External Cavity Laser Wavemeter for DWDM Stability
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Solution Overview
Problem
Existing external cavity type lasers with TO type packages lack precise wavelength control, making them unsuitable for dense wavelength division multiplexing (DWDM) applications that require stable wavelength intervals of 100 GHz, 50 GHz, or 25 GHz, as they are prone to wavelength instability due to temperature changes and current variations.
Innovation Solution
Incorporating a wavemeter with a TO type package that includes a laser diode chip, a collimating lens, a wavelength selective filter, and photodiodes to measure and adjust the laser beam wavelength by controlling the temperature of the thermoelectric element, ensuring precise wavelength stabilization regardless of current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a TO type external cavity laser package is used, then the device size and cost are reduced compared to butterfly packages, but wavelength stability deteriorates due to sensitivity to temperature changes and current variations
Solution Approach 1:
The patent implements a feedback control system using a wavemeter (photodiode detector) that continuously monitors the laser wavelength and provides feedback signals to adjust the grating angle or temperature, thereby compensating for wavelength drift caused by environmental changes and maintaining stable wavelength output in the compact TO package
Solution Approach 2:
The patent employs dynamic parameter adjustment by changing the grating angle or temperature of the diffraction grating in response to detected wavelength deviations, allowing the laser to maintain precise wavelength control despite the compact package's inherent sensitivity to environmental variations
2Measurement precision
If wavelength selective filtering is implemented to achieve precise wavelength control, then measurement precision improves, but device complexity increases due to additional optical components
Solution Approach 1:
The diffraction grating serves multiple functions simultaneously: it acts as both the wavelength-selective filtering element for the laser cavity and the dispersive element for the wavemeter, enabling wavelength control and measurement without requiring separate dedicated components for each function
Solution Approach 2:
The patent combines the laser cavity optics and wavemeter optics into a shared optical path using the common diffraction grating, merging multiple optical functions into a compact arrangement that achieves precise wavelength control without proportionally increasing device complexity
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 configuration allows for precise wavelength adjustment and stabilization, enabling the external cavity type laser to maintain wavelength stability within +/-100 pm, +/-50 pm, or +/-25 pm, meeting the requirements of advanced DWDM applications.
Implementation Method 1
a wavelength selective filter transmitting a beam having a selected specific wavelength therethrough
Implementation Method 2
a photodiode disposed on a path of the beam emitted from the laser diode chip and transmitting through the 45-degree partial reflection mirror
Implementation Method 3
a collimating lens installed on a path of a beam between the laser diode chip and the beam feedback partial reflection mirror to collimate the beam
Implementation Method 4
a beam feedback partial reflection mirror reflecting a portion of the beam emitted from the laser diode chip to feed the beam back to the laser diode chip
Data Source
AI summary
The present invention relates to an external cavity type laser provided with a wavemeter capable of precisely measuring a wavelength of a laser beam based on a transmission wavelength band of a wavelength selective filter inserted into a cavity regardless of a driving current of a laser diode chip. The external cavity type laser apparatus includes: a laser diode chip 100 emitting a laser beam; a beam feedback partial reflection mirror 500 reflecting a portion of the beam emitted from the laser diode chip 100 to feed the beam back to the laser diode chip 100; a collimating lens 200 installed on a path of a beam between the laser diode chip 100 and the beam feedback partial reflection mirror 500 to collimate the beam emitted from the laser diode chip 100; a 45-degree partial reflection mirror 300 converting a laser beam moving in parallel with a package bottom surface into a laser beam moving perpendicularly to the package bottom surface; a wavelength selective filter 400 transmitting a beam having a selected specific wavelength therethrough; a beam strength monitoring photodiode 600 disposed on a path of a beam moving from the collimating lens 200 to the 45-degree partial reflection mirror 300 and transmitting through the 45-degree partial reflection mirror 300; and a wavelength monitoring photodiode 700 disposed on a path of a beam moving from the wavelength selective filter 400 to the 45-degree partial reflection mirror 300 and transmitting through the 45-degree partial reflection mirror 300. A magnitude of a photocurrent flowing to the wavelength monitoring photodiode 700 is changed depending on a strength of a beam output oscillated in the laser diode chip 100 and a reflectivity at the wavelength selective filter 400, and a photocurrent flowing to the beam strength monitoring photodiode 600 is determined by the strength of the beam output outputted from the laser diode chip 100. Therefore, a value obtained by dividing the photocurrent flowing to the wavelength monitoring photodiode 700 by the photocurrent flowing to the beam strength monitoring photodiode 600 depends on only the reflectivity at the wavelength selective filter 400. Therefore, the value obtained by dividing the photocurrent flowing to the wavelength monitoring photodiode 700 by the photocurrent flowing to the beam strength monitoring photodiode 600 provides information on the wavelength of the laser beam based on the transmission band wavelength of the wavelength selective filter 400, and the wavelength of the laser beam may be figured out by measuring the value, and may be very precisely determined to be a predetermined wavelength.