ABSTRACT
We generate random numerical waveforms that mimic laser phase noise incorporating laser-resonance enhanced phase noise. The phase noise waveforms are employed in system simulators to estimate the resulting bit error rate penalties for differential quadrature phase shift keying signals. The results show that baudrate dependence of the bit error rate performance arises from laser-resonance phase noise. In addition, we show with supporting experimental results that the laser-resonance phase noise on the pumps in four-wave-mixing-based wavelength converters is responsible for large bit error rate floors.
ABSTRACT
We employ simple analytical models to construct the entire frequency-modulation (FM)-noise spectrum of tunable semiconductor lasers. Many contributions to the laser FM noise can be clearly identified from the FM-noise spectrum, such as standard Weiner FM noise incorporating laser relaxation oscillation, excess FM noise due to thermal fluctuations, and carrier-induced refractive index fluctuations from stochastic carrier generation in the passive tuning sections. The contribution of the latter effect is identified by noting a correlation between part of the FM-noise spectrum with the FM-modulation response of the passive sections. We pay particular attention to the case of widely tunable lasers with three independent tuning sections, mainly the sampled-grating distributed Bragg reflector laser, and compare with that of a distributed feedback laser. The theoretical model is confirmed with experimental measurements, with the calculations of the important phase-error variance demonstrating excellent agreement.
ABSTRACT
We investigate the effects of different phase noise processes of SGDBR laser on coherent systems. The SGDBR device operated well with QPSK modulation at 5 Gbaud, while the performance of 16-QAM was significantly degraded due to excess noise. The white FM noise mainly defines the ultimate performance of coherent reception, but the low frequency excess noise can potentially degrade the performance of systems that employ 16-QAM format at 5 Gbaud.
ABSTRACT
We propose a novel coherent self-heterodyne receiver structure based on phase modulation detection that potentially simplifies the front-end of a coherent optical receiver. The scheme has been demonstrated via simulations and experimentally for a 10 Gb/s DQPSK transmission system.
Subject(s)
Computer Communication Networks/instrumentation , Optical Devices , Signal Processing, Computer-Assisted/instrumentation , Telecommunications/instrumentation , Computer-Aided Design , Equipment Design , Equipment Failure Analysis , MicrowavesABSTRACT
Viewed historically and cross-culturally, orthostatic-induced dizziness, i.e., dizziness caused by standing up from a sitting or a lying position, forms a key aspect of many syndromes: irritable heart (American Civil War), effort syndrome (World War I and World War II), chronic fatigue syndrome (contemporary USA), Gulf War syndrome (contemporary USA), and orthostatic dysregulation (contemporary Japan). Among Vietnamese refugees attending a psychiatric clinic, this study documents a high rate of orthostatic panic (OP), as well as certain processes seemingly generating these panic attacks, viz., flashbacks and culturally specific catastrophic cognitions. Case examples are used to demonstrate OP's phenomenology and relevance to clinical care. To illustrate the mechanisms producing OP, we adduce the multiplex model of panic generation. Culturally appropriate care of Vietnamese refugees should include assessment and treatment of OP.
Subject(s)
Hypotension, Orthostatic/ethnology , Hypotension, Orthostatic/psychology , Panic Disorder/ethnology , Panic Disorder/etiology , Refugees/statistics & numerical data , Adult , Bipolar Disorder/ethnology , Bipolar Disorder/therapy , Cognitive Behavioral Therapy , Cross-Cultural Comparison , Female , Humans , Male , Mental Health Services/statistics & numerical data , Schizophrenia/ethnology , Schizophrenia/therapy , Stress Disorders, Post-Traumatic/psychology , Substance-Related Disorders/ethnology , Substance-Related Disorders/therapy , United States/epidemiology , Vietnam/ethnologyABSTRACT
This article discusses a culturally specific response to traumatic events: orthostatic panic attacks among Vietnamese refugees. We compared the rate and severity of orthostatic panic as well as the rates and severity of associated flashbacks a month before and a month after September 11, 2001. After that date, the rate and severity of orthostatic panic greatly increased, as did the rate and severity of associated flashbacks. The central role of orthostatic panic as a response to traumatic events is illustrated through a patient's vignette. An explanation of why September 11 so profoundly influenced this population is adduced, including an explanation of why it resulted in considerable worsening of orthostatic panic.
