AQ6375E Long Wavelength Optical Spectrum Analyzer 1200 to 2400 nm and 1000 to 2500 nm

High Performance LONG WAVELENGTH
The AQ6375E covers not only telecommunication wavelengths, but also the SWIR region which is often used for environmental sensing and medical applications.
・Lineup of 3 models [Standard, Extended and Limited]
・Covers wavelengths
     1200 to 2400 nm [Standard, and Limited]
     1000 to 2500 nm [Extended ]

Key feature summary

  • Lineup of 3 models [Standard, Extended and Limited]
  • Long wavelength range:
           1200 to 2400 nm [Standard, and Limited]
           1000 to 2500 nm [Extended ]
  • 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 0.05 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 2.5 μm 

      *Except Limited model

New Features

Purge feature

Due to the high resolution and sensitivity of the AQ6375E, 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 AQ6375E 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 AQ6375E 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.

* Except Limited model

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: 1200 to 2400 nm [Standard, and Limited], 1000 to 2500 nm [Extended ]

The AQ6375E 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 AQ6375E 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.

J011 Tm Aq6375 02
The spectrum of a white light source (yellow) and the background noise of AQ6375E (purple)

      *Except Limited model

High Resolution & Wide Dynamic Range *

The AQ6375E 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.

      *Except Limited model

High speed Measurement


High Speed Sweep

With a proprietary sweep technique the AQ6375E 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 AQ6375E 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 AQ6375E 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 AQ6375E uses a free-space optical input structure, i.e. no fiber is mounted inside the instrument.

J011 Tm Aq6375 06

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


DUT-oriented test apps simplify the test process

The appplication mode (APP) transforms an OSA into a versatile machine dedicated to a device under test (DUT). APP mode provides a DUT-specific user interface that navigates the user from configuration settings to test result output without worrying with other OSA settings. The AQ6375E comes pre-installed with several standard applications including DFB-LD testing, FP-LD testing and SC light source testing. Additional optional applications are available for download from the Yokogawa Test&Measurement website.

AQ6380 Optical Spectrum Analyzer App Menu | Yokogawa Test&Measurement
APP menu window

AQ6380 Optical Spectrum Analyzer APP WDM Test | Yokogawa Test&Measurement
SC light source test application


The AQ6375E 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.

New Functions

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.

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.

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 AQ6375E is equipped with GP-IB and Ethernet (10/100Base-T) interfaces, which can be used for remote access and control from an external PC to build automated test systems. 


The standard remote commands of the AQ6375E are compatible with SCPI, which is an ASCII text based standard code and format conforming to IEEE-488.2.

The AQ6375E supports proprietary remote programming codes of Yokogawa's best selling AQ6317 series for users to easily upgrade from their current automated test environment. 


Measurement applications and user-friendly multi-touch operation and connectivity

With over four decades perfecting the user experience, the Precision Makers of Yokogawa Test&Measurement developed the AQ6375E with an easy-to-use front-panel design and intuitive operability.

Large LCD touchscreen

The high-resolution, responsive 10.4-inch multi-touch capacitive touchscreen makes device operation simple and intuitive. Easily change the view and measurement conditions and perform analysis with just a touch. In the optical spectrum view, the waveform view can be zoomed or shifted by a simple tap and drag.

LCD Touchscreen AQ6380 Optical Spectrum Analyzer | Yokogawa Test&Measurement


Enhanced function keys

Operability is improved with the addition of frequently-used function keys on the front panel. These include sweep control (Auto/Single/Repeat/Stop), resolution, and sensitivity. The function keys can also be displayed as a pop-up on the screen.


Passive components (FBG)

In conjunction with a broadband light sources such as ASE, SLD, or Super Continuum (SC), the AQ6375E enables higher resolution and wider dynamic range measurements and performs evaluation of passive devices including FBG. In addition, the built-in optical filter analysis function simultaneously reports peak/bottom wavelength, level, crosstalk, and ripple width.

USB ports

The AQ6375E has USB ports that are compatible with a USB storage device, mouse, and keyboard. The file feature allows users to save data and screenshots to internal memory or USB storage for use in creating test reports. By connecting a mouse or keyboard to the USB port, you can comfortably operate the AQ6375E as if you were operating a PC.

Data access through LAN

The standard LAN port allows convenient access to files stored in the internal memory and enables remote updates for firmware from a PC.

The AQ6375E 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 AQ6375E 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.

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 AQ6375E 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 AQ6375E.

AQ6375E, 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.

AQ6375E 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.

1800nm DFB-LD

J011 Tm Aq6375 05

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


Gas detection and concentration measurements by Laser Absorption Spectroscopy

If the AQ6375E sweep is synchronized with a tunable laser, it will show the absorption spectrum of the gas mixture.

Hydrogen Cyanide H13C14N absorption spectrum measurement ‐ AQ6375E 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 AQ6375E 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.


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 AQ6375E 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 AQ6375E 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 AQ6375E is now equipped with Gas Purging Input and Output ports for the first time along with a suite of electrical interfaces (GP-IB, 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

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

Tm Aq6375 16

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

Numerical Aperture Conversion Fiber

By connecting a GI 50 or GI 62.5 optical fiber with a relatively large NA to the NA Conversion Fiber, the NA Conversion Fiber reduces the loss that occurs at the input and improves the measurement dynamic range during passive device measurements and the stability of optical level measurements during active device measurements.

751535-E5 Rack mounting kit

RACK MOUNTING KIT For an EIA-compliant Single-housing Rack


This application note introduces free space light measurement jigs for measuring the emission spectrum of a light source that propagates in free space or the optical transmission spectrum of an optical filter. It describes four types of jigs for light sources and one type for filters.

Application Note

OSA Macro Program Function

The OSA Macro Program Function enables automated measurement by creating programs for entry of measurement conditions and other tasks. Users can program a sequence of measurement procedures from entry of measurement conditions (e.g., wavelength sweep width, setting resolution) to analyses, data saving, output, and others and eliminates redundant procedures on the production line. The function acts as a controller of other connected devices through the LAN or RS232C port and allows users to build an automatic measuring system without using an external PC and input measurement conditions or output measured results while programs are running.


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.

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