Abstract: A solid-state imaging device includes: a sensor unit; a vertical scanning unit and a horizontal scanning unit; column amplifier units provided at respective vertical signal lines corresponding to columns in the sensor unit and amplifying signal charges read out to the vertical signal lines; a bias current adjustment unit controlling current flowing in the vertical signal lines by changing bias current of the column amplifier units; a signal processing unit processing signal charges read out to the vertical signal lines and amplified at the column amplifier units into image signals to be outputted; an output unit to which signals outputted from the signal processing unit are supplied; a drive signal generation unit supplying drive signals to the vertical scanning unit, the horizontal scanning unit, the signal processing unit and the output unit; and an input unit supplying plural drive mode signals to the drive signal generation unit.

Abstract: A document handling system includes an imaging area; a light source located in proximity to the imaging area; a raster imaging scanning system located in proximity to the imaging area; and a looped document path, located in proximity to the imaging area, having an entrance and an exit. The exit of the looped document path is positioned such that an exiting document is placed upon the imaging area a second time. Alternatively, the document handling system includes a semicircular document path, located in proximity to a first imaging area, having an entrance and an exit; and a second imaging area located in proximity to the exit of the semicircular document path. A bi-directional fiber optic element is located between the first and second imaging areas to transmit light from the light source to the second imaging area and light reflected from the second imaging area to the first imaging area.

Abstract: An image sensor including a plurality of photoelectric conversion elements arranged in a main scanning direction, a plurality of switching elements connected to respective ones of the photoelectric conversion elements, individually, and a controller for generating a clock signal to control the switching elements. The photoelectric conversion elements are divided into plural groups, each including a predetermined number (N) of the photoelectric conversion elements. The outputs from the photoelectric conversion elements in one group are read out simultaneously in response to the clock signal generated from the controller, thereby attaining a high speed reading of a document.

Abstract: A scanning device having a cable for connecting various parts is provided. A method is provided using a differential pair of clock generated signals to cancel each other, thereby reducing electromagnetic emissions. The differential pair is characterized by each being in phase with the other with regard to frequency, and each being the reverse of the other in amplitude.

Abstract: An image reading apparatus of the present invention converts respective pixel signals outputted from first, second and third shift registers to pixel data in an analog frontend IC and outputs pixel data as a serial data stream in a predetermined pattern. The address setting unit repeats add and subtract operation to the initial value according to the output pattern of the pixel data from the analog frontend IC to calculate pixel positions of the respective pixel data, and sets memory addresses corresponding to the pixel positions as destination memory addresses of the pixel data in an address register RR. The memory writing control unit writes the pixel data obtained from the analog frontend IC via a data sampling control unit in areas in the memory which correspond to the destination memory addresses. As a result, the amount of memory necessary for storing the pixel data can be reduced, and sorting operation of the pixel data can be executed with fewer memory access times.

Abstract: A document platen. A support member supports an end portion of the document platen from below in a sub scanning direction. A sensor module has a first protruding portion protruding in the sub scanning direction. The sensor module includes a first sensor, and a second sensor being shorter than the first sensor in length and being housed into the first protruding portion. A transport unit transports the sensor module in the sub scanning direction. When the sensor module is transported to an end part in the sub scanning direction, the support member is housed into a space disposed at a side of the first protruding portion in a main scanning direction.

Abstract: A scanning or copying system can include imaging elements and one or more system processors that are programmed or adapted to perform image processing methods and algorithms on image data, and in some instances, to enhance the image. Image data is acquired using imaging elements. Some imaging elements may have overlapping or rotated fields of view or employ differing resolutions. For each imaging element, its output is recombined together with the output of one or more other imaging elements. To perform the recombination, the system can extract features in an overlapping region and match these features in multiple images. In some instances, the features matched can be edges. Alternatively, the recombination can be performed by positioning each subimage with respect to a larger image through image matching and location techniques. Parameters from the recombined image can be extracted and these parameters can be used to correct for geometrical and spatial distortions and thereby enhance the image.

Abstract: The image reading device of the present invention includes (i) a sensor substrate which functions as a photoelectric transfer element having a photodetecting TFT and a pixel capacitor and (ii) a driving IC for applying a voltage to a gate electrode of the photodetecting TFT so as to drive the photodetecting TFT into an ON state or an OFF state. The driving IC applies a voltage, whose polarity is opposite to average polarity of a voltage making the photodetecting TFT in the OFF state, to the gate electrode of the photodetecting TFT in an arbitrary period. Thus, it is possible to provide the image reading device which can suppress variation of a photodetecting TFT property (resistance value) which is observed in a short time.

Abstract: A contact image sensor is provided including a housing, a slit plate a lens, one or two light sources and a light-receiving element array mounted on a light-receiving element array substrate. The housing contains the slit plate, the lens, the one or two light sources and the light-receiving element array substrate. The optical system of the contact image sensor is aligned and one or more depressions are formed on an end of the substrate for the alignment. Power to the one or two light sources is applied through one or more leads. Each of the one or more depressions is large enough so that each of the leads can be passed through the respective depressions.

Abstract: A method of changing driving sequence to output a charge coupled device signal, the method is applied to a scanner. The scanner has a pixel processor and a charge coupled device. A plurality of charge signals detected by the charge coupled device is sequentially output to the pixel processor according to the driving sequence. In the method of changing the driving sequence to output the charge coupled device signal, a fast driving sequence is provided. The fast driving sequence has a period equal to 1/N of the original driving sequence. According to the fast driving sequence, the charge signal is sent to the pixel processing circuit. The charge signals are sampled by the processing circuit according to a sampling sequence, and the data obtained by sampling is output.

Abstract: The scanning apparatus includes a movable chassis and a main board fixed on the body. A charge-coupled device module and a front end processing device are disposed on the chassis. An application-specific integrated circuit is positioned on the main board. After the charge-coupled device module detects a light analog signal, the application-specific integrated circuit communicates with the front end processing device through a command interface. Therefore, the light analog signal is converted into the light digital signal by the front end processing device, and then the light digital signal encoded into low voltage differential signaling form is transmitted to the application-specific integrated circuit for proceeding the subsequent image processing.

Abstract: To set at least the main portion of a read original on an image reading apparatus while avoiding a discontinuous portion, the position of the discontinuous portion of photoelectric conversion element arrays is indicated, or an original holder to be used to set the original while avoiding the discontinuous portion is arranged.

Abstract: A print media sensor mounting assembly includes a housing having a sensor mounting element. The sensor mounting element has a sensor position movably mounted therein for movement of the sensor position amongst a plurality of positions corresponding to a width of a print media web.

Abstract: A document reading apparatus arranged to reduce inconsistencies in the output signals of its linear image sensor is provided. The document reading apparatus includes a linear image sensor, a light source control circuit, and a light source driver. The light source control circuit has a pulse generator that generates control pulses having a prescribed frequency and a pulse period that is shorter than an accumulation period of the linear image sensor, the accumulation period being indicated by a timing signal that represents the accumulation period and a non-accumulation period. The light source control circuit also has a synchronization output unit that outputs a prescribed number of trigger pulses in synchronization with the timing signal and the control pulses. The light source driver drives the light source in response to the trigger pulses.

Abstract: A pixel circuit includes a silicon substrate having a photodiode that converts light intensity into a voltage signal and two metal layers disposed on the substrate having a pixel control circuit. The first metal layer includes a row trace and a reset trace and the second metal layer includes a column trace and a voltage supply trace. The row trace carries a signal that activates a switch for coupling the photodiode to the column trace during a readout phase and clears the voltage at the photodiode during a reset phase. The column trace interfaces with a signal capture circuit in a CMOS array of pixels for capturing a digital image that corresponds to each voltage level at each photodiode.

Abstract: A device and a method for inputting information are provided. The device includes: a rod; a movable ring fitted over the rod such that the rod is inserted through the movable ring, the movable ring moving in at least one of a longitudinal direction and a rotation direction of the rod; and a detector provided on the rod to sense a movement of the movable ring on the rod so as to generate information corresponding to the movement of the movable ring.

Abstract: There is disclosed an image read apparatus including an image sensor including: first and second sensors including light receiving devices arranged in one row; a first shift register for outputting the pixel signals of all the light receiving devices of the first sensor; and second and third shift registers for outputting the even-numbered and odd-numbered pixel signals of the light receiving devices of the second sensor, in which invalid data is prevented from being written in a memory. The pixel signals outputted from the first to third shift registers constituting a CCD image sensor with the same transfer clock are selected and taken in via an AFE in a time division. The taken pixel data is successively sampled in a data sampling block and stored in a memory. Moreover, when the sampling timing is controlled in a take-in signal generation circuit, the pixel data stored in the memory is limited to indicate the pixel number of each shift register.

Abstract: An image sensor unit has an electric discharge light emitting lamp for producing an illumination beam. The lamp includes a first electrode and a second electrode facing each other and defining a discharge space between them along the longitudinal axis of the lamp. A first light emitting layer and a second light emitting layer are provided in the discharge space so as to face each other and to cover the first and second electrodes, respectively. A dielectric material is inserted between the first electrode and the first light emitting layer, and between the second electrode and the second light emitting layer. At least one of the first and second light emitting layers is arranged so as to define an uncovered region, in which at least one of the dielectric material, the first electrode, and the second electrode is exposed to the discharge space.

Abstract: The scanner comprises first and second sensors 21, 22 wherein light receiving elements with 600 dpi resolution are arranged, a first shift register 25 which outputs all the pixel signals received from light receiving elements in the first sensor 21, and a second shift register 26 which outputs pixel signals received from even numbered light receiving elements in the second sensor 22, and selectively executes quality oriented image reading with 300 dpi resolution by utilizing one pixel signal composed of added pixel signals received from two light receiving elements arranged next to each other, or speed oriented image reading with 300 dpi resolution by utilizing pixel signals received from the second shift register.

Abstract: Scanning type device for detection of a photonic flux emitted by a scene containing at least one acquisition channel (V) comprising: several useful detectors (1) aligned with the scanning, each associated with a preamplifier (2), each receiving the same fraction of photonic flux from the scene and supplying information to the preamplifiers, a time delay integration device (4), integrating signals emitted by preamplifiers. The channel (V) cooperates with at least one calibration device (8) comprising: a calibration detector (9) on the input side of the useful detectors (1), receiving the fraction of photonic flux before the detectors (1), a device for generating a stimulus (11) from a fraction of the flux, and with at least one stimulus distribution device (13) for applying it to preamplifiers (2) before they have received the information from the associated useful detectors. Application particularly to imagery or to spectrometry.

Abstract: In an image reading apparatus, with respect to the first to third transfer clock signals for controlling shift registers in an image sensor, the second and third transfer clock signals have a cycle which is double the cycle of the first transfer clock signal, and the third transfer clock signal is shifted by a half cycle relative to the second transfer clock signal. Accordingly, the transfer timing of pixel signals in a second shift register is a half cycle shifted relative to the transfer timing in a third shift register, while the second and third shift registers operate with a transfer cycle which is double the transfer cycle of pixel signals in the first shift register. By this transfer control, the order of pixel signal output generally follows the order of the arrangement in the primary scanning direction of light receiving elements constituting the image sensor.

Abstract: An image reading apparatus for reading an image using a monochrome image sensor and a color image sensor having three shift registers which requires a reduced manufacturing cost and is less affected by the influence of external noises. The image reading apparatus comprises an analog frontend IC with three channels and having programmable gain amplifiers (PGA) for the respective channels capable of adjusting gains, an analog/digital converter (ADC) and a multiplexer (MUX) for sequentially providing signals amplified by the respective PGAs to the analog/digital converter built-in. The image reading apparatus amplifies pixel signals output from the respective channels of the monochrome image sensor or the color image sensor by providing the pixel signals to the corresponding PGAs, and converts the amplified pixel signals into pixel data through the analog/digital converter.

Abstract: A carrier device for a contact image sense optical scanner. The carrier device incorporates a pair of magnets with identical poles facing each other or a fluid filled sealed chamber for exerting an equal pressure on a scanning module within the scanner and maintaining close contact with a document platform throughout a scanning operation.

Abstract: An image reading device includes light-emitting diode chips (11A-11C) and a light guide (3) having a main region (3A) and a subsidiary region (3B). The subsidiary region (3B) includes a light incident surface (31) located above the light source (11A-11C) and an inclined surface (32). The light source (11A-11C) is offset in a direction receding from the main region (3A) with respect to the center (C2) as viewed in the primary scanning direction of the light incident surface (31).

Abstract: A contact image sensor module for scanning the image of a planar object comprises a white organic electroluminescent device, a plurality of cylindrical lenses, a color filter, and a contact image-sensing element. The white organic electroluminescent device emits white light which illuminates the planar object to result in reflected light. The cylindrical lenses direct the reflected light to the color filter, and the filtered light forms an image in the contact image-sensing element.

Abstract: A scanning circuit having rearranged circuit modules at each end of a flat cable. After the rearrangement, the flat cable carries scanning control signals produced by a conventional IC communication interface instead of timing signals and carries digital image data instead of easily distorted and interfered analog image signals.

Abstract: A solid-state image-pickup device including a multiplier configured to perform digital-gain processing for a sensor signal output from an analog-to-digital converter configured to convert an analog signal of an image sensor into a digital signal is provided. The solid-state image-pickup device includes a signal generator configured to generate randomly distributed signals, and an adder configured to add the randomly distributed signals to at least one signal with step-like discrete gradation, the signal being output from the multiplier.

Abstract: An apparatus for displacing a movable platen (50) in orthogonal first and second directions within a fixed plane of a surface (62). The movable platen is suspended from a stationary housing (80). A first actuator (40) provides a first linear displacement along the first direction and a second actuator (40) provides a second linear displacement along the second direction. A lever member (70) is pivoted at a flexure element (62) and is coupled to the stationary housing (80). The position of the flexure element along the lever member defines a working arm (58) of the lever member between the flexure element and the movable platen and an effort arm (76) of the lever member between the flexure element and point of contact of the actuator. The travel distance of the movable platen relative to the first linear displacement of the first actuator is proportional to the ratio of the length of the working arm to the length of the effort arm.

Abstract: A locking apparatus for a movable carry module, comprises a controller using to fix the movable carry module of an electric device. The controller has a movable locking shaft normality stretch in the movable carry module, and applies to fix the movable carry module. The electric device supplies the electric power to the controller when receiving the external electric power, and then the locking shaft departs from the movable carry module, such that the movable carry module can move freely.

Abstract: An image reading device includes a CCD which photoelectrically converts optical information and outputs an image signal in an analog form, a PGA which receives an output from the CCD, amplifies the output with a programmable gain, and outputs the output, an ADC which receives an output from the PGA, A/D-converts the output, and outputs an image signal in a digital form, and a CPU which calculates a gain which makes an output from the ADC match a reference value by using an output from the ADC and the reference value, thereby setting a gain for the PGA. This arrangement makes it possible to set a gain in a short period of time and shorten the first copy time in an image forming apparatus or MFP system using the image reading device of this invention.

Abstract: A scanner system for imaging a transparent media object comprising an illumination source for concurrently illuminating a first and second scan line of a media object, and a carriage comprising a photosensitive device located within the carriage and a light pipe affixed to a surface of the carriage is provided. The carriage is configured to receive on a first region of the photosensitive device light passed through the first scan line and the light pipe is adapted to redirect light passing through the second scan line onto a second region of the photosensitive device. The photosensitive device is operable to sample light directed onto the first and second regions.

Abstract: An optical module with movable reflective mirrors is provided in the invention. The optical module, which is set in a scanner for the scanning of documents, comprises the following elements: a first carriage comprising a first reflective mirror, a lens and a photoelectric sensing device, wherein the first carriage moves along the scanning direction to scan the document to be scanned; a second carriage comprising a second reflective mirror, a lens and a photoelectric sensing device, wherein the second carriage can make relative movement corresponding to the first carriage along the scanning direction; and a third carriage comprising a third reflective mirror, a lens and an photoelectric sensing device, wherein the third carriage can make relative movement corresponding to the first carriage along the scanning direction.

Abstract: An image reading device ready to operate at higher speed is built as an IC chip having a plurality of processing sections, of which each has a plurality of image reading photoelectric conversion elements, a plurality of transistors for reading a photoelectric conversion signal from the image reading photoelectric conversion elements, a signal selection circuit for sequentially selecting the plurality of transistors, and a signal output line by way of which the photoelectric conversion signal is transmitted.

Abstract: Embodiments of the claimed subject matter comprise a movable locking device for a scanner. In one embodiment, the movable locking device is used to affix a moving mechanical part inside a scanner, such as inside an optical chassis of the scanner. In this embodiment, the scanner comprises a platform, a lifting cover and a hinge set. The scanner uses the hinge set to allow the lifting cover to rotate relatively to the platform. The locking device includes a movable structure member and a buckling groove, in which the movable structure member includes a stopping piece and a holding rod used as the axis of rotation of the hinge set.

Abstract: An image sensor is disclosed, in which the image sensor changes the diameter of a lens from the center area of a chip to an edge thereof to obtain uniform sensitivity as a whole. The image sensor includes a plurality of light-receiving portions for converting a signal corresponding to the light of an object to an electrical signal, and a pixel array area having a plurality of micro lenses formed above the light receiving portions and respectively corresponding to the light-receiving portions to focus the light. In the image sensor, the respective micro lenses change their diameters from the center of the pixel array area to the edge thereof.

Abstract: To provide a close contact type sensor promoting a light utilizing efficiency, there is provided a close contact type sensor featured in that in a close contact type sensor having a sensor circuit portion and an irradiation window portion, a plurality of the irradiation windows are arranged and positions and sizes of the irradiation windows are matched to positions and sizes of opening portions of LCD utilized as a light source.

Abstract: An image pickup apparatus includes an image sensor in which main and auxiliary pixels are bidimensionally arranged for outputting a high and a low output signal, respectively. The user of the camera is allowed to select a desire image quality mode appearing on a monitor by operating a control panel. In a dynamic range priority mode, the high and low output signals are smoothly combined with each other to produce an image signal with a broadened dynamic range. In a resolution priority mode, the high and low output signals are not combined in order to guarantee resolution. In a sensitivity priority mode, the low output signal is added to the high output signal in order to raise the saturation point of the first output signal and therefore sensitivity. Further, in a color reproducibility priority mode, a white balance correcting method is changed depending upon the color temperature of a scene.

Abstract: A chassis locking apparatus capable of being unlocked spontaneously is used for fixing the chassis in a scanner. The locking apparatus includes a groove interlinking next to the electric socket, a push rod in the groove, and a revolving locking element. By means of the strength of inserting the plug into the socket on the scanner, the push rod is pushed to move along the groove and hit the locking element, which is originally fixed on the chassis, to make the locking element rotate so that the chassis locking apparatus can be unlocked spontaneously. Therefore, no effort is necessary for a user to unlock the chassis locking apparatus by hand before using the scanner, which is convenient and timesaving.

Abstract: An image sensor device for outputting digital signals and a method thereof are disclosed. The image sensor device has a sensor module, a photoelectric converter module, an encoder module and a decoder module integrated with each other. The digital signals are outputted by the photoelectric converter module, are transferred to the series outputs by the encoder module, and then the decoder module takes the place of the ADC for transferring the series outputs to parallel digital signal outputs. Hence the present invention improves the defects (such as transmission interference, transmission decay and power consumption) of the analog signal, and removes the ADC from the image sensor device for reducing production costs. Furthermore, the image sensor device has some advantages for providing good image quality, easy assembly and reducing both power consumption and cost.

Abstract: An image reader includes an image sensor including a plurality of light receiving elements. The plurality of light receiving elements receive a reflection light from a document and perform photoelectric conversion. The image reader further includes an MTF calculation portion which calculates an MTF of the image sensor based on image data which is obtained by reading a predetermined MTF detection pattern. Moreover, the image reader includes an image processing portion which divides the plurality of light receiving elements into a first MTF region and a second MTF region. The image processing portion performs a first image process on the plurality of image signals which are outputted from the light receiving elements in the first MTF region and a second image process on the plurality of image signals which are outputted from the light receiving elements in the second MTF region.

Abstract: A solid-state image sensor produces an image including plural sub-images, which are rapidly read out and outputted via output circuits. The image sensor has its imaging surface divided into corresponding plural sub-areas producing image data, which is transferred by the horizontal transfer path in both left and right directions and outputted from the output circuits, whose amplifier characteristics are determined as follows. Optical black (OB) data from an OB area on the imaging surface is transferred in the left direction by the horizontal transfer path and outputted from one output circuit as total OB data. OB data is transferred by the horizontal transfer path in both left and right direction and outputted from the output circuits as left and right OB data. An output circuit characteristics determiner uses the total, and left and right OB data to determine the amplifier characteristics of the output circuits.

Abstract: An apparatus for scanning a photograph with PictBridge capability is provided, which includes a light source, an image sensor, a signal converter, a PictBridge encoder, and a universal serial bus (USB) controller. The light source projects a scanning light onto an object to be scanned. Upon contacting with the object to be scanned, the scanning light is reflected as a reflected light. The image sensor receives the reflected light and then transmits an image signal to the signal converter to be converted into a digital image data. The digital image signal is encoded by the PictBridge encoder to a direct-printing code. Finally, the USB controller encodes the direct-printing code into a universal serial bus signal and transmits to a printer via a USB wire, so as to print the image by the printer.

Abstract: An analog-to-digital converter in an image sensor is implemented with a plurality of comparator units. Each comparator unit has a respective capacitor array and respective switches integrated therein. Such capacitors and switches across the comparator units are operated for generating ramp voltages for such comparator units for performing analog-to-digital conversion with correlated double sampling. Thus, circuit area and power consumption of the CMOS image sensor may be minimized.

Abstract: An aspect of the invention provides an image reading apparatus including: first and second light emitters that emit lights; a light guide unit that guides the lights emitted from the first and second light emitters to irradiate a document with the light; a photoelectric conversion unit that converts reflected light from the document into an image signal; and a control unit that controls the first light emitter to emit light for a first time period in a unit time period and controls the second light emitter to emit light for a second time period misaligned from the first time period in the unit time period.

Abstract: An image reading apparatus, comprising an image reading module having an image sensor to read an image from a document and a timing generator to generate a driving clock to control the image sensor, a main controller to output an enabling clock to the timing generator, and an analog-to-digital (A/D) converter to convert an analog signal output from the image sensor into a digital signal.

Abstract: A mirror attachment structure for an image-reading apparatus that includes a carriage for mounting a light source for illuminating a document and a photoelectric conversion device for receiving light from the document includes a reinforcement sheet metal member. The reinforcement sheet metal member includes first and second sections that do not lie in the same plane and a mirror that is fixed to one of the sections. The carriage supports the reinforcement sheet metal member. The reinforcement sheet metal member may be formed into a proper shape by bending. The mirror may be directly bonded to the reinforcement sheet metal member, mounted on a support attached to the reinforcement sheet metal member, or formed directly on the reinforcement sheet metal member by evaporating aluminum onto the reinforcement sheet metal member.

Abstract: Disclosed is an image reading apparatus which includes an illumination system, a reading unit, and an imaging optical system for imaging imagewise information provided on a surface of an original as illuminated by the illumination system, upon a surface of the reading unit. The imaging optical system includes, in an order from the original surface side, a first lens group of negative refractive power, a second lens group of positive refractive power, and a third lens group of negative refractive power. The image reading apparatus has a focal point position adjusting function and a focal length changing function based on movement of at least one of the lens groups of the imaging optical system. In the imaging optical system, a condition 0.01<R×K/F<1.00 is satisfied where R is resolution per single line in a main scan direction of said image reading apparatus, K is picture element size of the reading unit, and F is F number of the imaging optical system at a largest imaging magnification.

Abstract: An image reading unit includes an image sensor for converting light from a document into an electric signal, and a circuit board provided with the image sensor on one side. In the image reading unit, a heat dissipating member for controlling a temperature of the image sensor is attached to one side of the circuit board, and a shield member for reducing a noise is provided on the other side of the circuit board. The heat dissipating member and the shield member are connected by a heat conductive member. Also, the heat dissipating member is interposed between the image sensor and the circuit board.

Abstract: A CCD scanner is provided with a regulating circuit, which stores electric-current set values of LED elements of respective colors. The regulating circuit also stores desired values corresponding to optimum light amounts of the LED elements of the respective colors. By utilizing the electric-current set value and the desired value, binary search is performed for the LED elements every color. During the binary search, the light amount of the LED element is regulated, and an electric-current value thereof is determined so as to obtain the optimum light amount. By using the determined electric-current value, the LED element is turned on to read an image.

Abstract: An optical mechanism installed in an office machine, which has a machine base defining an internal space, and a paper-feeding mechanism arranged on the machine base, the paper-feeding mechanism having an inside receiving space and a bottom incident zone for the passing of light. The optical mechanism has an optical-path device formed of an image sensor and an optical module and mounted in the internal space inside the machine base, and a light-focusing structure mounted in the receiving space inside the paper-feeding mechanism above the incident zone for increasing optical path.