Abstract: A carrier recovery loop for a burst type QPSK system. A QPSK signal source of frequency f.sub.1 has its output frequency doubled and then doubled again to produce a signal of 4f.sub.1 with the QPSK modulation thereby removed. Also provided are first and second phase locked loops comprising a common voltage controlled oscillator (VCO), and separate ones of first and second phase detectors, respectively, with each detector having a characteristic output which varies sinusoidally with linear variation of the phase difference of the two signals supplied thereto and with the negative-going cross-over transitions of the characteristic output constituting unstable nulls. A third x2 frequency multiplier connects the output of the VCO to the first phase detector, and a fourth x2 frequency multiplier connects the output of the third x2 frequency multiplier to the second phase detector.

Abstract: A coupler for interconnecting transmission lines in an optical communication system. In a preferred embodiment it comprises an elongated bi-conically shaped rod of transparent material which continues into two cylindrical mixing rods. The lines are split up into two groups coupled to respective ones of the two plane endfaces of the coupler. The dimensions of each tapered central portion are determined such that the radiation pattern in the common plane of the identical minor bases is substantially hemispherical no matter what the direction of propagation of the light modes along the axis from one end to the other, given the numerical aperture of the associated transmission lines.

Abstract: A reciprocal coupler for connecting anyone of a plurality of optical signal transmission lines to all the other transmission lines in an optical communication system.The coupler comprises an elongated transparent optical mixing rod optically coupled by a first endface to each of the waveguides forming the lines to be interconnected and by its second endface to both ends of return guides provided by a fiber bundle which form a loop.

Abstract: An arrangement for measuring by correlation the lag produced by the transmission of a coded signal through a delaying medium and which permits a high signal-to-noise ratio and high accuracy. The received coded signal is applied to two correlators followed by a subtractor to form a discriminator circuit utilized to lock the frequency of a generator which provides two reference coded signal utilized respectively for correlation and to form an automatic tracking loop. The lag measurement is obtained by state-decoding of the transmission coded signal and of one of the reference coded signal and by pulse counting at a period sub-multiple of the bit period.

Abstract: A coupler for coupling in the same manner any one of a plurality of optical signal transmission lines to all of the other transmission lines. The coupler comprises at least three elongated frusto-conical shaped arms of transparent material coupled together by their minor bases through a connecting medium and connected by their major bases to end faces of optical transmission lines respectively. The base diameters and the axial length of these arms are determined such that each minor base has a hemispherical radiation pattern given the numerical aperture of the associated transmission line.

Abstract: A bit stream with a bit rate equaling the frequency of a train of accompanying clock pulses is transcoded into a two-level signal voltage having a reduced rate of changeover compared with the rate of alternation between 0 and 1 bits. Upon any shift from one kind of bit (e.g., 0) to the other kind of bit (e.g., 1), a transition between signal-voltage levels occurs in the middle of a clock-pulse cycle; the first bit of the first-mentioned kind (0) in a succession of a plurality of such bits, after a shift from the other kind of bit (1), is translated into a transition between signal-voltage levels occurring at the end of the corresponding clock-pulse cycle. Transcoding is accomplished with the aid of a three-stage shift register whose stage outputs are logically combined.