A method to reduce laser phase noise by external compensation is presented and numerically evaluated. In this work, a theoretical framework and simulation results are provided and the feasibility of the method is shown.

A dither-free bias control technique for correcting bias drifts in electro-optic in-phase and quadrature modulators is presented and experimentally verified. The technique eliminates the need to apply a dither signal to the bias electrodes, and instead relies on the effects of the electrical modulation signals on the optical power. It is suited for applications where the modulation signals are of low frequency and would spectrally overlap with a conventional dither signal.

Distributed fiber sensing based on correlation-aided phase-sensitive optical time domain reflectometry is presented. The focus is on correlation as an enabler for high spatial resolution. Results from different applications are presented.

A deployed fiber with in-house and underground sections is interrogated with a coherent correlation OTDR. The origin and propagation speed of a hammer-generated pressure wave in the underground section is detected and acoustic signals are monitored.

Fiber optic sensing is becoming an important means to physically secure today’s network infrastructure. However, a network-wide deployment of the monitors will require cost reduction of the interrogator system, which can only be achieved by highly integrated system components. In this contribution, we report on the use of an in-house designed single-chip coherent transceiver for acoustic fiber sensing. The transceiver on the basis of silicon photonics contains a high-speed dual-polarization IQ-modulator as well as a coherent receiver with balanced photodiodes and trans-impedance amplifiers, as defined by the OIF integrated coherent transmit-receive optical sub assembly (IC-TROSA) implementation agreement. The laser, used for transmission and as local oscillator, is provided external to the photonic integrated circuit and can be chosen according to the line-width requirements of the sensing system. The acoustic sensing demonstration is using a correlation-based optical time domain reflectometry with coherent detection. This method is able to detect, besides the amplitude information, the phase of the back-scattered signal, which has a significantly higher sensitivity to environmental effects on the fiber, like temperature and strain. As a proof of concept, sensing of an acoustic signal after a fiber span of 20 km is demonstrated by evaluating the obtained phase information, providing information on external dynamic events up to a frequency of 1.75 kHz.

Superimposed temperature variations and dynamic strain applied through a 400 Hz acoustic signal on a 195 m single-mode fiber section are successfully measured using a coherent correlation optical time domain reflectometry as an interrogator.

We report on methods to monitor the transmission path in optical networks using a correlation-based OTDR technique with direct and coherent detection. A high probing symbol rate can provide picosecond-accuracy of the fiber propagation delay, while a sensitive phase detection with a high repetition rate allows the monitoring of dynamic effects in the vicinity of the fiber. We discuss various approaches to evaluate the measured traces and show the results of a few monitoring applications.

The immense growth of data traffic that traverses modern networks, calls for immediate solutions to tackle the challenges that arise in terms of speed, capacity, cost and energy efficiency. This manuscript outlines the key technological aspects of the PICaboo project, that aims to develop novel building blocks and photonic integrated circuits for the next generation of optical metro and access networks enhanced with optical signal processing functionalities exploiting the generic foundry model approach.

The development of a wavelength selective switch (WSS) for space-division multiplexing (SDM) applications is discussed, covering system aspects and applicability of an SDM-WSS in an optical network as well as the development of the free-space optics and of the Liquid-Crystal-on-Silicon (LCoS) Spatial Light Modulator (SLM), including the flexible driving solution.

A coherent optical subassembly (COSA) is evaluated for coherent-correlation optical time domain reflectometry (CC-OTDR) based fibre sensing. Even though the COSA was originally designed for digital communication applications, acoustic signals with frequencies up to 360 Hz can be detected after 50 km of transmission.

We review the application of correlation for fiber optical sensing using direct or coherent detection. The Correlation-OTDR with direct detection provides a group delay measurement resolution in the order of a few picoseconds, while coherent detection enables dynamic event evaluation by analyzing the phase information.

The use of optical fiber as sensor as well as transmission medium for sensing data is discussed, enabling the use of optically active sensors without power supply at distances of tens of kilometers. Depending on the interrogation system, a spatial resolution of less than a millimeter can be achieved. The basic sensing principle is optical time-domain reflectometry (OTDR) with direct detection or coherent detection of the Rayleigh back-scattered or Fresnel reflected signal. Spatial resolution is improved by a cross-correlation between the transmitted sequence and the received signals.

In this paper, we report on the development progress of correlation-based optical time domain reflectometry (OTDR). Substituting the direct detection receiver with a coherent receiver enables to extract the phase and polarization information of the reflected signal. Furthermore, due to the mixing of a weak probe signal with a strong local oscillator the sensitivity of the receiver improved. This improvement was demonstrated by analyzing the reflection from an angled physical contact (APC) connector. To further quantify the improvements, we compare the direct detection correlation OTDR (C-OTDR) with the coherent detection correlation OTDR (CC-OTDR) with respect to the spatial and amplitude resolution.

Utilizing a Coherent-Correlation-OTDR, 2000 draw tower gratings in 100 meter fiber with a spatial resolution of 50 mm were successfully interrogated. Spooling of the fiber results in variations of the FBG reflection spectra.

A correlation optical time-domain reflectometry (C-OTDR) method is presented, which measures the propagation delay with an accuracy of a few picoseconds. This accuracy is achieved using a test signal data rate of 10 Gbit/s and employing cross-correlation and pulse fitting techniques. In this paper we introduce and evaluate the basic signal processing steps, investigate the measurement accuracy, and discuss applications for monitoring link delay and chromatic dispersion of long fiber spans as well as temperature sensing applications.

Raman amplifiers and rare-earth doped fiber amplifiers are promising candidates for increasing the capacity of fiber optical links by opening up new wavelength ranges in the near future. These technologies are compared in different scenarios considering short-term and mid-term availability of qualified components.

Opening new wavelength bands is the most economic step for further increasing the capacity of optical transmission links. Characteristics of different amplifier technologies for signal amplification in different wavelength bands are detailed. In particular, the suitability of these technologies for short–term and mid–term implementation is considered. An important criterion is the availability of qualified components, notably the required pump laser diodes. On this basis, solutions for the near–term and the mid–term are discussed.

Single–fiber bidirectional transmission systems using the same wavelength for both directions suffer from reflection induced interference. Experimental results demonstrate the dependence of system performance and of the threshold of the forward error correction (FEC) on signal waveform variations induced by fiber effects. Larger signal distortions lead to slightly larger impact of the interference, but reduce the shift of the FEC threshold to smaller bit error ratios.

Exploiting new wavelength bands for data transmission is the most economic step for further increasing the capacity of optical links. Important aspects of the most relevant amplifier technologies supporting this step are discussed.

Using a Correlation-OTDR, we characterized the temperature-induced group delay variations of two nested antiresonant nodeless hollow core fibers. The temperature sensitivity of both is substantially less than for SSMF with some dependency on coating type.