Instrumentation system for determination and compensation of electro-optic modulator transfer function drift

Abstract

This paper presents an instrumentation system developed to improve the operation of an electro-optic modulator (EOM). During their operating time, EOM are subject to a drift of the optical transfer function; therefore the initial tuning of the bias point no longer corresponds to the best characteristics of the device. Because of this drift the EOM no longer behaves linearly and there is degradation during time of the performances of the system in which the EOM is included. To determine the drift, a low frequency modulation signal (at 500 Hz) is applied to the EOM and the second harmonic component at 1 kHz is detected. A new criterion is introduced for estimating the nonlinearity and for compensating the drift of the transfer function, keeping the optical bias point at the quadrature position. Temperature changes significantly influence the EOM characteristics. Thus, the instrumentation system has to be simultaneously developed with temperature control and drift compensation of the optical transfer function. The design is based on PSOC microcontrollers for tuning the different parameters, for data acquisition and regulation process. By setting the temperature to some specific values, it is possible to test the behaviour of the modulator. Finally, by using both temperature and bias point control, a significant reduction of the nonlinearity can be obtained during 2 h of experiment: the biasing point at the quadrature point of the transfer function which corresponds to the most linear behaviour can be stabilized within ±0.22% of the half-wave voltage. All the works presented here were carried out with a Mach–Zehnder intensity modulator made of lithium niobate, but it is also possible to apply this method to other kinds of material, for example polymer material.

An arbitrary-function light power controller

“…Based on these requirements, we have designed a simple feedback-based arbitrary-function light power controller (AFPC) for our everyday laboratory experiments. Previously published approaches for compensating bias drifts have used active bias voltage stabilization based on bias modulation 2,3 and/or temperature stabilization. 2 The state-of-the-art photonic arbitrary waveform generator described in Ref.…”

“…Previously published approaches for compensating bias drifts have used active bias voltage stabilization based on bias modulation 2,3 and/or temperature stabilization. 2 The state-of-the-art photonic arbitrary waveform generator described in Ref. 4 uses three serially connected Mach-Zehnder modulators, driven by six digital 12.5 Gb/s signals.…”

Performance enhancement for long distance BOTDR sensing system based on high extinction ratio probe pulse generator

“…Traditionally, an optical coupler (OC) is used to feedback a small part (1% for example) of the EOM output signal for ER stabilization [9][10][11] . Stabilizer adds a small disturbance signal upon the modulator and analyzes the variation of the …”

Modelling and experimental linearisation of electric field sensing using electrode‐less LiNbO 3 interferometers and incoherent light

“…In electrode-less AMZIs sensors, an optical bias can be realised by introducing an optical phase shift, either by a difference on the lengths of the optical arms or by modifying the refractive index in the optical waveguides [1][2][3][4]. However, as the fabrication tolerances of the optical waveguides do not ensure fixing the operating point, additional elaborated active adjusting can be implemented [5,6]. Without any bias of the sensor, the physical variable will be imprinted in any region of its EOTF.…”