Lattice-Shifted Photonic Crystal Waveguide for High-Speed Modulation
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Solution Overview
Problem
Current high-speed optical modulators face challenges in achieving a high on/off extinction ratio (ER) and low power consumption while maintaining a compact size, as they often require precise tuning, high carrier densities, and suffer from high optical loss and unit capacitance, limiting their speed and efficiency.
Innovation Solution
A photonic integrated circuit (PIC) with a lattice-shifted photonic crystal optical waveguide and a semiconductor-oxide-semiconductor diode, which uses slow light to enhance modulation efficiency, reducing the modulator length and optical loss while maintaining a wide bandwidth, by incorporating geometric features like periodic patterns or trenches to create a slow-light effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If carrier-injection phase modulation is used to achieve efficient modulation, then modulation efficiency is improved, but modulation speed is limited to around 1 Gb/s by minority-carrier diffusion
Solution Approach 1:
The patent changes the fundamental parameter of carrier dynamics by using carrier-accumulation mode with a very thin oxide barrier layer (less than 10 nm) instead of traditional carrier-injection or carrier-depletion modes. This parameter change allows carriers to accumulate at the oxide interface under forward bias, enabling both high efficiency and high speed (greater than 10 Gb/s) modulation by eliminating minority-carrier diffusion limitations while maintaining strong phase modulation.
2Speed
If carrier-depletion phase modulation is used to achieve fast modulation speed, then modulation speed is improved, but modulation efficiency deteriorates because it is hard to deplete a lot of charge
Solution Approach 1:
The patent inverts the traditional carrier-depletion approach by using carrier-accumulation mode. Instead of depleting carriers to achieve fast modulation, the invention accumulates carriers at the oxide interface under forward bias. This inversion allows the diode to operate in a regime where both high speed and high efficiency are achieved simultaneously, as carriers accumulate rather than deplete, enabling strong phase modulation with fast response.
3Length of moving object
If carrier-accumulation phase modulation is used to achieve high speed and short MZI length, then modulator length is reduced, but optical loss increases due to polycrystalline-silicon scattering and absorption
Solution Approach 1:
The patent changes the material parameter by using single-crystal silicon instead of polycrystalline silicon in the optical waveguide regions. This material parameter change dramatically reduces optical loss from polycrystalline-silicon scattering and absorption, allowing the short MZI (around 0.5 mm) achieved through carrier-accumulation modulation to have acceptable optical loss while maintaining high speed and compact size.
4Use of energy by moving object
If carrier-accumulation phase modulation is used to achieve high carrier-mobility and low voltage operation, then voltage operation is reduced, but unit capacitance increases which limits modulation speed due to RC limits
Solution Approach 1:
The patent changes the geometric parameter by using a very thin oxide barrier layer (less than 10 nm) in the semiconductor-oxide-semiconductor diode structure. This parameter change reduces the unit capacitance while maintaining the carrier-accumulation effect, thereby reducing the RC time constant and enabling modulation speeds greater than 10 Gb/s even with low voltage operation (less than 2V).
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 significantly increases modulation efficiency, allowing for shorter modulator lengths, reduced optical loss, and higher data rates, achieving an ER of greater than 7 dB at low voltage with reduced power consumption and capacitance, enabling data rates beyond 10 Gb/s.
Implementation Method 1
uses light slowed by a lattice-shifted photonic crystal optical waveguide to enhance a semiconductor-oxide-semiconductor diode
Implementation Method 2
lattice-shifted photonic crystal optical waveguide
Implementation Method 3
most of the reported high-speed optical modulators implemented using silicon are based on the free-carrier plasma dispersion effect, i.e., the index of refraction of silicon decreases as densities of electrons and holes (i.e., free carriers) increase
Implementation Method 4
the index of refraction is modulated, and the optical phase of propagating laser light is modulated
Implementation Method 5
the phase modulation can then be converted into optical intensity modulation (i.e., on/off switching) by building the phase-modulation optical waveguide into a ring-resonator modulator or a Mach-Zehnder interferometer (MZI)
Data Source
AI summary
A photonic integrated circuit (PIC) is described. This PIC includes a semiconductor-barrier layer-semiconductor diode in an optical waveguide that conveys an optical signal, where the barrier layer is an oxide or a high-k material. Moreover, semiconductor layers in the semiconductor-barrier layer-semiconductor diode may include geometric features (such as a periodic pattern of holes or trenches) that create a lattice-shifted photonic crystal optical waveguide having a group velocity of light that is lower than the group velocity of light in the first semiconductor layer and the second semiconductor layer without the geometric features. The optical waveguide is included in an optical modulator, such as a Mach-Zehnder interferometer (MZI).