Precise broadband frequency modulated laser

#Many laser applications require the laser's frequency to be changed in time (“frequency modulated”) in an extremely controlled and predictable manner over large optical frequency bandwidths. Many of these applications require the optical frequency to change linearly and monotonically in time (to form a “linear frequency chirp,” called simply a “chirp” hereinafter). For instance, researchers have actively linearized an optical frequency radio frequency (RF) sideband to improve the performance of frequency-modulated, continuous-wave (FM-CW) laser detection and ranging (LADAR). Other researchers have actively linearized the carrier optical frequency for reading out spectral information recorded in optical crystal transitions.

#Previous work has demonstrated techniques for providing feedback through circuits that drive a laser to provide stable, highly linear laser output for low optical bandwidth systems. This previous work exhibits frequency tuning, including highly linear chirps, with bandwidths of up to 10 gigaHertz (GHz, 1 GHz=109 cycles per second, also called Hertz and abbreviated Hz).

#Previous techniques for precise laser tuning are observed to break down for extremely large tuning bandwidths, such as a bandwidth greater than 50 GHz, which is 5 times more frequency tuning bandwidth than demonstrated by the previous work. Broadband chirps greater than 50 GHz have been produced but with deviations from linearity of about 1 percent (%) or more. Therefore, there is a need for a broadband frequency modulated laser that is highly precise and accurate for bandwidths greater than about 50 GHz. For example there is a need for a broadband chirped laser that produces a chirp that deviates from linearity by less than 1% for bandwidths greater than 50 GHz.

#The embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings, in which:

#FIG. 1A is a graph of optical frequency versus time for two chirps, one of which is time delayed relative to the other, according to one embodiment;

#FIG. 1B is a graph of range determination (distance or length metrology) using chirps, according to one embodiment;

#An apparatus, method and software are disclosed for providing precise and/or accurate broadband frequency modulated optical waveforms. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention. It is apparent, however, to one skilled in the art that the embodiments of the invention may be practiced without these specific details or with an equivalent arrangement. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention.

#Although several embodiments of the invention are discussed with respect to a broadband chirped laser for frequency modulated continuous wave (FMCW) laser detection and ranging (LADAR) applications, embodiments of the invention are not limited to this context. It is explicitly anticipated that the broadband chirped laser is useful in many applications, including scanning, imaging, time delay determination, dimensional metrology, surface characterization, arbitrary waveform generation, TeraHertz (THz, 1 THz=1012 Hz) generation through nonlinear processes such as photomixing, or coherent spectral readout/analysis of unknown optical or TeraHertz signals, among others, alone or in some combination. It is further anticipated that non-linear or non-monotonic precise and accurate broadband modulated optical waveforms are generated and used in various applications.

#Some general embodiments are described at a high level first. More details for various components described herein and specific embodiments are provided below. Additional information, measurements and theory that underpin these embodiments in the context of high precision ranging applications are also provided in more detail below.