JP2558895B2 - Fiber Optic Superluminescent Light Source - Google Patents

Description

TECHNICAL FIELD The present invention relates to a light source having a broad emission spectrum using a rare earth element-doped optical fiber.

“Prior art and its problems” Since ordinary LEDs do not have a good far-field pattern, the coupling efficiency with a single-mode optical fiber is extremely low. As a light source developed for the purpose of improving the coupling efficiency with a single mode optical fiber, there is a super luminescence diode (hereinafter abbreviated as SLD). SLD is LED
Wide emission spectrum (poor time coherence)
However, the far field pattern is improved compared to LEDs.

However, in general, since the cross-sectional shape of the active layer that contributes to light emission is rectangular in the SLD, the emitted light is light that has some polarization characteristics, and is not depolarized light such as natural light that does not have polarization characteristics. . Further, since its life is short, there was a practical problem.

On the other hand, there has been proposed an SLD using a rare earth element-doped optical fiber obtained by adding a rare earth element to an optical fiber. However, in such an SLD, because the waveguide structure of the optical fiber is not designed in consideration of the relationship between the wavelength of the pumping light and the cutoff wavelength of the rare earth element-doped optical fiber,
The rare earth element-doped optical fiber operates as a multimode fiber at the wavelength of the excitation light. Therefore, there is a disadvantage that the mode shape of the excitation light propagating in the rare earth element-doped optical fiber changes and the excitation light intensity changes due to temperature fluctuations.

Further, since the intensity of the spontaneous emission light emitted by the rare earth element is proportional to the intensity of the excitation light, there is a disadvantage that the intensity of the spontaneous emission light also changes due to the above mode shape change. Further, the shape of the emission spectrum of the spontaneous emission light emitted from the rare earth element also changes depending on the excitation light intensity, so that there is a disadvantage that a stable emission spectrum cannot be obtained.

And an optical filter is used to cut the residual excitation light at the emission end of the optical fiber, and a normal optical filter has polarization characteristics depending on its insertion angle, but conventionally no attention has been paid to this point. Therefore, the light obtained from the above-mentioned optical filter does not have depolarization characteristics that completely have polarization characteristics.
It wasn't a rized light.

In order to solve such a problem, a rare earth element is added to the core of the optical fiber, and one end surface or both end surfaces of the optical fiber is polished obliquely with respect to the center axis of the optical fiber to suppress laser oscillation. Then, a method has been proposed in which the rare earth element existing in the core is excited by injecting the excitation light into the rare earth element-doped optical fiber, and the spontaneous emission light emitted from the rare earth element is used. (K. Liu et al. “10mW superfl
uorescent single-mode fiber souce at 1060nm ", Elec
tron, lett., 23, pp. 1320-1321 (1987))
The emission spectrum of LD is shown.

However, it is generally known that the slanted end face has polarization characteristics, and depolarize that does not have polarization characteristics completely.
I haven't got a d light.

In addition, there are problems in the stability of the emission spectrum shape and the intensity of the emitted light, and the end face treatment of the rare-earth element-doped optical fiber to obtain emitted light that does not have polarization characteristics and the insertion angle of the filter to block the excitation light. However, there is a problem that sufficient attention has not been paid to the above, and it has not been possible to easily obtain light having no polarization characteristics.

The present invention, in order to solve the above problems in a superluminescent light source using a rare earth element-doped optical fiber, by proposing a waveguide structure of the rare earth element-doped optical fiber and a method of configuring the light source, It is something that can be obtained.

"Means for Solving the Problems" The optical fiber superluminescent light source of the present invention comprises:
In an optical fiber superluminescent light source composed of a rare earth element-doped optical fiber and an excitation light source for exciting the rare earth element doped in the rare earth element-doped optical fiber, one end face on the excitation light source side is the central axis of the optical fiber With respect to the diagonal, the other end surface is vertically polished, respectively, its cutoff wavelength is a rare earth element-doped optical fiber shorter than the excitation light wavelength, and a coupling means for coupling the excitation light to the rare earth element-doped optical fiber, The solution was to block the excitation light, pass only the spontaneous emission light emitted from the rare earth element, and to provide an optical filter inserted perpendicularly to the spontaneous emission light.

[Examples] Hereinafter, the present invention will be described in detail.

FIG. 1 shows the outline of one embodiment of the optical fiber SLD of the present invention. In the figure, reference numeral 1 indicates an oscillation wavelength of 810 nm and 9
A pumping light source near 80 nm or 1480 nm, reference numeral 2 is a lens as a coupling system for coupling the pumping light emitted from the pumping light source 1 to the rare earth element-doped optical fiber 3, and reference numeral 3 is a rare earth element-doped optical fiber. The rare earth element-doped optical fiber 3 is made by adding erbiul (Er) as a rare earth element to a single mode fiber, and is designed so that its cutoff wavelength is shorter than the pumping light wavelength. is there. The end face of the rare earth element-doped optical fiber 3 on the excitation light source side is oblique to the center axis of the optical fiber,
The other end face is vertically polished. Reference numeral 4 is a thin-film bandpass filter, which blocks excitation light,
In order to allow the spontaneous emission light emitted from the rare earth element-doped optical fiber 3 to pass through, it has a pass band at about 1500 nm at normal incidence. The bandpass filter 4 is inserted so as to be perpendicular to the light emitted from the rare earth element-doped optical fiber 3. Reference numeral 5 is a single-mode optical fiber whose both end surfaces are polished vertically, has the same waveguide parameter as the rare earth element-doped optical code 3, and does not contain Er. The single mode optical fiber 5 and the rare earth element-doped optical fiber 3 are arranged close to each other so that the coupling loss is low.

In such an optical fiber SLD, first, the excitation light emitted from the excitation light source 1 is coupled to the rare earth element-doped optical fiber 3 by the lens 2. Er added to the rare earth element-doped optical fiber 3 is excited by this excitation light,
Emits spontaneous emission light around 1500 nm. The spontaneous emission light is vertically incident on the band pass filter 4 through the rare earth element-doped optical fiber 3 together with the excitation light. The excitation light is blocked by the bandpass filter 4, and the spontaneous emission light passes through the bandpass filter 4 and is guided to the single mode optical fiber 5. As a result, at the emission end of the single mode optical fiber 5, it is possible to obtain light having a wide emission spectrum near 1500 nm and no polarization characteristics.

In this example, Er was used as the rare earth element,
The optical fiber SLD of the present invention is not limited to this, using 800 nm as the pumping light wavelength and setting the pass wavelength of the bandpass filter to 1060 nm, neodymium (Nd)
It is also possible to obtain light with a broad emission spectrum with no polarization characteristics around 1060 nm by adding to the optical fiber.

"Effect of the invention" As described above, the optical fiber superluminescent light source of the present invention, the cut-off wavelength of the single mode optical fiber doped with a rare earth element is made shorter than the oscillation wavelength of the excitation light, and one end surface thereof is While polishing obliquely to the center axis of the fiber, by using the bandpass filter of the vertical incidence piece to block the excitation light, there is no polarization characteristics,
It is possible to obtain light with a wide emission spectrum.

Moreover, since the light source of the present invention can emit light having no polarization characteristic, it can be used as a light source for an optical fiber sensor such as an optical fiber gyro.

Especially in an optical fiber gyro, its optical system is usually composed of a polarized optical fiber and a polarizer. However, if a light source having no polarization characteristic of the present invention is used, a polarizer is not necessary for the optical system, and therefore all are simple. It can be configured with only one mode optical fiber, and the bottom cost can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of an optical fiber superluminescent light source of the present invention, and FIG. 2 is an emission spectrum of a conventional light source. 1 ... Excitation light source, 2 ... Lens, 3 ... Rare earth element-doped optical fiber, 4 ... Bandpass filter, 5 ... Single-mode optical fiber.

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Claims (1)

(57) [Claims] 1. An optical fiber superluminescent light source comprising a rare earth element-doped optical fiber and an excitation light source for exciting the rare earth element added to the rare earth element-doped optical fiber, wherein one end surface on the excitation light source side is A rare earth element-doped optical fiber that is polished obliquely to the center axis of the optical fiber and has the other end surface perpendicular to it, and its cutoff wavelength is shorter than the excitation light wavelength, and the excitation light is coupled to the rare earth element-doped optical fiber. And an optical filter that blocks excitation light and passes only spontaneous emission light emitted from the rare earth element, and is inserted perpendicularly to the spontaneous emission light. Luminescent light source