Optical Transmitter Module Using External Light Reflection
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Solution Overview
Problem
Current optical transmitter modules face challenges in extending modulation bandwidth due to limitations in directly modulated laser (DML) technology, including low fabrication yield, increased cost, and decreased optical coupling efficiency when integrated with silica arrayed waveguide grating (AWG) chips, and are restricted by a modulation bandwidth below 28 GHz.
Innovation Solution
An optical transmitter module is designed with a DML-based transmitter and a vertically polished AWG chip, optically coupled with a spaced distance of 10 μm to 15 μm, utilizing an external light reflection effect to enhance modulation bandwidth, and incorporating a spot-size converter and anti-reflection coatings to minimize optical coupling loss and optimize lasing wavelength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a distributed feedback laser and an electro-absorption modulator are co-integrated to form an EML for 100 Gbps PAM4 transmission, then the modulation bandwidth is improved, but the fabrication yield is lowered
Solution Approach 1:
The system is divided into separate functional modules: a DML chip for light generation and modulation, and a silica AWG chip for wavelength multiplexing. This segmentation allows each component to be optimized and manufactured independently, avoiding the fabrication yield issues of co-integrated EML while maintaining high-speed transmission capability through external optical coupling.
Solution Approach 2:
An external optical coupling interface serves as an intermediary between the DML chip and the silica AWG chip. This intermediary enables the system to achieve high-speed transmission without requiring complex co-integration, thus preserving fabrication yield while extending modulation bandwidth through proper optical alignment and coupling design.
2Reliability
If anti-reflection coating is applied to the waveguide output end to minimize light reflection, then the lasing wavelength and SMSR characteristics are improved, but light reflection from the vertically polished silica AWG chip still deteriorates these characteristics
Solution Approach 1:
The light reflection from the vertically polished silica AWG chip, which was previously a harmful factor deteriorating lasing characteristics, is converted into a beneficial feedback mechanism. By carefully controlling the optical coupling and using the reflected light, the system achieves extended modulation bandwidth while maintaining stable lasing wavelength and SMSR characteristics.
3Speed
If the modulation bandwidth of DML is extended by placing a passive section at the front or rear of the DML chip to induce photon-photon resonance, then the modulation bandwidth is improved, but the degree of integration increases leading to decreased manufacturing yield and increased cost
Solution Approach 1:
The passive section required for photon-photon resonance is extracted from the DML chip structure and implemented externally through the optical coupling system. This extraction maintains the modulation bandwidth extension benefit while avoiding the increased device complexity and integration issues that would result from incorporating the passive section directly into the chip.
4Reliability
If a mutual tilt structure is applied between the DML waveguide and the silica AWG chip waveguide to overcome light reflection, then the lasing characteristics are improved, but optical coupling efficiency and module manufacturing yield decrease
Solution Approach 1:
Instead of applying a mutual tilt structure that affects the entire interface, the solution uses localized anti-reflection coating at the waveguide output end and optimizes the optical coupling interface properties. This localized approach maintains lasing characteristics while preserving optical coupling efficiency and manufacturing yield.
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 achieves an increased modulation bandwidth of 5 GHz to 10 GHz, securing a side mode suppression ratio (SMSR) of 35 dB or more and high optical output power, while maintaining a low-cost and high-yield manufacturing process.
Implementation Method 1
a directly modulated laser chip array including one or more directly modulated laser (DML) chips
Implementation Method 2
a cross section of the waveguide at the output end is subjected to anti-reflection coating
Implementation Method 3
an arrayed waveguide grating (hereinafter referred to as 'AWG') chip that is vertically polished
Implementation Method 4
a wavelength multiplexer that multiplexes the multi-channel optical signals
Implementation Method 5
utilizing an external light reflection effect to enhance modulation bandwidth
Implementation Method 6
a photon-photon resonance (PPR) phenomenon is being induced
Data Source
AI summary
Disclosed is an optical transmitter module including a directly modulated laser transmitter based on a directly modulated laser (DML) and an arrayed waveguide grating (AWG) chip that is vertically polished. The directly modulated laser transmitter includes a directly modulated laser chip array including one or more directly modulated laser chips, an impedance matching circuit that allows each of the one or more directly modulated laser chips to operate at a critical speed of 100 Gbps per channel or higher, and a radio frequency-flexible printed circuit board (RF-FPCB) that transmits a radio frequency (RF) modulating signal to the directly modulated laser chip array. The arrayed waveguide grating chip includes an optical waveguides that transfer multi-channel optical signals and a wavelength multiplexer that multiplexes the multi-channel optical signals. The directly modulated laser transmitter and the arrayed waveguide grating chip are spaced apart from each other and are optically coupled in chip-to-chip.