Ring-resonator-based wavelength filters

Microring resonators (MR) represent a class of filters with characteristics very similar to those of Fabry–Perot filters. However, they offer the advantage that the injected and reflected signals are separated in individual waveguides, and in addition, their design does not require any facets or gratings and is thus particularly simple. MRs evolved from the fields of fibre optic ring resonators and micron scale droplets. Their inherently small size (with typical diameters in the range between several to tens of micrometres), their filter characteristics and their potential for being used in complex and flexible configurations make these devices particularly attractive for integrated optics or VLSI photonics applications.\ud MRs for filter applications, delay lines, as add/drop multiplexers, and modulators will be covered in detail in this chapter, while other applications such as in optical sensing, in spectroscopy or for coherent light generation (MR lasers) are outside the scope of this chapter.\ud This chapter focuses primarily on 4-port microrings, while 2-port devices will play a minor role here and are covered in more detail in Chap. 9. The present chapter starts with design considerations, the functional behaviour, and key characteristics of a single microring resonator and continues with the design of cascaded MRs allowing the implementation of higher order filters. Finally, complex devices like add-drop filters, tuneable dispersion compensators, all-optical wavelength converters, and tuneable cross-connects are treated.\u

Simultaneous chromatic dispersion, polarization-mode-dispersion and OSNR monitoring at 40Gbit/s

A novel method for independent and simultaneous monitoring of chromatic dispersion ( CD), first-order PMD and OSNR in 40Gbit/s systems is proposed and demonstrated. This is performed using in-band tone monitoring of 5GHz, optically down-converted to a low intermediate-frequency (IF) of 10kHz. The measurement provides a large monitoring range with good accuracies for CD (4742 +/- 100ps/nm), differential group delay (DGD) (200 +/- 4ps) and OSNR (23 +/- 1dB), independently of the bit-rate. In addition, the use of electro-absorption modulators (EAM) for the simultaneous down-conversion of all channels and the use of low-speed detectors makes it cost effective for multi-channel operation. (C) 2008 Optical Society of Americ

Coherent quantum measurement for the direct determination of the degree of polarization and Polarization Mode Dispersion compensation

An example of a coherent measurement for the direct evaluation of the degree of polarization of a single-mode optical beam is presented. It is applied to the case of great practical importance where depolarization is caused by polarization mode dispersion. It is demonstrated that coherent measurement has the potential of significantly increasing the information gain, compared to standard incoherent measurements.Comment: 4 pages + 3 figure

Nonlinear effects with a focus on cross phase modulation and its impact on wavelength division multiplexing optical fibre networks

The demand for faster data transmission is ever increasing. Wavelength division multiplexing (WDM) presents as a viable solution to increase the data transmission rate significantly. WDM systems are based on the ability to transmit multiple wavelengths simultaneously down the fibre. Unlike time division multiplexing (TDM) systems, WDM systems do not increase the data transfer by increasing the transmission rate of a single channel. In WDM systems the data rate per channel remains the same, only multiple channels carry data across the link. Dense wavelength division multiplexing (DWDM) promises even more wavelengths packed together in the same fibre. This multiplication of channels increases the bandwidth capacity rapidly. Networks are looking into making use of technology that will ensure no electronic signal regeneration at any point within the DWDM network. Examples are; reconfigurable optical add/drop multiplexers (ROADM) and optical cross connect (OXC) units. These components essentially enable network operators to split, combine and multiplex optical signals carried by optical fibre. WDM allows network operators to increase the capacity of existing networks without expensive re-cabling. This provides networks with the flexibility to be upgraded to larger bandwidths and for reconfiguration of network services. Further, WDM technology opens up an opportunity of marketing flexibility to network operators, where operators not only have the option to rent out cables and fibres but wavelengths as well. Cross phase modulation (XPM) poses a problem to WDM networks. The refractive index experienced by a neighbouring optical signal, not only depends on the signal’s intensity but on the intensity of the co-propagating signal as well. This effect leads to a phase change and is known as XPM. This work investigates the characteristics of XPM. It is shown that, in a two channel WDM network, a probe signal’s SOP can be steered by controlling a high intensity pump signal’s SOP. This effect could be applied to make a wavelength converter. Experimental results show that the degree of polarization (DOP) of a probe signal degrades according to a mathematical model found in literature. The pump and probe signals are shown to experience maximum interaction, for orthogonal probe-pump SOP vector orientations. This may be problematic to polarization mode dispersion compensators. Additionally, experimental results point out that the SOP of a probe signal is much more active in the presence of a high intensity pump, as compared to the single signal transmission scenario

Multicanonical Monte Carlo Method Applied to the Investigation of Polarization Effects in Optical Fiber Communication Systems

Polarization-mode dispersion (PMD) is a major source of impairments in optical fiber com‐ munication systems. PMD causes distortion and broadens the optical pulses carrying infor‐ mation and lead to inter-symbol interference. In long-haul transmission systems it is necessary to limit the penalty caused by polarization effects [1], so that the probability of ex