Wide Temperature Range Operation of a 1.55-$mu$m 40-Gb/s Electroabsorption Modulator Integrated DFB Laser for Very Short-Reach Applications

We present the uncooled operation of a 1.55- mum 40-Gb/s InGaAlAs electroabsorption modulator (EAM) integrated distributed-feedback (DFB) laser within a temperature range of 95degC (-15degC to 80degC ). To the best of our knowledge, this is the largest temperature range reported so far for such a 40-Gb/s EAM integrated DFB laser. We designed the EAM to operate at high speed by reducing the electrical parasitics, and we achieved a 3-dB frequency bandwidth of over 39 GHz for an EAM length of less than 150 mum. We demonstrated a 2-km single-mode fiber (SMF) transmission at 40-Gb/s over a wide temperature range of -15degC to 80degC by adjusting only the bias voltage to the EAM while keeping the modulation voltage swing constant at 2.0 V when the temperature changed. We achieved a dynamic extinction ratio of over 8.2 dB and a 2-km SMF transmission with a power penalty of less than 2 dB over a wide temperature range.     

1.3-μ m InGaAlAs Short-Cavity DBR Lasers for Uncooled 10-Gb/s Operation With Low Drive Current

We present a novel 1.3-mum laser, a short-cavity distributed-Bragg-reflector (DBR) laser that enables uncooled, 10-Gb/s operation with low drive currents. The laser consists of a short InGaAlAs multiple-quantum-well active region butt-jointed to an InGaAsP-DBR region. A fabricated laser with a 75-mum active region demonstrated 100 degC, 10-Gb/s operation at a record low drive current of 14-mA peak-to-peak (mA_p-p) with an average output power of -3 dBm     

High-Performance Directly Modulated 1.3- μm Undoped InAs–InGaAs Quantum-Dot Lasers

In this letter, we report on experimental results of directly modulated single-transverse mode 1.3-mum InAs-InGaAs quantum-dot (QD) lasers in a wide temperature range. A 3.125-Gb/s data modulation over temperature with an extinction ratio up to 10 dB is reported. Moreover, 10-Gb/s eye patterns at 15 degC and 50 degC and 5-Gb/s modulation in the whole explored temperature range (15 degC-85 degC) are demonstrated. These results were obtained by exploiting heterostructures containing six layers of high modal gain InAs QDs grown without incorporation of p-doping in the active region or tunnelling injection structure implementation. QD lasers exhibited a saturation modal gain as high as 36.3 cm^-1, ground state lasing from short cavities down to 400-mum length and a characteristic temperature of about 110 K in a large temperature range between 15 degC and 85 degC     

12.5-gb/s direct Modulation up to 115/spl deg/C in 1.3-/spl mu/m InGaAlAs-MQW RWG DFB lasers with notch-free grating structure

Direct modulation at 12.5 Gb/s of 1.3-/spl mu/m InGaAlAs distributed feedback (DFB) ridge waveguide (RWG) lasers with low-resistance notch-free gratings running up to 115/spl deg/C is experimentally demonstrated. It was achieved by the combination of the high differential gain of an InGaAlAs MQW active layer, high characteristic temperature of RWG structure, and low-resistance notch-free grating. Moreover, successful transmission of 10-Gb/s modulated signals over 30-km standard single-mode fiber was achieved with the laser running at up to 115/spl deg/C. These results confirm the suitability of this type of laser for use as the cost-effective light source in 12.5-Gb/s and 10-Gb/s datacom applications.     

Cavity Mode—Gain Peak Tradeoff for 1320-nm Wafer-Fused VCSELs With 3-mW Single-Mode Emission Power and 10-Gb/s Modulation Speed Up to 70 °C

Room-temperature cavity mode red-shift of about 45nm from the photoluminescence peak is found to be optimal for tradeoff between high modulation bandwidth and good high-temperature performance for InAlGaAs(InP)-AlGaAs fused vertical-cavity surface-emitting lasers (VCSELs) employing tunnel junction carrier injection. Single-mode output power up to 5.4 and 3.1 mW, at 25 degC and 75 degC, respectively, and open eye diagrams exhibiting fall time values close to 40 ps at 10-Gb/s modulation up to at least 70 degC have been obtained for such VCSELs emitting at 1320-nm wavelength     

10-Gb/s Direct Modulation up to 100 $^{circ}$C Using 1.3- $mu$m-Range Metamorphically Grown Strain Compensated InGaAs–GaAs MQW Laser on GaAs Substrate

We have realized 10-Gb/s direct modulation up to 100degC using a metamorphic InGaAs multiple-qunatum well (MQW) laser on a GaAs substrate. The highly strained InGaAs quantum well (QW) and strain-compensated GaAs barrier layer allowed 1.3-mum-range lasing and an increased number of QWs (six). This laser with a 200-mum-long short cavity and a narrow ridge had maximum relaxation oscillation frequencies of 13 and 6 GHz at 25degC and 100degC, respectively. A 10-km single-mode fiber error-free transmission was successfully obtained at a temperature of 85degC .     

Transmission properties of 1.3-/spl mu/m InGaAlAs MQW FP lasers in 10-gb/s uncooled operation

Limitations on transmission by an uncooled InGaAlAs Fabry-Perot (FP) laser in 10-Gb/s operation are experimentally and theoretically investigated. The InGaAlAs laser has both high relaxation-oscillation frequency and superior light-current characteristics over a wide temperature range, making it suitable for uncooled operation at 10 Gb/s. Over most of the temperature range used in transmission testing with standard-dispersion fiber, a small power penalty of 1 dB for a bit error rate (BER) of 10/sup -12/ was obtained in transmission over 4-7 km at the measured temperature range, whereas an error floor was seen in transmission over greater distance, despite the negative chromatic dispersion between the fiber and laser light. Theoretical analysis of these results indicates that mode-partition noise (MPN) imposes the major limitation on transmission distance. Moreover, the minimum transmission distance was estimated as 2.1 km, even when the production tolerance of lasing characteristics and zero-dispersion range of installed fiber are taken into account.     

Design and Fabrication of Low-Driving-Voltage Electroabsorption Modulators Operating at 40 Gb/s

In this paper, a design for low-driving-voltage InGaAlAs/InAlAs electroabsorption modulators (EAMs) operating at 40 Gb/s is described. The theoretical calculation clarified that the tensile-strained InGaAlAs/InAlAs multiquantum-well layers with thin wells provide large and steep extinction characteristics. This was experimentally confirmed. We modeled an EAM with a low-loss coplanar waveguide for both the input and output ports and designed an optimized core structure that assures a sufficient extinction ratio and electrical-to-optical bandwidth for 40-Gb/s operation, in terms of well number and core length. A fabricated device driven by a peak-to-peak voltage as low as 1.1 V shows a 3-dB bandwidth of over 50 GHz and an RF extinction ratio of 10 dB. Error-free operation at 40 Gb/s is confirmed.     

10-Gb/s, 80-km SMF Transmission From 0 to 80 $^{circ}$C by Using L-Band InGaAlAs-MQW Electroabsorption Modulated Laser With Twin Waveguide Structure

A 10-Gbit/s, 1.58-mu m, InGaAlAs electroabsorption modulator (EAM) integrated distributed-feedback (DFB) laser (EML) with a twin waveguide (TWG) structure is operated experimentally over a wide temperature range of 0 to 80degC. We introduce an InGaAlAs multi-quantum well (MQW) system for both LD and EAM MQWs, because this material has temperature-tolerant characteristics. These layers are grown using single step epitaxial growth, and the device was fabricated with a very simple process. Moreover, successful transmission through an 80-km single-mode fiber (SMF) was achieved with the device running at up to 80degC. These results confirm the suitability of this type of laser for use as a cost-effective and low-power consumption light source in 10-Gbit/s optical network systems.     

Low insertion loss and low dispersion penalty InGaAsP quantum-well high-speed electroabsorption modulator for 40-Gb/s very-short-reach, long-reach, and long-haul applications

We present a metal-organic-chemical-vapor-deposition-grown low-optical-insertion-loss InGaAsP/InP multiple-quantum-well electroabsorption modulator (EAM), suitable for both nonreturn-to-zero (NRZ) and return-to-zero (RZ) applications. The EAM exhibits a dynamic (RF) extinction ratio of 11.5 dB at 1550 nm for 3 Vp-p drive under 40-Gb/s modulation. The optical insertion loss of the modulator in the on-state is -5.2 dB at 1550 nm. In addition, the EAM also exhibits a 3-dB small-signal response (S21) of greater than 38 GHz, allowing it to be used in both 40-Gb/s NRZ and 10-Gb/s RZ applications. The dispersion penalty at 40 Gb/s is measured to be 1.2 dB over /spl plusmn/40 ps/nm of chromatic dispersion. Finally, we demonstrate 40-Gb/s transmission performance over 85 km and 700 km.     

Highly Reliable 1.5-μm DFB Laser With High-Mesa SIBH Structure

The degradation behavior of 1.5-mum uncooled distributed feedback (DFB) lasers with a semi-insulating buried heterostructure during constant-power aging is investigated. Long-term stability is achieved by suppressing the t^0.5 deterioration in the current increase rate (second-stage degradation). The improvement in reliability is attributed to the fact that some defects on the grating interface are simultaneously suppressed by the mutual diffusion that occurs when growing the SI-InP layer. We realized a DFB laser with high reliability (< 1000 failure digits) at 95 degC that is capable of error-free 2.5-Gb/s 80-km transmission at -20degC to 100 degC     

Temperature insensitive 1.3 /spl mu/InGaAs=GaAs quantum dot distributed feedback lasers for 10 Gbit=s transmission over 21km

Long wavelength monomode InGaAs/GaAs quantum dot (QD) distributed feedback (DFB) lasers with emission wavelength around 1325 nm are presented. Threshold currents below 19 mA for operating temperatures up to 70degC and output powers of 10 mW at 25degC (6 mW at 70degC) are observed. Error-free 10 Gbit/s transmission over 21 km fibre with an extinction ratio of 8.5 dB at room temperature (5.1 dB at 70degC) is demonstrated. The low threshold, low temperature sensitivity and high modulation speed were realised using complex coupled DFB lasers with ten stacks of self-organised MBE-grown QD layers and p-type modulation doping     

A 1.7 Gb/s ASK and a 622 Mb/s incoherent FSK transmissionexperiment using a 1.55-μm multiquantum well distributed feedbacklaser

A multiple-quantum-well distributed-feedback (MQW-DFB) laser with narrow linewidth and low frequency chirp at low output power may experience linewidth rebroadening at high output power. the rebroadening is mostly due to a large carrier-induced change of refractive index, which also causes a large frequency modulation response for the MQW-DFB lasers. Using a 1.55-μm MQW-DFB laser, a 622-Mb/s amplitude-shift-keying (ASK) transmission experiment employing 200-km of fiber and an erbium-doped fiber amplifier has been demonstrated having a dispersion power penalty less than 9.8 dB. The receiver sensitivities at BER=10^-9 of the ASK system are -34.5 dBm and -42.5 dBm for 1.7-Gb/s and 622-Mb/s modulation, respectively. A 622-Mb/s incoherent frequency-shift-keying (FSK) transmission experiment using the same laser has also achieved a receiver sensitivity of -42.5 dBm     

Semiconductor light sources for 40-Gb/s transmission systems

The status and prospects of semiconductor light sources for 40-Gb/s transmission systems are reviewed in regard to the following three topics: direct modulation, external modulation, and pulse sources for return-to-zero format. Included are discussions on direct modulation of a 1.3-/spl mu/m distributed feedback laser for 40-Gb/s very-short-reach optical links, progress made in developing external modulators based on electroabsorption of multiple quantum wells, and mode-locked lasers for carrier-suppressed return-to-zero modulation format.     

Evaluation of 4-Gbit/s optical fiber transmission distance with direct and external modulation

Transmission characteristics for a recently modulated measured distributed-feedbacked (DFB) laser and an externally modulated DFB laser using a Ti:LiNbO/sub 3/, Mach-Zehnder modulator at 4 Gb/s are discussed. The transmission characteristics are estimated by an advanced eye-pattern analysis method. The maximum measured fiber dispersion with a directly modulated laser is 100 to 140 ps/nm when the chirp power penalty is 1 dB. However, for external modulation, there is no power penalty after transmission over a 2220-ps/nm dispersive fiber. This confirms that external modulation has superior transmission characteristics. The modulation scheme for 4-Gb/s systems in terms of these results is discussed.<>     

Bidirectional Transmission Using Tunable Fiber Lasers and Injection-Locked Fabry–PÉrot Laser Diodes for WDM Access Networks

We propose and demonstrate the use of fiber ring lasers and Fabry-Perot laser diodes (FP-LDs) for wavelength-division-multiplexing access networks. The fiber ring laser not only generates downstream data traffic but also serves as the wavelength-selecting injection light source for the FP-LD located at the subscriber site. Moreover, it is wavelength tunable and can be applied to dynamic wavelength assignment networks. The ring laser has a tunable range of 30 nm in the C-band and a power fluctuation smaller than 0.6 dB. For 10-Gb/s downstream and 1.25-Gb/s upstream transmissions over 10-km single-mode fiber, power penalties less than 0.9 and 0.5 dB are demonstrated, respectively. A 40-dB sidemode suppression ratio is obtained for the FP-LD injection-locking at 1544.8 nm.     

Modulation and demodulation techniques in optical heterodyne PSKtransmission systems

Modulation and demodulation techniques are described for an optical PSK heterodyne transmission system operating at 560 Mb/s and 1.2 Gb/s. Performance limitations affecting the receiver sensitivity in a 1.2-Gb/s DPSK system, such as laser phase noise, phase modulation depth, IF center frequency deviation, and local laser power, are studied. High receiver sensitivities for PSK systems were achieved. The applicability of the Mach-Zehnder modulator as a phase modulator for 1.2-Gb/s DPSK is also demonstrated. A 1.2-Gb/s DPSK transmission of over 100 km, using polarization diversity with novel polarization-insensitive automatic frequency control in an attempt to overcome signal fading caused by polarization fluctuation in the transmitting fiber, is also described. A receiver sensitivity of less than -42.8 dBm and varying within 1.4 dB for all states of polarization was achieved. A multichannel high-definition TV (HDTV) transmission experiment using a DPSK polarization-diversity tunable receiver is described     

1.244-Gb/s 32-channel transmission using a shelf-mountedcontinuous-phase FSK optical heterodyne system

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^-9 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     

High-Performance and Low-Cost 40-Gb/s CWDM Optical Modules

High-performance and low-cost 40-Gb/s optical modules using four different wavelength uncooled 10-Gb/s distributed-feedback (DFB) lasers are proposed and demonstrated. The 40-Gb/s optical module was integrated with coarse wavelength division multiplexing (CWDM) thin-film filters which enabled four 10-Gb/s transmission channels output through a single fiber. The 10-Gb/s DFB laser was packaged by commercialized low-cost coaxial TO-Can technology. The results of the 40-Gb/s optical module showed that the output optical power was above ${-}1$ dBm per channel and the system power budget was 12 dB. The transmission distance with a single-mode fiber reached more than 30 km at a bit-error-rate of $10^{{-}9}$. Compared with conventional 40-Gb/s optical modules, the module is easy to fabricate and is low cost. This proposed high-performance 40-Gb/s CWDM optical module demonstrates not only the feasibility of a 30 km transmission, but also shows the low-cost possibility of ensuring the application of WDM-passive optical network fiber-to-the-home systems.      

Uncooled 25°-85°C) 10 Gbit/s operation of 1.3 μm-range metamorphic Fabry-Perot laser on GaAs substrate

The first direct modulation of a 1.3 mum-range metamorphic laser diode on a GaAs substrate has been realised. A 200 mum-long device had threshold currents as low as 5.2 and 11.4 mA at 25 and 85degC, respectively. This laser also achieved 10 Gbit/s direct modulation up to 85degC.