Electroabsorption Modulated Laser Research Articles

High-performance EML grown on taper-masked pattern substrates by ultra-low-pressure MOCVD

A novel in-plane bandgap energy controlling technique by ultra-low pressure (22 mbar) selective area growth (SAG) has been developed. To our knowledge, this is the lowest pressure condition during SAG process ever reported. In this work, high crystalline quality InGaAsP–InP MQWs with a photoluminescence (PL) full-width at half-maximum (FWHM) of less than 35 meV are selectively grown on mask-patterned planar InP substrates by ultra-low pressure (22 mbar) metal-organic chemical vapor deposition (MOCVD). In order to study the uniformity of the MQWs grown in the selective area, novel tapered masks are designed and used. Through optimizing growth conditions, a wide wavelength shift of over 80 nm with a rather small mask width variation (0–30 μm) is obtained. The mechanism of ultra-low pressure SAG is detailed by analyzing the effect of various mask designs and quantum well widths. This powerful technique is then applied to fabricate an electroabsorption-modulated laser (EML). Superior device characteristics are achieved, such as a low threshold current of 19 mA and an output power of 7 mW.

Monolithic integration of electroabsorption modulator and DFB laser for 10-Gb/s transmission

A strained InGaAsP-InP multiple-quantum-well DFB laser monolithically integrated with electroabsorption modulator by ultra-low-pressure (22mbar) selective-area-growth is presented. The integrated chip exhibits superior characteristics, such as low threshold current of 19mA, single-mode operation around 1550nm range with side-mode suppression ratio over 40dB, and larger than 16dB extinction ratio when coupled into a single-mode fiber. More than 10GHz modulation bandwidth is also achieved. After packaged in a compact module, the device successfully performs 10-Gb/s NRZ transmission experiments through 53.3km of standard fiber with 8.7dB dynamic extinction ratio. A receiver sensitivity of −18.9dBm at bit-error-rate of 10−10 is confirmed.

Cost-effective optical chirped duobinary transmitter using an electroabsorption modulated laser

We propose and demonstrate a cost-effective way to implement a 10-Gb/s chirped duobinary (CDB) transmitter using an electroabsorption modulated laser (EML) followed by a LiNbO/sub 3/ Mach-Zehnder modulator both driven with binary signals. Successful transmission is achieved over 285 km of dispersion-uncompensated standard single-mode fiber without significantly increasing the complexity and cost of the transmitter, compared to conventional duobinary transmitters. The demonstrated CDB signals exhibit a superior performance to conventional duobinary signals, in terms of back-to-back receiver sensitivity and transmission distance. We achieve consistent transmission performance with three EMLs obtained from two different vendors, each having different chirp and transmission characteristics. Therefore, we believe the use of EMLs greatly reduces the implementation issues of 10-Gb/s CDB transmission systems.

Waveguiding Effect in Electroabsorption Modulator: Passivation Layers and Their Impact on Extinction Ratios

Waveguide structures of the stand-alone electroabsorption (EA) modulator and the electroabsorption modulated laser (EML) are investigated using the 3D beam propagation method. The EA waveguide structures with InP-based passivation layers show saturation in the extinction ratio (ER) due to the stray light traveling through the passivation layers. This paper demonstrates that narrower passivation layers suppress stray-light excitation in the EA waveguide, increasing the ER. A taper structure in the isolation section of the EML waveguide can reduce the mode mismatch and suppress the excitation of the stray light, increasing the ER further. Low-index-polymer passivation layers can confine the mode more tightly in the active waveguide, yielding an even higher ER.

Photonic integration using asymmetric twin-waveguide (ATG) technology: part II-devices

Asymmetric twin-waveguide (ATG) technology has been shown to be a versatile and high-performance platform for the integration of a wide range of photonic integrated circuits. Following the conceptual and theoretical description in the preceding paper, here we discuss several archetype ATG-based photonic integrated devices and circuits. We present results on the three basic device classes that span the entire range of photonic component needs: light emitters, detectors, and light transporting devices (e.g., waveguides) that have been realized using the twin waveguide platform. Specifically, we discuss Fabry-Pe/spl acute/rot and wavelength-tunable lasers, high-bandwidth p-i-n photodiodes, a polarization-insensitive arrayed waveguide grating receiver with integrated p-i-n photodiodes, as well as combinations of functions including integrated electroabsorption-modulated lasers, and a semiconductor optical amplifier integrated with a p-i-n photodiode. Finally, we address potential integration challenges and novel applications of the ATG scheme, and avenues for improvement.

Operation of 1550-nm electroabsorption-Modulated laser at 40/spl deg/C for 10-gb/s, 40-km transmission

Semicooled operation at 40/spl deg/C of electroabsorptive modulator integrated laser (EML) for intermediate reach communication has been demonstrated. Reproducible operation at the elevated temperature was achieved through a device parameter optimized based on the temperature dependence of the dc characteristics of EML and a design of multi-quantum-well structure providing both relevant output power and high-frequency bandwidth at 40/spl deg/C. Good eye pattern and near zero chirp with the average power over 0 dBm are obtained at 40/spl deg/C, with an estimated lifetime over 20 years.

Low-cost coolerless integrated laser-modulator for 10 Gbit/s transmissions at 1.5 µm

For short and medium reach network applications, a low-cost and high performance integrated laser-electroabsorption modulator source for 1.5 µm transmissions is proposed. Coolerless and isolator-free 10 Gbit/s transmission over 50 km, for temperature ranging from 10 to 80°C is demonstrated.

Study of Internal Wavelength Locker Integrated 10 Gbps Electro-Absorption Modulated Laser Modules in Metro DWDM Applications

Several different divergences are tested in the several internal wavelength locker schemes for 10 Gbps electro-absorption modulated laser (EML) module. A 10 Gbps EML module with a simple and robust internal wavelength locker for metro dense WDM application is successfully demonstrated. The wavelength aging over 2000 h is done at elevated temperature of 70°C. The average wavelength drift of 10 modules is measured to be ± 5 pm. These modules can be successfully applied to the 10 Gbps DWDM systems with 50 GHz channel spacing.

Dispersion compensation in an optical communications system with an electroabsorption modulated laser and a fiber grating

The robustness of an optical communications system with an electroabsorption modulated laser (EML) to dispersion mismatch is investigated, where a fiber grating is used for dispersion compensation. We use 12-nm bandwidth 1360-ps/nm dispersion fiber gratings, which were fabricated to match the dispersion of 80 km of standard fiber, and an EML transmitter in a 10-Gb/s communications system testbed. We demonstrate a maximum power penalty <2 dB over a wide range of standard fiber lengths (30-110 km).

Widely tunable EAM-integrated SGDBR laser transmitter for analog applications

A widely tuneable electroabsorption-modulated sampled-grating distributed Bragg reflector laser, integrated with a semiconductor optical amplifier is characterized for analog applications. The wavelength can be tuned anywhere from 1522 to 1573 nm. The suboctave spurious-free dynamic range (SFDR) is between 125-127 dBHz/sup 4/5/ measured at eight sampled wavelengths over the tuning range. The broad-band SFDR is in the range of 103-107 dBHz/sup 2/3/ limited by third-order intermodulation products or 95-98 dBHz/sup 1/2/, limited by second-order intermodulation products.

Integrated 1.3-/spl mu/m DFB laser electroabsorption modulator based on identical MQW double-stack active layer with 25-GHz modulation performance

1.31-/spl mu/m electroabsorption modulators monolithically integrated with a DFB laser diode have been realized using an identical InGaAsP-InP multiple quantum-well-layer structure composed of two different QW types. Low laser threshold currents <13 mA and high 3-dBe cutoff frequency up to /spl sim/25 GHz have been measured.

40-Gb/s RZ transmission over 1200 km using an integrated electroabsorption-modulated laser

We report single-channel 40-Gb/s signal transmission over nonzero dispersion-shifted fiber using an integrated electroabsorption-modulated laser in the transmitter for data modulation. Return-to-zero format pseudolinear transmission over 1200 km is achieved with a measured Q of 15.6 dB or bit-error rate of 10/sup -9/.

Correlation between dispersion penalty and time-resolved chirp for an integrated widely tunable electroabsorption-modulated SGDBR laser across the EDFA gain bandwidth

We report, for the first time, the experimental relationship between time-resolved chirp and dispersion penalty across the 30-nm tuning range of a sampled-grating distributed Bragg reflector semiconductor-optical-amplifier electroabsorption-modulator laser. The extinction ratio, time-resolved chirp, and dispersion power penalties at transmission distances of 200, 275, and 350 km are presented for various values of effective alpha. Finally, a suitable method of computing the effective alpha from time-resolved spectroscopy is also presented.

An optical FSK transmitter based on an integrated DFB laser-EA modulator and its application in optical labeling

An optical frequency-shift-keying (FSK) transmitter based on an integrated distributed feedback laser-electroabsorption modulator is proposed and demonstrated. The feasibility of its application in optical labeling is also validated by the experimental results. The generated optical signal, consisting of a 10-Gb/s intensity-modulated payload and a 312-Mb/s FSK label, can be recovered error free after transmission over 88-km standard single-mode fiber.

Novel and simple model of 10-Gb/s electroabsorption modulated lasers and its experimental validation of transmission performance due to overshoot of optical signals

We have experimentally and theoretically investigated the transmission performance of 10-Gb/s electroabsorption modulated lasers (EMLs) due to the overshoot of optical pulses. When a highly negative bias voltage is applied to EMLs, the overshoot becomes larger due to nonlinear transfer curves of EMLs. In order to further understand the overshoot effect of optical pulses from EMLs on transmission performance, we propose a novel and simple EML model based on the frequency response (magnitude and phase) and the transfer curves (P-V and /spl alpha/-V) of EMLs. Although the model does not solve the rate equations and the wave equations, it can accurately predict output pulse shapes and the frequency chirp as well as the transmission performance with reducing simulation time. Using the EML model, we can calculate the overshoot and dispersion power penalty due to modulation bandwidth and group delay difference in 10-Gb/s EMLs. Our results suggest that the overshoot should be considered to accurately predict the transmission performance of 10-Gb/s EMLs.

Reduction in reflection-induced chirp from photonic integrated sources

Previously electroabsorption modulated lasers (EMLs) have been demonstrated using source lasers with grating strengths of two or less (k/sub r/L /spl les/ 2.0). Spatial holeburning was believed to limit the magnitude of the optimal grating strength. However, those standard-grating-strength lasers are sensitive to reflections from modulator output facet, integrated amplifiers, combiners, fiber tip, etc. and are a barrier to making integrated modules for long-span transmission. EMLs having record-strength (K/sub r/L > 6) gratings are fabricated. Output power >9.5 dBm, sidemode suppression ratio beyond 50 dB, single-mode yield >60% at high power, and power penalty <0.3 dB at 10 Gb/s for 75 km of fiber are demonstrated.

Long-haul DWDM/SCM transmission of 64- and 256-QAM using electroabsorption modulated laser transmitters

We report the first eight-wavelength hybrid dense wavelength-division multiplexing/subcarrier multiplexing (DWDM/SCM) transmission over 800 km (ten spans) of standard single-mode fiber, with 1.04-Gb/s payload on each wavelength in 35 6-MHz 64-quadrature amplitude modulated (QAM) channels, without dispersion compensation. Forward error-correction coding (FEC) was used to achieve error-free performance. Error-free performance on the majority of channels was also achieved for 64-QAM without FEC and for 256-QAM with FEC over 400 km. We used electroabsorption modulated laser transmitters.

Electroabsorption modulated laser for long transmission spans

Strain-compensated AlGaInAs quantum-well electroabsorption modulated lasers (EMLs) transmit at 10 Gbits/s on uncompensated transmission spans of >75 km of standard fiber and >225 km of MetroCor fiber. Details of the design, fabrication, and testing are presented. A complex-coupled distributed feedback (DFB) grating is used to enable high output power. The epitaxy and chip structure are described. The paper studies what is needed to accomplish long-span transmission in terms of minimum physical requirements for laser mode control, facet reflection, index grating strength, laser-modulator matching, laser-modulator electrical isolation, modulator extinction ratio, modulator capacitance, linewidth enhancement factor, etc. The interaction of the modulator with the laser is analyzed and a requirement for this structure is computed for the electrical isolation resistance between modulator and laser contacts. Stability of the laser source is discussed and a method is derived for determining the grating's gain-coupling coefficient at operating power. Chirp due to the modulator is analyzed. Nonzero chirp of the modulator is shown to have beneficial impact on the quality of the signal after transmission. The effect of a bias-dependent alpha parameter is analyzed. Because bit-error rate is a strong function of mean alpha parameter and not a strong function of the range of alpha during nonreturn-to-zero modulation, we determine that tuning the chirp of the EML modulator to suit different fiber types (MetroCor, SMF-28, etc.) is practical. Specific tradeoffs are also required. Experimental results verify the analysis.

Linearity enhancement of an electroabsorption modulated laser by dual-parallel modulation

A novel linearization process in an electroabsorption-modulated laser (EML) is proposed and experimentally demonstrated. A dual-parallel modulation scheme is used to compensate the nonlinear component of the EML by controlling the dc bias voltages of each EML separately. The validity of the proposed modulation scheme is confirmed through simulations and experiments. From a dual-parallel modulation experiment at 8 GHz, a reduction of 23 dB in IMD3 and a following increase of linear dynamic range of 19.6 dB are achieved compared to those of a single EML operation.

A supercontinuum source based on an electroabsorption-modulated laser for long distance DWDM transmission

We describe a 40-channel X 9.953 Gbit/s dense wavelength-division multiplexed (DWDM) transmitter based on spectrum-slicing of supercontinuum light generated from an electroabsorption-modulated laser (EML). Error-free transmission of all channels over 544 km of standard fiber is demonstrated.