Abstract

The optical senior design class at the University of Rochester strives to tackle engineering problems through engineering processes and design. The ASML fiber team was tasked with designing a broadband fiber coupler. The Broad Wavelength Range Single Mode Fiber Coupling Optic project aims to investigate and model the coupling effects for discrete wavelengths in the broadband range of 400 to 2000 nm through an optical system. The usage of the coupler will be incorporated into ASML lithography machine. The final design is to be modeled in OpticStudio, rendered in, and tested to achieve coupling efficiency around 75%.

We accomplished our goal by modeling the design using OpticStudio with off-the-shelf parts from Optimax, and conducted performance analysis to determine parameter tolerances. We had freedom to design our own rotationally symmetric lenses and mirrors with the addition of an optional aspheric surface. Our design process could include custom parts, as long as these parts fulfill manufacturing tolerances of Optimax. We aimed to use this design to explore possible modes of manufacturing within volume, cost, and material specifications. To read more background information on fiber coupling process, please refer to the design document below.

Requirements/Fitness of Use

Must include a 10 mm beam of diffraction limited broadband source in free space, into a fiber optic cable
Perform optimally for 10 discrete wavelengths ranging between 400-2000nm
Maintain a numerical aperture of 0.15 for an object located at infinity
Be rotationally symmetric
Incorporate spherical lenses, mirror surfaces, and an optional single aspheric surface

Desirables within System

Materials for lenses be chosen from the preferred glass list (Optimax)
Volume of the design does not exceed 300x100x100 mm^3
Zernike aberrations are minimized
Coupling efficiency of the optical power into the fiber is maximized
The system does not exceed 6 surfaces (3 elements)

We are not responsible for…

Producing a design that performs optimally for all wavelengths within the range of 400-2000nm outside of the 10 selected discrete wavelengths chosen for the design
The coupling design at the fiber output

Risk Analysis

Risk	Description	Impact	Probability	Mitigation
Laser (Leukos Rock 400 5)	High-power laser to gather sufficient signal, may hurt eyes (2-5W)	High	Low	Laser Safety Glasses and appropriate laser safety training from facility
CTE (optical and mechanical)	The lens selection needs to withstand and not be reshaped by laser thermal impact	High	Low	Filter preferred glass catalog to ensure selection accounts for high power laser
Signal	Unable to fit the beam into a single mode design with enough output	High	Low	Ensure that photon budget thoroughly considers the input beam
Time	Unable to thoroughly create and tolerance a final design in time	High	Low	Communicate with customer when specifications reach a breaking point in order to reframe the expectations
Transmission (weight wavelengths)	Developing a system that requires too many elements leading to transmission decay	Medium	High	Design with uncoated specification in mind limiting performance by access to elements
Packaging	Fiber couplers need to be used in very small circumstances	Medium	Low	Set strong constraints in the early design specifications to ensure proper packaging
Clean room environment inside machine	Cleanroom grade ISO 5	Medium	High	Design must aim to not contribute to particle contamination within the machine

Final 10 Wavelength Design

For the final Single Mode Broadband Fiber Coupler design, we utilized 3 elements, and a singular aspheric element to counter a system that achieved optimal coupling effencicy across 10 wavelengths.

Above is 2D representation of the 10 wavelength optic fiber coupler configuration modeled in OpticStudio.

Feature	Value
NA	0.148
Field	0° on-axis
Focal Length	123.9
Diameter	38.79
Length	149.32
Aspheric Surfaces	2
Transmission	96.57%

Wavelength (um)	Coupling Efficiency (%)
486	69.76%
532	64.09%
655	70.58%
755	75.08%
980	59.65%
1064	58.97%
1220	64.12%
1550	76.94%
1645	73.95%
1752	64.49%

ASML Broadband Single-mode Fiber Coupler

DCORE4 Team

Mentors

Abstract

Conclusion