This paper presents a brief review and discussion on the opportunities and challenges facing the optical components and sub-systems vendors. Specifically, this paper discusses some of the current components and sub-system development on the low loss CWDM filters, wavelength blockers, PLC switch arrays, wavelength selective switches, optical protection switching sub-systems, tunable filters and DCMs, and in addition, the fiber-coupled short-wavelength diode-lasers for medical applications.
Design of a high bit rate burst mode clock and data recovery (BMCDR) circuit for gigabit passive optical networks (GPON) is described. A top-down design flow is established and some of the key issues related to the behavioural level modeling are addressed in consideration for the complexity of the BMCDR integrated circuit (IC). Precise implementation of Simulink behavioural model accounting for the saturation of frequency control voltage is therefore developed for the BMCDR, and the parameters of the circuit blocks can be readily adjusted and optimized based on the behavioural model. The newly designed BMCDR utilizes the 0.18um standard CMOS technology and is shown to be capable of operating at bit rate of 2.5Gbps, as well as the recovery time of one bit period in our simulation. The developed behaviour model is verified by comparing with the detailed circuit simulation.
As the development of the technology, fiber-to-the-home (FTTH) becomes a feasible solution to meet the increasing demand on bandwidth. Due to the massive number of end users, cheap and reliable components become the bottleneck to deploy the new technology. Triplexer is one of the key components in the FTTH and is used by every end user. Currently, the available triplexers are either based on bulk optics or fiber optics with large size and high price due to manual labor involved. Planar lightwave circuit (PLC) is a possible technology for massive production and cost reduction. However, it is very challenging to design such bi-directional triplexer on PLC. The first challenge is that three channels, at λ=1310nm, 1490nm, and 1555nm, are separated unevenly over a very large wavelength range; Secondly, the bandwidths of the three channels, Δλ=100nm, 20nm, and 10nm, are very different. In the paper, we proposed a novel design by combining both coarse WDM and dense WDM. In the design, a multi-mode interference (MMI) device is used for coarse WDM to separate the 1310nm from the other two channels. The dense WDM for the remaining two channels is performed by an array waveguide gratings (AWG). The MMI and AWG are built on the same wafer with monolithic integration. Initial simulation results show it is a very promising device.
A low cost and high performance 4-(lambda) WDM DFB laser array employing a new strong gain-coupling laser design and a novel compact package approach is developed for optical network application. The WDM4 laser array is capable of simultaneous operation with 2.5 Gb/s 100 km NDS fiber transmission.
High density wavelength division multiplexing (DWDM) requires several channels with a fixed wavelength spacing of 1 - 2 nm. This can be achieved by fabricating arrays of distributed feedback (DFB) lasers, using a photomask method to print the gratings with a different period for each DFB laser in the array. The grating phase mask is fabricated first, using e-beam lithography and reactive ion etching. The parallel exposure of all gratings using such a mask is orders of magnitude faster than direct wafer writing, using e-beam lithography. The characteristics of 8-channel gain coupled DFB laser arrays designed for a 2 nm channel spacing are reported. The required performance, achievable yield (i.e. cost), packaging requirements and reliability will determine whether these arrays are suitable for use in DWDM systems.
A simple theory is presented for the analysis of optical channel-dropping filters for dense WDM applications. It combines the orthogonal coupled-mode theory based on normal modes and the nonorthogonal coupled-mode theory based on isolated waveguide modes. Analytical solution is obtained for the power dropped in the resonant channel. The interplay between mutual coupling and direct Bragg reflection is discussed.
We present experimental results showing a reduction of relative intensity noise (RIN) in partly gain-coupled InGaAsP/InP multiquantum-well DFB lasers. By comparing with conventional index-coupled lasers, it is found that even a small gain-coupling improves significantly the feedback insensitivity of DFB lasers. The mechanism of the RIN reduction and the less feedback sensitivity are believed to be a combined effect of the high relaxation frequency and heavy damping rate, the stronger internal mode discrimination, the facet reflectivity immunity, and the flatter carrier distribution in the gain-coupling structure.