Fiber Alignment Station

Role in QLT Fabrication

The fiber alignment station couples light from external fibers into the chip's edge-coupled waveguides and collects output for measurement. This is the MOST IMPORTANT characterization tool ● without it, we cannot verify that the chip works at all.

Tests Requiring This Station

Alignment Requirements

Alignment Physics

Waveguide mode field:     ~3 μm diameter (1/e² at 1550 nm)
SMF-28 mode field:        ~10.4 μm diameter (1550 nm)
Lensed fiber spot size:   ~2.5 μm (typical)

Coupling loss vs. misalignment (Gaussian mode overlap):
0.0 μm offset → 0.0 dB loss (perfect coupling)
0.5 μm offset → 0.5 dB loss
1.0 μm offset → 2.0 dB loss
2.0 μm offset → 8.0 dB loss (effectively uncoupled)

Sub-micron alignment accuracy is ESSENTIAL.
This is why a precision multi-axis stage is required.

Technical Specifications

Process Integration

Initial Assembly (Week 2 after delivery)

ASSEMBLY PROCEDURE (4–8 hours):

STEP 1: Mount breadboard on optical table
├── Bolt MB1218 (12"×18") to optical table with 1/4"-20 cap screws
└── Level with precision level (± 0.01°)

STEP 2: Mount NanoMax stages (input + output)
├── Position input stage (left side) ● bolt to breadboard
├── Position output stage (right side) ● bolt to breadboard
├── Set stages ~50 mm apart (chip will go between)
└── Align optical axis heights (both at 75 mm nominal)

STEP 3: Install fiber holders
├── Attach AMA009 angle brackets to stages
├── Mount HFF001 V-groove fiber clamps
├── Load input fiber (lensed SMF-28 or PM fiber)
├── Load output fiber (SMF-28 cleaved or lensed)
└── Secure with strain reliefs (HFS001)

STEP 4: Mount alignment camera
├── Install microscope column above chip position
├── Mount 10× or 20× objective in HCS013 holder
├── Connect USB camera (CS165MU1)
└── Focus on chip facet plane

STEP 5: Connect piezo controllers (if using MAX312D/311D)
├── Connect PAA100 drive cables from stages to BPC303/MDT693B
├── Connect PAA622 feedback cables (closed-loop only)
├── Power on controllers; verify all 3 axes respond
└── Set voltage limits: 0–75V range

STEP 6: Fiber-to-fiber verification
├── Remove chip; bring input and output fibers tip-to-tip
├── Launch 1550 nm from tunable laser
├── Adjust stages to maximize power meter reading
├── Record maximum throughput (should be > -3 dB for butt-coupled)
└── This verifies the station is functioning properly

Chip Alignment Protocol

CHIP ALIGNMENT (15–30 minutes per facet):

STEP 1: Mount chip on vacuum chuck or clip holder between stages
STEP 2: Use camera to visually locate input waveguide facet
STEP 3: Coarse X-Y positioning: use differential micrometers to bring fiber tip
within ~50 μm of facet (visible on camera)
STEP 4: Coarse Z positioning: close fiber-to-facet gap to ~10–20 μm
STEP 5: Fine alignment with piezos (if equipped):
├── Switch to piezo control mode
├── Launch ~1 mW CW at 1550 nm
├── Monitor output power on power meter
├── Raster-scan X-Y over ±20 μm in 0.5 μm steps
├── Find peak coupling position
├── Optimize Z (gap) for maximum power
└── Record peak coupled power and position
STEP 6: Lock position (tighten set screws if manual; hold piezo voltage if active)
STEP 7: Repeat for output fiber on opposite facet
STEP 8: Record total insertion loss: IL = P_in - P_out (dBm)
Target: < 8 dB total (< 3 dB per facet + < 2 dB propagation)

Vendor Options & Pricing

Thorlabs (Primary ● Fastest Delivery)

Newport/MKS (Alternative)

Newport 561D-XYZ stage: $2,640 each (stainless steel crossed-roller bearings, 6 mm X/Z, 13 mm Y, <100 μrad angular deviation). SM-13 vernier micrometers: $105 each. 561-FH bare fiber holder: $393. 561-TILT tilt platform: $741. 561-GON goniometer: $1,088.

PI (Physik Instrumente) ● Premium

Turnkey Systems

Vendor Contact Information

Facility Requirements

Safety & Handling

Laser Safety

Mechanical Safety

• Never crash fiber tip into chip facet ● approach slowly with piezo jogging (0.5 μm steps)
• Lensed fiber tips are fragile (~$200 each) ● handle with care; store in protective tubes
• Stage set screws must be tightened after alignment ● vibration can drift loose screws
• Maximum load on NanoMax stage: 1 kg ● do not overload with heavy optics

Fiber Handling Best Practices

• Always clean fiber connectors before insertion (Cletop cassette or IPA wipe)
• Inspect connectors with fiber scope (Thorlabs FS201, ~$1,500) if coupling loss is high
• PM fiber must be rotated to align polarization axis ● use HFR007 fiber rotator
• Bare fiber cleave quality affects coupling ● verify cleave angle < 1° under microscope