E.G. Churin

Design of free space WDM router based on holographic concave grating

A design for a 91/spl times/91 router with 0.33 nm channel spacing using a stationary anastigmatic Littrow mount of a holographic concave grating is reported. A simplified method of concave grating analysis is developed for the evaluation of the wavelength router performance. The coupling losses for all routed channels are within -0.9 dB and the power penalty due to coherent crosstalk caused by aberrations and diffraction at the aperture is negligibly small.

The influence of aperture size and shape on crosstalk level in free-space grating demultiplexers for WDM networks

A simple method is presented to calculate crosstalk caused by aberrations and diffraction at the aperture edges in free-space grating demultiplexers for wavelength-division multiplexed (WDM) communication systems. The influence of circular and square aperture sizes is described for ideal and aberrated optical systems. It is shown that aperture enlargement is not critical to aberrations whilst providing significant crosstalk reduction. The minimum crosstalk value is obtained when the dispersion plane is parallel to the diagonal of the square aperture. -60 dB crosstalk is attainable for moderately aberrated systems with 80 channels (0.5 nm spacing) in the range 1530-1570 nm.

Free-space, dense WDM router based on a new concave grating configuration

A 91/spl times/91 switchless wavelength router using a concave Littrow mount-based holographic grating is designed. Coupling losses for all channels, spaced by 0.33 nm, are within -0.9 dB. In this device, the coherent crosstalk due to aberrations and diffraction at the aperture leads to a negligible penalty.

Optimization of Rowland circle mounts for grating demultiplexers and narrow-band spectrographs.

A simple equation for the parameters of the Rowland circle grating mount is derived that ensures that the astigmatism and the meridional spherical aberration are stationary at the wavelength of correction. This is important in optimizing the design of grating multiplexers-demultiplexers and cross connects in wavelengthdivision multiplexed networks and high-resolution narrow-band spectrographs. An analysis of aberrations in three-dimensional and planar two-dimensional optical schemes is presented, and it is shown that in the wavelength range of 1530-1570 nm diffraction-limited performance can be achieved for 160 channels in a three-dimensional multiplexer-demultiplexer and for more than 800 channels for a planar free-space scheme.

Transmission passband, optical crosstalk and cascadability of free-space concave grating demultiplexer for dense WDM networks

We describe the performance of a 100 channel free-space concave grating demultiplexer with 1dB transmission passband of ±7GHz (FWHM 14–22GHz). The influence of optical aberrations and defocusing on the transmission spectrum is demonstrated. Crosstalk between neighbouring channels separated by >0.3nm is lower than −25dB and no penalty due to crosstalk is observed using 2.6Gbit/s directly modulated DFB lasers. Penalty-free transmission through a cascade of 30 demultiplexers is demonstrated in an optical fibre recirculating loop experiment, and the permitted tolerances on the laser frequency misalignments for a larger number of cascaded demultiplexers are investigated.

Concave grating and convex mirror double dispersion spectrograph for optical network applications

The concave grating stationary anastigmatic spectrograph has been modified into a novel retroreflective scheme by introducing a convex mirror concentric to the intermediate image. This provides double dispersion, diffraction-limited imaging of a long entrance slit, and substantial compensation of the stationary chromatic astigmatism. One can realize 140 independent multi/demultiplexers with 160 channels each simultaneously in the described device for optical network applications. Ray-tracing spot diagrams are presented.

Low-crosstalk, loss and PDL grating demultiplexer for application in terabit WDM routed networks

We report on the performance of a diffraction grating demultiplexer for narrow channel spacings of /spl les/50 GHz (/spl les/0.4 nm). The device exhibited a fiber-to-fiber loss of 3.8 dB, very low adjacent channel crosstalk of -43 dB, background crosstalk of -55 dB and polarization dependence of <0.3 dB. The transmission performance with 16/spl times/10 Gbit/s channels is also reported.

Free-space grating demultiplexer for densely-spaced, subnanometer wavelength-routed optical networks

We report on the diffraction-limited performance of a free-space aberration corrected concave grating demultiplexer. The fibre-to-fibre loss was less than 9 dB and channel isolation better than 25 dB for channel spacing of 0.4 nm, in the wavelength range 24 nm around 1.5 /spl mu/m. This device has applications in wavelength routing crossconnects and in optical spectrum analysers.