AQ6375B Long Wavelength Optical Spectrum Analyzer 1200 - 2400 nm (DISCONTINUED)

Notice: This product was discontinued on Jun 30, 2022.

High Performance LONG WAVELENGTH
The AQ6375B is a bench-top optical spectrum analyzer covering the long wavelengths, 1200 to 2400 nm, with the added benefits of gas purging input ports / output ports, a built-in cut filter for high order diffracted light, and a novel double speed mode which increases the sweep speed up to 2 times compared to the standard sweep mode.


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Key feature summary

  • Long wavelength range: 1200 to 2400 nm
  • Gas purging ports to reduce water vapor effects
  • Built-In cut filter for high order diffracted light
  • Double Speed Mode to further enhance fast measurement speed
  • High sensitivity down to -70 dBm
  • High resolution to 0.050 nm
  • Wide close-in dynamic range (55dB)
  • Fast auto-calibration
  • Free space optical input for maximum flexibility, low maintenance, and high reliability  
  • Applicable to single-mode and multimode fibers
  • Excellent performance for environmental gas sensing Laser Spectroscopy 
  • Indispensable tool for R&D and manufacturing of optical devices in the wavelength range from telecom band to 2.4μm 

New Features

Purge feature

Due to the high resolution and sensitivity of the AQ6375B, it can actually detect the presence of water molecules in the air. The water vapor is detected in the upper Near-IR wavelength region and could overlap with or mask the spectral characteristics of the actual device under test in that particular region.

By continuously supplying a pure purge gas such as nitrogen to the monochromator through the ports on the back panel, the AQ6375B can reduce the influence of water vapor absorptions and provide more reliable and accurate measurements than ever before.

Built-in cut filter for high order diffracted light

Due to the diffractive technology used, the monochromator in some circumstances could generate high order diffracted light, which appears at wavelengths equal to the integral multiple of input wavelengths.

By cutting incoming light below 1150 nm with the built-in filter, the AQ6375B drastically reduces the influence of high order diffracted light on the measurement. Thus, the measured data are always reliable and replicate the real signal under test.

Double speed mode

Increases the sweep speed up to 2 times compared to the standard sweep mode, with only a 2 dB penalty to the standard sensitivity value.

Long Wavelength Range: from 1200nm to 2400nm

The AQ6375B covers not only the wavelength span used in communications, but also the 2µm region which is used for environmental sensing, medical, biology and industrial applications.

High Sensitivity: down to -70dBm

The AQ6375B can measure optical power from +20dBm down to -70dBm thanks to its high-dynamic and very low noise components and circuits used for photo detection. This enables precise measurements of both high power and low power sources.

Measurement sensitivity can be chosen among 7 values according to the measurement speed required by the specific test to be performed.

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The spectrum of a white light source (yellow) and the background noise of AQ6375B (purple)

High Resolution & Wide Dynamic Range

The AQ6375B uses a double-pass monochromator structure to achieve high wavelength resolution (0.05 nm) and wide close-in dynamic range (55 dB). Thus, closely allocated signals and noise can be separately measured.

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Measured HeNe Laser (1523 nm), Close-in Dynamic range: @ peak±0.8 nm

High speed Measurement


High Speed Sweep

With a proprietary sweep technique the AQ6375B achieves a much faster sweep speed than conventional measurement systems, which use a monochromator. Max. sweep time is only 0.5 sec. for 100 nm span.

Fast command processing and data transfer


Applying a fast microprocessor, the AQ6375B achieves very fast command processing speed and Ethernet interface provides up to 100 times faster data transfer speed than GP-IB.

Fast auto-calibration

The AQ6375B has a built-in reference light source for wavelength calibration and optical alignment of the monochromator components, allowing it to deliver always-accurate measurements. 
The calibration and alignment process takes less on the unit take than 2 minutes and is fully automatic. 
NOTE: The wavelength calibration can also be performed by using an external reference source.

Free-Space Optical Input

The AQ6375B uses a free-space optical input structure, i.e. no fiber is mounted inside the instrument.

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This smart solution is:

  • WORRY-FREE, as no internal fiber can be scratched or get dirty
  • MAINTENANCE-FREE, as no internal fiber has to be cleaned
  • VERSATILE, as the instrument accepts both /PC and /APC connectors
  • DUAL PURPOSE, as the instrument accepts both Single-Mode and Multi-Mode fibers without being affected by the high insertion loss from MM-SM fibers matching

The AQ6375B has been designed to increase productivity of R&D and Production personnel.

The software has pre-installed analysis functions for the most common optoelectronic (passive and active) devices. The automatic calculation of the major parameters of the device under test will contribute to its fast characterization.

Moreover, the AQ6375B has the capability to be programmed to perform automatic measurements while controlling other lab equipment.

New Functions

Data logging function 

Records analysis results such as distributed feedback laser diode (DFB-LD) analysis data and multi-peak measurements at up to 10,000 points per channel with time stamps.

Smoothing function

Reduces the noise on the measured spectrum.

Built-in analysis functions to increase your testing efficiency

Spectrum Width Analysis

You can display the spectrum width and center wavelength using the following 4 types of calculation:

  • THRESH method
  • ENVELOPE method
  • RMS method
  • PEAK RMS method

Notch Width Measurement

With this function it is possible to measure pass bandwidth / notch width from the measured waveform of a filter with V-type or U-type wavelength characteristics.

Light Source Analysis

Light source parameters can be analyzed from the measured waveform of each type of light source among DFB-LD, FP-LD and LED.PMD Measurement

It is possible to measure the Polarization Mode Dispersion (PMD) of a DUT (such as an optical fiber) by using the instrument in combination with an Analyzer, Polarization Controller, Polarizer, and an Amplified Spontaneous Emission (ASE) light source, High-output LED light source, or other wideband light source.

WDM Analysis

With this function it is easy to analyze WDM transmission signals. You can also measure OSNR of a DWDM transmission system with 50 GHz spacing. Measurements of WDM signal wavelength, level, wavelength interval, and OSNR can be made collectively on up to 1024 channels, and the analysis results can be displayed in a data table.

Optical Amp Analysis

Gain and Noise figure measurements can be made on signal light waveforms going into optical amplifiers, as well as light leaving the optical amplifiers.

Optical Filter Characteristics Measurement

Optical filter characteristics can be measured from the measured waveforms of the light, from source, going into optical filters, as well as from the measured waveforms of light being output from optical filters. Analysis can be performed not only on optical filters with one mode, but also multimode filters (e.g WDM Filters).

Measurement of Level Fluctuations in Single-Wavelength Light

This function is used to measure changes over time in the level of a specific wavelength level. The sweep width is set to 0 nm, and measurement of the single-wavelength light is taken. The horizontal axis is the time axes. It is useful for purposes such as optical axis alignment when a light source is input to an optical fiber.

Template Analysis

The template function compares preset reference data (template data) with a measured waveform. In addition, if a function for displaying the target spectrum (target line) on the measurement screen is used, the target spectrum can be referenced while adjusting the optical axis of an optical device.

Go/No Go Judgment

The Go/No Go test function compares the active trace waveform against reference data (template data) preset by the user, and performs a test on the measured waveform (Go/No Go test).
This function can be used effectively in situations such as pass/fail tests on production lines.

Analysis between Line Markers / in the Zoom Area

The instruments perform the analysis of the signal contained into boundaries selected by means of line markers or zoomed area.

Building Automated Test Systems


The AQ6375B is equipped with GP-IB, RS-232, and Ethernet (10/100Base-T) interfaces, which can be used for remote access and control from an external PC to build automated test systems. Built-in Macro Programming function is also available to implement simple auto test programs on the unit it self.


The standard remote commands of the AQ6375B are compatible with SCPI, which is an ASCII text based standard code and format conforming to IEEE-488.2.

The AQ6375B supports proprietary remote programming codes of Yokogawa's best selling AQ6317 series for users to easily upgrade from their current automated test environment. 

Macro programming enables user to easily create test procedures by recording the user's actual key strokes and parameter selections. An external PC is not required because the macro program can also control external equipment through the remote interfaces.

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LabVIEW® DRIVER available

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AQ6375B Viewer - Emulation and Remote Control Software (Optional)

AQ6375Viewer is PC application software designed to work with Yokogawa's AQ6375B Optical Spectrum Analyzer. 

The software has exactly the same user interface and functions as the AQ6375B so that you can easily display and analyze waveform data.

Allows to control AQ6375B from anywhere on the Ethernet network. Because of fast data transfer speed of Ethernet, measurement data can be updated in real time. Note: The data update speed varies depending on network performance and conditions.

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The AQ6375B is the right instrument to test & characterize

  • passive optical components like FBGs, Filters, specialty fibers (e.g. Thulium doped)
  • active optoelectronics devices like semiconductor LASERs and Supercontinuum light sources used in industrial, telecom and medical/biomedical applications and environmental analysis.

Moreover, its peculiar characteristics and high-level performance make the AQ6375B the ideal OSA to measure gas concentration in the air using Laser Absorption Spectroscopy.

Passive and active devices characterization

Characterization of Fiber Bragg Gratings (FBGs)

A Fiber Bragg Grating (FBG) is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. This is achieved by creating a periodic variation in the refractive index of the fiber core, which generates a wavelength specific dielectric mirror. An FBG can therefore be used as an inline optical filter to block certain wavelengths, or as a wavelength-specific reflector.

The primary application of Fiber Bragg Gratings is in optical communications systems. They are specifically used as notch filters. They are also used in optical multiplexers and demultiplexers with an optical circulator, or optical add-drop multiplexer (OADM).

Fiber Bragg gratings can then be used also as direct sensing elements for strain and temperature, in fact the Bragg wavelength of the FBG can be tuned by strain and temperature change applied by a piezoelectric transducer. Specifically, fiber Bragg gratings are finding uses in instrumentation applications such as seismology, pressure sensors for extremely harsh environments, and as downhole sensors in oil and gas wells for measurement of the effects of external pressure, temperature, seismic vibrations and inline flow measurement.

Fiber Bragg gratings are created by "inscribing" or "writing" systematic (periodic or aperiodic) variation of refractive index into the core of a special type of optical fiber using an intense ultraviolet (UV) sources such as KrF or ArF excimer lasers.

However, the functional wavelength of FBG is not the writing wavelength, and for non-communication applications mentioned above (strain and temperature sensors) FBGs tuned on 2-3µm region are used. For testing such FBGs, the AQ6375B is the perfect instrument.

Characterization of Supercontinuum Light Sources

Supercontinuum light is generated by promoting highly nonlinear optical processes in special materials, e.g. photonic crystal fiber, by pumping them with a mode-locked pulsed laser (typically a femtosecond Ti:Sapphire laser).

Supercontinuum light can be best described as ‘broad as a lamp, bright as a laser', in fact it matches the characteristics of incandescent and fluorescent lamps - i.e. very broad spectrum - with the characteristics of lasers - i.e. high spatial coherence and very high brightness, which enables optimum coupling to a fibre and outstanding single-mode beam quality.

The Supercontinuum light sources are nowadays finding applications in a diverse range of fields, including optical coherence tomography, frequency metrology, fluorescence lifetime imaging, optical communications, gas sensing and many others.

Detecting the multi-wavelength optical pulses generated by a Supercontinuum light sourcewith AQ6375.

AQ6375, thanks to its premium performance, is the right instrument to tests and characterize Supercontinuum light sources during their production and after-production quality check processes.

Characterization of Lasers used in Medical applications

Specific LASERs emitting around 2µm are used nowadays as tools for endoscopic surgery, like Thulium laser used for surgical treatment of prostate cancer.

AQ6375B is the best instrument to test and characterize such kind of LASERs during their production and after-production quality check processes.

Characterization of semiconductor LASERs used in Laser Absorption Spectroscopy

Laser Absorption Spectroscopy is a measurement technique used to detect and measure the gases concentration in the air, in open or closed environment.

As shown in figure 1 below, the Laser Absorption Spectroscopy uses a laser that oscillates in a single vertical mode and can measure concentration of a gas molecule by slightly modulating the oscillation wavelength of the laser around the absorption wavelength specific to the gas to be detected and by detecting a change in light spectrum due to molecule absorption.

The lasers used in Absorption Spectroscopy require excellent single-mode operation performance, which directly determines the limits of detection. Furthermore such lasers should produce a stable oscillation in the absorption region in order to achieve sensitive detection of the gas of interest. Most of the greenhouse gases, for example CO2, SO2, NOX and CH4, have strong absorption lines in the 2µm wavelength region.

Figure 2 shows the result of measurement of the spectrum of a DFB-LD that oscillates in the near-infrared region of 2µm with the single vertical mode.

2010nm DFB-LD

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Resolution: 50 pm, Span: 20 nm
Sensitivity: HiGH1/CHOP


Gas detection and concentration measurements by Laser Absorption Spectroscopy

If the AQ6375B sweep is synchronized with a tunable laser, it will show the absorption spectrum of the gas mixture under test, like figure 3.

Hydrogen Cyanide H13C14N absorption spectrum measurement ‐ AQ6375B synchronous sweep with tunable laser source.

The global warming gases, called greenhouse gases, like CO2, SO2, NOX and CH4, has strong absorption lines in the 2µm wavelength region. The presence and concentration of those gases in the atmosphere can be determined by measuring the optical absorption spectrum of the gas mixture under test.

Thanks to its Free Space Optical Input, the AQ6375B can also measure the absorption spectrum of an air column using the Sun as light source and transferring by a MultiMode fiber the light passed-through the mixture.

Figure 4: Absorption lines of some gases in SW-IR and MW-IR (IR-B DIN) region

Figure 5: measurement setup to detect a specific gas in the air, e.g. Methane (CH4):

Cavity Ring-Down Spectroscopy applications (CRDS)

CRDS is a highly sensitive optical spectroscopic technique that enables measurement of absolute optical extinction by samples that scatter and absorb light. It has been widely used to study gaseous samples which absorb light at specific wavelengths, and in turn to determine mole fractions down to the parts per trillion level. The technique is also known as cavity ring-down laser absorption spectroscopy (CRLAS).

A typical CRDS setup consists of a laser that is used to illuminate a high-finesse optical cavity, which in its simplest form consists of two highly reflective mirrors. When the laser is in resonance with a cavity mode, intensity builds up in the cavity due to constructive interference. The laser is then turned off in order to allow the measurement of the exponentially decaying light intensity leaking from the cavity. During this decay, light is reflected back and forth thousands of times between the mirrors giving an effective path length for the extinction on the order of a few kilometers.

If something that absorbs light is placed in the cavity, the amount of light decreases faster-it makes fewer bounces before it is all gone. A CRDS setup measures how long it takes for the light to decay to 1/e of its initial intensity, and this "ringdown time" can be used to calculate the concentration of the absorbing substance in the gas mixture in the cavity.

Cavity ring down spectroscopy is a form of laser absorption spectroscopy. In CRDS, a laser pulse is trapped in a highly reflective (typically R > 99.9%) detection cavity. The intensity of the trapped pulse will decrease by a fixed percentage during each round trip within the cell due to both absorption and scattering by the medium within the cell and reflectivity losses.

One of the major applications of CRDS is breath analysis:

The following graph shows the spectra of the biomarker hydrogen cyanide (HCN) along with water vapor (H2O) at atmospheric pressure and at concentrations typically found in exhaled human breath:

The AQ6375B has the right characteristics to be an effective instrument to measure the output of CRDS systems.


Photonics is nowadays more and more applied in medical diagnostic. For example let's consider blood analysis.

Many components of blood have absorption wavelength in the VIS and NIR region:
Neutral fat: 656, 724, 756, 796, 882, 1040, 1972, 2270, 2354, 2444nm
Phosphorus: 514, 576, 770, 1132, 1178, 1234, 1250, 1992, 2008, 2384nm
Potassium: 428, 690, 1228, 1380, 1382, 1952, 2260, 2340, 2396, 2416nm
Lactic acid: 412, 506, 516, 646, 1918, 1976, 1990, 2040, 2378nm
Albumin: 604, 1726, 1858, 2192, 2194, 2218, 2220, 2222, 2224, 2248nm
Glucose: 1500 - 1800nm

Yokogawa's AQ6375B and AQ6373B cover the whole range of absorption wavelengths of these substances and therefore detect their presence and concentration by means of Laser Absorption Spectroscopy.

A complete suite of connection interfaces

For the first time, the AQ6375B is now equipped with Gas Purging Input and Output ports for the first time along with a suite of electrical interfaces (GP-IB, RS-232, USB, RJ-45 Ethernet, SVGA video output, analog (voltage) output, trigger input & output) which allow the user to easily operate it locally in the lab as well as remotely.

Front View

Optical interfaces
The AQ6375B adopts a universal type optical connector system for optical input and calibration output enabling direct coupling to major optical connectors (FC, SC or ST). The connectors can be replaced by users.

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USB interfaces
2 ports are available on the front panel, supporting keyboard, mouse, memory stick and external HDD.

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Note: USB ports can't be used for instrument's remote control. For this purpose the instrument has an Ethernet RJ45 port on its back panel.

Rear View

AQ6375B Rear View

AQ6375B Rear Key

LCA Reduced emission of CO2 about 24% compared to the previous model.

PDFResults of Life Cycle Assessment

To accurately measure pulsed light using an optical spectrum analyzer (OSA), it is necessary to understand the characteristics of the OSA and select the appropriate measurement method and settings.


Lack of reliable high-speed internet access in rural regions, due to complicated logistics and the considerable costs involved to extend land-based networks to these areas, has inspired a wave of next-generation applications that will provide greater accessibility and reliability. Making use of “space laser” networks, these revolutionary solutions can relay digital traffic via low Earth orbit (LEO) satellite systems to provide low-latency, high-speed broadband services to communities typically beyond the reach of standard wireless and fiber networks.

Case study
Case Study | Laval University Speeds Up Advanced Photonics Research  
(Laval University Photonics Research Case Study)

Laval University is a research institution world renowned for optics and photonics technology research and training, and are the founders of The Center for Optics, Photonics, and Lasers (COPL).

The university's researchers needed a faster and more efficient and practical solution to measure the spectral performance of lasers and optics beyond traditional telecom wavelengths. To achieve this, they contacted Yokogawa Test&Measurement and collaborated to develop a breakthrough grating-based optical spectrum analyzer that could cover MWIR wavelengths up to 5.5 um. Click to learn how productivity in the research lab dramatically increased for precise characterization of laser sources, and active/passive optical components in the fields of communications, medical diagnosis, advanced optical sensing, and environmental and atmospheric sensing.


The extreme test requirements of our research called for an OSA with extended MIR spectrum bandwidth capabilities up to 5μm, but we couldn’t find one on the market capable of measuring optical inputs at these wavelengths. Yokogawa Test&Measurement rose to the challenge and developed a new OSA model for us that would. Not only do we now have an instrument that is practically custom-made for our needs, it provides repeatable, accurate, and trusted measurement outputs and is easy to learn and use. Their equipment and ability to create a new optical measurement solution has definitely increased the overall efficiency and productivity of our research team.

— Martin Bernier, PhD, P.Eng., Full Professor, Centre de Optique, Photonique, et Laser, Université Laval


In a research paper published on, a team of researchers from the University of Virginia, Peking University, Shanxi University, and California Institute of Technology use a Yokogawa Test&Measurement Optical Spectrum Analyzer in order to achieve spectrum measurements above 1200 nm.

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