Michael J. Hayduk

Self-starting passively mode-locked tunable femtosecond Cr4+:YAG laser using a saturable absorber mirror

Abstract We have demonstrated self-starting, passive mode-locking of a Cr 4+ :YAG laser using a saturable absorber mirror structure. Highly stable femtosecond pulses tunable from 1488 to 1535 nm were generated with average output powers ranging from 40 to 80 mW. Nearly transform limited pulses of 120 fs duration were obtained at 1488 nm.

Harmonically mode-locked glass waveguide laser with 21-fs timing jitter

We report on experimental jitter results of a 10-GHz mode-locked laser. The laser is an actively harmonically mode-locked fiber laser using an erbium-doped glass waveguide as the gain medium. Amplitude noise and corresponding phase noise effects are greatly reduced by the inclusion of an intracavity high-finesse fiber Fabry-Pe/spl acute/rot etalon. Typical results show timing jitter of 21-fs root mean square, integrated from 10 Hz to 100 MHz.

Photonic analog-to-digital conversion techniques using semiconductor saturable absorbers

There has been much recent interest in the use of photonics for analog to digital conversion. It is anticipated that the use of photonic analog to digital converters (ADCs) will far surpass the performance of electronic ADCs in terms of both sampling speed and resolution. We have designed a novel photonic ADC module that incorporates the use of semiconductor linear absorbers to perform the data quantization at speeds up to 100 GS/s with 4 bits of resolution. The use of the passive materials in this flash photonic ADC architecture makes this module a candidate for insertion into future space-based platforms. Experimental characterization results will be presented for the semiconductor materials used in the data conversion process.

Gamma-ray induced responses in an erbium doped fiber laser

Many people are investigating photonic analog-to-digital converters (ADCs) for use in a digital receiver as a plausible solution to increase the bandwidth and resolution over that currently offered by electronic ADCs. A key component of a photonic ADC is a mode-locked fiber laser. A preliminary evaluation of the capability of utilizing this type of laser in space based ionizing environments and applications is required. This paper explains the effects of exposing an erbium-doped fiber laser (EDFL) to a total gamma-ray dose of 1 Mrad (Si). The performance of the laser is characterized in a passive fashion, i.e. before and after the irradiation. Predictions are offered to the extent of radiation induced damage that the fiber laser can endure before breaking down. The results of the evaluation will allow for further optimization of the EDFL for use in space-based architectures and applications.

Wavelength-based analog-to-digital conversion

This paper provides a comprehensive understanding of a tunable wavelength-based photonic high-speed analog-to- digital converter (ADC) approach and its anticipated performance. Analytic models, experimental data, and simulation results will provide the fundamental limits on the expected conversion speed and bit resolution. A thorough in situ study of the photonic signal conversion system under simulated space radiation conditions is required to precisely determine its performance in either a natural or man-made space environment. Although this study has not yet been performed on the entire system, preliminary performance predictions will be made based on previously published studies on the individual components within the system. The photonic components of particular interest that will be discussed in the context of radiation hardness includes the edge emitting laser diode with a MQW tuning element, the processor filters, the delay equalizers and the photodetectors.

Mode-locked Cr4+:YAG laser: model and experiment

Abstract A mode-locked Cr 4+ :YAG laser was simulated using a complex Landau-Ginzburg equation. The pulse widths and spectrum were determined as a function of laser tuning over a range from 1470 nm to 1550 nm. Simulations exhibit the same trend as the experimental data and the magnitudes are in reasonable agreement, as well. We are able to analytically estimate the pulse width, which is controlled by the cavity dispersion and the pulse energy. We find that the absorber saturation is responsible for determining the pulse energies. The experimentally observed pulse widths widen for long wavelengths; our simulations attribute this to dispersion and to a wavelength-dependent reduction of the saturable absorber modulation combined with the effect of gain saturation.

Diamond shaped ring laser characterization, package design and performance

A semiconductor diamond-shaped ring laser was fabricated and packaged for further test and analysis as an element in digital photonic logic. The optical characteristics of the ring laser were quantified in order to design a prototype package. The mode field was found to be quasi-circular. Based on the mode field of the laser, coupling curves were calculated and Corning OptiFocustrade lensed fiber was chosen to use for the four fiber outputs. Each fiber placement was actively optimized. Output power measurements were made for each facet before and after fiber coupling. Reflections from fiber tips were found to affect the final output power distribution of the device even though the fibers were anti-reflection (AR) coated, and additional effort was put into minimizing its variance. The packaged devices were tested for performance in digital photonic logic applications. Tests conducted to this point indicate that the packaging enabled a multiple port device of this type to be sufficiently portable for field testing

Comparison of radiation-induced passive and dynamic responses in two erbium-doped fiber lasers

Erbium-doped fiber lasers (EDFLs) may soon find applications in space as high bit rate optical communication systems and photonic analog-to-digital converters (ADCs). The rapid advancement in digital signal processing systems has led to an increased interest in the direct digitization of high-frequency analog signals. The potential high bandwidth, reduced weight, and reduced power requirements makes photonics an attractive technology for wide-band signal conversion as well as for use in space-based platforms. It is anticipated that photonic ADCs will be able to operate at sampling rates and resolutions far greater than current electronic ADCs. The high repetition rates and narrow pulse widths produced by EDFLs allow for high-speed impulse sampling of analog signals thus making it a vital component of a photonic ADC. In this paper we compare the results of exposing two differently constructed erbium-doped mode-locked fiber lasers (EDFLs) to gamma-rays. Each experiment is fully explained. The performance of EDFL1 was characterized in a passive fashion, i.e. before and after the irradiation. EDFL2s performance was monitored in situ. The onset, growth and extent of ionization induced damage under time-resolved operational conditions is presented. The in situ studies clearly revealed ionization induced shifts of the EDFL optical spectrum to shorter wavelengths and with corresponding changes to the emission spectral width. The results of the evaluation will allow for further optimization of an EDFL for use in space-based architectures and applications.

Terahertz Optical Frequency Comb Generation by Spectral Filtering of Broadband Spontaneous Amplified Emissions From a Semiconductor Optical Amplifier

In this paper, we describe a fiber-optics-based system for the generation of optical frequency comb using amplified spontaneous emissions from a semiconductor optical amplifier (SOA) as signal source. The continuous-wave (CW) spectrum from the SOA ranges from 1480 nm to 1680 nm. A Solc-Sagnac birefringent interferometer filters the CW into a comb of discrete spectral lines with line spacing of 600 GHz, producing comb signals than span 182-230 THz.

Injection characterization of packaged bi-directional diamond shaped ring lasers at 1550 nm

The Air Force Research Laboratory, Binoptics Corp., and Infotonics Technology Center worked collaboratively to package and characterize recently developed diode based ring lasers that operate at 1550 nm in a diamond shaped cavity. The laser modes propagate bi-directionally; however, uniaxial propagation may be induced by optical injection or by integrating a mirror. Round trip cavity length was 500 μm in 3.5 μm wide ridge waveguides, and four polarization-maintaining lensed fibers provided access to the input and output modes. A signal from a tunable diode laser, incident at one port, served to injection lock both of the counter-propagating circulating modes. When the input signal was time-encoded by an optical modulator, the encoding was transferred to both modes with an inverted time-intensity profile. Performance, in terms of fidelity and extinction ratio, is characterized for selected pulsed and monochromatic formats from low frequencies to those exceeding 12 GHz. A rate equation model is proposed to account for certain aspects of the observed behavior and analog and digital applications are discussed.