Abstract: A receiver for a differentially phase shift keying formatted optical signal, such as an RZ-DPSK formatted optical signal. Dither control loops are provided for controlling path length in a demodulator and/or for controlling the center wavelength of an optical band pass filter. A feedback loop is provided for controlling the gain of a pre-amplifier, and a method of protecting against optical transients by disabling a pre-amplifier is also provided. A preset delay may be provided to compensate for the differential delay in paths associated with the demodulator arms. When the signal is an RZ-DPSK modulated signal, a clock for retiming data from the optical signal may be derived from a signal on the data path.

Abstract: I branch is provided with a first interferometer, a first balanced optical detector, and a first data recovery circuit. Q branch is provided with a second interferometer, a second balanced optical detector and a second data recovery circuit. In I branch, a mixer multiples input signal of the first data recovery circuit with output signal of the second recovery circuit. An averaging circuit averages output signal of the mixer. In Q branch, a mixer multiples input signal of the second data recovery circuit with output signal of the first recovery circuit. An averaging circuit averages output signal of the mixer. A first phase control apparatus controls the phase of a phase shifter comprised in the first interferometer based on the output signal of the averaging circuit. A second phase control apparatus, in the same manner, controls the phase of a phase shifter comprised in the second interferometer.

Abstract: A light receiver has a photoelectric conversion circuit which converts an input optical signal into an electrical signal, an electric amplifier which amplifies the electrical signal output from the photoelectric conversion circuit, a threshold adjustment circuit which outputs a threshold value according to signal information in the optical signal, and an optical signal loss detection circuit which compares amplitude of the electric signal output from the electric amplifier with the threshold value output from the threshold adjustment circuit and outputs results of the comparison.

Abstract: A method for receiving an optical signal is included where an ingress signal is split into a first portion and a second portion. A relative delay is induced between the first portion and the second portion, which are optically interfered to generate at least one interfered signal. Quality criteria of a monitored signal at least based on the at least one interfered signal is monitored so that a relative delay based in the quality criteria may be adjusted.

Abstract: A variable dispersion compensating unit compensates an optical signal, and changes the compensation amount according to a control signal that has a given frequency. After demodulation of the compensated optical signal, error conditions of the signal are monitored and an error signal is output. A band pass filter filters the error signal for a component having a frequency equal to or less than the given frequency. Based on the component and on the control signal, a synchronous detecting circuit generates a compensation amount modification signal. The compensation amount modification signal is superposed on the control signal.

Abstract: A bandpass filter circuit 10 of the present invention includes: transconductance amplifier circuits 1 to 3; a common-mode feedback circuit 4 which outputs a first control signal to the transconductance amplifier circuit 1 so that a D.C. voltage level of a differential output of the transconductance amplifier circuit 1 is at a predetermined level; a common-mode feedback circuit 5 which outputs a second control signal to the transconductance amplifier circuit 2 so that a D.C. voltage level of a differential output of the transconductance amplifier circuit 2 is at a predetermined level; and capacitors C1 to C3. Each of the members are connected as shown in FIG. 1. With the configuration, a bandpass filter circuit capable of adjusting constants such as a Q-value is realized.

Abstract: An optical communication system combines strong electrical pre-filtering of data at the transmitter and digital feedback equalization (DFE) at the receiver to enhance spectral efficiency. The system can be applied to optical networking and digital communication systems, including binary modulated systems optical network systems.

Abstract: Apparatus and methods for noise-feedback controlled optical systems are disclosed. In one aspect, an apparatus includes a receiver adapted to receive an optical signal and to convert the optical signal to a corresponding electrical signal, and a control circuit coupled to the receiver. The control circuit includes a monitoring component adapted to monitor a noise level of at least a portion of the electrical signal and to adjust a gain of the receiver based on the noise level. In an alternate aspect, an optical system includes a transmitter, a receiver, and a monitoring component adapted to monitor a noise level of at least a portion of the electrical signal and to adjust at least one of an amplification of the transmitter and a gain of the receiver based on the noise level.

Abstract: An optical interconnect includes an optical transmitter having a plurality of optical sources; a light sensing array configured to receive optical beams emitted from the optical sources; and a beam tracking module in communication with the light sensing array. The beam tracking module is configured to calculate a displacement of at least one of the optical beams by extrapolating an extremum from cross-correlation data obtained between at least a portion of a sample reading from the light sensing array and at least a portion of a plurality of shifted versions of a reference reading from the light sensing array. A related method includes calculating a displacement of an optical beam by extrapolating an extremum from cross-correlation data obtained between a sample reading of the optical beam and at least a portion of a plurality of shifted versions of a reference reading from the light sensing array.

Abstract: In an IR communication network, a method is described to optimize channel performance in the presence of strong and varying IR interference. The method controls of the channel gain based on quantitative measurement of the channel noise.

Abstract: An optical signal, which is a low-speed signal superimposed on a high-speed phase modulated optical signal by intensity modulation, is used. In an optical receiver apparatus 40, a received signal is split, and one of the split signals is O/E converted and low frequency component alone is extracted via a filter 46. A clock is extracted from low-frequency component by CDR, and is compared with a preset frequency. Using the frequency difference obtained, dispersion compensation is performed with low accuracy. Next, the amount of phase control of the delay interferometer 21 is adjusted so that the amplitude of the electrical signal is maximized. An error rate is measured, and fine adjustment is performed to improve the error rate.

Abstract: The waveform deterioration detection range is broadened and multi bit rates can be handled. A chromatic dispersion compensator (or polarization mode dispersion compensator) (102) receives a waveform-deteriorated NRZ optical signal entered through an input fiber (101) and compensates it. On the other hand, an optical detector (106) receives part of output light and a sampling circuit (A/D converter) (107) performs asynchronous sampling of received waveform intensity. A control circuit (110) calculates the nth even moment (n is 4 or more) from an obtained waveform amplitude histogram and performs control to minimize its value.

Abstract: A receiving circuit comprises a transimpedance amplifier 3 including an inversion amplifier 2 for amplifying an input current IN, and a feedback resistance R1 connected between an input and an output of the inversion amplifier 2, a comparison circuit 4 for comparing an output OUT of the transimpedance amplifier 3 with a certain desired reference value, and outputting a result of the comparison, and a control circuit for holding the comparison result, and generating an AGC signal 20 for adjusting a gain of the transimpedance amplifier 3. The transimpedance amplifier 20 has a function capable of gain adjustment in accordance with the input AGC signal 20. The control circuit 5 performs gain adjustment until the output OUT of the transimpedance amplifier 3 exceeds the reference value so that an appropriate gain is obtained.

Abstract: An optical receiver includes: a converting unit that converts an optical signal into an electrical signal; an amplifying unit that amplifies the electrical signal; a regenerating unit that regenerates the amplified electrical signal; a correcting unit that performs correction of an error included in the regenerated electrical signal; a monitoring unit that performs monitoring of an optical current flowing through the converting unit; and a control unit that calculates a decision threshold based on a result of the correction and a result of the monitoring.

Abstract: An optical reception apparatus according to the present invention comprises: a branching section that branches an optical signal input thereto into two; first and second delay interferometers arranged on optical paths through which the branched lights are propagated; first and second photoelectric converting sections that receive the output lights from the delay interferometers; a clock recovery circuit for recovering a clock signal based on a data signal output from one of the photoelectric converting sections; a multiplexing section that multiplexes data signals from the photoelectric converting sections in accordance with the clock signal; and a delay interferometer control section that resets operating conditions of the delay interferometers when the frame synchronization is not achieved. Thus, it becomes possible to perform the demodulation processing on the signal light which is differential phase shift keying modulated using a quadrature phase component, utilizing a general-purpose framer.

Abstract: A system and method implementing dual stage carrier frequency offset compensation (FOC) in a coherent receiver for an optical communication system. In the first stage, a feed forward FOC function compensates for relatively slowly drifting frequency offsets. In a second stage, a decision-feedback FOC function compensates for relatively quickly drifting frequency offsets. The feed forward frequency offset compensation may be implemented with a feed forward carrier phase estimation function and the decision-feedback frequency offset compensation may be implemented with a decision-feedback carrier phase estimation function.

Abstract: An optical receiver of the present embodiment has a light-receiving block, a discriminating block, a detecting block, a controlling block, and an adjusting block. The light-receiving block generates complementary signals in accordance with a photo current output from a semiconductor light-receiving element which receives an optical signal. The discriminating block has a differential amplifier having input terminals connected to output terminals of the light-receiving block via respective coupling capacitors. The detecting block generates an intensity signal corresponding to the photo current. The controlling block generates a first signal in accordance with a dispersion signal corresponding to dispersion of an optical transmission line, a distance signal corresponding to the distance of the optical transmission line, and an intensity signal.

Abstract: A control device with a switchable bandwidth including: an integrating element with a first capacitance, which is charged and discharged by at least one current; at least one second capacitance, which can be connected in parallel with the first capacitance via a first switch; and at least one voltage follower, via which the voltage present at the first capacitance can be fed to the second capacitance. In this case, the first switch is open if the voltage present at the first capacitance is fed to the second capacitance by means of the voltage follower. The first switch is closed if the second capacitance is connected in parallel with the first capacitance. The invention enables a further capacitance to be supplementary connected without a disturbance signal arising.

Abstract: A learning remote “learns” both a digital code carried by an infrared operational signal as well as a timing characteristic (for example, time period) of a carrier used to modulate the operational signal. When the photodiode of the learning remote is close to the transmitter of the remote to be learned from, a low frequency saturation current is superimposed on the intelligence signal. Rather than using a fixed reference voltage to detect when the carrier component of the intelligence signal transitions, an adaptive reference voltage (VAR) is used. A comparator compares a photocurrent voltage to VAR. Because VAR is maintained between the envelope of positive peaks and the envelope of negative peaks of the photocurrent voltage despite changes in the low frequency current, the comparator detects each transition of the carrier component. A microcontroller timer determines the time between transitions output by the comparator and thereby determines the timing characteristic.

Abstract: An automatic threshold voltage adjustment circuit, a method of automatically adjusting threshold voltage and an optical receiver for an optical communication system. In one embodiment, the circuit includes: (1) an amplitude detector configured to detect an amplitude of a received optical signal, (2) a variable resistor coupled to the amplitude detector and including a field-effect transistor configured to operate in a triad mode to provide a resistance that varies substantially linearly based on the amplitude and (3) an operational amplifier coupled to the variable resistor and configured to apply a variable gain based on the resistance to an input threshold voltage to yield an adapted threshold voltage.

Abstract: An optical receiver is provided as a device capable of detecting a small optical power with satisfactory accuracy and detecting the optical power in a wide dynamic range. In the optical receiver a bias generator applies a variable voltage to an avalanche photodiode (APD). First and second current sensors generate first and second detected signals according to a photocurrent. A controller calculates an optical power, using either one of the detected signals. The first current sensor includes a current mirror circuit and generates a first detected signal by measuring an electric current proportional to the photocurrent. The second current sensor is disposed between the bias generator and the current mirror circuit, and the maximum of the photocurrent detectable by this second current sensor is greater than the maximum of the photocurrent detectable by the first current sensor.

Abstract: A wavelength division multiplexing optical transmission apparatus for transmitting wavelength division multiplexing optical signals, the apparatus including a plurality of optical transmitting units outputting optical signals having a different wavelength from each other, a plurality of optical intensity modulating units intensity-modulating the optical signals, and a wavelength multiplexing unit multiplexing the optical signals. The plurality of optical intensity modulating units sets the amount of wavelength chirp adapting to each wavelength of the optical signals for the optical signals outputted from each of the plurality of optical transmitting units, and the wavelength multiplexing unit multiplexes the optical signals having the amount of wavelength chirp set respectively and then outputs the multiplexed optical signals.

Abstract: A receiver for coherent detection of a PSK modulated optical carrier includes an optical detector, digital-to-analog converters, and a digital module. The optical detector is configured to mix the modulated optical carrier with two phase components of a reference optical carrier and to produce analog output signals representative of optical signals produced by said mixing. The digital-to-analog converters are connected to receive the analog output signals and to produce digital signals from the received analog output signals. The digital module is connected to receive the digital signals and to perform one of compensating the received digital signals for a conjugate phase misalignment between the mixed components, extracting phase of the received digital signals, and estimating a frequency offset between the two carriers from the received digital signals.

Abstract: An apparatus and method for detecting an output power level of an optical receiver, in order to hold output signal levels constant over changing input optical levels. A photodetector detects an optical signal, and a current from the photodetector is applied an amplifier. The amplifier may be either a differential trans-impedance amplifier, or a dual trans-impedance amplifier coupled to a differential output amplifier. An output of the amplifier is applied o a signal detector, wherein an output signal of the signal detector is an indication of an output power level of the optical receiver.

Abstract: Methods and systems for controlling optical power attenuation are provided. A method comprises periodically measuring an optical power of an optical signal received by an optical receiver and periodically measuring a first attenuation control signal voltage. When the optical power measurement is outside a target power range, the method continues with calculating a target voltage necessary to maintain the optical power measurements at a target power level; calculating a second attenuation control signal based on the target voltage, wherein the second attenuation control signal is calculated to provide an over-damped transient response that maintains the second attenuation control signal within a usable range of a variable optical power attenuator; applying a second attenuation control signal voltage based on the second attenuation control signal to the variable optical power attenuator; and adjusting attenuation of the optical signal based on the second attenuation control signal voltage.

Abstract: An optical reception circuit and an identification level controlling method for an optical reception circuit are disclosed wherein reception sensitivity degradation arising from transmission waveform degradation by chromatic dispersion can be suppressed. The optical reception circuit includes a photoelectric converter for converting reception light into an electric signal, a pre-amplifying unit for amplifying the electric signal, a main amplifier for amplifying an output of the pre-amplifying unit, a monitor for monitoring the output of the pre-amplifying unit, and a controller for controlling an identification level in the main amplifier based on an output of the monitor. The monitor includes a limiter amplifier for amplifying the output of the pre-amplifying unit, and an average value detector for detecting a time average value of an output amplitude of the limiter amplifier.

Abstract: A system, method, and computer readable medium for measurement of burst mode optical power over multiple bursts, comprises mirroring a photodiode current of an optical signal burst, converting the mirrored photodiode current to a capacitor voltage, comparing the capacitor voltage to a pre-determined threshold voltage, and accumulating a burst time necessary for the capacitor voltage to reach the pre-determined threshold voltage.

Abstract: A burst optical receiver includes an optical signal inlet, an optical-electrical signal converter, an AC coupling network, an integrator feedback network, and an electrical signal outlet. The AC coupling network is electrically communicated with the optical-electrical signal converter, and blocks the electric signal having the frequency ranges lower than a predetermined threshold frequency, and allows the electric signal having the frequency ranges above the threshold frequency to pass through. The integrator feedback network is electrically communicated with the AC coupling network, and recurrently modifies the electric signal from the AC coupling network in such a manner to minimize noise mixed with the electric signal such that the electric signal is sufficiently contrasted with the noise for maximizing a signal-to-noise ratio of the electric signal.

Abstract: A calculation processing unit controls temperature of a Peltier device based on a slope of a waveform obtained by subtracting a waveform of a B-arm monitoring signal from a waveform of an A-arm monitoring signal and a value obtained by subtracting a value B of the B-arm monitoring signal from a value A of the A-arm monitoring signal. Similarly, the calculation processing unit controls a phase of the A-arm and a phase of the B-arm. An A-arm side micro-controller controls temperature of an A-arm side heater 22 based on the value of the A-arm monitoring signal, and controls the phase of the A-arm. A B-arm side micro-controller controls temperature of a B-arm side heater based on the value B of the B-arm monitoring signal, and controls the phase of the B-arm.

Abstract: Branches are grouped into a group 1 including first and second branches, and a group 2 including third and fourth branches. The signal after being passed through a dual pin photodiode in one branch included in the group 1 and being at the earlier stage of a CDR circuit is obtained. Also, from the later stage of the CDR circuit in the other branch in the group 1 is obtained. The obtained signals are passed through low pass filters, and an average value over a plurality of symbols is obtained. The signal from the earlier stage of the CDR circuit is multiplied by the signal from the later stage, and they are averaged. The obtained value reflects the phase difference of the two delay interferometers in the group 1. The group 2 is monitored by using the same method.

Abstract: In an optical telecommunication system in which an intensity of an arriving optical signal is different for each packet, detected is an optical intensity for each packet with little error. For this purpose, contrived is to detect an average optical intensity across header parts for each packet by focusing on the fact that the header part comprising the preamble and delimiter of a packet is in a bit pattern which includes approximately the same numbers of “0” and “1”.

Abstract: The present invention provides an optical receiver that enables to vary the sensitivity depending on the transmission speed. The optical receiver provides a photodiode to generate the photocurrent, the pre-amplifier to convert the photocurrent to the voltage signal, the lead pin to supply the bias voltage to the photodiode, and the control block to generate the switching signal for varying the current-to-voltage conversion efficiency and the frequency bandwidth of the pre-amplifier based on the control signal. The control signal is commonly provided from the lead pin through which the bias voltage is applied. The control block interprets the signal applied to the lead pin and generates the switching signal.

Abstract: A communications system includes an optical receiver for receiving optical signals and for converting the optical signals into electrical signals, a transimpedance amplifier (“TIA”) for filtering the electrical signals, a limiting amplifier coupled with the TIA, an automatic threshold control (“ATC”) coupled with the TIA for providing a reference voltage for the limiting amplifier. The ATC further includes a common emitter circuit and an emitter follower circuit, wherein logic high signals and logical low signals in the electrical signals are determined based on the reference voltage output from the ATC.

Abstract: A bandwidth adjustable transimpedance amplifier. The bandwidth adjustable transimpedance amplifier includes a feedback path with a selectable resistance. The bandwidth adjustable transimpedance amplifier is preferably implemented with a photodiode in a five pin package for an optical transceiver system, with a single pin providing a monitor out function and a rate select input.

Abstract: Disclosed is a Photonic Phase Locked Loop (PPLL) detector/discriminator, which makes possible a system for optically transmitting electromagnetic signals through a transmission medium (such as optical fiber, optical waveguide, underwater, in biological tissue, or in free space) with high sensitivity and extremely high dynamic range exceeding what is possible with present optical intensity modulated (AM) systems. Information is encoded on an optical carrier through the use of phase modulation (PM) or frequency modulation (FM). This information is subsequently demodulated into an accessible form through the use of the PPLL.

Abstract: A low-cost configuration of, and at the same time to control the variable dispersion compensator at a high speed in a variable dispersion compensator for compensating the wavelength dependent accumulated dispersion resulting from the wavelength dependency of the transmission fiber and fixed dispersion compensator in a long-distance high-speed WDM transmission system. In order to achieve the object mentioned above, the wavelength dependent representative characteristic of the transmission fibers 4-1 . . . n, and the wavelength dependent representative characteristic of the DCFs 13-1 . . . n are recorded and maintained in advance in the dispersion control circuit 5-1 . . .

Abstract: A method and system for initializing a coherent optical receiver. Upon detection of an optical signal, a multi-bit digital sample stream of the optical signal is digitally processed to initialize each one of a plurality of adaptive control blocks of the coherent optical receiver. The adaptive control blocks include at least a dispersion compensation block and a clock recovery block. The dispersion compensation block is initialized before initializing the clock recovery block.

Abstract: An electronic circuit includes: a differential amplifier circuit into which a digital input signal and a reference signal are fed; a feedback circuit outputting an average of amplitude of the input signal; and a peak holding circuit outputting a signal held based on an output signal of the feedback circuit as the reference signal.

Abstract: A data-aided, multi-symbol phase estimation (MSPE) scheme is described for improving receiver sensitivity in the direct-detection of optical differential multi-level phase-shift keying (ODmPSK) signals including optical differential quadrature phase-shift keying (ODQPSK) signals, ODQPSK signals with amplitude shift keying (ODQPSK+ASK), optical differential 8-level phase-shift keying (OD8PSK) signals with eight phase levels, and optical differential phase-shift keying signals with more than eight phase levels. The use of data-aided MSPE substantially reduces the “differential detection penalty,” with receiver sensitivity approaching that of coherent detection schemes.

Abstract: An optical transmitter for an optical communication system is provided. Included in the transmitter is a first optical delay element configured to generate a second optical signal from a first optical signal. A second optical delay element is configured to generate a fourth optical signal from a second optical signal. An optical multiplexer is configured to combine the third and fourth optical signals to produce a fifth optical signal. Also included is an optical modulator configured to alter a pulse width of the fifth optical signal to generate a sixth optical signal. An optical delay controller is configured to control the first optical delay element and the second optical delay element based on the sixth optical signal.

Abstract: A signal identification method for efficiently identifying Dense Wavelength Division Multiplexing (DWDM) channel modulation formats, signal powers, and center frequency detuning of signals that may be used in conjunction with telecom-grade monitoring equipment. The method utilizes least-square curve fitting estimates applied to a set of curves, each curve is characteristic of a modulation format and rate. For each least-square estimate an error value is calculated, and a curve fit with the least error is selected as the identified signal format for a signal.

Abstract: The invention relates to a receiver circuit having an optical receiving device, a plurality of amplifiers that are connected to the receiving device, and circuit means or a control circuit for individually activating and deactivating the individual amplifiers. In this case, the amplifiers each differ from one another in at least one parameter such as gain, and only one amplifier is activated at a given point in time, while the other amplifiers are deactivated. The invention makes it possible to match the receiver circuit to widely varying transmission rates.

Abstract: The present invention provides an optical transceiver to reduce a crosstalk in sufficient. The optical receiving unit of the invention includes an O/E-converter, a signal processing unit, and an offset voltage setting unit. The input of the signal processing unit, connected to the output of the O/E-converter, receives an electrical signal from the O/E-converter. The offset voltage VOFF of the signal processing unit is kept constant, independent of the phase difference between signal in the optical transmitting unit and in the optical receiving unit, by the offset voltage setting unit.

Abstract: A light sensor having a photocurrent subsection and an interface circuit is disclosed. The photocurrent subsection includes a photodetector, an amplifier, a diode and an impedance element. The first photodetector generates a current between a first node and a power rail in response to being illuminated with light. The interface circuit generates an output signal that is related to the logarithm of the intensity of light that is incident on the photodetector. The impedance element is constructed in a manner that compensates for the thermal dependency of the impedance through the diode. Additional photocurrent subsections can be added to further reduce the thermal dependency of the output signal.

Abstract: Techniques to control an optical receiver having a control loop using Bit Error Rate (BER). In one implementation, a bit error rate (BER) associated with a received optical signal is determined. Indication of the BER to a control loop adapted is provided to adjust the optical signal in a manner tending to reduce the BER. The received optical signal is adapted in a manner tending to increase the BER such that the control loop operates within an active control region.

Abstract: A method for receiving an optical signal is included where an ingress signal is split into a first portion and a second portion. A relative delay is induced between the first portion and the second portion, which are optically interfered to generate at least one interfered signal. Quality criteria of a monitored signal at least based on the at least one interfered signal is monitored so that a relative delay based in the quality criteria may be adjusted.

Abstract: A system and method are provided for calibrating orthogonal polarity in a multichannel optical transport network (OTN) receiver. The method accepts a composite signal and separates the polarization of the signal into a pair of 2n-phase shift keying (2n-PSK) modulated input signals via Ix and Qx optical signal paths, where n?1. Likewise, a pair of 2p-PSK modulated input signals are accepted via Iy and Qy optical signal paths where p?1. Polarization-adjusted I?x, Q?x, I?y, and Q?y signals are generated. An average magnitude is compared to either 2×the absolute magnitude of (I?x and Q?x), or 2×the absolute magnitude of (I?y and Q?y). The average magnitude value can be used that is either 2×(a predetermined peak signal amplitude), or the sum of the absolute magnitudes of (I?x and Q?x) and (I?y and Q?y). The polarization-adjusted I?x, Q?x, I?y, and Q?y signals are modified until the magnitude comparison is about zero.

Abstract: A burst optical receiver includes an optical signal inlet, an optical-electrical signal converter, an AC coupling network, an integrator feedback network, and an electrical signal outlet. The AC coupling network is electrically communicated with the optical-electrical signal converter, and blocks the electric signal having the frequency ranges lower than a predetermined threshold frequency, and allows the electric signal having the frequency ranges above the threshold frequency to pass through. The integrator feedback network is electrically communicated with the AC coupling network, and recurrently modifies the electric signal from the AC coupling network in such a manner to minimize noise mixed with the electric signal such that the electric signal is sufficiently contrasted with the noise for maximizing a signal-to-noise ratio of the electric signal.

Abstract: An optical communications system using forward error correction (FEC) to correct errors in signals carried by the system. Optical signals on the system are dropped at nodes and converted to electrical signals by avalanche photodiodes (APDs) at the node receivers. An FEC chip operates on the electrical signal to correct errors. The error rate is used to control the APD bias voltage which affects signal noise and therefore error rate. The errors in a predetermined interval are counted and a determination made as to whether the error rate is rising with time. The bias voltage is derived from the value of a counter whose count is incremented each interval. If the error rate is rising, the counting direction is changed.

Abstract: An optical transmitter has a resonance wavelength characteristic that varies with the refractive index of the optical transmitter. The optical transmitter receives a narrow band injected wavelength signal from an incoherent light source. The controller substantially matches a resonant wavelength of the optical transmitter to the wavelength of the injected wavelength signal by changing the refractive index of the optical transmitter to substantially match the resonant wavelength of the optical transmitter and the wavelength of the injected wavelength signal. A detector measures a parameter of the optical transmitter to provide a feedback signal to a controller to determine when the resonant wavelength of the optical transmitter and the wavelength of the injected wavelength signal are substantially matched.