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US 2015/0146751 A1Published application
High-stability light source system and method
AssigneeUSL Technologies, LLC
InventorJohn P. Downing
Life of this patent
Estimating the term…
Abstract
A light source system that generates stable optical power over time and temperature in which a feedback control circuit is operative to receive a temperature signal and a sample signal and in response thereto generate a control signal to a driver circuit to maintain a power level of the light output substantially constant over an operative temperature range defined by Tmin and Tmax.
Claims24
A light source assembly, comprising:
- a semiconductor light emitter structured to emit light, the semiconductor light emitter comprising one from a group containing resonant-cavity light-emitting diodes, edge-emitting light-emitting diodes, and super luminescent diodes, wherein the light has a peak wavelength and bandwidth in bands in the group comprising ultraviolet-, visible-, and infrared-emission bands;
- a driver circuit having a first input terminal, a second input terminal structured to receive a reference signal, and an output terminal, the driver circuit operative to supply a drive signal on the output terminal to excite light emissions from the semiconductor light emitter;
- a lens operative to receive the light and to collimate the light into substantially parallel light rays;
- a beamsplitter comprising a plate of optically transparent material having a first surface and a second surface, the beamsplitter positioned to capture and reflect a first portion of the light rays having a first power and transmit a remaining unreflected second portion of the light rays having a second power;
- a photodetector circuit having a photodetector with an active area having spatially uniform responsivity over the active area of the photodetector and responsivity that changes less than 0.2% per year and operative to capture substantially all of the reflected first portion of the light rays in the active area and to convert the captured light rays to an electrical sample signal;
- a thermally conductive support member comprised of material having thermal conductivity in excess of 220 W/m·° K, the semiconductor light emitter and the photodetector mounted on the thermally conductive support member to maintain them at substantially the same temperatures;
- a temperature sensor coupled to the thermally conductive support member and operative to produce a temperature signal representative of the temperature of the semiconductor light emitter and the photodetector;
- and
- a feedback control circuit having a first input terminal coupled to the temperature sensor, a second input terminal coupled to the photodetector circuit, and an output terminal coupled to the first terminal of the driver circuit, the feedback control circuit forming a feedback loop between the photodetector circuit and the first input terminal of the driver circuit and operative to provide a control signal on the output terminal to the first input terminal of the driver circuit.
6 more elements
A method for calibrating a feedback control circuit and the reference control circuit in a light source assembly, the method comprising:
- determining from component test data whether interpolation or numerical solution of a function will be used to minimize a net control error in operation of the light source;
- providing a characterization of a variation in peak wavelength with temperature in the light source and forward current through a semiconductor light emitter within a production lot;
- providing a computer programmed to control the calibrating of the feedback control circuit and the reference control circuit, including providing a temperature signal and a correction factor;
- providing a program enabling a microprocessor in the feedback control circuit to digitize and store a calibration temperature signal and a correction factor;
- providing a program enabling the microprocessor in the feedback control circuit to do a numerical iteration to determine an optimal correction factor for each calibration temperature;
- providing a means for temporarily bonding a thermally conductive support member to a temperature control apparatus capable of controlling the temperature of the thermally conductive member to an accuracy of 0.1° C. and having a stability of ±0.01° C.;
- providing a NIST-traceable photodetector or spectrophotometer for monitoring output light power of the light source in absolute units;
- setting the temperature control apparatus to a reference temperature, either Tmin or Tmax, and allowing the temperature signal to stabilize;
- setting the output light power of the light source to an absolute reference level P0;
- recording the absolute reference level P0 in the computer;
- signaling the microprocessor to store a first calibration temperature and the corresponding correction factor;
- setting the temperature-control apparatus to the next calibration temperature and allowing the temperature signal to stabilize;
- signaling the microprocessor to determine by numerical iteration the value of the correction factor that minimizes a difference between the output optical power and the absolute reference level P0;
- recording the temperature signal and the correction factor in memory;
- and
- setting the temperature-control apparatus to the next calibration temperature and allowing the temperature signal to stabilize.
13 more elements
A system, comprising:
- a support formed of thermally conductive material;
- a semiconductor light emitter mounted on the support;
- a driver circuit operative to generate a driver signal to the semiconductor light emitter and to receive a reference signal;
- a device structured to receive the light and to reflect a first portion of the light and to output a second portion of the light;
- a detector circuit mounted on the support and operative to receive the first portion of the light and generate a sample signal in response to reception of the first portion of light;
- a temperature sensor disposed on the support and operative to generate a temperature signal;
- and
- a feedback control circuit operative to receive the temperature signal and the sample signal and in response thereto to generate a control signal to the driver circuit to maintain a power level of the second portion of light substantially constant over an operative temperature range defined by Tmin and Tmax.
5 more elements
A method, comprising:
- receiving a reference signal and a control signal and generating a driver signal in response to receipt of the reference signal and the control signal;
- generating a beam of light from a light source in response to the driver signal;
- reflecting a first portion of the beam of light and outputting a second portion of the beam of light;
- receiving the first portion of the beam of light at a detector circuit and generating a sample signal in response to reception of the first portion of the light;
- sensing a temperature of the light source and the detector circuit and generating a temperature signal;
- and
- receiving the temperature signal and the sample signal in a feedback control circuit and generate the control signal to maintain a power level of the second portion of light substantially constant over an operative temperature of Tmin and Tmax.
4 more elements
Dependencies are inferred from the claim text.