Superluminescent Light Emitting Diodes for OCT, Current Sensors and FOG


Shenzhen Box Optronics provides 830nm, 850nm, 1290nm, 1310nm, 1450nm, 1470nm, 1545nm, 1550nm, 1580nm, 1600nm and 1610nm sled butterfly package laser diode and driver circuit or sled module, sled broadband light source (superluminescent diode), 14 pin butterfly package and 14pin DIL package. Low, medium and high output power, wide spectrum range, fully meet the needs of different users. Low spectral fluctuation, low coherent noise, direct modulation up to 622MHz optional. Single mode pigtail or polarization maintaining pigtail is optional for output, 8 pin is optional, integrated PD is optional, and optical connector can be customized. The superluminescent light source is different from other traditional sleds based on ASE mode, which can output broadband bandwidth at high current. Low coherence reduces Rayleigh reflection noise. The high power single-mode fiber output has a wide spectrum at the same time, which cancels the receiving noise and improves the spatial resolution (for OCT) and detection sensitivity (for sensor). It is widely used in fiber optical current sensing, fiber optical current sensors, optical & Medical OCT, optical fiber gyroscopes, optical fiber communications system and so on.

Compared with the general broadband light source, SLED light source module has the characteristics of high output power and wide spectrum coverage. The product has desktop (for laboratory application) and modular (for engineering application). The core light source device adopts a special high output power sled with 3dB bandwidth of more than 40nm.

SLED broadband light source is an ultra wideband light source designed for special applications such as optical fiber sensing, fiber optic gyroscope, laboratory, University and Research Institute. Compared with the general light source, it has the characteristics of high output power and wide spectrum coverage. Through the unique circuit integration, it can place multiple sleds in a device to achieve the output spectrum flattening. The unique ATC and APC circuits ensure the stability of output power and spectrum by controlling the output of sled. By adjusting APC, the output power can be adjusted in a certain range.

This kind of light source has higher output power on the basis of the traditional broadband light source, and covers more spectral range than the ordinary broadband light source. The light source is divided into desktop light source module for engineering use. During the general core period, special light sources with a bandwidth of more than 3dB and a bandwidth of more than 40nm are used, and the output power is very high. Under the special circuit integration, we can use multiple ultra wideband light sources in one device, so as to ensure the effect of flat spectrum.

The radiation of this kind of ultra wideband light source is higher than that of semiconductor lasers, but lower than that of semiconductor light-emitting diodes. Because of its better characteristics, more series of products are gradually derived. However, ultra wideband light sources are also divided into two types according to the polarization of light sources, high polarization and low polarization.

830nm, 850nm SLED diode for Optical coherence tomography(OCT):

Optical coherence tomography (OCT) technology uses the basic principle of weak coherent light interferometer to detect the back reflection or several scattering signals of incident weak coherent light from different depth layers of biological tissue. By scanning, two-dimensional or three-dimensional structure images of biological tissue can be obtained.

Compared with other imaging technologies, such as ultrasonic imaging, nuclear magnetic resonance imaging (MRI), X-ray computed tomography (CT), etc., OCT technology has higher resolution (several microns). At the same time, compared with confocal microscopy, multiphoton microscopy and other ultra-high resolution technologies, OCT technology has greater tomography ability. It can be said that OCT technology fills the gap between the two kinds of imaging technology.

Structure and principle of optical coherence tomography

Broad ASE spectrum sources (SLD) and broad gain Semiconductor Optical Amplifiers are used as a key components for OCT light engines.

The core of OCT is optical fiber Michelson interferometer. The light from the super luminescent diode (SLD) is coupled into the single-mode fiber, which is divided into two channels by 2x2 fiber coupler. One is the reference light collimated by the lens and returned from the plane mirror; the other is the sampling light focused by the lens to the sample.

When the optical path difference between the reference light returned by the mirror and the backscattered light of the measured sample is within the coherent length of the light source, the interference occurs. The output signal of the detector reflects the backscattered intensity of the medium.

The mirror is scanned and its spatial position is recorded to make the reference light interfere with the backscattered light from different depths in the medium. According to the position of the mirror and the intensity of the interference signal, the measured data of different depths (z direction) of the sample are obtained. Combined with the scanning of the sample beam in the X-Y plane, the three-dimensional structure information of the sample can be obtained by computer processing.

Optical coherence tomography system combines the characteristics of low coherence interference and confocal microscopy. The light source used in the system is broadband light source, and the commonly used is super radiant light emitting diode (SLD). The light emitted by the light source irradiates the sample and the reference mirror through the sample arm and the reference arm respectively through the 2 × 2 coupler. The reflected light in the two optical paths converges in the coupler, and the interference signal can only occur when the optical path difference between the two arms is within a coherent length. At the same time, because the sample arm of the system is a confocal microscope system, the beam returned from the focus of the detection beam has the strongest signal, which can eliminate the influence of the scattered light of the sample outside the focus, which is one of the reasons why OCT can have high performance imaging. The interference signal is output to the detector. The intensity of the signal corresponds to the reflection intensity of the sample. After the processing of the demodulation circuit, the signal is collected by the acquisition card to the computer for gray imaging.

1310nm SLED diode for Fiber optic gyroscopes

A key application for SLED is in navigation systems, such as those in avionics, aerospace, sea, terrestrial, and subsurface, that use fiber-optic gyroscopes (FOGs) to make precise rotation measurements, FOGs measure the Sagnac phase shift of optical radiation propagating along a fiber-optic coil when it rotates around the winding axis. When a FOG is mounted within a navigation system, it tracks changes in orientation.

The basic components of a FOG, as shown, are a light source, a single-mode fiber coil (could be polarization-maintaining), a coupler, a modulator, and a detector. Light from the source is injected into the fiber in counter-propagating directions using the optical coupler.

When the fiber coil is at rest, the two light waves interfere constructively at the detector and a maximum signal is produced at the demodulator. When the coil rotates, the two light waves take different optical path lengths that depend on the rotation rate. The phase difference between the two waves varies the intensity at the detector and provides information on the rotation rate.

In principle, gyroscope is a directional instrument which is made by using the property that when the object rotates at high speed, the angular momentum is very large, and the rotation axis will always point to a direction stably. The traditional inertial gyroscope mainly refers to the mechanical gyroscope. The mechanical gyroscope has high requirements for the process structure, and the structure is complex, and its accuracy is restricted by many aspects. Since the 1970s, the development of modern gyroscope has entered a new stage.

Fiber optic gyroscope (FOG) is a sensitive element based on optical fiber coil. The light emitted by laser diode propagates along the optical fiber in two directions. The angular displacement of the sensor is determined by different light propagation paths.

Structure and principle of optical coherence tomography

1310nm SLED diode for Fiber optic current sensors

Fiber Optic Current Sensors are resistant to effects from magnetic or electrical field interferences. Consequently, they are ideal for the measurement of electrical currents and high voltages in electrical power stations.

Fiber Optic Current Sensors are able to replace existing solutions based on the Hall effect, which tend to be bulky and heavy. In fact, those used for high-end currents can weigh as much as 2000kg compared to Fiber Optic Current Sensors sensing heads, which weigh less than 15kg.

Fiber optic current Sensors have the advantage of simplified installation, increased accuracy and negligible power consumption. The sensing head usually contains a semiconductor light source module, typically an SLED, which is robust, operates in extended temperature ranges, has verified lifetimes, and is cost