FROZEN MODE REGIME FOR LIGHT AMPLIFICATION AND GENERATION
Abstract
The amplification per unit length of light propagating through optical gain material is inversely proportional to the group velocity [Sigman lasers]. This is because the optical amplification process is essentially a time domain process which depends on the rate of the stimulated emission generation. The longer the light interacts with the gain material the more stimulated emission is generated. Consequently, the slower the group velocity, the larger the gain per unit length. This property is manifested in conventional lasers cavities. The lasing mode of a Fabry-Perot cavity based laser, for example, is a standing wave with zero group velocity. Similar scenario occurs in the band-edge lasing in conventional distributed feedback (DFB) lasers exhibiting a regular band edge (RBE) point [23]. In such lasers, lasing is obtained at the edge of the passband/bandgap where the group velocity vanishes, thus giving rise to large modal gain. Another example is the recently introduced degenerate band edge laser [21] that operates in proximity of a degenerate band edge. However, the band diagram of a conventional DFB laser, and even of the degenerate band edge (DBE) laser, is symmetric around the bandgap edge, thus supporting waves with both positive and negative group velocities. Consequently, in all of the above examples the lasing mode is a standing wave and the laser emits in both directions. The frozen light mode, associated with a stationary inflection points (SIP) constitute a different type of slow wave. Here, the zero group velocity points does not occur at the edge of a bandgap as depicted in Figure 1. Mathematically, the main difference is manifested by the dispersion relations. The dispersion relation of periodic structures used in DFB lasers in the vicinity of the band-edge is quadratic in the wavenumber - ?-?_0?(k-k_0 )^2, while at the frozen mode point (a.k.a. SIP) the dispersion relation is cubic in the wavenumber - ?-?_0?(k-k_0 )^3.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 12, 2021
- Source ID
- FA86552017052
Entities
People
- Jacob Scheuer
Organizations
- Air Force Office of Scientific Research
- Tel Aviv University
- United States Air Force