JPH02157635A - Device for inspecting stability of light wavelength - Google Patents

Abstract

PURPOSE:To accomplish detection with high sensitivity with a simple small-sized constitution by constituting a spectral system by the use of a hologram lens. CONSTITUTION:A laser light beam to be measured from a semiconductor laser 1 passes through an optical fiber 2 and spectrally divided by the hologram lens 3, then is made incident on an optical sensor 5 by setting the clad of a single optical fiber 4 for receiving light as an optical fine aperture. The output from the sensor 5 is recorded by a recording device 6 and the stability of the laser light beam which is easy to be changed by a temperature, etc., is inspected. By constituting the spectral system by the user of the hologram lens without necessitating a precision spectrometer incorporating a diffraction grating or an optical spectral analyzer, etc., the inspection of stability of light wavelength can be performed with high sensitivity by the simple small-sized economy device. Then, the same result is obtained by using a sensor or an optical sensor array corresponding to may fibers for receiving light arrayed in a line.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an apparatus for inspecting the stability of the emission wavelength of a light source such as a semiconductor laser.

(Prior Art) Semiconductor lasers are widely used as light sources for optical fiber communications, optical disks, etc., but stabilization of the output wavelength is required for high performance. However, they usually have shortcomings in stability, such as the fact that the emission wavelength tends to fluctuate due to temperature changes. Further, variations in characteristics are likely to occur in the product. Therefore, when using a device that requires wavelength stability, it is necessary to test it in advance. However, conventional inspections require either a custom optical system using a precision spectrometer with a built-in diffraction grating, or an expensive spectroscopic device called an optical spectrum analyzer with a built-in optical interference system. The former has a problem in that it requires a particularly large installation space. In addition, whichever method is adopted, the inspection equipment becomes expensive, so there is a problem in that the cost of inspecting the semiconductor laser increases.

(Problems to be Solved by the Invention) An object of the present invention is to provide an optical wavelength stability testing device that can easily test the stability of the emission wavelength by simply configuring a spectroscopic system using a hologram lens. .

(Means for Solving the Problem) The optical wavelength stability inspection device of the present invention includes a hologram lens that receives emitted light from a light source to be inspected, and a single or single It consists of a plurality of minute optical apertures arranged in a row, an optical sensor that receives light that passes through each of the optical apertures, and a device that records the output of the optical sensor.

That is, the present invention allows light emitted from a semiconductor laser (or an optical fiber that receives light from the semiconductor laser) to be transmitted through an optical aperture (core of an optical fiber, pinhole, etc.) installed at a specific position via a hologram lens. The stability of the emission wavelength of a semiconductor laser is tested by measuring the intensity of light that enters a slit (such as a slit) and passes through this optical aperture.

In the conventional technology, inspection was performed using a precision spectrometer with built-in gratings and interference systems, but as explained below, the present invention simplifies inspection by combining an extremely simple hologram lens and optical power detection. There is a big difference between the two.

(Embodiment) FIG. 1 is a plan view showing the configuration of a first embodiment of the present invention, in which 1 is a semiconductor laser to be inspected, 2 is an optical fiber,
3 is a hologram lens, 4 is a light receiving optical fiber, 5 is an optical sensor, 6 is a recording device, 7 is an optical connector, and 8 is an optical fiber for coupling a semiconductor laser. In this embodiment, the inspection device of the present invention includes a main body surrounded by a broken line and a recording device 6. As shown in this figure, it may be connected only electrically to the main body, or it may be physically integrated with the main body. This recording device has a simple and economical configuration because it is a combination of a small number of small parts such as a light guiding section and a hologram lens, and a light receiving electric system.

The light emitted from the semiconductor laser 1 is transmitted through optical fibers 8 and 2.
The light passes through the thin plate-shaped hologram lens 3 and is focused by the diffraction effect of the hologram lens 3. The end face of the light-receiving optical fiber 4 is installed at this point to receive light. The light entering the light-receiving optical fiber is guided to an optical sensor 5 attached to the other end and its intensity is measured. This measured value is recorded on the recording device 6.

The principle of the present invention utilizes the fact that the focal point position of a thin film hologram lens depends on the wavelength of light. The light-receiving end face of the light-receiving optical fiber is attached to the position where the light is most focused. Thereafter, when the wavelength of the semiconductor laser changes, the focusing position of the light moves, and the amount of light entering the light-receiving optical fiber decreases, so the output of the optical sensor changes. Therefore, a change in the emission wavelength of the semiconductor laser can be measured as a change in the output of the optical sensor.

The present invention utilizes the characteristic that the position of the focal point of light by a hologram lens differs depending on the wavelength of incident light. Therefore, the hologram lens essential to the configuration of the present invention will be explained.

A hologram lens is a hologram made to have the function of a condensing lens. A typical hologram is created by simultaneously irradiating a substrate coated with a photosensitive material with two beams from the same laser under appropriate conditions, and recording the interference fringes. These interference fringes act as a kind of diffraction grating, thereby exerting a specific effect on the incident light.

As is well known, the diffraction angle of light changes significantly depending on the wavelength. The larger the wavelength, the larger the diffraction angle. Therefore, by utilizing the effect of diffraction, the focusing position of light by the hologram lens moves as the wavelength changes. This phenomenon is described, for example, in the article ``Grating Lens'' published in Journal of Applied Physics, Vol. 57, No. 5, pp. 759-761 (198B).

Examples of photosensitive materials for producing holograms include sulfur salts, dichromate gelatin, photopolymers, and thermoplastics, and hologram lenses can be produced using any of these materials. Usually due to the need to protect the photosensitive material,
After recording, a glass plate is attached to the photosensitive surface and sealed. The shape of the hologram lens is simply laminated glass, which is thin and easy to handle. For the purpose of reducing aberrations, two holograms are sometimes pasted together to form a single hologram lens, but the handling is the same.

FIG. 2 is an explanatory diagram of the optical effect of the hologram. Second
Figure (a) shows that when the optical fibers 2.4 are on the same axis, (
b) and (c) are cases where they are not on the same axis. The light emitted from the optical fiber 2 passes through the hologram lens as shown by the solid line, and then is received by the central core of the optical fiber. When the wavelength changes to the longer side, the light beam after passing through the hologram lens changes as shown by the broken line.

In addition to the function of condensing light on the same axis like a normal optical lens, a hologram lens can also have the function of bending the optical axis as shown in FIGS. 2(b) and 2(c).

As shown in FIG. 2(a), when the optical axis does not change as in a general condensing lens, the position of the focusing point simply moves back and forth on the optical axis as the wavelength changes.

Therefore, only the spot diameter of the light beam changes at the end face of the light-receiving optical fiber. On the other hand, in the case where the optical axis is bent and focused as shown in FIGS. 2(b) and 2(c), the angle at which the optical axis is bent itself changes as the wavelength changes. Therefore, in addition to the change in the spot diameter of the luminous flux, the spot position will shift from the axis of the receiving optical fiber.
The change in the amount of light incident on the light-receiving optical fiber is greater than in the former case. Therefore, the latter method has the advantage of increasing sensitivity. In the former case, if the diffraction efficiency of the hologram lens is not high, a part of the light component (O-order diffracted light) that travels straight without being diffracted will be incident on the end face of the optical fiber, but in the latter case, the 0-order diffracted light will be spaced out. Since the signals are separated from each other, there is no fear of such noise.

FIG. 3 is a principle diagram for explaining the change in luminous flux when the wavelength of light changes. FIG. 3(a) shows the change in the direction of the light beam due to the hologram.

Let the incident angles of the rays of wavelength λ and λ2 incident on the same position of the hologram be α1. α2 and the exit angle are 01. Let it be θ2. At this time, the following relationship is given.

Based on this relational expression, the magnitude of the axis deviation will be explained by taking the case of FIG. 2(b) as an example. As shown in Figure 3(b), the angle between the optical axis of the light emitted from the hologram lens and the optical axis of the light incident on the hologram lens is θ, and the wavelength is λ.
If the wavelength changes by Δλ, then 2(1
), α1=α2=O1λ, =λ, λ2=λ,
+Δλ, θ, =θ, θ2=θ+Δ. At this time, the amount of change Δθ in the optical axis of the emitted light is approximately given by the following equation.

λ Also, the distance from the hologram lens to the focal point of light is L
Then, the amount of axis deviation ΔX of the focal point with respect to the optical fiber is Jx=L·Δθ.

So, for example, λ=0.78μ age, θ=45°, L=5
01 and Δλ=0.1 rv, Δx 'i
2 μm is obtained. That is, a wavelength change of 0.1 .mu.m causes an axis misalignment of about 2 .mu.m. optical fiber 2,
If a single-mode optical fiber is used as the light-receiving optical fiber 4, the diameter of the optical fiber core is between 5 and 10 mm.
μm, and the diameter of the light spot produced by the hologram lens can be reduced to the same size. Core diameter 10μ
When m optical fibers are butted against each other and light is incident from one to the other, if an axial deviation of 2 .mu.- is applied from a state where there is no axial deviation, it can be calculated that the reduction in received light power will be more than 10%.

Therefore, in this embodiment, a change in received light power due to an axis deviation of 2 μm can be sufficiently detected.

0, In- wavelength resolution is generally difficult even with a spectrometer using a diffraction grating. Note that when it is desired to lower the sensitivity, that is, when it is desired to detect large fluctuations in wavelength, the light-receiving end face of the light-receiving optical fiber 4 may be shifted to a position where the beam diameter is large. The optical fiber 2 and the light-receiving optical fiber 4 may be multimode optical fibers with a large core diameter.

Note that, assuming that there are variations in the emission wavelength of the semiconductor laser, it is first necessary to be able to set the light receiving optical fiber to receive the light at the beginning of the inspection. For this purpose, at least one of the position of the output end face of the optical fiber 2, the inclination of the hologram lens, and the position of the light receiving end face of the light receiving optical fiber may be made adjustable.

In this embodiment, a light-receiving optical fiber was used as the element that receives the light emitted from the hologram near the condensing point, but instead, a pinhole was placed, and the optical sensor receives the light that passed through the pinhole. You may choose to accept it. Also, slits may be used instead of pinholes. However, in the case of slits, the slits are arranged so that the length direction is perpendicular to the plane of the paper. Note that in the case of slits, there is an advantage that positioning in the direction perpendicular to the plane of the drawing becomes very easy.

The above explanation was based on a narrowly defined hologram lens produced by optical interference, but it is also possible to use a lens produced by a broadly defined hologram (computer generated hologram) produced using lithography technology.

In computer generated holograms, the phase difference of interference light on the hologram surface is virtually calculated by a computer, and based on this, the shape of the surface of the substrate is processed using methods such as electron beam exposure and ultraviolet exposure. The phase of the light changes when it passes through this hologram substrate, producing an effect similar to that of a hologram in the narrow sense of the optical interference method described above. With this technology,
A hologram lens can be produced and can also be used in the present invention. The simplest design is the same as what is traditionally called a Fresnel lens, except for its smaller dimensions. This technique also makes it possible to create a hologram that focuses light by bending its optical axis.

FIG. 4 is a plan view showing the configuration of a second embodiment of the present invention. After the light from the semiconductor laser 1 enters the device of the present invention via the optical connector 7, it is split into two. One of the lights enters the hologram lens 3 as in the first embodiment. The other light passes through the optical fiber 2' and reaches the optical sensor 5.
The signal from this optical sensor is transmitted to the recording device 6.

Further, the focused light from the hologram lens 3 is received by two optical fibers 4.4. Each incident light beam is detected by optical sensors 5, 5, and a signal is transmitted to recording device 6.

By receiving the light through two optical fibers 4.4, the direction and amount of change in wavelength can be determined from the difference in light intensity between the two. The relationship between the difference in light intensity and the amount of wavelength change is calibrated in advance. Note that the measured value of the light intensity difference is normalized by the light intensity value from the optical sensor 5' to avoid the influence of intensity fluctuations of the light emitted from the semiconductor laser. In the first embodiment, these calculations are performed by a recording device. Fluctuations in the intensity of the light emitted from the semiconductor laser affect measurement errors; By simultaneously measuring the intensity of the signal and using this to standardize the wavelength-varying signal light, the measurement error can be reduced.In the case of a semiconductor laser that has an output terminal for the intensity monitor signal, There is no need to branch out the light as in the case of the above method, and the signal from the terminal can be input directly to the recording device.

In the second embodiment, there are two optical fibers that receive the light from the hologram lens, but if more optical fibers are lined up and any two optical fibers are used, it can be used over a wide wavelength range. This optical fiber that enables measurement of wavelength changes may also be a multi-core optical fiber having a plurality of cores.

FIG. 5 is a plan view showing the configuration of the third embodiment of the present invention, in which the focused light by the hologram is transmitted to the array type optical sensor 5#.
It receives light at If the spacing between the light receiving elements is sufficiently narrow, changes in wavelength can be successively measured as changes in the position of the focused light by searching for the light receiving element that exhibits the maximum measured intensity. When the spacing between the light receiving elements is large, the change in wavelength can be measured based on the difference in measured intensity for arbitrary light receiving elements, as in the second embodiment.

(Effects of the Invention) As explained above, the wavelength stability of a semiconductor laser, which has conventionally been measured using an expensive and large precision spectrometer, can be measured using a hologram lens and an optical fiber that is sensitive to changes in the position of the light beam. By using optical coupling, measurements can be made with a simple and compact optical system. Since the number of component parts is reduced, the inspection device can be significantly smaller and lower in price while maintaining high sensitivity. Therefore, if the present invention is used, it is possible to speed up the inspection by testing a large number of semiconductor lasers in parallel, and reduce the inspection cost, so the present invention provides great convenience in the use of semiconductor lasers. It is something.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing the configuration of the first embodiment of the present invention, Fig. 2 is a principle diagram explaining the optical action of a hologram lens, and Fig. 3 is a change in luminous flux when the wavelength of light changes. FIG. 4 is a plan view showing the configuration of the second embodiment, and FIG. 5 is a plan view showing the configuration of the third embodiment. 1... Semiconductor laser, 2.2' optical fiber 3... Hologram lens 4.4'... Optical fiber for light reception

Claims (1)

[Scope of Claims] 1. A hologram lens that receives light emitted from a light source to be inspected, and a single or a plurality of minute optical apertures arranged in a row installed near a light condensing position by the hologram lens; , an optical wavelength stability inspection device comprising: an optical sensor that receives light passing through each of the optical apertures; and a device that records the output of the optical sensor. 2. In the optical wavelength stability testing device as set forth in claim 1, an array type optical sensor is provided by a hologram lens in place of both the optical aperture that receives the focused light by the hologram lens and the optical sensor attached thereto. An optical wavelength stability inspection device characterized in that it is installed near a light condensing position.