Lasers and Optoelectronic Components Used with Lasers
Paul D. Hale
Fees are subject to change without notice.
The NIST Quantum Electronics and Photonics Division develops and maintains the U.S. national standards for the characterization of lasers, along with detectors and other optical and optoelectronic components used with lasers and in laser-based systems. These standards support applications of lasers in manufacturing, electronics, medicine, communications, and the military, among other fields, and are generally used to provide calibrations of instruments used in these areas.
For calibrating instruments used to measure the power or energy emitted by a laser, specially designed standards consisting of several types of isoperibol (constant temperature environment) calorimeters have been developed and used for many years. Low-level laboratory standards are realized using solid-state photodetectors and other thermal detectors. Well-characterized transfer standards (calibrated against the primary standards) are also maintained as laboratory standards for calibrations and for use in Measurement Assurance Program (MAP) intercomparisons. As part of a continuing process, new standards are being developed and implemented to improve accuracy and dynamic range. In addition, the Division has developed an ultra-high accuracy laser power measurement capability using a laser optomized cryogenic radiometer (LOCR). The laboratory standards and secondary transfer standards are used in specially designed, beamsplitter-based calibration systems that allow various power and energy detectors to be compared to the standards.
The Quantum Electronics and Photonics Division maintains the capability of measuring other laser parameters, for example, beam profile and relative intensity noise. Because these measurements are generally less well defined than power and energy measurements, they are undertaken as Special Tests, after consultation with the customer. Instruments used in optical communications generally accept or receive optical power through a connectorized optical fiber. Wavelength ranges of interest are generally centered on 850 nm, 1300 nm, and 1550 nm. In addition to power measurements in these ranges, calibrations of the frequency response (or impulse response) of detectors and analog and digital receivers used in optical communications can be provided. NIST also provides several Standard Reference Materials for calibrating instruments used in optical communications.
The Quantum Electronics and Photonics Division can also characterize many other optical and optoelectronic components used with lasers. Within existing capabilities, Special Test measurements can be provided. Those needing such measurements are invited to contact the Division.
Table 4 Laser Power and Energy Measurement Capabilities
Within the ranges listed in Table 4, NIST can perform calibrations at the power (or energy) and wavelength specified by the customer. These ranges are determined by the combined limits of our standards and available laser sources. For these measurements, the instrument to be measured is sent to NIST, where it is then compared to the appropriate laboratory reference standard using a calibrated beamsplitter measurement system. Normally, the response of the detector is characterized but no physical adjustments are made to the test instrument. At the completion of the calibration measurements, the instrument and a calibration report are sent to the customer. The calibration report summarizes the results of the measurements and provides a detailed listing of the associated measurement uncertainties. The laboratory standard isoperibol calorimeters used as references for these measurements were designed and built at NIST and all their critical parameters (electrical calibration coefficient, absorptivity, window transmittance, etc.) have been evaluated for the laser wavelengths and energies for which they are used. The characteristic voltage response of the standard isoperibol calorimeters is described by first principles of thermodynamics and linear system analysis. Accurate quantitative responsivity characterization (including linearity and stability) of the calorimeters is accomplished by periodically performed, electrical heater calibrations.
The laser power and energy measurements are accomplished using a calibrated beamsplitter arrangement in which both the standard and the test meter are exposed to the laser beam simultaneously. In addition to the isoperibol calorimeters, solid-state photodiodes and trap detectors are used as laboratory standards, especially at powers below 1 mW. The beamsplitters used in these systems have been characterized for all specific wavelengths for which they are used. Small angles of incidence are used to minimize polarization and angular position uncertainties. The laser sources used for these calibration measurements with the primary standards consist of the following types (subject to change): (1) Helium-Cadmium (325 nm) (2) Helium-Neon (632.8 nm), (3) Argon ion (488.0 nm and 514.5 nm), (4) Nd:YAG (532 nm, 1064 nm and 1319 nm CW, and 1064 nm Q-switched), (5) diode laser (830 nm and 1550 nm), (6) Carbon dioxide (10.6 µm), (7) KrF excimer (248 nm), and (8) ArF excimer (193 nm).
The Measurement Assurance Program (MAP) is available at the wavelengths and powers listed in Table 4. The laser MAP intercomparisons are implemented by means of transfer standards, which have been evaluated and characterized relative to the national primary standards. The measurement system and primary standards discussed above are used to calibrate the transfer standards for the intercomparisons. The characteristics of these transfer standards are well understood, and their associated accuracies do not differ significantly from those associated with direct comparisons to the primary standards. For a specified wavelength and power or energy, the appropriate transfer standard is selected and sent from NIST to the MAP participant. The participant calibrates the NIST transfer standard using their measurement system and then returns both his data and the transfer standard to NIST. Before and after the NIST transfer standard is shipped to the participant, NIST performs calibration measurements on the detector to provide continuity during the intercomparison. At the completion of the intercomparison, NIST evaluates the participants' measurement results relative to the NIST calibration results on this same meter. A MAP intercomparison report summarizing the intercomparison and listing the associated measurement uncertainties is then submitted to the participant. Customers who have the capability and require higher accuracy may request MAP services using appropriate high-accuracy transfer standards such as the photodiode trap detectors.
Optical fiber power meters are calibrated using an automated calibration system in which the test meter and the laboratory standard are alternately exposed to a stable diode laser source. During the measurement process, the input power to the test meter is monitored with a fiber coupler and reference detector assembly. Table 5 summarizes the current capabilities of this system. The laboratory standard used for these measurements is an electrically calibrated pyroelectric radiometer (ECPR) that has been calibrated with a laser optimized cryogenic radiometer (LOCR) primary standard. Various diode laser sources are used to provide the available wavelengths. The calibrations can be accomplished with either a collimated beam or a connectorized fiber configuration. We can accommodate most commonly used fiber connectors (such as FC/PC, ST, biconic, SC, SMA, FC/APC, HMS-10 etc.).
Table 5 Measurement Capabilities of Automated Calibration System for Optical Fiber Power Meters
NIST maintains a set of calibrated transfer standards, which are available for MAP intercomparisons of optical fiber power meters. These transfer standards are calibrated at the wavelengths listed in Table 5using the optical fiber power meter calibration system discussed above. If the MAP is to be conducted using a fiber with attached connector, then the customers are asked to provide the specific fiber and connector which is used in their laboratories. As in the laser MAP procedures listed above, measurements are made on the NIST transfer standard both before and after the MAP participant's measurements are conducted. At the conclusion of the MAP process, a calibration report that summarizes the measurements and associated uncertainties is sent to the participant.
Low-Level Laser Radiometer Calibrations and Measurement Assurance Program (MAP) and Calibrations (42150M and 42151C)
NIST has designed and constructed special silicon and germanium diode detectors to measure pulse energy and peak power of low-level, 1064 nm laser pulses of about 10 ns to 150 ns duration. These diode detectors have been evaluated for spatial uniformity, bandwidth, and linearity, and are used as transfer standards for intercomparisons. The output response of each detector has been calibrated against a transfer standard which, in turn, has been calibrated against the C-series calorimeter. The system for calibrating these transfer standards uses a CW Nd:YAG laser whose radiation is acousto-optically modulated to produce short, well defined pulses. The beam intensity is attenuated to low-levels using a multiple reflection precision wedge beamsplitter. The transfer standards are available for intercomparisons at the powers listed in Table 6. Calibration Service 42151C provides calibration of transfer standards similar to those described above for the MAP service that are provided by the customer.
Table 6 Low-Level MAP Transfer Standards
NIST measures the frequency response of photodetectors using the difference frequency beat note from 2 single frequency lasers operating at 850 nm, 1319 nm, or 1550 nm. Measurements can be performed between 50 GHz and approximately 1 MHz, depending on the wavelength. Normalized frequency response is proportional to the ratio of the generated microwave power to the DC power supplied through the bias current. A photodetector suitable for calibration includes a connectorized fiber pigtail and precision coaxial microwave connector. A calibration service is offered for the highest accuracy measurement, attained when the photodiode and power sensor are calibrated as one unit. A transfer standard of this type can be used to determine the optical modulation index of an arbitrary optical source with sinusoidal modulation. Options available include measurement of frequency response of a separate photodetector using NIST power sensors or normalization to optical power to give absolute response. These options degrade the measurement uncertainty due to power sensor calibration and fiber connector insertion loss, respectively. Measurements may also include correction for electrical impedance mismatch when separate power sensors are used.
NIST uses a mode-locked laser to generate optical pulses of approximately 100 fs duration at a wavelength of 1550 nm or 775 nm. The electrical impulse resulting from the optical input to the photodetector is measured by use of an electro-optic sampling technique. The measured waveform is Fourier-transformed; distortions due to impedance mismatch and loss are removed to give the magnitude and phase response of the photodiode. Results are reported at 200 MHz increments from dc to 110 GHz. Photodetectors suitable for testing must have a 75 ± 5 cm length pigtail and a 1.0 mm coaxial (male) electrical connector. The photodetector should be evaluated for linearity prior to measurement to ensure equivalence between time-domain and frequency-domain characterizations of the small-signal response. Photodetectors, suitable for calibration, are available for purchase from NIST. Customers who wish to submit their own photodetectors for calibration are strongly encouraged to contact Paul Hale to determine the suitability of their photodetector.
A laser optomized cryogenic radiometer (LOCR) is available in our measurement laboratory for ultra-high accuracy calibrations for laser power. Using this instrument as a reference, expanded (k=2) uncertainties as low as 0.05 % are available on request for certain wavelengths and measurement conditions. These high accuracy measurements are appropriate only for certain transfer standards (such as photodiode trap detectors) capable of maintaining high accuracies.
Spectral Responsivity Measurements of Laser and Optical Fiber Power Meters (or Detectors Used with Lasers) (42164C)
Spectral responsivity measurements on laser power meters and detectors used with lasers can be performed over the wavelength region 450 nm to 1700 nm. These spectral response measurements are accomplished using broadband light sources in conjunction with a scanning monochromator. These measurement results are not valid for measurement comparisons with fibers attached. High resolution spectral responsivity measurements can be performed over limited wavelength regions centered on 850 nm, 1300 nm, and 1550 nm using tunable laser diode systems (see for example 42130C).
Special Test for Spatial Uniformity of Laser and Optical Fiber Power Meters (or Detectors Used with Lasers) (42165S)
Detector uniformity is measured using a specially designed system which provides a small beam of laser radiation (at nominal wavelengths of 850 nm, 1300 nm, or 1550 nm) which is scanned across the detector surface. The resulting detector output response is displayed graphically and analyzed statistically. This information is useful for characterizing the quality of a detector and for identifying interference effects caused by, for example, windows with parallel surfaces. Other wavelengths are available upon request.
Calibration for Linearity Measurements of Optical Fiber Power Meters (or Detectors Used with Lasers) (42166C)
Linearity of optical fiber power meters and detectors used with lasers can be measured at the three nominal wavelength regions of 850 nm, 1300 nm and 1550 nm using automated NIST-designed measurement systems. These systems are based on dual beam superposition, in which the radiation from two optical paths is incident (both jointly and individually) onto the detector. The system can provide linearity characterizations covering a 60 dB to 90 dB power range. Various other wavelengths and powers are also available upon request.
Special Test for Linearity Measurements of High-Power Laser Meters (or Detectors Used with Lasers) (42167S)
Linearity of high-power laser power meters and detectors can be measured at 1064 nm and 10.5 µm using automated NIST-designed measurement systems. These systems are based on a set of specially designed reflective chopper wheels, where the chopper attenuation factor is measured at various power levels. The system can provide linearity characterizations covering a 2 W to 900 W power range.
The Quantum Electronics and Photonics Division conducts research not described specifically above on a variety of problems in the characterization of optoelectronics components. Consequently, we are interested in discussing and supporting all measurements involving laser detectors, sources, components, and instrumentation. Examples of measurement areas include beam profile, relative intensity noise (RIN), optical density or attenuation, and polarization (retardance).
In support of instrumentation used with optical fiber power systems, various optical fiber power related measurements are available by request and prearrangement. These include power measurements at customer-selected wavelengths (in the ±20 nm regions around 850 nm, 1300 nm, and 1550 nm), optical attenuator characterization, high power measurements, and power meter measurements involving unusual connector or fiber types.
Special Test for Optical Fiber and Fiber Component Measurements (other than Fiber Power), by Prearrangement (42190S)
The Quantum Electronics and Photonics Division conducts research in a variety of areas relating to the characterization of optical fibers and fiber components. Most calibration support is in the form of Standard Reference Materials (SRMs). Occasionally, when support is needed in an area where an SRM is not available or cannot be used, we can perform special tests, by prearrangement. Examples include measurements of chromatic dispersion, polarization mode dispersion (PMD), fiber geometrical parameters, and mode-field diameter.
Spectral Responsivity Measurements of Laser and Optical Fiber Power Meters (or Detectors Used with Lasers) (42210C)
NIST spectral responsivity measurements on laser power meters and detectors used with lasers can be performed over the wavelength region 450 nm to 1700 nm. A co-requisite for this service is three or more high resolution absolute responsivity measurements performed over limited wavelength regions near 670 nm, 850 nm, 1300 nm, and 1550 nm using tunable laser diode systems (see for example 42130C). The measurement results from the laser-based measurements are reconciled with measurements accomplished using broadband light sources in conjunction with a scanning monochromator over the wider wavelength region. Because of the necessary data analysis (curve fitting), these measurement results are provided at lower accuracy than those provided in 42164C, but are valid for meter comparisons with or without fibers attached.
This measurement Service compares laser beam diameter measurements made with the NIST beam diameter measurement system with those made by a test meter (or device under test, DUT) (usually a laser beam profiler). The measured beam diameter is the second-order moment (or 4σ) beam diameter defined by the International Organization for Standardization (ISO). A test laser beam, generated with a single-mode optical fiber and an optical fiber collimator at a wavelength of 830 nm, is used as a stable source for laser beam diameter measurements. The nominal beam diameter is 2.2 mm with a typical expanded (k=2) uncertainty of 0.3%.
Table 7 Measurement Capabilities of Laser Beam Diameter Calibration
References-Optical Fiber Power Meter Measurements
Optical Fiber Power Meter Nonlinearity Calibrations at NIST , I. Vayshenker, S. Yang, X. Li, T. R. Scott, C. L. Cromer, NIST Spec. Publ. 250-56 (Aug. 2000).
Nonlinearity of Optical Power Meters, I. Vayshenker, S. Yang, X. Li, and T.R. Scott, Natl. Inst. Stand. Technol. Spec. Publ. 905, pp. 101-104, (1996).
Errors Due to Connectors in Optical Fiber Power Meters, I. Vayshenker, X. Li, D. Keenan and T.R. Scott, Natl. Inst. Stand. Technol. Spec. Publ. 905, pp. 49-52, (1996).
Automated measurement of nonlinearity of optical fiber power meters, I. Vayshenker, S. Yang, X. Li, and T.R. Scott, Proc. Int. Symp. IMEKO, Vol. 2550, San Diego, CA (July 11-12, 1995).
Optical Detector Nonlinearity: Simulation, S.Yang, I. Vayshenker, X. Li, M. Zander and T.R. Scott, Natl. Inst. of Stand. Technol. Tech. Note 1376, (May 19, 1995).
Accurate Measurement of Optical Detector Nonlinearity, S. Yang, I. Vayshenker, X. Li, and T.R. Scott, Proc. Natl. Conf. Stand. Lab. Workshop and Symp., Session 5A, 353-362, (July-Aug., 1994).
Optical Power Meter Calibration Using Tunable Laser Diodes, I. Vayshenker, X. Li, and T.R. Scott, Proc. Natl. Conf. Stand. Lab. Workshop and Symp., Session 5A, 362-372, (July-Aug., 1994).
Optical Detector Nonlinearity: A Comparison of Five Methods, S. Yang, I. Vayshenker, X. Li, and T.R. Scott, Digest, Conf. Precision Electromagnetic Measurements, pp. 455-456, (June-July 1994).
Calibrated Optical Fiber Power Meters: Errors Due to Variations in Connectors, Xiaoyu Li and R. L. Gallawa, Fiber and Integrated Optics, Vol. 7 (1988).
Calibration of optical fiber power meters: the effect of connectors, R. L. Gallawa and Xiaoyu Li, Appl. Opt. 26, 1170 (Apr. 1987).
Optical fiber power meters: a round robin test of uncertainty, R. L. Gallawa and Shao Yang, Appl. Opt.25, 1066 (Apr. 1986).
References-Optoelectronic Frequency Response and Impulse Response