JP3146653B2 - Optical information processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information processing apparatus using coherent light or an optical information processing apparatus used in an optical applied measurement control field.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing an optical information processing apparatus using a semiconductor laser. This optical information processing apparatus records and reproduces information on an optical disk. 830n or less
Recording and reproduction for light having a wavelength of m will be described in detail with reference to the drawings. Light P emitted from semiconductor laser 21
After passing through a lens 40 and a beam splitter 41, the light 1 is irradiated on an optical disk 43 as a medium by a lens 42. Recording is performed on the medium with the output of the semiconductor laser of 30 mW. Reading is performed at an output of 2 mW. At this time, after irradiating the medium through the same optical path as writing, the reflected light is conversely collimated by the lens 42, reflected by the beam splitter 41, and condensed by the lens 44,
The signal is read by the detector 44 made of Si. The numerical aperture (NA) of the lens 42 was 0.6, and the focused spot size was 1.1 μm.

On the other hand, there is a configuration in which a Fresnel lens is used instead of a normal lens. FIG. 7 shows light collection by a Fresnel lens. The Fresnel lens 34 utilizes diffraction, and as shown in FIG.
It can be close to 00%. The thickness of the film on which the pattern is formed can be as thin as 1.7 μm.

[0004]

In the configuration using the optical information processing apparatus as described above, the output of the semiconductor laser differs between the reading and the writing, and the wavelength varies due to the difference in the driving current. In addition, individual differences between semiconductor lasers are large, and wavelength variations of about ± 10 nm have occurred. For this reason, there is a problem that the focal position changes when the light is condensed by the Fresnel lens. This will be described.
Although the wavelength of the semiconductor laser is 830 nm, the wavelength of the laser is 5 n
The focal position changed by 2 μm just by shifting by m, causing aberration.

Therefore, the present invention uses a compact laser light source and a Fresnel lens which can obtain a stable oscillation wavelength even when the environmental temperature changes as well as being not influenced by current changes and individual differences. The purpose is to achieve the compounding and compounding.

[0006]

[0007]

According to the present invention, there is provided an optical information processing apparatus comprising: a semiconductor laser; a substrate on which an optical waveguide, a grating and an optical modulator are formed; a Fresnel lens;
Having a beam splitter, light from the semiconductor laser enters the optical waveguide, part of the light is returned to the semiconductor laser by the grating, and light emitted from the optical waveguide passes through the lens and the beam splitter. Then, the medium is irradiated with light.

[0008]

The optical information processing apparatus of the present invention is small, lightweight,
A low-cost Fresnel lens is used, and a laser light source having a constant oscillation wavelength is used to prevent chromatic aberration. Due to the feedback from the grating formed on the optical waveguide, a constant oscillation wavelength is always obtained for the wavelength of the semiconductor laser even when the temperature and the current change. Also, there is no individual difference in oscillation wavelength, and the same wavelength can be obtained with all laser light sources. This will be described in detail. When the driving current of the semiconductor laser changes, the refractive index of the material of the semiconductor laser changes, and the oscillation wavelength tends to change accordingly. However, since the feedback wavelength from the grating is constant, oscillation occurs at that wavelength. In other words, the oscillation wavelength λ is λ = 2N, where Λ is the period of the grating and N is the refractive index of the optical waveguide. Here, since the period Λ and the refractive index N are constant, the oscillation wavelength λ is also constant. Therefore, even if the current changes between reading and writing, the focal position of the Fresnel lens does not change, and no aberration occurs. Also, there is no delay for switching.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical information processing apparatus according to the present invention will be described. FIG. 1 shows the configuration of the optical information processing apparatus. In this embodiment, LiTaO ₃ was used as the substrate. The light P1 emitted from the semiconductor laser 21 enters the optical waveguide 2 formed on the substrate 22. Light P1 incident propagates through the optical waveguide 2 in TM ₀₀ mode which is the lowest order mode, is partially fed back to the semiconductor laser by the grating. Thereby, the wavelength-stabilized laser light P1 is emitted from the optical waveguide 2, and
Used as a laser beam. This beam is collimated by a Fresnel lens 35, passes through a beam splitter 41, and is irradiated by a Fresnel lens 36 on an optical disc 43, which is a recording medium. Conversely, the reflected light is collimated by the Fresnel lens 36, reflected by the beam splitter 41, condensed by the Fresnel lens 37, and then read by the Si detector 45.
The material of the Fresnel lens is SF8 (refractive index 1.68),
The numerical aperture (NA) is 0.6. Further, the size of the condensed light spot was 1.1 μm. The beam was stable, so that a high-density optical information processing device could be realized. The size of the laser light source is compact within 4 mm square. In addition, the wavelength of the return light from the optical disk surface does not change, and the relative noise intensity (RIN) is -140 dB.
/ Hz was good.

Next, a method for manufacturing a Fresnel lens will be described. Drawing is performed by using an electron beam exposure apparatus on a resist applied on glass as a master to form a pattern, and then transferred to glass by dry etching. Replicas are taken from the master thus produced and mass-produced. Therefore, the cost can be significantly reduced.

The configuration of the laser light source used here will be described with reference to the drawings. FIG. 2 shows a configuration diagram of the laser light source. The laser light source basically includes a Si submount 20, a semiconductor laser 21, and a substrate 22 on which an optical waveguide is formed. A grating 3 of Ta ₂ O ₅ is formed on the optical waveguide 2 of the substrate 22. The light P1 emitted from the semiconductor laser 21 fixed to the Si mount 20 is directly introduced into the optical waveguide 2. This is the semiconductor laser 21
This is because the positions of the active layer and the optical waveguide 2 are adjusted to the same height with respect to the Si submount.

The light P1 entering the optical waveguide 2 is partially reflected by the grating and is returned to the semiconductor laser. Therefore, the semiconductor laser oscillates at a wavelength determined by the period of the grating and the refractive index of the substrate.

The optical waveguide 2 was manufactured by proton exchange in pyrophosphoric acid. Hereinafter, a method of manufacturing an optical waveguide and a grating on a substrate will be described with reference to FIG. FIG.
20A, Ta is sputter-deposited on the LiTaO ₃ substrate 1a to a thickness of 20 nm, and then the Ta is patterned using a normal photo process and dry etching. To form the incident taper, a part of the LiTaO ₃ substrate on which the pattern of Ta was formed was immersed in pyrophosphoric acid at 260 ° C. for 30 minutes, and proton exchange was performed. Form a proton exchange layer. Then at a temperature of 420 ° C. 20
Heat-treat for minutes. Thereby, an incident taper portion having a thickness of 5 μm is formed. This greatly improves the coupling efficiency with the semiconductor laser. In order to further form the optical waveguide 2, proton exchange was performed at 260 ° C. for 12 minutes in pyrophosphoric acid,
After a proton exchange layer having a thickness of 0.5 μm is formed immediately below the slit, heat treatment is performed at 420 ° C. for 1 minute. Next, FIG.
In forming at 30nm thick a Ta ₂ O ₅ 6 as a membrane. Next, in FIG. 4C, Ta ₂ O _{5 is formed} by using photolithography and dry etching.
Is formed. This is grating 3
Becomes The grating period is 1.9 μm, and 10 times the primary period of 0.19 μm is used. As described above, the cycle can be used if it is an integral multiple of the primary cycle. Thereafter, SiO ₂ 5 serving as a protective film is formed to a thickness of 2 μm by sputtering. By adjusting this thickness, the active layer of the semiconductor laser is made to have the same height as the active layer. Finally, an incoming / outgoing surface is formed by polishing. The thickness of the optical waveguide 2 is 1.9 μm and the length is 3 mm. The reflectivity of the grating is 10%. With this amount of reflection, the wavelength can be sufficiently stabilized.

Next, bonding is performed on the Si submount 20 having a length of 4 mm with the active layer side of the semiconductor laser 21 facing down. While attaching the lead wire and illuminating the semiconductor laser,
The substrate 22 on which the optical waveguide is formed is bonded at a position where the light P1 emitted from the optical waveguide 2 is maximized. Through the above steps, a compact laser light source was manufactured.

FIG. 4 shows the current dependence of the wavelength of the manufactured laser light source. Conventionally, for a 40 mA change in current,
Although the wavelength changed by as much as 5 nm, the laser light source of the present invention showed no wavelength change and was very stable. As a result, the optical information processing device stably operated without a change in the focal position of the Fresnel lens. In addition, because the Fresnel lens is used, the size and weight can be reduced.

Although three Fresnel lenses are used in this embodiment, one Fresnel lens can be used. Further, the present invention can be applied to other configurations using a Fresnel lens.

A description will be given of a second embodiment of the optical information processing apparatus according to the present invention. First, the configuration of the second embodiment of the optical information processing apparatus according to the present invention is the same as that of the first embodiment. In this embodiment, a proton exchange optical waveguide manufactured by using proton exchange in a LiNbO ₃ substrate and a modulation electrode are used as an optical waveguide for a laser light source. The light P1 emitted from the semiconductor laser 21 enters the optical waveguide 2 formed on the substrate 22. Light P1 incident propagates through the optical waveguide 2 in TM ₀₀ mode which is the lowest order mode, is partially fed back to the semiconductor laser by the grating. Thus, the wavelength-stabilized laser light P1 is emitted from the optical waveguide 2 and used as a laser beam. This beam is collimated by a Fresnel lens 35, passes through a beam splitter 41, and is irradiated by a Fresnel lens 36 onto an optical disc 43, which is a recording medium. Conversely, the reflected light is collimated by the Fresnel lens 36, reflected by the beam splitter 41, condensed by the Fresnel lens 37, and then read by the Si detector 45. The material of the Fresnel lens is plastic (refractive index 1.48), and the numerical aperture (NA) is 0.6. Further, the size of the condensed light spot was 1.1 μm. The beam was stable, so that a high-density optical information processing device could be realized.

FIG. 5 shows the configuration of the light modulator. In FIG. 5, reference numeral 22 denotes a + Z plate (the + side of the substrate cut out perpendicular to the Z axis).
LiNbO ₃ substrate, 2 formed optical waveguide, 3 formed by grating made of Ta ₂ O ₅ , 10 incident portion of light P1, 12 exit portion of light P1, 15 electrode of Al formed on optical waveguide It is. LiNbO ₃ has a large electro-optic effect and can change the refractive index by an electric field. By forming the optical waveguide in the vicinity of the cutoff thickness, switching, that is, modulation can be performed. That is, by changing the voltage applied to the optical waveguide, the refractive index is reduced, and the optical waveguide is cut off, so that the beam cannot be propagated. When a + voltage is applied to the optical waveguide and the side of the optical waveguide is dropped to the ground, lines of electric force run and an electric field is applied. As a result, the refractive index of the optical waveguide is reduced, and the guided light escapes to the substrate as a radiation mode and does not exit from the emission portion, thereby enabling switching. In FIG. 5, the electrode width is 4 μm, the electrode interval is 5 μm, and the thickness is 200 nm. Without SiO _{2 serving as a} protective film, the electrode 15 made of metal and the optical waveguide 2 come into direct contact, and the propagation loss increases. The length of this element is 10 mm.

In FIG. 5, a semiconductor laser beam (wavelength
840 nm) is guided from the incident part 10 to a single mode.
And propagated back by the grating 3 to the semiconductor laser.
The user was wavelength stabilized. A voltage of 10 V is applied to the electrode 15.
The refractive index to 10 ^-FourLower and cut the beam
I was able to At this time, the electric field is 2 × 10⁶V / m. Next
A pulse-like modulation voltage having a peak voltage of 10 V is applied to this electrode.
(Repeated 200 ps). 500MHz frequency
The output light also responded to the modulation voltage. this
Output is obtained by applying a modulation voltage to the electrodes
be able to. Thus, even during modulation, the semiconductor laser
The recording / reproduction is stable without changing the oscillation wavelength
ing.

In this embodiment, LiNbO ₃ having a large electro-optical effect is used as the substrate, but other ferroelectric materials such as LiTaO ₃ are also effective. In multimode propagation with respect to light, the output is unstable and impractical, and a single mode is effective.

The light incident method may be a structure via a lens other than the direct coupling. Further, although Si is used as the submount, any other material having good thermal conductivity such as Cu or C may be used. In the embodiment, LiNbO ₃ and LiTaO ₃ are used as crystals, but ferroelectrics such as KNbO ₃ and KTP, MN
It is also applicable to organic materials such as A and glass materials.

[0022]

As described above, according to the optical information processing apparatus of the present invention, a compact, lightweight and inexpensive optical information apparatus is constructed by using a Fresnel lens as a lens and a laser light source having a stable wavelength as a laser. can do. Further, according to the optical information processing apparatus of the present invention, the laser output can be modulated by controlling the voltage applied to the optical waveguide. Also, there is no change in the focal position during modulation.

Further, by using a laser light source having a stable wavelength by the optical information processing apparatus of the present invention, a spot free from aberration can be easily obtained stably, and it is strong against return light from a medium. The effect is extremely large.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical information processing apparatus according to a first embodiment of the present invention;

FIG. 2 is a configuration diagram of a laser light source used in the optical information processing apparatus of the present invention.

FIG. 3 is a manufacturing process diagram of a laser light source used in the optical information processing apparatus of the present invention.

FIG. 4 is a characteristic diagram showing a relationship between a driving current of a semiconductor laser and an oscillation wavelength.

FIG. 5 is a configuration diagram of an optical modulator used in an optical information processing device according to a second embodiment of the present invention.

FIG. 6 is a configuration diagram of a conventional optical information processing apparatus.

FIG. 7 is a sectional view of a Fresnel lens.

[Explanation of symbols]

 Reference Signs List 2 optical waveguide 3 grating 4 incident taper 15 electrode 20 Si submount 21 semiconductor laser 22 substrate on which optical waveguide is formed P1 light 35, 36, 37 Fresnel lens 40, 42, 44 lens 41 beam splitter

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-62982 (JP, A) JP-A-59-216116 (JP, A) JP-A-4-106990 (JP, A) JP-A-1- 268181 (JP, A) JP-A-64-46995 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (3)

(57) [Claims] A semiconductor laser, a substrate on which an optical waveguide, a grating and an optical modulator are formed, a Fresnel lens, and a beam splitter, wherein light from the semiconductor laser enters the optical waveguide; An optical information processing apparatus, wherein a part of the optical information is returned to the semiconductor laser by the grating, and the medium is irradiated with light emitted from the optical waveguide after passing through the lens and the beam splitter. 2. An optical information processing apparatus according to claim 1, characterized in that a structure for applying a modulation voltage to the electrodes as the light modulation unit. 3. A process according to claim 1, characterized in that the incident taper portion on the side against the semiconductor laser of the optical waveguide is formed
Serial mounting of the optical information processing apparatus.