ITU Wavelength Research Articles

Compact photonic crystal multichannel drop filter for CWDM systems

A novel photonic crystal channel drop filter (PCCDF) is proposed to drop four coarse wavelength division multiplexing (CWDM) channels at 1490 nm, 1510 nm, 1530 nm and 1550 nm. A special coupled dual-loop design was used for multichannel forward/backward dropping for the first time. Due to the reduced number of the dropping resonators with this design, the proposed multichannel PCCDF has a very compact size (338 μ m2). High transmission efficiencies at the four ITU wavelengths (87.87%, 93.99%, 85.40% and 84.24%) can be obtained simultaneously. Furthermore, the same dimension parameters (lattice constant and rod radius) of the dual-loop resonators are helpful for easy fabrication. The proposed device could be used in future photonic integrated circuit-based CWDM communication systems.

Monolithically Integrated 4-Channel-Selectable Light Sources Fabricated by the SAG Technology

The monolithic integration of four 1.5-μm InGaAsP/InP distributed feedback (DFB) lasers with a 4 × 1 multimode-interference (MMI) optical combiner using the selective area growth and butt-joint regrowth technologies is proposed and demonstrated. A dry-etching stop layer is grown to guarantee the etching depth of MMI. The four channels could match the ITU wavelength grid of 200-GHz well with a simple integrated thin-film heater, covering the wavelength range of 1552.3-1556.3 nm. The average output power of LD is 2.8 mW with a 150-mA current, and the threshold current is 20-22 mA at 25°C. The four channels can operate separately or simultaneously.

A flattop PLC polymer waveguide interleaver based on folded two-stage-cascaded Y-junction Mach–Zehnder interferometers

We demonstrate realization of a flattop Y-Junction Planar Optical Waveguide Interleaver (YJPOWI) with a channel spacing of 100GHz through a novel scheme of folded cascaded two-stage unbalanced Mach–Zehnder interferometers (MZI) fabricated on a polymer Planar Lightwave Circuit (PLC) platform. The characteristic 0.5dB passbands of the interleaver centered at ITU wavelength grids at its two output ports were 50 and 45GHz, respectively. The operating bandwidth of the device spanned the entire C band of a fiber amplifier and it is compact in size (1.3×1.4cm2). In addition, the device is easy to fabricate and do not require any individual heater to trim its performance.

Graeco-Latin-routed, self-wrapping, FSR-interleaved, AWG-based access network

Feature Issue on Passive Optical Network Architectures and TechnologiesWe describe, to the best of our knowledge, a novel WDM-TDM switched access network architecture featuring cascaded 16×16 and 1×32 arrayed waveguide gratings (AWGs), such that the AWG free spectral ranges (FSRs) have been matched to provide cascaded, cyclical, Graeco-Latin-routing protocols for downstream and upstream routing. In particular, use of FSR-multiplexed wavelengths allows greatly reduced cross talk between upstream and downstream signals and also doubling of the available network bandwidth capacity, while maintaining the same N×N AWG in the central office. Alternatively, this allows significant increase in the number of end users served by the network. We provide theoretical and simulation studies of our bidirectional access network topology, and experimental proof of principal results. Three sets of simulations with data rates from 2.5, 5.0, and 10.0Gbits/s have been performed for downstream and upstream transmissions. For the experimental part, eight ITU wavelengths were multiplexed at the exchange point and successfully transmitted at 2.5Gbits/s for simultaneous bidirectional transmission. Bit-error-rate measurements show error-free transmission is achievable for both directions with minimal cross talk between the channels.

A Novel Simple and Low-cost Wavelength Reconfigurable Optical Add/Drop Multiplexer

Optical Add/Drop Multiplexer (OADM) is a key component of DWDM system. In this paper a novel configuration of a wavelength-reconfigurable OADM is presented, which is based on a low-cost narrow-band filter array and a program-controlled micro mechanical actuator. This filtering system could provide a stable and flexible tuning from one ITU wavelength to another. An elaborate design is used to simplify the complicated configuration of the traditional OADM system. The new device could get applications in the metropolitan network and the access network because of its low cost and good performance.

DBR module with 20-mW constant coupled output power, over 16 nm (40 x 50-GHz spaced channels)

To replace DFB lasers in wavelength-division-multiplexing (WDM) systems, tunable lasers should provide the same output power (20 mW) and remain simple devices. We propose a two-section DBR laser with optimized design. The required settings to reach all the achievable ITU wavelengths with constant output power are simply derived from very few initial characterizations. We obtain a record 20-mW coupled output power, constant over 16 nm (=40 channels 50-GHz spaced). For the first time, power performances comparable with DFB lasers are obtained; DBR lasers are now competitive candidates for an integration in WDM systems.