Fabry-Perot Fiber Optic Filter

DATASHEET

The FPTF is a fiber-coupled Fabry-Perot Tunable Filter based on a fiber tip-gap etalon cavity driven by a piezoelectric actuator. It features narrow linewidth, wide tuning range, low optical loss, and fast tuning speed. The tuning range exceeds 100 nm, corresponding to the etalon's first-order free spectral range (FSR). Tuning beyond one FSR enters higher interference orders, potentially degrading signal quality. The piezo actuator supports scanning rates up to ~1 kHz, with resonant operation near 30 kHz. Due to inherent piezo drift, closed-loop feedback is recommended for wavelength stabilization. A full-function controller with small-amplitude dithering is available for precise tuning and control. The filter remains transparent outside its tuning band. The FPTF provides a cost-effective solution for high-speed wavelength scanning, spectroscopy, and tunable source applications requiring moderate finesse and rapid tuning.

Features

• Narrow Line Width
• Wide Tune Range
• Low IL and PDL
• Fast Tuning Speed
• USB, RS232, I2C Control Interfaces
• Gaussian-Shaped Passband

Specifications

Notes:

1. Finesse ± 20%
2. It is defined as the total light coupled out over the filter's spectral passing band. Measured using a broadband light source with integration of the transmission peak. Extra loss can occur if the laser source does not match the filter profile. A special filter can be made to match the application. The smaller the fiber core, the higher the loss. Excluding connector loss
3. Bandwidth tolerance are ± 20%
4. It related to the linewidth, the narrower, the smaller

Note: The specifications provided are for general applications with a cost-effective approach. If you need to narrow or expand the tolerance, coverage, limit, or qualifications, please click this link.

Applications

• FBG Sensing Interrogation
• Wavelength Scanning

Mechanical Dimension (mm)

A diagram shows the mechanical dimensions of the filter. Key measurements include:

• Boot: 1
• NEG: 7.6
• POS: 45.7
• Overall length (including 1m 900µm Loose Tube): 73.5
• Width: 57.2
• Length: 52.1
• 4-M26: 18
• 13.9
• 14.2
• For Mounting Only

*Product dimensions may change without notice. This is sometimes required for non-standard specifications.

Typical Transmission Curve

A graph displays the typical transmission curve of the filter. The X-axis represents Wavelength (nm) from 1500 to 1600, and the Y-axis represents Transmission from 0.0 to 1.0. Several curves are shown, each corresponding to a different applied voltage (0V, 10V, 13V, 15V, 16.5V, 17.5V, 18V), illustrating the wavelength shift with applied voltage.

Typical Wavelength Tuning vs Voltage

A graph illustrates the relationship between applied voltage and transmission peak wavelength. The X-axis represents Transmission Peak (nm) from 1510 to 1580, and the Y-axis represents Applied Voltage (V) from 0 to 12. A curve shows that as the transmission peak wavelength increases, the applied voltage also increases. The linewidth is indicated as 0.06-0.08nm.

Bandwidth/Linewidth Definition

A diagram defines bandwidth and linewidth. It shows a spectral response curve with the peak at f₀. The -3 dB points are labeled fL and fH, and the 0 dB line is shown above the peak. The linewidth (Δλ) is indicated as the difference between fH and fL, and the finesse (F) is related to the free spectral range (FSR) and linewidth.

Ordering Information

* ± 20nm

** Linewidth = FSR / finesse; 100/400=0.25nm, 100/1000=0.1nm, 100/2000=0.05nm, 100/5000=0.02nm, 100/1000=0.01nm, (Finesse ± 20%)

Red is special order with NRE

Controllers

Piezoelectric devices have material related temperature dependence and hysteresis, resulting in drift and poor repeatability. The mechanical devices also have intrinsic resonance frequencies; operation should below these frequencies. The controller can stabilize and lock the peak positions as well as perform scanning. It needs to follow a complex setup/tuning procedure. Scan mode is used primarily for sweeping the filter through a range of wavelengths for applications such as (un-calibrated) optical spectrum analysis and WDM channel monitoring. Locked mode locks onto a particular narrow line source and performs a scan with tuning stability by compensating electrical, thermal, and mechanical slow variations. It uses an internal photodetector that taps a small portion of the input light to form a closed-loop feedback control with a small amplitude dither at about 2kHz.

$2450

Operation Manual

1. Only available along with the product shipment.

How to test the insertion loss of a tunable optical filter

The filter only works in a specific range. Beyond this range, extra peaks may show. These peaks can be blocked with special order. Please follow these instructions to do an optical insertion loss test:

1. Connect a broadband fiber-coupled laser source to OSA, sweep one time over the specified range of the tunable filter, and then fix the curve in Trace A as a reference.
2. Connect the broadband laser source to the fiberoptic tunable filter fiber as input, then connect the other fiber port of the tunable filter as the output to the OSA.
3. Set OSA Trace B as 'write,' Trace C as 'Calculate: B-A.' Auto sweep Trace C from the specific range. Tune the micrometer to shift the peak at a different wavelength. Use 'Peak search' to record IL at a different wavelength.

Application Notes

Fiber Core Alignment

Note that the minimum attenuation for these devices depends on excellent core-to-core alignment when the connectors are mated. This is crucial for shorter wavelengths with smaller fiber core diameters that can increase the loss of many decibels above the specification if they are not perfectly aligned. Different vendors' connectors may not mate well with each other, especially for angled APC.

Fiber Cleanliness

Fibers with smaller core diameters (<5 µm) must be kept extremely clean, contamination at fiber-fiber interfaces, combined with the high optical power density, can lead to significant optical damage. This type of damage usually requires re-polishing or replacement of the connector.

Maximum Optical Input Power

Due to their small fiber core diameters for short wavelength and high photon energies, the damage thresholds for device is substantially reduced than the common 1550nm fiber. To avoid damage to the exposed fiber end faces and internal components, the optical input power should never exceed 20 mW for wavelengths shorter 650nm. We produce a special version to increase the how handling by expanding the core side at the fiber ends.