A direct B-integral measurement, and SPM compensation method in fiber optic CPA systems is demonstrated. For a pair
of input pulses, the chirped nature of the amplification transforms a nonlinear phase change into a temporal amplitude
change resulted in a satellite side pulses generation. The SHG autocorrelation measurement of these satellite pulses is
directly correlated to B-integral value. Then the accumulated SPM is removed by precompensation of the spectral
phase. The degree of compensation again confirmed the described B-integral measurement result.
We report a scheme for controlling pulse width in a robust self-starting mode-locked ytterbium fiber laser using a
semiconductor saturable absorber mirror (SESAM). We demonstrate that the pulse width in a mode-locked laser made
of all-normal-dispersive fiber can be adjusted by changing ump power to the laser or by adjusting the axial position of
the SESAM with respect to a focusing beam. We have obtained optical pulse width of 7.4 ps and the adjustable range
was 2 ps without dispersion compensators in the all-normal-dispersive cavity and provides a high reliability of turn-key
operation. We have explained that the principle of position dependent pulse width change in a mode-locked laser with a
SESAM and verified with numerical simulations.
Experimental proof-of-concept is presented for a quasi-holographic solution to polarization-sensitive optical coherence tomography (PS OCT). Due to decoupling between the reference and sample beams by polarization, the solution seems acceptable to acquisition and communication of optical data in the nonlaboratory environment. The nonlab environment implies uncontrollable disturbances, e.g., temperature changes and mechanical effects happening under shop testing in industry or routine examinations in common clinics and hospitals. For mapping the collagen-related depolarization ratio of light backscattered from the human dermis, a phenomenological model is evolved from the theory of light depolarization in crystalline polymers. The model yielded a simplified intensity-based estimation algorithm. The design concept and the model rely on a submillimeter tumor thickness as a proofed prognostic factor and an important criterion for complementary functional diagnostics of skin cancers in their early phase. Choice of the model is inspired by similarity of structural and optical properties between liquid-crystal collagen fibers in the dermis and birefringent crystalline lamellae in some polymer materials. The model gives a plausible interpretation of a peculiarity of cumulative birefringence in the abnormal skin dermis. Following a top-down approach to design, the authors attempt to contribute to bridging the gap between practitioners' concerns and academic studies.
It is critical to know the free spectral range (FSR) of an etalon for telecommunication applications. In this
paper, we have improved the Pound-Drever-Hall (PDH) based technique for measuring the FSR of an
etalon by 2 orders of magnitude. This improved technique results 1 part in 106 precision. To our knowledge
this is the most precise measurement of FSR.
Frequency skewed optical pulses are generated via both a composite cavity structure in a fiberized semiconductor optical amplifier ring laser and a frequency skew loop outside the laser cavity. The composite cavity technique is similar to rational harmonic mode-locking, however it is based on cavity detuning rather than frequency detuning. These frequency skewed pulses are ideal for range detection applications since their interference results in a range dependent RF signal. The intracavity frequency skewed pulse train showed superior performance in both stability and signal quality.
Mode-locked laser designs for both time and frequency domain based applications are presented. It is shown that for
strictly time domain applications, simple laser cavity designs can produce pulse trains at 10 GHz with sub-5 fs relative
timing jitter (1 Hz-100 MHz) using only commercially available components. Frequency stabilized sources maintain
low timing jitter while achieving 1MHz maximum frequency deviations for optical spectra consisting of ~200 10 GHz
spaced frequencies. Methods of characterizing pulse-to-pulse timing jitter by examining the photodetected spectrum are
reviewed. The effects of the phase noise of an rf source used to drive an actively mode-locked laser on the laser's
amplitude and timing fluctuations is also discussed.
Frequency stabilized modelocked lasers have recently garnered much attention owing to their potential in metrology, communications, and signal processing applications. The possibility of optical source technology that is economical, compact, and electrically efficient suggests that semiconductor gain media could allow frequency stabilized ultrafast sources to rapidly gain a foothold in communication and signal processing applications. This work will summarize recent work in the area of stabilized modelocked semiconductor diode lasers, and highlight unique features that will impact photonic signal processing applications.
A novel method incorporating time division multiplexing technique with optical parabolic phase modulation has been introduced to overcome the limitations on optical generation of chirped RF signals. Extension of the frequency span and frequency sweep time of a RF chirp signal has been experimentally realized. A chirped RF signal with a center frequency of 100 MHz, frequency span of 20 MHz and sweep time of 200 ns has been generated via this novel method. This chirp signal agrees well with the chirp signal generated by conventional methods.
We report on supermode noise suppression of a harmonically modelocked laser by optical injection. The modelocked
laser was injection locked to a CW narrow linewidth source. Injection locking selects a single supermode group
reducing the supermode noise spurs in the photodetected signal by 20 dB to a level of -130 dBc/Hz.
This paper discusses use of optical frequency combs generated by modelocked semiconductor lasers for coherent photonic signal processing applications. Key in our approach is a high Q cavity, supermode suppression and low spontaneous emission. Targeted applications of the stabilized optical frequency combs lie in areas of metrology, optical sampling, arbitrary waveform generation and communications using coherent detection.
Using an intracavity Pound-Drever-Hall technique, simultaneous optical frequency comb stabilization within ±3 MHz range and supermode phase noise suppression were demonstrated for a 10 GHz harmonically modelocked semiconductor ring laser resulting in timing jitter of 63.5 fs integrated from 10 Hz to 10 MHz.
A novel time division multiplexing technique has been incorporated with optical serrodyne phase modulation to generate a single microwave tone with up to 1 MHz tunability. Sideband spurs due to finite phase reset time in ordinary serrodyne phase modulation have been suppressed to more than 40 dB below the carrier. These results show that endless phase modulation can easily be achieved using this novel technique.
We report on low noise performance of a 10 GHz actively mode-locked laser. The laser is a fiberized ring laser using a commercially available semiconductor optical amplifier (SOA) as the gain medium. The noise properties as a function of cavity length and optical spectrum are investigated. It is found that supermode noise is reduced when the cavity length is increased past a certain threshold. Best performance is achieved with a 20 meter cavity whose pulses are down chirped. No active feedback control is utilized to reduce the noise, yet the integrated jitter is only 29 fs (10Hz-100MHz).
Modelocked semiconductor diode lasers are used as compact sources for multiwavelength generation. The generation of multiple wavelengths can be grouped into 2 general categories: 1) multiple continuous wave, phase locked optical frequencies, or 2) multiple, synchronized modelocked wavelength channels. Applications of these sources are demonstrated in areas of optical sampling, access networks, and arbitrary waveform generation.
This paper presents experimental results of using a diamond shaped semiconductor optical amplifier as the optical gain element in a high power external cavity semiconductor laser. An average output power of 740 mW is demonstrated in continuous wave operation while 400 mW of average power is obtained in both passive and hybrid modelocked operation, with subsequent optical amplification in an identical semiconductor optical amplifier. The modelocked laser operates at a repetition rate of 1.062 GHz. Optical pulses are generated with a temporal duration of 5 psec, which implies a pulse energy of 377 pJ, and a peak power of 60 watts. Further reduction of the optical pulsewidth to 1.3 psec is also achieved by using dispersion compensation techniques. These results show the promise of novel semiconductor optical amplifier devices for use as gain elements in external cavity semiconductor lasers. The generated output pulse characteristics from modelocked operation is sufficient for use in novel 3-dimensional data storage applications, and in large scale commercial printing and marking applications.
In this paper, we present the intracavity gain dynamics of hybrid modelocked external cavity semiconductor lasers. Using the pump-probe method, the optical gain and transmittance of a modelocked external cavity laser diode and saturable absorber were measured, respectively. The pulse shaping processes were measured by investigating the chirp of the optical pulse at the output coupler, before and after the saturable absorber. These measurements were obtained by a spectrally resolved cross correlation technique. In comparison with the previous studies of the single pass dynamics in semiconductor optical amplifiers, the dynamics of the nonlinearities affecting the pulse shaping within the laser cavity is less dramatic owing to the longer intracavity pulse widths. It was also observed that the linear GVD plays an important role in the shaping of the pulse envelop and linearizing the pulse chirp.
KEYWORDS: Semiconductor lasers, Optical amplifiers, Laser systems engineering, Ultrafast phenomena, Semiconductors, Diodes, Systems modeling, Laser optics, High power lasers, Oscillators
An ultrafast modelocked semiconductor laser diode system has been used to seed a flashlamp pumped Cr:LiSAF regenerative amplifier system, producing subpicosecond pulses with millijoule output pulse energy. This system has the potential to eliminate argon ion pumped based ultrafast laser systems.
KEYWORDS: Optical amplifiers, Semiconductor lasers, Semiconductors, Systems modeling, Optical semiconductors, Mode locking, Laser systems engineering, High power lasers, Prisms, Dispersion
Semiconductor diode lasers are playing important roles in high speed information processing, telecommunications, and high speed measurement and diagnostic systems. This paper presents recent developments in the generation, amplification, and utilization of high power modelocked optical pulses from traveling wave semiconductor optical amplifier devices.
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