Journal of Lightwave Technology

Published by Institute of Electrical and Electronics Engineers
Online ISSN: 0733-8724
Publications
Article
Polarization independent (<0.01 dB) switching is achieved at 1.55 μm in a strongly guiding, fused tapered fiber null coupler acoustooptic switch. An intermediate degree of fusion of the dissimilarly sized fibers is shown experimentally to have the form birefringence required to render the mode-splitting coupler polarization insensitive. The effect of the degree of fiber fusion on the acoustic wavelength of flexural waves is studied theoretically and experimentally, and precise control over the degree of fiber fusion is obtained for coupler waist cross-sectional dimensions as small as 6 μm
 
Article
This paper studies integrated silicon photodiodes (PDs) implemented in standard CMOS technologies. A new PIN PD structure utilizing deep n-well is presented, and compared with conventional vertical and lateral PIN PDs at 850-nm wavelength and different bias conditions. Prototype PDs were fabricated in a 0.18-mum standard CMOS technology, and their DC, impulse and frequency responses were characterized. A 70 times 70 mum<sup>2</sup> PD with the new structure achieved a 3-dB bandwidth of 2.2 GHz in small signal at 5-V bias, whereas conventional lateral and vertical PIN PDs could only operate up to 0.94 GHz and 1.15 GHz, respectively. At 5-V bias, the impulse response of the new PD exhibited a full-width at half-maximum pulsewidth of 127 ps, versus 175 and 150 ps for the conventional lateral and vertical ones, respectively. At 15.5-V bias, the bandwidth of this new PD reached 3.13 GHz, with an impulse response pulsewidth of 102 ps. The responsivity of all prototype PDs was measured at approximately 0.14 A/W up to 10-V bias, which corresponded to a quantum efficiency of 20%. The responsivity of the new PD could be further increased to 0.4 A/W or 58% quantum efficiency, when operating in the avalanche region at 16.2-V bias.
 
Article
Several new glass fiber production processes have been studied in the past for low-cost production. Although some of them are still being considered for overcladding, mechanically shaped preforms (MSP) have been demonstrated to be the only remaining candidates to combine economic non CVD processing and low loss, with a published value of 0.63 dB/km and a size of 30 fkm/preform [1]. Improved processing has now resulted in a minimum loss of 0.27 dB/km at 1550 nm. Preforms capable of yielding 150 fkm have been produced. Although already considerably improved, reboiling during preform stretching and fiber pulling is identified as the last remaining problem of the process.
 
Article
A laminated structure composed of alternating layers of Ge and SiO <sub>2</sub> (Ge-LAMIPOL) is usable as a miniaturized polarizer at 790-850 nm in fiber optic gyroscopes, for instance. However, peeling of the sputter deposited layers, due to the weak binding strength between Ge and SiO<sub>2</sub>, is a serious problem during the slicing process in preparation for assembly in the fiber. In order to improve the adhesive strength, the 1-nm-thick Si layers are inserted between Ge and SiO<sub>2</sub> layers. The Si layer functions as the adhesive layer via the Si-O bonding formation in place of the weaker Ge-O bond. The new Ge-LAMIPOL, including 125 layers of (1-nm Si)/(4.5-nm Ge)/(1-nm Si)/ (800-nm SiO<sub>2</sub>) is successfully prepared without any fracture. The extinction ratio and the insertion loss were 51 and 0.33 dB at 850 nm, respectively, corresponding to 59.6 and 0.36 dB as the designed values
 
Article
Very high speed optical links are studied. Applicable areas for systems using light-emitting diodes (LED'S) or laser diodes (LD's) with short transmission length are clarified. A new type differential mode inversion (DMI) decoder is proposed and it is shown that the DMI code is suitable as the line code for very high speed intra-office optical links. By using DMI code. a 400-Mbit/s information rate optical transmission experiment employing a 1.3-μm InGaAsP LED and a 0.5-km graded-index multimode optical fiber (GIF) as well as a 1.6-Gbit/s information rate optical transmission experiment using a 1.3-μm InGaAsP/InP Fabry-Perot-type LD and a 10-km single-mode optical fiber (SMF) are carried out. These results show that the feasibility of a 400-Mbit/s intra-office optical link using the LED and GIF, as well as a 1.6-Gbit/s intra-office optical link using the LD and SMF, are confirmed and this optical transmission technology has high-speed performance up to 3.2 Gbit/s.
 
Article
We report an Er-doped superfluorescent fiber source (SFS) with a record mean-wavelength stability of ±0.5 ppm over 17 h. This breakthrough was achieved in a double-pass SFS by implementing several improvements, namely 1) controlling all the parameters that affect its mean wavelength, including the pump diode temperature and current, 2) reducing polarization-induced drifts in mean wavelength with a Faraday rotator mirror and a long Er-doped fiber (EDF), and 3) getting rid of polarization controllers to eliminate polarization-dependent loss. The long-term mean-wavelength variations of this SFS were due almost entirely to variations in the EDF temperature. When the SFS temperature was allowed to vary, by calibrating its mean-wavelength dependence on temperature, it was possible to predict the mean wavelength to a ±2-ppm precision by simply measuring the EDF temperature. The same configuration was also implemented with a different Er-doped fiber to achieve an even lower dependence on EDF temperature. When controlling the temperature of this second SFS to about ±0.5°C, it exhibited a stability of ±0.5 ppm over 17 h. These new developments constitute an important step toward a practical high-grade fiber-optic gyroscope.
 
Article
We achieved the first 10-GHz subpicosecond pulses in the 1000-nm band by employing the higher order soliton effect in a 190-m photonic crystal fiber (PCF). We obtained 0.5-ps pulses at 1063 nm by compressing 11-ps pulses from a harmonically mode-locked Yb fiber laser with a 10-GHz repetition rate, which was stabilized with phase-locked-loop technology. This light source is attractive in terms of realizing a hundreds-of-gigabits-per-second optical-time-division-multiplexing transmission over a low-loss PCF in the 1000-nm band
 
Article
This paper describes an optical transceiver designed for power-efficient connections within high-speed digital systems, specifically for board- and backplane-level interconnections. A 2-Gb/s, four-channel, dc-coupled differential optical transceiver was fabricated in a 0.5-μm complementary metal-oxide-semiconductor (CMOS) silicon-on-sapphire (SoS) process and incorporates fast individual-channel power-down and power-on functions. A dynamic sleep transistor technique is used to turn off transceiver circuits and optical devices during power-down. Differential signaling (using two optical channels per signal) enables self-thresholding and allows the transceiver to quickly return from power-down to normal operation. A free-space optical link system was built to evaluate transceiver performance. Experimental results show power-down and power-on transition times to be within a few nanoseconds. Crosstalk measurements show that these transitions do not significantly impact signal integrity of adjacent active channels.
 
Article
The dark current properties of In<sub>x</sub>Ga<sub>1-x</sub>As photodiodes, where x is varied from 0.53 to 0.82 for extending the long wavelength cutoff from 1.7 to 2.6 μm, are described. Detailed analyses of optoelectrical parameters of In<sub>0.82</sub>Ga <sub>0.1</sub>As photodiodes are presented. Dark current, which is a critical parameter and limits the operation of the photodiode, is analyzed and compared with the experimental values. Typical characteristics of photodiodes with cutoff wavelengths of 1.7 μm ( x =0.53), 2.2 μm ( x =0.72), and 2.6 μm ( x =0.82) are presented. The typical and best values of the dark currents obtained are presented
 
Article
An optical fiber grating demultiplexer-multiposition switch having seven demultiplexing channels and six position-switching channels is demonstrated. This device consists of a unique fiber array in which 42 output fibers are aligned radially around an input fiber, a single gradient-index (GRIN)-rod lens and a rotatable blazed reflection grating. In this device, seven demultiplexing channels can be switched to six different directions by rotating blazed reflection grating. Therefore, this device can realize total transmission channels of 42. The device had a working band of 0.64-0.88 μm, a channel separation of 35-42 nm and a 3 dB band width of 18-22 nm. The deviations of center wavelengths among the switching channels were suppressed less than 3 nm
 
Article
A novel type of electrooptic phase modulator suitable for deep modulation at higher frequencies has been designed and constructed. This modulator can produce an extremely broad optical sideband, which is useful for forming ultrashort optical pulses. In experiments, phase modulation with a modulation index of 34 rad has been successfully obtained at 9.35 GHz, and thereby optical sidebands extending over as wide as 640 GHz have been attained. The sidebands produced are broad enough to form single-picosecond pulses using the chirping-compression method.
 
Article
The bandwidth characteristics of single and multimode optical fibers have been investigated with single and multilongitudinal mode laser sources operating at 0.8, 1.3, and 1.5 μm. It is shown that single-mode fiber with a cutoff wavelength of 1.3 μm can support 1 Gb/s transmission over at least 7.5 km with a 0.8-μm laser source.
 
Article
A simple modification is proposed to the dual-core spectral filter design which extends the range of single wavelength transmission considerably, making the filter characteristic nonperiodic in the wavelength range 0.8 μm<λ<1.6 μm. Also, a spectral filter based on collinear triple-core fiber is proposed which provides a substantially lower sidelobe level than the dual-core filter. Transmission characteristics of the proposed filters are calculated and compared with those of the unmodified dual-core filter. The advantages of the proposed filters, particularly for application in wavelength division multiplexed systems are addressed
 
Article
An optical-fiber crossbar switch has been constructed using fully integrated GaAs optoelectronic receivers, custom monolithic GaAs laser drivers, and an electrical 32×32 silicon crossbar switch. 470 Mb/s operation has been achieved with a bit error rate of less than 10<sup>-12</sup>. The approach uses a monolithic GaAs optoelectronic integrated receiver to convert optical signals into electrical signals that are fed into an Si 32×32 electronic crossbar switch. The switch outputs are used to drive laser transmitters consisting of a custom monolithic GaAs IC laser driver and a 0.85 μm GaAs/AlGaAs laser. The system could be reconfigured in 1 μm, limited by the control logic, with the switch chip capable of reconfiguration in 35 ns. No errors are induced by reconfiguration
 
Article
Highly efficient and small-size erbium-doped fibers with a gain coefficient of 4.9 dB/mW and a strained quantum-well-type InGaAs laser diode with a lasing wavelength of 0.98 μm as a pumped light source. As a result, the module 4×6×1.5 cm, realized a maximum net gain of 33 dB with an electricity consumption of only 175 mW, which corresponds to a drive current of 80 mA. The module consists of four individual components: a pumping laser diode submodule, a wavelength-division-multiplexing-type fiber coupler, a polarization-insensitive optical isolator, and an erbium-doped single-mode fiber coil
 
Article
We demonstrate error-free dense-wavelength-division multiplexing (DWDM) transmission of 40 40-Gb/s channels with 100-GHz spacing over 10 000 km dispersion-managed fiber using carrier-suppressed return-to-zero differential-phase-shift keying (CSRZ-DPSK), enhanced foward-error correction, and all-Raman-amplified spans with 100-km terrestrial length.
 
Article
We studied a fiber-optic strain sensor based on interference between LP<sub>01</sub>-LP<sub>02</sub> modes of a circularly symmetric few-mode fiber (FMF). A simple theoretical analysis for predicting the performance characteristics of such a sensor is developed. Fiber elongations producing differential phase shift of 2π (δl<sub>2π</sub>) between the two modes are measured, which is found to be independent of sensing length of the fiber as predicted by theory. A good agreement between the experimental and theoretical values of δl<sub>2π</sub> is observed. Theoretical calculations predict that the sensitivity of such a sensor is maximum for fibers with V=4.82 and increases with the increase in the core cladding index difference Δn
 
Article
Full-duplex transmission over a 60 GHz radio-on-fiber access system based on the optical heterodyne technique is verified in this paper. With this technique, an optical carrier generator on the transmitting side consolidates the functions of wavelength and polarization control for optical heterodyne detection in uplinks and optical millimeter-wave generation in downlinks, on behalf of each optical transmitter/receiver. Therefore, the whole system configuration can be significantly simplified. A full-duplex 1.0 Gbit/s transmission experiment over 10 km of single-mode fiber, which represents an access network transmission, is demonstrated using the simultaneous modulation/photodetection operation of an electroabsorption modulator (EAM). Bit error rates of less than 10 $^{-9}$ were obtained in both the uplink and downlink without noticeable mutual interference, even though the laser source and the EAM is shared by both links, and no significant dispersion-induced degradation was observed. Moreover, the experimental results showed that an optical link budget of 9.2 dB can be achieved with the experimental configuration.
 
Article
An optical-heterodyne-detection method for a 60-GHz radio-on-fiber uplink is proposed and verified in this paper. The main point of this proposal is that all the functions needed for the optical heterodyne detection, i.e., the local/carrier light sources, the automatic frequency control of these light sources, and a polarization-diversity-detection circuit, are consolidated in one transmitting-side module to realize a simple system configuration. This proposal realizes an adequate optical uplink budget with low-cost optical receivers that consist of just one IF-band photodetector and one envelope detector. A 1.0-Gb/s transmission experiment over 10 km of single-mode fiber, which represents access-network transmission, is demonstrated using a 61.0-GHz amplitude-shift-keying signal as a 60 GHz-band uplink signal. A BER of less than 10-9 was obtained at an uplink SSB signal power of -40 dBm regardless of the polarization state of the optical uplink signal, and no significant dispersion-induced degradation was noted.
 
Article
A planar InP-based InGaAs heterostructure avalanche photodiode (APD) with a preferential lateral extended guard ring is proposed. Optimum design and device fabrication are described for the planar-structure APD using various-donor-concentration n-InP avalanche layers, separated from the light-absorbing InGaAs layer. High performance results are low dark current, high speed, low noise, and uniform avalanche gain without edge breakdown. The APD yielded a sensitivity as high as -37.4 dBm for a 2-Gb/s 1.57-μm wavelength return-to-zero sequence with 10<sup>-9</sup> bit error rate
 
Article
A practical 1.3 μm optical fiber amplifier with reliable 1.01-μm band laser diode pump light sources and an efficient praseodymium-doped In/Ga-based fluoride fiber is presented. A praseodymium-doped In/Ga-based fluoride fiber is characterized using measurable parameters, and amplified characteristics are theoretically analyzed. Signal output power of +16.2 dBm (42 mW) is achieved for an amplifier pumped by four 1.01-μm band laser diodes. By using the amplifier as a power booster, data of 2.5 Gb/s is successfully transmitted more than 100 km
 
Article
We designed a 1.06-mum single-quantum-well (SQW) InGaAs/AlGaAs planar tapered amplifier that was injected with seed light of a fiber Bragg grating stabilized laser diode through a fiber biconical microlens. To increase the amplifier output, the microlens with approximately 3- and 11-mum radii on vertical and horizontal axes, respectively, provides high coupling efficiency between the laser diode and the amplifier. The microlens also controls propagation in the tapered gain area to suppress the filament formation. In addition, the small radii of the microlens reduce near-end reflection at the amplifier input to prevent parasitic laser oscillation of the amplifier. We demonstrated near-diffraction-limited output of 5.5 W with the beam quality factor M<sup>2</sup> of 1.5 by using a 3-mm-long amplifier having an optical confinement factor of 1.2%.
 
Article
We propose and demonstrate a double-clad neodymium (Nd)-doped fiber amplifier (IVDFA) at 1.06 μm for a compact configuration of a high-power optical amplifier. The proposed 125 μm first cladding diameter in the double-clad fiber, provides the single-mode propagation of the signal lightwave into its doped core without misguiding the signal lightwave into the outer core (first cladding), by simply splicing with a standard single-mode fiber. Furthermore a fiber grating in a single-mode core of the double-clad fiber allows the double-pass configuration for the signal lightwave at 1.06 μm and also allows the pump lightwave coupling at 0.81 μm into the first cladding without employing a bulk dichroic mirror. We demonstrate the signal output power of 110 mW for a 550-mW pump input from a multimode fiber coupled pump source. Theoretical results predict an efficient high-power operation of the amplifier by improving the signal scattering loss in the double-clad fiber
 
Article
We report the development of CW 1.06- and 1.32-μm fiber lasers made of short sections of Nd:YAG single crystal fibers optically end-pumped either with an Argon-ion laser ( lambda = 0.5145mu m) or a single laser diode ( lambda = 0.817mu m). High conversion efficiencies, a few milliwatt thresholds and 10-20 mW output powers are reported, as well as a good coupling efficiency to a standard single-mode fiber. Loss mechanisms and means of reduction are also investigated for a variety of fiber lasers in either guided or unguided configurations.
 
Article
A new high capacity lightwave transmission system has been developed using GaAs semicustom logic arrays and a DFB single-mode laser, and is presently in production. The architecture of this product is designed for in-service upgrade of a 565-Mbit/s product. This paper reviews the technical characteristics and design considerations of the Rockwell LTS-21130 lightwave transmission system.
 
Article
1.14 b/s/Hz spectrally efficient 50×85.4-Gb/s copolarized return-to-zero differential quaternary phase-shift keying (RZ-DQPSK) signals have been transmitted over 300 km of nonzero dispersion-shifted fiber (NZ-DSF), using optical prefiltering and conventional C-band erbium-doped fiber amplifier (EDFA) repeaters. In this study, in order to enhance the spectral efficiency, the impact of optical prefiltering on the RZ-DQPSK signal was experimentally investigated in comparison to the DQPSK signal, and we found that the RZ-DQPSK signal had better sensitivity with almost the same nonlinear tolerance than the DQPSK signal even with 65-GHz bandwidth optical prefiltering.
 
Article
The 1.2/1.3 mu m band single-mode fiber WDM was developed with various factors such as characteristics, stability, and cost of the device in practical use taken into consideration. It uses ball-lens collimators in the optical coupling system. Utilizing its coupling characteristics could realize a low-loss high-stability WDM. An insertion loss variation is less than 0.25 dB throughout the wide temperature range of from -40°C to +70°C.
 
Article
A total capacity of 40 Gb/s is achieved using a shelf-mounted continuous-phase frequency-shift-keying (CPFSK) optical heterodyne frequency-division-multiplexing (FDM) transmission system with 32 optical channels and a bit-rate of 1.244-Gb/s per channel. For achieving a stable bit-error-rate (BER) characteristics with high-sensitivity, narrow-linewidth laser diodes, a channel-spacing stabilization circuit, and an optical tuner are developed. The obtained sensitivity at a BER of 10<sup>-9</sup> for fiber transmission over 121 km ranges from -45.1 to -44.2 dBm, which is 9.8-10.7 dB lower than the shot-noise-limited sensitivity. The crosstalk penalty is suppressed to within 0.1 dB. The developed system has feasibility achieving a distribution system which can distribute more than 250 HDTV (high definition television) signals or 1250 current-standard TV signals to about 8000 subscribers 10 km from the office, or a 40-Gb/s trunk-line system with a fiber span of more than 50 km
 
Article
The intensity noise and the performance in a 1.7 Gb/s digital system of 1.3 μm InGaAsP multilongitudinal mode lasers is discussed. The total intensity noise, mode partitioning, and the impact of dispersion on optical noise are measured. It is found that under CW conditions the total simulated emission from unpackaged lasers is inherently quiet, with an integrated optical signal-to-noise ratio (SNR) of 26.8±1.5 dB over a bandwidth of 1.5 GHz and 5 mW/facet. The optical SNR decreased as a function of increasing reflection. Intense mode partitioning decreased the SNR of the main mode by ~20 dB and reduced the effective coherence length to ~2 cm in glass fiber. At 1.7 Gb/s, the power penalities associated with laser bias and fiber dispersion are reported. The best receiver sensitivity is obtained when the laser is biased 1.3 mA below threshold. In general, it is found that as the bit rate increases, the optimum transmitter design becomes progressively more restrictive
 
Article
A simple technique for frequency-locking 1.3- and 1.5-μm lasers to an excited-state atomic transition of noble gases using the optogalvanic effect is described. Many of the atomic transitions useful for these spectral regions are tabulated. The performance of frequency-locked lasers under direct frequency modulation is analyzed. It is shown that neither the frequency stability nor the receiver sensitivity shows any serious degradation when a frequency-locked laser is used in a frequency shift keying (FSK) transmission experiment
 
Article
We propose that Dy<sup>3+</sup>-doped chloride crystals be considered as candidates for amplification of the 1.3 μm signal used by the telecommunications network. While several of these types of crystals can provide gain at the specified operating wavelength of 1.31 μm, and furthermore offer adequate bandwidth, we have focused our attention on LaCl<sub>3</sub>:Dy as an illustrative case to explore in greater depth. Spectroscopic measurements were made on un-oriented samples of this material; excited-state lifetimes and LaCl<sub>3</sub>:Dy<sup>3+</sup> Judd-Ofelt parameters are reported. Wavelength-resolved absorption and emission cross sections are presented for the 1.3 μm W&rlhar2;Z band. Pump-probe measurements (using 0.92 μm and 1.32 μm, respectively) prove that the observed gain properties of LaCl<sub>3</sub>:Dy are consistent with those predicted on the basis of the spectroscopic cross sections. The Dy:chloride gain media appear to have fundamental optical characteristics amenable to superior 1.3 μm telecom amplifier performance, although many fabrication issues would have to be addressed to produce a practical amplifier
 
Article
The practical properties of nine types of 1.3-μm Fabry-Perot laser modules were determined so as to construct a bidirectional transmission system. Time compression multiplexing (TCM) transmission is employed and the modules must act as both transmitter and receiver. Many modules are tested and it is found that the responsivity of a laser module is roughly proportional to the module's output power. The main source of variation in responsivity is determined to be due to coupling effects. Optical characteristics are measured over the range -15 to +65°C. The maximum transmission distance for narrow-band ISDN (integrated services digital network) services over single-mode fibers is determined for a bit rate of 3.5 Mb/s
 
Article
Transmissions of a 6-GHz 8-phase phase-shift-keyed (8φ-PSK) signal over a 12.5-km single-mode fiber with a 5-dB power margin and bit-error-rate (BER) of 10<sup>-10</sup> and a 6-GHz 16-ary quadrature-amplitude-modulated (QAM) signal over the same distance with a 2-dB power margin and BER of 10<sup>-12</sup> were demonstrated. The 8φ-PSK digital modem operated at 78Mb/s and the 16-QAM digital modem operated at 90 Mb/s. A high-speed multimode InGaAsP laser diode and a high-speed p-i-n diode were used in both fiber-optic transmission systems. Floor characteristics and power penalties observed in the BER performances of both systems were found to be caused by the intensity noise of the laser diode, particularly the reflection-induced intensity noise
 
Article
A new 1.3/1.55 μm WDM/photodiode(PD) module has been designed and fabricated for use in optical access networks. A 1.3 μm-PD and a 1.55 μm-PD were arranged in series along the optical axis in a coaxial package. The 1.3 μm-PD with an In<sub>0.66</sub>Ga<sub>0.34 </sub>As<sub>0.76</sub>P<sub>0.24</sub> photosensitive layer (λ <sub>g</sub>=1.42 μm) absorbs 1.3 μm digital optical signals and it is transparent to 1.55 μm wavelength. The 1.55 μm-PD with an In <sub>0.53</sub>Ga<sub>0.47</sub>As photosensitive layer absorbs 1.55 μm analog optical signals. Responsivity of the module is 0.82 A/W at 1.31 μm wavelength and 0.75 A/W at 1.55 μm wavelength, respectively. IMD2 of the 1.55 μm-PD measured by two-tone method was -76.1 dBc at Pf(1.55 μm) of -6 dBm. Bit error rate (BER) of the 1.3 μm-PD was measured at 28.8 Mb/s by using an amplifier with bandwidth of 200 MHz and was found to be less than 10<sup>-8</sup> at Pf(1.3 μm) of -30 dBm
 
Article
Twelve-channel 14-Mb/s/channel 1-km parallel optical-fiber transmission using a 1×12 low-drive-current 1.3-μm light-emitting diode (LED) linear array and an InGaAs p-i-n photodiode linear array, with the LED drive current as low as 12 mAp-p/channel, is discussed. No receiver sensitivity degradation has been observed under simultaneous 12-channel operation. The skew was less than 6 ns after transmission through a 1-km-long 12-channel optical-fiber cable, which was sufficiently small for 14-Mb/s parallel transmission
 
Article
A novel tunable filter using a Fourier grating is studied and discussed. It consists of a Fourier grating, a collimator lens, single-mode fibers, and a computer controlled rotary actuator. It has very low polarization dependence of less than 0.3 dB, an insertion loss of less than 3 dB, and a narrow bandwidth of 1.5 nm. Wavelength selection was realized by rotating the grating, which was controlled by a computer. The device is able to select the light at the desired wavelength from more than 100 WDM optical data streams with 2 nm spacing in the range of 1.3-1.55 μm
 
Article
A 250-Mbit/s three-station fiber-optic ring local computer network was built and successfully demonstrated. A conventional token protocol was employed for bus arbitration to maximize the bus efficiency under high loading conditions, and a non-return-to-zero (NRS) data encoding format was selected for simplicity and maximum utilization of the ECL-circuit bandwidth.
 
Article
We developed a hybrid integrated optical module for 1.3/1.55-μm wavelength-division multiplexing (WDM) full-duplex operation. The optical circuit was designed to suppress the optical and electrical crosstalk using a wavelength division multiplexing filter, and an optical crosstalk of -43 dB and an electrical crosstalk of -105 dB were achieved with a separation between the transmitter laser diode and the receiver photodiode of more than 9 mm. We used the optical circuit design to fabricate an optical module with a bare chip preamplifier in a package. This module exhibited a full duplex operation of 156 Mbit/s with a minimum sensitivity of -35.2 dBm at a bit error rate of 10<sup>-10</sup>
 
Article
For an application to a high-speed LED driver, a shunt drive circuit which is eminently suitable for GaAs IC's has been developed. This circuit has been embodied in a monolithic GaAs IC. A compact hybrid IC of an LED transmitter, i.e., a combination of this GaAs IC and a high-speed LED, has been fabricated. A high bit rate (NRZ 4000 M bit/s) transmission was demonstrated by using this LED transmitter.
 
Article
Group delay dispersion (GDD) of ~15 ps/nm has been measured in a near-traveling-wave optical amplifier at a wavelength where measured gain ripple was ~2 dB, using the envelope phase-shift technique. This is compared to a measured GDD of ~180 ps/nm in a single-facet antireflection-coated amplifier biased below threshold with a gain ripple of ~17 dB. It is shown that these results agree qualitatively with standard theory. An important result is that GDD increases with the square of amplifier length. GDD can be reduced by an order of magnitude if gain ripple is reduced to 0.5 dB
 
Article
Compressively and tensile strained InGaAsP-InP MQW Fabry-Perot and distributed feedback lasers emitting at 1.3-μm wavelength are reported. For both signs of the strain, improved device performance over bulk InGaAsP and lattice-matched InGaAsP-InP MQW lasers was observed. Tensile strained MQW lasers show TM polarized emission, and with one facet high reflectivity (HR) coated the threshold currents are 6.4 and 12 mA at 20 and 60°C, respectively. At 100°C, over 20-mW output power is obtained from 250-μm-cavity length lasers, and HR-coated lasers show minimum thresholds as low as 6.8 mA. Compressively strained InGaAsP-InP MQW lasers show improved differential efficiencies, CW threshold currents as low as 1.3 and 2.5 mA for HR-coated single- and multiple quantum well active layers, respectively, and record CW output powers as high as 380 mW for HR-AR coated devices. For both signs of the strain, strain-compensation applied by oppositely strained barrier and separate confinement layers, results in higher intensity, narrower-linewidth photoluminescence emissions, and reduced threshold currents. Furthermore, the strain compensation is shown to be effective for improving the reliability of strained MQW structures with the quantum wells grown near the critical thickness. Linewidth enhancement factors as low as 2 at the lasing wavelength were measured for both types of strain. Distributed feedback lasers employing either compressively or tensile strained InGaAsP-InP MQW active layers both emit single-mode output powers of over 80 mW and show narrow linewidths of 500 kHz
 
Article
A distributed feedback (DFB) laser emitting at 1.3 μm for gigabit lightwave communication systems has been developed. The distributed feedback structure has been introduced in a newly developed buried heterostructure and designs for stable single-mode operation, high speed modulation, and low noise have been done. Threshold current of 10-15 mA, differential efficiency of around 0.28 mW/mA, low noise, small signal modulation bandwidth of 13.9 GHz, and satisfactory modulation waveform at 5-Gbit/s NRZ modulation have been attained with high single-mode operation yield.
 
Article
Performance and reliability for InGaAsP/InP 1.3-μm wavelength high-speed surface-emitting DH light emitting diodes (LED's) have been investigated. High-speed and high-radiance performances were obtained by the optimal design of both structural parameters and LED driving circuit. Rise and fall times were both 350 ps and peak optical power coupled to a 50-μm core 0.20 NA graded-index fiber at the 100-mA pulse current was -15.8 dBm with 6-dB optical ON/OFF ratio. A 2-Gbit/s non-return-to-zero (NRZ) pulse transmission over a 500-m span was carried out. Feasibility of using surface-emitting LED's in a high-speed optical communication system has been confirmed. Accelerated aging tests on high-speed LED's were carried out. The half-power lifetimes have been estimated to be more than 1 times 10^{8} h at 50°C ambient temperature.
 
Article
A compact polarization-independent optical circulator for 1.3μm is described. The device utilizes birefringent plates (rutile) for beam splitting, YIG plus a single-order quartz half-wave plate for polarization rotation, and a slotted 45° glass prism for beam steering. The fiber-to-fiber insertion loss is 2.0 or 2.5 dB and the isolation is 25 or 35 dB, depending upon the ports in question. The use of birefringent plates for beam splitting and combining eliminates the need for multiple dielectric coatings for polarization beam splitting, requires only optical plate processing, virtually eliminates sensitivity to translational misalignment of individual beam-splitting/combining components, and reduces the required number of optical-quality surfaces.
 
Article
Transverse-mode-stabilized, 1.3-μm, GaInAsP/InP, buried-crescent (BC) lasers fabricated using a reactive ion beam etching (RIBE) technique are presented. Yields of single-transverse-mode operation as high as 95% are achieved with low threshold currents of 11-25 mA. Transverse-mode stability under both high-power and long-term operation (50°C, 20 mW, 1000 h) is demonstrated. A coupling efficiency into a single-mode fiber of 63% and a coupled power of 40 mW at 160 mA are achieved. Stable continuous-wave operation is also confirmed under a constant power of 5 mW (50 and 70°C) and 20 mW (50°C) in an aging test
 
Article
High performance of newly developed InGaAsP P-substrate buried crescent (PBC) laser diodes is described. It is shown that the PBC laser has superior characteristics to the conventional buried crescent (BC) laser with n-InP substrate. The maximum output power of 140 mW under a CW condition is realized at room temperature. CW light output power of 10 mW up to 110°C is achieved. A maximum CW temperature of 135°C is obtained. Stable CW operations have been confirmed in 70°C 5-mW and 70°C 20-mW aging tests. The reason for the high performance is discussed in relation to the leakage current which flows through the current blocking layers.
 
Article
We investigate electrooptic directional-coupler modulators operating at the wavelength of 1.3 μm, to have high linearity in their response function. The inverse Fourier transform technique was used to synthesize the spatially varying coupling function from a specified response function. The resulting coupling function was then used to determine the shape of the modulator structure. Modulators to have the response function of the form of a triangular (“linear”) function have been designed, fabricated, and tested. The third-order intermodulation-limited spurious-free dynamic range, at -130-dBm normalized noise floor, of 96.2 dB/Hz<sup>2/3</sup> was obtained
 
Article
We describe leakage current calculation in several real-index-guided laser structures using an electrical equivalent circuit model. The structures analyzed are different types of buried heterostructures in which heterojunctions are used for lateral carrier confinements. The device types are: 1) the etched-mesa buried heterostructure (EMBH); 2) the channeled-substrate buried heterostructure (CSBH); 3) the double-channel planar buried heterostructure (DCPBH); 4) the planar buried heterostructure (PBH); and 5) the buried crescent (BC). Adequate current confinement is necessary in a laser structure for both linearity and low threshold operation. Thus leakage current, i.e., the difference between the injected current and the current through the active region, should be small. We have identified the main leakage paths in these structures and the parameters (the relevant layer thicknesses and doping levels) that determine the magnitude of the leakage current. The effect of nonradiative recombination sites on junction parameters and the consequent increase in leakage current is discussed.
 
Article
The coupling constant that determines the characteristics of distributed feedback laser diodes (DFB LDs) is controlled by employing the metalorganic chemical vapor deposition (MOCVD) technique and inserting a barrier layer between the active layer and the guiding layer. It is shown that the measured coupling constant is in good agreement with the designed coupling constant. Lasers with a small coupling constant have a large slope efficiency. Lasers with the above structure are expected to have a long life, comparable to that of conventional DFB LDs
 
Top-cited authors
Peter Winzer
  • Alcatel Lucent
Alan Kersey
  • CytoVeris Inc.
Teoman Erdogan
  • Medical Park Hospitals
Jianping Yao
  • University of Ottawa
Heather J Patrick
  • National Institute of Standards and Technology