Yinchieh Lai

Soliton transmission control

The Gordon-Haus limit of long-distance soliton transmission can be partially overcome through the use of linear filters in each amplifier stage. New limits are derived, and they show the possibility of increased bit rates and/or distances of propagation.

Quantum theory of soliton squeezing: a linearized approach

A linearized quantum theory of soliton squeezing and detection is presented. The linearization reduces the quantum problem to a classical one. The classical formulation provides physical insight. It is shown that a quantized soliton exhibits uncertainties in photon number and phase, position (time), and momentum (frequency). Detectors for the measurement of all four operators are discussed. The squeezing of the soliton in the fiber is analyzed. An optimal homodyne detector for detection of the squeezing is presented that suppresses the noise associated with the continuum and the uncertainties in position and momentum.

Theory of cascaded quarter wave shifted distributed feedback resonators

The theory of lambda /4 shifted DFB resonators, both series coupled and side coupled, is developed. The theory is limited to loss-free high-Q resonators. If the actual losses are too high, the internal losses of the structures, all of which are compatible with laser diode structures, can be compensated by gain via carrier injection. The theory of a simple transmission resonator is reviewed and extended to a side-coupled resonator. >

Narrow-band optical channel-dropping filter

Waveguide couplers are combined with lambda /4 shifted distributed feedback (DFB) resonators to produce narrowband channel dropping filters. The bandwidth of the filter can be made much narrower than the stopband of the grating. It is possible to remove the spurious responses of the grating filter by appropriate dispersion characteristics for the coupled waveguides. However, in some practical applications it may not be necessary to do this, if all channels can be accommodated within half the grating bandwidth of the filters. >

Narrow-band distributed feedback reflector design

The theory is developed for a narrowband distributed feedback reflector that reflects at the center of the grating stopband and transmits at frequencies to either side. A perturbational method of analysis is presented which simplifies the algebra and provides helpful insight. The approximate analysis is compared with the exact results. It is shown that the approximate solution is good in the operating region of practical devices. The proposed tunable narrowband reflector can perform well at a reasonable bandwidth of about 40 GHz. >

Femtosecond gain dynamics and saturation behavior in InGaAsP multiple quantum well optical amplifiers

Femtosecond pump‐probe experiments on InGaAs/InGaAsP multiple quantum well optical amplifiers reveal ultrafast dynamics that are similar to, but quantitatively different from, those observed in bulk amplifiers. Pulse energy saturation of the amplifier gain is also studied using 150 fs and 20 ps pulses and is found to be pulsewidth dependent. The measured saturation energies are 200 fJ and 6 pJ, respectively.

Short pulse gain saturation in InGaAsP diode laser amplifiers

The saturation behavior of InGaAsP optical amplifiers is studied for input pulsewidths of 15 ps and 150 fs. The measured output saturation energies are 150 and 40 fJ, respectively. A simple rate equation model based on pump-probe results predicts the observed pulsewidth-dependent saturation behavior.<<ETX>>

Direct generation of a 10 GHz 816 fs pulse train from an erbium-fiber soliton laser with asynchronous phase modulation.

By employing the technique of asynchronous mode locking, we have successfully demonstrated direct generation of stable 10 GHz 816 fs pulse trains with a supermode-suppression ratio >70 dB from a hybrid mode-locked Er-fiber laser. When the modulation frequency deviates from the cavity harmonic frequency by 15-40 kHz, stable femtosecond soliton pulses are formed. Our results demonstrate that asynchronous mode locking can act as an effective mechanism for achieving a shorter pulse width and for stabilizing high-repetition-rate pulse trains in soliton fiber lasers.

Stable new bound soliton pairs in a 10 GHz hybrid frequency modulation mode-locked Er-fiber laser

We report what is, to our knowledge, the first experimental observation of stable new bound soliton pairs at the 10 GHz repetition rate in a hybrid FM harmonic mode-locked Er-fiber laser (1177 soliton pairs simultaneously in the laser cavity). The two solitons in the soliton pair have the identical pulse shape and are with the antiphase (pi phase difference). Their time separation is about three times the FWHM soliton width and varies with the phase modulation strength. The corresponding mechanism for explaining the formation as well as the superior stability of these closely bound soliton pairs is also given.

Simple analytical method of cavity design for astigmatism-compensated Kerr-lens mode-locked ring lasers and its applications

An analytical method based on a renormalized q parameter for Gaussian-beam propagation and properly matched self-consistent complex q parameters is proposed to aid in the design of arbitrary-astigmatism-compensated Kerr-lens mode-locked ring cavity lasers. The q parameters throughout the ring cavity can be calculated by solution of an algebraically quadratic equation for an arbitrarily thick Kerr medium when the intracavity laser power is less than the self-trapping power. The Kerr-lens mode-locking strength at the curved mirror was calculated over the stable range. The results indicate that the astigmatism is best compensated so that the stable range of x and y directions have optimal overlapping. Although to maximize the hard-aperturing effect the curved mirror separation must be at the far edge of the stable range, pump and cavity field matching inside the Kerr medium is also necessary. In addition, the insertion of a vertical slit is more effective than insertion of a horizontal slit. A spiking phenomenon is found in the intracavity z scan curve, which can be observed only with thick Kerr materials and a high laser power.