Electroabsorption Modulator Device Research Articles

80Gb/s NRZ Ge waveguide electro-absorption modulator.

We demonstrate a Ge electro-absorption modulator (EAM) in L band with a 3 dB electro-optical bandwidth beyond 67 GHz at -3 V bias voltage. The Eye diagram measurement shows a data rate of over 80 Gbps for non-return-to-zero on-off keying (NRZ-OOK) modulation at a voltage swing of 2.3 Vpp and the wavelength of 1605 nm. Through the comparison of multi-device results, it is proved that the introduction of the annealing process after CMP can increase the mean static extinction ratio of the EAM from 7.27 dB to 11.83 dB, which confirms the manufacturability of the device. The dynamic power consumption of the device is 6.348 fJ/bit. The performance of our device is comprehensive. The Ge EAM device also has excellent performance as a photodetector (PD) in the C and L communication bands. The responsivity of the device is 1.04 A/W at the wavelength of 1610 nm, resulting in ∼0.87 mW of static power consumption at -3 V bias voltage under 0.28 mW of optical input and the 3 dB opto-electric bandwidth of the devices are beyond 43 GHz at -3 V bias.

Design of a 50-Gb/s Hybrid Integrated Si-Photonic Optical Link in 16-nm FinFET

This article presents an electro-absorption modulator (EAM)-based single-mode (SM) 50-Gb/s non return to zero (NRZ) Si-photonic optical link in a 16-nm FinFET. The EAM device is modeled to include its electrical and optical properties. The transmitter (TX) uses T-coil based over-peaking to improve modulation efficiency and relax transimpedance amplifier’s (TIA’s) bandwidth and noise requirement. The receiver (RX) uses a three-stage TIA with T-coils to improve bandwidth. The link sensitivity is −10.9-dBm optical modulation amplitude (OMA) at bit error rate (BER) < 10−12 with 2-dB link margin at 50 Gb/s. The combined power efficiency of the RX, TX, and clocking is 3.16 pJ/bit and the external laser consumes 1.15 pJ/bit with 10% wall-plug efficiency.

System-on-Packaging with Electroabsorption Modulator for a 60-GHz Band Radio-Over-Fiber Link

A system-on-packaging (SoP) with an electroabsorption modulator (EAM) for a 60 GHz band radio-over-fiber (RoF) link is described. The system consists of an EAM device, a microstrip filter, and a low noise amplifier (LNA). The microstrip filter was used to achieve impedance matching between the EAM device and the LNA and to reject the local oscillator (LO) frequency of the heterodyne system. The frequency response and the effect of the EAM bias voltage were measured for a simple RF/optical link. A 60 GHz band RoF link with 2.5 GHz intermediate frequency (IF) was prepared to measure the transmission characteristics of the 16 QAM data.

Optically Decoupled Loss Modulation in a Duo-Cavity VCSEL

We have proposed and demonstrated the principle of optical decoupling in a vertical-cavity surface-emitting laser (VCSEL)-electroabsorption modulator device by use of a duo-cavity device architecture. This technique promises ultrahigh-frequency modulation of the VCSEL output due to the elimination of the resonance influences on the intrinsic modulation transfer function. By adjusting spectral detuning between the resonances of the duo-cavity configuration, optical decoupling of output modulation by an electroabsorption modulator can be achieved. A flat ( 3 dB) response up to 20 GHz has been measured by proper detuning of the resonances.

Large electro-optic effect in tensile strained Ge-on-Si films

The authors report the first observation of a large, strain-enhanced, electro-optic effect in the weakly absorbing regime for Ge epitaxial films grown directly on Si substrates. The field dependence of absorption in the Ge films was measured from spectral responsivity measurements of Ge-on-Si p-i-n diodes. The experimental data were analyzed using the generalized Franz-Keldysh formalism [H. Shen and F. H. Pollak, Phys. Ref. B 42, 7097 (1990)] and the valence band edge shifts of the light- and heavy-hole energy positions were in response to biaxial stress. With measured Δα∕α∼3 and derived Δn∕F=280pm∕V, the material has significant potential for field-induced phase or electroabsorption modulator devices.

Development of Packaging Technologies for High-Speed ($≫40$Gb/s) Optical Modules

We developed high-speed optoelectronics packaging technologies for a waveguide photodiode and a traveling wave electro-absorption modulator device for 40-Gb/s digital communication systems. The effects of the device and the packaging designs on the broadband performance were investigated to optimize broadband characteristics. For the receiver, inductive peaking was used for bandwidth control and an internal bias tee was implemented; in addition, two types of preamplifier devices were used to develop high-gain receiver and wide-bandwidth receiver. In the optical-to-electrical response, a 3-dB bandwidth of the high-gain module was about 32 GHz as compared to 42 GHz for the wide-bandwidth module. The clear 40-Gb/s nonreturn-to-zero (NRZ) eye diagrams showed a good system applicability of these modules. In addition, an optimized modulator module showed a 3-dB bandwidth of 38 GHz in the electrical-to-optical response, an electrical return loss of less than 10 dB at up to 26 GHz, an rms jitter of 1.832 ps, and an extinction ratio of 5.38 dB in a 40-Gb/s NRZ eye diagram

Development and RF characteristics of analog 60-GHz electroabsorption modulator module for RF/optic conversion

We developed an analog 60-GHz module for RF/optic conversion by using an electroabsorption modulator (EAM) device associated with a traveling-wave electrode. The impedance matching of the module was accomplished with the 30-/spl Omega/ termination such that the resonance was precisely located at 60 GHz and the fractional bandwidth at S/sub 11/=-15 dB was as large as 1.0 GHz. The RF/optic conversion gain of the EAM device revealed a strong dependence on the input optical power and was closely related with the slope change in the optical transmission characteristic with reverse bias. From the EAM module with the composite-type multiple-quantum-well electroabsorption core consisting of both 8- and 12-nm quantum wells, we obtained the optimal RF/optic conversion gain at the reverse bias between 1.5-2 V in a wide range of input optical power from -6 to +9 dBm. In the same bias range, the third-order intermodulation distortion was <-49.5 dBc as obtained with RF input of -7.5 dBm.

Experimental study of NRZ format wavelength conversion using electroabsorption modulator

In this paper, NRZ format wavelength conversion using cross absorption modulation (XAM) in InGaAsP MQW electroabsorption modulator (EAM) is investigated experimentally in detail for the first time, to the best of our knowledge. The influence of two key operating parameters, input signal power and bias voltage of EAM, on wavelength conversion performance is studied. Experimental results indicate that there exists optimal bias voltage for fixed input signal power and that there exists also optimal input signal power for fixed bias voltage and the lowest power penalty of 0.9dB is obtained by optimizing these two parameters. The physical explanations are given for these results based on operating characteristic of EAM device. Finally, the probe light wavelength dependence of wavelength conversion is studied for span of 1530–1560nm.

Extinction ratio improvement of an electroabsorption modulator by using Be as a p-type dopant with small diffusion coefficient

Beryllium (Be) has been applied as an acceptor in the p-type cladding layer and the contact layer of an InGaAsP-based electroabsorption modulator (EAM) fabricated by metalorganic chemical vapor deposition (MOCVD). The concentration of diffused dopants in the absorption layer of the EAM was significantly reduced by employing Be instead of zinc (Zn) which has been conventionally used as an acceptor for MOCVD-grown III–V semiconductors. Numerical simulation of the diffusion of Be and Zn in the EAM device structure showed that the diffusion of Be was dominated by interstitials with small diffusion coefficient, while the diffusion of Zn was dominated by a fast diffusion mechanism of a divacancy-related complex which was not observed in the Be-doped EAM. The measured extinction ratio of the Be-doped EAM was higher by approximately 40% than that of the Zn-doped counterpart. The improvement of the extinction ratio is due to improved uniformity of the electric field applied to the absorption layer of the EAM.

Microstructural and optical properties of strain compensated In xGa 1− xAs/In yAl 1− yAs multiple quantum wells

Transmission electron microscopy (TEM) and photocurrent (PC) measurements were carried out to investigate the microstructural and excitonic transitions in In 0.52Ga 0.48As/In 0.55Al 0.45As multiple quantum wells (MQWs). TEM images showed that high-quality 11-period strain-compensated In 0.52Ga 0.48As/In 0.55Al 0.45As MQWs had high-quality heterointerfaces. Based on the TEM results, a possible crystal structure for the In 0.52Ga 0.48As/In 0.55Al 0.45As MQWs is presented, and their strains are compensated. The results for the PC data at 300 K for several applied electric fields showed that several excitonic transitions shifted to longer wavelengths as the applied electric field increased. These results indicate that the strain-compensated In 0.52Ga 0.48As/In 0.55Al 0.45As MQWs hold promise for electroabsorption modulator devices.

Comparison of electroabsorption in asymmetric triangular and rectangular GaAs/AlxGa1−xAs multiple quantum wells

We present the first detailed experimental comparison of electroabsorption in equivalent rectangular and asymmetric triangular multiple quantum wells. The absorption spectra are extracted from reflectance and transmittance measurements on molecular beam epitaxy-grown samples. With absorption edges at the same photon energy, the asymmetric triangular quantum well is much wider than its rectangular well counterpart which reduces its absorption coefficient by approximately a factor of nine compared to the rectangular well, in agreement with theoretical estimates. Implications for electroabsorption modulator devices are discussed.