JP2738759B2 - Light head - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical head used for an optical disk device or the like.

[Conventional technology]

For information on integrated optical systems for reading information from and reading and writing information from conventional optical information media, see ANRITSU NE
WS, Vol. 7, No. 36, 1988.

[Problems to be solved by the past]

In the conventional example (ANRITSU NEWS, Vol. 7, No. 36, 1988), a semiconductor laser is used as a light source, and reflected light from an optical information medium (here, a magneto-optical disk) is converted into three light beams. The light was propagated through the waveguide using a caching grating coupler (hereinafter GC).

In this configuration, the semiconductor laser changes in environmental temperature,
Focusing when wavelength fluctuates due to return light
The GC cannot convert light into light that propagates guided light, leaving a problem that the optical characteristics of the element deteriorate.

An object of the present invention is to realize, with a simple manufacturing process, an optical configuration that always maintains a predetermined optical performance stably even when the wavelength of a semiconductor laser fluctuates, and optimizes light use efficiency. It is an object of the present invention to provide a method for performing the above.

[Means for solving the problem]

In order to achieve the above object, the diffraction grating (hereinafter referred to as CCG)
Was provided in contact with the waveguide.

Further, the thickness of the GC and the thickness of the CCG are matched.

Further, the line-to-space ratio of the GC is set to a value other than 1: 1.

In the above-mentioned GC, the width of the space is twice or more the width of the line (the line-to-space ratio is 1: 2 or more).

Alternatively, the line width is twice or more the space (the line-to-space ratio is 2 or more: 1).

[Action]

The GC is provided in contact with the waveguide. Here, by providing the CCG in contact with the waveguide, the pattern surfaces of the GC and the CCG can be made the same. Thereby, in the patterning process, the positioning accuracy between the GC and the CCG is improved, and the positioning can be performed by a simple operation, so that the manufacturing process can be simplified.

Further, by making the thicknesses of the GC and the CCG the same, the GC and the CCG can be loaded in the same process. This allows
This simplifies the manufacturing process and reduces damage to the device caused in the manufacturing process, so that a highly reliable device can be obtained.

In addition, by setting the GC line-to-space ratio to other than 1: 1, the GC
Excess radiation loss coefficient (Optical integrated circuit: Nishihara, Haruna, Suhara: Corona: 1985, defined in Section 93.)
And a high light use efficiency is obtained.

In addition, by setting the width of the space to be twice or more the line width (the line-to-space ratio is 1: 2 or more), a region having high light use efficiency is used.

Similarly, by setting the line width to be at least twice the space width (the line-to-space ratio is at least 2: 1), a region having particularly high light use efficiency is used.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to the drawings. 1 is an overhead view of the present embodiment, FIG. 2 is a sectional view of FIG. 1, and FIG. 3 is a partially enlarged view of FIG.

First, an optical basic operation state of the present embodiment will be described with reference to FIG. 1 and FIG.

Light emitted from the semiconductor laser 5 is converted into parallel light by the lens 3a. Part of this light passes through the substrate 1 and the lens
The light is condensed by 3b and forms a focal point on the optical information medium 20. An information bit 21 is formed on the optical information medium 20.
With this bit, the plane of polarization of the light reflected by the optical information medium 20 changes.

The reflected light is converted into parallel light by the lens 3b, and part of the parallel light is diffracted by the CCGs 12a, 12b, and 12c. The diffracted light is reflected by the dielectric multilayer reflective film 7a and totally reflected at the bottom surface of the substrate. The light diffracted by the CCG 12a enters the GC 11a, and
Light diffracted by the CG 12b enters the GC 11b, and light diffracted by the CCG 12c enters the GC 11c. Light incident on each GC is coupled to light propagating through the waveguide 2 by the action of diffraction of the GC. (Here, converting light inside the waveguide to light outside the waveguide and vice versa will be referred to as coupling.) The lenses 10a and 10b combine the light coupled by the GC 11a. The light is incident on both photodetectors while forming a focal point near the boundary between the photodetectors 6a and 6b installed adjacent to each other. Also,
The lenses 10c and 10d pass the light combined by the GC 11b to the photodetector 6
Inject into c. The lenses 10e and 10f allow the light combined by the GC 11c to be incident on both photodetectors while forming a focal point near the boundary between the photodetectors 6d and 6e provided adjacent to each other. The light detected by the photodetector is sent to a signal processing device, which reads out information bits 21 on the optical information medium 20, detects a focus error amount, and detects a track error amount.

Here, when condensing the light combined by each of the GCs 11a, 11b, and 11c to the photodetectors 6a to 6e, the lenses 10a, 10b, and 10c
The drawings of the embodiments are illustrated as realizing the light collecting function by combining two convex lenses, such as 10d, 10e and 10f. By combining two or more waveguide-type convex lenses in this manner, a combined lens for a waveguide having a short combined focal length can be obtained, and the size of the substrate 1 can be reduced. As a result, the effect that the whole can be downsized can be obtained.

When such miniaturization is not always necessary, the functions of the lenses 10a and 10b shown here are constituted by a single waveguide lens. At this time, the optical configuration on the waveguide becomes simpler, and the process of manufacturing the optical system on the waveguide can be simplified.

Here, for each waveguide lens, Optical Integrated Circuit, Hiroshi Nishihara et al., Ohmsha, 1985, and Optical Integrated Circuit (Basic and Application), Japan Society of Applied Physics, Optical Society, Ed., Asakura Shoten 1988 ,It is described in.

The light collimated by the reflective lens 3b in the optical information medium 20 is
The situation of being diffracted by the CCGs 12a-12c and being coupled to the guided light by the GCs 11a-11c is shown in more detail in FIG. FIG. 3 is a part of a cross-sectional view of the substrate 1 of FIG. 1, and is a cross-sectional view including a CCG 12b and a GC 11b.

In this embodiment, since the semiconductor laser 5 is used as a light source as shown in FIG. 1, the oscillation wavelength of the semiconductor laser is actually affected by the ambient temperature, the intensity of the current injected into the semiconductor laser, return light, and other effects. It may change during operation. In such a case, there is a problem that the light cannot be efficiently coupled in the GC due to a change in the light coupling condition in the GC. However, by diffracting the light by the CCG before the light is incident on the GC, the light can always be coupled in the GC with high efficiency. This means
This is the same as described in Japanese Patent Application No. 1-66196.

Such a wavelength variation countermeasure using GC and CCG is effective. However, it cannot be denied that there is a complication that a CCG needs to be separately provided. Therefore, one technical issue is how to easily produce CCG.

As a simple method for producing GC and CCG, as shown in FIGS. 1 and 2, it is conceivable to form both on the same surface. As described in Hiroshi Nishihara et al., Optical Integrated Circuits, Ohmsha, Ltd., 1985, GC and CCG are manufactured using the same method as in the semiconductor manufacturing process. When GC and CCG are on the same surface, both can be produced simultaneously. Therefore, the production of the grating and the CCG becomes easy.

Further, the lenses 10a to 10c and 11a to 11c can be provided on the same plane as the GC and the diffraction grating. By doing so, many parts including the lens can be manufactured at the same time, and the manufacture of the element becomes easy.

As an example of a process for simultaneously producing the grating and the CCG, the process shown in FIG. 4 can be considered. That is, in the exposure step shown in FIG. 4A), the waveguide 2 is provided on the substrate 1, and further, the loading layer 900, the conductive layer 901 such as metal or ITO, and the resist layer 902 are provided. However, the loading layer 900 is finally processed to become CCG or grating. In addition, the conductive layer 901 is not always necessary especially when a charge gap (charge of the substrate) does not occur, such as a reduction exposure projection method and a contact exposure method. Lens layer 902 with electron beam
In some cases, it is necessary to directly draw a drawing pattern on the substrate, and the prevention of charge gap is performed.

In the development step of FIG. 4B), the pattern written on the resist layer 902 is developed. A necessary portion of the resist is removed.

In the etching step of FIG. 4C), etching is performed using the resist 902 as a mask, and the conductive layer 901 and the loading layer 9 are etched.
Etch 00.

In the unnecessary part removing step of FIG. 4D), the resist layer 902 and the conductive layer 901 are removed.

Through the above steps, CCG and GC can be simultaneously manufactured, and the manufacturing steps can be simplified.

Simultaneous production of CCG and GC, an example of which is shown in FIG. 4, has the feature that the thickness of CCG and GC is the same, as well as the simplification of the process.

The thickness of the GC is determined by the radiation loss coefficient (Optical Integrated Circuit, written by Hiroshi Nishihara, Ohmsha, 1985,
93). The thickness of the CCG is determined so that an appropriate diffraction efficiency can be obtained. Each optimized thickness may not necessarily match. Conversely, if the thicknesses of the two are matched, the light use efficiency may not always be optimal.

The thickness of the GC with good coupling efficiency is the same as that of CCG with good diffraction efficiency.
Is often thicker than the thickness of By making the thickness of both the same, the GC may be thicker than the optimum thickness. Also, the CCG may be thinner than optimal. In GC, the radiation loss coefficient (defined by Hiroshi Nishihara et al., Optical Integrated Circuits, Ohmsha, 1985, p. 93) may be too large. As a result, the binding efficiency in GC decreases. In GC, the diffraction efficiency may not be sufficient because there is not enough thickness.

One means for resolving such a contradiction will be disclosed hereinafter. In the conventional GC, as shown in FIG. 5 (a), the ratio of the grid line (the loaded portion) to the space (the unloaded portion) was 1: 1 or a value close thereto. On the other hand, as shown in FIG. 5B, consider that the ratio of line to space is not 1: 1. FIG. 6 shows an example of the calculation results of the coupling efficiency in GC using the ratio of line and pitch (sum of line and space) as a parameter. However, as the calculation conditions, the case where the thickness of the GC is thicker than the optimum value and the case where the radiation loss coefficient is too large is selected.

As shown in FIG. 6, since the radiation loss coefficient is too large, the coupling efficiency is low when the line / pitch ratio in the conventional GC is around 0.5. However, when the line / pitch ratio leaves 0.5 and becomes 0.33 or less, or 0.66 or more,
The radiation loss coefficient decreases and the coupling efficiency increases. In particular, the range where this effect is large is, as described above, the line /
This is the case when the pitch ratio is 0.33 or less, or 0.66 or more.
This is because the line width is less than half the space width, or
The line width is equal to or more than twice the space width.

By adjusting the line / space ratio as described above,
While simplifying the process, the coupling efficiency in GC can be improved, and the light use efficiency can be improved.

〔The invention's effect〕

According to the present invention, since the pattern surfaces of the GC and the CCG can be arranged on the same waveguide surface, in the patterning process, the positioning accuracy between the GC and the CCG is improved, and the positioning can be performed by a simple operation. Can be simplified.

[Brief description of the drawings]

1 is a perspective view showing an embodiment of the present invention, FIG. 2 is a longitudinal sectional view of FIG. 1, FIG. 3 is a partially enlarged view of FIG. 2, and FIG.
And CCG, or even a process diagram of lens production,
FIG. 5 is an enlarged sectional view of the GC, and FIG.
FIG. 4 is an explanatory diagram of a relationship between coupling efficiencies in GC. DESCRIPTION OF SYMBOLS 1 ... board | substrate, 2 ... waveguide, 3a ... lens, 3b ... lens, 5 ... semiconductor laser, 6a-6e ... photodetector, 7a ...
Dielectric multilayer reflective film, 10a to 10f ... Lens, 11a, 11b, 11c
… Grating coupling, 12a, 12b, 12c… Diffraction grating, 20… Optical information medium, 21… Information bit, 900… Loading layer, 901… Conductive layer, 902… Resist layer

Claims (1)

(57) [Claims] 1. A planar waveguide for transmitting light emitted from a light source and reflected from a recording medium, a grating coupler for converting the reflected light to light propagating through the planar waveguide, and the reflected light. An optical head comprising: a diffraction grating that diffracts light propagating outside the planar waveguide; wherein the grating coupler and the diffraction grating are provided in contact with a same plane above the waveguide, and the diffraction grating is provided. And the grating coupler is provided at substantially the same thickness above the planar waveguide, and the space width of the grating coupler is at least twice the line width or the line width is at least twice the space width. Light head.