High-speed photodetectors for full-wavelength-band WDM transmission systems at 40Gb/s and beyond

The capacity of the WDM system can be increased by increasing the useable optical bandwidth or using the available bandwidth more efficiently since bit. Ultra-wide-band WDM transmissions with high bit rates in the full-WDM-wavelength range from the O to U bands (1260-1675 nm) are also very attractive for achieving high-capacity WDM transmission at low cost. This paper represents the high-speed photodetectors with a 3-dB bandwidth of more than 50 GHz for full-wavelength-band WDM transmission systems at 40Gb/s and beyond. The photodetector is a back-illuminated lattice-mismatched InGaAs PIN photodiode that we designed and fabricated to operate with a 3-dB cut-off frequency to values above 40 GHz, in the full-WDM-wavelength range from the O to U bands, by applying a small junction diameter and reduced the thickness of the light-absorbing InGaAs layer with a lattice-mismatch of +0.2% to InP. For our photodiode modules, a 3-dB bandwidth as high as 65 GHz was achieved at a bias voltage of 3 V and the responsivities at wavelengths of 1310, 1552 and 1670 nm were 0.6, 0.65 and 0.55 A/W, respectively. 40Gb/s receivers and 10Gb/s PIN/TIA modules were described as applications of the FWB-PDs. The photodiode modules operating up to the bandwidth of 50GHz and above in the full-WDM-wavelength range can drive the development to 40Gb/s WDM transmission systems using RZ or NRZ format and the additional new channels in the U band.