Xiaoyu X. Li

A TRANSFER STANDARD FOR OPTICAL FIBER POWER METROLOGY

We have developed and evaluated a transfer standard for the calibration of optical fiber power meters over the wavelength range from 750–1800 nm. The transfer standard is an optical-trap detector consisting of two germanium (Ge) photodiodes, and a spherical mirror. The photodiodes and mirror are contained in a package that is thermally stable and accepts a variety of optical fiber connectors. Spatial uniformity measurements indicate that the variation of detector response as a function of beam position is less than ±0.15%. Comparison of the absolute responsivity for three different input conditions indicates that the detector responsivity is nearly the same for collimated beams transmitted through air, as for diverging input from an optical fiber. Small measurement-result differences between collimated and diverging inputs still remain and are discussed briefly.

Nonlinearity Measurements of High-Power Laser Detectors at NIST

We briefly explain the fundamentals of detector nonlinearity applicable to both electrical and optical nonlinearity measurements. We specifically discuss the attenuation method for optical nonlinearity measurement that the NIST system is based upon, and we review the possible sources of nonlinearity inherent to thermal detectors used with high-power lasers. We also describe, in detail, the NIST nonlinearity measurement system, in which detector responsivity can be measured at wavelengths of 1.06 µm and 10.6 µm, over a power range from 1 W to 1000 W. We present the data processing method used and show measurement results depicting both positive and negative nonlinear behavior. The expanded uncertainty of a typical NIST high-power laser detector calibration including nonlinearity characterization is about 1.3 %.

Power measurement standards for high-power lasers: comparison between the NIST and the PTB

We report the results of the first laser high-power measurement comparison between the Physikalisch-Technische Bundesanstalt (PTB, Germany), and the National Institute of Standards and Technology (NIST, USA). Laser power transfer standards were calibrated at both national standards laboratories between 82 W and 127 W at 1.06 µm and between 85 W and 554 W at 10.6 µm. Relative agreement between the standards of the two laboratories was demonstrated to lie between 5 × 10−3 and 7 × 10−3, which is well within the combined uncertainties.

Reflective attenuator for high-energy laser measurements

A high-energy laser attenuator in the range of 250 mJ (20 ns pulse width, 10 Hz repetition rate, 1064 nm wavelength) is described. The optical elements that constitute the attenuator are mirrors with relatively low reflectance, oriented at a 45 degrees angle of incidence. By combining three pairs of mirrors, the incoming radiation is collinear and has the same polarization orientation as the exit. We present damage testing and polarization-dependent reflectance measurements for 1064 nm laser light at 45 degrees angle of incidence for molybdenum, silicon carbide, and copper mirrors. A six element, 74 times (18 dB) attenuator is presented as an example.

Optical detector nonlinearity: a comparison of five methods

We derived a set of unified equations for five methods to evaluate nonlinearity of power meters and detectors. We performed computer simulations of these methods. The simulations assist in design of a measurement system to meet a target accuracy. Measurements verified the simulations.<<ETX>>

Optical-Fiber Power Meter Comparison between NIST and PTB

We describe the results of a comparison of reference standards between the National Institute of Standards and Technology (NIST-USA) and Korea Research Institute of Standards and Science (KRISS-R.O. Korea) for optical fiber-based power measurements at wavelengths of 1302 nm and 1546 nm. We compare the laboratories’ reference standards by means of a temperature-controlled optical trap detector. Measurement results showed the largest difference of less than 2.5 parts in 103, which is within the combined standard (k=1) uncertainty for the two laboratories’ reference standards.

Reflective Optical Chopper Used in NIST High-Power Laser Measurements

For the past ten years, NIST has used high-reflectivity, optical choppers as beamsplitters and attenuators when calibrating the absolute responsivity and response linearity of detectors used with high-power CW lasers. The chopper-based technique has several advantages over the use of wedge-shaped transparent materials (usually crystals) often used as beam splitters in this type of measurement system. We describe the design, operation and calibration of these choppers. A comparison between choppers and transparent wedge beampslitters is also discussed.

High-Power Diode Laser Array Metrology

NIST has been tasked by DARPA to provide wall plug efficiency and spectral measurements of high-power high-efficiency laser diodes and arrays for DARPA’s Super High Efficiency Diode Sources (SHEDS) program. To meet the needs for this project, the Optoelectronics Division has developed a new laboratory at NIST to measure electrical power, optical power, wavelength and line width, and junction temperature for lasers supplied by project participants. We describe a novel flowing-water optical power meter (FWOPM) that we have developed to meet the unique optical power measurement challenges presented by these lasers. We have also developed a new method for determining the average laser junction temperature through a simple model of laser waste heat as a function of drive current and cooling temperature. In addition, we present a preliminary uncertainty analysis that yields ∼1 % uncertainty (with a confidence interval of 95 %) for the efficiency measurements. We intend to continue offering these measurements as part of the NIST Calibration Services for optical radiation measurements, which are available to anyone for a fee.NIST has been tasked by DARPA to provide wall plug efficiency and spectral measurements of high-power high-efficiency laser diodes and arrays for DARPA’s Super High Efficiency Diode Sources (SHEDS) program. To meet the needs for this project, the Optoelectronics Division has developed a new laboratory at NIST to measure electrical power, optical power, wavelength and line width, and junction temperature for lasers supplied by project participants. We describe a novel flowing-water optical power meter (FWOPM) that we have developed to meet the unique optical power measurement challenges presented by these lasers. We have also developed a new method for determining the average laser junction temperature through a simple model of laser waste heat as a function of drive current and cooling temperature. In addition, we present a preliminary uncertainty analysis that yields ∼1 % uncertainty (with a confidence interval of 95 %) for the efficiency measurements. We intend to continue offering these measurements as...

Comparison of optical-power meters between the NIST and the PTB

We describe the results of a comparison of optical-power meters undertaken by the National Institute of Standards and Technology (NIST, USA) and the Physikalisch-Technische Bundesanstalt (PTB, Germany) at nominal wavelengths of 1300 nm and 1550 nm. Both laboratories used thermal detectors as reference standards, which were compared using a germanium trap detector as a transfer standard. Measurement results showed differences of less than 1 part in 103, well within the combined uncertainty for both laboratories.

Bilateral optical fiber power meter linearity comparison between NMIJ and NIST

Optical fiber power meter (OFPM) linearity standards of NMIJ (Japan) and NIST (USA) are compared using a commercial OFPM as a transfer standard at 1310 nm and 1550 nm over a power range [-60 dBm, 0 dBm]. At both wavelengths the comparison indicates an agreement between the two laboratories within the combined uncertainty. At 1550 nm the uncertainties are larger, which is attributed to unstable operation of the transfer standard at this wavelength.