Waveguide type optical detection apparatus

A waveguide type optical detection apparatus which is provided on an optical integrated circuit that has a waveguide for transmitting a light from point to point through the waveguide, one or more sets of two adjacent photodetectors provided on the waveguide, and one or more light-insensitive areas existing between the two adjacent photodetectors of each set. The waveguide type optical detection apparatus includes a waveguide focusing part and one or more reflection parts, the waveguide focusing part being provided on the waveguide for allowing a light beam passing through the waveguide to be focused on each of the two adjacent photodetectors of each set, and the reflection parts provided adjacent to each of the light-insensitive areas for reflecting each of light beams sent from the waveguide focusing means forward each of the two adjacent photodetectors of each set so that the light beams are received by the photodetectors. The waveguide type optical detection apparatus can be applied to a pickup for an optical disk and a photodetector array for an optical spectrum analyzer.

BACKGROUND OF THE INVENTION 
The present invention generally relates to optical detection apparatus, and 
more particularly to a waveguide type optical detection apparatus which is 
applied to several optical integrated circuit units such as an optical 
disk pickup, an optical spectrum analyzer photodetector array or the like. 
Generally, an optical waveguide, or a waveguide in which a 
light-transmitting material is used for transmitting information in the 
form of electric signals from point to point through the material, is 
commonly used for detecting a focus position in an optical disk pickup, 
for positioning a movable object, and for other purposes. A conventional 
waveguide optical detection apparatus, as disclosed, for example, in 
Japanese Published Patent Application No. 63-71946, provides an example of 
an optical waveguide apparatus which is built for detecting a focus 
position. On such an optical waveguide, a grating coupler is provided for 
transmitting in the air a light beam from a light source onto an optical 
disk and introducing a light reflected on the surface of the optical disk 
back to the waveguide. Also provided on the optical waveguide are a set of 
two adjacent photodetectors which are located on one end surface of the 
waveguide to receive a light beam sent from the grating coupler. In the 
case of such a conventional apparatus, the accuracy of the detection 
greatly depends on the width of the area between the adjacent 
photodetectors, and on the distance from the photodetectors to the grating 
coupler. To achieve better accuracy for the optical detection apparatus, 
it is necessary to either make the photodetector-to-coupler distance 
longer, or make the width of the area between the adjacent photodetectors 
narrower. The extent of the above described distance, however, is limited 
due to the design and overall size of the optical detection apparatus, and 
therefore it is not possible to have a distance which exceeds a prescribed 
maximum distance. The above described width is also limited due to the 
physical restriction inherent in developing a closely-aligned 
photodetector design on the optical waveguide. Therefore, there still 
remains the need to develop a new improved waveguide type optical 
detection apparatus which offers better detection accuracy. 
In addition, a conventional waveguide optical apparatus which is adapted to 
an optical disk pickup unit is disclosed, for example, in an engineering 
research report entitled "AN INTEGRATED-OPTIC DISK PICKUP DEVICE", 
OQE85-72, pp. 39-46, Shingaku Giho, Vol. 85, No. 136, issued on Sept. 17, 
1985 by the Institute of Electronics and Communication Engineers of Japan 
(IECEJ). Such a waveguide optical apparatus provides a tiny, ligthtweight 
optical disk pickup unit which can be produced for experimental use. 
However, in the conventional waveguide optical detection apparatus 
disclosed by this published article, there also still remains some 
problems which must first be resolved before such a pickup unit can be 
manufactured for practical use. Hence, in recent years, it has been 
desired that further improvements be developed for an optical disk pickup 
unit and relevant units which can be manufactured for practical use. 
First, referring to FIG. 1, a description will be given of the 
above-discussed conventional waveguide optical apparatus which is applied 
to an optical integrated circuit for an optical disk pickup head. In this 
conventional apparatus, a silicon substrate 31, a buffer layer 32 and an 
optical waveguide layer 33 are laminated together into a thin-film 
integrated circuit structure. A semiconductor laser diode 34 of a light 
source is provided on an end surface of the silicon layer 33 for 
generating a laser beam, and the beam from the light source 34 is 
transmitted through the waveguide 33. The light beam traveling through the 
waveguide 33 passes through a grating 35 and a grating coupler 36, and is 
diffracted so that a converging light is propagated in the air until it 
reaches a surface of an optical disk 37. The light is then reflected on 
the surface of the optical disk 37 back to the grating coupler 36 and the 
light is again introduced into the waveguide. Then the light is diffracted 
by the grating 35 so as to split into two separate light beams, which are 
received by a set of two adjacent first photodetectors 38a, 38b, and a set 
of two adjacent second photodetectors 38c, 38d, respectively. 
Electric signals outputted from these photodetectors when exposed to light 
are picked up through a logic circuit connected to suitable electrodes of 
the photodetectors, as shown in FIG. 1. These outputs include a readout 
signal S, a focusing error signal Fo and a tracking error signal Tr. The 
signals thus obtained from the photodetectors are expressed as follows: 
EQU Fo=(S.sub.38a +S.sub.38d)-(S.sub.38b +S.sub.38c) 
EQU Tr=(S.sub.38c +S.sub.38d)-(S.sub.38a +S.sub.38b) 
EQU S=S.sub.38a +S.sub.38b +S.sub.38c +S.sub.38d 
In these formulas, S.sub.38a, S.sub.38b, S.sub.38c and S.sub.38d are output 
signals of the photodetectors 38a, 38b, 38c and 38d, respectively. 
Concerning the focusing error signal Fo, when the optical disk 37 moves 
away from the pickup unit, the value of the Fo becomes negative, or the Fo 
is smaller than 0, and on the contrary, when the optical disk 37 
approaches the focus position of the pickup unit, the value of the Fo 
becomes positive, or the Fo is greater than 0. Therefore, this allows for 
appropriate detection of the focus position by using the conventional 
apparatus. 
However, the conventional waveguide optical apparatus as shown in FIG. 1 
has light-insensitive areas between the adjacent photodetectors 38a, 38b 
and between the adjacent photodetectors 38c, 38d. In the light-insensitive 
areas, light beams being sent from the grating 35 cannot be received by 
the photodetectors because the light-insensitive areas are located where 
no photodetection function is provided. Usually, the width of the 
light-insensitive area between the adjacent photodetectors ranges from 
approximately 5 to 10 microns, and it is practically impossible to make 
this light-insensitive area width negligible or zero. 
For example, when detection of the focusing error signal is carried out 
with the light from the light source 34 being focused exactly on the 
optical disk 37, the light beams are thrown on the light-insensitive area 
between the photodetectors 38a and 38b as well as on the light-insensitive 
area between the photodetectors 38c and 38d. If the beam diameter is 
smaller than the light-insensitive area width, with the optical disk 
deviating from the focus position, the value of the Fo becomes zero and 
the focusing error signal is insensitive. And, if the beam diameter 
becomes almost at the same level as the light-insensitive area width, such 
"light-insensitive" condition of the focusing error signal is eliminated. 
However, when the optical disk deviates from the focusing position, the 
amount of change in the focusing error signal becomes excessively small, 
which worsens the sensitivity of the optical detection apparatus. 
Since the light-insensitive areas cannot be made narrower than the minimum 
level, an immediate solution to the problem is to enlarge the distance 
from the grating 35 to the photodetectors 38. However, such a solution 
requires the development of a larger optical disk pickup design, which is 
inconsistent with the desired development of a tiny, lightweight 
integrated optic unit. 
SUMMARY OF THE INVENTION 
Accordingly, it is a general object of the present invention to provide a 
novel and useful waveguide type optical detection apparatus in which the 
above described problems are eliminated. 
Another and more specific object of the present invention is to provide a 
waveguide type optical detection apparatus in which small reflector parts 
are provided at positions between adjacent photodetectors on a waveguide 
to substantially eliminate the problem of the above-described 
light-insensitive areas between the adjacent photodetectors. According to 
the present invention, it is possible to improve the sensitivity of a 
optical disk pickup or an optical RF spectrum analyzer, to which the 
waveguide type optical detection apparatus is applied, yet still provide 
the advantages of a tiny, lightweight apparatus. This is possible as light 
beams are reflected on the small reflector parts and are transmitted to 
the photodetectors, allowing the beams traveling toward the 
light-insensitive areas to be properly received by the photodetectors. 
Still another object of the present invention is to provide a waveguide 
type optical detection apparatus which allows the forming of the waveguide 
reflector part and the small reflector parts at the same time in the same 
manufacturing process. According to the present invention, it is possible 
to reduce the number of processes required for manufacturing the waveguide 
type optical detection apparatus. In addition, it is possible to improve 
the quality and accuracy of the thus formed waveguide type optical 
detection apparatus, which promotes reduction of quality variations in 
finished products during volume production. 
A further object of the present invention is to provide a waveguide type 
optical detection apparatus which has a set of photodetectors with a 
distance therebetween provided on a waveguide and nevertheless offers 
highly accurate detection of a focus position. According to the present 
invention, it is possible to provide better accuracy for detection of a 
focus position than the conventional optical detection apparatus, while 
using the photodetectors placed with a distance therebetween. 
Other objects and further features of the present invention will be 
apparent from the following detailed description when read in conjunction 
with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 2, 3A and 3B, a description will be given as to the 
operating principle waveguide type optical detection apparatus according 
to the present invention. 
In an integrated optic circuit structure shown in FIG. 2, two photodetector 
parts 2a, 2b are provided adjacent to each other on an end portion of a 
waveguide 1. There is a light-insensitive area 3 between the adjacent 
photodetector parts 2a and 2b, and due to this light-insensitive area 3 a 
light beam being aimed at the light-insensitive area 3 is not sensed by 
the two photodetector parts 2a and 2b. To avoid this, a small reflector 
part 4 having two equally slanting reflection surfaces is provided to 
allow the light beam aimed at the light-insensitive area 3 to be reflected 
so that the reflected beam is directed to either the photodetector part 2a 
or the photodetector part 2b. In the waveguide type optical detection 
apparatus, light beams 10a, 10b among those being transmitted through the 
waveguide 1 are received directly by the photodetector part 2a, and light 
beams 10f, 10g are received directly by the photodetector part 2b as shown 
in FIG. 2. And, light beams 10c, 10d are reflected on an upper-side 
slanting surface of the reflector part 4 so that the reflected beams are 
appropriately received by the photodetector part 2a. Also, light beams 
10e, 10h are reflected on a lower-side slanting surface of the reflector 
part 4 so that they properly enter the photodetector part 2b. Therefore, 
it is possible for the waveguide type light detection apparatus provided 
with the reflector part 4, as shown in FIG. 2, to substantially eliminate 
the presence of a light-insensitive area between the adjacent 
photodetector parts 2a and 2b, enabling the optical detection covering the 
entire waveguide 1 including the areas where the photodetector parts are 
provided. 
FIG. 3A shows a representative cross section of the photodetector part 2 of 
the waveguide type optical detection apparatus shown in FIG. 2. In an 
optical integrated circuit of the waveguide type optical detection 
apparatus, a buffer layer 6 is deposited on a silicon substrate 5, and on 
the buffer layer 6 a waveguide 1 is further deposited. A refractive index 
of the waveguide 1 is higher than that of the buffer layer 6. The 
photodetector part 2 is formed in the silicon substrate 5, for example, by 
adding any p-type dopant to the n-type material of the silicon substrate 
to create a p-n junction structure. In an area of the photodetector part 
2, the buffer layer 6 is made excessively thin, and a light beam 
transmitted through the waveguide 1 reaches the photodetector part 2 
through such a thin buffer layer. Thus, the photodetector part 2 receives 
the light, and electric signals due to the photo-electric conversion 
effect of the photodetector part 2 are picked up from the electrodes 8 and 
9 which are connected to the photodetector part 2. 
FIG. 3B shows a representative cross section of the reflector part 4 of the 
waveguide type optical detection apparatus shown in FIG. 2. The reflector 
part 4 is formed, for example, by removing a corresponding region of the 
waveguide 1 from the optical integrated circuit board which is made up of 
the substrate layer 5, the buffer layer 6 and the waveguide 1. And, in the 
cross section of this reflector part 4, a thickness greater than the 
thickness of the waveguide 1 is removed. To attain effective reflection of 
the light being transmitted through the waveguide 1, it is possible to 
carry out two methods for forming the reflector part 4. One method is to 
utilize total reflection of the transmitted light, while the other method 
is to form a single metal film or a dielectric multilayer reflective film 
on the boundary between the reflector part 4 and the waveguide 1. In the 
former method, the reflector part is formed such that the angle 
.theta..sub.i of incident light to the surface of the reflector part 4 
satisfies the following formula: 
EQU .theta..sub.i &gt;sin .sup.1 (1/N) 
In this formula, N is an effective refractive index of a material of the 
waveguide when the light is transmitted through the waveguide 1. The 
latter method is useful especially when the angle of the incident light to 
the surface of reflector part 4 is smaller than the value of sin.sup.-1 
(1/N). 
Although the photodetector part 2 in the above described embodiment is 
formed as a p-n junction photodiode, the present invention is not limited 
to this embodiment. For example, the photodetector part 2 may be formed 
like a p-i-n diode. And, the above described embodiment employs a buffer 
layer deposited on a silicon substrate, but it is possible for a 
dielectric substrate having no absorption and showing a refractive index 
smaller than that of the waveguide 1 to be used and no buffer layer is 
provided between such a dielectric substrate and the waveguide. Further, 
the photodetector part 2 may be built through forming of an amorphous 
silicon film. In addition, the reflector part 4 in the above described 
embodiment is built through etching which is performed for the 
corresponding region of the waveguide; however, it is also possible that 
at the time of forming the waveguide, the region of the waveguide 
corresponding to the reflector part 4 will not be formed by using a 
masking technique to create a cavity in the region of the waveguide. 
Referring next to FIG. 4, a description will be given of a first embodiment 
of a waveguide type optical detection apparatus according to the present 
invention, which is applied to an optical disk pickup. In an optical 
integrated circuit of the optical disk pickup, a buffer layer (not shown) 
is deposited on a silicon substrate, and on the buffer layer a waveguide 
21 is deposited. And provided in the optical integrated circuit are a 
grating 15, a focusing grating coupler 16, a plurality of photodetectors 
22a, 22b, 22c, 22d, a semiconductor laser diode 27, and a plurality of 
electrodes 29a, 29b, 29c, 29d respectively being connected to the 
photodetectors 22a, 22b, 22c, 22d. Further provided are a reflector part 
24a between the photodetectors 22a and 22b, and a reflector part 24b 
between the photodetectors 22c and 22d. The semiconductor laser diode 27, 
or a light source for generating a laser beam, is provided on an end 
surface of the waveguide 21 so that the laser beam from the semiconductor 
laser diode 27 is transmitted through the waveguide 21. The transmitted 
beam passes through the grating 15 and is diffracted by the grating 
coupler 16 so that light is transmitted through the air and thrown onto an 
optical data storage medium (not shown). Then, the light reflected on the 
surface of the optical data storage medium reenters the grating coupler 16 
and is transmitted again through the waveguide 21. The light is diffracted 
by the grating 15 and is split into two different beams of light. One of 
these beams is reflected by the reflector part 24a so that the 
photodetectors 22a, 22b can receive the reflected beam. The other beam is 
reflected by the reflector part 24b so that the photodetectors 22c and 22d 
can receive the reflected beam. Electric signals given from the 
photodetectors 22a, 22b, 22c, 22d are picked up from the electrodes 29a, 
29b, 29c, 29d respectively connected to the photodetectors 22a, 22b, 22c, 
22d. 
In the optical disk pickup shown in FIG. 4, the beams are thrown on a place 
between the photodetectors 22a and 22b and on a place between the 
photodetectors 22c and 22d, respectively, when a light beam is focused 
accurately on the optical data storage medium. As described above, the 
provision of the reflector parts 24a, 24b at the places corresponding to 
light-insensitive areas between the photodetectors allows all the beams 
from the grating 15 to be correctly received by any of the photodetectors 
22a, 22b, 22c, 22d. Each of the reflector parts 24a, 24b has two equal 
slanting surfaces defining two equal sides of an isosceles triangle with a 
vertex point to which the transmitted beam is directed. When the optical 
data storage medium comes closer to or moves away from the focus point of 
the grating coupler 16, even a small quantity of the light separated by 
each of the reflector parts 24a, 24b is changed. Accordingly, the quantity 
of the light received by each photodetector is also changed in an expected 
manner, so that one can get a focusing error signal with good sensitivity 
using the above described optical disk pickup. 
Referring next to FIG. 5, a description will be given of a second 
embodiment of a waveguide type optical detection apparatus according to 
the present invention, which is applied to a RF spectrum analyzer. As 
shown in FIG. 5, in an optical waveguide 41 which is made from 
titanium-diffused lithium niobate, conventional-type geodesic lenses 45 
and 46 are formed. The titanium-diffused lithium niobate is prepared by 
diffusing a small quantity of titanium (Ti) on a lithium-niobate substrate 
(not shown). A transducer 48 is provided to generate an elastic surface 
wave so that it is directed to a place between the two geodesic lenses 45 
and 46 and travels across a path of a transmitting light beam as shown in 
FIG. 5. A semiconductor laser diode 47, or a light source for generating a 
laser beam which is transmitted through the waveguide 41, is joined to an 
end surface of the waveguide 41. A photodetector array 40 including 
light-receiving parts 42a, 42b, 42c, 42d, 42e, 42f, 42g, 42h and 
alternately aligning light-insensitive areas 43a, 43b, 43c, 43d, 43e, 43f, 
43g is provided on the other end surface of the waveguide 41. And, at 
respective places corresponding to the light-insensitive areas 43a, 43b, 
43c, 43d, 43e, 43f, 43g of the array 40 in the waveguide 41, small 
reflector parts 44a, 44b, 44c, 44d, 44e, 44f, 44g are provided. Each of 
the small reflector parts has two slanting reflection surfaces. 
In the thus arranged RF spectrum analyzer, a light beam from the 
semiconductor laser diode 47 is collimated by the lens 45 on the light 
source side, and is focused by the lens 46 on the array side so that the 
beam converges on the light-receiving part 42g. In this state, if a RF 
signal to be subjected to spectrum analysis is applied to the transducer 
48, the transducer 48 generates an elastic surface wave and the generated 
wave is transmitted in the upward direction of FIG. 5, traveling across an 
area of the waveguide 41 between the lenses 45 and 46. The light being 
transmitted through the waveguide 41 is diffracted by the elastic surface 
wave, and the light being focused by the lens 46 is directed to an upper 
light-receiving part of the photodetector array 40 which is located above 
the light-receiving part 42g when no RF signal is applied. The light when 
the RF signal is applied is received by a different light-receiving part 
of the photodetector array 40 than the light-receiving part 42g. In the RF 
spectrum analyzer as shown in FIG. 5, such a difference in location 
between the part actually receiving the light and the light-receiving part 
42g depends on the frequency of the RF signal. When the RF signal has a 
high frequency, the light is directed to an upper light-receiving part 
near to the part 42a. When the RF signal has a low frequency, the light is 
directed to a lower light-receiving part near to the part 42f. This 
enables the frequency of the RF signal to be measured with the 
photodetector array 40. According to the present invention, the RF 
spectrum analyzer having the small reflector parts 44a, 44b, 44c, 44d, 
44e, 44f, 44g allows all possible frequencies of the RF signal to be 
measured with the photodetector array 40, thus achieving good accuracy of 
spectrum analysis. 
Referring next to FIG. 6, a description will be given of a third embodiment 
of a waveguide type optical detection apparatus according to the present 
invention. In FIG. 6, there is a waveguide reflection component 60 which 
utilizes total reflection. The waveguide reflection component 60 is 
provided on an optical waveguide 51 to define an end surface of the 
waveguide 51 having two symmetrically arranged concave parabolic surfaces. 
And a pair of first photodetectors 52a, 52b, and a pair of second 
photodetectors 52c, 52d are provided at appropriate positions on the 
waveguide. There exists a first light-insensitive area 53ab between the 
adjacent first photodetectors 52a and 52b, and a second light-insensitive 
area 53cd between the adjacent second photodetectors 52c and 52d. Small 
reflector parts 54ab and 54cd respectively are provided at places 
corresponding to the light-insensitive areas 53ab and 53cd along the line 
of a light being reflected on the end surface of the waveguide 51. In this 
waveguide reflection component 60, an incoming light P is reflected on the 
end surface 60 of the waveguide 51 and the reflected light is focused. 
When the incoming light P is a parallel beam of light, the reflected light 
converges at a point which corresponds with the focus of the parabolic 
surface of the waveguide reflection component 60. The small reflector 
parts 54ab, 54cd which are provided at points each corresponding to the 
parabolic surface's focus, allow the incoming beam of light to be directed 
toward the photodetectors 52a, 52b, 52c and 52d. The easily seen function 
of the small reflector parts is that an incoming light passes within the 
waveguide type light sensitive apparatus as if there were no 
light-insensitive area between the photodetectors 52a and 52b and between 
the sensitive devices 52c and 52d. 
Next, a description will be given of the method for producing the waveguide 
type optical detection apparatus of this embodiment. The waveguide type 
optical detection apparatus is produced, for example, through a 
photolithography technique. Basically, after an etching or diffusion 
process is ended, an end surface of an integrated optic waveguide is 
formed into an optical reflection surface by using a photomask defining a 
desired pattern of the optical waveguide reflection surface. And, the 
small reflector parts 54ab, 54cd between adjacent photodetectors are 
designed to be in the same layer of the integrated optic circuit structure 
as that of the waveguide reflection component 60. Therefore, the small 
reflector parts 54ab and 54cd to be formed between adjacent photodetectors 
can be produced in the same manufacturing step as that of the waveguide 
reflection component 60. This is achieved by simply adding a pattern for 
forming the small reflector parts to a photomask having a pattern for 
forming the waveguide reflection component. 
Both the waveguide reflection component 60 and the small reflector parts 
54ab, 54cd are formed through etching of the waveguide 51 to remove its 
thickness of the waveguide or more which is performed with masking 
patterns. Such etching may be carried out by including the masking 
patterns in the same photomask. 
FIG. 7 shows an example of a waveguide reflection component 62 which 
utilizes normal reflection. The waveguide reflection component 62 is 
provided at an end portion of the waveguide 51 and formed with a metal 
reflector part 64. In this embodiment, it is possible to provide a metal 
reflector part, similar to the metal reflector part 64, on the small 
reflector parts 54ab, 54cd as well. The provision of a metal reflector 
part on a small reflector part is optional for individual applications. 
The forming of such a metal reflector part is carried out by including 
each masking pattern for forming metal reflector parts on the small 
reflector parts 54ab, 54cd in a photomask for forming the metal reflector 
part 64. 
Referring next to FIG. 8A, a description will be given of the small 
reflector part 54 and the relation of the small reflector part 54 to the 
photodetectors 52a and 52b. The small reflector part 54 has two reflection 
surfaces. These reflection surfaces may be formed to have a cross section 
of a straight line, a curved line, or a number of straight lines 
approximate to a curved line. However, it is necessary that the small 
reflector part 54 be formed to have the reflection surfaces at angles not 
smaller than a total reflection angle to the incoming light when total 
reflection is utilized, or to have the reflection surfaces at angles not 
smaller than 45 degrees to the incoming light when normal reflection is 
utilized. 
Referring next to FIG. 8B, a description will be given of a modified small 
reflector part 54' formed between the photodetectors 52a and 52b. In this 
embodiment, the small reflector part 54' is provided so that a vertex at 
the common end of the two reflection surfaces of the device 54' is aligned 
approximately with a line at the front edges of the photodetectors 52a and 
52b. The small reflector part 54' has a shape and dimensions with a margin 
to provide overlaps between the small reflector part 54' and the 
photodetectors 52a, 52b, for minimizing an error of positioning of the 
device 54' with respect to the devices 52a, 52b. Although the error of 
positioning causes a slight change of the vertex location, it is possible 
to eliminate the problem of the light-insensitive areas and to maintain 
the function of making effective use of incoming light. 
In addition, when producing the above described waveguide type optical 
detection apparatus having a waveguide reflector part and a small 
reflector part, the waveguide reflector part and the small reflector part 
conventionally are formed in separate processes. The process for forming 
the waveguide reflector part is similar to the process for forming the 
small reflector part. Therefore, repeating such a similar forming process 
causes an increase of the number of processes, and accompanying this, 
there is an increase in the cost of manufacturing products. In addition, 
it is difficult to accurately position a photomask for both the circuit 
devices formed in different processes, when a photolithography is used. 
The waveguide reflector part and the small reflector part must be 
accurately positioned because the sensitivity of the measurement being 
carried out with the waveguide type optical detection apparatus greatly 
depends on the relative positions of the waveguide reflector part and the 
small reflector part which are formed on the optical integrated circuit. 
Accordingly, the conventional apparatus often experiences a problem that 
an error as to matching of a photomask on the circuit devices during 
manufacture worsens the optical detection accuracy by the waveguide type 
optical detection apparatus, thereby leading to a wider range of 
variations. 
Referring next to FIGS. 9, 10, and 11A through 11F, a description will be 
given of a fifth embodiment of a waveguide type optical detection 
apparatus according to the present invention. 
FIG. 9 shows a fifth embodiment of a waveguide type optical detection 
apparatus according to the present invention, and FIG. 10 shows an optical 
disk pickup to which the waveguide type optical detection apparatus of 
FIG. 9 is applied. As shown in FIG. 10, a light beam from a light source 
101 is collimated by a collimator lens 102 and a collimated light beam 
comes into a waveguide component 103. In the waveguide component 103, the 
collimated beam is reflected on a boundary surface between a substrate 105 
and a cladding 106 so that a reflected beam enters a focusing lens 104. 
The beam entering the focusing lens 104 is focused on a surface of an 
optical data storage medium 112A which is, for example, an optical disk, 
an optical card, etc. The beam is reflected on the surface of the optical 
data storage medium 112A back to the waveguide component 103 through the 
focusing lens 4. The waveguide component 103 is formed with an optical 
waveguide 107 on which a coupler 108 and a beam splitter 109 are provided. 
A part of the reentrant beam is diffracted by the coupler 108 and guided 
to the waveguide 7. The guided beam first enters the beam splitter 109 
which serves to focus an incoming beam. 
As shown in FIG. 9, the beam splitter 109 has two lens portions 109a and 
109b. The lens portions 109a and 109b are formed from a convex optical 
lens which is cut into two halves, and arranged sidewise on the waveguide 
with one of the cut surfaces of the two halves facing a direction opposite 
to the other cut surface and one half being aligned at its bottom in 
contact with the other half at its top. The beam passing through the beam 
splitter 109 is split into two separate beams P and Q which are 
respectively focused by the lens portions 109a and 109b, the two separate 
beams aiming at two different points. These points on which the beams P 
and Q are focused respectively correspond with positions of waveguide 
mirrors 113a and 113b which are provided on the waveguide component 103. 
The waveguide mirrors 113a and 113b each have a diamond shape with 
suitable reflection surfaces which are capable of reflecting a part of 
each of the beams P and Q properly to a position of the corresponding 
photodetector. However, the overall shape of the waveguide mirrors is not 
limited to that of the shown examples but is optional if the functions 
thereof are attainable as described herein. Also, the positions of the 
waveguide mirrors arranged on the waveguide are not restricted to the 
shown examples but are optional if the function is attainable as described 
above. The beam P is partially reflected by the waveguide mirror 113a, 
and, from the focus position on the waveguide mirror 113a, it is separated 
into a non-reflected diverging beam P1 and a reflected diverging beam P2, 
which respectively are received by photodetectors 110a and 110b. 
Similarly, the beam Q is partially reflected by the waveguide mirror 113b, 
and is separated into a reflected diverging beam Q1 and a non-reflected 
diverging beam Q2, which respectively are received by photodectors 110c 
and 110d. The photodetectors 110a and 110b constitute a set of first 
photodetectors and the photodetectors 110c and 110d constitute another set 
of second photodetectors. 
In the above described embodiment, two waveguide mirrors and two sets of 
first and second photodetectors are employed so as to obtain a focusing 
error signal as well as a tracking error signal. However, in the case 
where the detection of the focus position only is desired, the provision 
of a single waveguide mirror and a single set of photodetectors may be 
adequate for attaining such a desired purpose. In addition, the 
diamond-shaped waveguide mirrors 113a and 113b, may be formed by removing 
a thickness of at least waveguide 107 in the corresponding regions through 
a photolithographic technique (e.g. dry etching) into a concave portion, 
as shown in FIG. 10. The beam is totally reflected on an end surface of 
such a cut-out portion, which may otherwise be a metal film being formed 
on the boundary between the substrate and the cladding, such a metal film 
being capable of normally reflecting the beam on the surface fo such a 
metal film. 
The photodetctors 110a through 110d are, for example, a junction type 
photodiode which is formed on the substrate 105 as shown in FIG. 10. The 
photodetector 110a is designed to receive a light beam traveling through 
the waveguide 107. An electric signal change of the photodetectors when 
they are exposed to light is picked up from an electrode 111a connected to 
the photodetector 110a . Concerning the light source 101, a laser light 
source such as a semiconductor laser diode, or a light emitting diode may 
be used, but it is preferable to use 1y a light source capable to emitting 
a light with good coherence in the aspect of space. Concerning the 
substrate 105, a metal, a dielectric, a glass or the like may be used as 
the substrate 105 of the waveguide component 103, but in this embodiment a 
semiconductor such as silicon, gallium arsenide is employed. When a 
semiconductor substrate is used as the substrate 105 in the above 
described embodiment, a photodetector may be built within the 
semiconductor substrate. However, since in the above described embodiment 
the beam from the light source 101 is reflected on the substrate surface, 
if a refractive index of the substrate is smaller than that of the 
cladding, it is necessary to form a reflection metal film or the like 
between the substrate and the cladding. 
Concerning the cladding 106 and the waveguide 107, these are formed from a 
transparent material such as a dielectric. However, it should be noted 
that a refractive index of the waveguide 107 must be greater than that of 
the cladding 106. Concerning the coupler 108, a grating coupler is used in 
the above described embodiment, which may be formed into a grating having 
equally spaced straight lines. Such a grating coupler may be built, for 
example, by forming a substrate into a thin film and applying etching or 
diffusion or cutting to the thin film to create a grating. Concerning the 
photodetectors, a junction type photodiode is used in the above described 
embodiment. Instead of this type, a Schottky barrier diode may be used, or 
otherwise, an alpha-silicon photodiode is also usable when a particular 
type of substrate material is employed. 
FIG. 11A shows a condition of the focusing beam from the focusing lens 104 
which is focused accurately on the surface of a subject body, or an 
optical data storage medium 112A. This corresponds with the condition in 
which the focal point of the focusing lens 104 lies on the optical data 
storage medium 112A. The beam passing through the lens portion 109a of the 
beam splitter 109 is transmitted through the waveguide and converges on a 
focal point F. After passing through the focal point F, the beam diverges. 
When the optical data storage medium 112A moves away from the focusing lens 
104 and the position of the medium 112A increasingly deviates from the 
focal point of the lens 104, the light being introduced by the coupler 8 
into the waveguide slightly converges before entering the lens portion 
109a. As shown in FIG. 11B, the light passing through the lens portion 
109a is focused on a point F.sub.1 which is nearer to the lens portion 
109a than the point F. This show that the forwarding direction of the 
light P shown in FIG. 11B is rotated slightly in a clockwise direction 
from the forwarding direction of the light P shown in FIG. 11A. 
In contrast, when the optical data storage medium 112A comes closer to the 
focusing lens 104 and the deviation of the medium 112A from the focal 
point of the lens 104 is decreasing, the light being introduced by the 
coupler 8 into the waveguide slightly diverges before entering the lens 
portion 109a. As shown in FIG. 11C, the light passing through the lens 
portion 109a is focused on a point F.sub.2 which is farther from the lens 
portion 109a than the point F. This shows that the forward direction of 
the light P shown in FIG. 11C is rotated slightly in a counterclockwise 
direction from the forwarding direction of the light P shown in FIG. 11A. 
The waveguide mirror 113a, as shown in FIG. 11D, reflects a part of the 
light being aimed at the focal point F of the lens portion 109a (in this 
case, the medium 112A is at the focus position of the focusing lens 104), 
and the remaining part of the light travels straight throughout the focal 
point F with no reflection. Thus, the light is split into two separate 
light beams P1, P2. The relative positions of the lens portion 109, the 
photodetectors 110a, 110b and the waveguide mirror 113 are arranged on the 
waveguide, so that the beams P1 and P2 having the same quantity of light 
are received accurately by the photodetectors 110a and 110b, respectively. 
In the case where the quantities of light received by the photodetectors 
110a and 110b differ from each other, adjustment of the sensitivity of 
each of the photodetectors 110a and 110b may be performed to make electric 
signals from the photodetectors 110a and 110b of the same level. Thus, 
when the medium 112A is exactly at the focus position of the focusing lens 
104, an output A of the photodetector 110a is equal to an output B of the 
photodetector 110b. The relative positions of the lens portion 109b, the 
waveguide mirror 113b and the photodetectors 110c, 110d are arranged 
symmetrically with those of the lens portion 109a, the waveguide mirror 
113a, and the photodetectors 110a, 110b described above. 
When the medium 112A moves away from the focusing lens 104 and deviation 
from the focus position of the lens 104 starts increasing, the quantity of 
light received by the photodetectors 110a, 110d is increased and the 
quantity of light received by the photodetectors 110b, 110c is decreased 
as shown in FIG. 11E. In contrast, when the medium 112A approaches the 
focusing lens 104 and the deviation from the focus position of the lens 
104 is still decreasing gradually until the focus position is reached, the 
quantity of light received by the photodetectors 110b, 110c is increased 
and the quantity of light received by the photodetectors 110a, 110d is 
decreased, as shown in FIG. 11F. Accordingly, when the medium 112A is at 
the same position as the focus position of the focusing lens 104, the 
outputs A, B, C, D of the photodetectors 110a, 110b, 110c, 110d are 
represented by the following formula: 
EQU (A+D)-(B+C)=0 
Hence, it is possible to carry out automatic focusing control by performing 
a focusing servo with respect to the focusing lens 104 if the (A+D)-(B +C) 
is taken as a focusing error signal. In addition, in the case where the 
optical data storage medium 112 has a track that is used for tracking, it 
is possible to carry out automatic tracking control through a conventional 
push-pull technique if the (A +B)-(C+D) is taken as a tracking error 
signal. 
In the foregoing embodiments, the present invention is applied to an 
integrated optic disk pickup unit. However, the present invention is also 
applicable to a technique for positioning a movable object. For example, 
within the optical detection apparatus shown in FIG. 10, a movable object 
having a reflection surface is located in place of the optical data 
storage medium 112. If the relative positions of the focusing lens 104, 
the waveguide component 103 and the light source 101 are arranged with 
respect to a target point on the reflection surface of the object to be 
positioned, the above described focusing error signal becomes zero at the 
target point. Thus, positioning can be carried out by correctly adjusting 
the position of the object to be positioned while checking that the 
focusing error signal becomes zero. 
Finally, a few modified examples of an optical disk pickup to which the 
optical detection apparatus of the present invention is applied are 
described below, as shown in FIGS. 12 through 14. 
FIG. 12 shows a sixth embodiment of the optical detection apparatus which 
is applied to the optical disk pickup. Instead of the waveguide component 
103 of FIG. 9, a waveguide component 103A shown in FIG. 12 is used for the 
optical disk pickup. The positions where waveguide mirrors 113c, 113d 
which divide an incoming light beam traveling through the waveguide into 
two separate beams P and Q are provided on the waveguide are different 
from those in FIG. 9. The positions are opposite to those of the waveguide 
mirrors 113a, 113b in FIG. 9 with respect to the beams P, Q, respectively, 
and they are located at positions behind the focus positions of the lens 
portions 109a, 109b. The focusing error signal and the tracking error 
signal are the same as those in FIG. 9. 
FIG. 13 shows a seventh embodiment of the optical detection apparatus which 
is applied to the optical disk pickup. Instead of the waveguide component 
103 of FIG. 9, a waveguide component 103B shown in FIG. 13 is used for the 
optical disk pickup. A focusing grating coupler 108A and a waveguide prism 
190 are provided on the waveguide component 103B. The waveguide prism 190 
divides an incoming light beam traveling through the waveguide into two 
separate beams P1 and Q1. The focusing grating coupler l08A performs both 
coupling an focusing: coupling of an incoming light into the waveguide and 
focusing of an outgoing light traveling through the waveguide. In the 
waveguide, a converging light beam sent from the focusing grating coupler 
l08A is divided into the two light beams P1 and Q1 by the waveguide prism 
190, the light beam P1 is further separated into two beams by a waveguide 
mirror 113e and the light beam Q1 is further divided into two beams by a 
waveguide mirror 113f. Thus, these four separate light beams are properly 
received by the photodetectors 110a, 110b, 110c and 110d, respectively. 
Hence, electric signals A, B, C and D outputted from the photodetectors 
110a, 110b, 110c and 110d when exposed to light can be used for focusing 
control by the focusing error signal (A+D) -(B+D) as well as for tracking 
control by the tracking error signal (A+B)-(C+D). 
FIG. 14 shows an eighth embodiment of the present invention. Instead of the 
waveguide component 103 of FIG. 9, a waveguide component 103C shown in 
FIG. 14 is used for the optical disk pickup. A double-focusing grating 
coupler 108B is provided on the waveguide component 103C. The 
double-focusing grating coupler 108B divides a light beam traveling 
through the waveguide into two separate beams P2 and Q2. And the 
double-focusing grating coupler 108B also performs both coupling and 
focusing: coupling of an incoming light into the waveguide and focusing of 
an outgoing light traveling through the waveguide. In the waveguide, each 
of the two separate converging light beams P2 and Q2 sent from the 
focusing grating coupler 108A is further divided into two beams by a 
waveguide mirror 113g or a waveguide mirror 113h. Thus, these four 
separate light beams are properly received by the photodetectors 110a, 
110b, 110c and 110d, respectively. The focusing error signal and the 
tracking error signal are the same as those in FIG. 9. The positions of 
the waveguide mirrors 113g and 113h are the same as those of the waveguide 
mirrors 113c, 113d in FIG. 12. 
Further, the present invention is not limited to these embodiments but 
various variations and modifications may be made without departing from 
the scope of the present invention.