Extinction ratio

About: Extinction ratio is a research topic. Over the lifetime, 8541 publications have been published within this topic receiving 111908 citations.

An ultrafast light gate

Abstract: A device has been built which is capable of gating light on and off on the picosecond time scale. The gate is built in much the same fashion as traditional Kerr cells, the difference lying in the use of powerful optical pulses rather than electrical pulses to induce a birefringence in various liquids. In the experiment, powerful light pulses from a mode-locked Nd:glass laser, ∼5 psec in duration (wavelength 1.06µ), are used to induce a birefringence in a number of liquids including CSµ, nitrobenzene, chlorobenzene, dichloroethane and others. The transmission of the gate as a function of time is probed by means of 0.53µ green light pulses derived from the 1.06µ pulses by second harmonic generation. With CS 2 the transmission curve has a width of 8 psec; the peak transmission is 10% and the extinction ratio is 200. With nitrobenzene the curve has an exponentially falling tail on one side. The associated decay time is 32± 6 psec. Since 32 psec is a time characteristic of molecular reorientation times, this observation provides direct support for the long held belief that orientational effects dominate light induced refractive index changes in nitrobenzene.

Laser control circuit

Abstract: A laser diode control circuit maintains a desired average output power of the laser diode (10) by detecting (18) the optical output, amplifying (24) the detected output, and controlling a bias current (14) of the laser diode accordingly. A pilot tone (20) is combined with the detected output (18) and amplified therewith, and the amplified (24) level of the tone is detected (22) and used to control (26) a modulation current (16) for the laser diode. In one described arrangement the laser diode (10) is controlled to have a high extinction ratio with the bias current at the knee (42) of the diode's characteristic curve, and in another arrangement a lower extinction ratio is provided with the bias current above the knee (42).

Spectrally Efficient WDM Nyquist Pulse-Shaped Subcarrier Modulation Using a Dual-Drive Mach–Zehnder Modulator and Direct Detection

Abstract: High data transmission capacity is increasingly needed in shortand medium-haul optical communication links. Cost-effective wavelength division multiplexed (WDM) transceiver architectures, achieving high information spectral densities (ISDs) (>1 b/s/Hz) and using low-complexity direct detection receivers are attractive solutions for such links. In this paper, we assess the use of dual-drive Mach-Zehnder modulators (DD-MZMs), and compare them with in-phase quadrature (IQ)-modulators for generating spectrally-efficient single sideband Nyquist pulse-shaped 16-QAM subcarrier (N-SCM) modulation format signals. The impact of the extinction ratio (ER) of a modulator on the optical sideband suppression ratio (OSSR) was investigated for the SSB signals in WDM systems, together with the resulting impact on inter-channel crosstalk penalties. First, in back-to-back operation, an IQ-modulator with an ER of 30 dB and a DD-MZM with an ER of 18 dB were experimentally compared in a 6×25 Gb/s WDM system by varying the channel spacing. Following this comparison, 16 GHz-spaced 6×25 Gb/s WDM signal transmission was experimentally demonstrated using the DD-MZM. The experiment was performed using a recirculating loop with uncompensated standard single-mode fiber (SSMF) and EDFA-only amplification. The maximum achievable transmission distances for single channel and WDM signals were found to be 565 and 242 km, respectively, at a net optical ISD of 1.5 b/s/Hz. This is the first experimental comparison of such modulator types for SSB N-SCM signal generation and the highest achieved ISD using a DD-MZM in direct-detection WDM transmission.

Multi-channel modulation in a DWDM monolithic photonic integrated circuit

Abstract: We present a multi-channel modulation circuit monolithically integrated with one 25-GHz-spacing AWG for both MUX and DEMUX and eight channels of SOAs and EAMs. The circuit can generate individual optical signals for each DWDM channel with a high extinction ratio of >20 dB and loss compensation. The circuit size can be reduced to 15 /spl times/ 7 mm/sup 2/.