Abstract: For optical transmitters in DWDM network systems, a method of operating the semiconductor laser which provides the output of the optical transmitter. The output power and wavelength of the semiconductor laser is set by controlling the bias current and operating temperature according to a closed theoretical mathematical form. The form has the variables of output power, wavelength, bias current and temperature related to each other by empirically determined coefficients. In this manner the optical transmitter can efficiently vary its output power while maintaining its wavelength constant, or vary its wavelength while maintaining its output power constant.

Abstract: A network switch connecting N input optical fibers and N output optical fibers, each optical fiber carrying M wavelength channels. The network switch has a control unit, a plurality of demultiplexers connected to the input output optical fibers, a plurality of tunable channel units, a switch fabric and a plurality of combiners connected to the output optical fibers. The demultiplexers and tunable channel units provide the wavelength routing function and the switch fabric, which has M×N2 switch points, switches signals from input optical fiber to output fiber so that the switch can switch signals from one wavelength channel to another and from one input optical fiber to one or more output optical fibers of the optical network. The switch fabric is formed from a plurality of switch modules, one switch module for each incoming wavelength channel.

Abstract: The present invention provides for an optical transmission system for generating light signals at a plurality of predetermined wavelengths on an output fiber. The system has a plurality of modulated laser sources coupled to the output fiber and a feedback loop connected to the output fiber. The feedback loop includes a first subloop which generates electrical signals indicative of a total amount of light carried on the output fiber, and a second subloop which generates electrical signals indicative of an amount of light carried on the output fiber at the predetermined wavelengths. A control unit coupled to the plurality of laser sources receives the electrical signals from the first and second subloops and adjusts the laser source output wavelengths so that the output of each laser source is centered at one of the predetermined wavelengths. A comb filter is in the second subloop for transmitting light signals at the predetermined wavelengths.

Abstract: A method and apparatus for controlling the wavelength of a laser. Initially, the wavelength of the laser is coarsely tuned to within a predetermined window around a specified wavelength. After coarse adjustment, a wavelength control loop is activated to finely tune and lock the laser wavelength. In an embodiment, the control loop dithers the wavelength of the optical carrier signal from the laser. The optical carrier signal is then modulated (i.e., with data) in the normal manner. A portion of the modulated optical signal is filtered and detected. The amplitude and phase of the detected signal, which comprises the error signal, is processed and averaged. The averaged signal is then summed with a dither signal to provide a composite signal. A control signal corresponding to the composite signal is then generated and used to adjust the laser wavelength.

Abstract: A wavelength division multiplexer (WDM) in an optical fiber transmission system launches analog signals, for instance a multi-channel television signal. The WDM enhances signal quality by transmitting along a single fiber two different optical wavelength signals, each carrying identical RF information. This results in a 3 dB improvement in carrier to noise ratio. The WDM combines two or more wavelengths centered around for instance 1550 nm or 1310 nm. A typical difference between the two wavelengths is 3 nm. In other embodiments, more than two wavelengths are used. The receiver is for instance a single photosensitive element. The phase of the two RF signals is adjusted in the optical or RF domain to be the same upon arrival at the receiver. In other embodiments, the receiver includes two photosensitive elements, each receiving from a receiver end WDM a single wavelength. In this case, the phase adjustment may be applied at the receiver in the optical or RF domain.

Abstract: An optical transmission system enables launching at least 17 dBm of optical power at 1550 nm wavelength into an e.g. 50 km long span of standard telecommunications single-mode optical fiber, without incurring unacceptable penalties from stimulated Brillouin scattering, damage to optical phase modulators from excessive drive power or thermal effects, or signal degradations caused by the SBS suppression. High frequency modulation of the laser drive current is combined with lower frequency modulation of the phase of the laser output light that is itself varied over a range of approximately 25 MHz. This two tone modulation raises the SBS threshold to greater than 17 dBm in the 1550 nm wavelength region when the laser has a line width less than 10 MHz, under cw operation. By thereby dividing the task of spectral partitioning between the laser and the phase modulator, the RF input power level to the phase modulator is manageable and the laser operates in a regime that does not cause clipping.

Abstract: A generalized frequency dependent predistortion circuit for nonlinear optic devices such as semiconductor lasers and light emitting diodes includes a pre-filter and post-filter associated with a linearizer (distorter). A multi-channel sub-carrier electrical signal is input to a splitter which provides on a primary path a signal to a time delay and hence to a coupler to the secondary paths. In the first secondary path, a pre-filter provides a signal to a second order distorter. This signal is then subject to a post-filter and then to a variable attenuator. In the second secondary path, a third order distorter again has an associated pre-filter and post-filter with a variable attenuator downstream of the post-filter. The variable attenuators in each path provide frequency independent attenuation. In one version the distorters in both paths are nonlinear diode circuits. The second secondary path provides very low fundamental leak-through.

Abstract: A cascaded distortion compensation arrangement is disclosed which utilizes a plurality of pre-distortion components disposed in a series arrangement at the input to the transmitter and a plurality of post-distortion components disposed in a series arrangement at the output of the receiver. The various components may be modified, added and/or deleted to provide an arrangement suitable for the particular system.