Agere Systems Inc.

Agere Systems Guardian Corp.

Agere Systems Optoelectronics Guardian Corp.

Lucent Technologies Inc.

Triquint Technology Holding Co.

Other

Scott L Broutin

James Kevin Plourde

John William Stayt, Jr

George John Przybylek

David Alan Ackerman

Frank Stephen Walters

John W Stayt

Stephen A O'Brien

Laser wavelength stabilization is achieved by locating a low selectivity reference filter in a reference path of a laser beam. The low selectivity reference filter, with a periodicity greater than the control filter, is used together with a lookup table for the reference filter to resolve the uncertainty associated with the multivalued control filter. After the wavelength uncertainty for the control filter is resolved, the laser beam is stabilized based on the response of the control filter, as if the reference filter was not present.

Method and apparatus for stabilizing laser wavelength

A unique method and apparatus for locking on an absolute wavelength of laser light output by a laser package by actively compensating for a change in the temperature of an etalon optical filter is disclosed. Changes in etalon response characteristics due to temperature changes are compensated for by the addition (or subtraction) of an output voltage offset to the voltage control signal sent to the Thermo-Electric Cooler (TEC) from a controller within the laser package. The voltage offset is calculated by monitoring the etalon temperature. The voltage offset value provides for active compensation of changes in the etalon temperature and effectively 'readjusts' the output of the laser as if the etalon temperature itself had been readjusted.

Method and apparatus for active numeric temperature compensation of an etalon in a wavelength stabilized laser

Multiple operational parameters for a laser device are simultaneously controlled, optimized and/or stabilized by a software-based system with nested and interactive feedback control loops. Start-up mode, channel lock mode and channel change mode operations are described. The invention may be applied to a laser device with monolithic DBR tuning and gain sections, and also to systems with separate amplifiers. An optical filter system for normalizing-out changes in output power in relation to wavelength control is also disclosed.

Feedback control loop operating system for tunable source

The present invention provides a system and method for dynamically increasing the numeric gain applied to the temperature loop in a DBR laser control system in response to the anticipated wavelength change that occurs as a tuning current ramp is in progress. In accordance with a preferred embodiment of the invention, the feedback control signal to the laser's TEC is overcompensated for, and as a result, the system is forced to respond much faster, thermally, to the anticipated wavelength shift, thus providing improved real time wavelength stabilization to the control system. The implementation of the increased numeric gain can be carried out through software and/or firmware.

Control system for use with DBR lasers

A laser module characterization apparatus and method, the apparatus controlled by a computer, the apparatus having a laser module, an internal etalon transducer, an external etalon, and an external etalon transducer. The laser module comprising a laser source substantially simultaneously emitting a pair of substantially identical beams of light and an internal etalon adapted to receive a first of the pair of beams of light and to permit a portion of the first beam to pass through the internal etalon. The internal etalon transducer connected to the computer and responsive to the portion of the first beam. The external etalon adapted to receive a second of the pair of beams of light and to permit a portion of the second beam to pass through the external etalon. The external etalon transducer connected to the computer and responsive to the portion of the second beam.

Method and apparatus for characterizing laser modules

A method and apparatus for stabilizing the wavelength of a laser are disclosed. The invention provides a way to stabilize a laser for applications in dense wavelength division multiplexing (DWDM) systems where frequency spacing is crucial. The invention accomplishes laser stabilization by generating one or more optical paths which are passed through one or more filters to obtain one or more signals which are a function of frequency. Another optical path which does not contain a filter is generated to obtain a signal which is a function of power. The frequency signal(s) and the power reference signal are then converted from optical to electrical and from analog-to-digital. A microcontroller is then used to normalize one or more selected frequency paths with respect to the optical power path, process the signals via software code, and generate a signal which provides feedback to the laser for stabilization. By using a microcontroller; elements that lead to wavelength or frequency drift, or manufacturing component variations can be taken into account and the input signal to the laser can be adjusted accordingly.

Multiple path digital wavelength stabilization

A method for controlling tuning current values provided to a multichannel laser source. For each operating laser channel, a desired slope value of laser power as a function of tuning current is stored. The slope values of laser power as a function of tuning current is then measured. The tuning current is then adjusted until a slope value substantially close to said desired slope value is measured. The operating tuning current is set for the laser source that corresponds to the measured slope value.

Method and apparatus to select optimal operating conditions in a digital wavelength stabilized control system

A circuit for increasing the signal-to-noise ratio in an optical communication system and for stabilizing a laser wavelength. The circuit includes an impedance element disposed in parallel relation with the input capacitance of the circuit to increase the input capacitance for filtering out noise in the circuit to thereby achieve a high signal-to-noise ratio. The bandwidth of the noise signal is kept low to achieve high signal-to-noise ratios and efficient wavelength stabilization. By operating at low bandwidths, the input capacitance of the circuit does not dominate the shunt voltage and associated current due to the noise; rather, a feedback resistance associated with an operational amplifier dominates the magnitude of the noise current. Thus, the input capacitance can be increased without increasing noise current, which effectively filters the noise from the total current in the circuit and advantageously insures that the bandwidth of the noise is low and the signal-to-noise ratio of the circuit remains high.

Circuits and methods for achieving high signal-to-noise ratios and obtaining stabilized laser signals in dense wavelength division multiplexing systems

The invention in accordance with one aspect is a method of determining aging of a light emitting device which is capable of selectively emitting light having different wavelengths corresponding to different channels for light transmission as a function of tuning current supplied to the device. A tuning current is applied to the device which results in a wavelength corresponding to a desired channel. The slope of a curve which is light power from the device as a function of tuning current is determined by dithering about the applied tuning current. The determined slope is compared with a prior determined value in order to detect any change from the prior value. The voltage derived from a light signal passing through an optical filter can also be measured and compared to a prior value. These values may be used to determine aging of the device and the filter.

Detecting aging of optical components

A unique method and apparatus for locking on an absolute wavelength of laser light output by a laser package by actively compensating for a change in the temperature of an etalon optical filter is disclosed. Changes in etalon response characteristics due to temperature changes are compensated for by the addition (or subtraction) of an output voltage offset to the voltage control signal sent to the Thermo-Electric Cooler (TEC) from a controller within the laser package. The voltage offset is calculated by monitoring the etalon temperature. The voltage offset value provides for active compensation of changes in the etalon temperature and effectively &ldquo;readjusts&rdquo; the output of the laser as if the etalon temperature itself had been readjusted.

An apparatus controls a light source, which may be a laser. A first detector provides a first electrical signal representing an amplitude of a first light that is output by the light source. A filter receives the first light and provides a filtered light having an amplitude that depends on the amplitude and wavelength of the first light. A second detector provides a second electrical signal representing the amplitude of the filtered light. A switching device, such as a multiplexer, is capable of providing either the first electrical signal or the second electrical signal as its output signal. A common amplifier is coupled to the switching device. The common amplifier amplifies the output signal of the switching device, to alternately provide a first amplified signal and a second amplified signal, representing the first and second electrical signals, respectively. A processor receives the first and second amplified signals and generates a control signal that depends on the wavelength of the first light and is independent of the amplitude of the first light. The control signal may be, for example, a control signal for a thermoelectric cooler or a bias signal for a laser. The control signal is used to control the light source.

Method and apparatus for electrically switching a wavelength control system

A closed-loop feedback control system with a temperature tuned, wavelength stabilized laser module. The system uses a feedback control signal dependent upon a predetermined gain to control the temperature of the laser module. The laser module has an output connected to a controller via filtering and reference circuitry. The controller inputs etalon and reference signals from the filtering and reference circuitry to monitor the optical amplitude and wavelength of the laser module output, as well as the temperature of the laser module. When the controller detects a change in a slope of the etalon signal, the controller calculates a new numeric gain based on the changed slope. The new numeric gain and temperature of the laser module is used to generate a new control signal to maintain the output of the laser module at a desired wavelength. By monitoring the slope of the etalon signals, the system is capable of performing automatic closed-loop gain adjustment. As such, the system prevents strong oscillations of the control signal about a desired wavelength locking point, wavelength drift beyond system specifications and unwanted mode-hopping of the laser wavelength to undesired channels.

Automatic closed-looped gain adjustment for a temperature tuned, wavelength stabilized laser source in a closed-loop feedback control system

The output of a dedicated control laser element in a laser array, which closely tracks the output of the array, is directed to a discriminator and feedback control means through a closed loop feedback-based system to provide both wavelength stability and power control of the array without reducing the optical power output from the array. The output of a dedicated control laser element in a laser array is also directed to a discriminator and synchronous detection means and is frequency modulated with a local oscillator to reduce the electronic drift and stabilize the wavelength of the dedicated laser source.

Method to sense laser array power and wavelength and reduce drift for wavelength selection and stabilization

A method and apparatus for stabilizing the wavelength of a laser are disclosed. The invention provides a way to stabilize a laser for applications in dense wavelength division multiplexing (DWDM) systems where frequency spacing is crucial. The invention accomplishes laser stabilization by generating an optical path which is passed through a filter to obtain a signal which is a function of frequency. A second optical path which does not contain a filter is generated to obtain a signal which is a function of power. The signals are then converted from optical to electrical and from analog to digital, and a microcontroller is used to normalize the frequency path with respect to the optical power path, process the signals via software code, and generate a signal which provides feedback to the laser for stabilization. By using a microcontroller; elements that lead to wavelength or frequency drift, or manufacturing component variations can be taken into account and the input signal to the laser can be adjusted accordingly.

Two path digital wavelength stabilization

A wavelength stabilized laser system includes a laser that produces a laser light. The laser light has an amplitude and a wavelength that vary with the laser temperature. A first detector provides a first signal representing the amplitude of the laser light. A filter has a gain that is a function of the wavelength of the laser light. The filter receives the laser light and outputs a filtered light having an amplitude that varies with the wavelength of the laser light. A second detector provides a second signal representing the amplitude of the filtered light. A transformer has a primary and a secondary. The primary is electrically coupled to the first and second detectors. The primary of the transformer includes a first coil connected to the first detector and a second coil connected to the second detector. The first and second coils of the primary are opposite in polarity from each other. Thus, the secondary has a voltage that is proportional to the difference between the voltages of the first and second detectors. A controller is coupled to the secondary. The controller controls the wavelength of the laser based on a voltage of the secondary of the transformer.

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Kutztown, PA, United States of America

Scott L Broutin