dB. The multiplexer response is approximately periodic. In each period the multiplexer accepts, from each input waveguide, a total of N channels, and it efficiently transmits each channel to a particular output port. Similarly, each output port receives N channels, one from each input port. Thus, the total number of channels that can be transmitted simultaneously is N/sup 2/, which requires N optical frequencies. >
319Â citations
TL;DR: In this paper, the system fading caused by polarization-mode dispersion was investigated at 1.7 Gb/s using highly-birefringent, dispersion-shifted fiber at a fixed receiver power.
Abstract: System fading caused by polarization-mode dispersion is investigated at 1.7 Gb/s using highly-birefringent, dispersion-shifted fiber at 1.55 mu m. The observed fading, which is manifested by random fluctuations of the bit error rate for a fixed receiver power, is observed to depend on the environmental conditions of the fiber, with the time constant for fading varying from minutes to hours depending on the rate of change of the ambient temperature. The mean dispersion penalty inferred from the observed fluctuations in the bit error rate is consistent with a square-law dependence on the polarization-mode dispersion for small penalties. >
273Â citations
TL;DR: In this article, a novel theory of nonlinear gain, well-barrier hole burning, was proposed to explain the wide variations in the damping behavior of quantum well lasers.
Abstract: The reported wide variations in the damping behavior of quantum well lasers are explained by a novel theory of nonlinear gain, well-barrier hole burning. In the model a spatial hole develops perpendicular to the active region involving carriers moving between the wells and the barrier/confinement layers. The modified rate equations describing well-barrier hole burning are presented. An analytical approximation for the nonlinear gain coefficient epsilon , valid only under certain conditions, is given. A numerical solution is given for the case of high photon densities and large capture-times. It is shown how well-barrier hole burning explains the measurements of the increased spontaneous emission from the barrier/confinement region above threshold. Various higher-than-expected damping rates reported in some quantum well lasers are shown to be consistent with the model. >
212Â citations
TL;DR: In this paper, the value of the modulation chirp parameter that minimizes the transmission power penalty caused by fiber chromatic dispersion was experimentally identified using a unique Ti:LiNbO/sub 3/ modulator.
Abstract: Using a unique Ti:LiNbO/sub 3/ modulator, the value of the modulation chirp parameter that minimizes the transmission power penalty caused by fiber chromatic dispersion was experimentally identified. System experiments at 5 Gb/s using nonreturn-to-zero (NRZ) amplitude-shift-keyed (ASK) transmission with direct detection reception are discussed, and the optimum values of the modulation chirp parameter versus distance for transmission at 1.5 mu m wavelength over fibre having zero dispersion at 1.3 mu m are identified. 5 Gb/s NRZ transmission was achieved through distances of 128, 192, and 256 km of conventional fiber while incurring dispersion penalties of -0.5, 0.1, and 1.1 dB respectively, by operating at the quantum chirp value. >
212Â citations
TL;DR: In this article, a tunable signal gain equalization was demonstrated in three-stage Er/sup 3+/-doped fiber amplifiers using a waveguide type Mach-Zehnder (MZ) optical fiber.
Abstract: Tunable signal gain equalization is demonstrated in three-stage Er/sup 3+/-doped fiber amplifiers using a waveguide type Mach-Zehnder (MZ) optical fiber. A 29-channel multiplexed system is examined where signal wavelengths are positioned from 1.548 to 1.555 mu m. By adjusting the MZ transmittance with the external control current, tunable gain equalization is achieved at the output of each amplifier. >
194Â citations
TL;DR: In this article, eight different fibers were studied to examine upconversion as a function of erbium concentration below 1000 ppm by weight, and a computer model of two-particle up-conversion made it possible to estimate the up conversion coefficient used in a rate-equation model.
Abstract: Eight different fibers were studied to examine upconversion as a function of erbium concentration below 1000 ppm by weight. These experiments and a computer model of two-particle upconversion made it possible to estimate the upconversion coefficient used in a rate-equation model. A strong correlation was found between amplification reduction and parasitic upconversion in fibers with both Ge- and Ge/Al/P-cores when the erbium-doping concentration is in the range 70-840 ppm by weight. When plotting maximum amplification versus the 980 luminescence on a logarithmic scale, the slope was approximately -2 irrespective of the host material. The validity of the assumed two-particle upconversion model up to 4 mW of pump power is shown. >
169Â citations
TL;DR: In this article, an optical notch filter was incorporated within the length of all erbium-doped fiber amplifier, which made it possible to enhance the amplifier gain at wavelengths around 1550 nm.
Abstract: An optical notch filter was incorporated within the length of all erbium-doped fiber amplifier. Careful choice of the filter characteristics and location made it possible to enhance the amplifier gain at wavelengths around 1550 nm. An amplifier with 27-dB gain and 33-nm bandwidth was demonstrated. The saturation characteristics of the amplifier were uniform across its gain spectrum, making it ideal for wavelength division multiplexed (WDM) application. >
157Â citations
TL;DR: In this paper, a light emitting diode was grown on a GaAs substrate, lifted off, aligned and selectively deposited onto a silicon host substrate, and electrically contacted and tested.
Abstract: The authors report the selective and alignable deposition of patterned thin-film epitaxial GaAs/GaAlAs devices onto a host substrate such as silicon for low cost, manufacturable hybrid integrated optoelectronic circuits. The authors use a thin polyimide diaphragm as the transparent transfer medium for these patterned epitaxial devices. Each of these devices or a group of these devices on the polyimide is then optically aligned and selectively deposited onto the host substrate. The use of the polyimide transfer diaphragm also allows both the bottom and the top of the device to be processed while under substrate support. Using this technique, a light emitting diode 50*50 mu m in area and 2 mu m thick was grown on a GaAs substrate, lifted off, aligned and selectively deposited onto a silicon host substrate, and electrically contacted and tested. >
156Â citations
TL;DR: In this article, a simple model for carrier heating in semiconductor lasers from which the temperature dynamics of the electron and hole distributions can be calculated is presented and analytical expressions for two new contributions to the nonlinear gain coefficient, in are derived, which reflect carrier heating due to stimulated emission and free carrier absorption.
Abstract: A simple model is presented for carrier heating in semiconductor lasers from which the temperature dynamics of the electron and hole distributions can be calculated. Analytical expressions for two new contributions to the nonlinear gain coefficient, in are derived, which reflect carrier heating due to stimulated emission and free carrier absorption. In typical cases, carrier heating and spectral holeburning are found to give comparable contributions to nonlinear gain suppression. The results are in good agreement with recent measurements on InGaAsP laser diodes. >
154Â citations
TL;DR: In this article, an integrated standing-wave, single frequency, erbium fiber laser having a laser linewidth of less than 47 kHz was reported, which incorporated two highly reflective intracore Bragg reflectors which provided both cavity feedback and adequate longitudinal mode discrimination.
Abstract: An integrated standing-wave, single frequency, erbium fiber laser having a laser linewidth of less than 47 kHz is reported. The monolithic fiber laser incorporated two highly reflective intracore Bragg reflectors which provide both cavity feedback and adequate longitudinal mode discrimination. The narrow linewidth single-mode operation and monolithic construction may make this a valuable communications/sensor source. >
TL;DR: In this article, it was shown that the dynamics of optical pulse propagation in lumped amplified systems is described by the lossless nonlinear Schrodinger equation under the condition that the amplifier spacing is short compared to the nonlinear evolution length scale.
Abstract: It is shown that the dynamics of optical pulse propagation in lumped amplified systems is described by the lossless nonlinear Schrodinger equation under the condition that the amplifier spacing is short compared to the nonlinear evolution length scale. The errors involved in this description are quantified and are on the order of the square of the amplifier spacing. The authors also consider an alternative method of pulse preemphasis which has been proposed, and they show how it relates to the average soliton method presented. >
TL;DR: In this article, the authors derived expressions for second and third-order distortion using the time-domain form of the field envelope wave equation, and showed that the distortion predicted by these expressions agrees well with numerical simulation and reasonably well with experimental data.
Abstract: Transmission through dispersive and nonlinear optical fibers produces distortion in subcarrier intensity-modulated systems. Analytic expressions for second- and third-order distortion are derived using the time-domain form of the field envelope wave equation. The distortion predicted by these expressions agrees well with numerical simulation and reasonably well with experimental data. Significant composite second-order distortion is predicted in typical 1.55 mu m cable television systems. >
TL;DR: In this paper, the effects of external optical feedback on the spectra of VCSELs (vertical-cavity surface-emitting lasers) were measured and it was shown that the sensitivity to optical feedback is comparable to that of conventional edge-emiting lasers such as DFBs despite their significantly different structures.
Abstract: The measurement of the effects of external optical feedback on the spectra of VCSELs (vertical-cavity surface-emitting lasers) is reported. It is surprising that VCSELs have a sensitivity to optical feedback comparable to that of conventional edge-emitting lasers such as DFBs despite their significantly different structures. This is because the extremely short cavity length of VCSELs negates the effects of their highly reflective output mirrors. As in edge-emitting lasers, VCSELs exhibit well-defined regimes of feedback effects in their spectra. Since optical isolators cannot be easily applied to VCSELs due to their array structure, these lasers may be most useful in applications which are not sensitive to the spectral qualities of the light source. >
TL;DR: In this paper, loss and gain coefficients were used to evaluate fiber performance in 980-nm or 1480-nm pumped optical amplifiers with germano-silicate core fibers.
Abstract: Erbium-doped fibers are characterized using loss and gain coefficients, and one amplifier saturation parameter. With a large-signal amplifier model that resolves the amplified spontaneous emission spectrum, these easily measured parameters allow the fiber performance in 980-nm or 1480-nm pumped optical amplifiers to be assessed rapidly. In tests at 980-nm pump wavelength, good agreement between the theoretical and experimentally measured gains was obtained with amplifiers having either germano-silicate or germano-alumino-silicate core fibers. >
TL;DR: In this article, a highly linear electrooptic modulator has been designed, fabricated, and evaluated, which consists of only a simple modification to the directional coupler, and two-tone testing has demonstrated that, for an optical modulation depth of 30% per channel, the third-order intermodulation distortion is more than 30 dB lower than that of the conventional directional coupling or Mach-Zehnder modulators.
Abstract: A highly linear electrooptic modulator has been designed, fabricated, and evaluated. The design of this modulator consists of only a simple modification to the directional coupler. Two-tone testing has demonstrated that, for an optical modulation depth of 30% per channel, the third-order intermodulation distortion is more than 30 dB lower than that of the conventional directional coupler or Mach-Zehnder modulators. This improvement was not observed to be accompanied by any increase in second harmonic distortion. Also included are results of two-tone computer simulations which predict the improvement in linearity of this device for a range of modulation depths. >
TL;DR: In this article, a continuous grading of the heterointerfaces in the Bragg reflectors eliminated the energy-band discontinuities, thus improving carrier transport and resulting in a substantial reduction in the series resistance and threshold voltage of the laser diodes.
Abstract: GaAs/AlGaAs vertical-cavity top-surface-emitting lasers (VCSELs) with a continuously graded mirror composition have been grown by MOCVD, and planar devices with proton-implant current confinement have been characterized. Continuous grading of the heterointerfaces in the Bragg reflectors eliminated the energy-band discontinuities, thus improving carrier transport and resulting in a substantial reduction in the series resistance and threshold voltage of the laser diodes. These VCSELs have excellent room-temperature CW electrical characteristics, including some of the lowest series resistances, highest power efficiencies and lowest operating voltages ever reported. >
TL;DR: In this article, a finite-difference time-domain approach that solves the scalar wave equations is proposed and validated, and the propagation, reflection, scattering, and radiation of electromagnetic waves in weakly guiding optical devices are described explicitly in the time domain.
Abstract: A finite-difference time-domain approach that solves the scalar wave equations is proposed and validated. The propagation, reflection, scattering, and radiation of electromagnetic waves in weakly guiding optical devices are described explicitly in the time domain. The method is applied to the simulation of guided-wave devices such as directional couplers and distributed feedback reflectors. A comparison to known analytical solutions shows good agreement. >
NEC1
TL;DR: In this paper, the highly nondegenerate four-wave mixing (HNDFWM) process was applied to a 1.5- mu m InGaAsP semiconductor laser in optical-frequency conversion experiments on 1-Gb/s intensity-modulated signals in a 1-THz conversion range.
Abstract: The authors report the application of the highly nondegenerate four-wave mixing (HNDFWM) process to a 1.5- mu m InGaAsP semiconductor laser in optical-frequency conversion experiments on 1-Gb/s intensity-modulated signals in a 1-THz conversion range. This conversion is based on a subpicosecond ultrafast nonlinear gain process in the laser. The HNDFWM was generated through the use of an injection-locking technique. The possibility of applying this phenomenon to an optical fiber dispersion compensator is also discussed. >
TL;DR: In this article, it was shown that dispersion-shifted fiber can be employed in place of the regular fiber in order to counteract the dispersion effect, and other possible ways to reduce distortion are to use lasers with reduced chirp, presumably with a multiquantum-well laser structure, or lasers with well-controlled spatial hole burning.
Abstract: Experimental and theoretical results have shown that the composite second-order (CSO) nonlinearity of 1.5- mu m AM analog laser links is inadvertently affected by the coupling of laser chirp with fiber dispersion in regular single-mode fiber. To counteract the dispersion effect, it is shown that dispersion-shifted fiber can be employed in place of the regular fiber. Other possible ways to reduce distortion are to use lasers with reduced chirp, presumably with a multiquantum-well laser structure, or lasers with well-controlled spatial hole burning. Short fiber spans ( >
TL;DR: In this paper, the lasing action of organically modified silica gel (ORMOSIL) host media doped with laser dyes, rhodamine 6G, and Rhodamine B is described.
Abstract: The lasing action of organically modified silica gel (ORMOSIL) host media doped with laser dyes, rhodamine 6G, and rhodamine B is described. The laser is a monolithic design pumped transversely by a pulsed Nd:YAG laser. Conversion efficiencies as high as 39% were observed with usable lifetimes exceeding 50000 pulses. With a 500- mu J pump source, typical output energies of 200 mu J were produced. The values obtained for the lifetime go well beyond the photostability behavior reported in prior studies. Moreover, this work shows that a simple monolithic solid-state laser pumped by a pulsed Nd:YAG is capable of producing broadband spectral output of 100-kW peak power. More detailed investigations are currently underway with different dyes and pump cavity configurations. >
TL;DR: In this paper, the linewidth enhancement factor was measured with a simple dynamic self-heterodyne method and the carrier lifetime was investigated with a SOA without antireflection coating.
Abstract: Semiconductor optical amplifiers are used for investigation of the effective carrier lifetime and the linewidth enhancement factor. Contrary to semiconductor lasers, semiconductor optical amplifiers allow measurement at high levels of injected carrier density. The carrier lifetime and the linewidth enhancement factor are measured with a simple dynamic self-heterodyne method. Carrier lifetimes of 750 ps at the threshold current for the SOA without antireflection coating and 200 ps at high injection have been found. The linewidth enhancement factor is measured to be between 4 and 17 which fits with a simple empirical expression. >
TL;DR: In this paper, a two-contact InGaAsP semiconductor self-pulsating laser diode was used for all-optical clock extraction from 5 Gb/s RZ data.
Abstract: All-optical clock extraction from 5 Gb/s RZ data is demonstrated using a two-contact InGaAsP semiconductor self-pulsating laser diode. The saturable absorber region of the device was doped with zinc ions to reduce the carrier lifetime in this region such that strong self pulsations at frequencies up to 5.2 GHz were obtained. Injection of a 10- mu W optical data signal at a wavelength close to one of the Fabry-Perot wavelengths was sufficient to synchronize the self pulsations to the incoming data stream. The measured 3-dB RF electrical bandwidth of the synchronized optical clock signal was 10 Hz, approximately the same as that of the electrical transmitter clock. Initial bit-error-rate measurements for 2/sup 7/-1 5 Gb/s data result in a 0.5-dB receiver sensitivity penalty when using the optical clock signal compared to the transmitter clock. >
TL;DR: In this paper, a polarization-insensitive optical amplifier was realized at a wavelength of 1.55 mu m. The active layer consisted of a tensile-strained-barrier multiple quantum well (MQW) structure.
Abstract: A polarization-insensitive semiconductor optical amplifier was realized at a wavelength of 1.55 mu m. The active layer consisted of a tensile-strained-barrier multiple quantum well (MQW) structure. At a driving current of 150 mA, no dependence of the saturation characteristics on modes was obtained. The saturation output power at which the gain decreases 3 dB is 13.3 dBm. A slightly higher saturation output power of 14 dBm was measured at a driving current of 200 mA. No large difference was observed between transverse-electric (TE) and transverse-magnetic (TM) modes. A high gain of 27.5 dB at a polarization sensitivity of 0.5 dB and a high saturation output of 14 dBm were realized simultaneously by using a longer device with reduced residual facet reflectivities. >
TL;DR: In this article, a single wavelength tunable distributed-feedback laser diode (DFB LD) in the 1.65-mu m region is used to emit two different wavelengths of equal power which are modulated 180 degrees out of phase with each other at a frequency of 10 kHz.
Abstract: In the method described a single wavelength tunable distributed-feedback laser diode (DFB LD) in the 1.65- mu m region is used to emit two different wavelengths of equal power which are modulated 180 degrees out of phase with each other at a frequency of 10 kHz. One of the two wavelengths is frequency stabilized via a methane gas cell and a feedback system equipped with a lock-in amplifier. A sensitivity of 4 p.p.m.-m methane in 1-atm nitrogen has been achieved. This light source has greatly simplified the setup for the measurements of this kind. >
TL;DR: In this paper, a feedback-loop scheme based on a simple feedbackloop scheme was proposed to reduce transient gain fluctuations efficiently across the whole amplifier bandwidth using only a low-power optical feedback signal.
Abstract: Dynamic compensation of low-frequency gain fluctuations in saturated erbium-doped fiber amplifiers is demonstrated. This compensation, based on a simple feedback-loop scheme makes it possible to reduce transient gain fluctuations efficiently across the whole amplifier bandwidth using only a low-power optical feedback signal. Such an, automatic gain control technique could be applied to suppress data packet interference due to traffic bursts in multiple-access networks, as well as in the implementation of long-haul fiber systems using erbium fiber amplifiers. >
TL;DR: In this paper, a new photodetector structure is demonstrated that alleviates limitations imposed by the tradeoff between the transit-time contribution to the bandwidth and the quantum efficiency, and the external quantum efficiency has been enhanced by incorporating the structure into a resonant cavity.
Abstract: For p-i-n photodiodes and avalanche photodiodes (APDs) in the low-gain regime, there is a performance tradeoff between the transit-time contribution to the bandwidth and the quantum efficiency. A new photodetector structure is demonstrated that alleviates limitations imposed by this tradeoff. This structure utilizes a thin ( approximately=900 AA) depleted absorbing layer to reduce the transit time and achieve avalanche gain at low bias voltage (V/sub b/ approximately=9 V). The external quantum efficiency has been enhanced ( eta /sub e/>49%) by incorporating the structure into a resonant cavity. >
TL;DR: In this paper, a method for incorporating distributed feedback in a ridge waveguide laser by means of lateral gratings and a single growth step is discussed, where the necessary Bragg condition for distributed feedback is satisfied by etching gratings along the ridge in the top confining layer of the laser on either side of the contact stripe.
Abstract: A method for incorporating distributed feedback in a ridge waveguide laser by means of lateral gratings and a single growth step is discussed. The necessary Bragg condition for distributed feedback is satisfied by etching gratings along the ridge in the top confining layer of the laser on either side of the contact stripe. Both Fabry-Periot modes and a single emission peak away from the peak of the gain profile are observed in lasers with cleaved facets. The Bragg reflection emission peak does not shift with increasing drive current, which is characteristic of a distributed-feedback (DFB) laser. >
TL;DR: In this article, the authors studied the IM and FM characteristics of a vertical-cavity surface-emitting laser (VCSEM) at a very low bias (4.5 mA) and demonstrated five Gb/s pseudorandom direct intensity modulation with open eyes.
Abstract: The IM (intensity modulation) and FM (frequency modulation) characteristics of vertical-cavity surface-emitting lasers are studied. The laser has high FM efficiency and broad IM bandwidth (near 8 GHz) at a very low bias (4.5 mA). Five Gb/s pseudorandom direct intensity modulation of this laser with open eyes is demonstrated. >
TL;DR: In this article, the fabrication and characteristics of gain-coupled 1.55-mu m GaInAlAs quantum-well metal-clad ridge-waveguide distributed-feedback lasers are discussed.
Abstract: The fabrication and characteristics of gain-coupled 1.55- mu m GaInAlAs quantum-well metal-clad ridge-waveguide distributed-feedback lasers are discussed. The gain-coupling mechanism was provided by a thin ternary loss grating layer with an estimated gain-coupling strength of about 30/cm. For as-cleaved devices, the single-mode yield was as high as 70 and 95% for 600- and 800- mu m-long devices, respectively. Typical threshold currents were 40 and 55 mA, respectively. Both the high single-mode yield and the pronounced asymmetric spectra were calculated theoretically and give a strong indication that a significant amount of gain coupling was realized in the laser structure. For a 600- mu m-long device, a continuous-wave (CW) output power of 10 mW and a minimum linewidth of 1.6 MHz were measured. >