Filip Öhman

Enhancing light slow-down in semiconductor optical amplifiers by optical filtering

We show that the degree of light-speed control in a semiconductor optical amplifier can be significantly extended by the introduction of optical filtering. We achieve a phase shift of approximately 150 degrees at 19 GHz modulation frequency, corresponding to a several-fold increase of the absolute phase shift as well as the achievable bandwidth. We show good quantitative agreement with numerical simulations, including the effects of population oscillations and four-wave mixing, and provide a simple physical explanation based on an analytical perturbation approach.

Slow Light in a Semiconductor Waveguide for True-Time Delay Applications in Microwave Photonics

We have investigated the slow and fast light properties of a semiconductor waveguide device employing concatenated gain and absorber sections. This letter presents the experimental results as well as theoretical modeling. A large phase shift of 110deg and a true-time delay of more than 150 ps are demonstrated. The combination of amplitude and phase control of the modulated signal shows great promise for applications within microwave photonics.

Analytical expression for the bit error rate of cascaded all-optical regenerators

We derive an approximate analytical expression for the bit error rate of cascaded fiber links containing all-optical 2R-regenerators. A general analysis of the interplay between noise due to amplification and the degree of reshaping (nonlinearity) of the regenerator is performed.

Theory of Optical-Filtering Enhanced Slow and Fast Light Effects in Semiconductor Optical Waveguides

A theoretical analysis of slow and fast light effects in semiconductor optical amplifiers based on coherent population oscillations and including the influence of optical filtering is presented. Optical filtering is shown to enable a significant increase of the controllable phase shift experienced by an intensity modulated signal traversing the waveguide. The theoretical model accounts for recent experimental results and is used to analyze and interpret the dependence on material and device parameters. Furthermore analytical approximations are derived using a perturbation approach and are used to gain a better physical understanding of the underlying phenomena.

Voltage-controlled slow light in an integrated semiconductor structure with net gain

We demonstrate the use of coherent population oscillations (CPO) to realize a monolithically integrated semiconductor device which allows voltage controlled tuning of the group velocity corresponding to a phase shift of up to 55 degrees at a frequency of 10 GHz. By combining sections of slow and fast light, corresponding to absorption and gain, we demonstrate control of both the slow-down factor and the signal amplitude, which is important for applications as true-time delay in microwave photonics. The physics of CPO is discussed in relation to electromagnetically induced transparency (EIT). In particular, we demonstrate and explain the possibility of achieving transparency when using the effect of CPO despite the fact that it relies on only a partial saturation of an absorption line.

Noise and regeneration in semiconductor waveguides with saturable gain and absorption

We have modeled the noise properties of a novel waveguide device with regenerative properties. The device consists of alternating sections of saturable gain and absorption, which give a nonlinear power transfer function. We investigate the relative intensity noise spectra and signal-to-noise ratio after the device by both a small-signal analysis and large-signal simulation, and we show that the gain saturation gives noise redistribution at the mark level. We also examine the influence of the nonlinearity on the noise probability density function and show that the standard approximations of Gaussian and noncentral /spl chi//sup 2/ distributions do not give a satisfying description. The strength and weaknesses of the limiting cases of static transfer functions and linear noise transfer as well as the small-signal analysis are examined in the case of bit-error-rate estimation in a cascade of regenerators. The interplay between increased nonlinearity and noise is investigated and we show that the increased nonlinearity achieved by additional device sections can improve the cascadability although more amplified spontaneous emission noise is added.

All-Optical flip-flop operation using a SOA and DFB laser diode optical feedback combination

We report on the switching of an all-optical flip-flop consisting of a semiconductor optical amplifier (SOA) and a distributed feedback laser diode (DFB), bidirectionally coupled to each other. Both simulation and experimental results are presented. Switching times as low as 50ps, minimal required switch pulse energies below 1pJ and a repetition rate of 1.25GHz have been measured. Contrast ratios over 25dB have been obtained. The dependence on the pulse length and CW input power of the minimal required switch energy is investigated.

All-Optical Flip-Flop Based on an SOA/DFB-Laser Diode Optical Feedback Scheme

We report on the dynamic all-optical flip-flop (AOFF) operation of an optical feedback scheme consisting of a semiconductor optical amplifier (SOA) and a distributed feedback laser diode (DFB-LD), bidirectionally coupled to each other. The operation of the AOFF relies on the interplay between the optical powers in both the DFB-LD and the SOA. Switching times as low as 150ps for switch pulse energies of around 6 pJ and a repetition rate of 500MHz have been measured. The contrast ratio was measured to be above 12 dB

Modeling of bit error rate in cascaded 2R regenerators

This paper presents a simple and efficient model for estimating the bit error rate (BER) in a cascade of optical reamplification and reshaping (2R) regenerators. The model includes the influences of amplifier noise, finite extinction ratio (ER), and nonlinear reshaping. The interplay between the different signal impairments and the regenerating nonlinearity is investigated. It is shown that an increase in nonlinearity can compensate for an increase in noise figure or decrease in signal power. Furthermore, the influence of the improvement in signal ER along the cascade and the importance of choosing the proper threshold of the nonlinearity are investigated.

85 km Long Reach PON System Using a Reflective SOA-EA Modulator and Distributed Raman Fiber Amplification

We report on a bidirectional 85 km long reach PON system supported by distributed fiber Raman amplification with a record 7.5 Gb/s remote carrier modulated upstream signal by employing a reflective SOA-EA monolithically integrated circuit