Analog characterization of low-voltage MQW traveling-wave electroabsorption modulators

In this paper, high-speed traveling-wave electroabsorption modulators (TW-EAMs) with strain-compensated InGaAsP multiple quantum wells as the absorption region for analog optical links have been developed. A record-high slope efficiency of 4/V, which is equivalent to a Mach-Zehnder modulator with a V/sub /spl pi// of 0.37 V and a high extinction ratio of > 30 dB/V have been measured. A detailed study of the nonlinearity and the spurious-free dynamic range (SFDR) is presented. By optimizing the bias voltage and the input optical power, the SFDR can be improved by 10-30 dB. After minimizing the third-order distortion, an SFDR as high as 128 dB-Hz/sup 4/5/ is achieved at 10 GHz. A simple link measurement was made using this EAM and an erbium-doped fiber amplifier and a 50-/spl Omega/ terminated photodetector. At 10 GHz, a link gain of 1 dB is achieved at a detected photocurrent of 7.6 mA with higher gains at lower frequencies. The dependence of link gains on bias voltage, input optical, and radio frequency powers are investigated in detail.     

Proposal for quantum-dot electroabsorption modulator

Quantum-dot, electroabsorption materials are proposed to obtain low internal loss, large absorption modulation, and negative alpha parameters (blue chirped pulses). These characteristics come from the discrete state absorption associated with three dimensional confinement in quantum dots compared to the band absorption of quantum well, quantum wire, and bulk materials. In addition, type II quantum-dot structures are also proposed to obtain the same optical modulation characteristics with the potential for greater immunity to saturation effects.     

An electroabsorption modulator module for digital and analogapplications

This paper presents an electroabsorption modulator (EAM) module for digital and analog (D/A) applications. Optically broad-band operation of the EAM module is studied for such digital application as wavelength division multiplexing (WDM) systems. Utilizing anisotropic electroabsorption of a multiple quantum-well (MQW) EAM, 40- and 100-nm bandwidth operations in 2.5-Gb/s digital signal transmission over 200-km standard fiber are confirmed by the experiments and the simulations, respectively. For analog applications, low distortion and high link gain characteristics of the EAM module are investigated at the wavelength of 1535 nm. High spurious-free dynamic range of 123 dB·Hz^4/5 and high link gains of -10.3 dB with matching circuit and -20.6 dB without matching circuit are obtained using the EAM module     

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%     

InGaAsP electroabsorption modulator for high-bit-rate EDFA system

The total performance of an InGaAsP electroabsorption modulator was characterized. Low-driving voltage of 1.2-2.7 V, low fiber-to-fiber insertion loss of 8.4-7.8 dB, and small α-value of 0.1-0.4 were obtained in 40-nm-wide wavelength range from 1.53 to 1.57 μm. Static and dynamic modulation characteristics showed small dependence on the polarization and the power level of input light. Successful applications of a packaged EA modulator to ultralong-distance Er-doped fiber amplifier systems were confirmed by 16000-4550-km transmission experiments at 2.5-10 Gb/s     

电吸收调制器特性研究

针对电吸收调制器在光纤无线通信系统中的重要作用,分析了电吸收调制器的插入损耗和由电吸收调制器组成的光纤无线通信系统的误码率和噪声系数。发现在波长从1530~1570nm范围内插入损耗都比较小;在工作波长为1550nm的通信系统内实现了速率为2.5Gb/s信号在200km长度的标准光纤内传输。系统功率衰减很小,在选择合适的匹配阻抗下,通信系统噪声系数能够达到12dB左右。     

Strain-compensated MQW electroabsorption modulator for increasedoptical power handling

InGaAsP MQW electroabsorption modulators with compressive strain in the wells and tensile strain in the barriers provide easier escape of photogenerated holes and operate at higher intensities before suffering saturation. Hole escape from wells is enhanced by a reduced energy difference between heavy-hole states in the well and light-hole states in the barrier     

Compact and stable electroabsorption optical modulator modules

Very compact electroabsorption optical modulator modules that demonstrate high coupling efficiency and high stability have been developed. The modules show very good potential such as an insertion loss as low as 5 dB, or ultrahigh speed modulation of up to 46 GHz. The module fabrication techniques are also applicable to other optical devices that require fiber connections at both facets     

Measurement-based model for cross-absorption Modulation in an MQW electroabsorption modulator

A model for cross-absorption modulation in a multiple-quantum-well electroabsorption modulator is developed based on measurements of the escape time of photogenerated carriers, the dependence of the modulator absorption on the power and wavelength of the pump and probe signals, and the dependence of the /spl alpha/ parameter of the wavelength-converted signal on the power and wavelength of the pump and probe signals. Good agreement between calculated and measured results is demonstrated for static, small-signal and large-signal conditions. The accuracy and computational efficiency of the model in describing the intensity and phase modulation properties of a wavelength-converted signal make it suitable for computer simulations aimed at system design and performance evaluation.     

GaAs traveling-wave optical modulator using a modulated coplanar strip electrode with periodic cross-tie overlay

This paper proposes and analyzes a GaAs traveling-wave optical modulator which uses a modulated coplanar strip electrode with periodic cross-tie overlay. This slow-wave structure can be designed to satisfy phase velocity and impedance matching conditions simultaneously. The dominant conductor loss in the slow-wave structure is reduced using the modulated coplanar strip electrode. The calculated 3-dB modulation bandwidth (100 GHz) is much wider than the bandwidth limit (30 GHz) of conventional electrode structures that are limited by phase velocity mismatch.     

Novel bias control of electroabsorption waveguide modulator

A novel approach is proposed for controlling the bias of an electroabsorption waveguide modulator for maximum radio-frequency (RF) gain in analog fiber-optic links. It is based upon the correlation between the RF gain and the modulator DC photocurrent. It is found that, under various operating conditions, the modulator bias at which the modulator DC photocurrent experiences the largest change with incremental bias, coincides with the bias for the maximum RF gain. This approach eliminates the need for an external tracking photodiode, and can be useful in bias controls of a modulator array     

Enhanced performance in traveling-wave electroabsorption Modulators based on undercut-etching the active-region

A novel traveling-wave electroabsorption modulator (TWEAM) based on undercut-etching-active-region waveguide (UEAW) is proposed and demonstrated. By selectively wet-etching the InGaAsP from InP to reduce InGaAsP active region, the waveguide can reduce parasitic capacitance with high conductivity in n-InP and p-InP cladding layers. In comparison with conventional ridge-waveguide (RW) TWEAM, 3 dB lower optical-insertion-loss, at least 6 dB higher in radio-frequency-link gain (dc to 40 GHz), and faster electrooptical response (3-dB bandwidth of 25 GHz at 50 /spl Omega/-termination for UEAW and 15 GHz for RW) are obtained in UEAW-TWEAM. A 10-Gbs/s operation with low swing voltage of 0.6 V has been achieved in UEAW-TWEAM, a 3.2-dB enhancement over RW-TWEAM. It indicates the tradeoff in designing electroabsorption modulators can be greatly released.     

行波型LiNbO3电光调制器的电极优化设计

利用扩展点匹配方法对厚电极厚缓冲层的共面波导电光调制器的结构和性能参数进行了分析和研究,通过仿真选择合适的电极厚度和缓冲层厚度,所得的特性阻抗和有效折射率与采用保角变换法得到的结果吻合,优化了调制器性能,实现了宽带调制.这一分析方法简便快捷,能够处理电极有一定厚度的多层光波导调制器结构.     

Integrated tandem traveling-wave electroabsorption modulators for >100 Gbit/s OTDM applications

Integrated tandem traveling-wave electroabsorption modulators are demonstrated as high-speed optical short pulse generators and demultiplexers for >100 Gbit/s optical time-division-multiplexed systems. The tandem significantly increases the extinction ratio and further compresses the optical pulses in comparison to a single modulator. An extinction ratio of /spl sim/50 dB is achieved while optical pulses of 4-6 ps width at 30-40 GHz are generated.     

Standing-wave enhanced electroabsorption modulator for 40-GHz optical pulse generation

Compact 40-GHz optical pulse generators are crucial to the implementation of practical 160-Gb/s optical time-division-multiplexing systems with 40-Gb/s electrical time-division-multiplexing tributaries. In this letter, we report on a novel standing-wave enhanced mode of the electroabsorption modulator (EAM) which can improve the performance of a single EAM for 40-GHz pulse generation. Both experimental and theoretical results indicate that the distributed effect plays an important role in the high-frequency operation of the EAM and the length of the microwave termination line must be adjusted properly to maximize the performance.     

Noise transfer characteristics of cross-absorption modulation in an electroabsorption modulator

The pump-to-probe noise transfer characteristics of cross-absorption modulation in an electroabsorption modulator are investigated experimentally. The transfer of intensity noise from the pump signal to the wavelength-converted signal is assessed by considering the optical signal-to-noise ratio, power spectral density, and relative intensity noise of the optical signals.     

High-performance traveling-wave electroabsorption modulators utilizing mushroom-type waveguide and periodic transmission line loading

For the first time, periodic loaded electrodes and mushroom-type waveguide are combined to improve the performance of traveling-wave electroabsorption modulators (TWEAMs) based on the asymmetric intra-step-barrier coupled double strained quantum well (AICD-SQW). The electrical modulation response of periodic mushroom-type TWEAM is obtained by using equivalent circuit model, and is compared with simulation result of conventional mushroom-type TWEAM counterpart. The equivalent circuit model simulation results indicate that for the exemplary modulation length of 300 mm, the mushroom-type TWEAM with periodic transmission line loading can achieve much wider bandwidth about 99.7 GHz and 43.1 GHz than the conventional counterpart with about 43 GHz and 33 GHz for 35 W and 45 W terminations, respectively.     

Enhancement in electroabsorption waveguide modulator slopeefficiency at high optical power

An increase in transfer curve slope efficiency for a Franz-Keldysh effect InGaAsP-InP electroabsorption waveguide modulator is observed as the incident optical power is increased from 5.8 to 17 dBm. However, high-frequency RF measurements agree with the gain predicted from the low-power transfer curve at all optical powers. We attribute the increase in dc slope efficiency to a temperature-induced bandgap shrinkage of the electroabsorption material     

Polarization-independent and ultra-high bandwidth electroabsorption modulator in multiquantum-well deep-ridge waveguide technology

Electroabsorption modulators with polarization-independence of transmission (TE/TM sensitivity <0.4 dB at 1550 nm) over a wide wavelength range from 1540-1560 nm have been realized using tensile-strained InGaAs and InGaAsP quantum wells. Both designs show 42-GHz modulation bandwidth with a high bandwidth-to-drive-voltage ratio of >23 GHz/V. Polarization insensitivity of modulator transmission and chirp is demonstrated. Technical realization has been done in ridge waveguide technology with low-pressure MOVPE, reactive ion etching (RIE) for semiconductor etching and polyimide for planarization.     

A semi-empirical model for electroabsorption in GaAs/AlGaAsmultiple quantum well modulator structures

A semiempirical model for electroabsorption in GaAs/AlGaAs quantum wells that is simple and has sufficient accuracy to make it suitable as a fast design tool for multiple quantum well (MQW) optical modulators is proposed. The model is based on a higher-order perturbation approach which includes all bound solutions of the unperturbed Hamiltonian. To complete the model, semiempirical relationships are set up for both the zero-field absorption peak and the half-width at half-maximum (HWHM) values of the heavy-hole exciton. Comparison with extensive experimental data shows a remarkable agreement for a range of wells between 5 and 20 nm and for photon energies on the long wavelength side of the absorption peak. These wavelength and well-size ranges coincide with those needed for practical design