Electrical Modeling of Long-Wavelength VCSELs for Intrinsic Parameters Extraction

We present an efficient method to model the small-signal modulation response of a long-wavelength VCSEL chip using an equivalent electrical circuit. This circuit serves two distinct purposes. Based on T-Matrix formalism, it is used to remove the parasitics contribution originating from the electrical access of the chip in order to obtain the optical cavity intrinsic frequency response as defined by the rate equations. The same circuit is also used to extract the intrinsic cavity parameters since every circuit element represents a physical optical cavity entity. The extraction of reliable intrinsic parameters requires that the circuit element values be representative of the device under test. To achieve this, we have developed a new methodology based on static and dynamic measurements such as the S-parameters and the turn-on delay time. In accordance with this procedure, each element of the cavity is fixed without numerical optimization. The good agreement between measured and simulated curves confirm the validity of the technique used

A photonic QPSK modulation in 2 GHz with an RF signal from a microwave optoelectronic oscillator

International audienceThis article presents a photonic circuit that achieves direct carrier QPSK modulation of an RF signal from an optoelectronic oscillator (OEO) suitable for satellite data transmitter. The circuit was implemented with three Mach-Zehnder optical modulators. One modulator was used to construct an OEO to generate a carrier with a frequency equal to 2.019 GHz. The others two modulators were used to compose the microwave photonic I/Q modulator. The setup initially achieved a data rate of 50 Mbps in a QPSK scheme with an EVM of 7.5%. Using a root-raised-cosine filter, it was possible to reduce the EVM to 5%. The diagrams of the optoelectronic circuit and the modulation measurements are displayed. After the EVM analysis, the modulated signal was demodulated through an actual satellite receiver. Using the demodulator, it was possible to measure the BER and consequently the degradation analysis. The degradation for a bit rate of 100 Mbps was 0.07 dB using the OEO as RF generator. In this case, the values of Eb/N0 and BER were 11.37 dB and 10−7, respectively

Automatic bias control suitable for a microwave photonic vector modulator

The microwave photonic vector modulator (MPVM) sometimes shows an unmodulated carrier peak, which appears in the modulated signal. This peak results from an incorrect bias value or a Mach-Zehnder modulator (MZM) bias drift over time, which in turn leads to an imbalance in the I/Q signals. This paper describes a mathematical model of an MPVM output by showing the unmodulated carrier peak behavior. It also discusses a constellation imbalance resulting from this non-modulated peak. To control this non-modulated carrier peak and restore the constellation balance, an automatic bias control (ABC) is proposed and simulated through a co-simulation technique. Unlike previous methods, this ABC is based on the analysis of the I/Q signals to generate voltage steps for the photonic modulator bias. The I/Q signals were recovered through a direct-conversion receiver, and an algorithm was developed to analyze the I/Q amplitude and phase imbalance. Consequently, the photonic modulator bias is continuously monitored by analyzing the resulting modulated microwave signal. In this way, its operation is transparent under MZM bias variations or extinction ratio (ER) imperfection since only the I/Q and microwave signals are considered in the algorithm implementation. ABC is validated through a co-simulation technique using low and high-order modulation formats such as QPSK, 64QAM, and 256QAM

Multilevel behavioral simulation of VCSEL-based optoelectronic modules

International audienceThe assembly within a single optoelectronic interconnect module of different components, including vertical-cavity semiconductor lasers and photodiode arrays, optical fibers, and electronics implying electrical, optical, mechanical, and thermal interactions, introduces new constraints in the conception phase and necessitates a new and different approach for modeling and simulation. A promising solution, when conceiving optoelectronic microelectromechanical systems, is obtained by simulation with the multilevel language VHDL-AMS based on system component parameters and standards

The NIMPH Project

International audienceThe next generation of telecommunication satellites operating in the Ku and Ka bands consider radio over optical fibre (RoF) technologies as a good candidate for the future flexible payloads. During the last 10 years CNES has supported the evaluation of optical components for spatial requirements. At present, experimental feedback in real environment would accelerate the introduction of RoF technologies for spatial needs. It is in this context that Thales Alenia Space and CNES offered the opportunity to the students of Toulouse University to realize a nanosatellite dedicated to the orbital test of a RoF transmission. This 2 years old ongoing project is entitled: Nanosatellite to Investigate Microwave Photonics (NIMPH)