High-speed InGaAlAs/InAlAs multiple quantum well electrooptic phasemodulators with bandwidth in excess of 20 GHz

High-speed phase modulation (in the frequency bandwidth of 20 GHz, the highest yet reported for multiple quantum well (MQW) phase modulators) for waveguided InGaAlAs/InAlAs MQW optical modulators is reported. The modulator successfully operates at a long wavelength of 1-55 μm with a low required voltage for phase shift (Vπ=3.8 V), small intensity modulation depth below 1.5 dB, and without any modulation bandwidth degradation up to 20 GHz under high input optical power of 0 dBm in single-mode fiber     

InGaAlAs Multiple-Quantum-Well Optical Phase Modulators Based on Carrier Depletion

We fabricated carrier-depletion-type optical phase modulators which contain an InGaAlAs multiple-quantum well (MQW) in a p-n junction, and investigated their phase modulation characteristics at the wavelengths of 1.55-1.62 mum under reverse biased conditions. Fabricated devices showed large modulation efficiencies up to 89deg/mm/V and smaller wavelength-dependence than that of conventional MQW phase modulators. Carrier-depletion-type optical phase modulators are attractive for optical integrated devices such as optical matrix switches for future wavelength-division-multiplexing photonic networks.     

High-performance Mach-Zehnder modulators in multiple quantum wellGaAs/AlGaAs

We demonstrate Mach-Zehnder interferometric waveguide intensity modulators which employ electrorefraction due to the quantum-confined Stark effect in multiple quantum well (MQW) GaAs/AlGaAs. These devices exhibit average half-wave voltage-length products as low as 3.0 V·mm and extinction ratios greater than 23.8 dB, which are superior to any MQW devices of this type. An effective index based model is developed to extract linear and quadratic electro-optic coefficients from the modulation data. Also, the power handling limitations of MQW modulators are discussed in terms of device performance and catastrophic electrical failure     

Monolithic integration of an amplifier and a phase modulatorfabricated in a GRINSCH-SQW structure by placing the junction below thequantum well

We present results of a novel semiconductor optical amplifier device in which an amplifier and a phase modulator are integrated into a fundamental transverse-mode ridge waveguide. By placing the p-n junction below the quantum well (QW) during epitaxial growth and utilizing the effect of the electric field on the depletion width, the phase of the light from an integrated optical amplifier-modulator is varied. For a modulation reverse bias voltage range of 0.4 V, we have demonstrated a 360°/mm phase shift with less than 1.2 dB of amplitude modulation     

High-speed InGaAlAs/InAlAs multiple quantum well optical modulators

High-speed modulation over 22 GHz for waveguided InGaAlAs/InAlAs multiple quantum well (MQW) optical modulators is described. A large on/off ratio of over 25 dB is demonstrated with a low-drive voltage (6 V) operating in the 1.55-μm wavelength region. The design and characteristics of MQW p-i-n modulators are discussed. The causes of large-insertion loss and the required drive voltage bandwidth figure of merit for the MQW modulator are discussed. The frequency response measurements show that the response speed is limited by the RC time constant of the device. This suggests that the speed can be further enhanced by decreasing the size and capacitance of the device     

All-binary InAs/GaAs optical waveguide phase modulator at 1.06μm

We demonstrate the use of multiple [(InAs) (GaAs)]/GaAs short-period strained-layer superlattice quantum wells for optical waveguide modulation at 1.06 μm. We achieve π phase modulation with 2.3 V applied (V_π×L=4.6 V mm, or 39°/V mm) in the presence of negligible absorption change using this all-binary modulator     

GaInAsP buried channel ea modulator for 13?m fibre links

Double-heterostructure (DH) GaInAsP/InP buried channel waveguide electroabsorption (EA) modulators are demonstrated. They are designed for external intensity modulation of 1·3 ?m laser light and direct coupling to single-mode fibre. For a 650?m-long device, a 30 dB on/off ratio has been achieved at a bias voltage of ? 9 V. The substrate light is found to be a limiting factor of the measured extinction ratio for short modulators, but not for long (1·8 mm) modulators     

Numerical simulation of a silicon-on-insulator waveguide structurefor phase modulation at 1.3 μm

This paper presents an analysis of a silicon-on-insulator (SOI) waveguide structure to be used for phase modulation at 1.3 μm. The device consists of a two-dimensional (2-D) strip waveguide and a p⁺ /N^-/N⁺ lateral diode to realize the effective index modulation by free-carrier injection. We have calculated that an effective index modulation between 5·10^-4 and 10^-3 could be obtained with current densities in the range from 500 to 1600 A/cm². A detailed numerical simulation of the device transient response is also reported. We demonstrate that an effective index modulation of 5·10^-4 could be obtained with a cutoff frequency of about 100 MHz. The phase modulator has a predicted figure-of-merit (FoM) of 160°/V/mm and a chirp factor of 25. Due to its full compatibility with complementary metal-oxide-semiconductor (CMOS)-SOI technology, the device is interesting for low-cost silicon-based optoelectronic systems     

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     

A low-drive-voltage, high-speed monolithic multiple-quantum-wellmodulator/DFB laser light source

A high-speed InGaAs/InAlAs multiple-quantum-well (MQW) intensity modulator and an InGaAsP/InGaAs MQW distributed feedback laser were monolithically integrated by using a hybrid growth technique combining molecular beam epitaxy and metalorganic vapor phase epitaxy. An operating drive voltage of only 2.0 V, a 20-dB on/off ratio, and a 3-dB bandwidth greater than 15 GHz were obtained. This device operated stably in a single mode and with a side-mode suppression ratio of more than 50 dB     

Full polarization insensitivity of a 20 Gb/s strained-MQWelectroabsorption modulator

We report on a MQW electroabsorption modulator with tensile-strained wells. The device transmission is shown to be fully polarization insensitive, i.e. both in amplitude and phase. The modulation efficiency is over 20 GHz/V (bandwidth higher than 20 GHz and 1 V drive voltage) which is the highest figure of merit reported for any kind of polarization insensitive modulator. Full polarization independence is further demonstrated by 2.5 Gb/s transmission at 1.55 μm over 475 km of standard fiber without penalty at 10^-9 BER whatever the polarization     

Operating characteristics of InGaAs-GaAs MQW hetero-nipi waveguidemodulators

We report frequency response measurements of optical MQW nipi waveguide modulators, observing a -3-dB bandwidth as high as 110 MHz. These devices have only 900-Å-thick intrinsic regions, and thus can achieve very high fields with modest reverse bias voltages. We also measured absorption modulation (32 dB) and a phase change figure of merit as low as V_π×L=0.8 V mm at a detuning of 115 meV below the photoluminescence peak. We compare ion-implanted selective contacts with traditional selective metal contacts     

The effect of modulator nonlinearity on measurements of chirp inelectroabsorption modulators

Traditional techniques for measuring the chirp in external modulators assume that the optical intensity output of the modulator is a faithful representation of the applied voltage. For electroabsorption modulators, which can have highly nonlinear transmission- vs voltage characteristics, this is a poor approximation, especially when they are operated at high modulation indices. We demonstrate a new technique that makes use of the actual measured T(V) for the device under test, and show that this new technique permits measurement of chirp in modulators generating either NRZ signals or soliton pulses. We apply this technique to both bulk and MQW electroabsorption modulators, and show that traditional measurements significantly underestimate the α values of these devices     

An integrated hybrid device for binary-phase-shift-keyingsubcarrier modulation

We propose an integrated optical/radio frequency (RF) hybrid device for binary-phase-shift-keying subcarrier modulation that is based on optical amplitude modulation and interference with phase delay. The device consists of two multiple-quantum-well (MQW) electroabsorption (EA) modulators branched with two multimode interference (MMI) couplers. When an RF carrier was applied to one modulator and a digital signal to the other one, the phase modulation of the RF subcarrier was realized     

Saturation intensity and time response of InGaAs-InGaP MQW opticalmodulators

We report modulation saturation and time response measurements on InGaAs-InGaP MQW modulators. The measurements yield a saturation intensity of (3.7±0.1) kW/cm² for a 0-10 V swing and switching times between 10 and 90 ns, depending on the bias voltage and incident light intensity. The observed dependence indicates that field screening due to carrier build-up is the dominant physical mechanism determining both the speed and the saturation intensity. This conclusion is supported by results of theoretical calculations     

Design and realization of a 1.55-μm patterned vertical cavitysurface emitting laser with lattice-mismatched mirror layers

It is possible to grow defect-free strained layers on patterned substrates (mesas or grooves) up to thicknesses far exceeding the critical thickness. Defect nucleation and propagation are inhibited in such growth. We have exploited this property to propose a novel InP-based 1.55-μm vertical cavity surface emitting lasers (VCSEL's). Careful photoluminescence and transmission electron microscopy (TEM) studies have confirmed that there are no propagating defects in the GaAs/Al_xGa_1-xAs distributed Bragg reflector (DBR) grown on the patterned InP-based heterostructures, specifically in the multiquantum-well (MQW) region. Lasers were designed with InP/InGaAsP bottom mirrors, InAlAs-oxide current confinement and short-stack GaAs/Al _xO_y top DBR mirrors. An optimal reflectivity and a maximum wall plug efficiency are determined analytically for this structure. In addition, a theoretical analysis of the modulation response of this device is performed using a rate equation model. Both analyzes show the potential of such a device for implementation in practical designs where high power and modulation bandwidth are required. Lasers with 8-40 μm diameter have been fabricated and characterized. A threshold current of 5 mA is observed at 15°C for an 8 μm diameter device; and up to 60 μW of light output is recorded     

GaAs 850 nm modulators solder-bonded to silicon

GaAs/AlGaAs p-i-n multiple-quantum-well modulators solder-bonded to a silicon substrate are reported. The GaAs substrate is then chemically removed to allow operation at 850 nm. The gold contact to the modulator is used as the reflector. A change in reflectivity from 26% to 52% is achieved for a 0 to 10 V bias swing. The device has a modulation saturation intensity of 80 kW/cm², demonstrating superb heat-sinking and ohmic contact. The hybrid was cycled from 30°C to 100°C over a 100 times, and it showed no degradation, exhibiting the practicality of the technique     

Monolithic integration of InGaAs/InP DFB lasers and InGaAs/InAlAs MQW optical modulators

The first successful monolithic integration of InGaAsP/InP distributed feedback (DFB) lasers and InGaAs/InAlAs multiple quantum well (MQW) optical modulators using LPE (liquid phase epitaxy)/MBE (modlecular beam epitaxy) hybrid growth reported. A 14% light output modulation is observed in this integrated device.     

Low-drive-voltage MQW electroabsorption modulator for opticalshort-pulse generation

This paper reports on InGaAsP-InGaAsP tensile strained MQW electroabsorption (EA) modulators with a high modulation efficiency of 35 GHz/V that generate optical short pulses. We studied and optimized the multiple-quantum-well (MQW) structural parameters, barrier height, and well number, thickness, and strain in the absorption layer to ensure high attenuation efficiency and generate low duty cycle pulses. Low TE/TM polarization sensitivity was obtained by controlling strain. Stable, nearly transform-limited optical pulse trains with a narrow pulsewidth of 3.6 ps are generated by applying a 20-GHz sinusoidal modulation voltage (6 V_pp) to the EA modulator. This achieves a very small pulse duty cycle of 7.2%     

High-speed MQW electroabsorption optical modulators integrated withlow-loss waveguides

An MQW electro-absorption optical modulator integrated with low-loss input and output waveguides is proposed to achieve larger modulation bandwidth with a shorter modulation region, keeping the total device length large enough for easy fabrication and packaging. A fabricated 1-mm-long modulator with a modulation-region length of 50 μm shows a low insertion loss (7 dB), low driving voltage (V_{10 dB}=2.6 V), and large modulation bandwidth f_{3 dB} =40 (GHz) extrapolated from measurements up to 20 GHz. This modulator is suitable for application to ultra-high-speed fiber transmission systems