Laser Diode Wavelength Control via Junction Voltage
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Solution Overview
Problem
Conventional methods for controlling the emission wavelength of light emitting devices, such as laser diodes, face challenges due to temperature variations and thermal gradients, leading to systematic errors in wavelength stabilization, especially in applications requiring high spectral resolution like telecommunications and spectroscopy.
Innovation Solution
A method involving amplitude modulated current to determine dynamic resistance and active region voltage, allowing for precise temperature control of the light emitting device's active region, thereby stabilizing the emission wavelength despite internal and external temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thermistor is used to sense temperature at a short distance from the active region, then temperature precision is typically 0.01 °K, but there is a temperature gradient between the thermistor and the laser causing systematic error in emission wavelength when ambient temperature varies
Solution Approach 1:
The patent introduces an intermediary measurement approach by using the voltage drop across the laser diode junction as a mediator to infer the active region temperature. Instead of directly measuring temperature with a thermistor near the active region, the method uses electrical voltage characteristics that directly reflect the junction temperature, thereby eliminating the temperature gradient error between the sensor and the active region.
Solution Approach 2:
The patent replaces the mechanical/thermal sensing system (thermistor) with an electrical measurement system (voltage drop measurement). By substituting the thermal conduction-based temperature sensing with electrical voltage characteristics, the method directly accesses the junction temperature through electrical properties, avoiding the thermal gradient problem inherent in physical temperature sensors.
2Ease of operation
If conventional thermistor-based temperature control is used, then temperature can be monitored, but systematic errors occur due to temperature gradients between the thermistor and the laser active region
Solution Approach 1:
The patent enables the laser diode to measure its own active region temperature through its inherent electrical characteristics. The voltage drop across the junction serves as a self-diagnostic parameter that directly indicates the temperature of the active region without requiring external sensors. This self-service approach eliminates the need for separate temperature sensing components and their associated gradient errors.
3Illumination intensity
If injection current is increased to maintain light emission, then light output is sustained, but junction heating occurs causing thermal expansion and wavelength shift
Solution Approach 1:
The patent implements a feedback control mechanism that continuously monitors the voltage drop across the laser diode junction and uses this information to regulate the injection current. By feeding back the voltage measurement (which reflects junction temperature) to the current control system, the method dynamically adjusts the current to maintain stable wavelength operation while sustaining light emission, compensating for the heating effect in real-time.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves accurate and stable wavelength control with minimal systematic error, maintaining wavelength stability within ±0.03 pm/°C over a 15-35°C ambient temperature range, comparable to conventional thermistor-based control methods.
Implementation Method 1
Laser diode operating temperature is controlled conventionally using a thermoelectric cooler (TEC) such as a Peltier element
Implementation Method 2
A potential alternative technique is to use the voltage drop across the laser diode to measure the temperature of the junction. This technique has been widely used in diode based thermometers for several decades. Thermometers using the junction voltage of a diode can sense temperature in the range of 1 K-400K with sensitivity of 1mK
Implementation Method 3
determining a dynamic resistance indication of series resistance of the device, the series resistance comprising ohmic resistance of the device, and measuring a forward voltage of the device during said light emission
Data Source
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AI summary
This invention generally relates to a method of controlling emission wavelength of a light emitting device, and a system for wavelength control of a light emitting device, for example for wavelength stabilisation of a laser diode. One method of controlling emission wavelength of a light emitting device comprises: determining an indication of series resistance of the device, the series resistance comprising ohmic resistance of the device; providing a current through the device to maintain light emission of the device; measuring a forward voltage of the device during said light emission, the forward voltage being across an impedance comprising impedance of an active region of the device and the series resistance; determining an indicator of active region voltage on the basis of the measured forward voltage and the determined indicator of series resistance; and controlling a temperature of the device on the basis of the determined indicator of active region voltage.