Real-time experimental demonstration of
low-cost VCSEL intensity-modulated 1125Gb/s optical OFDM signal transmission over 25km PON systems

Abstract

The feasibility of utilising low-cost, un-cooled vertical cavity surface-emitting lasers (VCSELs) as intensity modulators in real-time optical OFDM (OOFDM) transceivers is experimentally explored, for the first time, in terms of achievable signal bit rates, physical mechanisms limiting the transceiver performance and performance robustness. End-to-end real-time transmission of 11.25 Gb/s 64-QAM-encoded OOFDM signals over simple intensity modulation and direct detection, 25 km SSMF PON systems is experimentally demonstrated with a power penalty of 0.5 dB. The low extinction ratio of the VCSEL intensity-modulated OOFDM signal is identified to be the dominant factor determining the maximum obtainable transmission performance. Experimental investigations indicate that, in addition to the enhanced transceiver performance, adaptive power loading can also significantly improve the system performance robustness to variations in VCSEL operating conditions. As a direct result, the aforementioned capacity versus reach performance is still retained over a wide VCSEL bias (driving) current (voltage) range of 4.5 mA to 9 mA (275 mVpp to 320 mVpp). This work is of great value as it demonstrates the possibility of future mass production of cost-effective OOFDM transceivers for PON applications.

REAM intensity modulator-enabled 10Gb/s colorless upstream transmission of real-time optical OFDM signals in a single-fiber-based bidirectional PON architecture

“…Making use of the OOFDM transceiver design and the experimental system setup described in Section 2.1, optimizations of transceiver and system operating conditions are first conducted in real-time to maximize the obtainable signal line rate by effectively compensating for the system frequency response roll-off effect through adaptive bit and power loading performed at the information-bearing subcarriers [18][19][20][21][22][23]. Figure 2(a) illustrates the obtained optimum subcarrier bit allocation profile corresponding to a raw signal bit rate of 10Gb/s, of which 8Gb/s can be employed to carry user data because of the use of a 25% cyclic prefix.…”

“…The received analog OFDM signal is digitized by the 8-bit ADC operating at 4GS/s. By employing real-time DSP procedures detailed in [18][19][20][21][22][23], all 15 data-carrying subcarriers in the positive frequency bins are used for automatic symbol alignment, channel estimation/equalization and data recovery. In addition, the BER analyzer continuously counts errors for every 88500 symbols, which corresponds to a total test pattern of 6 608 000 bits.…”

“…Recently, by making use of various commercially available, low-cost intensity modulators such as directly modulated distributed feedback (DFB) lasers [18] and vertical cavity surfaceemitting lasers (VCSELs) [19], we have experimentally demonstrated end-to-end real-time 11.25Gb/s OOFDM transmission over 25km SSMF-based PON systems employing IMDD. In a very similar IMDD transmission system architecture, record high 19.125Gb/s end-to-end real-time dual-band OOFDM signal transmissions over 25km SSMFs have also been experimentally achieved recently [20], utilizing low-cost components including an electroabsorption modulated laser-based intensity modulator, a 4GS/s digital-to-analogue converter (DAC), as well as a 4GS/s analogue-to-digital converter (ADC).…”

Effect of Injection Coherence on Noise and Bandwidth of Long-Cavity Colorless Laser Diode for Digital Modulation and Transmission

“…Transmission of the OFDM data was successively demonstrated with the distributed feedback laser diodes [44], [45], the vertical-cavity surface emitting laser diodes [46], [47], the DFBLD injection-locked WRC-FPLD [48], the DFBLD injection-locked low-resonant FPLD [49], the self-injectionlocked FPLD injection-locked FPLD [50], the DFBLD injection-locked RSOA [51] and the down-stream reused RSOA [52], [53]. The OFDM modulated WRC-FPLD or RSOA transmitter provides the high spectral usage to achieve the data rate of 4 or 7.5-10 Gbit/s by efficiently using the modulation bandwidth of only 1 GHz.…”

Half-cycle QAM modulation for VCSEL-based optical links

“…Multi-tone modulation (DMT), a subclass of orthogonal frequency division multiplexing (OFDM), is a promising technology for both increasing spectral efficiency and dispersion tolerance. High speed data transmission of DMT signal using VCSELs has been demonstrated recently [9][10]. However, to support high-speed data transmission, DMT requires fast analogue to digital (ADC) and digital to analogue (DAC) converters.…”