United States Patent   Patent Number: 4,707,803
Anthony, Jr. et al.  Date of Patent: Nov. 17, 1987
 EMULATOR FOR COMPUTER SYSTEM INPUT-OUTPUT ADAPTERS
 Inventors: Bruce O. Anthony, Jr.; Thomas M.
Heise; Frank P. Sheppard, all of
 Assignee: International Business Machines
Corporation, Armonk, N.Y.
 Appl. No.: 745,728
 Filed: Jun. 17, 1985
 Int. Cl." G06F 13/00; G06F 13/24
 U.S. CI 364/900
 Field of Search ... 364/200 MS File, 900 MS File
 References Cited
U.S. PATENT DOCUMENTS
4,042,914 8/1977 Curley et al 364/200
4,245,300 1/1981 Kaufman et al 364/200
4,493,028 1/1985 Heath 364/200
4,575,793 3/1986 Morel et al 364/200
4,591,978 5/1986 Peterson et al 364/200
Primary Examiner—Thomas M. Heckler
Assistant Examiner—Paul Kulik
Attorney, Agent, or Firm—Paul L. Sjoquist
An optical fiber communications system includes an optical pathway defined as a closed optical loop with a
signal source introducing a fixed frequency optical signal onto the loop as a reference signal for system wide propagation. Each terminal device in the system includes a thermally controllable bus tap resonator which can be controlled in a step-wise manner to support plural sets of resonant modes having corresponding different free spectral ranges with one mode of each supported set of resonant modes frequency locked to the system reference signal and another mode used for communications purposes. The bus tap resonators are thermally controlled to allow each terminal device to tune from a first set of resonant modes having a first free spectral range to another set of resonant modes having another free spectral range so that the frequency of the mode used for communications in the latter set will be different from that in the former set. The system reference signal source is preferably defined by a controllable resonant structure, such as a Fabry Perot cavity, which is controlled to lock to the frequency of a stabilized He-Ne laser. A laser diode operating in the desired wavelength band is controlled to lock the wavelength of its output to that of the one of the resonant modes of the stabilized Fabry Perot cavity to thus lock the frequency of the laser diode to that of the highly stable He-Ne laser.