A circuit that allows the control of a parameter in each arm of a Mach-Zehnder interferometer or modulator in push-pull mode using a single control terminal and a ground (or a differential driving circuit). The parameter that is controlled can be a phase shift, a modulation or an attenuation. The magnitude and the frequency of the parameter can be adjusted.

Provided is an optical waveguide element including a first interactive part, a first EO substrate line, a second interactive part, and a second EO substrate line. A relay substrate unit includes a first relay substrate line, a second relay substrate line, and a loss adjusting part. The loss adjusting part is provided to the relay substrate line in a combination in which an electrical loss is low so that an electrical loss in a combination of the first EO substrate line and the first relay substrate line, and an electrical loss in a combination of the second EO substrate line and the second relay substrate line become approximately the same as each other.

A sensor head of a test and measurement instrument can include an input configured to receive an input signal from a device under test (DUT), an optical voltage sensor having signal input electrodes and control electrodes or one set of electrodes, wherein the input is connected to the signal input electrodes, and a bias control unit connected to the control electrodes and configured to reduce an error signal or the input signal bias control signal are electrically combined and applied to a single set of electrodes.

A substrate (102) having a piezoelectric effect, optical waveguide (138a, 140a, 138b, 140b, and the like) formed on the substrate, and a plurality of bias electrodes (152a, 152b, and the like) that control an optical wave (s) which propagate through the optical waveguides are provided, and the bias electrodes are constituted and/or disposed such that an electrical signal applied to one of the bias electrodes is prevented from being received by another one of the bias electrodes through a surface acoustic wave.

An optical demultiplexer that includes at least one a hybrid phase shifter configured to receive a light signal over a fiber element, the light signal including polarized optical signals. Each phase shifter includes a thermo-optic phase shifter configured to phase shift the light signal, an electro-optic phase shifter configured to phase shift the light signal, and a coupler configured to maintain polarization of the polarized signal components. The optical demultiplexer also includes control circuitry configured to regulate the thermo-optic and electro-optic phase shifters.

A control system for variable transmittance windows is disclosed. The system comprises at least one electro-optic element, a local control circuit, and a feedback circuit. The local control circuit is in communication with the electro-optic element via a conductive supply. The feedback circuit is in communication with the conductive supply and configured to communicate a feedback signal to the local control circuit. The local control circuit is configured to receive the feedback signal and adjust an output voltage transmitted to the conductive supply in response to the feedback signal.

Apparatuses and methods for a temperature insensitive electro-absorption modulator and laser. The device comprising a laser capable of emitting light. The laser itself includes a laser gain section, a first mirror and a second mirror. Each of the mirrors are coupled to the laser gain section. The laser gain section contains quantum wells. The first mirror and the second mirror have a wavelength bandwidth sufficient for a lasing wavelength range of the laser. A modulator is coupled to the laser to receive the light and is capable of modulating the light to vary the output from the modulator. The modulator contains quantum wells and has a quantum well confinement factor that is greater than 0.1. An output coupler is coupled to the modulator and the output coupler has a back reflection that is less than half of a back reflection of the second mirror. The laser has a lasing wavelength that tracks the absorption spectrum of the modulator. The device is operated at a temperature range comprising a first temperature and a second temperature, wherein the second temperature is greater than the first temperature by at least 15 degrees Celsius.

An optical transmitter includes: optical modulation means; bias voltage output means for supplying the optical modulation means with a bias voltage on which a pilot signal is superimposed; pilot signal receiving means; and bias voltage control means. The bias voltage control means includes: training means for determining a control start voltage and a control direction of the bias voltage based on a pilot signal component at first and second bias voltage values; and feedback means for determining an appropriate bias voltage to compensate for a deviation of an operating point of the optical modulation means by analyzing the pilot signal component while adjusting the bias voltage in a stepwise fashion along the control direction from the control start voltage after the control start voltage and the control direction are determined.

Disclosed is technology for controlling a bias using an integrated circuit (IC) instead of using a pilot tone. A bias control apparatus includes a photodetector configured to convert at least a portion of data included in an output from an optical modulator to an electrical signal; a power detector configured to convert a root mean square (RMS) value of an amplitude of the converted data to an analog voltage; a comparator configured to compare the output voltage and a pre-stored track hold value; and a bias controller configured to control a bias voltage to be within a preset range from an optimal voltage based on the comparison result.

A system for centralized automatic bias control for a plurality of modulators, including a coupler for coupling output of each of the plurality of modulators to generate a combined modulator output. A pilot insertion device inserts a pilot tone into each of the plurality of modulators such that a different pilot tone frequency is inserted for each of the plurality of modulators. A monitoring device iteratively monitoring power (P.sub.t) of each inserted pilot tone over time to determine whether a current modulator bias is optimal for each of the plurality of modulators, and an adjuster device iteratively adjusts the modulator bias for each of the plurality of modulators for which the current modulator bias is determined to be sub-optimal until a threshold condition has been met.