NTT Research and Development 2008 Review of Activities

Since the VMUX/DEMUX^*1 includes fundamental optical node elements such as VOAs^*2, PDs^*3 and AWGs^*4 for wavelength multi/demultiplexing, it can be utilized in both fixed and reconfigurable OADM^*5 systems. Currently, these OADM systems are rapidly being deployed in metro-core and metro-access networks, and thus compact and inexpensive optical components including VMUX/DEMUX modules should be developed to reduce capital expenditures.

The best way of achieving compactness is to integrate these devices on a single chip by using PLC^*6 technology. Therefore, we developed an ultra-small single-chip 40-ch VMUX/DEMUX based on single-chip PLC integration and stacked PD integration techniques. The use of 2.5% -Δ silica-based waveguides greatly reduced the chip size without degrading optical performance. This chip includes two 40ch AWGs, 40 channels of VOAs with 8% tap couplers and power monitors for automatic VOA level control. The chip size was reduced to only 25 mm x 25 mm, and we could lay out 21 chips on a 6-inch wafer. The worst maximum transmittances of the VMUX and DEMUX were -5.6 dB (0 dB VOA attenuation state) and -3.9 dB, respectively, even though we employed the 2.5% -Δ silica-based waveguide. Moreover, the transmittance can be changed by changing the applied power of the VOAs. Good optical characteristics were obtained by using spot-size converters for low-loss fiber connection at input/output waveguides.

We will continue our research and development of densely integrated multi-function optical devices based on PLC technology with higher Δ waveguides.

• *1 VMUX/DEMUX: VOA-Multiplexer/Demultiplexer
• *2 VOA: Variable Optical Attenuator
• *3 PD: Photodiode
• *4 AWG: Arrayed-Waveguide Grating
• *5 OADM: Optical Add/Drop Multiplexing
• *6 PLC: Planar Lightwave Circuit