Optical Subassembly Impedance Matching via Relay Substrate
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Solution Overview
Problem
Existing optical subassemblies face challenges in securing space for mounting optical devices while matching characteristic impedance, particularly in high-speed, broadband applications operating within a wide temperature range, such as those required for CPRI interfaces in wireless base stations.
Innovation Solution
The optical subassembly design includes a dielectric material-filled coaxial line with a lead terminal, a device mounting substrate, a relay substrate with a conductor pattern, and a spacer to establish conduction, allowing for simultaneous space allocation and impedance matching, enhanced by a Peltier temperature regulator and bonding wires for improved high-frequency wave characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the diameter of the through-hole is increased to match the characteristic impedance of the coaxial line, then the characteristic impedance matching is improved, but the distance between the seat and the lead terminal increases, requiring a thicker dielectric substrate, which in turn requires widening the line width of the conductor pattern, decreasing the space for mounting the optical device
Solution Approach 1:
A relay substrate is introduced as an intermediary component between the lead terminal and the device mounting substrate. The relay substrate includes a conductor pattern that transmits the electric signal, and a spacer that establishes conduction between the rear surface of the relay substrate and the seat. This intermediary structure allows characteristic impedance matching to be achieved without directly increasing the through-hole diameter or thickening the dielectric substrate, thereby preserving the mounting space for the optical device.
2Reliability
If a Peltier temperature regulator is added to maintain stable operation in a wide temperature range, then the temperature stability is improved, but the device complexity increases
Solution Approach 1:
The Peltier temperature regulator is integrated with the existing TO-CAN-type TOSA module structure, merging the temperature control function into the housing assembly. The regulator is positioned to work in conjunction with the optical device and existing structural components, achieving temperature stability without requiring a completely separate or complex temperature control system.
3Reliability
If bonding wires are added to reinforce grounding of the sub-mount, then the high-frequency wave characteristics are improved, but the device complexity increases
Solution Approach 1:
The bonding wires perform multiple functions simultaneously: they provide grounding for the sub-mount, reinforce the electrical connection, and improve high-frequency wave characteristics. This self-service approach allows a single component to address multiple requirements without adding significant complexity to the overall structure.
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 effectively secures space for the optical device and matches characteristic impedance, achieving stable high-frequency wave transmission and operation across a wide temperature range, thus addressing the limitations of existing TO-CAN-type TOSA modules.
Implementation Method 1
a dielectric material, which is filled in a space between the first through-hole and the first lead terminal
Implementation Method 2
a spacer interposed between the third surface and the relay substrate to establish conduction between a rear surface of the relay substrate and the seat
Implementation Method 3
a configuration that uses the EML in combination with a temperature regulator, for example, a Peltier device
Data Source
AI summary
An optical subassembly includes an eyelet including a first through-hole penetrating from a first surface through a second surface; a first lead terminal, which is to be inserted into the first through-hole, and is configured to transmit an electric signal; a dielectric material, which is filled in a space between the first through-hole and the first lead terminal; a device mounting substrate, on which an optical device is to be mounted, and which includes a first conductor pattern configured to transmit the electric signal to the optical device; a metal block having mounted thereon the device mounting substrate; a temperature regulator placed between the metal block and the eyelet; a relay substrate including a second conductor pattern, which is configured to transmit the electric signal to the optical device; a seat, which protrudes from the first surface in a direction extended from the first through-hole, and has a third surface mounting the relay substrate; and a spacer interposed between the third surface and the relay substrate to establish conduction between a rear surface of the relay substrate and the seat.