VSR4 links use graded index multimode fibers (GIMMFs) as the transmission medium with operation wavelength 850nm. For cost reasons, VCSEL has been selected as the optical source to VSR4. The minimum bandwidth specification for 62.5um GIMMF in VSR4 is only 400 MHz•km for over-filled-launch (OFL) condition. The distance of 300 meters is limited over transmission rates of 1.25Gbit/s on the basis of this specification. In order to overcome the OFL bandwidth limit by selective excitation of a limited number of modes, conditioned launch technique is investigated. In this paper, based on a comprehensive dispersion theory of GIMMF, a model is built to simulate the transmission of optical signal in GIMMFs and a comparison between OFL and conditioned launch is analyzed. The result can be the guidelines for the best choice of techniques for various LAN and interconnect systems also.
This paper describes the design process and performance of the optimized parallel optical transmission module. Based on 1×12 VCSEL (Vertical Cavity Surface Emitting Laser) array, we designed and fabricated the high speed parallel optical modules. Our parallel optical module contains a 1×12 VCSEL array, a 12 channel CMOS laser driver circuit, a high speed PCB (Printed Circuit Board), a MT fiber connector and a packaging housing. The L-I-V characteristics of the 850nm VCSEL was measured at the operating current 8mA, 3dB frequency bandwidth more than 3GHz and the optical output 1mW. The transmission rate of all 12 channels is 30Gbit/s, with a single channel 2.5Gbit/s. By adopting the integration of the 1×12 VCSEL array and the driver array, we make a high speed PCB (Printed Circuit Board) to provide the optoelectronic chip with the operating voltage and high speed signals current. The LVDS (Low-Voltage Differential Signals) was set as the input signal to achieve better high frequency performance. The active coupling was adopted with a MT connector (8° slant fiber array). We used the Small Form Factor Pluggable (SFP) packaging. With the edge connector, the module could be inserted into the system dispense with bonding process.
This paper proposes a novel and innovative scheme for 10Gb/s parallel Very Short Reach (VSR) optical communication system. The optimized scheme properly manages the SDH/SONET redundant bytes and adjusts the position of error detecting bytes and error correction bytes. Compared with the OIF-VSR4-01.0 proposal, the scheme has a coding process module. The SDH/SONET frames in transmission direction are disposed as follows: (1) The Framer-Serdes Interface (FSI) gets 16×622.08Mb/s STM-64 frame. (2) The STM-64 frame is byte-wise stripped across 12 channels, all channels are data channels. During this process, the parity bytes and CRC bytes are generated in the similar way as OIF-VSR4-01.0 and stored in the code process module. (3) The code process module will regularly convey the additional parity bytes and CRC bytes to all 12 data channels. (4) After the 8B/10B coding, the 12 channels is transmitted to the parallel VCSEL array. The receive process approximately in reverse order of transmission process. By applying this scheme to 10Gb/s VSR system, the frame size in VSR system is reduced from 15552×12 bytes to 14040×12 bytes, the system redundancy is reduced obviously.
Performance of asynchronous phase-encoded OCDMA system is evaluated on the condition that receiver noise and the impact of fiber channel are neglected. Phase-encoded optical signal (pseudo random optical signal with low intensity) is analyzed in the view of stationary random process. The pseudo random optical signal with low intensity is seen as a sample function of a certain stationary random process which is ergodic in strict sense. The analysis results reveal that the variance of the corresponding random process is only inversely proportional to the code length while the root-mean-square width of the phase-encoded optical signal is proportional to the width of initial optical pulse and the code length F. The numerical results demonstrate that the better system performance can be achieved in case of larger code length and shorter initial optical pulse.
By designating different frequencies to different mark positions of the modified prime code, a frequency-time spreading code is proposed. The side lobe of auto-correlation and cross-correlation of the proposed code have relatively lower values. The scheme greatly improves the total number of the available codes in asynchronous optical code division multiple access (OCDMA) system. Numerical results show that the asynchronous OCDMA system using the proposed code has excellent performance in the presence of double hard limiters. We also introduce an encoding/decoding device which is based on the frequency-time spreading modified prime code.
Group velocity walk-off effect on frequency hopping optical code division multiple access (FH-OCDMA) system is analyzed. We develop a systematic method which employs transfer function considering encoder, fiber channel and decoder to analysis the FH-OCDMA system. The difference of group velocities affects system performance more seriously than dispersion effect. The results show that single mode fiber is not proper for the FH-OCDMA system even the transmission length is no more than 1 kilometer while the dispersion-shifted fiber is more suitable for FH-OCDMA system.