Sloped Passband Filter for Unregulated Laser Power Stability

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Solution Overview

Problem

Directly modulated lasers (DMLs) without active temperature control mechanisms face challenges in maintaining optical signal power within specified limits across varying temperatures, leading to unreliable output due to red-shifting and power variations.

Innovation Solution

Incorporating a sloped or graded passband filter that attenuates optical signals based on temperature and wavelength, ensuring the output power remains within specified limits by adjusting bias current and operating within allowable temperature ranges.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If a directly modulated laser diode (DML) without temperature control is used to provide high output power, then the optical signal power is increased, but the center wavelength red-shifts and output power decreases as temperature increases

Engineering Contradiction:

Improveoptical signal output powerVSAvoidwavelength stability and power consistency

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

An optical filter is introduced as an intermediary component between the DML and the optical fiber. This filter selectively transmits wavelengths within a specific range (λc ± δ) while blocking other wavelengths, thereby stabilizing the output characteristics without requiring temperature control of the laser diode itself

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention changes the operational parameters by defining a specific wavelength transmission window (λc ± δ) through the optical filter. This parameter-based approach allows the system to operate reliably across temperature ranges by accepting only signals within the specified wavelength bandwidth, effectively decoupling performance from temperature stability

Inventive Principle:

Principle #35Parameter changes

2Power

If the bias current is increased to maintain output power at higher temperatures, then the optical signal power is improved, but the laser diode may exceed maximum current limits and reduce reliability

Engineering Contradiction:

Improveoptical signal output powerVSAvoidexcessive current stress on laser diode

Core Design Contradiction:

PowerVSObject-affected harmful factors

Solution Approach 1:

The invention converts the harmful effect of temperature-induced wavelength drift into a beneficial filtering mechanism. The optical filter exploits the wavelength shift caused by temperature changes to maintain signal integrity, transforming what was previously a reliability issue into a self-regulating feature of the system

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Ease of manufacture

If an optical filter with fixed transmission characteristics is used, then the manufacturing is simplified, but it cannot compensate for temperature-induced wavelength shifts

Engineering Contradiction:

Improvefilter fabrication simplicityVSAvoidtemperature compensation capability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The optical filter is designed with specific transmission parameters (center wavelength λc and bandwidth 2δ) that are chosen to accommodate the expected temperature range. By carefully selecting these parameters during design, the filter provides temperature compensation while maintaining manufacturing simplicity, as no active control mechanisms are required

Inventive Principle:

Principle #35Parameter changes

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

The solution effectively maintains optical signal power within specified limits across temperature variations, enhancing the reliability and stability of DMLs and other thermally unregulated lasers in optical transmitters.

Implementation Method 1

The sloped or graded passband filter is configured to receive the optical signal and attenuate an output power of the optical signal in the first wavelength band

Methodology Applied

Scientific EffectOptical filtering: Filter (optical)

Data Source

PatentUS11303358B2Optical transmitter including a graded or sloped passband filter, and methods of making and using the same

Publication Date: 2022.04.12 SOURCE PHOTONICS INC

AI summary

Embodiments pertain to an optical transmitter, including a thermally unregulated light emitting device and a sloped or graded passband filter. The light emitting device is configured to receive a bias current and output an optical signal within a wavelength band. The sloped or graded passband filter is configured to attenuate an output power of the optical signal in the wavelength band. The light emitting device has a maximum bias current limit, a maximum operating temperature limit, and maximum and minimum output power limits, and the sloped or graded passband filter has an insertion loss in the wavelength band that decreases as the light emitting device temperature increases and/or the optical signal wavelength increases within the wavelength band. The attenuated optical signal is within the maximum and minimum output power limits when the bias current is at or below the maximum bias current limit and the light emitting device outputs the optical signal at or below the maximum operating temperature limit.