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To: ahhaha who wrote (298)	3/8/1999 8:07:00 PM
From: ahhaha	Respond to of 626

The link: patents.ibm.com The next page in the patent deals with formulae which determine laser 12 state values by which the thermal sink controller 18 can control the laser cavity so that the cavity is able to act like a transient thermodynamic system. From our previous discussion the cavity dimension effects the stability of the resonant modes. Too much instability invites chirping, mode hopping. The cavity dimension is a function of the heat distribution and intensity in space and time. As listed on page 4, the change in temperature is a function of cavity heat transfer coefficient, flux absorption, thermal diffusivity, time,thermal conductivity, density and dimension. Palmer had solved the heat variance problem applicable to this device in the idealization from flat plate heat transfer in a paper previously completed. As demonstrated the active temperature controller 20 can be provided which follows the non-linear response of the thermal mass of the heat sink of the Laser in real time. Using the equations demonstrated above, appropriate scaling and response factors may be provided which track the thermal characteristics of the transmission laser 12 and paradigm laser 40. Another factor is the control of the temperature of the laser cavity using the balancing heat source 20. Control of the balancing beat source 20 is established using a first feedback loop 13 and a second feedback loop 14. The first feedback loop 13 operates by stabilizing a natural emission frequency of the atoms of the cavity with a mode frequency of the cavity. The objective of the first feedback loop 13 is to ensure that only a single laser frequency (mode) is present and that the laser 12 is stable in producing that single mode during operation. In general, the gain region of a DFB laser must be regarded as relatively wide. As such, several longitudinal modes of operation may normally be present during operation of a DFB laser. Under the invention, the gain region of the DFB laser 12 may be narrowed by adjusting the corrugations, but temperature control is still necessary. This is because the position of the gain profile depends on the band gap and this phenomenon is extremely dependent upon variations in temperature. DEF: Band gap In a semiconductor material, the minimum energy necessary for an electron to transfer from the valence band into the conduction band, where it moves more freely. Consequently, a slight change in temperature could cause the position of the gain profile to shift sufficiently to cause the laser 12 to mode "hop" to another longitudinal mode more favorably disposed with regard to the gain profile. As a means of developing a solution to the gain profile problem, it can be assumed that a single mode is oscillating at frequency Vm, which is greater than the natural emission frequency of the atom, Vo The natural frequency and oscillating frequency Vm creates two "holes" in the distribution. The oscillation at frequency Vm, is a standing wave within the cavity, consisting of two waves traveling in opposite directions. The two waves can he designated by "+" and "-", respectively. Both waves have a frequency of Vm. The interaction of the waves traveling in the positive +Vm direction with the laser medium will be greatest for those atoms that have a velocity component direction of +Vx, such that Vo = Vm*((1+Vm)/c). There are, therefore, two groups of atoms whose stimulated emission contributes to the laser output intensity. The population inversion is reduced for these atoms and gain saturation occurs with regard to these atoms. DEF: Population Inversion The condition in which there are more atomic systems in the upper of two energy levels than in the lower, so stimulated emission will predominate over stimulated absorption. This condition may be described as a negative temperature. DEF: Hole Burning The dip or gap in the profile of a laser beam's line width when it is both homogeneously and inhomogeneously broadened. When an inhomogeneously broadened spectral line is saturated by incident light, the absorption profile of the beam will show a sharp dip because transition saturation is not uniform Two "holes" are burned and they are symmetrical about Vx = 0 and correspond to atoms with velocities of plus and minus Vx. Under the embodiment, we can change the frequency of the oscillating mode until the peak frequency of the laser line is equal to the natural emission frequency (i.e., Vm = Vo). This can be accomplished by varying the length of the cavity by small variations in the cavity temperature. In changing the temperature ever so slightly, only a single group of atoms can contribute to the lasing process, viz., those with zero-x component of velocity, and providing only a single 'hole' in the population inversion-velocity curve. When this happens the output power has been found to drop as the available inverted population is smaller than before. The small increase in power resulting from the slight deviation from the center frequency of the laser 12 is used as a feedback in the first feedback loop 12 to stabilize the frequency of the laser 12 at the line center by minimizing the output. Because of the power differences, any drift in the mode frequency will cause one mode to increase in power and the other to decrease. The first feedback loop 13 is used to monitor the two different power levels and to subsequently to provide a feedback signal to control the cavity length.

To: ahhaha who wrote (298)	3/9/1999 12:30:00 AM
From: George T. Santamaria	Read Replies (2) \| Respond to of 626

"The limit on throughput is the current fiber limit of say, 10 ter/sec." You mean that SR can mix microwave channels into one 1.0THz analog microwave channel and then drive an EO modulator with this signal? That is about the minimum analog signal handling requirement with a reasonable signal-to-noise ratio over a single path (waveguide? coax cable? wire? ether?)implied by your 10Tb data rate. "The cost advantage is 10 to 1 cheaper than the WDM equivalent. As WDM approaches its technological limit, cost comparisons are meaningless, since tweaked SR operates way above any theoretical WDM implementation. Do you know how this 10:1 cost advantage is achieved?" Could you please explain what constitutes the 10:1 cost advantage? Is it terminal equipment? Is it the cost of dark fiber?