Papers by Tuomo von Lerber
Perception, 1997
Noise in visual neurons, or variability in psychophysical experiments, may be quantified in terms... more Noise in visual neurons, or variability in psychophysical experiments, may be quantified in terms of photon fluctuations from an ‘equivalent’ steady illumination. The conversion requires assumptions on how photon signals are pooled in space and time, ie how to pass from the light flux to the numbers of photon events relevant to the Poisson statistics describing signal/noise. Real weighting profiles for the integration of photon events in space and time [the sensitivity distribution of the receptive field (RF) and the waveform of the impulse response (IR)] are commonly approximated by sharp-bordered apertures of ‘complete’, equal-weight summation of events. Such apertures based on signal equivalence cannot provide noise equivalence, however, because greater numbers of events summed with lower weights (as in reality) have lower variances than smaller numbers summed with full weight. Thus sharp-bordered apertures are necessarily smaller if defined for noise equivalence rather than for ...
ArXiv, 2017
A programmable optical computer has remained an elusive concept. To construct a practical computi... more A programmable optical computer has remained an elusive concept. To construct a practical computing primitive equivalent to an electronic Boolean logic, one should find a nonlinear phenomenon that overcomes weaknesses present in many optical processing schemes. Ideally, the nonlinearity should provide a functionally complete set of logic operations, enable ultrafast all-optical programmability, and allow cascaded operations without a change in the operating wavelength or in the signal encoding format. Here we demonstrate a programmable logic gate using an injection-locked Vertical-Cavity Surface-Emitting Laser (VCSEL). The gate program is switched between the AND and the OR operations at the rate of 1 GHz with Bit Error Ratio (BER) of 10e-6 without changes in the wavelength or in the signal encoding format. The scheme is based on nonlinearity of normalization operations, which can be used to construct any continuous complex function or operation, Boolean or otherwise.
The advent of optical fibers has greatly impacted the modern technology landscape. Most notably, ... more The advent of optical fibers has greatly impacted the modern technology landscape. Most notably, existing telecommunications infrastructure relies on optical fiber networks, which have the ability to transmit high-bandwidth data over considerable distances. Optical fibers have also visible foothold in the field of metrology, where they are used as sensors in various applications. An optical resonator is a basic building block of many optical devices, such as lasers, measurement probes, and optical signal processing equipment. In this dissertation we propose new methods and tools for metrology and general telecommunications sciences based on fiber optical resonators. Compared to conventional free-space technology, fiber resonators enable easy connectivity and they are shown to be robust against ambient perturbations. This thesis consists of two parts that concentrate on optical measurement and signal processing technology, respectively. The first part introduces new measurement schem...
Our Paper describes a novel all-optical memory intended for optical computing applications and ca... more Our Paper describes a novel all-optical memory intended for optical computing applications and capable of integrated implementation. The memory circuit is based on a pair of mutually coupled, injection-locked lasers. The memory is static and volatile, i.e., it does not require refresh, and its state can be changed at will, respectively. We aim for a solution that can be fabricated with standard integrated optical technologies. We prove mathematically that the interconnected laser system has steady states that quantify and retain phase information under suitable conditions. We show numerically that despite simplifications of the mathematical analysis, also rate-equation-based models confirm the essential findings. We believe the proposed memory is unique in storing phase information in an all-optical setting. In the Paper, we provide a comprehensive review of existing optical memory approaches and argue some of the benefits of our approach. Naturally, the perceived benefit must alway...
SIAM Journal on Applied Dynamical Systems
An analytical study of dynamical properties of a semiconductor laser with optical injection of ar... more An analytical study of dynamical properties of a semiconductor laser with optical injection of arbitrary polarization is presented. It is shown that if the injected field is sufficiently weak, then the laser has nine equilibrium points, however, only one of them is stable. Even if the injected field is linearly polarized, six of the equilibrium points have a state of polarization that is elliptical. Dependence of the equilibrium points on the injected field is described, and it is shown that as the intensity of the injected field increases, the number of equilibrium points decreases, with only a single equilibrium point remaining for strong enough injected fields. As an application, a complex-valued optical neural network with working principle based on injection locking is proposed.
Optical Fiber Communication Conference, 2017
We experimentally demonstrate BER reduction and orthogonal modulation using an injection locked s... more We experimentally demonstrate BER reduction and orthogonal modulation using an injection locked single-mode VCSEL. It allows us suppressing an amplitude noise of optical signal and/or double the capacity of an information channel.
Teknillinen korkeakoulu Sähkö- ja tietoliikennetekniikan osasto Mikro- ja nanotekniikan laborator... more Teknillinen korkeakoulu Sähkö- ja tietoliikennetekniikan osasto Mikro- ja nanotekniikan laboratorio Distribution:
ABSTRACT The combination of tunable narrowband laser sources with the highly sensitive photoacous... more ABSTRACT The combination of tunable narrowband laser sources with the highly sensitive photoacoustic (PA) detection scheme bears great potential for pollution monitoring. The PA technique compares favorably with other optical methods such as multipass transmission or cavity ringdown spectroscopy. In trace gas sensing, the main requirements are high sensitivity and selectivity, multicomponent capability and large dynamic range. PA spectroscopy can generally offer these features. As example the detection of ppb to sub-ppb gas concentrations even in multicomponent mixtures and isotopic selectivity have been demonstrated. This report discusses some main characteristics and recent results illustrated by some examples. The judgement of air and water quality is of great concern with regard to, e.g., emission control of pollutants, air quality surveillance at workplaces, public health issues, etc. It requires novel measurement techniques for the sensitive and selective monitoring of all kinds of trace species. Besides numerous conventional and well established methods, photoacoustic schemes have only more recently gained in importance, particularly in air monitoring. In combination with tunable lasers as narrowband light sources, photoacoustic detection offers the advantage of a noncontact and rather simple setup. The microphones (or piezoelectric devices in the case of liquids) are compact room temperature detectors whose output signal is directly proportional to the absorbed radiation power or energy. This paper reviews the main features of such devices and demonstrates the performance with illustrative examples. Most studies have been performed on gases and only few on liquids, emphasis will thus be put on trace gas detection. Main features of photoacoustic (PA) instruments in trace detection Table I lists some important requirements that are generally posed on a trace gas sensor and approaches for their realization with laser-based systems. A high sensitivity is achieved by both choosing an appropriate wavelength and a sensitive detection scheme. The preferred wavelength region for spectroscopic studies on molecules is the fundamental or mid-infrared wavelength range between, say, 3 and 15 µm, where molecules exhibit strong absorptions caused by vibrational-rotational transitions. In the near-IR wavelength range tunable lasers such as diode or solid state lasers are readily available, but molecular absorption cross sections of overtone and combination band transitions are lower by orders or magnitude [1]. In the mid-IR range, conventional thermal light sources can be used but at the expense of spectral power density and thus of performance. However, for many applications these sources may still be appropriate as has been demonstrated by various examples including commercial devices [2,3].
Scientific Reports, 2019
An all-optical computer has remained an elusive concept. To construct a practical computing primi... more An all-optical computer has remained an elusive concept. To construct a practical computing primitive equivalent to an electronic Boolean logic, one should utilize nonlinearity that overcomes weaknesses that plague many optical processing schemes. An advantageous nonlinearity provides a complete set of logic operations and allows cascaded operations without changes in wavelength or in signal encoding format. Here we demonstrate an all-optical majority gate based on a vertical-cavity surface-emitting laser (VCSEL). Using emulated signal coupling, the arrangement provides Bit Error Ratio (BER) of 10−6 at the rate of 1 GHz without changes in the wavelength or in the signal encoding format. Cascaded operation of the injection-locked laser majority gate is simulated on a full adder and a 3-bit ripple-carry adder circuits. Finally, utilizing the spin-flip model semiconductor laser rate equations, we prove that injection-locked lasers may perform normalization operations in the steady-stat...
Optical Metro Networks and Short-Haul Systems II, 2010
We present an optical receiver for RZ-DPSK signals that use photonic balancing. Photonic balancin... more We present an optical receiver for RZ-DPSK signals that use photonic balancing. Photonic balancing is achieved through pulse counter-propagation and collision in a saturated SOA. We explain the principles of photonic balancing and show how it can lead to an improvement in RZ-DPSK detection by 3 dB, similar to electrical balancing. We also show how this scheme can be used
Visual Neuroscience, 1998
Noise recorded in visual neurons, or variability in psychophysical experiments, may be quantified... more Noise recorded in visual neurons, or variability in psychophysical experiments, may be quantified in terms of quantal fluctuations from an “equivalent” steady illumination. The conversion requires assumptions concerning how photon signals are pooled in space and time, i.e. how to pass from light fluxes to numbers of photon events relevant to the Poisson statistics describing signal/noise. It is usual to approximate real weighting profiles for the integration of photon events in space and time (the sensitivity distribution of the receptive field [RF] and the waveform of the impulse response [IR]) by sharp-bordered apertures of “complete,” equal-weight summation of events. Apertures based on signal-equivalence cannot provide noise-equivalence, however, because greater numbers of events summed with smaller weights (as in reality) have lower variances than smaller numbers summed with full weight. Thus sharp-bordered apertures are necessarily smaller if defined for noise- than for signal...
Optics Communications, 2007
We investigate a new parallel all-optical clock recovery scheme based on heterodyne beats of an o... more We investigate a new parallel all-optical clock recovery scheme based on heterodyne beats of an optical sideband-filtered signal. The oscillating clock signal is recovered when the filtered sideband is combined with a stable local oscillator. The filtering is performed with an optical resonator, which by nature provides possibility for multiwavelength operation. The local oscillator could be realized by a multiwavelength laser, whose emission wavelengths are injection seeded with carrier wavelengths of the input data. The output signal of such a configuration benefits from a reduced bit-pattern effect and a stable offset level. The sideband filtering is demonstrated for 23 simultaneous channels at 100 GHz DWDM grid, each hosting a data stream of 10 Gbit/s.
Chemical Physics Letters, 2002
A new efficient algorithm for the extraction of time constants from exponentially decaying signal... more A new efficient algorithm for the extraction of time constants from exponentially decaying signals is presented. The method is based on a non-linear Newton fitting and it is demonstrated to yield significantly more accurate results than the commonly used weighted least square method under noisy signal conditions. Methods are compared by simulated and true experimental data obtained by a fiber
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Papers by Tuomo von Lerber