Optical waveguides – Integrated optical circuit
Reexamination Certificate
2001-02-20
2004-01-13
Sanghavi, Hemang (Department: 2874)
Optical waveguides
Integrated optical circuit
C385S088000, C385S049000, C372S043010, C372S050121, C372S038100, C372S026000
Reexamination Certificate
active
06678432
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical integrated device, a semiconductor laser module and an optical transmitter, particularly to a technology effectively applied to a technology for stabilizing output of laser beam radiated from a plurality of semiconductor lasers.
In WDM (Wavelength Division Multiplexing) optical communication, it is very important to adjust and maintain wavelengths of light sources having a plurality of different wavelengths respectively to predetermined wavelengths prescribed by Communication Standards. Therefore, there have been proposed various wavelength adjusting technologies. For example, there is disclosed a technology of controlling a laser oscillation wavelength of a semiconductor laser (laser diode: LD) in Japanese Patent Laid-open (Kokai) No. Hei 9-129959.
There is adopted normally a method of transmitting laser beams emitted from respective semiconductor lasers to a separately packaged wavelength monitoring package by using optical fibers and feeding back control signals in correspondence with deviations from predetermined wavelengths to the respective semiconductor lasers.
According to the method, the apparatus becomes large-sized. In recent years, there has been proposed a method of mounting a small-sized optical output and wavelength monitor using an etalon filter at a vicinity of a position of emitting light of a semiconductor laser chip and including the monitor in a single package to thereby constitute a semiconductor laser module. For example, there is disclosed a wavelength monitor (optical monitor integrated optical transmitter module) for wavelength division multiplexing optical fiber communication in Japanese Patent Laid-open (Kokai) No. Hei 10-79723. According to the apparatus, there is constructed a constitution of arranging DFB (distributed feedback)-LD in a pin package, irradiating laser beam to outside of the package by passing forward beam of the laser diode through a lens, an isolator and a lens and guiding backward beam to a PIN array via Fabri-Perot etalon.
The package, for example, the package in a box shape, is described in A. Kasukawa, “High Power Semiconductor Laser for Exciting a Fiber Amplifier”, Kogaku (Japanese Journal of Optics), Vol. 29, No. 3, 2000, pp. 148-151, Optical Society of Japan (in Japanese). According to the literature, there is described a laser module (pig-tail module) projecting a plurality of leads (external electrode terminals) to align from both sides of a box-type package in a shape of a parallelepiped.
Further, according to Japanese Patent Laid-open (Kokai) No. Hei 7-50443, there is described a distributed feedback type laser with a modulator. According to the literature, there is described a selective growth technique as a method of integrating optical semiconductor elements having different kinds of functions such as a semiconductor laser, an optical modulator, an optical switch, an optical detector and an optical amplifier on the same semiconductor substrate.
SUMMARY OF THE INVENTION
According to the conventional optical monitor integrated optical transmitter module, there is constructed a structure integrated to a single package, which is an excellent method for making apparatus small-sized and inexpensive. However, according to the method, a single laser diode is formed on a semiconductor chip (semiconductor laser chip).
In the meantime, in recent years, there has been proposed a chip (semiconductor laser chip) in which in order to emit a plurality of wavelengths of beams in a range at least covering a portion of a plurality of wavelengths prescribed by the wavelength division multiplexing optical fiber communication, not only a laser diode having a predetermined single wavelength but also a plurality of semiconductor lasers (laser diodes) are monolithically integrated on a single semiconductor substrate, further, a multiplexer for multiplexing forward beams of the lasers, an amplifier and a modulator are monolithically integrated (K.Kudo et al., 25th Optical Fiber Communication Conference, TuL5, (2000)).
Hence, the inventors have investigated to combine the above-described integrated semiconductor laser chip with a small-sized optical monitor and integrating thereof to a box-type package, conventionally used. However, according to the method, it is known that the following problem is posed by the method.
FIG. 18
is a simplified schematic view of an integrated laser chip which has been investigated by the inventors prior to the present invention.
A semiconductor chip
1
is monolithically integrated with a plurality of semiconductor lasers
14
a
through
14
d
, forward optical guides
15
, a multiplexer
16
, an amplifier
17
and a modulator
18
. Forward beam
60
of the semiconductor lasers
14
a
through
14
d
is guided to the multiplexer
16
by the forward optical guides
15
and is irradiated from an emitting face a of the semiconductor chip
1
by being successively guided by the amplifier
17
and the modulator
18
. Further, wirings, electrode pads and the like are omitted in the drawing (the same as in following views).
When the plurality of semiconductor lasers
14
a
through
14
d
are integrated in the single pitch, in order to avoid interference thereamong, it is necessary to arrange the semiconductor lasers to be remote from each other by a predetermined distance or more. According to the above-described publicly-known example (K.Kudo et al., 25th Optical Fiber Communication Conference, TuL5, (2000)), an area having a width of 80 &mgr;m is arranged for arranging 8 pieces of lasers. The range is further increased when a number of integrated lasers is increased.
This signifies that when optical intensities of the respective semiconductor lasers
14
a
through
14
d
are monitored, a backward radiation range L becomes large. According to the example of
FIG. 18
, L becomes about 40 &mgr;m. For an optical monitor element constituted by an optical receiving element, it is necessary that an incident position and an incident direction of beam fall within predetermined ranges. The range is about 10 and several &mgr;m although depending on the style of the optical monitor. Therefore, when a number of integrating semiconductor lasers becomes large, even in the case of arranging the semiconductor chip land an optical monitor element contiguously to each other, there poses a problem that the range of a position of emitting beam of the respective semiconductor laser exceeds a detectable area (area) of the optical monitor element.
The integrated laser chip (semiconductor chip)
1
is constructed by the constitution of multiplexing, amplifying and modulating forward beam irradiated from the respective semiconductor lasers
14
a
through
14
d
and emitting thereof from the extremely small area a at the front end of the chip. Hence, there is conceivable a method of constructing a constitution of dividing a portion of the forward beam and monitoring the forward beam by transmitting the forward beam to an optical monitor without adopting a method of monitoring backward beam. According to the method, although there can be avoided the problem of nonuniformity of monitor accuracy caused by a variation in a position of emitting beam by the respective semiconductor laser, there poses a problem that beam to be used for transmission is attenuated by the monitor. Further, according to the method, there also poses a problem that output of the semiconductor laser cannot be monitored directly since the output of the respective semiconductor laser is monitored through the amplifier.
It is an object of the present invention to provide an optical integrated device, a semiconductor laser module and an optical transmitter capable of highly accurately monitoring output beam of respective semiconductor lasers subjected to laser-array monolithic integration on a semiconductor substrate.
It is other object of the present invention to provide an optical integrated device for emitting backward beam of respective semiconductor lasers subjected to laser-array monolithic integratio
Shigeta Junji
Shirai Masataka
Tatsuno Kimio
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Knauss Scott
Sanghavi Hemang
LandOfFree
Optical integrated device, semiconductor laser module and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical integrated device, semiconductor laser module and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical integrated device, semiconductor laser module and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3239823