Performance of the coherent optical binary polarization-shift-keying heterodyne system in free space optical communications using a lognormal atmospheric turbulence model MIC-CPE 2010

In this paper, simulation results for the bit error rate (BER) performance and fading penalty of a coherent optical binary polarization shift keying (2PolSK) heterodyne system adopted for free space optical (FSO) communication links with a log-normal atmospheric turbulence model is presented. The conditional and unconditional BER expressions are derived, demonstrating the comprehensive similarity between the 2PolSK and binary frequency shift keying (2FSK) schemes with regards to the system sensitivity. The study shows that 2PolSK offers improved performance compared to the binary amplitude shift keying (2ASK

A MATLAB based simulation program for indoor visible light communication system

We report a simulation program for indoor visible light communication environment based on MATLAB and Simulink. The program considers the positions of the transmitters and the reflections at each wall. For visible light communication environment, the illumination light-emitting diode is used not only as a lighting device, but also as a communication device. Using the simulation program, the distributions of illuminance and root-mean-square delay spread are analyzed at bottom surface

Simultaneous transmission of audio and video signals using visible light communications

A visible light communication system for parallel transmission of high-quality audio and video signals using illumination white and red light-emitting diodes (LEDs) is presented in this paper. For video transmission, we adopts the pulse width modulation (PWM) scheme at the carrier frequency of 15 MHz, whereas for the analog audio signal, the Sony/Philips Digital standard is used. We show that successful simultaneous high-quality audio and video signal transmissions over a link span of 50 cm are possible without the need for optimized optics. For audio transmission, only the link span is doubled to 100 cm

Transient response of a passively mode-locked Er-doped fiber ring laser

In this study, we report on the transient response of a passively mode-locked erbium fiber ring laser as studied by switching the optical pumping of the erbium doped fiber on and off. We confirm that the laser can maintain its mode-locking state even while the pump is modulated, and describe the laser behavior and its typical transient response upon abrupt changes in the intensity of the optical pump

Effect of periodic optical pumping on dynamics of passive mode-locked fiber laser

We report on the effect of periodic optical pumping on a passively mode-locked fiber laser (MLFL) based on an erbium-doped fiber (EDF). We investigate the influence of various parameters (including average pump power into the fiber laser, the modulation frequency and duty cycle of the pump, and the polarization state of the light inside the cavity) on the transient response characteristic of the MLFL such as: relaxation oscillation (RO) build-up time (defined as the time delay from the onset of pumping to the generation of passively mode-locked pulses) and the power of the detected RF signal at the fundamental cavity-mode frequency (determined by the ring cavity length), which reflects the stability of mode-locking pulse train. We have found that the RO build-up time is inversely proportional to the average pump power while the RF power of the detected fundamental cavity mode (produced by the ring cavity) is proportional to the average pump power. A change in the duty cycle effectively leads the average pump power to vary, which in turn leads to changes in the transient response. The modulation frequency of the pump is rather related to the stability of the MLFL than its response time. Generally, the lower the modulation frequency, the more stable the mode-locked pulses generated in the fiber laser. Finally, the RO build-up time and, consequently, the pulse-generation time are highly sensitive to the state of polarization in the MLFL cavity

Scintillation effect on intensity modulated laser communication systems: a laboratory demonstration

This paper shows the impact of atmospheric turbulence-induced fading on the symbol decision position in the on-off keying (OOK) and the binary phase shift keying (BPSK) subcarrier intensity modulated (SIM) laser communication link. Weak turbulence is simulated in the laboratory using a chamber equipped with heating elements and fans. We have shown that in atmospheric turbulence, it is advantageous to employ modulation schemes such as pulse time and subcarrier intensity modulations that do not directly impress data on the optical irradiance as is the case with the OOK. For the OOK-modulated laser communication system, atmospheric turbulence imposes complexity on the symbol decision subsystem and by extension places a limit on the achievable bit error rate (BER) performance

Pulse-amplitude equalization in a rational harmonic mode-locked semiconductor ring laser using optical feedback

Abstract A novel method of pulse-amplitude equalization in a rational harmonic mode-locked semiconductor ring laser is proposed and experimentally demonstrated. This pulse-amplitude equalization method is based on two key points. One is that an optical pulse train introduced to a semiconductor optical amplifier (SOA) saturates the SOA gain quickly, and this can be used for the gain modulation of SOA. The gain modulation of SOA as a mode-locking process in a semiconductor ring laser can generate stable mode-locked pulse trains. The second point is that the SOA gain is equalized from pulse to pulse because the feedback optical pulse circulates inside the ring cavity. By combining the rational harmonic modelocking using a LiNbO 3 electro-optic modulator with the gain modulation of the SOA, amplitude-equalized optical pulse trains with the multiplied repetition rates of $10.00 GHz (the third rational harmonic) and$16.72 GHz (the fifth rational harmonic) were successfully demonstrated using optical feedback with pulse intensity matching. This scheme can be used for upgrading existing rational harmonic mode-locked semiconductor ring lasers to a semiconductor ring laser with equalized amplitudes at high pulse repetition rates.