1.3-$mu$ m VCSEL Transmission Performance up to 12.5 Gb/s for Metro Access Networks

We experimentally demonstrate 1.33-$mu$m vertical- cavity surface-emitting laser characterization (linewidth and chirp measurements) and very good propagation performances at multi-Gb/s in single-mode-fiber transmission. Error-free measurements are presented both for 10.3 Gb/s over 40 km and for 12.5 Gb/s over 20 km at different operating temperatures.      

Widely tunable negative-chirp SG-DBR laser/EA-modulated transmitter

Ten Gb/s low power penalty (<0.5 dB) error-free transmission was achieved through 75 km using a high-performance sampled-grating (SG) distributed Bragg reflector (DBR) laser/EAM transmitter. Large signal chirp measurements show negative chirp operation across the entire tuning range of the devices. An integration-oriented quantum-well-intermixing (QWI) process was employed for the realization of these devices.     

Extended 10 Gb/s fiber transmission distance at 1538 nm using aduobinary receiver

Chromatic dispersion penalties at 10 Gb/s and 1550 nm wavelength depend on the transmission bandwidth, not just the baseband information bandwidth. Duobinary transmission is known to reduce the transmission bandwidth relative to that of binary transmission. Using binary transmission, with both negative and zero chirp modulators, we present the first comparison of binary and duobinary reception and achieve an improvement in the chromatic dispersion limited transmission distance using duobinary reception. A 3.8 dB dispersion penalty is observed at 160 km using negative chirped binary transmission coupled to a receiver with a duobinary filter and decision circuit     

40-Gb/s Series-Push-Pull Mach&#8211;Zehnder Transmitter on a Dual-Quantum-Well Integration Platform

A series-push-pull Mach–Zehnder modulator is integrated with a sampled-grating distributed Bragg reflector laser on a dual-quantum-well integration platform. The device exhibited greater than 7.8-dB extinction at 40 Gb/s with a 2.5-V drive voltage across a wavelength range of 1541–1566 nm. Bit-error-rate measurements at 10 Gb/s showed error-free operation and negative chirp.     

Chirp reduction of directly modulated semiconductor lasers at 10Gb/s by strong CW light injection

The influence of strong light injection on the reduction of the dynamical linewidth broadening of directly current-modulated semiconductor lasers at high bit rates is theoretically investigated and experimentally verified for 10 Gb/s NRZ pseudorandom modulation with a large current swing of 40 mA pp. Significant chirp reduction and single-mode operation are observed for bulk DFB, quantum well DFB lasers at 10 Gb/s and a weakly coupled bulk DFB laser at 8 Gb/s, so that an improvement of the transmission performance using standard monomode fibers in the 1.55 μm low-loss wavelength region can be achieved for all these laser types, where dispersion otherwise causes severe penalties for long-haul transmission. The properties of injection-locked bulk DFB and quantum well DFB lasers with respect to high bit rate modulation have been systematically studied by the use of the rate equation formalism. A dynamically stable locking range of more than 30 GHz under modulation has been found for both laser types with injection ratios higher than 0.5     

Design of InGaAsP multiple quantum-well Fabry-Perot modulators forsoliton control

The use of synchronous optical modulators is effective in reducing the pulse timing jitter in long-distance soliton transmission. The inherently polarization-insensitive characteristics of the Fabry-Perot multiple quantum-well (MQW) electroabsorption modulator make it a potentially suitable device for this application. We investigate the intensity and phase modulation characteristics of symmetric and asymmetric Fabry-Perot modulators, and show that, by positioning the resonant wavelength <30 nm away from the exciton absorption peak to obtain negative chirp operation, both configurations can be used to successfully reduce timing jitter in a 20 Gb/s soliton system     

Dynamic and CW linewidth measurements of buried heterostructuredistributed feedback lasers

Measurements of frequency chirp as a function of modulation current, data rate, and bias level for the etched-mesa buried heterostructure distributed feedback (EMBH-DFB) laser are presented. The results show that the chirp increases with increasing modulation current and is significantly larger if the laser off-state is below threshold than if it is above-threshold. The 20-dB down chirp widths are in the range of 4 to 6 Å for 40 mA of modulation current at 5 Gb//s under above threshold bias. Using the EMBH-DFB laser, a system experiment over 22-km fiber at 16 Gb/s has been carried out which shows less than 0.5 dB dispersion power penalty. The continuous-wave (CW) linewidths of the asymmetric facet-coated DFB lasers are in the range of 10 to 40 MHz at 6 mW of output power. This wide range arises principally from a variation of the phase of the grating at the high-reflectivity coated facet     

Optimization of DFB lasers integrated with Franz-Keldysh absorptionmodulators

The influence of the residual facet reflectance on electroabsorption modulators monolithically integrated with DFB lasers is analyzed, for both index- and partly loss-coupled lasers. The optimum laser design is discussed from the standpoint of system requirements in long-distance 10 Gb/s transmission systems, requiring a minimum of chirp. The integrated device's performance will depend as much on the laser design as on the modulator. The DFB laser should be long (L>500 μm) with a coupling strength of about κ·L=2-3 and should have a high relaxation oscillation frequency. The residual reflectance should be less than 1·10^-4     

15-GHz modulation bandwidth, ultralow-chirp 1.55-μm directlymodulated hybrid distributed Bragg reflector (HDBR) laser source

A hybrid source has been realized, integrating a fast Fabry-Perot laser and a fiber grating. The device has shown very good performances in the 1530-1570-nm range, obtaining 16 mA of threshold current at 20°C, 1.6-mW fiber optical power and 48 dB of sidemode suppression ratio at 50 mA bias current. The cavity length was designed to achieve a good tradeoff between chirp reduction and increasing speed. The device has shown for the first time, to our knowledge, more than 15 GHz of small-signal modulation bandwidth, and 10-Gb/s modulation capability. Moreover, a penalty-free transmission experiment at 2.5 Gb/s over 100 km of standard fiber has confirmed the very low wavelength chirp of the device. These previous characteristics together with an extremely low temperature dependence (<0.02 nm/°C) make the hybrid distributed Bragg reflector (HDBR) particularly suitable for dense wavelength-division-multiplexing systems     

Dynamic and CW linewidth measurements of 1.55-μm InGaAs-InGaAsPmultiquantum well distributed feedback lasers

Measurement of the CW linewidth and frequency chirp as functions of modulation data rate and bias level for 1.55-μm InGaAsP multiquantum-well distributed feedback lasers grown by low-pressure MOCVD are presented. The results show that the CW linewidth of asymmetric facet-coated multiquantum-well DFB lasers can be as low as 2.0 MHz at 13.5 mW output power. The frequency chirp increases with modulation data rate and is significantly larger if the laser off-state is below threshold than if it is above threshold. The 20 dB down chirp widths are in the range of 1.9-5 Å for 40 mA peak-to-peak modulation current at 10 Gb/s under above-threshold bias     

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.<>     

适用于多种调制格式的低驱动电压LiNbO_3光调制器

提出并分析了一种适用于多种调制格式的低驱动电压LiNbO_3光调制器,通过延长设计LiNbO_3光调制器的波导结构,可显著降低其射频驱动电压及直流偏置电压.通过实验测试并分析了10Gb/s传输速率下的器件参数,包括光眼图,小信号S参数以及啁啾参数等.实验证明,该调制器的驱动电压由原有的5.8V降低至2.8V,更适于各种新型的编码调制格式的应用场合.

Abstract：

Proposed is the demonstration of a new design of LiNbO_3 modulators with low driving voltage (V_(Pi)).The low V_(pi) performance is achieved by extension design of the wave-guide inside the modulator.Experimental tests and analysis carried out on the performance of some key parameters of the modulator at 10 Gb/s transmission rate,including the optical eye,small signal S parameter,chirp parameter,etc.Results obtained indicate the driving voltage of the modulator reduces to 2.8 V in comparison with traditional 5 V,which is more suitable for the applications of increasingly-emerged novel modulation formats.     

Design and performance of externally modulated 1.5-μm lasertransmitter in the presence of chromatic dispersion

Key laser and modulator characteristics that impact the use of externally modulated lasers in the presence of chromatic dispersion, excluding effects due to fiber nonlinearities, are reviewed. After a brief consideration of transmission performance with directly modulated 1.5-μm DFB lasers which have limited application of up to 80 km at 2.5 Gb/s, the key design characteristics of externally modulated transmitters are discussed. Experimental results showing the effects of modulator chirp and laser linewidth at a 2.5-Gb/s transmission rate are presented. It is found that lasers with CW linewidth under 100 MHz have less than 2-dB dispersion penalty for 600 km of non-dispersion-shifted fiber. Lower dispersion penalties can be realized if the modulator chirp is tuned so as to narrow the transmitted pulses. Excellent modulator stability is demonstrated for 60 days of error- and degradation-free 2.5-Gb/s operation     

Dispersion penalty reduction using an optical modulator with adjustable chirp

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.<>     

On the transmission performances and the chirp parameter of amultiple-quantum-well electroabsorption modulator

The chirp parameter of a multiple-quantum-well (MQW) electroabsorption modulator was measured with accuracy for several operating wavelengths in the 1.5 μm window. It varied strongly with applied bias. Effective chirp parameter, defined as the ratio of phase change to transmission change between modulator on and off states, is about zero, or even negative. However, experimental transmission length on standard fiber at 10 Gb/s NRZ is much smaller than what is expected for such a low chirp parameter. It is demonstrated that the effective chirp parameter should not be computed from changes between on and off states, but from the average of the chirp parameter values in a 3 dB region of the most transparent states of the modulator. This simple rule allows us to predict transmission performances based on measurements of the chirp parameter, and can be used to optimize optical components without actually experimenting on a transmission system. The effective chirp parameter of the MQW electroabsorption modulator is found positive. This should be intrinsic to red-shift electroabsorption effects, such as the quantum confined Stark effect     

Eye-opening improved electroabsorption modulator/DFB laser diodewith optimized thickness of the separate-confinement heterostructurelayers

The separate-confinement heterostructure (SCH) of an electroabsorption modulator integrated with a distributed feedback laser diode (EAM-LD) was optimized to obtain a clear optical waveform (eye opening) without penalty of chirp characteristics. The electric field applied to the multiple-quantum-well (MQW) structure was controlled by employing the proper thickness of undoped SCH layers to attain gentle absorption characteristics of the EAM at the optical mark level. As a result, the eye opening of the modulated emission at 10 Gb/s was improved and the intersymbol interference was reduced. No severe drawback on chirp characteristics was found in an α-parameter measurement. EAM-LD's with the optimized SCH structure exhibited good transmission characteristics of power penalties under 1.5 dB at 10 Gb/s, and the reliability of 10 Gb/s transmission characteristics was also confirmed. We have also investigated how the optical waveform after transmission was affected by the dependence of the α-parameter on bias voltage. Measurement and numerical calculation of the optical waveform after transmission showed that the optical waveform was severely affected by the α-parameters at deep reverse voltages     

Modeling and optimization of low chirp LiNbO/sub 3/ Mach-Zehnder modulators with an inverted ferroelectric domain section

Domain inversion under coplanar waveguide electrodes is proposed to improve the frequency-chirping behavior of Z-cut LiNbO/sub 3/ Mach-Zehnder modulators. This is achieved by introducing a phase reversal electrode section in tandem with inverted ferroelectric domains. The method opens the way to broad-band single-drive modulators with predetermined chirp parameter. The experimental results obtained at 10 Gb/s confirm the possibility of lowering the chirp parameter of a Z-cut modulator, while keeping a halfwave voltage lower than 5 V.     

40-Gb/s Direct Modulation With High Extinction Ratio Operation of 1.3-μm InGaAlAs Multiquantum Well Ridge Waveguide Distributed Feedback Lasers

Direct modulation at 40 Gb/s of a 1.3-mum InGaAlAs distributed feedback ridge waveguide laser is experimentally demonstrated. By combination of the high differential gain of an InGaAlAs multiquantum well active layer, a short cavity length of 100 mum, and a low-resistance notch-free grating, it achieves high bandwidth of 29 GHz and high-extinction ratio of 5 dB at 40-Gb/s modulation. Moreover, the laser operates at a record maximum ambient temperature of 60degC under 40-Gb/s directly modulation. It also achieves 40-Gb/s modulated transmission over 2 km with a low power penalty of 0.25 dB at 25degC .     

Long wavelength quantum well lasers: Synopsis of the RACE “AQUA” project: MOVPE/MBE/GSMBE for InGaAsP/InP and InGaAlAs/InP high speed MQW DFB lasers

The technological limits for ultra high speed devices are now rapidly expanding due to the use of quantum well (QW) materials. This new class of materials gives the opportunity of tailoring materials parameters by controlling geometries on an atomic scale. They look very promising as materials for lasers, detectors and transistors suitable even above 10 Gb/s. It will be demonstrated that state of the art MQW structures can be realized in both material systems, InGaAsP/InP and InGaAlAs/InP. Parallel lateral laser structures (e.g. SIBH, BRS and TBH) have been designed to take full benefit of QW technology. Ultimate reduction of parasitics, whilst using potential low cost fabrication technologies is the basis for achieving high bitrate (10 Gb/s) MQW lasers, even with the stronger damping in QW material. Using the DFB-SIBH laser structure 10 Gb/s large signal experiments are successfully performed with bulk, MQW and SLMQW lasers. Extremely low fall times of 44 ps are achieved. Additional MQW based improvements are observed such as: −3 times higher differential gain, increased output power (>110 mW), 2.5 times lower chirp (Δλ_−20dB = 0.40 nm at 10 Gb/s modulation), and 2 dB gain in power budget at 10 Gb/s digital transmission.     

Effects of laser diode parameters on power penalty in 10 Gb/soptical fiber transmission systems

A composite tradeoff study based on the influence of key laser diode parameters on frequency chirp induced power penalty, extinction induced power penalty, the turn-on delay, and the dispersion transmission limit is presented for 10 Gb/s optical fiber transmission systems. The simulated results reveal that an optimum range of differential gain and nonlinear gain coefficient exists, and it is advantageous to set an extinction ratio that minimizes both the total power penalty and the turn-on delay. In addition, it is shown that a reduction of chirp and maximization of the dispersion transmission limit can be realized by designing the laser diode with a linewidth enhancement factor near -0.8