JP6233189B2 - Beam scanning apparatus, optical wireless communication system, and beam scanning method - Google Patents

Description

  The present invention relates to a beam scanning device, an optical wireless communication system, and a beam scanning method.

  The technique of scanning the beam can be used for various applications. For example, optical wireless communication, laser printer, barcode reader, and the like.

  2. Description of the Related Art Conventionally, as a laser beam scanning device, a laser beam scanning device that includes a wavelength tunable light source and a partially transmissive etalon and injects a laser beam from the tunable light source into the partially transmissive etalon is known ( For example, see Patent Documents 1 and 2).

JP 2009-145838 A JP 2006-323175 A

  However, in the conventional laser beam scanning devices disclosed in Patent Documents 1 and 2, secondary diffracted light is generated and becomes multimodal, and the secondary diffracted light becomes noise light. Therefore, when the emission angle is scanned by changing the laser light wavelength, there is a problem that secondary diffracted light that always becomes a noise component is attached. For example, in short-distance optical wireless communication, this secondary diffracted light becomes noise, so it is desirable to scan unimodal light.

  The present invention has been made to solve the above-described problems. For example, secondary diffracted light that becomes noise in optical wireless communication is suppressed, and the wavelength is changed to scan unimodal light. An object of the present invention is to realize a beam scanning apparatus capable of performing the above.

  The beam scanning device according to the present invention includes a wavelength tunable light source that outputs light by changing a wavelength, a plane wave converter that converts light output from the wavelength tunable light source into a plane wave, and a plane wave that is converted by the plane wave converter. The light intensity distribution conversion unit that multi-reflects the reflected light and converts the adjacent beams of the multiple reflected light into a single-peak light intensity distribution according to the wavelength, and the light intensity distribution conversion unit converts the light into a wavelength. A phase wavefront that changes the light emission direction according to the unimodal light intensity distribution according to this wavelength by converting the phase wavefront of the light converted into a corresponding unimodal light intensity distribution into a spherical wave And a conversion unit.

  According to the present invention, the beam scanning apparatus can scan unimodal light by changing the wavelength.

1 is a configuration diagram showing an optical wireless communication system including a beam scanning device according to a first embodiment of the present invention. 1 is a block diagram showing a beam scanning device according to a first embodiment of the present invention. Explanatory drawing for demonstrating the beam scanning apparatus by Embodiment 1 of this invention. 1 is a block diagram showing a beam scanning device according to a first embodiment of the present invention. Configuration diagram showing a beam scanning apparatus according to a second embodiment of the present invention.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing an optical wireless communication system including a beam scanning apparatus according to Embodiment 1 of the present invention. FIGS. 2 and 4 are block diagrams showing a beam scanning apparatus according to Embodiment 1 of the present invention. FIG. 3 is an explanatory diagram for explaining the beam scanning apparatus according to the first embodiment of the present invention. In each figure, the same numerals indicate the same or corresponding parts. 1, 2 and 4, a beam scanning apparatus according to Embodiment 1 of the present invention includes a wavelength tunable laser 1 as a wavelength tunable light source, a plane wave converter 2, a light intensity distribution converter 3, and a phase wavefront converter. 4 is provided. The optical wireless communication system including the beam scanning device further includes a receiving unit 5.

Next, the operation will be described. In FIG. 1, light emitted from the wavelength tunable laser 1 is converted into a plane wave by the plane wave converter 2 and input to the light intensity distribution converter 3. As will be described later, the light intensity distribution conversion unit 3 performs light intensity distribution conversion in accordance with the wavelength of the wavelength tunable laser 1, for example, λ ₁ and λ ₂ . Further, the light intensity distribution conversion unit 3 has a unimodal intensity distribution, and the intensity distribution can be spatially changed according to the wavelength. Thereafter, the phase wavefront conversion unit 4 can change the light emission direction by converting the phase wavefront from the plane wave. Therefore, the light can be emitted to the position of the receiving unit 5 by changing the wavelength and scanning the light.

  Next, a specific configuration and operation of each unit will be described. In FIG. 1, a wavelength tunable laser 1 is a semiconductor laser such as a DFB (Distributed Feed-Back) laser or a DBR (Distributed Bragg Reflector) laser. A fiber laser or the like may be used.

  When a semiconductor laser is used as the wavelength tunable laser 1, the wavelength can be easily changed by changing the temperature of the semiconductor laser. For example, a method of changing the temperature by arranging a semiconductor laser on a Peltier element Alternatively, there is a method in which a resistor such as a thin film resistor is arranged around the semiconductor laser to flow current and change the temperature. Further, carrier injection may be performed on the semiconductor laser, and wavelength shift may be performed by the carrier plasma effect.

  The plane wave conversion unit 2 includes a collimator lens 2a, and adjusts the focal length freely according to the spot size of the laser beam from the wavelength tunable laser 1, and expands it to a desired beam diameter in the light intensity distribution conversion unit 3. For example, when the beam diameter incident on the light intensity distribution conversion unit 3 is expanded to 0.5 mm by the collimator lens 2a, if the wavelength is 1550 nm, the spread angle of the Gaussian beam is about 0.094 °, which is a pseudo plane wave. Can be considered.

  In FIG. 2, Fabry-Perot interference using an etalon 3 a is used as the light intensity distribution conversion unit 3. An AR (Anti-Reflection) coating is applied to a part of the incident surface of the etalon 3a so that the light is incident without reflection, and a gold coating is applied to the other part so that the light is totally reflected inside. . On the other hand, a partial reflection coat is applied to the emission surface of the etalon 3a so that light is partially reflected. As shown in FIG. 2, the traveling direction of the plane wave from the plane wave converting unit 2 is the z direction, and the direction perpendicular to the paper surface is the y direction.

  In FIG. 2, as schematically shown by solid arrows, light incident on the etalon 3a is multiple-reflected inside the etalon, and a plurality of beams are emitted from the etalon 3a. In this plurality of beams, adjacent beam diameters are set so as not to become point light sources. For example, assuming that the light incident on the etalon 3a is a Gaussian beam having a spot size of 0.5 mm, the thickness of the etalon 3a is 2.0 mm. When the etalon internal ray angle θ is 1.5 °, the interval between beams emitted from the etalon 3a by multiple reflection is 0.186 mm. Therefore, the adjacent beams, which are adjacent beams, are sufficiently overlapped.

FIGS. 3A and 3B show the simulation results of the beam emitted from the etalon 3a. 3A and 3B, the vertical axis represents the light intensity (arbitrary unit indicated by au in the figure), and the horizontal axis represents the x-axis (mm unit) shown in FIG. The light intensity was calculated by setting the electric field reflectance of the incident surface of the etalon 3a to 0% or 100% and the electric field reflectance of the emission surface of the etalon 3a to 60%. In FIG. 3A, when the wavelength is λ ₁ = 1550.4 nm, a light intensity peak occurs at a position of 0.12 mm in the negative x direction. In FIG. 3B, the wavelength is λ ₂ = 1550.8 nm. In this case, a light intensity peak occurs in the positive x direction of 0.12 mm. Since the phase wavefront is close to a plane wave, it propagates to the phase wavefront conversion unit 4 while maintaining the light intensity distribution with almost no change in the emission angle.

  FIG. 4 shows a convex lens 4 a capable of spherical wave conversion as the phase wavefront conversion unit 4. In FIG. 4, the intensity distribution incident on the convex lens 4a is changed by spatially changing the intensity distribution of the light by the light intensity distribution conversion unit 3, and therefore, it is schematically shown by arrows of a solid line, a rough wavy line, and a fine wavy line. In this way, it is possible to convert to an emission angle corresponding to the light intensity distribution.

  1 and 4, when the distance to the position of the receiving unit 5 is very short, it can be used below the focal length of the convex lens 4 a, but light after imaging after the focal length is used. May be. In that case, since the light is a spherical wave, attenuation is increased. In addition, since the lens is displaced from the center position of the convex lens 4a and aberrations due to the lens are easily generated, it is preferable to use the vicinity of the lens center axis.

  As described above, in the beam scanning apparatus according to the first embodiment of the present invention, the light intensity distribution conversion unit 3 sets the beam diameters so that adjacent beams of a plurality of beams as plane waves that are multiple-reflected inside the etalon overlap each other. Therefore, the secondary diffracted light is suppressed to a unimodal light intensity distribution, the light intensity distribution is spatially changed according to the wavelength, and the phase wavefront conversion unit 4 responds to the light intensity distribution. Conversion to the emission angle is made. Thereby, in the beam scanning apparatus which scans light by changing a wavelength, there exists an effect that a unimodal light can be scanned.

  Further, in the optical wireless communication system including the beam scanning device according to the first embodiment of the present invention, the receiving unit 5 receives the unimodal optical signal scanned with the secondary diffracted light being suppressed. ing. As a result, noise as secondary diffracted light is suppressed, and there is an effect that optical space communication excellent in communication quality such as a signal-to-noise ratio can be performed.

Embodiment 2. FIG.
In the beam scanning apparatus according to the first embodiment of the present invention, Fabry-Perot interference is used, so that the output power of light varies according to FSR (Free Spectral Range) corresponding to the wavelength change. In contrast, the beam scanning apparatus according to the second embodiment of the present invention enables beam scanning with a constant light output.

  FIG. 5 is a block diagram showing a beam scanning apparatus according to Embodiment 2 of the present invention. In each figure, the same numerals indicate the same or corresponding parts. In FIG. 5, the beam scanning device according to the second embodiment includes an etalon 3b instead of the configuration of the beam scanning device according to the first embodiment, and in addition to the configuration of the beam scanning device according to the first embodiment, the light intensity light receiving unit 6 It has. Since the other configuration is the same as that of the beam scanning apparatus according to the first embodiment shown in FIGS. 1, 2, and 4, the description including the operation thereof is omitted.

  In FIG. 5, an AR coat is applied to a part of the incident surface of the etalon 3b so that the light is incident without reflection, and a partial reflection coat is applied to the other part so that the light is partially reflected inside. . On the other hand, a partial reflection coat is applied to the emission surface of the etalon 3b so that light is partially reflected.

  Next, the operation will be described. In FIG. 5, the wavelength tunable laser 1 is arranged offset from the optical axis of the collimating lens 2a, which is a plane wave converter, and the plane wave is incident on the etalon 3b obliquely. As a result, a fluctuation equivalent to the fluctuation of the light intensity given according to the FSR on the emission surface side after passing through the etalon 3b can be obtained on the incident surface side. The light intensity is monitored by arranging the light intensity light receiving unit 6, and a current is passed through the wavelength tunable laser 1 so as to compensate for the fluctuation of the light intensity generated after passing through the etalon 3b. Laser beam scanning is possible.

  When a semiconductor laser is used as the wavelength tunable laser 1 and the wavelength is changed by changing the temperature of the semiconductor laser or the like, the optical output power of the semiconductor laser varies as the wavelength changes, but the beam scanning apparatus according to the second embodiment Since the light intensity can be monitored by the light intensity light receiving unit 6, the light output is kept constant.

  As described above, in the beam scanning apparatus according to the second embodiment of the present invention, the light intensity light receiving unit 6 is disposed on the incident surface side of the etalon 3b on which the partial reflection coating is applied, and the light intensity is monitored. To compensate for fluctuations. Thus, in addition to the operational effect of the beam scanning apparatus according to the first embodiment, there is an operational effect that beam scanning with a constant light output becomes possible.

  Further, in the optical wireless communication system including the beam scanning device according to the second embodiment of the present invention, the receiving unit 5 receives a single-peak optical signal scanned with a constant optical output while suppressing secondary diffracted light. I try to receive it. Thereby, in addition to the operation and effect of the optical wireless communication system according to the first embodiment, there is an operation and effect that optical space communication with a constant light output and excellent stability can be performed.

  In the beam scanning devices according to the first and second embodiments of the present invention, numerical values such as the wavelength of light, the reflectance and dimensions of the etalon, and the diameter and interval of the beams are merely examples, and are not limited thereto.

  In the beam scanning apparatus according to the first and second embodiments of the present invention, the semiconductor laser as the wavelength tunable laser 1, the collimator lens 2a as the plane wave converter 2, the etalons 3a and 3b as the light intensity distribution converter 3, the phase The configuration of the convex lens 4a or the like as the wavefront conversion unit 4 is not limited to this, and a configuration that exhibits the same effect can be applied.

  Further, as described above, the beam scanning apparatus according to the first and second embodiments of the present invention is suitable for application to an optical wireless communication system, but is not limited to this. For example, a laser printer, a barcode reader, etc. In short, in any system where secondary diffracted light is suppressed and it is desired to use unimodal light scanned with a constant light output Has the same effect.

  1 tunable laser, 2 plane wave converter, 2a collimating lens, 3 light intensity distribution converter, 3a, 3b etalon, 4 phase wavefront converter, 4a convex lens, 5 receiver, 6 light intensity receiver.

Claims (5)

A variable wavelength light source that outputs light by changing the wavelength;
A plane wave converter for converting light output from the wavelength tunable light source into a plane wave;
A light intensity distribution converter that multi-reflects the light converted into a plane wave by the plane wave converter and converts the adjacent beams of the multi-reflected light into a unimodal light intensity distribution according to the wavelength; and
By converting the phase wavefront of the light converted into a unimodal light intensity distribution according to the wavelength by the light intensity distribution conversion unit into a spherical wave, according to the unimodal light intensity distribution according to this wavelength A phase wavefront converter for changing the light exit direction;
A beam scanning device comprising:   The light intensity distribution conversion unit multiplex-reflects the light converted into a plane wave by the plane wave conversion unit inside the etalon, and adjacent beams of the multiple reflection light overlap each other, thereby unimodal light intensity distribution according to the wavelength The beam scanning device according to claim 1, wherein the beam scanning device is converted into: A light intensity receiving unit that receives light from the light intensity distribution conversion unit and monitors fluctuations in light intensity, and
3. The beam scanning apparatus according to claim 1, wherein the beam is scanned with a constant light output based on a monitoring result of the light intensity light receiving unit. The beam scanning apparatus according to any one of claims 1 to 3,
A receiver for receiving an optical signal scanned by the beam scanning device;
An optical wireless communication system comprising: A wavelength variable step for changing the wavelength and outputting light,
A plane wave conversion step of converting the light output in the wavelength variable step into a plane wave;
A light intensity distribution conversion step of multiply-reflecting the light converted into the plane wave in the plane wave conversion step, and converting the light beams adjacent to the multiple reflection light into a unimodal light intensity distribution according to the wavelength; and
By converting the phase wavefront of the light converted into a unimodal light intensity distribution according to the wavelength in the light intensity distribution conversion step into a spherical wave, according to the unimodal light intensity distribution according to this wavelength A phase wavefront conversion step for changing the light emission direction;
A beam scanning method comprising:

Images