Heterodyne detection of wavelength-swept super-dense WDM signal employing spectrum shaping

Abstract

A spectrum shaping technique is proposed for a previously proposed wavelength-swept wavelength division multiplexing (WDM) transmitter to allow it to be employed for heterodyne detection in the receiver side. With this technique, image rejection for all channels is performed on the transmitting side using a single optical periodic filter, therefore image-induced crosstalk can be suppressed. Furthermore, the selective heterodyne detection of a multi-channel 1.0 Gbit/s/ch super-dense WDM is demonstrated using a 12.5 GHz MZI filter as the spectrum shaping filter.Introduction: Wavelength division multiplexing (WDM) is a promising technique for meeting the growing demand for increased bandwidth and various types of services in the optical access network. In future access networks (especially with regards to downlinks), we require techniques for super-dense WDM (SD-WDM) [1] so that we can provide attractive additional services, such as high-quality video distribution or ondemand services, within the narrow spectral range unoccupied by existing access systems. For such SD-WDM access systems, a key technology is a multi-wavelength optical transmitter, which generates plural wavelength channels and precisely locks the wavelength channel spacing. As a promising solution, we have already proposed a multiwavelength optical transmitter based on the time-domain modulation of a wavelength-swept light [2,3]. With this technique, we can realise a WDM signal with a super-dense grid, e.g. around 0.1 nm (12.5 GHz in the 1550 nm band), using only a single light source and a modulator. In [2,3], we demonstrated the generation and selective detection of a four-channel 1.25/2.5 Gbit/s SD-WDM signal with a direct detection scheme.In this Letter, we propose a spectrum shaping technique to apply heterodyne detection to the receiving sides. Heterodyne detection is a coherent detection method which offers the advantages of high sensitivity and fine wavelength selectivity compared with a direct detection scheme, and is expected to be a key technology in future fibre-optic networks including access areas [4,5]. Since heterodyne detection requires no phase synchronisation between the signal and the local light, the approach is easier to implement than homodyne detection. However, since there is a problem with respect to image-induced crosstalk [6], an image rejection operation is needed in all channels to achieve sufficient reception quality. With the proposal, the image rejection of all the channels is performed on the transmitting side using a single optical periodic filter. As proof of concept, we demonstrate the selective heterodyne detection of multi-channel 1.0 Gbit/s/ch SD-WDM with a 12.5 GHz spacing.

Ultrafast Wavenumber Linear-Step-Swept Source Based on Synchronous Lightwave Synthesized Frequency Sweeper

“…Wavelength-swept source has been widely used in dynamic fiber Bragg grating sensing [1], wavelength-division multiplexing (WDM) networks [2], swept source optical coherence tomography (SS-OCT) [3], frequency-modulated continuous-wave (FMCW) reflectometry [4], dispersion measurement [5], and remote sensing of the atmosphere [6], etc. In these systems, a rapid and linear k-space swept source is crucial for increasing the spectrum sampling efficiency and decreasing the complexity of data processing.…”