Characteristic analysis of the optical delay in frequency response of resonant cavity enhanced (RCE) photodetectors

With consideration of the modulation frequency of the input lightwave itself, we present a new model to calculate the quantum efficiency of RCE p-i-n photodetectors (PD) by superimposition of multiple reflected lightwaves. For the first time, the optical delay, another important factor limiting the electrical bandwidth of RCE p-i-n PD excluding the transit time of the carriers and RCd response of the photodetector, is analyzed and discussed in detail. The optical delay dominates the bandwidth of RCE p-i-n PD when its active layer is thinner than several 10 nm. These three limiting factors must be considered exactly for design of ultra-high-speed RCE p-i-n PD.

Zero biased Ge-on-Si photodetector with a bandwidth of 4.72 GHz at 1550 nm

High quality Ge was epitaxially grown on Si using ultrahigh vacuum/chemical vapor deposition (UHV/CVD). This paper demonstrates efficient germanium-on-silicon p-i-n photodetectors with 0.8 mu m Ge, with responsivities as high as 0.38 and 0.21 A/W at 1.31 and 1.55 mu m, respectively. The dark current density is 0.37 mA/cm(2) and 29.4 mA/cm(2) at 0 V and a reverse bias of 0.5 V. The detector with a diameter of 30 mu m, a 3 dB-bandwidth of 4.72 GHz at an incident wavelength of 1550 nm and zero external bias has been measured. At a reverse bias of 3 V, the bandwidth is 6.28 GHz.

Chirp-free optical modulation using a silicon push-pull coupling microring

We propose a silicon ring-based optical modulation method to perform chirp-free optical modulations. In this scheme, we locate the light to be modulated at the resonance of the ring and tune the coupling coefficient between the ring and the straight waveguide by using a push-pull coupling structure. The chirp-free phase modulation can be achieved by varying the coupling coefficient in a large range, which can modify the coupling condition of the ring such that the input light experiences an abrupt phase shift of pi at the output. If the coupling coefficient is adjusted in a small range such that the coupling condition of the ring is kept unchanged, only the intensity of the light will be modulated. This leads to chirp-free intensity modulation. Our simulations performed at 10 Gbits/s confirm the feasibility of the proposal. (C) 2009 Optical Society of America

Wavelength conversion based on degenerate-four-wave-mixing with continuous-wave pumping in silicon nanowire waveguide

We present a comprehensive numerical study on the all-optical wavelength conversion based on the degenerate four-wave-mixing with continuous-wave pumping in the silicon nanowire waveguide. It is well known that the conversion efficiency and the 3-dB bandwidth can be greatly affected by the phase-matching condition. Through proper design of the waveguide cross-section, its dispersion property can be adjusted to satisfy the phase-matching condition and therefore effective wavelength conversion can be achieved in a large wavelength range. Generally, the group velocity dispersion plays a dominant role in the wavelength conversion. However, the fourth-order dispersion takes an important effect on the wavelength conversion when the group velocity dispersion is near the zero-point. Furthermore, the conversion efficiency and the 3-dB bandwidth can also be affected by the interactive length and the initial pump power. Through the numerical simulation, the optimal values for the interactive length and the initial pump power, which are functions of the propagation loss, are obtained to realize the maximum conversion efficiency. (C) 2008 Elsevier B.V. All rights reserved.

Low threshold current density 1.5 mu m strained-MQW laser by n-type modulation-doping

1.5 mu m. n-type modulation-doping InGaAsP/InGaAsP strained multiple quantum wells grown by low pressure metalorganic chemistry vapor decomposition technology is reported for the first time in the world. N-type modulation-doped lasers exhibit much lower threshold current densities than conventional lasers with undoped barrier layers. The lowest threshold current density we obtained was 1052.5 A/cm(2) for 1000 mu m long lasers with seven quantum wells. The estimated threshold current density for an infinite cavity length was 94.72A/cm(2)/well, reduced by 23.3% compared with undoped barrier lasers. The n-type modulation doping effects on the lasing characteristics in 1.5 mu m devices have been demonstrated.

Subtraction of scattering parameters for small-signal modulation characteristics of laser diode

An extended subtraction method of scattering parameters for characterizing laser diode is proposed in this paper. The intrinsic response is extracted from the measured transmission coefficients of laser diode, and the parasitics of packaging net-work laser chip are determined from the measured reflection coefficient of laser diode simultaneously. It is shown that the theories agree well with the experimental results.

Effect of interaction between periodic delta-doping in both well and barrier layers on modulation of superlattice band structure

The modulation of superlattice band structure via periodic delta-doping in both well and barrier layers have been theoretically investigated, and the importance of interaction between the delta-function potentials in the well layers and those in the barrier layers on SL band structure have been revealed. It is pointed out that the energy dispersion relation Eq. (3) given in [G. Ihm, S.K. Noh, J.I. Lee, J.-S. Hwang, T.W. Kim, Phys. Rev. B 44 (1991) 6266] is an incomplete one, as the interaction between periodic delta-doping in both well and barrier layers had been overlooked. Finally, we have shown numerically that the electron states of a GaAs/Ga0.7Al0.3As superlattice can be altered more efficiently by intelligent tuning the two delta-doping's positions and heights. (c) 2007 Elsevier B.V. All rights reserved.

Directional-coupler-based Mach-Zehnder interferometer in silicon-on-insulator technology for optical intensity modulation

Based on silicon-on-insulator (SOI) technology, a Mach-Zehnder interferometer (MZI) is fabricated, in which two directional couplers serve as power splitter and combiner. The free carrier plasma dispersion effect of Si is adopted to achieve the phase modulation and the consequent intensity modulation of optical fields. The device presents an insertion loss of 2.61 dB and an extinction ratio of 19.6 dB. The rise time and fall time are 676 ns and 552 ns, respectively. Detailed analysis and explanation of the performance behaviors are also presented. (c) 2007 Society of Photo-Optical Instrumentation Engineers.

Measurement of chirp parameter and modulation index of a semiconductor laser based on optical spectrum analysis

A novel and simple method for measuring the chirp parameter, frequency, and intensity modulation indexes of directly modulated lasers is proposed in a small-signal modulation scheme. A graphical approach is presented. An analytical solution to the measurement of low chirp parameters is also given. The measured results agree well with those obtained using the conventional methods.

A short carrier lifetime semiconductor optical amplifier with n-type modulation-doped multiple quantum well structure

Semiconductor optical amplifiers (SOAs) with n-type modulation-doped multiple quantum well structure have been investigated. The shortened carrier lifetime is derived from the PL spectrum and electrical modulation frequency response measurement. The carrier lifetime in semiconductor optical amplifiers with any n-type-2-modulated doping multiple quantum well structure is less than 60% of that in the undoped partner. The shortest measured carrier lifetime of 236 ps in the MD-MQW SOA with sheet carrier density of 3 x 10(12) cm(-2) was only 38% of that in the undoped MQW SOA, which can increase the wavelength conversion efficiency via four wave mixing by a factor of about 7 and switching speed via XGM and XPM applications by a factor of 2.63.

Effect of substrate misorientation on the InAs/InAlAs/InP nanostructure morphology and lateral composition modulation in the InAlAs matrix

The authors report the self-organized growth of InAs/InAlAs quantum wires on nominal (001) InP substrate and (001) InP substrates misoriented by 2 degrees, 4 degrees, and 8 degrees towards both [-110] and [110]. The influence of substrate misorientation on the structural and optical properties of these InAs/InAlAs quantum wires is studied by transmission electron microscopy and photoluminescence measurements. Compared with that grown on nominal (001) InP substrate, the density of InAs/InAlAs quantum wires grown on misoriented InP(001) substrates is enhanced. A strong lateral composition modulation effect take place in the InAlAs buffer layers grown on misoriented InP substrates with large off-cut angles (4 degrees and 8 degrees), which induces a nucleation template for the first-period InAs quantum wires and greatly improve the size distribution of InAs quantum wires. InAs/InAlAs quantum wires grown on InP (001) substrate 8 degrees off cut towards [-110] show the best size homogeneity and photoluminescence intensity. (c) 2007 American Institute of Physics.

Characterization of parasitics in TO-packaged high-speed laser modules

An elaborate analysis of the parasitic network of high-speed through-hole packaging (TO)-type laser modules is presented using a small-signal equivalent circuit model. The intrinsic laser diode is obtained using the optical modulation technique, and is embedded into the model as a separate component. Three step-by-step measurements are made for determining the packaging parasitic network, including the test fixture, TO header, submount, bonding wire, and parasitics of the laser chip. A good agreement between simulated and measured results confirms the validation and accuracy of the characterization procedures. Furthermore, several key parasitic elements are found based on the simulation of the high-frequency responses of the packaged devices. It is expected that the 3-dB bandwidth of 12 GHz or more of the low-cost TO packaged laser module may be achieved using the proposed optimization method.

Potential frequency bandwidth estimation of TO packaging techniques for photodiode modules

Scattering parameters of photodiode chip, TO header and TO packaged module are measured, and the effects of TO packaging network on the high-frequency response of photodiode are investigated. Based on the analysis, the potential bandwidth of TO packaging techniques is estimated from the scattering parameters of the TO packaging network. Another method for estimating the potential bandwidth from the equivalent circuit for the TO packaged photodiode model is also presented. The results obtained using both methods show that the TO packaging techniques used in the experiments can potentially achieve a frequency bandwidth of 22 GHz.

Mach-Zehnder interferometers with asymmetric modulation arms in applications of high speed silicon-on-insulator based optical switches

Modulation arms with different widths are introduced to Mach-Zehnder interferometers (MZIs) to obtain improved performance. Theoretical analysis and numerical simulation have shown that when the widths of the two arms are properly designed to achieve an inherent m pi/2 (m is an odd integer) optical phase difference between the arms, the asymmetric MZI presents higher modulation speed. Furthermore, the carrier-absorption induced divergence of insertion losses in silicon-on-insulator (SOI) based MZI optical switches can be obviously improved.

A 1.5 mu m n-type InGaAsP/InGaAsP modulation-doped multiple quantum well DFB laser by MOCVD

1.5 mu m n-type InGaAsP/InGaAsP modulation-doped multiple quantum well (MD-MQW) DFB lasers have been fabricated successfully by low pressure metal organic chemical vapour deposition (LP-MOCVD) technology. The experimental results indicate that n-type MD-MQWs can effectively reduce the threshold Current compared with conventional multiple quantum well DFB lasers. Theoretical analysis indicates that such an effect is due to the much smaller absorption loss and lower Auger recombination, compared with that in an undoped MQW structure. Moreover, the introduction of n-type dopant of suitable levels of concentration in the barrier layers enhances the dynamic characteristics of DFB lasers, due to a coupling between the adjacent quantum well layers and tunnelling-assisted injection, which can reduce the relatively long capture time and increase the effective differential gain 1/X dG/dn .